Date/Time : 16 Jun 2023 15:00
Venue : S17 #04-04 (SR3)
Speaker : Zhu Feng, University of Wisconsin

Putting a hyperbolic metric on a complete finite-type surface gives us a linear representation (the holonomy representation) with many nice geometric and dynamical properties: for instance it is discrete and faithful, and in fact stably quasi-isometrically embedded. This picture can be generalised in (at least) two ways. First, the notion of geometric finiteness generalises this picture in the context of rank-one Lie groups such as PSL(2,R) or PSL(2,C). Second, Anosov representations generalise this picture to higher-rank Lie groups such as PSL(d,K) for d>2.

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Date/Time : 17 May 2023 14:00
Venue : S17 #04-06 (SR1)
Speaker : Susanne Brenner, Lousiana State University

Elliptic optimal control problems are infinite dimensional least-squares data fitting problems where the models are defined by second order elliptic boundary value problems. In the presence of pointwise constraints on the state variable, the traditional approach becomes more challenging due to the reduced regularity of the adjoint state. In this talk I will explain how to adopt finite element methods originally designed for fourth order elliptic boundary value problems to this class of optimal control problems and present a unified framework for their analysis.

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Date/Time : 17 May 2023 10:30
Venue : Block A #10-01 (Energy Studies Institute)
Speaker : Gazi Salah Uddin, Linköping University

Solar adoption exploded until 2015 in Bangladesh, setting a precedent for electrifying previously unconnected areas worldwide. This study tries to measure the welfare effects of solar adoption using the three rounds of the Bangladesh Integrated Household Surveys. We applied ordinary least squares and propensity score matching techniques to estimate the welfare effects of solar adoption. We found that solar adoption is associated with higher income, expenditure, asset value growth, and a massive reduction in kerosene expenditure than non-adopters. Other findings include solar households that leave sharecropping and pursue trading and poultry farming and children who benefit from solar adoption regarding education and nutrition.

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Date/Time : 15 May 2023 16:00
Venue : S17 #04-06 (SR1)
Speaker : Jeong Han Kim, Korea Institute for Advanced Study

Majority dynamics on a graph G is a deterministic process such that every vertex updates its +/- 1-assignment according to the majority assignment on its neighbor simultaneously at each step. Benjamini, Chan, O’Donnell, Tamuz and Tan conjectured that, in the Erdos-Renyi random graph G(n,p), the random initial +/- 1-assignment converges to a 99%-agreement with high probability whenever p = \omega(1/n). This conjecture was first confirmed for p > \lambda n^{-1/2} for a large constant \lambda by Fountoulakis, Kang and Makai. Although this result has been reproved recently by Tran and Vu and by Berkowitz and Devlin, it was unknown whether the conjecture holds for p < \lambda n^{-1/2} . We break this \Omega(n^{-1/2})-barrier by proving the conjecture for sparser random graphs G(n,p), where \lambda’ n^{-3/5} \log n < p < \lambda n^{-1/2} with a large constant \lambda’ > 0.

(Joint work with D. Chakraborti, J. Lee, and T. Tran)

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Date/Time : 12 May 2023 14:00
Venue : S17 #04-06 (SR1)
Speaker : Chan Hon Fu Raymond, City University of Hong Kong

With the advances in sensor technology, data has become ubiquitous. To make sense of data we have to solve higher and higher dimensional problems that may seem intractable. However, many high-dimensional problems have solutions that live in low-dimensional spaces. Sparsity is a way to exploit the low-dimensional structure of the solutions to obtain feasible solutions for high-dimensional problems. In this talk, we will see how sparsity can be applied to facilitate the solutions of imaging problems, including magnetic resonance imaging, single-molecule localisation microscopy, and ground-based astronomy.

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Date/Time : 10 May 2023 17:00
Venue : S17 #04-05 (SR2)
Speaker : Jan Baars,

For a Tychonov space X we define Cp(X) to be the linear subspace of R^X consisting of all real-valued continuous functions on X. Let βX be the ˇCech-Stone compactifaction of X and let X^* = βX \ X be the remainder of X. For u ∈ X^*, we denote Xu = X ∪ {u} ⊆ βX.

For the countable discrete space ω, elements of ω^* can be identified with free ultrafilters on ω. In 1990 Gul’ko proved in [3] for u, v ∈ ω^* that Cp(ωu) and Cp(ωu) are linearly home- omorphic if and only if ωu and ωv are homeomorphic. In [1] this result was generalized for finite sums of spaces ωu as follows: For n, m ≥ 1 and {u1,…,un, v1,…,vm} ⊆ ω∗, let X and Y be the direct sums of all ω_ui and ω_vi, respectively.

Then the spaces Cp(X) and Cp(Y) are linearly homeomorphic if and only X and Y are homeomorphic, in particular n = m. Gul’ko’s result does not hold for all spaces X. For example in [2] it was shown that for each ordinal space α, where ω < α < ω1 is a limit ordinal, there are u, v ∈ α^* such that Cp(αu) and Cp(αv) are linearly homeomorphic but αu and αv are not homeomorphic.

Here the references are as follows:

[1] J. Baars, On the lp-equivalence of ultrafilters, Bull. Pol. Acad. Sci. Math. Vol 70 No 1. (2022), 63–82.

[2] J. Baars and J. van Mill, Function spaces and points in ˇCech-Stone remainders, To appear in Topology Appl.

[3] S.P. Gul’ko, Spaces of continuous functions on ordinals and ultrafilters, Math. Notes, Vol. 47,4 (1990), 329–334.

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Date/Time : 04 May 2023 16:00
Venue : S17 #04-06 (SR1)
Speaker : Zhang Zhen, Southern University of Science and Technology

We develop energy stable and bound preserving schemes for phase-field surfactant model with moving contact lines. The desired properties of the schemes are rigorously proved. We numerically validate the accuracies of the schemes and apply them in simulating droplet impact problems. Qualitative agreements with experiments are obtained. Moreover, surfactants are observed to have effects on enhancing droplet deformation and reducing dissipations.

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Date/Time : 03 May 2023 15:00
Venue : S17 #04-04 (SR3)
Speaker : Marco Abate, University of Pisa

In this talk we shall describe the asymptotic behaviour of sequences of functions obtained by iteratively left-composing or right-composing holomorphic self-maps of a hyperbolic Riemann surface $X$. We shall consider in detail two cases: when the holomorphic self-maps to be composed have values in a Bloch subdomain of~$X$; and when the holomorphic self-maps to be composed are sufficiently close to a given self-map. This is a joint work with Argyrios Christodoulou and Ian Short.

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Date/Time : 27 Apr 2023 16:00
Venue : S17 #04-06 (SR1)
Speaker : Franck Sueur, University of Bordeaux

In this talk, I will give an overview of some recent results on the so-called transport-Stokes system which describes sedimentation of inertialess particles in a viscous flow. This system couples a transport equation and the steady Stokes equations in the full 3D space. I will address the Cauchy problem, the regularity of the particle trajectories and the controllability issue. We will see that the system has some similarity to the incompressible Euler system. Some of the exposed results have been obtained in collaboration with Amina Mecherbet.

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