4,941 research outputs found
Policy and Practice Brief: State and Federal Vocational Rehabilitation Programs
This brief provides an introduction to the state and federal vocational rehabilitation system outlined in the Rehabilitation Act of 1973. It provides a review of how the vocational rehabilitation system is integrated within the broader Workforce Investment Act along with a break down for eligibility and available services. Discussed is financial need criteria, statutory requirements for maximization of employment, comparable services requirements and individual rights and appeals
Interim Service ISDN Satellite (ISIS) network model for advanced satellite designs and experiments
The Interim Service Integrated Services Digital Network (ISDN) Satellite (ISIS) Network Model for Advanced Satellite Designs and Experiments describes a model suitable for discrete event simulations. A top-down model design uses the Advanced Communications Technology Satellite (ACTS) as its basis. The ISDN modeling abstractions are added to permit the determination and performance for the NASA Satellite Communications Research (SCAR) Program
Effect of damper on overall and blade-element performance of a compressor rotor having a tip speed of 1151 feet per second and an aspect ratio of 3.6
The overall and blade-element performance of two configurations of a moderately high aspect ratio transonic compressor rotor are presented. The subject rotor has conventional blade dampers. The performance is compared with a rotor utilizing dual wire friction dampers. At design speed the subject achieved a pressure ratio of 1.52 and efficiency of 0.89 at a near design weight flow of 72.1 pounds per second. The rotor with wire dampers gave consistently higher pressure ratios at each speed, but efficiencies for the two rotors were about the same. Stall margin for the subject rotor was 20.4 percent, but for the wire damped rotor only 4.0 percent
Traffic model for advanced satellite designs and experiments for ISDN services
The data base structure and fields for categorizing and storing Integrated Services Digital Network (ISDN) user characteristics is outlined. This traffic model data base will be used to exercise models of the ISDN Advanced Communication Satellite to determine design parameters and performance for the NASA Satellite Communications Applications Research (SCAR) Program
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
Performance of a 1380-foot-per-second-tip-speed axial-flow compressor rotor with a blade tip solidity of 1.3
Aerodynamic design parameters are presented along the overall and blade element performance, of an axial flow compressor rotor designed to study the effects of blade solidity on efficiency and stall margin. At design speed the peak efficiency was 0.844 and occurred at an equivalent weight flow of 63.5 lb/sec with a total pressure ratio of 1.801. Design efficiency, pressure ratio, and weight flow 0.814, 1.65, and 65.3(41.1 lb/sec/sq ft of annulus area), respectively. Stall margin for design speed was 6.4 percent based on the weight flow and pressure ratio values at peak efficiency and just prior to stall
Hybrid-parallel sparse matrix-vector multiplication with explicit communication overlap on current multicore-based systems
We evaluate optimized parallel sparse matrix-vector operations for several
representative application areas on widespread multicore-based cluster
configurations. First the single-socket baseline performance is analyzed and
modeled with respect to basic architectural properties of standard multicore
chips. Beyond the single node, the performance of parallel sparse matrix-vector
operations is often limited by communication overhead. Starting from the
observation that nonblocking MPI is not able to hide communication cost using
standard MPI implementations, we demonstrate that explicit overlap of
communication and computation can be achieved by using a dedicated
communication thread, which may run on a virtual core. Moreover we identify
performance benefits of hybrid MPI/OpenMP programming due to improved load
balancing even without explicit communication overlap. We compare performance
results for pure MPI, the widely used "vector-like" hybrid programming
strategies, and explicit overlap on a modern multicore-based cluster and a Cray
XE6 system.Comment: 16 pages, 10 figure
Radial propagation of geodesic acoustic modes
The GAM group velocity is estimated from the ratio of the radial free energy
flux to the total free energy applying gyrokinetic and two-fluid theory. This
method is much more robust than approaches that calculate the group velocity
directly and can be generalized to include additional physics, e.g. magnetic
geometry. The results are verified with the gyrokinetic code GYRO [J. Candy and
R. E. Waltz, J. Comp. Phys. 186, pp. 545-581 (2003)], the two-fluid code NLET
[K. Hallatschek and A. Zeiler, Physics of Plasmas 7, pp. 2554-2564 (2000)], and
analytical calculations. GAM propagation must be kept in mind when discussing
the windows of GAM activity observed experimentally and the match between
linear theory and experimental GAM frequencies.Comment: 9 pages, 6 figures. This article has been published in Physics of
Plasmas 5, 072503 (2009). It can be found at
http://link.aip.org/link/?PHPAEN/16/072503/
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