A multi-domain Chebyshev collocation method for predicting ultrasonic field parameters in complex material geometries

The use of ultrasound to measure elastic field parameters as well as to detect cracks in solid materials has received much attention, and new important applications have been developed recently, e.g., the use of laser generated ultrasound in non-destructive evaluation (NDE). To model such applications requires a realistic calculation of field parameters in complex geometries with discontinuous, layered materials. In this paper we present an approach for solving the elastic wave equation in complex geometries with discontinuous layered materials. The approach is based on a pseudospectral elastodynamic formulation, giving a direct solution of the time-domain elastodynamic equations. A typical calculation is performed by decomposing the global computational domain into a number of subdomains. Every subdomain is then mapped on a unit square using transfinite blending functions and spatial derivatives are calculated efficiently by a Chebyshev collocation scheme. This enables that the elastodynamic equations can be solved within spectral accuracy, and furthermore, complex interfaces can be approximated smoothly, hence avoiding staircasing. A global solution is constructed from the local solutions by means of characteristic variables. Finally, the global solution is advanced in time using a fourth order Runge-Kutta scheme. Examples of field prediction in discontinuous solids with complex geometries are given and related to ultrasonic NDE.     

Phase transition in gauge theories and multiple-point model

The phase transition in the regularized U(1) gauge theory is investigated by using the dual Abelian Higgs model of scalar monopoles. The corresponding-renormalization-group-improved effective potential, analogous to the Coleman-Weinberg one, is considered in the two-loop approximation for β functions, and the phase-transition (critical) dual and nondual couplings are calculated in the U(1) gauge theory. It is shown that the critical value of the renormalized electric fine-structure constant,α _crit≈0.208, obtained in this study agrees with the lattice result for compact QED: α _crit ^lat ≈0.20±0.015. This result and the behavior of α in the vicinity of the phase-transition point are compared with the multiple-point-model prediction for the values of α near the Planck scale. Such a comparison is very encouraging for the multiple point model assuming the existence of the multiple critical point at the Planck scale.     

Pulsed laser deposition of aluminum-doped ZnO films at 355 nm

Conducting, transparent films of aluminium-doped ZnO (AZO) have been produced at the laser wavelength 355 nm. The most critical property, the electric resistivity, is up to a factor of 8 above that for films produced at shorter wavelengths. In contrast, the transmission of visible light through the films is about 0.9 which is comparable to the transmission through films deposited with short-wavelength lasers. The polycrystalline structure of the films is similar to that of films produced by shorter wavelengths as well. PACS 81.15 Fg; 68.55.-a; 73.61.Le     

Local field theory of the dual string

We develop a (classical) local field theory which contains as a special solution the (classical) dual string recently discussed by Goddard, Goldstone, Rebbi and Thorn. The basic field is a gauge field F_μν(x), and the Lagrangian is given by $\text{(}\text{?1}\text{2α'}\text{)√F}{}^2$. We treat the case of closed strings (corresponding to the Shapiro-Virasoro model) where F_μν can be expressed in terms of potentials A_μ. Quantization of F_μν is briefly discussed, but a more thorough discussion is postponed.     

On the role of combined static hyperfine interactions for the interpretation of in-beam nuclear Larmor-precession measurements

Differential perturbed angular-distribution measurements have been performed for¹⁰⁷Cd and¹⁰⁹Cd in silver hosts. The data have been obtained at various target temperatures with and wthout applied magnetic fields. The theory of static, combined electric and magnetic hyperfine interaction has been applied for comparison of the zero-field quadrupole data and the external field Larmor-precession data.It is concluded that this combined interaction of the external magnetic field and the damage-induced, electric field gradients quantitatively accounts for the observed dependence of Larmor-precession amplitudes on time, temperature and field strength. The significance of the experimental time range for the appearance and thus for the interpretation of this dependence is demonstrated.     

Saturation of gauge-invariant Schwinger-model correlation functions by instantons

We draw some conclusions from the saturation of QED₂ correlation functions by non-quasiclassical instantons.     

Analysis of the ν6(A″2) band of cyclopropane-d6 recorded under high resolution

The parallel band ν₆(A″₂) of C₃D₆ near 2336 cm^?1 has been studied with high resolution (Δν = 0.020 – 0.024 cm^?1) in the infrared. The band has been analyzed using standard techniques and the following parameters have been determined: B″ = 0.461388(20) cm^?1, D″_J = 3.83(17) × 10^?7 cm^?1, ν₀ = 2336.764(2) cm^?1, α^B = (B″ ? B′) = 8.823(12) × 10^?4 cm^?1, β^J = (D″_J ? D′_J) = 0, and α^C = (C″ ? C′) = 4.5(5) × 10^?4 cm^?1.     

The Peierls instability in one-dimensional conductors with arbitrary bandfilling

Mean field calculations of the Peierls instability have been carried out for arbitrary bandfilling both in the case of free electrons as well as for the tightbinding approximation. New expressions for Δ(0) and T_p are derived which change the experimentally derived λ to a more reasonable value. Δ(0)/k_BT_p may differ significantly from the BCS value 1.76 in the tightbinding approximation.