161 research outputs found

    An Information-Theoretic Framework for Consistency Maintenance in Distributed Interactive Applications

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    Distributed Interactive Applications (DIAs) enable geographically dispersed users to interact with each other in a virtual environment. A key factor to the success of a DIA is the maintenance of a consistent view of the shared virtual world for all the participants. However, maintaining consistent states in DIAs is difficult under real networks. State changes communicated by messages over such networks suffer latency leading to inconsistency across the application. Predictive Contract Mechanisms (PCMs) combat this problem through reducing the number of messages transmitted in return for perceptually tolerable inconsistency. This thesis examines the operation of PCMs using concepts and methods derived from information theory. This information theory perspective results in a novel information model of PCMs that quantifies and analyzes the efficiency of such methods in communicating the reduced state information, and a new adaptive multiple-model-based framework for improving consistency in DIAs. The first part of this thesis introduces information measurements of user behavior in DIAs and formalizes the information model for PCM operation. In presenting the information model, the statistical dependence in the entity state, which makes using extrapolation models to predict future user behavior possible, is evaluated. The efficiency of a PCM to exploit such predictability to reduce the amount of network resources required to maintain consistency is also investigated. It is demonstrated that from the information theory perspective, PCMs can be interpreted as a form of information reduction and compression. The second part of this thesis proposes an Information-Based Dynamic Extrapolation Model for dynamically selecting between extrapolation algorithms based on information evaluation and inferred network conditions. This model adapts PCM configurations to both user behavior and network conditions, and makes the most information-efficient use of the available network resources. In doing so, it improves PCM performance and consistency in DIAs

    Satellite Networks: Architectures, Applications, and Technologies

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    Since global satellite networks are moving to the forefront in enhancing the national and global information infrastructures due to communication satellites' unique networking characteristics, a workshop was organized to assess the progress made to date and chart the future. This workshop provided the forum to assess the current state-of-the-art, identify key issues, and highlight the emerging trends in the next-generation architectures, data protocol development, communication interoperability, and applications. Presentations on overview, state-of-the-art in research, development, deployment and applications and future trends on satellite networks are assembled

    Eighth International Workshop on Laser Ranging Instrumentation

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    The Eighth International Workshop for Laser Ranging Instrumentation was held in Annapolis, Maryland in May 1992, and was sponsored by the NASA Goddard Space Flight Center in Greenbelt, Maryland. The workshop is held once every 2 to 3 years under differing institutional sponsorship and provides a forum for participants to exchange information on the latest developments in satellite and lunar laser ranging hardware, software, science applications, and data analysis techniques. The satellite laser ranging (SLR) technique provides sub-centimeter precision range measurements to artificial satellites and the Moon. The data has application to a wide range of Earth and lunar science issues including precise orbit determination, terrestrial reference frames, geodesy, geodynamics, oceanography, time transfer, lunar dynamics, gravity and relativity

    Third International Symposium on Space Mission Operations and Ground Data Systems, part 2

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    Under the theme of 'Opportunities in Ground Data Systems for High Efficiency Operations of Space Missions,' the SpaceOps '94 symposium included presentations of more than 150 technical papers spanning five topic areas: Mission Management, Operations, Data Management, System Development, and Systems Engineering. The symposium papers focus on improvements in the efficiency, effectiveness, and quality of data acquisition, ground systems, and mission operations. New technology, methods, and human systems are discussed. Accomplishments are also reported in the application of information systems to improve data retrieval, reporting, and archiving; the management of human factors; the use of telescience and teleoperations; and the design and implementation of logistics support for mission operations. This volume covers expert systems, systems development tools and approaches, and systems engineering issues

    Earth Resources: A continuing bibliography with indexes, issue 16, January 1978

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    This bibliography lists 543 reports, articles, and other documents introduced onto the NASA scientific and technical information system between October 1 and December 31, 1977. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

    Workshop on Planetary Atmospheres : November 6-7, 2007, Greenbelt, Maryland

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    The talks are organized along three themes: Atmospheres around bodies with solid surfaces (e.g., terrestrial planets, Titan, Io, Pluto, satellites, small bodies); Giant-planet atmospheres (Jupiter, Saturn, Uranus, and Neptune); Other topics (e.g., comets, extrasolar planets, solar wind/magnetosphere/atmosphere interactions)Sponsored by: Lunar and Planetary Institute, National Aeronautics and Space AdministrationScientific Organizing Committee: Don Banfield, Cornell University, Jay T. Bergstralh, NASA Langley Research Center, Mark Bullock, Southwest Research Institute, Philippe Crane, NASA Headquarters, Neil Dello Russo, Johns Hopkins University, Applied Physics Laboratory, Heidi B. Hammel, Space Science Institute, David L. Huestis, SRI International, Molecular Physics Laboratory, Carey M. Lisse, Johns Hopkins University, Applied Physics Laboratory, Julianne I. Moses, Lunar and Planetary Institute, Adam P. Showman, University of Arizona, Amy A. Simon-Miller, NASA Goddard Space Flight Center, Local Organizing Committee: Philippe Crane, NASA Headquarters, Monica Washington, NASA Research and Education Support Services.PARTIAL CONTENTS: Mars Water Cycle Simulations with the NASA/Ames GCM / R. M. Haberle, F. Montmessin, M. A. Kahre, J. L. Hollingsworth, and J. Schaeffer--Low Temperature Absorption of Sulfur Dioxide Between 280 and 330 nm / J. B. Halpern, D. Carliss, C. Knight, and J. F. Burris--Optical Properties of Titan Haze Laboratory Analogs Using Cavity Ring Down Spectroscopy / C. A. Hasenkopf, M. R. Beaver, M. A. Tolbert, O. B. Toon, and C. P. McKay--High Resolution IR Spectroscopy: A Laboratory Program in Support of Planetary Atmospheric Research / T. Hewagama, W. E. Blass, T. Kostiuk, and J. Delgado--Large-Scale Extratropical Cyclogenesis and Frontal Waves: Effects on Mars Dust / J. L. Hollingsworth, M. A. Kahre, and R. M. Haberle--Mathematics of Radiation Propagation in Planetary Atmospheres: Absorption, Refraction, Time Delay, Occultation, and Abel Inversion / D. L. Huestis--Planetary Atmospheres Discoveries by the Cassini Spacecraft / A. P. Ingersoll

    Third International Symposium on Space Mission Operations and Ground Data Systems, part 1

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    Under the theme of 'Opportunities in Ground Data Systems for High Efficiency Operations of Space Missions,' the SpaceOps '94 symposium included presentations of more than 150 technical papers spanning five topic areas: Mission Management, Operations, Data Management, System Development, and Systems Engineering. The papers focus on improvements in the efficiency, effectiveness, productivity, and quality of data acquisition, ground systems, and mission operations. New technology, techniques, methods, and human systems are discussed. Accomplishments are also reported in the application of information systems to improve data retrieval, reporting, and archiving; the management of human factors; the use of telescience and teleoperations; and the design and implementation of logistics support for mission operations

    Proceedings of the Ninth Annual Software Engineering Workshop

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    Experiences in measurement, utilization, and evaluation of software methodologies, models, and tools are discussed. NASA's involvement in ever larger and more complex systems, like the space station project, provides a motive for the support of software engineering research and the exchange of ideas in such forums. The topics of current SEL research are software error studies, experiments with software development, and software tools

    Thirteenth International Laser Radar Conference

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    One hundred fifteen papers were presented in both oral and poster sessions. The topics of the conference sessions were: spaceborne lidar applications; extinction/visibility; differential absorption lidar; winds and tropospheric studies; middle atmosphere; clouds and multiple scattering; pollution studies; and new systems
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