Equilibrium shape and dislocation nucleation in strained epitaxial nanoislands

We study numerically the equilibrium shapes, shape transitions and dislocation nucleation of small strained epitaxial islands with a two-dimensional atomistic model, using simple interatomic pair potentials. We first map out the phase diagram for the equilibrium island shapes as a function of island size (up to N = 105 atoms) and lattice misfit with the substrate and show that nanoscopic islands have four generic equilibrium shapes, in contrast with predictions from the continuum theory of elasticity. For increasing substrate-adsorbate attraction, we find islands that form on top of a finite wetting layer as observed in Stranski-Krastanow growth. We also investigate energy barriers and transition paths for transitions between different shapes of the islands and for dislocation nucleation in initially coherent islands. In particular, we find that dislocations nucleate spontaneously at the edges of the adsorbate-substrate interface above a critical size or lattice misfit.Comment: 4 pages, 3 figures, uses wrapfig.sty and epsfig.st

Curved One-Dimensional Wire as a Spin Rotator

We propose a semiconductor structure that can rotate the electron spin without using ferromagnetic contacts, tunneling barriers, external radiation etc. The structure consists of a strongly curved one-dimensional ballistic wire with intrinsic spin-orbit interactions of Rashba type. Our calculations and analytical formulae show that the proposed device can redistribute the current densities between the two spin-split modes without backscattering and, thus, serve as a reflectionless and high-speed spin switcher. Using parameters relevant for InAs we investigate the projection of current density spin polarization on the spin-quantization axis as a function of the Rashba constant, external magnetic field, and radius of the wire's curvature.Comment: 10 pages, 6 figures; replaced with considerably extended versio

Quantum transport in a curved one-dimensional quantum wire with spin-orbit interactions

The one-dimensional effective Hamiltonian for a planar curvilinear quantum wire with arbitrary shape is proposed in the presence of the Rashba spin-orbit interaction. Single electron propagation through a device of two straight lines conjugated with an arc has been investigated and the analytic expressions of the reflection and transmission probabilities have been derived. The effects of the device geometry and the spin-orbit coupling strength $\alpha$ on the reflection and transmission probabilities and the conductance are investigated in the case of spin polarized electron incidence. We find that no spin-flip exists in the reflection of the first junction. The reflection probabilities are mainly influenced by the arc angle and the radius, while the transmission probabilities are affected by both spin-orbit coupling and the device geometry. The probabilities and the conductance take the general behavior of oscillation versus the device geometry parameters and $\alpha$. Especially the electron transportation varies periodically versus the arc angle $\theta_{w}$. We also investigate the relationship between the conductance and the electron energy, and find that electron resonant transmission occurs for certain energy. Finally, the electron transmission for the incoming electron with arbitrary state is considered. For the outgoing electron, the polarization ratio is obtained and the effects of the incoming electron state are discussed. We find that the outgoing electron state can be spin polarization and reveal the polarized conditions.Comment: 7 pages, 8 figure

Energetics and atomic mechanisms of dislocation nucleation in strained epitaxial layers

We study numerically the energetics and atomic mechanisms of misfit dislocation nucleation and stress relaxation in a two-dimensional atomistic model of strained epitaxial layers on a substrate with lattice misfit. Relaxation processes from coherent to incoherent states for different transition paths are studied using interatomic potentials of Lennard-Jones type and a systematic saddle point and transition path search method. The method is based on a combination of repulsive potential minimization and the Nudged Elastic Band method. For a final state with a single misfit dislocation, the minimum energy path and the corresponding activation barrier are obtained for different misfits and interatomic potentials. We find that the energy barrier decreases strongly with misfit. In contrast to continuous elastic theory, a strong tensile-compressive asymmetry is observed. This asymmetry can be understood as manifestation of asymmetry between repulsive and attractive branches of pair potential and it is found to depend sensitively on the form of the potential.Comment: 11 pages, 9 figures, to appear in Phys. Rev.

Quantum corrections in the Boltzmann conductivity of graphene and their sensitivity to the choice of formalism

Semiclassical spin-coherent kinetic equations can be derived from quantum theory with many different approaches (Liouville equation based approaches, nonequilibrium Green's functions techniques, etc.). The collision integrals turn out to be formally different, but coincide in textbook examples as well as for systems where the spin-orbit coupling is only a small part of the kinetic energy like in related studies on the spin Hall effect. In Dirac cone physics (graphene, surface states of topological insulators like Bi_{1-x}Sb_x, Bi_2Te_3 etc.), where this coupling constitutes the entire kinetic energy, the difference manifests itself in the precise value of the electron-hole coherence originated quantum correction to the Drude conductivity $\sim e^2/h * \ell k_F$. The leading correction is derived analytically for single and multilayer graphene with general scalar impurities. The often neglected principal value terms in the collision integral are important. Neglecting them yields a leading correction of order $(\ell k_F)^{-1}$, whereas including them can give a correction of order $(\ell k_F)^0$. The latter opens up a counterintuitive scenario with finite electron-hole coherent effects at Fermi energies arbitrarily far above the neutrality point regime, for example in the form of a shift $\sim e^2/h$ that only depends on the dielectric constant. This residual conductivity, possibly related to the one observed in recent experiments, depends crucially on the approach and could offer a setting for experimentally singling out one of the candidates. Concerning the different formalisms we notice that the discrepancy between a density matrix approach and a Green's function approach is removed if the Generalized Kadanoff-Baym Ansatz in the latter is replaced by an anti-ordered version.Comment: 31 pages, 1 figure. An important sign error has been rectified in the principal value terms in equation (52) in the vN & NSO expression. It has no implications for the results on the leading quantum correction studied in this paper. However, for the higher quantum corrections studied in arXiv:1304.3929 (see comment in the latter) the implications are crucia

The research of qualitative indicators of gas pipelines during the operation

The operation of gas pipelines is a complex of technical measures, aimed at preservation of the main stock of gas pipeline transportation facilities. The purpose of these measures is to maintain and to restore the initial operational capabilities of gas pipelines, in general and in particular areas. The line section of gas pipelines has the largest size and cost. Naturally determined process of changing the quality of gas pipelines during the operation is accompanied by the accumulation and development of damages, failures; this determines the objective need to restore the quality of operation. The practical running of the line section of gas pipelines is characterized by a certain flow of failures; therefore it is necessary to ensure the required level of reliability of the gas pipeline during the entire period of operation. The quality control study of the inter-settlement gas pipeline section was conducted, and graphs of dependence of gas pipeline quality parameters on time were presented in the work.Keywords: line section of the gas pipeline, technological state, failures in operation, gas pipeline operation, control and quality parameters of the gas pipeline

Circulating markers of vascular damage as predictors of cardiovascular events in atherosclerosis and metabolic disorders

The article presents the results of cluster analysis of the contribution of immune inflammation and endothelial dysfunction (ED) markers to the frequency and severity of cardiovascular events (CVE) in cohorts of patients with asymptomatic atherosclerosis (AAS), coronary artery disease (CAD), type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS) during a 3-year prospective observation. Results Circulating markers of ED and immune inflammation, such as ET-1, IL-1β, TNF-α, antibodies to collagen type I and III, and antibodies to chondroitine sulfate (CS) contribute to cardiovascular (CV) manifestation in AAS. In CAD patients ET-1, eNOs, antibodies to collagen, as well as IL-6 and vWf  are the main contributors. In T2DM without clinical manifestation of CAD, the set of markers associated with the adverse events includes ET-1, eNOs, IL-6, anti-C, and anti-HA. In CAD combined with T2DM, the cluster of markers associated with the adverse events includes vWf, TNF-α, eNOs, IL-6, anti-C, anti-HA and CRP. In AAS without MS, the key contributors are ET-1 and vWf, and the presence of anti-C and anti-ChS; in AAS/MS patients, the key markers are IL-1β, TNF-α, anti-C, anti-ChS, anti-HA, and CRP. In CAD without MS, the cluster of markers associated with adverse events includes ET-1, eNOs and anti-HA; in CAD/MS it includes anti-C, ET-1, and IL-6. Conclusion. The obtained results confirm the role of systemic inflammation in the development of atherosclerosis-associated angiopathy in coronary pathology and disorders of carbohydrate metabolism, and also suggest a set of circulating markers as predictors of adverse CVE