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.     

滨海新区对外通道在促进区域发展中的作用

一、"三北"地区是滨海新区重要的服务区域 (一)滨海新区服务区域的界定 国务院20号文件将天津滨海新区定位为:"依托京津冀、服务环渤海、辐射‘三北'、面向东北亚,努力建设成为我国北方对外开放的门户、高水平的现代制造业和研发转化基地、北方国际航运中心和国际物流中心,逐步成为经济繁荣、社会和谐、环境优美的宜居生态型新城区."     

北京话的轻音和语法化

北京话是汉语发展变化最快的方言。北京话在语法化的过程中,轻音(包括轻声和语句轻音)是极为重要的形式标志和变化动因。本文就北京话轻音和语法化相关的问题作一些探讨,指出北京话构词后缀的产生、虚词的虚化都与轻音有着密切的关系。     

中国农地制度的合理性探微：一个组织的制度分析范式

中国农村土地制度长期坚持以集体所有和家庭承包为内核，这不仅是国家层面的主观需要，也有集体和家庭分别作为两种制度安排的内在合理性。集体和家庭都体现着长期历史的自然选择，法律的规定只是让原有的非正式制度显化为正式的制度安排，外加非正式制度的配合，农地制度更易形成有效率的制度结构；集体和家庭在不同时期表征不同的功能，节约不同层次的交易费用，它们均具有较强的适应农地制度变革的能力。深化农地集体所有制改革需契合客观存在的自然法序，注重正式制度与非正式制度的功能配合，增强中国农地制度的稳定性和灵活性。     

Organization and implementation of China's national sampling survey on fertility and birth control

The Planning and Statistical Department of the State Family Planning Commission of China in July 1988 implemented a fertility and birth control survey in China on 2.16 million married women ages 15-57 using stratified, systematic, clustered, and non-proportionate sampling. 3 questionnaires were used: household, married women, and sample unit covering basic status, family planning status, general characteristics of pregnancy and contraception, population flow, deaths since 1981, and socioeconomic status. The authors suggest several international cooperative research projects including: design of fertility and contraception survey; Chinese population growth; Chinese population dynamics; dynamics of marital and family status; fertility; contraception and birth control; mortality; migration; status of the nationalities of China; population development; regional fertility status; and others. Data from the survey will be available in June 1989.     

The effects of the age and structure of population on family change]

The age structure of a population is one basic factor of population research. It is not only affected by birth, death, immigration, and marriage, but it also reflected in changes of family size. The article analyzed it from two aspects: (1) the age structure of population acts on the size and structure of the family. The younger the age structure, the larger the family size. Otherwise, it is the opposite. According to the 1982 census, 35.4% of the population was 0-14 years in rural areas, and average family size was 4.6; but in urban areas 26.0% of the population was 0-14 years and family size was 3.9. The family was characterized as a nuclear family as industrialization in economic development increased and the population aged. In the 1982 census, 64.7% were nuclear family and 6% were aging population in China. Three- generation families (or more) have decreased dramatically. The change of family size and structure is affected by change of internal family age structure. The younger population (0-14 years) is dependent and 90% live with their parents. The adult population (15-59) years are more affected by marriage, birth and social economic action. Families are established in this age period and give much more effect to fertility. The aging population (over 60) years is facing changes. They appear to be a "Defect" family because the wife or husband has passed away. They change from independent to dependent. 78.3% population over 60 years were dependent on children or social welfare, only 21.7% were independent according to the survey in Beijing Changping County.     

Inefficiency of strategy-proof allocation mechanisms in pure exchange economies

In this paper I prove that in the standard model of 2×n (n2) pure exchange economies there is no allocation mechanism that is efficient, non-inversely-dictatorial, and strategy-proof. This strengthens two previous results on this subject by Hurwicz and by Dasgupta, Hammond, and Maskin.I thank Alvin Klevorick, William Thomson, and an anonymous referee of the journal for many helpful comments.     

大学生科技创新能力培养的实践——多重课堂

主要从大学生科技创新能力的内涵和特征、培养实施方案和实践探索等方面对大学生科技创新能力的培养理论和实践进行了系统研究,阐述了"多重课堂"的概念。     

FDI对我国三次产业影响作用的实证分析

利用自回归分布滞后(ADL)模型,结合我国1983到2006年的有关数据,对我国FDI对三次产业的影响作用作出实证分析,得出结论,FDI在短期内对我国经济增长起了较大的促进作用,但长期作用不显著.并结合我国经济现状分析了原因,提出要充分发挥其在经济增长中的作用,需调整FDI在三次产业之间以及产业内部的投资结构.