Caging dynamics in a granular fluid

We report an experimental investigation of the caging motion in a uniformly heated granular fluid, for a wide range of filling fractions, $\phi$. At low $\phi$ the classic diffusive behavior of a fluid is observed. However, as $\phi$ is increased, temporary cages develop and particles become increasingly trapped by their neighbors. We statistically analyze particle trajectories and observe a number of robust features typically associated with dense molecular liquids and colloids. Even though our monodisperse and quasi-2D system is known to not exhibit a glass transition, we still observe many of the precursors usually associated with glassy dynamics. We speculate that this is due to a process of structural arrest provided, in our case, by the presence of crystallization.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Design study of TDRS antenna gimbal system for LANDSAT-D

The conceptual design studies of a two axis antenna drive assembly for the TDRSS link communications subsystem for LANDSAT D are presented. The recommended antenna drive assembly is a simple and reliable design substantially similar to the antenna and solar array drives developed and space qualified for programs such as DSCS 2 and FltSatCom. The gimbal design tradeoff is presented, along with drive electronics

Twin CWG systems Final report

Construction, operation, and maintenance of twin control moment gyroscope system for space vehicle motion simulato

Design of the Annular Suspension and Pointing System (ASPS) (including design addendum)

The Annular Suspension and Pointing System is an experiment pointing mount designed for extremely precise 3 axis orientation of shuttle experiments. It utilizes actively controlled magnetic bearing to provide noncontacting vernier pointing and translational isolation of the experiment. The design of the system is presented and analyzed

On the Generalized Kramers Problem with Exponential Memory Friction

The time-dependent transmission coefficient for the generalized Kramers problem with exponential memory friction has recently been calculated by Kohen and Tannor [D. Kohen and D. J. Tannor, J. Chem. Phys. Vol. 103, 6013 (1995)] using a procedure based on the method of reactive flux and the phase space distribution function. Their analysis is restricted to the high friction regime or diffusion-limited regime. We recently developed a complementary theory for the low-friction energy-diffusion-limited regime in the Markovian limit [Sancho et al., cond-mat/9806001, to appear in J. Chem. Phys.]. Here we generalize our method to the case of an exponential dissipative memory kernel. We test our results, as well as those of Kohen and Tannor, against numerical simulations

Project Technical Report MSC/TRW Task KM-205 - SLP OWS Control System Digital Simulation Requirements

Digital simulation of AAP orbital workshop pointing control system and thrust attitude control system

Applications technology satellite gravity gradient stabilization system Quarterly progress report, 1 Nov. 1966 - 31 Jan. 1967

Gravity gradient stabilization system for applications technology satellit

Fluidisation and plastic activity in a model soft-glassy material flowing in micro-channels with rough walls

By means of mesoscopic numerical simulations of a model soft-glassy material, we investigate the role of boundary roughness on the flow behaviour of the material, probing the bulk/wall and global/local rheologies. We show that the roughness reduces the wall slip induced by wettability properties and acts as a source of fluidisation for the material. A direct inspection of the plastic events suggests that their rate of occurrence grows with the fluidity field, reconciling our simulations with kinetic elasto-plastic descriptions of jammed materials. Notwithstanding, we observe qualitative and quantitative differences in the scaling, depending on the distance from the rough wall and on the imposed shear. The impact of roughness on the orientational statistics is also studied

Performance interface document for users of Tracking and Data Relay Satellite System (TDRSS) electromechanically steered antenna systems (EMSAS)

Satellites that use the NASA Tracking and Data Relay Satellite System (TDRSS) require antennas that are crucial for performing and achieving reliable TDRSS link performance at the desired data rate. Technical guidelines are presented to assist the prospective TDRSS medium-and high-data rate user in selecting and procuring a viable, steerable high-gain antenna system. Topics addressed include the antenna gain/transmitter power/data rate relationship; Earth power flux-density limitations; electromechanical requirements dictated by the small beam widths, desired angular coverage, and minimal torque disturbance to the spacecraft; weight and moment considerations; mechanical, electrical and thermal interfaces; design lifetime failure modes; and handling and storage. Proven designs are cited and space-qualified assemblies and components are identified

Detailed Calculation of Test-Mass Charging in the LISA Mission

The electrostatic charging of the LISA test masses due to exposure of the spacecraft to energetic particles in the space environment has implications in the design and operation of the gravitational inertial sensors and can affect the quality of the science data. Robust predictions of charging rates and associated stochastic fluctuations are therefore required for the exposure scenarios expected throughout the mission. We report on detailed charging simulations with the Geant4 toolkit, using comprehensive geometry and physics models, for Galactic cosmic-ray protons and helium nuclei. These predict positive charging rates of 50 +e/s (elementary charges per second) for solar minimum conditions, decreasing by half at solar maximum, and current fluctuations of up to 30 +e/s/Hz^{1/2}. Charging from sporadic solar events involving energetic protons was also investigated. Using an event-size distribution model, we conclude that their impact on the LISA science data is manageable. Several physical processes hitherto unexplored as potential charging mechanisms have also been assessed. Significantly, the kinetic emission of very low-energy secondary electrons due to bombardment of the inertial sensors by primary cosmic rays and their secondaries can produce charging currents comparable with the Monte Carlo rates.Comment: 31 pages, 18 figures, 4 tables. to be published in Astroparticle Physics. Changed due to error found in normalisation of the simulation result