Theoretical consideration of effect of fishing mortality on growth and reproduction of fish populations

Summary An increase in fish mortality due to fishing can theoretically change the growth and reproduction of fish populations from the viewpoint of adaptation. We address the issue of how an iteroparous fish should convert surplus energy into somatic growth and reproduction at each age under given conditions of mortality. A model of life history, which maximizes the net reproductive rate using the discrete maximum principle, is improved employing a new relationship between body weight and surplus energy which we have recently proposed. The model is applied to the North Sea plaicePleuronectes platessa, for which it has been reported that the average length of young fish had increased whereas that of old ones had decreased for some decades. Although the model cannot directly explain the former phenomenon, the two phenomena can be interpreted as a change in the optimal life history due mainly to an increase in mortality.     

而今迈步从头越--写在《云南民族大学学报》(哲学社会科学版)创刊20周年之际

《云南民族大学学报》走过了20年的发展历程。正值20岁生日时,随着学校的更名,学报有了新的名称,赋予了新的意义:一流的大学需要一流的学报。认真总结20年的办刊经验,坚持刊物的特色和品位,以更名为契机,努力开创学报工作的新局面,这是时代赋予我们的使命。     

政治化文学新体制的营构--建国初期丁玲的文学批评与创作

建国初期,为了营构政治化文学新体制,丁玲以较多的批评文字和不多的创作发出了自己作为“小号兵”呐喊助阵的声音。从“文艺为政治服务”的理念和“政治第一”的批评标准出发,她在批评实践中对文学作品的主题、题材问题、作家“改造思想”问题以及形式问题给予了高度关注。同时,她还以自己的创作显示了新体制的“规范”,间接显露出了“小号兵的声音”。在她的批评和创作中,文学与政治一体化的关系,是贯穿始终的中心和基本线索;建立和显示新体制的规范,是她从事批评和创作的目的。     

爱沙尼亚职前教师教育课程建设的价值嬗变、架构及特征——以塔尔图大学为例

被誉为“爱沙尼亚的启蒙圣母”的塔尔图大学是爱沙尼亚最早开展师范教育的高校,既反映了本国职前教师教育发展的需求,也是职前教师教育课程发展的缩影。塔尔图大学职前教师教育课程建设的价值经历了从通过技能提升获得教师职业身份、培养理论基础夯实的从教人员到实现教师专业发展的终身性嬗变。在职前教师教育课程建设中,构建了以培养教师候选人的综合素养的课程目标,依托主题将教师教育知识统整为课程内容,推行“反思—探究”教学策略,优化课程实施方式及依托信息技术,完善课程评估手段,彰显出课程内容注重时代性、课程设置以学习者中心、课程谱系理论与实践有机交融以及课程制定与实施利益相关者共同参与的典型特征。     

Private Ownership versus Institutional Ownership: Exclusion Pricing of Initial Public Offerings

The authors examine the literature with respect to the pricing of initial public offerings and focus upon the relationship of pricing to the structure and conduct of the investment banking industry. Using a data base of all share offerings undertaken in the United States over a two and a half year period, the authors find that there is considerable evidence for the proposition that large, prestigious, and well capitalised investment banks tend to price their share offerings at a higher absolute level than those not meeting such characteristics. Using classical statistical methods, the authors find that the pricing strategy of investment banks is connected to their affiliation with investment funds and unit trusts. The motives for such pricing strategies, the authors argue, lie with the affiliation of investment banks with investment funds, suggesting that the pricing of new share offerings may be a means of excluding retail investors from participating in the strong returns such issues exhibit. The authors raise legal and regulatory implications of their findings in the context of the general consolidation observed within the investment banking industry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Objective Bayesian inference for the ratio of the scale parameters of two Weibull distributions

The Weibull distribution is widely used due to its versatility and relative simplicity. In our paper, the non informative priors for the ratio of the scale parameters of two Weibull models are provided. The asymptotic matching of coverage probabilities of Bayesian credible intervals is considered, with the corresponding frequentist coverage probabilities. We developed the various priors for the ratio of two scale parameters using the following matching criteria: quantile matching, matching of distribution function, highest posterior density matching, and inversion of test statistics. One particular prior, which meets all the matching criteria, is found. Next, we derive the reference priors for groups of ordering. We see that all the reference priors satisfy a first-order matching criterion and that the one-at-a-time reference prior is a second-order matching prior. A simulation study is performed and an example given.     

A simple algorithm for calculating values for folded normal distribution

Folded normal distribution originates from the modulus of normal distribution. In the present article, we have formulated the cumulative distribution function (cdf) of a folded normal distribution in terms of standard normal cdf and the parameters of the mother normal distribution. Although cdf values of folded normal distribution were earlier tabulated in the literature, we have shown that those values are valid for very particular situations. We have also provided a simple approach to obtain values of the parameters of the mother normal distribution from those of the folded normal distribution. These results find ample application in practice, for example, in obtaining the so-called upper and lower α-points of folded normal distribution, which, in turn, is useful in testing of the hypothesis relating to folded normal distribution and in designing process capability control chart of some process capability indices. A thorough study has been made to compare the performance of the newly developed theory to the existing ones. Some simulated as well as real-life examples have been discussed to supplement the theory developed in this article. Codes (generated by R software) for the theory developed in this article are also presented for the ease of application.     

Estimating ordered quantiles of two exponential populations with a common minimum guarantee time

The problem of estimating ordered quantiles of two exponential populations is considered, assuming equality of location parameters (minimum guarantee times), using the quadratic loss function. Under order restrictions, we propose new estimators which are the isotonized version of the MLEs, call it, restricted MLE. A sufficient condition for improving equivariant estimators is derived under order restrictions on the quantiles. Consequently, estimators improving upon the old estimators have been derived. A detailed numerical study has been done to evaluate the performance of proposed estimators using the Monte-Carlo simulation method and recommendations have been made for the use of the estimators.     

An EWMA chart for monitoring process mean

In the statistical process control literature, there exists several improved quality control charts based on cost-effective sampling schemes, including the ranked set sampling (RSS) and median RSS (MRSS). A generalized cost-effective RSS scheme has been recently introduced for efficiently estimating the population mean, namely varied L RSS (VLRSS). In this article, we propose a new exponentially weighted moving average (EWMA) control chart for monitoring the process mean using VLRSS, named the EWMA-VLRSS chart, under both perfect and imperfect rankings. The EWMA-VLRSS chart encompasses the existing EWMA charts based on RSS and MRSS (named the EWMA-RSS and EWMA-MRSS charts). We use extensive Monte Carlo simulations to compute the run length characteristics of the EWMA-VLRSS chart. The proposed chart is then compared with the existing EWMA charts. It is found that, with either perfect or imperfect rankings, the EWMA-VLRSS chart is more sensitive than the EWMA-RSS and EWMA-MRSS charts in detecting small to large shifts in the process mean. A real dataset is also used to explain the working of the EWMA-VLRSS chart.     

Multivariate normal estimation: the case (n < p)

Estimation in the multivariate context when the number of observations available is less than the number of variables is a classical theoretical problem. In order to ensure estimability, one has to assume certain constraints on the parameters. A method for maximum likelihood estimation under constraints is proposed to solve this problem. Even in the extreme case where only a single multivariate observation is available, this may provide a feasible solution. It simultaneously provides a simple, straightforward methodology to allow for specific structures within and between covariance matrices of several populations. This methodology yields exact maximum likelihood estimates.