National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

Quinolinic Acid: An Endogenous Neurotoxin with Multiple Targets

Abstract: Quinolinic acid (QUIN), a neuroactive metabolite of the kynurenine pathway, is normally presented in nanomolar concentrations in human brain and cerebrospinal fluid (CSF) and is often implicated in the pathogenesis of a variety of human neurological diseases QUIN is an agonist of N-methyl-D-aspartate (NMDA) receptor, and it has a high in vivo potency as an excitotoxin In fact, although QUIN has an uptake system, its neuronal degradation enzyme is rapidly saturated, and the rest of extracellular QUIN can continue stimulating the NMDA receptor However, its toxicity cannot be fully explained by its activation of NMDA receptors it is likely that additional mechanisms may also be involved In this review we describe some of the most relevant targets of QUIN neurotoxicity which involves presynaptic receptors, energetic dysfunction, oxidative stress, transcription factors, cytoskeletal disruption, behavior alterations, and cell death

Integral Sliding Mode Control for Nonlinear Systems With Matched and Unmatched Perturbations

Abstract: We consider the problem of designing an integral sliding mode controller to reduce the disturbance terms that act on nonlinear systems with state-dependent drift and input matrix. The general case of both, matched and unmatched disturbances affecting the system is addressed. It is proved that the definition of a suitable sliding manifold and the generation of sliding modes upon it guarantees the minimization of the effect of the disturbance terms, which takes place when the matched disturbances are completely rejected and the unmatched ones are not amplified. A simulation of the proposed technique, applied to a dynamically feedback linearized unicycle, illustrates its effectiveness, even in presence of nonholonomic constraints.

Chemical reactivity of aluminium with boron carbide

Abstract: The chemical reactivity of boron carbide (B4C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627–1000 °C). Al–B4C powder mixtures were cold pressed, heated for 1–450 h under 105 Pa of purified argon and characterized by X-ray diffraction (XRD) optical metallography (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Whatever the temperature in the investigated range, B4C has been observed to react with solid or liquid Al. As long as the temperature is lower than 933 K (660 °C), i.e. as long as Al is in the solid state, interaction proceeds very slowly, giving rise to the formation of ternary carbide (Al3BC) and to diboride (AlB2). At temperatures higher or equal to 933 K, Al is in the liquid state and the reaction rate increases sharply. Up to 1141 ± 4 K (868 ± 4 °C), the reaction products are Al3BC and AlB2: at temperatures higher than 1141 K, Al3 BC is still formed while Al3B48C2 (β-AlB12) replaces AlB2. In the three cases, interaction proceeds via the same mechanism including, successively, an incubation period, saturation of aluminium in B and C, nucleation and growth by dissolution–precipitation of Al3BC and a C-poor boride and, finally, the passivation of B4C by Al3BC. These results are discussed in terms of solid–liquid phase equilibria in the Al–B–C ternary system, with reference to the binary invariant transformation: α-AlB12 + L ⇔ AlB2, which has been found to occur at 1165 ± 5 K (892 ± 5 °C).

An Optical Spectroscopic Atlas of Low-Redshift Active Galactic Nuclei

Abstract: We present a spectral atlas of the Hβ region for 215 type 1 AGNs (luminous Seyfert 1/radio galaxy nuclei and low-z quasars) up to z ≈ 0.8. Line profiles and measures were derived from the database of intermediate resolution spectra (R 1000) with average continuum level S/N ratio ≈30. Parameters including rest frame equivalent width and FWHM are provided for the Fe IIopt blend at λ4570, Hβ, He II λ4686, and the [O III] λλ4959, 5007 emission lines. We extract clean broad component Hβ profiles and provide wavelength measurements at 0, 1/4, 1/2, 3/4, and 0.9 peak intensity levels in order to permit a quantitative definition of the Hβ broad component for statistical studies. We also discuss sources of uncertainty, selection effects, and biases in our sample. The data are especially important for tests of the eigenvector 1 parameter space occupation and correlation. We show that the I Zw 1 template Fe IIopt spectrum reproduces well the observed Fe IIopt emission for a wide range of line width and strength. A detailed analysis of the data within the eigenvector 1 context is deferred to a companion paper.