二种群系统线性变动且趋于平衡点的一个充分条件

对于二种群生物系统方程x′=x (1 -x-αy) ,y′=y (1 - βx - y)我们给出了二种群共同线性增长或减少 ,最终达到平衡点的一个充分条件     

Unstable and multiple child care arrangements and young children's behavior

Growing evidence suggests that child care instability is associated with child behavior problems, but existing studies confound different types of instability; use small, convenience samples; and/or control insufficiently for selection into child care arrangements. This study uses survey and calendar data from the Fragile Families and Child Well-Being Study to estimate the associations between three different types of child care instability—long-term instability, multiplicity, and the use of back-up arrangements—and children's internalizing, externalizing, and prosocial behaviors at age 3, controlling for a large number of child and family background characteristics. Long-term instability between birth and age 3, as measured in both the survey and calendar data, is associated with higher levels of externalizing behavior problems. Current multiplicity at age 3 (as measured by survey data) is associated with higher levels of both externalizing and internalizing behavior problems, but stable multiplicity over time (as measured using calendar data) is not. Finally, the use of back-up arrangements at age 3 is associated with higher levels of internalizing behaviors. We find no consistent differences in these results by the timing of instability, child gender, family income, or type of care.     

Research issues in evaluating learning pattern development in higher education

This article concludes the special issue of Studies in Educational Evaluation concerned with “Evaluating learning pattern development in higher education” by discussing research issues that have emerged from the previous contributions. The article considers in turn: stability versus variability in learning patterns; old versus new analytic techniques; handling missing observations; measures of effect size; predispositions versus processes; and why it should be so hard to improve the quality of student learning in higher education.     

Stability of total and free prostate specific antigen in serum submitted to intermittent cold storage conditions

The goal of this study was to determine the stability of Total Prostrate Specific antigen (PSA-T) and Free Prostrate Specific Antigen (PSA-F) in archival serum stored at 4°C and −20°C and subjected to temperature shift due to interruption in power supply. Our study showed that PSA-T was stable up to 285 days and PSA-F was stable for 158 days under these conditions. Since power supply interruption is an unavoidable problem in developing nations, our study has implication on the validity of measurement of PSA-T and PSA-F in serum that was not properly stored due to emergency situations and for certain types of retrospective studies.     

基于分形理论的土地利用空间行为特征——以江西东江源流域为例

为增进对土地利用空间行为变化的理解,以分形理论为指导,在RS和GIS技术支持下,建立了东江源流域土地利用空间数据库,运用分形模型和提取数据对江西东江源流域土地利用空间格局的变化进行了研究。获得了1985年和2000年两个时期各个土地利用类型的分形维数和不稳定性指数,并且参照了常用的景观指数,包括斑块密度指数、景观斑块形状破碎化指数和景观类型分离度指数,对土地利用空间行为变化进行了定量分析,研究结果显示,景观斑块破碎度指数由0. 945变为0. 936,呈下降趋势;其他林地和有林地等土地利用类型的稳定性呈上升趋势,而高覆盖度草地、水域、灌木林地、旱地、水田等土地利用类型的稳定性明显降低,说明近期应当对它们进行适当保护;对其他林地和有林地而言,分形维数降低的程度,一方面说明了土地斑块形态规整化改善的程度,另一方面也说明了人们改善土地形态的行为强度,如植树造林、退耕还林。     

Locating the equilibrium points of a predator–prey model by means of affine state feedback

A predator–prey model with prey-dependent functional response is considered. The set of all points in the positive quadrant of the state plane that can be made equilibrium points by means of an affine state-feedback control law is determined, and the values of the control parameters ensuring the desired equilibria are provided. It is shown how the asymptotic stability of the equilibrium points depends on simple geometric conditions. The problem of stabilizing unstable equilibrium points is also briefly discussed.     

萝卜红色素及其稳定性研究

对萝卜红色素的提取方法和基本性质进行研究。实验表明该色素的热稳定性较好 ,具有一定的抗氧化、还原性。淀粉和NaCl是使萝卜红色素增色的介质 ,蔗糖是其减色介质。该色素是一种很有开发价值的色素资源     

河南省某尾矿坝稳定性分析与计算

为了尾矿库安全生产,对尾矿坝稳定性影响因素进行分析,针对具体的工程实例依据相关规范结合勘察资料,采用Fellenius、Bishop等稳定性计算方法对某尾矿坝抗滑稳定性分析,得出了在正常水位、洪水水位和特殊水位条件下该坝的稳定性计算结果。     

少年射击运动员肌肉工作稳定性的表象训练效果研究

本文总结了肌肉工作稳定性的表象训练的实验结果,结果表明:实验室工作与实践应用有高度的一致性,实验包括了肌肉静力性工作和动力性工作稳定性实验,并在此基础上,以体校射击运动员为对象进行了实践验证,验证说明了表象训练可有效提高肌肉工作的稳定性,这对提高射击成绩有一定的现实意义。结果还提示,缺少心理训练基础的运动员,至少要持续3周以上的表象训练才能获得较理想的效果。     

Ranking dynamics and volatility

Scientific journals are ordered by their impact factor while countries, institutions or researchers can be ranked by their scientific production, impact or by other simple or composite indicators as in the case of university rankings. In this paper, the theoretical framework proposed in Criado, R., Garcia, E., Pedroche, F. & Romance, M. (2013). A new method for comparing rankings through complex networks: Model and analysis of competitiveness of major European soccer leagues. Chaos, 23, 043114 for football competitions is used as a starting point to define a general index describing the dynamics or its opposite, stability, of rankings. Some characteristics to study rankings, ranking dynamics measures and axioms for such indices are presented. Furthermore, the notion of volatility of elements in rankings is introduced. Our study includes rankings with ties, entrants and leavers. Finally, some worked out examples are shown.