延期支付条件下考虑坏账影响的三阶段经济订货模型

研究零售商处于强势地位的三级供应链结构中,考虑到顾客坏账率的影响,分析二阶延期支付策略下零售商的最优订货策略。分两种情形讨论了坏账影响下零售商的利息收入与利息支出,建立了相应的决策模型。通过模型的分析求解,得出零售商的最优订货周期和最优订货批量的判定方法,并进一步分析了各参数对零售商最优决策的影响。 最后,通过数值分析对有关结论进行了验证。     

Penalized weighted composite quantile regression in the linear regression model with heavy-tailed autocorrelated errors

In this paper, a penalized weighted composite quantile regression estimation procedure is proposed to estimate unknown regression parameters and autoregression coefficients in the linear regression model with heavy-tailed autoregressive errors. Under some conditions, we show that the proposed estimator possesses the oracle properties. In addition, we introduce an iterative algorithm to achieve the proposed optimization problem, and use a data-driven method to choose the tuning parameters. Simulation studies demonstrate that the proposed new estimation method is robust and works much better than the least squares based method when there are outliers in the dataset or the autoregressive error distribution follows heavy-tailed distributions. Moreover, the proposed estimator works comparably to the least squares based estimator when there are no outliers and the error is normal. Finally, we apply the proposed methodology to analyze the electricity demand dataset.     

近十年国内学者关于学术越轨问题的研究综述

学术越轨囊括了学术失范、学术不端和学术腐败的内容,表现为情节轻重不一的违反学术规范、违背科学精神和科学规律的行为。学术越轨的诱发因素包括学术“马太效应”,学术评价体制不完善,学术行政化,学术道德失律,图书馆、期刊社、出版社的不作为以及越轨行为低成本化等。学术越轨不仅影响学者的学术水平和学术声誉,还会损害高校、科研院所的形象和声誉,影响学术界的发展,阻碍社会前进的步伐。防治学术越轨,不仅要实现学术约束机制化、职业伦理制度化、评价体系完善化、终端系统功能化,还要防范研究生的学术越轨行为。目前,关于学术越轨的相关概念尚未达成共识,对学术越轨的防治方法研究不足,研究深度不够。     

《说文解字诂林》引经类文献略考

《说文解字诂林》引经类文献有21种。文章对这些文献进行目录学梳理,并从考辨字形、训释字义以及形义兼考三个方面对其分类,考察其特点,认为,这些文献反映了清儒对《说文》引经问题以及经学训诂与小学训诂差异的认识,其研究方法与结论对后世研究《说文》引经问题很有启发。     

Some properties of generalized ridge estimators

Exact expressions, in the form of infinite series expansions, are given for the first and second moments of two well known generalized ridge estimators. These series expansions are then evaluated using recursive formulas and computations are verified using approximations. Results are presented for the relative mean square error and bias of these estimators as well as their relative efficiency with respect to least squares.     

Ordinary least squares estimation of the functional errors-in-variables model with trended data:some monte carlo evidence

This note summarizes some Monte Carlo experiments that were designed to investigate the finite sample relevance of the asymptotic normality and efficiency of OLS in the errors-in-variables model with trended data. The experiments show that the normal approximation is not very satisfactory for sample size up to T=400, but that OLS is quite efficient relative to competing estimators when there is a trend in the exogenous variables of the model.     

On the Ratio of Two Folded Normal Distributions

A class of distributions associated with the ratio of two folded normal random variables is introduced which strictly includes the half standard Cauchy distribution. The properties of this class of distributions are studied, along with a graph of the possible shapes of its density functions. The salient features of this class are mathematical tractability and statistical applicability. Utility of the class of distributions is demonstrated by presenting four applications.     

Block–Savits Characterization and Star Ordering of Exponential Mixtures

Block and Savits (1980 Block , H. W. , Savits , T. H. ( 1980 ). Laplace transforms for classes of life distributions . Ann. Probab. 8 : 465 – 474 .[Crossref], [Web of Science ®] , [Google Scholar]) established a characterization of life distributions using the Laplace transform. In this article, we remark that one of the necessary conditions to be IFRA distribution is equivalent to the star ordering of exponential mixtures. It leads to the definition of two new classes of life distributions, called LIFR and LIFRA, and their dual classes: LDFR and LDFRA. It occurs that these classes have many useful aging properties and preserve known reliability operations. Properties of the classes are studied and relations with known classes are established.     

Some Asymptotic Properties of Ridge Regression in a System of Seemingly Unrelated Regression Equations

A discussion is made of asymptotic properties of an Operational Ordinary Ridge Regression estimator and comparison is made with the Operational Generalized Least Squares estimator. Also, some simulation experiments are carried showing efficiency gains can be made through the use of de Ridge estimator.     

Edgeworth and Moment Approximations: The Case of MM and QML Estimators for the MA(1) Models

Extending the results in Sargan (1976 Sargan , J. D. ( 1976 ). Econometric estimators and the Edgeworth approximation . Econometrica 44 : 421 – 448 .[Crossref], [Web of Science ®] , [Google Scholar]) and Tanaka (1984 Tanaka , K. ( 1984 ). An asymptotic expansion associated with the maximum likelihood estimators in ARMA models . J. Roy. Statist. Soc. B 46 : 58 – 67 . [Google Scholar]), we derive the asymptotic expansions of the distribution, the bias and the mean squared error of the MM and QML estimators of the first-order autocorrelation and the MA parameter for the MA(1) model. It turns out that the asymptotic properties of the estimators depend on whether the mean of the process is known or estimated. A comparison of the moment expansions, either in terms of bias or MSE, reveals that there is not uniform superiority of neither of the estimators, when the mean of the process is estimated. This is also confirmed by simulations. In the zero-mean case, and on theoretical grounds, the QMLEs are superior to the MM ones in both bias and MSE terms. We also discuss how the approximations are affected by moderate deviations from the unit root case. The results presented here are important for bias correction and increasing the efficiency of the estimators.