Pressure-Induced transitions in amorphous TlxSe100−x alloys

Abstract

The electrical resistivity of bulk semiconducting amorphous Tl_xSe_100?x alloys with 0 ≤ x ≤ 25 has been investigated up to a pressure of 14 GPa and down to liquidnitrogen temperature by use of a Bridgman anvil device. All the glasses undergo a discontinuous pressure-induced semiconducting-to-metal transition. X-ray diffraction studies on the pressure-recovered samples show that the high-pressure phase is the crystalline phase. The pressure-induced crystalline products are identified to be a mixture of Se having a hexagonal structure with a = 4·37 Å and c = 4·95 Å and TlSe having a tetragonal structure with a = 8·0 Å and c = 7·0 Å     

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.     

Reaction of a Ni-coated Al nanoparticle to form B2-NiAl: A molecular dynamics study

The kinetic reaction in a Ni-coated Al nanoparticle with equi-atomic fractions and diameter of approximately 4.5 nm is studied by means of molecular dynamics simulation, using a potential of the embedded atom type to model the interatomic interactions. First, the large driving force for the alloying of Ni and Al initiates solid state amorphization of the nanoparticle with the formation of Ni₅₀Al₅₀ amorphous alloy. Amorphization makes intermixing of the components much easier compared to the crystalline state. The average rate of penetration of Ni atoms can be estimated to be about two times higher than Al atoms, whilst the total rate of inter-penetration can be estimated to be of the order of 10^?2 m/s. The heat of the intermixing with the formation of Ni₅₀Al₅₀ amorphous alloy can be estimated at approximately ?0.34 eV/at. Next, the crystallization of the Ni₅₀Al₅₀ amorphous alloy into B2-NiAl ordered crystal structure is observed. The heat of the crystallization can be estimated as approximately ?0.08 eV/at. Then, the B2-NiAl ordered nanoparticle melts at a temperature of approximately 1500 K. It is shown that, for the alloying reaction in the initial Ni-coated Al nanoparticle, the ignition temperature can be as low as approximately 200 K, while the adiabatic temperature for the reaction is below the melting temperature of the nanoparticle with the B2-NiAl ordered structure.     

Mass Perturbation of a Body Segment: I. Effects on Segment Dynamics

Investigators often use mass perturbation of body segments as an experimental paradigm to study movement coordination. To analyze the effect of mass perturbation on small-amplitude oscillations, the authors linearize the equation of motion of a single segment moving in a vertical plane and derive the effect of added mass on the undamped eigenfrequency, the relative damping, and the low-frequency control gain of the segment. Mass addition results in a decrease in both the relative damping and the low-frequency control gain; the undamped eigenfrequency increases for mass addition between the pivot point and R₀ (where R₀ is the length of a point mass pendulum whose undamped eigenfrequency is identical to that of the unperturbed segment), decreases for mass addition beyond R₀, and remains unaffected for mass addition at R₀. For a typical lower leg + foot segment, R₀ is just proximal to the ankle joint. That location may explain the absence of an effect on oscillation frequency in studies in which mass has been added to the ankle. The authors' analysis provides a basis for a more effective application of mass perturbations in future experiments.     

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking

This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45°), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints—the intrinsic limb dynamics—in creating coordinated limb behavior out of nonspecific muscle activations.     

Interference Effects in Learning Similar Sequences of Discrete Movements

Three experiments were conducted to examine proactive and retroactive interference effects in learning 2 similar sequences of discrete movements. In each experiment, the participants in the experimental group practiced 2 movement sequences on consecutive days (1 on each day, order counterbalanced across participants) followed by retention tests on the third day. In all, 2 out of 8 target locations differed between the 2 sequences. Experiment 1 established the nature of the interference effects in the present setup. Clear evidence was found for button-specific proactive and retroactive interference effects. Experiments 2 and 3 further probed the mechanisms underlying those effects, by varying the numbers of repetitions (50 or 250) of the 1st and 2nd sequence (Experiment 2) and the hand, dominant or nondominant, with which the sequences were practiced (Experiment 3). Experiment 2 showed that after a mere 50 repetitions, the representation of the movement structure was strong enough to evoke the effects observed in Experiment 1. Experiment 3 revealed that learning with the dominant hand did not result in more pronounced interference effects compared with learning with the nondominant hand. In combination, these results suggest that changes in the representation of the movement structure are primarily responsible for the observed interference effects.     

Sexual identity and choice of sexual object: From bisexuality to implicate order

Abstract

Stensson J. Sexual Identity and Choice of Sexual Object: From Bisexuality to Implicate Order. Int Forum Psychoanal 1992; 1:93-97. Stockholm. ISSN 0803-706 X

Freud's concept of bisexuality leads to contradictory consequences. Seeing choice of sexual object in the light of unconscious primal phantasies as coding systems, unfolds new possibilities. Taking the primal scene phantasy as a preconceptual code for mature sexuality, I make a limited and preliminary attempt to outline some possible outcomes of interactions between primal scene and oral phantasies, taking help from the theoretical physicist David Bohm's ideas on implicate order.     

Gamma- and theta-band synchronization during semantic priming reflect local and long-range lexical–semantic networks

Anterior and posterior brain areas are involved in the storage and retrieval of semantic representations, but it is not known how these areas dynamically interact during semantic processing. We hypothesized that long-range theta-band coherence would reflect coupling of these areas and examined the oscillatory dynamics of lexical–semantic processing using a semantic priming paradigm with a delayed letter-search task while recording subjects’ EEG. Time–frequency analysis revealed facilitation of semantic processing for Related compared to Unrelated conditions, which resulted in a reduced N400 and reduced gamma power from 150 to 450 ms. Moreover, we observed greater anterior–posterior theta coherence for Unrelated compared to Related conditions over the time windows 150–425 ms and 600–900 ms. We suggest that while gamma power reflects activation of local functional networks supporting semantic representations, theta coherence indicates dynamic coupling of anterior and posterior areas for retrieval and post-retrieval processing and possibly an interaction between semantic relatedness and working memory.     

Where the division lies: Common ingroup identity moderates the cross-race facial-recognition effect

This research investigated the hypothesis that better recognition for own-race than other-race faces is a result of social categorization rather than perceptual expertise. More specifically, we explored how the salience of race or university group boundaries would affect recall of faces. Using a modified facial recognition paradigm, on each trial eight Black and White faces were spatially organized either by race or university affiliation to induce categorization primarily based on one of these dimensions. When grouped by race, participants had superior recall for own-race faces and university affiliation had no effect. When grouped by university, participants had superior recall for own-university faces and race had no effect. Using identical stimuli across conditions, recall was superior for ingroup targets on the experimentally induced dimension of categorization, supportive of a social categorization based explanation of the cross-race effect.