Showing papers by "Naval Postgraduate School published in 2007"

Efficient Nearly Orthogonal and Space-Filling Latin Hypercubes

Abstract: This article presents an algorithm for constructing orthogonal Latin hypercubes, given a fixed sample size, in more dimensions than previous approaches. In addition, we detail a method that dramatically improves the space-filling properties of the resultant Latin hypercubes at the expense of inducing small correlations between the columns in the design matrix. Although the designs are applicable to many situations, they were developed to provide Department of Defense analysts flexibility in fitting models when exploring high-dimensional computer simulations where there is considerable a priori uncertainty about the forms of the response surfaces.

Effectiveness of Fluoride in Preventing Caries in Adults

Abstract: To date, no systematic reviews have found fluoride to be effective in preventing dental caries in adults. The objective of this meta-analysis was to examine the effectiveness of self- and professionally applied fluoride and water fluoridation among adults. We used a random-effects model to estimate the effect size of fluoride (absolute difference in annual caries increment or relative risk ratio) for all adults aged 20+ years and for adults aged 40+ years. Twenty studies were included in the final body of evidence. Among studies published after/during 1980, any fluoride (self- and professionally applied or water fluoridation) annually averted 0.29 (95%CI: 0.16-0.42) carious coronal and 0.22 (95%CI: 0.08-0.37) carious root surfaces. The prevented fraction for water fluoridation was 27% (95%CI: 19%-34%). These findings suggest that fluoride prevents caries among adults of all ages.

X3D: Extensible 3D Graphics for Web Authors

Abstract: X3D is the ISO-standard scene-graph language for interactive 3D graphics on the Web. A new course is available for teaching the fundamentals of 3D graphics using Extensible 3D (X3D). Resources include a detailed textbook, an authoring tool, hundreds of example scenes, and detailed slidesets covering each chapter. The published book is commercially available, while all other coursemodule resources are provided online free under an open-source license. Numerous other commercial and open resources are available for X3D, which also serves as an interchange format. The supported course has been taught for many years, successfully introducing masters' students to the principles and techniques of 3D graphics without requiring programming experience. This course and module appears to be ready for undergraduate use. Expressing 3D within the domain of Extensible Markup Language (XML) for the Web is novel and has the potential to open up computer graphics to many new practitioners. This combined resource is intended broadly support computer graphics education and skills for web authors.

A prototype of an autonomous controller for a quadrotor UAV

Abstract: The paper proposes a complete real-time control algorithm for autonomous collision-free operations of the quadrotor UAV. As opposed to fixed wing vehicles the quadrotor is a small agile vehicle which might be more suitable for the variety of specific applications including search and rescue, surveillance and remote inspection. The developed control system incorporates both trajectory planning and path following. Using a differential flatness property the trajectory planning is posed as a constrained optimization problem in the output space (as opposed to the control space), which simplifies the problem. The trajectory and speed profile are parameterized to reduce the problem to a finite dimensional problem. To optimize the speed profile independently of the trajectory a virtual argument is used as opposed to time. A path following portion of the proposed algorithm uses a standard linear multi-variable control technique. The paper presents the results of simulations to demonstrate the suitability of the proposed control algorithm.

Computing is a natural science

Abstract: Information processes and computation continue to be found abundantly in the deep structures of many fields. Computing is not---in fact, never was---a science only of the artificial.

Self-contained Position Tracking of Human Movement Using Small Inertial/Magnetic Sensor Modules

Abstract: Numerous applications require a self-contained personal navigation system that works in indoor and outdoor environments, does not require any infrastructure support, and is not susceptible to jamming. Posture tracking with an array of inertial/magnetic sensors attached to individual human limb segments has been successfully demonstrated. The "sourceless" nature of this technique makes possible full body posture tracking in an area of unlimited size with no supporting infrastructure. Such sensor modules contain three orthogonally mounted angular rate sensors, three orthogonal linear accelerometers and three orthogonal magnetometers. This paper describes a method for using accelerometer data combined with orientation estimates from the same modules to calculate position during walking and running. The periodic nature of these motions includes short periods of zero foot velocity when the foot is in contact with the ground. This pattern allows for precise drift error correction. Relative position is calculated through double integration of drift corrected accelerometer data. Preliminary experimental results for various types of motion including walking, side stepping, and running document accuracy of distance and position estimates.

SHEBA flux–profile relationships in the stable atmospheric boundary layer

Abstract: Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used to examine the profile stability functions of momentum, φ m , and sensible heat, φ h , in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φ m and φ h in detail and includes ample data for the very stable case. New parameterizations for φ m (ζ) and φ h (ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ m follows a ζ 1/3 dependence, whereas φ h initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects of self-correlation, which occur in plots of φ m and φ h versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging.

The Coupled Boundary Layers and Air–Sea Transfer Experiment in Low Winds

Abstract: The Office of Naval Research's Coupled Boundary Layers and Air–Sea Transfer (CBLAST) program is being conducted to investigate the processes that couple the marine boundary layers and govern the exchange of heat, mass, and momentum across the air–sea interface. CBLAST-LOW was designed to investigate these processes at the low-wind extreme where the processes are often driven or strongly modulated by buoyant forcing. The focus was on conditions ranging from negligible wind stress, where buoyant forcing dominates, up to wind speeds where wave breaking and Langmuir circulations play a significant role in the exchange processes. The field program provided observations from a suite of platforms deployed in the coastal ocean south of Martha's Vineyard. Highlights from the measurement campaigns include direct measurement of the momentum and heat fluxes on both sides of the air–sea interface using a specially constructed Air–Sea Interaction Tower (ASIT), and quantification of regional oceanic variability over sca...

Moral courage in the workplace: moving to and from the desire and decision to act

Abstract: The article of record as published may be found at http://dx.doi.org/10.1111/j.1467-8608.2007.00484.x

Shoaling and shoreline dissipation of low?frequency waves

Abstract: The growth rate, shoreline reflection, and dissipation of low?frequency waves are investigated using data obtained from physical experiments in the Delft University of Technology research flume and by parameter variation using the numerical model Delft3D?SurfBeat. The growth rate of the shoaling incoming long wave varies with depth with an exponent between 0.25 and 2.5. The exponent depends on a dimensionless normalized bed slope parameter ?, which distinguishes between a mild?slope regime and a steep?slope regime. This dependency on ? alone is valid if the forcing short waves are not in shallow water; that is, the forcing is off?resonant. The ? parameter also controls the reflection coefficient at the shoreline because for small values of ?, long waves are shown to break. In this mild?slope regime the dissipation due to breaking of the long waves in the vicinity of the shoreline is much higher than the dissipation due to bottom friction, confirming the findings of Thomson et al. (2006) and Henderson et al. (2006). The energy transfer from low frequencies to higher frequencies is partly due to triad interactions between low? and high?frequency waves but with decreasing depth is increasingly dominated by long?wave self?self interactions, which cause the long?wave front to steepen up and eventually break. The role of the breaking process in the near?shore evolution of the long waves is experimentally confirmed by observations of monochromatic free long waves propagating on a plane sloping beach, which shows strikingly similar characteristics, including the steepening and breaking.

Boundary Objects in Design: An Ecological View of Design Artifacts

Abstract: Traditionally, Systems Analysis and Design (SAD) research has focused on ways of working and ways of modeling. Design ecology – the task, organizational and political context surrounding design – is less well understood. In particular, relationships between design routines and products within ecologies have not received sufficient attention. In this paper, we theorize about design product and ecology relationships and deliberate on how design products – viewed as boundary objects – bridge functional knowledge and stakeholder power gaps across different social worlds. We identify four essential features of design boundary objects: capability to promote shared representation, capability to transform design knowledge, capability to mobilize for action, and capability to legitimize design knowledge. We show how these features help align, integrate, and transform heterogeneous technical and domain knowledge across social worlds as well as mobilize, coordinate, and align stakeholder power. We illustrate through an ethnography of a large aerospace laboratory how two design artifacts – early proto-architectures and project plans – shared these four features to coalesce design processes and propel successful movement of designs across social worlds. These artifacts resolved uncertainty associated with functional requirements and garnered political momentum to choose among design solutions. Altogether, the study highlights the importance of design boundary objects in multi-stakeholder designs and stresses the need to formulate sociology-based design theories on how knowledge is produced and consumed in complex SAD tasks.

The role of management control systems in planned organizational change: An analysis of two organizations

Abstract: In the management control literature there is growing interest in the role of management control systems (MCS) in planned organizational change. The existing literature is concerned with either rational, technical change principles or more social and political interpretations of MCS facilitated change. This paper aims to extend this literature by combining technical approaches to MCS facilitated change with a behavioral approach in the study of two similar organizations. Moreover, the paper employs a holistic approach to change to develop a comprehensive understanding of the role of MCS in planned organizational change. A framework by Huy [Huy, Q. N. (2001). Time, temporal capacity, and planned change. Academy of Management Review 26(4), 601–623] is used to provide an integrative approach that focuses on both rational, systematic practices and the behavioral processes involved in their implementation. This is achieved by identifying four idealized intervention types: commanding, engineering, teaching and socializing. Understanding the application of these four intervention types requires analysis of the way they interact through time.

Ridging, strength, and stability in high-resolution sea ice models

Abstract: [1] In multicategory sea ice models the compressive strength of the ice pack is often assumed to be a function of the potential energy of pressure ridges. This assumption, combined with other standard features of ridging schemes, allows the ice strength to change dramatically on short timescales. In high-resolution (∼10 km) sea ice models with a typical time step (∼1 hour), abrupt strength changes can lead to large internal stress gradients that destabilize the flow. The unstable flow is characterized by large oscillations in ice concentration, thickness, strength, velocity, and strain rates. Straightforward, physically motivated changes in the ridging scheme can reduce the likelihood of abrupt strength changes and improve stability. In simple test problems with flow toward and around topography, stability is significantly enhanced by eliminating the threshold fraction G* in the ridging participation function. Use of an exponential participation function increases the maximum stable time step at 10-km resolution from less than 30 min to about 2 hours. Modifying the redistribution function to build thinner ridges modestly improves stability and also gives better agreement between modeled and observed thickness distributions. Allowing the ice strength to increase linearly with the mean ice thickness improves stability but probably underestimates the maximum stresses.

A Lagrangian Trajectory View on Transport and Mixing Processes between the Eye, Eyewall, and Environment Using a High-Resolution Simulation of Hurricane Bonnie (1998)

Abstract: The transport and mixing characteristics of a large sample of air parcels within a mature and vertically sheared hurricane vortex are examined. Data from a high-resolution (2-km horizontal grid spacing) numerical simulation of real-case Hurricane Bonnie (1998) are used to calculate Lagrangian trajectories of air parcels in various subdomains of the hurricane (namely, the eye, eyewall, and near environment) to study the degree of interaction (transport and mixing) between these subdomains. It is found that 1) there is transport and mixing from the low-level eye to the eyewall that carries air possessing relatively high values of equivalent potential temperature (e), which can enhance the efficiency of the hurricane heat engine; 2) a portion of the low-level inflow of the hurricane bypasses the eyewall to enter the eye, and this air both replaces the mass of the low-level eye and lingers for a sufficient time (order 1 h) to acquire enhanced entropy characteristics through interaction with the ocean beneath the eye; 3) air in the mid- to upper-level eye is exchanged with the eyewall such that more than half the air of the eye is exchanged i n5hi nthis case of a sheared hurricane; and 4) that one-fifth of the mass in the eyewall at a height of 5 km has an origin in the mid- to upper-level environment where e is much less than in the eyewall, which ventilates the ensemble average eyewall e by about 1 K. Implications of these findings for the problem of hurricane intensity forecasting are briefly discussed.

Swell and Slanting-Fetch Effects on Wind Wave Growth

Abstract: Wind-sea generation was observed during two experiments off the coast of North Carolina. One event with offshore winds of 9–11 m s−1 directed 20° from shore normal was observed with eight directional stations recording simultaneously and spanning a fetch from 4 to 83 km. An opposing swell of 1-m height and 10-s period was also present. The wind-sea part of the wave spectrum conforms to established growth curves for significant wave height and peak period, except at inner-shelf stations where a large alongshore wind-sea component was observed. At these short fetches, the mean wave direction θm was observed to change abruptly across the wind-sea spectral peak, from alongshore at lower frequencies to downwind at higher frequencies. Waves from another event with offshore winds of 6–14 m s−1 directed 20°–30° from shore normal were observed with two instrument arrays. A significant amount of low-frequency wave energy was observed to propagate alongshore from the region where the wind was strongest. The...

Accuracy of atlantic and eastern north pacific tropical cyclone intensity forecast guidance

Abstract: Five statistical and dynamical tropical cyclone intensity guidance techniques available at the National Hurricane Center (NHC) during the 2003 and 2004 Atlantic and eastern North Pacific seasons were evaluated within three intensity phases: (I) formation; (II) early intensification, with a subcategory (IIa) of a decay and reintensification cycle; and (III) decay. In phase I in the Atlantic, the various techniques tended to predict that a tropical storm would form from six tropical depressions that did not develop further, and thus the tendency was for false alarms in these cases. For the other 24 depressions that did become tropical storms, the statistical–dynamical techniques, statistical hurricane prediction scheme (SHIPS) and decay SHIPS (DSHIPS), have some skill relative to the 5-day statistical hurricane intensity forecast climatology and persistence technique, but they also tend to intensify all depressions and thus are prone to false alarms. In phase II, the statistical–dynamical models SH...

The Marine Stratus/Stratocumulus Experiment (MASE): Aerosol‐cloud relationships in marine stratocumulus

Abstract: The Marine Stratus/Stratocumulus Experiment (MASE) field campaign was undertaken in July 2005 off the coast of Monterey, California to evaluate aerosol-cloud relationships in the climatically important regime of eastern Pacific marine stratocumulus. Aerosol and cloud properties were measured onboard the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft. One cloud that was clearly impacted by ship emissions as well as the ensemble of clouds observed over the entire mission are analyzed in detail. Results at both the individual and ensemble scales clearly confirm the Twomey effect (first indirect effect of aerosols) and demonstrate drizzle suppression at elevated aerosol number concentration. For the ship track impacted cloud, suppressed drizzle in the track led to a larger cloud liquid water path (LWP) at the same cloud thickness, in accord with the so-called second indirect effect. Ensemble averages over all clouds sampled over the entire 13-flight mission show the opposite effect of aerosol number concentration on LWP, presumably the result of other dynamic influences (e.g., updraft velocity and ambient sounding profile). Individual polluted clouds were found to exhibit a narrower cloud drop spectral width in accord with theoretical prediction (M.-L. Lu and J. H. Seinfeld, Effect of aerosol number concentration on cloud droplet dispersion: A large-eddy simulation study and implications for aerosol indirect forcing, Journal of Geophysical Research, 2006). This field experiment demonstrates both the indirect aerosol effect on ship track perturbed clouds, as well as the subtleties involved in extracting these effects over an ensemble of clouds sampled over a 1-month period.

Water properties and circulation in Arctic Ocean models

Abstract: [1] As a part of the Arctic Ocean Model Intercomparison Project, results from 10 Arctic ocean/ice models are intercompared over the period 1970 through 1999. Models' monthly mean outputs are laterally integrated over two subdomains (Amerasian and Eurasian basins), then examined as functions of depth and time. Differences in such fields as averaged temperature and salinity arise from models' differences in parameterizations and numerical methods and from different domain sizes, with anomalies that develop at lower latitudes carried into the Arctic. A systematic deficiency is seen as AOMIP models tend to produce thermally stratified upper layers rather than the “cold halocline”, suggesting missing physics perhaps related to vertical mixing or to shelf-basin exchanges. Flow fields pose a challenge for intercomparison. We introduce topostrophy, the vertical component of V×∇D where V is monthly mean velocity and ∇D is the gradient of total depth, characterizing the tendency to follow topographic slopes. Positive topostrophy expresses a tendency for cyclonic “rim currents”. Systematic differences of models' circulations are found to depend strongly upon assumed roles of unresolved eddies.

Laboratory Experimentation of Autonomous Spacecraft Approach and Docking to a Collaborative Target

Abstract: A new laboratory test bed i s introduced, which enables the hardware -in -the -loop simulation of the autonomous approach and docking of a chaser spacecraft to a target spacecraft of similar mass. The test bed consists of a chaser spacecraft and a target spacecraft simulator s floating via air pads on a flat floor. The prototype docking interface mechanism of Defense Advanced Research Projec ts Agency’s (DARPA’s) Orbital Express mission is integrated on the spacecraft simulators. Relative navigation of the chaser spacecraft is obtained by fusing the measurements from a single -camera vision sensor and an inertial measurement unit , through Kalma n filters . The target is collaborative in the sense that a pattern of three infrared Light Emitting Diodes is mounted on it as reference for the relative navigation. Eight cold -gas on -off thrusters are used for the t ranslation of the chaser vehicle . They a re commanded using a non -linear control algorithm based on S ch mit t triggers. Furthermore, a reaction wheel is used for the vehicle rotation with a proportional derivative linear control. Experimental results are presented of both autonomous proximity maneu ver a nd autonomous docking of the chaser simulator to the non -floating target . The presented results validate the proposed estimation and control methods and demonstrate the capability of the test bed.

The Use of Remittance Income in Mexico

Abstract: Immigration affects sending countries through the receipt of remittance income. The impact of these cash transfers on households and communities has brought attention to remittances as a development mechanism. This study attempts to understand the degree to which household consumption is affected by the receipt of remittance income and the ways in which the broader communities may be impacted. Using household income and expenditure data for Mexico, expenditure patterns of remittance-receiving households are analyzed. Regression analysis indicates that remittance-receiving households spend a greater share of total income on durable goods, healthcare, and housing.

Trilevel Optimization in Power Network Defense

Abstract: We present a trilevel optimization model of resource allocation in electric power network defense. This model identifies the most critical network components to defend against possible terrorist attacks. The goal of defense is to minimize the economic cost that the attacks may cause, subject to resource constraints. We describe a decomposition approach for finding an optimal solution to the trilevel model, which is based on iteratively solving smaller nested bilevel problems. Our testing results demonstrate the advantages of trilevel optimization over bilevel optimization in network defense.

Moats and Drawbridges: An Isolation Primitive for Reconfigurable Hardware Based Systems

Abstract: Blurring the line between software and hardware, reconfigurable devices strike a balance between the raw high speed of custom silicon and the post-fabrication flexibility of general-purpose processors. While this flexibility is a boon for embedded system developers, who can now rapidly prototype and deploy solutions with performance approaching custom designs, this results in a system development methodology where functionality is stitched together from a variety of "soft IP cores," often provided by multiple vendors with different levels of trust. Unlike traditional software where resources are managed by an operating system, soft IP cores necessarily have very fine grain control over the underlying hardware. To address this problem, the embedded systems community requires novel security primitives which address the realities of modern reconfigurable hardware. We propose an isolation primitive, moats and drawbridges, that are built around four design properties: logical isolation, interconnect traceability, secure reconfigurable broadcast, and configuration scrubbing. Each of these is a fundamental operation with easily understood formal properties, yet maps cleanly and efficiently to a wide variety of reconfigurable devices. We carefully quantify the required overheads on real FPGAs and demonstrate the utility of our methods by applying them to the practical problem of memory protection.

Solving the Bi-Objective Maximum-Flow Network-Interdiction Problem

Abstract: We describe a new algorithm for computing the efficient frontier of the “bi-objective maximum-flow network-interdiction problem.” In this problem, an “interdictor” seeks to interdict (destroy) a set of arcs in a capacitated network that are Pareto-optimal with respect to two objectives, minimizing total interdiction cost and minimizing maximum flow. The algorithm identifies these solutions through a sequence of single-objective problems solved using Lagrangian relaxation and a specialized branch-and-bound algorithm. The Lagrangian problems are simply max-flow min-cut problems, while the branch-and-bound procedure partially enumerates s-t cuts. Computational tests reveal the new algorithm to be one to two orders of magnitude faster than an algorithm that replaces the specialized branch-and-bound algorithm with a standard integer-programming solver.

Evolution of microstructure and microtexture in fcc metals during high-pressure torsion

Abstract: Pure nickel and commercially pure (CP) aluminium were selected as model fcc materials for a detailed investigation of the experimental parameters influencing grain refinement and evolution of microstructure and microtexture during processing by high-pressure torsion (HPT). Samples were examined after HPT using microhardness measurements, transmission electron microscopy and orientation imaging microscopy. Processing by HPT produces a grain size of ∼170 nm in pure Ni and ∼1 μm in CP aluminium. It is shown that homogeneous and equiaxed microstructures can be attained throughout the samples of nickel when using applied pressures of at least ∼6 GPa after 5 whole revolution. In CP aluminium, a homogeneous and equiaxed microstructure was achieved after 2 whole revolutions under an applied pressure of 1 GPa. For these conditions, the distributions of grain boundary misorientations are similar in the centre and at the periphery of the samples. It is shown that simple shear texture develops in fcc metals subjected to high-pressure torsion. Some grain growth was detected at the periphery of the Al disk after 8 revolutions. The factors influencing the development of homogeneous microstructures in processing by HPT are discussed.