Structural duality of 1/3⟨111⟩ twin-boundary disconnections

We investigate the structure of 1/3?111? disconnections at Σ3 {111} twin boundaries in gold. Our high-resolution transmission electron microscopy (HREM) observations and atomistic simulations show that the core relaxation of this defect is dramatically affected by reversing the sign of the Burgers vector, as oriented with respect to the twin boundary. In particular, we find two distinct, relaxed structures: one with a localized core and the other with a dissociated core composed of a stacking fault terminated by a Shockley partial dislocation. An analysis of the specific pathways available for the defect to relax and of the elastic interactions of the components of the dissociated dislocation for these cases explains the structural difference.     

Long-term natural ageing of a dissociated dislocation in a Cu-13.43 at.% Al alloy

The nature of impurity-dislocation interactions is one of the key questions governing the strength and plasticity of solid-solution materials. To investigate the influence of impurities on the mechanical properties of intermetallic NiAl, the electronic structure and energy of NiAl with a <100>{010} edge dislocation and transition-metal impurities was calculated using the real-space tight-binding linear muffin-tin orbital method. The localized electronic states, appearing in the core of the dislocation, are found to lead to strong impurity-dislocation interactions via two mechanisms: firstly, chemical locking, due to strong hybridization between impurity electronic states and dislocation localized states; secondly, electrostatic locking, due to long-range charge oscillations caused by the electron localization in the dislocation core. The results obtained explain qualitatively why the solid-solution hardening effect in NiAl correlates with the electronic structure of impurities rather than with size misfit, as expected according to traditional views.     

Determination of electrostatic characteristics at a 24°, [001] tilt grain boundary in a SrTiO3 bicrystal by electron holography

The electrostatic potential and associated space charge across a 24°, [001] tilt boundary of SrTiO₃ ceramic have been determined using electron holography. The results reveal a positive charged interface with a negative space charge on either side. The form of the double Schottky barrier and the local charge-density distribution at the interface are derived from the results.     

Who is who in dissociation?: A plea for psychodynamics in a time of trauma1

Contemporary theories of dissociation and trauma for the most part have evolved outside of psychoanalysis. Psychoanalytic writings have also been regarded as being in opposition to trauma‐based notions of human psychopathology. The specific psychoanalytic contribution—the emphasis on unconscious conflict and meaning—is for the most part excluded from the discourse on dissociation, often resulting in a mechanic conceptualisation of trauma. In this paper, based on clinical material, the author argues in favour of including conflict, unconscious intention and personal meaning in understanding the kind of dissociation we see in cases of multiple personality pathology. Textual analysis of letters written to the analyst illustrates how events of abuse are defensively elaborated. The author demonstrates that patterns of affect regulation and dominant object–relational strategies can be captured through analysis of the discourse structure. She focuses on how an organised character pattern, revealed mainly through narrative style and the analyst's countertransference, serves protective purposes as well as wishfulfillment. She argues that dissociation in the form of multiple personalities may imply an active, strategic agent.     

Shape of prismatic dislocation loops in anisotropic α-Fe

Prismatic dislocation loops are the primary manifestation of radiation damage in crystals, and contribute to the phenomenon of radiation embrittlement. This undesirable effect, most serious for materials used in high-dose environments such as next-generation fission and future fusion reactors, results from the strong interaction between gliding dislocations, the carriers of plasticity, with the population of radiation-induced prismatic loops. Ferritic–martensitic steels, the most promising candidate materials for future high-dose applications, are based on iron and are known to become highly elastically-anisotropic at the high temperatures (>500°C) at which they must operate. In this article, we develop a novel modelling approach based on anisotropic elasticity theory to predict the shapes of prismatic loops in anisotropic crystals, paying particular attention to the technologically important case of α-iron. The results are compared with transmission electron microscope observations of the damage structure sustained by ultra-high-purity iron irradiated to a dose of approximately two displacements per atom.     

The displacement field of a triangular dislocation loop–a correction with commentary

A correction is made to a previous coordinate-free formulation of the displacement field of a triangular dislocation loop by Barnett [Phil. Mag. A 51 383 (1985)]. Then, taking account of the correction, it is shown that the formulation reduces to that given by Hirth and Lothe [Theory of Dislocations, 2nd edn (Wiley, New York, 1982) p. 146.], which is restricted to a specially chosen coordinate system.     

The dissociation of position and extent in Müller-Lyer figures

Three experiments were designed to determine whether Müller-Lyer figures cause a misperception of the positions of their fins and, if they do, whether it is commensurate with the distortion of extent. Observers marked the visible intersection of shaft and fins either with their unseen hands or with their visible hands after the figure had been removed from view. In the former case, no systematic distortions of position were evident. In the latter case, there were small, systematic distortions of position, which were significantly smaller when the observers fixated the target vertex than when they fixated the center of the figure. These differences are discussed in terms of the probable similarities between the control of eye movements and the control of pointing responses. Of particular importance is the finding that even the largest distortions of vertex position were much smaller than the distortions of shaft extent. The results appear to provide evidence of the independence of perceived position from perceived extent in Müller-Lyer figures and to contradict all existing theories of the illusion.     

Demonstration of the g · b x u = 0 edge dislocation invisibility criterion for electron channelling contrast imaging

Dislocations with a large edge component do not exhibit a full loss of diffraction contrast in the transmission electron microscope unless the conditions g b = 0 and g b x u = 0 are simultaneously met. Because of a similarity between transmission electron microscopy (TEM) diffraction contrast and electron channelling contrast in the scanning electron microscope, the same contrast rules would be expected to apply for electron channelling contrast imaging (ECCI). Using the characteristic edge dislocations formed in annealed FeAl, it is demonstrated that the same extinction conditions apply for TEM diffraction contrast and ECCI.     

Are you listening? Exploring a developmental knowledge–action dissociation in a speech interpretation task

Young children sometimes act inappropriately despite appearing to know what to do. Dissociations of this kind raise important questions about the organization and development of knowledge and action systems. The present study investigated a knowledge–action dissociation in 6–year–olds performing a speech interpretation task and tested the hypothesis that knowledge–action dissociations stem from a general difficulty resolving conflicting cues. When knowledge and action measures were equated in terms of the amount of conflict that needed to be resolved for a correct response, children’s knowledge no longer appeared to outstrip their ability to act appropriately. Implications of the findings for competing views of knowledge representation and knowledge–action system organization are discussed.     

What's in an author's name? Differential evaluations of performance as a function of author's name

Three hundred college students (150 female, 150 male) were asked to evaluate an academic article in the field of politics, psychology of women, or education (judged masculine, feminine, and neutral, respectively) that was written by either a male, a female, or an author with a sexually ambiguous name. The results indicated that ratings of the articles were differentially perceived and evaluated according to the name of the author. An article written by a male was valued more positively than if the author was not male. Furthermore, subjects' bias against women was stronger when they believed that sexually neutral authors were female.We thank Brad Waite for his help in data collection.     

Core structure of a〈100〉 superdislocations in a single-crystal superalloy during high-temperature and low-stress creep

A thorough TEM analysis has been carried out to study the dislocations cutting into γ′ phase in a single-crystal superalloy during uniaxial tensile creep under high-temperature and low-stress conditions. It is proved that the a〈100〉 edge superdislocation originates from the interfacial a〈100〉 dislocations and moves into the γ′ phase by pure climbing. And the dissociation of the a〈100〉 superdislocation core into two a/2〈101〉 superpartial dislocations during uniaxial tensile creep has been identified by HRTEM method for the first time.     

Receptivity’s Construction in Public Schools: a Component of Immigrant Integration in an Emerging Gateway

Community receptivity, a critical component in integration processes, is a place’s collective response to newcomers. It is a constructed context in which the experiences of settlement and adjustment for both immigrants and non-immigrants occur. Receptivity is fluid, shaped by multi-scalar components of a community’s political, economic, social, and cultural spheres. In traditional gateways, the evolving interplay of long-established forces guides receptivity. But in new gateways, front line providers that encounter the initial settlement needs of immigrants are the vanguard of constructing the broader community’s warmth of immigrant welcome. This case study of three elementary schools in Charlotte, NC demonstrates the role of public schools as a site of receptivity’s early construction within an emerging gateway. We argue that teachers are creating receptivity building blocks within their classrooms, guiding the construction of receptivity within their schools, among the school board, the school district, and the city as a whole.     

Prediction of the configuration of a ‘Bardeen–Herring’ dislocation climb source under dynamic conditions

Abstract

The sequence of events during the operation of a ‘Bardeen-Herring’ climb source is predicted by using a numerical method in which the dislocation is modelled as a set of finite straight elements. The configuration is determined as a function of the applied stress and an approximate analytical treatment is presented which describes the time dependence of the source operation.     

Does half a pizza equal half a box of chocolates?: Proportional matching in an analogy task

There is now a considerable literature demonstrating analogical reasoning in children as young as 3 and 4 years of age. Here, we used analogy as a sensitive measure of proportional understanding in young children. In two experiments, we examined whether children's performance in a proportional analogy task would be affected when concrete models evoking different kinds of conceptual referents were used as the basis for the analogies. We chose two different conceptual referents (pizza and chocolates) of the kind typically used in fractions instruction. In both experiments, children were shown a base substance by the experimenter (e.g., a whole pizza) from which a proportion was then removed (e.g., a half pizza). Children were asked to complete the analogy by removing an equivalent proportion of their own target set (e.g., a whole box of chocolates changed to half a box of chocolates). This proportional matching paradigm resulted in analogy problems of the form: 8/8 pizza: 4/8 pizza: 4/4 box of chocolates:2/4 box of chocolates. Results indicated that 3- to 4-year-old children do have an emergent understanding of proportional equivalence, even when the materials to be matched are not isomorphic.     

Feelings of error in reasoning—in search of a phenomenon

Recent research shows that in reasoning tasks, subjects usually produce an initial intuitive answer, accompanied by a metacognitive experience, which has been called feeling of rightness. This paper is aimed at exploring the complimentary experience of feeling of error (FOE), that is, the spontaneous, subtle sensation of cognitive uneasiness arising from conflict detection during thinking. We investigate FOE in two studies with the “bat-and-ball” (B&B) reasoning task, in its standard and isomorphic control versions. Study 1 is a generation study, in which participants are asked to generate their own response. Study 2 is an evaluation study, in which participants are asked to choose between two conflicting answers (normative vs. intuitive). In each study, the FOE is measured by the FOE questionnaire. Results show that the FOE is significantly present in the standard B&B task when participants give a wrong answer, that our questionnaire can measure it, and furthermore, that it is diagnostic of genuine error.     

A model for 〈c+a〉 dislocation transmission across nano-spaced parallel basal stacking faults in a HCP alloy

We develop a model for recently observed 〈c + a〉 dislocation transmission across nano-spaced parallel basal stacking faults in hexagonal close-packed (HCP) Mg microcrystalline grains. The model theoretically predicts nanospace-dependent yield strength that is in good agreement with experimental data. Additionally, it theoretically predicts activation volume and strain rate sensitivity.     

Dynamic properties of edge dislocations decorated by interstitial loops in α-iron and copper

Clusters of self-interstitial atoms (SIAs) in the form of parallel crowdions are created directly in high-energy displacement cascades produced in metals by neutron irradiation. They are equivalent to small perfect dislocation loops and, in isolation in pure metals, undergo fast thermally-activated glide in the direction of their Burgers vector. Their strain field and ability to glide allows long-range interaction with other extended defects. Indeed, dislocations decorated by dislocation loops are commonly observed after neutron irradiation. Dislocations gliding under applied stress also encounter these mobile defects. These effects influence mechanical properties and require further investigation. This paper presents results from an atomic-scale study of copper and α-iron at either 0?K or 300?K. Loop drag and breakaway effects are investigated for an edge dislocation under applied stress interacting with a row of SIA loops below its glide plane. The maximum speed at which a loop is dragged is lower in copper than iron, and the applied stress at which this occurs is also lower. These differences in the dynamics of cluster-dislocation interaction are determined by the atomic structure of the defects and cannot be investigated by continuum treatment.