Showing papers by "Naval Postgraduate School published in 1995"

Exploiting reality with multicast groups: a network architecture for large-scale virtual environments

Abstract: Describes a network software architecture for solving the problem of scaling very large distributed simulations. The fundamental idea is to logically partition virtual environments by associating spatial, temporal and functionally-related entity classes with network multicast groups. We exploit the actual characteristics of the real-world large-scale environments that are simulated by focusing or restricting an entity's processing and network resources to its area of interest via a local 'area of interest manager' (AOIM). Finally, we present an example of how we would implement this concept for ground vehicles. We have begun the design and construction of the AOIM for use with the NPSNET 3D vehicle simulator. NPSNET is currently the only distributed interactive simulation (DIS) protocol compliant simulator using IP multicast communications and is suitable for operation over the Internet.

The Central Role of Discourse in Large-Scale Change: A Social Construction Perspective:

Abstract: This article reconceptualizes the change process from a rational planning perspective to an interpretive perspective emphasizing the social construction of meaning. Discourse is viewed as the core of the change process through which our basic assumptions about organizing are created, sustained, and transformed. To illustrate the dynamics of meaning systems, examples are provided of organizations shifting from mechanistic assumptions to become more adaptive, responsive, quality-oriented organizations. Implications for researchers and managers are included.

Two-Person Zero-Sum Games for Network Interdiction

Abstract: A single evader attempts to traverse a path between two nodes in a network while a single interdictor attempts to detect the evader by setting up an inspection point along one of the network arcs. For each arc there is a known probability of detection if the evader traverses the arc that the interdictor is inspecting. The evader must determine a probabilistic "path-selection" strategy which minimizes the probability of detection while the interdictor must determine a probabilistic "arc-inspection" strategy which maximizes the probability of detection. The interdictor represents, in a simplified form, U.S. and allied forces attempting to interdict drugs and precursor chemicals as they are moved through river, road, and air routes in Latin America and the Caribbean. We show that the basic scenario is a two-person zero-sum game that might require the enumeration of an exponential number of paths, but then show that optimal strategies can be found using network flow techniques of polynomial complexity. To enhance realism, we also solve problems with unknown origins and destinations, multiple interdictors or evaders, and other generalizations.

Precision measurement of the proton spin structure function g1p

Abstract: We have measured the ratio [ital g][sup [ital p]][sub 1]/[ital F][sup [ital p]][sub 1] over the range 0.029[lt][ital x][lt]0.8 and 1.3[lt][ital Q][sup 2][lt]10 (GeV/[ital c])[sup 2] using deep-inelastic scattering of polarized electrons from polarized ammonia. An evaluation of the integral [integral][ital g][sup [ital p]][sub 1]([ital x],[ital Q][sup 2])[ital dx] at fixed [ital Q][sup 2]=3 (GeV/[ital c])[sup 2] yields 0.127[plus minus]0.004(stat)[plus minus]0.010(syst), in agreement with previous experiments, but well below the Ellis-Jaffe sum rule prediction of 0.160[plus minus]0.006. In the quark-parton model, this implies [Delta][ital q]=0.27[plus minus]0.10.

Hydrodynamic damping. flow-induced oscillations, and biharmonic response

Abstract: A brief review of damping is followed by a comparison of three sets of lift-force data for circular cylinders, subjected only to transverse oscillation. Then the significance of two-dimensional or biharmonic oscillations (in both the in-line and transverse directions) is discussed in light of experiments undertaken for that purpose, to simulate more closely the true nature of flow-induced oscillations.

Exploiting reality with multicast groups

Abstract: This article describes our investigation into developing large distributed simulations. The architecture we describe logically partitions virtual environments by associating spatial, temporal, and functional classes with network multicast groups. We exploit the actual characteristics of the real-world large scale environments being simulated by focusing or restricting an entity's processing and network resources to its area of interest via a local area-of-interest manager. For example, a simulated infantryman in a virtual environment doesn't need to know the condition of a simulated truck 20 virtual kilometres away. >

Toward an improved understanding of thruster dynamics for underwater vehicles

Abstract: This paper proposes a novel approach to modeling the four quadrant dynamic response of thrusters as used for the motion control of ROV and AUV underwater vehicles. The significance is that these vehicles are small in size and respond quickly to commands. Precision in motion control will require further understanding of thruster performance than is currently available. The model includes a four quadrant mapping of the propeller blades lift and drag forces and is coupled with motor and fluid system dynamics. A series of experiments is described for both long and short period triangular, as well as square wave inputs. The model is compared favorably with experimental data for a variety of differing conditions and predicts that force overshoots are observed under conditions of rapid command changes. Use of the model will improve the control of dynamic thrust on these vehicles.

Precision measurement of the deuteron spin structure function g1d

Abstract: This work was supported by Department of Energy Contracts No. DE-AC05-84ER40150 (CEBAF), No. W-2795-Eng-48 (LLNL), No. DE-AC0376SF00515 (SLAC), No. DE-FG03-88ER40439 (Stanford), No. DE-FG05-88ER40390 and No. DEFG05-86ER4026 (Virginia), and No. DE-AC02-76ER00881 (Wisconsin); by National Science Foundation Grants No. 9114958 (American), No. 9307710 (Massachusetts), No. 9217979 (Michigan), No. 9104975 (ODU) and No. 9118137 (U. Penn.); by the Schweizersche Nationalfonds (Basel); by the Commonwealth of Virginia (Virginia); by the Centre NAtional de la Recherche Scientifique and the Commissariat a l'Energie Atomique (French groups); and by the Japanese Ministry of Education, Science and Culture (Tohoku).

Task scheduling in multiprocessing systems

Abstract: The complex problem of assigning tasks to processing elements in order to optimize a performance measure has resulted in numerous heuristics aimed at approximating an optimal solution. This article addresses the task scheduling problem in many of its variations and surveys the major solutions. The scheduling techniques we discuss might be used by a compiler writer to optimize the code that comes out of a parallelizing compiler. The compiler would produce grains of sequential code, and the optimizer would schedule these grains such that the program runs in the shortest time.

Wind-Driven Motions in the Northeast Pacific as Measured by Lagrangian Drifters

Abstract: Analysis is presented of the time-dependent motion of 47 surface drifters in the northeast Pacific during fall 1987 and 16 drifters in fall and winter 1989/90. The drifters were designed at 15-m depth and were designed to have wind-produced slips less than 2 cm s−1 for wind speeds up to 20 m s−1. The coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days. For periods between 5 and 20 days, drogue motion at 15-m depth is found to be highly coherent with local wind with an average phase of 70° to the right of the rotating wind vector. These results differ from analyses of FGGE-type drifters as reported by McNally et al. and Niiler in the same area. A model of wind-produced slip as a function of drifter design is used to provide a possible explanation of the differences. A linear regression, which accounts for 20%–40% of the current variance, gives water motion al 0.5% of wind speed and 68° to the right of the wind vector. Assuming an Ekman-type balance,...

Efficient dynamic simulation of an underwater vehicle with a robotic manipulator

Abstract: In this paper, an efficient dynamic simulation algorithm is developed for an underwater robotic vehicle (URV) with a manipulator. It is based on previous work on efficient O(N) algorithms, where N is the number of links in the manipulator, and has been extended to include the effects of a mobile base (the URV body). In addition, the various hydrodynamic forces exerted on these systems in underwater environments are also incorporated into the simulation. The effects modeled in this work are added mass, viscous drag, fluid acceleration, and buoyancy forces. With efficient implementation of the resulting algorithm, the amount of computation with inclusion of the hydrodynamics is almost double that of the original algorithm for a six degree-of-freedom land-based manipulator with a mobile base. Nevertheless, the amount of computation still only grows linearly with the number of degrees of freedom in the manipulator. >

Large-Scale Circulation Variability over the Tropical Western North Pacific. Part I: Spatial Patterns and Tropical Cyclone Characteristics

Abstract: The basic structure of the variability of the large-scale circulations over the tropical western Pacific is investigated with respect to its influence on tropical cyclone characteristics. A vector empirical orthogonal function analysis and fuzzy cluster algorithm are applied to a 9-yr dataset to define six recurrent 700-mb circulation patterns that represent large-scale variabilities associated with the monsoon trough and subtropical ridge. Five of the cluster patterns, which contain 48% of the sample, define combinations of active (inactive) monsoon trough and strong (weak) subtropical ridge circulations. The sixth cluster, which contains 26% of the data sample, depicts small deviations from the long-term climatology. After the cluster centers are defined, the fuzzy cluster coefficients are used to identify a seventh cluster, which contains the remaining 26% of the circulation patterns that could not be classified within any of the original six clusters. The 700-mb circulation patterns are physi...

Nonlinear H/sub /spl infin// control and its application to rigid spacecraft

Abstract: The problem of H/sub /spl infin// control of a rigid spacecraft with three control torques and disturbances is addressed. The Hamilton-Jacobi-Isaacs inequality for H/sub /spl infin// feedback design is solved. An H/sub /spl infin// suboptimal feedback is given, and the stability properties of the closed-loop system are studied. >

Implementing requirements traceability: a case study

Abstract: Many standards that mandate requirements traceability as well as current literature do not provide a comprehensive model of what information should be captured and used as a part of a traceability scheme. Therefore, the practices and usefulness of traceability vary considerably across systems development efforts, ranging from very simplistic practices just aimed at satisfying the mandates to very comprehensive traceability schemes used as an important tool for managing the systems development process. We present a case study of a systems development organization, employing a comprehensive view of traceability. A model describing the traceability practice in the organization, perceived benefits of such a scheme and lessons learnt from implementing it are presented.

Monsoonal Interactions Leading to Sudden Tropical Cyclone Track Changes

Abstract: Sudden poleward track changes of tropical cyclones embedded in monsoon gyres in the western North Pacific are documented. During these track changes, which are generally not well forecast, the cyclones are often accompanied by a separate comma-shaped area of gale-force winds and deep convection along the eastern periphery. This monsoon surge is distinct from the tropical cyclone. Synoptic analyses often reveal a building anticyclone to the east or southeast of the monsoon gyre. The hypothesis that the sudden track change is initiated by a binary interaction of the tropical cyclone and monsoon gyre is tested with a nondivergent barotropic model. Tropical cyclone-scale vortices with initial positions within the eastern semicircle of a larger monsoon gyre-scale vortex initially coalesce with the monsoon gyre and then exhibit sudden poleward track changes that are similar to the observations. During the coalescence phase, the large and relatively weak monsoon gyre undergoes a β-induced dispersion in ...

Sympathetic nucleation: an overview

Abstract: Sympathetic nucleation is defined as the nucleation of a precipitate crystal at an interphase boundary of a crystal of the same phase when these crystals differ in composition from their matrix phase throughout the transformation process. Following a brief history of the discovery and interpretation of this phenomenon, the means of identifying the presence of sympathetic nucleation are described. The morphological configurations most frequently produced by sympathetic nucleation are illustrated. Heterogeneous nucleation theory is then applied to explain sympathetic nucleation. Particular emphasis is placed upon the driving force for sympathetic nucleation, since many of the effects of phase diagram geometry and supersaturation upon sympathetic nucleation can be simply explained upon this basis.

NPSNET: a multi-player 3D virtual environment over the Internet

Abstract: in the Proceedings of the 1995 Symposium on Interactive 3D Graphics, 9 - 12 April 1995, Monterey, California.

VISUAL OBJECT-ORIENTED PROGRAMMING: Concepts and Environments

Abstract: Maps the intersection between visual programming and object technology for software developers. Describes emerging research and a few classic systems, recounts experiences of using the available visual programming languages in commercial setting to help new explorers avoid some of the pitfalls and d

Multiple-valued logic

Abstract: The ultimate usefulness of a number system depends on its implementation. Multiple-valued logic has been implemented in charge-coupled devices (CCD). In this technology, logic values are encoded as charge. For example, prototype four-valued logic devices have been implemented at the University of Twente (Enschede, Holland). Hitachi has implemented a 16-valued memory that stores the equivalent of 10/sup 6/ bits. CCD is more compact than any other VLSI technology. Although it is slower than CMOS (complementary metal oxide semiconductor), it is much faster than the disk and has the potential of replacing the disk. The use of multiple-valued logic in CCD increases its storage capacity significantly. Multiple-valued logic has also been implemented in current-mode CMOS. >

Evaluation of physical processes in an idealized extratropical cyclone using adjoint sensitivity

Abstract: An adjoint model is used to examine the sensitivity of an idealized dry extratropical cyclogenesis simulation to perturbations of predictive variables and parameters during the cyclone life cycle. the adjoint sensitivity indicates how small perturbations of model variables or parameters anywhere in the model domain can influence cyclone central pressure. Largest sensitivity for both temperature and wind perturbations is located between 600 and 900 hPa in the baroclinic zone above the developing cyclone. Perturbations of a given size have more influence on cyclone intensity when located in high-sensitivity regions (the middle and lower troposphere in this simulation). the effects of physical processes can be interpreted with adjoint sensitivity by considering perturbations that are proportional to temperature and wind tendencies in the basic state (nonlinear forecast). In the early phase of the cyclone life cycle, temperature advection near the steering level in the lower troposphere (about 800 hPa) is strongly cyclogenetic and resembles a Charney mode of baroclinic instability. During the phase of most rapid deepening, temperature advection in the lower troposphere remains important, while interpretation of sensitivity to wind perturbations suggests that increased vorticity in the middle and upper troposphere above the surface low-pressure centre may also be significant for cyclone intensification. Adjoint techniques can provide insight into spatial and temporal sensitivity not easily obtained from other methods. Higher sea surface temperature (SST) has a cyclogenetic effect mainly in a localized region corresponding to the cyclone warm sector. Outside the areas of high sensitivity, small perturbations of SST have very little effect on central pressure of the forecast cyclone. When strong upward sensible-heat flux, Fs, exists, it can have a cyclogenetic (preconditioning) influence early in the cyclone life cycle, although downward Fs in the cyclone warm sector is anticyclogenetic during the phase of most rapid deepening. the sensitivity indicates that Fs can be cyclogenetic in one location and anticyclogenetic at the same time in another location, so that Fs effects on cyclone intensity are partially self-cancelling. Surface momentum stress is anticyclogenetic, with sensitivity highly localized in the cyclone warm sector.

Principles of Programming Languages: Design, Evaluation, and Implementation

Abstract: PREFACE Concept Directory I. History, Motivation, and Evaulation II. Design and Implementation III. Principles IV. Implementation INTRODUCTION 1. The Beginning: Pseudo-Code Interpreters 1.1 History and Motivation 1.2 Design of a Pseudo-Code 1.3 Implementation 1.4 Phenomenology of Programming Languages 2. Emphasis on Efficiency: FORTRAN 2.1 History and Motivation 2.2 Design: Structural Organization 2.3 Design: Control Structures 2.4 Design: Data Structures 2.5 Design: Name Structures 2.6 Design: Syntactic Structures 2.7 Evaluation and Epilog 3. Generality and Hierarchy: ALGOL-60 3.1 History and Motivation 3.2 Design: Structural Organization 3.3 Design: Name Structures 3.4 Design: Data Structures 3.5 Design: Control Structures 4. Syntax and Elegance: ALGOL-40 4.1 Design: Syntactic Structures 4.2 Descriptive Tools: BNF 4.3 Design: Elegance 4.4 Evaluation and Epilog 5. Return to Simplicity: PASCAL 5.1 History and Motivation 5.2 Design: Structural Organization 5.3 Design: Data Structures 5.4 Design: Name Structures 5.5 Design: Control Structures 5.6 Evaluation and Epilog 6. Implementation of Block Structured Languages 6.1 Activation Records and Context 6.2 Procedure Call and Return 6.3 Display Method 6.4 Blocks 6.5 Summary 7. Modularity and Data Abstraction: ADA 7.1 History and Motivation 7.2 Design: Structural Organization 7.3 Design Data Structures and Typing 7.4 Design: Name Structures 8. Procedures and Concurrency: ADA 8.1 Design: Control Structures 8.2 Design: Syntactic Structures 8.3 Evaluation and Epilog 9. List Processing: LISP 9.1 History and Motivation 9.2 Design: Structural Organization 9.3 Design: Data Structures 10. Functional Processing: LISP 10.1 Design: Control Structures 10.2 Design: Name Structures 10.3 Design: Syntactic Structures 11. Implementation of Recursive List-Processors: LISP 11.1 Recursive Interpreters 11.2 Storage Reclamation 11.3 Evaluation and Epilog 12. Object-Oriented Programming: SmallTalk 12.1 History and Motivation 12.2 Design: Structural Organization 12.3 Design: Classes and Subclasses 12.4 Design: Objects and Message Sending 12.5 Implementation: Classes and Objects 12.6 Design: Object-Oriented Extensions 12.7 Evaluation and Epilog 13. Logic Programming: Prolog 13.1 History and Motivation 13.2 Design: Structural Organization 13.3 Design: Data Structures 13.4 Design: Control Structures 13.5 Evaluation and Epilog 14. Principles of Language Desing 14.1 General Remarks 14.2 Principles BIBLIOGRAPHY INDEX

Modeling Ocean Circulation

Abstract: Ocean numerical models have become quite realistic over the past several years as a result of improved methods, faster computers, and global data sets. Models now treat basin-scale to global domains while retaining the fine spatial scales that are important for modeling the transport of heat, salt, and other properties over vast distances. Simulations are reproducing observed satellite results on the energetics of strong currents and are properly showing diverse aspects of thermodynamic and dynamic ocean responses ranging from deep-water production to EI Nino. Now models can represent not only currents but also the consequences for climate, biology, and geochemistry over time spans of months to decades. However, much remains to be understood from models about ocean circulation on longer time scales, including the evolution of the dominant water masses, the predictability of climate, and the ocean9s influence on global change.

A simple neutrally buoyant sensor for direct measurement of particle velocity and intensity in water

Abstract: Acoustic particle velocity is commonly inferred from measurement of pressure or pressure gradient; however, in water, direct measurement is simple. A moving‐coil sensor embedded in a neutrally buoyant package produces a voltage directly proportional to the particle velocity in the surrounding fluid for frequencies above the mass‐spring resonance. Leslie et al. [J. Acoust. Soc. Am. 28, 711–715 (1956)] built such a sensor by mounting a moving‐coil element inside a hollow brass sphere. The sensor described in this paper is identical in principle but is considerably easier to fabricate. Useful from tens of hertz to several kilohertz, this sensor consists of a glass‐ microballoon‐and‐epoxy composite cast around a small, commercial geophone. The sensor is inexpensive, rugged, and has good immunity to interference. In conjunction with a pressure hydrophone, acoustic intensity can be measured without the errors associated with subtraction of nearly equal signals (as in the two‐hydrophone method).

Economic aspects of configuring cellular networks

Abstract: This paper addresses economic aspects of configuring cellular networks. Major components of costs and revenues and the major stakeholders are identified and a model is developed to determine the system configuration (e.g. cell size, number of channels, etc.) which will maximize the annual expected net revenues to the system operator. Key properties relating the various parameters of interest are derived. The results of computational experiments are presented and their implications are discussed. The computational results show that the optimal net revenue curves have a saw-tooth structure with two types of teeth; Large ones that come from switching between cellular technologies, and smaller jumps come the discretenes of base stations. The importance of capturing a high fraction of potential users, in early stages of cellular system introduction is investigated. Finally, the cost of competition and its implications for the regulatory agency and the cellular service providers are analyzed. It is shown that by dividing the available frequency spectrum between too many system operators, the overall value of the cellular system is reduced when compared to an approach which uses division of the overall service area into a larger number of service areas, each with only two system operatos. The above results have profound implications on public policies for frequency spectrum allocation.

Computing the 2‐median on tree networks in O(n lg n) time

Abstract: Location of facilities on tree networks is an important problem in transportation and telecommunication systems. For tree networks, the best-known algorithm to find 2-medians has a time complexity of O(n 2 ). By exploiting the properties relating the 1-median and the 2-medians in tree networks, and the properties inherent in tree structure, an improved algorithm is developed for computing the 2-median. The time complexity of this algorithm is O(n lg n). The details of the algorithm are described along with an illustrative example.

Effects of Aerosol Particles on the Microphysics of Coastal Stratiform Clouds

Abstract: Aerosol particles can act as cloud condensation nuclei and thereby influence the number and size of droplets in clouds. Consequently, anthropogenic particles have the potential to influence global climate by increasing cloud albedo and decreasing precipitation efficiencies. Enhanced cloud reflectances associated with increases in panicle number have been observed, but our understanding of these interactions has been hindered by incomplete empirical studies and models of limited scope. In this study, aerosol and droplet size distributions were measured on 13 research flights in stratiform clouds within 300 km west of the northern California coast. The chemical composition of the droplet solute was also assessed. Microphysical and chemical properties indicated that most of the clouds were influenced by pollution from the North American continent, but pristine marine clouds were sampled on one flight during westerly flow conditions. Data from this flight and another, representing a pristine and poll...