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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Sparse distributed memory

Sparse distributed memory was proposed be Pentti Kanerva as a realizable architecture that could store large patterns and retrieve them based on partial matches with patterns representing current sensory inputs. This memory exhibits behaviors, both in theory and in experiment, that resemble those previously unapproached by machines - e.g., rapid recognition of faces or odors, discovery of new connections between seemingly unrelated ideas, continuation of a sequence of events when given a cue from the middle, knowing that one doesn't know, or getting stuck with an answer on the tip of one's tongue. These behaviors are now within reach of machines that can be incorporated into the computing systems of robots capable of seeing, talking, and manipulating. Kanerva's theory is a break with the Western rationalistic tradition, allowing a new interpretation of learning and cognition that respects biology and the mysteries of individual human beings.

Denning, Peter J.↗
NASA NTRS1991

Vienna FORTRAN: A FORTRAN language extension for distributed memory multiprocessors

Exploiting the performance potential of distributed memory machines requires a careful distribution of data across the processors. Vienna FORTRAN is a language extension of FORTRAN which provides the user with a wide range of facilities for such mapping of data structures. However, programs in Vienna FORTRAN are written using global data references. Thus, the user has the advantage of a shared memory programming paradigm while explicitly controlling the placement of data. The basic features of Vienna FORTRAN are presented along with a set of examples illustrating the use of these features.

Chapman, Barbara↗
NASA NTRS1990

An empirical investigation of sparse distributed memory using discrete speech recognition

Presented here is a step by step analysis of how the basic Sparse Distributed Memory (SDM) model can be modified to enhance its generalization capabilities for classification tasks. Data is taken from speech generated by a single talker. Experiments are used to investigate the theory of associative memories and the question of generalization from specific instances.

Danforth, Douglas G.↗
NASA NTRS1992

Formal verification of a set of memory management units

This document describes the verification of a set of memory management units (MMU). The verification effort demonstrates the use of hierarchical decomposition and abstract theories. The MMUs can be organized into a complexity hierarchy. Each new level in the hierarchy adds a few significant features or modifications to the lower level MMU. The units described include: (1) a page check translation look-aside module (TLM); (2) a page check TLM with supervisor line; (3) a base bounds MMU; (4) a virtual address translation MMU; and (5) a virtual address translation MMU with memory resident segment table.

Schubert, E. Thomas↗
NASA NTRS1990

The optical implementation of inner product neural associative memory

A liquid-crystal TV spatial light modulator (LCTV SLM) input device and LCTV nonlinear thresholding element are presently used to accomplish an all-optical implementation of an inner-product neural associative memory. This architecture represents an alternative to the vector-matrix multiplication method of the Hopfield model, which is most often employed by neural network associative memory models. LCTV SLM experimental results are presented and discussed.

Liu, Hua-Kuang↗
NASA NTRS1992

High speed, nondestructive readout from thin-film ferroelectric memory

High-speed polarization-direction-dependent photoresponse from ferroelectric lead zirconate titanate (PbZr(0.53)Ti(0.47)O3) thin films sandwiched between conducting electrodes to form a memory capacitor is reported. Laser pulses with a full width at half maximum of around 10 ns at 532-nm wavelength are utilized to readout the photoresponse signal from individual polarized elements. Such readout is repeated over a million times, with no detectable degradation in the photoresponse or the remanent polarization suggesting its potential as a nondestructive readout (NDRO) of nonvolatile polarization state in thin-film ferroelectric memories. In principle both electronic as well as thermal mechanisms could be triggered by such photon exposure of ferroelectric thin films. A comparison of the photoresponse from capacitors with semitransparent and opaque top electrodes suggests that the observed NDRO signal is primarily due to thermally triggered mechanisms.

Thakoor, Sarita↗
NASA NTRS1993

Optoelectronic Inner-Product Neural Associative Memory

Optoelectronic apparatus acts as artificial neural network performing associative recall of binary images. Recall process is iterative one involving optical computation of inner products between binary input vector and one or more reference binary vectors in memory. Inner-product method requires far less memory space than matrix-vector method.

Liu, Hua-Kuang↗
NASA NTRS1993

Shape-Memory-Alloy Release Mechanism

Release-nut mechanism activated by electric current applied to shape-memory alloy. Separates attached objects quickly by remote control. Does not create hazard or cause damage. Shape-memory release-nut mechanism unaffected by moisture or vacuum. Requires sustained current lasting 5 seconds or longer, and insensitive to electromagnetic interference. Mechanism can be reused.

Mckinnis, Darin↗
NASA NTRS1992

Scalable problems and memory bounded speedup

In this paper three models of parallel speedup are studied. They are fixed-size speedup, fixed-time speedup and memory-bounded speedup. The latter two consider the relationship between speedup and problem scalability. Two sets of speedup formulations are derived for these three models. One set considers uneven workload allocation and communication overhead and gives more accurate estimation. Another set considers a simplified case and provides a clear picture on the impact of the sequential portion of an application on the possible performance gain from parallel processing. The simplified fixed-size speedup is Amdahl's law. The simplified fixed-time speedup is Gustafson's scaled speedup. The simplified memory-bounded speedup contains both Amdahl's law and Gustafson's scaled speedup as special cases. This study leads to a better understanding of parallel processing.

Sun, Xian-He↗
NASA NTRS1992

Optical implementation of terminal-attractor-based associative memory

For the purpose of reducing the spurious states in a Hopfield neural net for associative memory, we invoke terminal attractors. In achieving the optical implementation of the terminal-attractor-based associative memory (TABAM) as described in this paper, we first prove the existence of the terminal-attractor model with binary neuron representation. We then present several one- and two-dimensional optical architectures for the TABAM. Finally, as an example, we experimentally demonstrate an inner-product optical neural model using liquid-crystal spatial light modulators with engineering approximations and discuss how to apply the inner-product model to build a two-dimensional parallel processing TABAM.

Liu, Hua-Kuang↗
NASA NTRS1993

The performance of disk arrays in shared-memory database machines

In this paper, we examine how disk arrays and shared memory multiprocessors lead to an effective method for constructing database machines for general-purpose complex query processing. We show that disk arrays can lead to cost-effective storage systems if they are configured from suitably small formfactor disk drives. We introduce the storage system metric data temperature as a way to evaluate how well a disk configuration can sustain its workload, and we show that disk arrays can sustain the same data temperature as a more expensive mirrored-disk configuration. We use the metric to evaluate the performance of disk arrays in XPRS, an operational shared-memory multiprocessor database system being developed at the University of California, Berkeley.

Katz, Randy H.↗
NASA NTRS1994

Half-State Readout In Vertical-Bloch-Line Memory

Potentially narrow margins of chirality-based chopping of magnetic stripes avoided. Half-state readout is experimental method of readout in Vertical-Bloch-Line (VBL) memory. Based on differential deflections of magnetic stripe domains in which data bits stored. To give meaning to explanation of half-state readout, see "Vertical-Bloch-Line Memory" (NPO-18467).

Katti, Romney R.↗
NASA NTRS1994

Improved Reading Gate For Vertical-Bloch-Line Memory

Improved design for reading gate of vertical-Bloch-line magnetic-bubble memory increases reliability of discrimination between binary ones and zeros. Magnetic bubbles that signify binary "1" and "0" produced by applying sufficiently large chopping currents to memory stripes. Bubbles then propagated differentially in bubble sorter. Method of discriminating between ones and zeros more reliable.

Wu, Jiin-Chuan↗
NASA NTRS1993

Unipolar terminal-attractor based neural associative memory with adaptive threshold

A unipolar terminal-attractor based neural associative memory (TABAM) system with adaptive threshold for perfect convergence is presented. By adaptively setting the threshold values for the dynamic iteration for the unipolar binary neuron states with terminal-attractors for the purpose of reducing the spurious states in a Hopfield neural network for associative memory and using the inner product approach, perfect convergence and correct retrieval is achieved. Simulation is completed with a small number of stored states (M) and a small number of neurons (N) but a large M/N ratio. An experiment with optical exclusive-OR logic operation using LCTV SLMs shows the feasibility of optoelectronic implementation of the models. A complete inner-product TABAM is implemented using a PC for calculation of adaptive threshold values to achieve a unipolar TABAM (UIT) in the case where there is no crosstalk, and a crosstalk model (CRIT) in the case where crosstalk corrupts the desired state.

Liu, Hua-Kuang↗
NASA NTRS1993

Static Computer Memory Integrity Testing (SCMIT): An experiment flown on STS-40 as part of GAS payload G-616

This experiment investigated the integrity of static computer memory (floppy disk media) when exposed to the environment of low earth orbit. The experiment attempted to record soft-event upsets (bit-flips) in static computer memory. Typical conditions that exist in low earth orbit that may cause soft-event upsets include: cosmic rays, low level background radiation, charged fields, static charges, and the earth's magnetic field. Over the years several spacecraft have been affected by soft-event upsets (bit-flips), and these events have caused a loss of data or affected spacecraft guidance and control. This paper describes a commercial spin-off that is being developed from the experiment.

Hancock, Thomas↗
NASA NTRS1993

Optoelectronic associative memory

An associative optical memory including an input spatial light modulator (SLM) in the form of an edge enhanced liquid crystal light valve (LCLV) and a pair of memory SLM's in the form of liquid crystal televisions (LCTV's) forms a matrix array of an input image which is cross correlated with a matrix array of stored images. The correlation product is detected and nonlinearly amplified to illuminate a replica of the stored image array to select the stored image correlating with the input image. The LCLV is edge enhanced by reducing the bias frequency and voltage and rotating its orientation. The edge enhancement and nonlinearity of the photodetection improves the orthogonality of the stored image. The illumination of the replicate stored image provides a clean stored image, uncontaminated by the image comparison process.

Chao, Tien-Hsin↗