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31.
Abstract Recent observation of the acoustic saturation and of phonon echoes in crystalline quartz after light irradiation with fast neutrons indicates that there are the same low-energy atomic tunnelling systems as in Si02 glass. We report measurements of the diffuse X-ray scattering and of the lattice parameter change from neutron irradiated quartz single crystals studying the strength and symmetry of strain defects and their local correlations. For dose 3 × 1018 n/cm2 the diffuse scattering close to the Bragg peaks together with the lattice parameter change shows that the neutrons create defective regions with a volume change of 29 mean atomic volumes. The distortion field of these regions shows no high symmetry. The radius of the heavily strained region is ~ 10 Å. For higher doses the regions grow a little bit but mainly new defective regions are built. According to the various volume fractions of defective regions at various doses the first strong amorphous halo at about K≈ 1.5 A?1 was detected. Since this amorphous scattering is isotropic and during annealing the regions disappear mainly without changing their size we are led to the conclusion that the defective regions are glass-like in nature. So the size of the tunnelling system has to be smaller than 20 Å. 相似文献
32.
A. D. Fitt D. P. Mason E. A. Moss 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(6):1049-1067
The propagation of a two-dimensional fluid-driven fracture in impermeable rock is considered. The fluid flow in the fracture
is laminar. By applying lubrication theory a partial differential equation relating the half-width of the fracture to the
fluid pressure is derived. To close the model the PKN formulation is adopted in which the fluid pressure is proportional to
the half-width of the fracture. By considering a linear combination of the Lie point symmetries of the resulting non-linear
diffusion equation the boundary value problem is expressed in a form appropriate for a similarity solution. The boundary value
problem is reformulated as two initial value problems which are readily solved numerically. The similarity solution describes
a preexisting fracture since both the total volume and length of the fracture are initially finite and non-zero. Applications
in which the rate of fluid injection into the fracture and the pressure at the fracture entry are independent of time are
considered. 相似文献
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35.
L. Haeggqwist L. Schimansky-Geier I. M. Sokolov F. Moss 《The European physical journal. Special topics》2008,157(1):33-42
We study the diffusion coefficient of Active Brownian particles in
two dimensions. In addition to usual attributes of active motion we
let the particles turn in preferred directions over random times.
This angular motion is modeled by an effective Lorentz force with
time dependent frequency switching between two values at
exponentially distributed random times. The diffusion coefficient is
calculated by the Taylor-Kubo formula where distributions found from
a Fokker-Planck equation or from a continuous time random walk
approach have been inserted for averaging. Eventually properties
of the diffusion coefficient will be discussed. 相似文献
36.
Conditions have been found for the efficient palladium mediated cyclisation-carbonylation of bromodienes to give gamma,lambda-unsaturated acids. 相似文献
37.
[reaction: see text] The copper metallomicellar hydrolysis of O-methyl O-4-nitrophenyl phenylphosphonothioate to O-methyl phenylphosphonothioic acid takes place with effectively complete inversion at phosphorus. 相似文献
38.
Neiman A Schimansky-Geier L Moss F Shulgin B Collins JJ 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):284-292
We study, in terms of synchronization, the nonlinear response of noisy bistable systems to a stochastic external signal, represented by Markovian dichotomic noise. We propose a general kinetic model which allows us to conduct a full analytical study of the nonlinear response, including the calculation of cross-correlation measures, the mean switching frequency, and synchronization regions. Theoretical results are compared with numerical simulations of a noisy overdamped bistable oscillator. We show that dichotomic noise can instantaneously synchronize the switching process of the system. We also show that synchronization is most pronounced at an optimal noise level-this effect connects this phenomenon with aperiodic stochastic resonance. Similar synchronization effects are observed for a stochastic neuron model stimulated by a stochastic spike train. 相似文献
39.
40.
Previously reported endovesicular reactions in the cleavage of -nitrophenyl diphenyl phosphate by hydroxide (or fluoride) ions in vesicles of dihexadecyldimethylammonium bromide appear to be artifacts. 相似文献