Showing papers by "Naval Postgraduate School published in 1990"

Cognitive Elements of Empowerment: An “Interpretive” Model of Intrinsic Task Motivation

Abstract: This article presents a cognitive model of empowerment. Here, empowerment is defined as increased intrinsic task motivation, and our subsequent model identifies four cognitions (task assessments) as the basis for worker empowerment: sense of impact, competence, meaningfulness, and choice. Adopting an interpretive perspective, we have used the model also to describe cognitive processes through which workers reach these conclusions. Central to the processes we describe are workers' interpretive styles and global beliefs. Both preliminary evidence for the model and general implications for research are discussed.

A stable tracking control method for an autonomous mobile robot

Abstract: A stable tracking control rule is proposed for nonholonomic vehicles. The stability of the rule is proved through the use of a Liapunov function. Inputs to the vehicle are a reference posture (x/sub r/, y/sub r/, theta /sub r/)/sup t/ and reference velocities ( nu /sub r/, omega /sub r/)/sup t/. The major objective of this study is to propose a control rule to find reasonable target linear and rotational velocities ( nu , omega )/sup t/. Linearizing the system's differential equation is useful for deciding parameters for critical dumping for a small disturbance. In order to avoid slippage, a velocity/acceleration limitation scheme is introduced. Several simulation results are presented with or without the velocity/acceleration limiter. The control rule and limiting method proposed are robot independent and hence can be applied to various kinds of mobile robots with a dead reckoning ability. This method was implemented on the autonomous mobile robot Yamabico-11. Experimental results obtained are close to the results with the velocity/acceleration limiter. >

Generative Metaphor Intervention: A New Approach for Working with Systems Divided by Conflict and Caught in Defensive Perception:

Abstract: This article proposes that one way to help a group liberate itself from dysfunctional conflict and defensive routine is through the introduction of generative metaphor. By intervening at a tacit, i...

Atmospheric absorption of sound: Update

Abstract: Best current expressions for the vibrational relaxation times of oxygen and nitrogen in the atmosphere are used to compute total absorption. The resulting graphs of total absorption as a function of frequency for different humidities should be used in lieu of the graph published earlier by Evans et al (1972).

Significance of observation strategy on the design of robot calibration experiments

Abstract: This article examines the factors influencing the identification and observability of kinematic parameters during robot calibration. A generalized calibration experiment has been simulated using two different identification techniques. Details of the identification techniques and considerations for implementing them using standard IMSL routines are presented. The factors considered during the simulations include: initial estimates of parameters, measurement accuracy and noise, encoder resolution and uncertainty, selection of measurement configurations, number of measurements, and range of motion of the joints during observations. Results are tabulated for the various cases and suggestions are made for the design of robot calibration experiments.

The use of self checks and voting in software error detection: an empirical study

Abstract: The results of an empirical study of software error detection using self checks and N-version voting are presented. Working independently, each of 24 programmers first prepared a set of self checks using just the requirements specification of an aerospace application, and then each added self checks to an existing implementation of that specification. The modified programs were executed to measure the error-detection performance of the checks and to compare this with error detection using simple voting among multiple versions. The analysis of the checks revealed that there are great differences in the ability of individual programmers to design effective checks. It was found that some checks that might have been effective failed to detect an error because they were badly placed, and there were numerous instances of checks signaling nonexistent errors. In general, specification-based checks alone were not as effective as specification-based checks combined with code-based checks. Self checks made it possible to identify faults that had not been detected previously by voting 28 versions of the program over a million randomly generated inputs. This appeared to result from the fact that the self checks could examine the internal state of the executing program, whereas voting examines only final results of computations. If internal states had to be identical in N-version voting systems, then there would be no reason to write multiple versions. >

A Comparison of Password Techniques for Multilevel Authentication Mechanisms

Abstract: : Various mechanisms for authenticating users of computer-based information systems have been proposed. These include traditional, user-selected passwords, system-generated passwords, passphrases, cognitive passwords and associative passwords. While the mechanisms employed im primary passwords are determined by the operating systems' manufacturers, system designers can select any password mechanism for secondary passwords, to further protect sensitive applications and data files. This paper reports on the results of an empirically based study of passwords characteristics. It provides a comparative evaluation on the memorability and users' subjective preferences of the various passwords mechanisms, and suggest that cognitive passwords and associative passwords seem the most appropriate for secondary passwords. Keywords: Computer security.

Snow/Cloud Discrimination with Multispectral Satellite Measurements

Abstract: An algorithm is developed and evaluated for discriminating between clouds, snow-covered land and snow-free land in satellite image data. The multispectral technique uses daytime images of NOAA AVHRR channels 1 (0.63 μm), 3 (3.7 μm), and 4 (11.0 μm). Reflectance is derived for channel 3 by using the channel 4 emission temperature to estimate and remove the channel 3 thermal emission. Separation of clouds from snow and land is based primarily on the derived channel 3 reflectance. Observed reflectance in channel 3 is 0.02 to 0.04 for snow, 0.03 to 0.10 for land, 0.02 to 0.27 for ice clouds and 0.08 to 0.36 for liquid clouds. These ranges overlap for thin cirrus and snow, so the routine attempts analysis of cirrus based on differences in transmission between channels 3 and 4. Six case were analyzed and the total cloud cover was verified against a total of 110 surface observations in the standard categories of clear, scattered, broken and overcast. One of the cases is presented in detail to illustrate...

An optimal branch-and-bound procedure for the constrained path, moving target search problem

Abstract: A searcher and target move among a finite set of cells C = 1, 2, ',N in discrete time. At the beginning of each time period, one cell is searched. If the target is in the selected cell j, it is detected with probability qj. If the target is not in the cell searched, it cannot be detected during the current time period. After each search, a target in cell j moves to cell k with probability pjk. The target transition matrix, P = [pjk] is known to the searcher. The searcher's path is constrained in that if the searcher is currently in cell j, the next search cell must be selected from a set of neighboring cells Cj. The object of the search is to minimize the probability of not detecting the target in T searches.

Influence of dislocation density and distribution on the aging behavior of 6061 AlSiCw composites

Abstract: Precipitation hardening metal-matrix composites (MMCs) are known to age more rapidly than the unreinforced matrix alloys. It has been proposed that the accelerated aging is due to some dislocation defect mechanism which enhances nucleation, growth or both. Theoretical Avrami-type precipitation curves were generated assuming dislocation density dependent nucleation only and dislocation density dependent nucleation and growth. Curves were generated for both uniform dislocation density (to model cold work) and a dislocation density gradient (to model MMCs). These theoretical results were compared to precipitation curves generated by differential scanning calorimetry of unstrained and plastically strained unreinforced 6061 Al and 10 vol.% SiC whisker reinforced 6061 Al MMC. It was found on aging that β′ precipitation in the MMC initiates earlier and is completed later than in the unreinforced alloy with the same amount of plastic work as the composite. The reaction rate order for β′ precipitation was also determined from the calorimetric studies. These experimental results were interpreted in terms of the theoretical calculations. It is concluded that the matrix dislocation density distributions of metal-matrix composites can strongly influence macroscopically observed nucleation and growth rates.

A graph model for software evolution

Abstract: A graph model of software evolution is presented. The author seeks to formalize the objects and activities involved in software evolution in sufficient detail to enable automatic assistance for maintaining the consistency and integrity of an evolving software system. This includes automated support for propagating the consequences of a change to a software system. The evolution of large and complex software systems receives particular attention. >

Optimal grid-free path planning across arbitrarily contoured terrain with anisotropic friction and gravity effects

Abstract: The authors address anisotropic friction and gravity effects as well as ranges of impermissible-traversal headings due to overturn danger or power limitations. The method does not require imposition of a uniform grid, nor does it average effects in different directions, but reasons about a polyhedral approximation of terrain. It reduces the problem to a finite but provably optimal set of possibilities and then uses A* search to find the cost-optimal path. However, the possibilities are not physical locations but path subspaces. The method also exploits the insight that there are only four ways to optimally traverse an anisotropic homogeneous region: (1) straight across without braking, which is the standard isotropic-weighted-region traversal; (2) straight across without braking but as close as possible to a desired impermissible heading; (3) making impermissibility-avoiding switchbacks on the path across a region; and (4) straight across with braking. The authors prove specific optimality criteria for transitions on the boundaries of regions for each combination of traversal types. >

Observation of a kink soliton on the surface of a liquid.

Abstract: When a long channel of shallow liquid is driven parametrically, there can occur a 180\ifmmode^\circ\else\textdegree\fi{} kink in the phase of the fundamental cross mode of the surface. The kink is stable and localized, and is nonpropagating in the limit where the system is uniform. The weakly nonlinear theoretical description is a damped driven nonlinear Schr\"odinger equation supplemented with second harmonics. The kink is a robust state even at amplitudes where the perturbation expansion leading to this equation is unjustified.

Observational Evidence for Predictions of Tropical Cyclone Propagation Relative to Environmental Steering

Abstract: Theories of vortex motion due to the variations of the Coriolis parameter and environmental vorticity are compared to observations of tropical cyclone motion relative to computed “steering flows” using previously published composite data. The composite results are manipulated to obtain a vector quantity for the difference between tropical cyclone motion and steering, and this vector difference is termed “propagation.” The properties of these propagation vectors within various composite data stratifications provide tentative support for nonlinear numerical results such as: (i) the general magnitude and direction of the β-induced propagation; (ii) the dependence of such propagation on the outer-wind strength of the tropical cyclone; and (iii) the dependence of such propagation on the direction of the environmental vorticity gradient. Ambiguities in the composite data are discussed with respect to linear and nonlinear theories of tropical cyclone propagation, and several new composite data stratific...

User authentication by cognitive passwords: an empirical assessment

Abstract: The concept of cognitive passwords is introduced, and their use as a method to overcome the dilemma of passwords that are either difficult to remember or easily guessed is suggested. Cognitive passwords are based on personal facts, interests, and opinions that are likely to be easily recalled by a user. A brief dialogue between a user and a system, where a user provides a system with exact answers to a rotating set of questions, is suggested to replace the traditional authentication method using a single password. The findings of an empirical investigation focusing on memorability and ease-of-guessing of cognitive passwords, are reported. They demonstrate that cognitive passwords are easier to recall than conventional passwords, while being difficult for others, even those close to the users, to guess. >

A divide and conquer method for unitary and orthogonal eigenproblems

Abstract: LetH?? n xn be a unitary upper Hessenberg matrix whose eigenvalues, and possibly also eigenvectors, are to be determined. We describe how this eigenproblem can be solved by a divide and conquer method, in which the matrixH is split into two smaller unitary upper Hessenberg matricesH 1 andH 2 by a rank-one modification ofH. The eigenproblems forH 1 andH 2 can be solved independently, and the solutions of these smaller eigenproblems define a rational function, whose zeros on the unit circle are the eigenvalues ofH. The eigenvector ofH can be determined from the eigenvalues ofH and the eigenvectors ofH 1 andH 2. The outlined splitting of unitary upper Hessenberg matrices into smaller such matrices is carried out recursively. This gives rise to a divide and conquer method that is suitable for implementation on a parallel computer. WhenH?? n xn is orthogonal, the divide and conquer scheme simplifies and is described separately. Our interest in the orthogonal eigenproblem stems from applications in signal processing. Numerical examples for the orthogonal eigenproblem conclude the paper.

Software engineering with abstractions

Abstract: Table of Contents. Introduction. Requirements Analysis. Functional Specification. Architectural Design. Implementation. Evolution. Support Environment. Research. Directions. Appendices.

Investigating the cost/schedule trade-off in software development

Abstract: The author has studied the effects of schedule compression or stretch-out on total project cost within a much broader effort to study and predict the dynamics of the entire development process. The resulting cost/schedule tradeoffs were examined. Much of this project involved developing a comprehensive system-dynamics model. He used the model to conduct three simulation experiments. (1) He investigated the effects of different levels of schedule compression and stretch-out on total project cost in man-days and compared the results to those reported in the literature. (2) He addressed the stealthy role undersizing plays in schedule compression. (3) He investigated how different levels of managerial commitment affect the project's final cost and completion time. The results of all three experiments are presented and discussed. >

Defense spending and state economic growth

Abstract: Little evidence is currently available on the regional growth effects of federal defense spending. In this study, econometric models for state personal income and manufacturing employment between 1976 and 1985 are specified and estimated. Pooled cross-sectional time-series data are used, and the estimation procedure corrects for serial correlation, heteroscedasticity, and contemporaneous cross-sectional correlation. The results indicate that aggregate defense spending has a positive effect on both growth measures. However, when defense expenditures are disaggregated, only investment-type outlays appear to consistently affect state economic growth.

Remote sensing of ocean wave spectra by interferometric synthetic aperture radar

Abstract: Ocean surface waves can be clearly observed by SAR in the interferometric configuration (INSAR) due to the ability of INSAR to provide images of the local surface velocity field It is shown here that INSAR can be used to obtain wavenumber spectra that are in agreement with power spectra measured in situ This new method has considerable potential to provide instantaneous spatial information about the structure of ocean wave fields

An efficient Snell's law method for optimal-path planning across multipole two-dimensional, irregular, homogeneous-cost regions

Abstract: We are exploring a new approach to high-level optimal-path planning when homogeneous irregularly shaped regions of a plane have different traversal costs per unit distance. It is based on the simple idea that optimal paths must be straight in homogeneous regions, and so those regions need not be subdivided for path planning. Our approach uses optics anal ogies, ray tracing, and Snell's Law and reduces the problem to an efficient graph search with a variety of pruning criteria. The time and space of our algorithm is O(V 2) in an intui tively average case, where V is the number of region vertices. In experiments in which space is held constant, an imple mentation of our algorithm was not only dramatically faster but also gave better cost solution paths than a representative implementation of the chief competing technique, grid-based wavefront propagation. This appears to be because of the quite different and considerably smaller search space required for our more intelligent algorithm.

Events data and policy analysis

Abstract: In the 1960s and 1970s the creation and analysis of coded international events data became a major tool for the analysis of international relations and crises Unlike other quantitative projects developed by the academic community, the events data approach was transformed to applied research and used by various national security bureaucracies in the US government The approach was eventually rejected due to an aversion by bureaucrats to quantitative analysis systems and procedures which did not incorporate their expertise, organizational objectives and need for user-friendly and timely presentation The lessons learned from this case can be used to inform current efforts by academics to transfer basic research to the foreign policy making community

Relation between GDSS use and group task complexity: an experimental study

Abstract: A laboratory experiment was conducted to explore the influence of GDSS (group decision support systems) on decision quality, decision time, and user satisfaction under different levels of group-task complexity. Forty-eight groups each consisting of three members were assigned to four experimental treatments that differed in setting (non-GDSS or GDSS) and in group decision task complexity (low complexity or high). The findings indicate that, compared to working in a non-GDSS setting, the particular GDSS setting used (i) was more effective in solving complex problems, (ii) required more time for a low-complexity task but not for a high-complexity task, and (iii) resulted in lower satisfaction for a low-complexity task but a higher satisfaction for a high-complexity task. These findings help identify what type of group problems are better suited for GDSS use. >

Modeling Studies of Eddies in the Leeuwin Current: The Role of Thermal Forcing

Abstract: A high resolution, multilevel, primitive equation (PE) model is used to investigate the generation and stability of the Leeuwin Current and eddies off the west coast of Australia. Two numerical experiments are conducted to investigate the roles of the Indian Ocean temperature field and the North West (NW) Shelf waters in generating both the current and eddies. In the first experiment an alongshore temperature gradient, typical of the Indian Ocean temperature field, is imposed, while in the second experiment the additional effects of the NW Shelf waters are considered. In the first experiment, the meridional Indian Ocean temperature gradient is sufficient to drive a poleward surface flow (the Leeuwin Current) and an equatorial undercurrent. The surface flow is augmented by onshore geostrophic flow and accelerates downstream. In the second experiment, the inclusion of the NW Shelf waters completely dominates in the NW Shelf equatorial source region. The effects of the NW Shelf waters weaken away fr...

Free Surface Effects on the Near-Inertial Ocean Current Response to a Hurricane

Abstract: During the passage of hurricane Frederic in 1979, four ocean current meter arrays in water depths of 100–950 m detected both a baroclinic and a depth-independent response in the near-inertial frequency band. Although the oceanic response was predominately baroclinic, the hurricane excited a depth-independent component of 5–11 cm s−1. The origin and role of the depth-independent component of velocity is investigated using a linear analytical model and numerical simulations from a 17-level primitive equation model with a free surface. Both models are forced with an idealized wind stress pattern based on the observed storm parameters in hurricane Frederic. In an analytical model, the Green's function (K0) is convolved with the wind stress curl to predict a sea surface depression of approximately 20 cm from the equilibrium position. The near-inertial velocities are simulated by convolving the slope of the sea surface depression with a second Green's function. The barotropic current velocities rotate ...

Algorithm 686: FORTRAN subroutines for updating the QR decomposition

Abstract: Let the matrix A E R”““, m 2 n, have a QR decomposition A = QR, where Q E R”“” has orthonormal columns, and R E R”“” is upper triangular. Assume that Q and R are explicitly known. We present FORTRAN subroutines that update the QR decomposition in a numerically stable manner when A is modified by a matrix of rank one, or when a row or a column is inserted or deleted. These subroutines are modifications of the Algol procedures in Daniel et al. [5]. We also present a subroutine that permutes the columns of A and updates the QR decomposition so that the elements in the lower right corner of R will generally be small if the columns of A are nearly linearly dependent. This subroutine is an implementation of the rank-revealing QR decomposition scheme recently proposed by Chan [3].

A Numerical Simulation of the Mei-Yu Front and the Associated Low Level Jet

Abstract: A two-dimensional frontal model was used to study the structure and behavior of the Mei-Yu front over East Asia. The Mei-Yu front is characterized by mixed midlatitude-baroclinic and tropical-convective properties, with frequent occurrence of a low-level jet (LLJ) that is highly correlated with heavy convective rainfall. The quasi-steady state responses to a large-scale stretching deformation forcing were obtained by integrating the perturbation equations from an initial state of seasonal-mean zonal flow. Two major sets of experiments were conducted to simulate different midlatitude and subtropical conditions. The midlatitude front extends deeply into the upper troposphere with a strong poleward tilt, whereas the subtropical front is confined to the lower troposphere with less tilt, in good agreement with observations. Along the sloping front, slantwise updrafts develop with a multiband structure. This updraft is more evident in the subtropical cases and in the more moist midlatitude cases. For t...