Phase transitions in manganites with substitution of divalent ions for manganese

Experimental data are presented for the position of phase boundaries “orthorhombic-rhombohedral structure” and “semiconductor-metal” in manganites of La_{1 ? c + x} Sr _{c ? x} ²⁺ Mn_{1 ? x} Me _x ²⁺ O_{3 + γ} (Me = Mg, Zn, Ni) systems depending on the concentration of substituting divalent cations (0.15 ≤ c ≤ 0.35; 0.025 ≤ x ≤ 0.100).     

Metamagnetic states in single crystal HoNi<Subscript>2</Subscript>B<Subscript>2</Subscript>C at <Emphasis Type="Italic">T</Emphasis> ≈ 1.9 K: Torque magnetometry study

Metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi₂B₂C have been studied at T ≈ 1.9 K with a Quantum Design torque magnetometer. With increasing field, transitions to antiferromagnetic, ferrimagnetic, non-collinear, and saturated paramagnetic states take place. The critical fields of the transitions depend crucially on the angle θ between applied field and the easy axis [110]. Measurements of torque along the c axis have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab planes) and with changing field at fixed angle over a wide angular range. Two new phase boundaries in the region of the non-collinear phase have been observed, and the direction of the magnetization in this phase has been precisely determined. At low field the antiferromagnetic phase is observed to be multidomain. In the angular range around the hard axis (?6° ≤ ? ≤ 6°, where ? is the angle between the field and hard axis [100]) the magnetic behavior is found to be “frustrated” with a mixture of phases with different directions of the magnetization.     

The supergroup manifold formulation of the Wess-Zumino multiplet revisited: The supercurrent and the supergravity auxiliary fields

In this paper we provide a consistent first-order group-manifold formulation of the Wess-Zumino system. It is shownhow the well-known auxiliary fields of the ($\text{1}\text{2}$, 0, 0) system arise by supplementing Bianchi identities with the “second-order constraints”; that is, those equations allowing the transition from the first order to the second order of the theory. When the ($\text{1}\text{2}$, 0, 0) multiplet is coupled to N = 1 supergravity and the torsion “second-order constraint” is implemented, we get a non-minimal set of auxiliary fields (scalar, pseudoscalar axial vector and a spinor). We argue this to be the fundamental set of auxiliary fields. The so-called “minimal set” is not coordinate invariant and can be recovered only by adding a non-geometrical constraint.     

Phase transformations in equiatomic alloy TiZr at pressure up to 70 kbar

The effect of pressure on the α ? β and ω ? β transformations in the equiatomic alloy TiZr is studied by the differential thermal analysis (DTA) and calorimetric technique. The α-β equilibrium at atmospheric pressure occurs at a temperature of 579°C, and the heat of transition ΔH is 40.9±2.0 J/g. As the pressure increases up to 28 kbar, the temperature of the α-β equilibrium linearly decreases, dT/dP=?2.2±0.3 K/kbar. In the pressure range 28–48 kbar, the β-phase undergoes a transition to the two-phase (α + ω) state upon cooling to room temperature. At pressures above the triple point with the coordinates P=49±3 kbar and T=460±30°C, the cooling of the β-phase gives rise to only the hexagonal ω-phase with the unit cell parameters a=4.843 Å, c=2.988 Å, and c/a=0.617 under normal conditions. The slope of the ω-β equilibrium boundary is positive at pressures up to 70 kbar, dT/dP≈0.46 K/kbar. The ω → α transformation at atmospheric pressure proceeds in the temperature range T=425–470°C with the enthalpy of transition ΔH=2.8 J/g.     

Numerical simulation of transitional flow on a wind turbine airfoil with RANS-based transition model

This paper presents a numerical investigation of transitional flow on the wind turbine airfoil DU91-W2-250 with chord-based Reynolds number Re_c = 1.0 × 10⁶. The Reynolds-averaged Navier–Stokes based transition model using laminar kinetic energy concept, namely the k ? k_L ? ω model, is employed to resolve the boundary layer transition. Some ambiguities for this model are discussed and it is further implemented into OpenFOAM-2.1.1. The k ? k_L ? ω model is first validated through the chosen wind turbine airfoil at the angle of attack (AoA) of 6.24° against wind tunnel measurement, where lift and drag coefficients, surface pressure distribution and transition location are compared. In order to reveal the transitional flow on the airfoil, the mean boundary layer profiles in three zones, namely the laminar, transitional and fully turbulent regimes, are investigated. Observation of flow at the transition location identifies the laminar separation bubble. The AoA effect on boundary layer transition over wind turbine airfoil is also studied. Increasing the AoA from ?3° to 10°, the laminar separation bubble moves upstream and reduces in size, which is in close agreement with wind tunnel measurement.     

Flow visualization of relaminarization phenomena in curved pipes and the related measurements

Flow visualization results for secondary flow phenomena at the exit of 90° and 180° bends and helically coiled pipes (1, 2 and 5 turns), (radius of curvatureR _c=381 mm, inside pipe diameterd=37.5 mm, curvature ratiod/2R _c=0.049) and in the downstream straight pipe (l/d=30) are presented to study the stabilizing (relaminarization) effect in curved pipes with fully developed entry turbulent air flow and the destabilizing (re-transition from laminar to turbulent flow) effect in the downstream straight region. The entry Reynolds numbers areRe=2200, 3200, 4300 and 5300). The related measurement results using a hot-film anemometer are presented for developing profiles of the time-mean streamwise velocity distribution and the axial turbulence intensity field in the 180° return bend and in the downstream straight pipe for Reynolds numbersRe=3200, 4300, 6300 and 8200. The time traces showing the output of the hot-film sensor are also presented for developing fluctuating velocity field in the 180° bend and in the downstream straight pipe for the same Reynolds number range. Some aspects of the relaminarization phenomena in curved pipes and the re-transition phenomena from laminar to turbulent flow in the downstream straight pipe are clarified by the present experimental investigation.     

Neutron-neutron quasifree scattering in the 2H(n,nn)p reaction at En = 14.1 MeV

Neutron-neutron quasifree scattering has been studied in the deuteron break-up reaction ²H(n, nn)p at E_n = 14.1 MeV. Two coplanar and symmetric configurations have been investigated in a kinematically complete experiment where the detection of the spectator particle was not possible. The experimental cross sections are compared with “exact” calculations derived from Faddeev-type equations solved with S- and P-wave nucleon-nucleon separable interactions. These calculations agree both in shape and magnitude with the differential cross section for the θ₁ = ? θ₂ = 40° configuration (E_p^min = 0). At θ₁ = ? θ₂ = 30° (E_p^min = 180 keV). however, the absolute value of the measured cross section is too high and an observed structure in the shape of the differential cross section is in sharp conflict with the now available “exact” calculations.     

EPR study of Mn2+ around the ferroelastic transition point of Pb3(PO4)2

The spin Hamiltonian parameters of Mn²⁺ have been measured above and below the transition point (180°C) of the lead phosphate. They show that Mn²⁺ substitutes a Pb_I ion. Between 175 and 180°C the principal axis OX of the fine tensor is parallel to the wave vector of the soft mode which condensates at the transition point. An exaltation of the linewidth is observed. The linewidth remains constant within 5°C of T_c; in this temperature range, the “static regime” is achieved, and the correlation time of the fluctuations is less than 10^?8 sec.     

Systematic Experiment on Star Anomaly in pd Break up at E/A = 9.5 MeV

We measured pd breakup cross section at E _d = 19 MeV (E/A = 9.5 MeV) at Star configuration at 120° ≤ inclination angle α ≤ 180°, i.e. apart from Space Star configuration (α = 90°), and found that pd Star cross section at 120° ≤ α ≤ 180° agree with pd calculation, contrary to Köln data. By our systematic experiments on Star configurations so far and recent reliable pd calculations, existence of Space Star anomaly has been established in pd breakup at E/A = 9.5 and 13 MeV. Also it has been confirmed that no anomaly exist at Star configurations apart from Space Star.     

Mixing of P wave axial vector resonances

An analysis is given of the mixing of the axial vector kaon resonances by use of new data from SLAC. Mass values, decay widths and branching ratios of the SLAC work may be compatible with SU(3) and/or “pair creation model” classifications for a mixing angle λ ≈ ?35° ± 10°. The mass values and coupling strengths proposed by Basdevant and Berger, from a different parametrization of the same data, can be fitted in an SU(3) and/or broken SU(6)_w model with a larger mixing angle λ ≈ ?80°. Such a mixing would mean that the lower kaonic state is closely related to the 1^+? nonet in contrast to expectations from duality and/or one-gluon exchange mixing schemes. We also discuss the mixing of the charmed D meson states.     

Pulsed NMR frequency shifts in superfluid 3He

We report the first measurements of the NMR frequency in ³He A and B under conditions where the net magnetization, M, is tipped far from its equilibrium direction along H_O. In ³He A the frequency shift ω - γH_O varies from the continuous wave value at tipping angle Φ = 0 to a negative shift at Φ = 180°. In ³He B no frequency shift is observed, however for Φ ? 100° a beat pattern is seen to develop in the free induction decay envelope.     

Soluble renormalization groups and scaling fields for low-dimensional Ising systems

A variety of one-dimensional Ising spin systems, including staggered and parallel magnetic fields, alternating and second neighbor interactions, four-spin coupling, etc., are discussed in terms of renormalization group theory. A continuous range of distinct renormalization groups is constructed in exact closed form, analyzed in detail, and compared with exactly calculated thermodynamic properties. Fixed point linearization yields relevant, irrelevant, and marginal operators. All groups yield identical “critical” behavior (at T = 0) with η = 1, δ = ∞, γ = ν = 2 ? α, and with identical linear scaling fields. A generalization of Wegner's analysis to discrete groups yields explicit power series for the nonlinear scaling fields; these are seen to depend on the particular renormalization group and, hence, are physically nonunique. A planar, multiconnected “truncated tetrahedron” model of effective dimensionality log₂ 3 is analyzed via a dedecoration and star-triangle group revealing highly singular behavior as T → T_c = 0.     

Anomalous thermoelastic behaviour of cubic potassium cyanide

The temperature dependence of all elastic constants of cubic potassium cyanide has been measured by ultrasonic methods in the range from -105.4 to 181°C. Until about 180°C all elastic wave velocities increase with higher temperatures. The behaviour of the shear constant c₄₄ is given by c₄₄ = a · logT/T₀ with a = 0.219 · 10¹¹dyn.cm^?2 and T₀ = 153.7°K with a good approximation. These unusual effects are assigned to the librational vibrations and orientational jumping processes of the CN-ions. The phase transition at -105.5°C is a consequence of the low c₄₄ value.     

Microwave spectrum and hydrogen bonding in 1-aziridineethanol

From its microwave spectrum, 1-aziridineethanol,

$\text{CH}{}_2\text{CH}{}_2\text{NCH}{}_2\text{CH}{}_2\text{OH}$

is found to have a gauche OCCN configuration, maintained by an OH?N-type hydrogen bond. The normal species rotational constants (MHz), A = 8528.87(25), B = 2069.74(2), and C = 2020.41(2), are consistent with a small (～6°) distortion from the “staggered” configuration about the central CN bond. Assuming a “normal” hydroxyl group, the hydroxy d₁ data suggest a decrease in the O?N distance upon bridge deuteration of ～0.003 Å. The dipole moment is 2.77(5) D, with 2.34(3), 1.45(6), and 0.3(3) D “a,” “b,” and “c” components, respectively.     

Two schemes ofη−η′-mixing

Proceeding from the expansion of composite operators in interpolating hadronic fields, the width of the decays η(η′)→γγ andJ/ψ→η(η′)γ have been calculated. Two mechanisms of pseudoscalar field mixing (“mass-mixing” and “current-mixing”) are considered. In the given schemes, the values of η?η′-mixing angle θ _p are, respectively, (?15.0±1.8)^o and (?19.7±2.2)^o.     

The Wigner transition as a bifurcation

The Wigner transition from a low-density electron gas to an “electron solid” is described as a second-order phase transition. Using bifurcation theory, the corresponding critical mean interelectron spacing is found to lie in the range 3.92 < d_c/a_o ? 6.03.     

Microwave spectrum,centrifugal distortion,substitution structure,and dipole moment of sulfine,CH2SO

The microwave spectrum of the reactive species sulfine (CH₂SO) has been studied. Assignments of 86 transitions of the ground vibrational state normal isotopic species, with J up to 60, have allowed a thorough centrifugal distortion analysis. With planarity implied by the I_c-I_a-I_b value of 0.1333 amu $\text{A}\text{?}{}^2$, spectral assignments of seven other isotopic modifications have resulted in the following substitution bond lengths and angles: CH_syn = 1.085 Å, CH_anti = 1.077 Å, CS = 1.610 Å, SO = 1.469 Å, ?HCH = 121.86^°, ?SCH_syn = 122.51^°, ?SCH_anti = 115.63^°, and ?CSO = 122.51^°. From Stark effect measurements of the normal and d₂ species, the dipole moment has been determined to be 2.994 D, oriented 25.50° relative to the SO bond and 9.61° relative to the normal species “a” axis. At an initial pressure of 30 mTorr in a clean brass waveguide, the lifetime of sulfine at 25°C is ～30 min.     

Hydrogen-like atom in a superstrong magnetic field: Photon emission and relativistic energy level shift

Following our previous work, additional arguments are presented that in superstrong magnetic fields B ? (Zα)² B ₀, B ₀ = m ² c ³/e? ≈ 4.41 × 10¹³ G, the Dirac equation and the Schrödinger equation for an electron in the nucleus field following from it become spatially one-dimensional with the only z coordinate along the magnetic field, “Dirac” spinors become two-component, while the 2 × 2 matrices operate in the {0; 3} subspace. Based on the obtained solution of the Dirac equation and the known solution of the “onedimensional” Schrödinger equation by ordinary QED methods extrapolated to the {0; 3} subspace, the probability of photon emission by a “one-dimensional” hydrogen-like atom is calculated, which, for example, for the Lyman-alpha line differs almost twice from the probability in the “three-dimensional” case. Similarly, despite the coincidence of nonrelativistic energy levels, the calculated relativistic corrections of the order of (Zα)⁴ substantially differ from corrections in the absence of a magnetic field. A conclusion is made that, by analyzing the hydrogen emission spectrum and emission spectra at all, we can judge in principle about the presence or absence of superstrong magnetic fields in the vicinity of magnetars (neutron stars and probably brown dwarfs). Possible prospects of applying the proposed method for calculations of multielectron atoms are pointed out and the possibility of a more reliable determination of the presence of superstrong magnetic fields in magnetars by this method is considered.     

Polarization properties of Li2−x Na x Ge4O9 (0.2 ≤ x ≤ 0.3) crystals

The polarization switching in sinusoidal fields and the pyroelectric properties of Li_2?x Na _x Ge₄O₉ (0.2 ≤ x ≤ 0.3) crystals are measured in the temperature range T _c ?T ≤ 40 K. The behavior of the P?E hysteresis loops with variations in temperature is investigated for crystals with phase transition temperatures T _c < 300 K and T _c > 300 K. It is shown that, for crystals with phase transition temperatures T _c < 300 K, the temperature dependence of the hysteresis loop exhibits a behavior typical of crystals with second-order phase transitions. The crystals with phase transition temperatures T _c > 300 K are characterized by double hysteresis loops in the temperature range T _c ?T ₁ ≈ 30 K. The correlation between the polarization properties and possible structural transformations of the Li_2?x Na _x Ge₄O₉ crystals due to the change in the concentration ratio of Na and Li ions is discussed.     

Regeneration amplitude of KS0 from KL0 in carbon

We have measured the transmission regeneration amplitude for carbon. The invariant amplitude $\text{[?(0) ?}\text{?}\text{(0)]/P}$ varies from 5.909 ± 0.066 mb at 4.5 GeV/c to 3.933 ± 0.152 mb at 9.5 GeV/c. The results agree with optical model calculations using measured kaon-nucleon total cross sections. The data also provide a value for the ω trajectory intercept α_ω(0) = 0.42 ± 0.04.