Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations

Hippocampal Memory Recovery After Acute Stress: A Behavioral, Morphological and Molecular Study

Indexación: Scopus.Laboratory of Neuroplasticity and Neurogenetics, Department of Biochemistry and Molecular Biology, Faculty of Chemistry and Pharmaceutical Sciences, Universidad de Chile, Santiago, Chile, 2Laboratorio Farmacología del Comportamiento, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile, 3Department of Kinesiology, Faculty of Health Sciences, Universidad Católica del Maule, Talca, Chile, 4Facultad de Psicología, Universidad de Talca, Talca, Chile, 5Instituto de Ciencias Biomédicas, Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago, Chile, 6Escuela de Química y Farmacia, Facultad de Medicina, Universidad Andres Bello, Santiago, Chile.This study was supported by the following grants: Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) 1120528 (JLF), Fondo Central de Investigación, Universidad de Chile ENL025/16 (JLF).Several studies have shown that a single exposure to stress may improve or impair learning and memory processes, depending on the timing in which the stress event occurs with relation to the acquisition phase. However, to date there is no information about the molecular changes that occur at the synapse during the stress-induced memory modification and after a recovery period. In particular, there are no studies that have evaluated—at the same time—the temporality of stress and stress recovery period in hippocampal short-term memory and the effects on dendritic spine morphology, along with variations in N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits. The aim of our study was to take a multidimensional approach to investigate concomitant behavioral, morphological and molecular changes induced by a single restraint stress exposure (2.5 h) and a recovery period of 6 and 24 h in rats. We found that acute stress elicited a reduced preference to explore an object placed in a novel position (a hippocampal-dependent task). These changes were accompanied by increased activity of LIM kinase I (LIMK; an actin-remodeling protein) and increased levels of NR2A subunits of NMDA receptors. After 6 h of recovery from stress, rats showed similar preference to explore an object placed in a novel or familiar position, but density of immature spines increased in secondary CA1 apical dendrites, along with a transient rise in GluA2 AMPA receptor subunits. After 24 h of recovery from stress, the animals showed a preference to explore an object placed in a novel position, which was accompanied by a normalization of NMDA and AMPA receptor subunits to control values. Our data suggest that acute stress produces reversible molecular and behavioral changes 24 h after stress, allowing a full reestablishment of hippocampal-related memory. Further studies need to be conducted to deepen our understanding of these changes and their reciprocal interactions.Adaptive stress responses are a promising avenue to develop interventions aiming at restoring hippocampal function impaired by repetitive stress exposure. © 2018 Aguayo, Tejos-Bravo, Díaz-Véliz, Pacheco, García-Rojo, Corrales, Olave, Aliaga, Ulloa, Avalos, Román-Albasini, Rojas and Fiedler.https://www.frontiersin.org/articles/10.3389/fnmol.2018.00283/ful

Cysteinyl-tRNA synthetase is a direct descendant of the first aminoacyl-tRNA synthetase

AbstractThe gene encoding the cysteinyl-tRNA synthetase of E. coli was cloned from an E. coli genomic library made in λ2761, a lambda vector which can integrate and which carries a chloramphenicol resistance gene. A thermosensitive cysS mutant of E. coli was lysogenised and chloramphenicol-resistant colonies able to grow at 42°C were selected to isolate phages containing the wild-type cysS gene. The sequence of the gene was determined. It codes for a 461 amino-acid protein and includes the sequences HIGH and KMSK known to be involved in the ATP and TRNA binding respectively of class I synthetases. The cysteinyl enzyme has segments in common with the cytoplasmic leucyl-tRNA synthetase of Neurospora crassa, the tryptophanyl-tRNA synthetase of Bacillus stearothermophilus, and the phenylalanyl-tRNA synthetase of Saccharomyces cerevisiae. Sequence comparisons show that the amino end of the cysteinyl-tRNA synthetase has similarities with prokaryotic elongation factors Tu; this region is close to the equivalent acceptor binding domain of the glutaminyl-tRNa synthetase of E. coli. There is a further similarity with the seryl enzyme (a class II enzyme) which has led us to propose that both classes had a common origin and that this was the ancestor of the cysteinyl-tRNA synthetase

Modélisation hydrologique globale conceptuelle appliquée aux petits bassins versants en zone semi-aride du nord-Mexique

Dans le cadre d'une collaboration entre le CENID-RASPA (Centro National de Investigación Disciplinaria - Relación Agua, Suelo, Planta y Atmosfera, México) et l'IRD (anciennement ORSTOM, France), sept petites retenues du ranch Atotonilco, ranch d'élevage extensif situé au Nord-Mexique dans une zone semi-aride montagneuse, ont été équipées pour l'enregistrement en continu des niveaux d'eau (1996-1998). Des pluviomètres et pluviographes ont été installés sur leurs bassins versants (0,15 à 4,10 km2) et répartis sur toute la surface du ranch (450 km2). Par ailleurs, une soixantaine de petits barrages équipent ce ranch. En période pluvieuse ils complètent l'alimentation en eau du bétail, assurée principalement par des forages. L'objectif général de l'étude menée par le CENID-RASPA est d'analyser quel est et quel pourrait être le rôle de ces petits barrages dans l'alimentation en eau du ranch.À l'échelle des bassins versants, l'analyse des relations entre la hauteur de pluie et la lame ruisselée montre que la prise en compte de l'intensité de pluie est nécessaire pour expliquer le ruissellement. Dans ce but, un modèle hydrologique global conceptuel a été défini utilisant les notions :- d'intensité de pluie limite du ruissellement (IL),- d'indice des pluies antérieures (IK)- de pluie utile (PUIL), somme des pluies dont l'intensité, pour une même averse, dépasse la valeur limite IL.Les averses sans ruissellement et avec un faible ruissellement servent à définir la relation entre IL et IK. Deux paramètres définissent les relations hydro-pluviométriques : le coefficient de croissance parabolique E et le paramètre de position F, associé à l'origine des ruissellements. Le paramètre de position F varie en fonction de l'indice des pluies antérieures et tend à s'annuler pour une forte valeur de IK. Le paramètre E varie peu pour un même bassin, sauf lorsque deux averses sont espacées de moins de 24 heures et lorsque le couvert végétal herbeux est très dégradé. Dans ces deux cas, le coefficient E est nettement plus élevé, parfois trop élevé pour l'utilisation d'une relation parabolique.Les relations ainsi définies ont été utilisées pour calculer de longues séries d'apports journaliers dans les petits barrages du ranch Atotonilco (ESTRADA AVALOS, 1999).In a co-operative programme between CENID RASPA (Centro National de Investigación Disciplinaria - Relación Agua, Suelo, Planta y Atmosfera, México) and IRD (formerly ORSTOM, France), seven small dams were equipped for hydrological measurements in an extensive breeding system, the ranch Atotonilco, located in a semi-arid area of northern Mexico. The main aim of the equipment was to follow the surface water in the water supply system of the ranch (ESTRADA AVALOS, 1999). In order to analyse the role of the seven small dams, it was necessary to understand the hydrological conditions of their filling and emptying. Also, manual and automatic rain gauges were installed on small experimental watersheds (0.15 to 5 km2) and on the ranch (450 km2), and in addition evaporation pans and a floating pan were placed on the banks of a few dams and in a reservoir (THIEBAUX, 2000).The aim of this paper is to present the overall conceptual hydrological model used to calculate runoff in the small catchments in the Atotonilco ranch, considering that it was necessary to utilise the rainfall intensities to explain the surface runoff. Hydrological observations were made from 1996 to 1998 on the Atotonilco ranch. Spatial analysis of the rainfall demonstrated the existence of several types of storms: those with a small extension (17 km2), with a middle extension (160 km2) or with a great extension (more than 450 km2). The average distance between two isohyets with a deviation of 10 mm varied from 2 to 3 km. In this semi-arid area, obtaining rainfall measurements of good precision requires a dense rain gauge network. On the small catchment scale it was necessary to put three or four rain gauges in each river basin.On the scale of small catchments, the analysis of the relationship between the amount of rainfall and surface runoff showed that rainfall intensity explained very clearly the surface runoff. This led us to the construction of a lumped model using the following criteria:- rainfall intensity limit of surface runoff (IL), with a time step of 30 min,- forward rainfall index (IK),- useful rainfall (PUIL), sum of the depths of rainfall with intensities higher than the limit value of IL.Experimental measures without runoff and with surface runoff have been used to describe the variation of the rainfall intensity limit of the surface runoff (IL), which decreases exponentially with increasing forward rainfall index (IK). This index IK is defined as the sum of the previous rainfall andthe previous index, which decreases in an exponential manner with the time interval ?t expressed in days (and partial days) between two successive showers (LINSLEY et al., 1949). The interval dt, which defines the rainfall intensity, depends on the time of concentration in the small catchments. On the Atotonilco ranch, the correlations between rainfall intensities for different intervals and surface runoff demonstrated that a 30-min interval provided the best results. However, we did not obtain significant correlations between surface runoff and different values of the exponential decreasing coefficient of IL as a function of IK (a).Considering the results obtained by ESTRADA AVALOS (1999) on the scale of experimental plots (60 m2), we have chosen the value a ?=0.1 day-1. This value increases IK during the rainy season when increasing soil moisture and grass cover growth, but these two factors have opposite effects on the surface runoff.Two parameters define the quadratic relationships between the useful depth of rainfall and the surface runoff: the parabolic increasing coefficient (E) and the position coefficient (F). It is possible to determine the position coefficient F with the value of the useful rainfall (PUIL0) which gives a null value to the depth of surface runoff.Using the observations collected from 1996-1998, we demonstrated that the position coefficient F decreased linearly with an increasing forward rainfall index IK. In addition, the parabolic increasing coefficient E was constant in the same basin, except when the storms were spaced less than 24 h apart and when the grass cover was low at the beginning of the rainfall season (1996). In these two cases, the runoff aptitude of the watersheds was clearly greater resulting in a higher E coefficient, which was sometimes too high for a parabolic relationship. It would be better to extrapolate above the limit value of PUIL taking into consideration that the additional runoff is equal to the additional useful rainfall.In order to validate the calibration of this model we used the criterion of NASH and SUTCLIFFE (1970). This criterion was calculated only for the year of 1996 but for two scenarios: the first scenario considered the parameter F as a constant and the second scenario allowed for a linear decrease of this parameter with the forward rainfall index IK. The results demonstrated that it was always better to use, for the position parameter F, a linearly decreasing relationship with the index IK.The relationships defined for the seven experimental catchments in the Atotonilco ranch were used to calculate long daily chronic inflows into the little dams (ESTRADA AVALOS, 1999). The hydrological parameters were also mixed with the natural characteristics of the small catchments in order to perform a principal components analysis of the relationships between hydrological parameters and natural criteria. Rules for the transposition of the parameters of this quadratic model on the Atotonilco ranch were established using the results of the analysis

Kinetics of Particles Adsorption Processes Driven by Diffusion

The kinetics of the deposition of colloidal particles onto a solid surface is analytically studied. We take into account both the diffusion of particles from the bulk as well as the geometrical aspects of the layer of adsorbed particles. We derive the first kinetic equation for the coverage of the surface (a generalized Langmuir equation) whose predictions are in agreement with recent simulation results where diffusion of particles from the bulk is explicitly considered.Comment: 4 page

PLoS One

Estimating and selecting risk factors with extremely low prevalences of exposure for a binary outcome is a challenge because classical standard techniques, markedly logistic regression, often fail to provide meaningful results in such settings. While penalized regression methods are widely used in high-dimensional settings, we were able to show their usefulness in low-dimensional settings as well. Specifically, we demonstrate that Firth correction, ridge, the lasso and boosting all improve the estimation for low-prevalence risk factors. While the methods themselves are well-established, comparison studies are needed to assess their potential benefits in this context. This is done here using the dataset of a large unmatched case-control study from France (2005-2008) about the relationship between prescription medicines and road traffic accidents and an accompanying simulation study. Results show that the estimation of risk factors with prevalences below 0.1% can be drastically improved by using Firth correction and boosting in particular, especially for ultra-low prevalences. When a moderate number of low prevalence exposures is available, we recommend the use of penalized techniques

Examining Incoming Credit Differences Between First-Year and Transfer Students

In this study, the difference in the number of initial credits between incoming transfer and first-year students entering a land grant university in a professional education program was examined (N = 488). A multivariate analysis of variance revealed that transfer students transferred significantly more total credits and more credits that counted toward degree programs than did first-year students. Undergraduates who had graduated from small high schools transferred more credits and more credits that counted than did those from large high schools. However, first-year students transferred a significantly higher percentage of total credits that counted toward the degree programs than did transfer students. Implications for advisors, institutions, and policy makers are discussed

Chirality, magnetism and light

No abstract available