Modification of the magnetic structure of UAs — Appearance of an incommensurate phase below TN in UAs0.97Se0.03, studied by neutron diffraction from a single crystal

The magnetic structure of UAs_0.97Se_0.03 has been studied by neutron diffraction from a single crystal in zero applied magnetic field. It is found to be antiferromagnetic, of type-IA (++--) below T_o = 75.6 K and of type-I (+-+-) above T_o. The type-I persists till T_IC = 113.5 K, while above it and up to T_N = 122 K an incommensurate phase appears, thereby modifying the magnetic structure in pure UAs. The k-value of the wavevector $\text{K}$ (along cubic axes) is changing from 0.642 at T_N to 0.652 at T_IC. The transitions at T_o and T_IC are first-order while the transition at T_N is second-order. The ordered magnetic moment is 2.15 μ_B at T = 4.2 K, it varies smoothly to 1.95 μ_B at T = 75.4 K and drops drastically to 1.47 μ_B at T = 76 K.     

Effect of Cd impurity on the electrical properties of a-Se80Te20

Temperature dependence of dark and photoconductivity is studied in amorphous films of Se₈₀Te_20−xCd_x in the temperature range (300 K to 380 K) with a view to see the effect of Cd impurity on a-Se₈₀Te₂₀ binary alloy. It is observed that, at low concentration of Cd (x = 0.5), the dark and photoconductivity increase at all temperatures. However, at higher concentration of Cd (x = 10), an appreciable reduction in these parameters occurs in the same temperature range. The photosensitivity (σ_ph/σ_d) remains unchanged at x = 0.5 but decreases quite significantly at x = 10. The results are explained in terms of impurity doping at x = 0.5 and alloying effect at x = 10.     

Large transverse momentum particle production at 90° in proton-proton collisions at the ISR

Total charged particle fluxes above 1.2 GeV/c transverse momentum at 90° have been measured at the CERN Intersecting Storage Rings for c.m. energies between 23.2 and 52.7 GeV. In addition, charged pion spectra above 3 GeV/c have been obtained at 44.4 and 52.7 GeV, as well as gamma-ray spectra at the same energies. The upper limit to produce a single electron above 3 GeV/c at 90° is less than 1.2 × 10^?33cm²/sr at 90% confidence level.     

Conformal Structures of Static Vacuum Data

In the Cauchy problem for asymptotically flat vacuum data the solution-jets along the cylinder at space-like infinity develop in general logarithmic singularities at the critical sets at which the cylinder touches future/past null infinity. The tendency of these singularities to spread along the null generators of null infinity obstructs the development of a smooth conformal structure at null infinity. For the solution-jets arising from time reflection symmetric data to extend smoothly to the critical sets it is necessary that the Cotton tensor of the initial three-metric h satisfies a certain conformally invariant condition (*) at space-like infinity, it is sufficient that h be asymptotically static at space-like infinity. The purpose of this article is to characterize the gap between these conditions. We show that with the class of metrics which satisfy condition (*) on the Cotton tensor and a certain non-degeneracy requirement is associated a one-form κ with conformally invariant differential dκ. We provide two criteria. If h is real analytic, κ is closed, and one of its integrals satisfies a certain equation then h is conformal to static data near space-like infinity. If h is smooth, κ is asymptotically closed, and one of its integrals satisfies a certain equation asymptotically then h is asymptotically conformal to static data at space-like infinity.     

Two regimes of vortex penetration into platelet-shaped type-II superconductors

Vortex penetration into a thin superconducting strip of a rectangular cross section is considered at an increasing applied magnetic field H _a , taking an interplay between the Bean-Livingston and the geometric barriers in the sample into account. We calculate the magnetic field H _p at which the penetration begins and show that two regimes of vortex penetration are possible. In the first regime, vortices appearing at the corners of the strip at H _a = H _p immediately move to its center, where a vortex dome starts to develop. In the second regime, the penetration occurs in two stages. In the first stage, at H _a < H _p , tilted vortices penetrate into the edge regions of the strip, where novel domes are shown to be formed at the top, bottom, and lateral surfaces. In the second stage, at H _a = H _p , the vortex propagation to the center becomes possible. The difference between the regimes manifests itself in slightly different dependences of the magnetic moment of the strip on H _a .     

Effect of Al concentration and hydrostatic pressure on the néel temperature of CrAl alloys

As determined from ? vs T measurements, the T_N vs Al content curve for CrAl alloys exhibits three distinct regions. The first region extends from 0 to about 2 at.% Al. Here the Néel temperature decreases linearly in two stages, with an abrupt change in slope occurring at about 1.2 at.% Al. From 2 to 4 at.% Al no T_N value could be defined from the resistivity measurements. Finally, at concentrations higher than 4 at.% Al, T_N was observed to increase with increasing Al content. The variation of dT_N/dp with Al concentration was found to be similar to the T_N curve in the first region. Exceptionally high values of dT_N/dp were found.     

Adsorption isotherms of oxygen on tungsten (100), (110) and (111) surfaces in the pressure range 10−9 to 10−4 torr and temperature range 1500 to 2600 k,as measured by AES

This paper is a continuation of a previous investigation of oxygen adsorption on tungsten at high temperature using Auger electron spectroscopy. In this paper the adsorption isotherms of oxygen on (100), (110) and (111) faces of tungsten are reported. It is shown that these isotherms can be described by an equation of the form pO₂ = AF(θ) exp [?q(θ)/ kT]. The coverage depended functions F(θ) and q(θ) evaluated from the isotherms are different for all three investigated faces. The isosteric adsorption energy q has following initial values at very low oxygen coverage: q₁₀₀ = 6.1 eV, q₁₁₀ = 6.8 eV and q₁₁₁ = 6.5 eV. Increasing the oxygen coverage has only small influence on q₁₁₁; it changes from the initial value to q₁₁₁ ≈ 6.0 eV at θ ≈ 0.3 and remains constant at this value up to θ ≈ 1. q₁₁₀ shows the strongest dependence on oxygen coverage. It decreases rapidly at low coverages, slowly at moderate coverages and reaches the value q₁₁₀ = 5.0 atθ ≈ 1. The variation of q₁₁₀ with increasing oxygen coverage is monotonie from the initial value to q₁₁₁ = 4.9 eV at θ ≈ 1. Assuming that the atomic oxygen is the dominant species leaving the tungsten surface at high temperatures the functions F(θ) are used to calculate the oxygen equilibration probability ζO₂ (high temperature sticking probability) as a function of oxygen coverage θ. The main characteristic of ζO₂(θ) for all three faces is that it shows a maximum for (100) and (111) faces at θ = 0.3 and for (110) face at θ = 0.55.     

Measurements of the inclusive pd breakup cross section at low and intermediate energies

Inclusive measurements of the D(p, p)pn reaction were made at incident proton energies of 248?MeV and 13?MeV, to investigate the global feature of the pd breakup reaction at intermediate and low energies. At 248?MeV, the cross section and analyzing power A _y were measured at four angles from 7° to 20°. The data largely disagree with Faddeev calculations even if 2π-exchange three-nucleon force (2π3NF) or Δ-isobar is included, and the disagreement increases at forward angles. At 13?MeV, the cross section was measured at eight angles from 10° to 70°. The data are well reproduced by a recent pd Faddeev calculation, and the effects of Δ-isobar at 13?MeV are very small.     

The electrochemistry of InP in Br2/HBr solutions and its relevance to etching behaviour

Etch rate-potential curves of p-InP in HBrandBr₂/HBr solutions in the dark and under illumination were correlated with current-potential curves. It was found that InP is etched via a “chemical” mechanism both by HBrandBr₂. In aqueous HBr solutions InP is only etched at a significant rate at concentrations higher than 5 mol/ℓ. The Br₂ etchants contained 4.5M HBr; in this case HBr only serves to complex Br₂toBr^-₃. The etch rate in Br₂/HBr solutions is mass-transport controlled at InP(001) and kinetically controlled at InP with the (111) In orientation. The macroscopically obtained results are consistent with the profiles etched at resist edges in InP. The electrochemistry of Br₂ at p-InP under illumination reveals some interesting aspects with regard to the agreement between the etch rate and the Br₂ reduction.     

Systematic measurement of the D(p, pp)n cross section at KUTL

Systematic measurement of the D(p, pp)n cross section at E _p = 13 MeV at star configurations at various inclined angle α is in progress at Kyushu University tandem accelerator laboratory (KUTL). The measured cross section at space star (α = 90°) is about 12% below the recent pd calculation. The next measurement is being made at 0° < α < 90° to see if the large anomaly of about 25% found by the Köln group (2006) at backward α exists also at forward α.     

Gravity modulation study on opposed flame spread over thin solid fuels

In this work a numerical investigation has been carried out to study the effect of g-jitter on zero-gravity (0g_e) opposed flow spreading flame over thin solid fuels. For comparison simulations have also been carried out for normal gravity (1g_e) downward spreading flames. G-jitter is emulated by gravity modulation of sinusoidal (A_ge sin(2πt/T_ge)) gravity perturbation (g-perturbation) of a particular time-period (T_ge) and amplitude (A_ge) over a selected base gravity level (0g_e or 1g_e). The response of flames at 0g_e base gravity and at 1g_e base gravity was different to the imposed g-perturbation. While at 0g_e the mean and the amplitude of the oscillatory flame spread rate (FSR) magnified with increase in the time period of g-perturbation, interestingly for the 1g_e flame a maximum mean FSR and oscillation amplitude occurs at certain perturbation time period. Further, at very small perturbation time-periods (T_ge) the FSR at 1g_e was lower than the steady state FSR. The amplitude of oscillatory FSR increased with increase in perturbation amplitude (A_ge). However, the 0g_e flame which is little affected (compared to 1g_e flame) at small perturbation amplitude (A_ge) is affected severely at large perturbation amplitude (A_ge). Both the gas phase and fuel pyrolysis (or fuel response) follow perturbation signal with a lag but fuel pyrolysis is more sluggish and lags behind gas phase. The phase lag between fuel pyrolysis and gas increases at smaller time-periods (T_ge) and tends to enhance the effect of external perturbation whereas at larger time-periods (T_ge) this lag inhibits the effect of external perturbation.     

Infrared emission and lasing due to magnetoelectric-photo effect in InSb: Spectroscopy

Spectroscopic investigations have been carried out on IR emission (and induced absorption) of bulky InSb subjected to a magnetic field H across a current density J passing through it at 80–300 K. Significant contribution of deep-level acceptors, such as Cu⁻ and Cu⁻⁻, to the radiative recombination has been observed at low excitations by J × H force at 80 and 300 K. While at high excitations the emission due to band-to-band recombination dominates even at low temperatures, and at further high excitations notable line narrowing in the spectral line has been disclosed at 80 K, demonstrating occurrence of lasing mostly in a form of multi-mode oscillations but occasionally with single-mode oscillation.     

Longitudinal polarization transfer in the T→p, →n)3He reaction

The longitudinal polarization of neutrons has been measured for the reaction $\text{T}\text{→p}\text{,}\text{→n}\text{)}{}^3\text{He}$ with the incident proton beam longitudinally polarized. Measurements were performed at 0° for proton energies from 4 to 15 MeV and an angular distribution was measured at 10 MeV. The data determine the polarization transfer coefficient K_z^z′, which is equivalent to the Wolfenstein A′ parameter for nucleon-nucleon scattering. The quantity K_z^z′ at 0° increases from about 0.3 at 3 MeV incident energy to 0.9 at 9 MeV, and then decreases to 0.5 at 15 MeV. The data are computed with R-matrix calculations which reproduce the qualitative shape of the data at 0° and the angular distribution at 10 MeV.     

Transformation of phase to (x,y,z)-coordinates for the calibration of a fringe projection profilometer

In this work we present a phase to (x,y,z)-coordinates transformation method for the calibration of a fringe projection profilometer. Our technique is divided in two parts: (1) phase to z transformation (for axial calibration) based on the typical polynomial fitting which uses a flat plane placed at several z positions to measure the phase of the projected fringes. (2) Phase to x and y transformation (for transverse calibration) based on the use of a crossed gratings pattern and a Fourier phase measurement method to determine x and y coordinates at several z positions. As will be shown the use of the crossed gratings pattern and the Fourier phase measurement method for transverse calibration is advantageous in several aspects: an unique image can give us x and y information at once. It provides x and y coordinates at each pixel in the image avoiding the use of interpolation methods. We present some experimental results and explain the viability of the proposed technique.     

Resolution effects and scaling in numerical simulations of passive scalar mixing in turbulence

The effects of finite grid resolution on the statistics of small scales in direct numerical simulations of turbulent mixing of passive scalars are addressed in this paper. Simulations at up to 2048³ grid points with grid spacing Δx varied from about 2 to 1/2 Batchelor scales (η_B) show that most conclusions on Schmidt number (Sc) dependence from prior work at less stringent resolution remain qualitatively correct, although simulations at resolution Δx≈η_B are preferred and will give adequate results for many important quantities including the scalar dissipation intermittency exponent and structure functions at moderately high orders. For Sc≥1, since η_B=ηSc^−1/2 (where η is the Kolmogorov scale), the requirement Δx≈η_B is more stringent than the corresponding criterion Δx≈η for the velocity field, which is thus well resolved in simulations aimed at high Schmidt number mixing. A simple argument is given to help interpret the effects of Schmidt and Reynolds numbers on trends towards local isotropy and saturation of intermittency at high Schmidt number. The present results also provide evidence for a trend to isotropy at high Reynolds number with fixed Sc=1.0. This is a new observation apparently not detected in less well resolved simulations in the past, and will require further investigation in the future.     

Electron paramagnetic resonance in deuterated nickel fluosilicate

Electron paramagnetic resonance measurements in single crystals of NiSiF₆. 6D₂O were made at K, Ku and Ka bands at 4.2 K and between 77 K and 300 K. The measured g values were in the range 2.23–2.26, while the zero-field splitting parameter D varied from ?(0.185 ± 0.005) cm^?1 at 4.2 K to ?(0.53 ± 0.01) cm^?1 at 298 K. The parameters of the trimolecular hexagonal unit cell were determined to be approximately a = 9.28 Å, c = 9.58 Å from powder X-ray diffraction measurements at room temperature.     

Temperature dependence of the current-voltage characteristics of the Al/Rhodamine-101/p-Si(1 0 0) contacts

The current-voltage (I-V) characteristics of Al/Rhodamine-101/p-Si/Al contacts have been measured at temperatures ranging from 280 to 400 K at 20 K intervals. A barrier height (BH) value of 0.817 eV for the Al/Rh101/p-Si/Al contact was obtained at the room temperature that is significantly larger than the value of 0.58 eV of the conventional Al/p-Si Schottky diode. While the barrier height Φ_b0 decreases the ideality factors (n) become larger with lowering temperature. The high values of n depending on the sample temperature may be ascribed to decrease of the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. Therefore, at all temperatures, it has been seen that the I-V characteristics show three different regions, the ohmic behavior at low voltages, and the space charge limited current with an exponential distribution of traps at high voltages.     

Measurement of antiproton-proton small-angle elastic scattering at low momentum

Two high statistics measurements of antiproton-proton small-angle elastic scattering, at p = 233 MeV/c and p = 272 MeV/c, are presented. The measurements were carried out at the LEAR facility at CERN. By the Coulomb-nuclear interference method, values are obtained for the real-to-imaginary ratio ρ of the p̄p forward nuclear scattering amplitude and for its exponential slope b: ρ = + 0.041 ± 0.026 and b = 71.5 ± 4.5 (GeV/c)⁻² at 233 MeV/c and ρ = −0.014 ± 0.027 and b = 47.7 ± 2.7 (GeV/c)⁻² at 272 MeV/c. The method to derive these values is discussed in detail and so are the uncertainties contributing to their systematic error. The results are compared with predictions from forward dispersion relation calculations and with predictions from p̄p potential models.     

Observation of the vortex-glass transition in YBa2Cu3O7 by phase-resolved current-voltage measurements

Abstract. We report on investigations of the current-dependent ac impedance Z at 17 Hz of a YBa₂Cu₃O₇ thinfilm microbridge in magnetic fields from 1 to 8 T. A phasesensitive lock-in technique was applied and supplemented by a pulsed method for high current densities. Above the vortex-glass transition temperature T _g a constant Z(j) is observed with low current densities j, and a power-law behavior at high currents. Below T _g, the curvature of the Re Z vs. j curve is negative in a log-log plot. The Re Z(j) isotherms can be collapsed onto two universal scaling functions according to the predictions of the vortex-glass model. Close to and below T _g, a phase lag between current and voltage appears, which saturates to finite values at low j and to zero at high j. The phase lag within the constant-Z(j) region remains below the critical value, predicted theoretically by Dorsey, if T > T _g and approaches 90° at T < T _g indicating the freezing of the vortices into the dissipation-free vortex-glass state.     

Paramagnetic resonance linewidth of EuO near the curie temperature

Measurements of the EPR linewidth ΔH of EuO at 9 GHz are reported in the temperature range of 66–300° K, with particular attention to the region near T_c (69.6° K). Comparison with the earlier data of Eastman at 25 GHz in the critical region shows considerable suppression of ΔH at 25 GHz. The temperature-dependent behavior of ΔH in EuO at 9 GHz is similar to the observations in CrBr₃ and it is in qualitative agreement with the zero-field predictions of Huber and Maleev. The quantitative discrepancies are believed to be due to the effect of the resonance magnetic field on EPR spin dynamics near T_c and an inadequate decoupling of the four-spin correlation functions used in the theories.