共查询到20条相似文献,搜索用时 171 毫秒
1.
Aamir Shahzad Syed Irfan Haider Muhammad Kashif Muhammad Shahzad Shifa Tariq Munir Mao-Gang He 《理论物理通讯》2018,69(6):704-710
The thermal conductivity of complex fluid materials(dusty plasmas) has been explored through novel Evan-Gillan homogeneous non-equilibrium molecular dynamic(HNEMD) algorithm. The thermal conductivity coefficient obtained from HNEMD is dependent on various plasma parameters(Γ, κ). The proposed algorithm gives accurate results with fast convergence and small size effect over a wide range of plasma parameters. The cross microscopic heat energy current is discussed in association with variation of temperature(1/Γ) and external perturbations(P_z). The thermal conductivity obtained from HNEMD simulations is found to be very good agreement and more reliable than previously known numerical techniques of equilibrium molecular dynamic, nonequilibrium molecular dynamic simulations. Our new investigations point to an effective conclusion that the thermal conductivity of complex dusty plasmas is dependent on an extensive range of plasma coupling(Γ) and screening parameter(κ) and it varies by the alteration in these parameters.It is also shown that a different approach is used for computations of thermal conductivity in 2D complex plasmas and can be appropriate method for behaviors of complex systems. 相似文献
2.
Shear viscosity is examined throughout the entire range of strongly coupled states of two-dimensional complex (dusty) plasma liquids (CDPLs). We have employed equilibrium molecular dynamics (EMD) simulation to compute the shear viscosity coefficients of CDPLs. In the strongly coupled liquid region, the values of valid viscosity coefficient can be estimated only in order of magnitude. The variations in the valid viscosity coefficients with screening strength (κ) and Coulomb coupling strengths (Γ) are observed. A systematic dependence of shear viscosity on κ is observed for an intermediate and higher Γ. The investigations showed that the position of the minimum viscosity coefficient shifts towards higher Γ as κ increases. The computational results for the entire range of liquid states of the strongly coupled dusty plasma obtained using the shear autocorrelation functions are in good agreement with the available simulation results and experimental data. It is shown that new simulations extended the range of plasma states (Γ, κ) used in our earlier simulation results for the existence of a finite minimum possible viscosity coefficient and it is also dependent on plasma states. 相似文献
3.
We consider the thermal conductivity of steeply repulsive inverse power fluids (SRP) in which the particles interact with a pair potential, φ(r) = ε(σ/r)n. The time correlation function for the heat flux, Cλ(t), and the time average, Cλ(0) are calculated numerically by molecular dynamics simulations, and accurate expressions for these are also derived for the SRP fluid. We show, by molecular dynamics simulations, that close to the hard-sphere limit this time correlation function has the same analytic form as for the shear and pressure correlation functions for the shear and bulk viscosity, i.e. Cλ(t)/Cλ(0) = 1 ?T* (nt*)2 + 0((nt*)4), where T* = k B T/ε, is the reduced temperature, k B is Boltzmann's constant and t* = (ε/σ2)1/2 t is the reduced time. The thermal conductivity for the limiting case of hard spheres is numerically very close to that given by the traditional Enskog relation. At low densities the normalized relaxation times are typically largest for the thermal conductivity, followed by shear and then bulk viscosity. Close to the maximum fluid density, the latter two increase rapidly with density (especially for the shear) but continue a monotonic decline for the thermal conductivity. This reflects the relative insensitivity of the thermal conductivity to the approach to the fluid-solid phase boundary. 相似文献
4.
5.
Kinetic theory has been applied to study the damping characteristics of dust ion acoustic waves (DIAWs) in a dusty plasma comprising q‐non‐extensive distributed electrons and ions, while the dust particles are considered extensive following the Maxwellian velocity distribution function. It is found that the results of the three‐dimensional velocity distribution function are more accurate compared to the results of the one‐dimensional velocity distribution function. The numerical solution of the dispersion relation is carried out to study the effect of the non‐extensivity parameter q on the dispersion, the damping rate, and the range of the values of the normalized wavenumber ( k λD) for which the DIAWs are weakly damped. It is found that the change in the value of the electron non‐extensivity parameter qe has a minor effect on the dispersion, the damping rate, and the range of the values of the normalized wavenumber ( k λD) for which the DIAWs are weakly damped, while on the other hand, ion non‐extensivity parameter qi has a strong effect on these arguments. The effect of other parameters, such as the ratio of electron to ion number density and ratio of electron to ion temperature, on the damping characteristics of DIAWs is also highlighted. 相似文献
6.
O. Utéza N. Sanner B. Chimier A. Brocas N. Varkentina M. Sentis P. Lassonde F. Légaré J. C. Kieffer 《Applied Physics A: Materials Science & Processing》2011,105(1):131-141
Surface ablation of a dielectric material (fused silica) by single femtosecond pulses is studied as a function of pulse duration
(7–450 fs) and applied fluence (F
th<F<10F
th). We show that varying the pulse duration gives access to high selectivity (with resolution ∼10 nm) for axial removal of
matter but does not influence the transverse ablation selectivity, which only depends on the normalized applied fluence F/F
th. The ablation efficiency is shown to be inversely dependent on the pulse duration and saturates with respect to the applied
fluence earlier at ultra-short pulse durations (≤30 fs). The deduced optimal fluence F
opt corresponding to the highest ablation efficiency for each pulse width defines two regimes of laser application. Below F
opt, the removed material depth can be accurately adjusted in a large range (∼40–200 nm) as a function of the applied fluence
and the morphology of the ablated pattern almost reproduces the Gaussian beam distribution. Above F
opt, the material removal depth tends to saturate and the morphology of the ablated pattern evolves to a top-hat distribution.
The coupled evolution of depth and morphology is related to the dynamics of formation of dense plasma at the surface of the
material, acting as an ultra-fast optical shutter. 相似文献
7.
利用区熔法、机械合金化、放电等离子烧结(SPS)技术、热压法等多种工艺制备了p型碲化铋基热电材料.在300—500K的温度范围内测量了各热电性能参数,包括电导率(σ)、塞贝克系数(α)和热导率(κ),研究了制备工艺对热电性能的影响.结果表明,所制备的块体材料与同组成区熔晶体相比,性能优值ZT均有不同程度的提高.其中,利用区熔法结合SPS技术可获得热电性能最佳的块体材料,其ZT值达1.15.
关键词:
碲化铋
放电等离子烧结
区熔法
热电性能 相似文献
8.
A complete analysis of the phonon conductivity κ, still lacking in the literature, is presented in the two-mode conduction model for Germanium. First a method is derived from which the correction term κc of the Callaway model is separated into its longitudinal and transverse parts and then the effects of strong phonon dispersion and the role of longitudinal and transverse phonons on κc are studied. For this purpose we have also proposed some new empirical expressions for the three phonon relaxation rates τ3ph−1's which are valid in the entire temperature range. This improvised model, when applied simultaneously to the phonon conductivity data of both normal and enriched Ge, yields some new results. These are (i) κc neglected by the earlier workers in the two-mode phonon conduction model, gives a substantial contribution beyond the conductivity maximum and (ii) the longitudinal phonons are the major carriers of heat at high temperature. 相似文献
9.
Yu. V. Khrustalyov O. S. Vaulina 《Journal of Experimental and Theoretical Physics》2013,116(5):876-885
New data on heat transfer in two-dimensional Yukawa systems have been obtained. The results of a numerical study of the thermal conductivity for equilibrium systems with parameters close to the conditions of laboratory experiments in dusty plasma are presented. The Green-Kubo relations are used to calculate the heat transfer coefficients. The influence of dissipation (internal friction) on the heat transfer processes in nonideal systems is studied. New approximations are proposed for the thermal conductivity and diffusivity for nonideal dissipative systems. The results obtained are compared with the existing experimental and numerical data. 相似文献
10.
对烟颗粒的光散射进行模拟计算是研究火灾烟颗粒光散射特性的重要手段,目前对于火灾烟颗粒光散射的数值计算多采用球形或椭球模型.实际上,火灾烟颗粒的形貌与球形和椭球均存在着显著差异.扫描电子显微镜图像表明,烟颗粒具有近似分形的结构.本文利用离散偶极近似方法计算了随机取向的火灾烟颗粒分形凝团以及同体积的球形颗粒的光散射Muller矩阵,并对两者的归一化Muller矩阵元素随散射角的分布进行了比较.研究表明:火灾烟颗粒分形模型和球形模型的归一化矩阵元素F11(θ)/ 相似文献
11.
We have carried out million‐particle equilibrium molecular dynamics simulations of 3‐dimensional Yukawa liquids in order to determine the shear viscosity coefficient. The computations have been executed on Graphics Processing Unit (GPU) architectures with our largely parallelized code. The results cover the strongly coupled liquid phase, with Γ up to the vicinity of the freezing transition, for the 1 ≤ κ ≤ 3 domain of the screening parameter of the Yukawa potential. The good agreement of the present results with those obtained from earlier simulations of significantly smaller systems (consisting of several hundred to several thousand particles) verifies that the viscosity data derived in these smaller scale simulations are also acceptable (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
Investigation of the diocotron instability of an infinitely wide sheet electron beam by using the macroscopic cold-fluid model theory
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting walls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low-frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ωc to a wider usage range, which is restricted to be much larger than the plasma frequency ωp in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λb, which is greatly dependent on the parameter ωc/ωp. The larger ωc/ωp is, the smaller λb will be needed. Moreover, the system parameters, including the wave number kx of the perturbations and the relativistic mass factor γb, will also influence the growth rate of diocotron instability obviously. 相似文献
13.
We consider the spectral statistics of the superposition of a random diagonal matrix and a GUE matrix. By means of two alternative superanalytic approaches, the coset method and the graded eigenvalue method, we derive the two-level correlation functionX2(r) and the number varianceΣ2(r). The graded eigenvalue approach leads to an expression forX2(r) which is valid for all values of the parameterλgoverning the strength of the GUE admixture on the unfolded scale. A new twofold integration representation is found which can be easily evaluated numerically. Forλ?1 the Breit–Wigner widthΓ1measured in units of the mean level spacingDis much larger than unity. In this limit, closed analytical expressions forX2(r) andΣ2(r) can be derived by (i) evaluating the double integral perturbatively or (ii) anab initioperturbative calculation employing the coset method. The instructive comparison between both approaches reveals that random fluctuations ofΓ1manifest themselves in modifications of the spectral statistics. The energy scale which determines the deviation of the statistical properties from GUE behavior is given by. This is rigorously shown and discussed in great detail. The Breit–WignerΓ1width itself governs the approach to the Poisson limit forr→∞. Our analytical findings are confirmed by numerical simulations of an ensemble of 500×500 matrices, which demonstrate the universal validity of our results after proper unfolding. 相似文献
14.
15.
V. E. Fortov V. S. Filinov A. P. Nefedov O. F. Petrov A. A. Samaryan A. M. Lipaev 《Journal of Experimental and Theoretical Physics》1997,84(3):489-496
We have compared experimental measurements of ordered structures in a thermal plasma containing macroparticles of CeO2 at atmospheric pressure and a temperature around 1700 K with the results of numerical Monte Carlo calculations for the Yukawa
model. We describe several distinctive features of the way the experiments were done, including how the ordered macroparticle
structures were detected. We discuss a theoretical model of the behavior of an equilibrium system of charged macroparticles
in a plasma and the effective interaction potential between them. Good agreement between the experimental and numerical results
is noted, and possible reasons for the observed discrepancies are discussed.
Zh. éksp. Teor. Fiz. 111, 889–902 (March 1997) 相似文献
16.
AbstractIn this study, the elastic, electronic, optical and thermoelectric properties of CaTiO3 perovskite oxide have been investigated using first-principles calculations. The generalised gradient approximation (GGA) has been employed for evaluating structural and elastic properties, while the modified Becke Johnson functional is used for studying the optical response of this compound. In addition to ground state physical properties, we also investigate the effects of pressure (0, 30, 60, 90 and 120 GPa) on the electronic structure of CaTiO3. The application of pressure from 0 to 90 GPa shows that the indirect band gap (Γ-M) of CaTiO3 increases with increasing pressure and at 120 GPa it spontaneously decreases transforming cubic CaTiO3 to a direct (Γ-Γ) band gap material. The complex dielectric function and some optical parameters are also investigated under the application of pressures. All the calculated optical properties have been found to exhibit a shift to the higher energies with the increase of applied pressure suggesting potential optoelectronic device applications of CaTiO3. The thermoelectric properties of CaTiO3 have been computed at 0 GPa in terms of electrical conductivity, thermal conductivity and Seebeck coefficient. 相似文献
17.
Lu-Chun Du 《Physica A》2010,389(6):1189-1933
A time-delayed tumor cell growth model with correlated noises is investigated. In the condition of small delay time, the stationary probability distribution is derived and the stationary mean value (〈x〉st) and normalized varianceλ2 of the tumor cell population and state transition rate (κ) between two steady states are numerically calculated. The results indicate that: (i) The delay time (τ) enhances the coherence resonance in 〈x〉st as a function of the multiplicative noise intensity (D) and increases 〈x〉st as a function of the additive noise intensity (α), i.e., τ enhances fluctuation of the system, however, the strength (λ) of correlations between multiplicative and additive noise plays a contrary role to τ on these; (ii) τ enhances the coherence resonance in κ as a function of D and increases κ as a function of α, i.e., τ speeds up the rate of state transition, however, λ also plays a contrary role to τ on these. 相似文献
18.
The thermal conductivity (κ) of single crystals of tetragonal uniaxial antiferromagnets USb2 (T N = 202 K) and UBi2 (T N = 180.8 K) has been measured along the a-axis (κa ) over the temperature range from 0.5 to 300 K and along the c-axis (κc ) from 0.5 to 70 K. The as-grown samples have residual resistivity ratio (RRR) values of about 500–600 and 100–150 for UBi2 and USb2, respectively. The anisotropy of the thermal conductivity (κa (T)/κc (T) ~ 5) and the low-T Lorenz ratios are discussed in relation to Fermi surface topology for both compounds. 相似文献
19.
香蕉叶片Chla荧光动力学参量对激发光强的反应 总被引:5,自引:4,他引:1
在蓝色激发光(λm=660nm)作用下,香蕉叶片的叶绿素a(Chla)发出波长为720~740nm的荧光信号,荧光强度随时间呈现有规律的变化.随着激发光强的增加,荧光动力学参量F0和FVI/FV呈上升趋势,FV/F0与FV/FM逐渐达到饱和,而CA和T1/2呈下降趋势.研究结果表明,保证香蕉叶片光合机构高速有序运转的适宜光强在20~60μmol·m-2·s-1之间,过量的光强将造成叶片光合机构的损伤.讨论了香蕉叶片诸荧光动力学参量的生物学意义及其随激发光强度增加而变化的原因. 相似文献
20.
Abstract The nonlinear decrease of Gibbs free energy (gF) for the formation of Frenkel defects in Agx accounts for the anomalous increase of electrical conductivity and self-diffusion in this system. Using an analytical expression for gF(T) the excess heat capacity for Frenkel defects is calculated. A comparison with experimental data indicates that all the anomalies of heat capacity at high temperature is not accounted for. A contribution from Schottky defects is thus probable. 相似文献