An Improved Sideband Current Harmonic Model of Interior PMSM Drive by Considering Magnetic Saturation and Cross-Coupling Effects

The sideband current harmonics, as parasitic characteristics in permanent-magnet synchronous machine (PMSM) drives with space vector pulsewidth modulation technique, will increase the corresponding electromagnetic loss, torque ripple, vibration, and acoustic noises. Therefore, fast yet accurate evaluation of the resultant sideband current harmonic components is of particular importance during the design stage of the drive system. However, the inevitable magnetic saturation and cross-coupling effects in interior PMSM drives would have a significant impact on the current components, while the existing analytical sideband current harmonic model neglects those effects. This paper introduces a significant improvement on the analytical model by taking into account these effects with corresponding nonlinear factors. Experimental results are carried out to underpin the accuracy improvements of the predictions from the proposed model over the existing analytical one. The proposed model can offer a very detailed and insightful revelation of impacts of the magnetic saturation and cross-coupling effects on the corresponding sideband current harmonics

Two stage sorption type cryogenic refrigerator including heat regeneration system

A lower stage chemisorption refrigeration system physically and functionally coupled to an upper stage physical adsorption refrigeration system is disclosed. Waste heat generated by the lower stage cycle is regenerated to fuel the upper stage cycle thereby greatly improving the energy efficiency of a two-stage sorption refrigerator. The two stages are joined by disposing a first pressurization chamber providing a high pressure flow of a first refrigerant for the lower stage refrigeration cycle within a second pressurization chamber providing a high pressure flow of a second refrigerant for the upper stage refrigeration cycle. The first pressurization chamber is separated from the second pressurization chamber by a gas-gap thermal switch which at times is filled with a thermoconductive fluid to allow conduction of heat from the first pressurization chamber to the second pressurization chamber

Cost-Sensitive Decision Tree with Multiple Resource Constraints

Resource constraints are commonly found in classification tasks. For example, there could be a budget limit on implementation and a deadline for finishing the classification task. Applying the top-down approach for tree induction in this situation may have significant drawbacks. In particular, it is difficult, especially in an early stage of tree induction, to assess an attribute’s contribution to improving the total implementation cost and its impact on attribute selection in later stages because of the deadline constraint. To address this problem, we propose an innovative algorithm, namely, the Cost-Sensitive Associative Tree (CAT) algorithm. Essentially, the algorithm first extracts and retains association classification rules from the training data which satisfy resource constraints, and then uses the rules to construct the final decision tree. The approach has advantages over the traditional top-down approach, first because only feasible classification rules are considered in the tree induction and, second, because their costs and resource use are known. In contrast, in the top-down approach, the information is not available for selecting splitting attributes. The experiment results show that the CAT algorithm significantly outperforms the top-down approach and adapts very well to available resources.Cost-sensitive learning, mining methods and algorithms, decision trees

Exploring scientific creativity of eleventh grade students in Taiwan

textAlthough most researchers focus on scientists’ creativity, students’ scientific creativity should be considered, especially for high school and college students. It is generally assumed that most professional creators in science emerge from amateur creators. Therefore, the purpose of this study is to investigate the relationship between students’ scientific creativity and selected variables including creativity, problem finding, formulating hypotheses, science achievement, the nature of science, and attitudes toward science for finding significant predictors of eleventh grade students’ scientific creativity. A total of 130 male eleventh-grade students in three biology classes participated in this study. The main instruments included the Test of Divergent Thinking (TDT) for creativity measurement, the Creativity Rating Scale (CRS) and the Creative Activities and Accomplishments Check Lists (CAACL) for measurement of scientific creativity, the Nature of Scientific Knowledge Scale (NSKS) for measurement of the nature of science, and the Science Attitude Inventory II (SAI II) for measurement of attitudes toward science. In addition, two instruments on measuring students’ abilities of problem finding and abilities of formulating hypotheses were developed by the researcher in this study. Data analysis involved descriptive statistics, Pearson product-moment correlations, and stepwise multiple regressions. The major findings suggested the following: (1) students’ scientific creativity significantly correlated with some of selected variables such as attitudes toward science, problem finding, formulating hypotheses, the nature of science, resistance to closure, originality, and elaboration; (2) four significant predictors including attitudes toward science, problem finding, resistance to closure, and originality accounted for 48 % of the variance of students’ scientific creativity; (3) there were big differences between students with a higher and a lower degree of scientific creativity on the variables of family support, career images, and readings about science; and (4) many students were confused about the creative and moral levels on NSKS and the concept of “almighty of science” and purposes of science on SAI II. The results of this study may provide a more holistic and integrative interpretation of students’ scientific creativity and propose better ways of evaluating students’ scientific creativity. In addition, the research results may encourage teachers to view scientific creativity as an ability that can be enhanced through various means in classroom science teaching.Science and Mathematics Educatio