Noticias en español
Seminars appear in decreasing order in relation to date. To find an activity of your interest just go down on the list. Normally seminars are given in English. If not, they will be marked as Spanish Only.
Energy flux enhancement, intermittency and turbulence via Fourier triad phase dynamics in the 1-D Burgers equation.
Abstract: We present a theoretical and numerical study of Fourier space triad phase dynamics in 1-D stochastically forced Burgers equation at Reynolds number Re ≈ 27000. We show that Fourier triad phases over the inertial range display a collective behaviour characterised by intermittent periods of synchronisation and alignment, reminiscent of Kuramoto model (1984) and directly related to shock collisions in physical space. These periods of synchronisation favour efficient energy fluxes across the inertial range towards small scales,...
Progressive Decoupling of Linkages in Optimization with Elicitable Convexity
ABSTRACT: A method called the Progressive Decoupling Algorithm is described for solving variational inequalities and optimization problems in which a subspace captures “linkages” that can be relaxed. The approach is inspired by the Progressive Hedging Algorithm in convex stochastic programming and resembles the Partial Inverse Method of Spingarn, but retains more parametric flexibility than the latter. It is able even to work when mononicity or convexity is not directly present but can be “elicited”. The role...
Preferential Attachment Random graphs with edge-step functions
Abstract: Nowadays, modeling and understanding the evolution and properties of concrete networks are important questions for many areas in the scientific community. The huge amount of data generated these days combined with new computing power allowed us to see concretely how many entities, such as our own society, are organized and connected. These findings naturally motivated the investigation of many models that intended to reproduce the properties observed empirically. In this seminar, in its first moment, we will introduce which kind of...
Well-posedness for viscous compressible fluids with only bounded density
Abstract: In this talk, we consider the well-posedness issue for the barotropic Navier-Stokes equations. We consider initial velocity fields which have (slightly) sub-critical regularity, and initial densities which are (essentially) only bounded; in particular, we can consider densities having discontinuities across an interface. We are able to establish a local in time existence and uniqueness result in any space dimension, generalising previous results due to Hoff. The proof combines a maximal regularity approach with the study of...
Cross-diffusion and entropy in population dynamics
Abstract: In Population dynamics, reaction-cross diffusion systems model the evolution of the populations of competing species with a segregation effect between individuals. For these strongly coupled, often nonlinear systems, a question as basic as the existence of solutions appears to be extremely complex. We introduce an approach based on duality and entropy methods. We prove the existence of weak solutions in a general setting of reaction-cross diffusion systems, as well as some qualitative properties of the solutions. This is a joint...
Fair Auctions with Asymmetrically Informed Bidders
Abstract: (With Aranyak Mehta and Uri Nadav) Agents often arrive to auctions with different levels of informations about their own value for the object sold. In such asymmetric settings, it may be optimal to charge different reservation prices to discriminate between bidders. However, it is often infeasible to expressly treat different bidders in the same auction differently, particularly in on-line settings. We characterize optimal nondiscriminatory mechanisms in the presence of informational asymmetries and compares them to the revenue of...
Estimación de variación total y volatilidad en modelos unificados de GARCH-Ito con saltos.
Estimación de variación total y volatilidad en modelos unificados de GARCH-Ito con saltos. Resumen: Los modelos discretos de GARCH y continuos de Drift-Difusión son ampliamente utilizados en campos como finanzas y neurociencia. El modelo GARCH-Ito, introducido recientemente por Wang y Kim, superpone un modelo GARCH en tiempos discretos en el modelo de Ito para la volatilidad instantánea. En este trabajo, se propone una metodología conjunta para la estimación de la variación cuadratica para trayectorias con discontinuidades, utilizando...
Minicuro: Sarnak Conjecture: a link between ergodic theory and number theory
Abstract: In these series of talks we will look how several conjecture in number theory have a translation in ergodic theory and how applications go from one theory to the other. We focus mostly in the mechanisms allowing to pass from one theory to the other. No pre-requisists in number theory are needed. Date: 10:30 AM, Monday 14, Wednesday 16, Thursday 17, January 2019.
Applications of noisy quantum devices
Abstract: Near-term applications of early quantum devices rely on accurate estimates of expectation values to become relevant. Decoherence and gate errors lead to wrong estimates. This problem was, at least in theory, remedied with the advent of quantum error correction. However, the overhead that is needed to implement a fully fault-tolerant gate set with current codes and current devices seems prohibitively large. In turn, steady progress is made in improving the quality of the quantum hardware and we believe that we can build machines in...
A Linear Programming Based Approach to the Steiner Tree Problem with a Fixed Number of Terminals
Abstract: We present a set of integer programs (IPs) for the Steiner tree problem with the property that the best solution obtained by solving all, provides an optimal Steiner tree. Each IP is polynomial in the size of the underlying graph and our main result is that the linear programming (LP) relaxation of each IP is integral so that it can be solved as a linear program. However, the number of IPs grows exponentially with the number of terminals in the Steiner tree. As a consequence, we are able to solve the Steiner tree problem by solving...
