Internal and External Fluctuation Activated Non-equilibrium Reactive Rate Process

The activated rate process for non-equilibrium open systems is studied taking into account both internal and external noise fluctuations in a unified way. The probability of a particle diffusing passing over the saddle point and the rate constant together with the effective transmission coefficient are calculated via the method of reactive flux. We find that the complexity of internal noise is always harmful to the diffusion of particles. However the external modulation may be beneficial to the rate process.Comment: 10 pages, 1 figure (containing 2 subgraphs). arXiv admin note: text overlap with arXiv:cond-mat/9911028 by other author

A Simulation Analysis of the Relationship between Retail Sales and Shopping Center Rents

This article examines the variation in rents per square foot among regional shopping centers in the United States in response to variation in retail sales per square foot. The analysis breaks new ground by treating base and percentage rents as endogenous functions of retail sales. The analysis further distinguishes between de facto, if not de jure, fixed and percentage leases, and between new versus existing leases. Simulation results suggest that shopping center rents can easily increase in the short-run as retail sales decrease, or they can easily decrease as retail sales increase. In addition, the results suggest that shopping center rents per square foot generally react more aggressively to an increase in retail sales per square foot over time than to a decrease in retail sales per square foot, all else equal.

An order (n) algorithm for the dynamics simulation of robotic systems

The formulation of an Order (n) algorithm for DISCOS (Dynamics Interaction Simulation of Controls and Structures), which is an industry-standard software package for simulation and analysis of flexible multibody systems is presented. For systems involving many bodies, the new Order (n) version of DISCOS is much faster than the current version. Results of the experimental validation of the dynamics software are also presented. The experiment is carried out on a seven-joint robot arm at NASA's Goddard Space Flight Center. The algorithm used in the current version of DISCOS requires the inverse of a matrix whose dimension is equal to the number of constraints in the system. Generally, the number of constraints in a system is roughly proportional to the number of bodies in the system, and matrix inversion requires O(p exp 3) operations, where p is the dimension of the matrix. The current version of DISCOS is therefore considered an Order (n exp 3) algorithm. In contrast, the Order (n) algorithm requires inversion of matrices which are small, and the number of matrices to be inverted increases only linearly with the number of bodies. The newly-developed Order (n) DISCOS is currently capable of handling chain and tree topologies as well as multiple closed loops. Continuing development will extend the capability of the software to deal with typical robotics applications such as put-and-place, multi-arm hand-off and surface sliding

Effects of motion on jet exhaust noise from aircraft

The various problems involved in the evaluation of the jet noise field prevailing between an observer on the ground and an aircraft in flight in a typical takeoff or landing approach pattern were studied. Areas examined include: (1) literature survey and preliminary investigation, (2) propagation effects, (3) source alteration effects, and (4) investigation of verification techniques. Sixteen problem areas were identified and studied. Six follow-up programs were recommended for further work. The results and the proposed follow-on programs provide a practical general technique for predicting flyover jet noise for conventional jet nozzles

Control and structural optimization for maneuvering large spacecraft

Presented here are the results of an advanced control design as well as a discussion of the requirements for automating both the structures and control design efforts for maneuvering a large spacecraft. The advanced control application addresses a general three dimensional slewing problem, and is applied to a large geostationary platform. The platform consists of two flexible antennas attached to the ends of a flexible truss. The control strategy involves an open-loop rigid body control profile which is derived from a nonlinear optimal control problem and provides the main control effort. A perturbation feedback control reduces the response due to the flexibility of the structure. Results are shown which demonstrate the usefulness of the approach. Software issues are considered for developing an integrated structures and control design environment

Breakdown of the lattice polaron picture in La0.7Ca0.3MnO3 single crystals

When heated through the magnetic transition at Tc, La0.7Ca0.3MnO3 changes from a band metal to a polaronic insulator. The Hall constant R_H, through its activated behavior and sign anomaly, provides key evidence for polaronic behavior. We use R_H and the Hall mobility to demonstrate the breakdown of the polaron phase. Above 1.4Tc, the polaron picture holds in detail, while below, the activation energies of both R_H and the mobility deviate strongly from their polaronic values. These changes reflect the presence of metallic, ferromagnetic fluctuations, in the volume of which the Hall effect develops additional contributions tied to quantal phases.Comment: 11 pages, 3 figures, final version to appear in Phys. Rev. B Rapi