Thermal expansion and elasticity of PdFe<Subscript>3</Subscript>N within the quasiharmonic approximation

We have explored the bulk modulus and the thermal expansion of PdFe₃N (space group Pm[`3] mPm\overline 3 m) using ab initio phonon dynamics within the quasiharmonic approximation in the temperature range from 50 to 1000 K. PdFe₃N possesses a linear thermal expansion coefficient common for typical ceramics. The calculated average linear thermal expansion coefficient of 6.4 × 10^-6 K^-1 is consistent with the average measured coefficient of 6.7 × 10^-6 K^-1. We have shown here that the thermal behavior of this compound can be understood based on the electronic structure and the lattice dynamics thereof. PdFe₃N exhibits both metallic as well as covalent-ionic bonding. The Fe–N covalent-ionic bonding suppresses the lattice vibrations of the PdFe₃ matrix. The bulk modulus of 188 GPa for PdFe₃N decreases by 15% in the temperature range studied, which is expected due to presence of stiff Fe–N bonds.     

A method to polarise antiprotons in storage rings and create polarised antineutrons

An intense circularly polarised g \gamma -beam interacts with a cooled antiproton beam in a storage ring. Due to spin-dependent absorption cross-sections for the reaction g+[`(p)]?p<sup>-</sup>+[`(n)]\ensuremath \gamma+\overline{p}\rightarrow\pi^{-}+\overline{n} a built-up of polarisation of the stored antiprotons takes place. Figures of merit around 0.1 can be reached in principle over a wide range of antiproton energies. In this process polarised antineutrons with polarisation P_[`(n)] \succ 70%\ensuremath P_{\overline{n}} \succ 70\% emerge. The method is presented for the case of a 300MeV/c cooled antiproton beam.     

Magnetic Moments of Single-Crystal Tb–Sm Alloys

In the present paper, the magnetic properties of Tb_1–xSm_x alloys with different samarium contents are investigated along the <11 [`2]\overline 2 0 > (b), < 10 [`1]\overline 1 0 \gt; (a), and <0001> (c) crystallographic directions in magnetic fields up to 50 kOe in the temperature interval 4.2–400 K. It is demonstrated that small additions of the light rare-earth samarium metal to the heavy rare-earth terbium metal increase the specific magnetization and the effective magnetic moments.     

Features of the crystal structure of disperse carbides in alpha titanium

Investigations of disperse nonmetallic inclusions in unalloyed alpha titanium VT1-0 have been performed by using transmission electron (including scanning and high-resolution) microscopy. Characteristic electron energy losses spectroscopy has shown that these inclusions are titanium carbide particles. It has been revealed that the disperse carbides are formed in the titanium hcp matrix as a phase based on the fcc sublattice of titanium atoms. The inclusion–matrix orientation relationship corresponds to the well-known Kurdyumov–Sachs and Nishiyama–Wassermann relationships [ 2[`11] 0 ]<sub>\upalpha</sub> ||[ 011 ]<sub>\updelta</sub> \text and ( 000[`1] )_\upalpha ||( 1[`1] 1 )_\updelta {\left[ {2\overline {11} 0} \right]_{{\upalpha }}}\parallel {\left[ {011} \right]_{{\updelta }}}{\text{ and }}{\left( {000\overline 1 } \right)_{{\upalpha }}}\parallel {\left( {1\overline 1 1} \right)_{{\updelta }}} .     

Spin exchange during collisions of potassium atoms: Complex cross sections

Singlet (X ¹Σ⁺) and triplet (a ³Σ⁺) potentials of interaction of two potassium atoms residing in the ground state (4s ² S _1/2) are presented. Based on the given interaction potentials, the complex cross sections of spin exchange q = [`(q)] + i[`([`(q)])]q = \bar q + i\overline{\overline q} for the system under investigation are calculated. Obtained dependences of the real and imaginary parts of the spin-exchange cross section on temperature allow one to obtain information both on the broadening of a magnetic resonance line of K atoms and on the frequency shift of the magnetic resonance during collision.     

Normal-metal hot-electron bolometer with Andreev reflection from superconductor boundaries

This paper describes the design and experimental testing of a high-sensitivity hot-electron bolometer based a film of normal metal, exploiting the Andreev reflection from superconductor boundaries, and cooled with the help of a superconductor-insulator-normal metal junction. At the measured thermal conductivity, G≈6×10⁻¹² W/K, and a time constant of τ=0.2 μs, and a temperature of 300 mK, the estimated noise-equivalent power NEP=5×10⁻¹⁸ W/Hz^1/2, assuming that temperature fluctuations are the major source of noise. At a temperature of 100 mK, the thermal conductivity drops to G≈7×10⁻¹⁴ W/K, which yields NEP=2×10⁻¹⁹ W/Hz^1/2 at a time constant of τ=5 μs. The microbolometer has been designed to serve as a detector of millimeter and FIR waves in space-based radio telescopes. Zh. éksp. Teor. Fiz. 115, 1085–1092 (March 1999)     

Laminar natural convection between vertical isothermal heated plates with different temperatures

Numerical investigation of laminar free convection heat transfer in the vertical parallel plate channel with asymmetric heating is presented. Both inlet and exit effects are included into the analysis. A numerical solution is obtained for a Prandtl number of 0.71 and for modified Rayleigh number [`(Ra)]\overline {Ra} = 10⁻¹ ÷ 10⁵, and varying heating ratio T_R = 0 ÷ 1 and aspect ratio A = 10. Fully elliptic Navier-Stokes and energy equations are solved using the finite volume techniques with staggered grid arrangements. The obtained results show a strong influence of the temperature ratio on local and average heat transfer coefficient on the hot and cold plates. With reduction of T_R the heat transfer parameter on the hot wall grows, and on the cold one, on the contrary, it decreases. As a result, the total heat exchange from two plates depends poorly on the parameter T_R.     

Raman scattering in a near-surface n-GaAs layer implanted with boron ions

Structure in the Raman scattering spectra of near-surface n-GaAs layers (n=2×10¹⁸ cm⁻³) implanted with 100 keV B⁺ ions in the dose range 3.1×10¹¹–1.2×10¹⁴ cm⁻² is investigated. The qualitative and quantitative data on the carrier density and mobility and on the degree of amorphization of the crystal lattice and the parameters of the nanocrystalline phase as a result of ion implantation are obtained using a method proposed for analyzing room-temperature Raman spectra. Fiz. Tverd. Tela (St. Petersburg) 41, 1495–1498 (August 1999)     

Study of $$qqqc\bar c$$ five quark system with three kinds of quark-quark hyperfine interaction

The low-lying energy spectra of five quark systems uudc[`(c)]uudc\bar c (I = 1/2, S = 0) and udsc[`(c)]udsc\bar c (I = 0, S = 1) are investigated with three kinds of schematic interaction: the chromomagnetic interaction, the flavor-spin-dependent interaction and the instanton-induced interaction. In all the three models, the lowest five-quark state (uudc[`(c)]uudc\bar c or udsc[`(c)]udsc\bar c) has an orbital angular momentum L = 0 and the spin-parity J ^P = 1/2⁻; the mass of the lowest udsc[`(c)]udsc\bar c state is heavier than the lowest uudc[`(c)]uudc\bar c state.     

Experimental research of temperature and velocity fields in high-temperature flow of liquid heavy metal coolant

Presented are the results of experimental research of temperature and velocity fields for lead and lead-bismuth coolant flows in channels having circular and annular cross sections under varying oxygen content in the coolant and varying characteristics of insulating coatings. Tests are performed under the following operating conditions: (1) lead-bismuth eutectic—temperature T = 400−520°C, thermodynamic oxygen activity a = 10⁻⁵–10⁰, average flow velocity of the coolant w = 0.12−1.84 m/s, value of magnetic induction B = 0−0.85 T, Reynolds number Re = (0.24–3.5) × 10⁵, Hartmann number Ha = 0−500, and Peclet number Pe = 320−4600; (2) lead coolant-T = 400−550°C, a = 10⁻⁵−10⁰, w = 0.1−1.5 m/s, Re = (2.36−2.99) × 10⁵, and Pe = 500−7000.     

Probe measurements in a discharge with liquid nonmetallic electrodes in air at atmospheric pressure

Discharges with liquid nonmetallic electrodes of much interest for applications are investigated. It is found that a dc discharge between two streams of tap water in air at atmospheric pressure is stable at a currentof 40≤I≤100 mA. The discharge exists in the diffuse (volume) form with a relatively low current density (∼0.2 A/cm²) and a high (above one kilovolt) voltage drop across the air gap (∼1 cm) between the water electrodes. The current density and voltage depend only slightly on the discharge current. Probe measurements show that three regions can be distinguished in the discharge: two electrode regions (1–2 mm in length) and a discharge column with a constant electric field of ≈0.8 kV/cm (i.e., E/N≈20 Td, because the gas in the discharge is heated up to 1500–2000 K). The average electric field strength near the electrodes is E≈2–3×10³ V/cm (E/N≈60–80 Td). The charged particle density in the column is n ∼ 10¹² cm⁻³. The probe measurements of n agree with the previous microwave absorption measurements. The water vapor concentration in the column is also estimated from probe measurements.     

On distribution over the cathode surface of the current due to positive ions in discharge with oscillating electrons

The mechanisms of processes determining distribution of positive ions on the cathode surface in a discharge with oscillating electrons are studied. At low pressures P≤5×10⁻⁵ torr over the entire range of anode length variation l _a=0.5–11 cm, the ion current distribution over the cathode radius J _i(r) features a single maximum in the center and drops steeply with distance from the axis. At pressures P=1–4×10⁻⁴ torr, the distribution J _i(r) for short anodes (l _a<6 cm) is similar to the previous one but, for long anodes (l _a=6–10 cm), new maxima at higher J _i values have been detected. A physical explanation for the obtained results is proposed.     

Non-steady-state photo-EMF in nanostructured GaN and polypyrrole within porous matrices

We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=442 nm, I ₀=0.045–0.19 W/cm², T=293 K) and σ=(3.5–4.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=532 nm, I ₀=2.3 W/cm², T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L _D=0.18 μm.     

Analysis of the <Emphasis Type="Italic">Y</Emphasis>(4140) and related molecular states with QCD sum rules

In this article, we assume that there exist scalar D^*[`(D)]<sup>*</sup>{D}^{\ast}{\bar {D}}^{\ast}, D<sub>s</sub><sup>*</sup>[`(D)]_s^*{D}_{s}^{\ast}{\bar{D}}_{s}^{\ast}, B^*[`(B)]<sup>*</sup>{B}^{\ast}{\bar {B}}^{\ast} and B<sub>s</sub><sup>*</sup>[`(B)]_s^*{B}_{s}^{\ast}{\bar{B}}_{s}^{\ast} molecular states, and study their masses using the QCD sum rules. The numerical results indicate that the masses are about (250–500) MeV above the corresponding D ^*–[`(D)]<sup>*</sup>{\bar{D}}^{\ast}, D <sub>s</sub> <sup>*</sup>–[`(D)]_s^*{\bar {D}}_{s}^{\ast}, B ^*–[`(B)]<sup>*</sup>{\bar{B}}^{\ast} and B <sub>s</sub> <sup>*</sup>–[`(B)]_s^*{\bar {B}}_{s}^{\ast} thresholds, the Y(4140) is unlikely a scalar D_s^*[`(D)]<sub>s</sub><sup>*</sup>{D}_{s}^{\ast}{\bar{D}}_{s}^{\ast} molecular state. The scalar D<sup>*</sup>[`(D)]^*D^{\ast}{\bar{D}}^{\ast}, D_s^*[`(D)]<sub>s</sub><sup>*</sup>D_{s}^{\ast}{\bar{D}}_{s}^{\ast}, B<sup>*</sup>[`(B)]^*B^{\ast}{\bar{B}}^{\ast} and B_s^*[`(B)]<sub>s</sub><sup>*</sup>B_{s}^{\ast}{\bar{B}}_{s}^{\ast} molecular states maybe not exist, while the scalar D￠<sup>*</sup>[`(D)]^￠*{D'}^{\ast}{\bar{D}}^{\prime\ast}, D_s^￠*[`(D)]<sub>s</sub><sup>￠*</sup>{D}_{s}^{\prime\ast}{\bar{D}}_{s}^{\prime\ast}, B<sup>￠*</sup>[`(B)]^￠*{B}^{\prime\ast}{\bar{B}}^{\prime\ast} and B_s^￠*[`(B)]_s^￠*{B}_{s}^{\prime\ast}{\bar{B}}_{s}^{\prime\ast} molecular states maybe exist.     

Upper Bounds for Coarsening for the Deep Quench Obstacle Problem

The deep quench obstacle problem models phase separation at low temperatures. During phase separation, domains of high and low concentration are formed, then coarsen or grow in average size. Of interest is the time dependence of the dominant length scales of the system. Relying on recent results by Novick-Cohen and Shishkov (Discrete Contin. Dyn. Syst. B 25:251–272, 2009), we demonstrate upper bounds for coarsening for the deep quench obstacle problem, with either constant or degenerate mobility. For the case of constant mobility, we obtain upper bounds of the form t ^1/3 at early times as well as at times t for which E(t) ￡ \frac(1-[`(u)]<sup>2</sup>)4E(t)\le\frac{(1-\overline{u}^{2})}{4}, where E(t) denotes the free energy. For the case of degenerate mobility, we get upper bounds of the form t <sup>1/3</sup> or t <sup>1/4</sup> at early times, depending on the value of E(0), as well as bounds of the form t <sup>1/4</sup> whenever E(t) ￡ \frac(1-[`(u)]²)4E(t)\le\frac{(1-\overline{u}^{2})}{4}.     

The Combined Effect of Connectivity and Dependency Links on Percolation of Networks

Percolation theory is extensively studied in statistical physics and mathematics with applications in diverse fields. However, the research is focused on systems with only one type of links, connectivity links. We review a recently developed mathematical framework for analyzing percolation properties of realistic scenarios of networks having links of two types, connectivity and dependency links. This formalism was applied to study Erdős-Rényi (ER) networks that include also dependency links. For an ER network with average degree [`(k)]\bar{k} that is composed of dependency clusters of size s, the fraction of nodes that belong to the giant component, P <sub>∞</sub>, is given by P<sub>￥</sub>=p<sup>s-1</sup>[1-exp(-[`(k)]pP_￥) ]^sP_{\infty}=p^{s-1}[1-\exp{(-\bar{k}pP_{\infty})} ]^{s} where 1−p is the initial fraction of randomly removed nodes. Here, we apply the formalism to the study of random-regular (RR) networks and find a formula for the size of the giant component in the percolation process: P _∞=p ^s−1(1−r ^k ) ^s where r is the solution of r=p ^s (r ^k−1−1)(1−r ^k )+1, and k is the degree of the nodes. These general results coincide, for s=1, with the known equations for percolation in ER and RR networks respectively without dependency links. In contrast to s=1, where the percolation transition is second order, for s>1 it is of first order. Comparing the percolation behavior of ER and RR networks we find a remarkable difference regarding their resilience. We show, analytically and numerically, that in ER networks with low connectivity degree or large dependency clusters, removal of even a finite number (zero fraction) of the infinite network nodes will trigger a cascade of failures that fragments the whole network. Specifically, for any given s there exists a critical degree value, [`(k)]<sub>min</sub>\bar{k}_{\min}, such that an ER network with [`(k)] ￡ [`(k)]_min\bar{k}\leq \bar{k}_{\min} is unstable and collapse when removing even a single node. This result is in contrast to RR networks where such cascades and full fragmentation can be triggered only by removal of a finite fraction of nodes in the network.     

Analysis of the X(1835) and related baryonium states with Bethe-Salpeter equation

In this article, we study the mass spectrum of the baryon-antibaryon bound states p [`(p)] \bar{{p}} , S \Sigma [`(S)] \bar{{\Sigma}} , X \Xi [`(X)] \bar{{\Xi}} , L \Lambda [`(L)] \bar{{\Lambda}} , p [`(N)] \bar{{N}}(1440) , S \Sigma [`(S)] \bar{{\Sigma}}(1660) , X \Xi [`(X)]<sup>￠</sup> \bar{{\Xi}}^{{\prime}}_{} and L \Lambda [`(L)] \bar{{\Lambda}}(1600) with the Bethe-Salpeter equation. The numerical results indicate that the p [`(p)] \bar{{p}} , S \Sigma [`(S)] \bar{{\Sigma}} , X \Xi [`(X)] \bar{{\Xi}} , p [`(N)] \bar{{N}}(1440) , S \Sigma [`(S)] \bar{{\Sigma}}(1660) , X \Xi [`(X)]^￠ \bar{{\Xi}}^{{\prime}}_{} bound states maybe exist, and the new resonances X(1835) and X(2370) can be tentatively identified as the p [`(p)] \bar{{p}} and p [`(N)] \bar{{N}}(1440) (or N(1400)[`(p)] \bar{{p}} bound states, respectively, with some gluon constituents, and the new resonance X(2120) may be a pseudoscalar glueball. On the other hand, the Regge trajectory favors identifying the X(1835) , X(2120) and X(2370) as the excited h^￠ \eta^{{\prime}}_{}(958) mesons with the radial quantum numbers n = 3 , 4 and 5, respectively.     

Electromagnetic structure of W± bosons in the e–e+ → W+W– reaction

A model-independent analysis of anomalous gauge coupling constants of W ^± bosons is presented and the corresponding restrictions on them and on the electromagnetic characteristics of W ^± bosons following from the experiments on measuring the e⁺ e^- ? W⁺ W^- ? ( e