Uploaded May 2026 | Updated September 2026, 2 weeks ago
Title: Fluctuations across the scales: Partial Differential Equations, Geometry and Noise
Speaker: Nicolas Dirr, Cardiff University
Abstract: Multi-scale analysis of physical systems leads to “noisy” effective models on larger scales, i.e. deterministic (partial) differential equations perturbed by some small amount of randomness. This noise is a feature, not a bug: there are situations where the remaining small noise has visible effects on the macroscopic scale. Moreover the structure of the noise retains the memory of the smaller scales, so that crucial information can be gained from this noise. The effective equations on the macroscale are not only themselves closely related to geometry (e.g. mean curvature flows), but the noise itself comes with a geometric structure: small fluctuations define “weights” on tangent space, i.e. a thermodynamic metric.
Profile: Nicolas Dirr studied mathematics at the the universities of Tuebingen and Bonn in Germany with a year abroad in Cambridge/UK and obtained is Diploma in Mathematics in 1998 from Bonn, followed by a PhD from University of Leipzig/Germany in 2002 under supervision of Prof. Stephan Luckhaus. After postdoctoral positions at the University of Texas at Austin and the Max-Planck-Institut for Mathematics in the Sciences (Junior research group leader), he went as lecturer to Bath, UK and then as Reader and from 2016 Professor to the University of Cardiff, Wales, UK.
His research interest lies at the interface of nonlinear partial differential equations and stochastic processes. His research is in pure mathematics but motivated by modelling real world systems. This includes scaling limits of interacting particle systems, fluctuating hydrodynamics, geometric evolution equations, homogenization, control problems and mean field games, gradient flows and, recently, models for the visual cortex.
Find out more about the TSVP on the program website: oist.jp/visiting-program
#OIST #OIST-TSVP #Theoretical #Science #VisitingProgram #Okinawa #TSVP #NicolasDirr #PartialDifferentialEquations #Geometry #Noise #MultiScaleAnalysis #MeanCurvatureFlow
Title: Fluctuations across the scales: Partial Differential Equations, Geometry and Noise
Speaker: Nicolas Dirr, Cardiff University
Abstract: Multi-scale analysis of physical systems leads to “noisy” effective models on larger scales, i.e. deterministic (partial) differential equations perturbed by some small amount of randomness. This noise is a feature, not a bug: there are situations where the remaining small noise has visible effects on the macroscopic scale. Moreover the structure of the noise retains the memory of the smaller scales, so that crucial information can be gained from this noise. The effective equations on the macroscale are not only themselves closely related to geometry (e.g. mean curvature flows), but the noise itself comes with a geometric structure: small fluctuations define “weights” on tangent space, i.e. a thermodynamic metric.
Profile: Nicolas Dirr studied mathematics at the the universities of Tuebingen and Bonn in Germany with a year abroad in Cambridge/UK and obtained is Diploma in Mathematics in 1998 from Bonn, followed by a PhD from University of Leipzig/Germany in 2002 under supervision of Prof. Stephan Luckhaus. After postdoctoral positions at the University of Texas at Austin and the Max-Planck-Institut for Mathematics in the Sciences (Junior research group leader), he went as lecturer to Bath, UK and then as Reader and from 2016 Professor to the University of Cardiff, Wales, UK.
His research interest lies at the interface of nonlinear partial differential equations and stochastic processes. His research is in pure mathematics but motivated by modelling real world systems. This includes scaling limits of interacting particle systems, fluctuating hydrodynamics, geometric evolution equations, homogenization, control problems and mean field games, gradient flows and, recently, models for the visual cortex.
Find out more about the TSVP on the program website: oist.jp/visiting-program
#OIST #OIST-TSVP #Theoretical #Science #VisitingProgram #Okinawa #TSVP #NicolasDirr #PartialDifferentialEquations #Geometry #Noise #MultiScaleAnalysis #MeanCurvatureFlow









![Feng Liu: Excitonic Bose Einstein Condensation in Flat Bands (TSVP Talk at OIST)
Find out more about the TSVP on the program website: https://www.oist.jp/visiting-program.
Abstract: An excitonic insulator (EI) phase can be stabilized in narrow-gap semiconductors/semimetals when spontaneously formed excitons, bound bosonic pairs of electrons and holes, condense at low temperatures. The search for excitonic Bose-Einstein condensate (BEC) in intrinsic semiconductors has received tremendous attention in the past decade, but so far convincing evidence remains lacking. Several material candidates have been recently proposed computationally, but these studies are limited to single exciton calculations and the effects of interactions, if included, are approximated using mean-field approach. In this talk, I will discuss our recent work investigating the role of topological flat bands (FBs) in promoting excitonic BEC. First, I will show that flat valence and conduction bands (so-called yin-yang FBs) of quantum semiconductors [1], such as the one having a diatomic Kagome lattice as exemplified in a superatomic graphene, conspire to indicate a triplet EI state, based on DFT-GW and BSE calculations for a single exciton formation. Next, using exact diagonalization method to solve an extended Hubbard lattice model of yin-yang FBs, I will show directly spontaneous BEC of triplet excitons, based on analyses of multi-exciton formation energies and wave functions [2]. I will demonstrate the critical role of FBs in promoting quantum coherence, as evidenced by off-diagonal long-range order in many-exciton states. These works significantly enriches FB and excitonic physics while providing a unique platform for material realization of spinor BEC and spin superfluidity.
Profile: Feng Liu received his B.Sc. in Engineering physics from Tsinghua University in 1984 and earned his Ph.D. in 1990 at Virginia Commonwealth University in Chemical physics. He is currently a Distinguished and Ivan B. Cutler endowed chair Professor in the Department of Materials Science and Engineering at the University of Utah. His research interests lie in the theoretical modeling and computer simulation, from electronic to atomic and to mesoscopic scales, to study a wide spectrum of physical behavior of materials, with a special focus on surfaces/interfaces, thin films and low-dimensional materials. His best-known work includes theoretical modeling of strain-induced self-assembly of quantum dots and quantum wires in epitaxial growth of thin films, prediction of organic two-dimensional topological materials and surface-based topological states, and prediction of many-body quantum states of yin-yang flat bands. He is recipient of 2023 American Physical Society Davisson-Germer Prize in Surface Physics. He is a Fellow of American Physical Society. He served as Divisional Associated Editor of Physical Review Letters. He is a founding editor-in-chief for Coshare Science, a new international journal of video research articles.
#OIST #OIST_TSVP #Theoretical #Science #VisitingProgram #Okinawa #TSVP Feng Liu: Excitonic Bose Einstein Condensation in Flat Bands (TSVP Talk at OIST)](https://i.ytimg.com/vi/XOZ9nIou5JE/mqdefault.jpg)
