On the mechanism of phase transformation in Ag2Se

A differential thermal analysis ΔT _y (T) in vacuum has been performed, and the temperature gradient ΔT _x (T) along the Ag₂Se sample during the transition α → β has been studied. It has been shown that the transitions α → α′ and β′ → β are displacive transitions and that the transition α′ → β′ is a reconstructive transition. It has been found that the temperature gradient along the sample during the transition α′ → β′ passes through a deep minimum due to a strong increase in the specific heat capacity.     

Heat conductivity of a nonlinear β-FPU lattice

In this work, we propose a new approach to the computation of heat conductivity in nonlinear systems. The total heat conductivity process is decomposed into two parts: one part is an equilibrium process at the same temperature T of either end of the lattice, which does not transfer energy and the other is a nonequilibrium process at temperature ΔT of one end and a zero temperature of the opposite end of the lattice. This approach makes it possible to somewhat reduce the time of computation of heat conductivity at ΔT → 0. The threshold temperature T _thr is found to behave as T _thr ∼ N ⁻³, where N is the lattice length. The threshold temperature conventionally separates two mechanisms of heat conductivity: at T < T _thr, phonon heat conductivity is dominant; at T > T _thr, the contribution of soliton heat conductivity increases with increasing temperature. The problem of the computation of heat conductivity in the limit ΔT → 0 reduces to the heat conductivity of a harmonic lattice with time-dependent bond rigidities determined by an equilibrium process at temperature T. An exact expression for the temperature dependence of sound velocity in a lattice with a β-FPU potential at T < 10 is derived. A numerical experiment confirmed the existence of solitons and breathers that correspond to a modified Korteweg-de Vries (KdV) equation. The problem of the quantitative contribution of solitons and breathers to heat conductivity requires further study.     

T Violation in Neutrino Oscillation above GUT Scale

We study the Planck scale effects in the neutrino sector on the asymmetry between T-conjugate oscillation probabilities. ΔP _T =P(ν _α →ν _β )−P(ν _β →ν _α ), in a three flavor neutrino mixing. In this paper, we discuss some aspect of T violation effects in three flavor neutrino oscillation.     

Quantum measurement and pure dephasing

The prerequisite of quantum measurement is a transformation of an initially off-diagonal density matrix _ρmα;nβ describing an interacting measured object and measuring device into a diagonal density matrix _{ρmα;mαδmnδαβ} . The latter density matrix describes a proper mixture of states having definitem-values. On the other hand, the irreversible relaxation (towards the thermodynamic equilibrium) is also characterized by transformation of an initially off-diagonal matrix into a diagonal one. It has been shown that the process of irreversible relaxation can be used to perform quantum measurement, provided the duration Δt of the measurement is much larger thanT ₂, the phase relaxation time, and much smaller thanT ₁, the population relaxation time:T ₂ ≪ Δt ≪T ₁. Agedanken experiment describing this kind of measurement is provided. Aπ/2-pulse transforms an initials _z = −1/2 state into superposition ofs _z = ±1/2 states. The irreversible relaxation leads to the proper mixture ofs _z = 1/2 ands _z = −1/2 state. Results of the measurements are verified by the second electromagnetic pulse.     

Influence of Thomson effect on the resultant local Seebeck coefficient in thermoelectric composite materials

The resultant local Seebeck coefficient α _R (=α _S−α _T) at the interface of a thermoelement has not yet been measured, although it is an important factor governing the thermoelectric efficiency, where α _S is the local Seebeck coefficient and α _T is the one caused by the Thomson effect. It is shown in this paper that α _S, α _T, and α _R of the p- and n-type Cu/Bi–Te/Cu composites are obtained analytically and experimentally on the assumption that the local temperature of the composite on which the temperature difference ΔT is imposed varies linearly with changes in position along the composite. They were indeed estimated as a function of position from the local experimental data of R,ΔI,ΔT, and V generated by applying an additional current of ±I to the composite, where R is the electrical resistance and ΔI is a current generated by the composite. As a result, it was found that the absolute values of α _S at the hot interface of the p- and n-type composites are approximately 1.5 and 1.4 times higher than their lowest values in the middle region of the composite, respectively, while those of α _T are less than 8% of α _S all over the composite and are so small that the relation α _R≈α _S can be held. We thus succeeded in measuring α _R at the interfaces of the composite.     

Phenomenological theory of the magnetoelectric effect in some boracites

An explanation is given for the narrow peak in the temperature dependence of the component α ₃₂ of the magnetoelectric effect tensor near the transition at T=T _c to the m′m2′ phase observed in the boracites. A phenomenological approach is used which is based on the symmetry of the cubic phase of the crystals. The change in the sign of α ₂₃ and α ₃₂ observed in some of the boracites as the temperature is lowered is attributed to the low value of T _c. Zh. éksp. Teor. Fiz. 111, 536–546 (February 1997)     

Effects of current density on electropulsing-induced phase transformations in a Zn–Al based alloy

Phase transformations of an electropulsing-treated ZA22 alloy were studied after tensile deformation by using scanning electron microscopy and transmission electron microscopy. It was found that electropulsing tremendously accelerated phase transformations consequentially in the two stages: (a) quenching from supersaturated state approaching the final stable state, i.e., α+ε→T′+η, and (b) up-quenching from the final stable state to a higher temperature state, i.e., T′+η→α+ε. The mechanism of electropulsing-induced phase transformation is discussed from the point of view of Gibbs free energy, and electropulsing kinetics.     

Focal switch of cosine-Gaussian beams

The focal switch of cosine-Gaussian (CsG) beams passing through a system with the aperture and lens separated is studied analytically and numerically. It is shown that the focal switch of CsG beams can appear not only for the apertured case, but also for the unapertured case. The necessary condition for the focal switch is that truncation parameter α > α_c and the beam parameter β > β_c, α_c, β_c being the corresponding critical values. There exists a maximum of the relative transition height Δz _sw as α varies, and Δz _sw increases with increasing β and decreasing N _w. The normalized axial intensity minimum I _min / I _max decreases with an increase of α and β, and I _min / I _max remains unchanged as N _w varies.     

New physics hints in B decays and collider outlook

There are currently two hints for new physics involving CP violation in b → s transitions: ΔS ≡ S _f − S _J ^ϕK ≠ 0, and difference in direct CP asymmetry ΔA _Kπ ≡ A _K+π ⁰ − A _K+π ⁻ ≠ 0. We explore the two scenarios with a large and unique new CP phase in b ↔ s transitions. Motivated by ΔS ≠ 0, we update on the right-handed strange-beauty squark sb _1R at TeV scale. Motivated by ΔA _Kπ ≠ 0, we explore sequential fourth generation t′ and b′ quarks. Both scenarios can survive constraints such as SM level b → sγ, sll and B _s mixing, and predict sizable CP violation in B _s mixing. The fourth generation picture predicts sizable K _L → π ⁰ vv. Direct search for sb _R, b′ and t′ at hadronic colliders, such as Tevatron Run II and LHC, can complement further CP violation studies at these machines, as well as at the future Super B factory.     

Glass: Kohlrausch exponent,fragility, anharmonicity

The thermodynamical and mechanical properties of (fragile and strong) glass are modeled based on a generalised activation energy relationship log _τ = ΔG _β /RTn(T′) process of glass-forming liquids. This cooperative process involves 1/n(T′) elementary β motions of activation Gibbs energy ΔG _β dependent on the equivalent temperature T′, the temperature of the liquid in equilibrium having the volume of the glass, function of temperature and aging conditions. From this modified VFT law the relaxation of any properties (V , H , stress, creep) can be calculated and approximated by the Kohlrausch function. This model predicts consistency relationships for: a) the temperature (and aging time) variation of the Kohlrausch exponent; b) the temperature dependence of the stabilisation time domain of strong and fragile glass; c) the linear relation between the activation parameters (E ^* energy, S ^* entropy, V ^* volume) of the α and β transition. The Lawson and Keyes (LK) relations are recalled and it is shown that these relations (somewhat equivalant to the compensation law or Meyer-Neldel rule) are observed generally in glass. Morever the (macroscopic) ratios ΔH/ΔV observed during aging or after a temperature jump and the (microscopic) ratio E ^*/V ^* are found equal to κγ (κ compressibily, γ Grüneisen parameter), in agreement with the LK predictions. From various experiments and in agreement with predictions of this model we conclude that the Grüneisen parameter γ _B (pressure derivative of the bulk modulus) and the Mean Square Displacement (MSD) characterising the anharmonicity of solids (and liquids) are the main parameters which govern the relaxation properties of the glass state. Linear relations between the parameters γ _B , the fragility m, and the Kohlrausch exponent n _g at T _g are explained. These correlations underscore a strong relationship between the fragilty of glass formers and the extent of the anharmonicity in the interatomic interactions.     

Time-Scales to Equipartition in the Fermi–Pasta–Ulam Problem: Finite-Size Effects and Thermodynamic Limit

We investigate numerically the common α+β and the pure β FPU models, as well as some higher order generalizations. We consider initial conditions in which only low-frequency normal modes are excited, and perform a very accurate systematic study of the equilibrium time as a function of the number N of particles, the specific energy ε, and the parameters α and β. While at any fixed N the equilibrium time is found to be a stretched exponential in 1/ε, in the thermodynamic limit, i.e. for N→∞ at fixed ε, we observe a crossover to a power law. Concerning the (usually disregarded) dependence of T _eq on α and β, we find it is nontrivial, and propose and test a general law. A central role is played by the comparison of the FPU models with the Toda model.     

Investigation of thermal expansion,phase diagrams,and barocaloric effect in the (NH4)2WO2F4 and (NH4)2MoO2F4 oxyfluorides

The thermal expansion along the principal crystallographic axes of the (NH₄)₂WO₂F₄ and (NH₄)₂MoO₂F₄ oxyfluorides has been studied. The anomalous behavior of α _i (T) due to the phase transitions has been revealed at T ₁ = 271.4 K and T ₂ ≈ 180 K for the molybdate and at T ₁ = 201.5 K and T ₂ ≈ 161 K for the tungstate. The quantities dT/dp and dT/dσ _i , which characterize the dependence of the phase transition temperatures on the hydrostatic and uniaxial pressures, have been determined from analyzing the results of studies of the thermal expansion and heat capacity with the use of the Pippard relations. The p-T and α _i -T phase diagrams reflect different characters of the influence of the pressure on the stability of the initial and distorted phases of the oxyfluorides. The magnitudes of the extensive and intensive barocaloric effects determined in the vicinity of the structural phase transitions are as follows: ΔS _BCE varies from approximately −10 to −17 J/mol K and ΔT _AD ≈ 8−17 K for the molybdate and ΔS _BCE varies from approximately −10 to −17 J/mol K and ΔT _AD ≈ 8−13 K for the tungstate.     

Kinetics of glass transition and thermal stability of?Se58Ge42?xPbx?(9≤x≤20) glasses

Se₅₈Ge_42−x Pb _x (9≤x≤20) glasses have been prepared using conventional melt quenching technique. Differential Scanning Calorimetric (DSC) measurements show single glass transition and double crystallization, which indicate the occurrence of phase separation in the samples. The phases present in the samples were identified using XRD. The kinetics of the glass transition has been studied in terms of the variation of glass transition temperature with composition and heating rate. In addition to this, activation energy of the glass transition (E _t ) has also been evaluated and its composition dependence is also investigated. The thermal stability of these glasses has been investigated using various stability criteria: Deiztal first glass criterion, ΔT, Saad and Poulain weighted thermal stability, H′ and the S-parameter. The values of these parameters were obtained using various characteristic temperatures such as the glass transition temperature, T _g , the onset temperature of crystallization, T _c , and the peak crystallization temperature, T _p . The values of stability parameters show that the phase corresponding to second crystallization is more stable than the phase corresponding to first one. The stability in terms of the lead (Pb) content has been determined considering the values of stability parameters of the phase corresponding to second peak. It was found that the stability increases with the lead content.     

Di-pion emission in heavy quarkonia decays

The dipion spectrum for the ϒ(nS) → ϒ(n′S) transition with n < 4 has the form dw/dq ∼ (phase space) |η − x|², with x = q ² − 4m _π² / (ΔM)² − 4m _π² < q ² ≡ M _ππ², and ΔM = M(nS) − M(n′S). The parameter η is calculated and the spectrum is shown to reproduce the experimental data for all three types of decays: 3 → 1, 2 → 1, and 3 → 2 with η ≈ 0.5, 0, and −3, respectively. The text was submitted by the author in English.     

Absorption spectrum and excitons in thin films of the solid electrolyte RbCu4Cl3I2

We have investigated the absorption spectrum of thin films of the superionic conductor RbCu₄Cl₃I₂ synthesized on NaCl crystalline substrates. It is shown that the electron and exciton excitations in the energy interval 3–6 eV are associated with optical transitions in the CuHal sublattice, and the edge of the fundamental band is controlled by optical transitions in the Cu(II)Hal sublattice. It is found that the large band gap of this compound (E _g =3.86 eV) in comparison with those of CuCl and CuI is a result of the small number of Cu ions in the second coordination sphere. The temperature dependence of the spectral position and half-width of the low-temperature exciton band reveals features associated with the phase transitions γ→β (T _c1=170 K) and β→α (T _c2=220 K) and with disordering of the cation sublattice attendant to the transition to the superionic state. Fiz. Tverd. Tela (St. Petersburg) 40, 1022–1026 (June 1998)     

K*0 and φ meson production in proton–nucleus interactions at ?s=41.6\textGeV\sqrt{s}=41.6\text{GeV}

The inclusive production cross sections of the strange vector mesons K^*0, K̄^*0, and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to p_T = 3.5 GeV/c. The atomic number dependence is parametrised as σ_pA=σ_pN*A^α, where σ_pN is the proton–nucleon cross section. Within the phase space accessible, α(K^*0)=0.86±0.03, α(K̄^*0)=0.87±0.03, and α(φ)=0.96±0.02. The total proton–nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are σ_pN→K*0=(5.06±0.54) mb, σ_pN→K̄*0=(4.02±0.45) mb, and σ_pN→φ=(1.17±0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K^± mesons, the measured values of α for φ mesons coincide with those of K⁺ mesons for all transverse momenta, while the enhancement for K^*0/K̄^*0 mesons is smaller.     

Thermal expansion of orthorhombic and tetragonal phases of the highT c superconductors RE1Ba2Cu3O y (RE=Y,Gd, Dy)

Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases of RE₁Ba₂Cu₃O _y (RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77–300 K. All the superconducting samples exhibit a jump Δα at their respective transition temperatures,T _c. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content.     

Thermoelectric transport properties in disordered systems near the Anderson transition

We study the thermoelectric transport properties in the three-dimensional Anderson model of localization near the metal-insulator transition (MIT). In particular, we investigate the dependence of the thermoelectric power S, the thermal conductivity K, and the Lorenz number L₀ on temperature T. We first calculate the T dependence of the chemical potential μ from the number density n of electrons at the MIT using an averaged density of states obtained by diagonalization. Without any additional approximation, we determine from the behavior of S, K and L₀ at low T as the MIT is approached. We find that and K decrease to zero at the MIT as and show that S does not diverge. Both S and L₀ become temperature independent at the MIT and depend only on the critical behavior of the conductivity. Received 5 February 1999     

Effect of contacts between γ-Fe2O3 nanoparticles on their phase-transition temperature

The effect of mechanical contacts between γ-Fe₂O₃ particles on the temperature of the γ-α structural transition in them is established by magnetic studies and differential thermal analysis (DTA). The sample in which γ-Fe₂O₃ particles had no mechanical contacts with one another remained in the ferromagnetic state up to T _C = 630°C and had two exothermal DTA peaks. The first peak almost coincided with the Curie temperature, while the second peak attributed to the γ → α structural transition corresponded to 760°C. The magnetic transition for particles with a larger number of contacts was shadowed by the γ → α structural transition with a temperature lowered to 550°C.     

A comprehensive,time-resolved SANS investigation of temperature-change-induced sponge-to-lamellar and lamellar-to-sponge phase transformations in comparison with <Superscript>2</Superscript>H -NMR results

Time-resolved small-angle neutron scattering (TR-SANS) was employed to observe temperature-induced phase transitions from the sponge (L ₃ to the lamellar ( L _α phase, and vice versa, in the water-oil (n -decane)-non-ionic surfactant ( C₁₂E₅ system using both bulk and film contrast. Samples of different bilayer volume fractions φ and solvent viscosities η were investigated applying various amplitudes of temperature jump ΔT . The findings of a previous ²H -NMR study could be confirmed, where the lamellar phase formation was determined to occur through a nucleation and growth process, while it was concluded that the L ₃ -phase develops in a mechanistically different and more rapid manner involving uncorrelated passage formation. Likewise, the kinetic trends of the nucleation and growth transition (decreased transition time with increase of φ and ΔT were witnessed once again. Additionally, NMR and SANS data that demonstrate a strong dependency of that process on solvent viscosity η are presented. Contrariwise, it is made evident via both SANS and NMR results that the L _α -to-L ₃ transition time is independent (within experimental sensitivity) of the varied parameters (φ , ΔT , η . Unusual scattering evolution in one experiment, originating from a highly ordered lamellar phase, intriguingly hints that a major rate determining factor is the disruption of long-range order. Furthermore, the bulk contrast investigations give insight into structure peak shifts/development during the transitions, while the film contrast experiments prove the bilayer thickness to be constant throughout the phase transitions and show that there is no evidence for a change in the short-range order of the bilayer structure. The latter was considered possible, due to the different topology of the L ₃ and L _α phases. Lastly, an unexpected yet consistent appearance of anisotropic scattering is detected in the L ₃ -to- L _α transitions.