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.

Magnetization curves of antiferromagnetic heisenberg spin-1/2 ladders

Abstract: Magnetization processes of spin-1/2 Heisenberg ladders are studied using strong-coupling expansions, numerical diagonalization of finite systems and a bosonization approach. We find that the magnetization exhibits plateaux as a function of the applied field at certain rational fractions of the saturation value. Our main focus are ladders with 3 legs where plateaux with magnetization one third of the saturation value are shown to exist.

Kilohertz Quasi-periodic Oscillation Peak Separation Is Not Constant in the Atoll Source 4U 1608–52

Abstract: We present new Rossi X-Ray Timing Explorer observations of the low-mass X-ray binary 4U 1608-52 during the decay of its 1998 outburst. We detect, by a direct fast Fourier transform method, the existence of a second kilohertz quasi-periodic oscillation (kHz QPO) in its power density spectrum, which was previously only seen by means of the sensitivity-enhancing "shift and add" technique. This result confirms that 4U 1608-52 is a twin kHz QPO source. The frequency separation between these two QPOs decreased significantly, from 325.5±3.4 to 225.3±12.0 Hz, as the frequency of the lower kHz QPO increased from 470 to 865 Hz, in contradiction with a simple beat-frequency interpretation. This change in the peak separation of the kHz QPOs is closely similar to that previously seen in Scorpius X-1 but takes place at a 10 times lower average luminosity. We discuss this result within the framework of models that have been proposed for kHz QPO. Beat-frequency models where the peak separation is identified with the neutron star spin rate, as well as the explanations previously proposed to account for the similar behavior of the QPOs in Sco X-1, are strongly challenged by this result.

Relationship between texture and corrosion resistance in hot-dip galvanized steel sheets

Abstract: The addition of lead or antimony to the zinc bath promotes both excessive growth of the zinc crystals and a dendritic solidification in the form of spangles. This phenomenon affects not only the zinc coating texture but also its surface appearance and corrosion resistance. Therefore, the effects of the zinc bath chemical composition (changed by the addition of lead or antimony) on the texture and corrosion behaviour of hot-dip galvanized steel sheets were evaluated. Standardized salt spray tests as well as exposure to a 0.5 M NaClO4 solution test were employed. The surface texture was analyzed using X-ray diffraction (XRD). In order to study the corrosion performance, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques were employed. From the experimental results it was concluded that the characteristic texture of zinc coatings was not modified by an increase in the antimony content, but an increment in the lead content produced a crystallographic preferential orientation with the pyramidal family planes parallel to the coating surface. This last effect deteriorates not only the surface appearance but also the corrosion resistance of the galvanized steel sheets.

Genotoxic evaluation of the pyrethroid lambda-cyhalothrin using the micronucleus test in erythrocytes of the fish Cheirodon interruptus interruptus

Abstract: In order to develop experimental models able to detect genotoxic effects of pollutants in aquatic organisms, the genotoxicity of the pyrethroid lambda-cyhalothrin was studied using the micronucleus test in erythrocytes of Cheirodon interruptus interruptus. The frequency of micronuclei was examined in blood smears obtained from fishes exposed in vivo to three different concentrations (0.05; 0.01; 0.001 ug/l) of the compound and sacrificed at nine sampling times (24, 48, 72, 96 h and 8, 12, 15, 19 and 23 days). As a positive control fishes were exposed to 5 mg/l of cyclophosphamide. Results obtained demonstrated the genotoxic effects of the pyrethroid in the experimental model employed. The variation in the micronuclei frequencies in the different sampling times could be related to the blood cell kinetics and the erythrocyte replacement. The results could be considered as a validation of the MN test in fishes for the assessment of genotoxic pollutants.