Novel self-excited alternating operation of coupled commutator machines

Through the coupling of commutator machines, self-excited alternating power can be spontaneously generated with no external electrical excitations. Standard frequency- domain analysis is applied to the various equivalent circuits for each configuration. Conventional series and shunt self-excited generators are shown to have a single pole in the right-half s plane, indicating growing exponential solutions, whereas coupled generators are shown to have a pair of complex conjugate poles in the right-half s plane, indicating overstable modes, which oscillate as they grow, resulting in self-excited two-phase alternating power generation. Because of this interesting result, the analysis is extended to consider N-coupled generators which shows the existence of many overstable modes, resulting in multi-frequency, multi-phase power generation. The existence of electromechanical alternating self-excitation is demonstrated with the periodic speed reversals of a separately exited d.c. motor, which has its armature in series with the field and armature windings of a generator. Experimental results are presented which indicate that the linear circuit representation is appropriate for the onset and early time interval of these self-excited machines. The magnetic saturation characteristic limits the exponential growth so that a steady state results. These devices are of use in low-frequency, high-power applications, as well as serving as a model for other spontaneous mechanisms in nature.     

An action research study into the role of student negotiation in enhancing perceived student engagement during English speaking classes at university level in Turkey

A major issue in English language teaching in Turkey and other monolingual countries is the teaching of spoken English. This article reports the initial and final stages of an action research study which used student negotiation to enhance student engagement in speaking classes. The research was conducted in the English Language Teaching Department of a university in Turkey and involved the provision of student-negotiated speaking classes for one term during which qualitative and quantitative data collected from students through questionnaires on a weekly basis informed the design of the speaking activities. The results of content analysis and Wilcoxon signed-rank tests showed that student negotiation promoted student engagement through providing speaking classes appropriate to students’ needs and interests, which resulted in more positive perceived speaking ability and greater willingness to communicate. This study demonstrates the significance of student negotiation in speaking classes and has implications for enhancing student engagement in speaking classroom activities.     

REPLICATING AND EXTENDING RESEARCH ON THE PARTIAL ASSIGNMENT COMPLETION EFFECT: IS SUNK COST RELATED TO PARTIAL ASSIGNMENT COMPLETION STRENGTH?

After students acquire a skill, mastery often requires them to choose to engage in assigned academic activities (e.g., independent seatwork, and homework). Although students may be more likely to choose to work on partially completed assignments than on new assignments, the partial assignment completion (PAC) effect may not be very powerful. The current studies were designed to replicate previous research and determine whether the amount of sunk effort was related to PAC effect strength. Together, these studies (1) provide the only current replication of PAC effect; (2) support previous research, which suggests that the PAC effect is not very powerful; and (3) extend the theoretical research on PAC effects by showing that sunk effort did not influence PAC effect strength. Discussion focuses on implications for educators and directions for future theoretical research designed to identify the causal mechanism responsible for the PAC effect.     

Age Differences in the Dimensions of Perceived Control during Middle Childhood: Implications for Developmental Conceptualizations and Research

2 studies investigated developmental differentiation of children's causal beliefs across middle childhood. Grounded in meta-theories suggesting that development is characterized by progressive differentiation, hypotheses were derived from theory and research on the multiple dimensions of children's perceived control and on developmental changes in children's concepts of causal constructs. Age differences in the organization of children's causal perceptions were explored and replicated ( N 's = 294 and 240, ages 7–12). Analyses of factor structure of children's beliefs about the effectiveness of 5 causes for school success and failure (effort, ability, powerful others, luck, and unknown factors) revealed that beliefs became more differentiated with age. At ages 7–8, 2 dimensions were found, 1 marked by unknown and 1 by the remaining causes. At ages 9–10, 3 factors were present, marked by "internal,""external," and unknown means. By ages 11–12, 4 factors were indicated, marked by effort, ability, "external," and unknown causes. Findings suggested that different theories of perceived control may provide more useful accounts of the dimensions of causal beliefs at different ages. Implications were derived for measurement of perceived control and investigation of developmental change in its effects on children's motivation and behavior.     

IS IT BETTER TO OFFER MANY OR FEW ELECTIVES IN A BIBLE DEPARTMENT

This article, and the one following, were delivered as addresses by their respective authors at the annual meeting of the Professors’ and Research Associated Section of the Division of Christian Education, National Council of Churches, St. Louis, February, 1960. ‐‐ Editor.     

Associations Between Perceived Material Deprivation,Parents’ Discipline Practices,and Children's Behavior Problems: An International Perspective

This study investigated the association between perceived material deprivation, children's behavior problems, and parents’ disciplinary practices. The sample included 1,418 8- to 12-year-old children and their parents in China, Colombia, Italy, Jordan, Kenya, the Philippines, Sweden, Thailand, and the United States. Multilevel mixed- and fixed-effects regression models found that, even when income remained stable, perceived material deprivation was associated with children's externalizing behavior problems and parents’ psychological aggression. Parents’ disciplinary practices mediated a small share of the association between perceived material deprivation and children's behavior problems. There were no differences in these associations between mothers and fathers or between high- and low- and middle-income countries. These results suggest that material deprivation likely influences children's outcomes at any income level.