Managing complexity： A problem of chaos in fisheries policy

This work intends to present chaos theory （and dynamical systems such as the theories of complexity）, in terms of interpretation of ecological phenomena. The chaos theory applied in the context of ecological systems, especially in the context of fisheries has allowed the recognition of the relevance of this kind of theories to explain fishing phenomena and fisheries policies. It has permitted new advances in the study of marine systems, contributing to the preservation of fish stocks. This paper deals with the way how to manage fisheries taking chaos in account of the problem.     

Adaptive rational equilibrium with forward looking agents

In adaptive rational equilibrium dynamics (ARED) agents choose between a costly rational expectation forecast and a cheap naive forecast, and the fractions using each of the two strategies evolve over time and are endogenously coupled to the market equilibrium price dynamics. In this setting, agents are backward looking in the sense that strategy selection is based on experience measured by relative past realized profits. When the selection pressure to switch to the more profitable strategy is high, instability and complicated chaotic price fluctuations arise.
In this paper we investigate the ARED with forward looking agents, whose strategy selection is based upon expected profits. Our findings suggest that forward looking behavior dampens the amplitude of price fluctuations, but local instability of the steady state remains. The global dynamics depends upon how sophisticated the forward looking behavior is. With perfectly forward looking agents, prices converge to a stable 2-cycle, whereas with forward looking agents who are boundedly rational concerning their estimate of expected profits, small amplitude chaotic price fluctuations might arise.
We also establish an equivalence relationship between a heterogeneous agent model with switching of strategies and a representative agent framework, where the representative agent optimally chooses between the benefits of a high quality forecast and the associated information gathering costs. To an outside observer it is impossible to distinguish between the two.     

ALGORITHMIC METHODS FOR SINGLE SERVER SYSTEMS WITH REPEATED ATTEMPTS

In many practical situations customers applying for service and finding the server busy will not join a queue, but make a new attempt to enter service after some time. In this paper we study single server systems with repeated attempts both for infinite-source input and finite-source input where the service times are general and the reattempt times are exponential. Numerically stable recursion schemes are derived by which the time-average and customer-average steady-state probabilities can be effectively computed.     

关联规则中支持度变化的数据重挖掘算法研究

使用关联规则进行数据挖掘时,使用者为了达到一定的挖掘效果,经常需要不断地改变关联规则的支持度阈值(support)。文中提出了一种从大型数据库中挖掘关联规则的快速算法。该算法以经典的Apriori算法为基础,可以在提出新的支持度后,直接在首次挖掘的基础上进行再一次挖掘。结果表明,它较Apriori算法的实现速度有明显的提高。     

基于混沌理论的民用航空运输系统突发事件应对研究

首先介绍了混沌学的基本概念,并举例说明民航运输系统在突发事件时所发生的混沌现象;其次运用混沌学理论对民航运输系统的突发事件的发生机理进行了分析;最后,提出了民航改进大面积航班延误、避免混沌现象发生的措施。     

On the index tracking and the statistical arbitrage choosing the stocks by means of cointegration: the role of stock picking

In this paper, we propose a new methology for Index Tracking (IT) by means of cointegration which provides some significant improvements on that field. As the quality of the tracking portfolio (TP) depends highly on the stock selection procedure, we propose picking the stocks using a model selection technique based on optimizing the cointegration level of the TP and the benchmark index instead of selecting, as in previous papers the assets by ad hoc decisions. To illustrate an empirical application of these techniques we use daily closing prices in the Dow Jones Industrial Average (DJIA) index over two different periods; one period which goes from 1 January 1990 to 31 December 2001 previously used by other authors, and the bear and a turmoil period, which goes from January 2007 to May 2012, inside the current financial crisis. Using only five assets we are able to successfully track the DJIA index and our results improve the IT technique based on cointegration that chooses stocks with maximum capitalization level. We also have compared our results with a more traditional procedure based on correlation and again our results reveal superiority. The empirical illustration not only has been focused on the TP itself, but has also been extended to tracking the index with an added profitability of 5, 10, 15 or 20% and to long-short strategies, producing profitable results.     

经济预测的混沌分析

未来经济发展状况一直是人们探讨的问题。由于经济现象纷繁复杂,现有的经济预测理论与方法还不能对此给予完全合理的解释和有效的预测,经济预测的实效往往不佳,为此,以混沌理论为基础,对经济现象的可预测性、影响经济预测精度的原因以及如何提高经济预测精度进行了探讨。     

Digital Signatures

Abstract

The growing use of the Internet for business makes digital signatures a crucial issue. This article discusses three methods used in digital signatures: symmetric encryption, asymmetric encryption and signature dynamics. In addition, the need for consistent laws governing digital signatures in all of the United States, and indeed in the world, is discussed.