SRD倍频器自给偏压温度补偿研究

由世界贸易组织上海研究中心、上海市对外服务有限公司、上海对外贸易学院、上海海关高等专科学校主办的“世界贸易组织与中国服务贸易研讨会”于1997年4月19～20日在上海银河宾馆举行。世界贸易组织总干事雷纳托·鲁杰罗应邀出席了这次研讨会,并在会上发表专题演讲。现将鲁杰罗先生的演讲编译刊载如下,以飨读者。     

一种有效解决VHF频率资源短缺问题的方法

针对我国航空通信中VHF(Very High Frequency)频率资源紧张的现状，提出将信道间隔从25kHz减小到8．33kHz的解决方法。根据对选择连续信道概率的理论分析，提出了减小信道间隔后将同波道类型频点分散到不同频谱，同时设置预留区的规划方案。在规划过程中，考虑抑制干扰和灵活指配等因素，结合现有通信系统台站频率使用情况，对频率资源进行整合，说明将信道间隔减小到8．33kHz是行之有效的方法。     

基于混频向量自回归模型的宏观经济预测

本研究利用中国宏观经济指标构建了基于贝叶斯估计的混合频率向量自回归模型(MF-BVAR),并对该模型预测中国宏观经济运行情况的效果进行了检验。本文模型在允许多变量、不同频数据共存的条件下提高了模型估计的自由度,从而实现高精度预测。实证结果显示,在对宏观经济管理部门所关注的核心经济变量CPI、RPI和GDP等进行预测时,MF-BVAR模型相对于目前广泛应用的同频向量自回归模型和MIDAS模型,预测精度都有显著改善。本文亦发现房地产投资对于模型预测能力的重要作用,从样本外预测的角度佐证了房地产部门对于中国宏观经济的重要影响。本文也验证了中国股票市场表现不能对预测宏观经济运行提供额外贡献。     

Does CPI Granger-cause WPI? New extensions from frequency domain approach in Pakistan

The present study significantly contributes to the economic literature by investigating the direction of causality between WPI and CPI by applying frequency domain causality approach developed by Lemmens et al. (2008) based on spectral approach. We use monthly frequency data covering the period of 1961–2010 in case of Pakistan. Our results provide evidence of cointegration between the variables. Furthermore, we find unidirectional causal relationship running from CPI to WPI that varies across frequencies i.e., CPI Granger-causes WPI at lower, medium as well as higher level of frequencies reflecting long-run, medium and short-run cycles. This implies that CPI should be a leading indicator for important policy decisions pertaining to monetary or fiscal policies in Pakistan.     

Frequency of international expansion through high control market expansion modes and interlocked directorships

This study investigates director interlock as a mechanism by which an MNC learns and adopts high control market expansion modes that other MNCs use. Using data on greenfields and acquisitions by S&P 500 firms in the period 2003–2010, we find a significant relationship between the use of high control market expansion modes by interlocked MNCs and the frequency of international expansion of a focal MNC through such modes in unrelated industries, with the relationship stronger for the depth of interlocked director experience. The findings contribute to the literatures around the frequency of international expansion and microfoundations of international strategy.     

改革开放30年我国科技合作研究热点分析——基于词频分析视角

从中国期刊全文数据库(CNKI)中下载了1979-2008年与科技合作相关的文献题录数据,利用科学计量学的词频分析方法,得到了科技合作领域的若干研究热点;运用知识可视化软件Pajek,对这些关键词进行共现分析,勾勒出改革开放30年来我国科技合作研究的热点和特点,并对今后的研究趋势进行了初步预测。     

The investment value of the frequency of analyst recommendation changes for the ordinary investor

We find that analysts who frequently revise their stock recommendations outperform those who do not. This result holds for portfolios formed on the basis of favorable changes in recommendations as well as unfavorable changes. The frequency of revision captures information incremental to factors known to identify superior recommendations. Although much of the frequently revising analysts' advantage follows events proxied by abnormally high returns or trading volume, it does not appear to derive from more public events such as earnings announcements. Further, these analysts outperform their counterparts even over the short-run, suggesting that this is not simply a “quantity over quality” phenomenon. In summary, our results imply that the superior profitability of frequently revising analysts emanates at least partly from their ability to generate private information using their superior skill. Overall, the ordinary investor is better off following the advice of analysts who revise their recommendations more frequently.     

皮带机电控系统实施变频技术改造的研究与应用

文章简单介绍了跃进煤矿2-5区皮带机设备的运行现况和电控系统改造的必要性,较详细地阐述了实施改造期间采用的主要控制设备和各自具备的功能,以及实施改造后电控系统的主要技术性能指标、特点和应用效果。     

一种新的快速跳频频率合成器

本文提出一种新的快速跳频频率合成器方案。它通过采用脉冲内插变频鉴相和取样—保持—直接电压预置两种方法,使得电路具有换频速度快、输出信号频谱纯、以及易达到高的频率分辨率等优点,且实现容易。文中给出了实现框图和部分关键电路,并对其工作原理作了详细的说明。最后,对环路性能进行了分析。     

250KHz谐振自激直流变换器

谐振自激直流变换器,利用功率场效应管的栅极输入电容与微型线性电感(几微亨至几十微享)之间的并联谐振,产生数百千赫的自激振荡,完成高频直流-直流变换.由于不需要传统的可饱和变压器作控制元件,这种变换器电路简单、效率较高,而且更容易实现高频化.本文分析了高频谐振自激变换器的工作原理,并给出了一个250KHz谐振自激变换器的实例.