diff --git a/data/conferencias.yml b/data/conferencias.yml index 3c725da..d27851f 100644 --- a/data/conferencias.yml +++ b/data/conferencias.yml @@ -91,8 +91,8 @@ nombre: Luz Roncal afiliacion: UBCAM -Basque Center for applied mathematics web: https://sites.google.com/view/luzroncal - start: 2021-09-16T11:00-0300 - end: 2021-09-14T12:00-0300 + start: 2021-09-17T11:00-0300 + end: 2021-09-17T12:00-0300 - titulo: Characterizations of Nonnegative polynomials of some varieties abstract: | I will describe some recent results on the characterization of those polynomials that are nonnegative on a variety \(X\) in \(R^n\). In the first part of the talk I will explain why this is an interesting problem it turns out to have a wealth of applications ranging from nonconvex optimization to stochastic control. In the second part of the talk I will explain how this problem can be approached on algebraic curves and surfaces, presenting ongoing joint work with G. Blekherman (GA Tech), R. Sinn (U. Lepizig) and G.G. Smith (Queen's U). @@ -118,11 +118,11 @@ I will then consider the problem of determining the best set of potential confounding variables at the stage of the design of a planned observational study aimed at assessing the population average causal effect of a point exposure personalized, i.e. dynamic, or static treatment. Given a tentative non-parametric graphical causal model, possibly including unobservable variables, the goal is to select the "best" set of observable covariates in the sense that it suffices to control for confounding under the model and it yields a non-parametric estimator of ATE with smallest variance. For studies without unobservables aimed at assessing the effect of a static point exposure we show that graphical rules recently derived for identifying optimal covariate adjustment sets in linear causal graphical models and treatment effects estimated via ordinary least squares also apply in the non-parametric setting. We further extend these results to personalized treatments. Moreover, we show that, in graphs with unobservable variables, but with at least one adjustment set fully observable, there exist adjustment sets that are optimal minimal (minimum), yielding non-parametric estimators with the smallest variance among those that control for observable adjustment sets that are minimal (of minimum cardinality). In addition, although a globally optimal adjustment set among observable adjustment sets does not always exist, we provide a sufficient condition for its existence. We provide polynomial time algorithms to compute the observable globally optimal (when it exists), optimal minimal, and optimal minimum adjustment sets. This is joint work with Ezequiel Smucler and Facundo Sapienza. pdf: '' speaker: - nombre: Andrea Rotnizky + nombre: Andrea Rotnitzky afiliacion: Universidad di Tella, Buenos Aires web: https://www.hsph.harvard.edu/andrea-rotnitzky/ - start: 2021-09-15T11:00-0300 - end: 2021-09-15T12:00-0300 + start: 2021-09-17T11:00-0300 + end: 2021-09-17T12:00-0300 - titulo: Inviscid dissipation and turbulence abstract: 'Turbulence is a phenomenon of wide theoretical and practical interest and an area of research with intense current activity. Mathematical modeling of turbulence relies, in an essential manner, on a thorough understanding of solutions of the Navier-Stokes @@ -157,7 +157,7 @@ nombre: Gustavo Ponce afiliacion: University of California web: http://web.math.ucsb.edu/~ponce/ - start: 2021-09-14T011:00 + start: 2021-09-14T11:00-0300 end: 2021-09-14T12:00-0300 - titulo: Transfer operators and atomic decomposition abstract: Since the groundbreaking contributions of Ruelle, the study of transfer operators has been one of the main tools to understand the ergodic theory of expanding maps, that is, discrete dynamical systems that locally expand distances. Questions on the existence of interesting invariant measures, as well the statistical properties of such dynamics system, as exponential decay of correlations and Central Limit Theorem, can be answered studying the spectral properties of the action of these operators on suitable spaces of functions. Using the method of atomic decomposition, we consider new Banach spaces of functions (that in some cases coincides with Besov spaces) that have a remarkably simple definition and allows us to obtain very general results on the quasi-compactness of the transfer operator acting in these spaces, even when the underlying phase space and expanding map are very irregular. Joint work with Alexander Arbieto (UFRJ-Brazil). diff --git a/data/sesiones.yml b/data/sesiones.yml index 278d7c8..dcfddde 100644 --- a/data/sesiones.yml +++ b/data/sesiones.yml @@ -457,8 +457,8 @@ abstract: | Smooth periodic travelling waves in the Camassa–Holm (CH) equation are revisited in this talk. We show that these periodic waves can be characterized in two different ways by using two different Hamiltonian structures. The standard formulation, common to the Korteweg–de Vries (KdV) equation, has several disadvantages, e.g., the period function is not monotone and the quadratic energy form may have two rather than one negative eigenvalues. We explore the nonstandard formulation common to evolution equations of CH type and prove that the period function is monotone and the quadratic energy form has only one simple negative eigenvalue. We deduce a precise condition for the spectral and orbital stability of the smooth periodic travelling waves and show numerically that this condition is satisfied in the open region of three parameters where the smooth periodic waves exist. This is a joint work with Dmitry E. Pelinovsky (McMaster University), AnnaGeyer (Delft University of Technology) and Renan H. Martins (State University of Maringa). - start: 2021-09-17T16:45 - end: 2021-09-17T17:30 + start: 2021-09-16T15:00 + end: 2021-09-16T15:45 speaker: Fábio Natali (Universidade Estadual de Maringá, Brasil) - titulo: Spectral stability of monotone traveling fronts for reaction diffusion-degenerate Nagumo equations abstract: This talk addresses the spectral stability of monotone traveling front solutions for reaction diffusion equations where the reaction function is of Nagumo (or bistable) type and with diffusivities which are density dependent and degenerate at zero (one of the equilibrium points of the reaction). Spectral stability is understood as the property that the spectrum of the linearized operator around the wave, acting on an exponentially weighted space, is contained in the complex half plane with non-positive real part. The degenerate fronts studied in this paper travel with positive speed above a threshold value and connect the(diffusion-degenerate) zero state with the unstable equilibrium point of the reaction function. In this case, the degeneracy of the diffusion coefficient is responsible of the loss of hyperbolicity of the asymptotic coefficient matrices of the spectral problem at one of the end points, precluding the application of standard techniques to locate the essential spectrum. This difficulty is overcome with a suitable partition of the spectrum, a generalized convergence of operators technique, the analysis of singular (or Weyl) sequences and the use of energy estimates. The monotonicity of the fronts, as well as detailed descriptions of the decay structure of eigenfunctions on a case by case basis, are key ingredients to show that all traveling fronts under consideration are spectrally stable in a suitably chosen exponentially weighted L2 energy space. @@ -471,8 +471,8 @@ $$i u_t +\Delta u+|x|^{-b}|u|^{2\sigma} u = 0, \,\,\, x\in \mathbb{R}^N,$$ with \(N\geq 3\) and \(0 \lt b \lt \min\{\frac{N}{2},2\}\). We focus on the intercritical case, where the scaling invariant Sobolev index \(s_c=\frac{N}{2}-\frac{2-b}{2\sigma}\) satisfies \(0 \lt s_c \lt 1\). In this talk, for initial data in \(\dot H^{s_c}\cap \dot H^1\), we discuss the existence of blow-up solutions and also a lower bound for the blow-up rate in the radial and non-radial settings. This is a joint work with Mykael Cardoso (Universidade Federal do Piauí, Brasil). - start: 2021-09-16T15:00 - end: 2021-09-16T15:45 + start: 2021-09-17T16:45 + end: 2021-09-16T17:30 speaker: Luiz Gustavo Farah (Universidade Federal de Minas Gerais, Brasil). - titulo: A sufficient condition for asymptotic stability of kinks in general (1+1)-scalar field models abstract: | @@ -1729,13 +1729,7 @@ Zero-range processes are interacting particle models where particles jump between different sites according to rates that only depend on the number of particles at the current position. In this talk we will focus on the case when the rates decrease with the number of particles, inducing a condensation phenomenon where a macroscopic number of particles occupies the same position. I will present recent results that identify the coarsening dynamics of the process as fluid limit. These techniques can be applied to derive fluid limits for Jackson networks with rates that depend on the number of customers in the queue. Joint work with Johel Beltrán, Daniela Cuesta, Milton Jara and Matthieu Jonckheere. start: 2021-09-13T16:45 end: 2021-09-13T17:30 - speaker: Inés Armendáriz (Universidad de Buenos Aires, Argentina) - - titulo: A martingale approach to lumpability - abstract: | - The martingale problem introduced by Stroock and Varadhan is an efficient method to prove the convergence of a sequence of stochastic processes which are derived from Markov processes. In this talk we present two examples to illustrate this approach: the density of particles per site of a sequence of condensing zero range processes and the number of sites occupied by a system of coalescing random walks evolving on a transitive finite graph. Both examples exhibit a sort of asymptotic lumpability. - start: - end: - speaker: Johel Beltran (Pontificia Universidad Católica del Perú, Perú) + speaker: Inés Armendáriz (Universidad de Buenos Aires, Argentina) - titulo: Cutoff thermalization for Ornstein-Uhlenbeck systems with small Lévy noise in the Wasserstein distance abstract: | This talk presents recent results on the cutoff phenomenon for a general class of asymptotically exponentially stable Ornstein-Uhlenbeck systems under ε-small additive Lévy noise. The driving noise processes include Brownian motion, α-stable Lévy flights, finite intensity compound Poisson processes and red noises and may be highly degenerate. Window cutoff thermalization is shown under generic mild assumptions, that is, we see an asymptotically sharp ∞/0-collapse of the renormalized Wasserstein distance from the current state to the equilibrium measure με along a time window centered in a precise ε-dependent time scale tε . In many interesting situations such as reversible (Lévy) diffusions it is possible to prove the existence of an explicit, universal, deterministic cutoff thermalization profile. The existence of this limit is characterized by the absence of non-normal growth patterns in terms of an orthogonality condition on a computable family of generalized eigenvectors of the drift matrix Q. With this piece of theory at hand we provide a complete discussion of the cutoff phenomenon for the classical linear oscillator with friction subject to ε-small Brownian motion or α-stable Lévy flights. Furthermore, we cover the highly degenerate case of a linear chain of oscillators in a generalized heat bath at low temperature.