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.

Shifts in bacterial communities of two caribbean reef-building coral species affected by white plague disease

Abstract: Coral reefs are deteriorating at an alarming rate mainly as a consequence of the emergence of coral diseases. The white plague disease (WPD) is the most prevalent coral disease in the southwestern Caribbean, affecting dozens of coral species. However, the identification of a single causal agent has proved problematic. This suggests more complex etiological scenarios involving alterations in the dynamic interaction between environmental factors, the coral immune system and the symbiotic microbial communities. Here we compare the microbiome of healthy and WPD-affected corals from the two reef-building species Diploria strigosa and Siderastrea siderea collected at the Tayrona National Park in the Caribbean of Colombia. Microbiomes were analyzed by combining culture-dependent methods and pyrosequencing of 16S ribosomal DNA (rDNA) V5-V6 hypervariable regions. A total of 20 410 classifiable 16S rDNA sequences reads were obtained including all samples. No significant differences in operational taxonomic unit diversity were found between healthy and affected tissues; however, a significant increase of Alphaproteobacteria and a concomitant decrease in the Beta- and Gammaproteobacteria was observed in WPD-affected corals of both species. Significant shifts were also observed in the orders Rhizobiales, Caulobacteriales, Burkholderiales, Rhodobacterales, Aleteromonadales and Xanthomonadales, although they were not consistent between the two coral species. These shifts in the microbiome structure of WPD-affected corals suggest a loss of community-mediated growth control mechanisms on bacterial populations specific for each holobiont system.

Large surface magnetic contribution in amorphous ferromagnetic nanoparticles

Abstract: We present magnetization measurements on \ensuremath{\sim}3-nm $({\mathrm{Fe}}_{0.26}{\mathrm{Ni}}_{0.74}{)}_{50}{\mathrm{B}}_{50}$ ferromagnetic amorphous nanoparticles. Our results show evidence of the surface contribution to the magnetic properties in the $M(H),$ $M(T)$ and relaxation measurements. We observe a large increase in the magnetization with decreasing temperature, a nonsaturated component in the $M(H)$ curves, the presence of two maxima in the zero-field-cooling $M(T)$ data, and two viscosity regimes in magnetization relaxation data. The results have been interpreted by a simple model where we consider each single-domain particle as a core plus shell system with a uniaxial anisotropy acting on the core and a surface anisotropy acting on the shell. Monte Carlo simulations based in this core-shell model qualitatively reproduce all the observed phenomena.

Measurement of the prompt J/ψ and ψ(2S) polarizations in pp collisions at s=7 TeV

Abstract: The polarizations of prompt J/ψJ/ψ and ψ(2S)ψ(2S) mesons are measured in proton–proton collisions at View the MathML sources=7 TeV, using a dimuon data sample collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.9 fb−1. The prompt J/ψJ/ψ and ψ(2S)ψ(2S) polarization parameters λϑλϑ, λφλφ, and λϑφλϑφ, as well as the frame-invariant quantity View the MathML sourceλ˜, are measured from the dimuon decay angular distributions in three different polarization frames. The J/ψJ/ψ results are obtained in the transverse momentum range 14

Effect of Solution pH on the Adsorption of Paracetamol on Chemically Modified Activated Carbons.

Abstract: Paracetamol adsorption in acidic, neutral and basic media on three activated carbons with different chemistry surfaces was studied. A granular activated carbon (GAC) was prepared from coconut shell; starting from this sample, an oxidized activated carbon (GACo) was obtained by treating the GAC with a boiling solution of 6 M nitric acid, so to generate a greater number of oxygenated surface groups. In addition, a reduced activated carbon (GACr) was obtained by heating the GAC at 1173 K, to remove the oxygenated surface groups. Paracetamol adsorption was higher for GACr due to the lower presence of oxygenated surface functional groups. Moreover, adsorption was highest at neutral pH. The magnitude of the interactions between paracetamol molecules and activated carbons was studied by measuring the immersion enthalpies of activated carbons in solution of paracetamol at different concentrations and pH values and by calculating the interaction enthalpy. The highest value was obtained for GACr in a paracetamol solution of 1000 mg L−1 at pH 7, confirming that paracetamol adsorption is favoured on basic activated carbons at pH values near to neutrality. Finally, the Gibbs energy changes confirmed the latter result, allowing explaining the different magnitudes of the interactions between paracetamol and activated carbons, as a function of solution pH.