Viewing students consistently: how stable are teachers’ expectations?

ABSTRACT

Over the past 50 years, research has shown that teacher expectations can influence student outcomes. Many studies have examined within-year effects. There is, however, a paucity of research that has investigated the stability of teachers’ expectations across a single year, and there are no studies that have examined stability beyond 1 year. The current study examined the stability of 94 teachers’ expectations within 3 separate years and across 3 years in mathematics and reading. In both subject areas, teachers’ expectations remained relatively stable from beginning to end-of-year for each separate year and also across 3 years. Additionally, teachers who under- or overestimated their students by more than half a standard deviation continued to do so across all periods in the study. This was despite the teachers having different students each year. The study suggests that teachers view students’ capabilities similarly despite having different student cohorts.     

非自治扩散的两种群Lotka-volterra模型的持久性

考虑具有扩散的捕食——被捕食系统,得到系统的最终有界性,对应周期系统正周期解的存在性、唯一性以及全局渐近稳定性.     

大坝与坝基稳定性分析研究

大坝与坝基的稳定一直是工程师密切关注的一个安全问题. 论文提出2种分析重力坝和坝基稳定的方法: 一种是基于刚体极限平衡原理的直接分析方法, 它将坝体和岩基作为不变形的刚体, 利用该方法可直接计算出可能滑动面的安全因数; 另一种是基于弹塑性理论的间接分析方法, 它采用非线性有限元方法分析大坝和坝基的应力和变形. 根据收敛和突变准则来确定稳定安全度.结果表明:工程建筑物的破坏不仅仅是由于施加荷载的原因,同时也与组成材料的性质有关.     

基于随机化的排序过程分析

随机化算法的流程和结果受所使用的随机函数的影响，按影响的性质和程度分为“随机不影响算法的执行结果”、“随机影响执行结果的正确性”、“随机影响执行结果的优劣”三种情况，主要表现在算法的时间效率上．用随机函数全部或部分地抵消最坏输入，可使算法的时间效率不完全依赖于输入的好坏，通过对输入的适当控制，使得执行结果相对稳定．     

Geometrical nonlinear stability analyses of cable-truss domes

The nonlinear finite element method is used to analyze the geometrical nonlinear stability of cabletruss domes with different cable distributions. The results indicate that the critical load increases evidently when cables, especially diagonal cables, are distributed in the structure. The critical loads of the structure at different rise-span ratios are also discussed in this paper. It was shown that the effect of the tensional cable is more evident at small rise-span ratio. The buckling of the structure is characterized by a global collapse at small rise-span ratio; that the torsional buckling of the radial truss occurs at big rise-span ratio; and that at proper rise-span ratio, the global collapse and the lateral buckling of the truss occur nearly simultaneously. Project (No. 50278086) supported by the National Natural Science Foundation of China     

比率依赖型捕食扩散模型的一个注记

讨论了在齐次Neumann边界条件下具有比率依赖型捕食反应扩散模型.应用比较原理和建立与正解的上下确界相关的迭代格式,得到了一些改进的结果,即惟一的正常数平衡态是全局渐近稳定的.该结果说明了2种群最终在空间上均匀分布.所提出的方法也适用于其他一些模型.应用于讨论一些反应扩散系统非正常数平衡态的不存在性,该方法相当简单但是十分有效.     

甲苯二异氰酸酯三元聚合反应的研究

为了制备高活性聚氨酯交联固化剂,用2,4二异氰酸基甲苯(TDI)三元聚合反应合成了具有3个活性异氰酸根的六元环结构异氰脲酸酯.用红外光谱、凝胶色谱(GPC)及化学分析法对反应条件进行了优化研究,并对产物进行了表征.利用凝胶色谱法对TDI三聚体及多聚体的形成过程进行过程跟踪,并对TDI三聚体的稳定性进行了研究.结果表明采用Cat-3作催化剂,在(60±2)℃下反应,可制得分子量为530~550,Mw/Mn=1.10,NCO质量分数为(25.0±0.5)%窄分子量分布的TDI三聚体;随着反应时间延长,TDI会进一步多元聚合生成多聚结构;而加入质量分数为0.4%的苯甲酰氯作为稳定剂,可有效抑制多元聚合的发生,所制备的TDI三聚体稳定性可在半年以上.     

常温常湿CO氧化催化剂(Au/Fe2O3)的研究

研究了不同方法制备的催化剂(Au／Fe2O3)在常温常湿条件下对CO的氧化反应的作用及其自身的稳定性。结果表明，加料顺序、焙烧温度、沉淀剂种类、金含量等菌素对催化剂的稳定性均有较大影响，其中以K2CO3或Na2CO3为沉淀剂，金含量3％，焙烧温度250-350℃制得的催化剂具有较好的稳定性和抗水性，于25℃连续加入水蒸气反应430h可保持CO完全转化。X衍射实验结果表明，催化剂的稳定性与单质金及α-Fe2O3的粒径成反比，并与金和铁的化学状态有关。     

关于Dirichlet L-函数加权均值的推广

利用Kloostermann和估计、特征和估计及其解析方法给出了Dirichlet L-函数加权均值分布问题的一个推广,得到一个有趣的加权均值分布的渐近公式.     

Research on disturbance properties of suspensions near the injection area of moving jet

The equation of the suspension-gas non-streamwise complex disturbance velocity ratio near the injection area of moving jet was theoretically derived by using a phase-coupled model and stability theory. Then the ratio curves were obtained by the finite difference method based on the asymptotic method and the Euler conservative difference scheme. Analysis of the curves yielded conclusions on the disturbance properties of suspensions and effects of the natures of the flow-field and the properties of the suspensions on the suspensions ability to track the disturbed gas flow are presented in this paper. Projects supported by the State Education Commussion’s Trans-century Training Program Fund for Talents