Search results for "duc"
showing 10 items of 58590 documents
Influence of the MgO barrier thickness on the lifetime characteristics of magnetic tunnelling junctions for sensors
2016
Magnetic tunnelling junctions increasingly enter the market for magnetic sensor applications. Thus, technological parameters such as the lifetime characteristics become more and more important. Here, an analysis of the lifetime characteristics of magnetic tunnelling junctions using the Weibull statistical distribution for CoFeB/MgO/CoFeB junctions is presented. The Weibull distribution is governed by two parameters, the characteristic lifetime η of the population and the shape parameter β, which gives information about the presence of an infant mortality. The suitability of the Weibull distribution is demonstrated for the description of dielectric breakdown processes in MgO-based tunnelling…
Light-induced nonthermal population of optical phonons in nanocrystals
2017
Raman spectroscopy is widely used to study bulk and nanomaterials, where information is frequently obtained from spectral line positions and intensities. In this study, we monitored the Raman spectrum of ensembles of semiconductor nanocrystals (NCs) as a function of optical excitation intensity (optical excitation experiments). We observe that in NCs the red-shift of the Raman peak position with increasing light power density is much steeper than that recorded for the corresponding bulk material. The increase in optical excitation intensity results also in an increasingly higher temperature of the NCs as obtained with Raman thermometry through the commonly used Stokes/anti-Stokes intensity …
Review of the PEA Method for Space Charge Measurements on HVDC Cables and Mini-Cables
2019
This review takes into account articles and standards published in recent years concerning the application of the Pulsed Electro Acoustic (PEA) method for space charge measurement on High Voltage Direct Current (HVDC) cables and mini-cables. Since the 80s, the PEA method has been implemented for space charge measurements on flat specimens in order to investigate space charge phenomena and to evaluate the ageing of dielectrics. In recent years, this technique has been adapted to cylindrical geometry. Several studies and experiments have been carried out on the use of the PEA method for full size cables and HVDC cable models. The experiments have been conducted using different arrangements of…
MD Simulation Investigation on the Binding Process of Smoke-Derived Germination Stimulants to Its Receptor
2019
Karrikins (KARs) are a class of smoke-derived seed germination stimulants with great significance in both agriculture and plant biology. By means of direct binding to the receptor protein KAI2, the compounds can initiate the KAR signal transduction pathway, hence triggering germination of the dormant seeds in the soil. In the research, several molecular dynamics (MD) simulation techniques were properly integrated to investigate the binding process of KAR1 to KAI2 and reveal the details of the whole binding event. The calculated binding free energy, -7.00 kcal/mol, is in good agreement with the experimental measurement, -6.83 kcal/mol. The obtained PMF profile indicates the existence of thre…
Switching and redox isomerism in first-row transition metal complexes containing redox active Schiff base ligands.
2014
International audience; The reversible redox isomerisms in first row transition metal complexes of the type ML2 were studied. The six ML2 complexes (M = Mn(III) (), Fe(II) (), Co(III) (), Ni(II) (), Cu(II) () and Zn(II) ()) were synthesized with a redox active Schiff base ligand [2-(3,5-di-tert-butyl-2-hydroxyphenylamino)-4-chlorophenol] (H3L) presenting different oxidation states from -2 to 0 (L(2-), L(-) and L(0)). EPR spectra and magnetic susceptibility measurements indicate the presence of complexes of the type [Mn(III)(L(2-))(L(-))] () with S = 1/2, [Fe(II)(L(-))2] () with S = 2, [Co(III)(L(2-))(L(-))] () with S = 1/2, [Ni(II)(L(-))2] () with S = 1, [Cu(II)(L(-))2] () with S = 1/2 and …
Heavy enzymes and the rational redesign of protein catalysts
2019
Abstract An unsolved mystery in biology concerns the link between enzyme catalysis and protein motions. Comparison between isotopically labelled “heavy” dihydrofolate reductases and their natural‐abundance counterparts has suggested that the coupling of protein motions to the chemistry of the catalysed reaction is minimised in the case of hydride transfer. In alcohol dehydrogenases, unnatural, bulky substrates that induce additional electrostatic rearrangements of the active site enhance coupled motions. This finding could provide a new route to engineering enzymes with altered substrate specificity, because amino acid residues responsible for dynamic coupling with a given substrate present…
El pensamiento espontáneo docente sobre la ciencia y su enseñanza
2018
<span>En las dos últimas décadas la investigación en didáctica de las ciencias ha centrado su atención en el aprendizaje y, en particular, se ha caracterizado por haber estudiado en profundidad el conocimiento inicial de los estudiantes en muy diversos dominios de las ciencias. Desde hace pocos años el énfasis está derivado -y cada vez con mayor interés- hacia el estudio de la enseñanza y, en particular, hacia el de su principal artífice: el profesorado.</span>
Sostenibilidad y laboratorios escolares
2018
<span>Actualmente no es ninguna exageración afirmar que estamos viviendo una situación de verdadera emergencia planetaria, marcada por toda una serie de graves problemas estrechamente relacionados entre sí, tales como: superpoblación, contaminación, agotamiento de recursos naturales, cambio climático, pérdida de biodiversidad, lluvia ácida y destrucción de la capa de ozono. Dichos problemas, lejos de disminuir, son cada vez más intensos y extienden su impacto sobre todo el planeta. Así, en cuanto al calentamiento global, se afirma que la gravedad es tal, que si no se pone freno antes de una decena de años, después será ya demasiado tarde (Gore, 2007).</span>
La motivación de los estudiantes y la enseñanza de la Química. Una cuestión controvertida
2018
<span>El tema de la motivación de los estudiantes hacia el aprendizaje de cualquier materia científica constituye una seria preocupación para el profesorado. En primer lugar, porque los docentes constatan una falta general de interés de los alumnos hacia las disciplinas científicas como la Física y la Química. Esta percepción ha sido corroborada por los propios estudiantes en diferentes trabajos de investigación. En efecto, los propios estudiantes señalan como principales causantes de su actitud desfavorable, de su desinterés hacia la ciencia y su aprendizaje, a la enseñanza de una ciencia descontextualizada...</span>
Dificultades para la incorporación a la enseñanza de los hallazgos de la investigación e innovación en didáctica de las ciencias
2018
<span>La importancia social concedida, desde hace ya décadas, a la educación científica (Dewey 1916; Langevin, 1926) ha ido creciendo y ha experimentado, últimamente, un cambio cualitativo. En efecto, la tradicional importancia concedida a las inversiones en educación científica y tecnológica, para hacer posible el desarrollo futuro de un país, ha dejado paso al convencimiento de que la alfabetización científica de todos los ciudadanos y ciudadanas ha pasado a constituir una exigencia urgente, un requisito también para el desarrollo inmediato.</span>