Delocalized-localized transition in a semiconductor two-dimensional honeycomb lattice

We report the magneto-transport properties of a two-dimensional electron gas in a modulation-doped AlGaAs/GaAs heterostructure subjected to a lateral potential with honeycomb geometry. Periodic oscillations of the magneto-resistance and a delocalized-localized transition are shown by applying a gate voltage. We argue that electrons in such artificial-graphene lattices offer a promising approach for the simulation of quantum phases dictated by Coulomb interactions

Comparative study of hormonal counterregulation during GCIIS-guided hypoglycemia tests using human Proinsulin and Human Insulin (recombinant DNA)

Schlechte Scanvorlage

On three topical aspects of the N=28 isotonic chain

The evolution of single-particle orbits along the N=28 isotonic chain is studied within the framework of a relativistic mean-field approximation. We focus on three topical aspects of the N=28 chain: (a) the emergence of a new magic number at Z=14; (b) the possible erosion of the N=28 shell; and (c) the weakening of the spin-orbit splitting among low-j neutron orbits. The present model supports the emergence of a robust Z=14 subshell gap in 48Ca, that persists as one reaches the neutron-rich isotone 42Si. Yet the proton removal from 48Ca results in a significant erosion of the N=28 shell in 42Si. Finally, the removal of s1/2 protons from 48Ca causes a ~50% reduction of the spin-orbit splitting among neutron p-orbitals in 42Si.Comment: 12 pages with 5 color figure

Beta-decay half-lives and beta-delayed neutron emission probabilities of nuclei in the region below A=110, relevant for the r-process

Measurements of the beta-decay properties of r-process nuclei below A=110 have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. Beta-decay half-lives for Y-105, Zr-106,107 and Mo-111, along with beta-delayed neutron emission probabilities of Y-104, Mo-109,110 and upper limits for Y-105, Zr-103,104,105,106,107 and Mo-108,111 have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.Comment: 21 pages, 10 figures, article accepted for publication in Physical Review

Scattering Mechanisms in a High Mobility Low Density Carbon-Doped (100) GaAs Two-Dimensional Hole System

We report on a systematic study of the density dependence of mobility in a low-density Carbon-doped (100) GaAs two-dimensional hole system (2DHS). At T= 50 mK, a mobility of 2.6 x 10^6 cm^2/Vs at a density p=6.2 x 10^10 cm^- was measured. This is the highest mobility reported for a 2DHS to date. Using a back-gated sample geometry, the density dependence of mobility was studied from 2.8 x 10^10 cm^-2 to 1 x 10^11 cm^-2. The mobility vs. density cannot be fit to a power law dependence of the form mu ~ p^alpha using a single exponent alpha. Our data indicate a continuous evolution of the power law with alpha ranging from ~ 0.7 at high density and increasing to ~ 1.7 at the lowest densities measured. Calculations specific to our structure indicate a crossover of the dominant scattering mechanism from uniform background impurity scattering at high density to remote ionized impurity scattering at low densities. This is the first observation of a carrier density-induced transition from background impurity dominated to remote dopant dominated transport in a single sample.Comment: 4 pages, 5 figures, prepared with LaTex2

Unstable Attractors: Existence and Robustness in Networks of Oscillators With Delayed Pulse Coupling

We consider unstable attractors; Milnor attractors $A$ such that, for some neighbourhood $U$ of $A$, almost all initial conditions leave $U$. Previous research strongly suggests that unstable attractors exist and even occur robustly (i.e. for open sets of parameter values) in a system modelling biological phenomena, namely in globally coupled oscillators with delayed pulse interactions. In the first part of this paper we give a rigorous definition of unstable attractors for general dynamical systems. We classify unstable attractors into two types, depending on whether or not there is a neighbourhood of the attractor that intersects the basin in a set of positive measure. We give examples of both types of unstable attractor; these examples have non-invertible dynamics that collapse certain open sets onto stable manifolds of saddle orbits. In the second part we give the first rigorous demonstration of existence and robust occurrence of unstable attractors in a network of oscillators with delayed pulse coupling. Although such systems are technically hybrid systems of delay differential equations with discontinuous `firing' events, we show that their dynamics reduces to a finite dimensional hybrid system system after a finite time and hence we can discuss Milnor attractors for this reduced finite dimensional system. We prove that for an open set of phase resetting functions there are saddle periodic orbits that are unstable attractors.Comment: 29 pages, 8 figures,submitted to Nonlinearit

Reducing orbital eccentricity in binary black hole simulations

Binary black hole simulations starting from quasi-circular (i.e., zero radial velocity) initial data have orbits with small but non-zero orbital eccentricities. In this paper the quasi-equilibrium initial-data method is extended to allow non-zero radial velocities to be specified in binary black hole initial data. New low-eccentricity initial data are obtained by adjusting the orbital frequency and radial velocities to minimize the orbital eccentricity, and the resulting ($\sim 5$ orbit) evolutions are compared with those of quasi-circular initial data. Evolutions of the quasi-circular data clearly show eccentric orbits, with eccentricity that decays over time. The precise decay rate depends on the definition of eccentricity; if defined in terms of variations in the orbital frequency, the decay rate agrees well with the prediction of Peters (1964). The gravitational waveforms, which contain $\sim 8$ cycles in the dominant l=m=2 mode, are largely unaffected by the eccentricity of the quasi-circular initial data. The overlap between the dominant mode in the quasi-circular evolution and the same mode in the low-eccentricity evolution is about 0.99.Comment: 27 pages, 9 figures; various minor clarifications; accepted to the "New Frontiers" special issue of CQ