A multi-scale spatial ecological model of a wet sclerophyllous forest subject to recurrent fires is presented. The model is specified in a Discrete Event Systems framework (DEVS) (Zeigler, 1990) interfaced with a Geog...
A multi-scale spatial ecological model of a wet sclerophyllous forest subject to recurrent fires is presented. The model is specified in a Discrete Event Systems framework (DEVS) (Zeigler, 1990) interfaced with a Geographic Information System (GIS), and includes the ability to simulate landscape dynamics at several levels of resolution simultaneously. This is achieved by encoding a modular hierarchical representation of the forest landscape components into a set of nested, interconnected, and spatially referenced dynamic models. The results of the landscape dynamics simulations are displayed as sequences of maps through time, illustrating the potential of this modeling methodology for dealing with complex hierarchical structures that operate at several spatial and temporal resolutions.
An interlaboratory measurement round-robin was conducted by the University of Colorado and three industrial members of the Electronic Industries Association. A computational definition of mode transition matrices (MTM...
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An interlaboratory measurement round-robin was conducted by the University of Colorado and three industrial members of the Electronic Industries Association. A computational definition of mode transition matrices (MTM's) is presented, and its relationship to the basic theory of power propagation in multimode fibers is detailed. Measured data from the round-robin were used to calculate MTM's for the test components, which included four connectors, two sections of fiber cable, two power splitters, and two short fiber segments. The diagonal elements of the (2 x 2) MTM's determined from the near-field data were found to have a laboratory-to-laboratory standard deviation of approximately 10% of the average value. The off-diagonal elements were found to have a standard deviation approaching their mean value. The inherent launch dependence of MTM's is investigated as a source of the observed variation. Other sources of uncertainty such as errors in determining the core radius are also considered. Finally the implications of these results for the problem of characterizing components' intensive multimode fiber systems are discussed.
The stability of GaAs/Si superlattices grown on GaAs substrates using molecular beam epitaxy is described. Typical superlattice structures consisted of ten periods of thin (less than 6.5Å thick) layers of pseudom...
The stability of GaAs/Si superlattices grown on GaAs substrates using molecular beam epitaxy is described. Typical superlattice structures consisted of ten periods of thin (less than 6.5Å thick) layers of pseudomorphic silicon alternating with thick GaAs layers. We have examined the As2/Ga flux conditions required for the growth of high quality superlattices and have found that the structural perfection is extremely sensitive to the V/III flux ratio. The best superlattices were grown under condition that were just barely enough arsenic to produce a stable (2×4) surface reconstruction in the GaAs layers; increases in the arsenic overpressure resulted in a progressive trend towards 3-D growth of the GaAs on the pseudomorphic Si. In addition, we have examined the stability of GaAs/Si superlattices towards post-growth annealing. Double crystal x-ray diffraction scans showed little change in superlattice structure following rapid thermal anneals at 800°C; at 900°C, however, all but the first order satellite reflections disappeared. We attribute this behavior to the relaxation of pseudomorphic strin and the generation of misfit dislocations at the higher anneal temperature.
Performance evaluation of shipboard electronic systems entails debugging the systems in a laboratory environment, placing them in service and relving on svstem operators to provide feedback. General testing can be per...
Performance evaluation of shipboard electronic systems entails debugging the systems in a laboratory environment, placing them in service and relving on svstem operators to provide feedback. General testing can be performed at selected sites by system designers, but each site where equipment is to be installed can offer unique problems. It is impossible to predict all the scenarios. Unique problems are more the rule than the exception when equipment is destined for Navy ships. Ship deployments make for difficult logistics when sending test teams to evaluate system failures. So, out of necessity, if newly installed equipment receives the proper inputs and generates the proper outputs, it is accepted and becomes the sailor's responsibilitv to maintain. In cases where documentation is ambiguous or incomplete, it is left to the sailor's ingenuity to continue testing and training on equipment. This is generallv obtained through computer simulations and back-to-back testing which can provide results for ideal conditions, but does not take the dynamics of interference into account. Remote site testing is the only way to get a true representation of equipment performance and training problems. Electronic system operators on board Navy vessels are fortunate, thev have help. There exists an organization available near major naval ports worldwide whose existence is to test electronic systems performance. The testing utilizes electronic systems as they would normally be configured for operations. This organization is the Shipboard Electronic Svstem Evaluation Facility (SESEF).
作者：
SHEA, JGThe Author:holds bachelor and master of engineering degrees in mechanical engineering
a M.Eng. in engineering management and is currently fulfilling requirements for the M.S. and Ph.D. degrees in computer science at the University of Louisville. He is employed as program manager Phalanx Advanced Engineering Development at the Naval Ordnance Station Crane Div. NavSurfWarCen Louisville Ky. During his tenure with Phalanx Mr. Shea has contributed to system reliability improvement system performance upgrading and the development of the Phalanx HOL (RISC) Computer. Mr. Shea is a member of ASNE the Institute of Electrical and Electronics Engineers American Institute of Aeronautics and Astronautics Society for Computer Simulation International Test & Evaluation Association and the Military Operations Research Society.
Knowledge-based modeling and simulation bridges the gap between ''conventional'' artificial intelligence implementations (such as expert systems) and more traditional computer-aided design techniques. ...
Knowledge-based modeling and simulation bridges the gap between ''conventional'' artificial intelligence implementations (such as expert systems) and more traditional computer-aided design techniques. We are currently developing software, whose primary function is to capture a user-input design specification and produce a ''virtual'' rapid prototvpe in the form of executable rule-based code. This code can then be exercised either as an interactive part of a hardware-in-the-loop testbed simulator or as a component of an object-oriented ''behavioral'' simulation environment. While the Phalanx Testbed is the immediate beneficiary of this work, the techniques described have a wide range of application in the modeling of conceptual design and performance characteristics. This paper describes the system architecture and software tools that we are applying to generate virtual rapid prototypes for use in the Phalanx Testbed. Particular attention is paid to defining the intelligent knowledge-capture mechanisms and model generation methodologies that we are using to translate design knowledge and performance requirements into rule-based simulations. The object-oriented programming approach to the merging of ''new'' data with previouslv-captured and stored data is discussed, and the issues of verifying and validating prototypes generated using such partiallv ''reengineered'' models are examined. An application currently in use as an investigative prototype for testbed development, a simple position controller servomechanism used to control the azimuth angle of a target-tracking sensor, is used to illustrate the process.
作者：
MITTURA, AKARP, MSPEAndrew Mittura:is currently a senior program engineer with SYSCON Corp. He began his career in the Combat System Installation and Integration Office of NavSea in 1978. He has worked as a system engineer on the Seafire program at NSWCDD
on the NATO Anti-air Warfare Program while at FMC Corporation and for the past four years on the Aegis Combat System with SYSCON. Current efforts include performance assessment studies of the Aegis combat system and combat system architecture and connectivity analysis. Mr. Mittura received a B.S. in electrical engineering from Penn State University in 1978 and an M.S. in engineering management from Catholic University of America in 1982. He is a licensed professional engineer with the State of Virginia. Mitchel S. Karp:cofounded K&K Software Engineering
Inc. in February 1970. He is currently secretary/treasurer and senior system engineer. His involvement in combat systems began with NTDS in 1963. He has been involved in the Aegis Program since 1968 and has worked in all aspects of combat system development including computer programming tactical analysis software development and management. He has given several seminars on real-time software development and documentation. He currently is working under contracts to NSWCDD in the areas of combat system architecture and connectivity configuration management and documentation. Mr. Karp received a B.S. in engineering physics from Lehigh University in 1958.
The Navy's focus has shifted from global war scenarios to preparedness for the prospect of involvement in regional, littoral contingencies and conflicts. Operationally, shipboard personnel will need the ability to...
The Navy's focus has shifted from global war scenarios to preparedness for the prospect of involvement in regional, littoral contingencies and conflicts. Operationally, shipboard personnel will need the ability to shift focus from the combat system multimission roles to that of only a single mission. From a development perspective, combat systems must accommodate a continual infusion of technology in a budget constrained environment. Combat system architecture is the single most important feature affecting combat system flexibility, from both an operational and developmental aspect. There is a fundamental partitioning of combat svstem functions into detect, command, and engage in a horizontal integration approach that enhances this needed flexibilitv. This fundamental partitioning is currently applied to individual weapon systems, but not to combat svstems as a whole. Instead, self-contained weapon systems are often developed and then vertically integrated to form a combat svstem, causing reduced flexibility. The battle organization is the principal driving requirement for combat system architecture. This paper shows that that the battle organization is best supported by a horizontally integrated combat system of detect, command, and engage. It concludes that a horizontally integrated combat svstem architecture of detect, command, and engage should be a candidate for future combat systems.
The use of an electromagnetic analysis of 3-D planar structures is described with respect to the educational requirements of students from the college freshman level through the graduate level. The analysis is intende...
The use of an electromagnetic analysis of 3-D planar structures is described with respect to the educational requirements of students from the college freshman level through the graduate level. The analysis is intended primarily for microwave use; however, there is also significant potential interest from the student of high speed digital design. The analysis is used for passive planar circuits with any number of layers. The third dimension is represented by vias. A mature graphical user interface is provided allowing rapid capture of structure geometry, color visualization, and animation of the resulting current distributions. The software is also explicitly designed to work in conjunction with popular circuit theory based microwave software and with SPICE.
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