227 research outputs found
Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals
We observe experimentally that ensembles of quantum dots in three-dimensional (3D) photonic crystals reveal strongly nonexponential time-resolved emission. These complex emission decay curves are analyzed with a continuous distribution of decay rates. The log-normal distribution describes the decays well for all studied lattice parameters. The distribution width is identified with variations of the radiative emission rates of quantum dots with various positions and dipole orientations in the unit cell. We find a striking sixfold change of the width of the distribution by varying the lattice parameter. This interpretation qualitatively agrees with the calculations of the 3D projected local density of states. We therefore conclude that fluorescence decay of ensembles of quantum dots is highly nonexponential to an extent that is controlled by photonic crystals
The Kazhdan-Lusztig conjecture for W-algebras
The main result in this paper is the character formula for arbitrary
irreducible highest weight modules of W algebras. The key ingredient is the
functor provided by quantum Hamiltonian reduction, that constructs the W
algebras from affine Kac-Moody algebras and in a similar fashion W modules from
KM modules. Assuming certain properties of this functor, the W characters are
subsequently derived from the Kazhdan-Lusztig conjecture for KM algebras. The
result can be formulated in terms of a double coset of the Weyl group of the KM
algebra: the Hasse diagrams give the embedding diagrams of the Verma modules
and the Kazhdan-Lusztig polynomials give the multiplicities in the characters.Comment: uuencoded file, 29 pages latex, 5 figure
21-cm synthesis observations of VIRGOHI 21 - a possible dark galaxy in the Virgo Cluster
Many observations indicate that dark matter dominates the extra-galactic
Universe, yet no totally dark structure of galactic proportions has ever been
convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm
source we found in the Virgo Cluster using Jodrell Bank, was a possible dark
galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible
gravitational source to account for it. We have now imaged VIRGOHI 21 in the
neutral-hydrogen line and find what could be a dark, edge-on, spinning disk
with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has
unquestionably been involved in an interaction with NGC 4254, a luminous spiral
with an odd one-armed morphology, but lacking the massive interactor normally
linked with such a feature. Numerical models of NGC 4254 call for a close
interaction ~10^8 years ago with a perturber of ~10^11 solar masses. This we
take as additional evidence for the massive nature of VIRGOHI 21 as there does
not appear to be any other viable candidate. We have also used the Hubble Space
Telescope to search for stars associated with the HI and find none down to an I
band surface brightness limit of 31.1 +/- 0.2 mag/sq. arcsec.Comment: 8 pages, accepted to ApJ, uses emulateapj.cls. Mpeg animation (Fig.
2) available at ftp://ftp.naic.edu/pub/publications/minchin/video2.mp
Gate-tunable Superconductivity in Hybrid InSb-Pb Nanowires
We present a report on hybrid InSb-Pb nanowires that combine high spin-orbit
coupling with a high critical field and a large superconducting gap. Material
characterization indicates the Pb layer of high crystal quality on the nanowire
side facets. Hard induced superconducting gaps and gate-tunable supercurrent
are observed in the hybrid nanowires. These results showcase the promising
potential of this material combination for a diverse range of applications in
hybrid quantum transport devices.Comment: 11 pages, 3 figure
Molecular scale structure and dynamics at an ionic liquid/electrode interface
The structural arrangement and dynamics of ions near the IL/electrode interface during charging and discharging was studied by a combination of time resolved X-ray reflectivity and impedance spectroscopy.</p
Anyons in discrete gauge theories with Chern-Simons terms
We study the effect of a Chern-Simons term in a theory with discrete gauge
group H, which in (2+1)-dimensional space time describes (non-abelian) anyons.
As in a previous paper, we emphasize the underlying algebraic structure, namely
the Hopf algebra D(H). We argue on physical grounds that the addition of a
Chern-Simons term in the action leads to a non-trivial 3-cocycle on D(H).
Accordingly, the physically inequivalent models are labelled by the elements of
the cohomology group H^3(H,U(1)). It depends periodically on the coefficient of
the Chern-Simons term which model is realized. This establishes a relation with
the discrete topological field theories of Dijkgraaf and Witten. Some
representative examples are worked out explicitly.Comment: 18 page
An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey, using
both ground-based and Hubble Space Telescope images, of a complete sample of
nearby barred S0--Sa galaxies in the field, with a particular emphasis on
identifying and measuring central structures within the bars: secondary bars,
inner disks, nuclear rings and spirals, and off-plane dust. A discussion of the
frequency and statistical properties of the various types of inner structures
has already been published. Here, we present the data for the individual
galaxies and measurements of their bars and inner structures. We set out the
methods we use to find and measure these structures, and how we discriminate
between them. In particular, we discuss some of the deficiencies of ellipse
fitting of the isophotes, which by itself cannot always distinguish between
bars, rings, spirals, and dust, and which can produce erroneous measurements of
bar sizes and orientations.Comment: LaTeX, 66 pages (including 42 figures, 36 in color). To appear in The
Astrophysical Journal Supplement. Full-resolution and text-only versions
available at http://www.iac.es/galeria/erwin/research
The asymptotic dynamics of three-dimensional Einstein gravity with a negative cosmological constant
Liouville theory is shown to describe the asymptotic dynamics of
three-dimensional Einstein gravity with a negative cosmological constant. This
is because (i) Chern-Simons theory with a gauge group
on a space-time with a cylindrical boundary is equivalent to the non-chiral
WZW model; and (ii) the anti-de Sitter boundary conditions implement
the constraints that reduce the WZW model to the Liouville theory.Comment: 10 pages in LaTeX, LaTeX problem fixe
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