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.     

A preliminary study on quantitative relations among growth, reproduction and mortality in fishes

Summary As a quantitative approach to the life histories of fishes, the present paper attempted to predict a relation among reproduction, growth and mortality numerically with a technique of control theory, the discrete maximum principle. A method for predicting the relation was derived on the postulate that natural selection maximized the net reproductive rate subject to a few constraints. The derived method was applied to Atlantic cod and Atlantic herring populations in the Southern Gulf of St. Lawrence as numerical examples. The examples demonstrated that the theoretical reproductive effort and body weight were well consistent with the observed ones every age but the theoretical survival rates were slightly different from the observed ones. For the reasons mentioned below, however, it should be interpreted that the examples rather support the adopted postulate to a certain degree. First, in general, it is very difficult to obtain good estimates of the rates with traditional methods. Second, intense fishing pressure possibly changes the life history parameters to some extent in fish populations. Moreover, the examples also suggested that, to examine the postulate in further detail, similar analyses had to be made with the data of many fish populations on which intense fishing pressure had not been exerted.     

Measuring Information Behavior: A Time Budget Survey in Japan

This paper discusses the results of a time budget survey which was conducted nationwide in Japan in 1995 on ‘information behavior’, that is, the amount of time people spent communicating and using information media ranging from conversations to computers. We propose a three-dimensional time budget survey as a method for measuring information behavior in actual life. The method classifies information behavior into 24 categories and measures them with respect to three factors, i.e. time, location and purpose of behavior. Our survey revealed that the total time spent on information behavior was about seven hours per day, of which about 45% was spent watching TV. The displacement effect of PC use on TV watching was estimated by a “time-shift matching” design. The results demonstrated that use of a PC does not significantly affect TV viewing, despite a large difference in TV viewing time between PC users and non-users.     

东亚近代史中的中日甲午战争

甲午战争虽然已逾百年,但我们从东亚近代史的历史研究视野看,甲午战争的意义不仅仅限于中国和日本两国之间.甲午战争不仅改变了东亚世界的国际秩序,也改变了日本人对国家、天皇的认识,影响了日本整个近代社会.同时,甲午战争不仅是中日五十年战争的开始,也是"大日本帝国体制"从开始到发展、到崩溃的起点.     

Interannual fluctuations in recruitment and growth of the sardine,Sardinops melanostictus, in the sea of Japan and adjacent waters

Recruitment and growth of the sardineSardinops melanostictus fluctuated markedly in the Sea of Japan and adjacent waters between 1978 and 1993. Stock size was calculated using Virtual Population Analysis and average body length in each age class was determined by the number of annual rings on the scales. There is an inverse correlation between average water temperature at a depth of 50 m in the coastal area of the mainland of Japan in winter (January to March) and recruitmentR defined as the number of individuals at 1 year old. There is also an inverse correlation between spawning stock sizeE and reproductive success in (R/E). A multiple regression model using spawning stock size and water temperature in winter as independent variables can explain 73% of variance in reproductive success. It suggests that both density-dependent and density-independent factors perform important roles determining reproductive success. There is an inverse correlation between body length and stock size and this suggests that there is a density-dependent effect on the growth of the sardine.     

Determinants of Long-Term Unions: Who Survives the “Seven Year Itch”?

Most studies of union formation focus on short-term probabilities of marrying, cohabiting, or divorcing in the next year. In this study, we take a long-term perspective by considering joint probabilities of marrying or cohabiting by certain ages and maintaining the unions for at least 8, 12, or even 24 years. We use data for female respondents in the 1979 National Longitudinal Survey of Youth to estimate choice models for multiple stages of the union-forming process. We then use the estimated parameters to simulate each woman’s sequence of union transitions from ages 18–46, and use the simulated outcomes to predict probabilities that women with given characteristics follow a variety of long-term paths. We find that a typical, 18 year-old woman with no prior unions has a 22 % chance of cohabiting or marrying within 4 years and maintaining the union for 12+ years; this predicted probability remains steady until the woman nears age 30, when it falls to 17 %. We also find that unions entered via cohabitation contribute significantly to the likelihood of experiencing a long-term union, and that this contribution grows with age and (with age held constant) as women move from first to second unions. This finding reflects the fact that the high probability of entering a cohabiting union more than offsets the relatively low probability of maintaining it for the long-term. Third, the likelihood of forming a union and maintaining it for the long-term is highly sensitive to race, but is largely invariant to factors that can be manipulated by public policy such as divorce laws, welfare benefits, and income tax laws.     

Educational Inequality

Abstract. This paper develops a theoretical model of the inequality in wages and salaries associated with differences in years of schooling (educational inequality, for short). Our model assumes that in the long run individual decisions to become more educated equalize the lifetime earnings of more educated workers and comparable less educated workers. Given this assumption, our model implies that innovations that increase the relative demand for more educated labor, and which cause short‐run increases in educational inequality, in the long run induce offsetting increases in the relative supply of more educated labor. But our model also has the novel implication that innovations that increase differences between the wages and salaries received by workers with the same years of education who are more or less able (ability premiums, for short) cause a smaller fraction of workers to choose to become more educated. Consequently, innovations that increase ability premiums in the long run also cause educational inequality to be larger than otherwise. In applying our theory to recent changes in educational inequality in the USA, we suggest that, to the extent that innovations that increase ability premiums are contributing to educational inequality, the increases in educational inequality during the 1980s and 1990s are unlikely to be reversed soon.     

A computational algorithm for the loss probability in the M/G/1+PH queue

This article develops a computational algorithm for the loss probability in the stationary M/G/1 queue with impatient customers whose impatience times follow a phase-type distribution (M/G/1+PH). The algorithm outputs the loss probability, along with an upper-bound of its numerical error due to truncation, and it is readily applicable to the M/D/1+PH, M/PH/1+PH, and M/Pareto/1+PH queues.     

几首苏东坡词编年考

对苏东坡词<浣溪沙>三首、<临江仙>一首、<双荷叶>一首、<减字木兰花>一首的写作时间进行了考证.     

Relationship between surplus energy and body weight in fish populations

Summary This paper theoretically analyses the relationship between surplus energy, which is available for either somatic growth or reproduction, and body weight. From the data of metabolism and growth of the biwamasu,Oncorhynchus rhodurus, obtained by Miura et al., a Bernoulli's differential equation is induced to represent the relationship between body weight and the sum of surplus energy and active metabolic rate. Solving this equation gives the amount of surplus energy,f(W_x), as follows:f(W_x) = (αW _x ^1−γ +β^1−γ)^1/(1−γ)−W_x, in which α, β and γ are constants andW _x is body weight at agex. The function is applied to ten fish populations and consequently it is found to be useful for a wider age range and a wider variety of fishes than the conventional function.