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.

Searches for new physics using the tt̄ invariant mass distribution in pp collisions at √s=8 TeV

Abstract: Searches for anomalous top quark-antiquark production are presented, based on pp collisions at sqrt(s) = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 inverse femtobarns, were collected with the CMS detector at the LHC. The observed ttbar invariant mass spectrum is found to be compatible with the standard model prediction. Limits on the production cross section times branching fraction probe, for the first time, a region of parameter space for certain models of new physics not yet constrained by precision measurements.

Dynamics of rules and resources: three new field experiments on water, forests and fisheries

Abstract: Most common-pool resource experiments, inspired by the ground-breaking work of Ostrom, Gardner and Walker (1994), involve a typical structure of a static non-linear social dilemma with a rival but nonexcludable good that is extracted by a number of players. However there are specific ecological features of relevant common-pool resources that can be incorporated into an experimental design and tested in the field or the lab. Stock effects, spatial effects or vertical downstream externalities are issues that natural scientists and economists have studied in forests, fisheries or watershed management although experimental works on these ecological aspects are rather scarce. We designed three resource specific games to capture particular characteristics of common-pool resources and apply them in six villages in Thailand and Colombia. In each village we recruited 60 people and conducted three games. A water irrigation game capturing the downstream externalities and collective action problem of provision and appropriation stages where all players need to contribute to a public project that produces water which is then extracted sequentially by each of the players starting with the one located upstream, leaving the remaining water to the next player downstream, and so on. In our forestry game players start with a number of standing trees that can be cut by any of the players; in any round each player can extract between zero and a fixed number of trees. The remaining trees regrow at a certain rate and the resulting trees are then left for the next round for individual extraction. The game ends at a maximum number of rounds or when no trees are left. Finally, the fisheries game involves two possible fishing sites that can have high or low levels of stock. Each player needs to decide where to fish between the two sites and her individual effort of fishing. Depending on the aggregate level of fishing effort in each site, the stock level will change for the following round and will determine the fishing returns. All games involve a social dilemma where individual interests clash with the socially optimal outcome. Lessons can be derived regarding the design of better resource management rules and a better understanding of how resource specific dynamics affect the social dilemmas in commonpool resources. 1 The authors wish to thank the NSF grant within the HUMAN AND SOCIAL DYNAMICS PROGRAM for their funding. More details about the research project can be found in: http://www.public.asu.edu/~majansse/dor/nsfhsd.htm 2

Cattle and Weedy Shrubs as Restoration Tools of Tropical Montane Rainforest

Abstract: "En los ultimos 150 anos, una gran proporcion de los bosques de America Latina se han convertido en pastizales. Cuando se abandonan estos pastos, los pastos pueden retrasar el restablecimiento de especies lenosas y limitar la regeneracion forestal. En este estudio, exploramos el uso del ganado para facilitar el establecimiento de vegetacion lenosa en pastos de montana colombianos, dominados por los pastos africanos Pennisetum clandestinum (Kikuyo) y Melinis minutiflora (Yaragua). Primero, describimos la vegetacion lenosa y herbacea en pastizales y pastos sin pastoreo. En segundo lugar, probamos el efecto del pastoreo y la adicion de semillas en el establecimiento y crecimiento de especies lenosas. Tambien determinamos si el efecto del pastoreo era diferente en P. clandestinum y M. minutiflorapastizales Descubrimos que la baja densidad de ganado bovino aumento considerablemente la densidad, el numero de ramas por individuo (una medida de ""arbusto"") y el area basal de especies lenosas, pero tambien redujo la riqueza y diversidad de especies de plantas lenosas. En la zona de pastoreo, los arbustos Baccharis latifolia (Chilca) y Salvia sp. (Salvia) fueron los mas abundantes. El efecto combinado del pastoreo y la sombra de los arbustos redujo la vegetacion herbacea en un 52 a 92%. En el experimento de pastoreo / adicion de semillas, el pastoreo aumento el establecimiento de plantulas lenosas, particularmente del arbusto Verbesina arborea(camargo), pero el mayor efecto fue la adicion de semillas. Cuando los pastos son una barrera importante para la regeneracion, el pastoreo puede facilitar el establecimiento de arbustos que crean un microhabitat mas adecuado para el establecimiento de especies de arboles forestales montanos."