Nonparametric scaled equation of state and approximation of <Emphasis Type="Italic">P</Emphasis>-ρ-<Emphasis Type="Italic">T</Emphasis> data near the vapor-liquid critical point

We present a new scaled equation of state adequately describing the P-ρ-T data for fluids near the vapor-liquid transition point and compare this equation to the Schofield parametric equation of state. A comparative analysis of the approximation of data for He⁴, C₂H₄, and H₂O in the critical region shows that both these equations correctly describe the behavior of thermodynamic functions asymptotically close to the critical point.     

Crossover from high-temperature vortex-liquid to low-temperature vortex-glass behavior in single phase HgBa2Ca2Cu3O8+δ superconductor

The ρ-T curves in our single phase HgBa₂Ca₂Cu₃O_8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ₀exp(−U_eff/κ_BT). It can be transformed to another form d(lnρ)/d(1/T)=−U_eff+TdU_eff/dT, then this becomes a plot of the activation energy U_eff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems.     

Richtungseffekte der Lichtausbeute von Anthrazen bei Beschü\ mit Protonen im Energiebereich 200–600 keV

The results of the three-dimensional liquid droplet model are compared with experiment and other phenomenological theories. The homogeneity assumption of the scaling laws holds both above and belowT _c , and various series expansions can be derived. But there is a nonanalyticity near the critical isotherm aboveT _c for fixed “field” μ?μ(p _c ,T); and liquid and gas are not symmetric about the critical isochore aboveT _c . Both results contradict the usual scaling assumptions and experiment. The equation of state is fixed if the density on the coexistence curve and the critical pressure are known. Therefore we can derive various relations between critical quantities. They are compared with experiment and the corresponding relations in the Vicentini-Missoni ansatz, the parametric representation, and the generalized Landau ansatz. The disagreement ranges from about 20% to one order of magnitude.     

Correlation of volumetric properties of binary mixtures of some ionic liquids with alcohols using equation of state

In our previous paper, we extended the Tao and Mason equation of state (TM EOS) to pure ionic liquids. Here we apply TM EOS based on statistical?Cmechanical perturbation theory to binary mixtures of ionic liquids. Three temperature-dependent quantities are needed to use the equation of state: the second virial coefficient, B ₂, effective van der Waals co-volume, b, and a scaling factor, ??. The second virial coefficients are calculated from a correlation that uses the normal boiling temperature and normal boiling density. ?? and b can also be calculated from the second virial coefficient by scaling. In this procedure, the number of input parameters, for calculation of B ₂, ??, and b reduced from 5 (i.e., critical temperature, critical pressure, acetric factor, Boyle temperature T _B, and the Boyle volume ?? _B) to 2 (i.e., T _bp and ?? _bp). At close inspection of the deviations given in this work, the TM EOS predicts the densities with a mean AAD of 1.69%. The density of selected system obtained from the TM EOS has been compared with those calculated from perturbed-hard-sphere equation of state. Our results are in favor of the preference of the TM EOS over another equation of state. The overall average absolute deviation for 428 data points that calculated by perturbed-hard-sphere equation of state is 2.60%.     

Electrical behavior of some silver-doped lanthanum-based CMR materials

With a view to understand the structural, magnetic and electrical properties of La_1−xAg_xMnO₃ (x=0.05-0.3), a series of samples were prepared by polyvinyl alcohol (PVA) gel route. It has been found that both the metal-insulator and ferro- to paramagnetic transition temperatures after increasing up to the composition x=0.20, are found to remain constant thereafter. The electrical resistivity vs. temperature plot of the sample x=0.10 is found to exhibit an insulating behavior below 36 K, while the sample, x=0.20 exhibits two peaks, and the observed behavior is explained on the basis of the phase separation model. The low-temperature (T<T_P), electrical resistivity data were analyzed by a theoretical model, ρ=ρ₀+ρ₂T²+ρ_4.5T^4.5, indicating the importance of grain/domain boundary effects, electron-electron and two-magnon scattering processes. The low-temperature resistivity data (T<50 K) were fitted to an equation, which is based on the combined effect of weak localization, electron-electron and electron-phonon scattering.     

Simulation studies of gas-liquid transitions in two dimensions via a subsystem-block-density distribution analysis

The finite-size scaling analysis of the density distribution function of subsystems of a system studied at constant total density is studied by a comparative investigation of two models: (i) the nearest-neighbor lattice gas model on the square lattice, choosing a total lattice size of 64×64 sites. (ii) The two-dimensional off-lattice Lennard-Jones system (truncated at a distance of 2.5 σ, σ being the range parameter of the interaction) withN=4096 particles, applying the NVT ensemble. In both models, the density distribution functionP _L (ρ) is obtained forL×L subsystems for a wide range of temperaturesT, subblock linear dimensionsL and average densities <ρ>. Particular attention is paid to the question whether accurate estimates of critical temperatureT _c and critical density ρ _c can be obtained. In the lattice gas model these critical parameters are known exactly and the limitations of the approach can thus be definitively asserted. The final estimates for the Lennard Jones problem areT _c =0.47±0.01 (in units of the Lennard Jones energy ε) and ρ _c (in units of σ²), a comparison with previous estimates is made.     

Exploiting the flexibility of a family of models for taxation and redistribution

In this paper we present and discuss results of Monte Carlo numerical simulations of the two-dimensional Ising ferromagnet in contact with a heat bath that intrinsically has a thermal gradient. The extremes of the magnet are at temperatures T ₁?<?T _c ?<?T ₂, where T _c is the Onsager critical temperature. In this way one can observe a phase transition between an ordered phase (T?<?T _c ) and a disordered one (T?>?T _c ) by means of a single simulation. By starting the simulations with fully disordered initial configurations with magnetization m????0 corresponding to T?=???, which are then suddenly annealed to a preset thermal gradient, we study the short-time critical dynamic behavior of the system. Also, by setting a small initial magnetization m?=?m ₀, we study the critical initial increase of the order parameter. Furthermore, by starting the simulations from fully ordered configurations, which correspond to the ground state at T?=?0 and are subsequently quenched to a preset gradient, we study the critical relaxation dynamics of the system. Additionally, we perform stationary measurements (t??????) that are discussed in terms of the standard finite-size scaling theory. We conclude that our numerical simulation results of the Ising magnet in a thermal gradient, which are rationalized in terms of both dynamic and standard scaling arguments, are fully consistent with well established results obtained under equilibrium conditions.     

Analysis of the transport coefficients for simple dense fluids: The diffusion and bulk viscosity coefficients

The analysis of transport coefficients based on the modified Enskog theory (MET), discussed in a previous publication, has been extended to include the self-diffusion coefficient (D) and the bulk viscosity coefficient (η_v). Specifically, calculated values according to the MET are compared with experiment over the range for which data are available. Fluids considered are argon, nitrogen and methane. Agreement between theory and experiment for densities less than about twice the critical density (ρ_c) is generally within about 10%. However, much of the data was taken at densities well in excess of 2_ρc in which case agreement is still not unsatisfactory. Deviations exceeding 10% between theoretical and experimental self-diffusion coefficients were observed for densities in the approximate range 0.9 ? _ρ/ρc ? 2.0. It is possible that these deviations are due to long range correlated molecular motions which are not present in the MET. The sound absorption is also briefly considered. Finally, the behavior of η_v and D at low densities is discussed.     

Scaling models of thermodynamic properties on the coexistence curve: Problems and some solutions

Models consistent with the scaling theory of critical phenomena and capable of describing the thermodynamic properties F of substances on the coexistence curve, such as the density of the liquid ρ _l , density of the gas ρ _g , order parameter f _s , mean coexistence curve diameter f _d , and saturation pressure P _s are discussed. The models are presented in the form of equations F = (τ, D, C), where τ = (T _c ? T)/T _c , and D = (α, β, T _c , ρ _c , P _c , ...) are the critical characteristics, such as T _c , ρ _c , and P _c (temperature, density, and pressure, respectively), α and β are the scaling exponents, and C are adjustable coefficients. The authors developed combined models f(τ, D, C) for describing the indicated properties of a number of compounds (CH₄, NH₃, SF₆, water, methanol, ethanol, diethyl ether, and freons R134a, R143a, and R236ea). The coefficients C were determined based on experimental data over a wide temperature range, including the critical point. The equations derived are used to perform practical calculations, including estimates of the first and second derivatives of the saturation pressure with respect to the temperature in the critical region.     

Critical parameters near the ferromagnetic-paramagnetic phase transition in La0.7A0.3(Mn1−xbx)O3 (A=Sr; B=Ti and Al; x=0.0 and 0.05) compounds

The critical parameters provide important information concerning the interaction mechanisms near the paramagnetic-to-ferromagnetic transition. In this paper, we present a thorough study for the critical behavior of La_0.7A_0.3(Mn_1−xB_x)O₃ (A=Sr; B=Ti and Al; x=0.0 and 0.05) polycrystalline samples near ferromagnetic-paramagnetic phase transition temperature by analyzing isothermal magnetization data. We have analyzed our dc-magnetization data near the transition temperature with the help of the modified Arrot plot, Kouvel-Fisher method. We have determined the critical temperature T_C and the critical parameters β, γ and δ. With the values of T_C, β and γ, we plot M×(1−T/T_C)^−β vs. H×(1−T/T_C)^−γ. All the data collapse on one of the two curves. This suggests that the data below and above T_C obey scaling, following a single equation of state. Critical parameters for x=0 and x_Ti=0.05 samples are between those predicted for a 3D-Heisenberg model and mean-field theory and for x_Al=0.05 samples the values obtained for the critical parameters are close to those predicted by the mean-field theory.     

Anisotropic<Emphasis Type="Italic">s</Emphasis>-wave or<Emphasis Type="Italic">d</Emphasis>-wave pairing? Analysis of experiments on ion irradiation of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-x</Subscript> films

The effect of ion irradiation on the superconducting transition temperatureT _c and resistivityρ _ab (T) of YBa₂Cu₃O_7-x films with different oxygen content (initial temperatureT _c0≈90 K and 60 K) is studied experimentally. The dependenciesT _c /T _c0 on residual resistivityρ _o are obtained in very wide range 0.2<T _c /T _c0 <1 andρ _o μΩ·cm. The critical values ofρ _o , corresponding to the vanishing of superconductivity, are found to be an order of magnitude larger then those predicted by theory ford-wave pairing. At 0.5÷0.6<T _c /T _c0<1 the experimental data are in close agreement with theoretical dependencies, obtained for the anisotropics-wave superconductor within the BCS-framework.     

Polisher density into Preston equation

For the polishing process, Preston (1927) [1] proposed wear, h, is proportional to the work given by a frictional force, f_fr, on the glass. He assumed f_fr does not depend on relative velocity, v, between the glass and the tool. Téllez et al. (2007) [2] found frictional force depends on v. We have experimentally found that f_dr depends on relative velocity, v, and concentration, ρ, of the polisher suspension. Then Preston equation has to be modified i.e. h = h(f_fr(v), ρ).     

Scaling of the temperature-dependent resistivity in SrFe2−xNixAs2

We show that the zero-field normal-state resistivity of temperature-dependent resistivity ρ(T) of SrFe_2?xNi_xAs₂ can be reproduced by the expression ρ(T) = ρ₀ + c T exp(?2Δ/T). ρ(T) can be scaled using both this expression where the energy scale Δ, c and the residual resistivity ρ₀ are scaling parameters and a recently proposed model-independent scaling method (H.G. Luo, Y.H. Su, T. Xiang, Phys. Rev. B 77 (2008) 014529). The scaling parameters have been calculated and the compositional variation of 2Δ(x) has been determined. This dependence show almost a linear decreasing in the underdoped regime similar to that reported for cuprates. The existence of a universal metallic ρ(T) curve in a wide temperature range which, however, is restricted for the underdoped compounds to temperatures above a structural and anitiferromagnetic transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in SrFe_2?xNi_xAs₂ (x = 0–0.3).     

Magnetic and electrical behavior of La1−xAxMnO3 (A=Li, Na, K and Rb) manganites

With a view to understand the magnetic and electrical behavior of monovalent substituted lanthanum manganites, a series of materials were prepared by sol-gel route by sintering at 1200 °C. The X-ray diffraction data were analyzed using Rietveld refinement technique and it has been found that all the samples were found to crystallize into rhombohedral structure with R3¯c space group. The values of ferro to paramagnetic (T_C) and metal-insulator transition (T_P) temperatures were obtained using ac susceptibility and electrical resistivity data, respectively. It has been found that sodium-, potassium- and rubidium-doped samples exhibit two peaks in the electrical resistivity vs. temperature plots. The observed behavior has been explained on the basis of oxygen deficiency present in the samples. The electrical resistivity data were analyzed using various theoretical models and it has been concluded that the electrical resistivity data in the low-temperature regime (T<T_P) can be explained using the equation ρ_(T)=ρ₀+ρ₂T²+ρ_4.5T^4.5, signifying the importance of the grain/domain boundary, electron-electron and two magnon scattering processes. On the other hand, the high-temperature resisitivity data (T>T_P) were explained using variable range and small polaron hopping mechanisms.     

Multiple photon excitation of the v2 + v6 combination band of SF6 in a bulk and in a pulsed free jet

Multiple photon excitation of the v₂ + v₆ combination band of SF₆ in a bulk at T ≈ 295 K and cooled in a pulsed free jet up to T_V ≈ 160 K and T_R ≈ 40 K by a pulsed TEA CO₂ laser has been investigated. Obtained results are compared with the data on the v₃ vibration excitation. At exciting energy fluences ø = 0.1?2.5 J cm^-2 the levels in the region of the discrete vibrational states (v=3?5) are found mainly to be excited. Multiphoton absorption spectra at room temperature have a sharp resonant structure. The fraction of interacting molecules is considerably (3–7 times) less compared than that for the case of v₃ vibration excitation. Multiphoton absorption of the v₂ + v₆ and v₃ vibrations of SF₆ is shown to be proportional to the dipole moments of the corresponding transitions.     

Study of some co-precipitated manganite perovskite samples-doped iron

Polycrystalline La_0.70Sr_0.30Mn_1−yFe_yO₃ (0.05?y?0.07) samples are prepared by the co-precipitation method and have been studied. The substitution of Mn³⁺ by Fe³⁺ reduces the number of available hopping sites for the Mn e_g(↑) electron and suppresses the double exchange (DE), resulting in the reduction of the metal–semiconductor transition temperature (T_P) and the flux density saturation (B_s). Low-temperature resistivity (ρ) data (below T_P) well fit with the relation ρ(T)=ρ₀+ρ₂T², indicating the importance of grain/domain boundary effects and electron–electron scattering processes in the conduction of these materials. On the other hand, at high temperature (T_P<T<θ_D/2) conductivity data satisfy the variable range hopping (VRH) model. For T>θ_D/2 the small polaron hopping model is more appropriate than the VRH model.     

Variational calculations of asymmetric nuclear matter

We report on variational calculations of the energy E(ρ, β) of asymmetric nuclear matter having ? = ?_n + ?_p = 0.05 to 0.35 fm^?3, and β = (?_n ? ?_p/g9 = 0 to 1. The nuclear h used in this work consists of a realistic two-nucleon interaction, called v₁₄, that fits the available nucleon-nucleon scattering data up to 425 MeV, and a phenomenological three nucleon interaction adjusted to reproduce the empirical properties of symmetric nuclear matter. The variational many-body theory of symmetric nuclear matter is extended to treat matter with neutron excess. Numerical and analytic studies of the β-dependence of various contributions to the nuclear matter energy show that at ? < 0.35 fm^?3 the β⁴ terms are very small, and that the interaction energy EI(ρ, β) defined as E(ρ, β) ? T_F(ρ, β), where T_F is the Fermi-gas energy, is well approximated by EI₀(?) + β²EI₂(ρ). The calculated symmetry energy at equilibrium density is 30 MeV and it increases from 15 to 38 MeV as ? increases from 0.05 to 0.35 fm^?3.     

Equation of state for rotating nuclei at finite temperature

The equation of state ω(T, I) is derived for temperatures in the range0 ? T ? 0.5 MeV and spins in the range 0 ? I ? 24. It is demonstrated that if the yrast line backbends, then the equation of state contains a critical point at temperature T_c, and that backbending disappears for T > T_c.