11,281 research outputs found
Quantum glass phases in the disordered Bose-Hubbard model
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal
disorder is determined using Quantum Monte Carlo simulations. A sequence of
quantum glass phases intervene at the interface between the Mott insulating and
the Superfluid phases of the clean system. In addition to the standard Bose
glass phase, the coexistence of gapless and gapped regions close to the Mott
insulating phase leads to a novel Mott glass regime which is incompressible yet
gapless. Numerical evidence for the properties of these phases is given in
terms of global (compressibility, superfluid stiffness) and local
(compressibility, momentum distribution) observables
Creating topological interfaces and detecting chiral edge modes in a 2D optical lattice
We propose and analyze a general scheme to create chiral topological edge
modes within the bulk of two-dimensional engineered quantum systems. Our method
is based on the implementation of topological interfaces, designed within the
bulk of the system, where topologically-protected edge modes localize and
freely propagate in a unidirectional manner. This scheme is illustrated through
an optical-lattice realization of the Haldane model for cold atoms, where an
additional spatially-varying lattice potential induces distinct topological
phases in separated regions of space. We present two realistic experimental
configurations, which lead to linear and radial-symmetric topological
interfaces, which both allows one to significantly reduce the effects of
external confinement on topological edge properties. Furthermore, the
versatility of our method opens the possibility of tuning the position, the
localization length and the chirality of the edge modes, through simple
adjustments of the lattice potentials. In order to demonstrate the unique
detectability offered by engineered interfaces, we numerically investigate the
time-evolution of wave packets, indicating how topological transport
unambiguously manifests itself within the lattice. Finally, we analyze the
effects of disorder on the dynamics of chiral and non-chiral states present in
the system. Interestingly, engineered disorder is shown to provide a powerful
tool for the detection of topological edge modes in cold-atom setups.Comment: 18 pages, 21 figure
Stationary state volume fluctuations in a granular medium
A statistical description of static granular material requires ergodic
sampling of the phase space spanned by the different configurations of the
particles. We periodically fluidize a column of glass beads and find that the
sequence of volume fractions phi of post-fluidized states is history
independent and Gaussian distributed about a stationary state. The standard
deviation of phi exhibits, as a function of phi, a minimum corresponding to a
maximum in the number of statistically independent regions. Measurements of the
fluctuations enable us to determine the compactivity X, a temperature-like
state variable introduced in the statistical theory of Edwards and Oakeshott
[Physica A {\bf 157}, 1080 (1989)].Comment: published with minor change
1995 atmospheric trace molecule spectroscopy (ATMOS) linelist
The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment uses a Fourier-transform spectrometer on board the Space Shuttle to record infrared solar occultation spectra of the atmosphere at 0.01-cm^(-1) resolution. The current version of the molecular spectroscopic database used for the analysis of the data obtained during three Space Shuttle missions between 1992 and 1994 is described. It is an extension of the effort first described by Brown et al. [Appl. Opt. 26, 5154 (1987)] to maintain an up-to-date database for the ATMOS experiment. The three-part ATMOS compilation contains Line parameters of 49 molecular species between 0 and 10000 cm^(-1), The main list, with nearly 700,000 entries, is an updated version of the HITRAN 1992 database. The second compilation contains supplemental line parameters, and the third set consists of absorption cross sections to represent the unresolvable features of heavy molecules. The differences between the ATMOS database and other public compilations are discussed
Quantum Metallicity on the High-Field Side of the Superconductor-Insulator Transition
We investigate ultrathin superconducting TiN films, which are very close to
the localization threshold. Perpendicular magnetic field drives the films from
the superconducting to an insulating state, with very high resistance. Further
increase of the magnetic field leads to an exponential decay of the resistance
towards a finite value. In the limit of low temperatures, the saturation value
can be very accurately extrapolated to the universal quantum resistance h/e^2.
Our analysis suggests that at high magnetic fields a new ground state, distinct
from the normal metallic state occurring above the superconducting transition
temperature, is formed. A comparison with other studies on different materials
indicates that the quantum metallic phase following the magnetic-field-induced
insulating phase is a generic property of systems close to the disorder-driven
superconductor-insulator transition.Comment: 4 pages, 4 figures, published versio
An Extension of the Fractional Parentage Expansion to Nonrelativistic and Relativistic Dibaryon Calculations
The fractional parentage expansion method is extended from
nonrelativistic to and relativistic dibaryon calculations. A
transformation table between physical bases and symmetry bases for the
dibaryon is provided. A program package has been written for
dibaryon calculation based on the fractional parentage expansion method.Comment: 15 pages text plus 18 pages tables, latex, no figure
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
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Goodbye to Projects? Briefing Paper 1: An Overview: Projects and Principles.
YesThis briefing paper reports on research exploring ten detailed case studies of livelihoods-oriented interventions operating in Tanzania, Lesotho, South Africa and Uganda. Analysing these interventions through an audit of sustainable livelihood `principles¿ (as a proxy for best practice) revealed general lessons both about the practical opportunities and challenges for employing sustainable livelihoods approaches to the design, implementation, monitoring and evaluation of development interventions and also about the changing format of development interventions.Department for International Developmen
Influence of tensor interactions on masses and decay widths of dibaryons
The influence of gluon and Goldstone boson induced tensor interactions on the
dibaryon masses and D-wave decay widths has been studied in the quark
delocalization, color screening model. The effective S-D wave transition
interactions induced by gluon and Goldstone boson exchanges decrease rapidly
with increasing strangeness of the channel. The tensor contribution of K and
mesons is negligible in this model. There is no six-quark state in the
light flavor world studied so far that can become bound by means of these
tensor interactions besides the deuteron. The partial D-wave decay widths of
the N state to spin 0 and 1 final states
are 12.0 keV and 21.9 keV respectively. This is a very narrow dibaryon
resonance that might be detectable in relativistic heavy ion reactions by
existing RHIC detectors through the reconstruction of the vertex mass of the
decay product and by the COMPAS detector at CERN or at JHF in
Japan and the FAIR project in Germany in the future.Comment: 19 pages, 5 figure
Quark Delocalization, Color Screening, and Nuclear Intermediate Range Attraction
We consider the effect of including quark delocalization and color screening,
in the nonrelativistic quark cluster model, on baryon-baryon potentials and
phase shifts. We find that the inclusion of these additional effects allows a
good qualitative description of both.Comment: 10 pages, LaTeX, 4 figures in PostScript after text, LA-UR-91-215
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