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BEGIN:VEVENT
SUMMARY:Johan Ulander (Chalmers University of Technology)
DTSTART;VALUE=DATE-TIME:20230830T111500Z
DTEND;VALUE=DATE-TIME:20230830T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/1
DESCRIPTION:Title: Boun
dary-preserving numerical schemes for stochastic (partial) differential eq
uations\nby Johan Ulander (Chalmers University of Technology) as part
of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk we con
sider stochastic (partial) differential equations whose solutions remain i
n some (half-)bounded domain. This includes\, for example\, models for hea
t flow whose solutions remain positive. In general\, classical numerical s
chemes do not have the property of remaining in such domain. In this half-
way seminar\, I present some novel ideas for developing and analysing boun
dary-preserving numerical schemes for stochastic (partial) differential eq
uations. The presentation is based on joint works with Charles-Edouard Br
éhier\, David Cohen\, and Lluís Quer-Sardanyons.\n
LOCATION:https://researchseminars.org/talk/cam/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yoshio Komori (Kyushu Institute of Technology)
DTSTART;VALUE=DATE-TIME:20230906T111500Z
DTEND;VALUE=DATE-TIME:20230906T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/2
DESCRIPTION:Title: Spli
t S-ROCK methods for high-dimensional stochastic differential equations\nby Yoshio Komori (Kyushu Institute of Technology) as part of CAM semina
r\n\nLecture held in MV:L14.\n\nAbstract\nWe propose explicit stochastic R
unge--Kutta (RK) methods for high-dimensional It\\^{o} stochastic differen
tial equations. By providing a linear error analysis and utilizing a Stran
g splitting-type approach\, we construct them on the basis of orthogonal R
unge--Kutta—Chebyshev methods of order 2. Our methods are of weak order
2 and have high computational accuracy for relatively large time-step size
\, as well as good stability properties. In addition\, we take stochastic
exponential RK methods of weak order 2 as competitors. It is shown that th
e proposed methods can be very effective on high-dimensional problems whos
e drift term has eigenvalues lying near the negative real axis and whose d
iffusion term does not have very large noise. This is a joint work with Pr
of. Kevin Burrage.\n
LOCATION:https://researchseminars.org/talk/cam/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sagy Ephrati (University of Twente)
DTSTART;VALUE=DATE-TIME:20230920T111500Z
DTEND;VALUE=DATE-TIME:20230920T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/3
DESCRIPTION:Title: Stoc
hastic modeling for coarse computational geophysical fluid dynamics\nb
y Sagy Ephrati (University of Twente) as part of CAM seminar\n\nLecture he
ld in MV:L14.\n\nAbstract\nStochasticity has been employed systematically
in geophysical fluid dynamics (GFD) to model uncertainty. Additionally\, f
ully resolving geophysical flows is computationally expensive due to the l
arge range of scales of motion present in these flows. These computational
costs are efficiently mitigated by performing GFD simulations on coarse c
omputational grids and modeling the effects of unresolved scales on resolv
ed scales. On such grids\, the uncertainty due to unresolved small-scale m
otions has to be taken into account as well as the loss of accuracy due to
poorly resolved spatial derivatives. In this presentation\, we discuss ho
w data assimilation methods can be used to derive data-driven stochastic f
orcing for coarse computational GFD. We will show that a straightforward a
lgorithm\, based on several simplifying assumptions\, already leads to qua
litatively accurate outcomes at strongly reduced computational costs.\n
LOCATION:https://researchseminars.org/talk/cam/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Akash Sharma (Chalmers University of Technology and University of
Gothenburg)
DTSTART;VALUE=DATE-TIME:20230913T111500Z
DTEND;VALUE=DATE-TIME:20230913T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/4
DESCRIPTION:Title: Rand
om walks for approximating boundary value problems\nby Akash Sharma (
Chalmers University of Technology and University of Gothenburg) as part of
CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nWe will present numer
ical method to simulate reflected stochastic differential equations. We ge
neralize this algorithm to approximately solve linear Robin boundary value
problems via their probabilistic representations. In next part of the tal
k\, we will present numerical schemes to simulate confined Langevin dynami
cs which results in approximate solution of specular boundary value proble
ms. We obtain rate of convergence of these algorithms and verify them with
numerical experiments. This is a joint work with Prof. Benedict Leimkuhle
r (University of Edinburgh) and Prof. Michael V. Tretyakov (University of
Nottingham).\n
LOCATION:https://researchseminars.org/talk/cam/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ioanna Motschan-Armen (Chalmers University of Technology and Unive
rsity of Gothenburg)
DTSTART;VALUE=DATE-TIME:20230927T111500Z
DTEND;VALUE=DATE-TIME:20230927T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/5
DESCRIPTION:Title: Eule
r-Maruyama approximations of the stochastic heat equation on the sphere\nby Ioanna Motschan-Armen (Chalmers University of Technology and Univers
ity of Gothenburg) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAb
stract\nThe stochastic heat equation on the sphere driven by additive isot
ropic Wiener\nnoise is approximated by a spectral method in space and forw
ard and backward Euler–\nMaruyama schemes in time. The spectral approxim
ation is based on a truncation of the series\nexpansion with respect to th
e spherical harmonic functions. Optimal strong convergence rates\nfor a gi
ven regularity of the initial condition and driving noise are derived for
the Euler–\nMaruyama methods. Besides strong convergence\, convergence o
f the expectation and second\nmoment is shown\, where the approximation of
the second moment converges with twice the\nstrong rate. Numerical simula
tions confirm the theoretical results.\nThis is joint work with Annika Lan
g.\n
LOCATION:https://researchseminars.org/talk/cam/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mohammad Asadzadeh (Chalmers & University of Gothenburg)
DTSTART;VALUE=DATE-TIME:20231011T111500Z
DTEND;VALUE=DATE-TIME:20231011T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/6
DESCRIPTION:Title: On N
itsche approach for a finite element scheme for Maxwell equations\nby
Mohammad Asadzadeh (Chalmers & University of Gothenburg) as part of CAM se
minar\n\nLecture held in MV:L14.\n\nAbstract\nWe show improved convergence
for a $h-p$\, streamline diffusion (SD)\, Nitsche's scheme for the Vlasov
-Maxwell (VM) system. The standard Galerkin for VM equations\, as 1st orde
r hyperbolic\, suffers from the draw-back of poor convergence. We have imp
roved this convergence rate using: \n\n(i) The SD method that adds artific
ial diffusion to the system.\n\n(ii) The $h-p$ approach to gain adaptivity
feature. \n\n(iii) Combined\, differentiated\, Maxwell equations to rende
r the first order hyperbolic system to a second order hyperbolic equation
(not applicable to Vlasov part). \n\n(iv) Add of {\\sl symmetry} and {\\sl
penalty} terms to reach final step of Nitsche's scheme.\n\nNumerical exam
ples are justifying the theory.\n
LOCATION:https://researchseminars.org/talk/cam/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBA
DTSTART;VALUE=DATE-TIME:20231018T111500Z
DTEND;VALUE=DATE-TIME:20231018T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/8
DESCRIPTION:by TBA as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Institutionsdag
DTSTART;VALUE=DATE-TIME:20231025T111500Z
DTEND;VALUE=DATE-TIME:20231025T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/9
DESCRIPTION:by Institutionsdag as part of CAM seminar\n\nLecture held in M
V:L14.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBA
DTSTART;VALUE=DATE-TIME:20231101T121500Z
DTEND;VALUE=DATE-TIME:20231101T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/10
DESCRIPTION:by TBA as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Luigi Romano (Chalmers University of Technology)
DTSTART;VALUE=DATE-TIME:20231108T121500Z
DTEND;VALUE=DATE-TIME:20231108T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/11
DESCRIPTION:Title: Fin
ite element modelling of linear rolling contact problems\nby Luigi Rom
ano (Chalmers University of Technology) as part of CAM seminar\n\nLecture
held in MV:L14.\n\nAbstract\nThis Master's thesis deals with the numerical
approximation of linear hyperbolic problems appearing in rolling contact
mechanics. First\, the existence and uniqueness of strict solutions to the
considered equations\, which contain nonlocal and boundary terms\, are an
alysed within the framework provided by the semigroup theory. Then\, the s
pace semi-discrete problem is formulated using the discontinuous Galerkin
finite element method (DGMs)\, by replacing the unbounded operator appeari
ng in the abstract formulation with a finite-dimensional one. Quasi-optima
l error convergence is obtained for the space semi-discrete scheme by intr
oducing upwind regularisation. Time discretisation is then achieved by rel
ying on explicit first and second-order Runge-Kutta algorithms (RK1 and RK
2\, respectively)\, yielding quasi-optimal convergence in time owing to ce
rtain refined CFL conditions. In particular\, the considered RK2 schemes c
over the explicit midpoint method\, Heun's second-order method\, and Ralst
on's method.\n
LOCATION:https://researchseminars.org/talk/cam/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Moritz Hauck (Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20231115T121500Z
DTEND;VALUE=DATE-TIME:20231115T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/12
DESCRIPTION:Title: Gua
ranteed lower energy bounds for the Gross-Pitaevskii problem using mixed f
inite elements\nby Moritz Hauck (Chalmers and GU) as part of CAM semin
ar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk\, we present a low
est order Raviart-Thomas finite element discretization that provides guara
nteed lower bounds on the ground state energy of the nonlinear Gross-Pitae
vskii problem. We emphasize that due to their conformity\, classical discr
etization methods such as the $\\mathcal P^1$ or $\\mathcal Q^1$ finite el
ement methods can only provide upper bounds on the ground state energy. Fu
rthermore\, we establish an a priori error analysis for the Raviart-Thomas
discretization of the Gross-Pitaevskii problem. Optimal convergence rates
are shown for the primary and dual variables as well as for the eigenvalu
e and energy approximations.\n
LOCATION:https://researchseminars.org/talk/cam/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Johannes Borgqvist (University of Oxford\, Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20231122T121500Z
DTEND;VALUE=DATE-TIME:20231122T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/13
DESCRIPTION:Title: Lie
symmetries for constructing\, selecting and analysing mechanistic models
in mathematical biology\nby Johannes Borgqvist (University of Oxford\,
Chalmers and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbs
tract\nGiven the abundance of experimental data\, two of the most fundamen
tal questions in mechanistic modelling of biological data concern model co
nstruction and model selection. A common type of data is time series data
describing how some quantity\, e.g. population size or protein abundance\,
changes over time. Given such a time series\, it is often possible to con
struct numerous candidate mechanistic models consisting of ordinary differ
ential equations based on physical principles encoding distinct biological
hypotheses. Worse still\, numerous candidate models of the same time seri
es often describe the same data equally well\, and thus they cannot be dis
tinguished based on their fit to data. In these situations it is therefore
difficult to select one candidate model and thereby infer a biological me
chanism underlying the biological data. In this presentation\, we tackle t
he two fundamental problems of model construction and model selection by m
eans of Lie symmetries (or simply just symmetries) of ordinary differentia
l equations. These are\, simply put\, (one parameter pointwise) transforma
tions known as $\\mathcal{C}^{\\infty}$ diffeomorphisms which map a soluti
on curve to another solution curve. Symmetries are commonly used in mathem
atical physics and they are the basis for numerous Nobel prizes but they a
re almost unheard of in mathematical biology.\n\nTo solve the classical mo
del selection problem\, we have developed and implemented a methodology fo
r model selection based on symmetries. We implement this framework on actu
al experimental data describing the age-related increase in cancer risk. I
mportantly\, we infer experimentally validated hypotheses underlying diffe
rent cancer types using the symmetry based framework which the standard me
thodology based on model fitting fails to do. \n\nThereafter\, we switch f
ocus to model construction in the context of travelling wave models of col
lective cell migration. These models consists of a single second order ODE
describing how the population density $u(z)$ changes with respect to a tr
avelling wave variable $z=x-ct$ where the constant $c$ is referred to as t
he wave speed. Moreover\, certain such models of reaction diffusion type a
s well as other models with density dependent diffusion are known to have
specific analytical solutions of a simple form for certain wave speeds. Th
ese analytical solutions have been obtained by means of ansätze based on
series expansions\, and using these methods it is difficult to define the
class of models which have simple analytical solutions. To tackle this pro
blem\, we consider a set of symmetries referred to as a Lie Algebra consis
ting of two symmetries that has been used to find analytical solutions of
a second order ODE encapsulating numerous oscillatory models such as the v
an der Pol oscillator. Based on differential invariants\, we derive the mo
st general class of models for which this Lie Algebra is manifest. Thereaf
ter\, we implement Lie's algorithm based on step-wise integration in order
to demonstrate how first integrals and (if possible) analytical solutions
of all ODEs in our class of models are obtained. Using this general class
of models\, we construct a sub-class of models characterised by the previ
ously mentioned simple analytical solution. Lastly\, we demonstrate how th
is sub-class encapsulates the previously known models with analytical solu
tions and we quantify the action of the symmetries in this Lie algebra on
these analytical solutions. In total\, this work demonstrates how classes
of mechanistic models can be constructed based on mathematical properties
encoded by a Lie Algebra in contrast to the standard way of model construc
tion based on physical assumptions that are hard to validate.\n
LOCATION:https://researchseminars.org/talk/cam/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Michael Roop (Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20231129T121500Z
DTEND;VALUE=DATE-TIME:20231129T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/14
DESCRIPTION:Title: Lie
-Poisson methods for incompressible magnetohydrodynamics on the sphere
\nby Michael Roop (Chalmers and GU) as part of CAM seminar\n\nLecture held
in MV:L14.\n\nAbstract\nWe present a novel structure preserving numerical
method for Lie-Poisson systems on the dual of semidirect product Lie alge
bras. The method fully preserves the underlying geometry\, namely the Lie-
Poisson structure and all the Casimirs\, and nearly preserves the Hamilton
ian function. We illustrate the method on two models describing the motion
of magnetic fluids\, the equations of incompressible magnetohydrodynamics
\, and the Alfvén wave turbulence equations. For the latter case\, we rev
eal the formation of large scale quasi-periodic vortex blob dynamics.\n\nT
his is a joint work with Klas Modin.\n
LOCATION:https://researchseminars.org/talk/cam/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBA
DTSTART;VALUE=DATE-TIME:20231206T121500Z
DTEND;VALUE=DATE-TIME:20231206T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/15
DESCRIPTION:by TBA as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tommy Svensson and Anders Logg (Chalmers)
DTSTART;VALUE=DATE-TIME:20231213T121500Z
DTEND;VALUE=DATE-TIME:20231213T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/16
DESCRIPTION:Title: Sus
tainable Urban C-V2X with Intelligent Radio Environment Twinning\nby T
ommy Svensson and Anders Logg (Chalmers) as part of CAM seminar\n\nLecture
held in MV:L14.\n\nAbstract\nUbiquitous connectivity to power Information
and communication technologies (ICTs) is crucial for the modern society.
Besides\, ICT also has an important role for accelerating economic process
es that enable sustainability. As one part of ICT in smart and sustainable
cities\, cellular vehicle to everything (C-V2X)-based automated driving w
ill be crucial for fully autonomous or remotely operated vehicles in urban
environments. To this end\, different communication technologies have bee
n developed to improve the efficiency and reliability of the network perfo
rmance\, such as millimeter wave communications and reconfigurable intelli
gent surface (RIS). However\, challenges remain especially in urban areas
where the performance is normally hard to be evaluated before deployments.
Fortunately\, digital twinning can embed artificial intelligence and ICT
to provide a digital replica of real-life environments. With specific char
acteristics\, the replica is almost a cloned version of the original syste
m\, and is able to constantly update the properties with real-time data fr
om sensors. In this presentation\, we will present recent progress in our
AoA-ICT Seed Project on programmable\, and environmental-suitable communic
ation paradigm for C-V2X in dense city environments empowered by digital t
winning.\n
LOCATION:https://researchseminars.org/talk/cam/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eric Lindström (Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20240226T121500Z
DTEND;VALUE=DATE-TIME:20240226T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/17
DESCRIPTION:Title: Mul
tidimensional Coefficent Inverse Problems for Maxwellian Systems in Conduc
tive Media with Applications in Medical Imaging\nby Eric Lindström (C
halmers and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstr
act\nThe talk will present a new method for medical imaging in the context
of coefficient inverse problems (CIPs) in maxwellian systems. The main ai
m is to find potential tumors in human breasts by reconstructing the value
and shape of spatial functions describing the dielectric properties of va
rious tissue types. The algorithms used for the hybrid method will be intr
oduced\, together with some theoretical results which discuss the well-pos
edness of the underlying problem\, as well as the convergence of the recon
structing method. We will also look at numerical results achieved by apply
ing our method to anatomically realistic data.\n
LOCATION:https://researchseminars.org/talk/cam/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Rupp (Lappeenranta-Lahti University of Technology)
DTSTART;VALUE=DATE-TIME:20240219T121500Z
DTEND;VALUE=DATE-TIME:20240219T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/18
DESCRIPTION:Title: Par
tial differential equations on hypergraphs and networks of surfaces\nb
y Andreas Rupp (Lappeenranta-Lahti University of Technology) as part of CA
M seminar\n\nLecture held in MV:L14.\n\nAbstract\nAlbeit many physical\, s
ociological\, engineering\, and economic processes have been described by
partial differential equations posed on domains which cannot be described
as subsets of linear spaces or smooth manifolds\, there is still a lack of
mathematical tools and general purpose software specifically addressing t
he challenges arising from the discretization of these models.\n\nThis pre
sentation establishes a general approach to formulate partial differential
equations (PDEs) on networks of (hyper)surfaces\, referred to as hypergra
phs. Such PDEs consist of differential expressions with respect to all hyp
eredges (surfaces) and compatibility conditions on the hypernodes (joints\
, intersections of surfaces). These compatibility conditions ensure conser
vation properties (in case of continuity equations) or incorporate other p
roperties – motivated by physical or mathematical modeling. We illuminat
e how to discretize such equations numerically using hybrid discontinuous
Galerkin (HDG) methods. These methods consist of local solvers (encoding t
he differential expressions on hyperedges) and a global compatibility cond
ition (related to our hypernode conditions). We complement the physically
motivated compatibility conditions by a derivation through a singular limi
t analysis of thinning structures yielding the same results.\n
LOCATION:https://researchseminars.org/talk/cam/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Brynjulf Owren (NTNU Trondheim)
DTSTART;VALUE=DATE-TIME:20240212T121500Z
DTEND;VALUE=DATE-TIME:20240212T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/19
DESCRIPTION:Title: Sta
bility of numerical methods on Riemannian manifolds\nby Brynjulf Owren
(NTNU Trondheim) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbs
tract\nStability of numerical integrators play a crucial role in approxima
ting the flow of differential equations. Issues related to convergence and
step size limitations have been successfully resolved by studying the sta
bility properties of numerical schemes. Stability also plays a role in the
existence and uniqueness to the solution of the nonlinear algebraic equat
ions that need to be solved in each time step for an implicit method.\nHow
ever\, very little has up to now been known about stability properties of
numerical methods on manifolds\, such as Lie group integrators. An interes
t in these questions has recently been sparked by the efforts in construct
ing ODE based neural networks that are robust against adversarial attacks.
In this talk we shall discuss a new framework for B-stability on Riemanni
an manifolds. A method is B-stable if the numerical method exhibits a non-
expansive behaviour in the Riemannian distance measure when applied to pro
blems which have non-expansive solutions.\nWe shall in particular see how
the sectional curvature of the manifold plays a role\, and show some surpr
ising results regarding the non-uniqueness of geodesic implicit integrator
s for positively curved spaces.\n
LOCATION:https://researchseminars.org/talk/cam/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrea Papini (Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20240304T121500Z
DTEND;VALUE=DATE-TIME:20240304T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/20
DESCRIPTION:Title: Tur
bulence enhancement of coagulating processes\nby Andrea Papini (Chalme
rs and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\n
We present and investigate the collision-coalescence process of particles
in the presence of a fluid velocity field\, examining the relationship bet
ween flow properties and enhanced coagulation. Our research focuses on two
main aspects. Firstly\, we propose a novel modeling approach for turbulen
t fluid at small scales\, employing a Gaussian random field with non-trivi
al spatial covariance. Secondly\, we derive rigorous partial differential
equations (PDEs) and stochastic partial differential equations (SPDEs) fro
m this model\, capturing the physical characteristics of particles suspend
ed in the fluid. From an Eulerian perspective\, we analyze a kinetic parti
cle system subjected to environmental transport noise. Specifically\, we r
igorously study a modified version of Smoluchowski’s coagulation equatio
n\, which incorporates velocity dependence akin to the Boltzmann equation.
By utilizing techniques rooted in unbounded elliptic semigroup theory and
weighted Sobolev space inequalities\, we establish the existence and uniq
ueness of classical solutions for the case of a spatially homogeneous init
ial distribution. Moreover\, from a Lagrangian viewpoint\, we employ this
particle system to gain insights into the collision rate at a steady state
for particles uniformly distributed within a medium. Considering a partic
le-fluid model\, we perform two scaling limits. The first limit\, involvin
g the number of particles\, yields a stochastic Smoluchowski-type system\,
with the turbulent velocity field still governed by a noise stochastic pr
ocess. The second scaling limit pertains to the parameters of the noise\,
specifically targeting the direction associated with small-scale turbulenc
e. This limit leads to a deterministic equation with eddy dissipation in t
he velocity variable. We conduct numerical simulations of this equation sy
stem and demonstrate the influence of turbulence on rain formation. Our qu
alitative findings reveal a steady increase in coagulation efficiency with
escalating turbulent kinetic energy of the fluid. Additionally\, we obser
ve a power-law decay over time and in relation to the turbulence parameter
. Furthermore\, we recover fundamental laws governing the collision rate a
nd relative velocity of moving particles in the high Stokes number regime.
\n
LOCATION:https://researchseminars.org/talk/cam/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Verena Schwarz (University of Klagenfurt)
DTSTART;VALUE=DATE-TIME:20240318T121500Z
DTEND;VALUE=DATE-TIME:20240318T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/21
DESCRIPTION:Title: Hig
her-order approximation and optimality for jump-diffusion SDEs with discon
tinuous drift\nby Verena Schwarz (University of Klagenfurt) as part of
CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nIn this talk we consi
der the approximation of jump-diffusion stochastic differential equations
with discontinuous drift\, possibly degenerate diffusion coefficient\, and
Lipschitz continuous jump coefficient. We present a jump-adapted higher-o
rder scheme\, the so-called transformation-based jump-adapted quasi-Milste
in scheme. For this scheme\, we provide a complete error analysis: We prov
e convergence order $3/4$ in $L^p$ for $p\\in[1\,\\infty)$. Further\, we p
rovide lower error bounds for non-adaptive and jump-adapted approximation
schemes of order $3/4$ in $L^1$. This yields optimality of the transformat
ion-based jump-adapted quasi-Milstein scheme.\n\nThis is joint work with P
awel Przybylowicz and Michaela Szölgyenyi.\n
LOCATION:https://researchseminars.org/talk/cam/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stefano Di Giovacchino (University of L'Aquila)
DTSTART;VALUE=DATE-TIME:20240408T111500Z
DTEND;VALUE=DATE-TIME:20240408T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/22
DESCRIPTION:Title: Sto
chastic backward error analysis: application to Hamiltonian systems and op
timization algorithms\nby Stefano Di Giovacchino (University of L'Aqui
la) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nBackwar
d error analysis is a powerful tool in order to capture the long-term beha
viour of numerical integrators. In this talk\, we address our attention on
providing a backward error analysis (both in the strong and weak sense) f
or classes of numerical methods. From one hand\, the attention will be dev
oted to symplectic methods and Poisson integrators for stochastic Hamilton
ian and Poisson systems. Here\, we present strategies for deriving stochas
tic modified equations for the aforementioned integrators and we study the
m for obtaining long-term estimates on the Hamiltonian errors along the nu
merical dynamics.\nFrom the other hand\, the weak backward error approach
will be developed towards stochastic optimization algorithms\, with the ai
m of gaining insights of their behaviour.\nThis talk is based on joint res
earches with Raffaele D'Ambrosio (University of L'Aquila)\, Desmond J. Hig
ham and Konstantios C. Zygalakis (University of Edinburgh).\n
LOCATION:https://researchseminars.org/talk/cam/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fanny Seizilles (University of Cambride)
DTSTART;VALUE=DATE-TIME:20240415T111500Z
DTEND;VALUE=DATE-TIME:20240415T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/23
DESCRIPTION:Title: The
Bayesian approach to inverse Robin problems\nby Fanny Seizilles (Univ
ersity of Cambride) as part of CAM seminar\n\nLecture held in MV:L14.\n\nA
bstract\nWe investigate the Bayesian approach to certain elliptic boundary
value problems of determining a Robin coefficient on a hidden part of the
boundary from Cauchy data on the observable part. Such a nonlinear invers
e problem arises naturally in the initialisation of large-scale ice sheet
models. In this talk we will specifically focus on the computational routi
ne to estimate posterior densities for the Robin coefficient.\n\n\nThe Bay
esian approach is motivated for a prototypical Robin inverse problem by sh
owing that the posterior mean converges in probability to the data-generat
ing ground truth as the number of observations increases. Related to the s
tability theory for inverse Robin problems\, a logarithmic convergence rat
e for Sobolev-regular Robin coefficients is established\, whereas for anal
ytic coefficients an algebraic rate can be attained. Our numerical results
on synthetic data illustrate the convergence property in two observation
settings. (Joint work with Aksel Kaastrup Rasmussen\, Ieva Kazlauskaite an
d Mark Girolami).\n
LOCATION:https://researchseminars.org/talk/cam/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Zheng Zhao (Uppsala University)
DTSTART;VALUE=DATE-TIME:20240205T121500Z
DTEND;VALUE=DATE-TIME:20240205T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/24
DESCRIPTION:Title: Mom
ent quadrature for stochastic filtering\nby Zheng Zhao (Uppsala Univer
sity) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nStoch
astic filtering is an important estimation problem for time series. In thi
s talk\, we present a class of filters that represent the filtering distri
butions by their moments. The key enablement is a quadrature method that u
ses orthonormal polynomials spanned by the moments. We show that this mome
nt-based filter is asymptotically exact in the order of moments\, and that
the filter is also computationally efficient and is in line with the stat
e of the art.\n
LOCATION:https://researchseminars.org/talk/cam/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Axel Ringh (Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20240506T111500Z
DTEND;VALUE=DATE-TIME:20240506T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/25
DESCRIPTION:Title: Gai
n and phase type multipliers for structured feedback robustness\nby Ax
el Ringh (Chalmers and GU) as part of CAM seminar\n\nLecture held in MV:L1
4.\n\nAbstract\nOne of the most fundamental problems in control theory is
feedback stability analysis. That is\, the problem of determining if two s
ystems interconnected via feedback will be stable. In the case of linear t
ime-invariant systems\, under mild conditions the solvability of a set of
linear matrix inequalities (LMIs) is a both necessary and sufficient condi
tion for stability. Nevertheless\, models of reality are always imperfect\
, and in robust stability analysis one therefore instead consider the prob
lem if a feedback interconnection between a nominal system and a set of un
certainties is stable for all uncertainties in the set. In this talk\, I w
ill present new results on that robustness to certain forms of structured
uncertainties is equivalent with the existence of certain forms of structu
red solutions to the LMIs. The talk is aimed to be self-contained\; no pri
or knowledge on control theory is needed\, and all relevant concepts will
be introduced and explained.\n
LOCATION:https://researchseminars.org/talk/cam/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Klas Modin (Chalmers and GU)
DTSTART;VALUE=DATE-TIME:20240129T121500Z
DTEND;VALUE=DATE-TIME:20240129T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/26
DESCRIPTION:Title: The
reversibility paradox in matrix hydrodynamics\nby Klas Modin (Chalmer
s and GU) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract\nS
ome time ago\, Milo Viviani and myself unveiled numerical simulations of i
ncompressible 2-D hydrodynamics on the sphere indicating a connection betw
een the long-time behavior of 2-D Euler equations and integrability condit
ions for "blob dynamics". After presenting these results\, I was asked an
insightful question:\n\nThe phase space underlying the model in the simula
tions is compact. Because the dynamics in the model is also Hamiltonian\,
we have Poincaré recurrence. But the dynamics in the simulations\, leadin
g to blob formations\, seem contractive. Isn't the mechanism for blob form
ations instead induced by fictitious dissipation\, introduced via the nume
rical time-discretization?\n\nI didn’t have a good answer at the time\,
but the question stayed with me. Today I have an answer\, which is the sub
ject of this talk.\n
LOCATION:https://researchseminars.org/talk/cam/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eddie Wadbro (Karlstad University)
DTSTART;VALUE=DATE-TIME:20240422T111500Z
DTEND;VALUE=DATE-TIME:20240422T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/27
DESCRIPTION:Title: Mat
erial distribution topology optimization for boundary-effect-dominated pro
blems\nby Eddie Wadbro (Karlstad University) as part of CAM seminar\n\
nLecture held in MV:L14.\n\nAbstract\nIn the classical design optimization
using the material distribution method (density-based topology optimizati
on)\, a material indicator function represents the presence or absence of
material within the domain. The first part of this talk provides an introd
uction to material distribution topology optimization with an emphasis on
mathematical morphology\, non-linear filters\, and length scale control.\n
\nTo use the material distribution approach for boundary-effect-dominated
problems\, we need to identify the boundary of the design at each iteratio
n\; this talk discusses two methods to achieve this. The first is to use a
boundary strip indicator function defined on the elements of the computat
ional mesh. The second is to use a boundary indicator function defined on
the mesh faces (edges in 2D and facets in 3D). The second part of my prese
ntation covers the main ideas behind both approaches and showcases results
from two applications\, one suitable for each approach.\n
LOCATION:https://researchseminars.org/talk/cam/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ragnar Winther
DTSTART;VALUE=DATE-TIME:20240429T111500Z
DTEND;VALUE=DATE-TIME:20240429T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/28
DESCRIPTION:Title: Wha
t about $p$?\nby Ragnar Winther as part of CAM seminar\n\nLecture held
in MV:L14.\n\nAbstract\nThe title of this talk refers to a question frequ
ently asked by Ivo Babuska\, from the late 1980s and on\, following variou
s talks \non finite element methods. More precisely\, what can we say abou
t the properties of finite element methods as we raise the polynomial degr
ee? Even today the so called $p$-method is less understood\,\nand the corr
esponding analysis is less canonical\, than the traditional approach of me
sh refinement\, i.e.\, the $h$-method.\nIn recent years Rick Falk and I ha
ve developed a theory which represents a new tool to analyze finite elemen
t methods of high polynomial degree\,\nwhich we refer to as the bubble t
ransform. The key idea is to construct a decomposition into local bubbles
which \nsimultaneously covers all possible polynomial degrees.\nThe purpos
e of this talk is to give a review of this theory\, and to discuss \npoten
tial applications.\n
LOCATION:https://researchseminars.org/talk/cam/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Easter Monday
DTSTART;VALUE=DATE-TIME:20240401T111500Z
DTEND;VALUE=DATE-TIME:20240401T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/29
DESCRIPTION:by Easter Monday as part of CAM seminar\n\nLecture held in MV:
L14.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBC
DTSTART;VALUE=DATE-TIME:20240527T111500Z
DTEND;VALUE=DATE-TIME:20240527T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/30
DESCRIPTION:by TBC as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBC
DTSTART;VALUE=DATE-TIME:20240610T111500Z
DTEND;VALUE=DATE-TIME:20240610T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/31
DESCRIPTION:by TBC as part of CAM seminar\n\nLecture held in MV:L14.\nAbst
ract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christian Lubich (University of Tübingen)
DTSTART;VALUE=DATE-TIME:20240409T111500Z
DTEND;VALUE=DATE-TIME:20240409T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/32
DESCRIPTION:Title: Reg
ularized dynamical nonlinear parametric approximation\nby Christian Lu
bich (University of Tübingen) as part of CAM seminar\n\nLecture held in M
V:L14.\n\nAbstract\nThis talk is about the numerical approximation of solu
tions to initial value problems of high-dimensional ordinary differential
equations or evolutionary partial differential equations such as the Schr\
\"odinger equation by nonlinear parametrizations $u(t)=\\Phi(q(t))$ with t
ime-dependent parameters $q(t)$\, which are to be determined in the comput
ation. Our motivation comes from approximations by multiple Gaussians in q
uantum dynamics\, by tensor networks\, and by neural networks. In all thes
e cases\, the parametrization is typically irregular: the derivative $\\Ph
i'(q)$ can have arbitrarily small singular values and may have varying ran
k. The talk is about approximation results for a regularized approach\, wh
ich can still be successfully applied in such irregular situations\, even
if it runs counter to the basic principle in numerical analysis to avoid s
olving ill-posed subproblems when aiming for a stable algorithm.\nThe talk
is based on joint work with Jörg Nick\, Caroline Lasser and Michael Feis
chl.\n
LOCATION:https://researchseminars.org/talk/cam/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Malin Rau (Universität Hamburg)
DTSTART;VALUE=DATE-TIME:20240311T121500Z
DTEND;VALUE=DATE-TIME:20240311T130000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/33
DESCRIPTION:Title: Asy
nchronous Opinion Dynamics in Social Networks\nby Malin Rau (Universit
ät Hamburg) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbstract
\nOpinion spreading in society decides the fate of elections\, the success
of products\, and the impact of political or social movements.\nA promine
nt model to study opinion formation processes is due to Hegselmann and Kra
use. It has the distinguishing feature that stable states do not necessari
ly show consensus\, i.e.\, the population of agents might not agree on the
same opinion.\n\nWe focus on the social variant of the Hegselmann-Krause
model. There are $n$ agents\, which are connected by a social network. The
ir opinions evolve in an iterative\, asynchronous process in which agents
are activated one after another at random. When activated\, an agent adopt
s the average of the opinions of its neighbors having a similar opinion (w
here similarity of opinions is defined using a parameter $\\varepsilon$).
Thus\, the set of influencing neighbors of an agent may change over time.
To the best of our knowledge\, social Hegselmann-Krause systems with async
hronous opinion updates have only been studied with the complete graph as
social network.\n\nWe show that such opinion dynamics are guaranteed to co
nverge for any social network. We provide an upper bound of $\\mathcal{O}(
n|E|^2 (\\varepsilon/\\delta)^2)$ on the expected number of opinion update
s until convergence to a stable state\, where $|E|$ is the number of edges
of the social network\, and $\\delta$ is a parameter of the stability con
cept. For the complete social network\, we show a bound of $\\mathcal{O}(n
^3(n^2 + (\\varepsilon/\\delta)^2))$ that represents a major improvement o
ver the previously best upper bound of $\\mathcal{O}(n^9 (\\varepsilon/\\d
elta)^2)$.\n
LOCATION:https://researchseminars.org/talk/cam/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ioanna Motschan-Armen (Chalmers & GU)
DTSTART;VALUE=DATE-TIME:20240617T091500Z
DTEND;VALUE=DATE-TIME:20240617T100000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/34
DESCRIPTION:Title: App
roximation of semilinear stochastic heat equations on the sphere\nby I
oanna Motschan-Armen (Chalmers & GU) as part of CAM seminar\n\nLecture hel
d in MV:H12.\n\nAbstract\nStochastic partial differential equations are us
ed to describe various physical processes that are perturbed by noise. Som
e of those occur on curved surfaces\, for example spheres. In this talk se
milinear stochastic heat equations with additive noise on the unit sphere
are considered. Approximations in space and time are presented in order to
simulate and analyse solutions. The space approximation is derived using
the spectral method\, with spherical harmonic functions. In order to obtai
n time discretization on an equidistant time grid the Euler--Maruyama sche
me is applied. For the semilinear stochastic heat equations on the sphere
with additive isotropic Wiener noise\, strong convergence rates in space a
nd time are derived\, taking regularity of the initial condition and the d
riving noise into account. Furthermore convergence of the expectation and
the second moment is analysed for the corresponding linear equation. The t
heoretical results are confirmed by numerical simulations.\n\nMidterm-Semi
nar\n
LOCATION:https://researchseminars.org/talk/cam/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:TBC: Charles-Edouard Bréhier
DTSTART;VALUE=DATE-TIME:20241007T111500Z
DTEND;VALUE=DATE-TIME:20241007T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/35
DESCRIPTION:by TBC: Charles-Edouard Bréhier as part of CAM seminar\n\nLec
ture held in MV:L14.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Probably no seminar
DTSTART;VALUE=DATE-TIME:20240923T111500Z
DTEND;VALUE=DATE-TIME:20240923T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/36
DESCRIPTION:by Probably no seminar as part of CAM seminar\n\nLecture held
in MV:L14.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Workshop STINT: Sweden-China
DTSTART;VALUE=DATE-TIME:20241014T111500Z
DTEND;VALUE=DATE-TIME:20241014T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/37
DESCRIPTION:by Workshop STINT: Sweden-China as part of CAM seminar\n\nLect
ure held in MV:L14.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/cam/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrii Dmytryshyn (Örebro University)
DTSTART;VALUE=DATE-TIME:20240902T111500Z
DTEND;VALUE=DATE-TIME:20240902T120000Z
DTSTAMP;VALUE=DATE-TIME:20240804T044546Z
UID:cam/38
DESCRIPTION:Title: Eig
enstructures of low-rank matrix polynomials\nby Andrii Dmytryshyn (Ör
ebro University) as part of CAM seminar\n\nLecture held in MV:L14.\n\nAbst
ract\nChallenging and intriguing mathematical problems involving matrix po
lynomials arise in various applications. These problems often revolve arou
nd the eigenstructures of the polynomials\, emphasizing the importance of
the eigenstructures. In this talk we consider the set of matrix polynomial
s of bounded rank and degree and describe the eigenstructures that these p
olynomials typically have\, so called generic eigenstructures. We also fin
d such generic eigenstructures for the sets of symmetric and skew-symmetri
c matrix polynomials. Notably\, these symmetries have drastic effect on ge
neric eigenstructures\, for example\, on whether we can anticipate the app
earance of eigenvalues in the eigenstructures or not. \nThis talk is prima
rily based on joint work with Froilán Dopico and Fernando De Téran.\n
LOCATION:https://researchseminars.org/talk/cam/38/
END:VEVENT
END:VCALENDAR