An Uqp(u2)U_{qp}(u_2) Rotor Model for Rotational Bands of Superdeformed Nuclei

A nonrigid rotor model is developed from the two-parameter quantum algebra $U_{qp}({\rm u}_2)$. [This model presents the $U_{qp}({\rm u}_2)$ symmetry and shall be referred to as the qp-rotor model.] A rotational energy formula as well as a qp-deformation of E2 reduced transition probabilities are derived. The qp-rotor model is applied (through fitting procedures) to twenty rotational bands of superdeformed nuclei in the $A \sim 130$, 150 and 190 mass regions. Systematic comparisons between the qp-rotor model and the q-rotor model of Raychev, Roussev and Smirnov, on one hand, and a basic three-parameter model, on the other hand, are performed on energy spectra, on dynamical moments of inertia and on B(E2) values. The physical signification of the deformation parameters q and p is discussed.Comment: 24 pages, Latex File, to appear in IJMP

Dirac and Klein-Gordon particles in one-dimensional periodic potentials

We evaluate the dispersion relation for massless fermions, described by the Dirac equation, and for zero-spin bosons, described by the Klein-Gordon equation, moving in two dimensions and in the presence of a one-dimensional periodic potential. For massless fermions the dispersion relation shows a zero gap for carriers with zero momentum in the direction parallel to the barriers in agreement with the well-known "Klein paradox". Numerical results for the energy spectrum and the density of states are presented. Those for fermions are appropriate to graphene in which carriers behave relativistically with the "light speed" replaced by the Fermi velocity. In addition, we evaluate the transmission through a finite number of barriers for fermions and zero-spin bosons and relate it with that through a superlattice.Comment: 9 pages, 12 figure

Cleaved surface of i-AlPdMn quasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness

Roughness of i-AlPdMn cleaved surfaces are presently analysed. From the atomic scale to 2-3 nm, they are shown to exhibit scaling properties hiding the cluster (0.45 nm) aperiodic structure. These properties are quantitatively similar to those observed on various disordered materials, albeit on other ranges of length scales. These properties are interpreted as the signature of damage mechanisms occurring within a 2-3 nm wide zone at the crack tip. The size of this process zone finds its origin in the local temperature elevation at the crack tip. For the very first time, this effect is reported to be responsible for a transition from a perfectly brittle behavior to a nanoductile one.Comment: 8 page

The phase diagram of the lattice Calogero-Sutherland model

We introduce a {\it lattice} version of the Calogero Sutherland model adapted to describe $1/d^2$ pairwise interacting steps with discrete positions on a vicinal surface. The configurational free energy is obtained within a transfer matrix method. The full phase diagram for attractive and for repulsive interaction is deduced. For attraction, critical temperatures of faceting transitions are found to depend on step density.Comment: latex PRBCalogSuth.tex, 6 files, 4 pages [SPEC-S00/900

Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {\guillemotright}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO3 layers, especially in view of their integration in devices.Comment: In press in J. Appl. Phy

Co/Ni element ratio in the galactic cosmic rays between 0.8 and 4.3 GeV/nucleon

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere, gives an upper limit for this ratio of 0.093±0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope 59Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible 59Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed

In memoriam two distinguished participants of the Bregenz Symmetries in Science Symposia: Marcos Moshinsky and Yurii Fedorovich Smirnov

Some particular facets of the numerous works by Marcos Moshinsky and Yurii Fedorovich Smirnov are presented in these notes. The accent is put on some of the common interests of Yurii and Marcos in physics, theoretical chemistry, and mathematical physics. These notes also contain some more personal memories of Yurii Smirnov.Comment: Submitted for publication in Journal of Physics: Conference Serie

The First Swift BAT Gamma-Ray Burst Catalog

We present the first Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains bursts detected by the BAT between 2004 December 19 and 2007 June 16. This catalog (hereafter BAT1 catalog) contains burst trigger time, location, 90% error radius, duration, fluence, peak flux, and time averaged spectral parameters for each of 237 GRBs, as measured by the BAT. The BAT-determined position reported here is within 1.75' of the Swift X-ray Telescope (XRT)-determined position for 90% of these GRBs. The BAT T_90 and T_50 durations peak at 80 and 20 seconds, respectively. From the fluence-fluence correlation, we conclude that about 60% of the observed peak energies, Epeak, of BAT GRBs could be less than 100 keV. We confirm that GRB fluence to hardness and GRB peak flux to hardness are correlated for BAT bursts in analogous ways to previous missions' results. The correlation between the photon index in a simple power-law model and Epeak is also confirmed. We also report the current status for the on-orbit BAT calibrations based on observations of the Crab Nebula.Comment: 63 pages, 23 figures, Accepted in ApJS, Corrected for the BAT ground position, the image significance, and the error radius of GRB 051105, Five machine-readable tables are available at http://swift.gsfc.nasa.gov/docs/swift/results/bat1_catalog