Showing papers by "Naval Postgraduate School published in 2011"

Vision-based hand-gesture applications

Abstract: Body posture and finger pointing are a natural modality for human-machine interaction, but first the system must know what it's seeing.

Search and pursuit-evasion in mobile robotics

Abstract: This paper surveys recent results in pursuit-evasion and autonomous search relevant to applications in mobile robotics. We provide a taxonomy of search problems that highlights the differences resulting from varying assumptions on the searchers, targets, and the environment. We then list a number of fundamental results in the areas of pursuit-evasion and probabilistic search, and we discuss field implementations on mobile robotic systems. In addition, we highlight current open problems in the area and explore avenues for future work.

Remote data checking using provable data possession

Abstract: We introduce a model for provable data possession (PDP) that can be used for remote data checking: A client that has stored data at an untrusted server can verify that the server possesses the original data without retrieving it. The model generates probabilistic proofs of possession by sampling random sets of blocks from the server, which drastically reduces I/O costs. The client maintains a constant amount of metadata to verify the proof. The challenge/response protocol transmits a small, constant amount of data, which minimizes network communication. Thus, the PDP model for remote data checking is lightweight and supports large data sets in distributed storage systems. The model is also robust in that it incorporates mechanisms for mitigating arbitrary amounts of data corruption.We present two provably-secure PDP schemes that are more efficient than previous solutions. In particular, the overhead at the server is low (or even constant), as opposed to linear in the size of the data. We then propose a generic transformation that adds robustness to any remote data checking scheme based on spot checking. Experiments using our implementation verify the practicality of PDP and reveal that the performance of PDP is bounded by disk I/O and not by cryptographic computation. Finally, we conduct an in-depth experimental evaluation to study the tradeoffs in performance, security, and space overheads when adding robustness to a remote data checking scheme.

Towards a new generation axion helioscope

Abstract: We study the feasibility of a new generation axion helioscope, the most ambitious and promising detector of solar axions to date. We show that large improvements in magnetic field volume, x-ray focusing optics and detector backgrounds are possible beyond those achieved in the CERN Axion Solar Telescope (CAST). For hadronic models, a sensitivity to the axion-photon coupling of gaγ few × 10−12 GeV−1 is conceivable, 1–1.5 orders of magnitude beyond the CAST sensitivity. If axions also couple to electrons, the Sun produces a larger flux for the same value of the Peccei-Quinn scale, allowing one to probe a broader class of models. Except for the axion dark matter searches, this experiment will be the most sensitive axion search ever, reaching or surpassing the stringent bounds from SN1987A and possibly testing the axion interpretation of anomalous white-dwarf cooling that predicts ma of a few meV. Beyond axions, this new instrument will probe entirely unexplored ranges of parameters for a large variety of axion-like particles (ALPs) and other novel excitations at the low-energy frontier of elementary particle physics.

Model Uncertainty in a Mesoscale Ensemble Prediction System: Stochastic versus Multiphysics Representations

Abstract: A multiphysics and a stochastic kinetic-energy backscatter scheme are employed to represent model uncertainty in a mesoscale ensemble prediction system using the Weather Research and Forecasting model. Both model-error schemes lead to significant improvements over the control ensemble system that is simply a downscaled global ensemble forecast with the same physics for each ensemble member. The improvements are evident in verification against both observations and analyses, but different in some details. Overall the stochastic kinetic-energy backscatter scheme outperforms the multiphysics scheme, except near the surface. Best results are obtained when both schemes are used simultaneously, indicating that the model error can best be captured by a combination of multiple schemes.

Job Search and Voluntary Turnover in a Boundaryless world: a Control Theory Perspective

Abstract: We propose a cybernetic model of job search and voluntary turnover that is based on the need to remain employable in a volatile economy. The model depicts the process by which individuals engage in ongoing cycles of job search activities that can increase the likelihood of voluntary turnover, which, in turn, provides opportunities to develop additional career competencies. We then examine the implications of the model for future research on the turnover process.

Securing electronic medical records using attribute-based encryption on mobile devices

Abstract: We provide a design and implementation of self-protecting electronic medical records (EMRs) using attribute-based encryption on mobile devices. Our system allows healthcare organizations to export EMRs to locations outside of their trust boundary. In contrast to previous approaches, our solution is designed to maintain EMR availability even when providers are offline, i.e., where network connectivity is not available. To balance the needs of emergency care and patient privacy, our system is designed to provide fine-grained encryption and is able to protect individual items within an EMR, where each encrypted item may have its own access control policy. We implemented a prototype system using a new key- and ciphertext-policy attribute-based encryption library that we developed. Our implementation, which includes an iPhone app for storing and managing EMRs offline, allows for flexible and automated policy generation. An evaluation of our design shows that our ABE library performs well, has acceptable storage requirements, and is practical and usable on modern smartphones.

Foreword to the Special Issue on Spectral Unmixing of Remotely Sensed Data

Abstract: The 19 papers in this special issue focus on the state-of-the-art and most recent developments in the area of spectral unmixing of remotely sensed data.

How Probabilistic Risk Assessment Can Mislead Terrorism Risk Analysts

Abstract: Traditional probabilistic risk assessment (PRA), of the type originally developed for engineered systems, is still proposed for terrorism risk analysis. We show that such PRA applications are unjustified in general. The capacity of terrorists to seek and use information and to actively research different attack options before deciding what to do raises unique features of terrorism risk assessment that are not adequately addressed by conventional PRA for natural and engineered systems—in part because decisions based on such PRA estimates do not adequately hedge against the different probabilities that attackers may eventually act upon. These probabilities may differ from the defender’s (even if the defender’s experts are thoroughly trained, well calibrated, unbiased probability assessors) because they may be conditioned on different information. We illustrate the fundamental differences between PRA and terrorism risk analysis, and suggest use of robust decision analysis for risk management when attackers may know more about some attack options than we do.

An Estimation of Turbulent Characteristics in the Low-Level Region of Intense Hurricanes Allen (1980) and Hugo (1989)

Abstract: This study analyzes the flight-level data collected by research aircraft that penetrated the eyewalls of category 5 Hurricane Hugo (1989) and category 4 Hurricane Allen (1980) between 1 km and the sea surface. Estimates of turbulent momentum flux, turbulent kinetic energy (TKE), and vertical eddy diffusivity are obtained before and during the eyewall penetrations. Spatial scales of turbulent eddies are determined through a spectral analysis. The turbulence parameters estimated for the eyewall penetration leg are found to be nearly an order of magnitude larger than those for the leg outside the eyewall at similar altitudes. In the low-level intense eyewall region, the horizontal length scale of the dominant turbulent eddies is found to be between 500 and 3000 m, and the corresponding vertical length scale is approximately 100 m. The results suggest also that it is unwise to include eyewall vorticity maxima (EVM) in the turbulence parameter estimation because the EVMs are likely to be quasi-two-dimensional vortex structures that are embedded within the three-dimensional turbulence on the inside edge of the eyewall. This studyis afirstattempt at estimatingthe characteristics of turbulent flow in the low-leveltroposphereof an intense eyewall using in situ aircraft observations. The authors believe that the results can offer useful guidance in numerical weather prediction efforts aimed at improving the forecast of hurricane intensity. Because of the small sample size analyzed in this study, further analyses of the turbulent characteristics in the high-wind region of hurricanes are imperative.

On the entrepreneurial genesis of new markets: effectual transformations versus causal search and selection

Abstract: The generation of new markets is an emerging area of interest among researchers working in the traditions of evolutionary economics And true to those traditions, the current study incorporates empirical evidence from psychology and cognitive science to develop micro-foundations for evolutionary theories of new market generation In this paper we present an in-depth analysis of how expert entrepreneurs use effectual logic to conceptualize the creation of new markets Our results challenge received wisdom based on search and selection processes and move beyond combinatorial ideas to develop instead a “transformational” view of market genesis

Light propagation through anisotropic turbulence.

Abstract: A wealth of experimental data has shown that atmospheric turbulence can be anisotropic; in this case, a Kolmogorov spectrum does not describe well the atmospheric turbulence statistics. In this paper, we show a quantitative analysis of anisotropic turbulence by using a non-Kolmogorov power spectrum with an anisotropic coefficient. The spectrum we use does not include the inner and outer scales, it is valid only inside the inertial subrange, and it has a power-law slope that can be different from a Kolmogorov one. Using this power spectrum, in the weak turbulence condition, we analyze the impact of the power-law variations α on the long-term beam spread and scintillation index for several anisotropic coefficient values ς. We consider only horizontal propagation across the turbulence cells, assuming circular symmetry is maintained on the orthogonal plane to the propagation direction. We conclude that the anisotropic coefficient influences both the long-term beam spread and the scintillation index by the factor ς2−α.

Crafting a usable microkernel, processor, and I/O system with strict and provable information flow security

Abstract: High assurance systems used in avionics, medical implants, and cryptographic devices often rely on a small trusted base of hardware and software to manage the rest of the system. Crafting the core of such a system in a way that achieves flexibility, security, and performance requires a careful balancing act. Simple static primitives with hard partitions of space and time are easier to analyze formally, but strict approaches to the problem at the hardware level have been extremely restrictive, failing to allow even the simplest of dynamic behaviors to be expressed. Our approach to this problem is to construct a minimal but configurable architectural skeleton. This skeleton couples a critical slice of the low level hardware implementation with a microkernel in a way that allows information flow properties of the entire construction to be statically verified all the way down to its gate-level implementation. This strict structure is then made usable by a runtime system that delivers more traditional services (e.g. communication interfaces and long-living contexts) in a way that is decoupled from the information flow properties of the skeleton. To test the viability of this approach we design, test, and statically verify the information-flow security of a hardware/software system complete with support for unbounded operation, inter-process communication, pipelined operation, and I/O with traditional devices. The resulting system is provably sound even when adversaries are allowed to execute arbitrary code on the machine, yet is flexible enough to allow caching, pipelining, and other common case optimizations.

Optimal Rendezvous Trajectories of a Controlled Spacecraft and a Tumbling Object

Abstract: This paper formulates and solves the problem of minimum-time and minimum-energy optimal trajectories of rendezvous of a powered chaser and a passive tumbling target, in a circular orbit. Both translational and rotational dynamics are considered. In particular, ending conditions are imposed of matching the positions and velocities of two points of interest onboard the vehicles. A collision-avoidance condition is imposed as well. The optimal control problems are analytically formulated through the use of the Pontryagin minimum principle. The problems are then solved numerically, by using a direct collocation method based on the Gauss pseudospectral approach. Finally, the obtained solutions are verified through the minimum principle, solved by a shooting method. The simulation results show that the pseudospectral solver provides solutions very close to the optimal ones, except in the case of presence of singular arcs when it may not provide a feasible solution. The computational time needed by the pseudospectral solver is a small fraction of the one needed by the indirect approach, but it is still considerably too large to allow for its use in real-time onboard guidance.

Design principles for virtual worlds

Abstract: In this research note, we examine the design, development, validation, and use of virtual worlds. Our purpose in doing so is to extend the design science paradigm by developing a set of design principles applicable to the context of virtual environments, particularly those using agent-based simulation as their underlying technology. Our central argument is that virtual worlds comprise a new class of information system, one that combines the structural aspects of traditional modeling and simulation systems in concert with emergent user dynamics of systems supporting emergent knowledge processes. Our approach involves two components. First, we review the characteristics of agent-based virtual worlds (ABVWs) to discern design requirements that may challenge current design theory. From this review, we derive a set of design principles based on deep versus emergent structures where deep structures reflect conventional modeling and simulation system architectures and emergent structures capture the unpredictable user-system dynamics inherent in emergent knowledge processes, which increasingly characterize virtual worlds. We illustrate how these design challenges are addressed with an exemplar of a complex mirror world, a large-scale ABVW we developed called Sentient World. Our contribution is the insight of partitioning ABVW architectures into deep and emergent structures that mirror modeling systems and emergent knowledge processes respectively, while developing extended design principles to facilitate their integration. We conclude with a discussion of the implications of our design principles for informing and guiding future research and practice.

The Price Effects of Cash Versus In-Kind Transfers

Abstract: This paper compares how cash and in-kind transfers affect local prices. Both types of transfers increase the demand for normal goods, but only in-kind transfers also increase supply. Hence, in-kind transfers should lead to lower prices than cash transfers, which helps consumers at the expense of local producers. We test and confirm this prediction using a program in Mexico that randomly assigned villages to receive boxes of food (trucked into the village), equivalently-valued cash transfers, or no transfers. The pecuniary benefit to consumers of in-kind transfers, relative to cash transfers, equals 11% of the direct transfer.

A position paper on data sovereignty: the importance of geolocating data in the cloud

Abstract: In this paper we define the problem and scope of data sovereignty - the coupling of stored data authenticity and geographical location in the cloud. Establishing sovereignty is an especially important concern amid legal and policy constraints when data and resources are virtualized and widely distributed. We identify the key challenges that need to be solved to achieve an effective and un-cheatable solution as well as propose an initial technique for data sovereignty.

Surface freshening in the Arctic Ocean's Eurasian Basin: An apparent consequence of recent change in the wind‐driven circulation

Abstract: [1] Data collected by an autonomous ice-based observatory that drifted into the Eurasian Basin between April and November 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008. Sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0.5 m of liquid freshwater to the ocean (comparable to the freshening by melting estimated for those previous years), while the observed change in upper-ocean salinity over the melt period implies a freshwater gain of about 0.7 m. Results of a wind-driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the Eurasian Basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the Beaufort Gyre. This flux is likely associated with a 2009 shift in the large-scale atmospheric circulation to a significant reduction in strength of the anticyclonic Beaufort Gyre and the Transpolar Drift Stream.

Simple kinematic models for the environmental interaction of tropical cyclones in vertical wind shear

Abstract: . A major impediment to the intensity forecast of tropical cyclones (TCs) is believed to be associated with the interaction of TCs with dry environmental air. However, the conditions under which pronounced TC-environment interaction takes place are not well understood. As a step towards improving our understanding of this problem, we analyze here the flow topology of a TC immersed in an environment of vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called manifolds, can be identified under the assumptions of steady and layer-wise horizontal flow. The manifolds are shown to divide the flow around the TC into distinct regions. The manifold structure in our numerical experiment is more complex than the well-known manifold structure of a non-divergent point vortex in uniform background flow. In particular, one manifold spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the layer of strong inflow associated with surface friction and below the outflow layer in the upper troposphere. From the perspective of a steady and layer-wise horizontal flow model, the eyewall is well protected from the intrusion of environmental air. In order for the environmental air to intrude into the inner-core convection, time-dependent and/or vertical motions, which are prevalent in the TC inner-core, are necessary. Air with the highest values of moist-entropy resides within the limit cycle. This "moist envelope" is distorted considerably by the imposed vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. In a first approximation, the distribution of high- and low-θe air around the TC at low to mid-levels is governed by the stirring of convectively modified air by the steady, horizontal flow. Motivated by the results from the idealized numerical experiment, an analogue model based on a weakly divergent point vortex in background flow is formulated. The simple kinematic model captures the essence of many salient features of the manifold structure in the numerical experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for the point-vortex model. The results indicate distinct scenarios of environmental interaction depending on the ratio of storm intensity and vertical-shear magnitude. Further implications of the new results derived from the manifold analysis for TCs in the real atmosphere are discussed.

Rising Closures Of Hospital Trauma Centers Disproportionately Burden Vulnerable Populations

Abstract: Closures of hospital trauma centers have accelerated since 2001. These closures may disproportionately affect disadvantaged communities. We evaluate how driving time between ZIP code areas and the nearest trauma centers—a proxy for access, given the time-sensitive nature of trauma care—changed nationwide during 2001–07. By 2007, sixty-nine million Americans (24 percent of the population) had to travel farther to the nearest trauma center than they did in 2001, and almost sixteen million people had to travel an additional thirty minutes or more. Communities with disproportionately high numbers of African American residents, uninsured people, and people living in poverty, as well as people living in rural areas, were more likely than others to be thus affected. Because mortality from traumatic injuries has also worsened for these vulnerable populations, policy makers should learn more about the possible connections—and consider such measures as paying trauma centers serving these communities higher amounts ...

Incidence of physician-diagnosed osteoarthritis among active duty United States military service members.

Abstract: Objective. To examine the incidence of osteoarthritis and the influence of demographic and occupational factors associated with this condition among active duty US service members between 1999 and 2008. Methods. To determine the total number of incident cases of osteoarthritis, the Defense Medical Surveillance System (DMSS) was queried by sex, race, age, branch of military service, and rank using code 715 of the International Classification of Diseases, Ninth Revision, Clinical Modification. Multivariable Poisson regression analysis was used to estimate incidence rates, rate ratios, and 95% confidence intervals (95% CIs) for osteoarthritis per 1,000 person-years. Results. A total of 108,266 incident cases of osteoarthritis were documented in the DMSS within a population that experienced 13,768,885 person-years at risk of disease during the study period. The overall unadjusted incidence rate among all active duty US service members during the study period was 7.86 cases per 1,000 person-years. Significant demographic and occupational risk factors for osteoarthritis included sex, age, race, branch of service, and rank (P 40 years experienced an adjusted incidence rate for osteoarthritis that was 19 times higher than that for those ages <20 years (rate ratio 18.61 [95% CI 17.57– 19.57]). Black service members experienced significantly higher incidence rates of osteoarthritis than those in the white and “other” race categories. Conclusion. Rates of osteoarthritis were significantly higher in military populations than in comparable age groups in the general population.

Dynamics of fingering convection I: Small-scale fluxes and large-scale instabilities

Abstract: (Received ?? and in revised form ??) Double-diffusive instabilities are often invoked to explain enhanced transport in stablystratified fluids. The most-studied natural manifestation of this process, fingering convection, commonly occurs in the ocean’s thermocline and typically increases diapycnal mixing by two orders of magnitude over molecular diffusion. Fingering convection is also often associated with structures on much larger scales, such as thermohaline intrusions, gravity waves and thermohaline staircases. In this paper, we present an exhaustive study of the phenomenon from small to large scales. We perform the first three-dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport. Our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions. We then develop a generalized mean-field theory to study the stability of fingering systems to large-scale perturbations, using our calculated turbulent fluxes to parameterize small-scale transport. The theory recovers the intrusive instability, the collective instability, and the instability as limiting cases. We find that the fastest-growing large-scale mode depends sensitively on the ratio of the background gradients of temperature and salinity (the density ratio). While only intrusive modes exist at high density ratios, the collective and -instabilities dominate the system at the low density ratios where staircases are typically observed. We conclude by discussing our findings in the context of staircase formation theory.

A sliding time window heuristic for open pit mine block sequencing

Abstract: The open pit mine block sequencing problem (OPBS) seeks a discretetime production schedule that maximizes the net present value of the orebody extracted from an open-pit mine. This integer program (IP) discretizes the mine’s volume into blocks, imposes precedence constraints between blocks, and limits resource consumption in each time period. We develop a “sliding time window heuristic” to solve this IP approximately. The heuristic recursively defines, solves and partially fixes an approximating model having: (i) fixed variables in early time periods, (ii) an exact submodel defined over a “window” of middle time periods, and (iii) a relaxed submodel in later time periods. The heuristic produces near-optimal solutions (typically within 2% of optimality) for model instances that standard optimization software fails to solve. Furthermore, it produces these solutions quickly, even though our OPBS model enforces standard upper-bounding constraints on resource consumption along with less standard, but important, lower-bounding constraints.

Solving Defender-Attacker-Defender Models for Infrastructure Defense

Abstract: This paper (a) describes a defender-attacker-defender sequential game model (DAD) to plan defenses for an infrastructure system that will enhance that system's resilience against attacks by an intelligent adversary, (b) describes a realistic formulation of DAD for defending a transportation network, (c) develops a decomposition algorithm for solving this instance of DAD and others, and (d) demonstrates the solution of a small transportation-network example. A DAD model generally evaluates system operation through the solution of an optimization model, and the decomposition algo- rithm developed here requires only that this system-operation model be continuous and convex. For example, our transportation-network example incorporates a conges- tion model with a (convex) nonlinear objective function and linear constraints.

Association between ambulance diversion and survival among patients with acute myocardial infarction.

Abstract: Context Ambulance diversion, a practice in which emergency departments (EDs) are temporarily closed to ambulance traffic, might be problematic for patients experiencing time-sensitive conditions, such as acute myocardial infarction (AMI). However, there is little empirical evidence to show whether diversion is associated with worse patient outcomes. Objective To analyze whether temporary ED closure on the day a patient experiences AMI, as measured by ambulance diversion hours of the nearest ED, is associated with increased mortality rates among patients with AMI. Design, Study, and Participants A case-crossover design of 13 860 Medicare patients with AMI from 508 zip codes within 4 California counties (Los Angeles, San Francisco, San Mateo, and Santa Clara) whose admission date was between 2000 and 2005. Data included 100% Medicare claims data that covered admissions between 2000 and 2005, linked with date of death until 2006, and daily ambulance diversion logs from the same 4 counties. Among the hospital universe, 149 EDs were identified as the nearest ED to these patients. Main Outcome Measures The percentage of patients with AMI who died within 7 days, 30 days, 90 days, 9 months, and 1 year from admission (when their nearest ED was not on diversion and when that same ED was exposed to Results Between 2000 and 2006, the mean (SD) daily diversion duration was 7.9 (6.1) hours. Based on analysis of 11 625 patients admitted to the ED between 2000 and 2005, and whose nearest ED had at least 3 diversion exposure levels (3541, 3357, 2667, and 2060 patients for no exposure, exposure to Conclusion Among Medicare patients with AMI in 4 populous California counties, exposure to at least 12 hours of diversion by the nearest ED was associated with increased 30-day, 90-day, 9-month, and 1-year mortality.

Mapping the U.S. West Coast surface circulation: A multiyear analysis of high‐frequency radar observations

Abstract: signals with phase speeds of O(10) and O(100 to 300) km day −1 and time scales of 2 to 3 weeks The signals with slow phase speed are only observed in southern California It is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of Point Conception The seasonal transition of alongshore surfacecirculationforcedbyupwelling‐favorablewindsandtheirrelaxationiscapturedinfine detailSubmesoscaleeddies,identifiedusingflowgeometry,haveRossbynumbersof01to3, diameters in the range of 10 to 60 km, and persistence for 2 to 12 days The HFR surface currents resolve coastal surface ocean variability continuously across scales from