High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

GRAVITY’S ROLE IN ACCELERATED RUNNING - A COMPARISON OF AN EXPERIENCED POSE® AND HEEL-TOE RUNNER

The purpose of this study was to determine gravity’s role in accelerated running using an experienced male Pose® and heel-toe runner as a comparison. A two-step accelerated run found that maximum horizontal acceleration of the centre of mass (COM) occurred before maximum horizontal ground reaction force (GRF). Maximum horizontal and angular acceleration of the arms and trunk occurred at or before maximum horizontal acceleration of the COM. At maximum horizontal GRF both participants’ stance feet were vertically accelerated. It is suggested that acceleration of the COM occurs via a gravitational torque with GRF being the consequence of, not the cause of these movements. Therefore, practitioners might find this novel perspective helpful when applied to accelerated running

Theoretical backgrounds of nonlinear THz spectroscopy of semiconductor superlattices

We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.Comment: 14 page

Superlattice with hot electron injection: an approach to a Bloch oscillator

A semiconductor superlattice with hot electron injection into the miniband is considered. The injection changes the stationary distribution function and results in a qualitative change of the frequency behaviour of the differential conductivity. In the regime with Bloch oscillating electrons and injection into the upper part of the miniband the region of negative differential conductivity is shifted from low frequencies to higher frequencies. We find that the dc differential conductivity can be made positive and thus the domain instability can be suppressed. At the same time the high-frequency differential conductivity is negative above the Bloch frequency. This opens a new way to make a Bloch oscillator operating at THz frequencies.Comment: RevTeX, 8 pages, 2 figures, to be published in Phys. Rev. B, 15 Januar 200

Preparation of Low Friction MoSex/nc-Mo Coatings Containing Spherical Mo Nanoparticles

The possibility of preparation of nanocomposite coatings consisting of a solid lubricant matrix (MoSex) and nanocrystalline metal particles (nc-Mo) was demonstrated using pulsed laser deposition from synthesized target MoSe2.The particles had spherical shapes and their sizes were about 5 - 50 nm. The content of the nc-Mo nanoparticles in the MoSex/nc-Mo coatings was varied by changing the laser irradiation regimes and the conditions of expansion of the laser plume from the target to substrate. It was established that the tribological properties of the nanocomposite coatings MoSex/nc-Mo are depended on the concentration of nanoparticles in the bulk of the coatings as well as on the structure of the coating matrix. The MoSex/nc-Mo coating with increased crystalline order of matrix obtained on a steel substrate reduced the friction coefficient to ~0.04 during steel ball sliding in air of laboratory humidity. Probable mechanisms of nanoparticle formation were proposed and a role of these particles in the wear of the nanocomposite MoSex/nc-Mo coatings was discussed

Disentangling genetic and environmental effects on the proteotypes of individuals

Proteotypes, like genotypes, have been found to vary between individuals in several studies, but consistent molecular functional traits across studies remain to be quantified. In a meta-analysis of 11 proteomics datasets from humans and mice, we use co-variation of proteins in known functional modules across datasets and individuals to obtain a consensus landscape of proteotype variation. We find that individuals differ considerably in both protein complex abundances and stoichiometry. We disentangle genetic and environmental factors impacting these metrics, with genetic sex and specific diets together explaining 13.5% and 11.6% of the observed variation of complex abundance and stoichiometry, respectively. Sex-specific differences, for example, include various proteins and complexes, where the respective genes are not located on sex-specific chromosomes. Diet-specific differences, added to the individual genetic backgrounds, might become a starting point for personalized proteotype modulation toward desired features

Exciton spin decay modified by strong electron-hole exchange interaction

We study exciton spin decay in the regime of strong electron-hole exchange interaction. In this regime the electron spin precession is restricted within a sector formed by the external magnetic field and the effective exchange fields triggered by random spin flips of the hole. Using Hanle effect measurements, we demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te quantum wells. The calculations provide a consistent description of the experimental results, which is supported by independent measurements of the parameters entering the model.Comment: 5 pages, 3 figure