11,939 research outputs found
Dipole-dipole instability of atom clouds in a far-detuned optical dipole trap
The effect of the dipole-dipole interaction on the far-off-resonance optical
dipole trapping scheme is calculated by a mean-field approach. The trapping
laser field polarizes the atoms and the accompanying dipole-dipole energy shift
deepens the attractive potential minimum in a pancake-shaped cloud. At high
density the thermal motion cannot stabilize the gas against self-contraction
and an instability occurs. We calculate the boundary of the stable and unstable
equilibrium regions on a two-dimensional phase diagram of the atom number and
the ratio of the trap depth to the temperature. We discuss the limitations
imposed by the dipole-dipole instability on the parameters needed to reach
Bose-Einstein condensation in an optical dipole trap.Comment: 8 pages, 3 figure
Light Transmission Through Metallic-Mean Quasiperiodic Stacks with Oblique Incidence
The propagation of s- and p-polarized light through quasiperiodic
multilayers, consisting of layers with different refractive indices, is studied
by the transfer matrix method. In particular, we focus on the transmission
coefficient of the systems in dependency on the incidence angle and on the
ratio of the refractive indices. We obtain additional bands with almost
complete transmission in the quasiperiodic systems at frequencies in the range
of the photonic band gap of a system with a periodic alignment of the two
materials for both types of light polarization. With increasing incidence angle
these bands bend towards higher frequencies, where the curvature of the
transmission bands in the quasiperiodic stack depends on the metallic mean of
the construction rule. Additionally, in the quasiperiodic systems for
p-polarized light the bands show almost complete transmission near the
Brewster's angle in contrast to the results for s-polarized light. Further, we
present results for the influence of the refractive indices at the midgap
frequency of the periodic stack, where the quasiperiodicity was found to be
most effective.Comment: 10 pages, 7 figure
N=2 central charge superspace and a minimal supergravity multiplet
We extend the notion of central charge superspace to the case of local
supersymmetry. Gauged central charge transformations are identified as
diffeomorphisms at the same footing as space-time diffeomorphisms and local
supersymmetry transformations. Given the general structure we then proceed to
the description of a particular vector-tensor supergravity multiplet of 24+24
components, identified by means of rather radical constraints
Dilute Birman--Wenzl--Murakami Algebra and models
A ``dilute'' generalisation of the Birman--Wenzl--Murakami algebra is
considered. It can be ``Baxterised'' to a solution of the Yang--Baxter algebra.
The vertex models are examples of corresponding solvable
lattice models and can be regarded as the dilute version of the
vertex models.Comment: 11 page
The relationship of marine stratus to synoptic conditions
The marine stratus which persistently covered most of the eastern Pacific Ocean, had large clear areas during the FIRE Intensive Field Operations (IFO) in 1987. Clear zones formed inside the large oceanic cloud mass on almost every day during the IFO. The location and size of the clear zones varied from day to day implying that they were related to dynamic weather conditions and not to oceanic conditions. Forecasting of cloud cover for aircraft operations during the IFO was directed towards predicting when and where the clear and broken zones would form inside the large marine stratus cloud mass. The clear zones often formed to the northwest of the operations area and moved towards it. However, on some days the clear zones appeared to form during the day in the operations area as part of the diurnal cloud burn off. The movement of the clear zones from day to day were hard to follow because of the large diurnal changes in cloud cover. Clear and broken cloud zones formed during the day only to distort in shape and fill during the following night. The field forecasters exhibited some skill in predicting when the clear and broken cloud patterns would form in the operations area. They based their predictions on the analysis and simulations of the models run by NOAA's Numeric Meteorological Center. How the atmospheric conditions analyzed by one NOAA/NMC model related to the cloud cover is discussed
A Concept for Attribute-Based Authorization on D-Grid Resources
In Germany's D-Grid project numerous Grid communities are working together to provide a common overarching Grid infrastructure. The major aims of D-Grid are the integration of existing Grid deployments and their interoperability. The challenge lies in the heterogeneity of the current implementations: three Grid middleware stacks and different Virtual Organization management approaches have to be embraced to achieve the intended goals. In this article we focus oil the implementation of an attribute-based authorization infrastructure that not only leverages the well-known VO attributes but also campus attributes managed by a Shibboleth federation
Creation of a dipolar superfluid in optical lattices
We show that by loading a Bose-Einstein condensate (BEC) of two different
atomic species into an optical lattice, it is possible to achieve a
Mott-insulator phase with exactly one atom of each species per lattice site. A
subsequent photo-association leads to the formation of one heteronuclear
molecule with a large electric dipole moment, at each lattice site. The melting
of such dipolar Mott-insulator creates a dipolar superfluid, and eventually a
dipolar molecular BEC.Comment: 4 pages, 2 eps figure
Anharmonicity Induced Resonances for Ultracold Atoms and their Detection
When two atoms interact in the presence of an anharmonic potential, such as
an optical lattice, the center of mass motion cannot be separated from the
relative motion. In addition to generating a confinement-induced resonance (or
shifting the position of an existing Feshbach resonance), the external
potential changes the resonance picture qualitatively by introducing new
resonances where molecular excited center of mass states cross the scattering
threshold. We demonstrate the existence of these resonances, give their
quantitative characterization in an optical superlattice, and propose an
experimental scheme to detect them through controlled sweeping of the magnetic
field.Comment: 6 pages, 5 figures; expanded presentatio
- âŠ