Self-assembly formation of the ordered nanostructure arrays induced by Be interaction with Si(1 1 1) surface

Formation of the beryllium (Be) submonolayers on the Si(1 1 1)7 × 7 surface has been studied using scanning tunneling microscopy. It has been found that Be interaction with Si(1 1 1) at 500-700 °C results in a self-assembly formation of the four various types of the highly-ordered nanostructure arrays. The nanostructure arrays develop on top of the “soft” silicide layer, which period and orientation alter with the nanostructure growth: the shorter the nanostructure period, the larger the rotation angle. The main structural parameters of the silicide layer and nanostructure arrays have been established.     

On a geometric inequality

An inequality is obtained connecting the characteristics of a figureG with the characteristics of similar images of a convex figureg contained inG and containingG. In the case wheng is a disk the well-known inequality of Bonnesen is obtained.Translated from Ukrainskií Geometricheskií Sbornik, No. 30, 1987, pp. 49–52.     

Anode-Shape Determination with Allowance for Electrolyte Properties in Problems of Dimensional Electrochemical Machining of Metals

Based on the boundary-element technique, a method for determining the contour of an anode-workpiece with a prescribed shape of a cathode-tool is suggested for plane problems of dimensional electrochemical machining of metals. Within the scope of the assumptions made, the original problem is reduced to the problem of a fictitious flow of an ideal fluid with free surfaces. The allowance for the machining mode and electrolyte properties yields a nonlinear condition at the free surface.     

Focusators into a ring

Using numerical and analytical approaches, we have computed the optical elements (focusators) required for focusing laser light into a narrow ring, a wide ring and a set of rings. A numerical comparison of the various computational techniques is reported. Finally the operation of a fabricated rotor axicon to focus light into a ring is reported.     

Atomic and electronic structures of Ag/Si(100)-c(6 × 2) surface: A first-principles study

Using the experimental data obtained mainly with the scanning tunneling microscopy observations, density functional theory calculations have been applied to examine an atomic structure of the Ag/Si(100)-c(6 × 2) reconstruction. A set of structural models has been proposed having a similar Si(100) substrate reconstruction which incorporates rows of top Si atom dimers and troughs in between the rows. Stability of about twenty models with various Ag coverage ranging from 1/6 to 1 ML has been tested, that allows reducing the number of plausible models to four. Two of these four models have been attributed to the “regular” intrinsic Ag/Si(100)-c(6 × 2) reconstruction, while the other two to its defect-induced modification. The latter is observed in the local areas near defects and domain boundaries and exhibits 3 × 2 periodicity. Comparing the results of calculations with the experimental STM images, it has been concluded that while the Si(100) substrate reconstruction is solid, the Ag subsystem is flexible due to the presence of the lightly bonded mobile Ag atoms.     

Partial-Wave Decomposition for Meson-Exchange Currents in Few-Nucleon Systems

 We develop an approach for calculating matrix elements of meson-exchange current operators between three-nucleon basis states in -coupling and a three-nucleon bound state. The contributions generated by π- and ρ-exchanges are included into the consideration. The matrix elements are expressed in terms of multiple integrals in momentum space. We apply a technique of partial-wave decompositions and carry out some angular integrations in closed form. Different representations appropriate for numerical calculations are derived for the matrix elements of interest. The momentum dependences of the matrix elements are studied and benchmark results are presented. The approach developed is of interest for investigations of deuteron-proton radiative capture and ³He photo- and electrodisintegration when the interactions in the initial or final states are taken into account by solving the Faddeev equations. Received April 2, 1999; accepted for publication December 30, 1999     

片层硅酸盐用于热固性PU/PLS复合可能性探讨

高岭土(Kaolinite)和蒙脱土(Montromollite)等粘土,被广泛用作添加剂来改善聚合物的耐热性能。文章用各种先进技术对高岭土与蒙脱土的形态、组成和结构进行表征比较。电子透射电镜及电子探针(TEM/EDX)结果显示高岭土较蒙脱土有较大的粒径和较小的硅铝比,TEM还显示出这些粘土是由片层粒子堆积而成。热重分析(TGA)的结果表明蒙脱土由于失去吸附水从60 ℃升温至90 ℃失重明显(约7%),而高岭土在此温度下几乎不失水。高岭土脱除结构羟基官能团脱水失重的温度大约在510 ℃,低于蒙脱土的670 ℃。室温下光声傅里叶变换(PAS-FTIR)红外光谱显示蒙脱土在羟基吸收区有较强的吸附水的吸收,1 650 cm-1处孤立的弱吸收谱带可给予左证。变温红外和TGA的结果显示,片层硅酸盐表面的结构羟基从100～500 ℃非常稳定,它可以和异氰酸酯基团(NCO)封端的预聚物反应形成热固性PU/PLS复合聚合物。     

Rotation of multimodal Gauss–Laguerre light beams in free space and in a fiber

A gradient algorithm is proposed for design of phase diffractive optical elements (DOEs) that can form the light beams being effectively a superposition of a small number of nonradially symmetric Gauss–Laguerre modes with a preset energy contribution of each mode. We show that under certain conditions there is a rotation of the cross-section of such light beams. The rotation of multimodal Gauss–Laguerre light beams propagating in a fiber with quadratic dependence of the refractive index is discussed.