窄带中频数字接收机高速信号处理技术

窄带中频数字接收机在雷达对抗侦察中得到了广泛应用，其高速信号处理技术是目前研究的重点。本文详细介绍了数字雷达告警接收机高速信号处理技术的发展现状和关键技术，最后通过对该技术的全面分析指出了值得深入研究的领域。     

浅析企业人才的"留"与"流"

文章分析了人才在企业管理和促进企业发展中的重要性,提出在人才招聘中应注意的三个方面因素,全方位分析了留住人才与人才流动之间的关系.     

《石油沥青纸胎油毡》国家标准的修订

《石油沥青纸胎油毡》国家标准进行了第三次修订。本文介绍了修订的理由、修订的内容与依据，并与国内外同类产品标准进行了比较。     

The effect of ionic interaction on the miscibility and crystallization behaviors of poly(ethylene glycol)/poly(L‐lactic acid) blends

The effect of end groups (2NH₂) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH₂)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH₃, and 2CH₃)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH₂) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH₂) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH₂)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH₂)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

西气东输工程用X70热轧板卷屈服强度检测值波动大的探讨

对西气东输工程用X70热轧板卷检验过程中出的屈服强度σ0.5波动大的情况进行了分析，认为拉伸试样弯曲是主要原因。这一问题可通过反复压平试样，确保试样的平直度以及适当提高钢的强度的方法加以解决。     

Studies of substrate specificities of lipases from different sources

Although lipases are widely applied in a wide variety of reactions, available information on the factors that are responsible for the substrate specificities of lipases from different sources is scarce. In this paper, nine lipase‐producing microorganism strains were isolated from oil‐containing samples. The properties of these enzymes, including pH optima, temperature optima, thermal stability, and pH stability, vary significantly with the different sources from which these lipases were isolated. The substrate specificities of the nine lipases, including fatty acid and positional specificities, were also studied. The fatty acid specificities of the nine lipases were observably different toward 15 substrates with different carbon chain lengths, different saturation degrees and different side chains. The lipases from S₃ Penicillium citrinum (PCL), MJ₁ Aspergillus niger (ANL), MJ₂ Aspergillus oryzae (AOL), YM Bacillus coughing (BCL), S₉ Geotrichum candidum (GCL), and S₁₁ Candida lypolytica (CLL) showed the strongest specificities to short‐chain esters, and the other lipases showed strong selectivity for medium‐ or long‐chain and branched esters. The positional specificities were examined by analyzing the hydrolytic products of triolein catalyzed by the nine lipases, using TLC. The lipases can be mainly classified into two groups by their specificities for the ester bond at position 2 of triglycerides; one group can selectively hydrolyze the ester bond at position 2 of the triglycerides, the other group cannot. All these nine lipases were divided into four groups by hierarchical clustering analysis on the basis of the results of fatty acid and positional specificities.     

An online technique for monitoring the insulation condition of AC machine stator windings

A novel online technique for monitoring the insulation condition of ac machine stator windings is proposed in this paper. The concept is to measure the differential leakage currents of each phase winding from the terminal box in a noninvasive manner to assess the insulation condition during motor operation. The conventional differential CTs used for phase fault protection can be replaced with high performance current sensors to measure the leakage current with higher accuracy. Indicators for insulation condition such as the capacitance and dissipation factor are calculated based on the measurements to provide a low cost solution for online insulation condition assessment. A simplified online insulation system model is derived for analysis and interpretation of the measured data. Experimental results on a 15-hp induction motor under simulated insulation degradation conditions show that the proposed technique is a very sensitive method capable of detecting incipient signs of insulation degradation.