Showing papers by "Naval Postgraduate School published in 1997"

Current issues in recrystallization: a review

Abstract: The current understanding of the fundamentals of recrystallization is summarized. This includes understanding the as-deformed state. Several aspects of recrystallization are described: nucleation and growth, the development of misorientation during deformation, continuous, dynamic, and geometric dynamic recrystallization, particle effects, and texture. This article is authored by the leading experts in these areas. The subjects are discussed individually and recommendations for further study are listed in the final section.

The omni-directional treadmill: a locomotion device for virtual worlds

Abstract: The Omni-Directional Treadmill (ODT) is a revolutionary device for locomotion in large-scale virtual environments. The device allows its user to walk or jog in any direction of travel. It is the third generation in a series of devices built for this purpose for the U.S. Army’s Dismounted Infantry Training Program. We first describe the device in terms of its construction and operating characteristics. We then report on an analysis consisting of a series of locomotion and maneuvering tasks on the ODT. We observed user motions and system responses to those motions from the perspective of the user. Each task is described in terms of what causes certain motions to trigger unpredictable responses causing loss of balance or at least causing the user to become consciously aware of their movements. We conclude that the two primary shortcomings in the ODT are its tracking system and machine control mechanism for centering the user on the treads.

From Preponderance to Offshore Balancing: America's Future Grand Strategy

Abstract: I T h e Soviet Union's collapse transformed the international system dramatically, but there has been no corresponding change in U.S. grand strategy. In terms of ambitions, interests, and alliances, the United States is following the same grand strategy it pursued from 1945 until 1991: that of preponderance.' Whether this strategy will serve U.S. interests in the early twenty-first century is problematic. Hence, in this article my purpose is to stimulate a more searching debate about future U.S. grand strategic options.2 To accomplish this, I compare the strategy of preponderance to a proposed alternative grand strategy: offshore balancing.

A Type-Based Approach to Program Security

Abstract: This paper presents a type system which guarantees that well-typed programs in a procedural programming language satisfy a noninterference security property. With all program inputs and outputs classified at various security levels, the property basically states that a program output, classified at some level, can never change as a result of modifying only inputs classified at higher levels. Intuitively, this means the program does not “leak” sensitive data. The property is similar to a notion introduced years ago by Goguen and Meseguer to model security in multi-level computer systems [7]. We also give an algorithm for inferring and simplifying principal types, which document the security requirements of programs.

An overview of the 1995 SWARM shallow-water internal wave acoustic scattering experiment

Abstract: An overview is given of the July-August 1995 SWARM shallow-water internal wave acoustic scattering experiment. This experiment studied both acoustic propagation through and scattering by the linear and nonlinear internal waves found on the Mid-Atlantic Bight continental shelf, as well as the physical oceanography of the internal wavefield. In order that their goal of explaining the nature of the acoustic scattering should not be hindered by incomplete environmental knowledge, numerous instruments, both ship-deployed and moored, measured the acoustics, geophysics, and oceanography. In this paper, the authors show some of the results from the first year's analysis of the environmental and acoustic data. The environmental measurements, which are a key input to the analyses of the acoustic data, are given slightly more emphasis at this point in time. Some of the more interesting oceanographic, geophysical, and acoustical results the authors present are: evidence for the dominance of the lee-wave mechanism for soliton production, evidence for the "solibore internal tide" the "dnoidal wave" description of solitons, the inversion of chirp sonar data for bottom properties, propagation loss extraction from air-gun data, and the intensity and travel-time fluctuations seen in propagating acoustic normal modes. Directions for future research are outlined.

Mesoscale Interactions in Tropical Cyclone Genesis

Abstract: With the multitude of cloud clusters over tropical oceans, it has been perplexing that so few develop into tropical cyclones. The authors postulate that a major obstacle has been the complexity of scale interactions, particularly those on the mesoscale, which have only recently been observable. While there are well-known climatological requirements, these are by no means sufficient. A major reason for this rarity is the essentially stochastic nature of the mesoscale interactions that precede and contribute to cyclone development. Observations exist for only a few forming cases. In these, the moist convection in the preformation environment is organized into mesoscale convective systems, each of which have associated mesoscale potential vortices in the midlevels. Interactions between these systems may lead to merger, growth to the surface, and development of both the nascent eye and inner rainbands of a tropical cyclone. The process is essentially stochastic, but the degree of stochasticity can be reduced by the continued interaction of the mesoscale systems or by environmental influences. For example a monsoon trough provides a region of reduced deformation radius, which substantially improves the efficiency of mesoscale vortex interactions and the amplitude of the merged vortices. Further, a strong monsoon trough provides a vertical wind shear that enables long-lived midlevel mesoscale vortices that are able to maintain, or even redevelop, the associated convective system. The authors develop this hypothesis by use of a detailed case study of the formation of Tropical Cyclone Oliver observed during TOGA COARE (1993). In this case, two dominant mesoscale vortices interacted with a monsoon trough to separately produce a nascent eye and a major rainband. The eye developed on the edge of the major convective system, and the associated atmospheric warming was provided almost entirely by moist processes in the upper atmosphere, and by a combination of latent heating and adiabatic subsidence in the lower and middle atmosphere. The importance of mesoscale interactions is illustrated further by brief reference to the development of two typhoons in the western North Pacific.

Eliminating covert flows with minimum typings

Abstract: A type system is given that eliminates two kinds of covert flows in an imperative programming language. The first kind arises from nontermination and the other from partial operations that can raise exceptions. The key idea is to limit the source of nontermination in the language to constructs with minimum typings, and to evaluate partial operations within expressions of try commands which also have minimum typings. A mutual progress theorem is proved that basically states that no two executions of a well-typed program can be distinguished on the basis of nontermination versus abnormal termination due to a partial operation. The proof uses a new style of programming language semantics which we call a natural transition semantics.

Shape-based tracking of left ventricular wall motion

Abstract: An approach for tracking and quantifying the nonrigid, nonuniform motion of the left ventricular (LV) endocardial wall from two-dimensional (2-D) cardiac image sequences, on a point-by-point basis over the entire cardiac cycle, is presented. Given a set of boundaries, motion computation involves first matching local segments on one contour to segments on the next contour in the sequence using a shape-based strategy. Results from the match process are incorporated with a smoothness term into an optimization functional. The global minimum of this functional is found, resulting in a smooth flow field that is consistent with the match data. The computation is performed for all pairs of frames in the temporal sequence and equally sampled points on one contour are tracked throughout the sequence, resulting in a composite flow field over the entire sequence. Two perspectives on characterizing the optimization functional are presented which result in a tradeoff resolved by the confidence in the initial boundary segmentation. Experimental results for contours derived from diagnostic image sequences of three different imaging modalities are presented. A comparison of trajectory estimates with trajectories of gold-standard markers implanted in the LV wall are presented for validation. The results of this comparison confirm that although cardiac motion is a three-dimensional (3-D) problem, two-dimensional (2-D) analysis provides a rich testing ground for algorithm development.

Formal methods: promises and problems

Abstract: Successfully applying formal methods to software development promises to move us closer to a true engineering discipline. The authors offer suggestions for overcoming the problems that have hindered the use of formal methods thus far.

Decision support on demand: Emerging electronic markets for decision technologies

Abstract: For the individual or organization wishing to employ a scientific approach in solving decision problems, there is a plethora of relevant concepts, methods, models, and software. Yet, relative to their potential or to peer software such as database technologies, decision technologies are little used in real-world decision making. We argue that at least some of the problems that restrict the use of decision technologies are rooted in the use of conventional market mechanisms to distribute them. We propose the development of electronic markets for decision technologies, and explain how features of modem information networks offer a solution to these problems. We present a framework for comparing alternative electronic markets for decision technologies, survey and analyze several such emerging markets, and present some details on our own research initiative — DecisionNet. A distinctive feature of DecisionNet is that it consists of software agents that perform — at the market level —; functions (such as user accounting, billing and setting up the interface to a decision technology) that would otherwise need to be developed for each consumer, provider, or technology.

Phase Transition of the El Niño–Southern Oscillation: A Stationary SST Mode

Abstract: A stationary SST mode is proposed to understand the physical mechanisms responsible for the phase transition of the El Nino-Southern Oscillation. This stationary SST mode differs from the original delayed oscillator mode and the slow SST mode in the sense that it considers both balanced and unbalanced thermocline depth variations and does not take into account the zonal propagation of SST. Within this mode, the Walker circulation acts as a positive feedback mechanism to amplify and maintain an existing interannual SST anomaly, whereas the Hadley circulation acts as a negative feedback mechanism that dismisses the original anomaly and causes the phase shift from a warm (cold) to a cold (warm) episode. The key to the cause of interannual oscillations in the stationary SST mode lies in the zonal-mean thermocline depth variation that is not in equilibrium with the winds. Because of the nonequilibrium, this part of the thermocline depth anomaly tends to have a phase lag with the wind (or SST) anomaly and therefore holds a key for the interannual oscillation. The zonally asymmetric part of the thermocline depth anomaly, on the other hand, is always in Sverdrup balance with the winds. Such a phase relationship agrees well with observations and with GCM simulations. The stationary SST mode strongly depends on the basin width, on the air-sea coupling strength, and on the seasonal-cycle basic state. For a reasonable parameter regime, it depicts an interannual oscillation with a period of 2-7 years. This stationary SST mode is also season dependent: it has a maximum growth rate during the later part of the year and a negative growth rate during the northern spring, which may explain the occurrence of the mature phases of the El Nino in the northern winter and a rapid drop of the lagged correlation of the Southern Oscillation index in the boreal spring.

IEEE Standard For A Software Quality Metrics Methodology Revision And Reaffirmation

Abstract: The IEEE Standard 1061 is due for revision and reaffirmation. This workshop will give participants an opportunity to propose possible modifications to the standard and to comment on the modifications proposed by the workshop leaders. The workshop leaders will organize a set of issues to provide a framework for discussion. The results of this workshop will become one of the inputs to revising the standard for the reaffirmation ballot.

A wall-following method for escaping local minima in potential field based motion planning

Abstract: A wall-following method for escaping local minima encountered by the potential field based motion planning method used in real-time obstacle avoidance is presented. The new algorithm switches to a wall-following control mode when the robot falls into a local minimum. A switches back to the potential field guided control mode when a certain condition is met. A simple switch condition derived from monitoring the distance from the robot's position to the goal position is shown to be effective in escaping local minima in typical laboratory environments. A provision is built into the algorithm, allowing the robot to follow a wall in a different direction if the first attempt fails. The new algorithm is implemented on a Nomad 200 mobile robot. Simulation and experimental results are presented to demonstrate the usefulness of the method.

Line and circle formation of distributed physical mobile robots

Abstract: The formation problem of distributed mobile robots was studied in the literature for idealized robots. Idealized robots are able to instantaneously move in any directions, and are equipped with perfect range sensors. In this study, we address the formation problem of distributed mobile robots that are subject to physical constraints. Mobile robots considered in this study have physical dimensions and their motions are governed by physical laws. They are equipped with sonar and infrared range sensors. The formation of lines and circles is investigated in detail. It is demonstrated that line and circle algorithms developed for idealized robots do not work well for physical robots. New line and circle algorithms, with consideration of physical robots and sensors, are presented and validated through extensive simulations. © 1997 John Wiley & Sons, Inc.

Reliability modeling for safety-critical software

Abstract: Software reliability predictions can increase trust in the reliability of safety critical software such as the NASA Space Shuttle Primary Avionics Software System (Shuttle flight software). This objective was achieved using a novel approach to integrate software-safety criteria, risk analysis, reliability prediction, and stopping rules for testing. This approach applies to other safety-critical software. The authors cover only the safety of the software in a safety-critical system. The hardware and human-operator components of such systems are not explicitly modeled nor are the hardware and operator-induced software failures. The concern is with reducing the risk of all failures attributed to software. Thus, safety refers to software-safety and not to system-safety. By improving the software reliability, where the reliability measurements and predictions are directly related to mission and crew safety, they contribute to system safety. Software reliability models provide one of several tools that software managers of the Shuttle flight software are using to assure that the software meets required safety goals. Other tools are inspections, software reviews, testing, change control boards, and perhaps most important-experience and judgement.

Virtual reality transfer protocol (VRTP) design rationale

Abstract: The capabilities of the Virtual Reality Modeling Language (VRML) permit building large-scale virtual environments (LSVEs) using the Internet and the World Wide Web. However, the underlying network support provided by the hypertext transfer protocol (http) is insufficient for LSVEs. Additional capabilities for lightweight peer-to-peer communications and network monitoring need to be combined with the client-server capabilities of http. To accomplish this task, we present a detailed design rationale for the virtual reality transfer protocol (VRTP). VRTP is designed to support VRML in the same manner as http was designed to support HTML. Since VRTP must be highly optimized on individual desktops and across the Internet, a Cyberspace Backbone (CBone) is also needed for VRTP development and testing. VRTP appears to be a necessary next step in the deployment of all-encompassing interactive internetworked 3D worlds.

Optimizing Submarine Berthing with a Persistence Incentive

Abstract: Submarine berthing plans reserve mooring locations for inbound U.S. Navy nuclear submarines prior to their port entrance. Once in port, submarines may be shifted to different berthing locations to allow them to better receive services they require or to make way for other shifted vessels. However, submarine berth shifting is expensive, labor inten- sive, and potentially hazardous. This article presents an optimization model for submarine berth planning and demonstrates it with Naval Submarine Base, San Diego. After a berthing plan has been approved and published, changed requests for services, delays, and early arrival of inbound submarines are routine events, requiring frequent revisions. To encourage trust in the planning process, the effect on the solution of revisions in the input is kept small by incorporating a persistence incentive in the optimization model. q 1997 John Wiley & Sons, Inc. Naval Research Logistics 44: 301 - 318, 1997. Although the Cold War has ended, United States Navy submarines remain very capable and effective ships of war: A smaller number of submarines operated from fewer submarine bases will continue to play a significant role in national defense. The wise use of time and resources while submarines are in port will improve the state of readiness of a smaller fleet. While in port, a submarine completes preventive and corrective maintenance, replenishes stores, and conducts training and certification tests to maintain high material and personnel readiness. Ideally, a submarine in port should devote its time exclusively to these activities. However, submarines frequently spend time shifting berths. Some shifts are necessary and some are not. Services such as ordnance loading and the use of special maintenance equip- ment require that a submarine be moored at a specific location. During periodic maintenance upkeep, personnel from a submarine tender assist the submarine crew, and berthing near the tender is preferable. During training, inspection, and other periods, it is desirable to berth closer to shore, near squadron offices and training facilities. When conditions permit,

Measuring user satisfaction in an outsourcing environment

Abstract: Outsourcing is a term that encompasses a variety of approaches to contracting for information technology (IT) services. It is defined as a transfer of any particular IT activity or a combination of activities from an organization using them to one or more external service providers. IT outsourcing leads to significant changes in the management processes of the IT organization. For example, while IT managers have always had the responsibility for ensuring that users within their organization maintain a high degree of satisfaction, they now have to monitor the quality of service, even though they are no longer the providers of the service. This gets further complicated when only some parts of the IT functions are outsourced while others are provided by an internal IT department. Thus, developing a comprehensive set of measurement tools and mechanisms is an important step toward monitoring the quality of service provided by both an outside source and an IT department. This paper investigates the usefulness of an existing user-satisfaction measurement instrument for identifying problem areas in a multiprovider outsourcing environment, where an external service provider and an internal IT department each has different roles in the system. It discusses the rationale for measuring user satisfaction and the instruments to carry out the measurement procedure. It reports the results of implementing and testing a previously developed, documented, and validated user-satisfaction instrument in an outsourcing environment and draws practical conclusions from the results.

Models of Tropical Cyclone Wind Distribution and Beta-Effect Propagation for Application to Tropical Cyclone Track Forecasting

Abstract: A model of the tangential wind speed in the outer regions of tropical cyclones is proposed based on approximate conservation of angular momentum. The purpose is to derive an operationally useful model of the beta-effect propagation (BEP), which barotropic numerical models have shown to be primarily related to the outer wind structure. The functional dependence of the predicted BEP speeds over a range of latitudes and the radii Ro at which the cyclonic winds are reduced to zero is determined from dimensional analysis. Given the empirical nature of the profile and imprecise estimates of Ro, only four tropical cyclone sizes or outer wind structures are defined based on the magnitude of the BEP speeds and their relative contributions to the total motion. A second aspect of BEP from the barotropic model integrations is the development of a trailing anticyclone to the southeast of the tropical cyclone as a result of Rossby wave dispersion. The four tropical cyclone size categories or outer wind structu...

On a stochastic knapsack problem and generalizations

Abstract: We consider an integer stochastic knapsack problem (SKP) where the weight of each item is deterministic, but the vector of returns for the items is random with known distribution. The objective is to maximize the probability that a total return threshold is met or exceeded. We study several solution approaches. Exact procedures, based on dynamic programming (DP) and integer programming (IP), are developed for returns that are independent normal random variables with integral means and variances. Computation indicates that the DP is significantly faster than the most efficient algorithm to date. The IP is less efficient, but is applicable to more general stochastic IPs with independent normal returns. We also develop a Monte Carlo approximation procedure to solve SKPs with general distributions on the random returns. This method utilizes upper- and lower-bound estimators on the true optimal solution value in order to construct a confidence interval on the optimality gap of a candidate solution.

Sixth-order difference scheme for sigma coordinate ocean models

Abstract: How to reduce the horizontal pressure gradient error is a key issue of using σ-coordinate ocean models, especially of using primitive equation models for coastal regions. The error is caused by the splitting of the horizontal pressure gradient term into two parts and the subsequent incomplete cancellation of the truncation errors of those parts. Due to the fact that the higher the order of the difference scheme, the less the truncation error and the more complicated the computation, a sixth-order difference scheme for the σ-coordinate ocean models is proposed in order to reduce error without increasing complexity of the computation. After the analytical error estimation, the Semi-spectral Primitive Equation Model is used to demonstrate the benefit of using this scheme. The stability and accuracy are compared with those of the second-order and fourth-order schemes in a series of calculations of unforced flow in the vicinity of an isolated seamount. The sixth-order scheme is shown to have error red...

Measurement of the proton and deuteron spin structure function g1 in the resonance region

Abstract: We have measured the proton and deuteron spin structure functions g[sup p][sub 1] and g[sup d][sub 1] in the region of the nucleon resonances for W2 < 5GeV2 and Q2(similar, equals)0.5 and Q2(similar, equals)1.2GeV2 by inelastically scattering 9.7 GeV polarized electrons off polarized 15NH3 and 15ND3 targets. We observe significant structure in g[sup p][sub 1] in the resonance region. We have used the present results, together with the deep-inelastic data at higher W2, to extract Gamma (Q2)(equivalent)01 g1(x,Q2)dx. This is the first information on the low-Q2 evolution of Gamma toward the Gerasimov-Drell-Hearn limit at Q2 = 0.

Activity Delay in Stochastic Project Networks

Abstract: In this paper we deal with a stochastic project network and consider the impact of activity delay to maximize the expected present value of a project. It is shown that in certain situations, delaying the onset of an activity from its earliest start time can indeed increase the present value of a project due to the postponing of associated negative cash flows. Furthermore, a project that could otherwise be rejected negative expected present value may become profitable positive expected present value due to delay. We demonstrate that even activities on the critical path, as determined by each activity's expected duration, may be profitably delayed. Optimal and approximate procedures are developed to determine the amount of delay of the various activities.

Lake‐induced atmospheric circulations during BOREAS

Abstract: Lake-induced atmospheric circulations over three lakes ranging from 3 to 10 km width are analyzed using data from three aircraft during the 1994 Boreal Ecosystem-Atmosphere Study (BOREAS). A well-defined divergent lake breeze circulation is observed over all three lakes during the day. Under light wind conditions, the lake breeze is not very sensitive to the water temperature, and the strength of the divergence over the lake decreases with increasing lake size. The boundary-layer development over the surrounding land can be very important for generating a horizontal pressure difference which drives the lake breeze. Diurnal and seasonal variations of lake breezes are investigated on the basis of repeated passes from the different aircraft at different altitudes from late spring to early fall of 1994. The lake breeze divergence increases with time during the day and reaches a maximum around 1300 LST. The latent heat flux over 10-km-wide Candle Lake increases steadily from spring to fall as the lake temperature increases. The latent heat flux over the land reaches a maximum during the summer due to evapotranspiration. The lake effect on area-averaged fluxes sometimes leads to a negative heat transfer coefficient for an averaging scale of several times the lake width.

Use of the symmetrical number system in resolving single-frequency undersampling aliases

Abstract: The relationship between the discrete Fourier transform (DFT) and the symmetrical number system (SNS) is examined as a means of resolving single-frequency undersampling aliases (f>f/sub s//2). It is shown that the DFT naturally encodes the frequency information of a signal in a format that is in the same form as the SNS. Consequently, aliases that result from undersampling a signal can be resolved exactly using r/spl ges/2 channels. To demonstrate the concept, two- and three-channel examples are presented. Using the SNS properties of the DFT, the undersampling aliases can be easily resolved to a much greater extent than previously possible.

Software metrics model for integrating quality control and prediction

Abstract: A model is developed that is used to validate and apply metrics for quality control and quality prediction, with the objective of using metrics as early indicators of software quality problems. Metrics and quality factor data from the Space Shuttle flight software are used as an example. Our approach is to integrate quality control and prediction in a single model and to validate metrics with respect to a quality factor. Boolean discriminant functions (BDFs) were developed for use in the quality control and quality prediction process. BDFs provide good accuracy for classifying low quality software because they include additional information for discriminating quality: critical values. Critical values are threshold values of metrics that are used to either accept or reject modules when the modules are inspected during the quality control process. A series of nonparametric statistical methods is also used in the method presented. It is important to perform a marginal analysis when making a decision about how many metrics to use in the quality control and prediction process. We found that certain metrics are dominant in their effects on classifying quality and that additional metrics are not needed to accurately classify quality. This effect is called dominance. Related to the property of dominance is the property of concordance, which is the degree to which a set of metrics produces the same result in classifying software quality. A high value of concordance implies that additional metrics will not make a significant contribution to accurately classifying quality; hence, these metrics are redundant.

An inner quality approach to reducing stress and improving physical and emotional wellbeing at work

Abstract: This exploratory field study examined the impact of an Inner Quality Management program (IQM) on a group of Motorola employees. IQM is a training program designed to help people increase productivity through improved health, communication, goal clarity, positive mood and job satisfaction, and through the reduction of tension, burnout, physical symptoms of stress and negative mood. Both psychological and physiological measures were assessed in the 6-month study. The study involved three groups: managers, engineers and factory workers. Results showed that contentment, job satisfaction and communication significantly increased after the training, while tension, anxiety, nervousness and physical symptoms of stress significantly decreased. Blood pressure in hypertensive individuals decreased, and there was a reduction in sympathetic nervous activity. Implications for workplace wellbeing are discussed.© 1997 John Wiley & Sons, Ltd.