Chain ratio type estimator for ratio of two population m3ans using auxiliary characters

In this paper we have proposed chain ratio type estimators for ratio of two population means using two auxiliary characters. The expressions for bias and mean square error of these estimators have been derived. A comparison of the proposed estimator with that of double sampling estimator has been made in terms of mean square error. An emperical study has also been made.     

Matrix mean square error comparisons based on a certain covariance structure

For two given estimators of a parameter vector the covariance structure of their difference is used to compare them in terms of their mean square error matrices. The results obtained are applied to the covariance adjustment technique and regression     

A Generalized Class of Ratio Type Exponential Estimators of Population Mean Under Linear Transformation of Auxiliary Variable

Recently, Shabbir and Gupta [Shabbir, J. and Gupta, S. (2011). On estimating finite population mean in simple and stratified random sampling. Communications in Statistics-Theory and Methods, 40(2), 199–212] defined a class of ratio type exponential estimators of population mean under a very specific linear transformation of auxiliary variable. In the present article, we propose a generalized class of ratio type exponential estimators of population mean in simple random sampling under a very general linear transformation of auxiliary variable. Shabbir and Gupta's [Shabbir, J. and Gupta, S. (2011). On estimating finite population mean in simple and stratified random sampling. Communications in Statistics-Theory and Methods, 40(2), 199–212] class of estimators is a particular member of our proposed class of estimators. It has been found that the optimal estimator of our proposed generalized class of estimators is always more efficient than almost all the existing estimators defined under the same situations. Moreover, in comparison to a few existing estimators, our proposed estimator becomes more efficient under some simple conditions. Theoretical results obtained in the article have been verified by taking a numerical illustration. Finally, a simulation study has been carried out to see the relative performance of our proposed estimator with respect to some existing estimators which are less efficient under certain conditions as compared to the proposed estimator.     

PREDICTION OF THE FINITE POPULATION DISTRIBUTION FUNCTION UNDER GAUSSIAN SUPERPOPULATION MODELS

This article considers optimal prediction of the finite population distribution function under Gaussian superpopulation models, which allows auxiliary prior information to be incorporated into the estimation process. Large sample approximations for the variance of the optimal predictors are derived in some special important cases. A small scale Monte Carlo study illustrates comparisons between the optimal predictor and some others which are proposed in the literature. The conclusion is that the optimal predictor can be considerably more efficient in situations where the normal superpopulation model is adequate.     

Testing for ordered failure rates under general progressive censoring

For exponentially distributed failure times under general progressive censoring schemes, testing procedures for ordered failure rates are proposed using the likelihood ratio principle. Constrained maximum likelihood estimators of the failure rates are found. The asymptotic distributions of the test statistics are shown to be mixtures of chi-square distributions. When testing the equality of the failure rates, a simulation study shows that the proposed test with restricted alternative has improved power over the usual chi-square statistic with an unrestricted alternative. The proposed methods are illustrated using data of survival times of patients with squamous carcinoma of the oropharynx.     

双排双波浪带散热水箱传热性能研究

对双排双波浪带散热水箱的结构形式、换热和阻力试验结果进行了分析。采用非线性拟合法得到气侧的换热系数αa，并与桑塔纳管翅式散热水箱的气侧换热系数进行了对比，结果表明，此散热水箱具有较高的换热系数。     

Pooling multivariate data under W, LR and LM tests

Two independent random samples are drawn from two multivariate normal populations with mean vectors μ1 and μ2 and a common variance-covariance matrix Σ. Ahmed and Saleh (1990) considered preliminary test maximum likelihood estimator (PMLTE) for estimating μ1 based on the Hotelling's T _N ², when it is suspected that μ1=μ2. In this paper, the PTMLE based on the Wald (W), Likelihood Ratio (LR) and Lagrangian Multiplier (LM) tests are considered. Using the quadratic risk function, the conditions of superiority of the proposed estimator for departure parameter are derived. A max-min rule for the size of the preliminary test of significance is presented. It is demonstrated that the PTMLE based on W test produces the highest minimum guaranteed efficiencies compared to UMLE among the three test procedures.     

激活优势:家长主义浪潮下家长参与的群体差异

基于对同一城区两个初中班级的跟踪调查，本文考察了中国家长参与的特征以及不同群体在适应上的差异。文章发现，通过资源激活、能力塑造和责任伦理，城区学校在新的教育情势下建构起有关家长参与的话语。家长参与在学校空间的公共事务上发育缓慢，在家庭空间的私人事务上却发展迅猛，不同群体之间差异较大。基于参与意识、参与能力和参与行为的差异，不同群体的家长参与表现为：外来务工群体被唤起教育失败者的经验，采用被动应对的策略；城市普通工薪群体激发出难以胜任的经验，采用模仿依循的策略；中产群体则激活出教育成功者的经验，采用主动建构的策略。由此，家校之间成为阶层运作的重要场域空间。     

DAM—II数字模拟多功能实验箱的研发

通过对DAM—II数字模拟多功能实验箱的研发 ,剖析了现有电子技术基础实验设备装置存在的问题 ,如 :标准化问题、兼容性问题等。阐述了实验装置研发中应重视的开发方法和思路 ,对“二次开发”在电技术中的应用和“标准化”在电子技术实验设备装置设计中的必要性、重要性作了探讨     

SPZ1100/40双线铁路箱梁造桥机的设计

根据双线整孔简支箱梁节段预制拼装的施工要求，对造桥机的结构形式、梁段就位方式、走行方式、支承方式、下托梁和调位落架装置等进行了技术比较，确定了SPZ1100/40造桥机的总体构思。详细介绍了该机的构造和技术特点。实践证明，该机的设计和应用是成功的，为我国铁路简支梁向大跨方向的发展提供了先进的施工技术，具有广阔的应用前景。