Group algebras of Kleinian type and groups of units

The algebras of Kleinian type are finite-dimensional semisimple rational algebras A such that the group of units of an order in A is commensurable with a direct product of Kleinian groups. We classify the Schur algebras of Kleinian type and the group algebras of Kleinian type. As an application, we characterize the group rings RG, with R an order in a number field and G a finite group, such that the group of units of RG is virtually a direct product of free-by-free groups.     

Dependence of calculated electron effective attenuation lengths on transport mean free paths obtained from two atomic potentials

We report changes in electron effective attenuation lengths (EALs) resulting from use of transport mean free paths (TMFPs) obtained from the Dirac–Hartree–Fock (DHF) potential instead of the Thomas–Fermi–Dirac (TFD) potential in an algorithm used in the National Institute of Standards and Technology (NIST) Electron Effective‐Attenuation‐Length Database (SRD 82). TMFPs from the former potential are believed to be more reliable than those obtained from the latter potential. We investigated changes in the EALs for selected photoelectron and Auger‐electron lines in four elemental solids (Si, Cu, Ag, and W), for Si 2p photoelectrons of varying energy in SiO₂, and for photoelectrons excited by Al Kα X rays in four candidate gate‐dielectric materials (HfO₂, ZrO₂, HfSiO₄, and ZrSiO₄). For each material, we computed the change in the average EAL for a range of overlayer‐film thicknesses from zero to a maximum value corresponding to attenuation of the substrate signal to 10% of its original value. This EAL change was a maximum for electrons emitted normally from the surface and decreased monotonically with increasing emission angle. The maximum EAL change varied between ?4.4% and 2.6% for the three groups of materials. We found that the maximum EAL change correlated mainly with the TMFP change. We found that TMFP changes in other solids could generally lead to maximum EAL changes between ?2.6% and 1.9% for electron energies between 500 and 2000 eV. For lower energies, the maximum EAL changes could be larger for some solids. Our revised EALs for Si 2p photoelectrons in SiO₂ excited by Mg and Al Kα X rays agree within 0.5% with values reported by Seah and Spencer from a detailed analysis of SiO₂ film‐thickness measurements by XPS and other techniques. Copyright © 2006 John Wiley & Sons, Ltd.     

绕圆柱体自由表面磁流体流动和传热的研究

本文对在不同雷诺数下,绕圆柱体的磁流体自由表面流动及传热进行了模拟,分析了磁场对绕流圆柱尾迹和涡分离的影响,获得了两种雷诺数下的电磁力密度、流场和温度场分布。结果表明,磁场不仅影响了流动的形态,而且对湍流有抑制作用,降低了自由表面的更新机制,从而减少了传热能力;在相同的Hartmann数下,相比低雷诺数下的流动换热情况,高雷诺数下的湍流不能被完全抑制,自由表面与尾迹的相互作用也较强,因而自由表面换热也较强。     

电子碰撞诱导原子从低激态向高激态弛豫

本文根据空心阴极放电中电子能量分布的物理图象,分析了原子从低激态向高激态弛豫的可能途径。建立高低激态集居数密度增量的关系。讨论高激态集居数密度增量获得可观量的条件。根据此条件分别选取钠原子的基态3s~2S_(1/2)和铜原子的亚稳态4s~2D_(3/2)为与激光共振的下能级,并激发具有较大自发发射几率的3s~2S_(1/2)→3p~2P°_(1/2)(和3p~2P°_(3/2))和4s~2D_(3/2)→4p~2P°_(1/2)跃迁,在远离上能级的高激态上观测到敏化荧光,并精确测得这些态的自发发射系数比值,而在更高激态上没有观测到敏化荧光,表明讨论中提出的条件是合理的。     

反光板(合作目标)反射率测量仪

本文介绍了反光板（合作目标）反射率测量仪的研制。仪器采用对称双光路比较测量法，给定两束相等光通量的光束，分别作为参考光束和测试光束，并用分束器实现原光路取样，从而解决了合作目标反光板入射光线与反射光线重合不能用常规测试方法来检测的难题。由于采用对称双光路的方法，入射光通量是相对恒定的，不受外界因素影响，从而使反射率测量仪达到精度高、重复性好和环境要求低的设计要求。     

Gamma radiation effects on an amine antioxidant added in an ethylene-propylene copolymer

The aim of this work was to compare the gamma radiation induced effects on samples of an ethylene-propylene copolymer antioxidant free with samples loaded with an antioxidant characterised by the presence of an -NH functional group. The employed techniques were Electron Spin Resonance spectroscopy (ESR) and High Performance Liquid Chromatography (HPLC). Stable radicals R---NO° due to the interaction of free radicals produced in the irradiated polymer with the antioxidant have been observed by ESR at room temperature. The time evolution of the ESR signals following the irradiation was examined at different doses. The amount of antioxidant not involved in the oxidation reactions has been determined using HPLC.     

The stress driven instability in elastic crystals: Mathematical models and physical manifestations

Summary Equilibrium equations and stability conditions for the simple deformable elastic body are derived by means of considering a minimum of the static energy principle. The energy is supposed to be sum of the volume (elastic) and the surface terms. The ability to change relative positions of different material particles is taken into account, and appropriate natural definitions of the first and second variations of the energy are introduced and calculated explicitly. Considering the case of negligible magnitude of the surface tension, we establish that an equilibrium state of a nonhydrostatically stressed simple elastic body (of any physically reasonable elastic energy potential and of any symmetry) possessing any small smooth part of free surface is always unstable with respect to relative transfer of the material particles along the surface. Surface tension suppresses the mentioned instability with respect to sufficiently short disturbances of the boundary surface and thus can probably provide local smoothness of the equilibrium shape of the crystal. We derive explicit formulas for critical wavelength for the simplest models of the internal and surface energies and for the simplest equilibrium configurations. We also formulate the simplest problem of mathematical physics, revealing peculiarities and difficulties of the problem of equilibrium shape of elastic crystals, and discuss possible manifestations of the above-mentioned instability in the problems of crystal growth, materials science, fracture, physical chemistry, and low-temperature physics.     

The measure of a translated ball in uniformly convex spaces

Let (E, ¦·¦) be a uniformly convex Banach space with the modulus of uniform convexity of power type. Let be the convolution of the distribution of a random series inE with independent one-dimensional components and an arbitrary probability measure onE. Under some assumptions about the components and the smoothness of the norm we show that there exists a constant such that |{·<t}–{·+r<t}|r ^q , whereq depends on the properties of the norm. We specify it in the case ofL spaces, >1.     

Circuit-switching networks with FIFO plus justifying blockout service on infinite graphs

A class of circuit-switching open queueing networks is discussed. The main result of the paper is that if extra message flows are not too intensive and the path distribution is mainly concentrated on the paths of (graph) distance 1 (nearest neighbour connections), then the network has a unique stationary working regime, no matter how large the configuration graph of the network is. Standard properties of this regime are established such as decay of correlation and continuity.