Pressure and temperature driven phase transitions in HgTe quantum wells

We present theoretical investigations of pressure and temperature driven phase transitions in HgTe quantum wells grown on CdTe buffer. Using the 8-band \textbf{k$\cdot$p} Hamiltonian we calculate evolution of energy band structure at different quantum well width with hydrostatic pressure up to 20 kBar and temperature ranging up 300 K. In particular, we show that in addition to temperature, tuning of hydrostatic pressure allows to drive transitions between semimetal, band insulator and topological insulator phases. Our realistic band structure calculations reveal that the band inversion under hydrostatic pressure and temperature may be accompanied by non-local overlapping between conduction and valence bands. The pressure and temperature phase diagrams are presented.Comment: 9 pages, 8 figures + Supplemental material (5 pages

Temperature-dependent magnetospectroscopy of HgTe quantum wells

We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and inter-band transitions from zero-mode Landau levels, which split from the bottom conduction and upper valence subbands, and merge under the applied magnetic field. To describe experimental results, realistic temperature-dependent calculations of Landau levels have been performed. We show that although our samples are topological insulators at low temperatures only, the signature of such phase persists in optical transitions at high temperatures and high magnetic fields. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases in HgTe quantum wells

Temperature-driven single-valley Dirac fermions in HgTe quantum wells

We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness $d_c$. Our results, obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K, clearly indicate a change of the band-gap energy with temperature. The quantum well wider than $d_c$ evidences a temperature-driven transition from topological insulator to semiconductor phases. At the critical temperature of 90 K, the merging of inter- and intra-band transitions in weak magnetic fields clearly specifies the formation of gapless state, revealing the appearance of single-valley massless Dirac fermions with velocity of $5.6\times10^5$ m$\times$s$^{-1}$. For both quantum wells, the energies extracted from experimental data are in good agreement with calculations on the basis of the 8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages

Modeling of contact interaction of a heated plane rigid elliptical punch with a transversally isotropic elastic half-space

On the base of a rigorous mathematical model, the problem of the contact interaction of a heated flat punch of an elliptical section with a transversely isotropic elastic half-space is investigated. It is assumed that the half-space surface is the isotropy plane of a transversely isotropic material, and also that there is a smooth (without friction) contact. Expressions of contact stresses and displacements of a heated flat elliptical punch are found explicitly. In the form of a simple inequality, a condition for separating the elastic material from the surface of a flat elliptical punch is obtained. Numerical calculations are carried out. Contact interaction of a heated flat punch is studied taking into account the separation of material from the punch

Statistical Moments and Scintillation Level of Scattered Electromagnetic Waves in the Magnetized plasma

Statistical characteristics of scattered ordinary and extraordinary electromagnetic waves in the magnetized plasma are considered using the smooth perturbation method. Diffraction effects and polarization coefficients are taken into account. Second order statistical moments of scattered radiation are obtained for arbitrary correlation function of electron density fluctuations. Broadening of the spatial power spectrum and displacement of its maximum, wave phase structure function and the angle-of-arrivals are obtained for three-dimensional spectral function containing anisotropic Gaussian and power-law spectral functions. Scintillation level of scattered radiation is analyzed for different parameters characterizing anisotropic plasma irregularities for the ionospheric F-region. The spectral widths (first and second moments) of the power spectrum and scintillation periods are calculated for “frozen-in” drifting elongated plasma irregularities using the experimental data

An improvement of the Berry--Esseen inequality with applications to Poisson and mixed Poisson random sums

By a modification of the method that was applied in (Korolev and Shevtsova, 2009), here the inequalities $$\rho(F_n,\Phi)\le\frac{0.335789(\beta^3+0.425)}{\sqrt{n}}$$ and $$\rho(F_n,\Phi)\le \frac{0.3051(\beta^3+1)}{\sqrt{n}}$$ are proved for the uniform distance $\rho(F_n,\Phi)$ between the standard normal distribution function $\Phi$ and the distribution function $F_n$ of the normalized sum of an arbitrary number $n\ge1$ of independent identically distributed random variables with zero mean, unit variance and finite third absolute moment $\beta^3$. The first of these inequalities sharpens the best known version of the classical Berry--Esseen inequality since $0.335789(\beta^3+0.425)\le0.335789(1+0.425)\beta^3<0.4785\beta^3$ by virtue of the condition $\beta^3\ge1$, and 0.4785 is the best known upper estimate of the absolute constant in the classical Berry--Esseen inequality. The second inequality is applied to lowering the upper estimate of the absolute constant in the analog of the Berry--Esseen inequality for Poisson random sums to 0.3051 which is strictly less than the least possible value of the absolute constant in the classical Berry--Esseen inequality. As a corollary, the estimates of the rate of convergence in limit theorems for compound mixed Poisson distributions are refined.Comment: 33 page

Manganese catalysts to obtain olefins from C1-C4 alkanes

Oxidative transformations of C1-C4 alkanes into olefins on oxide manganese catalysts were under study. We also studied oxidative coupling of methane (OCM) into ethylene on deposited and applied on the silicon dioxide catalysts. We studied the influence of chemical composition of catalyst and promotors on the OCM. Adding a little amount of ethane and propane hydrocarbons to methane allows increasing the concentration of ethylene in gases and significantly increasing productivity in ethylene. The study also shows the impact of the amount of manganese and promotors applied on SiO2 on the yield of olefins during the conversion of C3-C4 alkanes

Funds Management as Relation System in Business Company for Highly Effective Finance Administration

Particularly relevant in a period of increasing competition in all sectors of the economy, where the major indexes falling rapidly, is cost management in enterprises of different types. At the moment, there is a period of rapid growth of the completion of the majority of companies, and the transition in the process of mergers and acquisitions. The productivity of domestic branded business - processes rapidly is of paramount importance not only for the efficient operation, as well as to maintain its place in the market. The stumbling block in achieving operational efficiency of any enterprise is the existence of an effectively functioning system of the enterprise. Also note that the fundamental nature of the competitive position of the company in today's market is characterized by high efficiency of its financial management system of the company. financial management system is a set of tools with which the company's management can rapidly generate accurate information about every aspect of the company. As well as to monitor for compliance with its performance tactical objectives and strategic plans, moreover, fully analyze the problems that arise in the operation of various types of enterprises, and to seek the best options for their solutions. Keywords: financial administration, financial management, budgeting, transaction, financial resources, financial leverage JEL Classifications: G02, G3, G3