Determination of the nature of stacking-fault tetrahedra in electron-irradiated silver by high-resolution structural imaging

Abstract

High-resolution structural imaging has been used to show that the great majority of stacking-fault tetrahedra produced in thin foils of electron-irradiated silver are of vacancy nature.     

Dislocation dissociation and stacking-fault energies in Ge1-xSix alloys

Dislocations in deformed Ge_1-xSi_x alloys in the whole range 0 < x < 1 have been investigated by means of weak-beam transmission electron microscopy. They are dissociated into Shockley partial dislocations bounding intrinsic stacking-faults. The intrinsic stacking-fault energy in the alloys decreases from 61 +/- 10 to 55 +/- 10 mJm^-2 with increasing Si content.     

Observation of a novel stacking-fault nucleation mechanism in melt-textured YBa2Cu3O7

The dislocation substructure of melt-textured YBa₂Cu₃O₇-Y2BaCuO₅ composites deformed under uniaxial compressive stress and a superposed gaseous confining pressure has been investigated by transmission electron microscopy. Observations reveal the generation of perfect dislocations in (001) as well as out of this plane. Screw segments of the latter lying on (001) are seen to act as Frank-Read sources for ? 〈301〉 partials bounding YBa₂Cu₄O₈-type stacking faults, according to a mechanism previously anticipated from theoretical considerations by one of the present authors.     

Dynamic formation and destruction process of stacking fault tetrahedra in single-crystal Ni during nanoscale cryo-rolling

Stacking fault tetrahedra (SFTs) are known to form during the rolling process of face-centered cubic metals and to deteriorate their structural properties. However, the atomistic mechanism of formation and destruction of SFTs during such material processing is still unclear. We have performed molecular dynamics simulations of the nanoscale cryo-rolling process for single-crystal nickel and here report the mechanism behind the formation and collapse of SFTs. It is found that SFTs are formed through dissociation of Shockley partial dislocation loops in the specimen. On the other hand, destruction of SFTs occurs under compressive stress and follows an inverse Silcox-Hirsch mechanism.     

The production of nominal compounds in aphasia

This study reports the difficulties of aphasic patients in producing nominal compounds in German. In a picture naming task with semantically relatively transparent targets it was found that the word frequency of the components determined the accuracy of the patients' performance. A second picture naming task using relatively opaque targets, and a further naming task in which patients were confronted with aurally presented object paraphrases using very opaque targets, are reported. The error patterns of all three tasks give evidence for morpheme-based mis-productions (e.g., componential substitutions), however, in declining proportions with decreasing semantic transparency. Access to final (or basic) components was clearly superior to initial (or determinative) components suggesting position-specific access routines.     

The role of scheduling in learning through observation

In the 2 experiments reported in the present article, participants (N = 40, Experiment 1; N = 60, Experiment 2) learned to solve complex puzzles under different schedules of physical practice, observation, or a combination of the two. The results of both studies indicated that observation, in the absence of any physical practice, allows the development of an accurate but relatively nonfunctional cognitive representation. The data suggest that, even when the motor demands are minimal, the functional significance of the cognitive representation is not maximally realized until physical interaction with the task is possible. Thus, providing the participant with an interspersed practice schedule during acquisition enables that interaction to occur, thereby allowing the absolute number of physical practice trials to be reduced and replaced by observation trials, but leading to equivalent learning.     

The value of infant observation in the psychoanalytic training

The following case report is an attempt to describe how infant-mother observation is an exercise in a psychoanalytic mode of thinking and reacting, developing knowledge of object-relation theory. The aim of infant observation is not therapeutic; however, this paper suggests that it also might have a therapeutic side effect, creating mental space for the mother and thereby, helping her from becoming too engulfed by the intensive needs of the baby.     

The role of memory for compounds in cue competition

Revisions of common associative learning models incorporate a within-compound association mechanism in order to explain retrospective cue competition effects (e.g., [Dickinson, A., & Burke, J. (1996). Within-compound associations mediate the retrospective revaluation of causality judgements. Quarterly Journal of Experimental Psychology, 49B, pp. 60-80.]). These models predict a correlation between memory for compounds (as a measure for the strength of within-compound associations) and retrospective cue competition but not forward cue competition. This was indeed found in a study of [Melchers, K. G., Lachnit, H., & Shanks, D. (2004). Within-compound associations in retrospective revaluation and in direct learning: A challenge for comparator theory. Quarterly Journal of Experimental Psychology, 57B, pp. 25-54.]. We argue that a higher-order reasoning account of causal learning can also explain the evidence for the role of within-compound associations in cue competition. Moreover, this account predicts that if making inferences during the learning stage is impeded, a correlation between memory for compounds and forward cue competition should be found as well. The results of a new study confirmed this prediction.     

The emergence of conditioned reinforcement from observation

We report an experiment in which observations of peers by six 3-5-year-old participants under specific conditions functioned to convert a small plastic disc or, for one participant, a small piece of string, from a nonreinforcer to a reinforcer. Prior to the observational procedure, we compared each participant's responding on (a) previously acquired performance tasks in which the child received either a preferred food item or the disc (string) for correct responses, and (b) the acquisition of new repertoires in which the disc (string) was the consequence for correct responses. Verbal corrections followed incorrect responses in the latter tasks. The results showed that discs and strings did not reinforce correct responses in the performance tasks, but the food items did; nor did the discs and strings reinforce correct responses in learning new repertoires. We then introduced the peer observation condition in which participants engaged in a different performance task in the presence of a peer who also performed the task. A partition blocked the participants from seeing the peers' performance. However, participants could observe peers receiving discs or strings. Participants did not receive discs or strings regardless of their performance. Peer observation continued until the participants either requested discs or strings repeatedly, or attempted to take discs or strings from the peers. Following the peer observation condition, the same performance and acquisition tasks in which participants had engaged prior to observation were repeated. The results showed that the discs and strings now reinforced correct responding for both performance and acquisition for all participants. We discuss the results with reference to research involving nonhuman subjects that demonstrated the observational conditioning of reinforcers.     

The role of analogy in the interpretation of novel compounds

It was investigated whether the on-line interpretative processing of novel nominal compounds is affected by analogous lexicalized compounds. In Experiment 1, novel compounds were presented as nonwords in a lexical decision task. Constituent nouns of novel compounds were of high or low productivity as measured by the number of lexicalized compounds of which they were part. Effects of productivity and of compound interpretability on decision latencies were found to be additive, suggesting that the activated lexicalized compounds do not contribute to the interpretation of novel compounds. In Experiment 2, a semantic priming paradigm was used in a lexical decision task. Lexicalized compounds were presented as targets and novel compounds as primes. Second nouns of lexicalized and novel compounds were identical and first nouns of the two types of compounds were semantically related. Target compounds differed in frequency. Equal priming effects were obtained for high- and low-frequency target compounds, indicating that novel compounds do not activate more strongly the most similar lexicalized compound. The role of analogous interpretative processing is considered in the context of alternative models for the interpretation of novel compounds.     

The interpretation of isolated novel nominal compounds

The lexical decision task was used to investigate interpretative processing of isolated novel compounds (noun-noun nominals). On the basis of interpretability ratings, novel compounds were classified as being of either high or low interpretability. In a lexical decision task in which novel compounds functioned as nonwords, a significant interference effect was found for compounds of high interpretability. In a naming task, no differences were found between the two types of novel compounds, but lexicalized compounds resulted in shorter latencies than did novel compounds. Novel compounds were also shown to be interpreted under conditions unfavorable to morphological decomposition, suggesting that the interpretation process is beyond strategic control by the subject. Equal semantic priming effects were obtained for members of established semantic categories and nouns of highly interpretable compounds. Interpretative processes dealing with a limited set of basic semantic relations and analogy with lexicalized compounds are discussed.     

The home observation assessment method (HOAM): real-time naturalistic observation of families in their homes.

The Home Observation Assessment Method (HOAM) is a new method developed to carry out objective coding of family interaction over extended time periods in a home setting. It is a computer-compatible coding system that permits on-line data reduction of interactional variables emphasizing contextual and structural dimensions of family behavior. To date, the HOAM has been applied to the study of 31 families observed for a total of over 250 sessions. Initial analysis of data from these sessions indicates that coder reliability is high and that the HOAM successfully measures dimensions of family behavior independent of architectural aspects of the home setting. Preliminary findings also indicate that although families differ dramatically along the interactional dimensions measured by the HOAM, all families studied spent remarkably little time in decision-making behavior, suggesting that behavior in the home is predominantly "maintenance-oriented."     

The role of knowledge of results frequency in learning through observation

The authors examined whether reduced knowledge of results (KR) frequency during observation of a model's performance enhances learning. As they viewed a timing task, observers (n = 54) received KR about the model's performance on each trial (100% KR) or on 1 out of 3 trials (33% KR). Controls (n = 18) received only physical practice; they did not take part in the observation session. The authors also wanted to dissociate the guidance effect of KR during physical practice from the guidance role played by the representation acquired during observation. Therefore, following the observation phase, participants physically performed the task with either the same or a different KR frequency than that experienced during observation. The effects of observation and physical practice on learning were assessed in delayed retention tests. The beneficial effect of reduced KR frequency during observation continued for the following physical practice phases. Possible explanations as to why KR influences observational learning are discussed.     

The role of typological variation in the processing of interfixed compounds

This study investigates the processing of interfixed compounds within a primed lexical decision paradigm. Results from an experiment on German are compared with those from a previous study on Greek and Polish, demonstrating that patterns of morphological priming in German differ from those obtained in the other two languages. In all experiments compounds were primed by initial morphemes with and without the interfix. In Greek and Polish priming was significantly facilitated in cases where the mophological prime was homophonous with a real word. In German, however, the effect of wordness was found for un-interfixed but not for interfixed primes. Our data suggest that patterns of morphological priming for a given structure may not be generalizable to analogous structures in other languages without a consideration of language-specific morphological properties.     

Theory and observation: The experimental nexus

Philosophical discussions of experiment usually focus exclusively on testing predictions. In this paper I compare G. Morpurgo's experimental test of the Gell‐Mann/ Zweig quark hypothesis with two neglected uses of experiment: constructing representations of new phenomena and inventing the instruments that produce such phenomena. These roles are illustrated by J. B. Biot's 1821 observations of electromagnetism and by Michael Faraday's invention of the first electromagnetic motor, also in 1821. The comparison identifies similarities between observation and experiment, showing how both observation and experiment actively engage the natural world and how each engagement shapes representation and subsequent empirical work. This challenges the post‐empiricist assumption of the sufficiency of knowing only the outcomes of experiments. I conclude that traditional views of observational access have looked in the wrong place for empirical constraints on theorizing. The active character of observation implies that a realist interpretation of experimenters’ discourse should be grounded in the fine structure of experimental practice rather than the supposedly decisive, golden events favoured by hypothetico‐deductive methodology.