Spin-wave instabilities in spin-transfer-driven magnetization dynamics

We study the stability of magnetization precessions induced in spin-transfer devices by the injection of spin-polarized electric currents. Instability conditions are derived by introducing a generalized, far-from-equilibrium interpretation of spin-waves. It is shown that instabilities are generated by distinct groups of magnetostatically coupled spin-waves. Stability diagrams are constructed as a function of external magnetic field and injected spin-polarized current. These diagrams show that applying larger fields and currents has a stabilizing effect on magnetization precessions. Analytical results are compared with numerical simulations of spin-transfer-driven magnetization dynamics.Comment: 4 pages, 2 figure

Efficient adaptive pseudo-symplectic numerical integration techniques for Landau-Lifshitz dynamics

Numerical time integration schemes for Landau-Lifshitz magnetization dynamics are considered. Such dynamics preserves the magnetization amplitude and, in the absence of dissipation, also implies the conservation of the free energy. This property is generally lost when time discretization is performed for the numerical solution. In this work, explicit numerical schemes based on Runge-Kutta methods are introduced. The schemes are termed pseudo-symplectic in that they are accurate to order p, but preserve magnetization amplitude and free energy to order q > p. An effective strategy for adaptive time-stepping control is discussed for schemes of this class. Numerical tests against analytical solutions for the simulation of fast precessional dynamics are performed in order to point out the effectiveness of the proposed methods

La modélisation d'accompagnement : une méthode de recherche participative et adaptative

Ce chapitre vise à présenter la diversité dans la mise en ½uvre d'un processus de modélisation d'accompagnement, mais aussi les points communs qui en émergent. L'objectif est de décrire pour mieux comprendre, sans intention normative. Nous nous appuyons sur l'analyse des cas d'études et des documents listés dans l'introduction. Notre analyse rassemble des cas concrets et des pratiques qui se réclament de la modélisation d'accompagnement et qui seront donc considérés comme tels dans notre analyse. La compatibilité de la diversité observée avec le cadre d'une adhésion aux principes initiaux de la charte sort du cadre de ce chapitre, elle est traitée dans la conclusion générale de l'ouvrage

Influenza di alcune pratiche di condizionamento sulla shelf-life di frutti di fico d'India della varietà "gialla"

"Gialla" cactus pears were subjected to various conditioning treatments (packaging, UV exposure and anaerobic shock) prior to were transferred to cold storage or retail conditions. Film packaging reduced significantly weight loss, chilling injury symptoms and maintained freshness of the fruit, while the anaerobic treatment acted only in reducing weight loss during the cold storage. Ultraviolet exposure was detrimental for the overall fruit quality

Variazioni qualitative dei frutti di arancio "Tardivo di san Vito" durante la frigoconservazione

"Tardivo di san Vito" orange fruits, a local late ripening cultivar, were cold stored. Harvesting took place in the second half of April from trees grafted on sour orange at the experimental station of CNR at Oristano. Fruit were selected for minimal blemishes and size and randomly divided in two plots before being cold stored at 3 or 8°C and 95% of relative humidity (RH) for 12 weeks. Fruits were transferred to 20°C and 70% RH after 6 and 12 weeks of cold storage to simulate shelf-life (SL). Fruits were inspected at harvest and at the end of both cold storage and SL periods for the following parameters: overall appearance, main chemical parameters (pH, titrable acidity, total soluble solids, ascorbic acid). Percent weight loss, decay and chilling injury incidence were also recorded at the above cited inspection times, except harvest. Results clearly indicate that "Tardivo di San Vito" orange fruit can withstand the lowest storage temperature of this trial. In fact, fruits show an excellent resistance to pathological breakdown, to chilling injury and maintain a good quality during the whole storage period. Si riferisce su una prova di frigoconservazione di frutti di arancio "Tardivo di san Vito", che costituisce una varietà locale a maturazione tardiva con discrete caratteristiche organolettiche. I frutti sono stati raccolti nella seconda decade di Aprile da alberi innestati su arancio amaro, presso l'agrumeto sperimentale del CNR ad Oristano. All'arrivo in laboratorio, dopo una selezione volta a scartare i frutti che presentavano difetti o danni meccanici, il campione e stato suddiviso in due lotti, corrispondenti a due regimi termici di conservazione. La refrigerazione è stata condotta alle temperature di 3 e 8°C e 90% di umidità relativa (UR) per un periodo totale di 12 settimane. Al termine della sesta e dodicesima settimana la metà di ogni lotto è stata trasferita a 20°C e 70% di UR per simulare le condizioni di mercato (SL). Alla raccolta e al termine dei succitati periodi sono stati determinati i seguenti parametri: analisi soggettiva dell'aspetto esterno, principali parametri chimici (pH, acidità titolabile, solidi solubili totali, acido ascorbico). Al termine di ogni periodo di conservazione sono state, inoltre, rilevate le percentuali di calo peso e di marciumi e rilevati i danni da freddo sull'epicarpo. I risultati ottenuti evidenziano una ottima conservabilità anche alla temperatura più bassa. Infatti, i frutti sono risultati resistenti alle alterazioni patologiche, agli stress da freddo e hanno mantenuto delle caratteristiche di commerciabilità accettabili per tutta la durata della prova

Alginate microspheres of Bacillus subtilis

La microencapsulación de organismos ha sido considerada como una alternativa de inmovilización de células, a finde que éstas puedan ejercer sus funciones en forma gradual. El objetivo del presente estudio fue elaborar microesferasde Bacillus subtilis ya sea en forma esporulada como vegetativa.Microesferas de Bacillus subtilis son preparadas utilizando alginato de sodio. Algunas propiedades típicas del sistemamicroencapsulado, tales como contenido de microorganismos, tamaño de partícula y tiempo de germinación han sidoestudiados. Las microesferas se prepararon mediante el método de coaservación-separación de fases, utilizando unaetapa intermedia de emulsión múltiple. Las condiciones de preparación han sido lo suficientemente benignas parano producir cambios en las propiedades biológicas generales del sistema, pero con la protección que le otorga lamatriz del hidrogel, la cual evita la directa comunicación con el medio externo.La viabilidad demostrada por las microesferas con las formas esporuladas fue significativamente superior a las delas formas vegetativas

Staphylococcal enterotoxins and enzymes in presence of essential oils

Nuestro objetivo fue investigar el efecto de concentraciones subinhibitorias de clavo, canela, y tomillo en el crecimiento de S aureus y en la producción de coagulasa, termonucleasa y enterotoxina. Con ese fi n se agregaron diferentes concentraciones de los aceites esenciales a Caldo Cerebro Corazón. La producción de enterotoxina en presencia y en ausencia de los aceites esenciales se determinó por la técnica de enzimoinmunoensayo (ELISA). Nuestros resultados indican que bajas concentraciones que no afectan el crecimiento, reducen la producción de la producción de las enzimas ensayadas y de enterotoxina El aceite esencial de tomillo es el que presenta mayor actividad pues al 0,04% produce la pérdida de la actividad de ambas enzimas y de la enterotoxicidad Esto es importante cuando consideramos su potencial aplicación en alimentos y en la industria farmacéutica.Our aim was to investigate the effect of subinhibitory concentrations of clove, cinnamon, and thyme essential oils on the growth of Staphylococcus aureus and its production of coagulase, thermonuclease and enterotoxin. Different concentrations of the essential oils were added to Brain Heart Infusion broth. The production of enterotoxin in the presence or absence of essential oils was estimated using the ELISA technique. Our results indicate that a lower concentration did not affect the growth S. aureus but reduced the production of metabolites. Thyme oil presents the most signifi cant effect, inhibiting the activity of both enzymes and the production of enterotoxin with 0,04%. There is a renewed interest in the potential application of these essential oils in the food and pharmaceutical industries to control staphylococcal poisoning