992 resultados para stability transition


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Lihasikojen E-vitamiinin tarve ruokittaessa vastapuidulla ohralla ja rehuun lisätyn E-vitamiinin vaikutus lihan pakastussäilyvyyteen ja syöntilaatuun

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We present an experimental study of the premartensitic and martensitic phase transitions in a Ni2MnGa single crystal by using ultrasonic techniques. The effect of applied magnetic field and uniaxial compressive stress has been investigated. It has been found that they substantially modify the elastic and magnetic behavior of the alloy. These experimental findings are a consequence of magnetoelastic effects. The measured magnetic and vibrational behavior agrees with the predictions of a recently proposed Landau-type model [A. Planes et al., Phys. Rev. Lett. 79, 3926 (1997)] that incorporates a magnetoelastic coupling as a key ingredient.

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We investigate the depinning transition occurring in dislocation assemblies. In particular, we consider the cases of regularly spaced pileups and low-angle grain boundaries interacting with a disordered stress landscape provided by solute atoms, or by other immobile dislocations present in nonactive slip systems. Using linear elasticity, we compute the stress originated by small deformations of these assemblies and the corresponding energy cost in two and three dimensions. Contrary to the case of isolated dislocation lines, which are usually approximated as elastic strings with an effective line tension, the deformations of a dislocation assembly cannot be described by local elastic interactions with a constant tension or stiffness. A nonlocal elastic kernel results as a consequence of long-range interactions between dislocations. In light of this result, we revise statistical depinning theories of dislocation assemblies and compare the theoretical results with numerical simulations and experimental data.

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The heat exchanged at the low-temperature first-order magnetostructural transition is directly measured in Gd5Ge4 . Results show that the origin and the temperature dependence of the heat exchanged varies with the reversible/irreversible character of the first-order transition. In the reversible regime, the heat exchanged by the sample is mostly due to the latent heat at the transition and decreases with decreasing temperature, while in the irreversible regime, the heat is irreversibly dissipated and increases strongly with decreasing temperature, reaching a value of 237 J/kg at 4 K.

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The occurrence of cardiovascular diseases (CVD) and related risk factors was evaluated in Seychelles, a middle level income country, as accumulating evidence supports increasing rates of CVD in developing countries. CVD mortality was obtained from vital statistics for two periods, 1984-5 and 1991-3. CVD morbidity was estimated by retrospective review of discharge diagnoses for all admissions to medical wards in 1990-1992. Levels of CVD risk factors in the population were assessed in 1989 through a population-based survey. In 1991-93, standardized mortality rates were in males and females respectively, 80.9 and 38.8 for cerebrovascular disease and 92.9 and 47.0 for ischemic heart disease. CVD accounted for 25.2% of all admissions to medical wards. Among the general population aged 35-64, 30% had high blood pressure, 52% of males smoked, and 28% of females were obese. These findings substantiate the current health transition to CVD in Seychelles. More generally, epidemiologic data on CVD mortality, morbidity, and related risk factors, as well as similar indicators for other chronic diseases, should more consistently appear in national and international reports of human development to help emphasize, in the health policy making scene, the current transition to chronic diseases in developing countries and the subsequent need for appropriate control and prevention programs.

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A spatially flat Robertson-Walker spacetime driven by a cosmological constant is nonconformally coupled to a massless scalar field. The equations of semiclassical gravity are explicitly solved for this case, and a self-consistent de Sitter solution associated with the Bunch-Davies vacuum state is found (the effect of the quantum field is to shift slightly the effective cosmological constant). Furthermore, it is shown that the corrected de Sitter spacetime is stable under spatially isotropic perturbations of the metric and the quantum state. These results are independent of the free renormalization parameters.

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Studies testing the High Energy Moisture Characteristic (HEMC) technique in tropical soils are still incipient. By this method, the effects of different management systems can be evaluated. This study investigated the aggregation state of an Oxisol under coffee with Brachiaria between crop rows and surface-applied gypsum rates using HEMC. Soil in an experimental area in the Upper São Francisco region, Minas Gerais, was studied at depths of 0.05 and 0.20 m in coffee rows. The treatments consisted of 0, 7, and 28 Mg ha-1 of agricultural gypsum rates distributed on the soil surface of the coffee rows, between which Brachiaria was grown and periodically cut, and compared with a treatment without Brachiaria between coffee rows and no gypsum application. To determine the aggregation state using the HEMC method, soil aggregates were placed in a Büchner funnel (500 mL) and wetted using a peristaltic pump with a volumetric syringe. The wetting was applied increasingly at two pre-set speeds: slow (2 mm h-1) and fast (100 mm h-1). Once saturated, the aggregates were exposed to a gradually increasing tension by the displacement of a water column (varying from 0 to 30 cm) to obtain the moisture retention curve [M = f (Ψ) ], underlying the calculation of the stability parameters: modal suction, volume of drainable pores (VDP), stability index (slow and fast), VDP ratio, and stability ratio. The HEMC method conferred sensitivity in quantifying the aggregate stability parameters, and independent of whether gypsum was used, the soil managed with Brachiaria between the coffee rows, with regular cuts discharged in the crop row direction, exhibited a decreased susceptibility to disaggregation.

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The closing of the RIO does not mean that the recovery process is complete for Iowa families and communities. The recovery process will continue for many years to come, and the Rebuild Iowa Transition Strategy has been drafted to provide a comprehensive set of recommended action steps to help the state complete long-term recovery efforts while better preparing the state for future disasters. This report begins with a review of the twelve major Rebuild Iowa Advisory Commission (RIAC) recommendations which have guided RIO’s work, followed by a summary of the major accomplishments toward each recommendation. Complete, detailed information on all the work that has been accomplished toward the RIAC recommendations can be found in the RIO’s Quarterly Reports. The identification of remaining needs and issues serves as the basis for the transition strategy.

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A stochastic nonlinear partial differential equation is constructed for two different models exhibiting self-organized criticality: the Bak-Tang-Wiesenfeld (BTW) sandpile model [Phys. Rev. Lett. 59, 381 (1987); Phys. Rev. A 38, 364 (1988)] and the Zhang model [Phys. Rev. Lett. 63, 470 (1989)]. The dynamic renormalization group (DRG) enables one to compute the critical exponents. However, the nontrivial stable fixed point of the DRG transformation is unreachable for the original parameters of the models. We introduce an alternative regularization of the step function involved in the threshold condition, which breaks the symmetry of the BTW model. Although the symmetry properties of the two models are different, it is shown that they both belong to the same universality class. In this case the DRG procedure leads to a symmetric behavior for both models, restoring the broken symmetry, and makes accessible the nontrivial fixed point. This technique could also be applied to other problems with threshold dynamics.

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RESUME L'étude de la médecine à la Faculté de l'Université de Lausanne est un cursus de six ans. Depuis la réforme générale du curriculum en octobre 1995, le programme de la deuxième année consacrée à l'étude de l'être humain sain a été transformé. L'enseignement intégré par système ou organe a été introduit en remplaçant l'enseignement par discipline. Parallèlement, un système d'évaluation de l'enseignement par les étudiants a été proposé. Il a été amélioré au fil des années et depuis l'année académique 1998-99, l'évaluation est devenue systémique et régulière. Notre étude présente et compare les résultats des évaluations de l'enseignement et des enseignants de neuf cours intégrés dispensés en deuxième année durant deux années académiques (1998-99 et 1999-2000). Une forte corrélation entre les résultats des deux années consécutives ainsi qu'une importante disparité des estimations à l'intérieure de chacune de deux années ont été observées. Ceci démontre un engagement sérieux des étudiants dans le processus d'évaluation, révèle la pertinence de leur analyse et leur bonne capacité de discernement. L'analyse de nos résultats montre que les évaluations effectuées par les étudiants peuvent constituer une source fiable d'informations et contribuer à l'amélioration du processus d'enseignement.

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We numerically study the dynamical properties of fully frustrated models in two and three dimensions. The results obtained support the hypothesis that the percolation transition of the Kasteleyn-Fortuin clusters corresponds to the onset of stretched exponential autocorrelation functions in systems without disorder. This dynamical behavior may be due to the large scale effects of frustration, present below the percolation threshold. Moreover, these results are consistent with the picture suggested by Campbell et al. [J. Phys. C 20, L47 (1987)] in the space of configurations.

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We study a model for water with a tunable intramolecular interaction Js, using mean-field theory and off-lattice Monte Carlo simulations. For all Js>~0, the model displays a temperature of maximum density. For a finite intramolecular interaction Js>0, our calculations support the presence of a liquid-liquid phase transition with a possible liquid-liquid critical point for water, likely preempted by inevitable freezing. For J=0, the liquid-liquid critical point disappears at T=0.