基于粒子群优化的模糊聚类分析

基于求解实优化问题时,粒子群优化算法优于遗传算法。在基于遗传算法的模糊C均值聚类算法基础上,给出了基于粒子群的模糊C均值聚类算法,试验结果表明:该算法克服了传统的模糊C均值聚类算法的缺陷,同时在收敛速度方面明显优于基于遗传算法的模糊C均值聚类算法。     

中国转基因食品安全管理的现状及对策

转基因食品是当今世界各国基因研究的重点。我国的转基因技术发展迅速,但科学界在转基因食品对人类健康和生态风险方面的认识存在局限性,政府应制定相应的政策、措施对其进行安全管理。本文介绍了转基因食品的概念及在我国的发展情况,分析了我国转基因食品安全管理的现状,阐述了转基因食品安全管理的重要性,并针对其中存在的问题,提出相应的对策。     

基于平衡计分卡的物流企业绩效评价指标体系研究

提出了物流企业绩效评价的基本原则，并以平衡计分卡的基本原理为依据，从财务、客户、内部业务流程、学习与发展等方面研究了物流企业绩效评价指标体系。     

Delaying integration of immigrant labor for the purpose of taxation

Delayed integration (DI) is a rule for taxing migrants. It requires that immigrants be taxed in the host country only after some period of transition. Conversely, emigrants are released from the obligation to pay taxes only after a certain period. DI is an alternative to the Employment Principle and the Home-Country Principle. The former governs the international taxation of labor. The latter is a close substitute for the Nationality Principle, on which US tax law is based. The paper studies DI in a setting which allows one to trade off the efficiency costs of distortionary taxation and of wasteful government.     

发挥热电联产的优势推动城市集中供热发展

热电联产集中供热是节约能源、减少环境污染的重要措施之一.目前我国热电联产集中供热的发展机遇和挑战共存,应发挥热电联产的优势,推动城市集中供热的发展.     

On a clear day you might see an environmental Kuznets curve

We shed some new light on the Environmental Kuznets curve (EKC) and show how it can be viewed as a particular form of equilibrium relationship, where technology and preference parameters determine the shape of the curve. In contrast to most of the literature on the EKC, we estimate a theoretically consistent model on long-run data (Swedish sulfur emission, covering the period 1900–2002). Furthermore, we test and date structural change. The model suggests four regimes, 1900–1918, 1919–1933, 1934–1967 and 1968–2002, generating four rather different patterns for pollution over time. The policy-conclusions are consonant with Pearce’s general view about the EKC: there is no theoretical presumption that it has an inverted U shape, nor should any country try to “grow out of the environmental problems” without analyzing the benefits and costs of so doing.     

Stock-flow matching and the performance of the labor market

We estimate outflow equations for vacancies and unemployed workers in Britain, departing from the stock-based analysis of matching in two ways. First, we deal with the temporal aggregation problem that arises when discrete time data are used to describe continuous time processes. Second, we allow for a stock-flow matching mechanism in which the stock of traders on one side of the market matches with the flow of traders on the other side. Our estimates are in line with the predictions of stock-flow matching in terms of higher exit rates of flows and of matching combinations between labor market stocks and flows. Furthermore, employer search effectiveness did not seem to decline between the 1960s and the 1990s. Nevertheless, some deterioration in worker search effectiveness is detected, however less severe than that implied by previous, stock-based work.     

On the impact of leverage constraints on asset prices and trading volume

Abstract. Researchers have used stylized facts on asset prices and trading volume in stock markets (in particular, the mean reversion of asset returns and the correlations between trading volume, price changes and price levels) to support theories where agents are not rational expected utility maximizers. This paper shows that this empirical evidence is in fact consistent with a standard infinite horizon – perfect information – expected utility economy where some agents face leverage constraints similar to those found in todays financial markets. In addition, and in sharp contrast to the theories above, we explain some qualitative differences that are observed in the price-volume relation on stock and on futures markets. We consider a continuous-time economy where agents maximize the integral of their discounted utility from consumption under both budget and leverage constraints. Building on the work by Vila and Zariphopoulou (1997), we find a closed form solution, up to a negative constant, for the equilibrium prices and demands in the region of the state space where the constraint is non-binding. We show that, at the equilibrium, stock holdings volatility as well as its ratio to stock price volatility are increasing functions of the stock price and interpret this finding in terms of the price-volume relation. We would like to thank the editor and two anonimous referees for valuable substantive comments. Our gratitude also to Franklin Allen, Kerry Back, Domenico Cuoco, Xavier Freixas, Sanford Grossman, Michel Habib, Lutz Hendricks, Richard Kihlstrom, Fernando Restoy, Mary Thomson, Jean-Luc Vila, participants to seminars at Birkbeck College, Carnegie-Mellon, Columbia, ESSEC, HEC, IAE, INSEAD, London Business School, London School of Economics, McGill, Michigan, National University of Singapore, Pompeu Fabra, North Carolina, Washington-St-Louis, Wharton, the Jornadas de Economía Financiera BBV, and the Meetings of the Society for Economic Dynamics and Control and the American Finance Association. Special thanks are due to Süleyman Basak for his enthusiastic support and many helpful suggestions. The usual disclaimer applies. We gratefully acknowledge the support of the BBV and Caja de Madrid Foundations and CREF (both authors) and of the Spanish Ministry of Education under DGICYT grant no. PB93-0388 (first author).     

Discrepancies between ex ante and ex post efficiency under identical subjective probabilities

Summary. Starr (1973) showed that, if people have different subjective probabilities, ex ante and ex post efficiency conflict. Conversely, under the simple preferences that he considered, the discrepancy between ex ante and ex post efficiency disappears when subjective probabilities are identical. Here I consider identical subjective probabilities, but more general preferences. First, risk attraction is admitted. Second, I dispense with the double requirement (dubbed IZU) of additive separability and state-independence of the utility of zero-date consumption, an unrealistic requirement when modeling the investment in durable goods. I find that, under IZU, and as long as ex post preferences satisfy the natural assumption of quasiconcavity (and satisfy some technical qualifications), an ex ante efficient allocation is indeed ex post efficient, but the converse is not necessarily true under risk attraction. If, on the other hand, IZU is violated, then one can have ex ante efficient allocations that are not ex post efficient, and vice-versa, even under risk aversion. Received: June 25, 1999; revised version: March 2001     

How many voters are needed for paradoxes?

Summary. This paper presents a general procedure for finding profiles with the minimum number of voters required for many important paradoxes. Borda's and Condorcet's classic examples are revisited as well as generalizations. Using Saari's procedure line, we obtain an upper bound for the minimum number of voters needed for a profile for which the Condorcet winner is not strictly top ranked for all weighted positional procedures. Also we give a simple upper bound on the minimum number of voters needed for a set of prescribed voting outcomes. In contrast to situations wherein small numbers of voters are needed, we consider paradoxes requiring arbitrarily large numbers of voters as well as large numbers of alternatives. Finally we indicate connections with statistical rank based tests. Received: April 18, 2001; revised version: May 25, 2001