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.

Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy

Abstract: A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.

Calls, colours, shape, and genes: a multi-trait approach to the study of geographic variation in the Amazonian frog Allobates femoralis

Abstract: Evolutionary divergence in behavioural traits related to mating may represent the initial stage of speciation. Direct selective forces are usually invoked to explain divergence in mate-recognition traits, often neglecting a role for neutral processes or concomitant differentiation in ecological traits. We adopted a multi-trait approach to obtain a deeper understanding of the mechanisms behind allopatric divergence in the Amazonian frog, Allobates femoralis. We tested the null hypothesis that geographic distance between populations correlates with genetic and phenotypic divergence, and compared divergence between mate-recognition (acoustic) and ecological (coloration, body-shape) traits. We quantified geographic variation in 39 phenotypic traits and a mitochondrial DNA marker among 125 individuals representing eight populations. Geographic variation in acoustic traits was pronounced and tracked the spatial genetic variation, which appeared to be neutral. Thus, the evolution of acoustic traits tracked the shared history of the populations, which is unexpected for pan-Amazonian taxa or for mate-recognition traits. Divergence in coloration appeared uncorrelated with genetic distance, and might be partly attributed to local selective pressures, and perhaps to Batesian mimicry. Divergence in body-shape traits was low. The results obtained depict a complex evolutionary scenario and emphasize the importance of considering multiple traits when disentangling the forces behind allopatric divergence. ©2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 826-838.

The Effect of Salt Concentration on Adsorption of Low-Charge-Density Polyelectrolytes and Interactions between Polyelectrolyte-Coated Surfaces.

Abstract: In this investigation surface force, X-ray photoelectron spectroscopy and ellipsometry techniques have been used to study the adsorption of a low-charge-density cationic polyelectrolyte on negatively charged surfaces. It is shown that the low cationicity of this polyelectrolyte induces an adsorption behavior which is limited by steric factors rather than by the substrate surface charge or potential. It is also established that an increase in ionic strength of the solution results in desorption of the polyelectrolyte accompanied by an increase in layer thickness. This phenomenon is typical of a screening-reduced adsorption regime where electrostatic interactions predominate in the adsorption process. An increase in layer thickness most often occurs as a result of an increased adsorbed amount. Here, however, the increase in layer thickness occurs despite a reduction in the adsorbed amount. This can be understood as resulting from a reduced polyelectrolyte-surface affinity and a swelling of the adsorbed layer. Finally, it is demonstrated that the employed techniques complement each other and reveal new information on the interaction forces and conformation of polyelectrolytes at the solid-liquid interface. Copyright 1998 Academic Press.

On measures of weak noncompactness

Abstract: In this paper an axiomatic approach to the notion of a measure of weak noncompactness is presented. Several properties of the defined measures are given. Moreover, we provide a few concrete realizations of the accepeted axiomatic system in some Banach spaces.