基于子带脉冲压缩的雷达宽带接收方法

宽带信号的大容量高速数据率,使宽带信号实时处理受到软硬件各方面的限制。本文详细研究了宽带信号的子带脉冲压缩处理方法,给出了过采样子带脉冲压缩系统的基本结构,并对该方法的详细性能进行仿真分析,有效地解决了宽带信号的实时处理问题。将该系统应用于实际工程中,对实测数据的处理结果证明了系统的正确性和有效性。     

Comparative study of a cascade cycle for simultaneous refrigeration and heating operating with ammonia,R134a,butane, propane,and CO2 as working fluids

In this paper, a cascade system for simultaneous refrigeration and heating is simulated with different working fluids. Ammonia, R134a, butane and propane are evaluated in the low-temperature (LT) cycle and carbon dioxide (CO₂) is used in the high cycle. The effects of the thermodynamic parameters on the cascade system are evaluated with the aim of finding the best working fluid performance and optimum design parameters. Coefficients of performance (COP) and exergetic efficiencies were estimated for each one of the cycles and for the entire system. The behaviour of these parameters is presented as a function of the internal heat exchanger effectiveness and main operating system temperatures. The results showed that the cascade system using butane in the LT cycle increased the COP up to 7.3% in comparison with those obtained with NH₃–CO₂. On the other hand, the cascade systems operating with the mixtures R134a–CO₂ and propane-CO₂ presented similar results reaching COPs up to 5% higher than those obtained with the NH₃–CO₂ system.     

A general methodology for energy comparison of intermediate configurations in two-stage vapour compression refrigeration systems

The aim of the present paper is to describe a general methodology suitable for analysing any intermediate configuration considered in staged vapour compression refrigeration cycles. This general methodology only depends on two basic parameters related to the subcooling and desuperheating obtained in the inter-stage system. A COP expression based on the two basic parameters was obtained from the general configuration. By means of its particularization to seven common configurations, it was then possible to make an energy comparison of the various configurations working with two fluids appropriated for the low temperature domain such as ammonia and R-404A.     

Microstructure comparison of ZK60 alloy under casting, twin roll casting and hot compression

The microstructures of ZK60 alloy under conventional direct as-casting (DC),twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM),electron backscatter diffraction (EBSD) and X-ray diffraction (XRD).The deformation condition of hot compression is 350 ℃,0.1 s?1.The microstructural evolution under TRC-HC deformation followed by annealing at different temperatures and time was discussed.The results show that TRC provides more modified microstructure compared with DC.Twins are found in TRC processing;dynamic recrystallization (DRX),shear bands and twins are found in TRC-HC.A short annealing time has little effect on hardness,while during a long time annealing,it is found that low annealing temperatures increase the micro-hardness and high temperature decreases it.     

Effects of temperature and strain rate on microstructure and mechanical properties of high chromium cast iron/low carbon steel bimetal prepared by hot diffusion-compression bonding

The objective of this study is to develop a hot diffusion-compression bonding process for cladding low carbon steel (LCS) to high chromium cast iron (HCCI) in solid-state. The influence of temperature (950–1150 °C) and strain rate (0.001–1 s⁻¹) on microstructure, hardness and bond strength of the HCCI/LCS bimetal were investigated. The interface microstructure reveals that the unbonded region can only be found for 950 °C due to lack of diffusion, while the intergrowth between the constituent metals occurred at and above 1100 °C. When bonding temperature increases to 1150 °C, a carbide-free zone was observed near the interface on the HCCI layer, and the thickness of the zone decreases with an increase of bonding strain rate. These evolutions indicate that the bond quality was improved by raising temperature and reducing strain rate due to the increase of element diffusion. The hot compression process of the bonding treatment not only changes the carbide orientation of the HCCI, but also increases the volume fraction of Cr–carbide. Based on the microstructural examinations and mechanical tests, the optimum bonding temperature and bonding strain rate are determined to be 1150 °C and 0.001 s⁻¹, respectively.     

Model and analysis of path compression for mobile Ad Hoc networks

Path compression techniques are efficient on-demand routing optimizing techniques for mobile Ad Hoc networks. However, there is no efficient model for path compression techniques. This paper analyzed the principles and characteristics of path compression algorithms and proposed dynamic model which provided theoretical basis to improve or propose path compression algorithms. This model took the mobility and expansibility of Ad Hoc networks into account and was efficient to analyze or evaluate path compression algorithms. The quantitative relationship and probability expression for pivotal compression events were given based on the model. The simulation results of SHORT (self-healing and optimizing routing techniques) and PCA (path compression algorithm) show that it is a correct and efficient dynamic model for path compression. Finally, some suggestions and application scenarios about the model were proposed.     

石英陶瓷与金属粘接压缩剪切强度的测定

采用Q/5S451-2005标准,对石英陶瓷与金属粘接压缩剪切强度试验进行了研究,讨论了胶层厚度、粘接面积、夹持方法、加载速度和试验温度等因素对测试结果的影响。结果表明,按照Q/5S451-2005标准的规定,能够完成天线罩粘接工序中剪切试样的测定。     

亚磷酸二甲酯尾气中氯甲烷回收的工艺实践

本文介绍了从亚磷酸二甲酯生产尾气中回收氯甲烷的工艺，采用降温干燥，固碱干燥和压缩相结合的方法，可使回收氯甲烷的浓度达９９％以上。     

Warm compression tests of aluminum alloy

Compression tests of aluminum alloy were experimentally investigated at specified temperatures ranging from 30 ‡C (room temperature) to 250 ‡C under a constant strain rate of 0.2 X 10^-3/s using powdered graphite as a lubricant throughout the tests. The effective stress method is found to show a significant fall in stress values beyond the barreling point, indicating a serious shortcoming over the barrel correction factor method within the tested temperature range. The compression curves obtained using the barrel correction factor method and the Bridgman remachining technique (no barreling allowed during the test) are found to have close values, even at higher temperatures. The true-stress versus true-strain curves and the barrel sizes obtained follow empirical power laws, even at higher test temperatures.     

Strain hardening of porous iron under uniaxial compression

A series of experiments was carried out with powder iron of 1–40% porosity including deformation by compression to various degree of deformation, and strain hardening curves were calculated. It was established that change in the loading sign relative to uniaxial tension had practically no effect on the strain hardening laws of the solid phase, although it basically changed the porosity contribution to the loading curve formation. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 106–112. January–February, 2000.