Density evolution during the growth of disc-shaped aluminium nanoparticles on a liquid surface

Aluminium (Al) nanoparticles (NPs) have been successfully fabricated on a liquid surface by thermal evaporation at room temperature. The Al NPs exhibit a disc-shaped morphology with mean diameter and height in the ranges 20–35 and 1.3–3.7?nm, respectively. As the nominal film thickness increases from 0.02 to 0.18?nm, the mean diameter and height are nearly independent of the thickness, implying that the density of the NPs increases during their growth. An explanation for this phenomenon is presented.     

Elastic solutions with arbitrary elastic inhomogeneity and anisotropy

An efficient numerical algorithm is proposed to accurately compute the elastic fields in two-dimensional (2D) or three-dimensional (3D) microstructures with arbitrary elastic inhomogeneity and anisotropy. It combines the equivalent inclusion method of Eshelby, the microelasticity theory of Khachaturyan, and the spectral iterative perturbation method of Hu and Chen. Its efficiency is compared with those of existing approaches in the literature. The method can be conveniently implemented in phase-field modeling of stress-dependent microstructure evolution and/or of mass/electrical transport.     

Posture-movement responses to stance perturbations and upper limb fatigue during a repetitive pointing task

Localized muscle fatigue and postural perturbation have separately been shown to alter whole-body movement but little is known about how humans respond when subjected to both factors combined. Here we sought to quantify the kinematics of postural control and repetitive upper limb movement during standing surface perturbations and in the presence of fatigue. Subjects stood on a motion-based platform and repetitively reached between two shoulder-height targets until noticeably fatigued (rating of perceived exertion = 8/10). Every minute, subjects experienced a posterior and an anterior platform translation while reaching to the distal target. Outcomes were compared prior to and with fatigue (first vs. final minute data). When fatigued, regardless of the perturbation condition, subjects decreased their shoulder abduction and increased contralateral trunk flexion, a strategy that may relieve the load on the fatiguing upper limb musculature. During perturbations, kinematic adaptations emerged across the trunk and arm to preserve task performance. In contrast to our expectation, the kinematic response to the perturbations did not alter in the presence of fatigue. Kinematic adaptations in response to the perturbation predominantly occurred in the direction of the reach whereas fatigue adaptations occurred orthogonal to the reach. These findings suggest that during repetitive reaching, fatigue and postural perturbation compensations organize so as to minimize interaction with each other and preserve the global task characteristics of endpoint motion.     

Do commodities reproduce themselves through human beings? Toward an ecology of goods

The argument of this paper—'an ecology of goods'—could be summarized as follows: Goods exist only in relation to each other. Goods form groups, and in time higher organizational levels, groups of groups, i.e. networks of artifacts emerge. Mass consumption society is the most developed manifestation of this organizing process. The process of association and dissociation of goods is only partly controllable through human decisions. Human beings making decisions about buying, using and disposing of goods are constrained by the “logic” of the general organizing process. This process emerges out of different kinds interactions between commodities and feedback cycles with unintended consequences. In routinization and institutionalization processes commodity interactions become stabilized, i.e. the fidelity of replicative cycles increases. From this perspective, a system of commodities could be seen as an entity, which reproduces itself in a continuous resource exchange with its co‐actors and environment. In a system there is both a tendency toward functional differentiation and integration with other systems. Accordingly, systems of goods are cyclic processes within processes rather than given stable entities. This approach places many theoretical and practical problems of consumer society in a new perspective.     

Personality,Parental, and Media Influences on Aggressive Personality and Violent Crime in Young Adults

Debate remains regarding the interaction between predictor variables for aggression, including family environment, media violence, and personality. The current study examined the contributions of gender and personality, exposure to physical abuse and violence in the family, and exposure to media violence in both television and in video games on violent criminal activity. Data from young adults (n = 355) indicated that personality characteristics and direct physical abuse significantly predicted violent crime. Exposure to television and video game violence were not significant predictors of violent crime. These results elucidate the complex interplay between multiple factors related to the etiology of violent crime. These results also call into question the belief that media violence is involved in the etiology of violent crime.     

When seeking influences believing and promotes posttraumatic adaptation

Background: Theory and evidence link social support processes and self-efficacy appraisals in the promotion of adaptation following traumatic events. Dynamic causal processes, however, have not been examined longitudinally or in the context of mass-violence. This study tested whether quantity of social support seeking indirectly reduced distress severity among student survivors of mass university shootings. Hypotheses specified that the indirect effects of social support seeking on distress severity would occur through positively influencing perceived social support and self-efficacy, and that these effects would emerge and become stronger as posttraumatic stress symptom severity increased. Design: Path analysis via Mplus 7.2 was used to test the hypothesized moderated-serial-mediation model (conditional indirect effects). Methods: The sample (N = 1191) consisted of students enrolled at Virginia Tech during the 16 April 2007 shootings. Data were collected via online surveys at two time points, 3–4 months and 1-year post-shootings. Results: Hypotheses were supported, showing that the indirect effects of social support seeking on distress reduction occurred through perceived social support, which in turn influenced self-efficacy. These effects emerged and grew in strength as PTS severity increased. Conclusions: Clinical implications, including the need to consider contextual determinants of posttraumatic recovery, are discussed.     

Changes in Limb Stiffness Under Conditions of Mental Stress

In 2 experiments, the effects of mental stress on limb stiffness were investigated. The relative contribution to arm stiffness of individual muscle activity, co-contraction, muscle reflexes, and postural adjustments were examined. In each experiment, participants (N = 24, Experiment 1; N = 16, Experiment 2) held their supinated hand under a tray that they were required to return to horizontal after it had been suddenly released. Electromyographic activity in the biceps and triceps muscles was recorded, as were elbow and wrist angles and tray displacement. In Experiment 1, mental arithmetic stress was shown to lead to decreased tray displacement (i.e., increased resistance) compared with displacements under the control, unstressed condition, as well as to increased elbow flexion before tray release. In Experiment 2, the increased resistance to perturbation caused by mental stress was found to be independent of initial elbow angle, but to vary as a function of the amount of upward force exerted before tray release. The authors conclude that stress-induced increases in limb stiffness result from changes in the initial position of the elbow, specified by its angle, together with the initial force exerted by participants to counteract the mechanical perturbations.     

Haptic and Visual Influences on Grasp Point Selection

When using precision grip to pick up objects, there are many possible pairs of grasp points that permit the thumb and index finger to exert opposed forces for secure grip. Previously, it was shown that individuals select grasp points so that the line between them (grasp axis) passes through or near the center of mass (CoM), thus minimizing the torque around the grasp axis during lifting. The accuracy of grasp axis selection depended on object spatial symmetry, indicating the importance of vision. The authors investigated how grasp point selection is influenced by haptic as well as visual information. Ten participants lifted cuboids whose CoM was located either symmetrically in the geometric center or asymmetrically toward one end. Results for the asymmetric cuboid revealed that grasp points migrated toward the asymmetric CoM from the geometric center. This was more pronounced in the presence of visual cues that reliably indicated the location of CoM. The results suggest that grasp point selection is influenced by a multimodal representation of CoM.     

The Use of Location and Distance in Reproducing Different Amplitudes of Movement

Experiments have demonstrated that in order to reproduce a standard movement, subjects can move for a certain distance or move to a certain location. Available evidence tentatively suggests the use of distance for short movements and location for long movements. However, this evidence is in conflict with the motor short-term memory characteristics of short and long movements. An experiment is reported which demonstrates that subjects spontaneously use distance for short movements and location for long movements, the procedure adopted being to shift by small amounts the starting-point of the estimation movements and test for a consequent shift in the end-point of the estimation. The experiment also revealed that using distance or location to reproduce a 40° movement resulted in equal accuracy, suggesting that the use of large amplitudes of movement has caused previous investigators to find that distance is less accurate than location.     

Comparing Online Adjustments to Distance and Direction in Fast Pointing Movements

It has been suggested that movements are planned in terms of direction and distance. If so, online adjustments to changes in the direction and distance of the movements may also differ. The authors therefore investigated whether fast online movement adjustments are the same for perturbations of the direction and of the distance. While subjects made fast pointing movements, the authors perturbed either target direction or distance or both shortly after movement initiation. Both kinds of perturbations resulted in accurate online adjustments. The latency and intensity of corrections for distance and direction perturbations were quite similar. This suggests that there might be one mechanism controlling both distance and direction perturbations.