粘弹性流体旋转流实验研究

利用粒子图像测速仪(PIV)对圆筒形容器内有自由表面变形的粘弹性流体旋转流动进行了实验研究.旋转流动由等速旋转的容器底面来驱动.实验工质为CTAC(十六烷基三甲基氯化铵界面活性剂)水溶液.测量了水、40×10-6、60×10-6和200×10-6CTAC水溶液在弗鲁德数为2.59至16.3范围内的旋转流动.PIV用来测量子午面内的二次流场,并从PIV图像中抽取自由面高度.结果表明在相似的弗鲁德数下,相比于水流CTAC水溶液旋转流动自由表面中心处的凹陷深度降低,随着溶液浓度或粘弹性升高,子午面内右上角的惯性涡被压缩且强度变得越来越弱.通过与水流动比较并做力平衡分析,定量估算了CTAC水溶液的第一正应力差或弱粘弹性.     

Validity of the Space-Time Enlargement Law for vacuum breakdown

This paper investigates, theoretically and experimentally, the applicability of the Space-Time Enlargement Law to vacuum-insulated systems. A discussion on how characteristics of possible vacuum breakdown mechanisms determine the distribution function of the breakdown voltage random variable is presented. By superimposing effects of electrode surface enlargement and inter-electrode gap enlargement, expressions for the mean value and standard deviation of the breakdown voltage random variable are obtained. In the case of time extensions, the assumption of complete independence of consecutive discharge processes is discussed. Experimental testing of the Enlargement Law was performed on Rogowski type two-electrode systems, with different electrode surface areas, inter-electrode gaps and vacuum pressures. Measurements were conducted using industrial ac voltage, dc voltage with 50 V/s rate of rise, standard atmospheric pulse voltage (1,2/50 μs), and commutational pulse voltage (250/2500 μs). The final conclusion, based on the comparison of theoretical considerations and the experimental results, is that the Space-Time Enlargement Law can be applied in the design phase during the development of vacuum devices, with certain limitations, regardless of the type of the applied voltage.     

The impact of social comparison information on motivation in patients with diabetes as a function of regulatory focus and self-efficacy.

Objective: Our aim was to determine whether the impact of upward and downward social comparison information on individuals' motivation to manage their diabetes is dependent on their regulatory focus (promotion or prevention focus) and self-efficacy. Design: The hypotheses were examined in a cross-sectional study. Patients with diabetes (N = 234) read a fictitious interview with a fellow patient, either an upward or a downward target, and they filled out questionnaires. Main Outcome Measures: Motivation to work on diabetes regulation. Results: High promotion-focused patients reported more motivation than low promotion-focused patients when confronted with the upward target (positive role model). High prevention-focused patients reported more motivation than low prevention-focused patients when confronted with the downward target (negative role model). This latter finding was qualified by patients' self-efficacy, as it applied only to patients with relatively high levels of self-efficacy. Conclusion: The current study highlights the importance of considering individual differences when using role models to encourage self-care activities in persons with diabetes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impact of social comparisons on the developing self-perceptions of learning disabled students.

Learning disabled (LD) children's self-perceptions were investigated using the Perceived Competence Scale for Children. This self-report instrument taps children's perceptions of their scholastic and athletic competence, social acceptance, and feelings of global self-worth. Participants in the study were 86 students in Grades 3–8 who attended a public school LD resource room. Results indicated that social comparison processes play an important role in the formation of LD students' perceived academic competence. LD students perceived themselves as becoming less academically competent across the grade span tested when they compared themselves with normally achieving students in their regular classes. When they compared their abilities with LD peers in their resource room, they maintained high perceptions of their own academic competence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Why do lower educated people continue smoking? Explanations from the longitudinal GLOBE study.

This article describes the effect of educational level on the decision to continue smoking among 1,354 initially smoking participants (age≥20 years) in the Dutch GLOBE study. The effect of education continued smoking was explained from baseline information (1991) on smoking characteristics, individual characteristics, and environmental factors. Smoking status was reassessed after 6.5 years. Lower educated smokers more often continued smoking (odds ratio 2.09). Poor perceived health and earlier smoking initiation in lower educated groups were main predictors of educational differences in smoking maintenance. Educational differences in chronic illness, perceived control, neuroticism, and emotional support also contributed to the explanation of educational differences in continued smoking. These results have important implications for intervention programs and policy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of internal stress and extensibility on the exterior durability of wood coatings

Different types of coatings were characterised for: swelling by moisture, moisture permeability, elastic modulus and extensibility. These data were used to calculate maximum internal stress. Internal stress was also measured directly whilst changing temperature and humidity. The stress data were compared to cracking and flaking results in both natural and accelerated weathering tests. Results showed that high levels of stress occur if there is a difference in swelling between coating and wood. In most cases stress relaxation took place rapidly. Comparing maximum stress, extensibility and cracking, a good correlation between these data was found. The ratio between maximum stress and extensibility appeared to be a very good predictor for crack formation.     

An Initial Experimental Assessment of the Dynamic Modelling in UML

The goal of this empirical study is to compare the semantic comprehension of three different notations for representing the dynamic behaviour in unified modelling language (UML): (a) sequence diagrams, (b) collaboration diagrams, and (c) state diagrams. Eighteen students of Informatics analysed the three types of diagrams within three different application domains. We performed a 3 × 3 factorial experimental design with repeated measures. The metrics collected were total time and total score. The main conclusion of this study is that the comprehension of the dynamic modelling in object-oriented designs depends on the diagram type and on the complexity of the document. The software project design written in the UML notation is more comprehensible, when the dynamic behaviour is modelled in a sequence diagram. While if it is implemented using a collaboration diagram, the design turns out to be less comprehensible as the application domain, and consequently, the document is more complex.     

Design-Operation of Multi-Hydropower Reservoirs: HBMO Approach

To illustrate and test the applicability and performance of the innovative honey-bee mating optimization (HBMO) algorithm in highly non-convex hydropower system design and operation, two problems are considered: single reservoir and multi-reservoir. Both hydropower problems are formulated to minimize the total present net cost of the system, while achieving the maximum possible ratio for generated power to installed capacity. The single hydropower reservoir problem is approached by the developed algorithm in 10 different runs. The first feasible solution was generated initially and later improved significantly and solutions converged to a near optimal solution very rapidly. In the application of the proposed algorithm to a five-reservoir hydropower system with 48 periods and a total of 230 decision variables, in early mating flights, the first feasible solution was identified and the results converged to a near optimal solution in later mating flights. In the case of the multi-reservoir problem, an efficient gradient-based nonlinear-programming solver (LINGO 8.0) failed to find a feasible solution and for the single hydropower reservoir design problem it performed much worse than the proposed algorithm.     

A Comparison Between Foundations of Metrology and Software Measurement

In this paper, we discuss basic issues related to measurements performed in the domains of software engineering and metrology. Similarities and differences are highlighted, with the aim of analyzing the level of knowledge in both domains. A theoretical approach is followed, allowing the proposal of a measurement process model, which is used as a guiding scheme throughout the paper to illustrate peculiarities arising when taking software measurements. Common ground between metrologists and software engineers are described by discussing foundations of measurement in the software context.     

Feminism and its discontents: A century of struggle with psychoanalysis: Book review.

Review of book: Feminism and Its Discontents: A Century of Struggle with Psychoanalysis. Cambridge, MA: Harvard University Press, 1998, 448 pp. Reviewed by Elaine Hoffman Baruch. (PsycINFO Database Record (c) 2010 APA, all rights reserved)