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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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The worst case timing margin of a synchronous design implemented with a field-programmable gate array (FPGA) is easy to perform using available FPGA design tools. However, it may be difficult to impossible to verify that worst case timing requirements are met for complex asynchronous logic design.
A method for the design of decentralized asynchronous controllers for spacecraft formations is presented.
This viewgraph presentation gives an overview of the Consultative Committee for Space Data Systems (CCSDS) Asynchronous Message Service (AMS). The topics include: 1) Key Features; 2) A single AMS continuum; 3) The AMS Protocol Suite; 4) A multi-continuum venture; 5) Constraining transmissions; 6) Security; 7) Fault Tolerance; 8) Performance of Reference Implementation; 9) AMS vs Multicast (1); 10) AMS vs Multicast (2); 11) RAMS testing exercise; and 12) Results.
Algorithm for synthesis of asynchronous sequential circuits
Asynchronous pulse-amplitude pulse width model of human operator performance
Asynchronous finite-state models of manual control systems in which human operator behaves as finite-state machine
Asynchronous finite state sequential nonlinear controller synthesis with few flip-flops for dynamic space vehicle systems
Asynchronous pulse amplitude, pulse width human operator model for producing discrete outputs in response to continuously presented Gaussian random inputs
Asynchronous pulse amplitude pulse width model of human operator
Asynchronous finite state sequential nonlinear controller synthesis with few flip-flops for dynamic space vehicle systems
Linear density gradients in isopycnic centrifugation technique for selecting synchronous daughter cells from asynchronous Chlorella cultures
Heuristic algorithm for computation of failures detection tests in asynchronous sequential logic circuits
The method of asynchronously sampling speech is based upon the derivatives of the acoustical speech signal. The following results are apparent from experiments to date: (1) It is possible to represent speech by a string of pulses of uniform amplitude, where the only information contained in the string is the spacing of the pulses in time; (2) the string of pulses may be produced in a simple analog manner; (3) the first derivative of the original speech waveform is the most important for the encoding process; (4) the resulting pulse train can be utilized to control an acoustical signal production system to regenerate the intelligence of the original speech.
Two asynchronous ac/dc/ac systems are modelled that utilize wind power to drive a variable or constant hertz alternator. The first system employs a high power 60-hertz inverter tie to the large backup supply of the power company to either supplement them from wind energy, storage, or from a combination of both at a preset desired current; rectifier and inverter are identical and operate in either mode depending on the silicon control rectifier firing angle. The second system employs the same rectification but from a 60-hertz alternator arrangement; it provides mainly dc output, some sinusoidal 60-hertz from the wind bus and some high harmonic content 60-hertz from an 800-watt inverter.
A class of interactive control systems is derived by generalizing interactive manipulator control systems. The general structural properties of such systems are discussed and an appropriate general software implementation is proposed. This is based on the fact that tasks of interactive control systems can be represented as a network of a finite set of actions which have specific operational characteristics and specific resource requirements, and which are of limited duration. This has enabled the decomposition of the overall control algorithm into a set of subalgorithms, called subcontrollers, which can operate simultaneously and asynchronously. Coordinate transformations of sensor feedback data and actuator set-points have enabled the further simplification of the subcontrollers and have reduced their conflicting resource requirements. The modules of the decomposed control system are implemented as parallel processes with disjoint memory space communicating only by I/O. The synchronization mechanisms for dynamic resource allocation among subcontrollers and other synchronization mechanisms are also discussed in this paper. Such a software organization is suitable for the general form of multiprocessing using computer networks with distributed storage.
A single channel model is shown to lack the capability to predict the visibility of asynchronous compound gratings. A constant Beta was assumed, based on Monte-Carlo simulations, and used to show that an SE of 6.73 (Limb, 1981) lies outside of an acceptable confidence interval. Potential imbalances between two eyes cannot be as large as 1.5 dB, which can only affect one eye, or one region of a retina. An average unbalance of 0.53 dB (SE = 0.12) employed in experiments to measure thresholds was compensated for by estimated threshold reductions. Trial-to-trial variability was included in the single channel model, as were considerations of retinal inhomogeneity. Temporal sensitivity for 2 and 4 c/deg grating patches were measured, and the amplitude response of a single channel at the two spatial frequencies was obtained. Threshold reductions with a Beta of 3.1 are then determined to not be significant enough to warrant adoption of the single channel model predictions.
Solving large, sparse, linear systems of equations is one of the fundamental problems in large scale scientific and engineering computation. A model of a general class of asynchronous, iterative solution methods for linear systems is developed. In the model, the system is solved by creating several cooperating tasks that each compute a portion of the solution vector. This model is then analyzed to determine the expected intertask data transfer and task computational complexity as functions of the number of tasks. Based on the analysis, recommendations for task partitioning are made. These recommendations are a function of the sparseness of the linear system, its structure (i.e., randomly sparse or banded), and dimension.
The de facto method for measuring airplane pilot workload is based upon subjective ratings. While researchers agree that such subjective data should be bolstered by using objective behavioral measures, results to date have been mixed. No clear objective technique has surfaced as the metric of choice. It is believed that this difficulty is in part due to neglect of theoretical work in psychology that predicts some of the difficulties that are inherent in a futile search for 'the one and only' best secondary task to measure workload. An initial study that used both subjective ratings and an asynchronous choice-reaction secondary task was conducted to determine if such a secondary task could indeed meet the methodological constraints imposed by current theories of attention. Two variants of a flight scenario were combined with two levels of the secondary task. Appropriate single-task control conditions were also included. Results give grounds for cautious optimism but indicate that future research should use synchronous secondary tasks where possible.