# Department Seminars & Colloquia

You can get notification if you subscribe the calendar in Google Calendar or iPhone calendar etc.

It has been told that deep learning is a black box. The universal approximation theorem was the key theorem which makes the stories going on. On the other hand, in the perspective of the function classes generated by deep neural network, it can be analyzed by in terms of the choice of the various activation functions. The piecewise linear functions, fourier series, wavelets and many other classes would be considered for the purpose of the tasks such as classification, prediction and generation models which heavily depend on the data sets. It might be a challenging problem for mathematicians to develop a new optimization theory depending on the various function classes.

In this talk, we present a Weisfielier-Leman Isomorphism test algorithm of featured graphs and how it can be used to extract representing features of nodes or entire graphs. This leads to a message passing framework of Aggregate-Combine of node-features which is one of the fundamental procedures to currently uesd graph neural networks. We proceed by showing various basic examples arised in real-world non-standard datasets like social network, knowledge graph and chemical compounds.

Global wellposedness and asymptotic stability of the Boltzmann equation with specular reflection boundary condition in 3D non-convex domain is an outstanding open problem in kinetic theory. Motivated by Guo’s L^2-L^\infty theory, the problem was completely solved for general C^3 domain, but it is still widely open for general non-convex domains. The problem was solved in cylindrical domain with analytic non-convex cross section. Generalizing previous work, we study the problem in general solid torus, a solid torus with general analytic convex cross-section. This is the first results for the domain which contains essentially 3D non-convex structure. This is a joint work with Chanwoo Kim and Gyeonghun Ko.

The past decade has witnessed a great advancement on the Tate conjecture for varieties with Hodge number $h^{2,0} = 1$. Charles, Madapusi-Pera and Maulik completely settled the conjecture for K3 surfaces over finite fields, and Moonen proved the Mumford-Tate (and hence also Tate) conjecture for more or less arbitrary $h^{2,0} = 1$ varieties in characteristic $0$.
In this talk, I will explain that the Tate conjecture is true for mod $p$ reductions of complex projective $h^{2,0} = 1$ varieties when $p \gg 0$, under a mild assumption on moduli. By refining this general result, we prove that in characteristic $p \geq 5$ the BSD conjecture holds for a height $1$ elliptic curve $E$ over a function field of genus 1, as long as $E$ is subject to the generic condition that all singular fibers in its minimal compactification are irreducible. We also prove the Tate conjecture over finite fields for a class of surfaces of general type and a class of Fano varieties. The overall philosophy is that the connection between the Tate conjecture over finite fields and the Lefschetz $(1,1)$-theorem over $C$ is very robust for $h^{2,0} = 1$ varieties, and works well beyond the hyperk\”{a}hler world.
This is based on joint work with Paul Hamacher and Xiaolei Zhao.

Please contact Wansu Kim at for Zoom meeting info or any inquiry.

Please contact Wansu Kim at for Zoom meeting info or any inquiry.

Please contact Wansu Kim at for Zoom meeting info or any inquiry.

(학사과정 학생 개별연구 결과 발표 세미나) Čech cohomology is the direct limit of cohomology taken from the cochain complex obtained by an open cover and a sheaf. In this talk we will derive some important results about Riemann surfaces such as Riemann-Roch theorem and Serre Duality, regarding low level Čech cohomologies. We will also discuss some basic structure and properties of Riemann surfaces using these results, focusing on genus and the embeddings.

For a given stable subalgebra of the formal power series ring, its Laurent extension, or others, we define an operator algebra over the subalgebra. One of the important operator algebras is the Weyl algebra or its generalization. We define generalized radical Weyl algebras (GRWA) and define the generalized radical Weyl algebra modules, we prove that the algebras and modules are simple. An automorphism of the GRWA define a twisted simple module as well. Since GRWA is an associative algebra, it has an ${\Bbb F}$-subalgebra which is a Lie algebra with respect to the commutator and we show that the Lie algebra is simple. We consider some other generalized Weyl algebra and its descended consequences as well.