共查询到20条相似文献,搜索用时 687 毫秒
1.
The embedded-atom method have been applied to study the strain field produced by the self-interstitial impurity at the octahedral
site in Ni. The calculation have been carried out consistently on the basis of discrete lattice theory, using Kanzaki method.
The atomic force constants are evaluated using Wills and Harrison interatomic potential. The dynamical matrix and external
force are evaluated considering the interaction up to first nearest neighbors. The atomic displacements are tabulated up to
20NN’s. These displacements are of oscillatory nature and of decreasing magnitude with NN’s distance. The physical properties
such as self-interstitial formation energy and volume change calculated using atomic displacements are in accordance with
the earlier studies. 相似文献
2.
耗散腔中多光子J-C模型中的密度算符间距 总被引:1,自引:1,他引:0
研究了腔场存在相位耗散时多光子J-C模型中光场、原子和系统的密度算符间距;讨论了原子初始态、光场强度以及腔场耗散系数对密度算符间距的影响;且比较了不同跃迁光子数下体系的密度算符间距。结果发现:①密度算符间距与原子的初始态密切相关。②光场和系统的密度算符间距在耗散腔中作减幅周期振荡最终达到稳定,达到稳定所需时间随腔的耗散系数增大而缩短;而原子的密度算符间距与腔的耗散无关。③随着光场初始强度的增加,光场和系统与各自初始态的偏离程度增大。④对于双光子跃迁,当腔场存在相位损耗时光场和系统的密度算符间距仍作减幅周期振荡,原子仍周期性的回到纯态。但由于光场与原子的纠缠和退纠缠速率加快,密度算符间距在每个周期内振荡加剧。 相似文献
3.
研究了腔场存在相位耗散时多光子J-C模型中光场、原子和系统的密度算符间距;讨论了原子初始态、光场强度以及腔场耗散系数对密度算符间距的影响;且比较了不同跃迁光子数下体系的密度算符间距.结果发现:①密度算符间距与原子的初始态密切相关.②光场和系统的密度算符间距在耗散腔中作减幅周期振荡最终达到稳定,达到稳定所需时间随腔的耗散系数增大而缩短;而原子的密度算符间距与腔的耗散无关.③随着光场初始强度的增加,光场和系统与各自初始态的偏离程度增大.④对于双光子跃迁,当腔场存在相位损耗时光场和系统的密度算符间距仍作减幅周期振荡,原子仍周期性的回到纯态.但由于光场与原子的纠缠和退纠缠速率加快,密度算符间距在每个周期内振荡加剧. 相似文献
4.
针对刃型位错的滑移运动, 构建包含外力场与晶格原子密度耦合作用的体系自由能密度函数, 建立剪切应变作用体系的晶体相场模型. 模拟了双相双晶体系的位错攀移和滑移运动, 计算了位错滑移的Peierls势垒和滑移速度. 结果表明: 施加较大的剪切应变率作用, 体系能量变化为单调光滑曲线, 位错以恒定速度做连续运动, 具有刚性运动特征; 剪切应变率较小时, 体系能量变化出现周期波动特征, 位错运动是处于低速不连续运动状态, 运动出现周期“颠簸”式滑移运动, 具有黏滞运动特征; 位错启动运动, 存在临界的势垒. 位错启动攀移运动的Peierls势垒要比启动滑移Peierls势垒大几倍. 位错攀移和滑移运动特征与实验结果相符合. 相似文献
5.
We present a strain analysis of an edge dislocation core, and a
detailed discussion of the Foreman dislocation model. In order to
examine the model, the quantitative measurement of strain field
around an edge dislocation in aluminum is performed, and
high-resolution transmission electron microscopy and geometric phase
analysis are employed to map the strain field of the edge
dislocation core in aluminum. The strain measurements are compared
with the Foreman dislocation model, showing that they are in good
agreement with each other when 0.7 ≤ a ≤ 1.5. 相似文献
6.
A method is presented to predict the root mean square displacement response of an open curved thin shell structure subjected to a turbulent boundary-layer-induced random pressure field. The basic formulation of the dynamic problem is an efficient approach combining classic thin shell theory and the finite element method, in which the finite elements are flat rectangular shell elements with five degrees of freedom per node. The displacement functions are derived from Sanders’ thin shell theory. A numerical approach is proposed to obtain the total root mean square displacements of an open curved thin structure in terms of the cross spectral density of random pressure fields. The cross spectral density of pressure fluctuations in the turbulent pressure field is described using the Corcos formulation. Exact integrations over surface and frequency lead to an expression for the total root mean square displacement response in terms of the characteristics of the structure and flow. An in-house program based on the presented method was developed. The total root mean square displacements of a curved thin blade subjected to turbulent boundary layers were calculated and illustrated as a function of free stream velocity and damping ratio. A numerical implementation for the vibration of a cylinder excited by fully developed turbulent boundary layer flow was presented. The results compared favorably with those obtained using software developed by Lakis and Païdoussis (J. Sound Vib. 25 (1972) 1–27) using cylindrical elements and a hybrid finite element method. 相似文献
7.
Molecular dynamics simulations are carried out to study the incipient dislocation plasticity in Ni3Al. Dislocation nucleation is found to occur preferentially at energetic atomic clusters with larger-than-average relative displacements. From the simulated distribution of the atomic relative displacements, a scaling model is proposed to predict the size dependence of the incipient plasticity condition in real-sized specimens. 相似文献
8.
Kyozi Kawasaki 《Annals of Physics》1984,154(2):319-355
A method is presented to obtain stochastic equations of motion for topological defects from the underlying TDGL-like stochastic dissipative field equations. The method makes use of virtual displacements of the Goldstone coordinates of topological defects. Effects of kinematical constraints among Goldstone coordinates are studied. The method is applied to modulated systems and we obtain stochastic equations of motion for interfaces (domain walls) and vortex lines (dislocation or defect lines). The driving force for a vortex line is found to include besides the usual surface tension force a new force due to misfit, which is an analogue of the Magnus force on a quantized vortex line and the Peach-Kochler force on a dislocation. A general expression for interactions between parts of interfaces is obtained in terms of asymptotic forms of field variables far from interfaces. 相似文献
9.
The interaction energy between atomic rows is calculated in the approximation of pairwise interaction. (This approximation is only valid for normal metals). The asymptotic behaviour of this energy is discussed as a function of the conduction electron number. This method fits computing with an iterative process the atomic configurations of a screw dislocation in a lithium lattice. Two configurations are found with three-fold symmetry, showing an asymmetry in (112) planes. 相似文献
10.
Numerical Investigation and Wind Tunnel Validation on Near-Wake Vortical Structures of Wind Turbine Blades 下载免费PDF全文
Zhenyu Zhang Li Chen & Tongguang Wang 《advances in applied mathematics and mechanics.》2016,8(4):556-572
Computational fluid dynamics (CFD) has been used by numerous researchers
for the simulation of flows around wind turbines. Since the 2000s, the experiments
of NREL phase VI blades for blind comparison have been a de-facto standard
for numerical software on the prediction of full scale horizontal axis wind turbines
(HAWT) performance. However, the characteristics of vortex structures in the wake,
whether for modeling the wake or for understanding the aerodynamic mechanisms
inside, are still not thoroughly investigated. In the present study, the flow around NREL
phase VI blades was numerically simulated, and the results of the wake field were
compared with the experimental ones of a one-to-eight scaled model in a low-speed
wind tunnel. A good agreement between simulation and experimental results was
achieved for the evaluation of overall performances. The simulation captured the complete
formation procedure of tip vortex structure from the blade. Quantitative analysis
showed the streamwise translation movement of vortex cores. Both the initial formation
and the damping of vorticity in near wake field were predicted. These numerical
results showed good agreements with the measurements. Moreover, wind tunnel wall
effects were also investigated on these vortex structures, and it revealed further radial
expansion of the helical vortical structures in comparison with the free-stream case. 相似文献
11.
Sun LD Hohage M Zeppenfeld P Balderas-Navarro RE Hingerl K 《Physical review letters》2006,96(1):016105
We show that reflectance difference spectroscopy (RDS) is sensitive to the inhomogeneous surface and thin film strain which builds up during hetero- and homoepitaxial growth. The RDS signal is affected by the local, mean square atomic displacements in the substrate resulting from the stress relaxation of strained adlayer islands. For layer-by-layer growth an oscillatory variation of the RDS intensity is observed. These results demonstrate the potentiality of RDS to probe the growth kinetics on structurally anisotropic surfaces. 相似文献
12.
In recent years, the phase field crystal (PFC) model has been confirmed as a good candidate to describe grain boundary (GB) structures and their nearby atomic arrangement. To further understand the mechanical behaviours of nanocrystalline materials, strain fields near GBs need to be quantitatively characterized. Using the strain mapping technique of geometric phase approach (GPA), we have conducted strain mapping across the GBs in nanocrystalline grains simulated by the PFC model. The results demonstrate that the application of GPA in strain mapping of low and high angles GBs as well as polycrystalline grains simulated by the PFC model is very successful. The results also show that the strain field around the dislocation in a very low angle GB is quantitatively consistent with the anisotropic elastic theory of dislocations. Moreover, the difference between low angle GBs and high angle GBs is revealed by the strain analysis in terms of the strain contour shape and the structural GB width. 相似文献
13.
González-Mozuelos P Yeom MS Olvera de la Cruz M 《The European physical journal. E, Soft matter》2005,16(2):167-178
We study small rod-like molecular electrolytes solutions with
their corresponding atomic counterions. The asymptotic length
scales (decay length and wavelength) of the structural
correlations are analyzed using the formalism of the dressed
interaction site theory (DIST). The correlation functions are
determined using the reference interaction site model equation
complemented with a mixed approach in which the hypernetted-chain
closure is used for the repulsive interactions, and the mean
spherical approximation is used for the attractive interactions.
The results from this scheme are in good agreement with the Monte
Carlo computer simulations reported here. The asymptotic
properties of the correlation functions of this molecular system
are compared against those corresponding to two related simple
(atomic) electrolyte models. The main conclusion is that the
molecular structure of the ions lowers by two orders of magnitude
the concentration at which the transition from monotonic to
oscillatory decay occurs. 相似文献
14.
利用Pegg-Barnett相位理论,研究了耗散腔中两个A型原子与相干态光场在Raman相互作用下光场的相位特性,并讨论了光场平均光子数和腔场耗散系数对光场相位特性的影响.结果表明:当腔不存在损耗时,光场相位分布概率以π/λ作周期性振荡;且在t=nπ/λ时刻,光场和原子是退纠缠的,相位分布概率曲线在极坐标图中呈单叶型结构;但在演化周期内,由于光场与原子的相互作用相位分布概率曲线会劈裂为多叶型结构.当腔场存在损耗时,相位分布概率的叶型结构会向中心扩散最终变为一个圆,即表明在考虑腔场耗散时光场的相位最终会变为随机分布;而且腔的耗散系数越大,光场相位越快趋于随机分布.另外,随光场的平均光子数增大,光场相位分布趋于集中.光场相位涨落受到腔场耗散的影响呈现出衰减周期振荡最终达到稳定值,而且达稳定值所需时间随耗散系数的增大而缩短. 相似文献
15.
《Physics letters. A》2006,357(2):92-96
The effects of an additional level and field on the dispersion and absorption characteristics of a four-level atomic medium based on a V-type are studied. The steady state solutions are given under two different fourth level damping rate relations, with the tunable weak probing field and resonant coupling and driving fields. 相似文献
16.
W. H. Robinson 《辐射效应与固体损伤》2013,168(1-4):339-346
In the amplitude independent region the dislocation damping is attributed to either phonon-drag (Granato-Lücke theory) or to the compensating charge-cloud surrounding electrically charged dislocations (Robinson-Birnbaum theory). The experimental results for the dependence of the damping on temperature, frequency and dislocation charge are compared with the two theories. Since it is found that in some cases it is necessary to include both forms of damping, a more complete theory is developed which includes both terms. In the amplitude dependent region the dislocation damping was thought to be due to the dislocations breaking away from pinning points or breaking through the compensating charge-cloud. Using the piezoelectric defect results for electrically charged dislocation in KCl the force-displacement hysteresis loop for the moving dislocations is determined together with the force-displacement curves for dislocations assuming phonon and charge-cloud damping. These results are found to be inconsistent with the “break away” models for amplitude dependence but instead to be consistent with the restoring force due to an elliptical compensation charge cloud, with a size proportional to the square root of the dislocation charge. 相似文献
17.
A rather simple semiclassical model is described for treating short-range correlation forces in the scattering of positrons from atoms at the energies below the thresholds of positronium formation in each of the considered systems. The present model allows one to introduce a non-empirical procedure for devising several damping functions, one for each of the perturbation terms which are included in the asymptotic expansion of the polarisation potential. It is shown by calculations, carried out for He, Ne and Ar as examples, that one can obtain very good agreement with experimental findings for surprisingly little computational effort, even for fairly complex atomic targets which would be otherwise out of reach for all but the most computationally intensive ab initio methods. 相似文献
18.
We use the dielectric-response formalism to evaluate the induced density of charge carriers in supported graphene due to an external moving charged particle in terms of its velocity and distance from graphene for several equilibrium charge carrier densities due to graphene doping. We show that, when the particle speed exceeds a threshold value, an oscillatory wake effect develops in the induced charge density trailing the particle. Strong effects are observed in the wake pattern due to finite size of the graphene–substrate gap, as well as due to strong coupling effects, and plasmon damping of graphene?s π electrons. 相似文献
19.
We obtain the singular asymptotic behavior of the stress field in the vicinity of a non-planar dislocation in three dimensions and the nearly singular behavior of the full self-force of the dislocation including both glide and climb forces, using asymptotic analysis. We also derive asymptotic formulas for the stress field in the vicinity of a curved dislocation segment. Numerical examples are presented to examine the asymptotic formulas. The obtained formulas can be used for qualitative understanding of the stress tensor associated with dislocations and efficient and accurate calculation of the stress tensor in dislocation dynamics simulations. 相似文献
20.
The propagation of nonlinear longitudinal waves in a plate is studied by taking into account the interaction of the longitudinal displacement component with the temperature field and the field of concentration of nonequilibrium atomic point defects. A nonlinear evolution equation is derived for describing the self-consistent thermoelastic longitudinal strain fields. It is shown that the thermoelastic effect on the strain waves manifests itself in the appearance of dissipative terms, which describe the heat transfer and the thermoelastic interaction caused by the strain-induced heat release due to the recombination of nonequilibrium atomic defects. The soliton solutions to the evolution equation are investigated, and the characteristic features of their damping are considered with allowance for the low-frequency and high-frequency losses. 相似文献