Ultimate 100‐m world records through extreme‐value theory

We use extreme‐value theory to estimate the ultimate world records for the 100‐m running, for both men and women. For this aim we collected the fastest personal best times set between January 1991 and June 2008. Estimators of the extreme‐value index are based on a certain number of upper order statistics. To optimize this number of order statistics we minimize the asymptotic mean‐squared error of the moment estimator. Using the thus obtained estimate for the extreme‐value index, the right endpoint of the speed distribution is estimated. The corresponding time can be interpreted as the estimated ultimate world record: the best possible time that could be run in the near future. We find 9.51 seconds for the 100‐m men and 10.33 seconds for the women.     

微气体轴承润滑模型研究

在微气体轴承特性分析中，通常采用基于滑移速度边界的润滑模型．对基于一阶滑移速度边界、二阶滑移速度边界、1．5阶滑移速度边界等三种润滑模型分别进行了推导，并给出了相应的描述微气体轴承动力特性的Reynolds方程．     

The Measurement and Analysis of Poverty and Inequality: An Application to Spanish Conurbations

Poverty as a multidimensional phenomenon can be approached from different points of view. In this paper we study poverty in large towns in Spain taking into consideration three different definitions: a) relative monetary poverty, or scarcity of resources as compared with population averages, b) poverty measured through physical indicators, i.e. deprivation of certain goods, and c) subjective poverty. This last one appears to be related to inequality, which is also considered and analyzed. The source of statistical information used is the Spanish Household Budget Survey of 1990–91. Possibilities and drawbacks of this survey in the analysis of poverty and inequality are also reviewed.     

Measurement Error and Nonlinearity in the Earnings-Returns Relation

There is a long history of research which examines the relation between unexpected earnings and unexpected returns on common stock. Early literature used simple linear regression models to describe this relation. Recently, a number of authors have proposed nonlinear models. These authors find that the earnings-returns relation is approximately linear for small changes but is 'S'-shaped globally. However, unexpected earnings are generated by the sum of a measurement error and a true earnings innovation, so the apparent nonlinearity could be an artifact of nonlinearity in the measurement errors. Using a research design that minimizes the presence of measurement errors, we provide evidence consistent with the hypothesis that measurement errors contribute to the nonlinearities in the earnings-returns relation. While we are not suggesting that the earnings-returns relation is linear, our evidence suggests that there is no advantage to using a nonlinear model for large firms that are widely followed by analysts.     

Parametric and Nonparametric Regression in the Presence of Endogenous Control Variables

The aim of this paper is to convey to a wider audience of applied statisticians that nonparametric (matching) estimation methods can be a very convenient tool to overcome problems with endogenous control variables. In empirical research one is often interested in the causal effect of a variable X on some outcome variable Y . With observational data, i.e. in the absence of random assignment, the correlation between X and Y generally does not reflect the treatment effect but is confounded by differences in observed and unobserved characteristics. Econometricians often use two different approaches to overcome this problem of confounding by other characteristics. First, controlling for observed characteristics, often referred to as selection on observables, or instrumental variables regression, usually with additional control variables. Instrumental variables estimation is probably the most important estimator in applied work. In many applications, these control variables are themselves correlated with the error term, making ordinary least squares and two-stage least squares inconsistent. The usual solution is to search for additional instrumental variables for these endogenous control variables, which is often difficult. We argue that nonparametric methods help to reduce the number of instruments needed. In fact, we need only one instrument whereas with conventional approaches one may need two, three or even more instruments for consistency. Nonparametric matching estimators permit     consistent estimation without the need for (additional) instrumental variables and permit arbitrary functional forms and treatment effect heterogeneity.     

群爆条件下弹丸壳体运动过程的动力学算法

结合爆轰物理学和材料学的有关理论,对弹药群爆时弹丸壳体的塑性膨胀变形过程进行了分析,建立了弹药群爆条件下的弹丸壳体运动速度的动力学算法,计算出了弹丸壳体膨胀破裂时的半径和形成破片的初速。     

Residual income past and future

This article considers the strengths and weaknesses of value-based management approaches based upon the residual income (RI) concept as the basis for incentive-based reward systems. The objective of these systems is to encourage optimal corporate investment selection by divisional managers and to encourage them to act as if they were independent owners of their divisions sharing a proportion of all losses and all profits. Part 1 of the article considers these systems in the light of the earlier RI debate in the 1960s and 1970s which raised a number of problems applicable to today's value-based systems. It also considers recent attempts to solve, perhaps, the major problem generated in the earlier debate—how to ensure that a single period RI is congruent with project net present value. Part 2 of the article provides a brief survey of current research into incentive systems based on RI. It then presents a possible programme of further research emphasising relevant research in finance theory.     

Robust Estimation of Beta Coefficients: Evidence from a Small Stock Market

In this paper we demonstrate that robust estimators improve the reliability of estimates of beta coefficients on small, thinly traded stock markets. We outline several different types of robust and bounded influence regression estimators and assess them using a jackknife methodology on data from the Johannesburg Stock Exchange. The empirical evidence confirms the hypothesis that robust estimators are more efficient than least squares estimators and indicates that least squares estimators may over-estimate systematic risk in some cases.     

The Determinants of Pharmaceutical R&D Expenditures: Evidence from Japan

During the past 20 years, the world pharmaceutical industry has experienced a dramatic increase in R&D intensity. We apply and extend a model developed by Grabowski and Vernon (2000, Journal of Evolutionary Economics, 10, 201–215) with a pooled data sample of the 15 publicly listed Japanese drug firms for the period 1987–1998. As in the original study, we find expected returns to be an important determinant of R&D spending in the Japanese drug industry, albeit considerably smaller than in the U.S., which is particularly obvious in the case of returns from newly introduced drugs. However, our results are sensitive to econometric model specification, in particular to controlling for serial correlation and to a dynamic specification of the baseline model. Likewise, estimates on financial constraints are sensitive to model specification, indicating that Japanese drug firms face small or no financial constraints. Our results are consistent with the general literature on R&D investment behaviour, yet raise some methodological questions with regard to the original study.