Modeling grain growth by the monte carlo method on isotropic grids

Results of modeling grain growth by the Monte Carlo method on grids consisting of Voronoi polyhedra for an isotropic distribution of the points on a plane and in space are reported. The influence of the grid structure on the properties of the model are discussed.     

蒙特卡罗方法的过程聚类EWMA控制图研究

以加工"过程"为研究对象,从零件成组加工技术出发,阐述了就如何利用EWMA控制图来进行统计聚类并进行过程质量监控等问题,提出通过统计聚类形成"零件族",对同一"零件族"采用统一的EWMA控制图的应用策略;引入聚类零件族的方差比ρ,利用蒙特卡罗模拟方法,对不同样本数量条件下的统计聚类EWMA控制图性能所产生的影响进行了详细的研究,最后给出了统计聚类的基本原则.     

Bayesian reconstruction for SPECT: Validation with monte carlo simulation,experimental phantom,and real patient data

A method for Bayesian image reconstruction from projections is applied to Monte Carlo simulation, experimental phantom, and real patient data from a SPECT acquisition system. This statistical image reconstruction method has three distinct aspects: (1) it uses a priori information about image density distribution of a multinomial process; (2) it considers a spatial correlation of nearby image elements; and (3) it incorporates the Poisson nature of photon detection fluctuation. The Monte Carlo simulation data are generated by computer codes for selected mathematical phantoms containing hot and cold rods. The experimental phantom data are acquired with a Triad SPECT system using radioactive phantoms containing hot and cold rods. The real patient data are obtained from a patient brain scan using the Triad SPECT system. A parallel beam geometry is used. The data are acquired from 120 projection angles uniformly distributed from 0 to 360 degrees. At each projection angle, a 128 X 128 projection image is measured. This 128 X 128 projection samples are equally spaced along the axis of detector rotation and perpendicular to the axis, respectively. Each image slice is reconstructed using a 128 X 128 pixel array. Comparisons between this Bayesian method and maximum likelihood method and filtered backprojection method are give. An improvement in noise suppression is demonstrated using the Bayesian method while image resolution is preserved.     

Influence of index table accuracy on roundness calibration in the multi-step method using monte carlo simulation

The precise and accurate roundness measurement is required year by year. The multi-step method is commonly used in the high-accuracy measurement for the roundness. The multi-step method is the self-calibration of the roundness capable of performing highly-advanced precise measurement. It depends on the reason that is able to separate measurement wave from the spindle rotation component and the form component of hemispherical master. But the mathematical models of the roundness measurement using that method are very complicated, describing numerous parameters and processes. So, recently, the Monte Carlo technique has attracted increasing attention as a very useful method for uncertainty estimation. This paper describes influences of the indexing angle accuracy and the noises generated by the roundness measuring machine, on the roundness measurements, both of which were analyzed by the Monte Carlo simulation. Furthermore, an example of hemispherical master is compared with the actual measurement data between when a reference guide plate is used utilizing the magnetic rotary encoder.     

CFD-DEM combined the fictitious domain method with monte carlo method for studying particle sediment in fluid

The interaction between a particle and the viscous fluid and then the particle-wall collision in the flow field plays an important role in the study of particulate flow. In this paper, we examine the velocity characteristics of a spheroidal particle sediment in the fluid and its rebound dynamics by applying the Computational Fluid Dynamics-Discrete Element Method (CFD-DEM). The Fictitious Domain method and Monte Carlo method are combined to improve the accuracy of the hydrodynamic force acting on the particle. A soft-sphere scheme of DEM is used to model the collision of particles, and the hydrodynamic force on the particle is fully solved directly from the CFD-DEM. The numerical results are verified by comparing the previous numerical and experimental results. The results are in good agreement with the corresponding published data. The simulation results show that the critical factor that affects the particle rebound is Stokes number (St). No rebound occurs when Stokes number is equal to 3.74. Initially, the results show that the ellipsoid particle shows large “wiggles” down the square tube at 45° angle with respect to the horizontal axis. These large “wiggles” gradually reduce after a time, and the ellipsoid finally settles into a stable horizontal state in the center of the square tube due to the effect of fluid viscosity dissipation.     

Application of the monte carlo method to the problem of flow in the boundary layer of a two-dimensional turbulent jet

A precise solution is found to the problem of flow in the boundary layer of a two-dimensional turbulent jet. The method of [1] is used here.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 4, pp. 725–728, April, 1972.     

Calculation of quantum-dot blinking using the gillespie monte carlo algorithm

We calculate the stochastic photoluminescence intensity of a single colloidal quantum dot in order to calculate the blinking behaviour of the optical emission. The combination of the long-lived dark state with a lifetime of the order of seconds together with the radiative recombination lifetimes in the nanosecond regime make the stochastic model of the system incredibly computer intensive. The stochastic behaviour of the single quantum dot using a system of rate equations for the probabilities of occupancy of the confined energy levels is calculated. A standard Monte Carlo algorithm is modified by introducing a time step that is dependent on the transitions possible in the state that the system occupies. The model is verified by comparison with the calculation using the standard algorithm and from the calculated probability densities. The improvement in computational time of this algorithm over the standard Monte Carlo method is also determined.     

Results of a monte carlo investigation of the diffuse attenuation coefficient

There has been a large effort to relate the apparent optical properties of ocean water to the inherent optical properties, which are the absorption coefficient a, the scattering coefficient b, and the scattering phase function rho(theta). The diffuse attenuation coefficient kdiff' has most often been considered an apparent optical property. However, kdiff' can be considered a quasi-inherent property kdiff' when defined as a steady-state light distribution attenuation coefficient. The Honey-Wilson research empirically relates kdiff' to a and b. The Honey-Wilson relation most likely applies to a limited range of water types because it does not include dependence on rho(theta). A series of Monte Carlo simulations were initiated to calculate kdiff' in an unstratified water column. The calculations, which reflected open ocean water types, used ranges of the single-scattering albedo omega(0) and the mean forward-scattering angle theta(m) for two analytic phase functions with different shapes. It was found that kdiff' is nearly independent of the shape of rho(theta) and can be easily parameterized in terms of a, b, and theta(m) for 0.11 相似文献   

Simulation of a gallium arsenide running wave amplifier with a schottky barrier by the monte carlo method

Process of transfer of electrons in a gallium arsenide running-wave amplifier with a Schottky barrier has been investigated. Simulation of the process has been implemented by the Monte Carlo method with the use of the three-valley (ΓLX) model of the GaAs conduction band with account for the nonparabolicity of the bands, scattering on phonons, and transport between valleys. The increment of spatial-charge wave (SCW) has been calculated; it has been shown that the amplification in such a device can be substantially greater than in a beam-instability amplifier. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 5, pp. 891–898, September–October, 1998.     

Sampling of time- and frequency-domain signals in monte carlo simulations of photon migration

We compare two fundamentally different ways to evaluate the time dependence in Monte Carlo simulations of photon migration: estimating the pulse response in time versus evaluating the transfer function at discrete points in the frequency domain. We show that these two methods differ in accuracy owing to quantization and sampling errors, whereas the statistical error is essentially the same for both methods. From our analysis we also derive alternative methods to sample the time-domain pulse response with reduced quantization and sampling error. Simulation results are included to illustrate our theoretical analysis.     

挂架载荷的动态标定及其数据处理方法研究

研究武器系统挂架载荷的动态标定及其数据处理方法,为挂架载荷力值的测量提供标定模型。采用对挂架上一特征点施加标准的脉冲和阶跃激励,测量应变片对激励的响应输出,通过非参数拟合,获得标定样本数据库,根据最近邻域法确定未知受力值。结果表明,基于非参数拟合的标定方法,可较好地解决复杂环境下应变片输出的噪声干扰,从而提高测量数据的稳健性。     

Some results from quantum monte carlo studies of the 2D Hubbard model

Quantum Monte Carlo calculations have provided insights into the magnetic, single-particle, and effective particle-particle interaction in the two-dimensional Hubbard model. Here we review some of these results.     

An experimental method to study the dynamic tensile failure of brittle geologic materials

An experimental method was developed to study the tensile failure of brittle geologic materials at strain rates of approximately 10 to 20/s. In these experiments, a cylindrical rod specimen is first loaded in static triaxial compression, then the axial pressure is released from each end simultaneously and very rapidly. The resulting rarefaction waves interact in the center of the rod to produce a dynamic tensile stress equal in magnitude to the original static compression. The pressure acting on the radial surface is approximately constant during the experiment. As an application of this method, several experiments were performed on concrete. Transient measurements were made of the axial load at each end, the confining pressure, and axial and circumferential surface strains at several locations along the length of the rod. Usually a single fracture occurred near the midpoint of the rod. In some experiments multiple fractures occurred. Assuming the peak observed strains in these experiments to be elastic the unconfined tensile strength of the concrete at a strain rate of 10 to 20/s was, on average, approximately 40% higher than the static splitting tensile strength. At the same strain rate, the tensile strength with 10 MPa confining pressure averaged approximately 100% higher than the static splitting tensile strength and 40% higher than the unconfined tensile strength at 10 to 20/s. Nonlinear analyses indicate that these estimates are reasonable, but that in general the assumption of elastic response is not valid. To match the measured strain histories with calculations requires that the rod be modeled inelastically.     

Analysis of experimental data on low-cycle fatigue in nonproportional deformation

We have analyzed experimental data on low-cycle fatigue in biaxial nonproportional deformation of various materials. To establish a correlation with the fatigue limit, we have proposed a strain parameter-the reduced range of strain. For most of the materials under consideration this correlation dependence can be obtained from uniaxial low-cycle fatigue experiments and can be represented by a linear function. Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 13–21, January–February, 2000.     

Path integral monte carlo simulations of thin4He films on a H2 surface

Atomatically thin⁴He films of up to three monolayers on molecular hydrogen (1,1,1) surfaces are studied at T = 0.5 K, using path integral Monte Carlo. We compute the binding energy of⁴He to the H₂ substrate as a function of⁴He coverage and obtain evidence of the prewetting transition. Density profiles perpendicular to the⁴He-H₂ interface are obtained, as well as the zero point motion and effective mass of⁴He parallel to the substrate surface. The superfluid density of⁴He vs. coverage is calculated, and the intermediate scattering function is computed, from which we estimate the speed of third sound. Finally, we calculate the vorticity-vorticity correlation function.     

A method of processing experimental data on the parameters of physical processes in information-measurement systems based on Mivar logical nets

A new method of computation-logic processing of information and experimental data on the basis of Mivar logic nets and productions for the creation of future information-measurement systems, control-measurement instruments, and diagnostic complexes is proposed.     

The processing of ultrafine-grained materials through the application of severe plastic deformation

The application of severe plastic deformation (SPD) to bulk metals provides the opportunity of achieving grain sizes in the submicrometer and nanometer range. Several different SPD processing techniques are now available including Equal-Channel Angular Pressing (ECAP), High-Pressure Torsion (HPT) and Accumulative Roll-Bonding (ARB). This paper examines the principles of grain refinement using ECAP and gives examples of the advantageous properties that may be achieved including increased strength at ambient temperatures and a superplastic forming capability at elevated temperatures. Invited paper presented in Symposium C at 5th Brazilian MRS Meeting, Florianópolis, Brazil.     

声纳动态测向的数据处理方法

提出白噪声多项式最优线性移动平滑滤波算法应用于分离声纳测向精度测量数据中的真实信号和随机噪声,并通过滤波方差比给出对随机误差的压缩程度;对声纳测向精度海上动态测量计算公式给出了完整的理论证明,并推导出更加精确的计算公式。试验结果表明,上述方法对声纳测向精度数据有效、适用。