Collapse and revival dynamics of superfluids of ultracold atoms in optical lattices

Recent experiments have shown a remarkable number of collapse-and-revival oscillations of the matter-wave coherence of ultracold atoms in optical lattices [Will et al., Nature 465, 197 (2010)]. Using a mean-field approximation to the Bose-Hubbard model, we show that the visibility of collapse-and-revival interference patterns reveal number squeezing of the initial superfluid state. To describe the dynamics, we use an effective Hamiltonian that incorporates the intrinsic two-body and induced three-body interactions, and we analyze in detail the resulting complex pattern of collapse-and-revival frequencies generated by virtual transitions to higher bands, as a function of lattice parameters and mean-atom number. Our work shows that a combined analysis of both the multiband, non-stationary dynamics in the final deep lattice, and the number-squeezing of the initial superfluid state, explains important characteristics of optical lattice collapse-and-revival physics. Finally, by treating the two- and three-body interaction strengths, and the coefficients describing the initial superposition of number states, as free parameters in a fit to the experimental data it should be possible to go beyond some of the limitations of our model and obtain insight into the breakdown of the mean-field theory for the initial state or the role of nonperturbative effects in the final state dynamics.Comment: 5 pages, 5 figures. This is the updated version published June 201

Are topological defects responsible for the 300 EeV cosmic rays?

We use of a hybrid matrix--Monte Carlo method to simulate the cascade through the cosmic background radiation initiated by UHE particles and radiation emitted by topological defects. We follow the cascade over cosmological distances and calculate the intensities of hadrons, gamma-rays and neutrinos produced. We compare our results with the observed cosmic ray intensity at 300 EeV and lower energies, and conclude that topological defects are most unlikely to be the origin of the most energetic cosmic ray events.Comment: 3 pages, compressed and uuencoded PostScript (111kb); Nucl. Phys. B., Proc. Suppl., vol 48, in press (TAUP95 Workshop

The braiding for representations of q-deformed affine sl2sl_2

We compute the braiding for the `principal gradation' of $U_q(\hat{{\it sl}_2})$ for $|q|=1$ from first principles, starting from the idea of a rigid braided tensor category. It is not necessary to assume either the crossing or the unitarity condition from S-matrix theory. We demonstrate the uniqueness of the normalisation of the braiding under certain analyticity assumptions, and show that its convergence is critically dependent on the number-theoretic properties of the number $\tau$ in the deformation parameter $q=e^{2\pi i\tau}$. We also examine the convergence using probability, assuming a uniform distribution for $q$ on the unit circle.Comment: LaTeX, 10 pages with 2 figs, uses epsfi

Application of numerical optimization to the design of wings with specified pressure distributions

A practical procedure for the optimum design of transonic wings is demonstrated. The procedure uses an optimization program based on the method of feasible directions coupled with an aerodynamic analysis program which solves the three-dimensional potential equation for subsonic through transonic flow. Two new wings for the A-7 aircraft were designed by using the optimization procedure to achieve specified surface pressure distributions. The new wings, along with the existing A-7 wing, were tested in the Ames 11 ft transonic wind tunnel. The experimental data show that all of the performance goals were met. However, comparisons of the wind tunnel results with the theoretical predictions indicate some differences at conditions for which strong shock waves occur

Improved electro-optical tracking system

Electro-optical tracking system employs a laser beam illuminating source, an electronic laser beam deflector, and an image dissector photomultiplier. An electronic scanning transmitter and receiver follows rapid movements or accelerations of the target

Analysis and compensation of an aircraft simulator control loading system with compliant linkage

A hydraulic control loading system for aircraft simulation was analyzed to find the causes of undesirable low frequency oscillations and loading effects in the output. The hypothesis of mechanical compliance in the control linkage was substantiated by comparing the behavior of a mathematical model of the system with previously obtained experimental data. A compensation scheme based on the minimum integral of the squared difference between desired and actual output was shown to be effective in reducing the undesirable output effects. The structure of the proposed compensation was computed by use of a dynamic programing algorithm and a linear state space model of the fixed elements in the system

Saline Conversion and Ice Structures from Artificially Grown Sea Ice

The environment of cold regions is generally viewed as inhospitable, primarily due to application of ideal processes and techniques suitable to temperate zones. The work herein is a step toward solving two environmental problems. The first involves the supply of inexpensive, potable water in Arctic regions, the lack of which is a severe detriment to development. Although water does exist in the Arctic, it is neither available in potable form during many months of the year nor does it occur in sufficient quantity near the point of use. Principally, this lack is caused by the aridness of the Arctic and the shallowness of fresh water sources which, for all practical purposes, do not exist but freeze completely each winter season. The remaining liquid water source is the sea. Arctic problems are then similar to other arid regions where the conversion of sea water to potable water or the transmission of potable water to desired locations is necessary. Cold temperatures generally preclude transmission except over very short distances. Desalination by freezing sea water is a much reported process and has been included among the desalination processes under study worldwide. The advantage of this method in the Arctic is the cold winter-time temperature for freezing and the existence of adequate solar energy in the summer for melting self purified ice. Power requirements are greatly reduced using these natural phenomena. The second aspect of this study concerns the use of artificially grown sea ice as a structural material, thinking primarily in terms of coastal facilities such as docks, jetties, islands, platforms, etc. At sufficiently high latitudes, the summer ablation can be controlled to the point where major structures can be maintained intact during the summer. The unit cost of material is quite low because of low energy requirements. The results of this study show that each of these sea water uses have considerable promise. Desalination to potable level was accomplished. Ice growth rates were obtained which indicate that ice structures of substantial size can be built.This project was accomplished under a matching grant between the Office of Water Resources Research, Department of the Interior, and the University of Alaska, Arctic Environmental Engineering Laboratory. Funds available under this grant purposefully did not anticipate the heavy logistic expense in moving the project and equipment from Fairbanks to Kotzebue, Alaska. Therefore, a major third contributor was the Alaska Air National Guard, Kulis Air Force Base, Alaska. The support offered by the officers and men of the Alaska Air National Guard was excellent and greatly appreciated

Research pressure instrumentation for NASA Space Shuttle main engine, modification no. 6

Research concerning the utilization of silicon piezoresistive strain sensing technology for space shuttle main engine applications is reported. The following specific topics were addressed: (1) transducer design and materials, (2) silicon piezoresistor characterization at cryogenic temperatures, (3) chip mounting characterization, and (4) frequency response optimization