Showing papers by "Naval Postgraduate School published in 2004"

A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

Abstract: . The last decade has seen tremendous advances in atmospheric aerosol particle research that is often performed in the context of climate and global change science. Biomass burning, one of the largest sources of accumulation mode particles globally, has been closely studied for its radiative, geochemical, and dynamic impacts. These studies have taken many forms including laboratory burns, in situ experiments, remote sensing, and modeling. While the differing perspectives of these studies have ultimately improved our qualitative understanding of biomass-burning issues, the varied nature of the work make inter-comparisons and resolutions of some specific issues difficult. In short, the literature base has become a milieu of small pieces of the biomass-burning puzzle. This manuscript, the second part of four, examines the properties of biomass-burning particle emissions. Here we review and discuss the literature concerning the measurement of smoke particle size, chemistry, thermodynamic properties, and emission factors. Where appropriate, critiques of measurement techniques are presented. We show that very large differences in measured particle properties have appeared in the literature, in particular with regards to particle carbon budgets. We investigate emissions uncertainties using scale analyses, which shows that while emission factors for grass and brush are relatively well known, very large uncertainties still exist in emission factors of boreal, temperate and some tropical forests. Based on an uncertainty analysis of the community data set of biomass burning measurements, we present simplified models for particle size and emission factors. We close this review paper with a discussion of the community experimental data, point to lapses in the data set, and prioritize future research topics.

Public deliberation in an age of direct citizen participation

Abstract: Citizen participation in the decisions that affect their lives is an imperative of contemporary society. For the first half of the 20th century, citizens relied on public officials and administrato...

Analysis of electric grid security under terrorist threat

Abstract: We describe new analytical techniques to help mitigate the disruptions to electric power grids caused by terrorist attacks. New bilevel mathematical models and algorithms identify critical system components (e.g., transmission lines, generators, transformers) by creating maximally disruptive attack plans for terrorists assumed to have limited offensive resources. We report results for standard reliability test networks to show that the techniques identify critical components with modest computational effort.

Arctic warming through the Fram Strait: Oceanic heat transport from 3 years of measurements

Abstract: We present estimates of volume and heat transport through Fram Strait for the period 1997 to 2000 from data of moored instruments. Full depth volume transports at 78° 55'N were in the order of 10 Sv both northwards and southwards with an annual mean net transport between 2 and 4 Sv to the south. The temperature of the northward flow of Atlantic Water had a strong seasonality with a minimum in winter. Nevertheless, the northward heat transport was highest in winter caused by the winter maximum of northward volume transport. During the three years of observation, the heat transport in the West Spitsbergen Current increased from 28 to 46 TW as a result of both increased speed and temperature. In contrast to the West Spitsbergen Current, the volume and heat transport of East Greenland Current remained fairly constant. An integration over a subsection of the East Greenland Current showed similar values of volume transport to that obtained by measurements in the 1980s (Foldvik et al., 1988). The southward heat transport through modified Atlantic Water weakened slightly between 1997 and 1999 despite increased temperatures.

Morphodynamic modeling of an embayed beach under wave group forcing

Abstract: [1] The morphodynamic response of the nearshore zone of an embayed beach induced by wave groups is examined with a numerical model. The model utilizes the nonlinear shallow water equations to phase resolve the mean and infragravity motions in combination with an advection-diffusion equation for the sediment transport. The sediment transport associated with the short-wave asymmetry is accounted for by means of a time-integrated contribution of the wave nonlinearity using stream function theory. The two-dimensional (2-D) computations consider wave group energy made up of directionally spread, short waves with a zero mean approach angle with respect to the shore normal, incident on an initially alongshore uniform barred beach. Prior to the 2-D computations, the model is calibrated with prototype flume measurements of waves, currents, and bed level changes during erosive and accretive conditions. The most prominent feature of the 2-D model computations is the development of an alongshore quasi-periodic bathymetry of shoals cut by rip channels. Without directional spreading, the smallest alongshore separation of the rip channels is obtained, and the beach response is self-organizing in nature. Introducing a small amount of directional spreading (less than 2°) results in a strong increase in the alongshore length scales as the beach response changes from self-organizing to being quasi-forced. A further increase in directional spreading leads again to smaller length scales. The hypothesized correlation between the observed rip spacing and wave group forced edge waves over the initially alongshore uniform bathymetry is not found. However, there is a correlation between the alongshore length scales of the wave group-induced quasi-steady flow circulations and the eventual alongshore spacing of the rip channels. This suggests that the scouring associated with the quasi-steady flow induced by the initial wave groups triggers the development of rip channels via a positive feedback mechanism in which the small scour holes start attracting more and more discharge.

Friendship and Advice Networks in the Context of Changing Professional Values

Abstract: In this article, I discuss the attributes of friendship and advice networks and hypothesize about their roles in maintaining and changing professional values. Advice networks sustain existing professional values in organizations. They are less likely to transmit new values because advice relations reflect current practice and may be negatively affected by changing values. Friendships rest on intimacy and trust rather than on existing task structures, so they can facilitate the development of new professional values without negatively affecting the friendship network. A longitudinal study of networks and teaching values in four public schools documented an initial alignment of advisors' and advisees' teaching values, followed by transmission of new teaching values through the friendship network. Changing professional values altered the advice network but did not affect the friendship network.

Internal solitons in the northeastern south China Sea. Part I: sources and deep water propagation

Abstract: A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. The goal of the observations was to quantify the water column variability in order to understand the along and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21-May 19, 2001 and sampled at 1-5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world's oceans. The waves arrived at the most offshore mooring in two clusters lasting 7-8 days each separated by five days when no waves were observed. Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The "critical point" /spl alpha/ where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.

The Effects of Climate Change on Water Resources in the West: Introduction and Overview

Abstract: The results of an experimental 'end to end' assessment of the effects of climate change on water resources in the western United States are described. The assessment focuses on the potential effects of climate change over the first half of the 21st century on the Columbia, Sacramento/San Joaquin, and Colorado river basins. The paper describes the methodology used for the assessment, and it summarizes the principal findings of the study. The strengths and weaknesses of this study are discussed, and suggestions are made for improving future climate change assessments. In the summer of 2000, the U.S. Department of Energy (DOE) funded a project to perform an experimental 'end-to-end' assessment of the effects of climate change on the western United States. The project was intended both to demonstrate and test a methodology for performing quantitative assessments of climate-driven environ- mental impacts. A second objective was to provide useful information to regional, state, and local decision-makers, whose job it will be to deal with the conflict- ing demands that climate change, population increases, and economic growth will place on the water resources of the West. The third objective was to demonstrate the potential value of an Accelerated Climate Prediction Initiative (ACPI). The ACPI was a DOE initiative to accelerate the development, improvement, and application of U.S. climate models and to provide the advanced computational facilities that would be needed to carry out this work. Although the ACPI was not funded, some of its spirit lives on in various DOE and other federal agency projects and programs designed to advance 'ultra-scale' computing and the science of climate simulation. In this volume, we hope to demonstrate what can be achieved if a highly qualified group of scientists are brought together, under relatively light management reins, to take an in-depth look at how future climate change might affect issues of real importance to the citizens of the United States. Other assessments have been made of the potential effects of climate change on the West (National Assessment Report, 2000), but this current work differs from previous assessments in important ways. The principal differences are as follows:

Pseudospectral Knotting Methods for Solving Nonsmooth Optimal Control Problems

Abstract: A class of computational methods for solving a wide variety of optimal control problems is presented; these problems include nonsmooth, nonlinear, switched optimal control problems, as well as standard multiphase problems. Methods are based on pseudospectral approximations of the differential constraints that are assumed to be given in the form of controlled differential inclusions including the usual vector field and differential-algebraic forms. Discontinuities and switches in states, controls, cost functional, dynamic constraints, and various other mappings associated with the generalized Bolza problem are allowed by the concept of pseudospectral (PS) knots. Information across switches and corners is passed in the form of discrete event conditions localized at the PS knots. The optimal control problem is approximated to a structured sparse mathematical programming problem. The discretized problem is solved using off-the-shelf solvers that include sequential quadratic programming and interior point methods. Two examples that demonstrate the concept of hard and soft knots are presented.

In‐situ measurements of velocity structure within turbidity currents

Abstract: [1] Turbidity currents are thought to be the main mechanism to move ∼500,000 m3 of sediments annually from the head of the Monterey Submarine Canyon to the deep-sea fan. Indirect evidence has shown frequent occurrences of such turbidity currents in the canyon, but the dynamic properties of the turbidity currents such as maximum speed, duration, and dimensions are still unknown. Here we present the first-ever in-situ measurements of velocity profiles of four turbidity currents whose maximum along-canyon velocity reached 190 cm/s. Two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year-long deployment.

Terrorism, Signaling, and Suicide Attack

Abstract: This article examines the strategic utility of suicide terrorism. Suicide terrorism, we suggest, can be thought of as a form of strategic "signaling." We define terrorism as a signaling game in which terrorist attacks are used to communicate a group's character and objectives to a set of target audiences. This is followed by an examination of the utility of suicide attacks as a signaling tactic. The relative effectiveness of suicide operations is evaluated in relation to other tactical options that are traditionally available to terrorist organizations. We go on to examine the institutional and social context of suicide terrorism, concluding with an examination of the evolutionary use of suicide attacks by Palestinian terrorist organizations and the Liberation Tigers of Tamil Eelam.‐

On climatological mass, heat, and salt transports through the Barents Sea and Fram Strait from a pan-Arctic coupled ice-ocean model simulation

Abstract: [1] The northward flow of Atlantic Water via the Barents Sea and Fram Strait is modeled, and climatological volume, heat, and salt fluxes into the Arctic Ocean are investigated. We argue that understanding of climate change in the region requires the knowledge of the mean circulation before its variability can be determined. Since estimates of long-term mean fluxes in the region are not available from observations, we present a modeling approach to quantify the climatological circulation and northward transports from the Norwegian Sea into the Arctic Ocean. A coupled ice-ocean model of the pan-Arctic region is configured at a 1/12° and 45-level grid and is integrated for 7 decades using a combination of daily-averaged 1979–2001 European Centre for Medium-Range Weather Forecasts data. Simulated water mass characteristics are compared with climatological atlas and selected observational data. The separation of the Norwegian Atlantic Current into Barents Sea and Fram Strait branches and their relative contributions to the total mass and property input into the Arctic Ocean are quantified. We emphasize the Barents Sea because fewer direct measurements of transports exist there and because water masses are significantly altered along this path by the seasonal ice melt/formation and the freshwater inputs. Under the given atmospheric forcing the Barents Sea outflow is shown to significantly contribute to the boundary flow continuing along the slopes of the Arctic Ocean. On the basis of model results, we argue that the contribution of the Barents Sea branch of Atlantic Water into the Arctic Ocean is equally, if not more, important than the Fram Strait branch.

Transient plasma ignition of quiescent and flowing air/fuel mixtures

Abstract: Transient plasmas that exist during the formative phase of a pulse-ignited atmospheric pressure discharge were studied for application to ignition of quiescent and flowing fuel-air mixtures. Quiescent methane-air mixture ignition was studied as a function of equivalence ratio, and flowing ethane-air mixture was studied in a pulse detonation engine (PDE). The transient plasma was primarily comprised of streamers, which exist during approximately 50 ns prior to the formation of an equilibrated electron energy distribution. Results of significant reduction in delay to ignition and ignition pressure rise time were obtained with energy costs roughly comparable to traditional spark ignition methods (100-800 mJ). Reduction in delay to ignition by factors of typically 3 in quiescent mixes to >4 in a flowing PDE (0.35 kg/s), and other enhancements in performance were obtained. These results, along with a discussion of a pseudospark-based pulse generator that was developed for these applications, will be presented.

On the Relationship between Western Maritime Continent Monsoon Rainfall and ENSO during Northern Winter

Abstract: Several studies have reported that Indonesian rainfall is poorly correlated with El Nino–Southern Oscillation (ENSO) events during the northern winter wet monsoon season. This work studies the relationship between the Nino-3 (5°S–5°N, 150°–90°W) sea surface temperature (SST) and the Maritime Continent monsoon rainfall during 1979–2002. The study indicates that the correlations are mostly negative except in the vicinity of Sumatra and Malay Peninsula (SMP, including the western sections of Java and Borneo), where the correlations range from zero to weakly positive. The monsoon rainfall during ENSO events is influenced by a pair of anomalous Walker cells and a low-level closed circulation centered near the Philippines. East of SMP, the rainfall is negatively correlated with Nino-3 SST. The anomalous low-level wind over the Indian Ocean west of SMP causes rainfall to also be correlated negatively with Nino-3 SST, but rainfall over SMP is sheltered from this effect because of the high mountains along...

The economic implications of exaptation

Abstract: Accounts of economic change recognize that markets create selective pressures for the adaptation of technologies in the direction of customer needs and production efficiencies. However, non-adaptational bases for technological change are rarely highlighted, despite their pervasiveness in the history of technical and economic change. In this paper the concept of exaptation -a feature co-opted for its present role from some other origin - is proposed as a characteristic element of technological change, and an important mechanism by which new markets for products and services are created by entrepreneurs. Exaptation is a missing but central concept linking the evolution of technology with the entrepreneurial creation of new markets and the concept of Knightian uncertainty.

Honeyfiles: deceptive files for intrusion detection

Abstract: This paper introduces an intrusion-detection device named honeyfiles. Honeyfiles are bait files intended for hackers to access. The files reside on a file server, and the server sends an alarm when a honey file is accessed. For example, a honeyfile named "passwords.txt" would be enticing to most hackers. The file server's end-users create honeyfiles, and the end-users receive the honeyfile's alarms. Honeyfiles can increase a network's internal security without adversely affecting normal operations. The honeyfile system was tested by deploying it on a honeynet, where hackers' use of honeyfiles was observed. The use of honeynets to test a computer security device is also discussed. This form of testing is a useful way of finding the faulty and overlooked assumptions made by the device's developers.

Aerosol–cloud drop concentration closure in warm cumulus

Abstract: Our understanding of the activation of aerosol particles into cloud drops during the formation of warm cumulus clouds presently has a limited observational foundation. Detailed observations of aerosol size and composition, cloud microphysics and dynamics, and atmospheric thermodynamic state were collected in a systematic study of 21 cumulus clouds by the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft during NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE). An “aerosol-cloud” closure study was carried out in which a detailed cloud activation parcel model, which predicts cloud drop concentration using observed aerosol concentration, size distribution, cloud updraft velocity, and thermodynamic state, is evaluated against observations. On average, measured droplet concentration in adiabatic cloud regions is within 15% of the predictions. This agreement is corroborated by independent measurements of aerosol activation carried out by two cloud condensation nucleus (CCN) counters on the aircraft. Variations in aerosol concentration, which ranged from 300 to 3300 cm^(−3), drives large microphysical differences (250–2300 cm^(−3)) observed among continental and maritime clouds in the South Florida region. This is the first known study in which a cloud parcel model is evaluated in a closure study using a constraining set of data collected from a single platform. Likewise, this is the first known study in which relationships among aerosol size distribution, CCN spectrum, and cloud droplet concentration are all found to be consistent with theory within experimental uncertainties much less than 50%. Vertical profiles of cloud microphysical properties (effective radius, droplet concentration, dispersion) clearly demonstrate the boundary layer aerosol's effect on cloud microphysics throughout the lowest 1 km of cloud depth. Onboard measurements of aerosol hygroscopic growth and the organic to sulfate mass ratio are related to CCN properties. These chemical data are used to quantify the range of uncertainty associated with the simplified treatment of aerosol composition assumed in the closure study.

Microstructural modification of as-cast NiAl bronze by friction stir processing

Abstract: The application of friction stir processing (FSP) to a cast NiAl bronze (NAB) material is presented as a means for selective modification of the near-surface layers by converting as-cast microstructures to a wrought condition in the absence of macroscopic shape change. This may enable selective surface hardening of cast components. The complex physical metallurgy of the NAB is reviewed, and microstructure changes associated with FSP for a selected set of processing parameters are examined by optical microscopy (OM) and transmission electron microscopy (TEM) methods. Direct temperature measurement in the stir zone is infeasible and, so, these microstructure changes are used to estimate peak temperatures in the stir zone. The persistence of a Fe3Al phase (κii) indicates that peak temperatures are below the solvus for this phase, while the presence of transformation products of the β phase, including fine Widmanstatten α, bainite, and martensite, indicates that peak temperatures exceed the eutectoid temperature for the reaction β → α+κiii throughout the stir zone.

Network structure and innovation ambiguity effects on diffusion in dynamic organizational fields

Abstract: Computational modeling simulated innovation diffusion through six prototypical interregional network structures and two distributions of partnering tendencies in dynamic organizational fields. Comp...

Systems engineering in an age of complexity

Abstract: This paper considers the creation of Complex Engineered Systems (CESs) and the Systems Engineering approach by which they are designed. The changing nature of the challenges facing Systems Engineering is discussed, with particular focus on the increasing complexity of modern systems. It is argued that modern complexity poses a major challenge to our ability to achieve successful systems and that this complexity must be understood, predicted and measured if we are to engineer systems confidently. We acknowledge previous work which concluded that, in complex systems, failures (“accidents”) may be inevitable and unavoidable. To further explore potential tools for increasing our confidence in complex systems, we review research in the field of Complexity Theory to seek potentially useful approaches and measures and find ourselves particularly interested in the potential usefulness of relationships between the magnitudes of events and their frequency of occurrence. Complexity Theory is found to have characterized naturally occurring systems and to potentially be the source of profitable application to the systems engineering challenge, viz., the creation of complex engineered systems. We are left with the tentative conclusion that truly complex systems, with our present understanding of complex behavior, cannot be designed with a degree of confidence that is acceptable given our current expectations. We recommend that the discipline of systems engineering must investigate this issue as a matter of priority and urgency and seek to develop approaches to respond to the challenge. © 2003 Wiley Periodicals, Inc. Syst Eng 7: 25–34, 2004

HF radar data assimilation in the Monterey Bay area

Abstract: [1] The utility of high-frequency (HF) radar data for improving numerical circulation model predictions is evaluated. Comparisons of the statistical properties of the (CODAR-type) HF radar data and the observed wind indicate a strong correlation between the dominant alongshore, upwelling-favoring wind-forcing and HF radar-derived surface currents along the central California coastline. Because inadequate knowledge of the wind stress is probably a significant source of error in the model solutions, the idea of using HF radar data to provide corrections to the model wind-forcing is promising. Different HF radar data assimilation schemes are compared and judged based on the correlations observed between model currents and independent observations from two mooring sites. Analysis of correlation maps between model-predicted and observed currents indicates a spatial and temporal shift between modeled and observed features. However, the impact of HF radar data assimilation reduces these spatial and temporal shifts. A significant improvement in the correlation between the model and observed subsurface currents is achieved when an Ekman-layer projection of the corrections is included. In this approach, assimilation of HF radar data produces additional Ekman pumping (vertical velocity) based on the horizontal pattern of model-observed velocity mismatch at the surface.

Military applications of agent-based simulations

Abstract: There continues to be increasing interest from a broad range of disciplines in agent-based and artificial life simulations. This includes the Department of Defense - which uses simulations heavily in its decision making process. Indeed, military conflicts can have many attributes that are consistent with complex adaptive systems - such as many entities interacting with some degree of autonomy, each of which is continually making decisions to satisfy a variety of sometimes conflicting objectives. In this paper, we present three applications of agent-based simulations used to analyze military problems. The first uses the MANA model to explore the ability of the U.S. Army's network-based Future Force to perform with degraded communications. The second studies how unmanned surface vehicles can be used in force protection missions with the Pythagoras model. The last example examines the standard Army squad size with an integrated effort using MANA, Pythagoras, and the high-resolution simulation JANUS.

Impression creep characterization of rapidly cooled Sn–3.5Ag solders

Abstract: The creep behavior of solders crucially influences solder joint reliability in microelectronic packages. This, in conjunction with the ongoing industry-wide transition to lead-free solders, has resulted in significant current emphasis on developing approaches for expeditiously creep testing miniaturized samples of a wide range of solder compositions to determine their suitability for packaging applications. Here we characterize the creep response of Sn–3.5Ag solders via impression creep testing. The tested microstructures represent a rapidly cooled state, resembling the highly refined microstructures often found in tiny microelectronic solder joints. It is shown that in the as-reflowed state, the solder creeps by a viscous glide-controlled mechanism at low stresses due to the presence of a non-equilibrium amount of dissolved Ag in Sn, and a particle-limited climb mechanism at high stresses. Following slight aging, which allows the dissolved solute concentration to drop to near-equilibrium levels, the low stress mechanism changes to dislocation climb-control. Based on these observations, a unified view of creep of Sn–3.5Ag solders is presented, which is consistent with observations of a transition from low to high stress sensitivity with increasing stress, which has been reported in several studies.