不同精度格式的格子Boltzmann热模型的传热分析

通过在格子Boltzmann (LBM)热模型中添加参数项,使得在对应的宏观传热方程中,消除了一阶非线性误差项,具备二阶精度.通过Rayleigh-Benard对流数值试算,初步探索该二阶精度格式及其对应的一阶精度格式三个热模型的传热特征和适应性,并做出相应对比分析.针对一二阶精度模型在Ra数极高或热传导系数极大时,Nu数的计算与经验值相比出现较大偏差,分析LBM对应宏观热传导方程的截断误差后,在平衡分布函数中引进一个调节因子.通过调节对应宏观传热方程的截断误差项系数,校正Nu数的计算偏差,提高模拟精度,拓展模拟范围,增强了LBM作为一个数值方法在传热中的适应性.     

Velocity distribution of flow with submerged flexible vegetations based on mixing-length approach

By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow velocities and Reynolds stress. The results show that hydraulic characteristics in non-vegetation and vegetation layers are totally different. In a region above the vegetation, Reynolds stress distribution is linear, and the measured velocity profile is a classical logarithmic one. Based on the concept of new-riverbed, the river compression parameter representing the impact of vegetation on river is given, and a new assumption of mixing length expression is made. The formula for time-averaged velocity derived from the expression requires less parameters and simple calculation, and is useful in applications.     

Minimizing sequences of variational problems with small parameters

A class of variational problems with small parameters is studied. Their zeroth-order asymptotic solutions are constructed. It is shown that the zeroth-order asymptotic solution is just the minimizing sequence of variational problems as the small parameter approaches to zero.     

基于区间参数摄动法的三维弹塑性区间有限元探讨

首次探讨了弹塑性问题的区间分析,推导了三维弹塑性问题的区间参数摄动法有限元计算公式,研制了相应的弹塑性区间有限元程序,通过算例分析得到结论:(1)采用增量法对弹塑性问题进行区间分析时,增量位移离差随着增量位移均值的增大而增大.(2)单元高斯点应力没有达到屈服极限之前,高斯点的应力离差很小;当单元高斯点应力达到屈服极限之后,高斯点应力离差逐渐增大.(3)是否考虑塑性矩阵的应力分量为弹塑性参数的隐函数,对应力高差计算的影响较小.     

On the uniqueness of large deflections of a uniform cantilever beam under a tip-concentrated rotational load

The problem of a uniform cantilever beam under a tip-concentrated load, which rotates in relation with the tip-rotation of the beam, is studied in this paper. The formulation of the problem results in non-linear ordinary differential equations amenable to numerical integration. A relation is obtained for the applied tip-concentrated load in terms of the tip-angle of the beam. When the tip-concentrated load acts always normal to the undeformed axis of the beam (the rotation parameter, β=0) there is a possibility of obtaining non-unique solution for the applied load. This phenomenon is also observed for other rotation parameters less than unity. When the tip-concentrated load is acting normal to the deformed axis of the beam (β=1), many load parameters are obtained for a tip-angle with different deformed configurations of the beam. However, each load parameter corresponds to a tip-angle, which confirms the uniqueness on the solution of non-linear differential equations.     

Experimentally Determining Bloch Parameters of Hamiltonian for Single-Qubit Systems

By considering the identification problem of unknown but fixed Hamiltonian H = S0σ0 ＋∑i=x,y,z Siσi where σi （i = x, y, z） are pauli matrices and σ0=I, we explore the feasibility and limitation of empirically determining the Hamiltonian parameters for quantum systems under experimental conditions imposed by projective measurements and initialization procedures. It may be unsurprising to physicists that one can not obtain the knowledge of So no matter what kind of projective measurements and initialization are permitted, but the observation draws our attention to the importance of the parameter identifiability under different experimental condition. It has also been revealed that one can obtain the knowledge of ｜Sz｜ and Sx^2＋Sy^2 at most when only the projective measurement {｜0/（0｜, ｜1/（1｜} is permitted to perform on and initialize the qubit. Further more, we demonstrated that it is feasible to distinguish ｜Sx｜, ｜Sy｜, and ｜Sz｜ even without any a priori information about Hamiltonian if at least two kinds of projective measurement or initialization procedures are permitted. It should be emphasized that both projective measurements and initialization procedures play an important role in quantum system identification.     

铜导线短路熔痕的XPS研究

利用氩离子溅射对熔痕样品进行了深度刻蚀,同时利用Cu的俄歇谱线和计算的俄歇参数值,对不同环境形成的铜导线短路痕迹的物相及元素分布规律进行了分析。根据刻蚀时间可将一次短路熔痕表面膜层分为三部分,即C含量迅速减少的近表面层;O含量变化不大,C含量逐渐消失且有Cu₂O相的中间层;无Cu₂O相,O含量显著减少的过渡层。而将二次短路熔痕表面膜层分为两部分：C含量迅速减少的近表面层;无Cu₂O相,C和O量逐渐减少层。由此可见,一次短路熔痕的表面膜层与基体分界明显,有显著的过渡层,而二次短路熔痕的表面膜层与基体分界不明显,无过渡层。综上所述,可以根据两种短路熔痕是否含有Cu₂O相以及定量分析结果来区分两种熔痕,为判断火灾原因提供新的技术依据。     

Theoretical study on the complexes of He, Ne and Ar

This paper investigates the effect of basis sets through the potential energy curves(PECs) of six rare gas complexes He 2,Ne 2,Ar 2,He-Ne,He-Ar,and Ne-Ar.The coupled cluster singles and doubles method with perturbative treatment of triple excitations,doubly augmented basis sets of d-aug-cc-pVQZ,bond functions,and basis set superposition errors are employed.The diffuse function is more effective than the polarization function on describing the dissociation energy.The PECs are fitted into analytical potential energy functions(APEFs) using three expressions.It is found that all the expressions are suitable for describing the complexes of rare gases.Based on these APEFs,the spectroscopic parameters are calculated and the results are compared with the theoretical and experimental data available in the literature.     

Uncertainty Relations in Terms of Fisher Information

By virtue of the well-known concept of Fisher information in the theory of statistical inference, we obtain an inequality chain which generalizes and refines the conventional Heisenberg uncertainty relations.     

MOBVE分布参数的估计及其改进

本文讨论由Marshall和Olkin引进的二元指数分布(MOBVE分布)的参数估计问题.这个分布关于某个控制测度的密度函数被提出.对于边缘分布相同的情形,本文给出了充分统计量并讨论了它的性质;对两个参数各提出了一个无偏估计并采用协方差改进法分别对其作了改进.