Size effects in multiferroic BiFeO3 nanodots: A first-principles-based study

An effective Hamiltonian scheme is developed to investigate structural and magnetic properties of BiFeO3 nanodots under short-circuit-like electrical boundary conditions. Various striking effects are discovered. Examples include (a) scaling laws involving the inverse of the dots' size for the magnetic and electric transition temperatures; (b) the washing out of some structural phases present in the bulk via size effects; (c) the possibility of tailoring the difference between the Neel and Curie temperatures, by playing with the size and electrical boundary conditions; and (d) an universal critical thickness of the order of 1.6 nm below which the dots do not possess any long-range ordering for the electrical and magnetic dipoles, as well as, for the oxygen octahedral tiltings.Comment: 3 figure

Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy

Deep level defects in n-type unintentionally doped a-plane MgxZn1−xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1−xO were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of Ec − 1.4 eV, 2.1 eV, 2.6 V, and Ev + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at Ec − 2.1 eV, Ev + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at Ev + 0.3 eV and Ec − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the Ev + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the Ec − 1.4 eV and Ec − 2.6 eV levels in Mg alloyed samples

Exocytosis of catecholamine (CA)-containing and CA-free granules in chromaffin cells.

Recent evidence suggests that endocytosis in neuroendocrine cells and neurons can be tightly coupled to exocytosis, allowing rapid retrieval from the plasma membrane of fused vesicles for future use. This can be a much faster mechanism for membrane recycling than classical clathrin-mediated endocytosis. During a fast exo-endocytotic cycle, the vesicle membrane does not fully collapse into the plasma membrane; nevertheless, it releases the vesicular contents through the fusion pore. Once the vesicle is depleted of transmitter, its membrane is recovered without renouncing its identity. In this report, we show that chromaffin cells contain catecholamine-free granules that retain their ability to fuse with the plasma membrane. These catecholamine-free granules represent 7% of the total population of fused vesicles, but they contributed to 47% of the fusion events when the cells were treated with reserpine for several hours. We propose that rat chromaffin granules that transiently fuse with the plasma membrane preserve their exocytotic machinery, allowing another round of exocytosis

Grupo Espejo: una propuesta psicoeducativa de acompañamiento

Se presenta un modelo de intervención integral y grupal que conjuga perspectivas psicológicas y educativas: Grupos Espejo. En el modelo se trabaja el enfoque psicoeducativo en relación a lo clínico como algo que conlleva una finalidad pedagógica, es decir, se promueve el reaprendizaje de los conflictos y tensiones que se viven y actualizan en las figuras del grupo. Se incluye una propuesta de evaluación de competencias psicoemocionales.ITESO, A.C

COVID-19 y salud reproductiva

El comportamiento de las enfermedades microbianas, ya sea por virus, bacterias o protozoos, y su respuesta inflamatoria son diferentes entre hombres y mujeres. Esta diferencia se hace notoria en la pandemia derivada por la enfermedad por coronavirus (COVID-19). Desde el reporte del primer caso de neumonía en diciembre de 2019, en Wuhan, China, la COVID-19 se ha diseminado a 212 países y territorios y, a la fecha, se ha confirmado más de 3,5 millones de casos, con una mortalidad mundial del 7%, lo que la convierte en una emergencia sanitaria internacional (1). Hasta ahora, en Colombia, hay más de 7000 casos confirmados, con más de 300 defunciones, de los cuales, más del 60% pertenecen al sexo masculino. Hasta el momento, la literatura científica disponible relacionada con la COVID-19 solo abarca ciertos aspectos de la salud reproductiva, tanto femenina como masculina, mientras se continúa recopilando más información que nos permita conocer y realizar un análisis más detallado de su impacto real en humanos durante el proceso infeccioso y las secuelas derivadas de este. Está confirmado que las condiciones médicas relacionadas con el síndrome metabólico y los estados de insulinorresistencia en hombres y mujeres agravan la presentación clínica y el pronóstico (2). La presente revisión pretende ilustrar los mecanismos relacionados con la respuesta inmunitaria diversa frente a las infecciones virales según el sexo del individuo, su compromiso gonadal y los efectos relacionados con la salud reproductiva masculina y femenina, que incluye la maternofetal y la posible transmisión vertical

A Novel Prototype Offset Multi Tubular Photoreactor (OMTP) for solar photocatalytic degradation of water contaminants

The design and operation of a new solar photoreactor prototype named Offset Multi Tubular Photoreactor (OMTP) is presented. The OMTP advances over the compound parabolic collector (CPC) photoreactor, which is one of the most efficient design for large-scale solar detoxification of water and wastewater. The OMTP design is based on a simple modification of the common CPC and included a supplementary set of tubes in the space occupied by the axes of intersection of the CPC reflective involutes. This new reactor configuration increased the irradiated reactor volume by 79% and the fluid residence time by up to 1.8-fold in comparison to the CPC, for the same solar irradiated area (footprint). The model parameters used for comparing and scaling the OMPT and CPC were β (reactor volume/total volume), α (area of absorption/total volume), αg (physical area/total volume), degradation efficiency ηα per unit area, and the operating volume. The total solar energy absorbed in the reactors (1.74 m2 footprint) was 15.17 W for the CPC and 21.86 W for the OMTP, which represents an overall gain of 44% for the latter. The performance of the OMTP and CPC were compared at the same value of solar exposure, β of 0.3 with optimal photocatalyst loading of 0.25 g/L titanium dioxide (TiO2 P25). The degradation efficiencies of methylene blue, dichloroacetic acid, 4-chlorophenol (120 ppm initial concentration) in the OMTP were up to 81%, 125%, 118% and 242% higher, respectively, in comparison to the CPC after 8000 J/m2 of accumulated solar energy. The OMTP should outperform the CPC in environmental and renewable energy applications of solar heterogeneous photocatalysis

Models and experimental results from the wide aperture Nb-Ti magnets for the LHC upgrade

MQXC is a Nb-Ti quadrupole designed to meet the accelerator quality requirements needed for the phase-1 LHC upgrade, now superseded by the high luminosity upgrade foreseen in 2021. The 2-m-long model magnet was tested at room temperature and 1.9 K. The technology developed for this magnet is relevant for other magnets currently under development for the high-luminosity upgrade, namely D1 (at KEK) and the large aperture twin quadrupole Q4 (at CEA). In this paper we present MQXC test results, some of the specialized heat extraction features, spot heaters, temperature sensor mounting and voltage tap development for the special open cable insulation. We look at some problem solving with noisy signals, give an overview of electrical testing, look at how we calculate the coil resistance during at quench and show that the heaters are not working We describe the quench signals and its timing, the development of the quench heaters and give an explanation of an Excel quench calculation and its comparison including the good agreement with the MQXC test results. We propose an improvement to the magnet circuit design to reduce voltage to ground values by factor 2. The program is then used to predict quench Hot-Spot and Voltages values for the D1 dipole and the Q4 quadrupole.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet, Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva, Switzerlan

Single phase a-plane MgZnO epilayers for UV optoelectronics: substitutional behaviour of Mg at large contents

High quality 1 μm thick a-plane MgxZn1−xO layers were produced by molecular beam epitaxy with Mg contents higher than 50%. Resonant Rutherford backscattering spectrometry combined with ion channeling revealed a uniform growth in both composition and atomic order. The lattice-site location of Mg, Zn and O elements was determined independently, proving the substitutional behaviour of Mg in Zn-sites of the wurtzite lattice. X-Ray diffraction pole figure analysis also confirms the absence of phase separation. Optical properties at such high Mg contents were studied in Schottky photodiodes

Repotenciación de alimentadores primarios para la reducción de pérdidas

Una manera efectiva de reducir las pérdidas de energía es a través de la repotenciación del conductor de los alimentadores primarios, que consiste en el aumento del calibre del conductor de la línea. El costo del conductor que se va a instalar, sumado con el costo de la mano de obra requerida para la instalación, debe ser compensado por el beneficio producido con la disminución del costo asociado a las pérdidas de energía. Este artículo desarrolla una metodología con la que se encuentra una propuesta de nueva configuración de calibres del conductor para cada segmento de los alimentadores del sistema, de tal manera que se minimicen los costos totales