飞灰冲蚀条件下材料抗磨性能的试验研究

本文首先综述了国内外学者在研究塑性材料耐冲蚀磨损性能方面所取得的主要成果,并在专门建立的灰磨试验台上,对电站燃煤锅炉对流受热面常用材料20号钢、12Cr_1MoV合金铜以及铜、铝四种塑性材料进行了耐飞灰冲蚀磨损性能的试验研究。提出用材料的体积磨损率来定义材料的耐冲蚀磨损性能系数。并用它表征塑性材料的抗磨性能。该系数可直接应用于计算燃煤锅炉对流受热面的安全烟速。     

On an asymptotic relative efficiency concept based on expected volumes of confidence regions

ABSTRACT

The paper deals with an asymptotic relative efficiency concept for confidence regions of multidimensional parameters that is based on the expected volumes of the confidence regions. Under standard conditions the asymptotic relative efficiencies of confidence regions are seen to be certain powers of the ratio of the limits of the expected volumes. These limits are explicitly derived for confidence regions associated with certain plugin estimators, likelihood ratio tests and Wald tests. Under regularity conditions, the asymptotic relative efficiency of each of these procedures with respect to each one of its competitors is equal to 1. The results are applied to multivariate normal distributions and multinomial distributions in a fairly general setting.     

A volume based approach to establish B-spline based expressions for density functions and its application to progressive hybrid censoring

We propose an approach to determine the distribution of particular linear combinations of hybrid censored order statistics which is based on the calculation of volumes of polytopes. For this purpose, we establish efficient and compact volume formulas in terms of B-splines. Further, we illustrate our approach for ten different progressive hybrid censoring schemes under an exponential assumption.     

Nonparametric and semiparametric estimation of the three way receiver operating characteristic surface

In many situations the diagnostic decision is not limited to a binary choice. Binary statistical tools such as receiver operating characteristic (ROC) curve and area under the ROC curve (AUC) need to be expanded to address three-category classification problem. Previous authors have suggest various ways to model the extension of AUC but not the ROC surface. Only simple parametric approaches are proposed for modeling the ROC measure under the assumption that test results all follow normal distributions. We study the estimation methods of three-dimensional ROC surfaces with nonparametric and semiparametric estimators. Asymptotical results are provided as a basis for statistical inference. Simulation studies are performed to assess the validity of our proposed methods in finite samples. We consider an Alzheimer's disease example from a clinical study in the US as an illustration. The nonparametric and semiparametric modelling approaches for the three way ROC analysis can be readily generalized to diagnostic problems with more than three classes.     

周邦彦卷入王寀、刘昺"谋逆"事件考辨

宋人庄绰与王明清曾谓周邦彦因受王寀、刘昺"谋逆"事件牵连而出知真定,然当代学者却反以为邦彦因反对蔡京而外任.此文则考出所谓王、刘"谋逆"事件纯属冤案,是当时郑居中与蔡京政治角逐的产物.但邦彦的确受此事件牵连,几乎获罪,因得到蔡京及其集团其他成员的营救而豁免,遂出知真定.     

舒伯特艺术歌曲的演唱风格

舒伯特是十九世纪欧洲浪漫主义音乐的奠基人,是艺术歌曲大师。演唱其艺术歌曲时应注意几方面问题:演唱者要根据不同的旋律风格和歌词内容处理歌曲,注意运用不同的音色、力度来刻画形象,准确把握歌曲的速度,注意轻声、半声、渐强、渐弱的运用,保持声音的流畅、语音的连贯及声音位置的准确。     

读《唐会要》札记一则

在检阅四库本《唐会要》卷七十四《选部上.论选事》和中华本《唐会要》卷七十六《贡举中.进士》时,发现二书或整段内容此有彼无,或史事时间序次歧互淆乱,或人名和官名互有出入,或文字衍脱讹误,凡此类可拾掇的问题不在少数。     

Passenger Rail Security,Planning, and Resilience: Application of Network,Plume, and Economic Simulation Models as Decision Support Tools

We built three simulation models that can assist rail transit planners and operators to evaluate high and low probability rail‐centered hazard events that could lead to serious consequences for rail‐centered networks and their surrounding regions. Our key objective is to provide these models to users who, through planning with these models, can prevent events or more effectively react to them. The first of the three models is an industrial systems simulation tool that closely replicates rail passenger traffic flows between New York Penn Station and Trenton, New Jersey. Second, we built and used a line source plume model to trace chemical plumes released by a slow‐moving freight train that could impact rail passengers, as well as people in surrounding areas. Third, we crafted an economic simulation model that estimates the regional economic consequences of a variety of rail‐related hazard events through the year 2020. Each model can work independently of the others. However, used together they help provide a coherent story about what could happen and set the stage for planning that should make rail‐centered transport systems more resistant and resilient to hazard events. We highlight the limitations and opportunities presented by using these models individually or in sequence.     

Tests for Cointegration Breakdown Over a Short Time Period

We derive a speculative trading model with endogenous informed trading that yields a conditionally heteroscedastic time series for trading volume and the squared price changes. We use half-hourly price-change and volume data for IBM during 1988 to test the model and estimate the structural parameters using the simulated method-of-moments estimation procedure. Although the model seems to do a reasonable job fitting the unconditional moments of the volume and the squared price change processes, it fares less well in fitting the relation between current trading volume and lags of trading volume and squared volume's (and its lag's) relation to squared price changes.     

基于Malmquist指数的客车企业效率研究

汽车行业是中国加入WTO后受冲击最大的行业之一。正确估计作为公共交通主要工具的客车企业的效率是研究、规划、调控该行业发展的重要依据。本文运用基于DEA模型的Malmquist研究了2002年到2005年中国客车类上市公司纯技术效率、规模效率、技术进步率和全要素生产率的变化。结果表明面对外资企业的冲击,多数企业的发展高于人们的预期,在激烈的竞争中保持住了竞争优势,并实现了一定程度的生产率提高,只是受发展环境的限制,提高速度低于国民经济增长速度。