University of Warsaw

About: University of Warsaw is a education organization based out in Warsaw, Poland. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 20832 authors who have published 56617 publications receiving 1185084 citations. The organization is also known as: Uniwersytet Warszawski & Warsaw University.

Multilevel Schwarz Methods for Elliptic Problems with Discontinuous Coefficients in Three Dimensions

Abstract: Multilevel Schwarz methods are developed for a conforming finite element approximation of second order elliptic problems. We focus on problems in three dimensions with possibly large jumps in the coefficients across the interface separating the subregions. We establish a condition number estimate for the iterative operator, which is independent of the coefficients, and grows at most as the square of the number of levels. We also characterize a class of distributions of the coefficients, called quasi-monotone, for which the weighted\(L^{2}\) -projection is stable and for which we can use the standard piecewise linear functions as a coarse space. In this case, we obtain optimal methods, i.e. bounds which are independent of the number of levels and subregions. We also design and analyze multilevel methods with new coarse spaces given by simple explicit formulas. We consider nonuniform meshes and conclude by an analysis of multilevel iterative substructuring methods.

An indirect search for weakly interacting massive particles in the sun using 3109.6 days of upward-going muons in super-kamiokande

Abstract: We present the result of an indirect search for high energy neutrinos from Weakly Interacting Massive Particle (WIMP) annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande. Data sets from SKI-SKIII (3109.6 days) were used for the analysis. We looked for an excess of neutrino signal from the Sun as compared with the expected atmospheric neutrino background in three upmu categories: stopping, non-showering, and showering. No significant excess was observed. The 90% C.L. upper limits of upmu flux induced by WIMPs of 100 GeV c-2 were 6.4 × 10–15 cm–2 s–1 and 4.0 × 10–15 cm–2 s–1 for the soft and hard annihilation channels, respectively. These limits correspond to upper limits of 4.5 × 10–39 cm–2 and 2.7 × 10–40 cm–2 for spin-dependent WIMP-nucleon scattering cross sections in the soft and hard annihilation channels, respectively.

Universal rate constants for reactive collisions of ultracold molecules.

Abstract: A simple quantum-defect model gives analytic expressions for the complex scattering length and threshold collision rates of ultracold molecules. If the probability of reaction in the short-range part of the collision is high, the model gives universal rate constants for $s$- and $p$-wave collisions that are independent of short-range dynamics. This model explains the magnitudes of the recently measured rate constants for collisions of two ultracold $^{40}\mathrm{K}^{87}\mathrm{Rb}$ molecules, or an ultracold $^{40}\mathrm{K}$ atom with the $^{40}\mathrm{K}^{87}\mathrm{Rb}$ molecule [S. Ospelkaus et al., Science 327, 853 (2010)].

Schwarz analysis of iterative substructuring algorithms for elliptic problems in three dimensions

Abstract: Domain decomposition methods provide powerful preconditioners for the iterative solution of the large systems of algebraic equations that arise in finite element or finite difference approximations...