Polarization properties of corner-cube retroreflectors: theory and experiment

Polarization properties of the corner-cube retroreflector are discussed theoretically by use of ray tracing and analytical geometry. The Jones matrices and eigenpolarizations of the six propagation trips of the corner-cube retroreflector are derived. An experiment is also set up for the determination of the linear eigenpolarizations and the output states of polarization for incident linearly polarized light. The experimental results are consistent with theoretical expectations.     

Fourier transform near-infrared spectrometer using a corner-cube integrated prism scanning interferometer

This paper describes a Fourier transform (FT) near-infrared spectrometer that uses an integrated prism scanning interferometer whose optical paths are stabilized by corner cubes. A combination of corner cubes and a retroreflection mirror, which is sometimes used in the conventional interferometer for FT spectrometers, is adopted and adapted to the integrated prism scanning interferometer through a special design. Without any degradation of spectroscopic properties, the optical path in the interferometer is highly stabilized and the moving distance of the stage is halved. These advantages provide a robust and portable FT spectrometer for field use.     

旋转柱面产生动态散斑的统计特性分析

高斯光束照射到以角速度ω 旋转的圆柱体表面时,反射空间将出现的动态散斑随着被测表面的运动连续变化,这是一个随机过程。研究了当旋转圆柱体表面满足弱散射体条件时,在菲涅尔衍射场形成的动态散斑的统计特性;给出了几种特定情况下描述动态散斑时间-空间相关性质的参数——动态散斑的空间相关长度,动态散斑的相关时间,动态散斑的平移距离和相关距离。这些参数表明动态散斑的统计特性与圆柱体曲率半径、入射光束、表面微观形貌、物体旋转角速度、光学几何结构因素有关;依据参数分析了动态散斑运动形式,动态散斑纯沸腾运动取决于观察面到散射屏出射平面的距离,投射到散射屏出射平面上的照明光波波面的曲率半径和散射体的曲率半径。     

Thermophysical properties of ceramic matrix composites produced by polymer pyrolysis

A unidirectional composite and a series of bidirectionally reinforced composites were fabricated using carbon fibre reinforcement in a silicon carbide matrix, which was produced by the pyrolysis of a polymer precursor. The thermal expansion over the temperature range 20–1000 °C has been measured and the thermal diffusivity measured over the temperature range 200–1200 °C. Thermal diffusivity data was converted to conductivity data using measured density and literature specific heat data. Metallographic examination has been carried out on the composites and the results are discussed in terms of the observed microstructural features.     

Anisotropic compressive properties of porous copper produced by unidirectional solidification

Porous copper whose long cylindrical pores are aligned in one direction has been fabricated by unidirectional solidification of the melt in a mixture gas of hydrogen and argon. The compressive yield strength of the porous copper with the cylindrical pores orientated parallel to the compression direction decreases linearly with increasing porosity. For the porous copper whose pore axes are perpendicular to the compressive direction, the compressive yield strength slightly decreases in the porosity range up to 30% and then decreases significantly with increasing porosity. The compressive stress–strain curves depend on the compressive direction with respect to the pore direction, which are due to the stress concentration around the pores and the buckling of the copper between the pores. From two different types of stress–strain curve, the energy absorption capacity of the porous copper with the pores parallel to the compressive direction is higher than that perpendicular to the compressive direction at a given porosity.     

TiC-xNi金属陶瓷的燃烧合成及其热物理性能

利用自蔓延高温燃烧民结合机械厂压力方法制备了TiC-Ni金属陶瓷,研究了ＴiC-Ni金属陶瓷材料的密度,比热度、比热容、热传导以及热膨胀性质随温度和组成的变化关系,结果表明：ＴiC-Ni材料的密度在w(Ni)为２０％时致密性达到最高,材料的比定压热容在浊试温度区内呈线性增加;ＴiC-Ni材料的热扩散率随度的升高基本呈增加趋势,热扩散率随Ｎi含量的增加而增加,热导率的变化与热扩散率的变化有相似的规律,材料的热膨胀系数随温度的升高单调递增,温度上升相同情况下,材料的热膨胀系数随Ｎi含量的增加而增加。     

Superconducting properties of V3Si produced by reactive diffusion

We have made a study of the superconducting properties of specially prepared V₃Si films. The films studied were produced in two steps. Vanadium was first sputtered onto silica glass substrates; then the film and substrate were heated. Above a definite threshold temperature the vanadium combined with the silicon atoms in the glass to form V₃Si.This research was supported by the National Aeronautics and Space Administration.     

Formation and properties of single texture polyethylene produced by rolling

The formation of single textured low density polyethylene by unidirectional rolling has been investigated. It was found to be associated with the shear of the sample during annealing, which is a reversal of the shear imparted by the rolling process. Single texture could be produced from double texture by compressing it obliquely in such a way as to simulate this shear. It is concluded that the material probably contains another component besides the single orientation of lamellae which would need to be taken into account when using it as a model for the study of lamellar properties.     

Aligning a reflection cavity by Anderson's method

The sounding rocket principle of equivalence measurement uses a set of four laser gauges operating in Fabry-Perot cavities to determine the relative acceleration of two test masses that are chemically different. One end of each cavity is a flat mirror on a test mass. Because the test masses are unconstrained and thus expected to rotate slightly during measurement, and because the distance measurements are made at the sub-picometer level, it is essential to have real-time alignment of the beam entering the cavity. However, the cavity must be used in reflection and space is limited. We show that Anderson's alignment method can be used in reflection, but that it requires that the Fabry-Perot cavity have mirrors with significantly unequal reflectivities.     

Optical properties of micrometer size water droplets studied by cavity ringdown spectroscopy

Optical extinction by homogeneous, pure water droplets of 30 to 70 microm diameter produced by a vibrating orifice aerosol generator has been studied by pulsed cavity ringdown (CRD) spectroscopy at lambda=560 nm under ambient conditions. Experimental sensitivity of better than 1% achieved in measurements of CRD times enabled detection of changes in laser light losses per pass due to changes in the number and size of particles within the laser beam volume. By systematically changing the droplet size in the cavity while recording the CRD time, a periodic modulation in the value of the loss per pass was observed. The modulation is caused by the oscillatory nature of the extinction efficiency, which was subsequently inferred and compared with the results of theoretical calculations based on Mie theory.     

Quantitative studies on electrode material properties by means of the cavity microelectrode

The determination of the number of active sites is a key issue in the evaluation of electrode materials for any electrochemical application. Nonetheless, and particularly in the case of powder materials, a commonly accepted method to determine the actual density of active sites is not yet available, mainly because a method to quantify the amount of material under investigation is missing. In this study, we propose the use of the cavity microelectrode (C-ME, i.e., a cylindrical recessed microdisk) of known volume, which enables the study of a known amount of material, thus allowing the quantitative evaluation of its properties. The validation of the method implied (i) the preparation of C-MEs with different radii and depths; (ii) the calibration of the relevant volumes by means of a "standard" powder, whose number of active sites can be easily determined by cyclic voltammetry; and (iii) their use for the quantification of specific parameters that identify the electrochemical properties of mixed IrO(2)-SnO(2) powders. The results evidence that the quantity of charge relative to the number of pseudocapacitance sites and the currents for the oxygen evolution reaction are proportional to the cavity volumes. This strategy allows the direct comparison of different materials for their rapid and accurate screening. In addition, thanks to the small amount of material required for the sample (typically 10-100 ng), the method can be safely listed among the nondestructive techniques.     

Some physical properties of thin MgO films produced by reactive evaporation

Films of magnesium oxide were deposited by reactive evaporation using an electron gun. The films were polycrystalline with a preferential 1 1 1 orientation when their thickness was greater than 2m. Based on the transmission coefficient in the visible and ultraviolet range, the optical gap was calculated to be E _g=4.3 eV. The a.c. and d.c. electrical properties were evaluated using a single model: conduction by electron hopping from a trap level to extended states in the conduction band. The ionization energy of this trap level, which was clearly due to oxygen vacancies, was E _i=(1.4±0.1) eV.     

Physical properties of cadmium selenide layers produced by solid-state substitution reactions

Hexagonal and cubic CdSe layers were produced on single-crystal CdS and ZnSe substrates by solid-state substitution reactions. The room-temperature conductivity of the layers is dominated by donor levels with ionization energies of 0.7 and 0.16 eV for α- and β-CdSe, respectively. The 300-K photoluminescence spectra of the layers show two emissions differing in origin: one is due to interband transitions, and the other to dissociation of excitons upon inelastic scattering from electrons.     

The optical properties of porous silicon produced by metal-assisted anodic etching

Porous silicon (PS) was obtained from n-type (100) mono-crystalline silicon wafers with different metal using two different illumination conditions. The visible photoluminescence (PL) may come from defect-related radiative centers on PS surface and adsorbed hydrogen atoms may be associated to the elimination of irradiative centers on PS surface, which can be proved by the infrared absorption spectra. The metal can be used as catalytic role to increase the etching rate under back illumination, but under front illumination, the metal can cancel light-generated carrier leading to the decrease of etching rate during anodic etching. Furthermore, the change of minority carrier lifetime is opposite to the change of PL efficiency of PS, which can be Confirmed by the results of μ-PCD measurements.     

Structure and properties of metal nitride films produced by ion implantation

Nitride films are grown on Ti, Ta, Mo, W, Ni, Si(111), and NaCl(100) substrates by ion implantation, and their phase composition, structure, and properties are studied. The films produced using a titanium target are multiphase and contain, in addition to TiN and Ti₂N (and minor amounts of nitrides of the substrate metal), TiO₂ and oxides of the substrate metal in the form of islands 0.04 to 0.2m in size, distributed at random over the film. The presence of several phases in the films determines their mechanical and electrical properties and ensures good adhesion and corrosion resistance.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 40–45.Original Russian Text Copyright © 2005 by Ignatenko, Klyakhina, Badekin.     

Silicon nanocrystallites produced via a chemical etching method and photoluminescence properties

Silicon nanocrystallites (NCs) were fabricated via a simple and inexpensive method. The Si powders were chemically etched in the mixture of hydrofluoric and nitric acid, followed by the ultrasonic vibration in benzene, de-ionized water, or ethanol. The as-prepared Si particles feature two different sizes of ~2 and ~10 nm, respectively. The smaller particles are Si NCs suspended in the solvent, and the larger ones are several small Si NCs wrapped in amorphous shell. As excited with line of 340–420 nm, the suspensions display violet-blue emissions, which relate to the quantum confinement effect. The photoluminescence intensity of benzene suspension is the strongest and that of ethanol is the weakest.     

Electrical and elastic properties of Cu-W graded material produced by vibro compaction

Self-formed W graded preform was produced by size segregation of weakly vibrated tungsten bimodal granular medium. The bimodal granular media bed was initially set up with larger W agglomerates placed on the bottom and with smaller agglomerates on the top of the container. During the vibro-compaction treatment the granular bed progresses through three distinguished compaction stages: percolation, diffusion like or hopping, and non-equilibrium steady state, which exhibit different packing factor and structures. Shorter vibration time results in a skeleton type of microstructure, while a graded structure was formed when the system reaches a non-equilibrium steady state. The vibrated beds were uniaxially pressed to manufacture sintered W preform with a graded interconnected porosity. High temperature sintering treatments complete the evolution of a steeper gradient in porosity predominantly through coalescence process. Electrical and elastic properties of the final materials, produced by infiltration of Cu into the sintered W preforms, are strongly influenced by the W microstructural evolution. It has been shown that the optimal microstructure for electrical properties consists of a highly 3D interconnected Cu phase (skeleton type of microstructure), while the graded structure exhibits higher E-modulus. This work was undertaken to better understand the nature of the graded structure and to study the relationship between the self-formed microstructure types, electrical and elastic materials properties.     

Comparison of properties of coatings produced by laser cladding and conventional methods

Abstract

Wear resistant coatings of hardfacing alloys can be produced with powders by using various techniques such as laser cladding (LC), plasma transferred arc (PTA) welding, atmospheric plasma spraying (APS), etc. The properties of coatings applied using these techniques differ slightly owing to the manufacturing process, despite having the same chemical composition. The coating microstructures and properties (such as hardness, wear resistance, and corrosion resistance) of nickel base hardfacing alloys produced by LC, PTA welding, and APS have been studied. Estimates of realistic coating thickness, coating rate, powder consumption, and the influence of temperature on the substrate material during LC, PTA welding, and APS are given.

MST/1696     

Development of mechanical properties in AA 8090 alloy produced by extrusion processing

Abstract

The effects of extrusion processing parameters on the mechanical properties of an AA 8090 alloy were monitored using a combination of hardness, tensile, andfracture toughness tests, and using light, transmission electron microscopy, and scanning electron microscopy. It was found that variations in the processing parameters affect the tensile properties to a greater extent in the as extruded condition than in the heat treated condition. In the former, the property changes occur as a result of both variation of grain structure and the solutionising effect during the process. In the latter, the tensile properties are controlled by the precipitation processes that occur, and the toughness remains essentially unaffected by changes in the processing conditions. Improved combinations of strength, ductility, and toughness are achieved when the material is subjected to suitable preaging treatments, which modify the precipitate morphology within the microstructure; the fracture surface characteristics of both tensile and fracture toughness test specimens reflect the microstructural changes.

MST/1115