Approximate estimation in nonlinear panel data models

This paper is concerned with the estimation of a general class of nonlinear panel data models in which the conditional distribution of the dependent variable and the distribution of the heterogeneity factors are arbitrary. In general, exact analytical results for this problem do not exist. Here, Laplace and small-sigma appriximations for the marginal likelihood are presented. The computation of the MLE from both approximations is straightforward. It is shown that the accuracy of the Laplace approximation depends on both the sample size and the variance of the individual effects, whereas the accuracy of the small-sigma approximation is 0(1) with respect to the sample size. The results are applied to count, duration and probit panel data models. The accuracy of the approximations is evaluated through a Monte Carlo simulation experiment. The approximations are also applied in an analysis of youth unemployment in Australia.     

Computing the probability of hash table/urn overflow

We analyze the probability of a random distribution of n balls into m urns of size b resulting in no overflows. This solves the computational problem associated with a classical combinatorial extreme-value distribution. The problem arose during the analysis of a technique, called perfect hashing, for organizing data in computer files. The results and techniques presented can be used to solve several problems in the analysis of hashing techniques     

Weighted Stochastic Restricted Estimation in Linear Measurement Error Models

This article discusses the consistent estimation of the parameters in a linear measurement error model when stochastic linear restrictions on regression coefficients are available. We propose some methodologies to obtain the consistent estimation when either the covariance matrix of the measurement errors or the reliability matrix of independent variables is known. Their finite- and large-sample properties are derived with not necessarily normal errors. A Monte Carlo simulation is carried out to study the the finite properties of the estimators.     

理工高校法律人才培养模式之检讨

通过抽样考察,可窥见我国理工高校法律人才培养模式总体现状欠佳,其主要存在这样几个问题:一是培养模式未彰显特色,培养目标指向趋于同质,定位模糊;二是培养机制缺乏制度化支撑,长久动力不足,人才培养缺乏竞争优势。理工高校应以应用复合型卓越法律人才培养目标的确立,特定法律人才培养机制的建构,特色法律专业课程的设计和教学方法的创新,以及法律人才培养模式的制度化保障等四个方面为进路,尽快改变理工高校法律人才培养的欠佳状况。     

Mapping Invasive Species Risks with Stochastic Models: A Cross-Border United States-Canada Application for Sirex noctilio Fabricius

Nonindigenous species have caused significant impacts to North American forests despite past and present international phytosanitary efforts. Though broadly acknowledged, the risks of pest invasions are difficult to quantify as they involve interactions between many factors that operate across a range of spatial and temporal scales: the transmission of invading organisms via various pathways, their spread and establishment in new environments. Our study presents a stochastic simulation approach to quantify these risks and associated uncertainties through time in a unified fashion. We outline this approach with an example of a forest pest recently detected in North America, Sirex noctilio Fabricius. We simulate new potential entries of S. noctilio as a stochastic process, based on recent volumes of marine shipments of commodities from countries where S. noctilio is established, as well as the broad dynamics of foreign marine imports. The results are then linked with a spatial model that simulates the spread of S. noctilio within the geographical distribution of its hosts (pines) while incorporating existing knowledge about its behavior in North American landscapes. Through replications, this approach yields a spatial representation of S. noctilio risks and uncertainties in a single integrated product. The approach should also be appealing to decisionmakers, since it accounts for projected flows of commodities that may serve as conduits for pest entry. Our 30-year forecasts indicate high establishment probability in Ontario, Quebec, and the northeastern United States, but further southward expansion of S. noctilio is uncertain, ultimately depending on the impact of recent international treatment standards for wood packing materials.     

BARTLETT CORRECTED LIKELIHOOD RATIO TESTS IN LOCATION-SCALE NONLINEAR MODELS

The paper derives Bartlett corrections for improving the chisquare approximation to the likelihood ratio statistics in a class of location-scale family of distributions, which encompasses the elliptical family of distributions and also asymmetric distributions such as the extreme value distributions. We present, in matrix notation, a Bartlett corrected likelihood ratio statistic for testing that a subset of the nonlinear regression coefficients in this class of models equals a given vector of constants. The formulae derived are simple enough to be used analytically to obtain several Bartlett corrections in a variety of important models. We show that these formulae generalize a number of previously published results. We also present simulation results comparing the sizes and powers of the usual likelihood ratio tests and their Bartlett corrected versions when the scale parameter is considered known and when this parameter is uncorrectly specified.     

The Relationship of Expectancies to the Transtheoretical Model of Change in College Smokers

Abstract

Efforts on the part of the sci en tific com mu nity have resulted in in creased knowl edge about to bacco ad die tion and im proved treat ment ef fi cacy. De spite these gains, how ever, our un der stand ing of to bacco ad die tion re mains in com plete. Two el e ments that may help il lu-mi nate the knowl edge of this ad die tion pro cess and pro vide im pli ca tions for treat ment are the Transtheoretical Model of Change and the con cept of ex pec tan cies. This project is a be gin ning step in ex plor ing the re la tion ship be tween the transtheoretical model and fac ets of ex pec tan cies among col lege smokers.     

跨文化交际教育中的交流模式解析

伴随着全球化进程，跨文化交际过程中对于交流技巧的关注愈来愈多。交流的方式及过程直接影响到交流效果的好坏，于是如何使用得当的方式处理交流过程中涉及的信息、意义便成为保障顺利交流的关键。文本试从解析交流过程中信息的产生及走向为出发点，重点探讨改进意义的方式，并最终建构跨文化交际教育中更为科学合理的交流模式。     

基于测井资料的低孔低渗储层产能预测研究

针对低孔低渗储层产能预测模型受敏感因素影响大，主次因素在低产情况下区别不明显，产能预测评价相对较困难等实际问题，以准噶尔盆地夏子街地区夏77井、夏79井为例，开展低孔低渗储层产能预测的前期试验研究，对多个产能预测模型及其适用条件进行了对比分析，从Darcy模型、Jones（1976）模型、Vogel/Harrison（1968）模型、裂缝模型中进行优选和调试。通过分析产能预测模型结果与测试结果在产量上的相关性，表明基于测井资料的预测结果与试油测试结果相当吻合，从而确认产能预测模型结果的可靠性。     

丙烯精馏塔的建模及其先进控制方法研究

精馏过程是化工、石油、医药等领域常见的生产过程，由于其非线性、时变性和强耦合等特点，使建模、控制与优化成为理论与实践研究中的难点。本文以一个二元丙烯精馏塔为研究对象，在由物料及能量平衡原理推导出精馏过程数学模型的基础之上，采用基于集结法的动力学模型降阶处理方法对原模型进行降阶，最后为该精馏塔模型设计了基于PID神经网络的解耦控制器。