高速钢回火行为的电子理论分析

运用固体与分子经验电子理论对Ｗ６Ｍｏ ５Ｃｒ４Ｖ２高速钢不同热处理状态的回火特性作了合金价电子结构的分析研究。通过马氏体内不同类型的价电子结构单元构成及其权重，用价电子结构信息ｎＡ和引入的新参量ＮＤ分析了回火硬度曲线上显示的二次硬化及峰值温度的变化，从而对高速钢回火的认识能够深入到价电子结构的层次。     

Evaluation of Photopolymerization Kinetics by Means of Transmittance Measurements

Polymeric resins are widely used for dental reconstruction, and most resins use camphorquinone as activator of the polymerization reaction, through the absorption of light at a defined wavelength range (from 400 nm to 460 nm). During the photopolymerization curing, transparency of these resins changes and transmittance variation can be detected by photodiode and bolometer measurements. This change can be used as an index of the reaction rate, and the kinetic parameter k (reaction rate) can be evaluated from transmittance data by means of nonlinear regression. The relation between k and the light intensity impinging on the resin sample can thus be obtained. In the present work, tests were carried out using the resin Enamel Plus HFO GE2. Results reveal the presence of two different polymerization reactions at two different intensity ranges. The obtained k values were used to predict the most suited curing times for different light intensities. The proposed methodology can be applied to different dental reconstruction materials, provided that the material is partially transparent and that its transparency changes during the polymerization reaction.     

高速干切削温度场的测量及仿真研究

分析了切削热的产生、热的传导以及切削温度的测量方法.对目前切削温度实验测量技术及数值模拟仿真技术的优缺点进行了比较.采用平面应变热力耦合切削模型,重点研究在高速干切削过程中,工件已加工表面的温度变化过程.根据试验测定工件材料的力学性能以及刀具-工件之间的摩擦特性,建立材料在切削变形过程中热产生以及热传导模型,并采用点跟踪的方法获取工件材料上任意位置点温度的变化过程.并将模拟计算得到的切削温度与实验测量结果进行了比较,两者具有较好的一致性.     

Power Measurements by Means of Thermally Excited Mechanical Vibrations

The periodic absorption of heat on the surface of a material produces a periodically varying temperature distribution in the material near the surface as well as an increase of the average temperature. The periodic component of temperature is largest on the surface and falls off with distance from the surface. This fact brings about periodic internal stresses. These stresses under proper circumstances can excite a mechanical system to oscillation. The amplitude of this oscillation is found theoretically and experimentally to be directly proportional to the power absorbed on the material surface over a wide range of power. This phenomenon was employed to construct several linear power detectors for microwave application in the X-and K-bands. By using piezoelectric and electromagnetic transducers, a voltage linearly proportional to the power was obtained.     

Filtering of Randomly Sampled Time-Stamped Measurements

This paper concerns the filtering of measurements that are taken by networked sensors at nonuniform intervals but that are accurately time stamped. Traditional digital filtering methods are difficult or impossible to use due to nonuniform sampling. Two filtering methods are described. Both are based on making an assumption about the signal behavior between measurements, such as the signal being constant between measurements. In the first method, a filter is formulated as an ordinary differential equation that is incrementally solved as measurements arrive. Such filtering is general; nonlinear and nontime invariant filters may be constructed. In the second method, signal convolution with a continuous-time finite impulse response filter is efficiently performed using a spline representation for the filter response. Such filters are ldquoFIR likerdquo in the sense that they have frequency-domain performance similar to FIR filters and have only slightly worse asymptotic computation time and memory requirements compared to FIR filters, yet have the advantage of being able to deal with nonuniformly sampled measurements. Examples of the operation of both sorts of filters are shown on actual measured data.     

Measurements of the Restrainer Content of Gelatin by a Photographic Means

An emulsion is prepared and chemically sensitized using the test gelatin and a suitable standard addition of thiosulphate sensitizer. The time and temperature of digestion are also controlled and the emulsion adjusted to optimum speed by varying the addition of a synthetic restrainer. The amount of synthetic restrainer required at optimum is an inverse measure of the restraining power of the gelatin and, if it is assumed that those gelatins which require the largest omount of added restrainer contain no natural restrainer, then by comparing the amount required by a test gelatin with this amount, the restraining power of the test gelatin is obtained in terms of the added restralner. Active gelatins had restraining powers broadly in line with their nucleic acid contents. Inert gelatins also showed considerable differences in restraining power but, as they contain negligible nucleic acid, these gelatins must contain other types of restrainer. The sensitometric properties at optimum are closely similar for most gelatins, even for some widely different gelatins, as the optimum, with each test gelatin, is reached under similar restrainer- sensitizer environment. Some gelatins differ from the majority and this is taken to indicate the presence of substances other than restrainers and sensitizers.     

Non-destructive Case Depth Determination by Means of Low-Frequency Barkhausen Noise Measurements

The availability of a fast and reliable method for non-destructive case depth determination which can be used to directly monitor the quality of various heat treatment processes is of great interest. Conventionally hardened steel components are analyzed by means of depth-resolved microhardness measurements providing the case hardening depth (CHD) of the material. However, as a consequence of mechanical destruction, the investigated part cannot be used in its original state anymore and needs to be replaced by a twin part whose properties might be different. In this work, a new approach of non-destructive CHD determination based on Barkhausen noise analysis with an excitation frequency of 0.5 Hz is described. The use of a low frequency allows to enhance the penetration depth of the external magnetic field and to reduce the eddy current damping of the filtered Barkhausen (BN) signal at the same time. In this way, simultaneous information about the hard case and the soft base material core is experimentally accessible. Various measurands derived from the detected BN signals are sensitive to the different magnetic properties of the case and the core. The so-obtained correlations with the measured CHD can be used for non-destructive CHD determination by means of appropriate calibration data. The investigated sample set consists of cylindrical parts of 18CrNiMo7-6 which were case-hardened and ground in order to provide graded CHD values up to 3.6 mm. The sensitivity of the tested low-frequency method will be quantitatively demonstrated over the complete range of interest and its potential for industrial applications will be discussed.     

Phase Retrieval From Fresnel Zone Intensity Measurements by use of Gaussian Filtering

The reconstruction of a complex-valued object from intensity measurements in the Fresnel zone region is considered. The reconstruction is based on the phase-retrieval method from Fresnel zone intensity data obtained by modulation of the object with a known Gaussian function and with its shifted functions along the horizontal and the vertical directions in rectangular coordinates. Two types of reconstruction system are presented. In the two systems a Gaussian amplitude filter and a Gaussian illuminating beam are used as the known Gaussian functions. Computer-simulated examples in two dimensions illustrate the performance of the reconstruction in these systems.     

Square-Root Extractor for Fluid Speed Measurements

A fluid speed measuring system based on Bernoulii's equation of flowing fluid is presented. The necessary square-root extraction is performed numerically to reach the advantages of numerical display and the possibility of using the device as a data source of the computer controlling the process. Simple recursive square-root extraction algorithm is derived and the statistics of the roundoff error is considered.     

表面粗糙度测量中的高斯滤波快速算法

应用高斯函数的逼近法和冲激响应不变法,设计出用于表面粗糙度测量的高斯数字滤波器,并给出了其零相移的递归滤波算法,算法简洁,易于实现。递归计算方法的计算量小,计算效率高。适当增加滤波器节数,在不增加很多计算量的情况下,可以达到很高的精度。文中给出的滤波器例子,传输偏差大约为2％和1％,处理一次表面测量轮廓数据,在当今最普通的计算机上,滤波时间小于1s。     

High-Resolution Shaft Speed Measurements Using a Microcomputer

A Motorola 6800 microcomputer has been applied to the measurement of instantaneous angular velocity at one degree intervals on a pair of coupled shafts. Velocity is determined by accurately measuring the time intervals between pulses produced by shaft encoders. Variations in relative velocity can be detected when precision timing is available. Using an essentially software approach time can be measured in 30-?s increments. The number of instructions in the timing loop can be reduced by adding a small amount of hardware to permit parallel data acquisition. Time increments of 12?s were obtained using inputs from two shafts. The results of measurements on a pair of shafts coupled by noncircular gears is included as an example.     

High Speed Shutters

The principles of single-shot high speed shutters are outlined including (lash, capping, electro-optic (Faraday and Kerr Cell) and image tube techniques. The limitations of transmission and response time are compared.     

Search for Spin Filtering by Electron Tunneling Through Ferromagnetic EuS Barriers in PbS

Perpendicular transport through single- and double-barrier eterostructures made up of ferromagnetic EuS layers embedded into a PbS matrix was investigated. Both resonant tunneling and probably spin filtering through EuS barrier were observed.     

High Speed Photography

The determination of the sulphur in the silver bromide grains of a photographic emulsion shows that the sulphur contents are several times greater than that corresponding to the gelatin adsorbed to the grains. The significance of the sulphur atom for the occurrence of effective chemisorption is indicated.     

遥感相机象移速度的滤波处理

在遥感相机对地面目标摄影的过程中,由于地面目标在相机象面上的象是运动的,即存在象移,这将导致相机分辨力下降.为获得较高的动态照象分辨力,必须对象移进行补偿,而补偿的关键是准确地获得当前的象移速度.本文采用统计实验方法,分析了采用计算法得到的象移速度的分布特性,给出了实用的象移速度滤波预处理、卡尔曼滤波、野值剔除方法.仿真结果表明,所给出的滤波处理方法效果明显,简单实用.     

遥感相机像移速度的滤波处理

在遥感相机对地面目标摄影的过程中 ,由于地面目标在相机象面上的象是运动的 ,即存在象移 ,这将导致相机分辨力下降。为获得较高的动态照象分辨力 ,必须对象移进行补偿 ,而补偿的关键是准确地获得当前的象移速度。本文采用统计实验方法 ,分析了采用计算法得到的象移速度的分布特性 ,给出了实用的象移速度滤波预处理、卡尔曼滤波、野值剔除方法。仿真结果表明 ,所给出的滤波处理方法效果明显 ,简单实用