National University of La Plata

About: National University of La Plata is a education organization based out in La Plata, Argentina. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 12993 authors who have published 30013 publications receiving 495118 citations. The organization is also known as: UNLP & Universidad Nacional de La Plata.

Did Humans Cause the Late Pleistocene-Early Holocene Mammalian Extinctions in South America in a Context of Shrinking Open Areas?

Abstract: Capitulo VII de Haynes, Gary (ed). American megafaunal extinctions at the end of the Pleistocene. Springer, Vertebrate Paleobiology and Paleoanthropology Series, 2009, 202 p. + 32 il. ISBN 978-1-4020-8793-6 (e-book).

Inhibition of Giardia intestinalis by Extracellular Factors from Lactobacilli: an In Vitro Study

Abstract: The aim of the present work was to evaluate the effect of spent culture supernatants of different strains of lactobacilli on giardia trophozoites. The growth of Giardia intestinalis strain WB, as well as the attachment to the human intestinal epithelial cell line Caco-2, was evaluated by using proliferation and adhesion assays with radiolabeled parasites. In addition, scanning electron microscopy and flow cytometric analysis were performed. The effect of spent culture supernatants from lactobacilli was strain dependent. Lactobacillus johnsonii La1 significantly inhibited the proliferation of G. intestinalis trophozoites. Although the effect was strongly pH dependent, it was not simply due to lactic acid. According to flow cytometric analysis, trophozoites were arrested in G1 phase but neither significant necrosis nor apoptosis could be detected. Bacterial cells or their spent culture supernatants were unable to modify trophozoite attachment to Caco-2 cells. However, trophozoites treated with spent culture supernatants had little, if any, proliferative capacity. These results suggest that La1 produces some substance(s) able to inhibit proliferation of Giardia trophozoites. Partial characterization of the factors involved in the antigiardiasic action showed that they have a low molecular mass and are inactivated by heating. On this basis, it seems worthwhile to explore how colonization of the proximal small bowel with these lactic acid bacteria could interfere with giardiasis in vivo.

Search for heavy neutrinos and right-handed W bosons in events with two leptons and jets in pp collisions at √s =7 TeV with the ATLAS detector

Abstract: This letter reports on a search for hypothetical heavy neutrinos, N, and right-handed gauge bosons, W-R, in events with high transverse momentum objects which include two reconstructed leptons and ...

High and intermediate-resolution spectroscopy of Be stars - An atlas of H$\gamma$, He I 4471 and Mg II 4481 lines

Abstract: We present an atlas of H ,H ei 4471 and Mg ii 4481 line proles obtained in a 10 year observation period of 116 Be stars, which enabled many of them to be observed at quite dierent emission epochs. From the best t of the observed He i 4471 line proles with non-LTE, uniform (Te; logg) and full limb-darkened model line proles, we determined the V sini of the program stars. To account, to some degree, for the line formation peculiarities related to the rapid rotation-induced non-uniform distributions of temperature and gravity on the stellar surface, the t was achieved by considering (Te; logg) as free parameters. This method produced V sini estimations that correlate with the rotational velocities determined by Slettebak (1982) within a dispersion 30 km s 1 and without any systematic deviation. They can be considered as given in the new Slettebak's et al. (1975) system. Only 13 program stars have discrepant V sini values. In some objects, this discrepancy could be attributed to binary eects. Using the newly determined V sini parameters, we found that the ratio of true rotational velocities V=Vc of the program Be stars has a very low dispersion around the mean value. Assuming then that all the stars are rigid rotators with the same ratio V (!)=Vc, we looked for the value of ! that better represents the distribution of V sini=Vc for randomly oriented rotational axes. We obtained ! =0 :795. This value enabled us to determine the probable inclination angle of the stellar rotation axis of the program stars. In the observed line proles of H ,H ei 4471, Mg ii 4481 and Fe ii 4351 we measured several parameters related to the absorption and/or emission components, such as: equivalent width, residual emission and/or absorption intensity, FWHM, emission peak separations, etc. The parameters related to the H line emission proles were used to investigate the structure of the nearby environment of the central star. From the characteristics of the correlations between these quantities and the inferred inclination angle, we concluded that in most of cases the H line emission forming regions may not be strongly flattened. Using a simple representation of the radiation flux emitted by the star+envelope system, we derived rst order estimates of physical parameters characterizing the H line emission formation region. Thus, we obtained that the total extent of the H region is Rf' 2:5 1:0 R and that the density distribution in these layers can be mimicked with a power law R ,w here =2 :5 +2:2 0:6 . The same approach enabled us to estimate the optical depth of the H line emission formation region. From its dependence with the aspect angle, we concluded that these regions are caracterized by a modest flattening and that the (equator)=(pole) density contrast of the circumstellar envelope near the star should be two orders of magnitude lower than predicted by models based on a priori disc-shaped circumstellar envelopes. We found that the separation between the emission peaks, p, and the full width at half maximum, 1=2 ,o f the H line emission are not only sensitive to kinematic eects, but to line optical depth as well. This nding agrees with previous theoretical predictions and conrms that Huang's (1972) relation overestimates the extent of the H line emission formation region.