矩形永磁体磁场分布的解析表达式

从分子环流模型出发,利用毕奥-萨伐尔定理,对于仅在一个方向均匀完全充磁的矩形永磁块体,导出了其外部空间磁场分布的解析表达式．该解析式能精确描述一块至多块按极性相反并列放置时矩形永磁体外部空间的磁场分布．针对单块永磁体,还分析了磁场分布与永磁体几何尺寸之间的依赖关系,以及磁场大小随外部空间点离开永磁体表面距离之间的关系;定量分析了横向磁场的强度均匀度和分布均匀度随永磁体几何尺寸和离开永磁体表面距离的变化规律．     

含正三角形孔口热电材料的断裂力学分析

采用复变函数方法研究了含正三角形孔口热电材料中受到无穷远处均匀电流密度和能量流作用下的断裂问题.在电绝缘和热绝缘边界条件下,获得了温度场和应力场的解析表达式,分析了三角形尺寸、能量流载荷对热电材料性能的影响.结果表明,能量流载荷和三角形尺寸的变化对环向能量流、环向应力、环向热流有较明显的影响.     

An electron-diffraction study of the effect of codeposition of foreign material on the structure of iron electrodeposits

An electron-diffraction study has been made of iron electrodeposits on copper (110) and (111) single-crystal faces. A comparison has been made of the orientation of these deposits under two sets of conditions: (a) when they reveal the incorporation of crystalline codeposits, and (b) when inclusions of foreign matter are absent. Ring radii measurements strongly suggest that the codeposit is hexagonal ferrous hydroxide. Further, it has been shown that, in the presence of codeposit, the iron electrodeposits (obtained at a particular current density) have crystal orientations which were normally obtained at higher current densities.     

Hall current effect on MHD mixed convection flow from an inclined continuously stretching surface with blowing/suction and internal heat generation/absorption

Hydromagnetic heat transfer by mixed convection along an inclined continuously stretching surface, with power-law variation in the surface temperature or heat flux, in the presence of Hall current and internal heat generation/absorption has been studied. The surface is considered to be permeable to allow fluid suction or blowing, and stretching with a surface velocity varied according to a power-law. Two cases of the temperature boundary conditions were considered at the surface. The governing equations have been transformed into non-similar partial differential equations which have been integrated by the forth-order Runge–Kutta method. The effect of Hall parameter, magnetic parameter, dimensionless blowing/suction parameter, space and temperature dependent internal heat generation/absorption parameters and buoyancy force parameters on the temperature, primary and secondary flow velocity have been studied parametrically. All parameters involved in the problem affect the flow and thermal distributions except the temperature-dependent internal heat generation/absorption in the case of prescribed heat flux (PHF). Numerical values of the local skin-friction and the local Nusselt numbers for various parametric conditions have been tabulated.     

On construction and (non)existence of c-(almost) perfect nonlinear functions

Functions with low differential uniformity have relevant applications in cryptography. Recently, functions with low c-differential uniformity attracted lots of attention. In particular, so-called APcN and PcN functions (generalization of APN and PN functions) have been investigated. Here, we provide a characterization of such functions via quadratic polynomials as well as non-existence results.     

均匀性度量的势函数模型

分析了均匀性度量应满足的基本条件，根据物理学的势和力的模型，提出了均匀性度量的势函数模型，该模型较好地解决了均匀性度量的可计算性、布点的均匀性调整方法等问题；而且具有均匀性度量所应该具有的所有优良性质，如旋转对称性、平移对称性、中心对称性等。最后给出了应用实例，并就低维投影的均匀性问题和势函数模型的改进作了讨论。      

A Stability Estimate for a Solution of the Problem of Determining the Dielectric Permittivity

We consider the problem of determining the dielectric permittivity for a nonconducting and nonmagnetic medium. As information we take the traces of the tangential components of the electromagnetic field on the lateral surface of a cylindrical domain. These traces correspond to a solution to some direct problem for the Maxwell system. The impulse source of the current flux lies outside the domain in which the coefficient is sought. The main result of the article is a stability estimate for a solution to the inverse problem in question.     

Iron ore production scheduling to improve product quality

Iron ore quality depends upon successive shipments being uniform in composition, not only in iron but also in several other minerals. The production process involves several stages of scheduling, from the mine face, through railing, stockpiling and ship loading. At each of these stages there is potential to improve the composition uniformity through appropriate scheduling procedures. This paper discusses a variety of algorithms and simulation models developed to aid these scheduling decisions.     

An approximate logic for measures

We present a logical framework for formalizing connections between finitary combinatorics and measure theory or ergodic theory that have appeared in various places throughout the literature. We develop the basic syntax and semantics of this logic and give applications, showing that the method can express the classic Furstenberg correspondence and to give short proofs of the Szemerédi Regularity Lemma and the hypergraph removal lemma. We also derive some connections between the modeltheoretic notion of stability and the Gowers uniformity norms from combinatorics.     

Isotropic background cosmic X-rays in the energy range 50–290 KeV

The observations of omnidirectional X-ray flux at the top of the atmosphere have been extended upto 200 KeV using a balloon-borne NaI (Tl) scintillator detector at Hyderabad, India. The omnidirectional flux at 60 KeV is found to be 0·0066±0·0014 photons/cm.² sec. ster. KeV. The X-ray flux in the energy range 50–290 KeV can be adequately represented by the spectrum Ke^?2.2±0.4. New upper limits to the hard X-ray flux from the quiet sun have also been obtained from the same measurement.     

Investigations of c-differential uniformity of permutations with Carlitz rank 3

The c-differential uniformity is recently proposed to reflect resistance against some variants of differential attack. Finding functions with low c-differential uniformity is attracting attention from many researchers. For even characteristic, it is known that permutations of low Carlitz rank have good cryptographic parameters, for example, low differential uniformity, high nonlinearity, etc. In this paper we show that permutations with low Carlitz rank have low c-differential uniformity. We also investigate c-differential uniformity of permutations with Carlitz rank 3 in detail.     

On canonical variables in integrable models of magnets

Three integrable models: the deformed Heisenberg, Landau-Lifschits, and Ishimori magnets are written in terms of the stereographic projection. The Hamiltonians of these models are obtained and certain problems related to the existence of exact solutions are studied. In particular, stability of solitions is studied for the Heisenberg marnet, simplest stationary solutions are obtained for the Landau-Lifschits magnet, and Hamiltonians and topological charges are calculated for several known solutions of the Ishimori model. Bibliography: 33 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 347, 2007, pp. 117–143.     

投影均匀分片拉丁超立方体设计

空间填充设计是有效的计算机试验设计,比如均匀设计、最大最小距离拉丁超立方体设计等.虽然这些设计在整个试验空间中有较好的均匀性,但其低维投影均匀性可能并不理想.对于因子是定量的计算机试验,已有文献构造了诸如最大投影设计、均匀投影设计等相适应的设计;而对于同时含有定性因子和定量因子的计算机试验,尚未有投影均匀设计的相关文献.文章提出了综合投影均匀准则,利用门限接受算法构造了投影均匀的分片拉丁超立方体设计.在新构造设计中,整体设计与每一片设计均具有良好的投影均匀性.模拟结果显示,与随机分片拉丁超立方体设计相比,利用新构造设计进行试验而拟合的高斯过程模型具有更小的均方根预测误差.     

Finite-element method simulation of rotating disk flow: effect of the transport of a chemical species

Electrochemical cells containing an iron rotating disk electrode which is dissolved in the electrolyte, an 1 M H₂SO₄ solution present a current instability in the plateau region, where the current is controlled by the mass transport. Dissolution of the electrode gives rise to a thin concentration boundary layer, due to a Schmidt number Sc = 2000. This boundary layer, together with the potential applied to the electrode, leads to an increase in the fluid viscosity and in a decrease in the diffusion coefficient, coupling the concentration and the chemical species field. Since the current is proportional to the concentration gradient at the interface, an instability of the coupled fields at Reynolds numbers attained in experimental conditions could be responsible for the current instability. Mangiavacchi [1] performed a linear stability analysis of the problem and showed that this is indeed the case. In this paper we review the main results of the stability analysis and present the main features of the FEM code recently developed in our group, to proceed with the investigation of the current instability observed in electrochemical cells. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Magnetic Procedure for the Stability Number

A magnet is a pair u, v of adjacent vertices such that the proper neighbours of u are completely linked to the proper neighbours of v. It has been shown that one can reduce the graph by removing the two vertices u, v of a magnet and introducing a new vertex linked to all common neighbours of u and v without changing the stability number. We prove that all graphs containing no chordless cycle C _k (k ≥ 5) and none of eleven forbidden subgraphs can be reduced to a stable set by repeated use of magnets. For such graphs a polynomial algorithm is given to determine the stability number.     

三维轴对称曲面击波驻点邻域的高阶理论

本文建立了三维轴对称小曲率曲面击波驻点邻域的次级条件,其中包括热传导、粘性、击波结构的影响.这些击波条件是在局部击波斜率代替局部击波曲率前提下建立的.在Prandtl数等于3/4条件下,获得了驻点邻域附近的击波质通量、滞止焓、动量的切向分量和法向分量的修正公式的显形式.     

Higher order global solution and normalized flux for singularly perturbed reaction-diffusion problems

In this paper a computational technique is proposed for obtaining a higher order global solution and global normalized flux of singularly perturbed reaction-diffusion two-point boundary-value problems. The HOC (higher order compact) finite difference scheme developed in Gracia et al. (2001) [4] and which is constructed on an appropriate piecewise uniform Shishkin mesh, has been considered to find an almost fourth order convergent solution at mesh points. Using these values, piecewise cubic interpolants based approximations for solution and normalized flux in whole domain have been defined. It has been shown that the global solution and the global normalized flux are also uniformly convergent. Moreover, for the global solution, the order of uniform convergence in the whole domain is optimal, i.e., it is the same as this one obtained at mesh points, whereas, for the global normalized flux, the uniform convergence is almost third order, except at midpoints of the mesh, where it is also almost fourth order. Theoretical error bounds have been provided along with some numerical examples, which corroborate the efficiency of the proposed technique to find good approximations to the global solution and the global normalized flux.     

Numerical simulation of Darcy–Forchheimer flow of third grade liquid with Cattaneo–Christov heat flux model

The main purpose of this research is to evaluate the impact of Darcy–Forchheimer flow in an incompressible third‐grade liquid through Cattaneo–Christov heat flux approach. The Cattaneo–Christov heat flux theory is adopted to govern the mathematical expression of energy, which involves the heat flux relaxation time chracteristics. Time‐dependent thermal conductivity is accounted. The steady problem is reduced to ordinary differential equations via suitable transformation. Numerical solutions for the resulting flow expressions have been computed with the help of Euler's explicit technique. Impact of influential variables on the velocity, temperature and skin‐friction coefficient have been demonstrated and discussed through graphs. Copyright © 2017 John Wiley & Sons, Ltd.     

Formation and performance of new Zr-Ti-Cu-Ni-Be-Fe bulk amorphous alloy

The formation of the new Zr-Ti-Cu-Ni-Be-Fe bulk amorphous alloy with high strength is reported. The effects of the iron atom on the glass forming ability, hardness, susceptibility and thermal stability of the amorphous alloy are investigated. The role of the iron in the formation of the bulk amorphous alloy is discussed.