基于空时分组编码的MC-CDMA下行链路合并方案

基于空时分组编码的发射分集技术利用空间和时间分集 ,能有效抗多径 ,增强信道可靠性。将空时分组编码应用到MC -CDMA下行链路中 ,构建了一种新的多载波CDMA系统 (ST -MC -CD MA) ,通过在每个子载波信道中获得空间分集增益来提高系统性能。具体实现时 ,依据传统MC -CDMA信号合并方案 ,提出了ST -MC -CDMA空时译码后相应的四种合并方案。仿真结果验证了这 4种合并方案的优、缺点 ;并进一步证明 :在频率选择性瑞利衰落信道中 ,该系统比采用相同合并方案的传统MC -CDMA有明显的性能改善。     

Determinants of Foreign Ownership in Newly Privatized Companies in Transition Economies

We investigate determinants of foreign ownership in newly privatized firms. We analyze data on privatized Czech firms to address two related general questions. First, what characteristics distinguish transition firms that attract a foreign investor? Second, how do firm‐specific characteristics influence the size of the foreign equity stake? Our results suggest that foreign investors i) seek safe, profitable firms in which they can exert unchallenged influence on corporate governance and then ii) structure their equity stakes to mitigate agency costs and political risk.     

Minimal efficiency of designs under the class of orthogonally invariant information criteria

Consider the linear regression model with uncorrelated errors and an experimental design . In the article, we address the problem of calculating the minimal efficiency of with respect to the class of orthogonally invariant information criteria, containing all Kiefers criteria of _p-optimality, among others. We show that the -minimal efficiency of is equal to the minimal efficiency of with respect to a finite class of criteria which generalize the criterion of E-optimality. We also formulate conditions under which a design is maximin efficient, i.e. the most efficiency-stable for criteria from . To illustrate the results, we calculated the -minimal efficiency of _p (in particular D, A and E) optimal designs for polynomial regression on [–1,1] up to degree 4. Moreover, for the quadratic model we explicitly constructed the -maximin efficient design.Acknowledgement. The author would like to thank prof. Pázman as well as an anonymous referee for useful and inspiring comments on earlier versions of this article.Supported by: VEGA grant of the Slovak Agency No. 1/0264/03     

Estimating a continuous time portfolio selection model: An application with UK data

An empirical assessment of a continuous time portfolio selection model is studied for the UK economy between 1970 and 1996. The estimates obtained from this study are both statistically significant and consistent with the model's predictions. The estimate of risk aversion parameter refers to low risk aversion which is consistent with the optimal risky asset holding parameter. Furthermore, the estimated parameters of the asset pricing relationship are also found to be consistent with the historical values of the stock prices. First version received: February 1998/final version received: March 1999     

Design and evaluation of ranking-type Delphi studies using best-worst-scaling

The ranking-type Delphi method has received widespread use in a large number of research areas. In order to rank a set of items, ranking-type Delphi studies use different ranking approaches which may be biased. This is intensified by the fact that the number of issues a participant can reasonably rank is limited. This paper describes an approach for the design and evaluation of ranking-type Delphi studies using best-worst-scaling (BWS). The statistical BWS design is based on a balanced incomplete block design to construct the comparison sets. The statistical evaluation encompasses the measurement of stability and consensus with the use of the coefficient of variation. Overall, our approach (1) enables to design a ranking with up to 22 items in a manner that participants can reasonably rank, (2) avoids and overcomes shortcomings of common ranking approaches, and (3) offers a statistical procedure for an unambiguous evaluation.     

CFM56-5B发动机反推失效故障分析

本文通过CFM56-5B发动机反推失效排故全过程的故障分析,提出了对CFM56-5B发动机在反推排故过程中和维护中的预防措施和建议。希望减少类似故障引起的多次部件拆换,减少排故时间。     

融合梯度和色度信息的分块均值漂移目标跟踪

针对在相似颜色干扰场景下传统均值漂移目标跟踪鲁棒性差的缺陷,提出Prewitt梯度和色度信息融合的分块均值漂移跟踪算法。首先,对跟踪框进行分块,并提取当前帧各子块特征;其次,利用Bhattacharyya距离计算参考目标区域与候选区域间各子块对应的相似程度,根据其相似程度分配各子块的权值,并通过融合规则对各子块相应特征进行融合构成新子块特征,在此基础上,将子块特征选择串接方式作为最终目标特征;最后,采用均值偏移原理迭代估计最终目标位置信息。实验结果表明,当场景中存在相似颜色干扰的情况下,相对于经典均值漂移算法,其准确度提高了84%左右。     

试论加气混凝土砌块墙体裂缝的产生原因

在用户对建筑质量进行评判的时候,建筑裂缝是他们对建筑进行评判的主要目测标准之一。粉煤灰加气混凝土砌块是一种轻质墙体材料,具有良好的隔热性能,施工较为简便而且价格低廉,但是施工不当会导致加气混凝土砌块墙体裂缝的产生。本文主要探讨了加气混凝土砌块墙体裂缝的产生原因,并提出了对策。