Model independent constraints from vacuum and in-medium QCD Sum Rules

We discuss QCD sum rule constraints based on moments of vector meson spectral distributions in the vacuum and in a nuclear medium. Sum rules for the two lowest moments of these spectral distributions do not suffer from uncertainties related to QCD condensates of dimension higher than four. We exemplify these relations for the case of the ω meson and discuss the issue of in-medium mass shifts from this viewpoint. Received: 22 December 1998 / Revised version: 13 January 1999     

Quark mass dependence of the pion vector form factor

We examine the quark mass dependence of the pion vector form factor, particularly the curvature (mean quartic radius). We focus our study on the consequences of assuming that the coupling constant of the ρ   to pions, g_ρππ$g_{\rho \pi \pi }$, is largely independent of the quark mass while the quark mass dependence of the ρ mass is given by recent lattice data. By employing the Omnès representation we can provide a very clean estimate for a certain combination of the curvature and the square radius, whose quark mass dependence could be determined from lattice computations. This study provides an independent access to the quark mass dependence of the ρππ   coupling and in this way a non-trivial check of the systematics of chiral extrapolations. We also provide an improved value for the curvature for physical values for the quark masses, namely 〈r⁴〉=0.73±0.09 fm⁴$〈r^4〉=0.73\pm 0.09{\text{fm}}^4$ or equivalently cV=4.00±0.50 GeV−4$c_V=4.00\pm 0.50{\text{GeV}}^{-4}$.     

Luminescence properties of Tb implanted ZnO

ZnO [0 0 0 1] crystals were irradiated at room temperature with Tb⁺ ions of 400 keV with fluences from 1×10¹⁶ to 2×10¹⁷ cm⁻². The implanted layer was examined by several methods, including radioluminescence (RL), Rutherford backscattering spectrometry (RBS) and optical spectroscopy. The optical extinction spectra were simulated using Mie scattering theory. Absorption spectra predicted by Mie theory for particles of decreasing diameter were compared with those obtained experimentally. Some qualitative agreement between theoretical and experimental data was achieved. It was also shown that the intensities of the characteristic green emission bands associated with Tb produced by ⁵D₄→⁷F_j=5,4 transitions have increased about 8 times after annealing. Optical spectroscopy and radioluminescence data have revealed that the ion implantation is a promising tool for synthesizing Tb nanoparticles in the ZnO surface. The Tb nanoparticles exhibit a rather weak plasma resonance.     

Surface magnetization,grain and domain structure in laser-scribed soft magnetic sheets

The local magnetic softening and simultaneous grain coarsening are observed in low carbon sheets due to the laser-scribing process as the results of the net mechanical stress relief. A very fine surface domain structure with domain walls of higher mobility is created within the scribed zone, in spite of the fact that local increase of microhardness of the laser-treated zone was detected.     

Implications of the JLab proton polarization data for the behavior of strange nucleon form factors

A special eight-resonance unitary and analytic model of nucleon electromagnetic structure is used to analyze first the classical proton form factor data obtained by the Rosenbluth technique, and then also the contradictory JLab proton polarization data on the ratio μ_p G _Ep(Q ²)/G _Mp(Q ²) , with the aim to investigate the implications of the latter for the behavior of strange nucleon form factors.     

p-type conduction in ZnO dual-acceptor-doped with nitrogen and phosphorus

A dual-acceptor doping method was proposed to produce p-type conduction in ZnO. Both nitrogen and phosphorus were used as the p-type doping agents. ZnO:(N, P) films were prepared by spray pyrolysis. The p-type conduction was achieved by thermal annealing at appropriate temperatures (500-700 ^°C) for 20 min in O₂ ambient. The lowest resistivity of , with a hole concentration and Hall mobility of 5.3×10¹⁷ cm⁻³ and 0.94 cm² V ⁻¹ s⁻¹, respectively, was obtained at an optimal annealing temperature of 600 ^°C. The p-type behavior was reproducible and stable. The introduction of nitrogen and phosphorus in ZnO were identified by secondary ion mass spectroscopy.     

Effect of composition on phase formation,microstructure and magnetic properties of Nd–Fe–B thin films

Nd–Fe–B hard magnetic thin films were deposited on a combined Cr/Ta buffer layer on heated MgO(1 0 0) substrates by pulsed laser deposition. The effect of composition on phase formation, morphology and magnetic properties was investigated. For a quantification of phase formation, hysteresis measurements along the hard axis are used. Optimum phase formation is obtained at a Nd/Fe ratio around 0.3. For this Nd content an excellent magnetic texture and a coercivity up to 1 T can be obtained; however, remanence is reduced and the films have a granular microstructure with high roughness. Also a certain B surplus is of benefit. However, with a too-high B or Nd surplus phase formation is more difficult.     

φ-meson photoproduction from nuclei

We study coherent and incoherent φ-meson photoproduction from nuclei. The available data are analyzed in terms of single- and coupled-channel photoproduction. It is found that the data on coherent photoproduction can be well reproduced within a single-channel optical model and show only little room for ω-φ mixing. These data indicate a normal distortion of the φ-meson in nuclei, which is compatible with the results obtained through the vector meson dominance model. The data on incoherent φ-meson photoproduction show an anomalous A-dependence resulting in a very strong φ-meson distortion. These data can be explained by a coupled-channel effect through the dominant contribution from the ω↦φ or the π↦φ transition or, more speculative, through the excitation of a cryptoexotic B _φ-baryon.     

Entropy of electromyography time series

A nonlinear analysis based on Renyi entropy is applied to electromyography (EMG) time series from back muscles. The time dependence of the entropy of the EMG signal exhibits a crossover from a subdiffusive regime at short times to a plateau at longer times. We argue that this behavior characterizes complex biological systems. The plateau value of the entropy can be used to differentiate between healthy and low back pain individuals.     

On the current status of OZI violation in πN and pp reactions

The available data on ω and φ production from πN and pp collisions are reanalyzed with respect to an OZI rule violation on the basis of transition matrix elements. The data are found to be compatible with a constant ratio R , which however, deviates substantially from the SU(3) prediction based on the present knowledge of the φ-ω mixing angle. Received: 5 July 1999 / Revised version: 20 October 1999