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 : 15 Mar 2019 14:00
Venue : S17 #04-06 SR1
Speaker : Nicholas M. Katz, Princeton University

We will discuss recent joint work with Antonio Rojas Leon and Pham Huu Tiep about writing down explicit rigid local systems on the affine line in characteristic p whose monodromy groups are various “interesting” finite groups.

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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 : 13 Mar 2019 14:00
Venue : S17 #04-06 SR1
Speaker : John Erik Fornaess, Norwegian University of Science and Technology

In complex analysis the most important domain is the unit disc. In fact all domains (at least simply connected and bounded) are biholomorphic, i.e. analytically equivalent, to the disc. In higher dimension, the natural analogue is the unit ball. But in higher dimension, the general domain is not biholomorphic to the ball. A basic question is then how well a general domain can be approximated by the ball. If we have a ball $B_r$ of radius $r<1$ contained in the unit ball $B_1$, then a domain $U$ with $B_r\subset U\subset B_1$ is said to be squeezed between the two balls. The larger we can choose $r,$ the closer the domain $U$ is to the ball. I will talk about this topic.

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Date/Time : 12 Mar 2019 15:00
Venue : S17 #05-11 SR5
Speaker : Zhe Sun , University of Luxembourg

Date/Time:12 Mar 2019 15:00 Venue: S17 #05-11 SR5 Speaker: Zhe Sun, University of Luxembourg McShane identities for higher Teichmüller theory and the Goncharov-Shen potential We describe a family of Mcshane-type identities for simple root length on positive surface group representations into PGL(n, R). It looks very similar to Mirzakhani’s generalized McShane identity for bordered surfaces which is used to again prove Witten-Kontsevich theorem, except new parameters appear. We find nice properties for these new parameters. Our techniques are based on a family of “generalized horocycle lengths” (called Goncharov-Shen potential), on the positive representation with parabolic monodromy around each boundary component. These horocycle lengths were introduced by Goncharov and Shen, who used their tropical versions to define positive integral points for parametrizing certain canonical bases and to formulate a homological mirror symmetry picture that provides a compactification of the character variety. This is joint work with Yi Huang. Add to calendar: 

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Date/Time : 11 Mar 2019 16:00
Venue : S17 #04-06 SR1
Speaker : Charles K. Chui , Menlo Park, California

Date/Time:11 Mar 2019 16:00 Venue: S17 #04-06 SR1 Speaker: Charles K. Chui, Menlo Park, California Inverse Problem on Assessment of our Health and Well-being Hormone balance is critical to our health and well-being, in that its imbalances commonly lead to fatigue, sleep changes, depression, loss of bone, hair loss, memory difficulty, heart disease, and cancer. Our endocrine system is in charge of secreting hormones, mainly from the endocrine glands to the blood stream, creating pulse signals that can be measured, most conveniently from our two wrists. Normal daily periods of hormone secretion are governed by the circadian rhythms. This lecture is concerned with the important inverse problem of assessing the health of the major endocrine glands from pulse data. Motivated by the published medical literature, we introduce a mathematical representation of pulse waveforms, with three parameters that govern the pulse strength, rate of secretion signal onset, and rate of secretion signal decay, respectively. We then formulate the mathematical model of the source signal in terms of the pulse waveforms, and discuss the inverse problem of recovering the source signal from pulse data. 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 : 06 Mar 2019 14:00
Venue : S17 #04-06 SR1
Speaker : Georgios Daskalopoulos, Brown University

Loosely speaking, Holomorphic rigidity of Teichmueller space states that the action of mapping class group uniquely determines the Teichmueller space as a complex manifold. I will sketch the main ideas involved in proving such result. The method of proof is through harmonic maps and fits into the framework of geometric superrigidity. In addition, I may discuss a harmonic maps proof of both the high rank and the rank one superrigidity of the mapping class group proved via other methods by Farb-Masur and Yeung.

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Date/Time : 06 Mar 2019 15:00
Venue : S17 #04-04 SR3
Speaker : Li Yunyue , National University of Singapore

Date/Time:06 Mar 2019 15:00 Venue: S17 #04-04 SR3 Speaker: Li Yunyue, National University of Singapore Multicomponent Elastic Imaging: New Insights from the Old Equations Elastic wave imaging has been a significant challenge in the exploration industry due to the complexities in wave physics and numerical implementation. We have separated the governing equations for P- and S-wave propagation without the assumptions of homogeneous Lamé parameters to capture the mode conversion between the two body waves in an isotropic, constant-density medium. The resulting set of two coupled second-order equations for P- and S-potentials clearly demonstrates that mode conversion only occurs at the discontinuities of the shear modulus. Applying the Born approximation to the new equations, we derive the PP, PS, SP, and SS imaging conditions from the first gradients of waveform matching objective functions. The resulting images are consistent with the physical perturbations of the elastic parameters, and, hence, they are automatically free of the polarity reversal artifacts in the converted images. When implementing elastic reverse time migration (RTM), we find that scalar wave equations can be used to back propagate the recorded P-potential, as well as individual components in the vector field of the S-potential. Compared with conventional elastic RTM, the proposed elastic RTM implementation using acoustic propagators not only simplifies the imaging condition, it but also reduces the computational cost and the artifacts in the images. We have demonstrated the accuracy of our method using 2D and 3D numerical examples. Add to calendar: 

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