Subtractive manufacturing with geminal powers:making good use of a bad wave function

The cluster Jastrow antisymmetric geminal power ansatz was recently introduced as a promising approach for treating weak and strong electron correlations simultaneously. One crucial aspect of this ansatz is that the Jastrow operator allows the geminal power to achieve size consistency through the deletion of unphysical ionic terms. Here, we present data suggesting that the effects of such deletions go much deeper, causing the geminal to ‘intentionally’ take on a highly unphysical form that, in the presence of the Jastrow's deletions, nonetheless results in an accurate final wave function, a process that we note is similar to the variation-after-projection approach of projected Hartree–Fock theory. Indeed, in both LiF and N₂, we show that the optimal geminal is quite unphysical if considered on its own, but in ways that the Jastrow easily corrects to yield a highly accurate final wave function.     

Corrections to finite-size-scaling in two dimensional Potts models

High resolution Monte Carlo simulations are used to examine the finite size behavior of Q-state Potts models in two dimensions. For Q = 3 we find that at the critical point bulk properties are subject to much larger corrections to finite size scaling than were previously realized. For Q = 4 we find that corrections to finite size scaling are subtle and that the multiplicative logarithmic correction is insufficient to correct the dominant terms.     

Cluster algorithms for anisotropic quantum spin models

We present cluster Monte Carlo algorithms for theXYZ quantum spin models. In the special case ofS=1/2, the new algorithm can be viewed as a cluster algorithm for the 8-vertex model. As an example, we study theS=1/2XY model in two dimensions with a representation in which the quantization axis lies in the easy plane. We find that the numerical autocorrelation time for the cluster algorithm remains of the order of unity and does not show any significant dependence on the temperature, the system size, or the Trotter number. On the other hand, the autocorrelation time for the conventional algorithm strongly depends on these parameters and can be very large. The use of improved estimators for thermodynamic averages further enhances the efficiency of the new algorithms.     

Copolymerization of Ethylene with 1,9‐Decadiene: Part II—Prediction of Molecular Weight Distributions

In the present work, adaptive orthogonal collocation and a Monte Carlo method are used to compute the molecular weight distributions (MWD) of ethylene/1,9‐decadiene copolymers produced with a constrained geometry catalyst. Predictions from each model are compared to each other and to the experimental MWDs, allowing for the evaluation of relative strengths and weaknesses of each mathematical modeling method. Comparisons with experimental results indicate that the rate of macromonomer incorporation in the growing polymer chains decays with the macromonomer radius of gyration. In all cases, the proposed models are able to fit appropriately the available experimental MWDs.     

Monte Carlo Simulations of Observation Time-Dependent Self-Diffusion in Porous Media Models

Observation time-dependent self-diffusion coefficients can be used to obtain microstructural information of porous media. This paper presents two different kinds of Monte Carlo simulations of the self diffusion process of fluids like water in porous systems, a lattice-free method and a lattice-based method. The results for simple porous media model geometries agree well with each other and with published analytical as well as semi-analytical equations. The use of these equations, which are important for the interpretation of Pulsed Field Gradient-Nuclear Magnetic Resonance (PFG-NMR) time-dependent diffusion data with respect to properties of porous media, is discussed.     

Calculation of pressure on an airfoil contour in an unsteady separated flow

Simple formulas for calculating the pressure and the total hydrodynamic reactions acting on an arbitrarily moving airfoil are derived within the framework of the model of plane unsteady motion of an ideal incompressible fluid. Several vortex wakes may be shed from the airfoil owing to changes in velocity circulation around the airfoil contour. Cases with nonclosed and closed contours are considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 109–113, May–June, 2008.     

Analysis of Concentration as Sampled in

The aim of this paper is to analyze the statistical properties of solute concentration in natural aquifers as sampled in observation wells, having a small diameter in comparison with the characteristic size of the heterogeneity in hydraulic properties. The analysis, in Langragian framework, takes advantage of the reverse formulation, where, instead of considering the destination of the injected particles, the origin of the particle being sampled is sought. In the case of small values of the log-conductivity variance _Y², it allows the derivation of an analytical expression for concentration mean, variance and pdf, while for aquifer characterized by high value in _Y², a numerical analysis based on a Monte Carlo approach using a reverse scheme is developed and applied for values of _Y² up to 2. In this case, the use of a Beta function to fit the concentration pdf proves valid for practical applications. The comparison between the numerical and the analytical results defines the range of validity of the analytical ones. The relative role of large-scale dispersion processes and pore-scale effects is analyzed in terms of global variance in order to point out limits and accuracy of the Eulerian scheme in comparison with the Lagrangian one.     

北斗双星/SINS组合导航系统滤波模型的一致性研究

北斗双星定位系统（简称双星定位）是我国自行建立的一种定位系统.根据北斗双星定位系统采用有源定位的特点,介绍了北斗双星与SINS组合的最优预测模型,该方法利用了双星定位系统提供的滞后定位信息对组合系统进行最优预测,进而校正惯导;同时为验证该滤波方法对状态估计的一致性,文中重点研究了滤波器一致性的准则,并给出了检验的统计量.理论研究和试验仿真证明,文中介绍的滤波器与系统是匹配的,具有较高的滤波性能和精度.     

圆管流动水击压力波测量及水力计算

为探索水击现象的物理过程和机理,研制了自循环定常流动管路瞬态特性计算机控制试验装置,并利用该装置进行圆管流动水击压力波实验测量。用12只扩散硅压力传感器测定圆管流动水击压力波瞬态分布及最大、最小压力值,由试验数据拟合出水击波波形,揭示了水击压力波传播方式、特性及衰减规律。通过分析随机捕捉测量技术方法,理论上推断出测量数据达到可信精度。在归纳分析试验数据基础上,得出最大压力随关阀时间的关系曲线,对圆管流动直接水击等概念进行了探讨,用数值分析方法拟合出水击最大压力水力计算修正方程式。     

岩石材料的冲击开裂机理

基于爆燃压裂造缝原理,研制了可以模拟爆燃加载环境的岩石冲击开裂实验装置,为进行动载下的岩石开裂机理研究提供了实验手段。根据动量和能量守衡原理等,建立了冲击峰值压力和加压速率计算模型,模型计算结果与16次钢质岩心实验结果间平均相对误差分别为2.56%和4.04%,具有较高的精度。39次岩石冲击开裂实验结果分析表明,冲击能量和平均加压速率是影响岩石开裂以及开裂能否形成多条裂缝的主要因素;多条开裂裂缝的形成更大程度上取决于平均加压速率,且存在明显的临界平均加压速率;基于实验结果的灰色关联分析和多元二次多项式回归,建立的裂缝条数计算相关公式具有较高的精度,为油气田开发中爆燃压裂技术的机理研究和施工参数设计与控制提供重要的依据。