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81.
A cluster model based on ab initio density-functional theory was used to model gallium-stabilized δ-plutonium alloys, and to calculate the electron-density distribution, its pressure dependence, bond lengths, elastic properties (second order and third order), and inelastic properties for Pu12Ga (7.7 at% Ga) and Pu18Ga (5.3 at% Ga). The electron distribution was found to contain localized, semi localized, and delocalized contributions, with the second possessing covalent character. Two of plutonium’s 8 valence electrons were found to be itinerant, consistent with a recent prediction based on an electrostatic model, with the electron configuration for plutonium being 7s0.57p0.55f1 (itinerant) and 6d15f5 (localized), and that for gallium being 4s14p2. Applied hydrostatic pressure shifts the charge density toward a more localized Pu(d)-based distribution. The onset of the pressure-induced δ-Pu to α-Pu phase change is accompanied by a ∼0.2 electron increase in the localized population that may serve as a driving force for the phase change. Interior bonding within the Pu12Ga subunits is stronger than that of the surrounding plutonium lattice, and the Pu-Ga bonds therein relax in a direction opposite to lattice strain. This study predicts covalency in metallic plutonium, both in the Pu-Ga bonding and in the Pu-Pu bonding. 相似文献
82.
Conway GD Borba DN Alper B Bartlett DV Gormezano C von Hellermann MG Maas AC Parail VV Smeulders P Zastrow KD 《Physical review letters》2000,84(7):1463-1466
Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB. 相似文献
83.
C. Chevallard M. Clerc P. Coullet J.-M. Gilli 《The European physical journal. E, Soft matter》2000,1(2-3):179-188
We have experimentally observed the pattern instabilities of an Ising wall formed in a nematic or cholesteric liquid crystal
layer. We have deduced an envelope equation, relevant close to the Fréedericksz transition, from which we derived an equation
for the dynamics of the interface in the vicinity of its bifurcation. In the case of the zig-zag instability, this model is
characterized by a conservative and variational order parameter whose gradient satisfies a Cahn-Hilliard equation. We have
also investigated the influence of slightly broken symmetries on the dynamical behaviour of the system. The disappearance
of the interface translational invariance or of the reflection symmetry along the wall axis may induce new interfacial patterns
which have been both experimentally and theoretically pointed out.
Received 5 August 1999 and Received in final form 13 September 1999 相似文献
84.
E. Hanelt A. Grewe K. -H. Schmidt T. Brohm H. -G. Clerc M. Dornik M. Fauerbach H. Geissel A. Magel G. Münzenberg F. Nickel M. Pfützner C. Scheidenberger M. Steiner K. Sümmerer B. Voss M. Weber J. Weckenmann C. Ziegler 《Zeitschrift für Physik A Hadrons and Nuclei》1993,346(1):43-46
The longitudinal-momentum distributions of projectile fragments from 0.8 A GeV136Xe and 1 A GeV197Au projectiles impinging on targets of beryllium and aluminium, respectively, have been measured using the projectile-fragment separator FRS at GSI. Different momentum distributions have been found for two different classes of fragmentation processes: the abundant hot fragmentation with several nucleons evaporated from the prefragments, and the rare cold fragmentation with only protons removed from the projectile, but no nucleons evaporated. The data are compared to model calculations.This article comprises part of the Ph.D. thesis of B. Voss 相似文献
85.
B. Blank S. Andriamonje R. Del Moral J. P. Dufour A. Fleury T. Josso M. S. Pravikoff S. Czajkowski Z. Janas A. Piechaczek E. Roeckl K. -H. Schmidt K. Sümmerer W. Trinder M. Weber T. Brohm H. -G. Clerc A. Grewe E. Hanelt A. Heinz A. Junghans C. Röhl S. Steinhäuser B. Voss M. Pfützner 《Zeitschrift für Physik A Hadrons and Nuclei》1995,352(1):69-75
At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of58Ni at 650 MeV/nucleon in a beryllium target. By means of aΔE—Bρ—TOF measurement, the fragments have been identified and their charge-changing probabilities in targets of CH2, C, Al, and Pb have been determined. We describe the results for the total charge-changing cross sections in this first paper, whereas a second article deals with the partial charge-changing cross sections. At the drip line, the measured charge-changing cross sections exhaust close to 100% of the total interaction cross sections as calculated with semiempirical models. The measurements at the proton drip line with low-Z targets indicate that only a very small increase of the cross sections may be observed, whereas the measurements with a lead target show that no significant increase of the total charge-changing cross sections is present which would be a hint for low-lying dipole strength. Our experimental data are compared to Glauber-type calculations. 相似文献
86.
88.
Dissipative localized structures exhibit intricate bifurcation diagrams. An adequate theory has been developed in one space dimension; however, discrepancies arise with the experiments. Based on an optical feedback with spatially modulated input beam, we set up a 1D forced configuration in a nematic liquid crystal layer. We characterize experimentally and theoretically the homoclinic snaking diagram of localized patterns, providing a reconciliation between theory and experiments. 相似文献
89.
L. Gordillo T. Sauma Y. Zárate I. Espinoza M.G. Clerc N. Mujica 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(1):39-49
Development of technologies based on localized states depends on our ability to
manipulate and control these nonlinear structures. In order to achieve this, the
interactions between localized states and control tools should be well modelled and
understood. We present a theoretical and experimental study for handling
non-propagating hydrodynamic solitons in a vertically driven rectangular water
basin, based on the inclination of the system. Experiments show that tilting the basin
induces non-propagating solitons to drift towards an equilibrium position through a
relaxation process. Our theoretical approach is derived from the parametrically driven
damped nonlinear Schr?dinger equationwhich models the system. The basin tilting effect is
modelled by promoting the parameters that characterize the system, e.g. dissipation,
forcing and frequency detuning, as space dependent functions. A motion law for these
hydrodynamic solitons can be deduced from these assumptions. The model equation, which
includes a constant speed and a linear relaxation term, nicely reproduces the motion
observed experimentally. 相似文献
90.
Marcel?G.?Clerc Micha??Kowalczyk Panayotis?SmyrnelisEmail authorView authors OrcID profile 《Journal of Nonlinear Science》2018,28(3):1079-1107
In this paper we study qualitative properties of global minimizers of the Ginzburg–Landau energy which describes light–matter interaction in the theory of nematic liquid crystals near the Fréedericksz transition. This model depends on two parameters: \(\epsilon >0\) which is small and represents the coherence scale of the system and \(a\ge 0\) which represents the intensity of the applied laser light. In particular, we are interested in the phenomenon of symmetry breaking as a and \(\epsilon \) vary. We show that when \(a=0\) the global minimizer is radially symmetric and unique and that its symmetry is instantly broken as \(a>0\) and then restored for sufficiently large values of a. Symmetry breaking is associated with the presence of a new type of topological defect which we named the shadow vortex. The symmetry breaking scenario is a rigorous confirmation of experimental and numerical results obtained earlier in Barboza et al. (Phys Rev E 93(5):050201, 2016). 相似文献