Electric Field Effect Analysis of Thin PbTe films on high-epsilon SrTiO3 Substrate

Thin PbTe films (thickness 500 - 600 angstrom), deposited on SrTiO3, have been investigated by electric field effect (EFE). The high resistivity of such thin films warrants a high sensitivity of the EFE method. The SrTiO3 substrate serves as the dielectric layer in the Gate-Dielectric-PbTe structure. Due to the large dielectric constant of SrTiO3, particularly at low temperatures, the electric displacement D in the film reaches the high value of about 10^8 V/cm, and the EFE introduced charge into the PbTe film amounts to ~ 8 microC/cm2. The high D permits to measure the EFE resistance and Hall constant over a wide region of D, revealing the characteristic features of their D-dependence. An appropriate theoretical model has been formulated, showing that, for such films, one can measure the dependence of the Fermi level on D. In fact, we demonstrate that shifting the Fermi level across the gap by varying D, the density-of-states of the in-gape states can be mapped out. Our results show, that the PbTe layers studied, possess a mobility gap exceeding the gap of bulk PbTe.Comment: 27 pages, 12 figure

Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion-implantation

We describe here the characteristics of two types of high-quality PbTe p-n-junctions, prepared in this work: (1) by thermal diffusion of In4Te3 gas (TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and Zn (Zn-IJ). The results, as presented here, demonstrate the high quality of these PbTe diodes. Capacitance-voltage and current-voltage characteristics have been measured. The measurements were carried out over a temperature range from ~ 10 K to ~ 180 K. The latter was the highest temperature, where the diode still demonstrated rectifying properties. This maximum operating temperature is higher than any of the earlier reported results. The saturation current density, J0, in both diode types, was ~ 10^-5 A/cm2 at 80 K, while at 180 K J0 ~ 10^-1 A/cm2 in TDJ and ~ 1 A/cm2 in both ion-implanted junctions. At 80 K the reverse current started to increase markedly at a bias of ~ 400 mV for TDJ, and at ~550 mV for IJ. The ideality factor n was about 1.5-2 for both diode types at 80 K. The analysis of the C-V plots shows that the junctions in both diode types are linearly graded. The analysis of the C-V plots allows also determining the height of the junction barrier, the concentrations and the concentration gradient of the impurities, and the temperature dependence of the static dielectric constant. The zero-bias-resistance x area products (R0Ae) at 80 K are: 850 OHMcm2 for TDJ, 250 OHMcm2 for In-IJ, and ~ 80 OHMcm2 for Zn-IJ, while at 180 K R0Ae ~ 0.38 OHMcm2 for TDJ, and ~ 0.1 OHMcm2 for IJ. The estimated detectivity is: D* ~ 10^10 cmHz^(1/2)/W up to T=140 K, determined mainly by background radiation, while at T=180 K, D* decreases to 108-107 cmHz^(1/2)/W, and is determined by the Johnson noise

Determining the boundary layers in the plane problem for three-layer strips. Part 1

We propose an exact solution of the problem on a boundary layer (a stress-strain state decreasing away from the boundary) for three-layer strips (rods) whose layers are made of different materials. We use the asymptotic integration method to obtain boundary eigenfunctions and a characteristic equation for the parameter describing the boundary layer decay rate. We study how the middle layer material affects the boundary layer extent. © Allerton Press, Inc., 2008

Determination of boundary layers in the plane problem for three-layer strips. Part 2

In the first part of this paper, we considered the exact statement of the plane elasticity problem in displacements for strips made of various materials (problem A, an isotropic material; problem B, an orthotropic material with 2G12 √E1E2). Further, we stated and solved the boundary layer problem (the problem on a solution decaying away from the boundary) for a sandwich strip of regular structure consisting of isotropic layers (problem AA). In the present paper, we use the solution of the plane problem to consider the problem for sandwich strips of regular structure with isotropic face layers and orthotropic filler (problem AB). © Allerton Press, Inc., 2009

Dynamics of Gaseous Disks in a Non-axisymmetric Dark Halo

The dynamics of a galactic disk in a non-axisymmetric (triaxial) dark halo is studied in detail using high-resolution, numerical, hydrodynamical models. A long-lived, two-armed spiral pattern is generated for a wide range of parameters. The spiral structure is global, and the number of turns can be two or three, depending on the model parameters. The morphology and kinematics of the spiral pattern are studied as functions of the halo and disk parameters. The spiral structure rotates slowly, and its angular velocity varies quasi-periodically. Models with differing relative halo masses, halo semi-axis ratios, distributions of matter in the disk, Mach numbers in the gaseous component, and angular rotational velocities of their halos are considered.Comment: 22 pages, 11 figure

Extensive molecular tinkering in the evolution of the membrane attachment mode of the Rheb GTPase

Rheb is a conserved and widespread Ras-like GTPase involved in cell growth regulation mediated by the (m)TORC1 kinase complex and implicated in tumourigenesis in humans. Rheb function depends on its association with membranes via prenylated C-terminus, a mechanism shared with many other eukaryotic GTPases. Strikingly, our analysis of a phylogenetically rich sample of Rheb sequences revealed that in multiple lineages this canonical and ancestral membrane attachment mode has been variously altered. The modifications include: (1) accretion to the N-terminus of two different phosphatidylinositol 3-phosphate-binding domains, PX in Cryptista (the fusion being the first proposed synapomorphy of this clade), and FYVE in Euglenozoa and the related undescribed flagellate SRT308; (2) acquisition of lipidic modifications of the N-terminal region, namely myristoylation and/or S-palmitoylation in seven different protist lineages; (3) acquisition of S-palmitoylation in the hypervariable C-terminal region of Rheb in apusomonads, convergently to some other Ras family proteins; (4) replacement of the C-terminal prenylation motif with four transmembrane segments in a novel Rheb paralog in the SAR clade; (5) loss of an evident C-terminal membrane attachment mechanism in Tremellomycetes and some Rheb paralogs of Euglenozoa. Rheb evolution is thus surprisingly dynamic and presents a spectacular example of molecular tinkering

PROSPECTS FOR THE DEVELOPMENT OF TOURISM IN THE CONDITION OF DIGITAL TRANSFORMATION

Digital and innovative technologies can significantly increase the level of development of the tourism sector, improve the quality of services and increase the competitiveness of tourism enterprises