Showing papers by "Naval Postgraduate School published in 1998"

Costate Estimation by a Legendre Pseudospectral Method

Abstract: We present a Legendre pseudospectral method for directly estimating the costates of the Bolza problem encountered in optimal control theory. The method is based on calculating the state and control variables at the Legendre‐Gauss‐Lobatto (LGL) points. An Nth degree Lagrange polynomial approximation of these variables allows a conversion of the optimal control problem into a standard nonlinear programming (NLP) problem with the state and control values at the LGL points as optimization parameters. By applying theKarush ‐Kuhn‐Tucker (KKT) theorem to the NLP problem, we show that the KKT multipliers satisfy a discrete analog of the costate dynamics including the transversality conditions. Indeed, we prove that the costates at the LGL points are equal to the KKT multipliers divided by the LGL weights. Hence, the direct solution by this method also automatically yields the costates by way of the Lagrange multipliers that can be extracted from an NLP solver. One important advantage of this technique is that it allows a very simple way to check the optimality of the direct solution. Numerical examples are included to demonstrate the method.

The virtual reality modeling language and Java

Abstract: The Virtual Reality Modeling Language (VRML) and Java provide a standardized, portable and platform- independent way to render dynamic, interactive 3D scenes across the Internet. Integrating two powerful and portable software languages provides interactive 3D graphics plus complete programming capabilities plus network access. Intended for programmers and scene authors, this paper provides a VRML overview, synopsizes the open development history of the specification, provides a condensed summary of VRML 3D graphics nodes and scene graph topology, describes how Java interacts with VRML through detailed examples, and examines a variety of VRML/Java future developments. Overview. The Web is being extended to three spatial dimensions thanks to VRML, a dynamic 3D scene description language that can include embedded behaviors and camera animation. A rich set of graphics primitives provides a common-denominator file format which can be used to describe a wide variety of 3D scenes and objects. The VRML specification is now an International Standards Organization (ISO) specification (VRML 97). Why VRML and Java together? Over twenty million VRML browsers have shipped with Web browsers, making interactive 3D graphics suddenly available for any desktop. Java adds complete programming capabilities plus network access, making VRML fully functional and portable. This is a powerful new combination, especially as ongoing research shows that VRML plus Java provide extensive support for building large-scale virtual environments (LSVEs). This paper provides historical background, a detailed overview of VRML 3D graphics, example VRML-Java test programs, and a look ahead at future work.

Experimental and Computational Investigation of the Knoller-Betz Effect

Abstract: The ability of a sinusoidally plunging airfoil to produce thrust, known as the Knoller-Betz or Katzmayr effect, is investigated experimentally and numerically. Water-tunnel experiments are performed providing flow visualization and laser Doppler velocimetry data of the unsteady wakes formed by the plunging foils. Vortical structures and time-averaged velocity profiles in the wake are compared with numerical computations from a previously developed inviscid, unsteady panel code that utilizes a nonlinear wake model

Secure information flow in a multi-threaded imperative language

Abstract: Previously, we developed a type system to ensure secure information flow in a sequential, imperative programming language [VSI96]. Program variables are classified as either high or low security; intuitively, we wish to prevent information from flowing from high variables to low variables. Here, we extend the analysis to deal with a multithreaded language. We show that the previous type system is insufficient to ensure a desirable security property called noninterference. Noninterference basically means that the final values of low variables are independent of the initial values of high variables. By modifying the sequential type system, we are able to guarantee noninterference for concurrent programs. Crucial to this result, however, is the use of purely nondeterministic thread scheduling. Since implementing such scheduling is problematic, we also show how a more restrictive type system can guarantee noninterference, given a more deterministic (and easily implementable) scheduling policy, such as round-robin time slicing. Finally, we consider the consequences of adding a clock to the language.

Mobile Agents

Abstract: From the Publisher: Like human agents, Internet agents can move independently in a network of locations to perform their tasks, all the while making independent decisions. Their behavior can provide astonishing solutions not even dreamed of today. Mobile Agents will help you understand their amazing potential for business applications and show you in detail how to create and use the power of agent technologies.

Stochastic Network Interdiction

Abstract: Using limited assets, an interdictor attempts to destroy parts of a capacitated network through which an adversary will subsequently maximize flow. We formulate and solve a stochastic version of the interdictor's problem: Minimize the expected maximum flow through the network when interdiction successes are binary random variables. Extensions are made to handle uncertain arc capacities and other realistic variations. These two-stage stochastic integer programs have applications to interdicting illegal drugs and to reducing the effectiveness of a military force moving materiel, troops, information, etc., through a network in wartime. Two equivalent model formulations allow Jensen's inequality to be used to compute both lower and upper bounds on the objective, and these bounds are improved within a sequential approximation algorithm. Successful computational results are reported on networks with over 100 nodes, 80 interdictable arcs, and 180 total arcs.

Trajectory Tracking for Autonomous Vehicles: An Integrated Approach to Guidance and Control

Abstract: . This paper addresses the problem of in- tegrated design of guidance and control systems for au- tonomous vehicles (AVs). In fact, it introduces a new methodology for integrated design of guidance and control for such vehicles. The methodology proposed leads to an efficient procedure for the design of controllers for AVs to accurately track reference trajectories defined in an iner- tia! reference frame. The paper illustrates the application of this procedure on the design of a tracking controller for the Unmanned Air Vehicle Bluebird. The design phase is summarized, and the performance of the resulting con- troller is assessed in simulation using dynamic models of the vehicle and its sensor suite.

Scheduling resources in multi-user, heterogeneous, computing environments with SmartNet

Abstract: It is increasingly common for computer users to have access to several computers on a network, and hence to be able to execute many of their tasks on any of several computers. The choice of which computers execute which tasks is commonly determined by users based on a knowledge of computer speeds for each task and the current load on each computer. A number of task scheduling systems have been developed that balance the load of the computers on the network, but such systems tend to minimize the idle time of the computers rather than minimize the idle time of the users. The paper focuses on the benefits that can be achieved when the scheduling system considers both the computer availabilities and the performance of each task on each computer. The SmartNet resource scheduling system is described and compared to two different resource allocation strategies: load balancing and user directed assignment. Results are presented where the operation of hundreds of different networks of computers running thousands of different mixes of tasks are simulated in a batch environment. These results indicate that, for the computer environments simulated, SmartNet outperforms both load balancing and user directed assignments, based on the maximum time users must wait for their tasks to finish.

Sensitivity Analysis and the Expected Value of Perfect Information

Abstract: Measures of decision sensitivity that have been applied to medical decision problems were examined. Traditional threshold proximity methods have recently been supple mented by probabilistic sensitivity analysis, and by entropy-based measures of sen sitivity. The authors propose a fourth measure based upon the expected value of perfect information (EVPI), which they believe superior both methodologically and prag matically. Both the traditional and the newly suggested sensitivity measures focus en tirely on the likelihood of decision change without attention to corresponding changes in payoff, which are often small. Consequently, these measures can dramatically over state problem sensitivity. EVPI, on the other hand, incorporates both the probability of a decision change and the marginal benefit of such a change into a single measure, and therefore provides a superior picture of problem sensitivity. To lend support to this contention, the authors revisit three problems from the literature and compare the r...

Measurements of the Proton and Deuteron Spin Structure Functions g1 and g2

Abstract: Measurements are reported of the proton and deuteron spin structure functions ${g}_{1}^{p}$ and ${g}_{1}^{d}$ at beam energies of 29.1, 16.2, and 9.7 GeV, and ${g}_{2}^{p}$ and ${g}_{2}^{d}$ at a beam energy of 29.1 GeV. The integrals ${\ensuremath{\Gamma}}_{p}={\ensuremath{\int}}_{0}^{1}{g}_{1}^{p}{(x,Q}^{2})dx$ and ${\ensuremath{\Gamma}}_{d}={\ensuremath{\int}}_{0}^{1}{g}_{1}^{d}{(x,Q}^{2})dx$ were evaluated at fixed ${Q}^{2}=3(\mathrm{GeV}{/c)}^{2}$ using the full data set to yield ${\ensuremath{\Gamma}}_{p}=0.132\ifmmode\pm\else\textpm\fi{}0.003(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.009(\mathrm{syst})$ and ${\ensuremath{\Gamma}}_{d}=0.047\ifmmode\pm\else\textpm\fi{}0.003\ifmmode\pm\else\textpm\fi{}0.006.$ The ${Q}^{2}$ dependence of the ratio ${g}_{1}{/F}_{1}$ was studied and found to be small for ${Q}^{2}g1(\mathrm{GeV}{/c)}^{2}.$ Within experimental precision the ${g}_{2}$ data are well described by the twist-2 contribution, ${g}_{2}^{\mathrm{WW}}.$ Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry ${A}_{2}$ was measured and found to be significantly smaller than the positivity limit $\sqrt{R}$ for both proton and deuteron targets. ${A}_{2}^{p}$ is found to be positive and inconsistent with zero. Measurements of ${g}_{1}$ in the resonance region show strong variations with $x$ and ${Q}^{2},$ consistent with resonant amplitudes extracted from unpolarized data. These data allow us to study the ${Q}^{2}$ dependence of the integrals ${\ensuremath{\Gamma}}_{p}$ and ${\ensuremath{\Gamma}}_{n}$ below the scaling region.

The relative performance of various mapping algorithms is independent of sizable variances in run-time predictions

Abstract: The author studies the performance of four mapping algorithms. The four algorithms include two naive ones: opportunistic load balancing (OLB), and limited best assignment (LBA), and two intelligent greedy algorithms: an O(nm) greedy algorithm, and an O(n/sup 2/m) greedy algorithm. All of these algorithms, except OLB, use expected run-times to assign jobs to machines. As expected run-times are rarely deterministic in modern networked and server based systems, he first uses experimentation to determine some plausible run-time distributions. Using these distributions, he next executes simulations to determine how the mapping algorithms perform. Performance comparisons show that the greedy algorithms produce schedules that, when executed, perform better than naive algorithms, even though the exact run-times are not available to the schedulers. He concludes that the use of intelligent mapping algorithms is beneficial, even when the expected time for completion of a job is not deterministic.

Observations of highly nonlinear internal solitons over the continental shelf

Abstract: Surface disturbances caused by strong, near-surface internal waves are widely seen in coastal regions as bands of slick and rough water propagating shoreward. These surface slicks are typically manifestations of optical and radar backscatter properties above internal solitons, and have strong surface current pulses associated with them. During a recent experiment studying coastal internal waves, extremely strong solitary internal wave packets were observed over a three week period on a very shallow and strongly stratified pycnocline off Northern Oregon. During periods of strongest tidal forcing, solitons were consistently observed on the leading edge of a semidiurnal internal tide bore, with pycnocline displacements up to 25m downward from a 7m initial depth in the first few solitons. The extreme nonlinearity of these internal waves is believed to be unique in ocean observations. This note characterizes these highly nonlinear Solitary Internal Waves (SIW) and presents a second order KdV model which reproduces the form of the displacements, and the small change in soliton width with amplitude predicted by this model.

The impact of a new emotional self-management program on stress, emotions, heart rate variability, DHEA and cortisol

Abstract: This study examined the effects on healthy adults of a new emotional self-management program, consisting of two key techniques, “Cut-Thru” and the “Heart Lock-In.” These techniques are designed to eliminate negative thought loops and promote sustained positive emotional states. The hypotheses were that training and practice in these techniques would yield lowered levels of stress and negative emotion and cortisol, while resulting in increased positive emotion and DHEA levels over a one-month period. In addition, we hypothesized that increased coherence in heart rate variability patterns would be observed during the practice of the techniques.

Retrieval of aerosol optical depth over land using two-angle view satellite radiometry during TARFOX

Abstract: A new aerosol optical depth retrieval algorithm is presented that uses the two-angle view capability of the Along Track Scanning Radiometer 2 (ATSR-2). By combining the two-angle view and the spectral information this so-called dual view algorithm separates between aerosol and surface contributions to the top of the atmosphere radiance. First validation of the dual view algorithm was performed during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX), which was conducted at the mid-Atlantic coast of the United States in July 1996. The satellite retrieved spectral aerosol optical depth is in good agreement with the aerosol optical depth from ground-based Sun/sky radiometers in three out of four cases. This shows the potential of aerosol retrieval over land using two-angle view satellite radiometry. Copyright 1998 by the American Geophysical Union.

Probabilistic noninterference in a concurrent language

Abstract: The authors previously give a type system that guarantees that well-typed multi-threaded programs are possibilistically noninterfering. If thread scheduling is probabilistic, however, then well-typed programs may have probabilistic timing channels. They describe how they can be eliminated without making the type system more restrictive. They show that well-typed concurrent programs are probabilistically noninterfering if every total command with a high guard executes atomically. The proof uses the concept of a probabilistic state of a computation, following the work of Kozen (1981).

Freshening of the upper ocean in the Arctic: Is perennial sea ice disappearing?

Abstract: During the Surface Heat Budget of the Arctic (SHEBA) deployment in October, 1997, multiyear ice near the center of the Beaufort Gyre was anomalously thin The upper ocean was both warmer and less saline than in previous years The salinity deficit in the upper 100 m, compared with the same region during the Arctic Ice Dynamics Joint Experiment (AIDJEX) in 1975, is equivalent to surface input of about 24 m of fresh water Heat content has increased by 67 MJ m−2 During AIDJEX the change in salinity over the melt season implied melt equivalent to about 08 m of fresh water As much as 2 m of freshwater input may have occurred during the 1997 summer, possibly resulting from decreased ice concentration from changes in atmospheric circulation early in the summer , in the classic albedo-feedback scenario Unchecked, the pattern could lead to a significantly different sea-ice regime in the central Arctic

Observations of the Internal Tide in Monterey Canyon

Abstract: Data from two shipboard experiments in 1994, designed to observe the semidiurnal internal tide in Monterey Canyon, reveal semidiurnal currents of about 20 cm s21, which is an order of magnitude larger than the estimated barotropic tidal currents. The kinetic and potential energy (evidenced by isopycnal displacements of about 50 m) was greatest along paths following the characteristics calculated from linear theory. These energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of Monterey Bay. Energy propagated shoreward during the April experiment (ITEX1), whereas a standing wave, that is, an internal seiche, was observed in October (ITEX2). The difference is attributed to changes in stratification between the two experiments. Higher energy levels were present during ITEX1, which took place near the spring phase of the fortnightly (14.8 days) cycle in sea level, while ITEX2 occurred close to the neap phase. Further evidence of phase-locking between the surface and internal tides comes from monthlong current and temperature records obtained near the canyon head in 1991. The measured ratio of kinetic to potential energy during both ITEX1 and ITEX2 was only half that predicted by linear theory for freely propagating internal waves, probably a result of the constraining effects of topography. Internal tidal energy dissipation rate estimates for ITEX1 range from 1.3 3 1024 to 2.3 3 1023 Wm 23, depending on assumptions made about the effect of canyon shape on dissipation. Cross-canyon measurements made during ITEX2 reveal vertical transport of denser water from within the canyon up onto the adjacent continental shelf.

Spatial Orientation and Wayfinding in Large-Scale Virtual Spaces: An Introduction

Abstract: ‘‘I have coasted this lake, in search of skins, afore the war, and have been here already; not at this very spot, for we landed yonder, where you may see the oak that stands above the cluster of hemlocks.’’ ‘‘How, Pathfinder, can you remember all these trifles so accurately?’’ ‘‘These are our streets and houses—our churches and palaces. Remember them, indeed! . . .’’ The Pathfinder, James Fenimore Cooper (1840)

Defensive democratization in Jordan.

Abstract: Jordans political-liberalization program initiated in 1989 represents the longest sustained such opening in the Arab world today. During this time Jordan has held three national parliamentary elections enacted a number of liberalizing laws removed many restrictions on the press and minimized the role that the security services or mukhabarat play in repressing opposition. Moreover the liberalization program has survived a number of severe challenges including the second Gulf War and the subsequent loss of Jordans major regional trading partner Iraq; the implementation of a difficult domestic austerity program; and the conclusion of a controversial peace treaty with Israel. Democratization in Jordan has not followed the same path as the recent democratic transitions in East Asia Latin America and Eastern Europe. By closely examining Jordans program of political liberalization since 1989 I will argue that the process is best understood as a series of pre-emptive measures designed to maintain elite privilege in Jordan while limiting the appeal of more fundamental political change. The regime has skillfully managed and directed a process that has throughout protected the four pillars of power in Jordan: the monarchy and its coterie the army and security services wealthy business elites and East Bank tribal leaders. It has simultaneously sought to undermine the only social force legally able to disrupt key regime policies the Islamist Muslim Brotherhood and its political party the Islamic Action Front (IAF). In other words uncertain about its ability to survive a deepening crisis the regime undertook sufficient reform to assure its political longevity but without altering the core structures of power in Jordan. I term this "defensive democratization." The concept of defensive democratization provides an additional nuance to our understanding of democratic transitions more generally by focusing attention on pre-emptive liberalizing strategies available to rentier states. This essay concludes by arguing that the strategy of defensive democratization in Jordan may not be able to withstand the likely political volatility in and Islamization of Palestinian politics in Jordan. (excerpt)

Bamboo-a portable system for dynamically extensible, real-time, networked, virtual environments

Abstract: Bamboo is a portable system supporting real-time, networked, virtual environments. Unlike previous efforts, this design focuses on the ability of the system to dynamically configure itself without explicit user interaction, allowing applications to take on new functionality after execution. In particular, this framework facilitates the discovery of virtual environments on the network at runtime. Fundamentally, Bamboo offers a compatible set of mechanisms needed for a wide variety of real-time, networked applications. Also included is a particular combination of these mechanisms supporting a dynamically extensible runtime environment. This paper serves as a general introduction to Bamboo. It describes the system's architecture, implementation and future directions. It also shows how the system can facilitate the rapid development of robust applications by promoting code reuse via community-wide exchange.

Scheduling short-term marine transport of bulk products

Abstract: A multinational company uses a personal computer to schedule a fleet of coastal tankers and barges transporting liquid bulk products among plants, distribution centres (tank farms), and industrial customers. A simple spreadsheet interface cloaks a sophisticated optimization-based decision support system and makes this system useable via a varity of natural languages. The dispatchers, whose native language is not English, and some of whom presumably speak no English at all, communicate via the spreadsheet, and view recommended schedules displayed in Gantt charts both internationally familiar tools. Inside the spreadsheet, a highly detailed simulation can generate every feasible alternate vessel employment schedule, and an integer linear set partitioning model selects one schedule for each vessel so that all loads and deliveries are completed at minimal cost while satisfying all operational requirements. The optimized fleet employment schedule is displyed graphically with hourly time resolution over a plann...

Unified formulation of robotic systems with holonomic and nonholonomic constraints

Abstract: Many robotic systems are subject to nonholonomic as well as holonomic constraints. Rolling contact between two rigid bodies is a typical example of such a system. In the study, a unified state space formulation of robotic systems subject to both holonomic and nonholonomic constraints is presented. The position-level holonomic constraints are first replaced by a set of velocity-level constraint equations that asymptotically converge to the original holonomic constraints. Having represented both holonomic and nonholonomic constraints in a common form, a state space representation of the constrained systems is then developed. A numerical algorithm for implementing the state space representation is also described. The proposed formulation eliminates the need to solve holonomic constraints either analytically or numerically, and ensures that holonomic constraints are always satisfied, particularly in computer simulations. The formulation makes it possible to treat systems with holonomic constraints, with nonholonomic constraints, or with both holonomic and nonholonomic constraints in a unified framework. Two examples are presented to illustrate the application of the unified formulation.

Three-tiered interest management for large-scale virtual environments

Abstract: In the past there have been several approaches taken. In NPSNET [1], the world is broken into hexagons, each representing a multicast group. Each entity sends state information to a multicast group corresponding to the local hexagon it is in, while at the same time subscribing to many surrounding hexagons via their multicast groups. This approach, while not exact, works well when entities are distributed evenly within the virtual environment, but fails if all entities are clumped within the same cell.

Navigating in natural environments: a virtual environment training transfer study

Abstract: The ability to use virtual environments as either an abstraction of a space, similar to a map, or as a simulation of the space itself has suggested to many that it would be a useful tool in terrain familiarization of unknown environments. Up to this point, all research in this area has focused on building interiors and urban environments which are significantly different from natural environments in terms of navigation cues and useful wayfinding techniques. The experiment we present uses a virtual environment, as compared to a map only or real-world conditions on navigation tasks in a natural environment. We show that navigation ability is more important to performance than the training method, with the virtual environment being most effective for intermediate orienteers as compared to advanced or beginner orienteers.

Wind-Driven South China Sea Deep Basin Warm-Core/Cool-Core Eddies

Abstract: The formation of the South China Sea (SCS) deep basin warm-core and cool-core eddies was studied numerically using the Princeton Ocean Model (POM) with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography. Numerical integration was divided into pre-experimental and experimental stages. During the preexperimental stage, we integrated the POM model for three years from zero velocity and April temperature and salinity climatological fields with climatological monthly mean wind stresses, restoring type surface salt and heat fluxes, and observational oceanic inflow/outflow at the open boundaries. During the experimental stage, we integrated the POM model for another 16 months under three different conditions: one control and two sensitivity runs (no-wind and no lateral transport). We take the fields of the last 12 months for analysis. The simulation under control run agrees well with earlier observational studies on the South China Sea surface thermal variabilities. In addition, the sensitivity study further confirms that the wind effect is the key factor for generation of the SCS deep basin warm/cool eddy and that the lateral boundary forcing is the major factor for the formation of the strong western boundary currents, especially along the southeast Chinese coast during both summer and winter monsoon seasons.

Distributed and Parallel Computing

Abstract: The state-of-the-art in high-performance concurrent computing -- theory and practice.-- Detailed coverage of the growing integration between parallel and distributed computing.-- Advanced approaches for programming distributed, parallel systems -- and adapting traditional sequential software.-- Creating a Parallel Virtual Machine (PVM) from networked, heterogeneous systems.This is the most up-to-date, comprehensive guide to the rapidly changing field of distributed and parallel systems.The book begins with an introductory survey of distributed and parallel computing: its rationale and evolution. It compares and contrasts a wide variety of approaches to parallelism, from distributed computer networks, to parallelism within processors (such as Intel's MMX), to massively parallel systems. The book introduces state-of-the-art methods for programming parallel systems, including approaches to reverse engineering traditional sequential software. It includes detailed coverage of the critical scheduling problem, compares multiple programming languages and environments, and shows how to measure the performance of parallel systems. The book introduces the Parallel Virtual Machine (PVM) system for writing programs that run on a network of heterogenous systems; the new Message Passing Interface (MPI-2)standard; and finally, the growing role of Java in writing distributed and parallel applications.

Highlights of Coastal Waves 1996

Abstract: Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address ...