Trees are ubiquitous. Probabilists may think of branching processes and ask about extinction or survival. The recursive structure of trees leads to functional equations for generating functions, of interest in analytic combinatorics. Trees also help organize power series expansions in various areas of analysis and mathematical physics, from numerics (Butcher trees) to renormalization (Gallavotti-Niccolo trees). The talk presents yet another application, namely inverse function theorems for functionals in measure spaces for which Banach inversion is not possible. Combined with cluster expansions from equilibrium statistical mechanics, the theorem allows for a rigorous derivation, in a restricted parameter regime, of density functionals used in analytic models of materials. The talk is based on joint work with Tobias Kuna and Dimitrios Tsagkarogiannis (arXiv:1906.02322 [math-ph]) and considerably improves earlier results based on Lagrange-Good inversion (J., Tate, Tsagkarogiannis, Ueltschi, CMP 2014).
In this talk we introduce a discrete model for atmospheric turbulence, which was originally derived by Helmholtz from the Euler equations.
We state some of it basic properties and show how we can derive an effective PDE, the so-called mean field limit, from the discrete Hamiltonian system, by using a variational principle.
Furthermore, we discuss the extension of these methods to generalized surface quasigeostrophic models and show how tools from probability theory can help us to get more information about turbulence phenomena.
The content of this talk is based on work in collaboration with Marco Romito (Uni Pisa), the presentation tries to avoid technicalities and to be accessible to a mixed audience.
In this talk we will look at the spectrum (eigenvalues) of the adjacency matrix of a graph, and ask whether the eigenvalues determine the graph. This is a difficult, but important problem which plays a special role in the famous graph isomorphism problem. It has been conjectured by van Dam and Haemers that almost every graph is determined by its spectrum. The mentioned problem has been solved for several families of graphs; sometimes by proving that the spectrum determines the graph, and sometimes by constructing nonisomorphic graphs with the same spectrum. In recent years this problem has attracted much interest. In this talk we will report on recent results concerning this conjecture.
One way to define Type A Schubert varieties is as matrix varieties, that is as a subset of SLn satisfying some extra conditions. The geometry of this variety is tightly connected to the combinatorics of the symmetric group Sn on n letters. Moreover to each element w in S_n there exists one such variety X_w. In this talk I will explain a new approach to a characterization which Schubert varietes X_w and X_v for different w,v in S_n share the same tangent cone at the identity.
This is joint work with Stephane Gaussent (Saint Etienne).
No prior knowledge of Schubert varieties will be assumed.
Though perhaps not true in high dimensions our experience in small dimension shows that beautiful objects do have symmetries. Symmetries are my guide to construct extremal codes and lattices. The notion of extremality stems from a very fruitful connection between codes and invariant theory of finite groups and its analogous relation between lattices and modular forms.
Invariant theory allows to upper bound the error correcting properties of codes in certain families. Codes achieving this upper bound are called extremal. In 1973 Neil Sloane published a short note asking whether there is an extremal code of length 72. Since then many mathematicians search for such a code, developing new tools to narrow down the structure of its symmetry group. We now know that, if such a code exists, then it has at most 5 symmetries.
The methods for studying this question involve explicit and constructive applications of well known classical theorems in algebra and group theory, like Burnside's orbit counting theorem and quadratic reciprocity, as well as basic representation theoretic methods and tools from the theory of quadratic forms.
Similar methods have been recently developed to study extremal lattices admitting certain symmetries. In my talk I will survey the results obtained on extremal codes and lattices and give some nice examples of the use of symmetries to reduce the search space.
After giving an overview on well known results on extreme values for sequences of independent identically distributed random variables, we turn to a class of models that exhibit a logarithmic correlation structure.
As it turns out a (sometimes hidden) branching structure helps to understand the effect of correlations. In this talk we will focus on one such model which is called branching random walk. I will explain how first and (truncated) second moment computations can be used to determine the order of the maximum.
We investigate the well-posedness of stochastic cross-diffusion systems. Such problems arise in many application areas like fluid dynamics of mixtures, cell biology and biofilm mmodeling. Cross-diffusion occurs if the gradient in the concentration of one species induces a flux of another species. Famous examples are given by the Maxwell-Stefan systems or bacterial biofilm models. The stochastic terms quantify the lack of knowledge of certain parameters or fluctuations which occur due to external perturbations. We explore a formal gradient-flow or entropy structure of these equations and an interplay between the entropy density and the stochastic terms in order to investigate properties of the solution.
This talk is based on a joint work with G. Dhariwal, F.Huber, A.Jüngel (Vienna University of Technology) and Christian Kuehn (Technical University of Munich).
The purpose of this talk is to present the relation between certain BMO--type seminorms and the total variation of SBV functions Recently, Bourgain, Brezis and Mironescu introduced a new BMO--type space $B\subset L^1(Q)$ on the unit cube $Q\subset \mathbb R^n$, by mean of the seminorm \begin{equation}\label{star} \| f\|_B= \sup_{0< \varepsilon
Existence of T-$\vec{p}(\cdot)$-solutions for some anisotropic quasilinear elliptic problem
Sarah Biesenbach RWTH Aachen University, GermanyOptimal convergence rates for the Cahn-Hilliard equation on the line
We explain how to derive optimal algebraic-in-time rates for the decay to equilibrium under the assumption that the initial data has a finite (not small) distance to the limit state. The method exploits the gradient flow structure, Nash-type inequalities and a duality argument to establish sharp estimates. We present two examples. This is joint work with Felix Otto and Maria Westdickenberg.
Nonlinear Vibration analysis of hyperelastic plates
Nonlinear vibration of hyperelastic plates with physical and geometrical nonlinearities is elaborated. The hyperelastic and the initial deflection affects on the frequency and time responses are investigated. The Lagrange equations are used and nonlinear partial differential equations governing the motion are formulated. Various hyperelastic models are considered based on the multimodal analysis and the Garlekin procedure.The associated nonlinear differential system is obtained. The time response is computed for various geometrical and material parameters. The harmonic balance method is implemented and the nonlinear frequency-amplitude responses are analysed.
Oksana Chernova Taras Shevchenko National University of Kyiv, UkraineEstimation in Cox proportional hazards model with measurement errors
I work on survival and event history analysis. Survival data often arise in medicine, engineering and insurance, where the outcome of interest is time to an event. Statistical inference is usually complicated by the presence of incomplete observations. For some subjects the event is not observed and only known that survival time exceeds some observed censoring time. Since its introduction, the proportional hazards model proposed by Cox has become the workhorse of regression analysis for censored data. I consider the case when covariates are observed with additive measurement errors and propose new approach for parameters estimation.
Noémie Combe Max Planck Institute for Mathematics in the Sciences, GermanyGauss Skizze operad & Frobenius manifolds
Consider a certain class of Frobenius manifolds: the space of complex polynomials of a fixed degree. The existence of a decomposition, indexed by ``Gauss drawings'' (which are bi-colored graphs verifying properties) is shown. Using this tool, and monodromy properties, we construct a (topological) operad: the Gauss skizze operad.
Rosa Antonia Kowalewski University of Lübeck, GermanyIncorporating a Deformation Prior and Object Boundary Constraints for Multiple Shape Registration
Lise Maurin Sorbonne Université, FranceRobustness of the Adaptive Biasing Force method under a non-gradient perturbation
New Estimators Based on the Characteristics of Geometric Distribution and Aftershock Data Application
In this study, we have considered ratio and product exponential estimators of geometric distributed population in simple random sampling (SRS). The mean square error (MSE) equations of the proposed estimators are obtained and compared in application with the classical ratio estimator. In addition, theoretical findings are supported by an empirical study to show the superiority of the constructed estimators over others with aftershock data of Turkey.
Anne Pein Technical University of Munich, GermanyRandom Attractors for Stochastic Partly Dissipative Systems
Anna Schilling Universität Heidelberg, GermanyHorofunction compactification of vector spaces
Any $n$-dimensional closed convex ball $B \subset \mathbb{R}^n$ containing the origin as an interior point defines a norm and therefore also a metric on $\mathbb{R}^n$ that has $B$ as its unit ball. The horofunction compactification, first defined by Gromov for any metric space, crucially depends on the metric of the space. Based on various examples we illustrate this construction and dependence and show that the horofunction compactification of $\mathbb{R}^n$ equipped with the norm defined by (some polyhedral) $B$ is homeomorphic to the dual unit ball $B^\circ$.
Caren Schinko Universität Augsburg, GermanyCompact hyperkähler manifolds
An irreducible hyperkähler manifold is a compact Kähler manifold with a holomorphic symplectic form. One can see these manifolds as higher-dimensional analogues of K3 surfaces. The poster shows a brief overview of compact hyperkähler manifolds with focus on examples.
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The enumeration of faces of various types of simplicial complexes is a promnent topic in algebraic, topological and geometric combinatorics. In this talk, I will first provide a short survey on what is known for general simplicial complexes, simplicial polytopes and triangulations of manifolds. In the second part, the focus lies on balanced simplicial complexes, i.e., simplicial complexes whose underlying graph permits a minimal proper coloring in the graph-theoretic sense.
I will discuss holomorphic foliations on a complex manifold from the point of view of the exceptional minimal set conjecture. In particular I am interested in curvature conditions for the holomorphic normal bundle of the foliation. The main result is that if the holomorphic normal bundle is positive in the sense of Griffiths, then the foliation does not admit a compact invariant set that is a complete intersection of smooth real hypersurfaces. As a by-product, we obtain classification results for compact Levi-flat CR manifolds.
Sylvie Paycha, University of Potsdam, on leave from the University Clermont-Auvergne
According to the principle of locality in physics, events taking place at different locations should behave independently, a feature expected to be reflected in the measurements. The latter are compared with theoretic predictions which use renormalisation techniques in order to deal with divergences from which one wants to derive finite quantities.
The purpose of this talk is to confront locality and renormalisation.
We shall present a multivariate approach to renormalisation which encodes locality as an underlying algebraic principle. It can be applied to various situations involving renormalisation, such as divergent multizeta functions and their generalisations, namely discrete sums on cones and discrete sums associated with trees.
This talk is based on joint work with P. Clavier, L. Guo and B. Zhang
The framework of port-Hamiltonian systems (PH systems) combines both the Hamiltonian approach and the network approach, by associating with the interconnection structure of the network model a geometric structure given by a Dirac structure. A Lanczos method for non-symmetric systems of linear equations that exploits the structure of PH systems has been derived. The results from a series of parametrized numerical experiments are presented to show the numerical stability and behavior of the solution depending on the parameters.
The language of D-modules permits an investigation of linear differential equations by algebraic methods. In this talk, I want to give an insight into computational aspects of the theory.
The formation of patterns or microstructures in materials can often be understood as the result of a competition between different energy contributions, for example an elastic bulk energy and a (higher order) surface energy. Among many others, typical examples include microstrcuctures in shape-memory alloys, shape formation in elastically strained thin crystalline films, and the formation of rafts in biomembranes. In this talk, I shall discuss some recent analytical results on the associated variational problems, which typically involve vectorial, non-convex nonlinear functionals.