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  • 1
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    Chemical Source Inversion using Assimilated Constituent Observations in an Idealized Two-dimensional System (2009)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: We present a source inversion technique for chemical constituents that uses assimilated constituent observations rather than directly using the observations. The method is tested with a simple model problem, which is a two-dimensional Fourier-Galerkin transport model combined with a Kalman filter for data assimilation. Inversion is carried out using a Green's function method and observations are simulated from a true state with added Gaussian noise. The forecast state uses the same spectral spectral model, but differs by an unbiased Gaussian model error, and emissions models with constant errors. The numerical experiments employ both simulated in situ and satellite observation networks. Source inversion was carried out by either direct use of synthetically generated observations with added noise, or by first assimilating the observations and using the analyses to extract observations. We have conducted 20 identical twin experiments for each set of source and observation configurations, and find that in the limiting cases of a very few localized observations, or an extremely large observation network there is little advantage to carrying out assimilation first. However, in intermediate observation densities, there decreases in source inversion error standard deviation using the Kalman filter algorithm followed by Green's function inversion by 50% to 95%.
    Keywords: Meteorology and Climatology
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    ISIS and META projects (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The ISIS project has developed a new methodology, virtual synchony, for writing robust distributed software. High performance multicast, large scale applications, and wide area networks are the focus of interest. Several interesting applications that exploit the strengths of ISIS, including an NFS-compatible replicated file system, are being developed. The META project is distributed control in a soft real-time environment incorporating feedback. This domain encompasses examples as diverse as monitoring inventory and consumption on a factory floor, and performing load-balancing on a distributed computing system. One of the first uses of META is for distributed application management: the tasks of configuring a distributed program, dynamically adapting to failures, and monitoring its performance. Recent progress and current plans are reported.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-186413 , NAS 1.26:186413
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Programming with process groups: Group and multicast semantics (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Process groups are a natural tool for distributed programming and are increasingly important in distributed computing environments. Discussed here is a new architecture that arose from an effort to simplify Isis process group semantics. The findings include a refined notion of how the clients of a group should be treated, what the properties of a multicast primitive should be when systems contain large numbers of overlapping groups, and a new construct called the causality domain. A system based on this architecture is now being implemented in collaboration with the Chorus and Mach projects.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-187975 , NAS 1.26:187975 , TR-91-1185 , AD-A233033
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    NASA TECHNICAL REPORTS
  • 4
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    Consistent detection of global predicates (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A fundamental problem in debugging and monitoring is detecting whether the state of a system satisfies some predicate. If the system is distributed, then the resulting uncertainty in the state of the system makes such detection, in general, ill-defined. Three algorithms are presented for detecting global predicates in a well-defined way. These algorithms do so by interpreting predicates with respect to the communication that has occurred in the system.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-188078 , NAS 1.26:188078 , TR-91-1200 , AD-A235282
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    From Earth to orbit (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Within this document, the National Research Council (NRC) assesses the requirements, benefits, technological feasibility, and roles of Earth-to-orbit transportation options that could be developed in support of the national space program. Among the topics covered are launch vehicles and infrastructure, propulsion, and technology.
    Keywords: SPACE TRANSPORTATION
    Type: NASA-CR-190216 , NAS 1.26:190216
    Format: application/pdf
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  • 6
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    Tools for distributed application management (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Distributed application management consists of monitoring and controlling an application as it executes in a distributed environment. It encompasses such activities as configuration, initialization, performance monitoring, resource scheduling, and failure response. The Meta system is described: a collection of tools for constructing distributed application management software. Meta provides the mechanism, while the programmer specifies the policy for application management. The policy is manifested as a control program which is a soft real time reactive program. The underlying application is instrumented with a variety of built-in and user defined sensors and actuators. These define the interface between the control program and the application. The control program also has access to a database describing the structure of the application and the characteristics of its environment. Some of the more difficult problems for application management occur when pre-existing, nondistributed programs are integrated into a distributed application for which they may not have been intended. Meta allows management functions to be retrofitted to such programs with a minimum of effort.
    Keywords: ADMINISTRATION AND MANAGEMENT
    Type: NASA-CR-186646 , NAS 1.26:186646
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  • 7
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    Design alternatives for process group membership and multicast (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Process groups are a natural tool for distributed programming, and are increasingly important in distributed computing environments. However, there is little agreement on the most appropriate semantics for process group membership and group communication. These issues are of special importance in the Isis system, a toolkit for distributed programming. Isis supports several styles of process group, and a collection of group communication protocols spanning a range of atomicity and ordering properties. This flexibility makes Isis adaptable to a variety of applications, but is also a source of complexity that limits performance. This paper reports on a new architecture that arose from an effort to simplify Isis process group semantics. Our findings include a refined notion of how the clients of a group should be treated, what the properties of a multicast primitive should be when systems contain large numbers of overlapping groups, and a new construct called the casuality domain. As an illustration, we apply the architecture to the problem of converting processes into fault-tolerant process groups in a manner that is 'transparent' to other processes in the system.
    Keywords: COMPUTER SYSTEMS
    Type: NASA-CR-189517 , NAS 1.26:189517 , TR91-1257 , AD-A245350
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  • 8
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    Supporting large scale applications on networks of workstations (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Distributed applications on networks of workstations are an increasingly common way to satisfy computing needs. However, existing mechanisms for distributed programming exhibit poor performance and reliability as application size increases. Extension of the ISIS distributed programming system to support large scale distributed applications by providing hierarchical process groups is discussed. Incorporation of hierarchy in the program structure and exploitation of this to limit the communication and storage required in any one component of the distributed system is examined.
    Keywords: COMPUTER SYSTEMS
    Type: NASA-CR-186346 , NAS 1.26:186346
    Format: application/pdf
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  • 9
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    Tools for distributed application management (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Distributed application management consists of monitoring and controlling an application as it executes in a distributed environment. It encompasses such activities as configuration, initialization, performance monitoring, resource scheduling, and failure response. The Meta system (a collection of tools for constructing distributed application management software) is described. Meta provides the mechanism, while the programmer specifies the policy for application management. The policy is manifested as a control program which is a soft real-time reactive program. The underlying application is instrumented with a variety of built-in and user-defined sensors and actuators. These define the interface between the control program and the application. The control program also has access to a database describing the structure of the application and the characteristics of its environment. Some of the more difficult problems for application management occur when preexisting, nondistributed programs are integrated into a distributed application for which they may not have been intended. Meta allows management functions to be retrofitted to such programs with a minimum of effort.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-186711 , NAS 1.26:186711 , TR-90-1136
    Format: application/pdf
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  • 10
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    From Earth to Orbit: An assessment of transportation options (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The report assesses the requirements, benefits, technological feasibility, and roles of Earth-to-Orbit transportation systems and options that could be developed in support of future national space programs. Transportation requirements, including those for Mission-to-Planet Earth, Space Station Freedom assembly and operation, human exploration of space, space science missions, and other major civil space missions are examined. These requirements are compared with existing, planned, and potential launch capabilities, including expendable launch vehicles (ELV's), the Space Shuttle, the National Launch System (NLS), and new launch options. In addition, the report examines propulsion systems in the context of various launch vehicles. These include the Advanced Solid Rocket Motor (ASRM), the Redesigned Solid Rocket Motor (RSRM), the Solid Rocket Motor Upgrade (SRMU), the Space Shuttle Main Engine (SSME), the Space Transportation Main Engine (STME), existing expendable launch vehicle engines, and liquid-oxygen/hydrocarbon engines. Consideration is given to systems that have been proposed to accomplish the national interests in relatively cost effective ways, with the recognition that safety and reliability contribute to cost-effectiveness. Related resources, including technology, propulsion test facilities, and manufacturing capabilities are also discussed.
    Keywords: SPACE TRANSPORTATION
    Type: NASA-CR-192729 , NAS 1.26:192729 , PB93-114684 , LC-92-60204
    Format: application/pdf
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