1,895 research outputs found
Contact resistance dependence of crossed Andreev reflection
We show experimentally that in nanometer scaled superconductor/normal metal
hybrid devices and in a small window of contact resistances, crossed Andreev
reflection (CAR) can dominate the nonlocal transport for all energies below the
superconducting gap. Besides CAR, elastic cotunneling (EC) and nonlocal charge
imbalance (CI) can be identified as competing subgap transport mechanisms in
temperature dependent four-terminal nonlocal measurements. We demonstrate a
systematic change of the nonlocal resistance vs. bias characteristics with
increasing contact resistances, which can be varied in the fabrication process.
For samples with higher contact resistances, CAR is weakened relative to EC in
the midgap regime, possibly due to dynamical Coulomb blockade. Gaining control
of CAR is an important step towards the realization of a solid state entangler.Comment: 5 pages, 4 figures, submitted to PR
Hypersomnia associated with bilateral posterior hypothalamic lesion - A polysomnographic case study
We examined an obese 58-year-old patient with a bilateral posterior hypothalamic lesion of unknown etiology. A 24-hour polysomnography revealed a markedly increased total sleep time (17.6 h). During daytime, only 3 continuous wake phases occurred. REM periods occurred only between 5 p.m. and 6 a.m. We conclude from our results that, similar to the results from animal experiments, the posterior hypothalamus in humans plays a critical role in the maintenance of wakefulness. Copyright (C) 2003 S. Karger AG, Basel
Discrete charges on a two dimensional conductor
We investigate the electrostatic equilibria of N discrete charges of size 1/N
on a two dimensional conductor (domain). We study the distribution of the
charges on symmetric domains including the ellipse, the hypotrochoid and
various regular polygons, with an emphasis on understanding the distributions
of the charges, as the shape of the underlying conductor becomes singular. We
find that there are two regimes of behavior, a symmetric regime for smooth
conductors, and a symmetry broken regime for ``singular'' domains. For smooth
conductors, the locations of the charges can be determined up to a certain
order by an integral equation due to Pommerenke (1969). We present a derivation
of a related (but different) integral equation, which has the same solutions.
We also solve the equation to obtain (asymptotic) solutions which show
universal behavior in the distribution of the charges in conductors with
somewhat smooth cusps. Conductors with sharp cusps and singularities show
qualitatively different behavior, where the symmetry of the problem is broken,
and the distribution of the discrete charges does not respect the symmetry of
the underlying domain. We investigate the symmetry breaking both theoretically,
and numerically, and find good agreement between our theory and the numerics.
We also find that the universality in the distribution of the charges near the
cusps persists in the symmetry broken regime, although this distribution is
very different from the one given by the integral equation.Comment: 46 pages, 46 figures, submitted to J. Stat. Phy
Spectra of comet P/Halley at R = 4 - 8 AU
Spectra of Comet Halley (lambda lambda = 3400-6500 A) were acquired at pre- and post-perihelion distances of 4.8 AU on 1985 Feb. 17 (Coma V equals 18.9 mag) and 1987 Feb. 1 (coma V = 15.9 mag) using the 4.5-m Multiple-Mirror Telescope (MMT) and the CTIO 4.0-m telescope, respectively. The CN(0,0) violet system band flux at 4.8 AU was approx. 15 times greater at the post-perhelion phase compared to pre-perihelion. Additional post-perihelion spectra, obtained on 1986 Nov. 28 to 30 with the MTT, showed CN(0,0) and very weak C3 4040 A emission. The MMT data are one-dimensional spectra (aperture: 5 arc sec diameter) obtained with an intensified Reticon while the CTIO data are two-dimensional spectra (slit length = 280 arc sec) obtained with a 2D-Frutti photon counting system. Extended CN(0,0) emission was detected in the 1987 Feb. 1 (at 4.8 AU) spectra to a distance of at least 70 arc sec in the solar and anti-solar directions. Additional CCD spectra obtained with the KPNO 2.2-meter telescope on 1988 Feb. 20 (at 7.9 AU) show scattered solar continuum approx. 32 arc sec diameter. However, no emission features were detected at 7.9 AU
The Effect of Precipitation and Temperature on Annualr Ring Growth in Four Species of Quercus
The present investigations were made from 11 trees of Quercus alba, 17 trees of Q. montana, 16 trees of Q. velutina and 9of Q. borealis maxima. All specimens were taken from the knobs area of Bartholomew and Brown counties in Indiana, from stumps left by lumbering operations carried on from July to September: 1934. Sections were brought to the laboratory and measurements were made with a binocular microscope suspended over the section. The annular ring widths of eight equidistant radii were taken on each of the 53 sections measured. During the measuring, medullary rays were followed instead of geometrical radii. In this manner the width of the annular growth was taken in a direction eliminating the error of oblique measurement. When a radius was completed, a number tag was placed at the end of the radius. This allowed for a recheck to be made at any desirable time. Annular ring measurements were taken of the years 1909-1933 inclusive, a growth period of twenty-five years. The measurement of eight radii per section aided in eliminating the errors of unequal growth along different radii in the same tree
Spin-charge separation in two-component Bose-gases
We show that one of the key characteristics of interacting one-dimensional
electronic quantum systems, the separation of spin and charge, can be observed
in a two-component system of bosonic ultracold atoms even close to a competing
phase separation regime. To this purpose we determine the real-time evolution
of a single particle excitation and the single-particle spectral function using
density-matrix renormalization group techniques. Due to efficient bosonic
cooling and good tunability this setup exhibits very good conditions for
observing this strong correlation effect. In anticipation of experimental
realizations we calculate the velocities for spin and charge perturbations for
a wide range of parameters
Extended coherence time on the clock transition of optically trapped Rubidium
Optically trapped ensembles are of crucial importance for frequency
measurements and quantum memories, but generally suffer from strong dephasing
due to inhomogeneous density and light shifts. We demonstrate a drastic
increase of the coherence time to 21 s on the magnetic field insensitive clock
transition of Rb-87 by applying the recently discovered spin self-rephasing.
This result confirms the general nature of this new mechanism and thus shows
its applicability in atom clocks and quantum memories. A systematic
investigation of all relevant frequency shifts and noise contributions yields a
stability of 2.4E-11 x tau^(-1/2), where tau is the integration time in
seconds. Based on a set of technical improvements, the presented frequency
standard is predicted to rival the stability of microwave fountain clocks in a
potentially much more compact setup.Comment: 5 pages, 4 figure
Excitations in two-component Bose-gases
In this paper, we study a strongly correlated quantum system that has become
amenable to experiment by the advent of ultracold bosonic atoms in optical
lattices, a chain of two different bosonic constituents. Excitations in this
system are first considered within the framework of bosonization and Luttinger
liquid theory which are applicable if the Luttinger liquid parameters are
determined numerically. The occurrence of a bosonic counterpart of fermionic
spin-charge separation is signalled by a characteristic two-peak structure in
the spectral functions found by dynamical DMRG in good agreement with
analytical predictions. Experimentally, single-particle excitations as probed
by spectral functions are currently not accessible in cold atoms. We therefore
consider the modifications needed for current experiments, namely the
investigation of the real-time evolution of density perturbations instead of
single particle excitations, a slight inequivalence between the two
intraspecies interactions in actual experiments, and the presence of a
confining trap potential. Using time-dependent DMRG we show that only
quantitative modifications occur. With an eye to the simulation of strongly
correlated quantum systems far from equilibrium we detect a strong dependence
of the time-evolution of entanglement entropy on the initial perturbation,
signalling limitations to current reasonings on entanglement growth in
many-body systems
Simultaneous visible and near-infrared spectrophotometry of Comet Austin 1989c
Simultaneous visible and near-infrared spectra of Comet Austin were obtained wit the 1.5 m and 2.3 m telescopes of the University of Arizona Observatories on 1990 May 16. The visible spectrum obtained with the IHW spectrograph covers the 3126-9490 A wavelength interval, while the near-infrared spectrum obtained with the germanium spectrometer covers the 9036-12794 A wavelength interval. Simultaneous measurements of integrated band fluxes are presented for the CN B 2Sigma(+) - X 2Sigma(+) (violet) and A 2Pi - X 2Sigma(+) (red) systems. A CN spectrum and CN band flux ratios calculated from a fluoresence equilibrium model are also presented. From a comparison between the observed and calculated CN spectra and band flux ratios, it is found that red system oscillator strengths determined from recent ab initio calculations appropriately describe the radiative properties of CN molecules
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