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.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

Abstract: A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca(2+) is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca(2+)-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca(2+) with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca(2+) channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca(2+) and SLO3 for K(+), which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Optically active metal nanoparticles

Abstract: Optical activity and its relation with chiral metal nanoparticles are revised in this tutorial review. The experimental evidence as well as the different mechanisms to explain the optical activity of ligand-protected nanoparticles are described, emphasizing the aspects that provide insights into this novel phenomenon at the nanoscale. The perspectives of this research field and a list of unsolved problems are presented. This tutorial review provides information for an interdisciplinary community working in synthesis, characterization and utilization of chiral metal nanoparticles.

Use of Tenebrio molitor (Coleoptera: Tenebrionidae) to Recycle Organic Wastes and as Feed for Broiler Chickens

Abstract: Several dried waste materials from different origins were used as a substrate to grow Tenebrio molitor L. Nutrient/amino acid values differed depending on both larval size/weight and substrate. These larvae were experimentally used as a broiler feedstuff. Seven-day-old chicks of a commercially available strain with an average weight of 126 g were randomly distributed into nine six-broiler groups. Three levels of Tenebrio molitor larvae (0, 5, and 10% dry weight) were used in a 19% protein content sorghum-soybean meal basal diet, to evaluate feed intake, weight gain, and feed efficiency. Results after 15 d showed no significant differences among treatments. These data indicate that Tenebrio molitor has the potential to be used as protein source for raising broilers.

Slab detachment control on mafic volcanic pulse and mantle heterogeneity in central Mexico

Abstract: Seismic tomography studies and plate reconstructions suggest that the Farallon slab broke off shortly before subduction ended off southern Baja California. However, the progress of detachment in time and space and its consequences on the volcanism of central Mexico have not so far been considered. Here I use the Neogene geologic record of central Mexico to propose a lateral propagation of slab detachment beneath the Trans-Mexican volcanic belt during the late Miocene. I suggest that the trace of the detachment is expressed by a short (2–3 m.y.), eastward-migrating pulse of mafic volcanism that took place from ca. 11.5 to ca. 6 Ma to the north of the Pliocene–Quaternary volcanic arc, as hot, subslab material flowing into the slab gap produced a transitory thermal anomaly in the mantle wedge. Slab detachment of the deeper and denser part of the plate was initiated in the southern Gulf of California area by the incoming of progressively younger oceanic lithosphere at the paleotrench that produced an increasing coupling between the Magdalena microplate and the overriding North American plate. The tear in the slab propagated eastward from the Gulf of California to the Gulf of Mexico, paralleling the southern Mexico trench system. The decrease in the Rivera–North America convergence rate between ca. 9 and 7 Ma appears to be related to the loss of slab pull after the detachment. Sparse oceanic-island–type basalts emplaced since the end of the Miocene in the Trans-Mexican volcanic belt are located above a trench-parallel slab window between the inferred detachment trace and the leading edge of the present slab, which has been detected seismically. In this context, the occurrence of these unusual intraplate magmas is easily explained by the infiltration of enriched asthenosphere into the subarc mantle.

Efficient CO2 to CO electrolysis on solid Ni–N–C catalysts at industrial current densities

Abstract: The electrochemical CO2 reduction reaction (CO2RR) to pure CO streams in electrolyzer devices is poised to be the most likely process for near-term commercialization and deployment in the polymer industry. The reduction of CO2 to CO is electrocatalyzed under alkaline conditions on precious group metal (PGM) catalysts, such as silver and gold, limiting widespread application due to high cost. Here, we report on an interesting alternative, a PGM-free nickel and nitrogen-doped porous carbon catalyst (Ni–N–C), the catalytic performance of which rivals or exceeds those of the state-of-the-art electrocatalysts under industrial electrolysis conditions. We started from small scale CO2-saturated liquid electrolyte H-cell screening tests and moved to larger-scale CO2 electrolyzer cells, where the catalysts were deployed as Gas Diffusion Electrodes (GDEs) to create a reactive three-phase interface. We compared the faradaic CO yields and CO partial current densities of Ni–N–C catalysts to those of a Ag-based benchmark, and its Fe-functionalized Fe–N–C analogue under ambient pressures, temperatures and neutral pH bicarbonate flows. Prolonged electrolyzer tests were conducted at industrial current densities of up to 700 mA cm−2. Ni–N–C electrodes are demonstrated to provide CO partial current densities above 200 mA cm−2 and stable faradaic CO efficiencies around 85% for up to 20 hours (at 200 mA cm−2), unlike their Ag benchmarks. Density functional theory-based calculations of catalytic reaction pathways help offer a molecular mechanistic basis of the observed selectivity trends on Ag and M–N–C catalysts. Computations lend much support to our experimental hypothesis as to the critical role of N-coordinated metal ion, Ni–Nx, motifs as the catalytic active sites for CO formation. Apart from being cost effective, the Ni–N–C powder catalysts allow flexible operation under acidic, neutral, and alkaline conditions. This study demonstrates the potential of Ni–N–C and possibly other members of the M–N–C materials family to replace PGM catalysts in CO2-to-CO electrolyzers.