The histidine phosphocarrier kinase/phosphorylase from bacillus subtilis is an oligomer in solution with a high thermal stability

The histidine phosphocarrier protein (HPr) kinase/phosphorylase (HPrK/P) modulates the phosphorylation state of the HPr protein, and it is involved in the use of carbon sources by Gram-positive bacteria. Its X-ray structure, as concluded from crystals of proteins from several species, is a hexamer; however, there are no studies about its conformational stability, and how its structure is modified by the pH. We have embarked on the conformational characterization of HPrK/P of Bacillus subtilis (bsHPrK/P) in solution by using several spectroscopic (namely, fluorescence and circular dichroism (CD)) and biophysical techniques (namely, small-angle X-ray-scattering (SAXS) and dynamic light-scattering (DLS)). bsHPrK/P was mainly a hexamer in solution at pH 7.0, in the presence of phosphate. The protein had a high conformational stability, with an apparent thermal denaturation midpoint of ~70¿ C, at pH 7.0, as monitored by fluorescence and CD. The protein was very pH-sensitive, precipitated between pH 3.5 and 6.5; below pH 3.5, it had a molten-globule-like conformation; and it acquired a native-like structure in a narrow pH range (between pH 7.0 and 8.0). Guanidinium hydrochloride (GdmCl) denaturation occurred through an oligomeric intermediate. On the other hand, urea denaturation occurred as a single transition, in the range of concentrations between 1.8 and 18 µM, as detected by far-UV CD and fluorescence

Caracterización de la durabilidad del hormigón sometido a ciclos hielo deshielo mediante modelos micromecánicos

En este trabajo se exponen los resultados previos de la caracterización de la durabilidad del hormigón frente a los ciclos hielo-deshielo mediante la micromecánica. Los modelos micromecánicos permiten estudiar las propiedades globales del material en función de las propiedades microestructurales de las fases constituyentes: propiedades elásticas, fracción de volumen, distribución y orientación de las heterogeneidades así como su geometría. El trabajo se divide en dos partes, un estudio teórico y una posterior validación experimental. En el estudio teórico se aborda el comportamiento de la velocidad a partir de la variación de las características microestructurales por este tipo de deterioro. Estas predicciones se han comparado con las medidas de velocidad ultrasónica, mostrando buenos resultados

Parallel Multi-Objective Evolutionary Algorithms: A Comprehensive Survey

Multi-Objective Evolutionary Algorithms (MOEAs) are powerful search techniques that have been extensively used to solve difficult problems in a wide variety of disciplines. However, they can be very demanding in terms of computational resources. Parallel implementations of MOEAs (pMOEAs) provide considerable gains regarding performance and scalability and, therefore, their relevance in tackling computationally expensive applications. This paper presents a survey of pMOEAs, describing a refined taxonomy, an up-to-date review of methods and the key contributions to the field. Furthermore, some of the open questions that require further research are also briefly discussed

Estudio de las observaciones en rayos X de varias fulguraciones solares originadas en la misma región activa

Se han analizado los datos en Rayos X en el rango de energía 3.5-3.0 keV obtenidos por el Hard X-ray Spectrometer (HXIS) del satélite SMM, correspondiente a cuatro fulguraciones solares originadas en la misma región activa. Se trata de buscar similitudes en la morfología del campo magnético que las produce y las posibles coincidencias en las formas de liberación de energía. Se ha encontrado un corrimiento en el abrillantamiento de los rayos X duros que nos permiten sugerir la presencia de reconección magnética como fuente de suministro de la energía liberada en la fulguración.Asociación Argentina de Astronomí

Fulguraciones solares en regiones activas complejas

Se analizan características de fulguraciones solares definidas a partir de datos obtenidos por el Harx X-Ray Imaging Spectrometer a bordo del SMM y de observatorios terrestres, que incluyan evolución espacio-temporal de los rayos X duros, dependencia con el tiempo del contenido de energía térmica en distintas estructuras magnéticas, dureza e impulsividad de la emisión de rayos X duros, relación con la intensidad y morfología del campo magnético. De las observaciones se deducen propiedades sobre la liberación y almacenamiento de energía en distintas zonas de la región activa donde se producen las fulguraciones.Asociación Argentina de Astronomí

Balance energético de la fulguración solar del 12 de noviembre de 1980

Estudiamos las características temporales y espaciales de la emisión en rayos X en el rango de energía 3.5-30 keV de la fulguración solar del 12 de noviembre de 1980. Los datos fueron obtenidos por el Hard X-Ray Imaging Spectrometer a bordo del satélite Solar Maximum Mission. Para nuestro análisis utilizamos también datos de otros intrumentos que volaron en el mismo satélite como el Hard-Ray Burst Spectrometer. Del balance de energía entre las distintas regiones del loop deducimos que, en la etapa de liberación primaria de energía en esta fulguración son importantes tanto el procesos de aceleración de partículas como la formación de regiones localizadas a alta temperatura.Asociación Argentina de Astronomí

Evaluation offreeze-thaw damage in concrete by ultrasonic imaging

This work studies the use of ultrasonic imaging as an evaluation tool in concrete subjected to freeze–thaw (F–T) cycles. To evaluate the damage in this deterioration process, ultrasonic velocity and attenuation images have been generated from concrete specimens with and without air-entraining agents. Two parameters have been proposed from these ultrasonic images according to our experimental setup: the non-assessable area proportion (NAAP) and a weighted average velocity in terms of the NAAP. The proposed parameters have been compared with the recommended failure criteria of the ASTM and Rilem standards, which employ ultrasonic contact measurements. The principal advantage of the use of ultrasonic images and the proposed methodology in comparison with the ultrasonic velocity measurements by contact is the possibility of detection of incipient damage caused by accelerated freeze–thaw cycles

Resorcinolic Lipids from Yucatecan Propolis

Propolis is a material produced by bees from a combination of plant exudates and wax, used to fill out cracks in the beehive and to defend against intruders and pathogenic microorganisms; it is recognized for its many biological activities and its chemical composition depends on the botanical sources close to the beehive. The objective of this investigation was to isolate and identify metabolites with antioxidant activity present in a propolis sample collected in Yucatan, Mexico. Purification of the bioactive metabolites was carried out using argentation chromatography, while the combination of 1H nuclear magnetic resonance (NMR), laser desorption ionization (LDI), gas chromatography-mass spectrometry (GC-MS) and biosynthetic origin data allowed their identification as resorcinolic lipids. Finally, the resin of Mangifera indica was identified as the botanical source of these metabolite

Observational evidences of the particle acceleration process in a solar flare

The electrons accelerated in solar flares give rise to X-ray emission through thick and thin bremsstrahlung when interacting with the plasma within the loops. We have made a detailed study of the behaviour of the hard X-ray emission for the Nov. 6 1980, 17:25 U.T. flare so as to identify these processes and get information about the energy release mechanism. The observations are in good agreement with a two component model: a thermal emission superimposed to a non-thermal one produced by a power law spectrum of accelerated electrons.Asociación Argentina de Astronomí