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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.

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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The Fringe Reading Facility at the Max-Planck-Institut fuer Stroemungsforschung

A Mach-Zehnder interferometer is used for optical flow measurements in a transonic wind tunnel. Holographic interferograms are reconstructed by illumination with a He-Ne-laser and viewed by a video camera through wide angle optics. This setup was used for investigating industrial double exposure holograms of truck tires in order to develop methods of automatic recognition of certain manufacturing faults. Automatic input is achieved by a transient recorder digitizing the output of a TV camera and transferring the digitized data to a PDP11-34. Interest centered around sequences of interferograms showing the interaction of vortices with a profile and subsequent emission of sound generated by this process. The objective is the extraction of quantitative data which relates to the emission of noise.

Becker, F.↗
NASA NTRS1988

Acquisition Technique For Spread-Spectrum Codes

Ability to lock onto signal increased with minimal equipment. Technique proposed to improve acquisition of spread-spectrum (pseudonoise) coded signal modulated by digital data signal. Divides correlation time into subintervals, integrates over subintervals, passes integrator outputs through square-law detectors, and adds detector outputs over all subintervals to reach decision regarding detection of code. Reduces effect of data-bit transitions at price of non-coherent-combining loss.

Cheng, Unjeng↗
NASA NTRS1988

The Shuttle Imaging Radar B (SIR-B) experiment report

The primary objective of the SIR-B experiment was to acquire multiple-incidence-angle radar imagery of a variety of Earth's surfaces to better understand the effects of imaging geometry on radar backscatter. A complementary objective was to map extensive regions of particular interest. Under these broad objectives, many specific scientific experiments were defined by the 43 SIR-B Science Team members, including studies in the area of geology, vegetation, radar penetration, oceanography, image analysis, and calibration technique development. Approximately 20 percent of the planned digital data were collected, meeting 40 percent of the scientific objectives. This report is an overview of the SIR-B experiment and includes the science investigations, hardware design, mission scenario, mission operations, events of the actual missions, astronaut participation, data products (including auxiliary data), calibrations, and a summary of the actual coverage. Also included are several image samples.

Cimino, Jo Bea↗
NASA NTRS1988

Langley advanced real-time simulation (ARTS) system

A system of high-speed digital data networks was developed and installed to support real-time flight simulation at the NASA Langley Research Center. This system, unlike its predecessor, employs intelligence at each network node and uses distributed 10-V signal conversion equipment rather than centralized 100-V equipment. A network switch, which replaces an elaborate system of patch panels, allows the researcher to construct a customized network from the 25 available simulation sites by invoking a computer control statement. The intent of this paper is to provide a coherent functional description of the system. This development required many significant innovations to enhance performance and functionality such as the real-time clock, the network switch, and improvements to the CAMAC network to increase both distances to sites and data rates. The system has been successfully tested at a usable data rate of 24 M. The fiber optic lines allow distances of approximately 1.5 miles from switch to site. Unlike other local networks, CAMAC does not buffer data in blocks. Therefore, time delays in the network are kept below 10 microsec total. This system underwent months of testing and was put into full service in July 1987.

Crawford, Daniel J.↗
NASA NTRS1988

Finite-dimensional modeling of network-induced delays for real-time control systems

In integrated control systems (ICS), a feedback loop is closed by the common communication channel, which multiplexes digital data from the sensor to the controller and from the controller to the actuator along with the data traffic from other control loops and management functions. Due to asynchronous time-division multiplexing in the network access protocols, time-varying delays are introduced in the control loop, which degrade the system dynamic performance and are a potential source of instability. The delayed control system is represented by a finite-dimensional, time-varying, discrete-time model which is less complex than the existing continuous-time models for time-varying delays; this approach allows for simpler schemes for analysis and simulation of the ICS.

Ray, Asok↗
NASA NTRS1989

Eight-Channel Spectrometer

Inexpensive, compact, battery-powered, eight-channel spectrometer produces 8-bit digital data in each channel and records data for subsequent reconstruction in analog form or for transmission to computer for analysis. Unit designed for use in analysis of rocket-exhaust plumes. Modified versions of spectrometer used to analyze combustion in boilers or gas turbines.

Huston, Steven W.↗
NASA NTRS1986

Further development of the dynamic gas temperature measurement system. Volume 2: Computer program user's manual

The Dynamic Gas Temperature Measurement System compensation software accepts digitized data from two different diameter thermocouples and computes a compensated frequency response spectrum for one of the thermocouples. Detailed discussions of the physical system, analytical model, and computer software are presented in this volume and in Volume 1 of this report under Task 3. Computer program software restrictions and test cases are also presented. Compensated and uncompensated data may be presented in either the time or frequency domain. Time domain data are presented as instantaneous temperature vs time. Frequency domain data may be presented in several forms such as power spectral density vs frequency.

Stocks, Dana R.↗
NASA NTRS1988

The California Cooperative Remote Sensing Project

The USDA, the California Department of Water Resources (CDWR), the Remote Sensing Research Program of the University of California (UCB) and NASA have completed a 4-yr cooperative project on the use of remote sensing in monitoring California agriculture. This report is a summary of the project and the final report of NASA's contribution to it. The cooperators developed procedures that combined the use of LANDSAT Multispectral Scanner imagery and digital data with good ground survey data for area estimation and mapping of the major crops in California. An inventory of the Central Valley was conducted as an operational test of the procedures. The satellite and survey data were acquired by USDA and UCB and processed by CDWR and NASA. The inventory was completed on schedule, thus demonstrating the plausibility of the approach, although further development of the data processing system is necessary before it can be used efficiently in an operational environment.

Hlavka, Christine A.↗
NASA NTRS1987

A review of computer aided interpretation technology for the evaluation of radiographs of aluminum welds

Industrial radiography is a well established, reliable means of providing nondestructive structural integrity information. The majority of industrial radiographs are interpreted by trained human eyes using transmitted light and various visual aids. Hundreds of miles of radiographic information are evaluated, documented and archived annually. In many instances, there are serious considerations in terms of interpreter fatigue, subjectivity and limited archival space. Quite often it is difficult to quickly retrieve radiographic information for further analysis or investigation. Methods of improving the quality and efficiency of the radiographic process are being explored, developed and incorporated whenever feasible. High resolution cameras, digital image processing, and mass digital data storage offer interesting possibilities for improving the industrial radiographic process. A review is presented of computer aided radiographic interpretation technology in terms of how it could be used to enhance the radiographic interpretation process in evaluating radiographs of aluminum welds.

Lloyd, J. F., Sr.↗
NASA NTRS1987

Classification of cloud fields based on textural characteristics

The present study reexamines the applicability of texture-based features for automatic cloud classification using very high spatial resolution (57 m) Landsat multispectral scanner digital data. It is concluded that cloud classification can be accomplished using only a single visible channel.

Welch, R. M.↗
NASA NTRS1989

On the self-noise in QASK decision-feedback carrier tracking loops

Quadrature amplitude-shift keying (QASK) is often used for transmitting two digital data streams in bandwidth-constrained communication systems. Previous analyses of the tracking performance of a decision-feedback carrier tracking loop, which can be used to provide a carrier reference for a QASK signal set, have neglected the effects of the self-noise in the derivation of the loop resonance. The authors incorporate the effects of the self-noise into the analysis of decision-feedback carrier tracking loops. It is demonstrated that failure to account for the self-noise will only result in a conservative assessment of the system's performance, contrary to what might be expected. All results obtained are in closed form and can easily be evaluated numerically for performance prediction purposes.

Hinedi, Sami↗
NASA NTRS1990

Optimal Allocation Of Tasks In Hypercube Computers

Uniform tasks distributed uniformly or else assigned to one processor. Investigation in theory of scheduling yielded optimal scheme for allocation of tasks among digital data processors in hypercube ensemble. Applies to tasks that require equal time to execute, performed in any order, and between any two of which equal amounts of communication required. Reduces overall processing time for given set of computational tasks.

Salama, Moktar A.↗
NASA NTRS1990

Fast, Capacious Disk Memory Device

Device for recording digital data on, and playing back data from, memory disks has high recording or playback rate and utilizes available recording area more fully. Two disks, each with own reading/writing head, used to record data at same time. Head on disk A operates on one of tracks numbered from outside in; head on disk B operates on track of same number in sequence from inside out. Underlying concept of device applicable to magnetic or optical disks.

Muller, Ronald M.↗
NASA NTRS1990

Monolithic Optoelectronic Integrated Circuit

Monolithic optoelectronic integrated circuit (OEIC) receives single digitally modulated input light signal via optical fiber and converts it into 16-channel electrical output signal. Potentially useful in any system in which digital data must be transmitted serially at high rates, then decoded into and used in parallel format at destination. Applications include transmission and decoding of control signals to phase shifters in phased-array antennas and also communication of data between computers and peripheral equipment in local-area networks.

Bhasin, Kul B.↗
NASA NTRS1990

Performance measurements for a laboratory-simulated 30/20 GHz communication satellite transponder

NASA has developed a digital satellite communications system simulator and test bed facility, known as the Systems Integration, Test and Evaluation (SITE) Project. The purpose of the facility is to evaluate satellite system components, develop and verify system concepts, and perform satellite system experiments. A recently completed set of experiments measured the performance of the 30/20 GHz satellite transponder portion of the system in terms of RF parameters and high rate digital data transmission. The results of these tests indicate the quality of data transmission which can be obtained under various transponder conditions, as well as the relative effects of degraded RF performance on the bit-error rate (BER) of transmitted data.

Kerczewski, Robert J.↗
NASA NTRS1990

A method of classification for multisource data in remote sensing based on interval-valued probabilities

An axiomatic approach to intervalued (IV) probabilities is presented, where the IV probability is defined by a pair of set-theoretic functions which satisfy some pre-specified axioms. On the basis of this approach representation of statistical evidence and combination of multiple bodies of evidence are emphasized. Although IV probabilities provide an innovative means for the representation and combination of evidential information, they make the decision process rather complicated. It entails more intelligent strategies for making decisions. The development of decision rules over IV probabilities is discussed from the viewpoint of statistical pattern recognition. The proposed method, so called evidential reasoning method, is applied to the ground-cover classification of a multisource data set consisting of Multispectral Scanner (MSS) data, Synthetic Aperture Radar (SAR) data, and digital terrain data such as elevation, slope, and aspect. By treating the data sources separately, the method is able to capture both parametric and nonparametric information and to combine them. Then the method is applied to two separate cases of classifying multiband data obtained by a single sensor. In each case a set of multiple sources is obtained by dividing the dimensionally huge data into smaller and more manageable pieces based on the global statistical correlation information. By a divide-and-combine process, the method is able to utilize more features than the conventional maximum likelihood method.

Kim, Hakil↗
NASA NTRS1990

Performance measurements for a laboratory-simulated 30/20 GHz communication satellite transponder

NASA has developed a digital satellite communications system simulator and test bed facility, known as the SITE (System Integratrion, Test and Evaluation) Project. The purpose of the facility is to evaluate satellite system components, develop and verify system concepts, and perform satellite system experiments. A recently completed set of experiments measured the performance of the 30/20 GHz satellite transponder portion of the system in terms of RF parameters and high rate digital data transmission. The results of these tests indicate the quality of data transmission which can be obtained under various transponder operating conditions, as well as the relative effects of degraded RF performance on the bit-error rate (BER) of transmitted data.

Kerczewski, Robert J.↗
NASA NTRS1989

A tone-aided dual vestigial sideband system for digital communications on fading channels

A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.

Hladik, Stephen M.↗