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991.
Moser Guillaume Tschamber Valérie Schönnenbeck Cornelius Brillard Alain Brilhac Jean-François 《Journal of Thermal Analysis and Calorimetry》2019,136(5):2145-2155
Journal of Thermal Analysis and Calorimetry - With high energy densities, metals appear as innovative energy carriers. In the present study, magnesium powder is considered as fuel for energy... 相似文献
992.
Guillaume Bal 《Communications in Mathematical Physics》2009,292(2):457-477
We consider the perturbation of parabolic operators of the form ∂
t
+ P(x, D) by large-amplitude highly oscillatory spatially dependent potentials modeled as Gaussian random fields. The amplitude of
the potential is chosen so that the solution to the random equation is affected by the randomness at the leading order. We
show that, when the dimension is smaller than the order of the elliptic pseudo-differential operator P(x, D), the perturbed parabolic equation admits a solution given by a Duhamel expansion. Moreover, as the correlation length of
the potential vanishes, we show that the latter solution converges in distribution to the solution of a stochastic parabolic
equation with multiplicative noise that should be interpreted in the Stratonovich sense. The theory of mild solutions for
such stochastic partial differential equations is developed.
The behavior described above should be contrasted to the case of dimensions larger than or equal to the order of the elliptic
pseudo-differential operator P(x, D). In the latter case, the solution to the random equation converges strongly to the solution of a homogenized (deterministic)
parabolic equation as is shown in [2]. A stochastic limit is obtained only for sufficiently small space dimensions in this
class of parabolic problems. 相似文献
993.
994.
Ferlat G Charpentier T Seitsonen AP Takada A Lazzeri M Cormier L Calas G Mauri F 《Physical review letters》2008,101(6):065504
We investigate the structural and vibrational properties of glassy B2O3 using first-principles molecular dynamics simulations. In particular, we determine the boroxol rings fraction f for which there is still no consensus in the literature. Two numerical models containing either a low or a high level of boroxol rings are tested against a gamut of experimental probes (static structure factor, Raman, 11B and 17O NMR data). We show that only the boroxol-rich model (f=75%) can reproduce the full set of observables. Total-energy calculations show that at the glass density, boroxol-rich structures are favored by about 6 kcal/(mol boroxol). Finally, the liquid state is explored in the 2,000-4,000 K range and a reduction of f to 10%-20% is obtained. 相似文献
995.
996.
Nief G Gautier F Dalmont JP Gilbert J 《The Journal of the Acoustical Society of America》2008,124(2):1320-1331
The issue of the influence of wall vibrations on the behavior of wind instruments is still under debate. The mechanisms of vibroacoustic couplings involved in these vibrations are difficult to investigate, as fluid-structure interactions are weak. Among these vibroacoustic interactions, the present study is focused on the coupling between the internal acoustic field and the mechanical behavior of the duct. For this purpose, a simplified single reed instrument consisting of a brass tube connected to a clarinet mouthpiece has been studied. A theoretical model of coupling between the plane inner acoustic wave and mechanical modes is developed and suggests that in order to obtain measurable effects of wall vibrations, the geometrical parameters of the studied tube have to be unusual compared to that of real instruments. For a slightly oval-shaped and very thin brass tube, it is shown theoretically and experimentally that a coupling between the inner plane acoustic wave and ovalling mechanical modes occurs and results in disturbances of the input impedance, which can slightly affect the tone color of the sound produced. It is concluded that the reported effects are unlikely to occur in real instruments except for some organ pipes. 相似文献
997.
Guillaume A Rousselet Cyril R Pernet Patrick J Bennett Allison B Sekuler 《BMC neuroscience》2008,9(1):1-22
Background
The zitter (zi/zi) rat, a loss-of-function mutant of the glycosylated transmembrane protein attractin (atrn), exhibits widespread age-dependent spongiform degeneration, hypomyelination, and abnormal metabolism of reactive oxygen species (ROS) in the brain. To date, the mechanisms underlying these phenotypes have remained unclear.Results
Here, we show differentiation defects in zi/zi oligodendrocytes, accompanied by aberrant extension of cell-processes and hypomyelination. Axonal bundles were relatively preserved during postnatal development. With increasing in age, the injured oligodendrocytes in zi/zi rats become pathological, as evidenced by the accumulation of iron in their cell bodies. Immunohistochemical analysis revealed that atrn expression was absent from an oligodendrocyte lineage, including A2B5-positive progenitors and CNPase-positive differentiated cells. The number and distribution of Olig2-positive oligodendrocyte progenitors was unchanged in the zi/zi brain. Furthermore, an in vitro differentiation assay of cultured oligodendrocyte progenitors prepared from zi/zi brains revealed their normal competence for proliferation and differentiation into mature oligodendrocytes. Interestingly, we demonstrated the accelerated recruitment of ED1-positive macrophages/microglia to the developing zi/zi brain parenchyma prior to the onset of hypomyelination. Semiquantitative RT-PCR analysis revealed a significant up-regulation of CD26 and IL1-β in the zi/zi brain during this early postnatal stage.Conclusion
We demonstrated that the onset of the impairment of oligodendrocyte differentiation occurs in a non-cell autonomous manner in zi/zi rats. Hypomyelination of oligodendrocytes was not due to a failure of the intrinsic program of oligodendrocytes, but rather, was caused by extrinsic factors that interrupt oligodendrocyte development. It is likely that macrophage/microglial activation in the zi/zi CNS leads to disturbances in oligodendrocyte differentiation via deleterious extrinsic factors, such as the cytokine IL1-β or ROS. Atrn might be involved in the activation of brain macrophages/microglia by suppressing excessive migration of monocytes into the CNS, or by accelerating the transformation of brain monocytes into resting microglia. Understanding the pathogenesis of the zi/zi rat may provide novel insights into the developmental interaction betweens macrophages/microglia and cells of an oligodendrocyte lineage. 相似文献998.
The structure and dynamics of vortex filaments that form the cores of scroll waves in three-dimensional oscillatory media described by the complex Ginzburg-Landau equation are investigated. The study focuses on the role that twist plays in determining the bifurcation structure in various regions of the (alpha,beta) parameter space of this equation. As the degree of twist increases, initially straight filaments first undergo a Hopf bifurcation to helical filaments; further increase in the twist leads to a secondary Hopf bifurcation that results in supercoiled helices. In addition, localized states composed of superhelical segments interspersed with helical segments are found. If the twist is zero, zigzag filaments are found in certain regions of the parameter space. In very large systems disordered states comprising zigzag and helical segments with positive and negative senses exist. The behavior of vortex filaments in different regions of the parameter space is explored in some detail. In particular, an instability for nonzero twist near the alpha=beta line suggests the existence of a nonsaturating state that reduces the stability domain of straight filaments. The results are obtained through extensive simulations of the complex Ginzburg-Landau equation on large domains for long times, in conjunction with simulations on equivalent two-dimensional reductions of this equation and analytical considerations based on topological concepts. 相似文献
999.
We address the general case of sampling the Fourier spectrum of an incoherent object by extending the possibilities of the computerized optical sampler described in a previous paper. Because such a spectrum is hermitian, pairs of sampling slits are still used as pupils of an imaging system; but we take advantage of multiple measurements performed in the image plane for computing the amplitude and phase of each spectral component. The principle of multiplexed measurements within a given frequencies band, using a white light source, is suggested as a conclusion. 相似文献
1000.
We report luminescence experiments performed in pure Ge at low temperature. Taking into account the splitting of the ground state of free excitons in this material, we show that their emission line shape is subject to a Gaussian broadening which seems to be due to the phonon lifetime. From this study, we deduce new values of the binding energy of electron-hole drops in Ge and Si which are respectively -2 and -5.6meV. 相似文献