University of Los Andes

About: University of Los Andes is a education organization based out in Bogotá, Colombia. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 17616 authors who have published 25555 publications receiving 413463 citations.

A fractional order epidemic model for the simulation of outbreaks of influenza A(H1N1)

Abstract: In this paper, we propose a nonlinear fractional order model in order to explain and understand the outbreaks of influenza A(H1N1). In the fractional model, the next state depends not only upon its current state but also upon all of its historical states. Thus, the fractional model is more general than the classical epidemic models. In order to deal with the fractional derivatives of the model, we rely on the Caputo operator and on the Grunwald–Letnikov method to numerically approximate the fractional derivatives. We conclude that the nonlinear fractional order epidemic model is well suited to provide numerical results that agree very well with real data of influenza A(H1N1) at the level population. In addition, the proposed model can provide useful information for the understanding, prediction, and control of the transmission of different epidemics worldwide. Copyright © 2013 John Wiley & Sons, Ltd.

Evidence for associated production of a single top quark and W Boson in pp collisions at √s=7 TeV

Abstract: Evidence is presented for the associated production of a single top quark and W boson in pp collisions at √s=7 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4.9 fb^(-1). The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the tt background from the signal. The observed signal has a significance of 4.0σ and corresponds to a cross section of 16_(-4)^(+5) pb, in agreement with the standard model expectation of 15.6±0.4_(-1.2)^(+1.0) pb.

Outside Directors, Board Interlocks and Firm Performance: Empirical Evidence from Colombian Business Groups

Abstract: We investigate the relation of board structure through the appointments of outside directors and the role of busy directors on firm return on assets within an environment of no regulation for privately held firms and voluntary adoption of corporate best practices for security issuers with family controlling blockholders. This study relies on a sample of an average of 335 firms per year for the 1996-2006 period, where 244 are private firms and 285 are affiliated to one of the seven largest non-financial business groups in the country. Five of these groups were, in 2006, still family-controlled. We find a positive relation between both the ratio of outside directors, and the degree of board interlocks, with firm return-on-assets. Outside busy directors turned out to be key drivers of improved firm performance. Appointments of outsiders are endogenous to firm ownership structure. Blockholder activism and contestability becomes an internal mechanism that improves director monitoring and ex-post firm valuation.