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BEGIN:VEVENT
SUMMARY:Chimere Anabanti (University of Technology (TU Graz) Austria)
DTSTART:20200611T130000Z
DTEND:20200611T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/1
DESCRIPTION:Title: On the classification of finite filled groups\nby Chimere An
abanti (University of Technology (TU Graz) Austria) as part of MESS (Mathe
matics Essex Seminar Series)\n\n\nAbstract\nWe give an introduction to pro
duct-free sets in finite groups\, discuss an application to Combinatorics\
, and conclude with what is known about filled groups.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dmitry Savostyanov (University of Essex)
DTSTART:20200618T130000Z
DTEND:20200618T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/2
DESCRIPTION:Title: Epidemiological models on networks: Numerical approaches and cha
llenges (Work in progress)\nby Dmitry Savostyanov (University of Essex
) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nMathem
atical modelling of infectious disease is an important area of applied mat
hematics. The Kermack--McKendrick compartmental SIR model is quite simple
but also quite powerful --- it describes the epidemics with a system of or
dinary differential equations (ODEs)\, which can be easily solved using a
suitable numerical method\, and predicts the behaviour of outbreaks very s
imilar to that observed in many recorded epidemics. Even though compartmen
tal models are almost hundred years old now\, they are still widely used n
ot only in a classroom\, but also to predict the development of dangerous
diseases and to inform Government strategies in case of emergency. The qua
lity of a mathematical model\, and our understanding of its assumptions an
d applicability in a particular scenario\, is therefore crucial to make co
rrect decisions to protect public health and respond to epidemics effectiv
ely when they occur. The fundamental assumption of a compartmental model i
s that the population is well-mixed: there is no firm boundary between sus
ceptible\, infected and recovered individuals. Everyone interacts with eve
ryone at once\, similar to chemical molecules in a mixture. Although this
assumption may be appropriate on a later stages of epidemic\, it clearly l
imits the model's capability to accurately describe and predict the early
stages\, when the infection is largely localised in one location and is ca
rried to other locations through a network of transport and/or social and
community links. If we consider how a disease progresses through a network
\, only neighbouring nodes can participate in transmission --- the network
is not well-mixed. Hence\, the compartmental model is no longer fit for p
urpose\, and has to be replaced with a probabilistic model\, where we esti
mate the probability for each node to be in susceptible\, infected or reco
vered state at a given time. Importantly\, the states of the neighbours
are not independent --- quite the opposite! --- a susceptible person in di
rect contact with an infected person is likely to become infected soon. Th
is means that instead of considering individual probabilities\, we have to
describe the evolution of the joint probability distribution\, accounting
for the states of all nodes at once. This high--dimensional problem strug
gles from the curse of dimensionality --- the number of unknowns grows exp
onentially with the number of nodes\, and traditional ODE solvers can't co
pe with he growing complexity when the number of nodes exceeds several ten
s. For this reason\, the problem is typically solved using Stochastic Simu
lation Algorithms (SSA)\, such as Monte Carlo and its variants. Using our
experience with high--dimensional problems\, such as Fokker--Planck\, Chem
ical Master Equation and Quantum Spin Dynamics\, we consider applying tens
or product algorithms to solve this high--dimensional ODE with high accura
cy\, and hence obtain a full probabilistic picture of the disease transfer
through the network. In preliminary experiments we find tensor product ap
proach to be successful in principle. In particular\, it can accurately es
timate the probabilities of rare events\, as well as higher moments of the
observed quantities\, where SSA often struggles. This is a work in progre
ss! The presented results are in preparation for publication. We will appr
eciate all feedback and suggestions regarding this work.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:George Kinnear (University of Edinburgh)
DTSTART:20200626T130000Z
DTEND:20200626T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/3
DESCRIPTION:Title: Teaching mathematics online with STACK\nby George Kinnear (U
niversity of Edinburgh) as part of MESS (Mathematics Essex Seminar Series)
\n\n\nAbstract\nAt the University of Edinburgh\, we have been increasing o
ur use of the STACK computer-aided assessment system to provide practice a
nd homework for students. I will give an overview of the features of STACK
\, and describe different ways it is being used across all years of our pr
ogramme. In particular\, I will show how STACK was a key part of the desig
n of a new optional course for incoming students\, "Fundamentals of Algebr
a and Calculus"\, which covers key topics from Advanced Higher and A-Level
syllabuses. The course is delivered almost entirely online\, as a series
of STACK quizzes which interleave textbook-style exposition with videos of
worked examples\, interactive applets\, and practice questions. I will de
scribe how ideas from education research and cognitive science (such as sp
acing and retrieval practice) informed the course design\, from its overal
l structure to the content of individual questions. I will also show some
results from our evaluation of the course\, including measures of the stud
ents' learning gains.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chris Antonopoulos (University of Essex)
DTSTART:20201015T140000Z
DTEND:20201015T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/4
DESCRIPTION:Title: An extended SIR model for the spread of COVID-19 in different co
mmunities\nby Chris Antonopoulos (University of Essex) as part of MESS
(Mathematics Essex Seminar Series)\n\n\nAbstract\nIn this paper\, we stud
y the effectiveness of the modelling approach on the pandemic due to the s
preading of the novel COVID-19 disease and develop an extended-susceptible
-infected-removed (eSIR) model that provides a theoretical framework to in
vestigate its spread within a community. The eSIR model is based upon the
well-known susceptible-infected-removed (SIR) model with the difference th
at a total population is not defined or kept constant per se and the numbe
r of susceptible individuals does not decline monotonically. To the contra
ry\, as we show herein\, it can be increased in surge periods! In particul
ar\, we investigate the time evolution of different populations and monito
r diverse significant parameters for the spread of the disease in various
communities\, represented by countries and the state of Texas in the USA.
The eSIR model can provide us with insights and predictions of the spread
of the virus in communities that recorded data alone cannot. Our work show
s the importance of modelling the spread of COVID-19 by the eSIR model tha
t we propose here\, as it can help to assess the impact of the disease by
offering valuable predictions. Our analysis takes into account data from J
anuary to June\, 2020\, the period that contains the data before and durin
g the implementation of strict and control measures. We propose prediction
s on various parameters related to the spread of COVID-19 and on the numbe
r of susceptible\, infected and removed populations until September 2020.
By comparing the recorded data with the data from our modelling approaches
\, we deduce that the spread of COVID-19 can be under control in all commu
nities considered\, if proper restrictions and strong policies are impleme
nted to control the infection rates early from the spread of the disease.\
n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anne-Sophie Kaloghiros (Brunel University)
DTSTART:20201112T150000Z
DTEND:20201112T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/5
DESCRIPTION:Title: K-stability of Fano 3-folds\nby Anne-Sophie Kaloghiros (Brun
el University) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbs
tract\nFano varieties are geometric shapes which are positively curved. Th
ey arise in a wide array of fields from theoretical physics to phylogeneti
c trees. In fact\, every geometric shape which can be parametrised (or cov
ered ) is - up to surgery - a family of Fano varieties. There are rich in
teractions between differential geometric and algebro-geometric properties
of Fano manifolds (and more generally of Kahler manifolds). An instance o
f this phenomenon was conjectured by Yau Tian and Donaldson ( and proved b
y Donaldson\, Chen and Sun): they proved that on Fano manifolds the exist
ence of special canonical metrics is equivalent to a stability property. T
his is an equivalence between properties that are subtle\, and still litt
le understood. I will discuss algebro-geometric approaches to this problem
and will present recent developments and their applications to our unders
tanding of Fano surfaces and 3-folds.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Murat Akman (University of Essex)
DTSTART:20201119T150000Z
DTEND:20201119T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/6
DESCRIPTION:Title: A Minkowski problem for nonlinear capacity\nby Murat Akman (
University of Essex) as part of MESS (Mathematics Essex Seminar Series)\n\
n\nAbstract\nThe classical Minkowski problem consists in finding a convex
polyhedron from data consisting of normals to their faces and their surfac
e areas. In the smooth case\, the corresponding problem for convex bodies
is to find the convex body given the Gauss curvature of its boundary\, as
a function of the unit normal. The proof consists of three parts: existenc
e\, uniqueness and regularity. In this talk\, we study a Minkowski problem
for certain measure associated with a compact convex set E with nonempty
interior and its A-harmonic capacitary function in the complement of E. He
re A-harmonic PDE is a non-linear elliptic PDE whose structure is modeled
on the p-Laplace equation. If \\mu_E denotes this measure\, then the Min
kowski problem we consider in this setting is that\; for a given finite Bo
rel measure \\mu on S^(n-1)\, find necessary and sufficient conditions for
which there exists E as above with \\mu_E =\\mu. We will discuss the exis
tence\, uniqueness\, and regularity of this problem in this setting. The t
alk will be related with the following papers: https://arxiv.org/abs/1906.
01576\, https://arxiv.org/abs/1810.03752\, https://arxiv.org/abs/1709.0044
7.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alastair Litterick (University of Essex)
DTSTART:20201126T150000Z
DTEND:20201126T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/7
DESCRIPTION:Title: Variations on a theme of J.-P. Serre: Complete reducibility in g
roups\, representations\, buildings and geometric invariant theory\nby
Alastair Litterick (University of Essex) as part of MESS (Mathematics Ess
ex Seminar Series)\n\n\nAbstract\nWhen studying modules or other algebraic
objects\, it is common to try and break things up and study the simple pi
eces. Complete reducibility asks the question: Under what conditions do th
ese simple objects fully describe the object we started with? In represent
ation theory this becomes: Under what condition is every module a direct s
um of its irreducible factors? This question\, which a priori has nothing
to do with geometry\, topology or combinatorics\, turns out to have deep c
onnections with all these other areas. In this talk we will look at these
connections\, and we will see how fundamental representation-theoretic res
ults have analogues and generalisations in other areas of pure mathematics
.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicola Walker (Centre for Environment\, Fisheries and Aquaculture
Science)
DTSTART:20201203T150000Z
DTEND:20201203T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/8
DESCRIPTION:Title: Cod on the menu? Using mathematical modelling to provide fisheri
es management advice\nby Nicola Walker (Centre for Environment\, Fishe
ries and Aquaculture Science) as part of MESS (Mathematics Essex Seminar S
eries)\n\n\nAbstract\nScientific advice on the management of fish stocks i
s often informed by mathematical assessment models that fit to information
from catches\, research surveys and life history. North Sea cod is a high
-profile and commercially important stock with a long history of highs and
lows. In particular\, the latest assessment estimates that the stock is b
elow safe biological limits\, which comes just two years after the fishery
was certified sustainable. Using North Sea cod as a case study\, Dr Walke
r will present the state-space assessment model (SAM) and detail the proce
ss of turning model outputs into scientific advice for fisheries managemen
t. She will discuss diagnostics for assessing the quality of input data an
d model fits and highlight some of the problems facing the assessment of t
his stock.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marina Iliopolou (University of Kent)
DTSTART:20210204T150000Z
DTEND:20210204T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/9
DESCRIPTION:Title: A discrete Kakeya-type inequality\nby Marina Iliopolou (Univ
ersity of Kent) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAb
stract\nThe Kakeya conjectures of harmonic analysis claim that congruent t
ubes that point in different directions rarely meet. In this talk we discu
ss the resolution of an analogous problem in a discrete setting (where the
tubes are replaced by lines)\, and provide some structural information on
quasi-extremal configurations. This is joint work with A. Carbery.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jesús M. Seoane (Universidad Rey Juan Carlos)
DTSTART:20210211T150000Z
DTEND:20210211T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/10
DESCRIPTION:Title: Relativistic chaotic scattering\nby Jesús M. Seoane (Unive
rsidad Rey Juan Carlos) as part of MESS (Mathematics Essex Seminar Series)
\n\n\nAbstract\n"The phenomenon of chaotic scattering is very relevant in
different fields of science and engineering. It has been mainly studied in
the context of Newtonian mechanics\, where the velocities of the particle
s are low in comparison with the speed of light. In this talk\, we analyze
global properties such as the escape time distribution and the decay law
of the Hénon-Heiles system in the context of special relativity. Our resu
lts show that the average escape time decreases with increasing values of
the relativistic factor β. As a matter of fact\, we have found a crossove
r point for which the KAM islands in the phase space are destroyed when β
≃ 0.4 [1]. On the other hand\, the study of the survival probability of
particles in the scattering region shows an algebraic decay for values of
β ≤ 0.4\, and this law becomes exponential for β >\; 0.4. Surprisin
gly\, a scaling law between the exponent of the decay law and the β facto
r is uncovered where a quadratic fitting between them is found. The result
s of our numerical simulations agree faithfully with our qualitative argum
ents. Besides\, we compute the basin entropy and the fractal dimension of
the set of singularities of the scattering function in function of β [2].
Finally\, we apply these results in the scattering in three-body problem
in relativistic regime [3]. We expect this work to be useful for a better
understanding of both chaotic and relativistic systems.\n[1] J. D. Bernal\
, J. M. Seoane\, and M. A. F. Sanjuán. Global relativistic effects in cha
otic scattering. Phys. Rev. E 95\, 032205 (2017).\n[2] J. D. Bernal\, J. M
. Seoane\, and M. A. F. Sanjuán. Basin entropy and fractal dimension in r
elativistic chaotic scattering. Phys. Rev. E 97 042214 (2018).\n[3] J. D.
Bernal\, J. M. Seoane\, J. C. Vallejo\, L. Huang\, and M. A. F. Sanjuán.
Influence of the gravitational radius o asymptotic behaviour of the relati
vistic Sitnikov problem. Phys. Rev. E 102 042204 (2020)."\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christina de Filippis (University of Turin)
DTSTART:20210225T150000Z
DTEND:20210225T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/11
DESCRIPTION:Title: Differentiable vs non-differentiable systems\nby Christina
de Filippis (University of Turin) as part of MESS (Mathematics Essex Semin
ar Series)\n\n\nAbstract\n"Nonautonomous\, nonuniformly elliptic functiona
ls are variational integrals characterized by quite a wild behavior of the
ellipticity ratio associated to their integrand\, in the sense that it ma
y blow up as the modulus of the gradient variable goes to infinity. We ana
lyze the interaction between the space-depending coefficient of the integr
and and a possible forcing term and derive optimal Lipschitz criteria for
minimizers. We catch the main model cases appearing in the literature\, su
ch as functionals with unbalanced power growth or with fast exponential gr
owth. We also find new borderline regularity results also in the uniformly
elliptic case\, i.e. when the ellipyicity ratio is uniformly bounded. Thi
s approach yields optimal regularity results for obstacle problems associa
ted for instance to iterated exponential models\, which have been treated
in [2] for the first time. Finally\, we look at general nonautonomous inte
grands with (p\,q)-growth and show general interpolation properties allowi
ng to get basic higher integrability results for either bounded or Hölder
continuous minimizers under improved bounds for the gap q-p.\nThis talk i
s based on papers [1\,2\,3].\nReferences\n[1] C. De Filippis\, G. Mingione
\, Interpolative gap bounds for nonautonomous integrals. Preprint (2020)\,
submitted.\n[2] C. De Filippis\, G. Mingione\, Lipschitz bounds and nonau
tonomous integrals. Preprint (2020)\, submitted. https://arxiv.org/pdf/200
7.07469.pdf\n[3] C. De Filippis\, G. Mingione\, On the regularity of minim
a of non-autonomous functionals. Journal of Geometric Analysis 30:1584-162
6\, (2020). https://doi.org/10.1007/s12220-019-00225-z"\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Charles Cox (University of Bristol)
DTSTART:20210304T150000Z
DTEND:20210304T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/12
DESCRIPTION:Title: Spread and infinite groups\nby Charles Cox (University of B
ristol) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\n
My recent work has involved taking questions asked for finite groups and c
onsidering them for infinite groups. There are various natural directions
with this. In finite group theory\, there exist many beautiful results reg
arding generation properties. One such notion is that of spread\, and Scot
t Harper and Casey Donoven have raised several intriguing questions for sp
read for infinite groups (in https://arxiv.org/abs/1907.05498). A group G
has spread k if for every g_1\, …\, g_k in G we can find an h in G such
that < g_i\, h > = G for i = 1\, ...\, k. For any group we can say that if
it has a proper quotient that is non-cyclic\, then it has spread 0. In th
e finite world there is then the astounding result - which is the work of
many authors - that this condition on proper quotients is not just a neces
sary condition for positive spread\, but is also a sufficient one. Harper-
Donoven’s first question is therefore: is this the case for infinite gro
ups? Well\, no. But that’s for the trivial reason that we have infinite
simple groups that are not 2-generated (and they point out that 3-generate
d examples are also known). But if we restrict ourselves to 2-generated gr
oups\, what happens? In this talk we’ll see the answer to this question.
The arguments will be concrete (*) and accessible to a general audience.\
n\n(*) at the risk of ruining the punchline\, we will find a 2-generated g
roup that has every proper quotient cyclic but that has spread zero.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nivedita Viswanathan (University of Edinburgh)
DTSTART:20210318T150000Z
DTEND:20210318T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/13
DESCRIPTION:Title: Understanding the notion of K-stability using 3-folds\nby N
ivedita Viswanathan (University of Edinburgh) as part of MESS (Mathematics
Essex Seminar Series)\n\n\nAbstract\nThe main objects of study in Algebra
ic geometry are ‘varieties’\, which are basically the geometric counte
rpart of solutions to polynomial equations. One of the most interesting qu
estions to ask about a variety\, is to determine whether it is ‘K-stable
’. A conjecture by Yau-Tian-Donaldson gives an algebro-geometric way of
looking at the notion of K-stability and many recent developments give ver
y explicit ways of determining this property. In this talk\, my goal woul
d be to give you a rough idea of why this is very interesting to study\, b
y looking at an explicit example of a Fano 3-fold. We will first look at t
he basic concepts that would be required to do this\, using some simple ex
amples and then take you through an example of a 3-fold slowly. We will
look at how best to describe the 3-fold using notions that are familiar to
us and then describe how one would determine the K-stability of the same.
This is joint work with Jesus Martinez Garcia\, Ivan Cheltsov\, Costya
Shramov\, Kento Fujita\, Carolina Araujo\, Ana-Maria Castravet\, Anne-Soph
ie Kaloghiros and Hendrick Suess.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mehmet Cihan (University of Essex)
DTSTART:20210325T150000Z
DTEND:20210325T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/14
DESCRIPTION:Title: Digraph groups and related groups\nby Mehmet Cihan (Univers
ity of Essex) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbst
ract\nGroups can be expressed in terms of a finite a digraph which vertic
es correspond to the generators and arcs correspond to the relators. Cu
no and Williams investigated when the number of vertices is equal the numb
er of arcs\, where the undirected graph is triangle free that means the gi
rth is at least 4\, and they proved that the corresponding group is either
finite cyclic or infinite. It is known that when the number of vertices
is more than the number of arcs\, then it is infinite. Therefore\, I inves
tigated when the number of vertices is less than or equal the number of ar
cs in my thesis. But it is more interesting when the undirected graph is w
ith triangle and therefore the underlying graph is complete graph. When we
directed the complete graph\, then it is known as tournaments. All known
examples are done by Mennicke and Johnson for a strong tournament with 3 v
ertices. In 1959\, Mennicke provided an example of a group defined by the
presentation M(a\, b\, c) =〈x\, y\, z | y^−1xy=x^a\, z^−1yz=y^b\, x^
−1zx=z^c〉\, which is finite in the case a=b=c ≥ 3. In 1997\, Johnso
n provided another group needing exactly three generators with presentatio
n J(a\, b\, c) =〈x\, y\, z|x^y=y^(b−2)x^−1y^(b+2)\, y^z=z^(c−2)y^
−1z^(c+2)\,z^x=x^(a-2)z^−1x^(a+2)〉 and which is finite in the cases
where a\, b\, and c are non-zero even integers. These are important since
they provide examples of finite groups needing exactly three generators.
In this talk\, I will talk about generalisation of their groups from 3 gen
erators to n generators for all strong tournaments.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Federica Armani (University of Essex)
DTSTART:20210429T140000Z
DTEND:20210429T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/15
DESCRIPTION:Title: Mathematics Anxiety: general overview\, what has been done and
what we need to do to help learners\nby Federica Armani (University of
Essex) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\n
Mathematical competence is an important ability to master often accompanie
d by a feeling of apprehension\, anxiety and fear which influence the achi
evements\, career choices or performance of an individual. This is called
Math Anxiety\, a feeling of tension and anxiety that interferes with the m
anipulation of numbers and the solving of mathematical problems in ordinar
y life and academic situations. In this seminar I will discuss this proble
m and show how tailored educational approaches in combination with motivat
ional and Mindset Theories can be used to mitigate the negative effects of
Math Anxiety. In the last part I will present the development and initial
results obtained from a mathematical puzzle I am using in research which
relies on counting abilities\, spatial reasoning\, working memory and expl
oits basic mathematical knowledge adapted and used in a different and more
engaging way in order to solve a series of puzzles.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marina Logares (Universidad Complutense de Madrid)
DTSTART:20210520T140000Z
DTEND:20210520T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/16
DESCRIPTION:by Marina Logares (Universidad Complutense de Madrid) as part
of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sergey Dolgov (University of Bath)
DTSTART:20210617T140000Z
DTEND:20210617T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/17
DESCRIPTION:Title: Deep tensor decompositions for sampling from high-dimensional d
istributions\nby Sergey Dolgov (University of Bath) as part of MESS (M
athematics Essex Seminar Series)\n\n\nAbstract\nCharacterising intractable
high-dimensional random variables is one of the fundamental challenges in
stochastic computation\, for example\, in the solution of Bayesian invers
e problems. The recent surge of transport maps offers a mathematical found
ation and new insights for tackling this challenge by coupling intractable
random variables with tractable reference random variables. In this talk
I will present a nested coordinate transformation framework inspired by de
ep neural networks but driven by functional tensor-train approximation of
tempered probability density functions instead. This bypasses slow gradien
t descent optimisation by a direct inverse Rosenblatt transformation. The
resulting deep inverse Rosenblatt transport significantly expands the capa
bility of tensor approximations and transport maps to random variables wit
h complicated nonlinear interactions and concentrated density functions. W
e demonstrate the efficiency of the proposed approach on a range of applic
ations in uncertainty quantification\, including parameter estimation for
dynamical systems and inverse problems constrained by partial differential
equations.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Georgios Amanatidis (University of Essex)
DTSTART:20201105T150000Z
DTEND:20201105T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/18
DESCRIPTION:Title: Rapid mixing of the switch Markov chain for strongly stable deg
ree sequences\nby Georgios Amanatidis (University of Essex) as part of
MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nThe switch Markov
chain has been extensively studied as the most natural Markov Chain Monte
Carlo approach for sampling graphs with prescribed degree sequences. We sh
ow that the switch chain for sampling simple undirected graphs with a give
n degree sequence is rapidly mixing when the degree sequence is so-called
strongly stable. Strong stability is satisfied by all degree sequences for
which the switch chain was known to be rapidly mixing based on Sinclair's
multicommodity flow method up until a recent manuscript of Erd\\H{o}s et
al. (2019). Our approach relies on an embedding argument\, involving a Mar
kov chain defined by Jerrum and Sinclair (1990). This results in a much sh
orter proof that unifies (almost) all the rapid mixing results for the swi
tch chain in the literature\, and extends them up to sharp characterizatio
ns of P-stable degree sequences. In particular\, our work resolves an open
problem posed by Greenhill and Sfragara (2017).\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anouchah Latifi (University of Qom)
DTSTART:20201029T150000Z
DTEND:20201029T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/20
DESCRIPTION:Title: Labyrinth walk: A chaotic non Hamiltonian conservative system t
hat does not admit an energy function\nby Anouchah Latifi (University
of Qom) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\n
Labyrinth Chaos and it conservative version\, Labyrinth walk are generic a
nd minimal models of a dynamical system discovered by Otto Rossler and Ren
e Thomas in order to identify the necessary mathematical conditions for th
e appearance of chaotic and hyperchaotic motion in continuous flows. It tu
rned out that in spite of its extreme simplicity these systems are full of
surprising properties. Simple and elegant as it is\, it still holds great
promise for elucidating aspects of chaotic dynamics that are not evident
in other systems. Our work highlights the incredible riches of this system
in its disconcerting simplicity and its importance in the context of dyna
mical systems and in other fields. This is joint work with Chris G. Antono
poulos and Vasileios Basios.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Simon Blackburn (Royal Holloway\, University of London)
DTSTART:20201210T150000Z
DTEND:20201210T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/21
DESCRIPTION:Title: How many finite rings are there?\nby Simon Blackburn (Royal
Holloway\, University of London) as part of MESS (Mathematics Essex Semin
ar Series)\n\n\nAbstract\nFor a positive integer $n$\, write $f(n)$ for th
e number of isomorphism classes of rings of order $n$. What can we say abo
ut $f(n)$? Determining $f(n)$ exactly for all $n$ looks unrealistic\, but
in 1970 Kruse and Price (J LMS) stated an asymptotic result that gives the
growth rate of $f(n)$ as $n\\rightarrow\\infty$. Sadly\, there are probl
ems with their proof. I will talk about recent joint work with K. Robin Mc
Lean (University of Liverpool) in which we fix the problems\, and improve
the error terms\, of the Kruse--Price result. No knowledge of ring theory
above a first undergraduate course will be assumed!\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Melissa Lee (University of Auckland)
DTSTART:20201217T090000Z
DTEND:20201217T100000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/22
DESCRIPTION:Title: The hunt for regular orbits of almost quasisimple groups\nb
y Melissa Lee (University of Auckland) as part of MESS (Mathematics Essex
Seminar Series)\n\n\nAbstract\nLet $G$ be a permutation group on $\\Omega$
. We say that $G$ has a regular orbit on $\\Omega$ if there exists $x \\in
\\Omega$ that is fixed only by the identity permutation. Regular orbits a
rise in a number of applications including the study of Frobenius groups a
nd the proof of the celebrated $k(GV)$-theorem\, which gives an upper boun
d on the number of conjugacy classes of certain affine groups where $|G|$
and $|V|$ are coprime. One of the major cases in the proof of the $k(GV)$
-theorem was a study of regular orbits of the so-called almost quasisimple
groups $G$ (i.e.\,$ G/F(G)$ is an almost simple group). In this talk\, af
ter giving some background and motivation\, I will discuss progress in my
quest to finish classifying all pairs $(G\,V)$ where $G$ is an almost quas
isimple group with a regular orbit on its irreducible module $V$. By the p
roof of the $k(GV)$-problem\, this boils down to the cases where $(|G|\,|V
|) >1$. I will also briefly discuss techniques used for this classificatio
n\, which involve some algebraic group theory\, character theory and compu
tational methods.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Antonio Marcos Batista (State University of Ponta Grossa\, Paraná
\, Brazil)
DTSTART:20210128T150000Z
DTEND:20210128T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/23
DESCRIPTION:Title: Extreme events in nonlinear wave interactions (dragon king)
\nby Antonio Marcos Batista (State University of Ponta Grossa\, Paraná\,
Brazil) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\n
Extreme events are by definition rare and exhibit unusual values of rele
vant observables. In literature\, it is possible to find many studies abou
t the predictability and suppression of extreme events. In this work\, w
e show the existence of dragon-kings extreme events in nonlinear thr
ee-wave interactions. Dragon-king extreme events\, identified by phase
transitions\, tipping points and catastrophes\, affects fluctuating syste
ms. We show that these events can be avoided by adding a perturbing smal
l amplitude wave to the system.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kelly Iarosz (Universidade Tecnológica Federal do Paraná UTFPR F
aculdade de Telêmaco Borba FATEB)
DTSTART:20210218T150000Z
DTEND:20210218T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/24
DESCRIPTION:Title: Our brain is not static\nby Kelly Iarosz (Universidade Tecn
ológica Federal do Paraná UTFPR Faculdade de Telêmaco Borba FATEB) as p
art of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nThe connecti
ons between brain neurons have the characteristic of being modified over t
ime due to several causes such as new experiences\, lesions\, brain pathol
ogies\, etc. This fenomenon is known as synaptic plasticity. We study the
capacity of neurons in a network to change temporarily or permanently thei
r connections and behavior\, as a function of their synchronous behavior.
Specifically\, an initial all-to-all topology evolves to a complex topolog
y. Moreover\, external perturbations can induce co-existence of clusters\,
those whose neurons are synchronous and those whose neurons are desynchro
nous. When the delay is increased the network presents a non-trivial topol
ogy. Regarding the synchronization\, only for small values of the synaptic
delay this phenomenon is observed.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jennifer Creaser (University of Exeter)
DTSTART:20210311T150000Z
DTEND:20210311T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/25
DESCRIPTION:Title: Domino effects on networks of bistable oscillatory nodes\nb
y Jennifer Creaser (University of Exeter) as part of MESS (Mathematics Ess
ex Seminar Series)\n\n\nAbstract\nMultistability has been identified as a
key mechanism in a diverse range of brain functions at different spatial s
cales. It is well known that the addition of noise in a multistable system
can induce random transitions between states. In a network\, the presence
of coupling introduces dependence between nodes leading to sequences of n
oise-induced transitions in a so called domino effect. The timing and orde
r of these domino cascades are emergent properties of the network. Analysi
s of the transient dynamics responsible for these transitions is crucial t
o understand the drivers of neurological disorders such as epilepsy. We co
nsider a general model of coupled bi-stable oscillators. Each node has two
stable states\; oscillating (active) and non-oscillating (quiescent). Esc
ape from the quiescent state is driven by additive noise and we assume the
timescale of transitions back again is long enough to be ignored. Escapes
are affected by changes in node dynamics\, coupling strength and synchron
isation. Using numerical and theoretical techniques we explore the interpl
ay between synchronisation and noise-induced escape. We consider amplitude
and phase-amplitude coupled motifs. In particular\, we find and investiga
te examples of three node symmetric networks where sequences of noise-indu
ced escapes are associated with various types of partial synchrony during
the sequence.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kyle Wedgwood (University of Exeter)
DTSTART:20210506T140000Z
DTEND:20210506T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/26
DESCRIPTION:Title: The curious case of rapid entrainment after jet lag\, and\, how
to get a single neuron to remember\nby Kyle Wedgwood (University of E
xeter) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\n"
This talk will cover two stories involving mathematical modelling (and som
e experiments) in neural systems.\n\nIn the first\, we will discuss the re
-entrainment problem of how our bodies synchronise with the external envir
onment following travel across time zones or shift work. To do so\, we ana
lyse a two-dimensional variant of the Forgers-Jewett-Kronauer model\, whic
h describes changes in core body temperature and neural activity in the br
ain region responsible for circadian rhythms\, forced by a 24-hour light/d
ark cycle. This model\, which has previously been used to explain the East
-West asymmetry in jet lag severity after travel\, predicts a counter-intu
itive rapid re-entrainment for sufficiently bright daylight. We explain th
is phenomenon via continuation of invariant manifolds of fixed points of a
24-hour stroboscopic map and explore the consequence of the arrangement o
f such manifolds on re-entrainment in a variety of scenarios.\n\nIn the se
cond story\, we will explore the capability of a neuron that is synaptical
ly coupled to itself\, to store and repeat patterns of precisely timed spi
kes\, which we regard as single cell 'memories'. Drawing on analogies from
semiconductor lasers\, we append a delayed self-coupling term to the oft
studied Morris-Lecar model of neuronal excitability and use bifurcation an
alysis to predict the number and type of memories the neuron can store. Th
ese results highlight the delay period as an important period parameter co
ntrolling the storage capacity of the cell. Finally\, we use the dynamic c
lamp protocol to introduce self-coupling to a mammalian cell and confirm t
he existence of the spiking patterns predicted by the model analysis."\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Constanza Rojas-Molina (CY Tech - Institut des Sciences et Techniq
ues - CY Cergy Paris Université)
DTSTART:20210513T140000Z
DTEND:20210513T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/27
DESCRIPTION:Title: Fractional random Schrödinger operators\, integrated density o
f states and localization\nby Constanza Rojas-Molina (CY Tech - Instit
ut des Sciences et Techniques - CY Cergy Paris Université) as part of MES
S (Mathematics Essex Seminar Series)\n\n\nAbstract\nIn this talk we will r
eview some recent results on the fractional Anderson model\, a random Schr
ödinger operator driven by a fractional laplacian. The interest on the la
tter lies in their association to stable Levy processes\, random walks wit
h long jumps and anomalous diffusion. We discuss in this talk the interpla
y between the non-locality of the fractional laplacian and the localizatio
n properties of the random potential in the fractional Anderson model\, in
both the continuous and discrete settings. In the discrete setting we stu
dy the integrated density of states and show a fractional version of Lifsh
itz tails. This coincides with results obtained in the continuous setting
by the probability community. This is based on joint work with M. Gebert (
LMU Munich).\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Billy Woods (University of Essex)
DTSTART:20210527T140000Z
DTEND:20210527T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/28
DESCRIPTION:Title: Iwasawa algebras and skew power series rings\nby Billy Wood
s (University of Essex) as part of MESS (Mathematics Essex Seminar Series)
\n\n\nAbstract\nIn this talk\, beginning with a faulty proof of Fermat’s
Last Theorem from the 19th century\, I’ll attempt to provide some moti
vation for the study of Iwasawa algebras\, which have now become a critica
l tool in many significant number-theoretic problems. I’ll give a couple
of ways to think about them algebraically\, contrast them with similar al
gebraic objects\, and outline some of what is known (and what is still unk
nown) about them\, including my own research. This is a talk about noncomm
utative algebra\, but I’ll try to keep the technical jargon to a minimum
\, so that much of this talk remains accessible even to those who haven’
t thought about abstract algebra in some time!\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Thanos Manos (CY Tech - Institut des Sciences et Techniques - CY C
ergy Paris Université)
DTSTART:20210603T140000Z
DTEND:20210603T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/29
DESCRIPTION:Title: Neural networks: desynchronization with synaptic and structural
plasticity\nby Thanos Manos (CY Tech - Institut des Sciences et Techn
iques - CY Cergy Paris Université) as part of MESS (Mathematics Essex Sem
inar Series)\n\n\nAbstract\n"Mathematical modelling is an important tool i
n understanding the basic mechanisms of the human brain as well as determi
ning its function and operation. In this talk\, I will discuss how such mo
dels\, based on ordinary differential equations can capture and describe t
he underlying dynamical evolution of interactions between a relatively sma
ll number of neurons within some brain area. Several brain diseases are ch
aracterized by abnormally strong neuronal synchrony. Coordinated Reset (CR
) stimulation was computationally designed to specifically counteract abno
rmal neuronal synchronization processes by desynchronization. In the prese
nce of spike timing-dependent plasticity (STDP) this leads to a decrease o
f synaptic weights and ultimately to an anti-kindling\, i.e.\, unlearning
of abnormal synaptic connectivity and abnormal neuronal synchrony. The lon
g-lasting desynchronizing impact of CR stimulation has been verified in pr
e-clinical and clinical proof of concept studies. However\, as yet it is u
nclear how to optimally choose the CR stimulation frequency\, i.e.\, the r
epetition rate at which the CR stimuli are delivered.\nThe first part of t
he talk is dedicated to systems with STDP and the design of optimal CR sti
mulation protocols. Namely\, protocols that manage to induce global (for d
ifferent system initiations) desynchronization but also show very good rob
ustness among different signals and network dependent variations. These fi
ndings can be implemented into stimulation protocols for first in man and
proof of concept studies aiming at further improvement of CR stimulation.\
nIn the second part\, I will present a computational model which account f
or combining different time scales with synaptic (STDP) and structural pla
sticity. The latter one refers to a mechanism that deletes or generates sy
napses in order to homeostatically adapt the firing rates of neurons to a
set point-like target firing rate in the course of days to months. Such a
model succeeds to explain a clinically relevant dynamic phenomenon which c
ould not be explained in the STDP-only models so far. It also provides a p
lausible mechanism that explains why CR stimulation may become more effect
ive (i.e.\, require less stimulation duration) when repeatedly delivered (
in the course of the treatment). This aspect is crucial from a clinical st
andpoint to further optimize dosing (and hence treatment outcome) of CR st
imulation."\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Helen Christodoulidi (University of Lincoln)
DTSTART:20210610T140000Z
DTEND:20210610T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/30
DESCRIPTION:Title: The role of KdV and Toda in the FPUT problem\nby Helen Chri
stodoulidi (University of Lincoln) as part of MESS (Mathematics Essex Semi
nar Series)\n\n\nAbstract\nThe celebrated Fermi-Pasta-Ulam-Tsingou model i
s a long chain of coupled nonlinear oscillators representing the simplest
one-dimensional analogue of atoms in a crystal. This system represents a b
enchmark in the history of nonlinear science: The FPUT problem sparked the
birth of both computational mathematics and integrable systems. Most nota
bly\, it is the first dynamical system numerically integrated on a compute
r while its enigmatic non-ergodic behaviour is puzzling the scientists for
over 65 years\, with innumerable works published. In this talk I will foc
us on the role of two integrable models\, namely I) the Korteweg-de Vries
equation (KdV)\, which describes waves on shallow water surfaces\, and II)
the Toda lattice\, in explaining FPUT's non-ergodic behaviour at low ener
gies.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kirk McDermott (Slippery Rock University)
DTSTART:20210624T140000Z
DTEND:20210624T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/31
DESCRIPTION:Title: On the shift dynamics of groups of Fibonacci type\nby Kirk
McDermott (Slippery Rock University) as part of MESS (Mathematics Essex Se
minar Series)\n\n\nAbstract\nA group is said to be cyclically presented if
it admits a presentation with a certain cyclic symmetry. Such a symmetry
induces a periodic automorphism of the group called the shift\, and its dy
namics strongly impacts the structure of the group. In this talk\, we inve
stigate the shift dynamics of the cyclically presented groups of Fibonacci
type. These groups have a rich history and have been studied from a varie
ty of perspectives\, from combinatorial group theory to 3-manifold topolog
y. We use these perspectives to study the shift dynamics and go on to intr
oduce topological and computational techniques for identifying fixed point
s.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ihechukwu Chinyere (University of Essex)
DTSTART:20210701T140000Z
DTEND:20210701T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/32
DESCRIPTION:Title: Hyperbolicity of certain cyclically presented groups\nby Ih
echukwu Chinyere (University of Essex) as part of MESS (Mathematics Essex
Seminar Series)\n\n\nAbstract\nIn his 1992 article titled “A funny prope
rty of sphere and equations over groups” Klyachko used the car-crash lem
ma to establish the Kervaire conjecture for torsion-free groups. Inspired
by this construction we use ant-lane argument to prove that certain cyclic
ally presented groups are hyperbolic.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marina Logares (Universidad Complutense de Madrid)
DTSTART:20211021T140000Z
DTEND:20211021T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/33
DESCRIPTION:Title: The many facets of Higgs bundles\nby Marina Logares (Univer
sidad Complutense de Madrid) as part of MESS (Mathematics Essex Seminar Se
ries)\n\n\nAbstract\nSince their origin in the late 80’s\, Higgs bundles
manifest as fundamental objects which are ubiquitous in contemporary math
ematics and theoretical physics. Some prominent examples of this ubiquity
are their role as integrable systems\, in Langlands duality and Mirror Sym
metry\, and in representation theory as character varieties. In this talk
we shall give an introduction to Higgs bundles\, together with a glimpse o
f how they play all these roles mentioned above.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dimitrios Mitsotakis (Victoria University of Wellington)
DTSTART:20220224T150000Z
DTEND:20220224T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/34
DESCRIPTION:Title: Nonlinear and dispersive waves in a basin\nby Dimitrios Mit
sotakis (Victoria University of Wellington) as part of MESS (Mathematics E
ssex Seminar Series)\n\n\nAbstract\nSurface water waves of significant int
erest such as tsunamis and solitary waves are nonlinear and dispersive wav
es. Unluckily\, the equations describing the propagation of surface water
waves known as Euler’s equations are immensely hard to solve. In this pr
esentation we show that among the so many simplified systems of PDEs propo
sed as alternative approximations to Euler’s equations there is only one
proven to be well-posed (in Hadamard’s sense) in bounded domains with s
lip-wall boundary conditions. We also show that the system obeys most of t
he physical laws that acceptable water waves equations must obey. Validati
on with laboratory data is also presented.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bernd Sturmfels (MPI Leipzig)
DTSTART:20211014T140000Z
DTEND:20211014T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/35
DESCRIPTION:Title: Linear PDE with Constant Coefficients\nby Bernd Sturmfels (
MPI Leipzig) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstr
act\nWe discuss practical methods for computing the space of solutions to
an arbitrary homogeneous linear system of partial differential equations w
ith constant coefficients. These rest on the Fundamental Principle of Ehre
npreis--Palamodov from the 1960s. We develop this further using recent adv
ances in computational commutative algebra.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alexei Vernitski (University of Essex)
DTSTART:20211028T140000Z
DTEND:20211028T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/36
DESCRIPTION:Title: Looking for ways of presenting knots which help artificial inte
lligence to learn to manipulate knots\nby Alexei Vernitski (University
of Essex) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstrac
t\nKnots (like the one presented in the picture) are difficult to begin to
study mathematically because mathematical notation works well with words
or matrices\, and a knot diagram cannot be easily represented as either. T
his is why in knot theory much effort is invested in representing knots in
the form of words or matrices (for example\, you might have heard of Gaus
s words or Goeritz matrices). Now suppose we want the computer to work wit
h knots\; then we face a different kind of problem\, namely\, the computer
does not possess human 2D and 3D intuition. To enable the computer to sta
rt exploring knots\, we need to trawl through existing representations of
knots (or invent new ones) looking for those which will compensate for the
computer not possessing human spatial intuition.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Agnid Banerjee (Tata Institute of Fundamental Research)
DTSTART:20211104T150000Z
DTEND:20211104T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/37
DESCRIPTION:Title: Strong unique continuation for heat operator with Hardy type p
otential\nby Agnid Banerjee (Tata Institute of Fundamental Research) a
s part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nI will ta
lk about strong unique continuation for the heat operator with Hardy type
potential. This is. based on a recent joint work with Nicola Garofalo and
Ramesh Manna. A strong unique continuation property for the heat operator
with Hardy type potential. J. Geom. Anal. 31 (2021)\, no. 6\, 5480–5504
.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pieter Kleer (Tilburg University)
DTSTART:20211118T150000Z
DTEND:20211118T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/39
DESCRIPTION:Title: MCMC methods for sampling graphs with given degree constraints<
/a>\nby Pieter Kleer (Tilburg University) as part of MESS (Mathematics Ess
ex Seminar Series)\n\n\nAbstract\n"Efficiently sampling graphs with given
degree constraints is an important open problem\, both in theory and pract
ice. In this talk\, I will give an overview of some Markov Chain Monte Car
lo algorithms for various type of degree constraints: Hard degree constrai
nts\, degree interval constraints and joint degree distribution constraint
s.\nThese algorithms are based on making small random changes (to a given
initial graph) that preserve the desired constraints. The goal is to under
stand how many of these small changes are needed until the resulting distr
ibution\, over the set of all graphs satisfying the given constraints\, is
close to the (uniform) stationary distribution of the induced Markov chai
n.\nBased on joint work with Georgios Amanatidis (University of Essex)."\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nikos Katzourakis (University of Reading)
DTSTART:20211125T150000Z
DTEND:20211125T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/40
DESCRIPTION:Title: Generalised vectorial $\\infty$-eigenvalue nonlinear problems f
or $L^\\infty$ functionals\nby Nikos Katzourakis (University of Readin
g) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\n"Let
$\\Omega \\Subset \\mathbb R^n$\, $f \\in C^1(\\mathbb R^{N\\times n})$ an
d $g\\in C^1(\\mathbb R^N)$\, where $N\,n \\in \\mathbb N$. In this talk I
will discuss the minimisation problem of finding $u \\in W^{1\,\\infty}_0
(\\Omega\; \\mathbb R^N)$ that satisfies\n$$\\big\\| f(\\mathrm D u) \\bi
g\\|_{L^\\infty(\\Omega)} \\! = \\inf \\Big\\{\\big\\| f(\\mathrm D v) \\b
ig\\|_{L^\\infty(\\Omega)} \\! : \\ v \\! \\in W^{1\,\\infty}_0(\\Omega\;\
\mathbb R^N)\, \\\, \\| g(v) \\|_{L^\\infty(\\Omega)}\\! =1\\Big\\}\,$$\nu
nder natural assumptions on $f\,g$. This includes the $\\infty$-eigenvalue
problem as a special case. I will describe the existence of a minimiser $
u_\\infty$ with extra properties\, derived as the limit of minimisers of a
pproximating constrained $L^p$ problems as $p\\to \\infty$. A central con
tribution and novelty of this work is that $u_\\infty$ is shown to solve a
divergence PDE with measure coefficients\, whose leading term is a diverg
ence counterpart equation of the non-divergence $\\infty$-Laplacian. The r
esults are new even in the scalar case of the $\\infty$-eigenvalue problem
. The talk is based on the preprint https://arxiv.org/abs/2103.15911."\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Livia Campo (University of Birmingham)
DTSTART:20211209T150000Z
DTEND:20211209T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/41
DESCRIPTION:Title: Morphing shapes: a guide to birational surgeries\nby Livia
Campo (University of Birmingham) as part of MESS (Mathematics Essex Semina
r Series)\n\n\nAbstract\n"Algebraic Geometry studies geometric shapes (alg
ebraic varieties) that are defined as solutions of polynomial equations in
many variables. Such shapes can be distinguished according to their curva
ture: positive\, zero\, or negative. In this talk I will focus on those wi
th positive curvature\, called Fano varieties.\nThe Minimal Model Program
offered a novel approach to the classification of Fano varieties. As a con
sequence\, many of them can be transformed into one another by performing
sequences of specific (birational) modifications. During my talk I will gi
ve an account of these birational surgeries carrying out a basic example\,
and I will describe a picture that illustrates this procedure in a more c
omplicated setting."\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theodoros Papazachariou (University of Essex)
DTSTART:20211216T150000Z
DTEND:20211216T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/42
DESCRIPTION:Title: GIT and K-stability for Fano varieties\nby Theodoros Papaza
chariou (University of Essex) as part of MESS (Mathematics Essex Seminar S
eries)\n\n\nAbstract\nIn algebraic geometry\, one studies varieties which
occur as solutions to polynomial equations. In particular\, we deal with p
rojective varieties which are the solution spaces of homogeneous polynomia
ls. An important category of geometric objects in algebraic geometry is sm
ooth Fano varieties\, which are varieties with positive curvature. As such
they can be thought of as higher dimensional analogues of the sphere. The
se have been classified in 1\, 8 and 105 families for curves\, surfaces an
d threefolds respectively\, while in higher dimensions the number of Fano
families is yet unknown\, although we know that their number is bounded. A
n important current problem is compactifying these families into moduli sp
aces\, i.e.\, spaces which parametrise objects with some common properties
. The aim for the above is so that we can study these families into more d
etails. In this talk I will discuss how one can obtain such compactificati
ons using Geometric Invariant Theory (GIT)\, which studies (algebraic) gro
up actions on varieties. I will also discuss how one can get similar compa
ctifications using the theory of K-stability\, and the links this has to G
IT.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:CANCELED DUE TO STRIKE
DTSTART:20211202T150000Z
DTEND:20211202T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/43
DESCRIPTION:Title: CANCELED DUE TO STRIKE\nby CANCELED DUE TO STRIKE as part o
f MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nThis week's semin
ar is cancelled due to industrial action on higher education.\nPlease see
https://www.theguardian.com/education/2021/nov/16/uk-universities-and-coll
eges-face-three-days-of-strikes-in-december for more details.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Zulkarnain (University of Essex)
DTSTART:20220120T150000Z
DTEND:20220120T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/44
DESCRIPTION:Title: Localisation of energy in the FPUT-a system with variability an
d its chaotic behaviour\nby Zulkarnain (University of Essex) as part o
f MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nFermi\, Pasta\, U
lam\, and Tsingou studied one-dimensional lattices to model the crystal ev
olution towards thermal equilibrium. They expected to observe the equipart
ition of energy as predicted by the Boltzmann-Gibbs (BG) statistics due to
nonlinearities in their model. However\, they noticed that almost all ene
rgy was back to its initial state after some period of steady state. This
phenomenon\, well-known as the FPUT recurrences\, led to numerous discover
ies in mathematics and physics. A recent study by Nelson et al. shows that
if variability is incorporated in the FPUT system\, it will limit the obs
ervance of recurrences. They numerically show that this variability can pr
event recurrences in this system. In this talk\, I will discuss two-modes
approximations in the normal mode coordinate to explain the localisation o
f energy for large enough variabilities. Moreover\, we also investigate th
e chaotic behaviour of the FPUT-α system for different numbers of particl
es as we increase the variabilities by computing the maximum Lyapunov expo
nent and the SALI of this system.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/44/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Huseyin Yildirim (University of Essex)
DTSTART:20220127T150000Z
DTEND:20220127T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/45
DESCRIPTION:Title: Network re-construction for the complex data generated from the
discrete and continuous models\nby Huseyin Yildirim (University of Es
sex) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nNet
work Inference for complex systems is crucial to infer connectivity among
variables in many subject areas\, ranging from finance to health sciences.
Therefore\, it is a rapidly developing area with newly proposed methods.
In this seminar talk\, I will present the Mutual Information (MI)\, double
normalised Mutual Information Rate (MIR) methods and their lagged version
s to reconstruct the initial network for artificial data generated by the
coupled logistic map\, coupled circle map\, and coupled Hindmarsh-Rose (HR
) model of neuronal activity. The authors in [1] have already showed that
the double normalised MIR can capture all links in the original network fo
r discrete and continuous dynamical models when specific conditions are me
t. Our study proposes that the lagged versions of MI and double normalised
MIR can infer network topology 100% successfully for small time series. F
inally\, our results show that the latter methods have better performance
when using the instantaneous frequency of the membrane potential in the HR
model as a probe to infer network structure.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/45/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Valerij Romanovskij (University of Maribor)
DTSTART:20220203T150000Z
DTEND:20220203T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/46
DESCRIPTION:Title: Integrability and limit cycles in polynomial systems of ODEs\nby Valerij Romanovskij (University of Maribor) as part of MESS (Mathema
tics Essex Seminar Series)\n\n\nAbstract\n"We discuss two problems related
to the theory of olynomial plane differential systems\, that is\, syst
ems of the form \n$$\\frac{dx}{dt}=P_{n}(x\,y)\, \\ \\ \\ \n\\frac{dy}{dt}
=Q_{n}(x\,y)\,\n$$\nwhere $P_{n}(x\,y)\, Q_{n}(x\,y)$ are polynomials of d
egree $n$\, $x$ and $y$ are real unknown functions.\n\nThe first one is t
he problem of local integrability\, that is\, the problem of finding loca
l analytic integrals in a neighborhood of singular points of system (1).
We present a computational approach to find integrable systems within gi
ven parametric families of systems and describe some mechanisms of integra
bility. \n\n\nThe second problem is called the cyclicity problem\, or the
local 16th Hilbert problem\, and is related to the stimation of the numbe
r of limit cycles arising in system (1) after perturbations of integrable
systems. The approach is algorithmic and is based on algorithms of computa
tional commutative algebra relying on the Groebner bases theory. \n"\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/46/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dimitra Kosta (University of Edinburgh)
DTSTART:20220210T150000Z
DTEND:20220210T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/47
DESCRIPTION:by Dimitra Kosta (University of Edinburgh) as part of MESS (Ma
thematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/47/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Zihui Zhao (University of Chicago)
DTSTART:20220217T150000Z
DTEND:20220217T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/48
DESCRIPTION:Title: Quantitative unique continuation\nby Zihui Zhao (University
of Chicago) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstr
act\nUnique continuation theorem is a fundamental property of harmonic fun
ctions\, as well as solutions to a large class of elliptic and parabolic P
DEs. It says that if a harmonic function vanishes to infinite order at a p
oint\, the function must vanish everywhere. In the same spirit\, there is
a large class of quantitative unique continuation theorems\, which use the
local information about the growth rate of a harmonic function to deduce
global information. In particular\, I will talk about how to estimate the
size of the singular set $\\{u=0=|\\nabla u|\\}$ of a harmonic function u.
This is joint work with Carlos Kenig.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/48/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alyssa Genschaw (Milwaukee School of Engineering)
DTSTART:20220303T150000Z
DTEND:20220303T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/49
DESCRIPTION:Title: Hausdorff Dimension of Caloric Measure\nby Alyssa Genschaw
(Milwaukee School of Engineering) as part of MESS (Mathematics Essex Semin
ar Series)\n\n\nAbstract\nCaloric measure is a probability measure support
ed on the boundary of a domain in R^{n+1} = R^n × R (space × time) that
is related to the Dirichlet problem for the heat equation in a fundamental
way. Equipped with the parabolic distance\, R^{n+1} has Hausdorff dimensi
on n+ 2. We prove that (even on domains with geometrically very large boun
dary)\, the caloric measure is carried by a set of Hausdorff dimension at
most n + 2 − beta_n for some beta_n > 0. The corresponding theorem for h
armonic measure is due to Bourgain (1987)\, but the proof in that paper co
ntains a gap. Additionally\, we prove a caloric analogue of Bourgain’s a
lternative. I will briefly discuss the results\, including how we fix the
gap in the original proof. This is joint work with Matthew Badger.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/49/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christian Bick (University of Exeter)
DTSTART:20220310T150000Z
DTEND:20220310T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/50
DESCRIPTION:Title: Coupled Oscillator Networks: Structure\, Interactions\, and Dyn
amics\nby Christian Bick (University of Exeter) as part of MESS (Mathe
matics Essex Seminar Series)\n\n\nAbstract\nThe collective dynamics of cou
pled oscillatory processes govern many aspects crucial to our lives\, whet
her it is the synchronous beating of our heart cells\, collective activity
of neurons in the brain\, or power grid networks that operate in a stable
frequency regime. In this talk we discuss how the collective network dyna
mics are shaped by the network structure (what oscillator is coupled to wh
at other oscillator) and the network interactions (how one oscillator is c
oupled to another). We discuss in particular how ""higher-order"" interact
ions\, which have attracted tremendous attention in recent years\, give ri
se to heteroclinic and chaotic dynamics.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/50/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dimitra Kosta (University of Edinburgh)
DTSTART:20220317T150000Z
DTEND:20220317T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/51
DESCRIPTION:Title: Unboundedness of Markov complexity of monomial curves in for n
≥ 4\nby Dimitra Kosta (University of Edinburgh) as part of MESS
(Mathematics Essex Seminar Series)\n\n\nAbstract\nComputing the complexit
y of Markov bases is an extremely challenging problem\; no formula is know
n in general and there are very few classes of toric ideals for which the
Markov complexity has been computed. A monomial curve $C$ in $ \\mathbb{A}
^3$ has Markov complexity $m(C)$ two or three. Two if the monomial curve
is a complete intersection and three otherwise. Our main result shows that
there is no $d \\in \\mathbb{N}$ such that $m(C) \\leq d$ for all monom
ial curves C in $ \\mathbb{A}^4$. The same result is true even if we rest
rict to complete intersections. We extend this result to all monomial curv
es in $ \\mathbb{A}^n$\, where $n \\geq 4$.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/51/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eabhnat Ni Fhloinn and Aidan Fitzsimons (Dublin City University)
DTSTART:20220324T150000Z
DTEND:20220324T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/52
DESCRIPTION:Title: Problem-solving Potential within the field of mathematics\n
by Eabhnat Ni Fhloinn and Aidan Fitzsimons (Dublin City University) as par
t of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nProblem-solvin
g Potential (PsP) is a triad construct\, developed as part of a doctoral s
tudy\, that encompasses a student's mindset\, their mathematical resilienc
e\, and their problem-solving skills\; which together influence the studen
t's potential in mathematical problem-solving. In this talk\, I will outli
ne that theory that underlines PsP\, its relevance to the teaching of math
ematics\, and the context and environment in which the PsP has been studie
d thus far.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/52/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos Zygalakis (University of Edinburgh)
DTSTART:20220428T140000Z
DTEND:20220428T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/53
DESCRIPTION:Title: Connections Between Optimization and Sampling Algorithms\nb
y Konstantinos Zygalakis (University of Edinburgh) as part of MESS (Mathem
atics Essex Seminar Series)\n\n\nAbstract\nOptimization and Sampling probl
ems lie in the heart of Bayesian inverse problems. The ability to solve su
ch inverse problems depends crucially on the efficient calculation of quan
tities relating to the posterior distribution\, giving thus rise to comput
ationally challenging high dimensional optimization and sampling problems.
In this talk\, we will connect the corresponding optimization and samplin
g problems to the large time behaviour of solutions to (stochastic) differ
ential equations. Establishing such a connection allows to utilise existin
g knowledge from the field of numerical analysis of differential equations
. In particular\, two very important concepts are numerical stability and
numerical contractivity. In the case of linear differential equations thes
e two concepts coincide\, but with the exception of some very simple Runge
-Kutta methods such the Euler method in the non-linear case numerical stab
ility doesn’t imply numerical contractivity [1]. However\, the recently
introduced framework of integral quadratic constraints and Lyapunov functi
ons [2\, 3] allows for bridging this gap between linearity and non-lineari
ty in the case of (strongly) convex functions. We will use this framework
to study a large class of strogly convex optimization methods and give an
alternative explanation for the good properties of Nesterov method\, as we
ll as highlight the reasons behind the failure of the heavy ball method [2
]. In addition\, using similar ideas [4]\, we will present a general frame
work for the non-asymptotic study of the 2-Wasserstein distance between th
e invariant distribution of an ergodic stochastic differential equation an
d the distribution of its numerical approximation in the strongly log-conc
ave case. This allows us to study in a unified way a number of different i
ntegrators proposed in the literature for the overdamped and underdamped L
angevin dynamics.\n\n\n[1] J. M. Sanz Serna and K. C. Zygalakis\, Contract
ivity of Runge–Kutta Methods for Convex\nGradient Systems\, SIAM Journal
on Numerical Analysis 58(4):2079-2092\, 2020.\n\n[2] L. Lessard\, B. Rech
t\, and A. Packard\, Analysis and design of optimization algorithms via in
tegral quadratic constraints\, SIAM Journal on Optimization\, 26(1):57–9
5\, 2016.\n\n[3] M. Fazlyab\, A. Ribeiro\, M. Morari\, and V. M. Preciado\
, Analysis of optimization algorithms via integral quadratic constraints:
nonstrongly convex problems\, SIAM Journal on Optimization\, 28(3):2654–
2689\, 2018.\n\n[4] J. M. Sanz Serna and K. C. Zygalakis\, Wasserstein dis
tance estimates for the distributions of numerical approximations to ergod
ic stochastic differential equations\, Journal of Machine Learning Researc
h\, 22\, 1--37\, 2021\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/53/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Riikka Kangaslampi (Tampere University)
DTSTART:20220519T140000Z
DTEND:20220519T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/54
DESCRIPTION:Title: Ollivier--Ricci curvature on graphs\nby Riikka Kangaslampi
(Tampere University) as part of MESS (Mathematics Essex Seminar Series)\n\
n\nAbstract\nCurvature is a fundamental notion in the study of smooth Riem
annian manifolds. This notion has been generalized in various ways from th
e smooth setting of manifolds to more general metric spaces. Several adapt
ations of Ricci curvature such as Bakry-Emery curvature\, Ollivier-Ricci c
urvature\, entropic curvature introduced by Erbar and Maas\, and Forman cu
rvature\, have emerged on graphs in recent years\, and there is very activ
e research on these notions. These discrete Ricci curvature notions have a
lso been shown to play significant roles in various applied fields.\n\nIn
this talk I will focus on the Ollivier-Ricci curvature in the discrete set
ting of combinatorial graphs. This curvature notion\, based on optimal tra
nsportation\, is due to Yann Ollivier. I will introduce the Ollivier-Ricci
curvature and present some examples\, basic properties and applications.
I will also discuss a few results like the classification of cubic graphs
with non-negative Ollivier-Ricci curvature and of cubic graphs with girth
five that have zero curvature\, as well as the behaviour of the Ollivier-R
icci curvature under graph products.\n\nThe talk is based on joint work wi
th D. Cushing\, S. Kamtue\, V. Lipiäinen\, S. Liu\, N. Peyerimhoff\, and
G.W. Stagg.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/54/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Istvan Kiss (University of Sussex)
DTSTART:20220526T140000Z
DTEND:20220526T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/55
DESCRIPTION:Title: Epidemics on networks: from exact to mean-field models includin
g results and challenges\nby Istvan Kiss (University of Sussex) as par
t of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\nThe contact st
ructure of a population plays an important role in the transmission of i
nfectious diseases. Often individuals are represented by nodes and contact
s between them by links. This gives rise to a network/graph which allows u
s to depart from the homogeneous random mixing assumption implied by the w
idely used population dynamic models based on ordinary differential equati
ons. While networks offer a great deal of flexibility to model heterogenei
ty in individuals and their contacts/mixing\, they lead to high-dimensiona
l models even when the number of nodes is small. Such network-based models
are difficult to analyse both analytically and numerically. In this talk\
, I will start from the exact formulation of an epidemic model on a networ
k and show how the exact model can be reduced to various mean-field models
(systems with a few ordinary differential equations). In particular\, I
will discuss the pairwise and edge-based compartmental models and will sho
w how the network manifest itself in these models and what analytic insigh
ts can be gained from these simplified approximations. I will briefly touc
h upon the relationship between these and the exact model. Finally\, I wil
l present a number of further extensions\, such as for non-Markovian epide
mic dynamics and adaptive networks\, and discuss future challenges.\n\n[1
] I Z Kiss\, J C Miller\, and P L Simon. Mathematics of Epidemics on Netwo
rks: from exact to approximate models. Springer\, 2017.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/55/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Esmaeel Asadi (Institute for Advanced Studies in Basic Science\, Z
anjan\, Iran)
DTSTART:20220512T140000Z
DTEND:20220512T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/56
DESCRIPTION:Title: geometry of integrable systems\; introduction by examples\n
by Esmaeel Asadi (Institute for Advanced Studies in Basic Science\, Zanjan
\, Iran) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAbstract\
nIf a curve moves in a certain way In a geometric space\, what would be th
e evolution of its invariants? In this talk we focus on some curve flow i
n low dimensional Euclidean space and see how it is related to evolution o
f its classical curvature and torsion in the form of integrable PDEs and d
iscuss the possible extension of the idea behind some multi-components int
egrable systems.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/56/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hamid Abban (Loughborough University)
DTSTART:20220609T140000Z
DTEND:20220609T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/57
DESCRIPTION:Title: Fano varieties: their geometry\, classification\, and parametri
sation\nby Hamid Abban (Loughborough University) as part of MESS (Math
ematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/57/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theresa Smith (University of Bath)
DTSTART:20220623T140000Z
DTEND:20220623T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/58
DESCRIPTION:Title: https://essex-university.zoom.us/j/97080588123\nby Theresa
Smith (University of Bath) as part of MESS (Mathematics Essex Seminar Seri
es)\n\n\nAbstract\nIn this talk\, I will present ongoing research I am car
rying out following a productive Knowledge Transfer Partnership with Mayde
n\, a Bath-based company that develops the most widely used electronic pat
ient record system in NHS psychological therapies services. The key statis
tical challenge in this project is predicting the likelihood of multiple c
ompeting outcomes while incorporating new data on subjects as it becomes a
vailable so that these predictions can be updated dynamically throughout a
course of psychological therapy. I will discuss two existing paradigms fo
r dynamic prediction: joint modelling and landmarking\, focusing on the tr
ade-offs in computational challenges and the statistical properties of the
two approaches. I will also discuss practical barriers to embedding these
approaches within decision support tools in a patient records systems.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/58/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Baha Tamimi (University of Essex)
DTSTART:20220630T140000Z
DTEND:20220630T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/59
DESCRIPTION:Title: The sandpile & Smith groups of certain classes of graphs\nb
y Baha Tamimi (University of Essex) as part of MESS (Mathematics Essex Sem
inar Series)\n\n\nAbstract\nThe Smith group and the sandpile group are gra
ph invariants. It is common to calculate these groups algorithmically usin
g the Smith normal form. We show an alternative combinatorial approach usi
ng Tietze transformation and apply it to calculate a subset of known graph
families like integral circulant graphs and walk regular graphs.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/59/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tiago Duarte-Guerreiro (University of Essex)
DTSTART:20221013T140000Z
DTEND:20221013T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/60
DESCRIPTION:Title: Non-solidity of Uniruled Varieties\nby Tiago Duarte-Guerrei
ro (University of Essex) as part of MESS (Mathematics Essex Seminar Series
)\n\nLecture held in NTC.1.04.\n\nAbstract\nThe minimal model program (MMP
) is a far-reaching conjecture in birational geometry that says that any c
omplex algebraic variety is built up from 3 basic building blocks: Mori fi
bre spaces\, Calabi-Yau fibrations and Canonically polarised varieties. Al
though the MMP is still conjectural\, in the seminal paper of Birkar\, Cas
cini\, Hacon and Mckernan\, (BCHM)\, the authors prove\, among other impor
tant results\, that varieties covered by rational curves (uniruled varieti
es) are birational to Mori fibre spaces. In this talk we give a criterion
to establish when such a Mori fibre space is a strict fibration\, that is\
, a Mori fibre space with strictly positive dimensional basis. Moreover\,
there are usually many different possible outcomes when applying the MMP
to a uniruled variety\, so it becomes natural to study their relations. If
time allows\, I will explain how to obtain explicit birational maps betwe
en certain Mori fibre spaces.\n\nThis is joint work with Livia Campo.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/60/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ryan Hynd (Penn University)
DTSTART:20221020T140000Z
DTEND:20221020T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/61
DESCRIPTION:Title: The Blaschke–Lebesgue theorem revisited\nby Ryan Hynd (Pe
nn University) as part of MESS (Mathematics Essex Seminar Series)\n\nLectu
re held in STEM 3.1.\n\nAbstract\nA curve of constant width has the proper
ty that any two parallel supporting lines are the same distance apart in a
ll directions. It turns out that a circle encloses the most area and a Re
uleaux triangle encloses the least area among all curves of a given width.
The latter fact was proved independently by Blaschke and Lebesgue. We wi
ll discuss this theorem\nand what is thought to be true for the analogous
shapes in three-dimensions.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/61/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sema Gunturkun (University of Essex)
DTSTART:20221027T140000Z
DTEND:20221027T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/62
DESCRIPTION:Title: Growth of the Hilbert function of ideals containing a regular s
equence\nby Sema Gunturkun (University of Essex) as part of MESS (Math
ematics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nFa
mous Macaulay’s theorem describes the growth of Hilbert functions of hom
ogeneous ideals in $K[x_1\,\\ldots\, x_n]$. Eisenbud\, Green and Harris c
onjectured a finer bound on the Hilbert function so that it associates wit
h the structure of the ideal such as the degrees of a regular sequence it
contains. In this talk\, we discuss the current state of this conjecture\
, and especially focus on the ideal containing a regular sequence of quadr
atic forms.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e05a6
7b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/62/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Annalisa Calini (College of Charleston\, USA)
DTSTART:20221103T150000Z
DTEND:20221103T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/63
DESCRIPTION:Title: Knotted solutions of the Vortex Filament Equation and their sta
bility properties\nby Annalisa Calini (College of Charleston\, USA) as
part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in STEM 3
.1.\n\nAbstract\nThe Vortex Filament Equation (VFE) or binormal flow–a l
ocalized induction approximation of the Biot-Savart law–describes the se
lf-induced dynamics of a vortex filament in a 3-dimensional ideal fluid. I
ts connection with the focusing cubic Nonlinear Schrödinger Equation (NLS
) through the Hasimoto map allows the use of tools from soliton theory to
construct large classes of solutions. \n\nIn this first part of this talk
I will focus on the construction of a family of knotted vortex filaments
coming from finite-genus solutions of the NLS\, including torus and cable
knots. These solutions do not exhibit self-crossing during the VFE evoluti
on\, thus representing physically plausible models of vortex filaments. In
the second part\, I will discuss a framework for studying the stability o
f finite-genus solutions of the VFE and present several interesting exampl
es.\n\nThe seminar presentation of Prof Calini at Essex is partially funde
d by Isaac Newton Institute for Mathematical Sciences\, Cambridge.\n\nhttp
s://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/pr
ojects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/63/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bruno Poggi (Universitat Autònoma de Barcelona)
DTSTART:20221110T150000Z
DTEND:20221110T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/64
DESCRIPTION:Title: $L^p$-solvability of the Poisson problem and its applications t
o the regularity problem.\nby Bruno Poggi (Universitat Autònoma de Ba
rcelona) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture hel
d in STEM 3.1.\n\nAbstract\nWe introduce the concept of $L^p$-solvability
of the Poisson problem\n\\[\n\\left\\{\\begin{array}{ll}-\\operatorname{d
iv}A\\nabla w=H-\\operatorname{div} F\,&\\text{in }\\Omega\,\\\\w=0\,&\\te
xt{on }\\partial\\Omega\,\\end{array}\\right.\n\\]\nunder certain natural
quantitative assumptions on $H$ and $F$\, with its corresponding new estim
ate (new even for the Laplacian)\, and study several applications. By $L^p
$ solvability\, we mean uniform bounds on the $L^p$ norm of the non-tangen
tial maximal function of $w$. An analogous concept is classical and centra
l for the theory of boundary value problems for \\emph{homogeneous} second
-order elliptic PDEs. Our main application is towards the $L^p$ Dirichlet-
regularity problem for elliptic operators $-\\operatorname{div} A\\nabla$
whose matrix $A$ satisfies the Dahlberg-Kenig-Pipher condition (this is\,
roughly speaking\, a Carleson measure condition on $|\\nabla A|^2\\operato
rname{dist}(\\cdot\,\\partial\\Omega)$)\, in the geometric generality of b
ounded Corkscrew domains with uniformly rectifiable boundaries. This solve
s an open problem from 2001. Other applications include new characterizati
ons of the $L^p$-solvability of the Dirichlet problem\, and a non-tangenti
al maximal function estimate for the gradient of the Green's function\, in
Corkscrew domains with Ahlfors-regular boundaries. This is joint work wit
h Mihalis Mourgoglou and Xavier Tolsa.\n\nhttps://findyourway.essex.ac.uk/
bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c2
30405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/64/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ben Fairbairn (Birbeck University London)
DTSTART:20221117T150000Z
DTEND:20221117T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/65
DESCRIPTION:Title: Beauville Surfaces\, Structures and Groups\nby Ben Fairbair
n (Birbeck University London) as part of MESS (Mathematics Essex Seminar S
eries)\n\nLecture held in STEM 3.1.\n\nAbstract\nVery roughly speaking\, a
Beauville surface is a complex surface constructed by allowing a finite g
roup G act on the product of two compact Riemann surfaces. These have nume
rous nice properties and are easier to study than most complex surfaces si
nce the entire construction can be internalised into the group which we ca
ll a Beauville group. Numerous questions about constructing these and what
properties they can have been posed over the past twenty years or so. In
this talk we will discuss a handful of approaches to these objects that ha
ve been taken.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-
05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/65/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jing Ping Wang (University of Kent)
DTSTART:20221124T150000Z
DTEND:20221124T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/66
DESCRIPTION:Title: POSTPONED: Quantisations of the Volterra hierarchy\nby Jing
Ping Wang (University of Kent) as part of MESS (Mathematics Essex Seminar
Series)\n\n\nAbstract\nTHIS TALK IS POSTPONED.\n\nIn this talk\, we’ll
discuss a recently emerged approach to the problem of quantisation based o
n the notion of quantisation ideals. We prove that the nonabelian Volterra
together with the whole hierarchy of its symmetries admit a deformation q
uantisation\, and that all odd-degree symmetries of the Volterra hierarchy
admit also a non-deformation quantisation. The quantisation problem for p
eriodic Volterra hierarchy will also be discussed. In particular\, we show
that the Volterra system with period 3 admits a bi-quantum structure\, wh
ich can be regarded as a quantum deformation of its classical bi-Hamiltoni
an structure. This is a joint work with S. Carpentier and A.V. Mikhailov r
ecently published on Letters in Math. Phys.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/66/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Roberto Camassa (University of North Carolina)
DTSTART:20221201T150000Z
DTEND:20221201T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/67
DESCRIPTION:Title: Fluid-boundary interaction: confinement effects\, stratificatio
n and transport\nby Roberto Camassa (University of North Carolina) as
part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in STEM 3.
1.\n\nAbstract\nArguably some of the most interesting phenomena in fluid d
ynamics\, both\nfrom a mathematical and a physical perspective\, stem from
the interplay\nbetween a fluid and its boundaries. This talk will present
some examples of how boundary effects lead to remarkable outcomes. Singu
larities can form in finite time as a consequence of the continuum assumpt
ion when material surfaces are in smooth contact with horizontal boundarie
s of a fluid under gravity. For fluids with chemical solutes\, the presenc
e of boundaries impermeable to diffusion adds further dynamics which can g
ive rise to self-induced flows and the formation of coherent structures ou
t of scattered assemblies of immersed bodies. These effects can be analyti
cally and numerically predicted by simple mathematical models and observed
in “simple” experimental setups.\n\n\nThe seminar presentation of Pro
f Camassa at Essex is partially funded by Isaac Newton Institute for Mathe
matical Sciences\, Cambridge.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-
e3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/67/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Shirsho Mukherjee (University of Essex)
DTSTART:20221208T150000Z
DTEND:20221208T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/68
DESCRIPTION:Title: Regularity of quasilinear equations with Hormander vector field
s of step two\nby Shirsho Mukherjee (University of Essex) as part of M
ESS (Mathematics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbs
tract\nIn this talk\, some recent results on the regularity theory of quas
ilinear subelliptic equations shall be presented.\n\nThe main prototype of
such equations is the $p$-Laplacian equation defined on vector fields whi
ch\, together with their commutators\, span the tangent space at every po
int. I shall illustrate the proof of weak solutions being locally $C^{1\,\
\alpha}$ for every \n$1 < p < \\infty$.\n\nThis is a joint work with Giova
nna Citti.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a6
7b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/68/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Argha Mondal (Sidho-Kanho-Birsha University\, India)
DTSTART:20221215T150000Z
DTEND:20221215T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/69
DESCRIPTION:Title: The role of Mathematical pathways in modelling Computational Ne
urosciences\nby Argha Mondal (Sidho-Kanho-Birsha University\, India) a
s part of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/69/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Asma Hassannezhad (University of Bristol)
DTSTART:20230119T150000Z
DTEND:20230119T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/71
DESCRIPTION:Title: Isoperimetric inequalities for mixed Steklov eigenvalues on a s
urface\nby Asma Hassannezhad (University of Bristol) as part of MESS (
Mathematics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract
\nThe talk aims to give an overview of isoperimetric inequalities for the
Steklov eigenvalues on a surface with boundary. The Steklov problem descr
ibes a vibrating free drum with its mass concentrated along the boundary.
Its eigenvalue parameter appears in the boundary condition. We discuss how
(possibly hidden) symmetries of the underlying domain can lead to extendi
ng classical isoperimetric inequalities for Steklov eigenvalues to mixed S
teklov eigenvalues.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-
b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/71/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Peter Higgins (University of Essex)
DTSTART:20230126T150000Z
DTEND:20230126T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/72
DESCRIPTION:Title: The Biker-hiker problem\nby Peter Higgins (University of Es
sex) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in
NTC 2.05.\n\nAbstract\nThere are $n$ travellers who have $k$ bicycles and
they wish to complete a journey in the shortest possible time. We investi
gate optimal solutions of this problem where each traveller cycles for $k/
n$ of the journey. Each solution is represented by an $n \\times n$ binary
matrix $M$ with $k$ non-zero entries in each row and column.\n\nWe determ
ine when such a matrix gives an optimal solution. This yields an algorithm
of complexity $O(n^2 log n)$ that decides the question of optimality of
$M$.\n\nWe introduce three symmetries of matrices that preserve optimality
\, allowing identification of minimal non-optimal members of this class. A
n adjustment to optimal solutions that eliminates unnecessary handovers of
cycles is established\, which maintains all other features of the solutio
n.\n\nWe identify two mutually transpose solution types\, the first unique
ly minimises the number of handovers\, while the second keeps the number o
f separate cohorts to $3$ while bounding their overall separation\, in the
case where $2k$ does not exceed $n$\, to under $2/n$ of the journey.\n\n
https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/searc
h/projects/23/60ef1a872031e800c2303f9b\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/72/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vanni Noferini (Aalto University)
DTSTART:20230202T150000Z
DTEND:20230202T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/73
DESCRIPTION:Title: The limit empirical spectral distribution of random matrix poly
nomials\nby Vanni Noferini (Aalto University) as part of MESS (Mathema
tics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nThree
famous classic results concern the distributions of the roots of a random
polynomial and the eigenvalues of a random matrix or pencil. Under relati
vely mild assumptions on the distribution of the coefficients\, the former
is known to converge to the uniform distribution on the unit circle when
the degree $k$ approaches infinity. Under similarly unrestrictive assumpti
ons on the distributions of the entries\, the distribution of a random mat
rix eigenvalues is known to converge to the uniform distribution on the un
it disk (when the entries have mean 0 and variance $1/n$) when the size $n
$ approaches infinity. Several mathematicians have also independently deri
ved the distribution of the generalised eigenvalues of a random pencil: in
this case\, the distribution is uniform on the Riemann sphere. However\,
until the present work nothing was to my knowledge known about the eigenva
lues of a general random matrix polynomial\, which could be thought as an
intermediate case between a random matrix or pencil ($k=1$) and a random p
olynomial ($n=1$).\n\nIn this talk I plan to first give some gentle introd
uction\, thought for non-experts on random variables and random matrices\,
to the known results mentioned above. I will then move on to describe rec
ent new results that we obtained about the limit spectral distributions of
a random matrix polynomial\, both in the regime $k\\to\\infty$ and in the
case $n\\to\\infty$. After discussing the (easier) nonmonic case\, I will
also comment on what changes if the random matrix polynomial is assumed t
o be monic\, i.e.\, having all random coefficients except the leading one
which is taken to be the identity matrix.\n\nThe main tools from our resul
ts come both from random matrix theory and\nfrom deterministic matrix theo
ry. In particular\, we exploit\n(1) the replacement principle\, proven by
Tao\, Vu and Krishnapur\,\n(2) the logarithmic potential approach as propo
sed by Girko\, and\n(3) classic perturbation theory results.\n\nThe talk i
s based on joint work with Giovanni Barbarino\, also at Aalto.\n\nhttps://
findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/projec
ts/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/73/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Barbara Baumeister (University of Bielefeld)
DTSTART:20230209T150000Z
DTEND:20230209T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/74
DESCRIPTION:Title: Presentations of Artin groups and quasi-Coxeter elements\nb
y Barbara Baumeister (University of Bielefeld) as part of MESS (Mathematic
s Essex Seminar Series)\n\n\nAbstract\nAre the braid groups or more genera
lly the Artin groups suitable for cryptography? A basic question is whethe
r we can write the elements of the\ngroup in a nice normal form. We will
discuss this question by applying\na method due to Garside to the (Artin)
groups related to quasi-Coxeter elements.\n\nParts are joint work with Der
ek Holt\, Georges Neaime and Sarah Rees.\n\nOnline talk via zoom\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/74/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Liana Heuberger (University of Bath)
DTSTART:20230216T150000Z
DTEND:20230216T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/75
DESCRIPTION:Title: POSTPONED\nby Liana Heuberger (University of Bath) as part
of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/75/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cristiano Spotti (Aarhus University)
DTSTART:20230223T150000Z
DTEND:20230223T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/76
DESCRIPTION:Title: POSTPONED\nby Cristiano Spotti (Aarhus University) as part
of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/76/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sokratis Zikas (University of Poiters)
DTSTART:20230302T150000Z
DTEND:20230302T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/77
DESCRIPTION:Title: POSTPONED\nby Sokratis Zikas (University of Poiters) as par
t of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/77/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Igor Freire (Universidade Federal do ABC)
DTSTART:20230309T150000Z
DTEND:20230309T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/78
DESCRIPTION:Title: Cauchy problems and equations describing pseudospherical surfac
es\nby Dr Igor Freire (Universidade Federal do ABC) as part of MESS (M
athematics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\
nIn 1986 Chern and Tenenblat introduced the notion of a differential equat
ion describing pseudospherical surfaces. Roughly speaking\, smooth solutio
ns of these equations give rise to metrics of a surface of Gaussian curvat
ure K=-1. In this talk we discuss pseudospherical surfaces emanating from
Cauchy problems. We show that well-posed problems lead to uniqueness of th
e metric of the corresponding surface\, and discuss some limitations and o
pen problems.\n\nSTEM 3.1 https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11
eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/78/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Adam Thomas (University of Warwick)
DTSTART:20230323T150000Z
DTEND:20230323T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/79
DESCRIPTION:Title: The power and beauty of small matrices\nby Dr Adam Thomas (
University of Warwick) as part of MESS (Mathematics Essex Seminar Series)\
n\nLecture held in STEM 3.1.\n\nAbstract\nIn this talk we will start with
the humble set of $2\\times 2$ matrices over the complex numbers. From her
e\, we gently build up to the world of Lie algebras and then present some
beautiful theorems showing that the $2\\times2$ matrices are actually stil
l running the show. We will discuss some results focussing on these small
Lie algebras when we move away from the complex numbers and end with some
ongoing work (joint with David Stewart\, Manchester) on the case where the
entries of our matrices come from a field of characteristic 2.\n\nhttps:/
/findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/proje
cts/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/79/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prof Peter Higgins (University of Essex)
DTSTART:20230427T140000Z
DTEND:20230427T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/80
DESCRIPTION:Title: Algebras defined by equations\nby Prof Peter Higgins (Unive
rsity of Essex) as part of MESS (Mathematics Essex Seminar Series)\n\nLect
ure held in 5S.4.19.\n\nAbstract\nThis seminar is designed to be a general
talk for all DMS members based\non work I have been doing with Marcel Jac
kson on Algebras defined by Equations.\n\nWe have proved two theorems of g
eneral algebra that explain exactly what properties a class of algebras mu
st have in order for it to be definable by a list of equations. These equ
ations allow definition by the logical quantifiers ‘for all’ $\\forall
$\, ‘there exists’ $\\exists$\, ‘And’ $\\land$\, and ‘Or’ $\\l
or$ (but not negation\, and so not implication).\n\nClasses that may be d
efined without the use of ‘there exists’ are called varieties and have
long been known (Birkhoff’s theorem) to consist of algebras that are cl
osed under the taking of homomorphic images of subalgebras of direct produ
cts (HSP closed). Varieties may always be defined by identities. For exam
ple $xy = yx$ is the identity for Commutativity. Our second theorem chara
cterises equational classes that may be defined without the use of the ‘
for all’ quantifier.\n\nI will state\, explain\, (but not prove) these t
heorems. However\, most of the talk will concentrate on concrete examples
of these equational classes and how they relate to the theorem and to one
another. Our theorems were originally motivated by classes of semigroups\
, as so many extensively studied semigroup classes are not varieties but a
re equational in our sense.\n\nI will not assume any knowledge of semigrou
ps but will introduce examples and relevant facts during the talk itself.
\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/s
earch/projects/23/60ef1a832031e800c2303abf\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/80/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Alexei Vernitski (University of Essex)
DTSTART:20230504T140000Z
DTEND:20230504T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/81
DESCRIPTION:Title: Hard flat knots and circulant Gauss diagrams\nby Dr Alexei
Vernitski (University of Essex) as part of MESS (Mathematics Essex Seminar
Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nThis will be an informa
l and\, hopefully\, entertaining talk about my ongoing research. I study h
ard flat knots\, that is\, those that require one or more applications of
Reidemeister move 3 before a simplifying Reidemeister move 1 or 2 can be a
pplied. I notice that flat diagrams of torus knots are examples of hard fl
at knots\, and they have especially symmetric\nGauss diagrams\, which I ca
ll circulant Gauss diagrams.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e
3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/81/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Yan-long Fang (UCL)
DTSTART:20230511T140000Z
DTEND:20230511T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/82
DESCRIPTION:Title: Carleman estimates on hyperbolic inverse problems\nby Dr Ya
n-long Fang (UCL) as part of MESS (Mathematics Essex Seminar Series)\n\nLe
cture held in STEM 3.1.\n\nAbstract\nLet us consider the damped wave opera
tor\n\\(\nP:=\\partial_t^2-\\Delta_g + Q_1\\partial_t + Q_0.\n\\)\nSuppose
$u$ solves $Pu=F$ on $\\mathbb{R}_+\\times \\Omega$ with some boundary co
nditions on $\\mathbb{R}_+\\times \\partial \\Omega$. Can we recover the d
amping term $Q_1$ or/and the potential term $Q_0$ from the partial boundar
y data $u|_{[0\,T]\\times \\Gamma}$\, where $\\Gamma \\subset \\partial \\
Omega$? If possible\, what are the conditions on $\\Gamma$\, initial data
of $u$ and $T$?\n\nIt is well known that Carleman type inequalities are ve
ry useful in establishing unique continuations for PDE problems. I will br
iefly explain how one could use Carleman inequalities to obtain some stabi
lity estimates of the operator $P$ subject to Dirichlet or Robin boundary
conditions. Moreover\, one could read out the conditions on $\\Gamma$\, th
e initial data and $T$ from the stability estimates. If time allows\, I wi
ll briefly\nexplain how one can use microlocal analysis to improve the sta
bility estimates obtained by Carleman inequalities.\n\nThe talk is based o
n a joint work with Daniel Lesnic.\n\nhttps://findyourway.essex.ac.uk/bcdc
98e0-e3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c23040
5d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/82/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Andrea Olivo (ICTP Italy)
DTSTART:20230518T140000Z
DTEND:20230518T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/83
DESCRIPTION:Title: Fourier transform of self-similar measures: decay outside of a
sparse set of frequencies and decay of smooth images\nby Dr Andrea Oli
vo (ICTP Italy) as part of MESS (Mathematics Essex Seminar Series)\n\nLect
ure held in STEM 3.1.\n\nAbstract\nIn this talk\, we are going to discuss
about the behaviour of self-similar measures and its Fourier transform. It
is known that\, in some particular cases\, the Fourier transform of a sel
f-similar measure does not go zero when the frequencies go to infinity. Ne
vertheless\, Kaufman and Tsujii proved that the Fourier transform of self-
similar measures on the real\nline has a power decay outside of a sparse s
et of frequencies. We will go over these results and present a version for
homogeneous self-similar\nmeasures on the complex plane.\n\nhttps://findy
ourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/projects/23
/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/83/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Sokratis Zikas (U Poitiers)
DTSTART:20230601T140000Z
DTEND:20230601T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/84
DESCRIPTION:Title: Unbounded algebraic subgroups of $\\mathrm{Bir}(C \\times \\mat
hbb{P}^n)$\nby Dr Sokratis Zikas (U Poitiers) as part of MESS (Mathema
tics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nThe c
lassification of maximal connected algebraic subgroups of the group of bir
ational transformations of $\\mathbb{P}^m\,$ for $m = 2$ and $3\,$ implies
that every connected algebraic subgroup of $\\mathrm{Bir}(\\mathbb{P}^m)$
is contained in a maximal one. Thus a natural question is whether a simil
ar statement is true for $\\mathrm{Bir}(C \\times \\mathbb{P}^n)\,$ where
$C$ is a curve of positive genus.\n\nIn this talk\, I will give a negative
answer to the previous question. The proof relies on the machinery of the
G-equivariant Sarkisov Program. \n\nThis is joint work with Pascal Fong.\
n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/se
arch/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/84/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Liana Heuberger (U Bath)
DTSTART:20230608T140000Z
DTEND:20230608T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/85
DESCRIPTION:Title: Combinatorial Reid's recipe for consistent dimer models\nby
Dr Liana Heuberger (U Bath) as part of MESS (Mathematics Essex Seminar Se
ries)\n\nLecture held in STEM 3.1.\n\nAbstract\nIn the first part of my ta
lk\, I will make a gentle introduction to the McKay correspondence for ADE
surface singularities: this relates a purely algebraic object (the McKay
quiver) with the geometry of a quotient variety. Reid's recipe is a genera
lisation of this correspondence in dimension three\, in the case of affine
toric varieties. I will describe an algorithm by Craw and Reid realising
this for quotient singularities\, and discuss its extension to any affine
toric Gorenstein variety. This is joint work with Alastair Craw and Jesus
Tapia Amador.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-0
5a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/85/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Alex Doak (U Bath)
DTSTART:20230525T140000Z
DTEND:20230525T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/86
DESCRIPTION:Title: Internal Solitary Waves in a three-layer model\nby Dr Alex
Doak (U Bath) as part of MESS (Mathematics Essex Seminar Series)\n\nLectur
e held in STEM 3.1.\n\nAbstract\nInside stratified fluids\, regions of rap
id density variation with respect to depth (pycnoclines) act as waveguides
for horizontally propagating internal waves. In this talk we shall examin
e internal waves by computing travelling wave solutions to a simplified th
ree-layer model. We will be presenting numerical solutions to both the ful
l Euler system\, and a reduced model called the three-layer Miyata-Choi-Ca
massa (MCC3) equations. We exploit structure within the model system to de
scribe the solution space seen in both the model and fully nonlinear theor
y. We relate large amplitude solutions to the so-called conjugate states o
f the system\, where the limiting solutions of many of the solution branch
es are a heteroclinic orbit between conjugate states (i.e. wavefront solut
ions). The talk will begin with an overview of water wave and bifurcation
theory for those less familiar with these fields\, allowing the talk to be
accessable to all those interested.\n\nhttps://findyourway.essex.ac.uk/bc
dc98e0-e3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230
405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/86/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prof Stephen Anco (Brock University)
DTSTART:20230615T140000Z
DTEND:20230615T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/87
DESCRIPTION:Title: CANCELLED\nby Prof Stephen Anco (Brock University) as part
of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/87/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Abdel Salhi (Essex)
DTSTART:20231012T140000Z
DTEND:20231012T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/88
DESCRIPTION:Title: The Ultimate Solution Approach to Intractable Problems\nby
Abdel Salhi (Essex) as part of MESS (Mathematics Essex Seminar Series)\n\n
Lecture held in STEM 3.1.\n\nAbstract\nThere is now strong belief that $\\
textrm{P} \\neq \\textrm{NP}$. This means that some very common problems c
annot be solved efficiently under current and so called Von Neumann type c
omputer architectures including parallel configurations.\n\nMoreover\, thi
s will remain the case for the foreseeable future and even in relatively l
ow dimensions. What one may hope to achieve when solving these problems\,
is the best possible solution given the available facilities within the al
lowed time. In other words\, attempting to find the absolute optimum\, is
not realistic. This makes the current definition of the optimum redundant
for\npractical purposes. Therefore\, a new definition of the optimum is re
quired as well as appropriate approaches to find it. This paper will put f
orward a definition for the practical or sensible\noptimum\, the s-optimum
\, consider its consequences and suggest what can be the ultimate approach
\nto finding it. Although this approach is generic and can be applied in a
ny context\, optimisation and search are the specific contexts with which
we will be concerned here.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c
3-11eb-b52e-05a67b7792fc/search/projects/23/60e\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/88/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dmitry Savostyanov (Essex)
DTSTART:20231019T140000Z
DTEND:20231019T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/89
DESCRIPTION:Title: Tensor product approach to Bayesian inference of networks from
epidemiological data\nby Dmitry Savostyanov (Essex) as part of MESS (M
athematics Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\
nEpidemiological modelling is crucial to inform healthcare policies and to
support decision making for disease prevention and control.\nThe recent o
utbreak of COVID-19 pandemic raised a significant scientific and public de
bate regarding the quality of the\nmathematical models used to predict the
effect of the pandemics and to choose an appropriate response strategy.\n
To accurately capture how the disease spreads\, we have to move beyond a u
sual assumption that the population is connected homogeneously (well--mixe
d)\, and towards network models of epidemics.\nUnfortunately\, their compl
exity grows exponentially with the size of the network --- these models su
ffer from the curse\nof dimensionality and usually rely on further approxi
mations to make them practically solvable.\nIn this talk we discuss how ep
idemiological models on networks can be solved accurately using the recent
ly proposed algorithms based on low--rank tensor product factorisations.\n
We also discuss the inverse problem of inferring a contact network from ep
idemiological data\, for which we employ Bayesian optimisation techniques.
\n\n\nThis is joint work with Sergey Dolgov (University of Bath\, UK).\nTh
is work is supported by the Leverhulme Trust Research Fellowship RF-2021-2
58.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792f
c/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/89/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Shirsho Murherjee (Essex)
DTSTART:20231026T140000Z
DTEND:20231026T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/90
DESCRIPTION:Title: Minkowski problem for p-harmonic measures\nby Shirsho Murhe
rjee (Essex) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture
held in STEM 3.1.\n\nAbstract\nAn account of Minkowski problems shall be
discussed including a brief history and contemporary developments followed
by our recent results in this direction corresponding to p-harmonic measu
res. This is a joint work with Murat Akman.\n\nhttps://findyourway.essex.a
c.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e
800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/90/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Taras Skrypnyk (Leeds)
DTSTART:20231102T150000Z
DTEND:20231102T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/91
DESCRIPTION:Title: CANCELLED: Classical non-skew-symmetric r-matrices and integra
ble spin models.\nby Taras Skrypnyk (Leeds) as part of MESS (Mathemati
cs Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nTHIS TA
LK IS CANCELLED. APOLOGIES FOR INCONVENIENCE.\n\nIn the present talk we wi
ll review a theory of classical non-skew-symmetric non-dynamical r-matric
es with spectral parameters and their usage the theory of integrable cla
ssical and quantum spin chains. We will explain the relation of these r-
matrices with the theory of infinite-dimensional almost-graded Lie algeb
ras with Kostant-Adler decomposition. We will present several classes of
examples of such the r-matrices\, naturally lying out of the Belavin-Drin
feld classification. In particular\, we will present classical r-matrices
related to integrable multidimensional tops (Manakov tops). We will also
outline a sub-class of the non-skew-symmetric classical r-matrices permit
ting to construct\, except for the linear tensor brackets\, also the quadr
atic tensor brackets that lead to Maillet and reflection equation algebras
. We will in details consider Gaudin models with and without external ma
gnetic field and their generalizations based on non-skew-symmetric classi
cal r-matrices. Applications of these models to the problem of isomonodro
mic deformations and to Kinizhnik-Zamolodchikov-type equations will be br
iefly discussed.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52
e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/91/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adam Jones (Cambridge)
DTSTART:20231109T150000Z
DTEND:20231109T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/92
DESCRIPTION:Title: Hensel lifting and the p-adic numbers\nby Adam Jones (Cambr
idge) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture held i
n STEM 3.1.\n\nAbstract\nOne of the oldest questions in mathematics\, and
the question which underlies the discipline of algebra\, is how can we sol
ve a polynomial equation? Specifically\, given an integer polynomial $F(X)
$\, does the equation $F(X)=0$ have a numerical solution\, and can we expr
ess this solution by a formula\, e.g. the quadratic formula? However\, an
easier problem might be to fix a prime number $p$\, and solve the correspo
nding congruence equation $F(X) = 0 \\:(\\textrm{mod}\\: p)$\, i.e. for wh
ich integer $n$ does $p$ divide $F(n)$? In this talk\, I will demonstrate
how solving the congruence can actually yield a solution to the equation!
More precisely\, start with an integer solution n to the congruence\, and
using a procedure developed by Kurt Hensel\, we can lift this to an actual
solution $N$\, i.e. $F(N)=0$. But this $N$ will may be an integer\, it wi
ll in fact take the form of something known as a $p$-adic number. I will d
escribe how p-adic numbers are defined\, how we can express them\, how we
can approximate them\, and how we can use them to determine the solvabilit
y of polynomial equations.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c
3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/92/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Zili Zhang (Tongji University\, China)
DTSTART:20231116T150000Z
DTEND:20231116T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/93
DESCRIPTION:Title: Simpson's correspondence and the P=W conjecture\nby Zili Zh
ang (Tongji University\, China) as part of MESS (Mathematics Essex Seminar
Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/93/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jing Ping Wang (Kent)
DTSTART:20231123T150000Z
DTEND:20231123T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/94
DESCRIPTION:Title: Symmetries of Differential--Difference Equations\nby Jing P
ing Wang (Kent) as part of MESS (Mathematics Essex Seminar Series)\n\nLect
ure held in STEM 3.1.\n\nAbstract\nIn this talk\, we’ll discuss symmetri
es of differential-difference equations (DDEs) and their applications. A D
DE is a functional relation among functions and their derivatives calculat
ed at several points of a lattice. Typical examples are Volterra chain and
Toda lattice equations. A DDE may possess discrete symmetries\, continuou
s point symmetries and Lie algebras of infinitesimal symmetries. Symmetry
reductions enable one to study symmetry-invariant solutions of DDEs and li
nk them with finite dimensional dynamical systems and Painleve equations.
For integrable equations infinite hierarchies of symmetries can be constru
cted using Lax representations\, recursion (Nijenhuis) operators or master
symmetries. Integrable DDEs has natural connections with integrable parti
al differential equations. This talk is based on a short review paper with
A.V. Mikhailov.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52
e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/94/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Naomi Andrew (Oxford)
DTSTART:20231130T150000Z
DTEND:20231130T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/95
DESCRIPTION:Title: Automorphisms of groups and actions on trees\nby Naomi Andr
ew (Oxford) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture
held in STEM 3.1.\n\nAbstract\nThe automorphisms (that is\, symmetries) of
a group do not vary particularly transparently with the group: for instan
ce\, changing a single integer in the presentation of a Baumslag--Solitar
group can turn a finite outer automorphism group into one which is not eve
n finitely generated. However\, in nice enough situations\, one can extrac
t information about the outer automorphism group from investigating the wa
ys the original group acts on trees. The challenge becomes ensuring you ar
e in such a situation\, and interpreting the information you get. I'll dis
cuss these ideas and how they play out in work on the outer automorphism g
roups of (some) free-by-cyclic groups. (Joint with Armando\nMartino)\n\nht
tps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/
projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/95/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yu Qiu (Tsinghua University\, China)
DTSTART:20231207T150000Z
DTEND:20231207T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/96
DESCRIPTION:Title: On cluster braid groups\nby Yu Qiu (Tsinghua University\, C
hina) as part of MESS (Mathematics Essex Seminar Series)\n\nAbstract: TBA\
n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/96/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dominic Bunnett (TU Berlin)
DTSTART:20231214T150000Z
DTEND:20231214T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/97
DESCRIPTION:Title: Moduli spaces of hypersurfaces and their topology\nby Domin
ic Bunnett (TU Berlin) as part of MESS (Mathematics Essex Seminar Series)\
n\nLecture held in STEM 3.1.\n\nAbstract\nA hypersurface is defined by the
vanishing of a single polynomial equation. One constructs a moduli space
of hypersurfaces by considering all equations and quotienting out by the g
roup action given by changing coordinates. In the classical setting of hyp
ersurfaces in projective space the group of coordinate changes is SLn whic
h is a reductive group. Thus techniques of geometric invariant theory can
be used to define notions of stability for hypersurfaces\, put algebraic s
tructure on the quotient space and even explicitly study the topology. In
this talk\, we revisit these classical techniques and extend them to the n
on-reductive setting\, which is the setting for many moduli problems. We w
ill compute the cohomology of the moduli spaces of some low degree del Pez
zo surfaces.\n\nRoom: STEM 3.1 https://findyourway.essex.ac.uk/bcdc98e0-e3
c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/97/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jesus Matrinez-Garcia (U Essex)
DTSTART:20240118T150000Z
DTEND:20240118T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/98
DESCRIPTION:Title: The Calabi Problem for Fano threefolds\nby Jesus Matrinez-G
arcia (U Essex) as part of MESS (Mathematics Essex Seminar Series)\n\n\nAb
stract\nAlgebraic varieties are the space of solutions to polynomial equat
ions in several variables. A typical example is the sphere which is a solu
tion to x^2+y^2+z^2=1\, however in algebraic geometry and for technical re
asons\, we reduce to the case of homogeneous polynomials with complex coef
ficients\,\nwhich gives yield to projective varieties. Then\, the Minimal
Model Programme predicts that projective varieties can be constructed from
three basic building blocks: varieties of positive\, negative and zero Ri
cci curvature. Of these\, varieties of positive curvature (known as Fano v
arieties) are the only ones which are known to belong to a finite number o
f deformation families (Birkar\, 2016\, for which he got a Fields Medal).
As such\, classifying Fano varieties is a reasonable (but difficult) goal.
\n\nIn the 1950s\, Calabi introduced the notion of Kaehler-Einstein metric
for ‘building blocks’. This is a metric that has constant Ricci curva
ture while giving the variety a Riemannian\, a symplectic and a complex st
ructure in a compatible manner. While varieties of negative and zero curva
ture are known to always admit a Kaehler-Einstein metric\, varieties of po
sitive curvature do not always admit it. The Calabi Problem consists in id
entifying which ones do. Thanks to work of Chen-Donaldson-Sun\, we know th
e existence of the metric (an analytic condition) is equivalent to the alg
ebro-geometric property of K-stability\, which is also very elusive. In th
is talk I will explain these notions in some detail and describe the state
-of-the-art\, which includes our classification of which of the 105 deform
ation families of smooth 3-dimensional Fano varieties have a member with a
Kahler-Einstein metric in them. This is joint work with Carolina Araujo\,
Ana-Maria Castravet\, Ivan Cheltsov\, Kento Fujita\, Anne-Sophie Kaloghir
os\, Constantin Shramov\, Hendrik Süß\, and Nivedita Viswanathan.\n\nhtt
ps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/p
rojects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/98/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Choi-Hong Lai (U Greenwich)
DTSTART:20240125T150000Z
DTEND:20240125T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/99
DESCRIPTION:Title: On defect correction methods for some nonlinear option pricing
problems\nby Choi-Hong Lai (U Greenwich) as part of MESS (Mathematics
Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nThis expan
sion of Black--Scholes model through a small perturbation of the option pr
ice leading to a discrete hedging is examined. The computation of such exp
ansion terms is to be worked out through a computational method known as d
efect correction method. Several examples are given to illustrate how thes
e computational defect correction method is performed. The method is then
applied to the Black Scholes model with a nonlinear volatility term. Numer
ical experiments demonstrate the accuracy of the method. Some current expe
riments and future are discussed towards the end of the talk.\n\nhttps://f
indyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/project
s/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/99/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Julian Weigt (Warwick)
DTSTART:20240208T150000Z
DTEND:20240208T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/100
DESCRIPTION:Title: Endpoint regularity of maximal functions\nby Julian Weigt
(Warwick) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture he
ld in STEM 3.1.\n\nAbstract\nGiven an integrable real valued function f on
ℝ^d\, its Hardy-Littlewood maximal function Mf maps a point x in ℝ^d
to the largest average value that can be achieved by averaging |f| over an
y ball centered in x. The classical Hardy-Littlewood maximal function theo
rem states that this maximal operator is a bounded operator on the Lebesgu
e space L^p(ℝ^d) if and only if 1 < p <= ∞. Indeed\, for every nonzero
function f in L^1(ℝ^d) its maximal function Mf is not even in L^1(ℝ^d
).\n\nIn 1997 Juha Kinnunen proved the corresponding result for the gradie
nt of the maximal function\, i.e. that the L^p(ℝ^d)-norm of the gradient
of the maximal function is controlled by the L^p(ℝ^d)-norm of the gradi
ent of the function if 1 < p <= ∞. However\, he provides no counterexamp
le in the endpoint\, leaving open the possibility that the gradient bound
in fact holds also for p = 1.\n\nIn 2004 Hajłasz and Onninen formally pos
ed the question if the Hardy-Littlewood maximal operator on ℝ^d satisfie
s the endpoint gradient bound. It has since attracted considerable attenti
on\, motivated by to the elementary nature of the maximal operator and by
the relative simplicity of the proof of the Hardy-Littlewood maximal funct
ion theorem and of Kinnunens 1997 result. Many special cases\, generalizat
ions and variations of this problem have been explored\, with partial succ
ess. The original question by Hajłasz and Onninen remains unanswered.\n\n
https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/searc
h/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/100/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Taras Skrypnyk (U Leeds)
DTSTART:20240201T150000Z
DTEND:20240201T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/101
DESCRIPTION:Title: Classical non-skew-symmetric r-matrices and integrable spin mo
dels\nby Taras Skrypnyk (U Leeds) as part of MESS (Mathematics Essex S
eminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nIn the present ta
lk we will review a theory of classical non-skew-symmetric non-dynamical r
-matrices with spectral parameters and their usage the theory of integrabl
e classical and quantum spin chains. We will explain the relation of these
r-matrices with the theory of infinite-dimensional almost-graded Lie alge
bras with Kostant--Adler decomposition. We will present several classes of
examples of such the r-matrices\, naturally lying out of the Belavin--Dri
nfeld classification. In particular\, we will present classical r-matrices
related to integrable multidimensional tops (Manakov tops). We will also
outline a sub-class of the non-skew-symmetric classical r-matrices permitt
ing to construct\, except for the linear tensor brackets\, also the quadra
tic tensor brackets that lead to Maillet and reflection equation algebras.
We will in details consider Gaudin models with and without external magne
tic field and their generalizations based on non-skew-symmetric classical
r-matrices. Applications of these models to the problem of isomonodromic d
eformations and to Kinizhnik--Zamolodchikov--type equations will be briefl
y discussed.\n\nhttps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05
a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/101/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nikolaos Fytas (U Essex)
DTSTART:20240222T150000Z
DTEND:20240222T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/103
DESCRIPTION:Title: Computer simulations in Statistical Physics: Crossing the barr
iers in complex and disordered systems\nby Nikolaos Fytas (U Essex) as
part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in STEM 3
.1.\n\nAbstract\nIn this talk I will present the basic ideas behind some o
f the most powerful numerical methods in Statistical Physics used for unra
velling the critical behaviour of complex magnetic spin models. These meth
ods are an asset especially for the study of disordered systems which feat
ure a rough free-energy landscape and\, when combined with theoretical app
roaches such as field theory\, finite-size scaling\, and the renormalisati
on group\, can provide clear-cut answers to longstanding problems in the f
ield. Selected examples of successful application of these methods will al
so be discussed\, mostly focusing on the problem of universality violation
s in the random-field Ising model but also in the determination of the ord
er of the transition in spin-1 models under the presence of a chemical pot
ential.\n\nRoom: STEM 3.1 https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11
eb-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/103/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gawin Brown (Warwick)
DTSTART:20240229T150000Z
DTEND:20240229T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/104
DESCRIPTION:Title: Moebius strips in higher dimensions\nby Gawin Brown (Warwi
ck) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in
STEM 3.1.\n\nAbstract\nYou can crush the central axis of a moebius strip t
o a point\, and the result is a disc. We see this\, for example\, when we
look down on a spiral staircase from above: the central axis on which\nthe
steps are attached is a line in reality but just a point in our view.\nTo
get a grip on the geometry of this\, we can write down equations that exp
lain how to glue two pieces of paper together to build a Moebius strip.\n\
nIn 3 dimensions (and over the complex numbers) there are infinitely many
possibilities for the analogous phenomenon.\nThe equations are now essenti
al as we cannot visualise them. We do not know them all\, but it seems tha
t after 40 years of trying we are now very close.\nAtiyah rediscovered one
case in the 50s as slight modifications of the singularity $xy = zt$ in 4
-space: visibly factorisation is not unique in this situation (since $xy$
and $zt$ are two different but equal products)\, and this provides the key
.\nThese modifications are called flops. They play an signficant role in t
he physics of string theory\, though I cannot explain that beyond tea time
stories.\n\nOnce we have some examples to hand\, I will sketch an on-goin
g project with Michael Wemyss (Glasgow) to construct and classify all flop
s using certain finite-dimensional non-commutative algebras: this amounts
to studying polynomials in variables $X$ and $Y\,$ but ones that do not co
mmute\, and is a simple problem to state\, but seems to be quite hard to s
olve.\n\nRoom: STEM 3.1 https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb
-b52e-05a67b7792fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/104/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alastair Litterrick (U Essex)
DTSTART:20240307T150000Z
DTEND:20240307T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/105
DESCRIPTION:Title: Elementary abelian subgroups: From algebraic groups to finite
groups\nby Alastair Litterrick (U Essex) as part of MESS (Mathematics
Essex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nAcross gro
up theory\, elementary abelian subgroups arise naturally in many contexts.
For instance\, they play an important role in modular representation theo
ry\, in local structure of groups\, and in the cohomology theory of variou
s spaces.\n\n This talk will present joint work with Jianbei An (Universit
y of Auckland) and Heiko Dietrich (Monash University\, Melbourne)\, in whi
ch we consider elementary abelian subgroups of reductive algebraic groups
in positive characteristic. In contrast with previous works which proceed
‘bottom up’\, beginning with elements of order p\, then elements of or
der p in their centralisers\, and so on\, we use a ‘top-down’ approach
building on work of R. Griess on maximal elementary abelian subgroups and
their normaliser structure. Such subgroups behave differently depending o
n whether or not they are toral (contained in a torus)\, and our results a
re two-fold. For toral subgroups\, we give an efficient combinatorial algo
rithm for enumerating subgroups and determining their normaliser and centr
aliser structure. For non-toral subgroups\, we complement work of J. Yu an
d Andersen et. al.\, and end up with a complete classification of subgroup
s which is independent of the ambient characteristic. The eventual aim is
to use these results to prove local structure results in finite groups of
Lie type\, via the Lang-Steinberg theorem\; I will close with a discussion
of the subtleties arising in this process.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/105/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Thomas Prellberg (Queen Mary U)
DTSTART:20240314T150000Z
DTEND:20240314T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/106
DESCRIPTION:Title: On the universality class of the special adsorption point of t
wo-dimensional lattice polymers\nby Thomas Prellberg (Queen Mary U) as
part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in STEM 3
.1.\n\nAbstract\nPolymers tethered to a surface undergo an (ordinary) adso
rption transition when the strength of the polymer-surface interaction is
increased. If there is also a bulk interaction present\, polymers undergo
a second order collapse transition\, which then changes the nature of the
surface adsorption transition. At the critical collapse point this is know
n as the special adsorption point. On the other hand\, collapsed polymers
are believed to form a surface-attached globule under adsorption\, but thi
s scenario is notoriously hard to see in simulations.\n\nIn 2019 we found
evidence that the surface adsorption transition of an interacting polymer
model placed on the square lattice displays a non-universal behaviour at t
his special adsorption point\, with surface exponents depending on the or
ientation of the surface with respect to the lattice axes. Through new ext
ensive Monte Carlo simulations\, utilising much longer configurations than
previously achieved\, we can now demonstrate that the different exponents
observed earlier are due to the presence of a previously unseen surface-a
ttached-globule phase which changes the multicritical nature of the specia
l adsorption point. We confirm this observation by considering modified su
rfaces. These results strongly indicate that at least two universality cla
sses exist for the special adsorption point on the square lattice.\n\nThe
method employed is based on stochastic enumeration techniques combined wit
h uniform sampling ideas.\n\nhttps://arxiv.org/abs/2305.09803\n\nRoom: STE
M 3.1 https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc
/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/106/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matthew Hyde (Warwick)
DTSTART:20240321T150000Z
DTEND:20240321T160000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/107
DESCRIPTION:Title: Quantitative rectifiability in metric spaces\nby Matthew H
yde (Warwick) as part of MESS (Mathematics Essex Seminar Series)\n\nLectur
e held in STEM 3.1.\n\nAbstract\nThe theory of quantitative rectifiability
was developed extensively by David and Semmes in the early 1990s\, partly
motivated by questions arising in harmonic analysis. They proved\, among
many other things\, the equivalence of Uniform Rectifiability (UR) and the
Bi-lateral Weak Geometric Lemma (BWGL). The first condition being a natur
al quantitative version of rectifiability\, the second\, a quantitative co
ndition measuring local approximations by affine subspaces. Their result c
an be seen as quantification of the equivalence between rectifiability and
the almost everywhere existence of approximate tangent planes. In this ta
lk we will discuss some history of the subject and report on recent work\,
with Bate and Schul\, which extends the theory to metric spaces.\n\nRoom:
STEM 3.1 https://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b77
92fc/search/projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/107/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prof Peter Higgins (U Essex)
DTSTART:20240502T140000Z
DTEND:20240502T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/108
DESCRIPTION:Title: Production optimization for agents of differing work rates
\nby Prof Peter Higgins (U Essex) as part of MESS (Mathematics Essex Semin
ar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nWe introduce a scheme
for producing\, in the least possible time\, p identical objects with n a
gents that work at differing speeds [2]. This involves halting the proces
s in order to transfer production across agent types. For the case of two
types of agent\, we construct a scheme\nbased on the Euclidean algorithm t
hat seeks to minimise the number of pauses in production (which works part
icularly well in the case of agent counts that are two consecutive Fibonac
ci numbers).\n\nThe problem is a variation of the Biker-Hiker problem [1]
that I spoke about in MESS in 2023\, and I will explain the interpretation
and contrast the formulas that link the topics. The underlying mathemati
cs is still simple but is rather different and indeed is thousands of year
s old: harmonic means and the Euclidean algorithm\, applied to Operational
Research ideas.\n\n[1] The Biker Hiker problem\, J. of Combinatorics\, V
olume 15\, Number 1\, 105–134\, (2024).\n[2] Production optimization for
agents of differing work rates\, Australia and New Zealand Industrial and
Applied Mathematics Journal\, submitted.\n\nSTEM 3.1 https://findyourway.
essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/projects/23/60ef1a
882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/108/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Josh Macdonald (Tel-Aviv U)
DTSTART:20240509T140000Z
DTEND:20240509T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/109
DESCRIPTION:Title: Modeling non-trophic planktonic interactions\nby Dr Josh M
acdonald (Tel-Aviv U) as part of MESS (Mathematics Essex Seminar Series)\n
\n\nAbstract\nAuthors: Joshua Macdonald (School of Zoology\, The George S
Wise Faculty of Life Sciences\, Tel Aviv University) and Gregory L. Britte
n (Woods Hole Oceanographic Institute)\n\nAbstract:\n\nNutrient-Phytoplank
ton-Zooplankton-Detritus (NPZD) models\, a cornerstone of quantitative bio
logical oceanography\, investigate plankton interactions and coexistence m
echanisms and explore mechanistic explanations for empirically observed ph
enomena. However\, classical NPZD models\ngenerally aggregate phytoplankto
n and zooplankton into a small number of highly simplified compartments. T
hese models are thus limited in their ability to answer questions related
to the effects and maintenance of planktonic biodiversity. Next-generation
biogeochemical models address this weakness in the NPZD framework by inco
rporating larger communities of phytoplankton and zooplankton connected vi
a networks of trophic and non-trophic interactions. Critically\, integrati
ng planktonic biodiversity into NPZD models requires parameterizing the ne
twork of\ninteractions between individual phytoplankton and zooplankton sp
ecies or functional groups. Despite the demonstrated importance of network
structure on planktonic dynamics\, significant uncertainties exist regard
ing the underlying structure of trophic interactions\, the importance of n
on-trophic interactions\, and how network structures depend on environment
al conditions.\n Here\, we pair a simulation-estimation approach\, differe
nt notions of identifiability analysis\, and model analysis to address the
se fundamental questions in network-based species-rich NPZD modeling: (i)
What data are required to confidently infer network structure from observe
d\nspecies/functional group abundance time series? (ii) What degree of net
work complexity can be inferred from a given set of observations? (iii) Ho
w much network information is contained in macro-ecological observations?\
n\nZoom only talk\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/109/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Pavlos Kassotakis (U Warsaw)
DTSTART:20240516T140000Z
DTEND:20240516T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/110
DESCRIPTION:Title: On quadrirational pentagon maps\nby Dr Pavlos Kassotakis (
U Warsaw) as part of MESS (Mathematics Essex Seminar Series)\n\nAbstract:
TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/110/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prof Gerald Williams (U Essex)
DTSTART:20240523T140000Z
DTEND:20240523T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/111
DESCRIPTION:Title: Incidence graphs of generalized polygons and star graphs of gr
oup presentations with cyclic symmetry\nby Prof Gerald Williams (U Ess
ex) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture held in
STEM 3.1.\n\nAbstract\nA generalized polygon is a point-line incidence str
ucture that includes projective planes (generalized 3-gons). Incidence gra
phs of generalized m-gons are connected bipartite graphs of diameter m and
girth 2m. Associated to any group presentation is a graph called the star
graph\, which encodes structural information about the group defined by t
he presentation. Transitional behaviour can occur for groups defined by pr
esentations whose star graph components are incidence graphs of generalize
d polygons\; such presentations are called “special”. A cyclic present
ation of a group is a type of group presentation that admits a cyclic symm
etry. In this talk I will discuss joint work with Ihechukwu Chinyere in wh
ich we classify the special cyclic presentations.\n\nRoom: STEM 3.1 https:
//findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/proj
ects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/111/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Manoj Kumar (NISER India)
DTSTART:20240606T140000Z
DTEND:20240606T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/112
DESCRIPTION:Title: Critical behavior of the three-dimensional random-field Potts
model\nby Dr Manoj Kumar (NISER India) as part of MESS (Mathematics Es
sex Seminar Series)\n\nLecture held in STEM 3.1.\n\nAbstract\nIn this talk
\, I will discuss the phase transitions and critical phenomena of three an
d four-state random field Potts models (RFPM) in three dimensions. A key u
niversal feature of these models is that their phase transition is governe
d by a zero-temperature random fixed point. We target the problem by deter
mining the ground states at temperature T=0. Although finding ground state
s in RFPM is known to be NP-hard\, we employ a computationally efficient g
raph cut algorithm to find excellent approximate ground states in polynomi
al time. From these states\, we evaluate various quantities such as magnet
ization\, Binder cumulant\, specific heat\, and susceptibility\, and extra
polate them to the limit of quasi-exact ground states. These results are o
btained for different system sizes\, and an extensive finite-size scaling
approach is implemented to estimate the critical point and the exponents t
hat characterize the singular behavior near the transition.\n\nSTEM 3.1 ht
tps://findyourway.essex.ac.uk/bcdc98e0-e3c3-11eb-b52e-05a67b7792fc/search/
projects/23/60ef1a882031e800c230405d\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/112/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dr Joshua Jackson (Sheffield)
DTSTART:20240613T140000Z
DTEND:20240613T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/113
DESCRIPTION:Title: Quotients by group actions and classification questions in alg
ebraic geometry\nby Dr Joshua Jackson (Sheffield) as part of MESS (Mat
hematics Essex Seminar Series)\n\nLecture held in NTC 3.05.\n\nAbstract\nA
notable feature of algebraic geometry is that the set parameterising geom
etric objects of a particular kind often itself has a geometric structure.
In many cases the best way to obtain and study that geometric structure i
s to quotient some easier space by a group action. The simplest example of
this phenomenon is\, in principle\, familiar to every undergraduate: the
space of linear endomorphisms of a vector space is itself a vector space (
the space of matrices) quotiented by the change-of-basis action of the gen
eral linear group. However\, unlike in more flexible geometries\, question
s of existence of the quotient in algebraic geometry can be highly non-tri
vial. I'll explain what kinds of obstacles arise\, what theorems we have\,
and give a tour through some applications.\n\nhttps://findyourway.essex.a
c.uk/search/60ef1a872031e800c2303fb0?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/113/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Emilian Parau (U East Anglia)
DTSTART:20241010T130000Z
DTEND:20241010T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/114
DESCRIPTION:Title: Stability of travelling waves in deep water\nby Emilian Pa
rau (U East Anglia) as part of MESS (Mathematics Essex Seminar Series)\n\n
\nAbstract\nWe present some new results on the stability of nonlinear wave
s in deep water. Two cases are investigated in detail. First the effect of
vorticity is examined\, using asymptotic and numerical methods based on c
onformal mappings to study the stability of the travelling waves. Then the
stability of nonlinear hydroelastic waves to superharmonic and subharmoni
c perturbations is considered.\n\nRoom: CTC.3.02 https://findyourway.essex
.ac.uk/search/62f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/114/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prof Peter Higgins (U Essex)
DTSTART:20241017T130000Z
DTEND:20241017T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/115
DESCRIPTION:Title: Generating all de Bruijn sequences using inverse Burrows-Wheel
er transforms\nby Prof Peter Higgins (U Essex) as part of MESS (Mathem
atics Essex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbstract\nThe
Burrows-Wheeler transform of a word $w$ is formed by taking the table cons
isting of all the cyclic conjugates of $w\,$ listing them alphabetically a
nd then taking the final column\, $BW(w).$ Remarkably $w$ may be recovered
by inverting $BW(w)$ in linear time with $BW(w)$ being much easier to com
press that a typical message word $w.$ [1]\n\nUnfortunately\, not all word
s arise as Burrows–Wheeler transforms of a word so\, in the original for
mat\, it was not possible to invert an arbitrary string. The extended BW t
ransform (eBWT) however does allow the inversion of an arbitrary word and
the result in general is a multiset (a set allowing repeats) of necklaces\
, which are cyclic classes of primitive words (words that are not powers o
f other words).\n\nFollowing on from [2]\, I discovered a connection betwe
en generalised BW transforms and de Bruijn words (an example of which is $
aaaabbababbbbaab$: regarded cyclically\, it has every factor over $\\{a\,b
\\}$ of length $4$ appearing exactly once). In [3]\, I generalised this i
dea to that of de Bruijn sets because that collection was exactly the outp
ut of inverting a particular word set that had an especially simple descri
ption.\n\nRecently\, Lipt\\´ak and Parmigiani in [4] applied my theorem t
o offer “the first practical algorithm able to generate all dB sequences
”.\n\n``… Higgins proved the following beautiful result (here given in
the restricted version for binary alphabets):\n\nA multiset $M$ is a bina
ry de Bruijn set of order $n$ if and only if $ebwt(M) \\in \\{ab\, ba\\}$
to the power $2^{n-1}$.''\n\nThey claim that this new `insight' allows for
the first algorithm of this kind as\, up till now\, the only approach was
the `naïve' application of the Fleury algorithm to find Euler cycles in
de Bruijn digraphs. They claim that their algorithm based on my theorem i
s ``10–12 times faster than random-Fleury for $n$ values between $17$ an
d $23$''\, which is the typical range utilised in applications of dB seque
nces in biology and other fields.\n\nIn this seminar I hope to put a littl
e flesh on the bones of this description.\n\nReferences:\n\n[1] Burrows M.
and D.J. Wheeler\, A block sorting data compression algorithm\, Technical
Report\, DIGITAL System Center\, 1994.\n\n[2] Higgins\, P.M.\, The semigr
oup of conjugates of a word\, International Journal of Algebra and Computa
tion\, Vol. 16\, No. 6 (2006)\, 1015-1029.\n\n[3] Higgins\, P.M.\, Burrows
-Wheeler transformations and de Bruijn words\, Theoretical Computer Scienc
e\, 457 (2012)\, 128-136.\n\n[4] Lipt\\´ak Z. and L. Parmigiani\, A BWT-
Based Algorithm for Random de Bruijn Sequence Construction\, in Soto\, J.A
.\, Wiese\, A. (eds) LATIN 2024: Theoretical Informatics. LATIN 2024. Lect
ure Notes in Computer Science\, vol 14578. Springer\, Cham. https://doi.or
g/10.1007/978-3-031-55598-5_9\n\nhttps://findyourway.essex.ac.uk/search/62
f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/115/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prof Dawid Kielak (U Oxford)
DTSTART:20241031T140000Z
DTEND:20241031T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/116
DESCRIPTION:Title: One-relator groups\nby Prof Dawid Kielak (U Oxford) as par
t of MESS (Mathematics Essex Seminar Series)\n\nLecture held in CTC.3.02.\
n\nAbstract\nI will survey the history of the study of one-relator groups\
, and discuss\nrecent developments.\n\nhttps://findyourway.essex.ac.uk/sea
rch/62f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/116/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gandhar Joshi (Open U)
DTSTART:20241107T140000Z
DTEND:20241107T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/117
DESCRIPTION:Title: Monochromatic arithmetic progressions in Sturmian sequences.\nby Gandhar Joshi (Open U) as part of MESS (Mathematics Essex Seminar S
eries)\n\nLecture held in CTC.3.02.\n\nAbstract\nWe are concerned with Stu
rmians: an interesting family of infinite symbolic sequences over a binary
alphabet. A monochromatic arithmetic progression (MAP) in a sequence is c
ounting how many times a particular symbol keeps appearing at a constant d
istance in a particular sequence. We ask if there is an infinite MAP for a
ny difference in a particular sequence.\n\nFirst\, we introduce some terms
and notation. Then we look at the famous Van der Waerden's theorem (1927)
followed by a brief history of our query for some related families of seq
uences. Then we will explain our technique that works for the Sturmians. I
n particular\, we will use the Fibonacci word\, a prototypical example of
the Sturmian sequences to prove that "the MAPs in Sturmians for any differ
ence are finite." This is an alternative proof to that in a recent paper b
y Durand and Goyheneche (2018) which feels more illustrative and elementar
y. If time permits\, we will provide the two definitive formulae to calcul
ate the length of the MAP of any difference in the Fibonacci word\, which
can be naturally extended to all the Sturmians. Also (again if time permit
s) mention an automatic theorem proving software that sort of paved our wa
y to the result.\n\n\nReferences:\n\n1. For a primer on Symbolic dynamics:
Queffelec: Substitution Dynamical Systems - Spectral Analysis doi:10.1007
/BFb0081890\n\n2. van der Waerden's theorem: van der Waerden\, B. L. (1927
). "Beweis einer Baudetschen Vermutung". Nieuw. Arch. Wisk. (in German). 1
5: 212–216.\n\n3. Dekking's criterion: The spectrum of dynamical systems
arising from substitutions of constant length | Probability Theory and Re
lated Fields doi:10.1007/BF00534241\n\n4. Durand and Goyheneche paper: De
cidability\, Arithmetic Subsequences and Eigenvalues of Morphic Subshifts
doi:10.36045/bbms/1576206359\n\nhttps://findyourway.essex.ac.uk/search/62f
111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/117/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marcelo Flamarion (Pontifical Catholic University of Peru)
DTSTART:20241121T140000Z
DTEND:20241121T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/118
DESCRIPTION:Title: Nonlinear Dynamics: Rogue Waves and Breather Structures\nb
y Marcelo Flamarion (Pontifical Catholic University of Peru) as part of ME
SS (Mathematics Essex Seminar Series)\n\n\nAbstract\nIn this talk\, we wil
l begin by discussing the formation of monstrous ocean waves known as rogu
e waves\, which pose serious risks to coastal regions\, small vessels\, an
d beachgoers. Interestingly\, similar phenomena have recently been observe
d in plasma physics and financial markets. We will then shift our focus to
breather structures—traveling\, oscillatory wave packets that arise as
solutions to classical integrable systems\, such as the modified Korteweg-
de Vries (mKdV) and Gardner equations—and present strong numerical evide
nce suggesting that these structures can also emerge in non-integrable mod
els. The talk is based on the works [1-4]\, in collaboration with Efim Pel
inovsky and Ekaterina Didenkulova.\n\n[1] Flamarion\, M.V.\, & Pelinovsky\
, E. (2024). Nonlinear random wave fields within a Boussinesq system. Phys
ics Letters A\, 520\, 129677.\n[2] Flamarion\, M.V.\, & Pelinovsky\, E. (2
023). Evolution and statistical analysis of internal random wave fields wi
thin the Benjamin–Ono equation. Journal of Marine Science and Engineerin
g\, 11\, 1853.\n\n[3] Flamarion\, M.V.\, Pelinovsky\, E.\, & Didenkulova E
. (2024). Dynamics of irregular wave fields in the Schamel equation framew
ork\, arXiv:2408.17411.\n\n[4]Flamarion\, M.V.\, & Pelinovsky\, E. (2024).
Wave evolution within the Cubic Vortical Whitham equation. arXiv:2409.194
24.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/118/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Shirsho Mukherjee (U Essex)
DTSTART:20241128T140000Z
DTEND:20241128T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/119
DESCRIPTION:Title: tbc\nby Shirsho Mukherjee (U Essex) as part of MESS (Mathe
matics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/119/
END:VEVENT
BEGIN:VEVENT
SUMMARY:John Nicholson (U Glasgow)
DTSTART:20241212T140000Z
DTEND:20241212T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/120
DESCRIPTION:Title: The topology of group presentations\nby John Nicholson (U
Glasgow) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture hel
d in CTC.3.02.\n\nAbstract\nGiven a finitely presented group\, can we clas
sify its collection of finite presentations? To make such a question tract
able\, we must first specify an equivalence relation on the class of prese
ntations. One way to do this is to build a 2-dimensional space from a grou
p presentation and say that two presentations are homotopy equivalent if t
heir corresponding spaces are. In\nthis talk\, I will give a light introdu
ction to the classification of group presentations up to homotopy equivale
nce\, and discuss how this topic connects to other areas of mathematics.\n
\nFirstly\, I will discuss Wall's D2 problem which asks if the homotopy ty
pes of group presentations are in one-to-one correspondence with certain c
hain complexes. In joint work with Tommy Hofmann\, we use algorithms from
algebraic number theory to rule out a longest standing potential counterex
ample (first proposed in 1977). Secondly\, I will discuss joint work with
Ian Hambleton which gives applications to the topology of closed smooth 4-
manifolds. Finally\, I will discuss joint work with Mikhail Khovanov and S
lava Krushkal in which we consider TQFT invariants for group presentations
.\n\nCTC.3.02 https://findyourway.essex.ac.uk/search/62f111e07a0f322989532
426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/120/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yuri Santos Rego (U Lincoln)
DTSTART:20241114T140000Z
DTEND:20241114T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/121
DESCRIPTION:Title: Fixed point theory and twisted conjugacy classes of linear gro
ups\nby Yuri Santos Rego (U Lincoln) as part of MESS (Mathematics Esse
x Seminar Series)\n\n\nAbstract\nThe study of fixed points of maps on 'nic
e' spaces underwent major developments after Lefschetz\, Brouwer\, Reideme
ister\, and Nielsen. There are examples of interesting manifolds whose sel
f-maps can have a prescribed number of (essential) fixed points\, though t
here is still much to be investigated in the area. This talk will be a 'cr
ash course' on fixed point theory for such spaces and their relationship w
ith the (algebraically defined) twisted conjugacy classes. We later focusi
ng on recent results for matrix groups\, and how some new spaces with nice
fixed-point properties can be constructed.\n\nThis is joint work with Pau
la M. Lins de Araujo.\n\nRoom: CTC.3.02 https://findyourway.essex.ac.uk/se
arch/62f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/121/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alastair Litterick (U Essex)
DTSTART:20241205T140000Z
DTEND:20241205T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/122
DESCRIPTION:Title: Varying flavours of complete reducibility\nby Alastair Lit
terick (U Essex) as part of MESS (Mathematics Essex Seminar Series)\n\nLec
ture held in CTC.3.02.\n\nAbstract\nOriginating with the familiar represen
tation-theoretic concept\, we have nowadays come to understand $G$-complet
e reducibility as a geometric property\, characterised using cocharacters
of $G$ and closure of $G$-orbits on certain varieties\, and as a combinato
rial property\, characterised via the action of subgroups on the spherical
building of $G$. This allows a number of generalisations. When a subgroup
$K$ of $G$ acts on $G^n$\, we are led to 'relative complete reducibility.
' In the presence of a Frobenius endomorphism $\\sigma$ acting on $G$ and
its building\, we arrive at so-called '$\\sigma$-complete reducibility'. A
nd finally\, we can replace $G$ by groups such as Kac-Moody groups: Infini
te-dimensional analogues with a twin building\, in which the notion of opp
osition (and hence complete reducibility) can still be defined and studied
.\n\nThis talk consists of joint work with Michael Bate\, Ben Martin\, Ger
hard Roehrle and their former students Chris Attenborough\, Falk Bannusche
r\, Maike Gruchot and Tomohiro Uchiyama\, and incipient joint work with my
PhD student Harvey Sykes.\n\nCTC.3.02 https://findyourway.essex.ac.uk/sea
rch/62f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/122/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Erol Vatansever (Izmir\, Turkey)
DTSTART:20250123T140000Z
DTEND:20250123T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/123
DESCRIPTION:Title: Computational Studies of Spin Systems: Quantum Monte Carlo Sim
ulations and Dynamic Phase Transitions\nby Erol Vatansever (Izmir\, Tu
rkey) as part of MESS (Mathematics Essex Seminar Series)\n\nLecture held i
n CTC.3.02.\n\nAbstract\nThis talk consists of two parts. In the first par
t\, I will present the Stochastic Series Expansion (SSE) Quantum Monte Car
lo method [1]\, a powerful and versatile approach for simulating quantum m
any-body systems\, particularly in the study of spin models. The discussio
n will begin with the foundational principles of the SSE technique\, based
on the series expansion of the partition function and stochastic sampling
to achieve high computational efficiency. Key features\, including operat
or-loop updates and the treatment of diagonal and off-diagonal terms\, wil
l be detailed to showcase the algorithm's capability in handling complex q
uantum interactions. Concrete examples\, such as simulations of the Heisen
berg models [2-4]\, will illustrate how the SSE method enables precise cal
culations of thermodynamic quantities\, uniform susceptibility\, staggered
magnetization\, and critical properties\, shedding light on phase transit
ions and emergent phenomena in low-dimensional quantum systems.\n\nIn the
second part of the talk\, I will focus on the behavior of ferromagnetic sy
stems driven by an oscillating magnetic field\, emphasizing dynamic phase
transitions and dynamic hysteresis. These phenomena result from the compet
ition between the period of the external field and the metastable lifetime
of the system. A comparative analysis will be presented\, contrasting fer
romagnetic systems in thermal equilibrium with those subjected to time-dep
endent magnetic fields. I will highlight the similarities between dynamic
and thermodynamic phase transitions\, noting that both often belong to the
same universality class and exhibit analogous phase diagrams [5-6]. Furth
ermore\, I will discuss recent experimental findings that show fluctuation
s in the dynamic order parameter and susceptibility leading to sharp sideb
ands\, known as metamagnetic anomalies\, in the dynamically paramagnetic p
hase near the critical point [7-8]. This behavior is particularly notewort
hy as it lacks an analog in equilibrium systems\, providing deeper insight
s into the nature of phase transitions in driven systems.\n\nReferences:\n
\n1. A.W. Sandvik\, AIP Conference Proceedings\, 1297 135 (2010).\n\n2. E.
Vatansever\, G.G. Grahovski\, N.G. Fytas\, The European Physical Journal
B 97 (3) 34 \n(2024).\n\n3. U. Kanbur\, E. Vatansever\, H. Polat\, Physica
l Review B 102 (6) 064411 (2020).\n\n4. U. Kanbur\, H. Polat\, E. Vatansev
er\, Physical Review E 102 (4) 042104 (2020).\n\n5. Z.D. Vatansever\, E. V
atansever\, A. Berger\, A. Vasilopoulos\, N.G. Fytas\, arXiv:2409.20152 (2
024).\n\n6. A. Vasilopoulos\, Z.D. Vatansever\, E. Vatansever\, N.G. Fytas
\, Physical Review E 104 024108 (2021).\n\n7. P. Riego\, P. Vavassori\, A
. Berger\, Physical Review Letters\, 118 117202 (2017).\n\n8. M. Quintana\
, A. Berger\, Physical Review Letters\, 131 116701 (2023).\n\nRoom: CTC.3.
02 https://findyourway.essex.ac.uk/search/62f111e07a0f322989532426?project
Id=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/123/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Abhishek Kumar (Coventry)
DTSTART:20250206T140000Z
DTEND:20250206T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/125
DESCRIPTION:Title: tbc\nby Abhishek Kumar (Coventry) as part of MESS (Mathema
tics Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/125/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jesús Miguel Seoane Sepúlveda (U Rey Juan Carlos\, Madrid)
DTSTART:20250213T140000Z
DTEND:20250213T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/126
DESCRIPTION:Title: Dynamics and Physics of Cancer\nby Jesús Miguel Seoane Se
púlveda (U Rey Juan Carlos\, Madrid) as part of MESS (Mathematics Essex S
eminar Series)\n\n\nAbstract\nIn this talk\, various studies on the dynami
cs of interactions between tumors and immune cells are presented [1-4]. A
probabilistic hybrid cellular automaton model is developed to describe the
spatiotemporal evolution of tumor growth and its interaction with cell-me
diated immune response. The model parameters are fitted to an ordinary dif
ferential equation model\, which has been previously validated [1] with in
vivo experiments. The cellular automaton is used to conduct in silico exp
eriments that\, along with mathematical analysis\, allow characterization
of the speed at which a tumor is lysed by a population of immune cells [2-
3]. Additionally\, the transient and asymptotic dynamics of cell-mediated
immune response to tumor growth are considered [4]. The cellular automaton
model is utilized to investigate and discuss the ability of cytotoxic cel
ls to maintain long periods of tumor mass latency\, as commonly observed i
n recurrent metastatic disease. Finally\, we apply this technique to simul
ate melanomas and their destruction by the immune system [5].\n\n[1] Alvar
o G. López\, Jesús M. Seoane\, and Miguel A.F. Sanjuán. A validated mat
hematical model of tumor growth including tumor-host interaction\, cell-me
diated immune response\, and chemotherapy. Bulletin of Mathematical Biolog
y 76\, 2884 (2014).\n\n[2] Alvaro G. López\, Jesús M. Seoane\, and Migue
l A.F. Sanjuán. Destruction of solid tumors by immune cells. Communicatio
ns in Nonlinear Science and Numerical Simulation 44\, 390 (2016).\n\n[3]
Alvaro G. López\, Jesús M. Seoane\, and Miguel A.F. Sanjuán. Decay dyn
amics of tumors. Plos ONE 11\, e0157689 (2016).\n\n[4] Alvaro G. López\,
Jesús M. Seoane\, and Miguel A.F. Sanjuán. Dynamics of the cell-mediated
immune response to tumor growth. Proc. R. Soc. A 375\, 20160291 (2017).\
n\n[5] Blanca Nieto\, Manuel Durán-Poveda\, Jesús M. Seoane\, and Miguel
A.F. Sanjuán. Destruction of solid tumors by immune cells. Communication
s in Nonlinear Science and Numerical Simulation 122\, 107248 (2023).\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/126/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xin Guan (Imperial College London)
DTSTART:20250227T140000Z
DTEND:20250227T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/127
DESCRIPTION:Title: Evolution of vortex sheets under a horizontal electric field\nby Xin Guan (Imperial College London) as part of MESS (Mathematics Ess
ex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbstract\nThe vortex sh
eet model is well-known to suffer from ill-posedness and curvature singula
rity due to the Kelvin-Helmholtz instability. Various regularization metho
ds\, such as incorporating vortex blob\, finite-thickness effect\, or surf
ace tension\, have been extensively studied\, and shown to suppress curvat
ure singularities. In this talk\, we investigate the regularization of a h
orizontal electric field on vortex sheets.\n\nElectric fields play a dual
role in the linear stability of fluid interfaces: an electric field vertic
al to the undisturbed interface destabilizes the system\, while a horizont
al one stabilizes the system. However\, it is unclear whether a horizontal
electric field can render the vortex sheet model well-posed in nonlinear
regime and suppress the curvature singularity. In this talk\, we partially
answer the question. Our study employs a hybrid approach combining numeri
cal simulations using boundary integral method with weakly nonlinear model
s based on Hamiltonian structure. Our results indicate that a horizontal e
lectric field does not suppress curvature singularity. Moreover\, there ar
e two distinct regimes where the singularity time exhibits different asymp
totic behaviors\, depending on the strength of both the vortex sheet and t
he electric field.\n\nhttps://findyourway.essex.ac.uk/search/62f111e07a0f3
22989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/127/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mark Blyth (U East Anglia)
DTSTART:20250306T140000Z
DTEND:20250306T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/128
DESCRIPTION:Title: Termination points in a class of inhomogeneous nonlinear ordin
ary differential equations\nby Mark Blyth (U East Anglia) as part of M
ESS (Mathematics Essex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbs
tract\nIn this talk I will discuss a particular class of nonlinear ordinar
y differential equations that are motivated by a problem in water waves. T
he equations have the form\n\\[\nu’’ + u^2 = a f(x)\n\\]\nand are pose
d on the real line for $u(x)\,$ with $u\\to0$ as $|x|\\to\\infty.$ \nHere
$a$ is a parameter. \nThe forcing term on the right-hand side is prescribe
d and is such that $f\\to0$ as $|x|\\to\\infty.$ \n\nI will describe the s
olutions to this problem for different values of the parameter $a.$ \nA pa
rticular point of interest is that when performing continuation in the par
ameter $a\,$ solution branches can terminate\, a most unusual feature. \nI
will provide an explanation of this phenomenon via an asymptotic construc
tion.\n\nhttps://findyourway.essex.ac.uk/search/62f111e07a0f322989532426?p
rojectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/128/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matheus Rolim Sales (U Essex)
DTSTART:20250220T140000Z
DTEND:20250220T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/129
DESCRIPTION:Title: Characterization of weakly chaotic dynamics in area-preserving
mappings\nby Matheus Rolim Sales (U Essex) as part of MESS (Mathemati
cs Essex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbstract\nIn two-
dimensional\, area-preserving mappings with hierarchical phase space\, cha
otic orbits can spend an arbitrarily long time around stability islands\,
during which they behave similarly to quasiperiodic orbits. This phenomeno
n is called stickiness\, and it is due to the presence of partial barriers
to the transport around the hierarchical levels of islands-around-islands
. The stickiness affects the convergence of the Lyapunov exponents\, makin
g the task of characterizing the dynamics more difficult\, especially when
only short time series are known. Due to the intrinsic property of dynami
cal systems that quasiperiodic orbits can have at most three different ret
urn times (Slater’s theorem)\, which is the time needed for the orbit to
return to a given region along the orbit\, in this talk\, we discuss the
use of the recurrence time entropy (RTE) (estimated from the recurrence pl
ots) to characterize the dynamics of nonlinear systems. We find that the R
TE is an alternative way of detecting chaotic orbits and sticky regions. F
urthermore\, the finite-time RTE distribution is multi-modal when sticky r
egions are present in the phase space\, and each mode corresponds to a dif
ferent hierarchical level in the islands-around-islands structure embedded
in the chaotic sea.\n\nhttps://findyourway.essex.ac.uk/search/62f111e07a0
f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/129/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Abhishek Kumar (Coventry U)
DTSTART:20250313T140000Z
DTEND:20250313T150000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/130
DESCRIPTION:Title: Linear and Nonlinear Stability of Stratified Flows: Instabilit
ies and Control\nby Abhishek Kumar (Coventry U) as part of MESS (Mathe
matics Essex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbstract\nWe
investigate the stability and control of stably stratified flow in a nearl
y semicylindrical cavity\, motivated by metallurgical casting processes wh
ere hot liquid metal is poured into a sump with cold walls and allowed to
solidify at the bottom. The flow domain features an upper free surface (fo
r fluid inflow) and porous lower boundaries (for fluid outflow) and is gov
erned by buoyancy-driven equations under the Boussinesq approximation\, wh
ich we solve using the spectral element method. Linear stability analysis
first reveals that the two-dimensional steady base flow becomes unstable t
o either oscillatory or non-oscillatory three-dimensional modes\, dependin
g on the inlet net mass flux. Further examination of the nonlinear evoluti
on via three-dimensional direct numerical simulations and the Stuart–Lan
dau equation demonstrates both supercritical and subcritical transitions f
or different parameter regimes [1].\n\nTo suppress these instabilities\, w
e employ a thermo-mechanical actuation strategy derived from receptivity a
nalysis\, utilising both direct and adjoint eigenmodes to pinpoint regions
of high sensitivity. Our receptivity maps identify the mid-section of the
inlet as particularly receptive\, guiding the design of time-dependent ac
tuation. Numerical experiments carried out using NEKTAR++ [2] show that ap
plying this receptivity-informed control effectively suppresses the unstab
le modes for a finite duration. Notably\, when the actuation amplitude is
maintained at a constant value over time\, a simpler approach suitable for
industrial settings\, the flow becomes re-destabilised after an initial s
tabilising phase. By contrast\, activating the actuation only during the s
tabilising stage of the mode evolution yields sustained stabilisation even
after the control input is removed. These findings highlight the effectiv
eness of receptivity-based strategies in suppressing instabilities and pro
pose a practically implementable route for long-term flow control [3].\n\n
References:\n\n[1] Kumar and Pothérat\, JFM (2020). \n\n[2] Moxey et al.
\, CPC (2020).\n\n[3] Kumar and Pothérat\, arXiv (2024).\n\nhttps://findy
ourway.essex.ac.uk/search/62f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/130/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Leïla Moueddene (University of Lorraine)
DTSTART:20250529T130000Z
DTEND:20250529T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/131
DESCRIPTION:Title: Critical and tricritical behavior of the d=3 Blume-Capel mode
through the zeros of the partition function\nby Leïla Moueddene (Univ
ersity of Lorraine) as part of MESS (Mathematics Essex Seminar Series)\n\n
\nAbstract\nWe investigate the location of the critical and tricritical po
ints of the three-dimensional\nBlume-Capel model by analyzing the behavior
of the first Lee-Yang zero\, the density of\npartition function zeros\, a
nd higher-order cumulants of the magnetization. Our analysis is\nconducted
through Monte Carlo simulations\, intentionally using only small system s
izes. We\ndemonstrate that this approach yields excellent results for stud
ying the critical behavior of\nthe model. Our findings indicate that at th
e tricritical point\, where logarithmic corrections are\nanticipated\, the
numerical results align closely with the theoretical exponents describing
\nthese corrections.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/131/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matteo Vannacci (U Florence\, Italy)
DTSTART:20250605T130000Z
DTEND:20250605T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/132
DESCRIPTION:Title: Representations over finite fields\, Probability and Zeta Func
tions\nby Matteo Vannacci (U Florence\, Italy) as part of MESS (Mathem
atics Essex Seminar Series)\n\n\nAbstract\nWe will start with a little int
roduction to profinite groups and their Haar measure. Then\, we will outli
ne the connection between the asymptotic growth of the number of represent
ations over finite fields of a profinite group $G$ and the probability of
generating its group algebra with Haar-random elements. Finally\, we will
see how to encode the number of representations over finite fields of a pr
ofinite group $G$ into a zeta function and how analytic invariants of this
zeta function remember properties of the group $G$.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/132/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Robert Hanson (U Essex)
DTSTART:20250612T130000Z
DTEND:20250612T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/133
DESCRIPTION:Title: tbc\nby Robert Hanson (U Essex) as part of MESS (Mathemati
cs Essex Seminar Series)\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/133/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Roberto Ribeiro (U Parana\, Brazil)
DTSTART:20250619T130000Z
DTEND:20250619T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/134
DESCRIPTION:Title: Full Euler Equations for Waves Generated by Vertical Seabed Di
splacements\nby Roberto Ribeiro (U Parana\, Brazil) as part of MESS (M
athematics Essex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbstract\
nIn this seminar\, we will present a study on the generation and propagati
on of surface water waves caused by vertical displacements of the ocean fl
oor. Besides\, we will discuss our initial results on horizontal displac
ements. One of the key motivations behind this study is the modeling of ts
unamis triggered by underwater earthquakes\, with the goal of gaining a be
tter understanding of their characteristics and behavior over time.\n\nThi
s is a topic of significant social and scientific relevance\, drawing inte
rest from fields such as engineering\, physics\, mathematics\, and oceanog
raphy. In our work\, we adopt the classical hydrodynamic equations as the
physical model for the phenomenon. Mathematically\, this leads to a Laplac
e problem with a free and moving boundary\, whose evolution — representi
ng the free surface of the ocean — is governed by a nonlinear system of
partial differential equations.\n\nWe have developed a numerical method ca
pable of accurately simulating both the generation and propagation of such
waves. A key feature of our approach is the use of a time-dependent confo
rmal mapping\, which captures the evolving geometry of the ocean floor and
the dynamic wave profile at the free surface. This enables the applicatio
n of pseudo-spectral methods for solving the equations with high accuracy.
\n\nIn the talk\, we will compare fully nonlinear results with those obtai
ned from classical linear models (in the case of vertical displacements)\,
and also discuss validation through laboratory experiments (for horizonta
l displacements).\n\nThis work is a collaboration with João Vitor P. Pole
tto - UFPR (Brazil)\, David Andrade - Universidad del Rosario (Colombia)\
, and Marcelo Flamarion - Pontificia Universidad Católica del Perú (Peru
).\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/134/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kimaro Kairuntu (U Essex)
DTSTART:20250626T130000Z
DTEND:20250626T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/135
DESCRIPTION:Title: Pricing Asian option under mean reversion and jumps\, based on
Fast Fourier Transform\, Artificial Neural Networks and Deep Learning met
hods\nby Kimaro Kairuntu (U Essex) as part of MESS (Mathematics Essex
Seminar Series)\n\nLecture held in CTC.3.02.\n\nAbstract\nWe propose an ef
ficient pricing approach for arithmetic Asian options by utilising machine
learning techniques\, specifically neural networks and deep learning\, in
scenarios where a closed-form formula is unavailable.\nOur method explici
tly incorporates mean reversion and jump components into the underlying pr
ice dynamics\, which are well-supported by empirical literature as signifi
cant anomalies in certain asset classes\, including commodities.\nThe appr
oach is specifically designed for discretely monitored European-style arit
hmetic Asian options.\nThe analytical solutions derived from our Fast Four
ier Transform are employed to generate option price values for training an
d testing our machine learning models.\nThe results are then benchmarked a
gainst Monte Carlo simulation-based pricing to assess accuracy and computa
tional efficiency.\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/135/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marcelo Flamarion (Pontifical Catholic University of Peru)
DTSTART:20250710T130000Z
DTEND:20250710T140000Z
DTSTAMP:20260424T222120Z
UID:EssexMaths/136
DESCRIPTION:Title: Modeling nonlinear wave phenomena using dynamical systems\
nby Marcelo Flamarion (Pontifical Catholic University of Peru) as part of
MESS (Mathematics Essex Seminar Series)\n\nLecture held in CTC.3.02.\n\nAb
stract\nIn this talk\, we explore how solitons interact with external forc
es in nonlinear PDEs\, focusing on Korteweg–de Vries (KdV) type equation
s that model shallow water waves. External forces—deterministic or stoch
astic—represent effects like wind stress\, variable bathymetry\, or loca
lized pressure. These inputs alter soliton stability and trajectory. We ex
amine the emergence of trapped waves\, where resonant interactions cause s
oliton dynamics to resemble those of a nonlinear oscillator\, evolving in
amplitude–phase space. In addition\, the flow structures beneath such so
litons are also discussed.\n\nRoom: CTC.3.02 https://findyourway.essex.ac.
uk/search/62f111e07a0f322989532426?projectId=essexc\n
LOCATION:https://stable.researchseminars.org/talk/EssexMaths/136/
END:VEVENT
END:VCALENDAR