基于线电压和零序电流相位的小电流接地故障分界方法

针对用户内部小电流接地故障波及公共电网事故频发,现有分界开关单相接地分界可靠性不高的情况,提出了基于广域测控系统的线电压和零序电流相位的分界新方法。综合分析比较故障时不同接地系统工频分量幅值与相位特征,加入对不同故障合闸角、不同接地电阻影响因素的判别。该方法不受接地系统类型、合闸角、接地电阻等因素影响,解决了小电流接地故障分界遇到的判别困难问题,实现了责任分界点的准确定位。

Bookmark标准设定中的分界分数估计方法比较

采用Reckase的模拟方法讨论3种分界分数估计方法和2种反应概率值(response probability,RP)对Bookmark标准设定中单个评委第一轮分界分数的影响.结果表明:将正确作答概率低于RP的第一个题目以及正确作答概率高于RP的最后一个题目的难度定位值(Bookmark difficulty location,BDL)均值作为分界分数估计值的方法(AVERAGE方法)在对预期分界分数(intended cut score,ICS)的返真性方面优于将书签前一个题目的BDL作为分界分数估计值的方法 (previous item,PI)和将书签两旁题目的BDL均值作为分界分数估计值的方法 (between items,BI);评委评判误差对AVERAGE方法设定的分界分数的影响最小,不同RP值对分界分数的设定也有影响.

Modeling Technology in Finite Element Analysis of Electrostatic Proximity Fuze Problem

In order to analyze the electrostatic field concerned with electrostatic proximity fuze problem using the available finite analysis software package, the technology to model the problem with a scale reduction object and boundary was presented. The boundary is determined by the maximum distance the sensor can detect. The object model is obtained by multiplying the terms in Poisson's equation with a scale reduction factor and the real value can be reconstructed with the same reverse process after software calculation. Using the finite element analysis program, the simulation value is close to the theoretical value with a little error. The boundary determination and scale reduction method is suitable to modeling the irregular electrostatic field around air targets, such as airplane, missile and so on, which is based on commonly used personal computer (PC). The technology reduces the calculation and storage cost greatly.

Decomposition method for solving parabolic equations in finite domains

This paper presents a comparison among Adomian decomposition method (ADM), Wavelet-Galerkin method (WGM), the fully explicit (1,7) finite difference technique (FTCS), the fully implicit (7,1) finite difference method (BTCS), (7,7) Crank-Nicholson type finite difference formula (C-N), the fully explicit method (1,13) and 9-point finite difference method, for solving parabolic differential equations with arbitrary boundary conditions and based on weak form functionals in finite domains. The problem is solved rapidly, easily and elegantly by ADM. The numerical results on a 2D transient heat conducting problem and 3D diffusion problem are used to validate the proposed ADM as an effective numerical method for solving finite domain parabolic equations. The numerical results showed that our present method is less time consuming and is easier to use than other methods. In addition, we prove the convergence of this method when it is applied to the nonlinear parabolic equation.

Ground states for asymptotically periodic quasilinear Schrdinger equations with critical growth

For a class of asymptotically periodic quasilinear Schr？dinger equations with critical growth the existence of ground states is proved.First applying a change of variables the quasilinear Schr？dinger equations are reduced to semilinear Schr？dinger equations in which the corresponding functional is well defined in H1 RN .Moreover there is a one-to-one correspondence between ground states of the semilinear Schr？dinger equations and the quasilinear Schr？dinger equations.Then the mountain-pass theorem is used to find nontrivial solutions for the semilinear Schr？dinger equations. Finally under certain monotonicity conditions using the Nehari manifold method and the concentration compactness principle the nontrivial solutions are found to be exactly the same as the ground states of the semilinear Schr？dinger equations.

Determining Atmospheric Boundary Layer Height with the Numerical Differentiation Method Using Bending Angle Data from COSMIC

This paper presents a new method to estimate the height of the atmospheric boundary layer(ABL) by using COSMIC radio occultation bending angle(BA) data. Using the numerical differentiation method combined with the regularization technique, the first derivative of BA profiles is retrieved, and the height at which the first derivative of BA has the global minimum is defined to be the ABL height. To reflect the reliability of estimated ABL heights, the sharpness parameter is introduced, according to the relative minimum of the BA derivative. Then, it is applied to four months of COSMIC BA data(January, April, July, and October in 2008), and the ABL heights estimated are compared with two kinds of ABL heights from COSMIC products and with the heights determined by the finite difference method upon the refractivity data. For sharp ABL tops(large sharpness parameters), there is little difference between the ABL heights determined by different methods, i.e.,the uncertainties are small; whereas, for non-sharp ABL tops(small sharpness parameters), big differences exist in the ABL heights obtained by different methods, which means large uncertainties for different methods. In addition, the new method can detect thin ABLs and provide a reference ABL height in the cases eliminated by other methods. Thus, the application of the numerical differentiation method combined with the regularization technique to COSMIC BA data is an appropriate choice and has further application value.

Some optimal dividend problems for a surplus process with interest

We derive some results on the dividend payments prior to ruin in the classical surplus process with interest.An integro-differential equation with a boundary conditions satisfied by the expected present value of dividend payments is derived and solved.Furthermore,we derive an integro-differential equation for the moment generating function,through which we analyze the higher moment of the present value of dividend payments.Finally,closed-form expressions for exponential claims are given.

Self-organized Critical Model Based on Complex Brain Networks with Hierarchical Organization

The dynamical behavior in the cortical brain network of macaque is studied by modelling each cortical areawith a subnetwork of interacting excitable neurons.We find that the avalanche of our model on different levels exhibitspower-law.Furthermore the power-law exponent of the distribution and the average avalanche size are affected by thetopology of the network.

Novel boundary element method for resolving plate bending problems

This paper discusses the application of the boundary contour method fo r resolving plate bending problems. The exploitation of the integrand divergence free property of the plate bending boundary integral equation based on the Kirc hhoff hypothesis and a very useful application of Stokes' Theorem are presented to convert surface integrals on boundary elements to the computation of bending potential functions on the discretized boundary points,even for curved surface elements of arbitrary shape. Singularity and treatment of the discontinued corne r point are not needed at all. The evaluation of the physics variant at internal points is also shown in this article. Numerical results are presented for some plate bending problems and compared against analytical and previous solutions.

Solving Linear Fredholm-Stieltjes Integral Equations of the Second Kind by Using the Generalized Midpoint Rule

In this paper, the approximate solution to the linear fredholm-stieltjes integral equations of the second kind （LFSIESK） by using the generalized midpoint rule （GMR） is introduced. A comparison resu｜ts depending on the number of subintervals ＂n＂ are calculated by using Maple 18 and presented. These results are demonstrated graphically in a particular numerical example. An algorithm of this application is given by using Maple 18.

Concept Design of a New Deep Draft Platform

The authors analyzed requirements for a new deepwater platform, from conceptual design to hydrodynamic analysis.The design incorporated Deep Draft Multi-Spar (DDMS) that allowed easy fabrication, reduced costs, and provided favorable motion performance.It also provided a dry tree system and other benefits.The conceptual design process included dimension estimation, general arrangements, weight estimation, weight distribution, stability analysis, etc.A high order boundary element method based on potential theory and the modified Morison equation was used to predict the hydrodynamic and viscous effects of this new concept platform.The response amplitude operators (RAOs) were acquired and compared with those of a typical Truss Spar.The response of the platform to the JONSWAP spectra of 3 different extreme ocean conditions was analyzed to evaluate the seakeeping ability of the new concept.The results revealed favorable motion performance due to all the degrees of freedom available.

Multi-domain Boundary Element Method with Dissipation

The wave diffraction and radiation around a floating body is considered within the framework of the linear potential theory in a fairly perfect fluid. The fluid domain extended infinitely in the horizontal directions but is limited by the sea bed, the body hull, and the part of the free surface excluding the body waterplane, and is subdivided into two subdomains according to the body geometry. The two subdomains are connected by a control surface in fluid. In each subdomain, the velocity potential is described by using the usual boundary integral representation involving Green functions. The boundary integral equations are then established by satisfying the boundary conditions and the continuous condition of the potential and the normal derivation across the control surface. This multi-domain boundary element method （MDBEM） is particularly interesting for bodies with a hull form including moonpools to which the usual BEM presents singularities and slow convergence of numerical results. The application of the MDBEM to study the resonant motion of a water column in moonpools shows that the MDBEM provides an efficient and reliable prediction method.

On the Singular Biharmonic Problems Involving Critical Sobolev Exponents

Abstract： Let Ω belong to R^N be a smooth bounded domain such that 0 ∈ Ω, N ≥ 5, 2^＊ ：2N/N-4 is the critical Sobolev exponent, and f（x） is a given function. By using the variational methods, the paper proves the existence of solutions for the singular critical in the homogeneous problem △^u-μ u/{x}^4=｜μ｜^2＊-2u＋f（x） with Dirichlet boundary condition on 偏dΩ under some assumptions on f（x） and μ.

Modeling of Water Vapor Condensation by Using Computer Methodology

The excessive moisture has an adverse effect on the building materials structure. Most standard construction materials are characterized by porous structure, resulting in the ability to absorb water in liquid and gaseous phases in the inner pores. Under certain conditions, water fills the pores within the structure of building material and then moves back to its surrounding. Many technical studies have shown that monitoring the moisture transport is mainly based on experimental methods. This work is based on models of transport of moisture in building physics, i.e., the description of the moisture behaviour of building materials based on physical laws models （KRISCHER, KIESSL）. The aim of this work is to obtain the parameters of distribution of moisture for calculation capillary conductivity coefficient for practical using by means of non-destructive method. The authors have now developed all the software required to perform a boundary element analysis of problems in potential flow. The examples which the authors can analyse will, however, be restricted to homogenous domains.

Challenge of Hydrodynamic Analysis for a Structure in Waves

Hydrodynamic analysis is one of the key steps in safety assessment ot a structure m waves, lvlany optloll~ axe available for answering challenge raised from marine and offshore energy industry, from costly three dimensional CFD to the efficient but not perfect boundary element models. Focus on the boundary element methods, analysis methods for the interaction of waves and structures are discussed. Those boundary element models cover frequency domain and time domain, linear and non-linear. Special attention is pay to the problems encountered in those models and approaches we adopted for their engineering solution.

Numerical Solution of Some Diffusion Problems in 3-Layered 3D Domain

In this paper we consider averaging and finite difference methods for solving the 3-D boundary-value problem in a multilayered domain. We consider the metal concentration in the 3 layered peat blocks. Using experimental data the mathematical model for calculating the concentration of metal at different points in peat layers is developed. A specific feature of these problems is that it is necessary to solve the 3-D boundary-value problems for the partial differential equations （PDEs） of the elliptic type of second order with piece-wise diffusion coefficients in the three layer domain. We develop here a finite-difference method for solving a problem of the above type with the periodical boundary condition in x direction. This procedure allows reducing the 3-D problem to a system of 2-D problems by using a circulant matrix.

Analysis of the Adjacent Terrain Effect on the Properties of Ground Motion

The explicit finite element analysis method combined with the artificial transmitting boundary theory is performed to evaluate the adjacent terrain effects on ground motion,and the influence of the distance between adjacent terrains on the topographical amplification effects on ground motion is studied. The results show that:( 1) Compared to the case of a single hill,the presence of adjacent hills has little effect on the shape of the spectral ratio curve,but has a significant effect on the value of spectral ratio,which is dependent on the locations of observation points.( 2) The presence of adjacent hills has a greater effect on high-frequency ground motion,and with the increase of the distance between adjacent hills,such an effect weakens gradually,and the effect of the composite topography combined with multiple hills on ground motion gradually approaches that of a single hill.

A survey on artificial boundary method Dedicated to Professor Shi Zhong-Ci on the Occasion of his 80th Birthday

The artificial boundary method is one of the most popular and effective numerical methods tor solving partial differential equations on unbounded domains, with more than thirty years development. The artificiM boundary method has reached maturity in recent years. It has been applied to various problems in scientific and engineering computations, and the theoretical issues such as the convergence and error estimates of the artificial boundary method have been solved gradually. This paper reviews the development and discusses different forms of the artificial boundary method.

Micro-CT evaluation and histological analysis of screwbone interface of expansive pedicle screw in osteoporotic sheep

Objective： To investigate the properties of screwbone interface of expansive pedicle screw （EPS） in osteoporotic sheep by micro-CT and histological observation. Methods： Six female sheep with bilateral ovariectomyinduced osteoporosis were employed in this experiment. After EPS insertion in each femoral condyle, the sheep were randomly divided into two groups： 3 sheep were bred for 3 months （Group A）, while the other 3 were bred for 6 months （Group B）. After the animals being killed, the femoral condyles with EPS were obtained, which were three-dimensionally-imaged and reconstructed by micro-CT. Histological evalu-ation was made thereafter. Results： The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expan-sive section, especially within the spiral marking. In the non- expansive section, however, there was no significant differ-ence between the interface and the distant parts. The regions of interest （ROI） adjacent to EPS were reconstructed and analyzed by micro-CT with the same thresholds. The three-dimensional （3-D） parameters, including tissue min- eral density （TMD）, bone volume fraction （BVF, BV/TV）, bone surface/bone volume （BS/BV） ratio, trabecular thickness （Tb.Th）, and trabecular separation （Tb.Sp）, were sig- nificantly better in expansive sections than non-expan-sive sections （P 〈 0.05）. Histologically, newly-formed bony trabeculae crawled along the expansive fissures and into the center of EPS. The newly-formed bones, as well as the bones at the bone-screw interface, closely contacted with the EPS and constructed four compartments. Conclusions： The findings of the current study, based on micro-CT and histological evaluation, suggest that EPS can significantly provide stabilization in osteoporotic cancellous bones.

Variable-step integration method for milling chatter stability prediction with multiple delays

This paper analyzes the stability of milling with variable pitch cutter and tool runout cases characterized by multiple delays,and proposes a new variable-step numerical integration method for efficient and accurate stability prediction. The variable-step technique is emphasized here to expand the numerical integration method,especially for the low radial immersion cases with multiple delays. First,the calculation accuracy of the numerical integration method is discussed and the variable-step algorithm is developed for milling stability prediction for single-delay and multiple-delay cases,respectively. The milling stability with variable pitch cutter is analyzed and the result is compared with those predicted with the frequency domain method and the improved full-discretization method. The influence of the runout effect on the stability boundary is investigated by the presented method. The numerical simulation shows that the cutter runout effect increases the stability boundary,and the increasing stability limit is verified by the milling chatter experimental results in the previous research. The numerical and experiment results verify the validity of the proposed method.