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Institution

Naval Postgraduate School

EducationMonterey, California, United States
About: Naval Postgraduate School is a education organization based out in Monterey, California, United States. It is known for research contribution in the topics: Tropical cyclone & Boundary layer. The organization has 5246 authors who have published 11614 publications receiving 298300 citations. The organization is also known as: NPS & U.S. Naval Postgraduate School.


Papers
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Proceedings ArticleDOI
01 Oct 2016
TL;DR: A new approach to detect and track UAVs from a single camera mounted on a different UAV, which finds spatio-temporal traits of each moving object through optical flow matching and classify those candidate targets based on their motion patterns compared with the background.
Abstract: Despite the recent flight control regulations, Unmanned Aerial Vehicles (UAVs) are still gaining popularity in civilian and military applications, as much as for personal use. Such emerging interest is pushing the development of effective collision avoidance systems. Such systems play a critical role UAVs operations especially in a crowded airspace setting. Because of cost and weight limitations associated with UAVs payload, camera based technologies are the de-facto choice for collision avoidance navigation systems. This requires multi-target detection and tracking algorithms from a video, which can be run on board efficiently. While there has been a great deal of research on object detection and tracking from a stationary camera, few have attempted to detect and track small UAVs from a moving camera. In this paper, we present a new approach to detect and track UAVs from a single camera mounted on a different UAV. Initially, we estimate background motions via a perspective transformation model and then identify distinctive points in the background subtracted image. We find spatio-temporal traits of each moving object through optical flow matching and then classify those candidate targets based on their motion patterns compared with the background. The performance is boosted through Kalman filter tracking. This results in temporal consistency among the candidate detections. The algorithm was validated on video datasets taken from a UAV. Results show that our algorithm can effectively detect and track small UAVs with limited computing resources.

80 citations

Journal ArticleDOI
TL;DR: A new computational method for finding feedback optimal control and solving HJB equations which is able to mitigate the curse of dimensionality is presented and an upper bound for the approximation error is proved.
Abstract: We address finding the semi-global solutions to optimal feedback control and the Hamilton–Jacobi–Bellman (HJB) equation. Using the solution of an HJB equation, a feedback optimal control law can be implemented in real-time with minimum computational load. However, except for systems with two or three state variables, using traditional techniques for numerically finding a semi-global solution to an HJB equation for general nonlinear systems is infeasible due to the curse of dimensionality. Here we present a new computational method for finding feedback optimal control and solving HJB equations which is able to mitigate the curse of dimensionality. We do not discretize the HJB equation directly, instead we introduce a sparse grid in the state space and use the Pontryagin’s maximum principle to derive a set of necessary conditions in the form of a boundary value problem, also known as the characteristic equations, for each grid point. Using this approach, the method is spatially causality free, which enjoys the advantage of perfect parallelism on a sparse grid. Compared with dense grids, a sparse grid has a significantly reduced size which is feasible for systems with relatively high dimensions, such as the 6-D system shown in the examples. Once the solution obtained at each grid point, high-order accurate polynomial interpolation is used to approximate the feedback control at arbitrary points. We prove an upper bound for the approximation error and approximate it numerically. This sparse grid characteristics method is demonstrated with three examples of rigid body attitude control using momentum wheels.

80 citations

Journal ArticleDOI
TL;DR: The second part of a two-part study examined the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework as mentioned in this paper, where several open issues were addressed concerning the formation of the storm's warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave's pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions.
Abstract: This is the second of a two-part study examining the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. Here several open issues are addressed concerning the formation of the storm’s warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave’s pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions. All but one of the experiments include ice microphysics as represented by one of several parameterizations, and the partition of convective versus stratiform precipitation is accomplished using a standard numerical technique based on the high-resolution control experiment. The transition to a warm-core tropical cyclone from an initially cold-core, lower tropospheric wave disturbance is analyzed first. As part of this transformation process, it is shown that deep moist convection is sustained near the pouch center. Both convecti...

80 citations

Journal ArticleDOI
TL;DR: This analysis uses transaction cost economics to contrast the differences between structures infused with information technology and traditional supply chains.
Abstract: Coordination is the management of dependencies between activities. Given that supply chains represent the functional integration of many interdependent activities associated with the flow of goods, coordination theory offers a framework for understanding and designing supply chains. Supply chains are separated into two distinct substructures: physical (dealing with the flow and storage of goods) and information (dealing with information associated with those goods). Optimization that alters the storage and movement of information and incorporates the impact of information technology leads to a distinct set of node connections and configurations for each substructure. Our analysis uses transaction cost economics to contrast the differences between structures infused with information technology and traditional supply chains.

79 citations

Journal ArticleDOI
TL;DR: The findings give an indication on how the current proposals to cut public spending could exacerbate the trauma closure particularly among areas with high shares of minorities and how the growth of Medicaid managed care population should be monitored.
Abstract: Emergency departments and trauma centers are key players of the health care safety net for all patients, especially the underserved. Trauma centers, in particular, have been shown to significantly reduce both morbidity and mortality in numerous studies, and are important public health institutions given that injury is the most important cause of lost years of life in the United States.1–5 Trauma centers, however, are not without costs; they have traditionally been viewed as unprofitable, and have been shown to serve higher proportions of Medicaid and uninsured patients compared with nontrauma centers and sustain greater losses for the care they provide.6,7 Specific concerns have been voiced by the Institute of Medicine (IOM) and other stakeholders regarding the underfunding of and uneven access to trauma centers, which are seen as particularly vulnerable to closure because of the high costs of care.7–11 One of the areas that has been relatively unexplored in trauma service studies is the identification of system-level risk factors of trauma center closures. Although there are, on average, an increasing number of trauma centers in the United States, the pattern of openings and closures has been very unstable. One of the few studies looking at closures in the past decade found approximately 60 trauma centers dropped their trauma designation from 1981 to 1991.12 The rate of closures has accelerated, with over 300 trauma centers closing in urban areas between 1990 and 2005. Current literature in this field is mainly descriptive data on the trends and characteristics of trauma centers.6,10,11,12–19 Although some works document the financial characteristics of trauma centers,6,12,13,18,20–22 to our knowledge, no study has conducted multivariate analysis examining the institutional risk factors of trauma center closures. Alongside financial considerations, however, it is also important to identify if these exits occur differentially in areas with higher shares of vulnerable populations (eg, poor, minority, uninsured) requiring this service. Although there are some outcomes-based studies documenting racial disparities in trauma care on a patient-level,23–26 no study investigates whether there is a differential closure rate of trauma centers among areas with varying shares of vulnerable populations. In this study, we aim to extend the work of this field by conducting a multivariate analysis of trauma center closures that occurred between 1990 and 2005. Specifically, we estimate the hazard rates of shutting down these trauma centers along several dimensions of risk factors, particularly: (1) whether financial pressure increases the risks of trauma center closure, holding other characteristics constant; and (2) whether vulnerable populations (such as minority or poor population) are more likely to be in areas with higher risks of trauma center closures.

79 citations


Authors

Showing all 5313 results

NameH-indexPapersCitations
Mingwei Chen10853651351
O. C. Zienkiewicz10745571204
Richard P. Bagozzi104347103667
Denise M. Rousseau8421850176
John Walsh8175625364
Ming C. Lin7637023466
Steven J. Ghan7520725650
Hui Zhang7520027206
Clare E. Collins7156021443
Christopher W. Fairall7129319756
Michael T. Montgomery6825814231
Tim Li6738316370
Thomas M. Antonsen6588817583
Nadia Magnenat-Thalmann6552114850
Johnny C. L. Chan6126114886
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202331
2022151
2021321
2020382
2019352
2018362