On the ultra-high-strain rate shock deformation in copper single crystals: multiscale dislocation dynamics simulations

Multiscale dislocation dynamics plasticity (MDDP) calculations are carried out to simulate the mechanical response of copper single crystals that have undergone shock loading at high strain rates ranging from 1?×?10⁶ to 1?×?10¹⁰?s^?1. Plasticity mechanisms associated with both the activation of pre-existing dislocation sources and homogeneous nucleation of glide loops are considered. Our results show that there is a threshold strain rate of 10⁸?s^?1 at which the deformation mechanism changes from source activation to homogeneous nucleation. It is also illustrated that the pressure dependence on strain rate follows a one-fourth power law up to 10⁸?s^?1 beyond which the relationship assumes a one-half power law. The MDDP computations are in good agreement with recent experimental findings and compare well with the predictions of several dislocation-based continuum models.     

Boundary effects on forced drainage through aqueous foam

The flow of liquid through foam confined in vertical tubes was investigated by measuring the velocity v_f of the liquid front forced down by gravity for various flow rates Q. The power law relating the velocity to flow rate of the incoming liquid (v_f     

Analysis of sintering of two cylindrical particles by lattice or grain-boundary diffusion at the initial stage

The sintering of two cylindrical particles by lattice or grain-boundary diffusion at the initial stage is analysed by a variational principle and use of the continuity equation. The expression for the growth rate by lattice or grain-boundary diffusion indicates that the length of the neck increases as a power of time.     

Growth of diamond crystals by combustion synthesis

Abstract

Low-pressure synthesis of diamond by activated chemical vapour deposition processes is attractive for producing diamond films for optical and electronic (i.e. non-abrasive) applications because of the ability of these processes to produce these films in large dimensions. The low growth rate (about 1 μm h^?1) has, however, precluded these processes for abrasive grain production on simple economic grounds. With the introduction of combustion synthesis of diamond at growth rates exceeding 100μmh^?1, this barrier seems less formidable than it once did. The synthesis of large (about 200 μm) well formed single crystals of diamond by the combustion process with growth rates of about 100μm h^?1, reported here, offers an opportunity to explore the potential of this process for abrasive grain production.     

Relation between volume,number of faces and three-dimensional growth laws in coarsening cellular patterns

Abstract

The recently established linear growth law for three-dimensional diffusive coarsening shows zero average growth for grains with 15·8 faces, while the average number of faces per grain in the pattern is 13·7 ± 0·1. In the better-known two-dimensional case, grains with six sides (the average number) show zero growth. We show that the three-dimensional zero growth value is a consequence only of the linear form of the law and the cubic dependence of average area per grain on the number of faces.     

Crystal growth and defect study of BiSbTe3

BiSbTe₃ single crystals have been grown by the Bridgman technique. Microscopic observations of the as-grown crystals reveal typical features, such as striations on the top free surface, which are attributed to the effect of growth conditions. A nitric-acid-based reagent capable of revealing dislocations has been developed and tested. Etch pits are produced at the dislocation sites, but some discrepancies have been observed on matched cleavage surfaces. The structural difference between the matched cleavage surfaces is discussed.     

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.     

Fractal growth of graphite nodules in iron

It has been found from a large number of statistical tests that graphite nodules in malleable iron grow with time according to a power law. The growth of the nodules and their fractal dimension have been investigated experimentally as a function of annealing time. Based on the assumption of carbon-diffusion-controlled growth in the initial stage, the growth equation is R _G = K ₁ t ^1/(D-1), where R _G is the radius of the graphite nodules, t the time, D the fractal dimension and K ₁ a constant. Assuming cementite-dissolution-controlled growth in the later stages of growth, the relation is R _G = K ₃ t ^3/D , where K ₃ is a constant. The fractal dimension, or the aggregate state of the graphite nodules, strongly influences the growth process.     

Microstructural development during transient directional solidification of a hypomonotectic Al–In alloy

Upward directional non-steady-state solidification experiments have been performed on a hypomonotectic Al–5.5?wt%In alloy. The alloy developed cellular as-solidified microstructure for tip growth rates, V _L, higher than 0.95?mm/s. The casting regions associated with V _L?<?0.95?mm/s were shown to be characterized by a microstructure formed by In droplets disseminated in the Al matrix. Tip growth rate and microstructural features, such as cell spacing and interphase spacing, have been experimentally determined. The experimental cell spacings have been compared with theoretical predictions furnished by the Hunt–Lu model. It was found that the experimental scatter lies below the minimum range of values theoretically predicted. Moreover, the experimental cell spacing evolution with V _L is characterized by a ?1.1 power law. The droplets’ interphase spacing, λ, is related to the growth rate by the Jackson–Hunt relationship (λ ² V _L?=?constant).     

Influence of crystallographic orientation on cyclic strain-hardening behaviour of copper single crystals

The cyclic strain-hardening behaviour of copper single crystals with various slip orientations is considered systematically. It is shown that the crystallographic orientation has a strong effect on the cyclic hardening behaviours of double- and multiple-slip-oriented copper single crystals. The initial cyclic hardening of differently oriented copper single crystals is mainly dependent on the modes and intensities of dislocation interactions between slip systems operating in the crystal, as well as on the possibility of cross-slip. A distinctive strain burst phenomenon has been frequently observed in the very early stage of cyclic hardening for critical double-slip-oriented crystals. A secondary cyclic hardening stage occurs readily late in cyclic deformation of coplanar doubleslip-oriented crystals.     

Initial sintering of cylindrical particles of different sizes by surface diffusion

Sintering of two cylindrical particles of different sizes by surface diffusion at the early stage is theoretically analysed. Formulae for the neck growth rate are derived using a variational principle and the continuity equation of vacancies. The size difference between two particles is found to influence the growth rate of the neck only when the difference is large.     

Hope and world survival

Abstract

Gives an overview and analysis of the role of the Pacific region in the world economy stressing the ongoing shift of growth potential and purchasing power. Japan's surplus is discussed as a tool to stimulate economic growth in the world. Trends in Pacific cooperation are given.     

The Tarasoff Warning and the Duty to Protect

Summary

Since the case of Tarasoff v. Regents of the University of California, mental health professionals have had an explicit legal duty to warn potential adult victims of violence. Subsequent case law expanded this standard to a broader duty-to-protect. Primary health care providers are increasingly treating psychiatric patients for whom the duty to protect is applicable. However, these providers are often unaware of the legal, ethical, and clinical issues involved. Assessment of violence risk should include demographic, psychiatric, and social dimensions. Interventions include notifying law enforcement authorities, potential victims, and possible use of psychiatric hospitalization to prevent aggressive behavior. The duty-to-protect as a standard-of-care has been applied to several other clinical situations, including impaired driving capacity, high-risk HIV behavior, and child sexual abuse. The article includes a step-by-step clinical protocol for evaluation and intervention in dangerous situations.     

Survey of plateau behaviour in the cyclic stress-strain curve of copper single crystals

Experimental results relating to the plateau behaviour in the cyclic stress-strain (CSS) curve of copper single crystals located on different sides of the stereographic triangle are summarized. Unlike the situation for single-sliporiented crystals, the crystallographic orientation has a strong effect on the plateau behaviour in the CSS curves of double- and multiple-slip-oriented crystals. The existence or non-existence of a plateau in the CSS curves, as well as the corresponding plateau stress amplitude, depend not only on the modes and intensities of dislocation interactions among slip systems operating in the crystals but also on the slip deformation characteristics associated with crystal orientations. The plateau region in CSS curve disappears only when multiple slip plays a determining role during cyclic deformation.     

Dislocation multiplication in bcc molybdenum: A dislocation dynamics simulation

Plastic deformation of Mo single crystals is examined by direct simulation of dislocation dynamics under stress. Initial dislocation populations are made to mimic real dislocation microstructures observed in transmission electron microscopy cross-sections of pure annealed Mo single crystals. No a priori sources for dislocation multiplication are introduced, and yet multiplication takes place through a sequence involving aggregation of grown-in superjogs, bowing of screw dislocation segments and fast lateral motion of edge segments, producing a large number of elongated loops and a characteristic cross-grid pattern of screw dislocations.     

Comparison of quasicrystalline (T2) and crystalline (R) structures in AlCuLi using high-resolution X-ray diffraction

Abstract

A high-resolution X-ray scattering experiment has been performed on quasicrystalline (T2) and crystalline (R) phases of AlCuLi alloys. Peak widths determined from the diffraction profile of the R phase are found to scale with momentum transfer G, similar to the strain-broadening effect seen in conventional crystals with small unit cells. A narrowing of peak widths on annealing is also observed. On the other hand, diffraction peak widths in I-phase samples obtained by rapid solidification are found to scale with phason momentum G ₁, similar to that observed in large faceted crystals. Thermal annealing of the I phase is found to have no effect on peak widths. Our findings are discussed in the light of models for crystals and quasicrystals.     

Le rapport à la loi et à ses représentants est-il altéré par le contact des adolescents avec les acteurs de la chaîne pénale ? Une revue systématique de la littérature

IntroductionAdolescents have the highest prevalence and incidence rates of delinquency. Several authors have suggested that the rejection of authority figures in adolescence may explain these rates. Other studies have also found a positive relationship between delinquency and negative attitudes toward the law and its representatives.ObjectiveThe objective was to make an inventory of the current scientific knowledge concerning the link between contact with the penal actors and the adolescents’ attitude towards the law and its representatives. We also want to identify the mediators of this link.MethodWe conducted a systematic review. Of the 802 articles identified, we selected those involving adolescents and focusing on contact with penal actors (i.e., law enforcement officers, court personnel, lawyers, prison personnel, security personnel, social workers) and on attitudes toward the law and its representatives. Our review finally covers the 46 articles corresponding to our inclusion and exclusion criteria.ResultsMost studies show that contact with penal actors lead to more negative attitudes toward the law and its representatives. Longitudinal studies suggest that this relationship is causal : contact with penal actors leads adolescents to have less positive attitudes towards the law and its representatives. However, there seem to be differences according to the type of contact studied.ConclusionThese results, questioning the penal responses brought to adolescents, will be discussed, both on a theoretical and practical level. Methodological issues will also be addressed.     

Using Relational-Cultural Theory to Conceptualize Couple Interventions in the Treatment of Sex Addiction

ABSTRACT

Sex addictions have become an increasing concern since the growth of the sex industry, sex in advertising, and the ease of Internet access to sex. This article uses the foundational principles of Relational-Cultural Theory (RCT) to conceptualize sexual addiction and its relational impact. Particular attention is paid to the principles of connection, mutuality, authenticity, power, and culture. In closing, the author offers some creative interventions for relational transformation for affected couples in order to move from a state of disconnection towards mutuality, growth, and connection.     

When is a cause the “same”? Incoherent generalization across contexts

A theory or model of cause such as Cheng's power (p) allows people to predict the effectiveness of a cause in a different causal context from the one in which they observed its actions. Liljeholm and Cheng demonstrated that people could detect differences in the effectiveness of the cause when causal power varied across contexts of different outcome base rates, but that they did not detect similar changes when only the cause–outcome contingency, ?p, but not power, varied. However, their procedure allowed participants to simplify the causal scenarios and consider only a subsample of observations with a base rate of zero. This confounds p, ?p, and the probability of an outcome (O) given a cause (C), P(O|C). Furthermore, the contingencies that they used confounded p and P(O|C) in the overall sample. Following the work of Liljeholm and Cheng, we examined whether causal induction in a wider range of situations follows the principles suggested by Cheng. Experiments 1a and 1b compared the procedure used by Liljeholm and Cheng with one that did not allow the sample of observations to be simplified. Experiments 2a and 2b compared the same two procedures using contingencies that controlled for P(O|C). The results indicated that, if the possibility of converting all contexts to a zero base rate situation was avoided, people were sensitive to changes in P(O|C), p, and ?p when each of these was varied. This is inconsistent with Liljeholm and Cheng's conclusion that people detect only changes in p. These results question the idea that people naturally extract the metric or model of cause from their observation of stochastic events and then, reasonably exclusively, use this theory of a causal mechanism, or for that matter any simple normative theory, to generalize their experience to alternative contexts.