Some concepts of mult1variate dependence

Several types of positive dependence are shown to be equiv-alent to the concept of a distribution with a density which is TP₂ in pairs. Among these is the concept of m^?-positive depend-ence of Alam and Wallenius. Using this result, all relationships among many of the most important concepts of positive dependence are determined. Furthermore, an application of the equivalences of these types of positive dependence yields a results of Ahmed, Langberg, Leon and Proschan.     

Dependence function for continuous bivariate densities

The notion of cross-product ratio for discrete two-way contingency table is extended to the case of continuous bivariate densities. This results in the “local dependence function” that measues the margin-free dependence between bivariate random variables. Properties and examples of the dependence function are discussed. The bivariate normal density plays a special role since it has constant dependence. Continuous bivariate densities can be constructed by specifying the dependence function along with two marginals in analogy to the construction of two-way contingency tables given marginals and patterns of interaction. The dependence function provides a partial ordering on bivariate dependence.     

Strong laws of large numbers for dependent heterogeneous processes: a synthesis of recent and new results

This paper surveys recent developments in the strong law of large numbers for dependent heterogeneous processes. We prove a generalised version of a recent strong law for Lz-mixingales, and also a new strong law for Lpmixingales. These results greatly relax the dependence and heterogeneity conditions relative to those currently cited, and introduce explicit trade-offs between dependence and heterogeneity. The results are applied to proving strong laws for near-epoch dependent functions of mixing processes. We contrast several methods for obtaining these results, including mapping directly to the mixingale properties, and applying a truncation argument.     

Small-Sample Methods for Cluster-Robust Variance Estimation and Hypothesis Testing in Fixed Effects Models

ABSTRACT

In panel data models and other regressions with unobserved effects, fixed effects estimation is often paired with cluster-robust variance estimation (CRVE) to account for heteroscedasticity and un-modeled dependence among the errors. Although asymptotically consistent, CRVE can be biased downward when the number of clusters is small, leading to hypothesis tests with rejection rates that are too high. More accurate tests can be constructed using bias-reduced linearization (BRL), which corrects the CRVE based on a working model, in conjunction with a Satterthwaite approximation for t-tests. We propose a generalization of BRL that can be applied in models with arbitrary sets of fixed effects, where the original BRL method is undefined, and describe how to apply the method when the regression is estimated after absorbing the fixed effects. We also propose a small-sample test for multiple-parameter hypotheses, which generalizes the Satterthwaite approximation for t-tests. In simulations covering a wide range of scenarios, we find that the conventional cluster-robust Wald test can severely over-reject while the proposed small-sample test maintains Type I error close to nominal levels. The proposed methods are implemented in an R package called clubSandwich. This article has online supplementary materials.     

Two-dimensional generalisations of dynamic programming for image analysis

Dynamic programming (DP) is a fast, elegant method for solving many one-dimensional optimisation problems but, unfortunately, most problems in image analysis, such as restoration and warping, are two-dimensional. We consider three generalisations of DP. The first is iterated dynamic programming (IDP), where DP is used to recursively solve each of a sequence of one-dimensional problems in turn, to find a local optimum. A second algorithm is an empirical, stochastic optimiser, which is implemented by adding progressively less noise to IDP. The final approach replaces DP by a more computationally intensive Forward-Backward Gibbs Sampler, and uses a simulated annealing cooling schedule. Results are compared with existing pixel-by-pixel methods of iterated conditional modes (ICM) and simulated annealing in two applications: to restore a synthetic aperture radar (SAR) image, and to warp a pulsed-field electrophoresis gel into alignment with a reference image. We find that IDP and its stochastic variant outperform the remaining algorithms.     

多氢酸酸化技术及其应用

砂岩储层酸化的常规土酸体系存在与矿物反应速度快、酸化液的有效距离短和容易产生二次沉淀等问题。现存的缓速酸酸液体系不能克服粘土和石英界面反应速率的巨大反差,新的深度酸化工艺可以在一定程度上增加酸液的穿透距离,但工艺繁琐,且仍然不能解决沉淀、堵塞问题。多氢酸体系与现存的HF酸体系相比,其反应速度慢,溶解能力强,且具有良好的防垢性能和分散性能,可以抑制井眼附近的地层伤害,有效控制二次沉淀等优点。本研究对多氢酸的酸度特性、溶蚀性能、润湿性、静态腐蚀性以及多氢酸的分散和防垢性能进行了室内测试,并对土酸、氟硼酸及多氢酸进行了酸化效果实验评价。室内实验及现场应用表明,多氢酸性能优越,可明显提高酸化效果。     

论跨国公司子公司衍生过程中的知识依赖

跨国公司在国外建立子公司是一种强有力的公司进入方式。母公司的知识存量,特别是有关技术和市场的隐性知识对新建子公司知识能力和生存发展有着深刻影响,子公司在其产生和成长过程中对母公司存在知识依赖。中国的跨国公司发展进程相对滞后,从知识管理的角度研究跨国公司子公司衍生发展的对策是一种有益的探索。     

新课改背景下数学师范生专业技能培养的探究

介绍新课改对数学教师的新要求,设想数学师范生专业技能的结构,并对数学师范生专业技能的培养原则及其措施进行了探究.     

抗战时期四联总处与战时盐业运输简

“七七事变”后,沿海各产盐区先后沦于敌手,大批存盐滞留盐场。为避免存盐资敌,满足战时军需民食对食盐的需求,国民政府根据当时“商疲力竭”的盐业运输实际现状,及时调整盐务运输政策,实行官商并运。抗战初期成立的国民政府最高经济与金融机构四联总处,根据战时盐业运输政策调整的实际需要,大力实施战时盐务贷款政策,利用国家各大银行的金融力量大力开展贴现与放款业务,尽力向国家所属盐运机关、盐商提供贷款。从资金方面确保战时盐业运输的顺利进行,为将沿海大批食盐抢运到内地创造了条件。伴随着战时盐业“官运”规模的扩大,四联总处提高对战时盐业运输的认识,将盐务贷款上升到关系抗战胜利的高度,对于国家所属盐务机关及各地盐运商的盐业运输贷款需求,尽量给予协助办理。历史证明,四联总处所实施的战时盐务贷款,在促进战时盐业运输,满足大后方军民食盐需求等方面起了重要作用,有助于战时食盐的抢运与运销。从而支持了抗战的胜利。