Prospecting Research: Knowing when to Stop

An important aim of many surveys is to undertake prospecting research: the search for new possibilities and an understanding of the diversity in a population. This paper develops a method—the extrapolation of resampled possibilities (ERP)—for predicting how much new information will be revealed by extending a sample. This is useful for deciding whether it is likely to be worthwhile sampling more cases, bearing in mind the costs and the benefits. The method avoids making any assumptions about the nature of the underlying population, apart from the information implicit in the existing sample.     

Optimal income transfers

A substantial literature addresses the design of transfer programs and policies, including the negative income tax, other means-tested transfers, the earned income tax credit, categorical assistance, and work inducements. This work is largely independent of that on the optimal nonlinear income tax, yet formulations of such a tax necessarily address how low-income individuals should be treated. This paper draws on the optimal income taxation literature to illuminate the analysis of transfer programs, including the level and shape of marginal tax rates (including phase-outs), the structure of categorical assistance, and the role of work inducements in an optimal income transfer scheme. JEL Classification H21 · H53 · I38     

低信噪比强窄带干扰条件下的LFM信号检测技术的比较与分析

研究了低信噪比强窄带干扰条件下的LFM信号检测技术,提出了基于短时傅里叶变换(STFT)的线性调频(LFM)信号增强技术、基于时频峰值滤波的强窄带干扰抑制技术和基于一维搜索的宽带LFM信号检测技术.试验结果表明,采用以上这些方法在低信噪比强窄带干扰情况下,对于LFM信号具有较高的正确检测概率及参数测量精度.     

Effect of caregiver feeding behaviours on child nutritional status in rural Ghana

A six‐month observational study involving 100 mothers with infants between the ages of 6 and 12 months was conducted in the Manya Krobo district of Ghana. The objective was to assess the role of caregiver feeding behaviours on child nutritional status using a modified positive deviance approach. Each child was in the study for 6 months, during which they were observed at home once a month. On each visit, data were collected on the child anthropometry, child meal frequency, diet diversity, responsiveness of caregiver during feeding, child’s appetite and feeding atmosphere as well as caregiver hygienic practices related to feeding. Using weight‐for‐age (WAZ) and length‐for‐age (LAZ) scores, the children were classified as positive or negative deviant children. The study revealed significant differences between the two groups of children in terms of caregiver feeding behaviours. Positive deviant children had significantly higher meal frequencies (3.1 ± 0.4 vs. 2.4 ± 0.6, P = 0.001), diet diversity scores (6.3 ± 0.6 vs. 3.7 ± 1.1, P = 0.001), were fed under better hygienic conditions (7.2 ± 0.9 vs. 4.2 ± 1.1, P = 0.001) and were much more interested in food during feeding (85.8% vs. 59.3%). Caregiver responsiveness during feeding was also significantly higher among the positive deviant group (6.5 ± 0.8 vs. 4.5 ± 0.9, P = 0.001). This study has demonstrated the tremendous effect of caregiver feeding behaviours on child nutritional outcomes and provides a scientific basis for introducing care during feeding as a component of intervention to improve child nutritional status in Ghana.     

Realistic Statistical Modelling of Financial Data

The aim of this paper is to present some of the stylized features of financial data which have received a lot of attention both from practitioners and those with more theoretical backgrounds. Some of the models resulting from these efforts are reviewed and discussed. To facilitate the discussion two data sets are used: one of these contains all US trades in IBM stocks in 1995 at NYSE.     

卫星监测站智能监控系统的设计与实现

在分析卫星监测站监控系统的需求和发展过程的基础上，提出了一套智能化监控系统的方案，并对系统的组成和核心功能进行了剖析，对其主要模块进行了详细设计。分析表明，该系统具有良好的可实现性，能够达到预期的功能。     

Auctions with asymmetric common-values: The first-price format

We study the performance of the first-price format in auctions with asymmetric common-values. We show that, contrary to the result for second-price auctions, a small advantage for one player translates only to small changes in bidders’ strategies, and the equilibrium remains close to the first-price equilibrium of the original game. We characterize the equilibrium bidding strategies and their behavior as the degree of asymmetry increases. Finally, we compare the revenues at the optimal auction, the first-price auction and the second-price auction.     

用MFSK调制实现水声远程信息传输

研究了一种基于多进制频移键控(MFSK)调制的水声远程信息传输技术，介绍了通过谱分析进行解调的方法。初步的海试结果表明，该技术可以实现80km距离、4bit／s数据率的信息可靠传输。     

Portfolio Value-at-Risk with Heavy-Tailed Risk Factors

This paper develops efficient methods for computing portfolio value-at-risk (VAR) when the underlying risk factors have a heavy-tailed distribution. In modeling heavy tails, we focus on multivariate t distributions and some extensions thereof. We develop two methods for VAR calculation that exploit a quadratic approximation to the portfolio loss, such as the delta-gamma approximation. In the first method, we derive the characteristic function of the quadratic approximation and then use numerical transform inversion to approximate the portfolio loss distribution. Because the quadratic approximation may not always yield accurate VAR estimates, we also develop a low variance Monte Carlo method. This method uses the quadratic approximation to guide the selection of an effective importance sampling distribution that samples risk factors so that large losses occur more often. Variance is further reduced by combining the importance sampling with stratified sampling. Numerical results on a variety of test portfolios indicate that large variance reductions are typically obtained. Both methods developed in this paper overcome difficulties associated with VAR calculation with heavy-tailed risk factors. The Monte Carlo method also extends to the problem of estimating the conditional excess, sometimes known as the conditional VAR.