共查询到20条相似文献,搜索用时 15 毫秒
1.
Salah Haggag 《General Relativity and Gravitation》1999,31(8):1169-1186
Kramer's formulation of Einstein's fieldequations for static perfect fluid cylinders isconsidered. Three approaches are followed in seekingsolutions of Kramer's equations. First, a particularintegral is found which reproduces a previously knownclass of four solutions. Second, a fairly general ansatzis suggested, whereby a class of six new solutions isderived. Finally, the problem for an incompressible perfect fluid, with constant energy density, isreduced to a single second order equation. All solutionsare regular everywhere. Constraints are imposed on thesolutions parameters such that energy conditions are satisfied and hence the solutions arephysically reasonable. 相似文献
2.
The transport process of a Brownian particle in a ratchet-like potential subjected to two exchanging Gaussian white noises is studied. The change of the temperatures is described by a stochastic dichotornic process. By making use of the perturbation method the probability current up to second order in small correlation time τ is obtained, and time-averaged current is evaluated numerically for a whole region of the parameters. For asymptotically fst temperature cycles, the present model yields larger current in comparison with the periodical temperature cycles. Depending on the temperature of cold heat reservoir, the current changes sign as a function of τ. 相似文献
3.
A. Camacho 《General Relativity and Gravitation》2003,35(2):319-325
The effects, upon the Klein–Gordon field, of nonconformal stochastic metric fluctuations, are analyzed. It will be shown that these fluctuations allow us to consider an effective mass, i.e., the mass detected in a laboratory is not the parameter appearing in the Klein–Gordon equation, but a function of this parameter and of the fluctuations of the metric. In other words, in analogy to the case of a nonrelativistic electron in interaction with a quantized electromagnetic field, we may speak of a bare mass, where the observed mass shows a dependence upon the stochastic terms included in the metric. Afterwards, we prove, resorting to the influence functional, that the energy–momentum tensor of the Klein–Gordon field inherites this stochastic behavior, and that this feature provokes decoherence upon a particle immersed in the region where this tensor is present. 相似文献
4.
G. Lambiase 《General Relativity and Gravitation》2002,34(9):1437-1444
Neutrino oscillations are analyzed in the Ellis-Mavromatos-Nanopoulos-Volkov (ENMV) model, where the quantum gravitational fluctuations of the space-time background are described by virtual D branes. Such fluctuations may induce neutrino oscillations if a violation of the equivalence principle or a tiny violation of the Lorentz invariance is imposed. In this framework, the oscillation length of neutrinos turns out to be proportional to E
–2
M, where E is the neutrino energy and M is the energy which is the scale characterizing the topological fluctuations in the vacuum. 相似文献
5.
In intermittent dynamical systems, the distributions of local Lyapunov exponents are markedly non-Gaussian and tend to be asymmetric and fat-tailed. A comparative analysis of the different time-scales in intermittency provides a heuristic explanation for the origin of the exponential tails, for which we also obtain an analytic expression deriving from a more quantitative theory. Application is made to several examples of discrete dynamical systems displaying intermittent dynamics. 相似文献
6.
LIANG Zhongcheng MING Hai ZHANG Jiangying LONG Yunze XIA Yong XIE Jianping ZHANG Qijin SHEN Weilun 《中国光学快报(英文版)》2000,9(3)
Polymer liquid crystals (PLC) with azobenzene moieties are promising materials for optical switching and image storage because the orientation of mesogens in thin films of this material may be modified by light. 相似文献
7.
LIANG Zhongcheng MING Hai ZHANG Jiangying LONG Yunze XIA Yong XIE Jianping ZHANG Qijin SHEN Weilun 《Chinese Journal of Lasers》2000,9(3):254
Polymerliquidcrystals(PLC)withazobenzenemoietiesarepromisingmaterialsforopticalswitchingandimagestoragebecausetheorientationofmesogensinthinfilmsofthismaterialmaybemodifiedbylight.Recently,wefoundthatthereorientationofazobenzenemesogenscanbeachievedbyt… 相似文献
8.
9.
A. P. Blokhin M. F. Gelin O. V. Buganov V. A. Dubovskii S. A. Tikhomirov G. B. Tolstorozhev 《Journal of Applied Spectroscopy》2003,70(1):70-78
The evolution of optically induced anisotropy in an equilibrium ensemble of free asymmetric tops under collisionless conditions has been investigated theoretically and experimentally. The dynamics of the orientation correlation functions has been studied, the results of femtosecond experiments on measurement of relaxation of the optically induced anisotropy for perylene in the gas phase are presented, and their interpretation within the framework of the theory developed is given. It is shown that in contrast to stationary anisotropy, its time kinetics has more complete characteristic information about the dynamics of vector correlations in a molecular ensemble. 相似文献
10.
Jozef Kowalewski Lawrence Werbelow 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,128(2):144-148
General comments related to the impact of the antisymmetric component of the electronic shielding tensor in context of nuclear magnetic relaxation studies are given. It is argued that in most conceivable applications of high field NMR, the effects associated with the antisymmetric component will be negligible. However, in certain situations, this conventional wisdom may fail and, as an extreme example, it is demonstrated that for highly nonaxially symmetric shieldings, motional anisotropy may accentuate dramatically therelativeimportance of the antisymmetry. 相似文献
11.
《Composite Interfaces》2013,20(7):489-513
Interfacial adhesion of sisal/coir hybrid fibre reinforced natural rubber (NR) composites has been characterized by restricted equilibrium swelling technique with special reference to the effects of fibre loading, orientation and bonding agent. The swelling parameters of NR composites with and without bonding agent were evaluated with three aromatic solvents, namely; benzene, toluene and xylene, by a sorption gravimetric method. As fibre content and penetrant size increase, the solvent uptake has been found to decrease due to the increased hindrance and good fibre–rubber interaction. The bonding agent added mixes showed enhanced restriction to swelling and it is seen that the ratio of change in volume fraction of rubber before and after swelling to the volume fraction of rubber before swelling (V 0 – V r/V 0) is lower for bonding agent added composites, when compared to an unbonded one. The anisotropic swelling studies were carried out to analyse the extent of fibre alignment and fibre–matrix interaction. In strongly bonded composites, the swelling has been mainly observed to take place in the thickness direction, as attested by optical photographs. The rubber–fibre interaction has also been examined by Lorenz–Parks and Kraus equations. 相似文献
12.
Local Modulation of Double Electromagnetically Induced Transparency Spectrum 总被引:1,自引:0,他引:1 下载免费PDF全文
The double electromagnetically induced transparency induced by two coupling fields can be realized in a fourlevel tripod-type atom. Such double transparency spectra can be locally modulated by using the weak coherent fields to perturb the coupling transitions. These investigations within this scheme can be independent of Doppler broadening by properly orienting these fieds. 相似文献
13.
The astrophysical applicability of the electrically and magnetically charged black hole solutions obtained in a model of nonlinear electrodynamics proposed by Kruglov is investigated. Theoretical calculations of the bending angles and gravitational redshifts from the theory of general relativity are studied numerically by using the stellar data of charged compact objects and a hypothetical quark star model. Calculations have revealed that although the theoretical outcomes differ from the linear Maxwell case, the plotted bending angles coincide with the linear case and it becomes hard to identify the effect of nonlinearity. However, the calculation of the redshift has shown that while the increase in the electric field leads to a decrease in the gravitational redshift,the presence of the strong magnetic field contributes to the gravitational redshift in an increasing manner. 相似文献
14.
15.
Lorenzo Rossi Fabrizio Dolcini Fabio Cavaliere Niccol Traverso Ziani Maura Sassetti Fausto Rossi 《Entropy (Basel, Switzerland)》2021,23(2)
When a parameter quench is performed in an isolated quantum system with a complete set of constants of motion, its out of equilibrium dynamics is considered to be well captured by the Generalized Gibbs Ensemble (GGE), characterized by a set of coefficients related to the constants of motion. We determine the most elementary GGE deviation from the equilibrium distribution that leads to detectable effects. By quenching a suitable local attractive potential in a one-dimensional electron system, the resulting GGE differs from equilibrium by only one single , corresponding to the emergence of an only partially occupied bound state lying below a fully occupied continuum of states. The effect is shown to induce optical gain, i.e., a negative peak in the absorption spectrum, indicating the stimulated emission of radiation, enabling one to identify GGE signatures in fermionic systems through optical measurements. We discuss the implementation in realistic setups. 相似文献
16.
Developing microrobots for precisely manipulating micro/nanoscale objects has triggered tremendous research interest for various applications in biology, chemistry, physics, and engineering. Here, a novel hypersonic‐induced hydrodynamic tweezers (HSHTs), which use gigahertz nano‐electromechanical resonator to create localized 3D vortex streaming array for the capture and manipulation of micro‐ and nanoparticles in three orientations: transportation in a plane and self‐rotation in place, are presented. 3D vortex streaming can effectively pick up particles from the flow, whereas the high‐speed rotating vortices are used to drive self‐rotation simultaneously. By tuning flow rate, the captured particles can be delivered, queued, and selectively sorted through the 3D HSHTs. Through numerical simulations and theoretical analysis, the generation of the 3D vortex and the mechanism of the particles manipulation by ultrahigh frequency acoustic wave are demonstrated. Benefitting from the advantages of the acoustic and hydrodynamic method, the developed HSHTs work in a precise, noninvasive, label‐free, and contact‐free manner, enabling wide applications in micro/nanoscale manipulations and biomedical research. 相似文献
17.
For nonsoft potential collision kernels with angular cutoff, we prove that under the initial condition f
0(v)(1+|v|2+|logf
0(v)|)L
1(R
3), the classical formal entropy identity holds for all nonnegative solutions of the spatially homogeneous Boltzmann equation in the class L
([0, ); L
1
2(R
3))C
1([0, ); L
1(R
3)) [where L
1
s
(R
3)={ff(v)(1+|v|2)
s/2L
1(R
3)}], and in this class, the nonincrease of energy always implies the conservation of energy and therefore the solutions obtained all conserve energy. Moreover, for hard potentials and the hard-sphere model, a local stability result for conservative solutions (i.e., satisfying the conservation of mass, momentum, and energy) is obtained. As an application of the local stability, a sufficient and necessary condition on the initial data f
0 such that the conservative solutions f belong to L
1
loc([0, ); L
1
2+
(R
3)) is also given. 相似文献
18.
《Composite Interfaces》2013,20(4-6):423-439
The surface behaviour of a two-phase polymer mixture depends on the chemical structure of the polymer components, the interaction between the two polymers and the processing conditions. The microscopic morphology and the surface composition need to be known in order to fully utilize the thin film properties. The technique of static time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to obtain the molecular surface composition of thin films of blends and block copolymers. The depth profiling tool of Nano-SIMS, a dynamic SIMS technique, helps to provide the chemical mapping of the surface in 2D and 3D. The surface morphology is investigated using AFM. Thin films of PS and PMMA diblock copolymers with molecular weight of 12K-12K and 10K-10K and blends of PS/PMMA (10K/10K) for thicknesses ranging from 5 nm to 50 nm are examined. For the blends, the ToF-SIMS spectra for all the thicknesses show the same behaviour of a high increase of PMMA on the surface after annealing. Nano-SIMS images reveal the formation of nanostructures on the annealed surfaces and AFM studies show these nanostructures to be droplets having distinct phase shift from the surrounding matrix. The droplet dimensions increase with the increase of the thickness of the film but the absolute intensity from the ToF-SIMS spectra for all the annealed films remains almost the same. For the copolymers, the ToF-SIMS spectra show that there is a decrease of PMMA on the surface for the annealed films when compared to the as-cast ones. AFM morphology reveals that, for different thicknesses, annealing induces different topographical features like droplets, holes, spinodal patterns, etc. but with no distinct phase shift between the patterns and the surrounding matrix. The two different copolymers of comparable molecular weight are found to exhibit very different topography even when the thickness of the films remained the same. The surface composition from the ToF-SIMS data, however, was not found to vary even when the topography was completely different. 相似文献
19.
V. N. Kravchenko N. YA. Minina A. M. Savin I. V. Berman O. P. Hansen C. B. Sorensen 《高压研究》2013,33(2):305-308
Anisotropy of the piezoresistance relaxations has been observed in p -(0 0 1)GaAs/Al 0.5 Ga 0.5 As heterostructures. The character of relaxation process depends on the direction of the applied uniaxial compression: after loading along [1 m 1 0] direction the specimen resistance relaxes down to the lower magnitude while after loading along [1 1 0] direction it relaxes up to the higher magnitude. Shubnikov-de Haas oscillations and Hall effect measurements indicate that variation of the carrier concentration j N in the quantum well during relaxation processes has different signs for uniaxial compression along [1 m 1 0] and [1 1 0] directions and correlates with the corresponding change of the resistance. The piezoelectric field that in GaAs can reach the magnitude E =1.152 2 10 6 V/m at uniaxial stress P =1 kbar along d 1 1 0 ¢ directions is supposed to be responsible for the metastable state after loading (unloading) and redistribution of carriers during the relaxation process. 相似文献
20.
建立了一维滑动弧裂解CO2的反应机理模型. 利用对流冷却的特征频率计算横向气流对流引起的等离子体组分损失. 将等离子体密度和温度的数值模拟结果与文献中滑动电弧等离子体反应器的实验数据进行了对比,吻合较好. 模拟结果表明,滑动弧裂解CO2会产生大量O和O2等活性助燃粒子以及可燃的CO. 随着对流冷却特征频率的增加,放电过程中最大电子数密度和电子温度减小,CO2转化率下降. 在整个CO2裂解机制中e+CO2→e+CO+O的贡献最大,准稳态中贡献率为90.63%,瞬态中贡献率为98.43%. 反应CO+O+M→CO2+M对CO2生成的贡献率最大. 在实际应用中,为提高CO2转化率,可以通过增大放电电流,增大e+CO2→e+CO+O的反应速率,同时选择合适的气体流量,避免过大的速度引起CO2转化率下降. 相似文献