Variations in Child Care by Grandparents During the First Three Years

Routine child care by grandparents was examined for 1,229 children who were participants in the National Institute of Child Health and Human Development (NICHD) Study of Early Child Care. Four groups were identified: extended full‐time care, extended part‐time care, sporadic care, and no routine care during the first three years. The odds of sporadic child care by grandparents were higher when mothers were relatively young and worked nonstandard hours. The odds of extended full‐time grandparent care versus extended part‐time grandparent care were higher for mothers of color and mothers with more extensive full‐time employment. All types of grandparent care were more likely when a grandparent lived in the household. These findings suggest that grandparent care is heterogeneous and may occur in response to different family circumstances.     

笙馨同音 宗旨如一──略论《文心雕龙》对《文选》的影响

《文心雕龙》书名是刘勰文学观点的集中体现，它强调的是精妙的艺术构思与精美的文学语言的有机结合；而《文选》的选文标准“事出于沉思，义归乎翰藻”，则是萧统文学观点的典型反映。其“沉思”之想与“文心”之思，“翰藻”之文与“雕龙”之采，名异而实同，都体现了他们注重内容与形式相结合的文学观点。《文心》所论文体３４种，《文选》３９种，两书基本相同的文体选目近２０种。其渊源有自，一目了然。     

关于本科生所做毕业设计的思考

提出了理工科院校本科生所做毕业设计的重要性 ,从师生互动、课题选择、经费支持等方面分析了造成本科生毕业设计质量差的主要原因 ,并提出了相应的解决方案。     

苏颂与"三舍人议案"评析

宋代熙宁"三舍人议案"是一个震动朝野、风闻天下,影响至今的重大历史事件.苏颂坚持法制,违抗皇命的大无畏精神值得称赞;"三舍人议案"中关于选才用人的争论有许多经验应该总结,其对现在的干部提拔任用将有所裨益;<宋史>说苏颂"明哲保身","务循故事"也值得商榷.     

Computational Comparison Studies of Quadratic Assignment Like Formulations for the In Silico Sequence Selection Problem in De Novo Protein Design

In this paper an O(n²) mathematical formulation for in silico sequence selection in de novo protein design proposed by Klepeis et al. (2003, 2004), in which the number of additional variables and linear constraints scales with the square of the number of binary variables, is compared to three O(n) formulations. It is found that the O(n²) formulation is superior to the O(n) formulations on most sequence search spaces. The superiority of the O(n²) formulation is due to the reformulation linearization techniques (RLTs), since the O(n²) formulation without RLTs is found to be computationally less efficient than the O(n) formulations. In addition, new algorithmic enhancing components of RLTs with inequality constraints, triangle inequalities, and Dead-End Elimination (DEE) type preprocessing are added to the O(n²) formulation. The current best O(n²) formulation, which is the original formulation from Klepeis et al. (2003, 2004) plus DEE type preprocessing, is proposed for in silico sequence search. For a test problem with a search space of 3.4×10⁴⁵ sequences, this new improved model is able to reduce the required CPU time by 67%.     

自然主义:现实主义到现代主义的中介

本文首先论述了自然主义文学理论产生的原由及自然主义理论比之以往文学的创新之处。其次,阐明自然主义文学以实证的手法、客观的态度,从生物学的角度写人的兽性,打破了以往的写作“禁区”,把不登大雅之堂的东西展现给读者,为现代主义作家描写“异化”现象作了铺垫。再次,自然主义客观真实的环境描写,表现了囿于各种环境中人的生物状态,及与浪漫主义、现实主义的环境描写实质上的不同,以及对现代主义的影响。     

论话语意图的选择、调控与整合功能--话语意图连贯功能之四

语篇的连贯有三个层次--语法(形式)、语义、语用.只有在第二和第三层次上连贯的语篇才是真正连贯的语篇.而位于第三层次的话语意图起核心的作用.没有它的选择、调控与整合功能,话语就无从建立"相关".     

Portfolio optimization: New capabilities and future methods

Summary  This paper addresses the problem of portfolio selection in finance. In many cases, currently available software to compute the efficient frontier runs into difficulty in problems with more than about 600 securities. To proceed beyond this size, it is often necessary to modify the problem in which case there is typically a loss of information. In this paper, we discuss a computer capability that can exactly compute mean-variance efficient frontiers of problems with up to 2,000 securities in very reasonable time (even if a problem’s covariance matrix is 100% dense). The paper also discusses an augmentation to the theory of portfolio selection that allows multiple objectives (such as dividends, liquidity, social responsibility, amount invested in R&D, and so forth) to be incorporated into the portfolio selection process. In such problems, the efficient set is no longer a “frontier,” but is now best described as a “surface” with the interesting property that it is composed of platelets (like on the back of a turtle). Moreover, the computer capability that can compute the exact efficient frontier of a mean-variance problem with up to 2,000 securities also has, after additional coding, the ability to compute exactly all platelets of the efficient surface of a tri-criterion portfolio problem with up to 400 securities.

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Zusammenfassung  In dieser Arbeit stellen wir einen leistungsf?higen Rechenalgorithmus vor, um den effizienten Rand (die nichtdominierten Alternativen) von Portfolio-Auswahlproblemen in der Finanzierung zu bestimmen. Wir bezeichnen den Berechnungsalgorithmus, der in Java programmiert ist, mit MPQ (multi-parametric quadratic programming). MPQ weist gegenüber bisherigen Berechnungsverfahren eine Reihe von Vorteilen auf: Es kann für umfangreiche Anwendungsf?lle genutzt werden, ist durch passable Rechenzeiten charakterisiert und kann die Menge effizienter Alternativen in einem Bruchteil bisher üblicher Rechenzeiten bestimmen.

     

摩擦市场中允许卖空的最优投资组合选择

资本市场的一个重要特征就是存在不确定因素,为了衡量其导致的风险,本文提出基于绝对偏差的新型函数,在一个存在摩擦的资本市场中构造均值-绝对离差(mean-absolute deviation,MAD)投资组合选择模型.该模型结构特殊性使其转化为线性规划问题,从而可利用单纯型法求解.实证分析比较了不同风险函数下投资组合的有效前沿,并验证了该方法的有效性.     

广义相对论的超维观念和降维方法

广义相对论运用降维方法研究空间弯曲导致的超维空间。球状有限无界闭合空间的提出实际上赋予超维物理意义。球状空间不同的对称性导致对空间第 4维的不同理解 :镜像对称使“无界”变为“镜界” ,“穿越赤道”变为“自我碰撞” ;中心对称使第 4维成为与原有 3维一样实在的空间维。弯曲状况不同的空间并存可以明显表现超 3维空间。近似开放空间的不均匀收缩导致局部闭合为“空洞” ,可作为显示超维的模型。宇宙可能包含无数并存的空间 ;具体时空的有限性 ,不能作为否认宇宙时空无限性的依据