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At least 325 records · Page 18

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NASA NTRS1989

A design philosophy for multi-layer neural networks with applications to robot control

A system is proposed which receives input information from many sensors that may have diverse scaling, dimension, and data representations. The proposed system tolerates sensory information with faults. The proposed self-adaptive processing technique has great promise in integrating the techniques of artificial intelligence and neural networks in an attempt to build a more intelligent computing environment. The proposed architecture can provide a detailed decision tree based on the input information, information stored in a long-term memory, and the adapted rule-based knowledge. A mathematical model for analysis will be obtained to validate the cited hypotheses. An extensive software program will be developed to simulate a typical example of pattern recognition problem. It is shown that the proposed model displays attention, expectation, spatio-temporal, and predictory behavior which are specific to the human brain. The anticipated results of this research project are: (1) creation of a new dynamic neural network structure, and (2) applications to and comparison with conventional multi-layer neural network structures. The anticipated benefits from this research are vast. The model can be used in a neuro-computer architecture as a building block which can perform complicated, nonlinear, time-varying mapping from a multitude of input excitory classes to an output or decision environment. It can be used for coordinating different sensory inputs and past experience of a dynamic system and actuating signals. The commercial applications of this project can be the creation of a special-purpose neuro-computer hardware which can be used in spatio-temporal pattern recognitions in such areas as air defense systems, e.g., target tracking, and recognition. Potential robotics-related applications are trajectory planning, inverse dynamics computations, hierarchical control, task-oriented control, and collision avoidance.

Vadiee, Nader↗

NASA NTRS1989

The role of the + or - 1 number system in multibit hardware correlators

The use of commercially available 1-bit LSI correlator chips whose main function is the correlation of sequences of plus ones and minus ones (rather than zeros and ones) as building blocks in the design of multibit correlators is investigated. A radix-2 number system in which the bit values are + or - 1 (no zero) is discussed. The development of a simple conversion algorithm to find the + or - 1 representation of a number given in 2's complement is presented. Some of the issues raised by this conversion algorithm are discussed. It is shown that, if the analog signal is available, there is a simple step to take before the analog-to-digital conversion in order to improve the overall precision. The construction of multibit correlators based on the + or - 1 system is compared to alternative approaches.

Zohar, Shalhav↗

NASA NTRS1990

Non-oscillatory central differencing for hyperbolic conservation laws

Many of the recently developed high resolution schemes for hyperbolic conservation laws are based on upwind differencing. The building block for these schemes is the averaging of an appropriate Godunov solver; its time consuming part involves the field-by-field decomposition which is required in order to identify the direction of the wind. Instead, the use of the more robust Lax-Friedrichs (LxF) solver is proposed. The main advantage is simplicity: no Riemann problems are solved and hence field-by-field decompositions are avoided. The main disadvantage is the excessive numerical viscosity typical to the LxF solver. This is compensated for by using high-resolution MUSCL-type interpolants. Numerical experiments show that the quality of results obtained by such convenient central differencing is comparable with those of the upwind schemes.

Nessyahu, Haim↗

NASA NTRS1991

Neural Networks Of VLSI Components

Concept for design of electronic neural network calls for assembly of very-large-scale integrated (VLSI) circuits of few standard types. Each VLSI chip, which contains both analog and digital circuitry, used in modular or "building-block" fashion by interconnecting it in any of variety of ways with other chips. Feedforward neural network in typical situation operates under control of host computer and receives inputs from, and sends outputs to, other equipment.

Eberhardt, Silvio P.↗

NASA NTRS1991

Waveform-Generating Program

GENERATE (Digital Generation of Complex Waveforms) computer program is flexible and reliable software tool for advanced generation of waveforms. User employs standard arithmetic operator (+, -, x, /, and parentheses) to simulate any combination of eight commonly used basic waveforms at desired amplitude and frequency. Creates data file based on user's selections from menu. Provides necessary equations describing eight basic waveforms and enables user to combine them arithmetically. Basic waveforms offered as building blocks; sine, ramp, exponential, logarithmic, step, clipped sine, square, and sawtooth. Also contains routine for plotting output waveform data on terminal with Tektronics (or equivalent) emulator, providing visual confirmation of desirability of waveform. Developed by use of VMS FORTRAN on DEC VAX 3600 computer.

Hopson, Charles B.↗

NASA NTRS1990

Situationally Driven Local Navigation for Mobile Robots

For mobile robots to autonomously accommodate dynamically changing navigation tasks in a goal-directed fashion, they must employ navigation plans. Any such plan must provide for the robot's immediate and continuous need for guidance while remaining highly flexible in order to avoid costly computation each time the robot's perception of the world changes. Due to the world's uncertainties, creation and maintenance of navigation plans cannot involve arbitrarily complex processes, as the robot's perception of the world will be in constant flux, requiring modifications to be made quickly if they are to be of any use. This work introduces navigation templates (NaT's) which are building blocks for the construction and maintenance of rough navigation plans which capture the relationship that objects in the world have to the current navigation task. By encoding only the critical relationship between the objects in the world and the navigation task, a NaT-based navigation plan is highly flexible; allowing new constraints to be quickly incorporated into the plan and existing constraints to be updated or deleted from the plan. To satisfy the robot's need for immediate local guidance, the NaT's forming the current navigation plan are passed to a transformation function. The transformation function analyzes the plan with respect to the robot's current location to quickly determine (a few times a second) the locally preferred direction of travel. This dissertation presents NaT's and the transformation function as well as the needed support systems to demonstrate the usefulness of the technique for controlling the actions of a mobile robot operating in an uncertain world.

Slack, Marc Glenn↗

NASA NTRS1990

An investigation of messy genetic algorithms

Genetic algorithms (GAs) are search procedures based on the mechanics of natural selection and natural genetics. They combine the use of string codings or artificial chromosomes and populations with the selective and juxtapositional power of reproduction and recombination to motivate a surprisingly powerful search heuristic in many problems. Despite their empirical success, there has been a long standing objection to the use of GAs in arbitrarily difficult problems. A new approach was launched. Results to a 30-bit, order-three-deception problem were obtained using a new type of genetic algorithm called a messy genetic algorithm (mGAs). Messy genetic algorithms combine the use of variable-length strings, a two-phase selection scheme, and messy genetic operators to effect a solution to the fixed-coding problem of standard simple GAs. The results of the study of mGAs in problems with nonuniform subfunction scale and size are presented. The mGA approach is summarized, both its operation and the theory of its use. Experiments on problems of varying scale, varying building-block size, and combined varying scale and size are presented.

Goldberg, David E.↗

NASA NTRS1991

Viscous flow simulations of internal store carriage and separation

The internal carriage of stores by the military aircraft is an option for possible reductions in the aerodynamic drag and the observability. Trade studies of this option require considering the aircraft and the stores together. In an effort to develop a computational fluid dynamic (CFD) code for such studies, an investigation was conducted from 1986 to 1990. The study was divided into five building-block steps. First, a full Navier-Stokes code was developed to simulate the unsteady, three-dimensional cavity flow. As the second step, this code was then used to simulate the flows past various missile configurations at angles of attack up to 44 deg. The effects of incidence as well as the turbulence on the leeside flows were computationally captured. The objective of this study has involved the interference flows of rather complex configurations with multiple, joint or disjoint, components of nonsimilar geometries. Hence, a hybrid domain decomposition (HDD) method was developed as the third step of the investigation. The strengths of the multiblock, zonal, and overlapped grids were judiciously combined and employed for the present problem. In the fourth step, the interference flow past a missile near a flat-plate wing was simulated using the HDD method. Finally, the fifth step involved the simulation of the internal store carriage and separation. Four different cases for two different configurations were simulated. The computational results of all five steps were successfully compared with the available wind tunnel test data. The unsteady aerodynamic forces on the separating store were computationally predicted. The CFD code developed for this project is called Viscous Internal Store Carriage Code (VISCC).

Baysal, Oktay↗

NASA NTRS1989

Moessbauer spectroscopy and scanning electron microscopy of the Murchison meteorite

Meteorites provide a wealth of information about the solar system's formation, since they have similar building blocks as the Earth's crust but have been virtually unaltered since their formation. Some stony meteorites contain minerals and silicate inclusions, called chondrules, in the matrix. Utilizing Moessbauer spectroscopy, we identified minerals in the Murchison meteorite, a carbonaceous chondritic meteorite, by the gamma ray resonance lines observed. Absorption patterns of the spectra were found due to the minerals olivine and phyllosilicate. We used a scanning electron microscope to describe the structure of the chondrules in the Murchison meteorite. The chondrules were found to be deformed due to weathering of the meteorite. Diameters varied in size from 0.2 to 0.5 mm. Further enhancement of the microscopic imagery using a digital image processor was used to describe the physical characteristics of the inclusions.

Brown, Christopher L.↗

NASA NTRS1990

Integrated space transportation evolution

The development of an evolutionary approach to a space transportation system to meet the needs of the Space Exploration Initiative and other earth orbital and planetary missions is discussed. Common architectures, a building block approach to space transportation elements, the development of alternative technologies are considered as essential steps to arriving at an integrated space transportation system. These aspects are addressed as they apply to both lunar and Mars technology.

Huffaker, Frederick↗

NASA NTRS1990

Technology needs of the Exploration Initiative

An overview of the U.S. Space Exploration Initiative (SEI) is presented. The two primary objectives of the initiative are a return to the moon to create a permanent lunar base and a human mission to Mars. Even though mission architectural concepts are not yet defined, previous studies indicate that the SEI will require developments in numerous areas, including advanced engines for space transportation, in-space assembly and construction to support permanent basing of exploration systems in space, and advanced surface operations capabilities including satisfactory levels of power and surface roving vehicles, and technologies to safely support human space operations of long duration. The process of mission definition has begun and it is shown that it is possible to identify a family of fundamental functional building blocks from which all SEI mission architectures will be constructed.

Aldrich, Arnold↗

NASA NTRS1990

Exploration Technology Program plans and directions

A summary of the proposed Space Exploration Initiative (SEI) needs that have been identified is presented along with a detailed review of the status of SEI technology planning. Plans are also being formulated to implement an Exploration Technology Program (ETP) that will develop the major technologies required for SEI. The ETP will provide in the near term clear demonstrations of potential exploration technologies, results of research to support SEI architecture decisions, and a foundation of mature technology that is ready to be applied in the first round of SEI missions. A family of functional building blocks has been defined from which both lunar and Mars SEI mission architectures can be constructed.

Aldrich, Arnold↗

NASA NTRS1990

Structural evaluation of composite fuselage structure fabricated using a THERM-X process

An experimental and analytical program has been implemented to evaluate the structural performance of complex composite parts made using THERM-X processing techniques. Preliminary analysis shows 22-percent cost savings for parts made with a THERM-X process over parts made with conventional manufacturing methods. Results of building-block tests from the coupon to the element level, which represent structural details of the curved integrally stiffened panel selected as the full-scale article, are also reported. Comparisons with baseline results and analytical predictions show that THERM-X processing yields parts with stiffness and strength comparable to or slightly better than conventional manufacturing procedures. Compression strength after low-speed impact damage (caused by a drop weight impactor) is also comparable to parts fabricated with conventional methods.

Kassapoglou, Christos↗

NASA NTRS1990

Elementary bipoles of active regions and ephemeral active regions

The general properties of elementary bipoles (EBs), the class of moving magnetic features identified by Frazier (1972) as building blocks of new solar active regions, are described, and variations in their characteristics are illustrated with extensive videomagnetograms obtained at Big Bear Solar Observatory during 1984-1989. Consideration is given to ephemeral active regions consisting of EBs with only one positive and one negative pole, multiple-pole ephemeral regions, reversed-polarity EBs, interactions among EBs and adjacent magnetic features, and the EBs of small and medium active regions. The detection of EBs prior to the appearance of arch filaments confirms the relationship found by Frazier.

Martin, Sara F.↗

NASA NTRS1990

Modelling and control of large space structures

Currently NASA, USA, has under active study and development several large structures for deployment in space. These include for instance beam-like trusses to serve as antenna masts and/or basic building blocks for Space Station construction. An important design consideration is that of assuring adequate stability of the structure in the space environment and in addition in the case of antennas, meeting stringent pointing accuracy requirements. This paper addresses some of the basic design considerations involved such as: (1) modeling flexible multibody dynamics, including sensors and actuators, (2) identifying/monitoring model parameters in orbit, and (3) integrated controls-structures optimization with emphasis on novel concepts and techniques.

Balakrishnan, A. V.↗

NASA NTRS1991

Advanced information processing system for advanced launch system: Avionics architecture synthesis

The Advanced Information Processing System (AIPS) is a fault-tolerant distributed computer system architecture that was developed to meet the real time computational needs of advanced aerospace vehicles. One such vehicle is the Advanced Launch System (ALS) being developed jointly by NASA and the Department of Defense to launch heavy payloads into low earth orbit at one tenth the cost (per pound of payload) of the current launch vehicles. An avionics architecture that utilizes the AIPS hardware and software building blocks was synthesized for ALS. The AIPS for ALS architecture synthesis process starting with the ALS mission requirements and ending with an analysis of the candidate ALS avionics architecture is described.

Lala, Jaynarayan H.↗

NASA NTRS1991

Ground support system methodology and architecture

A synergistic approach to systems test and support is explored. A building block architecture provides transportability of data, procedures, and knowledge. The synergistic approach also lowers cost and risk for life cycle of a program. The determination of design errors at the earliest phase reduces cost of vehicle ownership. Distributed scaleable architecture is based on industry standards maximizing transparency and maintainability. Autonomous control structure provides for distributed and segmented systems. Control of interfaces maximizes compatibility and reuse, reducing long term program cost. Intelligent data management architecture also reduces analysis time and cost (automation).

Schoen, P. D.↗

NASA NTRS1991

NASA Marshall Space Flight Center solar observatory report, January - June 1991

Given here is a summary of the solar vector magnetic field, H-alpha, and white-light observations made at the NASA/Marshall Space Flight Center (MSFC) Solar Observatory during its daily periods of operation. The MSFC Solar Observatory facilities consist of the Solar Magnetograph, an f/13, 30-cm Cassegrain system with a 3.5-cm image of the Sun, housed on top of a 12.8-meter tower; a 12.5-cm Razdow H-alpha telescope housed at the base of the tower; an 18-cm Questar telescope with a full aperture white-light filter mounted at the base of the tower; a 30-cm Cassegrain telescope located in a second metal dome; and a 16.5-cm H-alpha telescope mounted on side of the Solar Vector Magnetograph. A concrete block building provides office space, a darkroom for developing film and performing optical testing, a workshop, video displays, and a computer facility for data reduction.

Smith, James E.↗