5,640 research outputs found
SU(3) quasidynamical symmetry underlying the Alhassid--Whelan arc of regularity
The first example of an empirically manifested quasi dynamical symmetry
trajectory in the interior of the symmetry triangle of the Interacting Boson
Approximation model is identified for large boson numbers. Along this curve,
extending from SU(3) to near the critical line of the first order phase
transition, spectra exhibit nearly the same degeneracies that characterize the
low energy levels of SU(3). This trajectory also lies close to the
Alhassid-Whelan arc of regularity, the unique interior region of regular
behavior connecting the SU(3) and U(5) vertices, thus offering a possible
symmetry-based interpretation of that narrow zone of regularity amidst regions
of more chaotic spectra.Comment: 4 pages, LaTeX, 5 eps figure
Image Storage in Hot Vapors
We theoretically investigate image propagation and storage in hot atomic
vapor. A system is adopted for imaging and an atomic vapor cell is placed
over the transform plane. The Fraunhofer diffraction pattern of an object in
the object plane can thus be transformed into atomic Raman coherence according
to the idea of ``light storage''. We investigate how the stored diffraction
pattern evolves under diffusion. Our result indicates, under appropriate
conditions, that an image can be reconstructed with high fidelity. The main
reason for this procedure to work is the fact that diffusion of opposite-phase
components of the diffraction pattern interfere destructively.Comment: 11 pages, 3 figure
Diffraction limit of the sub-Planck structures
The orthogonality of cat and displaced cat states, underlying Heisenberg
limited measurement in quantum metrology, is studied in the limit of large
number of states. The asymptotic expression for the corresponding state overlap
function, controlled by the sub-Planck structures arising from phase space
interference, is obtained exactly. The validity of large phase space support,
in which context the asymptotic limit is achieved, is discussed in detail. For
large number of coherent states, uniformly located on a circle, it identically
matches with the diffraction pattern for a circular ring with uniform angular
source strength. This is in accordance with the van Cittert-Zernike theorem,
where the overlap function, similar to the mutual coherence function matches
with a diffraction pattern.Comment: 5 pages, 3 figure
Mass and Spin of Poincare Gauge Theory
We discuss two expressions for the conserved quantities (energy momentum and
angular momentum) of the Poincar\'e Gauge Theory. We show, that the variations
of the Hamiltonians, of which the expressions are the respective boundary
terms, are well defined, if we choose an appropriate phase space for asymptotic
flat gravitating systems. Furthermore, we compare the expressions with others,
known from the literature.Comment: 16 pages, plain-tex; to be published in Gen. Rel. Gra
Quasi-local Energy for Spherically Symmetric Spacetimes
We present two complementary approaches for determining the reference for the
covariant Hamiltonian boundary term quasi-local energy and test them on
spherically symmetric spacetimes. On the one hand, we isometrically match the
2-surface and extremize the energy. This can be done in two ways, which we call
programs I (without constraint) and II (with additional constraints). On the
other hand, we match the orthonormal 4-frames of the dynamic and the reference
spacetimes. Then, if we further specify the observer by requiring the reference
displacement to be the timelike Killing vector of the reference, the result is
the same as program I, and the energy can be positive, zero, or even negative.
If, instead, we require that the Lie derivatives of the two-area along the
displacement vector in both the dynamic and reference spacetimes to be the
same, the result is the same as program II, and it satisfies the usual
criteria: the energies are non-negative and vanish only for Minkowski (or
anti-de Sitter) spacetime.Comment: 16 pages, no figure
Nanoplasmonic Lattices for Ultracold atoms
We propose to use sub-wavelength confinement of light associated with the
near field of plasmonic systems to create nanoscale optical lattices for
ultracold atoms. Our approach combines the unique coherence properties of
isolated atoms with the sub-wavelength manipulation and strong light-matter
interaction associated with nano-plasmonic systems. It allows one to
considerably increase the energy scales in the realization of Hubbard models
and to engineer effective long-range interactions in coherent and dissipative
many-body dynamics. Realistic imperfections and potential applications are
discussed.Comment: 5 pages, 3 figures, V2: minor changes, V3: minor changes, added
supplemental materia
Thermo-mechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near infrared pump-probe diffraction experiments
The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of
metallic nano-disks has been studied by near infrared pump-probe diffraction
measurements, over a temporal range spanning from 100 fs to several
nanoseconds. The experiments demonstrate that, in these systems, a
two-dimensional surface acoustic wave (2DSAW), with a wavevector given by the
reciprocal periodicity of the array, can be excited by ~120 fs Ti:sapphire
laser pulses. In order to clarify the interaction between the nanodisks and the
substrate, numerical calculations of the elastic eigenmodes and simulations of
the thermodynamics of the system are developed through finite-element analysis.
At this light, we unambiguously show that the observed 2DSAW velocity shift
originates from the mechanical interaction between the 2DSAWs and the
nano-disks, while the correlated 2DSAW damping is due to the energy radiation
into the substrate.Comment: 13 pages, 10 figure
TOMEX: A Comparison of Lidar and Sounding Rocket Chemical Tracer
On October 26, 2000, a Black Brant V sounding rocket carrying a chemical tracer release was launched from the rocket range at White Sands, New Mexico, as part of the Turbulent Oxygen Mixing Experiment (TOMEX). The releases occurred approximately 150 km from the location of the Starfire Optical Range where the University of Illinois sodium lidar was operated to measure winds and temperatures in the mesosphere and lower thermosphere. The geometry for the experiment was such that the lidar beam was able to intersect the release point for the chemical tracer trail on the upleg part of the flight near an altitude of 95 km. In all, a total of five lidar beam directions were used to sample the region from approximately 85 to 105-km altitude in the vicinity of the releases. Combining the lidar Doppler velocity data from the various beam directions made it possible to produce profiles of vector horizontal winds that could be compared directly with the winds obtained from the triangulation of the chemical tracer trails
Constructing Fresnel reflection coefficients by ruler and compass
A simple and intuitive geometical method to analyze Fresnel formulas is
presented. It applies to transparent media and is valid for perpendicular and
parallel polarizations. The approach gives a graphical characterization
particularly simple of the critical and Brewster angles. It also provides an
interpretation of the relation between the reflection coefficients for both
basic polarizations as a symmetry in the plane
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