通用桥式起重机主梁自重对拱度的影响及修正

通用桥式起重机主梁上拱度是起重机的重要技术指标,因此生产检测中所测的拱度值必须保证是准确可靠的。而在进行起重机桥架结构时,由于各种条件的限制,支架位置常常处于0.8倍跨度处,此时主梁自重对主梁拱度产生的影响值会有偏差,造成测得的主梁上拱度值是不准确的,因此需要对该值进行修正。通过生产实践总结和理论计算相结合,可准确得出支架位置在0.8倍跨度处主梁自重对主梁上拱度的影响修正值,此时测得的拱度值再减去修正值后就是准确的拱度值。     

Validating the international tourist role scale

This study was designed to validate the international tourist role scale and the three dimensions it revealed. The purpose of this attitudinal scale was to measure the tourist role typology. United States adult outbound tourists flying with 11 major airlines returned useful questionnaires. This study validated the role scale as a reliable one that properly identified three conceptual dimensions of international tourist typology and successfully provided measures of tourists’ novelty-seeking preferences on the three dimensions. The study demonstrated, however, that the scale would measure the novelty-seeking preferences of international tourists more effectively if it were supplemented by other measures.     

浅析地基承载力特征值的深度修正

影响地基承载力特征值修正的因素较多，文章通过对地基破坏形式的分析得出地基承载力深度修正的实质，并分析不同情况下地基承载力深度修正时基础埋深的取值。     

Bias from Farmer Self‐Selection in Genetically Modified Crop Productivity Estimates: Evidence from Indian Data

In the continuing debate over the impact of genetically modified (GM) crops on farmers of developing countries, it is important to accurately measure magnitudes such as farm‐level yield gains from GM crop adoption. Yet most farm‐level studies in the literature do not control for farmer self‐selection, a potentially important source of bias in such estimates. We use farm‐level panel data from Indian cotton farmers to investigate the yield effect of GM insect‐resistant cotton. We explicitly take into account the fact that the choice of crop variety is an endogenous variable which might lead to bias from self‐selection. A production function is estimated using a fixed‐effects model to control for selection bias. Our results show that efficient farmers adopt Bacillus thuringiensis (Bt) cotton at a higher rate than their less efficient peers. This suggests that cross‐sectional estimates of the yield effect of Bt cotton, which do not control for self‐selection effects, are likely to be biased upwards. However, after controlling for selection bias, we still find that there is a significant positive yield effect from adoption of Bt cotton that more than offsets the additional cost of Bt seed.     

基于MAPGIS土地利用数据库的数据变更技术方法

土地利用数据的现势性和准确性是土地科学管理的关键，在县(市)级土地利用数据库的建设和日常使用维护中，数据变更工作非常重要。阐述在MAPGIS土地利用数据库管理系统下数据变更的解决方案及土地利用变更数据的外业调绘、制作变更图、数据采集、变更处理等技术方法。     

Consumption effects of genetic modification: what if consumers are right?⋆

This paper develops a model of differentiated consumers to examine the consumption effects of genetic modification (GM) under alternative labelling regimes and segregation enforcement scenarios. Analytical results show that if consumers perceive GM products as being different than their traditional counterparts, GM affects consumer welfare and, thus, consumption decisions. When the existence of market imperfections in one or more stages of the supply chain prevents the transmission of cost savings associated with the new technology to consumers, GM results in welfare losses for consumers. The analysis shows that the relative welfare ranking of the ‘no labelling’ and ‘mandatory labelling’ regimes depends on: (i) the level of consumer aversion to GM products; (ii) the size of marketing and segregation costs under mandatory labelling; (iii) the share of the GM product in total production; and (iv) the extent to which GM products are incorrectly labelled as non‐GM products.     

涡旋压缩机型线及其修正方法

文章在介绍涡旋压缩机工作原理的基础上,总结了涡旋式压缩机型线的啮合特点,并介绍了圆渐开线、正方形渐开线和变基圆渐开线作为其型线的方程和特点。最后,给出了常用的涡旋压缩机型线始端的修正方法。     

西安铁路枢纽客运系统扩能方案研究

西安铁路枢纽将有8个方向、7条铁路线引入,既有西安站已不能满足客流增长的需要。分析西安枢纽内影响客运能力的各项因素,结合西安枢纽的改扩建及西安城市规划,提出新建第二客运站——西安北站和辅助客运站——纺织城站,并对原西安站进行扩建的方案,形成西安枢纽客运系统二主一辅的格局。     

Consistent estimation in the bilinear multivariate errors-in-variables model

A bilinear multivariate errors-in-variables model is considered. It corresponds to an overdetermined set of linear equations AXB=C, A∈ℝ^m×n, B∈ℝ^p×q, in which the data A, B, C are perturbed by errors. The total least squares estimator is inconsistent in this case.  An adjusted least squares estimator is constructed, which converges to the true value X, as m →∞, q →∞. A small sample modification of the estimator is presented, which is more stable for small m and q and is asymptotically equivalent to the adjusted least squares estimator. The theoretical results are confirmed by a simulation study. Acknowledgements. We thank two anonymous reviewers for their suggestions and corrections.? A. Kukush is supported by a postdoctoral research fellowship of the Belgian office for Scientific, Technical and Cultural Affairs, promoting Scientific and Technical Collaboration with Central and Eastern Europe.? S. Van Huffel is a full professor with the Katholieke Universiteit Leuven.? I. Markovsky is a research assistant with the Katholieke Universiteit Leuven.? This paper presents research results of the Belgian Programme on Interuniversity Poles of Attraction (IUAP V-22), initiated by the Belgian State, Prime Minister's Office – Federal Office for Scientific, Technical and Cultural Affairs of the Concerted Research Action (GOA) projects of the Flemish Government MEFISTO-666 (Mathematical Engineering for Information and Communication Systems Technology), of the IDO/99/03 project (K.U. Leuven) “Predictive computer models for medical classification problems using patient data and expert knowledge”, of the FWO projects G.0078.01, G.0200.00, and G0.0270.02.? The scientific responsibility is assumed by its authors.     

The scope of application of management accounting methods in Polish enterprises

The transformation of Poland’s economic system in the 1990s as a result of transition from a centrally planned economy to a market-based system involves significant changes in the regulatory context and in accounting practice and education.This paper presents the scope of application of management accounting concepts and methods in 60 Polish enterprises covered by a questionnaire survey carried out by the author between November 1998 and December 1999 in enterprises located in central and southern Poland. The selected companies were interviewed by means of a postal survey, with inquiry forms delivered in person in some cases.The detailed analyses carried out in this paper and the conclusions presented are also based on information obtained from documentary evidence kept by the enterprises and from direct interviews conducted in the course of work in teams engaged in analysis and assessment of cost accounting practices and in management accounting system design in a number of large and medium Polish enterprises.The empirical research carried out is aimed at verification of a number of hypotheses including the following: • modification of cost accounting systems and implementation of management accounting tools in Polish enterprises is brought about by many different factors, the most important being growth of competition and ownership changes in business entities, • Polish enterprises mostly implement the methods and techniques of operational management accounting, • short-term budgeting for cost centres is the most widely used method of management accounting.