Magnetic-field effects in defect-controlled ferromagnetic Ga_{1-x}Mn_xAs semiconductors

We have studied the magnetic-field and concentration dependences of the magnetizations of the hole and Mn subsystems in diluted ferromagnetic semiconductor Ga_{1-x}Mn_xAs. A mean-field approximation to the hole-mediated interaction is used, in which the hole concentration p(x) is parametrized in terms of a fitting (of the hole effective mass and hole/local moment coupling) to experimental data on the Tc critical temperature. The dependence of the magnetizations with x, for a given temperature, presents a sharply peaked structure, with maxima increasing with applied magnetic field, which indicates that application to diluted-magnetic-semiconductor devices would require quality-control of the Mn-doping composition. We also compare various experimental data for Tc(x) and p(x) on different Ga_{1-x}Mn_xAs samples and stress the need of further detailed experimental work to assure that the experimental measurements are reproducible.Comment: RevTeX 4, 3 two-column pages, 4 colour figures; to appear in J Appl Phy

Front crawl arm stroke trajectories of physically impaired swimmers: A preliminary study

© 2019 Elsevier Masson SAS. Introduction: This study evaluated three-dimensional kinematic parameters of the front crawl stroke in physically impaired swimmers across a range of functional classification levels. Facts and Results: Eight highly-trained competitive swimmers (5 male and 3 female) from IPC classes S5 to S9 performed 50 m maximal front crawl trials while being video-taped by six cameras (four under- and two above water). The most distal point of the right upper limb was manually digitised at 50 Hz to allow three-dimensional reconstruction of the limb's trajectory through the water. Conclusion: The stroke presented large inter-swimmer variability, reflecting individual characteristics and severity of the impairment. The swimmers who combined shallow and narrow stroke movements produced a shorter trajectory. This study provides swimmers and coaches with an overview of the kinematic characteristics of a range of physically impaired swimmers

Physical properties of a generalized model of multilayer adsorption of dimers

This article investigates the physical and statistical properties of two-dimensional structures obtained with a dimer packing model, which may be of great interest in other scientific and technological areas besides theoretical physics. The study is based on extensive computer simulations in order to examine the effect of the orientational anisotropy of dimers deposited following a ballistic deposition process, leading to multilayer networks of complex morphologies dominated by branched fractal architectures. The geometric characteristics of the bulk and contours of these systems, and the transport properties, particularly the electrical conductivity were investigated by varying the orientational anisotropy of the dimers. The results provide information about the fundamental mechanisms underlying formation and behavior of such types of amorphous and disordered matter that are of paramount importance both to physics as well as to environmental and material sciences

Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator

Optomechanical cavities have proven to be an exceptional tool to explore fundamental and technological aspects of the interaction between mechanical and optical waves. Such interactions strongly benefit from cavities with large optomechanical coupling, high mechanical and optical quality factors, and mechanical frequencies larger than the optical mode linewidth, the so called resolved sideband limit. Here we demonstrate a novel optomechanical cavity based on a disk with a radial mechanical bandgap. This design confines light and mechanical waves through distinct physical mechanisms which allows for independent control of the mechanical and optical properties. Our device design is not limited by unique material properties and could be easily adapted to allow large optomechanical coupling and high mechanical quality factors with other promising materials. Finally, our demonstration is based on devices fabricated on a commercial silicon photonics facility, demonstrating that our approach can be easily scalable.Comment: 16 pages, 11 figure