Instituto Politécnico Nacional

About: Instituto Politécnico Nacional is a education organization based out in Mexico City, Mexico. It is known for research contribution in the topics: Population & Context (language use). The organization has 43351 authors who have published 63315 publications receiving 938532 citations. The organization is also known as: Instituto Politécnico Nacional & Instituto Politecnico Nacional.

Critical behavior of the electrical resistivity in magnetic systems

Abstract: The effect of critical fluctuations on the resistivity near magnetic and order-disorder phase transitions is discussed. It is shown that in all magnetic and electronic systems the asymptotic high-momentum spin correlation functions dominate the temperature dependence of the resistivity sufficiently close to the transition. The dependence on the parameters of the system of the critical behavior and the way in which this behavior is approached is discussed in detail. In particular, the importance of the transition from a classical to a proper critical behavior, for the interpretation of experimental results, is emphasized, and recent renormalization-group results for the form of the correlation functions are utilized. For semiconductors the effects of fluctuations on the band gap are also calculated. It is suggested that the Fisher-Langer relation between the temperature derivative of the resistivity and the specific heat should be valid over a considerable temperature range outside the critical region. Theoretical predictions are compared with available experimental results on the resistivity and band gaps. It is shown that these results can all be understood, at least qualitatively, in the Born approximation by using only the most general known properties of the system.

Constraints on the cosmic-ray density gradient beyond the solar circle from Fermi γ-ray observations of the third galactic quadrant

Abstract: We report an analysis of the interstellar ?-ray emission in the third Galactic quadrant measured by the Fermi Large Area Telescope. The window encompassing the Galactic plane from longitude 210? to 250? has kinematically well-defined segments of the Local and the Perseus arms, suitable to study the cosmic-ray (CR) densities across the outer Galaxy. We measure no large gradient with Galactocentric distance of the ?-ray emissivities per interstellar H atom over the regions sampled in this study. The gradient depends, however, on the optical depth correction applied to derive the H?I column densities. No significant variations are found in the interstellar spectra in the outer Galaxy, indicating similar shapes of the CR spectrum up to the Perseus arm for particles with?GeV to tens of?GeV energies. The emissivity as a function of Galactocentric radius does not show a large enhancement in the spiral arms with respect to the interarm region. The measured emissivity gradient is flatter than expectations based on a CR propagation model using the radial distribution of supernova remnants and uniform diffusion properties. In this context, observations require a larger halo size and/or a flatter CR source distribution than usually assumed. The molecular mass calibrating ratio, X CO = N(H2)/W CO, is found to be (2.08 ? 0.11) ? 1020 cm-2(K km s?1)?1 in the Local arm clouds and is not significantly sensitive to the choice of H I spin temperature. No significant variations are found for clouds in the interarm region.

Signalling of Trichomonas vaginalis for amoeboid transformation and adhesin synthesis follows cytoadherence

Abstract: Summary The cytoadherence of Trichomonas vaginalis, the sexually transmitted flagellated protozoan, to vaginal epithelial cells (VECs) is the key to infection. Electron microscopy revealed that in vitro-grown parasites having typical globular shape transformed rapidly after contact with VECs into thin, flat, amoeboid cells, maximizing the area of adhesion to the surface of VECs. Amoebic trichomonads formed filopodia and pseudopodia, which interdigitated at distinct sites on the plasma membrane of target cells. In contrast, the amoeboid transformation did not occur for T. vaginalis interacting with He La cells, the previously used in vitro host model cell. Initial parasitism of VECs by a single organism was followed by establishment of a monolayer of trichomonads on the host cell. Finally, parasites adhering to either VECs or HeLa cells were induced to synthesize greater amounts of the four previously described adhesins. Therefore, distinct signals after contact with either epithelial cell type leads to the morphological transformation and/or induction of adhesin synthesis by T. vaginalis.