发布时间： 2022-12-01
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**Organizing committee of Beijing-Saint Petersburg Mathematics Colloquium **

(1) Huijun Fan (SMS PKU, symplectic geometry and mathematical physics, geometric analysis)

(2) Feimin Huang (CAS, institute of applied mathematics, partial differential Equation, fluid mechanics)

(3) Sergey Kryzhevich (SPBU, differential and difference equations, dynamical systems, chaotic dynamics, structural stability, hyperbolic theory)

(4) Xiaonan Ma (Université de Paris, geometry, index theory)

(5) Maxim Vsemirnov (PDMI RAS, SPBU, number theory, algebra, combinatorics)

(6) Wenyuan Yang (BICMR, geometric group theory and Kleinian groups)

(7) Dmitry Zaporozhets (PDMI RAS, SPBU, Poisson-Voronoi tessellation zeros of random analytic functions and polynomials mixed volumes)

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**Lecture Series 38 ****—— December 1, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

**To Join Zoom Meeting:**

**https://us02web.zoom.us/j/81167390381?pwd=ZFhxdHdSQWxkQUsvUjRyZysyK2VYdz09**

**Meeting ID:** 811 6739 0381

**Password:** 654321

**Lecture 1****——On rationally integrable planar dual and projective billiards**

**Speaker:** Alexey Glutsyuk (Ecole Normale Supérieure de Lyon)

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** ../../docs/20221128151431652674.pdf

**Bio:** Professor Glutsyuk is an outstanding expert in real and complex dynamical systems: billiards, analytic theory of ordinary differential equations, holomorphic foliations, groups of transformations, and mathematical models for Josephson’s effect in superconductivity. He graduated from Moscow State University in 1993 and got his PhD in 1996 under the supervision of Yu.S. Ilyashenko. Alexey Glutsyuk obtained his habilitation at ENS Lyon in 2008 and his doctoral degree in Moscow in 2012. He has experience working at the Institute for Advanced Study in Princeton, Paul Sabatier University in Toulouse, Max Plank Institute in Bonn, and the Independent University of Moscow before obtaining his current position at ENS Lyon.

**Lecture 2****——Dirac operator and positive scalar curvature**

**Speaker:** Guoliang Yu (Texas A&M University)

**Time: **21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** In this talk, I will discuss an index theorem for Dirac operators on manifolds with corners and its application to Gromov's dihedral rigidity conjecture on scalar curvature. I will make this talk accessible to non-experts. This is joint work with Jinmin Wang and Zhizhang Xie.

**Bio:** Guoliang Yu is the Powell Chair in Mathematics and University Distinguished Professor at Texas A&M University. He was an invited speaker at the International Congress of Mathematicians in 2006. He is a Fellow of the American Mathematical Society and also a Simons Fellow in Mathematics. His research interests include large-scale geometry, K-theory, index theory, manifold topology and geometry, and operator algebras.

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**Lecture Series 37 ****—— November 17, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/758C625543237B2825C947F49E8D0D05

Valid Until: 2026-12-31 23:59

**Lecture 1****——Brownian chain break and some exit problems**

**Speaker:** Mikhail Lifshits (St. Petersburg State University)

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** Interacting Brownian particles are a popular model for various physical systems where a number of particles is subjected to inter-particle forces and ambient noise.

We investigate in depth the behaviour of one such model studied earlier both by physicists and mathematicians: a finite chain of Brownian particles, interacting through a pairwise quadratic potential, with one end of the chain fixed and the other end pulled away at slow speed.

We study the instant when the chain “breaks”, that is, the distance between two neighboring particles becomes larger than a certain limit. There are three different regimes depending on the relation between the speed of pulling and the Brownian noise. We prove weak limit theorems for the break time and the break position for each regime. The main tools used are weak dependence and Piterbarg-Pickands theorem on Gaussian large deviations.

As a byproduct, for a class of Gaussian stationary processes we obtain a limit theorem for the last exit time over a slowly growing linear boundary.

The work displays a series of joint works with F.Aurzada, F.Betz, and N.Karagodin.

**Bio:** Mikhail Lifshits is a professor at his alma mater St. Petersburg State University since 2000 and a board member of Saint Petersburg Mathematical Society. He got his Master degree in 1978, his PhD in 1981 from then Leningrad State University and received Doctor of Science degree in 1993. As an invited professor, M.Lifshits used to teach in France (Strasbourg, Lille, Paris), in USA (Georgia Tech), in Sweden (Linkoping); he also gave courses in Germany and Finland and many other places. He works in various areas of Random Processes Theory such as Gaussian processes, quantization, small deviations, exit probabilities, etc. as well as in applied Geostatistics. Prof. Lifshits wrote the monograph "Gaussian Random Functions" and textbooks "Lectures on Gaussian Processes" (Springer, 2014) and "Random Processes by Example" (World Scientific, 2015) which are extremely popular among students and young scientists. He is now Editor-in-Chief of the journal Probability Surveys and Associated Editor of Journal of Theoretical Probability, Theory of Probability and Applications, and some other journals.

**Lecture 2****——The random series-parallel graph**

**Speaker:** Zhan Shi（AMSS CAS）

**Time: **21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** I am going to make some elementary discussions on the random series-parallel graph of Hambly and Jordan (2004). Joint work with Xinxing Chen, Bernard Derrida and Thomas Duquesne.

**Bio:** Zhan Shi is Professor at AMSS, Chinese Academy of Sciences. Before joining AMSS, he was Professor at Sorbonne Université Paris VI. He received a PhD from Sorbonne Université Paris VI, under the joint supervision of Professors Marc Yor and Paul Deheuvels. Zhan Shi's research interests lie in probability theory, stochastic analysis and statistical physics.

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**Lecture Series 36 ****—— November 10, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/8F9C3126AFDD066C5842C7AB0185D10B

Valid Until: 2026-12-31 23:59

**Lecture 1****——On the structure and statistics of the set of classical knots**

**Speaker:** Andrei Malyutin (Saint Petersburg Department of Steklov Mathematical Institute)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** We study the structure and statistical characteristics of the set of classical knots. Particular points of this study are the statistics with respect to Thurston's classification (satellite/torus/hyperbolic) and the growth rates of the number of knots with respect to various complexity measures on the set of knots. New estimates for the growth rates of the number of prime knots with respect to the crossing number and arc index will be presented.

**Bio:** Andrei Malyutin is the deputy director of the Saint Petersburg Department of Steklov Mathematical Institute, a Professor at Saint Petersburg State University, having also an honorary degree of Professor of the Russian Academy of Sciences. He obtained his PhD in 2001 and got his Doctoral Degree (habilitation) in 2010. Andrey has some mathematical awards including the first prize in the International Mathematical Olympiad in 1992. His research interests include Geometric Topology, Geometric Group Theory, Dynamical Systems, Random Processes, etc. He provided solutions for a wide range of difficult problems, some of them going back to Markov and Poisson. Andrei is a member of the editorial board of several prestigious journals e.g. Algebra I Analiz.

**Lecture 2****——Taut foliations of 3-manifolds with Heegaard genus two**

**Speaker:** Tao Li (Boston College)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** Let M be a closed, orientable, and irreducible 3-manifold with Heegaard genus two. We prove that if the fundamental group of M is left-orderable then M admits a co-orientable taut foliation. This verifies part of the L-space Conjecture.

**Bio:** Tao Li is a professor at the Department of Mathematics at Boston College. He specializes in low-dimensional geometry and topology. He obtained his PhD in 2000 from Caltech. After a Bing Instructor at the University of Texas at Austin, he went to Oklahoma State University before moving to Boston. He was awarded twice the Simons Fellowship in 2015 and 2022 and was elected as a Fellow of the American Mathematical Society in 2016. He was an invited speaker at the 2014 ICM in Seoul.

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**Lecture Series 35 ****—— October 20, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/A060BCDC327122B952F2EE65455EB411

Valid Until: 2026-11-30 23:59

**Lecture 1****——Singular Weyl's law with Ricci curvature bounded below**

**Speaker:** Xianzhe Dai (University of California, Santa Barbara)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** The classical Weyl's law describes the asymptotic behavior of eigenvalues of the Laplace Beltrami operator in terms of the geometry of the underlying space. Namely, the growth order is given by (half of) the dimension and the limit by the volume. The study has a long history and is important in mathematics and physics. In a very recent joint work with S. Honda, J. Pan and G. Wei, we find two surprising types of Weyl's laws for some compact Ricci limit spaces. The first type could have power growth of any order (bigger than one). The other one has an order corrected by logarithm as some fractals even though the space is 2-dimensional. Moreover, the limits in both types can be written in terms of the singular sets of null capacities, instead of the regular sets. These are the first examples with such features for Ricci limit spaces. Our results depend crucially on analyzing and developing important properties of the examples constructed by J. Pan and G. Wei (GAFA 2022).

**Bio:** Xianzhe Dai is a professor at the Department of Mathematics at the University of California, Santa Barbara. He specializes in Differential Geometry and Geometric Analysis, in particular the Atiyah-Singer index theory. He obtained his PhD in 1989 from Stony Brook University. After a C. L. E Moore Instructorship at MIT, he went to the University of Southern California before moving to UCSB. He was a Sloan Research Fellow from 1993 to 1995.

**Lecture 2****——Formation of singularities of 2D soliton equations represented by $L,A,B$-triples**

**Speaker:** Iskander Taimanov (Sobolev Institute of Mathematics of RAS)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** We expose recent results on a certain geometrical mechanism of the formation of singularities of modified Novikov-Veselov and Davey-Stewartson II equations. The singular solutions are constructed by means of surface theory. These systems are represented by L,A,B-triples and we discuss the relation of such a mechanism to the degeneration of the zero level discrete spectra of the corresponding L-operators.

**Bio:** Iskander Asanovich Taimanov is an Academician of the Russian Academy of Sciences and an invited speaker of ICM’2022. He graduated from the Faculty of Mechanics and Mathematics of Moscow State University in 1983. In 1987, Iskander Taimanov defended his PhD thesis under the supervision of academician S. P. Novikov. In 1994, he defended his doctoral thesis at Steklov Institute of the Russian Academy of Sciences.

Now Prof. Taimanov works as a Principal Researcher at Sobolev Institute of Mathematics of the Siberian Branch of RAS being also the Chair of the Department of Geometry and Topology of Novosibirsk State University. Acad. Taimanov is a member of the board of directors of the Kazakh-British Technical University and participates on editorial boards of several prestigious journals. In September 2017, Acad. Taimanov was elected to the Presidium of the Russian Academy of Sciences.

Iskander Taimanov is an expert in research concerning geometry, calculus of variations, and soliton theory. Topics of his work are Morse–Novikov theory and Willmore surfaces. He is the author of the textbook Lectures on Differential Geometry.

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**Lecture Series 34 ****—— October 6, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recordinig: https://disk.pku.edu.cn:443/link/A60F3CA06FB856C9E5BA5A362C8714D0

Valid Until: 2026-11-30 23:59

**Lecture 1****——Aspects of the Bogomolov conjectures**

**Speaker:** Xinyi Yuan (Beijing International Center for Mathematical Research)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** The original Bogomolov conjecture (proved by Ullmo) asserts that a projective curve of genus greater than 1 over a number field has only finitely many points of small Neron-Tate heights. We will introduce this conjecture and the recent developments on other versions of it, including the geometric Bogomolov conjecture and the uniform Bogomolov conjecture.

**Bio:** Xinyi Yuan is currently a chair professor at Peking University. He got his Bachelor’s Degree from Peking University in 2003, and got his PHD from Columbia University in 2008. Before joining Peking University in 2020, he was an associate professor at UC Berkeley. He specializes in number theory and arithmetic geometry.

**Lecture 2****——On a conjecture due to J.-L. Colliot-****Thelene**

**Speaker:** Ivan Panin (St. Petersburg Department of Steklov Mathematical Institute)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** Let $R$ be a regular local ring containing a field, $K$ be its fraction field, $a\in R^{\times}$ be a unit, $n\geq 1$ be an integer, $1/2$ is in $R$. Particularly, we prove the following result. Suppose *a* is a sum of n squares in K. Then *a* is a sum of *n* squares in *R*. This is a partial case of a conjecture due to J.-L. Colliot-Thelene (1979). *The conjecture is solved in positive for regular local rings containing a field.*

In more details. If *R* contains rational numbers, then the conjecture is solved by the speaker in his Inventiones paper (2009). If *R* contains a finite field and the residue field of *R* is infinite, then the conjecture is solved by the speaker jointly with K.Pimenov in 2010 in their Doc. Math. paper. If *R* contains a finite field, then the conjecture is solved by S. Scully in 2018 in his Proceedings of the AMS paper. *If time permits, very recent progress in the topic will be discussed.*

**Bio:** Ivan Panin is a Chair of Algebra and Number Theory at Steklov Mathematical Institute at Sankt-Petersburg. He is a Corresponding Member of the Russian Academy of Sciences since 2003. He got his PhD in 1984 under the supervision of Andrei Suslin. Ivan Panin got his Habilitation in 1995. He was an invited speaker at ICM-2018 in Rio de Janeiro. He solved the Grothendieck--Serre conjecture on principal G-bundles (for regular local rings containing a field). He invented (jointly with A. Smirnov) a topic of oriented cohomology theories on algebraic varieties, stated and proved a Riemann--Roch type theorem for oriented cohomology theories. Jointly with G. Garkusha, he realised a project due to V.Voevodsky producing a machinery for computing motivic infinite loop spaces.

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**Lecture Series 33 ****—— September 22, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/2C3167F7FADFEB83417F8A3A80B9527E

Valid Until: 2026-10-31 23:59

**Lecture 1****——The pro-Chern-Schwarz-MacPherson class in Borel-Moore motivic homology**

**Speaker:** Fangzhou Jin (**Tongji University**)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:**** We show that the zero-dimensional part of the pro-Chern-Schwarz-MacPherson class defined by Aluffi is equal to the pro-characteristic class in limit Borel-Moore motivic homology. A similar construction also produces a quadratic refinement of this class in the limit Borel-Moore Milnor-Witt homology. This is a joint work with Peng Sun and Enlin Yang.**

**Bio:**** Fangzhou Jin is an assistant professor at Tongji University. He obtained his PhD at Ecole Normale Supérieure de Lyon in 2016 under the supervision of Frédéric Déglise. His work is related to foundational aspects of motivic homotopy theory, a theory introduced by Morel and Voevodsky which studies cohomology theories on algebraic varieties using geometric as well as categorical tools by importing ideas from algebraic topology.**

**Lecture 2****——Triangulated categories, weight structures, and weight complexes**

**Speaker:** Mikhail Bondarko (St. Petersburg State University)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** (Co)homology functors usually yield certain functors into triangulated categories. I will justify this claim and recall some basics on homotopy categories of complexes and other triangulated categories. Next, I define weight structures on triangulated categories; these were independently introduced by B. and D. Pauksztello. Weight structures give certain filtrations of triangulated categories; the definition is a certain cousin of that of t-structures. I will mention some methods of constructing weight structures as well as interesting "topological" and motivic examples. Weight structures give certain weight complex functors that are "usually" exact; they are also conservative up to "objects of infinitely large and infinitely small weights" (that is, weight complexes only kill extensions of objects of these two sorts). In particular, one has an exact conservative functor from geometric Voevodsky motives into complexes of Chow motives, whereas the corresponding weight spectral sequences vastly generalize Deligne’s ones. Weight complexes also enable one to calculate the corresponding pure functors; some of the latter are quite new and interesting.

The talk can be interesting to anyone who had some experience with (co)homology and categories.

**Bio:** Mikhail Bondarko is an associate professor at the St. Petersburg State University and also a professor of the Russian Academy of Sciences. He obtained his PhD in 2000 and got his Doctor Degree (habilitation) in 2007. He has some prestigious awards; this includes first prize in the Chinese Mathematical Olympiad in 1994. Currently, Bondarko studies triangulated categories (including motivic ones), weight structures, and t-structures on them. He also has several papers on formal groups, finite flat group schemes, and additive Galois modules.

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**Lecture Series 32 ****—— June 16, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/003A36414D9928A3A199EFE5BE0DF5E0

Valid Until: 2026-07-31 23:59

**Lecture 1****——Bounded elementary generation of Chevalley groups**

**Speaker:** Prof. Nikolai Vavilov

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:**** We discuss several results on bounded elementary generation and bounded commutator width for Chevalley groups over Dedekind rings of arithmetic type in positive characteristics. In particular, Chevalley groups of rank \ge 2 over polynomial rings F_q[t] and Chevalley groups of rank \ge 1 over Laurent polynomial F_q[t,t^{-1}] rings, where F_q is a finite field of q elements, are boundedly elementarily generated. We sketch several proofs, using reciprocity laws, symbols in algebraic K-theory, and surjective stability for K-functors. As a result, we establish rather plausible explicit bounds, that do not depend on q and are better than the known ones even in the number case. Using these bounds we can also produce sharp bounds of the commutator width of these groups. We also mention several applications (Kac---Moody groups, first order rigidity, etc.) and possible generalisations. This is joint work with Boris Kunyavskii and Eugene Plotkin.**

**Bio:**** Professor Nikolai Alexandrovich Vavilov works at Saint-Petersburg State University, Department of Mathematics and Computer Sciences (he was one of the co-founders of the Department) and at Saint Petersburg Department of Steklov Mathematical Institute. He is one of the best Russian algebraists having a big number of brilliant results in Structure theory and representations of algebraic groups, algebraic K-theory, overgroups of semisimple groups and tori. Prof. Vavilov graduated from Leningrad State University (now Saint Petersburg State University) and got his Doctor Degree (habilitation) in 1988. He has got a big number of prestigious awards and prizes and grew up dozens of students.**

Besides, Nikolai Alexandrovich intensively cooperates with Chinese colleagues. He is one of those people who launched the current program of Russian - Chinese collaboration.

**Lecture 2****——Arakelov geometry over adelic curves**

**Speaker:**** Prof. ****Huayi Chen**

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:**** Arakelov geometry is a theory of arithmetic geometry which combines algebraic geometry over an algebraic integer ring and complex analytic geometry to study the arithmetic properties of projective varieties over a number field. In a joint work with Atsushi Moriwaki, by using the adelic point of view of Chevalley and Weil, we extend Arakelov geometry to the setting of projective varieties over an arbitrary countable field. In this talk, I will explain the main ideas behind this theory, and the similarity and differences compared to the classical approach.**

**Bio:**** Huayi Chen is currently a Professor at Paris Diderot University and the Mathematics Institute of Jussieu–Paris Rive Gauche. He graduated from Peking University in 2000. In 2003, he got his Master's degree at Pierre and Marie Curie University. Then he got his PhD at Laurent Schwartz Mathematics Center, Ecole Polytechnique in 2006. His research interests include algebraic geometry, Arakelov geometry and Diophantine problems.**

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**Lecture Series 31 ****—— June 2, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/F98451EB7316CD31517990FA148AC092

Valid Until: 2026-07-31 23:59

**Lecture 1****——****On a geometric realization of the center of the small quantum group**

**Speaker:**** Prof. **Peng Shan (Yau Mathematical Sciences Center)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:**** **In Lie theory, the center of many important representation categories admits geometrical interpretations as singular cohomology of certain algebraic varieties. We will explain a new realization of this type, relating the center of the small quantum group to the cohomology of certain affine Springer fibres. As an application, we obtain a conjectural formula for the dimension of the center of the small quantum group. This is based on a joint work with R. Bezrukavnikov, P. Boixeda-Alvarez, and E. Vasserot.

**Bio:**** **Peng Shan is currently a Professor at Yau Mathematical Sciences Center, Tsinghua University. Her research interests lie in Geometric Representation Theory. In 2011, she received her Ph.D. from Paris Diderot University. After graduation, Peng Shan worked at MIT as C. L. E. Moore instructor. From 2011 to 2017, she was an associate researcher at the French National Center for Scientific Research. Also, she carried out research at the University of Caen-Normandie and Paris-Sud University. She is also the invited speaker at the ICM (2022). Prof. Shan Peng is on the editorial board of "J. Algebra" and has published many papers in top mathematics journals such as J. Amer. Math. Soc., Invent. Math., Duke Math. J. and Adv. Math.

**Lecture 2——Chevalley groups over rings of polynomials**

**Speaker:** Dr. Anastasia Stavrova (Saint Petersburg State University)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:**** **Let D be a Dedekind domain. In 1977, A. Suslin established that for any N>=3, and any n>=1, one has SL_N(D[x_1,...,x_n])=SL_N(D)E_N(D[x_1,...,x_n]), where E_N(D[x_1,...,x_n]) is the elementary subgroup of SL_N(D[x_1,...,x_n]), i.e. the subgroup generated by the unipotent elementary transformation matrices E+tE_ij, where E is the unit matrix, E_ij is the matrix with 1 at the position i,j and 0 everywhere else, and t is an arbitrary element of the polynomial ring D[x_1,...,x_n]. In particular, this implies that SL_N(Z[x_1,...,x_n])=E_N(Z[x_1,...,x_n]), where Z is the ring of integers. We discuss an extension of this result to all split simple linear algebraic groups (also called Chevalley groups) and to regular rings D of higher dimension.

**Bio:**** **Dr. Anastasia Stavrova is an expert in algebraic groups, non-associative algebra, and algebraic K-theory. She is a researcher in the Chebyshev Laboratory and Department of Mathematics and Computer Science at Saint Petersburg State University. Dr. Stavrova earned a specialist degree in mathematics at Saint Petersburg State University in 2005 and got her PhD in 2009 supervised by Nikolai Vavilov. She has got a great experience of working overseas (the University of Leiden, University of Padua, Ludwig Maximilian University of Munich, and the University of Duisburg-Essen). Also, she was Jerrold E. Marsden Postdoctoral Fellow at the Fields Institute in Canada. Anastasia Stavrova obtained a great number of brilliant results in Algebra and related areas. She won the Young Mathematician Prize of the Saint Petersburg Mathematical Society in 2009, the Young Russian Mathematics Scholarship in 2016. In 2018, she has got the G. de B. Robinson Award from the Canadian Mathematical Society.

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**Lecture Series 30 ****—— May 26, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/BC2A84C65A65A46B5303EFAE1C4212AA

Valid Until: 2026-06-30 23:59

**Lecture 1****——The non-positive curvature geometry of some fundamental groups of complex hyperplane arrangement complements**

**Speaker:**** Jingyin Huang (Ohio State University)**

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:**** A complex hyperplane complement is a topological space obtained by removing a collection of complex codimension one affine hyperplanes from C^n (or a convex cone of C^n). Despite the simple definition, these spaces have highly non-trivial topology. They naturally emerge from the study of real and complex reflection groups, braid groups and configuration spaces, and Artin groups. More recently, the fundamental groups of some of these spaces start to play important roles in geometric group theory, though most of these groups remain rather mysterious. We introduce a geometric way to understand classes of fundamental groups of some of these spaces, by equivariantly “thickening” these groups to metric spaces which satisfy a specific geometric property that is closely related to convexity and non-positive curvature. We also discuss several algorithmic, geometric and topological consequences of such a non-positive curvature condition. This is joint work with D. Osajda.**

**Bio:**** Jingyin Huang is an assistant professor and the Alice Louise Ridenour Wood Chair in Mathematics at Ohio State University. He completed his PhD at New York University in 2015. He is an expert in geometric group theory, which studies the deep connections between the algebraic properties of groups and the geometry of spaces they act on. His research focus on certain rigidity properties of discrete groups (quasi-isometric rigidity, measure equivalence and orbit equivalence rigidity), and the geometry of non-positively curved spaces and groups. He has been awarded a 2022 Sloan Research Fellowship.**

**Lecture 2——Combinatorics of Lipschitz polytope and beyond**

**Speaker:** Prof. Fedor Petrov

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:**** Let $(X, \rho)$ be a finite metric space. Consider the space of real functions on $X$ with zero mean. Equip it with Lipschitz norm $\|f(x)\|=\max |f(x)-f(y)|/\rho(x, y)$ and consider the unit ball in this norm, which is a certain convex polytope. The question on classifying metrics depending on the combinatorics of this polytope have been posed by Vershik in 2015. In a joint work with J. Gordon (2017), we proved that for generic metric space the number of faces of a given dimension is always the same. This fact is intimately related to regular triangulations of the root polytope (convex hull of the roots of root system $A_n$). In this survey-style talk, we discuss both this phenomenon and further relations of the subject, observed recently by several groups of mathematicians.**

**Bio:**** Prof. Fedor Petrov is an expert in Combinatorics, Convex Geometry, Functional Analysis and Geometry of Numbers. Being a former student of Prof. A.M. Vershik, now he plays a leading role in his research group. Prof. Petrov graduated from Saint Petersburg State University in 2004, got his PhD in 2007 and habilitation (Doctor of Sciences degree) in 2018. He is a Professor and a director of one of the educational programs at the Department of Mathematics and Computer Sciences of Saint Petersburg State University combining this with a research position at the Saint Petersburg Department of Steklov Mathematical Institute. Not only Prof. Petrov is an author of a big number of impressive results in the aforementioned areas, but also a jury member of several top mathematical contests for high school and university students. Besides, he is a member of the Council of the St. Petersburg Mathematical Society (since 2018).**

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**Lecture Series 29 ****—— May 19, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/872A119E054BC012A4A81977B8AA410E

Valid Until: 2026-06-30 23:59

**Lecture 1****——A violation of the uncertainty principle: indicator functions with thin spectrum and uniformly bounded partial Fourier integrals**

**Speaker:**** ****Sergey Kislyakov (**St.Petersburg Department of Steklov Mathematical Institute**)**

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:**** Given a set $a$ of finite measure on the real line, it is possible to find a set $b$ with the properties mentioned in the title and differing from $a$ as little as we want in the sense of measure. There is an analog of this claim for more or less general LCA groups. The discussion will be prefaced with a short survey of various results about conditions that may or may not be fulfilled simultaneously for a function and its Fourier transform. This is a joint work with P.Perstneva.**

**Bio:**** Sergey Vitalievich Kislyakov is one of the best Russian experts in Harmonic Analysis, Functional Analysis, Interpolation theory, Fourier Analysis and many other related fields, having obtained a great deal of outstanding results in these areas. Besides, he is the author of several books that are extremely popular both among students and mature researchers. Prof. Kislyakov is a Doctor of Mathematics, an Academician of the Russian Academy of Sciences (since 2016), and the Chief Editor of the "Algebra and Analysis" journal. He was Director of the Saint Petersburg Department of Steklov Mathematical Institute.**

**Lecture 2****——****Critical Point Sets of Solutions in Elliptic Homogenization**

**Speaker:** **Fanghua Lin (Courant Institute, NYU)**

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: ****In this talk, I shall outline a proof for bounds on H^(n-2)–Hausdorff measure of critical point sets of solutions in elliptic homogenization. The method works for solutions of elliptic equations with Lipschitz coefficients also. This is a joint work with Zhongwei Shen.**

**Bio: **Professor Fanghua Lin is a Silver Professor of Mathematics at the Courant Institute of Mathematical Sciences, New York University. He received his Ph.D. in 1985 from the University of Minnesota. His research interests are in nonlinear partial differential equations, geometric measure theory and applied & geometric analysis. Professor Lin has made significant contributions to the theory of liquid crystals, harmonic maps, Ginzburg-Landau equations and the theory of homogenization. He has also made important contributions to the studies of topological defects, vortices, quantitative unique continuation, nodal and critical sets of solutions of partial differential equations.

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**Lecture Series 28 ****—— May 5, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/BBD59D040E4E91A35EFFC9E42CEF593A

Valid Until: 2026-06-30 23:59

**Lecture 1****——Analysis on compressible Navier-Stokes equations with strong boundary layer**

**Speaker: **Tong Yang (City University of Hong Kong)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:**** It is a classical problem in fluid dynamics about the stability and instability of different hydrodynamic patterns in various physical settings, in particular in the high Reynolds number limit of laminar flow with the boundary layer. However, there are very few mathematical results on the compressible fluid despite the extensive studies when the fluid is governed by the incompressible Navier-Stokes equations. In this talk, we will present a new approach to studying the compressible Navier-Stokes equations in the subsonic and high Reynolds number regime where a subtle quasi-compressible and Stokes iteration is developed. As a byproduct, we show the spectral instability of the subsonic boundary layer. This is a joint project with Zhu Zhang.**

**Bio:**** Tong Yang is a Chair Professor of Mathematics at the City University of Hong Kong. He was President of the Hong Kong Mathematical Society from 2016 to 2020. He has been working in the fields of partial differential equations and kinetic theory. He served as an Editor-in-Chief of Analysis and Applications from 2013 to 2017 and is one of the founding Editors-in-Chief of Kinetic and Related Models launched in 2008. He also serves on several international journals, including the Editorial Advisory Board of London Mathematical Society: Bulletin and Journal, and SIAM Journal on Mathematical Analysis. He is a member of the European Academy of Sciences, The World Academy of Sciences and the Hong Kong Academy of Sciences. The awards and distinctions that he has received include the 2nd class State Natural Science Award of China in 2012 and the Croucher Senior Research Fellowship in 2011.**

**Lecture 2——Large bifurcation supports**

**Speaker:** Prof. Yulij Ilyashenko

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: ** The talk deals with a general problem of the bifurcation theory on the two-sphere. Consider a vector field with arbitrary degeneracies: complex singular points, multiple limit cycles and polycycles. What part of the phase portrait will bifurcate under a perturbation of this field, and what part will remain unchanged? Not only the degenerated parts of the phase portrait mentioned above will bifurcate; but some generic parts will also. A highly nontrivial question arises: WHO BIFURCATES? The answer will be given in the talk based on joint work with Natalya Goncharuk.

**Bio: **Prof. Yulij Ilyashenko is one of the most renowned Russian scientists working in Differential Equations, Dynamical Systems and Geometry. He obtained a big number of brilliant results in bifurcation theory and dynamics beyond uniform hyperbolicity. In particular, he proved the finiteness of the number of limit cycles for polynomial vector fields, thus giving a partial solution to Hilbert's 16^{th} problem (the previous proof provided by Dulac contained a serious gap).

Yulij Sergeevich Ilyashenko is the Rector of the Independent University of Moscow, vice-president of Moscow Mathematical Society, and Professor at Moscow State University, Cornell University, Higher School of Economics, and Steklov Mathematical Institute. Besides, Prof. Ilyuashenko is a member of the editorial boards of several prestigious journals including Ergodic Theory and Dynamical Systems, Journal of Dynamics and control systems and Main Editor of Moscow Mathematical Journal.

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**Lecture Series 27 —— April 7, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/C745583AE3B73B5E4E69ABDBAE6C8459

Valid Until: 2026-05-31 23:59

**Lecture 1——Extending periodic maps on surfaces over the 4-sphere**

**Speaker:** Prof. Shicheng Wang, Peking University

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** The topic indicated by the title has been addressed by Montesinos (1982) and Hirose (2002) using Rohlin intersection form, and by Ding-Liu-Wang-Yao (2012) using spin structures.

Based on the work above, we deduce a more computable criterion for extending periodic maps on surfaces over the 4-sphere.

Some applications are given. Results including:

(1) Let $F_g$ be the closed orientable surface of genus $g$ and $w_g$ be a periodic map of maximum order on $F_g$.

Then $w_g$ is extendable over $S^4$ for some smooth embedding $e: F_g\ to S^4$ if and only if $g=4k, 4k+3$.

(2) For infinitely many primes $p$, each periodic map of order $p$ on $F_g$ is extendable over $S^4$ for some smooth embedding $e: F_g\ to S^4$.

This is joint work with Zhongzi Wang.

**Bio:** Prof. Shicheng Wang is currently a Distinguished Professor at the Department of Mathematics, Peking University. He received a master's degree from Peking University in 1981 and a doctorate degree from UCLA in 1988. He has won the Shiing-Shen Chern Mathematics Award and the second prize of the National Natural Science Awards (China). Prof. Wang was an invited speaker at the ICM’2002 in Beijing. His research focuses on low-dimensional topology, involving geometric group theory, dynamical systems, and algebraic topology.

**Lecture 2——A Mozaic from Geometry, Dynamics, PDEs, and maybe more.**

**Speaker:** Prof. Dimitri Yu. Burago, Pennsylvania State University, State College PA

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** I am going to begin with some unsolved problems, which, in my opinion, deserve more attention that they receive. For some problems, there are partial solutions, which I would try to sketch or at least discuss. I plan then to go to problems where the progress is more substantial, as time permits. What I plan is indeed a mozaic. I am not sure how many topics I would be able to touch upon and which ones would be more of interest, my collaborators include D. Chen, S. Ivanov, B. Kleiner, Ya. Kurylev, M. Lassas, J. Lu, A. Novikov, L. Polterovich. Maybe, I would concentrate оn two or three topics, maybe many more short stories, depending on the reaction.

**Bio:** Dimitri Yurievich Burago is a worldwide renowned expert in Geometry, Topology and Dynamical Systems. He graduated from Saint Petersburg State University and has got his doctorate in 1994 under the supervision of Prof. Anatoly Vershik. Now he is working at Pennsylvania State University where he received the title of Distinguished Professor in Mathematics. Besides, Prof. Burago received many prestigious prizes including the Leroy P. Steele Prize by the American Mathematical Society. Also, he was an invited speaker of the ICM’1998 in Berlin.

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**Lecture Series 26 —— March 24, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/EE1E0EAC2E77FE3CF97E4E2B48DAAEA3

Valid Until：2026-04-30 23:59

**Lecture 1——On Lyapunov exponents of quasi-periodic cocycles**

**Speaker: **Jiangong You (Chern Institute of Mathematics, Nankai University)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **Lyapunov exponents are dynamical invariants. Quasi-periodic cocycles are a special important class of dynamical systems having strong background in quantum physics. Lyapunov exponents of a quasi-periodic cocycle depends sensitively on the smoothness of the cocycle, arithmetic property of the frequency and profile of the potential. So far the behind mechanism of the sensitivity has not been completely understood. In this talk, I will discuss the continuity, Holder regularity of the Lyapunov exponent as well as the quantitative version of Avila’s global theory. The talk is based on joint works with L. Ge, S. Jitomirskaya, Y. Wang, X. Zhao and Q. Zhou.

**Bio: **Jiangong You is a professor at Chern Institute of Mathematics of Nankai University. His research interests include Hamiltonian dynamics (especially KAM theory for Hamiltonian ODEs and PDEs), smooth ergodic theory (especially Lyapunov exponents) and mathematical physics (especially spectral theory of quasi-periodic Schrodinger operators).

**Lecture 2——Systems of isometries: dynamics and topology**

**Speaker:** Alexandra Skripchenko

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: **Systems of partial isometries of the interval represent a simple combinatorial object which appears in topology in connection with measured foliations on a surface (orientable or non-orientable), in dynamics as a nice model to study billiards in rational polygons and in geometric group theory as a way to describe actions of free groups on R-trees. We will discuss several classes of systems of isometries (interval exchange transformations, interval exchange transformations with flips, interval translation mappings, band complexes) and compare their basic dynamical properties: minimality, ergodicity, invariant measures etc. The talk is mainly based on the joint works with Artur Avila and Pascal Hubert and with Serge Troubetzkoy.

**Bio: **Prof. Alexandra Skripchenko is the Dean of Faculty of Mathematics at Higher School of Economics (HSE), Moscow. She is expert in Dynamical Systems, Low-dimensional Topology and Geometric Group Theory. In particular, she has got some outstanding results concerning interval exchange mappings and interval translation mappings. Having graduated from Moscow State University in 2009, Alexandra Skripchenko has got her PhD in 2012 and works at HSE since 2014.

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**Lecture Series 25 —— March 8, 2022（20:00-22:00 Beijing time / 15:00-17:00 St Petersburg time).**

Recording: https://disk.pku.edu.cn:443/link/EDA3BDF8D06B8765C1542BE7278C7D3B

Valid Until: 2026-06-30 23:59

**Lecture 1——Sharp asymptotics for arm events in critical planar percolation**

His main research interests are on the interface between analysis and probability including (but not limited to) Geometry of Gaussian fields, Growth models, Geometric function theory, Schramm-Loewner Evolution and critical lattice models.

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**Lecture Series 24 —— December 16, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/D51CB6937C05AB71E2B6F5627F6ECB52

Valid Until：2026-04-30 23:59

Prof. Zaporozhets is one of strongest researchers in Probability theory and Geometry, having major interests in Geometry of numbers, Stochastic Geometry, Convex Geometry, Poisson - Voronoi tessellation, zeros of random polynomials and random analytic functions.

Being a student of Acad. Il'dar Ibragimov, one of the most renowned experts in Probability and Statistics, Dmitry graduated from Saint Petersburg State University, defended his PhD thesis in 2005 and Doctoral thesis in 2015 (both thesis were devoted to Random Polynoms).

Later on, Prof. Zaporozhets has got the honorary degree of Professor of Russian Academy of Sciences.

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**Lecture Ser****ies ****23**** —— ****December** **02****, ****2021**（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).

Video: https://disk.pku.edu.cn:443/link/A863DD4C00B98F1807DB384C8909F353

Valid Until：2026-04-30 23:59

**Lecture 1——Gabor analysis for rational functions**

**Speaker: **Prof. Yuri Belov

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** Let $g$ be a function in $L^2(\mathbb{R})$. By $G_\Lambda$, $\Lambda\subset R^2$ we denote the system of time-frequency shifts of $g$, $G_\Lambda=\{e^{2\pi i \omega x}g(x-t)\}_{(t,\omega)\in\Lambda}$.

A typical model set $\Lambda$ is the rectangular lattice $\Lambda_{\alpha, \beta}:= \alpha\mathbb{Z}\times\beta\mathbb{Z}$ and one of the basic problems of the Gabor analysis is the description of the frame set of $g$ i.e., all pairs $\alpha, \beta$ such that $G_\Lambda_{\alpha,\beta}$ is a frame in $L^2(\mathbb{R})$. It follows from the general theory that $\alpha\beta \leq 1$ is a necessary condition (we assume $\alpha, \beta > 0$, of course). Do all such $\alpha, \beta $ belong to the frame set of $g$? Up to 2011 only few such functions $g$ (up to translation, modulation, dilation and Fourier transform) were known. In 2011 K. Grochenig and J. Stockler extended this class by including the totally positive functions of finite type(uncountable family yet depending on finite number of parameters) and later added the Gaussian finite type totally positive functions. We suggest another approach to the problem and prove that all Herglotz rational functions with imaginary poles also belong to this class. This approach also gives new results for general rational functions. In particular, we are able to confirm Daubechies conjecture for rational functions and irrational densities.

**Lecture 2—****—Planar Sobolev extension domains and quasiconformal mappings. **

**Speaker: **Yi Zhang

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** In 1979, Goldshtein et al. pointed out that a bounded simply connected planar domain is a W^{1,\,2}-extension domain if and only if it is a quasidisk. This result was later generalized by Jone to all dimensions, showing that uniform domains are W^{1,\,p}-extension domain for any 1\le p<\infty. However, there are simply connected W^{1,\,p}-extension domains in the plane which are not uniform when p\neq 2, pointed out by e.g. Maz'ya. In this talk I will present my joint work with Koskela and Rajala on this problem, and show its connection to the Ahlfors' quasiconformal reflection theorem.

**Bio: ** My main background is in complex analysis and geometric function theory. I have also done works on harmonic analysis, functional analysis, nonlinear elliptic partial differential equations (p-Laplacians and infinity Laplacian), free boundary problems, calculus of variations, eigenvalue problems of p-Laplacians and so on. Especially, I am interested in problems in the intersection of analysis and geometry.

B.S., Math & Applied Math, Beihang University, September 1, 2009 – June 30, 2013.

M.S., Mathematics, University of Jyväskylä (Supervisor: Pekka Koskela), August 1, 2013 – July 30, 2014.

Ph.D., Mathematics, University of Jyväskylä (Supervisor: Pekka Koskela), August 1, 2014 – July 30, 2017.

Doctoral Dissertation: Planar Sobolev extension domains. (Defended on May 5th, 2017)

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Video: https://disk.pku.edu.cn:443/link/5B3295FADF4652F5B3814A5112999F28

Valid Until：2026-04-30 23:59

**Lecture 1**——Symmetry Results in Two-Dimensional Inequalities for Aharonov–Bohm Magnetic Fields.

**Speaker:** Prof. Ari Laptev,

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Lecture 2**——Microscopic conservation laws for the derivative nonlinear Schrodinger equation

**Speaker:** Guixiang Xu (Beijing Normal University)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

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**Lecture Series 21 —— November 04, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/6D11936873F0A5E492B553AC48F3E6C6

Valid Until：2026-04-30 23:59

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**Lecture Series 20 — October 21, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/90A35E4EF58FF4E7D0841D0217747F5D

Valid Until：2026-04-30 23:59

**Lecture 1——Multiplication Between (Local) Hardy Spaces and Their Dual Spaces**

**Speaker: **Yang Dachun

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **It is well known that bilinear decompositions of products of (local) Hardy spaces and their dual spaces play an important role in the study on various problems from analysis. In this talk, we present some recent progresses on such bilinear decompositions of products of (local) Hardy spaces and their dual spaces. Some open questions are also mentioned in this talk.

**Bio: **Yang Dachun, Professor, School of Mathematical Sciences, Beijing Normal University. Focus on the research of the real-variable theory of function spaces and its applications. Rewarded by National Science Foundation for Distinguished Young Scholars of China in 2005.

**Lecture 2 —— Elementwise sub-representations of groups, and their automorphic analogue.**

**Speaker: **Dipendra Prasad, Prof.

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: **Suppose V and W are two finite dimensional representations of a group G such that for each element g of G, the eigenvalues of g (counted with multiplicity) on V are contained in the eigenvalues of g on W. What can we say about V and W? Such a question appears naturally in Automorphic representations which we will briefly discuss, but then focus on the abstract question on group representations.

**Bio: **Professor Dipendra Prasad works at Indian Institute of Technology Bombay (Mumbai, India) having the second position at Saint - Petersburg State University where he heads the Laboratory ‘Modern Algebra and Applications’ at the Department of Mathematics and Computer Science. He obtained his bachelor’s degree from the St. Xavier College, Mumbai in 1978 before moving to the Indian Institute of Technology Kanpur which he completed in 1980. From 1980–1985, Prasad worked as a research scholar at the Tata Institute of Fundamental Research, Mumbai (TIFR Mumbai). He then completed his PhD under the supervision of Benedict Gross at Harvard, in 1989.

Prof. Prasad is a worldwide known expert in Number Theory, Group Theory and Representation Theory (mainly, on Automorphic Representations and the Gan-Gross-Prasad conjecture).

He has got a big number of prestigious awards on national and international levels. In 2018, he was Invited Speaker of the International Congress of Mathematics in Rio de Janeiro.

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**Lecture Series 19 — October 7, 2021（19:00-21:00 Beijing time or 14:00-16:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/F1CEAE494B34A35B67CBA8BD214CB2FD

Valid Until：2026-04-30 23:59

**Lecture 1——Norm-resolvent convergence to zero-range models with internal structure in models with strong inhomogeneities**

**Speaker:** Alexander V. Kiselev

**Time: **19:00-20:00 Beijing time (14:00-15:00 St Petersburg time)

**Abstract:**

**Bio: **Dr. Alexander Kiselev, an outstanding expert in Mathematical Physics, whose interested include but not are limited to:

- Functional model for non-selfadjoint linear operators in Hilbert spaces

- Functional analysis;

- Stability Theory and Similarity Theory for non-selfadjoint linear operators;

- Theory of perturbations.

Having graduated from Saint Petersburg State University in 1996 (Faculty of Physics), Dr. Kiselev obtained his PhD degree in 2001. After that he was working in a big number of top-level universities including Dublin Institute of Technology, Universidad Nacional Autónoma de México, University College London, University of Bath, and Lomonosov Moscow State University,

The number of Alexander Kiselev’s collaborators and coauthors is very impressive as well as the number and scientific diversity of his research projects and students.

Now Dr. Kiselev is working at the Department of Mathematics and Computer Science of Saint Petersburg State University.

**Lecture 2 —— Elementwise sub-representations of groups, and their automorphic analogue.**

**Speaker: **Mingying Zhong

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **By identifying a norm capturing the effect of the forcing governed by the Poisson equation, we give a detailed spectrum analysis on the linearized Vlasov-Poisson-Boltzmann system around a global Maxwellian. It is shown that the electric field governed by the self-consistent Poisson equation plays a key role in the analysis so that the spectrum structure is genuinely different from the well-known one of the Boltzmann equation. Based on this, we give the optimal time decay rates of solutions to the equilibrium.

**Bio: **Zhong Mingying, Professor, College of Mathematics and Information Science, Guangxi University. Focus on the spectral analysis, Green's function and fluid dynamical limits of the kinetic equations with external force, such as the Vlasov-Poisson(Maxwell)-Boltzmann systems, and so on. Rewarded by National Natural Science Foundation--Outstanding Youth Foundation, 2019.

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**Lecture Series 18 — June 3, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/15CD646FE11B67512C30EDD28E594410

Valid Until：2026-04-30 23:59

**Lecture 1——Nevanlinna factorization in classes of analytic functions smooth up to the boundary.**

**Speaker:** N.A. Shirokov

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **The definition of all objects used in this announcement will be given in the talk. Let an analytical function f belong to the Hardy class Hp in the unit disc D. Then f may be represented as the product, f=IOf, where I is the so-called inner function, it means that |I(z)|<1 for z belonging D, and |I(z)|=1 for almost every z on the unit circle, and the so-called outer function Of is defined by values of |f(z)| on the unit circle. One of those two factors may be absent. The cited statement is the classical result, the factors I and Of are in a sense independent for the functions f from Hp. Let us consider a class X which is contained in H1 and consists of functions f continuous in the closed disc D--. Then f=IOf ,the inner function I is in general discontinuous in D-- what implies that the outer function Of is to compensate the points of discontinuity of the inner function I. The talk is devoted to the concrete way of this compensation and to the specific properties of outer functions belonging to the analytical Holder classes and to the classes of functions of variable smoothness. The consequences about the half-smoothness of an analytical function in comparison with the smoothness of its modulus on the boundary will be given too.

**Bio:** Professor Nikolai A. Shirokov is a worldwide renowned expert in harmonic and complex analysis which includes the theory of approximations, boundary properties of holomorphic functions and the theory of singular integrals. Having graduated from Saint Petersburg State University in 1971, he has got his Ph.D.in 1973, became Doctor of Science (Saint Petersburg department of Steklov Institute) in 1985 and got his Professor degree in 1988. Professor Shirokov is the author of 82 research publications (Scopus) and a supervisor of a big number of students (both graduate and undergraduate). In 2014 he was officially recognized as ‘the best teacher’ of Higher School of Economics which is one of the most prestigious Russian Universities. N.A. Shirokov heads the department of Math.Analysis of Saint Petersburg State University since 2005 and the Department of Applied Mathematics at Higher School of Economics (Saint Petersburg branch) since 2013.

**Lecture 2 —— Factoring Quasiconformal & quasisymmetric mappings**

**Speaker: **Jinsong Liu (Institute of Mathematics, Chinese Academy of Sciences)

**Time: **21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** It follows from the Measurable Riemann Mapping Theorem that we can always present a 2-dimensional quasi-conformal mapping as a composition of quasi-conformal mappings with smaller dilatation. In this talk we will construct n (≥3)-dimensional quasi-conformal homeomorphism between Euclidean spaces which admit no minimal factorization in linear, inner, or outer dilatation. If time permits, I will discuss the composition of quasi-symmetric mappings between metric spaces.

**Bio: **Jinsong Liu is a professor of institute of mathematics, Chinese Academy of Sciences. His research field is complex analysis and Teichmuller theory.

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**Lecture Series XVII — May 20, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/820DF463C85B66E00CB1FB0C1DDFB027

Valid Until：2026-04-30 23:59

**Lecture 1——Fractional Calculus for m-accretive Operators**

**Speaker: **Dr. Maxim Kukushkin, Moscow State University for Civil Engineering; Institute for Applied Mathematics and Automatization

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **In this report we aim to construct an abstract model of a differential operator with a fractional integro-differential operator composition in final terms, where modeling is understood as an interpretation of concrete differential operators in terms of the infinitesimal generator of a corresponding semigroup. We study such operators as a Kipriyanov operator, Riesz potential, difference operator. Along with this, we consider transforms of m-accretive operators as a generalization, introduce a special operator class and provide a description of its spectral properties.

**Bio: **Maksim Kukushkin is a specialist in boundary problems, fractional derivatives and operator theory being author of a wide range of publications in all these areas. He has got his PhD degree in 2016 and, after the worked at Moscow State University of Civil Engineering, Kabardino-Balkarian Scientific Center and Saint Petersburg State Transport University.

**Lecture 2 —— Cohn-Vossen inequality on certain noncompact Kahler manifolds**

**Speaker: **Prof. Gang Liu, East China Normal University

**Time: **21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: **We generalize the Cohn-Vossen inequality to certain noncompact Kahler manifolds. This is related to a conjecture of Yau.

**Bio:**Gang Liu graduated from the University of Minnesota. He was a postdoctoral fellow at the University of California, Berkeley, and an assistant professor at Northwestern University. Now he is a professor at the East China Normal University.

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**Lecture Series XVI — May 13, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/8A04293383593E6A308D71987895879D

Valid Until：2026-04-30 23:59

**Lecture 1——Newton’s aerodynamic problem: an overview of recent results and open questions**

**Speaker:** Alexander Plakhov University of Aveiro (Portugal) and Institute for Information Transmission Problems RAS (Moscow)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** Newton (1687) posed the problem of finding a convex axisymmetric bodies of the smallest aerodynamic drag. So, we are looking for the optimal curve which is the generatrix of the body. In 1993, a similar problem was formulated in a wider class of convex (not necessarily symmetric) bodies. This task proved to be much more difficult: it is about finding the optimal surface. The talk will provide an overview of recent results and methods used, and besides, we formulate some open questions. А special attention will be paid to the following statement. If all points of an open (in the relative topology) subset of the boundary of some optimal body are regular (that is, C ^ 1-smoothness holds), then this set does not contain any extreme points of the body. This statement is a strengthening of a similar result (Brock, Ferone, Kawohl, 1996), formulated for C ^ 2-smooth subsets.

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**Lecture Series XV——April 22, 2021（15:00-17:00 Beijing time or 10:00-12:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/29E2301EB5B100B243E8F3503523C0D5

Valid Until：2026-04-30 23:59

**Lecture 1—— POINT PROCESSES AND INTERPOLATION**

**Speaker: **Alexander BUFETOV (CNRS Steklov IITP RAS)

**Time:** 2021-04-22 15:00-16:00 Beijing time or 10:00-11:00 St Petersburg time

**Abstract: **The Kotelnikov theorem recovers a Paley-Wiener function from its restriction onto an arithmetic progression. A Paley-Wiener function can also be recovered from its restriction onto a realization of the sine-process with one particle removed. If no particles are removed, then the possibility of such interpolation for the sine-process is due to Ghosh, for general determinantal point processes governed by orthogonal projections, to Qiu, Shamov and the speaker. If two particles are removed, then there exists a nonzero Paley-Wiener function vanishing at all the remaining particles.

How explicitly to interpolate a function belonging to Hilbert space that admits a reproducing kernel, given the restriction of our function onto a realization of the determinantal pont process governed by the kernel? In the case of the zero set of the Gaussian analytic function, or, in other words, the determinantal point process governed by the Bergman kernel, in joint work with Qiu, the Patterson-Sullivan construction is used for uniform interpolation in dense subspaces of the Bergman space. The invariance of our point process under Lobachevskian isometries plays a key rôle.

For the sine-process, the Ginibre process, the determinantal point process with the Bessel kernel and the determinantal point process with the Airy kernel, A.A. Borichev, A.V. Klimenko and the speaker proved that if the function decays as a sufficiently high negative power of the distance to the origin, then the answer is given by the Lagrange interpolation formula.

**Bio: **Alexander Bufetov is an expert in Ergodic Theory, Probability, Dynamical Systems and Statistics.

He graduated from Moscow State University being student of Acad. Ya. Sinai, one of the worldwide greatest experts in Ergodic Theory. Later on, he has got his PhD from Princeton University. In 2011 he became Doctor of Sciences. In 2015 he won the prestigious Sofia Kovalevskaya price and, thereafter, has got a honorary degree of ‘Professor of Russian Academy of Science’. He is an author of an impressive number of outstanding results https://scholar.google.com/citations?user=nAkXSowAAAAJ&hl=ru.

Prof. Bufetov had a wide range of prestigious positions: at Mathematical Institute of Russian Academy of Sciences, Higher School of Economics, Rice Univeristy, Chebyshev Laboratory at Saint Petersburg State University etc. Now he is working at University Aix-Marseille at CNRS Director position.

**Lecture 2—— Differential Network Analysis via Lasso Penalized D-Trace Loss**

**Speaker:** Ruibin Xi (Peking University)

**Time:** 2021-04-22 16:00-17:00 Beijing time or 11:00-12:00 St Petersburg time

**Abstract: **

Biological networks often change under different environmental and genetic conditions. In this paper, we model the network change as the difference of two precision matrices and propose a novel loss function called the D-trace loss, which allows us to directly estimate the precision matrix difference without attempting to estimate precision matrices. Under a new irrepresentability condition, we show that the D-trace loss function with the lasso penalty can give consistent estimators in high-dimensional settings if the difference network is sparse. A very efficient algorithm is developed based on the alternating direction method of multipliers to minimize the penalized loss function. Simulation studies and a real data analysis show that the proposed method outperforms other methods.

**Bio: **

Dr. Ruibin Xi is an associate professor at School of Mathematical Sciences, Peking University. He obtained his PhD from Washington University in St. Louis and received post doc training at Harvard Medical School. His main research interests include statistical analysis of big biological data, cancer genomics, network and graphical models, Bayesian analysis and high-dimensional statistics.

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**Lecture Series XIV——April 8, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/1D59046D6638F95A152BF678ECE03FC3

Valid Until：2026-04-30 23:59

**Lecture 1——Transcendence Theory over Function Fields on Quotients of Bounded Symmetric Domains**

**Speaker: **Ngaiming Mok (The University of Hong Kong)

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **Finite-volume quotients of bounded symmetric domains Ω, which are naturally quasi-projective varieties, are objects of immense interest to Several Complex Variables, Algebraic Geometry, Arithmetic Geometry and Number Theory, and an important topic revolves around functional transcendence in relation to universal covering maps of such varieties. While a lot has already been achieved in the case of Shimura varieties by means of methods of Model Theory, Hodge Theory and Complex Differential Geometry, techniques for the general case of not necessarily arithmetic quotients Ω/Γ =: XΓ have just begun to be developed. For instance, Ax-type problems for subvarieties of products of arbitrary compact Riemann surfaces of genus ≥ 2 have hitherto been intractable by existing methods. We will explain how uniformization theorems for bi-algebraic varieties can be proven by analytic methods involving the Poincar´e-Lelong equation in the cocompact case (joint work with S.-T. Chan), generalizing in the absence of the emisimplicity theorem of Andr´e-Deligne for monodromy groups (proven for arithmetic lattices). Klingler-Ullmo-Yafaev (2016) resolved the hyperbolic Ax-Lindemann Conjecture for Shimura varieties in the affirmative ascertaining that the Zariski closure of the image π(S) of an algebraic subset S ⊂ Ω under the universal covering map π : Ω → XΓ is totally geodesic. I will explain how the arithmeticity condition can be dropped in the cocompact case by a completely different proof using foliation theory, Chow schemes, partial Cayley transforms and K¨ahler geometry.

**Bio: **莫毅明教授为香港大学明德教授与讲座教授，自1999年始兼任数学研究所所长。莫毅明1980年在斯坦福大学获得数学系哲学博士学位，旋即在普林斯顿大学开展其职业生涯，历任美国哥伦比亚大学正教授与法国巴黎大学（奥赛）正教授，1994年回香港任职香港大学数学系讲座教授。1984年莫毅明获美国斯隆研究基金，1985年获美国总统年青研究人员奖，1998年获香港裘槎优秀科研者奖，2007年获国家自然科学奖二等奖， 2009年获美国数学会伯格曼奖(Bergman Prize).莫毅明为美国数学会会士。莫毅明自1992年起担任“数学年鉴(Mathematische Annalen)”编辑委员，并于2002至2014年期间担任 “数学发明(Inventiones Mathematicae)”编辑委员。莫毅明1994年获邀在苏黎世于国际数学大会(ICM)做学术演讲，并获委任为ICM 2010(海得拉巴)的菲尔兹奖选委。2015莫毅明获选中国科学院院士与香港科学院院士。

**Lecture 2 ——A New Life of the Old Sieve**

**Speaker: **Yuri Matiyasevich

**Time: **21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: **Prime numbers are one of the most important objects of study in Number Theory. Greek mathematician Eratosthenes (276--194 B.C.) invented a method (known nowadays under his name) for revealing primes among all natural numbers. A more modern and powerful for tool for studying prime numbers is Riemann's zeta function. In recent years the speaker performed intensive computer calculations in the search for new properties of this function. Unexpectedly, the Sieve of Eratosthenes naturally appeared in one calculation with the non-trivial zeros of the zeta function. This form of the sieve demonstrates a rich fractal structure lacking in the original sieve. Later another calculation revealed a different kind of a sieve which is dual to the classical Sieve of Eratosthenes. So far no theoretical explanation was found for the observed phenomena. Calculation were not an easy computational task. They required calculations of several thousands of initial non-trivial zeros of the zeta function with several thousands decimal digits, and solving systems consisting of several thousands linear equations.

**Bio: **马蒂亚舍维奇教授是当代俄罗斯最著名的数学家之一，圣彼得堡数学学会主席。1966年，19岁的他在逻辑学方面取得了一些突破性的成果，应邀在当年莫斯科举行的国际数学家大会上作邀请报告。1970年，尤里-马蒂亚舍维奇解决了希尔伯特第十问题。到目前为止，他在其他经典领域，如四种颜色问题和黎曼问题上取得了广泛的突破性成果。 他获得了许多著名的奖项，包括洪堡奖、苏联科学院的Markov奖等。他曾获得奥弗涅大学克莱蒙费朗分校和皮埃尔和玛丽居里大学的荣誉学位。Matiyasevich教授是AMS、巴伐利亚科学院和许多其他科学团体的成员。Yuri Vladimirivich Matiyasevich自1970年起在圣彼得堡的斯捷科洛夫研究所工作，1995年成为圣彼得堡国立大学教授。 2002年起，他担任圣彼得堡市数学奥林匹克竞赛负责人。2008年，Matiyasevich教授当选为俄罗斯科学院正式院士。Matiyasevich院士培养了一大批优秀的学生，其中有多位教授和院士。

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**Lecture Series XIII——March 25, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

**To Join Zoom Meeting:**

Video: https://disk.pku.edu.cn:443/link/4459C670911CEF7FBFC326AC056FDDC5

Valid Until：2026-04-30 23:59

**Lecture 1—— Polynomial complexity and Sarnak conjecture**

**Speaker: **Prof. Wen Huang, University of Science and Technology of China(USTC)

**Bio:** Huang Wen received his Ph.D. from the Department of Mathematics, USTC in 2003. His research field is topological dynamical system and ergodic theory, related to the entropy and chaos theory, multipleergodic Theorem, Sarnak’s conjecture and so on. He and his collaborators proved the following results: 1) positive entropy implies weak horseshoes. 2) pointwise multiple ergodic theorem holds for distal measure-preserving systems. 3) Sarnak’s conjecture holds for dynamical systems with sub-polynomial measure complexity. He achieved many rewards: 2012 China National Science Funds for Distinguished Young Scientists; 2018 National Ten Thousand Talent Program Leading Scientists, P.R.China; 2018 Second Class National Natural Science Award, P.R.China（rank 2）.

**Lecture 2 ——Dynamical models of some sociological problems.**

**Speaker: **Sergei Yu. Pilyugin, Faculty of Mathematics and Computer Science,St. Petersburg State University.

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

We study both cases of finite and infinite groups of agents. We are mostly interested in the structure and stability of fixed points of the system and in conditions under which any positive trajectory tends to a fixed point.

**Bio: **Sergei Yu. Pilyugin is Former vice President of Saint Petersburg Mathematical Society, he is a professor at Faculty of Mathematics and Computer Science, St. Petersburg State University, Russia. His research interests are in dynamical systems (especially theory of attractors and shadowing theory) and in applications (including sociological models).

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**Lecture Series Ⅻ —— March 11, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

**To Join Zoom Meeting: **

Video: https://disk.pku.edu.cn:443/link/11FB200B91B098AB7C5E6A2D07EE6445

Valid Until：2026-04-30 23:59

**Lecture 1—— The J-equation and the deformed Hermitian-Yang-Mills equation.**

**Speaker: **Prof. Gao Chen, University of Science and Technology of China.

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **The deformed Hermitian-Yang-Mills (dHYM) equation is the mirror equation for the special Lagrangian equation. The "small radius limit" of the dHYM equation is the J-equation, which is closely related to the constant scalar curvature K\"ahler (cscK) metrics. In this talk, I will explain my recent result that the solvability of the J-equation is equivalent to a notion of stability. I will also explain my similar result on the supercritical dHYM equation.

**Bio: **Chen Gao got Bachelor's degree in Univeristy of Science and Techonology of China in 2012 and Ph.D. in Stony Brook University in 2017. Since then he has worked in IAS and University of Wisconsin-Madison. From January of 2021 he became a tenure-track professor in USTC.

**Lecture 2 ——Various types of spectra and spectral measures on Cayley graphs of finitely generated groups and their actions.**

**Speaker: **Tatiana Nagnibeda (University of Geneva)

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** We will be interested in the Laplacian on graphs associated with infinite finitely generated groups: Cayley graphs and more generally, Schreier graphs corresponding to some natural group actions. The spectrum of such an operator is a compact subset of the closed interval [0,2], but not much more can be said about it in general. Little is known about the associated spectral measures either. We will discuss various spectral problems arising in this context and stemming from the famous question “Can one hear the shape of a drum?”

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**Lecture Series Ⅺ—— January 28, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/5E58EEF73495E01118D5216AE2E12DA6

Valid Until：2026-04-30 23:59

**Lecture 1—— On local combinatorial formulas for Euler class of spherical fiber bundle. **

**Speaker: **Dr. Nikolai Mnev, Senior Research Fellow of Chebyshev Laboratory at Saint-Petersburg State University and Saint Petersburg Department of Steklov Mathematical Institute

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** We will discuss the classical problem on local combinatorial formulas of characteristic classes on example of Euler class. Suppose we have a PL spherical fiber bundle with a fiber S^n triangulated over the base simplicial complex. The bundle determines n+1 dimensional Euler characteristic class in the base. Local combinatorial formula for the Euler class is a universal combinatorial function of elementary triangulated S^n-bundles over n+1 simplices universally representing Euler cocycle of the bundle in simplicial cohomology of the base. Such functions exist for rational coefficients in cohomology. They can be constructed as "twisting cochains" -- explicit local chain-level formulas for Gysin homomorphism in the Gysin sequence of the bundle. To get an access to local chain combinatorics of spectral sequence of the bundle we may use Guy Hirsh homology model of the bundle as a local system and then applying homology perturbation theory obtain local formulas as certain measure of twisting in combinatorial Hodge structure of the elementary bundle. The answer can be interpreted and evaluated statistically as certain combinatorial counting using Catanzaro-Chernyak-Klein higher Kirchhoff theorems. The formulas are resulting in a combinatorial form of Gauss-Bonne theorem. For example we easily obtain otherwise difficult to access statement: One can triangulate only trivial and Hopf circle bundles over a 2-dimensional sphere if the base sphere is triangulated as the boundary of 3-simplex.

**Bio: **Dr. Nikiolay Mnev graduated from the faculty of Mathematics and Mechanics of Saint Petersburg State University in 1980. In 1986 he defended his PhD thesis under supervision of Prof. Anatoly Vershik. Since that time he works at Steklov Institute and, besides, he has got a position at Chebyshev Laboratory starting from its foundation in 2011. Additionally, Dr. Mnev curates the so-called Fizmatklub, the organization intended to boost the level of teaching maths in Saint Petersburg Universities by organizing additional lecture courses, delivered by leading specialists.

Dr. Nikolai Mnev’s research interests cover Algebraic Topology, Geometric Topology and Combinatorial Geometry. In 1991, he received Delbert Ray Fulkerson prize for outstanding papers in the area of discrete mathematics.

**Lecture 2 —— Recent developments in exact Lagrangian fillings.**

**Speaker:** Honghao Gao, Michigan State University

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** Legendrian knots and their exact Lagrangian fillings are important geometric objects to study in low dimensional contact and symplectic topology. It was not known whether there exists a Legendrian knot that admits infinitely many exact Lagrangian fillings. In 2020, this statement was proven affirmatively, and infinitely many Lagrangian fillings have been constructed for all torus links of infinite type (with Casals), a family of positive braid links (Casals-Zaslow), all positive braid links of infinite type (with Shen-Weng), two examples that are not positive braid links (Casals-Ng). In this talk, I will review these results, and explain the construction for the torus (3,6) link appeared in the work with R. Casals.

**Bio: **Honghao Gao received his PhD degree from Northwestern University in 2017, under the supervision of Eric Zaslow. He was previously a postdoc at Institut Fourier, and is currently a postdoc at Michigan State University. His research interest is in contact and symplectic topology.

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**Lecture Series Ⅹ—— January 14, 2021（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/0CA255AFF20FD43771B84685ECA5EEC9

Valid Until：2026-04-30 23:59

**Speaker:**Dr. Petr. Shpilev

**Time: **20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:** The lecture is based on a joint talk with Prof. Vyacheslav Melas. Within the framework of the report, a brief overview of the history of the development of the theory of optimal experiment designs will be given, the basic concepts, definitions, and some key results of this theory are considered.The problem of changing the dimension of the initial optimization task and some approaches to the solution of this problem will be considered on the examples of tasks of constructing specific optimal designs studied by the author of the report.

**Bio: **Dr. Shpilev graduate from the Faculty of Mathematics and Mechanics in 2004 and got his PhD degree in 2007. His research interests include: Optimal Experimental Design Theory, Regression Analysis, Statistics, Mathematical Simulation, Data Analysis, Computer Science, and Approximation Theory.

**Lecture 2 —— Exploring Stochastic Methods For Deep Learning and Reinforcement Learning**

**Speaker: **Zaiwen Wen, Beijing International Center for Mathematical Research.

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** Stochastic methods are widely used in machine learning. In this talk, we present a structured stochastic quasi-Newton method and a sketchy empirical natural gradient method for deep learning. We also introduce a stochastic quadratic penalty algorithm for reinforcement learning.

**Bio:** Wen's research interests include large-scale computational optimization and their applications in data sciences. Together with his coauthors, he has developed both deterministic and stochastic semi-smooth Newton algorithms for composite convex program and Newton type algorithms for Riemannian optimization, as well as academic software packages such as SSNSDP, ARNT, Arrabit, LMSVD and LMAFIT, etc. He was awarded the Science and Technology Award for Chinese Youth in 2016, and the Beijing Science and Technology Prize-Outstanding Youth Scholar Zhongguan Village Prize in 2020. He is an associate editor of Journal of the Operations Research Society of China, Journal of Computational Mathematics and a technical editor of Mathematical Programming Computation.

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Video: https://disk.pku.edu.cn:443/link/A59A44F4FDF41825DCBF8AE9578C8D2B

Valid Until: 2025-01-01

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**Lecture Series Ⅷ ——December 3rd, 2020（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/51D4B1FC28EA321B4C4BC25FEF15C28F

Valid Until: 2025-01-01

**Lecture 1——Graph-walking automata.**

**Speaker:Prof. Alexander Okhotin.**

**Time: 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time) .**

**Abstract:** Graph-walking automata are a model studied in theoretical computer science: they traverse an undirected graph by following its edges, and use a memory of constant size to plan their movements. Graph-walking automata can be regarded both as a model of a robot navigating an unknown environment, and as a generic model of computation, with the graph modelling its memory. This paper presents the known results on these automata, ranging from their limitations in traversing graphs, studied already in the 1970s, to the later work on the logical reversibility of their computations, including the most recent lower bounds on their size.

**Bio:**Alexander Okhotin (Ph.D. 2004, Queen's University) is a professor of theoretical computer science at St. Petersburg State University. His main research subjects are formal grammars, finite automata and their complexity.

**Lecture 2 ——Modeling and Verification of Concurrent and Distributed Systems: From Reo to Mediator.**

**Speaker: Prof. Meng Sun.**

**Time: **21:00-22:00 Beijing time (16:00-17:00 St Petersburg time) .

**Abstract:** In this talk I will introduce the channel-based coordination language Reo and the component-based modeling language Mediator, and show how to formalize and verify component-based concurrent and distributed system models in them. Reo provides a channel-based model which focuses on complex interactions among system components. Mediator supports a two-step hierarchical modeling approach: Automata, which provide an interface of ports, are the basic behavior units; Systems declare components or connectors through automata, and glue them together. With the help of Reo and Mediator, both components and systems can be modeled separately and precisely.

**Bio:**Meng Sun received his BSc and PhD degrees in applied mathematics from Peking University, in 1999 and 2005, respectively. He then spent one year as a postdoctoral researcher in National University of Singapore. From 2006 to 2010, he worked as a scientific staff member at CWI, the Netherlands. He has been a faculty member at Peking University since 2010 and became a full professor in 2017. Currently, his research interests mainly lie in software theory and formal methods. His recent work includes coordination models and languages, coalgebra theory, model checking, theorem proving, software testing, cyber-physical systems, service-oriented and cloud computing, modeling and verification of blockchain and smart contracts, big data analysis, theoretical foundations of machine learning, deep learning and their application in formal verification.

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**Lecture Series Ⅶ ——November 19th, 2020（20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/B06B1459AA07B80DD51E17F8406655C2

Valid Until: 2025-01-01

**Lecture 1——Deep CT Imaging by Unrolled Dynamics**

**Speaker:** Bin Dong, Beijing International Center for Mathematical Research, Peking University

**Time:** 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **In this talk, I will start with a brief review of the dynamics and optimal control perspective on deep learning (including supervised learning, reinforcement learning, and meta-learning), especially the so-called unrolled dynamics approach and its applications in medical imaging. Then, I will present some of our recent studies on how this new approach may help us to advance CT imaging. Specifically, I will focus on our thoughts on how to combine the wisdom from mathematical modeling with ideas from deep learning. Such combination leads to new data-driven image reconstruction models and new data-driven scanning strategies for CT imaging, and with a potential to be generalized to other imaging modalities.

**Bio:**Bin Dong received his B.S. from Peking University in 2003, M.Sc from the National University of Singapore in 2005, and Ph.D from the University of California Los Angeles (UCLA) in 2009. Then he spent 2 years in the University of California San Diego (UCSD) as a visiting assistant professor. He was a tenure-track assistant professor at the University of Arizona since 2011 and joined Peking University as an associate professor in 2014. His research interest is in mathematical modeling and computations in imaging and data science. A special feature of his research is blending different branches in mathematics which include: bridging wavelet frame theory, variational techniques, and nonlinear PDEs; bridging differential equations and optimal control with deep learning.

**Lecture 2 —— Gaussian random fields in machine learning**

**Speaker:** Viacheslav Borovitskiy, Department of Mathematics and Mechanics，Saint Petersburg State University.

**Time:** 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: **I will introduce the Gaussian process regression algorithm, a widely used approach to probabilistic modeling in machine learning, and talk about its applications and challenges associated with its use. In the end, I will mention our own recent research in this topic that was presented on International Conference on Machine Learning and will be presented on this year's conference on Neural Information Processing Systems.

**Bio:** He has graduated from Saint-Petersburg State University, Faculty of Mathematics and Mechanics. His main interests cover PDEs, Banach spaces, Satistics and Informatics.

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**Lecture Series VI - November 5th, 2020 （20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video: https://disk.pku.edu.cn:443/link/E68335CAFDAD6A71A943A348EF8FC42A

Valid Until: 2025-01-01

**Speaker:** Prof. Yanjun Liu, Jiangxi Normal University

**Abstract: **The question of which prime powers can occur as divisors of irreducible character degrees of finite groups has a long history. One related conjecture is given by Geoffrey Robinson in 1996, who conjectured that the p-part of character degrees in a p-block of a finite group can be bounded in terms of the center of a defect group of the block. I will mention recent progress on Robinson's conjecture for odd primes,and then turn to the question of when a p-block of a finite group G is also a q-block of G. A series related work have been done by Navarro-Willems,Bessenrodt-Mall-Olsson, Navarro-Turull-Wolf and etc. The block separation property is studied by Bessenrodt-Zhang and they proved that the nilpotency, p-nilpotency of a finite group can be characterized by intersections of principal blocks of some (quotient) groups. Thus it is natural to ask if the solvability or p-solvability of a finite group can also be characterized in this way. By introducing the so-called block graph of a finite group this problem was solved affirmatively. Finally, I will talk about a conjecture relating the trivial intersection of principal blocks to the existence of nilpotent Hall subgroups.

**Bio:** Dr. Yanjun Liu got Ph. D. from Peking University and is now working in Jiangxi Normal University. Recently He got Humboldt Research Fellowship based on his excellent work in some canonical conjecture of representation theory.

**Speaker:** Prof. Mikhail Gavrilovich, Saint Petersburg Department of Higher School of Economics

**Abstract:** We consider simplicial sets equipped with a notion of smallness, and observe that this slight “topological” extension of the “algebraic” simplicial language allows a concise reformulation of a number of classical notions in topology, e.g. continuity, limit of a map or a sequence along a filter, various notions of equicontinuity and uniformconvergence of a sequence of functions; completeness and compactness; in algebraic topology, locally trivial bundles as a direct product after base-change and geometric realisation as a space of discontinuous paths. These reformulations are elementary and can perhaps be used in teaching to give motivated examples of elementary concepts in category theory. Surprisingly, this category is not well-studied and thus these observations raise many easy but open problems, which we like to think are in line with goals of tame topology put by Grothendieck. In the talk, we will work through of a couple of example, briefly mention some others, and indicate a number of open problems, who we like to think are in line with the goals of tame topology put by Grothendieck.

We will preceed the main part of the talk by explaning a category-theoretic characterisaiton of finite solvable and nilpotent groups in terms of the Quillen lifting property, which is also used in reformulations of the notions of limit, compactness, and completeness, and others.

This talk is based on preliminary notes

http://mishap.sdf.org/by:gavrilovich/treplo-groups.pdf.

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**Lecture Series V - October 22th, 2020 （20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time).**

Video：https://disk.pku.edu.cn:443/link/FD9BF2C2F871B7FE56EFD891777A6E7E

Valid Until：2025-01-01 00：00

**Lecture 1—— Global existence and decay of solutions to Prandtl system with small analytic data**

**Speaker:** Prof. Ping Zhang, Mathematics Institute of Academy of Mathematics and Systems Science of Chinese Academy of Sciences, Beijing

**Time：**2020-10-22 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

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__Lecture Series IV ____- July 14th, 2020 （20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time）__

Video： Part I：https://disk.pku.edu.cn:443/link/ADEA1AC5CB6C898F8809E6FFBC93B54C

Part II：https://disk.pku.edu.cn:443/link/8395E85B327FAC1E80993F79F2CACCF2

Valid Until：2025-01-01 00：00

**Lecture 1 - WORD MAPS ON SIMPLE ALGEBRAIC GROUPS AND RELATED TOPICS**

**Speaker:** Prof. Nikolai Gordeev, Saint Petersburg State Pedagogical University

**Time：**2020-07-14 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract:(/upload/editor/file/20200711/11112603683.pdf)**

**Lecture 2 - Structure of Commutator Subgroups**

**Speaker:** Prof. Zuhong Zhang， Beijing Institute of Technology

**Time：**2020-07-14 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract: **

This talk is based on the joint works with R. Hazrat, A. Stepanov and N. Vavilov in the past decade. In his seminal paper, more than half a century ago, Hyman Bass initialed the study of commutator subgroups and commutator formulas over rings. Since then, it attracted great attend of many leading experts including A. Bak, A.A. Suslin, L.N. Vaserstein, etc.. Various commutator formulas have been obtained in stable and non-stable settings and for a range of classical and algebraic like-groups.

In this talk, we will describe some recent results on the study (higher/birelative) commutators in general linear groups $GL(n,A)$ as well as their elementary generators. we will also discuss some further related research and applications.

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__Lecture Series III ____- June 30th, 2020 （20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time）__

Valid Until: 2025-08-31 23:59

1. Admissible metrics on the measure space: new trend in the theory of mm spaces.

2. Classification of mm-spaces. Matrix distributions.

3.Thе actions of measure preserving groups in the space of admissible metrics in measure space. ($\ca M \subset L^1(X\otimes X, \mu \otimes \mu).

4.Average metrics, ergodic limit and asymptotic invariants,

5.Sclaing entropy. Scaling entropy function. Examples.

6.Theorem. Bounded scaling entropy and discrete spectra. Sequential entropy by Kushnirenko. All possible scalings.

7.New geometrical problems.

- infinite-dimensional groups and their Asymptotic Representation Theory;

- Lie groups;

- New methods of Representation Theory for finite symmetric groups;

- Combinatorial Probability Theory and limit forms for configurations (the Vershik-Kerov theorem on limit forms of Young diagrams, Bratelli-Vershik diagrams, etc) ;

- Universal objects in Combinatorics Geometry and Dynamical Systems;

- Dynamical Systems and Ergodic Theory;

- Non-holonomic Geometry and Mechanics;

- Random processes, random walks and random matrices;

- Optimization.

**Download **Slides:

Valid Until: 2025-07-31 23:59

It is an ideal situation if we can reduce a problem P stated for general ergodic or minimal systems to the same problem in their "simple factors". We will explain how one did so for the problem on the convergence of multiple ergodic averages in ergodic theory. Moreover, we will present a recent work by Glasner-Huang -Shao-Weiss-Ye on the similar problem in the topological setup.

On the way to do so, we will address the parallels between topological dynamics and ergodic theory, and their applications to combinatoric number theory.

**Bio: **Prof. Ye got his Ph. D. in Mechanics and Mathematics Department of Moscow State University in 1991, and then did postdoc work in ICTP during 1991-1993. He was a faculty of Mathematics School in USTC since 1993. He was selected as a member of the Chinese Academy Sinica in 2019. His research interests include topological dynamics, ergodic theory and combinatoric number theory.

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__Lecture Series II ____- June 16th, 2020 （20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time）__

Video：Part I：https://disk.pku.edu.cn:443/link/F3034E87D1FC25E824BBDB14302AB24E

Part II：https://disk.pku.edu.cn:443/link/E55DFDEE3CA697F5C15F978B04ABC727

Valid Until：2025-01-01 00：00

**Lecture 1 - Multiple structures for quasilinear equations by the variational method**

**Speaker: **Alexander Nazarov, PDMI RAS and Math&Mech Faculty, St. Petersburg State University

**Time：**2020-06-16 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: **

We study entire bounded solutions to the equations of variational nature. The model example here is $\Delta u - u + u^3 = 0$ in $\mathbb R^2$. Our approach is purely variational and is based on concentration arguments and symmetry considerations. This method allows us to construct in an unified way several types of solutions with various symmetries (radial, breather type, rectangular, triangular, hexagonal, etc.),both positive and sign-changing. It is also applicable for more general equations in any dimension.

The talk is based on the joint paper Lerman L.M., Naryshkin P.E., Nazarov A.I., Abundance of entire solutions to nonlinear elliptic equations by the variational method, Nonlinear Analysis -- TMA. 190 (2020), DOI 10.1016/j.na.2019.111590, 1-21.

**Lecture 2 - Periodic and quasi-periodic solutions of 1-d Q-curvature equation. **

**Speaker:** Jiang Meiyue, School of Mathematical Sciences, Peking University

**Time：**2020-06-16 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract（/upload/editor/file/20200609/09145940157.pdf）: **

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__Lecture Series I - June 2nd, 2020 （20:00-22:00 Beijing time or 15:00-17:00 St Petersburg time）__

**Lecture 1 - Spectral synthesis for systems of exponentials and reproducing kernels **

** VIDEO：** https://disk.pku.edu.cn:443/link/62236134E8043AD5871A88D2BA3F2868

**Expiration Time：2025-07-31 23:59**

**Speaker：**Anton Baranov (Saint Petersburg State University)

**Time：**2020-06-02 20:00-21:00 Beijing time (15:00-16:00 St Petersburg time)

**Abstract: ****Let $x_n$ be a complete and minimal system of vectors in a Hilbert space $H$. We say that this system is hereditarily complete or admits spectral synthesis if any vector in $H$ can be approximated in the norm by linear combinations of partial sums of the Fourier series with respect to $x_n$. It was a long-standing problem whether any complete and minimal system of exponentials in $L^2(-a,a)$ admits spectral synthesis. Several years ago Yu. Belov, A. Borichev and myself gave a negative answer to this question which implies, in particular, that there exist non-harmonic Fourier series which do not admit a linear summation method. At the same time we showed that any exponential system admits the synthesis up to a one-dimensional defect. In the talk we will also discuss related problems for systems of reproducing kernels in Hilbert spaces of entire functions (such as Paley-Wiener or Fock).**

**Lecture 2 - On gauged linear sigma model and related problems **

** VIDEO：**https://disk.pku.edu.cn:443/link/5034D664212B1B1DD783D05CA07B343D

**Expiration Time：2025-07-31 23:59**

**Speaker: **Prof. Huijun Fan (Peking University)

**Time：**2020-06-02 21:00-22:00 Beijing time (16:00-17:00 St Petersburg time)

**Abstract:** **Gauged linear sigma model was proposed by Witten in the early of 90's to explain the mirror symmetry phenomenon and the CY/LG correspondence conjecture. In this lecture, I will firstly formulate the mathematical framework of the GLSM, and then describe an algebraic way to construct the quantum invariants of GLSM in narrow case (for general gauge group) via quasimaps.
This was a joint work with Jarvis and Ruan. Finally I will report the recent progress in this field and related problems. **