Search NASA⌕ Search

SEARCH · Search NASA

Results for “parallel”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On-board landmark navigation and attitude reference parallel processor system

An approach to autonomous navigation and attitude reference for earth observing spacecraft is described along with the landmark identification technique based on a sequential similarity detection algorithm (SSDA). Laboratory experiments undertaken to determine if better than one pixel accuracy in registration can be achieved consistent with onboard processor timing and capacity constraints are included. The SSDA is implemented using a multi-microprocessor system including synchronization logic and chip library. The data is processed in parallel stages, effectively reducing the time to match the small known image within a larger image as seen by the onboard image system. Shared memory is incorporated in the system to help communicate intermediate results among microprocessors. The functions include finding mean values and summation of absolute differences over the image search area. The hardware is a low power, compact unit suitable to onboard application with the flexibility to provide for different parameters depending upon the environment.

Gilbert, L. E.↗
NASA NTRS1979

Circuit for automatic load sharing in parallel converter modules

A nondissipative circuit for automatic load sharing in parallel converter modules having push-pull power transistors is presented. Each transistor has a separate current-sensing transformer and an impedance-adjusting transformer in series with its collector. The impedance-adjusting transformer functions as a current-controlled variable impedance that is responsive to the difference between the peak collector current of the transistor and the average peak current of all collector currents of power transistors in all modules, thereby to control the collector currents of all power transistors with reference to the average peak collector current.

Nagano, S.↗
NASA NTRS1979

Solar Cell Modules with Parallel Oriented Interconnections

Twenty-four solar modules, half of which were 48 cells in an all-series electrical configuration and half of a six parallel cells by eight series cells were provided. Upon delivery of environmentally tested modules, low power outputs were discovered. These low power modules were determined to have cracked cells which were thought to cause the low output power. The cracks tended to be linear or circular which were caused by different stressing mechanisms. These stressing mechanisms were fully explored. Efforts were undertaken to determine the causes of cell fracture. This resulted in module design and process modifications. The design and process changes were subsequently implemented in production.

Source record↗
NASA NTRS1978

Parallel battery test results

The effects of disabling and enabling the charger on one of two batteries that are operating in a parallel mode are discussed.

Palandati, C.↗
NASA NTRS1978

Development of an optical parallel logic device and a half-adder circuit for digital optical processing

The paper describes the fabrication and operation of an optical parallel logic (OPAL) device which performs Boolean algebraic operations on binary images. Several logic operations on two input binary images were demonstrated using an 8 x 8 device with a CdS photoconductor and a twisted nematic liquid crystal. Two such OPAL devices can be interconnected to form a half-adder circuit which is one of the essential components of a CPU in a digital signal processor.

Athale, R. A.↗
NASA NTRS1978

Parallel compilation - A design and its application to SIMULA 67

A design for a separate compilation facility for the SIMULA 67 programming language is presented. The paper explores the problems with existing separate compilation schemes, and proposes a new scheme that allows top-down, bottom-up, or even parallel development and integration of program modules. An evaluation of the proposal and a discussion of its applicability to other languages are then given.

Schwartz, R. L.↗
NASA NTRS1980

A polymorphic reconfigurable emulator for parallel simulation

Microprocessor and arithmetic support chip technology was applied to the design of a reconfigurable emulator for real time flight simulation. The system developed consists of master control system to perform all man machine interactions and to configure the hardware to emulate a given aircraft, and numerous slave compute modules (SCM) which comprise the parallel computational units. It is shown that all parts of the state equations can be worked on simultaneously but that the algebraic equations cannot (unless they are slowly varying). Attempts to obtain algorithms that will allow parellel updates are reported. The word length and step size to be used in the SCM's is determined and the architecture of the hardware and software is described.

Parrish, E. A., Jr.↗
NASA NTRS1980

Analysis and identification of subsynchronous vibration for a high pressure parallel flow centrifugal compressor

The summary of a complete analytical design evaluation of an existing parallel flow compressor is presented and a field vibration problem that manifested itself as a subsynchronous vibration that tracked at approximately 2/3 of compressor speed is reviewed. The comparison of predicted and observed peak response speeds, frequency spectrum content, and the performance of the bearing-seal systems are presented as the events of the field problem are reviewed. Conclusions and recommendations are made as to the degree of accuracy of the analytical techniques used to evaluate the compressor design.

Kirk, R. G.↗
NASA NTRS1979

The dynamics and stability of radiatively driven gas clouds. I - Plane-parallel slabs

A combination of numerical and analytical techniques has been used to investigate the dynamics and stability of optically thin plane-parallel radiatively driven slabs of gas confined by the thermal gas pressure of a high-temperature low-density medium. Scaling laws allow the individual model 'clouds' to be characterized by a single free parameter, chi, a normalized column density which measures the strength of the acceleration due to radiation pressure relative to that due to thermal gas pressure. It is found that these clouds are stable and coherently accelerated only when chi is small. In this regime a simple slab model is constructed which accurately reproduces the more complex gasdynamic results. The low-chi clouds are marginally able to reach the high velocities seen in the atmospheres of quasi-stellar objects, but only if their motion is subsonic with respect to the external confining medium. This implies either that the medium is extremely hot and tenuous or that it is moving outward with the clouds.

Haas, M. R.↗
NASA NTRS1979

The Massively Parallel Processor and its applications

A long-term experimental development program conducted at Goddard Space Flight Center to implement an ultrahigh-speed data processing system known as the Massively Parallel Processor (MPP) is described. The MPP is a single instruction multiple data stream computer designed to perform logical, integer, and floating point arithmetic operations on variable word length data. Information is presented on system architecture, the system configuration, the array unit architecture, individual processing units, and expected operating rates for several image processing applications (including the processing of Landsat data).

Strong, J. P.↗
NASA NTRS1980

Evidence for parallel electric field particle acceleration in the dayside auroral oval

Electron and ion energy spectra and electron pitch angle distributions are presented for two sounding rocket flights in the dayside auroral zone. At times, effects of dc electric fields parallel to the magnetic field are evident in that: (1) within precipitation features, protons are decelerated by an amount of energy consistent with that which electrons gain and (2) electrons are sometimes aligned to within 3 deg (full width at half maximum) of the magnetic field. A maximum altitude for the accelerating region of several thousand kilometers is deduced from the narrow width of the pitch angle distribution and also from time-of-flight delays between the observation of accelerated electrons and decelerated protons.

Torbert, R. B.↗
NASA NTRS1980

Design of a massively parallel processor

The massively parallel processor (MPP) system is designed to process satellite imagery at high rates. A large number (16,384) of processing elements (PE's) are configured in a square array. For optimum performance on operands of arbitrary length, processing is performed in a bit-serial manner. On 8-bit integer data, addition can occur at 6553 million operations per second (MOPS) and multiplication at 1861 MOPS. On 32-bit floating-point data, addition can occur at 430 MOPS and multiplication at 216 MOPS.

Batcher, K. E.↗
NASA NTRS1980

Base drive for paralleled inverter systems

In a paralleled inverter system, a positive feedback current derived from the total current from all of the modules of the inverter system is applied to the base drive of each of the power transistors of all modules, thereby to provide all modules protection against open or short circuit faults occurring in any of the modules, and force equal current sharing among the modules during turn on of the power transistors.

Nagano, S.↗
NASA NTRS1981

One-dimensional models of quasi-neutral parallel electric fields

Parallel electric fields can exist in the magnetic mirror geometry of auroral field lines if they conform to the quasineutral equilibrium solutions. Results on quasi-neutral equilibria and on double layer discontinuities were reviewed and the effects on such equilibria due to non-unique solutions, potential barriers and field aligned current flows using as inputs monoenergetic isotropic distribution functions were examined.

Stern, D. P.↗
NASA NTRS1981

An approach to real-time simulation using parallel processing

A preliminary simulator design that uses a parallel computer organization to provide accuracy, portability, and low cost is presented. The hardware and software for this prototype simulator are discussed. A detailed discussion of the inter-computer data transfer mechanism is also presented.

Blech, R. A.↗
NASA NTRS1980

Distributed parameter system coupled ARMA expansion identification and adaptive parallel IIR filtering - A unified problem statement

A novel interconnection of distributed parameter system (DPS) identification and adaptive filtering is presented, which culminates in a common statement of coupled autoregressive, moving-average expansion or parallel infinite impulse response configuration adaptive parameterization. The common restricted complexity filter objectives are seen as similar to the reduced-order requirements of the DPS expansion description. The interconnection presents the possibility of an exchange of problem formulations and solution approaches not yet easily addressed in the common finite dimensional lumped-parameter system context. It is concluded that the shared problems raised are nevertheless many and difficult.

Johnson, C. R., Jr.↗
NASA NTRS1981

Transfer of line radiation in differentially expanding atmospheres. VI The plane parallel atmosphere with expanding and contracting regions

The non-LTE radiative transfer problem for a two level atom with complete redistribution over a Doppler profile is solved for a plane parallel slab (overlying a radiating photosphere) that has a velocity field which rises symmetrically from zero at either face to a central maximum. Since the velocity gradient reverses, distant layers of the slab become coupled by radiation that jumps intervening layers. The Feautrier method is used, but an iterative variant is also employed as a check in cases where poorly conditioned matrices are encountered. Approximations are developed to explain some of the principal features. It is found that the source function S tends to have two plateaus with values near 2/3 I sub 0 and 1/3 I sub 0, where I sub 0 is the photospheric continuum incident from below; the larger value lies nearer the photosphere. The upper layers sometimes exhibit a rise in S owing to interconnection by radiation to the base. It is noted that the radiation force is largest at the two faces and the midplane. Some line profiles are found to have unusually steep absorptions at rest frequency because of the low excitation in the uppermost, stationary layers.

Noerdlinger, P. D.↗