Crossover effects induced by lattice compressibility in random magnets

Crossover behaviour induced by lattice compressibility in a random magnet is studied using solutions of the renormalization group recursion relations to leading order in =4–d. An effective exponent of the magnetic susceptibility is introduced and the size of the crossover region is estimated. Crossover scaling functions for the free energy, specific heat, and magnetic susceptibility are also obtained.     

Odd crystal field in scheelite

Russian Physics Journal -     

Electrical conductivity of polycrystalline BiVO4 samples having the scheelite structure

Polycrystalline samples of the scheelite oxide BiVO₄ have been prepared with and without 1 m/o additions of CaO. Using impedance spectroscopy the electrical conductivity of these samples was measured in the temperature range 140–550°C and data for the low temperature regime (140–300°C) interpreted in terms of ionic conductivity due to oxygen ion vacancies. This interpretation suggested that the enthalpy of motion of anion vacancies in these materials is relatively low (∼ 0.33 eV).     

Crossover and finite-size effects in the (1+1)-dimensional Kardar-Parisi-Zhang equation

Crossover scaling of the surface width in the Kardar-Parisi-Zhang equation for surface growth is studied numerically. By means of a perturbative solution of the discretized equation and by comparison with the exact solution of the corresponding linear equation, the finite-size effects due to the spatial discretization are carefully analyzed. The dependence on the nonlinearity of both the finite-size and asymptotic scaling forms is then investigated.     

Dynamic Crossover in Metallic Glass Nanoparticles

We report the dynamic crossover behavior in metallic glass nanoparticles(MGNs)with the size reduction based on the extensive molecular dynamics(MD)simulations combined with the activation-relaxation technique(ART).The fragile-to-strong transition of dynamics can be achieved by just modulating the characteristic size of MGNs.It can be attributed to the abnormal fast surface dynamics enhanced by the surface curvature.By determining the potential energy surface,we reveal the hierarchy-to-flat transition of potential energy landscape(PEL)in MGNs,and demonstrate the intrinsic flat potential landscape feature of the MGN with size smaller than a critical size.Our results provide an important piece of the puzzle about the size-modulated potential energy landscape and shed some lights on the unique properties of MGs in nanoscale.     

Crossover interconnects in gradient-index planar optics

The point spread function (PSF) in gradient-index planar optics for implementation of crossover interconnects is studied. Gradient-index (GRIN) planar optics is made with refractive substrate providing a smart optical diffraction-limited imaging. We use as a figure of merit the space-bandwidth product (SBP) of the planar imaging system in order to estimate the number of data channels which can be handled in crossover interconnects. For a selfoc semirod-lens of 3 mm diameter, a crossover network configuration of 703 × 703 channels can be designed.     

Crossover dynamics in bond disordered lattices

The asymptotic dynamics of the percolation model for a bond disordered lattice is studied. The velocity autocorrelation function (VACF) is investigated for arbitrary concentration of disorder in two and three dimensions using an effective medium approximation (EMA). Corrections to the long time tails away from the percolation threshold and to the percolation tails at the threshold are calculated. A characteristic time scale for the long time tails is identified and found to diverge at the threshold. Sufficiently close to the threshold the two types of asymptotic dynamics can be identified clearly for times greater than and less than this characteristic time, respectively. An approximate scaling of the EMA equation is obtained near the threshold for investigation of the crossover region. More generally, the EMA equation is solved numerically for arbitrary concentration in two dimensions to exhibit the complete time dependence of the VACF in all domains near and far from the threshold.     

Crossover critical correlation function

The anomalous dimension index assumes its critical value for small momenta and vanishes for large momenta. We provide, in the form of a quadrature, a momentum dependent (k) which interpolates between the above limits. High- and low-momentum expansions for the spectral function are obtained, leading to a Padé approximant from which (k) is determined, thereby giving a crossover critical correlation function.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Crossover behavior in fluids with Coulomb interactions

According to extensive experimental findings, the Ginzburg temperature t_G for ionic fluids differs substantially from that of nonionic fluids [W. Schr?er, H. Weig?rtner, Pure Appl. Chem. 76, 19 (2004)]. A theoretical investigation of this outcome is proposed here by a mean field analysis of the interplay of short and long range interactions on the value of t_G. We consider a quite general continuous charge-asymmetric model made of charged hard spheres with additional short-range interactions (without electrostatic interactions the model belongs to the same universality class as the 3D Ising model). The effective Landau-Ginzburg Hamiltonian of the full system near its gas-liquid critical point is derived from which the Ginzburg temperature is calculated as a function of the ionicity. The results obtained in this way for t_G are in good qualitative and sufficient quantitative agreement with available experimental data.     

Crossover from BCS-superconductivity to Bose-condensation

Starting from a model of free Fermions in two dimensions with an arbitrary strong effective interaction, we derive a Ginzburg-Landau theory describing the crossover from BCS-superconductivity to Bose-condensation. We find a smooth crossover from the standard BCS-limit to a Gross-Pitaevski type equation for the order parameter in a Bose superfluid. The mean field transition temperature exhibits a maximum at a coupling strength, where the behaviour crosses over from BCS to Bose like with corresponding values of 2 Δ₀/T_c ≈ 5 which are characteristic for high T_c superconductors.     

Crossover Critical Behavior in the Three-Dimensional Ising Model

The character of critical behavior in physical systems depends on the range of interactions. In the limit of infinite range of the interactions, systems will exhibit mean-field critical behavior, i.e., critical behavior not affected by fluctuations of the order parameter. If the interaction range is finite, the critical behavior asymptotically close to the critical point is determined by fluctuations and the actual critical behavior depends on the particular universality class. A variety of systems, including fluids and anisotropic ferromagnets, belongs to the three-dimensional Ising universality class. Recent numerical studies of Ising models with different interaction ranges have revealed a spectacular crossover between the asymptotic fluctuation-induced critical behavior and mean-field-type critical behavior. In this work, we compare these numerical results with a crossover Landau model based on renormalization-group matching. For this purpose we consider an application of the crossover Landau model to the three-dimensional Ising model without fitting to any adjustable parameters. The crossover behavior of the critical susceptibility and of the order parameter is analyzed over a broad range (ten orders) of the scaled distance to the critical temperature. The dependence of the coupling constant on the interaction range, governing the crossover critical behavior, is discussed.