Using response times to detect aberrant responses in computerized adaptive testing

A lognormal model for response times is used to check response times for aberrances in examinee behavior on computerized adaptive tests. Both classical procedures and Bayesian posterior predictive checks are presented. For a fixed examinee, responses and response times are independent; checks based on response times offer thus information independent of the results of checks on response patterns. Empirical examples of the use of classical and Bayesian checks for detecting two different types of aberrances in response times are presented. The detection rates for the Bayesian checks outperformed those for the classical checks, but at the cost of higher false-alarm rates. A guideline for the choice between the two types of checks is offered.This study received funding from the Law School Admission Council (LSAC). The opinions and conclusions contained in this paper are those of the authors and do not necessarily reflect the policy and position of LSAC. The authors are most indebted to Wim M. M. Tielen for his computational assistance and to the US Defense Manpower Data Center for the permission to use the ASVAB data set in the empirical examples.     

Self-assembly-assisted growth of two-dimensional Penrose tiling

An algorithm for the growth of two-dimensional Penrose tiling, based on symmetry operations on a seed rhombus, is discussed and demonstrated. Independent of empirical matching rules, as suggested by Penrose [Bull. Inst. Math. Appl. 10 266 (1974)], and also overcoming the scaling-down operation, as proposed by Ramachandrarao et al. (Acta Crystallogr. A 47 210 (1991)], the present algorithm follows a mechanism akin to self-assembly and can be continued ad infinitum.     

Role of cross-slipping in formation of edge dislocations in heteroepitaxial systems GeSi-on-Si(001) and Ge-on-InGaAs/GaAs

Edge misfit dislocations (MDs) formed as result of reactions between 60° glissile threading dislocations and 60° MDs lying on an intersecting glide plane were found in strained GeSi-on-Si(001) and Ge-on-InGaAs/GaAs films. It was demonstrated that dislocations penetrating from the InGaAs buffer layer to the strained Ge film can provoke formation of not only 60° MDs, but also edge MDs on the interface even at minor mismatch of the lattice parameters of the film and the InGaAs/GaAs virtual substrate.     

Shape deformation by moving a glissile interface with one set of misfit dislocations

Transformation and misfit dislocations are used to describe the motion of glissile interfaces with one set of misfit dislocations in the framework of the Frank?Bilby equation. The sweep of these glissile interfaces brings about an invariant-plane-strain type shape deformation. Our approach explains the glissile motion of martensitic interfaces and small-angle symmetrical tilt grain boundaries. It is consistent with the phenomenological theory of martensite crystallography but more flexible.     

Stress in physical education teachers in Qatar

Stress is an area of interest among researchers and practitioners in many fields – including teaching. Much of the research on causes of stress for teachers has focused on teachers in general; only a few studies have focused on physical education teachers. Although there have been a few studies of causes of stress for physical education teachers in the Middle East, no studies have been conducted on physical education teachers in Qatar. Thus, the purpose of this study was to identify causes of stress for physical education teachers in Qatar at the beginning and end of the school year as well as any changes over the course of the year. A second purpose was to try to explain any differences in causes of stress according to: gender, nationality, type of school, and amount of experience. Results showed that there were different causes of stress for different groups of teachers which could be related to different backgrounds and experiences and different roles and responsibilities in society as a result of different cultural and social expectations and environmental factors.     

Atomic arrangement at the 3C-SiC/Si(001) interface revealed utilising aberration-corrected transmission electron microscope

The atomistic structure of the 3C-SiC/Si(001) interface has been investigated using a combination of aberration-corrected transmission electron microscopy and a newly developed image processing method for eliminating artificial contrast. The structures having periods four times longer than those of the silicon lattice have been observed distinctly in images taken along both Si[110] and Si[100] directions. Contrary to theoretical models proposed previously, the interface of the three-dimensional structural model that we constructed on the basis of our experiments has a silicon-rich configuration. We have clarified that the strain field induced by the two-dimensional misfit between Si(001)-(4?×?4) and SiC(001)-(5?×?5) is relaxed by the two-dimensional network of misfit dislocations; simple edge dislocations with [100] and [010] directions and Lomer dislocations with [110] and [110] directions. The atomistic structures of the Lomer dislocations have been also clarified.     

Person–Group Dissimilarity in Involvement in Bullying and Its Relation with Social Status

This study tested a person-group dissimilarity model for the relation between peer preference on the one hand, and bullying and victimization on the other. This model accounts for both individual and group (i.e., classroom) factors and postulates that children will be rejected by their peers when they display behaviors that deviate from the group norm. We tested the model in a sample of 2,578 early adolescents in 109 middle school classrooms. Multilevel analysis was used to account for our nested data when examining individual and group effects simultaneously in cross-level interaction terms. The results supported our hypotheses based on the dissimilarity model. Classroom norms of behavior appeared to affect the relation between involvement in bullying and peer preference, in that early adolescents who bullied were more likely to be rejected by their peers in a classroom where bullying was non-normative. In classrooms where bullying was normative, adolescents who bullied were less likely to be rejected or were even liked by their peers (i.e., positive scores on peer preference). The same was true for victimization, although victims still had low scores on peer preference even when victimization was normative. Theoretical and practical implications of these results are discussed in terms of directions for future research and intervention in bullying.     

Transient photoconductivity in n-type a-Si: H

Abstract

The long-time transient photocurrent decay in annealed and light-exposed P-doped a-Si: H is examined experimentally and by numerical modelling. The decay is a dispersive power law with sublinear index, extending to times longer than 1s, and the decay rate increases with temperature. Light exposure dramatically decreases the decay amplitude but does not affect the rate of decay. The phenomenon is discussed in terms of a comprehensive multiple-trapping model in which transport of thermalized electrons is essentially non-dispersive, and recombination of free carriers via defects is dispersive, owing to continued thermalization of excess holes. The slower recombination step is free-hole capture by D^? states, while the decay of the total excess ensemble is controlled by hole release from valence-band tail traps. The index of the excess photoelectron decay provides information on the valence-band tail states, which are exponentially distributed, with a characteristic energy estimated as 0·06 eV.