Random vibration analysis of switching apparatus based on Monte Carlo method

The performance in vibration environment of switching apparatus containing mechanical contact is an important element when judging the apparatus’s reliability. A piecewise linear two-degrees-of-freedom mathematical model considering contact loss was built in this work, and the vibration performance of the model under random external Gaussian white noise excitation was investigated by using Monte Carlo simulation in Matlab/Simulink. Simulation showed that the spectral content and statistical characters of the contact force coincided strongly with reality. The random vibration character of the contact system was solved using time (numerical) domain simulation in this paper. Conclusions reached here are of great importance for reliability design of switching apparatus.     

Homoharringtonine induces apoptosis of endothelium and down-regulates VEGF expression of K562 cells

Homoharringtonine (HHT) has currently been used successfully in the treatment of acute and chronic myeloid leukemias and has been shown to induce apoptosis of different types of leukemic cells in vitro. Emerging evidence suggests that angiogenesis may play an important role in hematological malignancies, such as leukemia. How ever, whether HHT can relieve leukemia by anti-angiogenesis is still unknown. We investigated the anti-angiogenesis potential of HHT with the human umbilical vein endothelial cell line (ECV304) and leukemic cell line (K562) in vitro. Cellular proliferation was determined by MTT assay and apoptosis was analyzed by flow cytometry. The mRNA expression of vascular endothelial growth factor (VEGF) was assessed by RT-PCR and VEGF protein production was detected by Western blot. Inhibition of cell proliferation and induction of apoptosis by HHT were discovered in ECV304 cells, and appeared in a dose- and time-dependent manner. Also, treatment with HHT caused down-regulation of VEGF mRNA expression in K562 cells in similar dose- and time-dependent manner and inhibition of VEGF protein production in K562 cells in response to the enhancing concentration of HHT. The results demonstrated that HHT could also induce apoptosis in endothelium and down-regulate VEGF expression in K562 cells. In conclusion, we believe HHT has anti-angiogenesis potential and speculate that HHT might exert its anti-leukemia effects via reduction of angiogenesis.     

THE VALIDITY AND RELIABILITY OF ORAL EXAMINATIONS IN ASSESSING COGNITIVE SKILLS IN MEDICINE1

In order to attempt to assess aspects of clinical competence, not adequately assessed by other means, the Center for the Study of Medical Education, University of Illinois College of Medicine together with the American Board of Orthopaedic Surgery developed oral examinations in formats specifically designed to yield information on high level cognitive functioning. The examinations were administered to 784 candidates for certification in January 1968. Reliability of the oral problem-solving component score pooled from four examiners was approximately .50. Assessment of content, construct, and concurrent validity made by questionnaire and factor analytic studies indicated that the oral tests identified factors not measured by multiple-choice tests and, therefore, significantly improved the relationship between supervisory evaluations and test scores.     

Wandel in der Fremdsprachenpolitik der DDR

Ohne Zusammenfassung     

The elusive nature of whole system improvement in education

Whole system improvement—where the vast majority of schools improve—is difficult to achieve. Some jurisdictions use what turns out to be ‘wrong’ policy drivers like testing and evaluation. Rather, success turns out to depend on changing the culture of schools and their relationship to the infrastructure of policies and regulation. I examined the six cases studies in the light of whole system change criteria. Two of the case studies, South Africa and India, represent limited but useful examples in that they focus on basic skills like literacy. A second set of two studies, Escuela Nueva and LCP in Mexico, represent strong examples of how bottom up strategies can spread to significant levels. The final two, Long Beach in the US and Ontario, are strong examples of how deep change can be accomplished by focusing on a few core priorities and then building a culture over a number of years to support and sustain the changes. The paper then draws conclusions about the conditions that will be required for large scale change to occur.     

一种用于宽动态范围上的高精度散射测量的标准方法

The co-effect of transmitted power fluctuation and system nonlinearity produce deviations in scatterometer measurement results . An internal calibration method to deal with this problem is proposed. The method can result in more precise scatterometric measurements in a wide range. The basic principle of the method is combining real-transmitted-power detection with the calibration of system nonlinearity. A practical scheme to implement the method is also presented, which is developed based on a special designed mechanism of a microwave radiometer-scatterometer combined system.     

The rewarding effects of number and surface area of food in rats

Visual cues have an important role in food preference for both rats and humans. Here, we aim to isolate the effects of numerosity, density, and surface area on food preference and running speed in rats, by using a forced-choice maze paradigm. In Experiment 1, rats preferred and ran faster for a group of multiple smaller pellets rather than a single large pellet, corroborating previous research (Capaldi, Miller, & Alptekin Journal of Experimental Psychology: Animal Behavior Processes, 15(1), 75–80, 1989). Further experiments tested the prevailing hypothesis that multiple food pieces are more reinforcing because they occupy a larger surface area. Experiment 2 controlled for numerosity by utilizing a continuous food: mashed potatoes flattened to cover a larger surface area or rounded into a ball. The rats preferred and ran faster for the flattened potatoes, suggesting surface area plays a role in quantity estimations. Finally, in Experiment 3, rats displayed no preference or difference in running speed between a group of scattered and clustered pellets when number of pellets were kept constant. Taken together, these results suggest that density has an important role in food perception—that is, the rewarding effect of higher numerosity or larger surface area is removed when the food does not fill out the entire space. Alternative explanations and implications for human diet are discussed.     

Using Variables in School Mathematics: Do School Mathematics Curricula Provide Support for Teachers?

This study employed content analysis to examine 3 popular middle-grades mathematics curricula in the USA on the support they provide for teachers to implement concepts associated with variables in school mathematics. The results indicate that each of the 3 curricula provides some type of support for teachers, but in a varied amount and quality. More specifically, whereas the University of Chicago School Mathematics Project (UCSMP) curriculum provides support for teachers on several aspects of using variables in school mathematics, the support found in the Connected Mathematics 2 and the Math Connects curricula focused mainly on one conception of variables—namely, the use of variables as quantity that varies in the Connected Mathematics 2 curriculum and the use of variables as specific unknowns in the Math Connects curriculum. Overall, the UCSMP curriculum provides the most support for teachers, followed by the Connected Mathematics 2 curriculum, with the Math Connects curriculum recording the least support for teachers to enact variable concepts. It is worth pointing out that, although the 3 curricula collectively provide guidance for teachers to implement variable ideas within meaningful real-world contexts, the supports identified in the respective curriculum were not sufficient in addressing all of the areas that are essential for teaching the many concepts associated with variables in school mathematics effectively. Recommendations for curriculum developers and for international researchers with interest in the roles of variables in school mathematics are provided.