El saber indígena y la administración colonial española: la visita a la provincia de mariquita de 1559

Trabajos recientes sobre la historia de América han incorporado métodos propios de las ciencias de la comunicación y de la semiótica, tendientes a ofrecer nuevas explicaciones sobre la naturaleza del colapso de las sociedades indígenas al momento de la conquista.1 Aunque los europeos no dejaron para Colombia los ricos testimonios propios de las culturas de México, Guatemala o Perú, como glifos y relatos de la conquista hechos por los mismos indígenas, al menos nos quedaron otros escritos cuya lectura puede conducirnos al análisis de realidades subsumidas en estratos cuya riqueza testimonial se oculta bajo la apariencia de un lenguaje repetitivo e intrascendente. Tal es el caso de las llamadas visitas tempranas que se hicieron a diferentes partes del actual territorio de Colombia en la década de 1550

Hydrogen adsorption on graphene: a first principles study

We present a systematic ab initio study of atomic hydrogen adsorption on graphene. The characteristics of the adsorption process are discussed in relation with the hydrogenation coverage. For systems with high coverage, the resultant strain due to substrate relaxation strongly affects H atom chemisorption. This leads to local structural changes that have not been pointed out to date, namely localized surface curvature. We demonstrate that the hydrogen chemisorption energy barrier is independent of the optimization technique and system size, being associated with the relaxation and rehybridization of the sole adsorbent carbon atom. On the other hand, the H desorption barrier is very sensitive to a correct structural relaxation and is also dependent on the degree of system hydrogenation. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010

Background studies for acoustic neutrino detection at the South Pole

The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the tiny flux of cosmogenic neutrinos expected on Earth. The energy threshold for this process depends strongly on the absolute noise level in the target material. The South Pole Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 m depth. The noise is very stable and Gaussian distributed. Lacking an in-situ calibration up to now, laboratory measurements have been used to estimate the absolute noise level in the 10 to 50 kHz frequency range to be smaller than 20 mPa. Using a threshold trigger, sensors of the South Pole Acoustic Test Setup registered acoustic pulse-like events in the IceCube detector volume and its vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to localize acoustic events. Monte Carlo simulations of sound propagating from the established sources to the SPATS sensors have allowed to check corresponding model expectations. An upper limit on the neutrino flux at energies $E_\nu > 10^{11}$ GeV is derived from acoustic data taken over eight months.Comment: 17 pages, 14 figure