Date/Time : 16 Oct 2024 15:00
Venue : S17 #05-11 (SR5)
Speaker : Raphael Winter, Cardiff University

We present new results on the kinetic Balescu-Lenard and Landau equations, which describe the collisional relaxation of plasma. The first result establishes global existence of solutions to the Balescu-Lenard equation for initial data close to equilibrium, while the second result shows a new blow-down mechanism for the Landau equation for a family of super-critical initial data. We also discuss the breakthrough result of Guillen and Silvestre who identify the Fisher information as a Lyapunov functional of the spatially homogeneous Landau equation. Joint work with Mitia Duerinckx and Maria Gualdani.

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Date/Time : 11 Sep 2024 15:00
Venue : S17 #05-11 (SR5)
Speaker : Yuxuan Wang, Tsinghua University

First examined by Riemann in 1860 in one-dimensional space, the Riemann problem has since been extensively studied and advanced by numerous scholars. Our talk will investigate the interaction of two approaching shocks in the context of spherical symmetry in three-dimensional space, presuming the fluid to be ideally barotropic. We will outline the proof of the local existence, uniqueness, and higher regularity of the solution to the shock interaction problem.

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Date/Time : 04 Sep 2024 15:00
Venue : S17 #05-11 (SR5)
Speaker : Meiyue Jiang, Peking University

In this talk we will first present an elementary treatment of the Brunn-Minkowski inequalities in dimension 2, which include the classical Brunn-Minkowski inequality, the $L^p$ and the log Brunn-Minkowski inequalities due to Lutwak and his collaborators, then we discuss a Brunn-Minkowski type inequality for the functional associated with the dual $L^p$−Minkowski problem. If time permits, a similar inequality for higher dimensional PDEs will be proposed.

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Date/Time : 23 Aug 2024 16:00
Venue : S17 #04-05 (SR2)
Speaker : Yixuan Wang, Caltech

We provide a general framework that could be potentially amenable to the stability of a large class of problems with type I singularities in a weighted Sobolev space and use nonlinear heat and complex Ginzburg-Landau equations as examples, which are joint works with Tom Hou, Van Tien Nguyen, and Jiajie Chen. A generalized dynamic rescaling formulation is introduced, with modulation parameters capturing the spatial translation and rotation symmetries of the equation and novel additional modulation parameters perturbing the scaling symmetry. This new formulation provides enough degrees of freedom to impose vanishing conditions on the rescaled solution, completely eliminating the unstable and neutrally stable modes of the linearized operator around the blowup profile. We then establish the full stability of the blowup using weighted energy estimates, without relying on a topological argument or a spectrum analysis. The log correction for the blowup rate is automatically inferred by refined estimates of the modulation parameters.

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Date/Time : 21 Aug 2024 15:00
Venue : S17 #04-05 (SR2)
Speaker : Van Tien Nguyen, National Taiwan University

Advanced mathematical techniques have been developed in the last two decades for precise construction of blowup solutions within the class of finite energy. However, the question of a complete classification of blowup dynamics remains open. In this talk, we consider the energy-critical nonlinear heat equation in $\mathbb{R}^3$  as a model example to illustrate our technique to archive such a blowup classification. It consists of two parts: 1) a review of different techniques for constructing finite-energy blowup solutions, and 2) a rigidity result of the finite-energy blowup.  

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Date/Time : 14 Aug 2024 10:00
Venue : S17 #06-11 (SR6)
Speaker : Jinxin Xue, Tsinghua University

The mean curvature flow is to evolve a hypersurface in Euclidean space using the mean curvatures at each point as the velocity field. The flow has good smoothing property, but also develops singularities. The singularities are modeled on an object called shrinkers, which give homothetic solutions to the flows. As there are infinitely many shrinkers that seem impossible to classify, it is natural to explore the idea of generic mean curvature flows that is to introduce a generic perturbation of the initial conditions. In this talk, we shall explain our work on this topic, including perturbing away nonspherical and noncylindrical shrinkers, and generic isolatedness of cylindrical singularities. The talk is based on a series of works jointly with Ao Sun.

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Date/Time : 01 Aug 2024 15:00
Venue : S17 #04-05 (SR2)
Speaker : Armin Schikorra, University of Pittsburgh

n-Laplace systems with antisymmetric potential are known to govern geometric equations such as n-harmonic maps between manifolds and generalized prescribed H-surface equations. Due to the nonlinearity of the leading order n-Laplace and the criticality of the equation they are very difficult to treat.

I will discuss some progress we obtained, combining stability methods by Iwaniec and nonlinear potential theory for vectorial equations by Kuusi-Mingione.

Joint work with Dorian Martino

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Date/Time : 17 Jul 2024 15:00
Venue : via Zoom
Speaker : Feng Shao, Peking University

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https://nus-sg.zoom.us/j/82730991505?pwd=LEzOeoXXrYPflm2EVK5xKzpiQCi6Pt.1

Meeting ID: 827 3099 1505
Passcode: 008679

In this talk, I will discuss the joint work with Dongyi Wei and Zhifei Zhang on the construction of self-similar smooth imploding solutions of isentropic relativistic Euler equations with isothermal equation of state $p=\frac1\ell\varrho$ for all $\ell>1$ in physical space dimension $d=2,3$ and for $\ell>1$ close to 1 in higher dimensions. This work is a crucial step toward solving long-standing open problem: finite time blow-up of the supercritical defocusing nonlinear wave equation.

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Date/Time : 29 May 2024 14:00
Venue : S17 #06-11 (SR6)
Speaker : Jaydeep Singh, Princeton University

An important class of finite-time blowup solutions to the Einstein-scalar field system was constructed by Christodoulou (’94), going by the name of k-self-similar naked singularities. In this talk we will motivate the study of these spacetimes from a PDE and general relativity perspective, and discuss the subtle issue of their (in-)stability. Our main results will show how the chief instability mechanism, a blue-shift along the past light-cone of the singularity, is highly sensitive to the space of perturbations considered.

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