Interactions of persistent slip bands with a grain boundary on the common primary slip plane in a copper bicrystal

In this letter, the dislocation patterns on the common primary slip plane in a fatigued \[1-34]-\[182-7] copper bicrystal with a Sigma=19b grain boundary (GB) have been investigated using the electron channelling contrast technique in a scanning electron microscope. The results show that the two-phase dislocation structure, such as veins and persistent slip band (PSB) walls, embedded within veins, can be clearly seen on the common primary slip plane. In particular, the interactions of PSBs with the GB are clearly revealed. It is found that there are three kinds of interaction mode between the GB and the dislocations during cyclic deformation, and those are discussed. It is suggested that the dislocations carried by PSBs cannot transfer through the GB continuously even though the bicrystal has a common primary slip plane and its surface slip bands are continuous across the GB.     

Solid-solution strengthening in ordered In x Ga1 − x P alloys

Ordered In _x Ga_{1??? x} P alloys have been grown on to GaAs(001) substrates by metal–organic vapour-phase epitaxy. Lattice-matched compositions of alloys (In _x Ga_{1??? x} P with x?≈?0.5) were used in order to produce epitaxial layers free of structural defects (threading dislocations). Growth temperature and substrate orientation were adjusted to control the degree η, of order, of the alloys in the range 0.3–0.5. Nanoindentation tests were carried out to measure the mechanical response of the heteroepitaxial layers. Transmission electron microscopy was used to characterize the structure as well as the plastic zones generated into the specimen by nanoindentation. Comparison of the alloys with binary references (InP and GaP bare substrates) showed strengthening, with the hardness and flow-stress values that are much larger than those of InP and of the same order of magnitude as those of GaP.     

The flow stress contribution of the dislocation 'forest' in bcc lattices

The athermal flow stress contribution by junction reactions of a glide dislocation with a 'forest' of density rho is usually written as tau = alpha mu b rho ^1/2. The strength coefficient alpha has been computed for the bcc lattice by virtual displacement of triple nodes following the method of Puschl et al. (1982, Physica status solidi (a), 74, 211). In the isotropic approximation, the values for glide dislocations with 0, 30, 60 and 90^o character are as alpha = 0.18, 0.21, 0.19 and 0.22 respectively. A comparison with values calculated previously by Frydman is made, and good agreement is found when differences in the cut-off radii of the linear elastic solution are accounted for.     

Deformed substructures in fine-grained tetragonal zirconia

Transmission electron microscopy (TEM) has been employed to examine the deformed microstructures of a high-purity tetragonal zirconia polycrystal containing 3mol% yttria. The TEM observations reveal that piled-up and tangled dislocations are developed within grains at a high stress, but such substructures do not appear at a lower stress, except for a small number of isolated dislocations. The stress-dependent deformed microstructures suggest that the dislocation substructures observed at a high stress are not due to any experimental artefacts. Applying a model proposed by Eshelby et al. to the observed pile-up dislocations, it can be estimated that a stress concentration of the order of 14-25 is generated around multiple-grain junctions during deformation.     

Determination of Peierls stress from acoustic harmonic generation

The interaction of acoustic waves with dislocations leads to aperiodic oscillations in the magnitude of the acoustic nonlinearity parameter β as a function of the acoustic drive amplitude σ _ampl. The magnitude and spacing of the oscillations depend on the value of the Peierls stress. A least-square curve fit of the β(σ _ampl) equation to experimental data taken of 99.999% pure aluminum monocrystals oriented for wave propagation along the [1?0?0] crystal axis yields the value 6.2?×?10⁴?Pa for the Peierls stress. The value is consistent with the smallest values reported in the literature for aluminum where for both theoretical and experimental studies the reported values range over three orders of magnitude.     

Threading dislocation with b=c+2a in 4H-SiC as determined by LACBED

The Burgers vectors of the so-called threading screw dislocations (a total of 28 dislocations) in 4H-SiC were determined by large-angle convergent-beam electron diffraction. A new type of TSD, that is, b = c + 2a dislocation, was identified. Thus, all of the four types of TSD predicted by Onda et al. [Phil. Mag. Lett. 93 (2013) p.591] were identified.     

Continuum and discrete models of dislocation pile-ups. II. Pile-up of screw dislocations at the interface in a bimetallic solid

The methodology developed in the precursor to this paper is used to find the positions of n screw dislocations in a pile-up against an interface bonding two crystalline solids. The pile-up is caused by a constant applied stress and, as n →∞, the dislocations are located with sufficient accuracy to predict the large but finite stress distribution at the interface. Such a prediction is impossible using a conventional continuum dislocation density.     

Is the Bifactor Model a Better Model or Is It Just Better at Modeling Implausible Responses? Application of Iteratively Reweighted Least Squares to the Rosenberg Self-Esteem Scale

Although the structure of the Rosenberg Self-Esteem Scale (RSES) has been exhaustively evaluated, questions regarding dimensionality and direction of wording effects continue to be debated. To shed new light on these issues, we ask (a) for what percentage of individuals is a unidimensional model adequate, (b) what additional percentage of individuals can be modeled with multidimensional specifications, and (c) what percentage of individuals respond so inconsistently that they cannot be well modeled? To estimate these percentages, we applied iteratively reweighted least squares (IRLS) to examine the structure of the RSES in a large, publicly available data set. A distance measure, d_s, reflecting a distance between a response pattern and an estimated model, was used for case weighting. We found that a bifactor model provided the best overall model fit, with one general factor and two wording-related group factors. However, on the basis of d_r?values, a distance measure based on individual residuals, we concluded that approximately 86% of cases were adequately modeled through a unidimensional structure, and only an additional 3% required a bifactor model. Roughly 11% of cases were judged as “unmodelable” due to their significant residuals in all models considered. Finally, analysis of d_s revealed that some, but not all, of the superior fit of the bifactor model is owed to that model's ability to better accommodate implausible and possibly invalid response patterns, and not necessarily because it better accounts for the effects of direction of wording.     

Disorganized infant attachment and preventive interventions: A review and meta‐analysis

Infant disorganized attachment is a major risk factor for problematic stress management and later problem behavior. Can the emergence of attachment disorganization be prevented? The current narrative review and quantitative meta‐analysis involves 15 preventive interventions (N = 842) that included infant disorganized attachment as an outcome measure. The effectiveness of the interventions ranged from negative to positive, with an overall effect size of d = 0.05 (ns). Effective interventions started after 6 months of the infant's age (d = 0.23). Interventions that focused on sensitivity only were significantly more effective in reducing attachment disorganization (d = 0.24) than interventions that (also) focused on support and parent's mental representations (d = ?0.04). Most sample characteristics were not associated with differences in effect sizes, but studies with children at risk were more successful (d = 0.29) than studies with at‐risk parents (d = ?0.10), and studies on samples with higher percentages of disorganized attachment in the control groups were more effective (d = 0.31) than studies with lower percentages of disorganized children in the control group (d = ?0.18). The meta‐analysis shows that disorganized attachments may change as a side effect of sensitivity‐focused interventions, but it also illustrates the need for interventions specifically focusing on the prevention of disorganization.     

The Peierls-Nabarro model revisited

We re-examine two important issues within the Peierls-Nabarro model, which are critical in obtaining accurate values for the Peierls stress. The first is related to the sampling scheme (double versus single counting) of the misfit energy across the glide plane and the second is the effect of atomic relaxation on the Peierls stress. We argue that the double-counting scheme is physically more appropriate. An analytical formula is derived for the Peierls stress of dislocations in alternating lattices. The atomic relaxation is shown to play an important role on the Peierls stress for narrow dislocations.     

Size effects and Hall–Petch relation in polycrystalline cobalt

The mechanical behaviour of polycrystalline hexagonal close-packed cobalt was investigated over a large range of grain size d in order to examine the occurrence of size effects. Crystallographic texture and amount of face centred cubic allotropic phase were maintained unchanged thanks to appropriate heat treatment procedures. The Hall–Petch (HP) relation exhibits two distinct behaviours from the very beginning of plastic strain levels. The conventional HP law is fulfilled for a number of grains across the thickness t higher than a critical value (t/d)_c = 14. For t/d lower than (t/d)_c, a multicrystalline regime is evidenced highlighting a strong reduction in flow stress. The high value of (t/d)_c is related to the low-stacking fault energy of cobalt in the basal plane. The size effect is predominant in the first work hardening stage where slip mechanisms and stacking faults predominate. In the second stage, driven by mechanical twinning processes, this effect is less sensitive. Finally, the size effect could also affect the end of the elastic stage, in link with nonlinear elasticity mechanisms.     

Evaluation of a Brief Mindfulness Program for People with Multiple Sclerosis Delivered in the Community Over Five Years

This study evaluated the effectiveness, change mechanisms, and sustainability of a brief mindfulness intervention for people with multiple sclerosis (PwMS) delivered in the community through a frontline service over five years. Participants were 126 PwMS. A single intervention condition design was used with pre-intervention, post-intervention and 2-month follow-up assessments. The primary outcome was distress. Secondary outcomes were perceived stress, quality of life (QoL) and fatigue, and the proposed change mechanisms: mindfulness, self-compassion, psychological inflexibility. Intention-to-treat analyses showed the primary outcome, distress (Cohen’s d = .25), and all secondary outcomes improved: perceived stress (d = .38), mental health QoL (d = .39), physical health QoL (d = .47), fatigue (d = .30), mindfulness (d = .29), self-compassion (d = .37), psychological flexibility (d = .44). Distress, stress and perceived stress continued to improve post-intervention to follow-up. Mindfulness emerged as a temporal mediator of perceived stress (BCa 95% CI). Self-compassion mediated concurrent improvements in distress, perceived stress, fatigue and physical health QoL, while greater psychological flexibility mediated concurrent reductions in distress (BCa 95% CI). Mindfulness home practice was unrelated to improvements on all outcomes except a marginal association with mindfulness. Of the socio-demographic and illness factors, lower disease severity predicted improvements in physical health QoL (p = .046). Improvements in outcomes were supported by qualitative feedback and participant satisfaction ratings. Twenty-one groups were offered with good participant engagement and wide geographical reach, suggesting sustained feasibility of the Mindfulness for MS program over five years. Findings support the delivery of the Mindfulness for MS program through a community-based service in partnership with a local university.

     

Reviewing,Categorizing, and Analyzing the Literature on Black–White Mean Differences for Predictors of Job Performance: Verifying Some perceptions and Updating/Correcting Others

In both theoretical and applied literatures, there is confusion regarding accurate values for expected Black–White subgroup differences in personnel selection test scores. Much confusion arises because empirical estimates of standardized subgroup differences (d) are subject to many of the same biasing factors associated with validity coefficients (i.e., d is functionally related to a point‐biserial r). To address such issues, we review/cumulate, categorize, and analyze a systematic set of many predictor‐specific meta‐analyses in the literature. We focus on confounds due to general use of concurrent, versus applicant, samples in the literature on Black–White d. We also focus on potential confusion due to different constructs being assessed within the same selection test method, as well as the influence of those constructs on d. It is shown that many types of predictors (such as biodata inventories or assessment centers) can have magnitudes of d that are much larger than previously thought. Indeed, some predictors (such as work samples) can have ds similar to that associated with paper‐and‐pencil tests of cognitive ability. We present more realistic values of d for both researcher and practitioner use. Implications for practice and future research are noted.     

Randomized controlled trial evaluating the effectiveness of a web-based stress management program among community college students

Background and Objectives: This study evaluated the effectiveness of a web-based stress management program among community college students that focused on increasing perceived control over stressful events. Design: Students (N = 257) were randomly assigned to a Present Control Intervention or a Stress-information only comparison group. Methods: Primary outcomes were perceived stress and stress symptoms; secondary outcomes were depression and anxiety. Self-report measures were completed online at preintervention, postintervention, and three-week follow-up. Intervention effects were estimated using linear mixed models. Seventy-five percent of the sample (n = 194) completed the pretest and comprised the intent-to-treat sample. Results: Participants in the intervention group reported significant increases in present control, and significant decreases in all four primary and secondary outcome measures from baseline to postintervention and follow-up. Within-group effect sizes were small to medium at postintervention (mean d = –.34) and follow-up (mean d = –.49). The mean between-group effect size on the four outcome measures was d = .35 at postintervention but d = .12 at follow-up, due to unexpected decreases in distress in the comparison group. Conclusions: Our online program is a cost-effective mental health program for college students. Limitations and future direction are discussed.     

Heterogeneity Coefficients for Mahalanobis' D as a Multivariate Effect Size

The Mahalanobis distance D is the multivariate generalization of Cohen's d and can be used as a standardized effect size for multivariate differences between groups. An important issue in the interpretation of D is heterogeneity, that is, the extent to which contributions to the overall effect size are concentrated in a small subset of variables rather than evenly distributed across the whole set. Here I present two heterogeneity coefficients for D based on the Gini coefficient, a well-known index of inequality among values of a distribution. I discuss the properties and limitations of the two coefficients and illustrate their use by reanalyzing some published findings from studies of gender differences.     

Effects of load direction on the mechanical properties of open-cellular epoxy with a cubic prism structure

The mechanical properties of open-cellular epoxies with a cubic prism structure have been investigated by compressive tests with angles between the beam and the load direction of 0^o (90^o) and 45^o. When the angle was 45^o, the stress fluctuated in a plateau region about a roughly constant flow up to a strain of 77%. However, when the angle was 0^o (90^o), the flow stress changed significantly with the strain passing through a series of peaks. The absorption energy per unit volume was found to be essentially independent of the angle between the beam and the load direction.     

The selection of judges for preference testing

A scheme for choosing a few individuals whose preferences for given objects are most representative of those of a larger group of individuals is proposed. The method involves (a) quantifying the preferences of each individual so as to discriminate optimally among objects, (b) testing statistically whether or not a common preference continuum may be assumed for the quantified preferences, (c) constructing a linear estimator of values for the objects on this continuum, if it may be assumed, and (d) selecting as judges the least number of individuals whose quantified preferences, when used with this estimator, determine values for the objects with acceptable accuracy. A numerical example based on food preferences is presented. Preparation of this paper has been supported in part by the Quartermaster Food and Container Institute for the Armed Forces. Views or conclusions expressed herein are those of the author and do not necessarily reflect the views or indorsement of the Department of Defense.     

The energetics and interactions of random dislocation walls

Abstract

Regular dislocation walls, where dislocations are spaced equally along the wall direction, are a popular idealization for modelling the arrangement and interactions of excess dislocations in plastic deformation. The assumption of regular walls is motivated by the fact that such walls represent minimum energy arrangements for dislocations of the same sign, and it allows to use the analytically known short-ranged stress fields of such walls for analyzing the structure of plastic boundary layers. In order to critically evaluate the physical robustness of models based on regular walls, we investigate their random counterparts and demonstrate that the energetics and interactions of such non-periodic dislocation arrangements differ completely from the periodic wall arrangements. Implications of our results for the modelling of plastic boundary layers and dislocation-grain boundary interactions are discussed.     

Experimental evidence of relaxation arising from the motion of geometrical kinks on screw dislocations in iron

Abstract

Internal friction measurements with a superimposed bias stress have provided evidence for geometrical kink migration on screw dislocations in iron. This intrinsic process causes a relaxation phenomenon in internal friction which has been identified with the occurrence of a subpeak (below 20 K) of the α-peak. The effect of different bias stress has allowed us to evaluate the kink migration energy, E ^m _k ? 0·001eV.