Colloquia & Seminars Archives - Page 148 of 152

Seminars: Colloquia & Seminars

Date
Time
Venue

Speaker
Affiliation
Title of Talk

12 Mar 2019
15:00
S17 #05-11 SR5

Zhe Sun
University of Luxembourg
McShane identities for higher Teichmüller theory and the Goncharov-Shen potential

McShane identities for higher Teichmüller theory and the Goncharov-Shen potential

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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11 Mar 2019
16:00
S17 #04-06 SR1

Charles K. Chui
Menlo Park, California
Inverse Problem on Assessment of our Health and Well-being

Inverse Problem on Assessment of our Health and Well-being

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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07 Mar 2019
16:00
S17 #05-12 SR4

Wu Bin

On Large Games with Bio-social Traits

On Large Games with Bio-social Traits

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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06 Mar 2019
14:00
S17 #04-06 SR1

Georgios Daskalopoulos
Brown University
Rigidity of Teichmueller space

Rigidity of Teichmueller space

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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06 Mar 2019
15:00
S17 #04-04 SR3

Li Yunyue
National University of Singapore
Multicomponent Elastic Imaging: New Insights from the Old Equations

Multicomponent Elastic Imaging: New Insights from the Old Equations

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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05 Mar 2019
15:00
S17 #05-12 SR4

Alan McLeay
University of Luxembourg
Mapping class groups, covers, and braids

Mapping class groups, covers, and braids

Date/Time : 05 Mar 2019 15:00
Venue : S17 #05-12 SR4
Speaker : Alan McLeay , University of Luxembourg

Date/Time:05 Mar 2019 15:00 Venue: S17 #05-12 SR4 Speaker: Alan McLeay, University of Luxembourg Mapping class groups, covers, and braids The mapping class group of a surface is the group of isotopy classes of boundary preserving homeomorphisms of the surface. Given a finite sheeted covering space between surfaces, we may ask what relationship, if any, exists between the two mapping class groups? In joint work with Tyrone Ghaswala we investigate this question for surfaces with non-empty boundary. I will discuss a classical theorem of Birman-Hilden and give new insight into a family of covering spaces related to the Burau representation of braid groups. Add to calendar:

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20 Feb 2019
15:00
S17 #04-06 SR1

Siva Athreya
ISI Bangalore
Strong existence and uniqueness for stable stochastic differential equations with distributional drift

Strong existence and uniqueness for stable stochastic differential equations with distributional drift

Date/Time : 20 Feb 2019 15:00
Venue : S17 #04-06 SR1
Speaker : Siva Athreya , ISI Bangalore

Date/Time:20 Feb 2019 15:00 Venue: S17 #04-06 SR1 Speaker: Siva Athreya, ISI Bangalore Strong existence and uniqueness for stable stochastic differential equations with distributional drift We consider the stochastic differential equation dX_t = b(X_t) dt + dL_t,where the drift b is a generalized function and L is a symmetric one dimensional alpha-stable Levy processes, alpha in (1, 2). We define the notion of solution to this equation and establish strong existence and uniqueness whenever b belongs to the Besov-Holder space C^\beta for beta > 1/2- alpha/2. This is joint work with Oleg Butkovsky and Leonid Mytnik. Add to calendar:

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20 Feb 2019
14:00
S17 #04-06 SR1

Alexander Drewitz
U. Cologne
Geometry of Gaussian free field sign clusters and random interlacements

Geometry of Gaussian free field sign clusters and random interlacements

Date/Time : 20 Feb 2019 14:00
Venue : S17 #04-06 SR1
Speaker : Alexander Drewitz , U. Cologne

Date/Time:20 Feb 2019 14:00 Venue: S17 #04-06 SR1 Speaker: Alexander Drewitz, U. Cologne Geometry of Gaussian free field sign clusters and random interlacements We consider two fundamental percolation models with long-range correlations: Level set percolation for the Gaussian free field (GFF) and percolation of the vacant set of random interlacements. Both models have been the subject of intensive research during the last decades. In this talk we focus on structural properties of the level set percolation of the GFF. In particular, we establish the non-triviality of a phase in which two infinite sign clusters dominate, and their complement only has small connected components. While the respective results are new for $\Z^d$ as the underlying graph, we also cover more intricate geometries such as transient graphs with subdiffusive random walk behavior. As a consequence, we answer an open problem on the non-triviality of the phase transition of the vacant set of Random Interlacements on such geometries. This talk is based on joint works with A. Prévost (Universität zu Köln) and P.-F. Rodriguez (IHES). Add to calendar:

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13 Feb 2019
15:00
S17 #04-06 SR1

Marko Hans Weber
Columbia University
Systemic Portfolio Diversification: Equilibrium Holdings and Policy Implications

Systemic Portfolio Diversification: Equilibrium Holdings and Policy Implications

Date/Time : 13 Feb 2019 15:00
Venue : S17 #04-06 SR1
Speaker : Marko Hans Weber, Columbia University

Date/Time:13 Feb 2019 15:00 Venue: S17 #04-06 SR1 Speaker: Marko Hans Weber, Columbia University Systemic Portfolio Diversification: Equilibrium Holdings and Policy Implications We study the implications of fire-sale externalities on optimal portfolio selection. Banks select their asset holdings to minimize expected execution costs triggered by the need to comply with regulatory leverage requirements. We show that if banks disregard the price impact caused by other banks’ liquidation actions, they hold an excessively diversified portfolio. Instead, banks seek systemic diversification when they account for other banks’ asset holdings: They reduce portfolio overlapping to decrease the likelihood of simultaneous deleveraging, sacrificing diversification benefits at the individual level. The bank’s equilibrium allocation is not socially efficient. A benevolent social planner aiming for minimum fire-sale externalities should provide incentives to increase banks’ diversity. A tax on portfolio overlaps aligns the private and social optimum. Social costs can be reduced by enforcing policies which mandate the split of a bank into smaller institutions with heterogeneous leverage ratios. Add to calendar:

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