Strict Positive Definiteness of a Product of Covariance Functions

Positive definiteness represents an admissibility condition for a function to be a covariance. Nevertheless, the more restricted condition of strict positive definiteness has received attention in literature, especially in spatial statistics, since it ensures that the kriging system has a unique solution. Most known covariance functions are isotropic but there are applications where isotropy is not appropriate, e.g., space-time covariance functions. One way to construct non-isotropic covariance functions is to use a product or a product-sum. In this article, it is given a necessary as well as a sufficient condition for a product of two covariance functions to be strictly positive definite. This result is extended to the well-known product-sum covariance model.     

A monte carlo comparison of regression trimmed means

Two proposals are made for constructing adaptive estimators of the parameters in a linear regression model. These estimators are based on regression trimmed means and use an idea of Jaeckel [(1971) Ann Math Statist 42, 1540-1552] and the bootstrap respectively. These adaptive trimmed means as well as some nonadaptive trimmed means are studied by Monte Carlo. A one-step biweight is also included for comparison purposes.     

A new nonparametric estimator for the mean of the selected population

A modified bootstrap estimator of the mean of the population selected from two populations is proposed which is a convex combination of the two sample means, where the weights are random quantities. The estimator is shown to be strongly consistent. The small sample behavior of the estimator is investigated and compared with some competitors by means of Monte Carlo studies. It is found that the newly proposed estimator has smaller mean squared error for a wide range of parameter values.     

地方政府融资平台现状及发展策略——基于四川省某融资平台公司调查分析

针对目前传统的机车信号测试环线安装在钢轨内侧腰部存在一定的磁屏蔽、安装相对不是很容易、施工钢轨穿孔困难等缺点,结合具体施工等实际因素,设计并实现了一种成本较为低廉、安装方便、削弱构成磁屏蔽的一种机车信号测试环线支架法。该方法采用自主设计,特定加工的环线支架固定在钢轨上,环线通过支架安装在钢轨外侧,高度基本与钢轨高度水平。实践证明,这种环线支架法较之前传统的安装方式使用效果良好、信号检测稳定,设计经过实践检验基本合理,能满足机车信号的正常检测,在一定程度上优化了设计,方便了施工,达到了预期目标。     

黄土泥岩接触面滑坡工程防护的数值模拟

以晋陕蒙接壤区黄土泥岩接触地带滑坡为工程研究背景,分析研究黄土泥岩接触面滑坡的工程防护。通过室内试验确定了黄土的基本物理力学参数。利用FLAC2D数值软件,对地区常见的挡墙和锚索工程防护措施,针对坡脚为15°和25°的滑坡模型进行了工程防护的数值模拟,对比其防护效果,并给出工程建议。     

勘探“人民文学”的“现代人学内涵”

以工农兵为本位的“人民文学”形态是在历史曲折中形成的 ,创作主体与对象主体的角色意识经过错位与置换 ,导致“人民文学”的现代人学内涵的失落或潜隐 ,有必要重新勘探与阐释     

The effect of context variables on cognitive effort in multiattribute binary choice

This article reports an empirical investigation of the cognitive effort required to decide in multiattribute binary choice using a variation of the Additive Difference strategy. In contrast with other studies, this paper focuses on the effect of various context variables (rather than task variables) on cognitive effort. In order to select the context variables to be manipulated, we used the model proposed by Shugan (1980; J. Consumer Res. 75 (1980) 99). Our results indicate that there is a positive relationship between the cognitive effort required to decide and the mean of the differences between the dimensions of the choice alternatives. We have also found an inverse relationship between cognitive effort and the variance of the differences between the dimensions of the choice alternatives. Finally, we have found that in negative correlation contexts the effort needed to decide is greater than in positive and null correlation contexts.     

Early Adolescents' Perceptions of Mothers' and Fathers' Parenting Styles and Problem Behavior

We investigated early adolescents' perceptions of parenting styles in mother–father–adolescent triads along with child self-reported problem behaviors (substance abuse and delinquency). We also examined the various combinations of mothers' and fathers' parenting styles by child gender in relation to problem behavior. Participants included 3,353 children (aged 12 to 14) from the National Longitudinal Survey of Youth—97. Results from our structural equation model indicated that mothers and fathers may use different parenting strategies and that permissive parenting may not be as detrimental as previously assumed. In addition, youth perceptions of each parent were equally important in explaining problem behavior among both daughters and sons, but the perception of an authoritarian mother showed stronger adverse effects on sons, even after controlling for poverty and peer influence.