Low temperature magnetoresistance of dirty thin films and quantum wires near a parallel-field-tuned superconducting quantum phase transition

We study the low temperature magnetoresistance of dirty thin films and quantum wires close to a quantum phase transition from a superconducting to normal state, induced by applying a parallel magnetic field. We find that the different corrections (Aslamazov-Larkin, density of states and Maki-Thompson) to the normal state conductivity, coming from the superconducting pair fluctuations, are of the same order at zero temperature. There are three regimes at finite temperatures. In the "quantum" regime, which essentially shows a zero-temperature-like behavior we find a negative magnetoresistance. Since in the "classical" regime the correction is positive, we predict a non-monotonic magnetoresistance at higher temperatures.Comment: Proceedings for SCES conference (2004

Biased diffusion in a piecewise linear random potential

We study the biased diffusion of particles moving in one direction under the action of a constant force in the presence of a piecewise linear random potential. Using the overdamped equation of motion, we represent the first and second moments of the particle position as inverse Laplace transforms. By applying to these transforms the ordinary and the modified Tauberian theorem, we determine the short- and long-time behavior of the mean-square displacement of particles. Our results show that while at short times the biased diffusion is always ballistic, at long times it can be either normal or anomalous. We formulate the conditions for normal and anomalous behavior and derive the laws of biased diffusion in both these cases.Comment: 11 pages, 3 figure

N* and Delta* decays into N pi0 pi0

Decays of baryon resonances in the second and the third resonance region into N pi0 pi0 are studied by photoproduction of two neutral pions off protons. Partial decay widths of N* and Delta* resonances decaying into Delta(1232) pi, N(\pi\pi)_{S}, N(1440)P_{11} pi, and N(1520)D_{13} pi are determined in a partial wave analysis of this data, and data from other reactions. Several partial decay widths were not known before. Interesting decay patterns are observed which are not even qualitatively reproduced by quark model calculations. In the second resonance region, decays into Delta(1232) pi dominate clearly. The N(\pi\pi)_{S}-wave provides a significant contribution to the cross section, especially in the third resonance region. The P_{13}(1720) properties found here are at clear variance to PDG values.Comment: 13 pages, 4 figures, long author's lis

Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in pi^0-photoproduction off the proton

At the electron accelerator ELSA a linearly polarised tagged photon beam is produced by coherent bremsstrahlung off a diamond crystal. Orientation and energy range of the linear polarisation can be deliberately chosen by accurate positioning of the crystal with a goniometer. The degree of polarisation is determined by the form of the scattered electron spectrum. Good agreement between experiment and expectations on basis of the experimental conditions is obtained. Polarisation degrees of P = 40% are typically achieved at half of the primary electron energy. The determination of P is confirmed by measuring the beam asymmetry, \Sigma, in pi^0 photoproduction and a comparison of the results to independent measurements using laser backscattering.Comment: 9 pages, 10 figures, submitted to EPJ

An unusual new sauropod dinosaur from the Late Cretaceous of Mongolia

© 2020, © The Trustees of the Natural History Museum, London 2020. All rights reserved. A new sauropod, Abdarainurus barsboldi gen. et sp. nov., is described based on several anterior and one middle caudal vertebrae and chevrons from the Late Cretaceous Alagteeg Formation at Abdrant Nuru, northern Gobi Desert, Mongolia. The new taxon is characterized by 16 unique or rare characters of the caudal skeleton, including opisthocoelous centra, longitudinal ridges on the neural canal walls, postprezygapophyseal processes, a hypertrophied postspinal fossa, mediolaterally constricted neural spines, and a deep pocket-like spinodiapophyseal fossa covered laterally by high postzygodiapophyseal lamina. Our preferred phylogenetic analysis places Abdarainurus as a basal titanosaurian sauropod, but this result could be affected by inadequate knowledge of basal titanosaurs. The new taxon likely represents a highly specialized lineage of Asian macronarian sauropods that was unknown previously. http://zoobank.org/urn:lsid:zoobank.org:pub::87174FD4-0616-4BD6-9209-C40C0455D2DA