Dipole of misfit dislocations in axially symmetric structures

The nucleation of a pair of misfit dislocations of Burgers vectors b 1 and b 2 with b 1 + b 2 = 0 has been studied for the case of an axially symmetric two-phase structure. Considering a cylindrical inclusion epitaxially stressed in a unbounded matrix, the variation in the total energy due to the formation of the dipole has first been determined as a function of the radius of the inclusion and the epitaxial stress. The conditions for nucleation of the dipole on the interface have then been investigated as a function of the ratio of the shear modulus and of the misfit stress.     

Precipitation of niobium carbonitrides in ferrite: chemical composition measurements and thermodynamic modelling

High-resolution transmission electron microscopy and electron-energy loss spectroscopy have been used to characterize the structure and chemical composition of niobium carbonitrides in the ferrite of a Fe–Nb–C–N model alloy at different precipitation stages. Experiments seem to indicate the coexistence of two types of precipitates: pure niobium nitrides and mixed sub-stoichiometric niobium carbonitrides. In order to understand the chemical composition of these precipitates, a thermodynamic formalism has been developed to evaluate the nucleation and growth rates (classical nucleation theory) and the chemical composition of nuclei and existing precipitates. A model based on the numerical solution of thermodynamic and kinetic equations is used to compute the evolution of the precipitate size distribution at a given temperature. The predicted compositions are in very good agreement with experimental results.     

Temperature dependence of nucleation rate in a binary solid solution

The influence of regression (partial dissolution) effects on the temperature dependence of nucleation rate in a binary solid solution has been studied theoretically. The results of the analysis are compared with the predictions of the simplest Volmer–Weber theory. Regression effects are shown to have a strong influence on the shape of the curve of nucleation rate versus temperature. The temperature T_M at which the maximum rate of nucleation occurs is found to be lowered, particularly for low interfacial energy (coherent precipitation) and high-mobility species (e.g. interstitial atoms).     

Identification of crystal nucleation and growth in an amorphous FeZr2 alloy by means of electrical resistance measurements

A polymorphous crystallization process in an amorphous FeZr₂ alloy has been investigated by means of accurate electrical resistance measurements (ERMs) at elevated temperatures. It was found that, upon crystallization of the amorphous alloy, the electrical resistance increased with increasing temperature, exhibiting three distinct stages. Quantitative microscopy observations revealed that the three stages originated from crystal nucleation, from subsequent growth of crystal nuclei and from coarsening of the crystallites respectively. The activation energies for the crystal nucleation and growth determined from the ERM data agree satisfactorily with the data in the literature. The success in identification of the crystal nucleation and growth processes by means of ERMs may originate from differences in electrical resistance changes due to the crystal formation and the crystalline-amorphous interface formation processes from the amorphous phase.     

The history of imitation in learning theory: the language acquisition process

The concept of imitation has undergone different analyses in the hands of different learning theorists throughout the history of psychology. From Thorndike's connectionism to Pavlov's classical conditioning, Hull's monistic theory, Mowrer's two-factor theory, and Skinner's operant theory, there have been several divergent accounts of the conditions that produce imitation and the conditions under which imitation itself may facilitate language acquisition. In tracing the roots of the concept of imitation in the history of learning theory, the authors conclude that generalized imitation, as defined and analyzed by operant learning theorists, is a sufficiently robust formulation of learned imitation to facilitate a behavior-analytic account of first-language acquisition.     

Do new Ethical Issues Arise at Each Stage of Nanotechnological Development?

The literature concerning ethical issues associated with nanotechnologies has become prolific. However, it has been claimed that ethical problems are only at stake with rather sophisticated nanotechnologies such as active nanostructures, integrated nanosystems and heterogeneous molecular nanosystems, whereas more basic nanotechnologies such as passive nanostructures mainly pose technical difficulties. In this paper I argue that fundamental ethical issues are already at stake with this more basic kind of nanotechnologies and that ethics impacts every kind of nanotechnologies, already from the simplest kind of engineered nanoproducts. These ethical issues are mainly associated with the social desirability of nanotechnologies, with the difficulties to define nanotechnologies properly, with the important uncertainties surrounding nanotechnologies, with the threat of ‘nano-divide’, and with nanotechnology as ‘dual-use technology’.     

Homogeneous nucleation of dislocation loops under stress in perfect crystals

We present an analysis and results on the homogeneous nucleation of a dislocation loop under stress in a perfect crystal. By using a variational boundary integral method in the Peierls-Nabarro framework, we have determined the saddle-point configurations of embryonic dislocation loops and their associated activation energies under stress levels up to the ideal shear strength. The high-energy barriers under the usual levels of applied shear stresses, differing markedly from the ideal shear strength, confirm the widely held view that thermal motion should play no role in such nucleation. The result provides means for more definitive solutions of fundamental problems involving homogeneous nucleation of dislocation loops and has significant implications for models based on the mechanism of nucleation of dislocations from a perfect crystal.     

The kinetic limit of superheating induced by semicoherent interfaces

The superheating behaviour of embedded particles induced by semicoherent interfaces has been observed in many circumstances. In this paper, a phenomeno‐ logical model for melt nucleation on misfit dislocations at a semicoherent interface is proposed. A kinetic limit for semicoherent-interface-induced superheating, which is in good agreement with the results of experiments and computer simulations, is derived from this model. Calculations and analyses based on the model reveal that melting prefers to initiate at the semicoherent interface and that superheating of embedded particles is possible for a melt nucleation contact angle less than 90°. Among the matrix-dependent parameters, the contact angle and the shear modulus of the matrix are found to be dominant in determining the superheating of embedded particles.     

A novel method for measurement of electronic work function of micro/nanostructure materials using a Kelvin probe system

Work function (WF) can be measured using the Kelvin probe (KP) technique to characterize surface behavior of micro/nanostructures grown on substrates such as metals or semiconductors. However, for such micro/nanostructures, substrates with different WF can strongly affect the measurements if they are exposed directly to face the Kevin probe tip. In this article, a model is proposed to investigate the WF of sparse ZnO nanorods grown on an Si substrate. It is demonstrated that theoretical results from the model are consistent with experimental observations performed using a KP system.     

Minority Influence,Social Change,and Social Stability

From Moscovici (Social influence and social change. London, Academic Press; 1976) on, a growing body of research on minority influence has been conducted within the social psychology mainstream. A general guideline of most of the research on this topic associates minority influence with social change and innovation. Minorities have been considered as challengers to social stability, and their dynamics have been considered in relation to the mechanisms through which social changes occur and established norms are modified and evolve in human society. In the present paper, we try to extend this viewpoint by suggesting that it represents only one side of a much more complex story. We consider the conditions under which minorities produce social change as well as the conditions under which they are, instead, inclined to defend the status quo. We then suggest that an integrative account of different approaches – namely, social identity, social dominance, and system justification – might contribute to expanding the theoretical frame of minority influence.     

The perception of speech rate from the sound-silence patterns of monologues

Two experiments asked whether listeners can judge word rate from a speech signal that has been degraded in various ways. In the first, the rates of spontaneous speech were increased by 42% and further transformed to produce tone-silence sequences. The tonesilence sequences were presented to listeners who judged the rate of each sequence. Results clearly indicated that listeners could differentiate the rates of the tone-silence sequences, suggesting that minimal nonlinguistic information may be sufficient to make grossly accurate estimates of speech rates. In the second study, listeners were presented with speech sequences involving three naturally produced rates (slow, moderate, and fast) in three conditions (clear, frequency-inverted, and tone-silence) such that different listeners participated in the three conditions, but heard all rates in each condition. Listeners in the clear and frequency-inverted conditions distinguished all three rates, but those in the tone-silence condition differentiated only the slow and moderate rates. Contrary to expectation, the gender and extroversion scores of the listeners did not affect their judgments.     

Oculomotor control and the maintenance of spatially and temporally distributed events in visuo-spatial working memory

Previous studies have demonstrated that working memory for spatial location can be significantly disrupted by concurrent eye or limb movement (Baddeley, 1986; Smyth, Pearson, & Pendleton, 1988). Shifts in attention alone can also interfere with spatial span (Smyth & Scholey, 1994), even with no corresponding movement of the eyes or limbs (Smyth, 1996). What is not clear from these studies is how comparable is the magnitude of effect caused by different forms of spatial disrupter. Recently, it has been demonstrated that limb movements produce as much interference with spatial span as do reflexive saccades (Lawrence, Myerson, Oonk, & Abrams, 2001). In turn this has led to the hypothesis that all spatially directed movement can produce similar effects in visuo-spatial working memory. This paper reports the results of five experiments that have contrasted the effect of concurrent eye movement, limb movement, and covert attention shifts on participants' working memory for sequences of locations. All conditions involving concurrent eye movement produced significantly greater reduction in span than equivalent limb movement or covert attention shifts with eyes fixated. It is argued that these results demonstrate a crucial role for oculomotor control processes during the rehearsal of location-specific representations in working memory.     

A new counter-example to Kelvin's conjecture on minimal surfaces

A survey of the published literature on undercooled metallic and oxide melts suggests that phase selection during solidification can be categorized as nucleation controlled or growth controlled. Common characteristics governing the phase-selection pathway have been identified for various alloy systems. It is recognized that when competing stable and metastable phases share the same crystalline characteristics and have comparable interface kinetic coefficients, the principle of nucleation control applies for primary phase formation in a deeply undercooled melt. However, there can be a difference of two or three orders of magnitude in the interface kinetic coefficients for competing phases, either between an ordered intermetallic compound and a disordered solid solution, or between a crystalline phase with a high level of complexity and a simple crystal. In such cases, the principle of growth control will apply; more specifically, the phase with the faster growth kinetics should be favoured and the competing counterpart with sluggish interface kinetics should be suppressed at high undercoolings. Some simple predictions are suggested on the basis of this principle when considering stable and metastable phase diagrams. The specific conditions under which the present categorization is applicable are outlined. Future work is required to elucidate phase competition under conditions of very rapid solidification.     

Elasticity theory of topological defects in carbon nanotubes and graphene

We develop elasticity theory to predict the energies of topological defects in carbon nanostructures. The theory is a simple, quantitatively accurate and transferable continuum approach to predicting defect formation energies that obviates the need for computationally expensive quantum mechanical methods. Thus the theory has the potential to serve as the basis for thermodynamic and multi-scale modelling of the structural properties of carbon nanostructures.     

Kinetic study of hydrogen-induced direct phase transformation in Y2Fe17 magnetic alloy on the basis of Kolmogorov’s model

The kinetics of the hydrogen induced direct phase transformation in Y₂Fe₁₇ magnetic alloy has been analysed within the framework of Kolmogorov’s kinetic model. It is established that the transformation can be classified as a diffusion-controlled transformation, which occurs by a mechanism of nucleation and growth with a decreasing nucleation rate of new phases, namely α-Fe and YH₂. A kinetic equation has been obtained that well describes the isothermal kinetic curves of the phase transformation in Y₂Fe₁₇ as a function of the transformation temperature.     

The Influence of Contraction Types on the Relationship Between the Intended Force and the Actual Force

Abstract

It has been demonstrated that the intended force (subjective estimation of force) does not always match to actual force without external feedback. The purpose of this study was to compare the influence of ballistic and tonic contractions on the relationship between the intended and actual force. Subjects produced isometric force at requested percentages of their MVC (20, 40, 60 and 80%) based on subjective estimation of force under two conditions (tonic and ballistic conditions). The tonic condition was to maintain force production, whereas the ballistic condition was to produce force as fast as possible. As a result, the actual force amplitude, the coefficient of variance and EMG amplitude were larger under the ballistic contraction compared with the tonic condition, even the same intended force levels. These results suggest that different motor unit activity and control systems in the ballistic and tonic contractions could alter the relationship between the intended force and the actual force.     

The effects of three methods of observation on couples in interactional research

Abstract

Reactivity to observation can affect both internal and external validity of experimental studies. Although the effects of observation have been well documented in groups and parent-child interaction, there have been few studies of observer effects on couples. This study assessed the effects of three different methods of observation—one-way mirror, audio-recording and video-recording—on 30 volunteer, nonclinical couples. No differences were found among couples in the three observational conditions on measures of interactional behavior on a problem-solving task, participant appraisals of self-consciousness, discomfort and reactivity for themselves and their spouses, or on pre-post observation measures of anxiety and feelings toward spouse. The results suggest that these different types of observation do not produce significantly different effects on nonclinical couples and that studies utilizing these three methods may be compared.     

Adaptation to auditory-visual discordance and ventriloquism in semirealistic situations

While “recalibration by pairing” is now generally held to be the main process responsible for adaptation to intermodal discordance, the conditions under which pairing of heteromodal data occur in spite of a discordance have not been studied systematically. The question has been explored in the case of auditory-visual discordance. Subjects pointed at auditory targets before and after exposure to auditory and visual data from sources 20° apart in azimuth, in conditions varying by (a) the degree of realism of the context, and (b) the synchronization be-tween auditory and visual data. In Experiment 1, the exposure conditions combined the sound of a percussion instrument (bongos) with either the image on a video monitor of the hands of the player (semirealistic situation) or diffuse light modulated by the sound (nonrealistic situation). Experiment 2 featured a voice and either the image of the face of the speaker or light modulated by the voice, and in both situations either sound and image were exactly syn-chronous or the sound was made to lag by 0.35 sec. Desynchronization was found to reduce adaptation significantly, while degree of realism failed to produce an effect. Answers to a question asked at the end of the testing regarding the location of the sound source suggested that the apparent fusion of the auditory and visual data—the phenomenon called “ventriloquism”— was not affected by the conditions in the same way as adaptation. In Experiment 3, subjects were exposed to the experimental conditions of Experiment 2 and were asked to report their impressions of fusion by pressing a key. The results contribute to the suggestion that pairing of registered auditory and visual locations, the hypothetical process at the basis of recalibration, may be a different phenomenon from conscious fusion.     

Some evidence for 'speech' as an acoustic feature.

Under conditions of serial recall of auditorily presented lists of digits, recall of the last item has been shown to be adversely affected by the presence of a redundant item following the list. This is known as 'the suffix effect' (Crowder & Morton, 1969). In a series of experiments it is shown that the size of this effect is not influenced by the phonological complexity of the suffix. Non-speech sounds, on the other hand, produce no suffix effect even when the subjects are forced to process them. Certain speech sounds were also found to produce no effect. It is concluded that these sounds lacked properties which are characteristic of speech sounds and so were classified as 'non-speech' and that as a result, these sounds are processed by a separate system from the speech sounds.     

Performance in free recall following rupture and repair of intracranial aneurysm

There have been many reports of global memory disorder following rupture and repair of intracranial aneurysms. These reports suggest a more anterior basis for the amnesic syndrome than the various sites in the diencephalon and the temporal lobe that have so far been implicated. Patients from a consecutive series of 76 cases of aneurysmal subarachnoid hemorrhage demonstrated a moderate deficit in free recall, but aneurysms at different sites within the cerebrovascular system did not produce significantly different degrees of impairment. The results are consistent with the idea that aneurysmal subarachnoid hemorrhage gives rise to diffuse cerebral damage, and do not necessitate any revision of conventionally accepted accounts of the neuropathology of amnesic conditions.