University of Buenos Aires

About: University of Buenos Aires is a education organization based out in Buenos Aires, Argentina. It is known for research contribution in the topics: Population & Context (language use). The organization has 29353 authors who have published 50947 publications receiving 1086007 citations. The organization is also known as: Universidad de Buenos Aires.

Measurement of the W boson helicity in top quark decays at D0

Abstract: The authors present a measurement of the fraction f{sub +} of right-handed W bosons produced in top quark decays, based on a candidate sample of t{bar t} events in the {ell}+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb{sup -1} collected by the D0 detector at the Fermilab Tevatron p{bar p} Collider at {radical}s = 1.96 TeV. They reconstruct the decay angle {theta}* for each lepton. By comparing the cos{theta}* distribution from the data with those for the expected background and signal for various values of f{sub +}, they find f{sub +} = 0.056 {+-} 0.080(stat) {+-} 0.057(syst). (f{sub +} < 0.23 at 95% C.L.), consistent with the standard model prediction of f{sub +} = 3.6 x 10{sup -4}.

Dystrophin deletions and cognitive impairment in Duchenne/Becker muscular dystrophy.

Abstract: Analyses of deletions in the dystrophin gene and of cognitive status were performed on patients with Duchenne (DMD) or Becker (BMD) muscular dystrophy in order to find a correlation between both features. Molecular study by multiplex and simplex PCR of dystrophin exons led to the identification of 51 deletions in 126 unrelated patients. Most of them were frameshift, in full agreement with severe clinical symptoms, three patients with a BMD-like phenotype had in-frame mutations. Deletions were localized with reference to the different dystrophin isoform sequences and were clustered in two main areas, 5' and central+ 3' end of the gene. Cognitive abilities were tested in 47 out of 51 patients with identified mutations, 23 of them being mentally impaired. Comparison of molecular and neuropsychological features showed that deletions localized in central and 3' parts of the gene (18 out of 23) are preferentially associated with mental impairment. Fourteen of them were found in the regulatory and coding sequences for the three CNS specific carboxy terminal isoforms. Therefore, though mutations with variable locations may lead to cognitive impairment, our results show that deletions in the distal portion of the gene are basically related to mental retardation.

Effect of culture parameters on the production of the edible mushroom Grifola frondosa (maitake) in tropical weathers

Abstract: Hitherto, little effort has been directed to improve culture conditions for commercial development of maitake (Grifola frondosa), an edible and medicinal fungus, due to the short history of cultivation, particularly in tropical weathers. The purpose of this research was analyzing the environmental factors required for successful basidiome development on synthetic substrates in Colombia. We evaluated different cereal grains (corn, barley, sorghum and rice) for spawn production; and industrial by-products (such as coffee spent-ground and oak-sawdust) as substrates for mushroom production. Exploiting these residues for G. frondosa solid culturing would primarily provide edible mushroom and simultaneously help in resolving their disposal problem. The use of corn grains as substrate for spawn production results an important factor for reducing crop cycle time. A cold shock to 10°C was requisite for basidiome formation. Coffee spent-ground was a good substrate for mycelial growth, but not for mushroom production. When using oak sawdust plus corn bran as substrate, we obtained consistent yields with combined high biological efficiency (BE) (35.3%), best quality mushrooms, and a crop cycle of 12–14 weeks. The results achieved in this investigation contribute to expand the knowledge on this fungus, and compare favorably with previous works in the northern hemisphere with respect to BE, mushroom quality and crop cycle time.

Reactive oxygen species production and redox state in parthenogenetic and sperm-mediated bovine oocyte activation.

Abstract: The knowledge concerning redox and reactive oxygen species (ROS)-mediated regulation of early embryo development is scarce and remains controversial. The aim of this work was to determine ROS production and redox state during early in vitro embryo development in sperm-mediated and parthenogenetic activation of bovine oocytes. Sperm-mediated oocyte activation was carried out in IVF-modified synthetic oviductal fluid (mSOF) with frozen-thawed semen. Parthenogenetic activation was performed in TALP plus ionomycin and then in IVF-mSOF with 6-dimethylaminopurine plus cytochalasin B. Embryos were cultured in IVF-mSOF. ROS and redox state were determined at each 2-h interval (7-24 h from activation) by 2',7'-dichlorodihydrofluorescein diacetate and RedoxSensor Red CC-1 fluorochromes respectively. ROS levels and redox state differed between activated and non-activated oocytes (P<0.05 by ANOVA). In sperm-activated oocytes, an increase was observed between 15 and 19 h (P<0.05). Conversely, in parthenogenetically activated oocytes, we observed a decrease at 9 h (P<0.05). In sperm-activated oocytes, ROS fluctuated throughout the 24 h, presenting peaks around 7, 19, and 24 h (P<0.05), while in parthenogenetic activation, peaks were detected at 7, 11, and 17 h (P<0.05). In the present work, we found clear distinctive metabolic patterns between normal and parthenogenetic zygotes. Oxidative activity and ROS production are an integral part of bovine zygote behavior, and defining a temporal pattern of change may be linked with developmental competence.

Influence of the number of layers on the equilibrium of a granular packing

Abstract: This paper reports an experimental study on avalanches in a granular material contained in a confined geometry. The granular packing is made of monosize glass beads initially poured into a box that is slowly inclined until an avalanche takes place at a critical angle ${\ensuremath{\theta}}_{M}$ (maximum angle of stability). The avalanche involves a decrease of the surface slope until a second critical angle ${\ensuremath{\theta}}_{r}$ (angle of repose) is reached. Both angles and the mass displaced out of the box during the avalanche are studied as a function of the height of the granular packing. In order to avoid cohesion effects, experiments are carried out in a humidity controlled environment. For small packings, up to approximately ten layers, the stability of the system is significantly affected by the rough surface at the bottom. In contrast, for thicker systems, critical angles do not depend on the height.