Effect of reliability of grounding of the shaft of a turboset on the operation of devices for control and protection of exciting circuits

Disturbance of the grounding of the shaft of a turboset or its absence for technical reasons can result in failure, misoperation, limitation of the operating zone, errors or limitation of the sensitivity of devices for control and protection of exciting circuits from single-point leakage, and electroerosion of elements of the turboset structure. Measures for increasing the reliability of the grounding of the shaft are discussed. __________ Translated from élektricheskie Stantsii, No. 3, March 2006, pp. 61–66.     

产业集聚效应的系统动力学模型研究

以系统动力学理论为基础，结合产业集聚效应的正反馈特征，对人才流、技术流、资金流和市场流的因果关系进行了探讨。通过产业集聚效应衡量方法的比较，构建系统动力学模型，分析制约产业集聚效应发挥的主要因素，提出加强政府投资力度、发挥市场机制作用和提高企业整体能力的建议。     

Separate when equal? Racial inequality and residential segregation

This paper sets out a new mechanism involving the emergence of middle-class black neighborhoods that can lead segregation in American cities to increase as racial inequality narrows. The formation of such neighborhoods requires a critical mass of highly educated blacks in the population, and leads to an increase in segregation when those communities are attractive for blacks who would otherwise reside in middle-class white neighborhoods. To assess the empirical importance of this “neighborhood formation” mechanism, we propose a two-part research design. First, inequality and segregation should be negatively related in cross section for older blacks if our mechanism operates strongly, as we find using both the 1990 and 2000 Censuses. Second, a negative relationship should also be apparent over time, particularly for older blacks. Here, we show that increased educational attainment of blacks relative to whites in a city between 1990 and 2000 leads to a significant rise in segregation, especially for older blacks, and to a marked increase in the number of middle-class black communities. These findings draw attention to a negative feedback loop between racial inequality and segregation that has implications for the dynamics of both phenomena.     

卷接包集控系统网络结构的规划分析

为解决绵阳卷烟厂卷包生产过程中存在的设备自控关联性差、连锁方式难以改变、分散的设备与生产运行难以监控、生产管理模式难以满足柔性化生产等问题,引进了卷包集控系统,并对该系统的三层网络结构进行了规划设计、对比分析。通过改变三个网络层次之间的连接方式、网络拓扑结构,使卷接包生产因集控系统网络故障引起的停机时间降到最低。应用效果表明,改进后的网络结构有利于缩小网络规模,控制网络风险,保证数据交换,避免I/O整体失控,有效提高了通信网络的安全性和稳定性及网络资源的利用率。     

采用闭环双口RAM实现深空动态模拟源的设计

深空探测具有时延长、运动速度大以及信号强度低的技术难点。在对上述技术难点进 行分析的基础上,提出了对深空动态模拟的解决办法：通过利用闭环双口RAM来解决模拟时 延较长的问题;改变读出双口RAM数据的速率来模拟卫星的运动速度;控制数控衰减器来模 拟深空的信号强度。实际的工程应用证明上述实现方法有效可行。     

一种适用于遥测测距信号的新型码跟踪环

遥测测距技术采用再生伪码作为上行链路信号。针对飞行器现有码跟踪环结构复杂、低信噪比条件下环路跟踪性能差的问题,提出了一种新的基于锁相环的码跟踪环结构,推导了环路的信号处理流程。该结构降低了环路实现的复杂度,改善了低信噪比条件下的相位测量精度,仿真进一步验证了方法的有效性和稳定性,较现有方法在信噪比为-10 dB时能提高1.5×10－3个码片的精度,适合遥测测距技术。     

一种针对压缩域信号的新型锁相环技术

针对通信信号压缩采样获得的压缩域信号频率、相位提取问题,提出了一种基于压缩感知的新型锁相环技术。通过深入研究压缩域的信号估计问题,提出了压缩域锁相环路,可以直接在压缩域同步跟踪信号频率和相位变化,不再需要高复杂度的信号重构处理。分析了环路模型及其估计性能,并针对该锁相环可行性和性能分别进行了仿真实验。仿真结果不仅验证了压缩域锁相环的可行性,同时表明该环路能够实现高动态信号的高精度频率提取。压缩域锁相环的应用潜力较大,例如可以作为压缩感知通信接收机的同步解调方法。     

粉喷桩施工的现代质量控制技术

阐述目前我国粉喷桩施工技术的发展现状及存在的问题 ,介绍计算机控制的粉喷钻机基本原理及各参量控制过程 .通过对两种机械施工结果的比较可知 ,由计算机控制施工的粉喷桩 ,桩体各段搅拌均匀 ,含粉量上下基本一致 ,无侧限抗压强度无大的变化 ,其轻便触探N10 可达加固前的 2倍以上 ,施工质量得到有效控制 ,避免普通施工机械施工所造成的上部质量明显好于下部的现象 ,使施工工艺更加完善     

Quantifying the effect of riparian forest versus agricultural vegetation on river meander migration rates,central Sacramento River,California, USA

Riparian forest vegetation is widely believed to protect riverbanks from erosion, but few studies have quantified the effect of riparian vegetation removal on rates of river channel migration. Measured historical changes in a river channel centreline, combined with mapped changes in floodplain vegetation, provide an opportunity to test how riparian vegetation cover affects the erodibility of riverbanks. We analysed meander migration patterns from 1896 to 1997 for the central reach of the Sacramento River between Red Bluff and Colusa, using channel planform and vegetation cover data compiled from maps and aerial photography. We used a numerical model of meander migration to back‐calculate local values for bank erodibility (i.e. the susceptibility of bank materials to erosion via lateral channel migration, normalized for variations in near‐bank flow velocities due to channel curvature). A comparison of migration rates for approximately 50 years before and after the construction of Shasta dam suggests that bank migration rates and erodibility increased roughly 50%, despite significant flow regulation, as riparian floodplains were progressively converted to agriculture. A comparison of migration rates and bank erodibilities between 1949 and 1997, for reaches bordered by riparian forest versus agriculture, shows that agricultural floodplains are 80 to 150% more erodible than riparian forest floodplains. An improved understanding of the effect of floodplain vegetation on river channel migration will aid efforts to predict future patterns of meander migration for different river management and restoration scenarios. Copyright © 2004 John Wiley & Sons, Ltd.     

LDPC码的树图法构造

LDPC码译码采用的是BP算法,但由于回路的存在,使译码重复迭代,特别是短长度的回路使LDPC码的性能下降.为此,用树图法分析了LDPC码的回路及其特性,给出了求解回路长度和所经过节点的方法,非常适合于计算机进行求解.同时也用树图的方法来构造LDPC码,可以在树生成的过程中了解其中的回路数目及长度.