15,675 research outputs found
Calculation of symmetric and asymmetric vortex seperation on cones and tangent ogives based on discrete vortex models
An inviscid discrete vortex model, with newly derived expressions for the tangential velocity imposed at the separation points, is used to investigate the symmetric and asymmetric vortex separation on cones and tangent ogives. The circumferential locations of separation are taken from experimental data. Based on a slender body theory, the resulting simultaneous nonlinear algebraic equations in a cross-flow plane are solved with Broyden's modified Newton-Raphson method. Total force coefficients are obtained through momentum principle with new expressions for nonconical flow. It is shown through the method of function deflation that multiple solutions exist at large enough angles of attack, even with symmetric separation points. These additional solutions are asymmetric in vortex separation and produce side force coefficients which agree well with data for cones and tangent ogives
Restoration of multichannel microwave radiometric images
A constrained iterative image restoration method is applied to multichannel diffraction-limited imagery. This method is based on the Gerchberg-Papoulis algorithm utilizing incomplete information and partial constraints. The procedure is described using the orthogonal projection operators which project onto two prescribed subspaces iteratively. Some of its properties and limitations are also presented. The selection of appropriate constraints was emphasized in a practical application. Multichannel microwave images, each having different spatial resolution, were restored to a common highest resolution to demonstrate the effectiveness of the method. Both noise-free and noisy images were used in this investigation
Observation of the Pairing Gap in a Strongly Interacting Fermi Gas
We study fermionic pairing in an ultracold two-component gas of Li atoms
by observing an energy gap in the radio-frequency excitation spectra. With
control of the two-body interactions via a Feshbach resonance we demonstrate
the dependence of the pairing gap on coupling strength, temperature, and Fermi
energy. The appearance of an energy gap with moderate evaporative cooling
suggests that our full evaporation brings the strongly interacting system deep
into a superfluid state.Comment: 18 pages, 3 figure
Ultracold molecules: vehicles to scalable quantum information processing
We describe a novel scheme to implement scalable quantum information
processing using Li-Cs molecular state to entangle Li and Cs
ultracold atoms held in independent optical lattices. The Li atoms will
act as quantum bits to store information, and Cs atoms will serve as
messenger bits that aid in quantum gate operations and mediate entanglement
between distant qubit atoms. Each atomic species is held in a separate optical
lattice and the atoms can be overlapped by translating the lattices with
respect to each other. When the messenger and qubit atoms are overlapped,
targeted single spin operations and entangling operations can be performed by
coupling the atomic states to a molecular state with radio-frequency pulses. By
controlling the frequency and duration of the radio-frequency pulses,
entanglement can either be created or swapped between a qubit messenger pair.
We estimate operation fidelities for entangling two distant qubits and discuss
scalability of this scheme and constraints on the optical lattice lasers
Lyapunov Spectra in SU(2) Lattice Gauge Theory
We develop a method for calculating the Lyapunov characteristic exponents of
lattice gauge theories. The complete Lyapunov spectrum of SU(2) gauge theory is
obtained and Kolmogorov-Sinai entropy is calculated. Rapid convergence with
lattice size is found.Comment: 7pp, DUKE-TH-93-5
Exploring the BEC-BCS Crossover with an Ultracold Gas of Li Atoms
We present an overview of our recent measurements on the crossover from a
Bose-Einstein condensate of molecules to a Bardeen-Cooper-Schrieffer
superfluid. The experiments are performed on a two-component spin-mixture of
Li atoms, where a Fesh\-bach resonance serves as the experimental key to
tune the s-wave scattering length and thus to explore the various interaction
regimes. In the BEC-BCS crossover, we have characterized the interaction energy
by measuring the size of the trapped gas, we have studied collective excitation
modes, and we have observed the pairing gap. Our observations provide strong
evidence for superfluidity in the strongly interacting Fermi gas.Comment: Proceedings of ICAP-2004 (Rio de Janeiro). Review on Innsbruck
BEC-BCS crossover experiments with updated Feshbach resonance positio
Resolution enhancement of multichannel microwave imagery from the Nimbus-7 SMMR for maritime rainfall analysis
A restoration of the 37, 21, 18, 10.7, and 6.6 GHz satellite imagery from the scanning multichannel microwave radiometer (SMMR) aboard Nimbus-7 to 22.2 km resolution is attempted using a deconvolution method based upon nonlinear programming. The images are deconvolved with and without the aid of prescribed constraints, which force the processed image to abide by partial a priori knowledge of the high-resolution result. The restored microwave imagery may be utilized to examined the distribution of precipitating liquid water in marine rain systems
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