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.
Improved Approximation Algorithms for 2-Dimensional Knapsack: Packing into Multiple L-Shapes, Spirals, and More.
In the 2-Dimensional Knapsack problem (2DK) we are given a square knapsack and a collection of n rectangular items with integer sizes and profits. Our goal is to find the most profitable subset of items that can be packed non-overlappingly into the knapsack. The currently best known polynomial-time approximation factor for 2DK is 17/9+eps<1.89 and there is a (3/2+eps)-approximation algorithm if we are allowed to rotate items by 90 degrees. In this talk, I will present a (4/3+eps)-approximation algorithms in polynomial time for both cases,...
Ciclos de largo dado en grafos orientados.
Resumen: En esta charla se mostrará que para todo l > 3, todo grafo orientado contiene un ciclo de tamaño exactamente l, bajo ciertas condiciones de tamaño y semigrado mínimo. Además se mostrarán conjeturas relacionadas y aplicaciones sobre panciclicidad.
About infinite energy solutions to the incompressible Navier-Stokes equations.
Abstract: We study estimates for the Navier–Stokes equations, in a sufficiently robust context to be applied to the construction of : 1) Discretely self-similar solutions, for initial data satisfying the weak condition to be locally square integrable. 2) Regular axially symmetrical solutions without swirl, for initial data which together with his gradient belong to a weighted Lebesgue space.
Scheduling in the Random-Oder Model.
Abstract: We study Online Makespan Minimization, one of the most basic scheduling problems, in the random-order model. Here jobs of a given input arrive in a uniformly chosen random order as opposed to the classical adversarial model, which considers worst-case orders. The random-order model originates from the Secretary Problem and has received quite some research interest over the last years. For scheduling, the random-order model provides beyond worst-case guarantees while still not being overly pessimistic. Furthermore, it leads to a...
Sumas iteradas para clasificación de series de tiempo.
Resumen La clasificación de series de tiempo es una tarea recurrente en ciencia de datos. Usualmente, los datos son transformados de alguna forma para producir una representación concisa, preservando simetrías de interés. En esta charla, presentaré una serie de trabajos que describen cómo las sumas iteradas de una serie de tiempo contienen todas las cantidades (features) polinomiales invariantes bajo realinamiento temporal (time warping). Describiré también como se transforma esta representación bajo la aplicación de cierta clase funciones no...
Virtual levels and virtual states of operators in Banach spaces.
Abstract: Virtual levels admit several equivalent characterizations: (1) there are corresponding eigenstates from L^2 or a space “slightly weaker” than L^2; (2) there is no limiting absorption principle in the vicinity of a virtual level (e.g. no weights such that the “sandwiched” resolvent remains uniformly bounded); (3) an arbitrarily small perturbation can produce an eigenvalue. We develop a general approach to virtual levels in Banach spaces and provide applications to Schroedinger operators with non selfadjoint...
Adaptive bin packing with overflow.
Abstract: Motivated by the allocation of virtual machines into servers in the cloud, we consider the online problem of packing items with random sizes into unit-capacity bins. Items arrive sequentially, but upon arrival an item’s actual size is unknown; only its probabilistic information is available to the decision maker. Without knowing this size, the decision maker must irrevocably pack the item into an available bin or place it in a new bin. Once packed in a bin, the decision maker observes the item’s actual size, and overflowing the bin...
Anisotropic harmonic maps and Ginzburg-Landau type relaxation.
Abstract: Consider maps $u:R^n\to R^k$ with values constrained in a fixed submanifold, and minimizing (locally) the energy $E(u)=\int W(\nablau)$. Here $W$ is a positive definite quadratic form on matrices. Compared to the isotropic case $W(\nabla u)=|\nabla u|^2$ (harmonic maps) this may look like a harmless generalization, but the regularity theory for general $W$’s is widely open. I will explain why, and describe results with Andres Contreras on a relaxed problem, where the manifold-valued constraint is replaced by an integral...
City logistics and smart delivery.
Abstract: he current and expected growing number of people living and working in cities and the limited space available inside city centres implies a greater exchange of inbound and outbound freight flows between city centres and their surrounding regions. Urban freight transports provide economic benefits to society but are also responsible for negative externalities such as congestion, air and water pollution, climate change, accidents and noise. Access restrictions are one of the most applied measures to control urban traffics in the...
