Orientation dependence of creep in Ni<Subscript>3</Subscript>Ge single crystals

The creep of Ni₃Ge alloy single crystals oriented along [001], \([\bar 139]\), \([\bar 234]\) and \([\bar 122]\) strain axes is investigated. It is established that the transition from an octahedral to a cubic slip raises the alloy’s resistance to creep deformation. The slip in cube planes demonstrates the high stability of the rate of steady-state creep with respect to changes in the testing temperature.     

Study of creep and features of the dislocation structure in single crystals of Ni3Ge alloy

Data from investigating the dislocation structure of Ni₃Ge alloy single crystals formed during creep are presented. The creep of the Ni₃Ge single crystals with the [001] orientation of the deformation axis was studied. It was found that a fragmented substructure with varying degrees of disorientation occurs in the areas of macrolocalized deformation. A polycrystalline substructure consisting of fragments with a low dislocation density is formed in the local areas.     

On possible deep subsurface states in topological insulators: The PbBi<Subscript>4</Subscript>Te<Subscript>7</Subscript> system

Theoretical studies of the bulk and surface electronic structures of PbBi₄Te₇ are presented. The PbBi₄Te₇ compound has a layered structure of five-layer (Bi₂Te₃) and seven-layer (PbBi₂Te₄) blocks alternating along the hexagonal axis. Analysis of the spin-orbit-induced inversion of the band gap edges indicates that this compound is a three-dimensional topological insulator. The topological properties of this compound are mainly determined by the PbBi₂Te₄ blocks. The Dirac cone is formed on the PbBi₄Te₇(0001) surface near the $ \bar \Gamma $ \bar \Gamma point for any block (either Bi₂Te₃ or PbBi₂Te₄) forming the surface. It is shown that the Dirac state can be localized not only on the surface but also deeply beneath it.     

Anisotropy of elastic strains and specific features of the defect structure of <Emphasis Type="Italic">a</Emphasis>-plane GaN epitaxial films grown on <Emphasis Type="Italic">r</Emphasis>-plane sapphire

The structural state of GaN epitaxial layers grown on r-plane sapphire through metal-organic vapor phase epitaxy has been investigated using X-ray diffraction. The interplanar spacings in two directions in the (11$ \bar 2 $ \bar 2 0) plane of the interface and in the direction perpendicular to it, as well as the diffraction peaks in the ϑ and ϑ-2ϑ scan modes in the Bragg and Laue geometries, are measured on double- and triple-crystal diffractometers. The intensity distribution maps for asymmetric Bragg reflections are constructed for two azimuthal positions of the sample. An analysis of the data obtained has demonstrated that the elastic strain is anisotropic and that the X-ray diffraction pattern parallel to the interface plane is broadened. The layers are contracted in the [1$ \bar 1 $ \bar 1 00] direction and unstrained in the [0001] direction. The broadening of the Bragg reflections in the [1$ \bar 1 $ \bar 1 00] direction is considerably larger than that in the [0001] direction. It is shown using the Williamson-Hall plots for the Bragg and Laue reflections that these broadenings are not related to different degrees of mosaicity but are determined by the local dilatations and misorientations around defects. The data obtained are analyzed, and the conclusions regarding the dislocation structure of the samples are drawn.     

The creep behavior of single-crystalline Ni<Subscript>3</Subscript>Ge alloys

The creep of single-crystalline Ni₃Ge alloys subjected to compression along the strain axis [001] has been investigated. The resulting creep curves have revealed low and high secondary-creep rates. Inverse hightemperature creep behavior has been observed.     

Effect of nonstoichiometry on the plastic behavior of Ni<Subscript>3</Subscript>Ge single crystals with the [001] orientation of the deformation axis

The effect of nonstoichiometry on the mechanical properties of Ni₃Ge alloy single crystals with the [001] orientation of the deformation axis has been investigated. It is shown that the limits of the temperature range of different stages shift to higher temperatures with an increase in nonstoichiometry. A change in the alloy composition only slightly affects the temperature dependence of the work hardening rate.     

Ternary thallium-based semimetal chalcogenides Tl-V-VI<Subscript>2</Subscript> as a new class of three-dimensional topological insulators

The results of the theoretical investigation of the bulk and surface electronic structures of Tl-V-VI₂ compounds, where V is the Bi or Sb semimetal and VI is the Se or Te chalcogen, are reported. It has been shown that these compounds are three-dimensional topological insulators. Both a topologically protected surface state, which forms a Dirac cone at the $ \bar \Gamma $ \bar \Gamma point, and occupied surface states, which are localized in the band gap, are present on the surface of these compounds.     

Symmetry analysis of ordered phases of the lower tungsten carbide W2C

The channels of disorder-order phase transitions through which there can arise orthorhombic (space group Pbcn) β′-W₂C, rhombohedral (space group P $ \bar 3 $ \bar 3 m1)β″-W₂C, and trigonal (space group P $ \bar 3 $ \bar 3 1m)ɛ-W₂C superstructures of the disordered lower hexagonal carbide β-W₂C have been determined. The distribution functions of carbon atoms in the superstructures under consideration have been calculated, and the physically admissible sequence of transformations associated with the ordering of the lower carbide β-W₂C that occur with a decrease in the temperature has been established.     

Investigation of creep in Ni3Ge alloy single crystals oriented along axes \left[ {\bar 234} \right] and \left[ {\bar 122} \right]

The creep of Ni₃Ge alloy single crystals is investigated at temperatures of 873, 923, and 973 K, which lie above the temperature of the anomalous peak behavior of mechanical properties with the deformation axis orientations $\left[ {\bar 234} \right]$ and $\left[ {\bar 122} \right]$ for which cubic slip is characteristic. It is shown that the steady state creep rate depends weakly on temperature.     

Structure and mechanical properties of Ni<Subscript>3</Subscript>Ge single crystals under severe plastic deformation and heating

Mechanical tests are performed for Ni₃Ge alloy single crystals in the intense plastic shear deformation scheme under quasi-hydrostatic pressure at different test temperatures. Dependences of resistance to shear deformation on the Bridgman anvils’ angle of rotation are obtained. The microrelief of the surface damage of Ni₃Ge single crystals fractured by plane bending after specimens were withdrawn from the Bridgman anvils is studied. X-ray diffraction patterns of deformed Ni₃Ge single crystals are obtained.     

Coupling running through the looking-glass of dimensional reduction

The dimensional reduction, in a form of transition from four to two dimensions, was used in the 90s of the past century in a context of the HE Regge scattering. Recently, it has got a new impetus in quantum gravity where it opens the way to renormalizability and finite short-distance behaviour. We consider a QFT model gφ⁴ with running coupling defined in both domains of different dimensionality; the $ \bar g $ \bar g (q ²) evolutions being duly correlated at the reduction scale q ∼ M. Beyond this scale, in the deep UV 2-dimensional region, the running coupling does not increase any more. Instead, it slightly decreases and tends to a finite value $ \bar g $ \bar g ₂(∞) < $ \bar g $ \bar g ₂(M ²) from above. As a result, the global evolution picture looks quite peculiar and proposes a base for the modified scenario of gauge couplings behavior with UV fixed points provided by dimensional reduction instead of leptoquarks.     

Directed flow of identified particles from Au+Au collisions at RHIC

We present the measurement of directed flow (v ₁) for the identified particles, namely, Λ, $ \bar \Lambda $ \bar \Lambda and K _s ⁰, as a function of rapidity and centrality in Au+Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV and 62.4 GeV. The measurement is based on the run IV data obtained by the STAR experiment at RHIC. In order to enhance event plane resolution, we use tracks reconstructed from the Forward Time Projection Chambers (FTPCs), together with the sideward deflection of spectator neutrons measured by the STAR’s Shower Maximum Detector at Zero Degree Calorimeters (ZDC-SMDs). We find that for 200 GeV, proton and antiproton v ₁ is less than 1%, the K _s ⁰ Λ, $ \bar \Lambda $ \bar \Lambda v ₁ is less than 2%; for 62 GeV, proton v ₁ is less than 1% and antiproton is less than 2%, v ₁ for K _s ⁰, Λ, $ \bar \Lambda $ \bar \Lambda is less than 2% in Au+Au collisions at 200 GeV.     

Confinement singularities in two-pion decays of mesons

We consider as an example the two-pion decay of the ρ meson, the ³ S ₁ q $ \bar q $ \bar q state of the constituent quarks—the decay being determined by the transition q $ \bar q $ \bar q → ππ contains information about confinement interactions. One can specify in this decay two types of transitions: (i) the bremsstrahlung radiation of a pion q → q + π (or $ \bar q $ \bar q → $ \bar q $ \bar q + π) with a subsequent fusion q $ \bar q $ \bar q → π, and (ii) the direct transition q $ \bar q $ \bar q → ππ. We demonstrate how in the amplitudes of the corresponding transitions the quark singularities have to disappear, i.e., what is the way the quark confinement at relatively short distances can be realized. We calculate and estimate the contributions of processes with bremsstrahlung radiation of the pion and of the direct transition q $ \bar q $ \bar q → ππ. The estimates demonstrate that the processes involving the direct transition q $ \bar q $ \bar q → ππ are necessary, but they cannot be determined unambiguously by the decay ρ(775) → ππ. We conclude that for the determination of the q $ \bar q $ \bar q → ππ transition more complete data on the resonance decays into the ππ channels are needed than those available at the moment.     

Effect of nonstoichiometry on the plastic behavior of Ni3Ge single crystals with the [$$ \bar 2 $$34] orientation of the deformation axes

The effect of nonstoichiometry on the mechanical properties of Ni₃Ge single crystals with the [\(\bar 2\)34] orientation of the deformation axis, which is suitable to cubic slip, has been investigated. The influence of change in the Ge concentration on the Ni₃Ge plastic properties under the conditions of cubic slip is established. The concentration dependence of the yield stress at different temperatures is obtained.     

Structure and lattice dynamics of the high-pressure phase in the ScF3 crystal

The high-pressure phase of the ScF₃ crystal has been studied using synchrotron radiation diffraction and Raman scattering. This phase existing in the pressure range 0.6–3.2 GPa is optically anisotropic: its structure is described by space group R $ \bar 3 $ \bar 3 c, Z = 2, and the transition is associated with the rotation of ScF6 octahedra around the threefold axis. The pressure dependences of the lattice parameters and the rotation angle have been determined. The number of lines in the Raman spectrum corresponds to the expected number for this structure; the recovery of soft modes has been observed above the phase transition.     

Anisotropic piezoeffect in microelectromechanical systems based on epitaxial Al<Subscript>0.5</Subscript>Ga<Subscript>0.5</Subscript>As/AlAs heterostructures

A microelectromechanical system is created that has the form of a cantilever-fitted microbar with a cross-sectional area of several square micrometers. The system is formed by applying epitaxial AlGaAs layers on the GaAs(001) surface and selective chemical etching of the AlAs layer lying under the bar. Two micro-cantilevers that are made on the same GaAs(001) wafer and directed along the [110] and [1$ \bar 1 $ \bar 1 0] orthogonal diagonal axes are studied. The static and dynamic characteristics of the systems are studied by white light optical interferometry. The deflection of the bars as a function of the applied voltage is measured in the static mode. An opposite shift of orthogonal microcantilevers on which the same voltage is applied is considered as direct evidence of the efficiency of a piezoeffect-based microengine. The calculated parameters of the micro-electromechanical system, the sensitivity and eigenfrequency, are in good agreement with the measurements.     

Thermoactive creep characteristics for single crystals of Ni3Ge alloy with different orientations

Results from investigating thermoactivated characteristics during the creep of Ni₃Ge alloy with L1₂ structure are presented. Single crystals deformed along axes [100], \([\bar 1 3 9]\) , \([\bar 1 2 2]\) , and \([\bar 2 3 4]\) are investigated. Creep activation energies are measured for the above orientations. It is found that the established rate of creep is described by the familiar law d?/dt = K ₂σ ⁿ . The magnitudes of exponent n are found and conclusions with respect to possible creep mechanisms are drawn. It is shown that the creep of samples oriented along different axes is due to dislocation processes that differ in activation energy.     

Effect of deformation axis orientation on the plastic behavior of Ni3Ge single crystals upon deviation of an alloy’s compound phase from stoichiometry

Results from studying the effect of deformation axis orientation on the mechanical properties of Ni₃Ge single crystals when the alloy compound deviates from stoichiometry are presented. The change in the alloy compound somewhat influences the material’s characteristics but does not affect the dependences of temperature or deformation. The influence of deformation axis orientation is more substantial. Changing the direction of the axes from [001] to $\left[ {\bar 2 3 4} \right]$ when an octahedral slip is initiated produces a cubic slip, bringing qualitative changes to the deformation process.     

Properties of neutral charmed mesons in <Emphasis Type="Italic">pA</Emphasis> interactions at 70 GeV

The results of data handling for the E-184 experiment involving the irradiation of the active target, consisting of carbon, silicon, and lead plates by a 70-GeV proton beam are presented. When the two-prong neutral charmed meson decay signal was selected and the cross section for charm production at a near-threshold energy was estimated (σ(c $ \bar c $ \bar c ) = 7.1 ± 2.4(stat.) ± 1.4(syst.) μb/nucleon), some properties of D ⁰ and $ \bar D^0 $ \bar D^0 were investigated. These include the atomic-weight dependence of the cross section on the target mass number (its A dependence); the differential cross sections dσ/dp _t ² and dσ/dx _F; and the dependence of the parameter α on x _F, p _t ², and p _lab. The experimental results are compared with the predictions of the FRITIOF7.02 program.     

Internal waves in a compressible two-layer model atmosphere: Hamiltonian description

We consider slow, compared to the speed of sound, motions of an ideal compressible fluid (gas) in a gravitational field in the presence of two isentropic layers with a small specific-entropy difference between them. Assuming the flow to be potential in each of the layers (v _{1, 2} = ▿ϕ_{1, 2}) and neglecting the acoustic degrees of freedom (div($ \bar \rho $ \bar \rho (z)▿ϕ_{1, 2}) ≈ 0, where $ \bar \rho $ \bar \rho (z) is the average equilibrium density), we derive the equations of motion for the boundary in terms of the shape of the surface z = η(x, y, t) itself and the difference between the boundary values of the two velocity field potentials: ψ(x, y, t) = ψ₁ − ψ₂. We prove the Hamilto nian structure of the derived equations specified by a Lagrangian of the form ℒ = ∫$ \bar \rho $ \bar \rho (η)η _t ψdxdy − ℋ{η, ψ}. The system under consideration is the simplest theoretical model for studying internal waves in a sharply stratified atmosphere in which the decrease in equilibrium gas density due to gas compressibility with increasing height is essentially taken into account. For plane flows, we make a generalization to the case where each of the layers has its own constant potential vorticity. We investigate a system with a model dependence $ \bar \rho $ \bar \rho (z) ∝ e ^−2αz with which the Hamiltonian ℋ{η, ψ} can be represented explicitly. We consider a long-wavelength dynamic regime with dispersion corrections and derive an approximate nonlinear equation of the form u _t + auu _x − b[−$ \hat \partial _x^2 $ \hat \partial _x^2 + α²]^1/2 u _x = 0 (Smith’s equation) for the slow evolution of a traveling wave.