An AI approach for scheduling space-station payloads at Kennedy Space Center

The Payload Processing for Space-Station Operations (PHITS) is a prototype modeling tool capable of addressing many Space Station related concerns. The system's object oriented design approach coupled with a powerful user interface provide the user with capabilities to easily define and model many applications. PHITS differs from many artificial intelligence based systems in that it couples scheduling and goal-directed simulation to ensure that on-orbit requirement dates are satisfied

SSME structural dynamic model development

A mathematical model of the Space Shuttle Main Engine (SSME) as a complete assembly, with detailed emphasis on LOX and High Fuel Turbopumps is developed. The advantages of both complete engine dynamics, and high fidelity modeling are incorporated. Development of this model, some results, and projected applications are discussed

Tracking ocean wave spectrum from SAR images

An end to end algorithm for recovery of ocean wave spectral peaks from Synthetic Aperture Radar (SAR) images is described. Current approaches allow precisions of 1 percent in wave number, and 0.6 deg in direction

Gravitational waves in preheating

We study the evolution of gravitational waves through the preheating era that follows inflation. The oscillating inflaton drives parametric resonant growth of scalar field fluctuations, and although super-Hubble tensor modes are not strongly amplified, they do carry an imprint of preheating. This is clearly seen in the Weyl tensor, which provides a covariant description of gravitational waves.Comment: 8 pages, 8 figures, Revte

The high-lying 6^6Li levels at excitation energy around 21 MeV

The $^3$H+$^3$He cluster structure in $^6$Li was investigated by the $^3$H($\alpha$,$^3$H $^3$He)n kinematically complete experiment at the incident energy $E_\alpha$ = 67.2 MeV. We have observed two resonances at $E_x^*$ = 21.30 and 21.90 MeV which are consistent with the $^3$He($^3$H, $\gamma$)$^6$Li analysis in the Ajzenberg-Selove compilation. Our data are compared with the previous experimental data and the RGM and CSRGM calculations.Comment: 12 pages, 6 figures. Accepted for publication in J. Phys. Soc. Jp

The ISIS synchrotron beam control and study programme

Progress on the beam control and study programme for the 800 MeV High Intensity Proton Synchrotron of the Spallation Neutron Source ISIS, is outlined. Recent hardware upgrades to diagnostics, instrumentation and computing have increased the amount, accuracy and availability of beam information. The measurement methods employed and their planned applications for beam control, optimisation and study are described. Work includes detailed study of longitudinal and transverse dynamics at high and low intensity. Results obtained so far and future plans are summarised. (6 refs)

Topological stability of stored optical vortices

We report an experiment in which an optical vortex is stored in a vapor of Rb atoms. Due to its 2\pi phase twist, this mode, also known as the Laguerre-Gauss mode, is topologically stable and cannot unwind even under conditions of strong diffusion. To supplement our finding, we stored a flat phase Gaussian beam with a dark center. Contrary to the optical vortex, which stays stable for over 100 microseconds, the dark center in the retrieved flat-phased image was filled with light at storage times as small as 10 microseconds. This experiment proves that higher electromagnetic modes can be converted into atomic coherences, and that modes with phase singularities are robust to decoherence effects such as diffusion. This opens the possibility to more elaborate schemes for two dimensional information storage in atomic vapors.Comment: 4 pages, 4 figures v2: minor grammatical corrections v3: problem with references fixed v4: minor clarifications added to the tex

Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties

Ferroelectric and dielectric properties of polydomain (twinned) single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a nonlinear thermodynamic theory, which has been developed recently for epitaxial ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3 (PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit strain-temperature" phase diagrams are calculated and compared with each other. It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar to the diagram of PbTiO3 films. They consist of only four different stability ranges, which correspond to the paraelectric phase, single-domain tetragonal ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of stable polarization states, involving at least one monoclinic polydomain state. Using the developed phase diagrams, the mean out-of-plane polarization of a poled PZT film is calculated as a function of the misfit strain and composition. Theoretical results are compared with the measured remanent polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane dielectric response of PZT films on the misfit strain in the heterostructure is also reported.Comment: 23 pages, 4 figure

(Giant) Vortex - (anti) vortex interaction in bulk superconductors: The Ginzburg-Landau theory

The vortex-vortex interaction potential in bulk superconductors is calculated within the Ginzburg-Landau (GL) theory and is obtained from a numerical solution of a set of two coupled non-linear GL differential equations for the vector potential and the superconducting order parameter, where the merger of vortices into a giant vortex is allowed. Further, the interaction potentials between a vortex and a giant vortex and between a vortex and an antivortex are obtained for both type-I and type-II superconductors. Our numerical results agree asymptotically with the analytical expressions for large inter-vortex separations which are available in the literature. We propose new empirical expressions valid over the full interaction range, which are fitted to our numerical data for different values of the GL parameter