Nuclear spin warm-up in bulk n-GaAs

We show that the spin-lattice relaxation in n-type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, that cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, that governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping can be studied and harnessed in much simpler model environment of n-GaAs bulk crystal.Comment: 5 pages, 4 figure

Ballistic spin transport in exciton gases

Traditional spintronics relies on spin transport by charge carriers, such as electrons in semiconductor crystals. This brings several complications: the Pauli principle prevents the carriers from moving with the same speed; Coulomb repulsion leads to rapid dephasing of electron flows. Spin-optronics is a valuable alternative to traditional spintronics. In spin-optronic devices the spin currents are carried by electrically neutral bosonic quasi-particles: excitons or exciton-polaritons. They can form highly coherent quantum liquids and carry spins over macroscopic distances. The price to pay is a finite life-time of the bosonic spin carriers. We present the theory of exciton ballistic spin transport which may be applied to a range of systems where bosonic spin transport has been reported, in particular, to indirect excitons in coupled GaAs/AlGaAs quantum wells. We describe the effect of spin-orbit interaction of electrons and holes on the exciton spin, account for the Zeeman effect induced by external magnetic fields, long range and short range exchange splittings of the exciton resonances. We also consider exciton transport in the non-linear regime and discuss the definitions of exciton spin current, polarization current and spin conductivity.Comment: 16 pages, 10 figures to be published in Phys. Rev.

The role of retraining technologies of personnel in ensuring financial stability of transport and industrial companies

The industry-based companies with state participation operating in the Russian Federation are significant producers of economic growth and core economic entities identifying the Russian labor market growth. In terms of risky business environment, the mechanism for implementing personnel development strategy at transport and industrial companies with state participation in the capital assets, which are based on an innovative personnel training and retraining system, determines the vector of ensuring their financial stability. Considering the latter, the risk management of transport and industrial companies’ personnel development is directly related to the strategy for the intangible assets formation. It also ensures institutionalization of promising systems of human capital management.peer-reviewe

Polariton Dispersion Law in Periodic Bragg and Near-Bragg Multiple Quantum Well Structures

The structure of polariton spectrum is analyzed for periodic multiple quantum well structures with periods at or close to Bragg resonance condition at the wavelength of the exciton resonance. The results obtained used to discuss recent reflection and luminescent experiments by M. H\"{u}bner et al [Phys. Rev. Lett. {\bf 83}, 2841 (1999)] carried out with long multiple quantum well structures. It is argued that the discussion of quantum well structures with large number of wells is more appropriate in terms of normal modes of infinite periodic structures rather then in terms of super- and sub- radiant modes.Comment: replaced with a new version, an error in one of the equations is correcte

Spin Texture in a Cold Exciton Gas

We report on the observation of a spin texture in a cold exciton gas in a GaAs/AlGaAs coupled quantum well structure. The spin texture is observed around the exciton rings. The observed phenomena include: a ring of linear polarization, a vortex of linear polarization with polarization perpendicular to the radial direction, an anisotropy in the exciton flux, a skew of the exciton fluxes in orthogonal circular polarizations and a corresponding four-leaf pattern of circular polarization, a periodic spin texture, and extended exciton coherence in the region of the polarization vortex. The data indicate a transport regime where the spin polarization is locked to the direction of particle propagation and scattering is suppressed.Comment: version 2 contains updated supplementary materia

Nanoscale investigation of polymer cement concretes by small angle neutron scattering

An analysis of dense cements, such as polymer cement concrete, is made to produce original innovative components for different types of constructing materials. These materials present good functional properties (ageing resistance, crack formation resistance, hardness, and stability of mechanical modules) and can be used for various applications. In this paper, experimental tests on Portland cement with added γ-Al 2 O 3 and redispersible dry polymer performed using small angle neutron scattering are reported. The objective of the investigation was to assess the key parameters of the material (e.g., porosity, fractal dimensions, and size distribution) at the nanoscale level as well as to obtain useful structural information for expanding the possibility of applications. The results obtained can contribute to the optimisation of the consistency of the material, the design of operating conditions of elements of structures and facilities, and the design of the procedures that support ecological criteria and enhance quality and safety levels. © 2017 Walter de Gruyter GmbH, Berlin/Boston

Orbital dynamics of "smart dust" devices with solar radiation pressure and drag

This paper investigates how perturbations due to asymmetric solar radiation pressure, in the presence of Earth shadow, and atmospheric drag can be balanced to obtain long-lived Earth centred orbits for swarms of micro-scale 'smart dust' devices, without the use of active control. The secular variation of Keplerian elements is expressed analytically through an averaging technique. Families of solutions are then identified where Sun-synchronous apse-line precession is achieved passively to maintain asymmetric solar radiation pressure. The long-term orbit evolution is characterized by librational motion, progressively decaying due to the non-conservative effect of atmospheric drag. Long-lived orbits can then be designed through the interaction of energy gain from asymmetric solar radiation pressure and energy dissipation due to drag. In this way, the usual short drag lifetime of such high area-to-mass spacecraft can be greatly extended (and indeed selected). In addition, the effect of atmospheric drag can be exploited to ensure the rapid end-of-life decay of such devices, thus preventing long-lived orbit debris

On selection of foxes for enhanced aggressiveness and its correlated implications

The results of a 35-year selection of foxes for aggressive response to humans are reported. Averaged estimates of the phenotypic manifestation of aggressiveness in all selection generations are presented. The dynamics of these estimates shows that the phenotypic response to the selection was obvious only in the first 12 generations. Subsequent selection did not alter the mean aggressiveness score. Analysis of variance was performed for the intergroup variability (among descendants of different mothers) and intragroup variability (among the offspring within a family). The intragroup variability was constantly low. Most likely, the trait is stabilized by maternal prenatal and early neonatal factors. The general tendency in the dynamics of intergroup variability is that it does not decrease over time during selection, no matter how long the population has been under it. It follows from the statistical indices of the phenotypic similarity between parents and offspring that additive interactions are insufficient for the explanation of the persisting variability. The contribution of epistatic interactions is not ruled out, though. Emphasis is laid on the correlated consequences of the selection for aggressiveness and their coordination with the consequences of the selection in the opposite direction, for elimination of aggressive response to humans, or for tameness. The parallelism of correlated changes in the selection in contrasting directions is illustrated by the examples of some physiological and morphological traits. The phenomenon is discussed in the light of classical notions of the resource of cryptic genetic variation and the role of selection in its phenotypic manifestation. Its interpretation also invokes molecular data pointing that some genetic pathways may regulate parameters of both aggression and tameness and that the selection processes in both directions may have some genetic targets in common