Date/Time : 04 Apr 2019 16:00
Venue : S17 #05-12 SR4
Speaker : Subhroshekhar Ghosh, National University of Singapore

Date/Time:04 Apr 2019 16:00 Venue: S17 #05-12 SR4 Speaker: Subhroshekhar Ghosh, National University of Singapore Two manifestations of rigidity in point sets : forbidden regions and maximal degeneracy A point process is said to be “rigid” if its local observables are completely determined (as deterministic functions of) the point configuration outside a local neighbourhood. For example, it has been shown in earlier work that, in the Ginibre ensemble (a.k.a. the 2D Coulomb gas at inverse temperature beta=2), the point configuration outside any bounded domain determines, almost surely, the number of points in the domain. In this talk, we will explore two recent manifestations of such rigidity phenomena. For the zeros of the planar Gaussian analytic function, we show that outside every large “hole”, there is a “forbidden region” which contains a vanishing density of points. This should be seen in contrast with the corresponding situation for classically understood models (e.g. random matrix ensembles), where no such effects are known to occur. In the second part of the talk, we will consider “stealthy” hyperuniform systems, which are systems whose structure function (i.e., the Fourier transform of the two-point correlation) vanishes near the origin. We show that such systems exhibit “maximal degeneracy”, namely the points outside a bounded domain determine, almost surely, the entire point configuration inside the domain. En route, we establish a conjecture of Zhang, Stillinger and Torquato that such systems have (deterministically) bounded holes. Based on joint works with Joel Lebowitz and Alon Nishry. Add to calendar: 

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Date/Time : 19 Mar 2019 16:00
Venue : S17 #05-12 SR4
Speaker : Dejan Gajic, University of Cambridge

Date/Time:28 Mar 2019 16:00 Venue: S17 #05-12 SR4 Speaker: Dejan Gajic, University of Cambridge Quasinormal modes on black hole spacetimes A fundamental problem in the context of Einstein’s equations of general relativity is to understand the evolution of small perturbations of stationary black hole solutions. It is expected that there is a discrete set of characteristic frequencies that play a dominant role at late times and carry information about the nature of the black hole, similar to the normal frequencies of a vibrating guitar string. These frequencies are called quasinormal frequencies and they are closely related to scattering resonances in the study of Schrödinger’s equation. I will consider the linear wave equation on black hole backgrounds as a toy model for the Einstein equations and give an introduction to quasinormal frequencies in this setting. Then I will discuss a new method of defining and studying quasinormal frequencies on asymptotically flat spacetimes, developed from joint work with Claude Warnick, which interprets the frequencies as honest eigenvalues of a natural operator acting on a Hilbert space. Add to calendar: 

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Date/Time : 14 Mar 2019 16:00
Venue : S17 #05-12 SR4
Speaker : Li Qianxiao, National University of Singapore

Date/Time:14 Mar 2019 16:00 Venue: S17 #05-12 SR4 Speaker: Li Qianxiao, National University of Singapore A Mean-field Optimal Control Formulation of Deep Learning In this talk, we discuss formulating, through a continuous-time approximation, deep supervised learning as a mean-field optimal control problem. We prove necessary conditions for optimality in the form of a mean-field Pontryagin’s maximum principle, as well as global characterizations of optimality using Hamilton-Jacobi-Bellman equations. Interesting learning algorithms derived from this approach will also be discussed. Add to calendar: 

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Date/Time : 07 Mar 2019 16:00
Venue : S17 #05-12 SR4
Speaker : Wu Bin,

Date/Time:07 Mar 2019 16:00 Venue: S17 #05-12 SR4 Speaker: Wu Bin On Large Games with Bio-social Traits This paper shows that, in a class of large games with traits model, distinguishing agent space and trait space via the nowhere equivalence condition is not only sufficient but also necessary for the existence of pure strategy Nash equilibrium and closed graph property. Furthermore, under the nowhere equivalence condition, we characterize Nash equilibria of large games with traits. Add to calendar: 

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Date/Time : 24 Jan 2019 16:00
Venue : S17 #05-12 SR4
Speaker : Xia Chao, Xiamen University

Date/Time:24 Jan 2019 16:00 Venue: S17 #05-12 SR4 Speaker: Xia Chao, Xiamen University Stability on two types of partitioning problems In this talk, two geometric variational problems, so-called partitioning problems for convex domains will be discussed. Type-I is on area minimizing hypersurfaces with volume constraint and Type-II is on area minimizing ones with wetting area constraint. The stationary points for Type-I are free boundary CMC hypersurfaces while the ones for Type-II are minimal hypersurfaces with constant contact angle. We study the stability problem, namely, the second variation for area functional is nonnegative under two types of admissible deformations. We show the uniqueness result for stable type-I or type-II stationary hypersurfaces in a Euclidean ball. This talk is based on joint works with Guofang Wang and Jinyu Guo. Add to calendar: 

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Date/Time : 07 Nov 2018 16:00
Venue : S17 #05-12 SR4
Speaker : An Xinliang, National University of Singapore

Date/Time:07 Nov 2018 16:00 Venue: S17 #05-12 SR4 Speaker: An Xinliang, National University of Singapore Formation of Singularity in General Relativity III Besides black holes, can other types of singularities form in gravitational collapse? What does the singularity look like? Will the singular information be censored in universe? In this talk, I will address above questions. Add to calendar: 

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Date/Time : 24 Oct 2018 16:00
Venue : S17 #05-12 SR4
Speaker : An Xinliang, National University of Singapore

Date/Time:24 Oct 2018 16:00 Venue: S17 #05-12 SR4 Speaker: An Xinliang, National University of Singapore Formation of Singularity in General Relativity I I will present three introductory talks on a mathematical approach to studying singularity formation in general relativity. In the first talk, basic concepts and theorems of space time geometry will be discussed. PhD students in 1st and 2nd years are welcome to attend. Add to calendar: 

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Date/Time : 18 Oct 2018 16:00
Venue : S17 #05-12 SR4
Speaker : An Xinliang, National University of Singapore

Date/Time:31 Oct 2018 16:00 Venue: S17 #05-12 SR4 Speaker: An Xinliang, National University of Singapore Formation of Singularity in General Relativity II In this talk, I will address an interesting physical question: can a black hole form dynamically in the vacuum? Without the help of matter, we will show that focusing of gravitational waves could lead to black hole formation. Add to calendar: 

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