Magnetisches Moment und Quadrupolmoment des 8,42 keV-Zustandes von Tm169 aus der Hyperfeinstrukturaufspaltung in Tm-Metall

The hyperfine transition from the 8·42 kev level to the groundstate of Tm¹⁶⁹ was investigated using the Mössbauer-Effect in Tm-metal in the temperature range between 5° K and 60° K. Well resolved hyperfine spectra were found between 5° K and 25° K indicating an internal magnetic field of about 7×10⁶ Oe and a large electric fieldgradient. The ratio of the magnetic moments of the 8·42 keV rotational state to the groundstateμ _a /μ _g =?2·33±0·04 was deduced from these measurements. The magnetic moment of the groundstate and the quadrupole moment of the 8·42 kev level were deduced from calculated internal fields. These data were analyzed in terms of the “Unified Nuclear Model” and the results compared with other known magnetic moments andM-1-transition probabilities in theK=1/2 rotational band of Tm¹⁶⁹. The complicated hyperfine spectra obtained above 25° K reveal the influence of complex magnetic ordering on the internal fields in Tm-metal.     

Kernresonanzabsorption nicht Doppler-verbreiterter Gammastrahlung in Re187

Nuclear resonant absorption of gamma-rays has been observed in nuclei of Re¹⁸⁷ bound in a crystal lattice. At a temperature of 20° K a small fraction of the gammaquanta of the 134 keV transition to the ground state is emitted with essentially no energy lost to recoil, the recoil momentum being taken up by the entire crystal, not by the individual nucleus. Nuclei of Re¹⁸⁷ similarly bound in a crystal lattice have been irradiated with such gamma-rays emitted without loss of energy, resulting in an oberservable resonance absorption. Using a relative velocity of the order of 10 cm/sec the line emitted with the natural line width has been shifted away from the absorption line, resulting in the destruction of the resonance phenomena. Analysis of the variation in transmission as a function of the Doppler shift of the emitted gamma-ray yields a value ofτ=(1,5±0,2) · 10^?11 sec for the lifetime of the 134 keV excited state in Re¹⁸⁷.     

Anti-de sitter/conformal-field-theory calculation of screening in a hot wind

One of the challenges in relating experimental measurements of the suppression in the number of J/psi mesons produced in heavy ion collisions to lattice QCD calculations is that whereas the lattice calculations treat J/psi mesons at rest, in a heavy ion collision a cc[over ] pair can have a significant velocity with respect to the hot fluid produced in the collision. The putative J/psi finds itself in a hot wind. We present the first rigorous nonperturbative calculation of the consequences of a wind velocity v on the screening length L(s) for a heavy quark-antiquark pair in hot N=4 supersymmetric QCD. We find L(s)(v,T)=f(v)[1-v(2)](1/4)/piT with f(v) only mildly dependent on v and the wind direction. This L(s)(v,T) approximately L(s)(0,T)/sqrt[gamma] velocity scaling, if realized in QCD, provides a significant additional source of J/psi suppression at transverse momenta which are high but within experimental reach.     

Control of the excitability of neuronal tissue by weak external forces

The spreading depression (SD) is a pronounced example of excitation-depression waves in excitable media, to which neuronal tissue according to its structure and functions belongs. SD waves can especially easily be observed in the vertebrate retina which is neuronal tissue and a true part of the central nervous system (CNS). According to the high intrinsic optical signal (IOS) concomitant with the retinal spreading depression (rSD), it can be monitored with standard video imaging techniques, thus the retina has been used in our studies as a suitable model system for neuronal tissue in general. In particular, the control of wave set-up and propagation in excitable media by weak external forces is of high interest. Accordingly, the interaction of rSD waves with DC and AC electromagnetic fields of low amplitude and frequency and with gravity has been investigated in this study. The dependence of rSD-wave propagation velocity on the given parameters as one important indication of excitability control has been investigated in detail. Our results with rSD waves are partially compared to another well known excitable medium, the Belousov-Zhabotinsky reaction, where some data about the effects of electrical fields and gravity have already been published.