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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1966

Nixie tube display unit employs time-shared logic

Cathodes of display tubes wired in parallel achieve input switching simplification of a Nixie tube display system. Use of time- shared logic energizes the appropriate anode and inhibits all unnecessary cathodes.

Gray, J.↗
NASA NTRS1987

Time-sharing visual and auditory tracking tasks

An experiment is described which examined the benefits of distributing the input demands of two tracking tasks as a function of task integrality. Visual and auditory compensatory tracking tasks were utilized. Results indicate that presenting the two tracking signals in two input modalities did not improve time-sharing efficiency. This was attributed to the difficulty insensitivity phenomenon.

Tsang, Pamela S.↗
NASA NTRS1989

Visual scanning with or without spatial uncertainty and time-sharing performance

An experiment is reported that examines the pattern of task interference between visual scanning as a sequential and selective attention process and other concurrent spatial or verbal processing tasks. A distinction is proposed between visual scanning with or without spatial uncertainty regarding the possible differential effects of these two types of scanning on interference with other concurrent processes. The experiment required the subject to perform a simulated primary tracking task, which was time-shared with a secondary spatial or verbal decision task. The relevant information that was needed to perform the decision tasks were displayed with or without spatial uncertainty. The experiment employed a 2 x 2 x 2 design with types of scanning (with or without spatial uncertainty), expected scanning distance (low/high), and codes of concurrent processing (spatial/verbal) as the three experimental factors. The results provide strong evidence that visual scanning as a spatial exploratory activity produces greater task interference with concurrent spatial tasks than with concurrent verbal tasks. Furthermore, spatial uncertainty in visual scanning is identified to be the crucial factor in producing this differential effect.

Liu, Yili↗
NASA NTRS1993

Distributed simulation using a real-time shared memory network

The Advanced Control Technology Branch of the NASA Lewis Research Center performs research in the area of advanced digital controls for aeronautic and space propulsion systems. This work requires the real-time implementation of both control software and complex dynamical models of the propulsion system. We are implementing these systems in a distributed, multi-vendor computer environment. Therefore, a need exists for real-time communication and synchronization between the distributed multi-vendor computers. A shared memory network is a potential solution which offers several advantages over other real-time communication approaches. A candidate shared memory network was tested for basic performance. The shared memory network was then used to implement a distributed simulation of a ramjet engine. The accuracy and execution time of the distributed simulation was measured and compared to the performance of the non-partitioned simulation. The ease of partitioning the simulation, the minimal time required to develop for communication between the processors and the resulting execution time all indicate that the shared memory network is a real-time communication technique worthy of serious consideration.

Simon, Donald L.↗
NASA NTRS1988

Performance modeling and measurement of real-time multiprocessors with time-shared buses

A closed queueing network model is constructed to address workload effects on computer performance for a highly reliable unibus multiprocessor used in real-time control. The queueing model consists of multiserver nodes and a nonpreemptive priority queue. Use of this model requires partitioning the workload into task classes. The time average steady-state solution of the queueing model directly produces useful results that are necessary in performance evaluation. The model is experimentally justified with the Fault-Tolerant Multiprocessor (FTMP) located at the NASA AIRLAB. Extensive experiments are performed on FTMP with a synthetic workload generator (SWG) to directly measure performance parameters, such as processor idle time, system bus contention, and task processing times. These measurements determine values for parameters in the queueing model. Experimental and analytic results are then compared.

Woodbury, Michael H.↗
NASA NTRS1983

The effects of cuing in time-shared tasks

The results of two divided-attention experiments involving the editing of route-way-point displays on an avionics computer unit are reported. Two side tasks were required of the subjects, and either no cue, verbal cues appearing on the CRT, or symbolic cues (lights on the keyboard adjacent to keys to be used) were given to facilitate the primary editing task. Forty female and 30 male undergraduates were trained in the separate and combined tasks and divided randomly into groups of 25 for the cuing tests. A second test with three 10-subject groups was conducted at least one month later to investigate the efficacy of cuing for infrequently used procedures. It is found that only symbolic cuing significantly improved primary-task performance, increasing editing accuracy in the repetitive tests and reducing editing time in the delayed tests. Verbal cuing, probably because it requires additional cognitive effort, has no significant beneficial effect. These results are considered important for designing instruments for work environments requiring the performance of concurrent tasks, and as aircraft cockpits.

Chechile, R. A.↗
NASA NTRS1975

Building a computer-aided design capability using a standard time share operating system

The paper describes how an integrated system of engineering computer programs can be built using a standard commercially available operating system. The discussion opens with an outline of the auxiliary functions that an operating system can perform for a team of engineers involved in a large and complex task. An example of a specific integrated system is provided to explain how the standard operating system features can be used to organize the programs into a simple and inexpensive but effective system. Applications to an aircraft structural design study are discussed to illustrate the use of an integrated system as a flexible and efficient engineering tool. The discussion concludes with an engineer's assessment of an operating system's capabilities and desirable improvements.

Sobieszczanski, J.↗
NASA NTRS1981

Time-sharing switch for vacuum brazing

Switching unit changes power and cooling-water connections between two vacuum-brazing machines. It allows both units to be powered by single radio-frequency (RF) generator. One machine can be used for brazing while bell jar of other is being evacuated (20 minute process) in preparation for brazing or is being cooled after brazing (10 minute process).

Stein, J. A.↗
NASA NTRS1986

Response modalities and time-sharing performance

An experiment performed to investigate the role of resource competition and asymmetric transfer in dual-task performance is described. It is shown that there is an advantage to mixed manual/speech response modality configurations that cannot be accounted for by asymmetric transfer. The present results support the multiple resources approach to the application of speech technology. Once speech recognition achieves an acceptable level of operational reliability, speech controls can be used to reduce resource competition and improve performance in multitask environments.

Vidulich, Michael A.↗
NASA NTRS1988

Speech responses and dual-task performance - Better time-sharing or asymmetric transfer?

The value of speech controls in a dual-task experiment that also evaluated asymmetric transfer effects is considered. There was no evidence of asymmetric transfer in spite of significant effects supporting the advantage of mixing manual and speech responses. The data suggest that speech controls can be used to enhance performance in operational multiple-task environments.

Vidulich, Michael A.↗
NASA NTRS1976

Timesharing without synchronization

The capacity region of a multiple-access channel has recently been identified as the convex hull (barred K) of a certain set (K) of points in the first quadrant of the (R1,R2) plane. For a pair of rates in K, a more or less standard random-coding argument can be used to show the existence of a good pair of codes. But for points in barred K-K, it is apparently necessary for the two senders to use some form of time sharing to achieve the desired rates. However, in order to share time, at least one of the senders must have knowledge of the other's phase; and in many practical situations this knowledge does not exist. This paper investigates the problems which arise in coding for multiple-access channels when the senders cannot synchronize with each other.

Mceliece, R. J.↗
NASA NTRS1977

Computer assisted thermal-vacuum testing

In testing complex systems and components under dynamic thermal-vacuum environments, it is desirable to optimize the environment control sequence in order to reduce test duration and cost. This paper describes an approach where a computer is utilized as part of the test control operation. Real time test data is made available to the computer through time-sharing terminals at appropriate time intervals. A mathematical model of the test article and environmental control equipment is then operated on using the real time data to yield current thermal status, temperature analysis, trend prediction and recommended thermal control setting changes to arrive at the required thermal condition. The data acquisition interface and the time-sharing hook-up to an IBM-370 computer is described along with a typical control program and data demonstrating its use.

Petrie, W.↗