Showing papers by "Naval Postgraduate School published in 2018"

Probability and Random Processes for Electrical and Computer Engineers

Abstract: With updates and enhancements to the incredibly successful first edition, Probability and Random Processes for Electrical and Computer Engineers, Second Edition retains the best aspects of the original but offers an even more potent introduction to probability and random variables and processes Written in a clear, concise style that illustrates the subject’s relevance to a wide range of areas in engineering and physical and computer sciences, this text is organized into two parts The first focuses on the probability model, random variables and transformations, and inequalities and limit theorems The second deals with several types of random processes and queuing theory New or Updated for the Second Edition: A short new chapter on random vectors that adds some advanced new material and supports topics associated with discrete random processes Reorganized chapters that further clarify topics such as random processes (including Markov and Poisson) and analysis in the time and frequency domain A large collection of new MATLAB®-based problems and computer projects/assignments Each Chapter Contains at Least Two Computer Assignments Maintaining the simplified, intuitive style that proved effective the first time, this edition integrates corrections and improvements based on feedback from students and teachers Focused on strengthening the reader’s grasp of underlying mathematical concepts, the book combines an abundance of practical applications, examples, and other tools to simplify unnecessarily difficult solutions to varying engineering problems in communications, signal processing, networks, and associated fields

A meta-analysis of the antecedents of work–family enrichment

Abstract: Summary This study meta-analytically examined theoretically derived antecedents of both directions of work–family enrichment (sometimes labeled facilitation or positive spillover), namely, work–family enrichment and family–work enrichment. Contextual and personal characteristics specific to each domain were examined. Resource-providing (e.g., social support and work autonomy) and resource-depleting (e.g., role overload) contextual characteristics were considered. Domain-specific personal characteristics included the individuals' psychological involvement in each domain, the centrality of each domain, and work engagement. Results based on 767 correlations from 171 independent studies published between 1990 and 2016 indicate that several contextual and personal characteristics have significant relationships with enrichment. Although those associated with work tend to have stronger relationships with work–family enrichment and those associated with family tend to have stronger relationships with family–work enrichment, several antecedent variables have significant relationships with both directions of enrichment. Resource-providing contextual characteristics tend to have stronger relationships with enrichment than do resource-depleting characteristics. There was very little evidence of gender being a moderator of relationships between contextual characteristics and enrichment. Lastly, meta-analytic structural equation modeling provided evidence that a theoretical path model wherein work engagement mediates between several contextual characteristics and enrichment is largely generalizable across populations.

A Suite of Exercises for Verifying Dynamic Earthquake Rupture Codes

Abstract: We describe a set of benchmark exercises that are designed to test if computer codes that simulate dynamic earthquake rupture are working as intended. These types of computer codes are often used to understand how earthquakes operate, and they produce simulation results that include earthquake size, amounts of fault slip, and the patterns of ground shaking and crustal deformation. The benchmark exercises examine a range of features that scientists incorporate in their dynamic earthquake rupture simulations. These include implementations of simple or complex fault geometry, off‐fault rock response to an earthquake, stress conditions, and a variety of formulations for fault friction. Many of the benchmarks were designed to investigate scientific problems at the forefronts of earthquake physics and strong ground motions research. The exercises are freely available on our website for use by the scientific community.

Interdependent Infrastructure as Linked Social, Ecological, and Technological Systems (SETSs) to Address Lock‐in and Enhance Resilience

Abstract: Traditional infrastructure adaptation to extreme weather events (and now climate change) has typically been techno-centric and heavily grounded in robustness—the capacity to prevent or minimize disruptions via a risk-based approach that emphasizes control, armoring, and strengthening (e.g., raising the height of levees). However, climate and nonclimate challenges facing infrastructure are not purely technological. Ecological and social systems also warrant consideration to manage issues of overconfidence, inflexibility, interdependence, and resource utilization—among others. As a result, techno-centric adaptation strategies can result in unwanted tradeoffs, unintended consequences, and underaddressed vulnerabilities. Techno-centric strategies that lock-in today’s infrastructure systems to vulnerable future design, management, and regulatory practices may be particularly problematic by exacerbating these ecological and social issues rather than ameliorating them. Given these challenges, we develop a conceptual model and infrastructure adaptation case studies to argue the following: (1) infrastructure systems are not simply technological and should be understood as complex and interconnected social, ecological, and technological systems (SETSs); (2) infrastructure challenges, like lock-in, stem from SETS interactions that are often overlooked and underappreciated; (3) framing infrastructure with a SETS lens can help identify and prevent maladaptive issues like lock-in; and (4) a SETS lens can also highlight effective infrastructure adaptation strategies that may not traditionally be considered. Ultimately, we find that treating infrastructure as SETS shows promise for increasing the adaptive capacity of infrastructure systems by highlighting how lock-in and vulnerabilities evolve and how multidisciplinary strategies can be deployed to address these challenges by broadening the options for adaptation. Plain Language Summary Instead of thinking of infrastructure as purely technological artifacts, we instead propose considering infrastructure as linked social, ecological, and technological systems (SETS). Adopting a SETS lens can help identify vulnerabilities that develop within infrastructure systems over time. Ultimately, adopting this SETS perspective will not only help us better understand our infrastructure systems, but also aid in the development strategies for adapting to the many challenges that our infrastructure will continue to face (climate change, interdependencies, technological evolution, growing complexity, etc.)

Double-Diffusive Convection

Abstract: Double-diffusive convection is a mixing process driven by the interaction of two fluid components which diffuse at different rates. Leading expert Timour Radko presents the first systematic overview of the classical theory of double-diffusive convection in a coherent narrative, bringing together the disparate literature in this developing field. The book begins by exploring idealized dynamical models and illustrating key principles by examples of oceanic phenomena. Building on the theory, it then explains the dynamics of structures resulting from double-diffusive instabilities, such as the little-understood phenomenon of thermohaline staircases. The book also surveys non-oceanographic applications, such as industrial, astrophysical and geological manifestations, and discusses the climatic and biological consequences of double-diffusive convection. Providing a balanced blend of fundamental theory and real-world examples, this is an indispensable resource for academic researchers, professionals and graduate students in physical oceanography, fluid dynamics, applied mathematics, astrophysics, geophysics and climatology.

Overview of the Arctic Sea State and Boundary Layer Physics Program

Abstract: A large collaborative program has studied the coupled air-ice-ocean-wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year.

Networks and Religion: Ties that Bind, Loose, Build-up, and Tear Down

Abstract: Social scientists who study religion generally believe that social networks play a central role in religious life. However, most studies draw on measures that are relatively poor proxies for capturing the effects of social networks. This book illustrates how researchers can draw on formal social network analysis methods to explore the interplay of networks and religion. The book's introductory chapters provide overviews of the social scientific study of religion and social network analysis. The remaining chapters explore a variety of topics current in the social scientific study of religion, as well as introducing a variety of social network theories and methods, such as balance theory, ego-network analysis, exponential random graph models, and stochastic actor-oriented models. By embedding social network analysis within a social scientific study of religion framework, Networks and Religion offers an array of approaches for studying the role that social networks play in religious belief and practice.

Optimal Synchronization of Heterogeneous Nonlinear Systems With Unknown Dynamics

Abstract: Optimal output synchronization of multi-agent leader–follower systems with unknown nonlinear dynamics is considered. The agents are assumed heterogeneous so that the dynamics may be nonidentical. A distributed observer is designed to estimate the leader state for each agent. A discounted performance function is defined for each agent, and an augmented Hamilton–Jacobi–Bellman (HJB) equation is derived to find its minimal value. The HJB solution depends on the trajectories of the local state and the distributed observer state. A control protocol based on the HJB solution assures that the synchronization error goes to zero locally asymptotically fast for all agents. The proposed approach has two main advantages compared to standard output synchronization methods. First, it is optimal in the sense that it not only makes the steady-state synchronization error zero, but also minimizes the transient error. Second, it does not require the explicit solution to the output regulator equations, though the HJB solutions implicitly provide optimal solutions to them. Finally, a reinforcement learning technique is used to learn the optimal control protocol for each agent without requiring any knowledge of the agents or the leader dynamics. Simulation studies on a notional multi-agent system validate the proposed approach.

Spring Land Surface and Subsurface Temperature Anomalies and Subsequent Downstream Late Spring‐Summer Droughts/Floods in North America and East Asia

Abstract: Author(s): Xue, Y; Diallo, I; Li, W; David Neelin, J; Chu, PC; Vasic, R; Guo, W; Li, Q; Robinson, DA; Zhu, Y; Fu, C; Oaida, CM | Abstract: Sea surface temperature (SST) variability has been shown to have predictive value for land precipitation, although SSTs are unable to fully predict intraseasonal to interannual hydrologic extremes. The possible remote effects of large-scale land surface temperature (LST) and subsurface temperature (SUBT) anomalies in geographical areas upstream and closer to the areas of drought/flood have largely been ignored. Here evidence from climate observations and model simulations addresses these effects. Evaluation of observational data using Maximum Covariance Analysis identifies significant correlations between springtime 2-m air temperature (T2nm) cold (warm) anomalies in both the western U.S. and the Tibetan Plateau and downstream drought (flood) events in late spring/summer. To support these observational findings, climate models are used in sensitivity studies, in which initial LST/SUBT anomaly is imposed to produce observed T2nm anomaly, to demonstrate a causal relationship for two important cases: between spring warm T2nm/LST/SUBT anomalies in western U.S. and the extraordinary 2015 flood in Southern Great Plains and adjacent regions and between spring cold T2nm/LST/SUBT anomalies in the Tibetan Plateau and the severe 2003 drought south of the Yangtze River region. The LST/SUBT downstream effects in North America are associated with a large-scale atmospheric stationary wave extending eastward from the LST/SUBT anomaly region. The effects of SST in these cases are also tested and compared with the LST/SUBT effects. These results suggest that consideration of LST/SUBT anomalies has the potential to add value to intraseasonal prediction of dry and wet conditions, especially extreme drought/flood events. The results suggest the importance of developing land data and models capable of preserving observed soil memory.

State of the world 2017: autocratization and exclusion?

Abstract: This article presents evidence of a global trend of autocratization. The most visible feature of democracy – elections – remains strong and is even improving in some places. Autocratization mainly affects non-electoral aspects of democracy such as media freedom, freedom of expression, and the rule of law, yet these in turn threaten to undermine the meaningfulness of elections. While the majority of the world’s population lives under democratic rule, 2.5 billion people were subjected to autocratization in 2017. Last year, democratic qualities were in decline in 24 countries across the world, many of which are populous such as India and the United States. This article also presents evidence testifying that men and wealthy groups tend to have a strong hold on political power in countries where 86% of the world population reside. Further, we show that political exclusion based on socio-economic status in particular is becoming increasingly severe. For instance, the wealthy have gained significantly mo...

Identifying network structure similarity using spectral graph theory

Abstract: Most real networks are too large or they are not available for real time analysis Therefore, in practice, decisions are made based on partial information about the ground truth network It is of great interest to have metrics to determine if an inferred network (the partial information network) is similar to the ground truth In this paper we develop a test for similarity between the inferred and the true network Our research utilizes a network visualization tool, which systematically discovers a network, producing a sequence of snapshots of the network We introduce and test our metric on the consecutive snapshots of a network, and against the ground truth To test the scalability of our metric we use a random matrix theory approach while discovering Erdos-Renyi graphs This scaling analysis allows us to make predictions about the performance of the discovery process

Higher Education and Prosperity: From Catholic Missionaries to Luminosity in India

Abstract: This paper estimates the impact of completed higher education on economic prosperity across Indian districts. To address the endogeneity of higher education, we use the location of Catholic missionaries circa 1911 as an instrument. Catholics constitute a very small share of the population in India and their influence beyond higher education has been limited. Our instrumental variable results find a positive effect of higher education on development, as measured by light density. The results are robust to alternative measures of development, and are not driven by lower levels of schooling or other channels by which missionaries could impact current income. This article is protected by copyright. All rights reserved.

A technical review and evaluation of implantable sensors for hearing devices

Abstract: Most commercially available cochlear implants and hearing aids use microphones as sensors for capturing the external sound field. These microphones are in general located in an external element, which is also responsible for processing the sound signal. However, the presence of the external element is the cause of several problems such as discomfort, impossibility of being used during physical activities and sleeping, and social stigma. These limitations have driven studies with the goal of developing totally implantable hearing devices, and the design of an implantable sensor has been one of the main challenges to be overcome. Different designs of implantable sensors can be found in the literature and in some commercial implantable hearing aids, including different transduction mechanisms (capacitive, piezoelectric, electromagnetic, etc), configurations microphones, accelerometers, force sensor, etc) and locations (subcutaneous or middle ear). In this work, a detailed technical review of such designs is presented and a general classification is proposed. The technical characteristics of each sensors are presented and discussed in view of the main requirements for an implantable sensor for hearing devices, including sensitivity, internal noise, frequency bandwidth and energy consumption. The feasibility of implantation of each sensor is also evaluated and compared.

ARCTIC CHANGE AND POSSIBLE INFLUENCE ON MID-LATITUDE CLIMATE AND WEATHER: A US CLIVAR White Paper.

Abstract: The Arctic has warmed more than twice as fast as the global average since the mid 20th century, a phenomenon known as Arctic amplification (AA). These profound changes to the Arctic system have coincided with a period of ostensibly more frequent events of extreme weather across the Northern Hemisphere (NH) mid-latitudes, including extreme heat and rainfall events and recent severe winters. Though winter temperatures have generally warmed since 1960 over mid-to-high latitudes, the acceleration in the rate of warming at high-latitudes, relative to the rest of the NH, started approximately in 1990. Trends since 1990 show cooling over the NH continents, especially in Northern Eurasia. The possible link between Arctic change and mid-latitude climate and weather has spurred a rush of new observational and modeling studies. A number of workshops held during 2013-2014 have helped frame the problem and have called for continuing and enhancing efforts for improving our understanding of Arctic-mid-latitude linkages and its attribution to the occurrence of extreme climate and weather events. Although these workshops have outlined some of the major challenges and provided broad recommendations, further efforts are needed to synthesize the diversified research results to identify where community consensus and gaps exist. Building upon findings and recommendations of the previous workshops, the US CLIVAR Working Group on Arctic Change and Possible Influence on Mid-latitude Climate and Weather convened an international workshop at Georgetown University in Washington, DC, on February 1-3, 2017. Experts in the fields of atmosphere, ocean, and cryosphere sciences assembled to assess the rapidly evolving state of understanding, identify consensus on knowledge and gaps in research, and develop specific actions to accelerate progress within the research community. With more than 100 participants, the workshop was the largest and most comprehensive gathering of climate scientists to address the topic to date. In this white paper, we synthesize and discuss outcomes from this workshop and activities involving many of the working group members.

Critical scaling near the yielding transition in granular media.

Abstract: We show that the yielding transition in granular media displays second-order critical-point scaling behavior. We carry out discrete element simulations in the low-inertial-number limit for frictionless, purely repulsive spherical grains undergoing simple shear at fixed nondimensional shear stress Σ in two and three spatial dimensions. To find a mechanically stable (MS) packing that can support the applied Σ, isotropically prepared states with size L must undergo a total strain γ_{ms}(Σ,L). The number density of MS packings (∝γ_{ms}^{-1}) vanishes for Σ>Σ_{c}≈0.11 according to a critical scaling form with a length scale ξ∝|Σ-Σ_{c}|^{-ν}, where ν≈1.7-1.8. Above the yield stress (Σ>Σ_{c}), no MS packings that can support Σ exist in the large-system limit L/ξ≫1. MS packings generated via shear possess anisotropic force and contact networks, suggesting that Σ_{c} is associated with an upper limit in the degree to which these networks can be deformed away from those for isotropic packings.

Recent Advances in Research and Forecasting of Tropical Cyclone Track, Intensity, and Structure at Landfall

Abstract: This review prepared for the fourth International Workshop on Tropical Cyclone Landfall Processes (IWTCLP-4) summarizes the most recent (2015-2017) theoretical and practical knowledge in the field of tropical cyclone (TC) track, intensity, and structure rapid changes at or near landfall. Although the focus of IWTCLP-IV was on landfall, this summary necessarily embraces the characteristics of storms during their course over the ocean prior to and leading up to landfall. In the past few years, extremely valuable observational datasets have been collected using both aircraft reconnaissance and new geostationary and low-earth orbiting satellites at high temporal and spatial resolution for TC forecasting guidance and research studies. Track deflections for systems near complex topography such as that of Taiwan and La Reunion have been further investigated, and advanced numerical models with high spatial resolution necessary to predict the interaction of the TC circulation with steep island topography have been developed. An analog technique has been designed to meet the need for longer range landfall intensity forecast guidance that will provide more time for emergency preparedness. Probabilistic track and intensity forecasts were also developed to better communicate on forecast uncertainty. Operational practices of several TC forecast centers are described herein and some challenges regarding forecasts and warnings for TCs making landfall are identified. This review concludes with insights from both researchers and forecasters regarding future directions to improve predictions of TC track, intensity, and structure at landfall.

On the design of a MEMS piezoelectric accelerometer coupled to the middle ear as an implantable sensor for hearing devices.

Abstract: The presence of external elements is a major limitation of current hearing aids and cochlear implants, as they lead to discomfort and inconvenience. Totally implantable hearing devices have been proposed as a solution to mitigate these constraints, which has led to challenges in designing implantable sensors. This work presents a feasibility analysis of a MEMS piezoelectric accelerometer coupled to the ossicular chain as an alternative sensor. The main requirements of the sensor include small size, low internal noise, low power consumption, and large bandwidth. Different designs of MEMS piezoelectric accelerometers were modeled using Finite Element (FE) method, as well as optimized for high net charge sensitivity. The best design, a 2 × 2 mm2 annular configuration with a 500 nm thick Aluminum Nitride (AlN) layer was selected for fabrication. The prototype was characterized, and its charge sensitivity and spectral acceleration noise were found to be with good agreement to the FE model predictions. Weak coupling between a middle ear FE model and the prototype was considered, resulting in equivalent input noise (EIN) lower than 60 dB sound pressure level between 600 Hz and 10 kHz. These results are an encouraging proof of concept for the development of MEMS piezoelectric accelerometers as implantable sensors for hearing devices.

Stability of a giant connected component in a complex network.

Abstract: We analyze the stability of the network's giant connected component under impact of adverse events, which we model through the link percolation. Specifically, we quantify the extent to which the largest connected component of a network consists of the same nodes, regardless of the specific set of deactivated links. Our results are intuitive in the case of single-layered systems: the presence of large degree nodes in a single-layered network ensures both its robustness and stability. In contrast, we find that interdependent networks that are robust to adverse events have unstable connected components. Our results bring novel insights to the design of resilient network topologies and the reinforcement of existing networked systems.

The Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS): Initial Benchmarks and Future Directions

Abstract: Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code-verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well-defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike-slip fault obeying rate-and-state friction, embedded in a 2D homogeneous, linear elastic half-space. Sequences of quasi-dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long-term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics.

Nightmares in United States Military Personnel With Sleep Disturbances.

Abstract: Study Objectives:Sleep disturbances are common in United States military personnel. Despite their exposure to combat and trauma, little is known about nightmares in this population. The purpose of ...

Ocean Stratification and Low Melt Rates at the Ross Ice Shelf Grounding Zone

Abstract: Ocean‐driven melting of ice shelves is a primary mechanism for ice loss from Antarctica. However, due to the difficulty in accessing the sub‐ice shelf ocean cavity, the relationship between ice shelf melting and ocean conditions is poorly understood, particularly near the grounding zone, where the ice transitions from grounded to floating. We present the first borehole oceanographic observations from the grounding zone of the Ross Ice Shelf, Antarctica's largest ice shelf by area. Contrary to predictions that tidal currents near grounding zones mix the water column, we found that Ross Ice Shelf waters were vertically stratified. Current velocities at middepth in the ocean cavity did not change significantly over measurement periods at two different parts of the tidal cycle. The observed stratification resulted in low melt rates near this portion of the grounding zone, inferred from phase‐sensitive radar observations. These melt rates were generally <10 cm/year, which is lower than average for the Ross Ice Shelf (∼20 cm/year). Melt rates may be higher at portions of the grounding zone that experience higher subglacial discharge or stronger tidal mixing. Stratification in the cavity at the borehole site was prone to diffusive convection as a result of ice shelf melting. Since diffusive convection influences vertical heat and salt fluxes differently than shear‐driven turbulence, this process may affect ice shelf melting and merits further consideration in ocean models of sub‐ice shelf circulation.

Theoretical Expressions for the Ascent Rate of Moist Deep Convective Thermals

Abstract: An approximate analytic expression is derived for the ratio λ of the ascent rate of moist deep convective thermals and the maximum vertical velocity within them; λ is characterized as a fun...

Optimal Motion Planning for Differentially Flat Systems Using Bernstein Approximation

Abstract: This letter presents a computational framework to efficiently generate feasible and optimal trajectories for differentially flat autonomous vehicle systems. We formulate the optimal motion planning problem as a continuous-time optimal control problem, and approximate it by a discrete-time formulation using Bernstein polynomials. These polynomials allow for efficient computation of various constraints along the entire trajectory, and are particularly convenient for generating trajectories for safe operation of multiple vehicles in complex environments. The advantages of the proposed method are investigated through theoretical analysis and numerical examples.

BGP Communities: Even more Worms in the Routing Can

Abstract: BGP communities are a mechanism widely used by operators to manage policy, mitigate attacks, and engineer traffic; e.g., to drop unwanted traffic, filter announcements, adjust local preference, and prepend paths to influence peer selection. Unfortunately, we show that BGP communities can be exploited by remote parties to influence routing in unintended ways. The BGP community-based vulnerabilities we expose are enabled by a combination of complex policies, error-prone configurations, a lack of cryptographic integrity and authenticity over communities, and the wide extent of community propagation. Due in part to their ill-defined semantics, BGP communities are often propagated far further than a single routing hop, even though their intended scope is typically limited to nearby ASes. Indeed, we find 14% of transit ASes forward received BGP communities onward. Given the rich inter-connectivity of transit ASes, this means that communities effectively propagate globally. As a consequence, remote adversaries can use BGP communities to trigger remote blackholing, steer traffic, and manipulate routes even without prefix hijacking. We highlight examples of these attacks via scenarios that we tested and measured both in the lab as well as in the wild. While we suggest what can be done to mitigate such ill effects, it is up to the Internet operations community whether to take up the suggestions.