Publications
Characterizing the optical variability of bright blazars: variability-based selection of fermi active galactic nuclei
November 20, 2012
Journal Article
Published in:
Astrophys. J., Vol. 760, No. 1, 20 November 2012, pp. 51-61.
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Summary
We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of y -ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability T , and driving amplitudes on short timescales ^sigma. Imposing cuts on minimum T and ^sigma allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several arcminute error ellipses of y -ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E >/ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other y -ray blazars and is likely to be the y -ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ~3 years in the rest frame of the jet, in contrast with the ~320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.
Summary
We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of y -ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid...
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Tower Flight Data Manager benefits assessment: initial investment decision interim report
November 19, 2012
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-394
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This document provides an overview of MIT Lincoln Laboratory's activities in support of the interim stage of the Initial Investment Decision benefits assessment for the Tower Flight Data Manager. It outlines the rationale for the focus areas, and the background, methodology, and scope in the focus areas of departure metering, sequence optimization, airport configuration optimization, and safety assessment. Estimates of the potential benefits enabled by TFDM deployment are presented for each of these areas for a subset of airports and conditions considered within the scope of the analyses. These benefits are monetized where possible. Recommendations for follow-on work, for example, to support future benefits assessment efforts for TFDM, are also discussed.
Summary
This document provides an overview of MIT Lincoln Laboratory's activities in support of the interim stage of the Initial Investment Decision benefits assessment for the Tower Flight Data Manager. It outlines the rationale for the focus areas, and the background, methodology, and scope in the focus areas of departure metering...
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Switchable electrowetting of droplets on dual-scale structured surfaces
November 7, 2012
Journal Article
Published in:
J. Vac. Sci. Technol. B, Microelectron. Process. Phenon., Vol. 30, No. 6, November 2012, 06F801.
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Summary
The authors report on the development of surfaces containing artificially fabricated structures of dual nanometer and micrometer surfaces that allow an aqueous droplet to be reversibly switched by electrowetting from a Cassie state with low adhesion to a Wenzel state with high adhesion. A variety of geometries were fabricated to study parameters that affect switchable wetting-dewetting. Nanometer parallel corrugations, posts, and holes were fabricated and combined with micrometer features consisting of parallel corrugations, streets, and checkerboard patterns of varying widths and pitches. It was observed that many combinations of the dual-textured surfaces produced superhydrophobic wetting states and aqueous droplets on these surfaces could be electrically controlled to switch from a Cassie state to a Wenzel state. Reversible switching between these wetting states occurred on specific combinations of surface geometries, namely surfaces that had parallel corrugations.
Summary
The authors report on the development of surfaces containing artificially fabricated structures of dual nanometer and micrometer surfaces that allow an aqueous droplet to be reversibly switched by electrowetting from a Cassie state with low adhesion to a Wenzel state with high adhesion. A variety of geometries were fabricated to...
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Multifunction Phased Array Radar wind shear experiment
November 5, 2012
Conference Paper
Published in:
26th Conf. on Sever Local Storms, 5-8 November 2012.
Summary
Terminal Doppler Weather Radars (TDWRs) provide near-ground wind shear detection that is critical for aircraft safety at 46 airports across the United States. These systems are part of the larger network of 510 weather and aircraft surveillance radars owned and operated by government agencies in the continental United States. As the TDWR and other radar systems approach their engineering design life cycles, the Federal Aviation Administration (FAA), National Weather Service (NWS), and Department of Defense (DoD) are considering potential replacement systems (OFCM 2006; Weber et al. 2007). One option under consideration that would maintain the current airspace coverage is a replacement network of 334 Multifunction Phased Array Radars (MPARs) (Weber et al. 2007). The MPAR network described by Weber et al. (2007) would include two classes of systems: A high-resolution, full-scale version with an 8-m diameter antenna, and a lower-resolution terminal version with a 4-m diameter antenna, termed Terminal MPAR, or TMPAR. As the proposed TMPAR design has lower azimuthal beam resolution and less sensitivity than TDWRs, it is crucial to determine the impacts of that design on the detection of low-altitude wind shear. The design of the SPY-1A PAR, a research radar at the National Weather Radar Test Bed in Norman, Oklahoma (Zrnić et al. 2007), makes it a good proxy for examining the potential wind shear detection performance of the TMPAR. Therefore, in spring 2012, the National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory organized and executed the MPAR Wind Shear Experiment (WSE) in collaboration with the FAA, NOAA's NWS Radar Operations Center, the University of Oklahoma Advanced Radar Research Center (OU ARRC), and the Massachusetts Institute of Technology Lincoln Laboratory (MIT LL). The primary objective of the MPAR WSE was to collect low-altitude observations with the SPY-1A PAR (hereafter, PAR) for comparison with observations from the nearby Oklahoma City (OKC) TDWR. Of particular interest is comparison of MIT LL wind shear detection algorithm performance using data from these two radars; this analysis is reported in Cho et al. (2013). Data were also collected from other radars in central Oklahoma to facilitate basic research on microbursts and other wind-producing storms. This paper provides an overview of the MPAR WSE and observed wind shear events.
Summary
Terminal Doppler Weather Radars (TDWRs) provide near-ground wind shear detection that is critical for aircraft safety at 46 airports across the United States. These systems are part of the larger network of 510 weather and aircraft surveillance radars owned and operated by government agencies in the continental United States. As...
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Shared information access services in SWIM segment 2: an architectural assessment
October 31, 2012
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-383
Summary
The System Wide Information Management (SWIM) program is a foundational program for the Federal Aviation Administration?s (FAA) Next Generation Air Transportation System (NextGen) initiative, with a goal of providing a common, scalable information management infrastructure. Though some benefits were realized in SWIM Segment 1 from the use of common software infrastructure components (i.e., the Progress FUSE software suite), the actual reuse of service interfaces was limited. The focus of SWIM Segment 2 is increasingly on shared services, with a goal of improved interoperability as well as increased software reuse. This report focuses on shared data access services, based on lessons learned in the SWIM Segment 1 Corridor Integrated Weather System (CIWS) SWIM Implementing Program (SIP) activity, the NextGen Network-Enabled Weather (NNEW) program, and a number of other Laboratory net-centric programs. The applicability of other information sharing architectures, such as the Web and content delivery overlay networks, to SWIM is also assessed. Based on this assessment, a number of recommendations are suggested to facilitate the development of shared services that are flexible enough to respond quickly to evolving NextGen requirements, while at the same time minimizing the overall SWIM software "footprint."
Summary
The System Wide Information Management (SWIM) program is a foundational program for the Federal Aviation Administration?s (FAA) Next Generation Air Transportation System (NextGen) initiative, with a goal of providing a common, scalable information management infrastructure. Though some benefits were realized in SWIM Segment 1 from the use of common software...
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Dynamic photoacoustic spectroscopy for trace gas detection
October 29, 2012
Journal Article
Published in:
Appl. Phys. Lett., Vol. 101, No. 18, 29 October 2012, 184103.
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Summary
We present a method of photoacoustic spectroscopy in which a laser beam tuned to an absorption feature of a gas is swept through its plume at the speed of sound. The resulting coherent addition of acoustic waves leads to an amplification of the signal without the need for a resonant chamber, thus enhancing the ability to remotely sense the gas. We demonstrate the concept using a tunable CO2 laser and SF6 gas in conjunction with a microphone. Sound pressure levels of 83 dB (relative to 20 uPa) are generated from a 15-ppm plume.
Summary
We present a method of photoacoustic spectroscopy in which a laser beam tuned to an absorption feature of a gas is swept through its plume at the speed of sound. The resulting coherent addition of acoustic waves leads to an amplification of the signal without the need for a resonant...
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Characterization of traffic and structure in the U.S. airport network
October 24, 2012
Conference Paper
Published in:
CIDU 2012: Conf. on Intelligent Data Understanding, 24-26 October, 2012.
Summary
In this paper we seek to characterize traffic in the U.S. air transportation system, and to subsequently develop improved models of traffic demand. We model the air traffic within the U.S. national airspace system as dynamic weighted network. We employ techniques advanced by work in complex networks over the past several years in characterizing the structure and dynamics of the U.S. airport network. We show that the airport network is more dynamic over successive days than has been previously reported. The network has some properties that appear stationary over time, while others exhibit a high degree of variation. We characterize the network and its dynamics using structural measures such as degree distributions and clustering coefficients. We employ spectral analysis to show that dominant eigenvectors of the network are nearly stationary with time. We use this observation to suggest how low dimensional models of traffic demand in the airport network can be fashioned.
Summary
In this paper we seek to characterize traffic in the U.S. air transportation system, and to subsequently develop improved models of traffic demand. We model the air traffic within the U.S. national airspace system as dynamic weighted network. We employ techniques advanced by work in complex networks over the past...
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Cognitive workload and visual attention analyses of the air traffic control Tower Flight Data Manager (TFDM) prototype demonstration
October 22, 2012
Conference Paper
Published in:
HFES 2012, Human Factors and Ergonomics Society 56th Annual Mtg., 22-26 October 2012.
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This paper presents two methods of analyzing air traffic controller activity: cognitive workload measurement through the novel comparison of controller-pilot verbal communications, and visual attention quantification through manual eye gaze analysis. These analyses were performed as part of an evaluation of the Tower Flight Data Manager (TFDM) prototype system. Cognitive workload analyses revealed that, when comparing participant controllers utilizing TFDM to a control group utilizing existing air traffic control (ATC) equipment, participants issued commands sooner than the control, and thus were perceived to have a lower workload. While visual attention data were not available for the control group, analyses of participant gaze data revealed 81.9% of time was spent in a head-down position, and 17.2% of time was spent head-up. Results are related back to system inefficiencies to find potential areas of improvement in design.
Summary
This paper presents two methods of analyzing air traffic controller activity: cognitive workload measurement through the novel comparison of controller-pilot verbal communications, and visual attention quantification through manual eye gaze analysis. These analyses were performed as part of an evaluation of the Tower Flight Data Manager (TFDM) prototype system. Cognitive...
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Estimating the monetizable safety benefits of prototype air traffic control technologies
October 22, 2012
Conference Paper
Published in:
HFES 2012, Human Factors and Ergonomics Society 56th Annual Mtg., 22-26 October 2012.
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The Federal Aviation Administration (FAA) utilizes a formal investment analysis process to support the development, procurement and deployment of new air traffic control technologies. It is often unclear how to estimate the impacts of a new technology on aviation safety, both in terms of the probability that incidents and accidents could be prevented and in terms of the potential financial savings associated with reduced aircraft damage and personal injuries. With this in mind, the focus of this paper is twofold: (1) demonstrating the application of a method for generating probabilistic estimates of safety benefits for a future air traffic control technology, and (2) monetizing and extrapolating safety impacts from historical data to provide a quantitative estimate of savings over the lifetime of a new technology. The technologies explored in this analysis involve electronic flight data, enhanced surveillance and decision support tools for the air traffic control tower environment. From this initial analysis, the estimated total monetizable safety benefit of deploying all of these capabilities in a new system with an expected 2015-2035 lifetime across a set of major airports in the US ranges from $155 million to $2.1 billion. Implications of key data assumptions driving the lower and upper-bound estimates are discussed.
Summary
The Federal Aviation Administration (FAA) utilizes a formal investment analysis process to support the development, procurement and deployment of new air traffic control technologies. It is often unclear how to estimate the impacts of a new technology on aviation safety, both in terms of the probability that incidents and accidents...
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DSKE: dynamic set key encryption
October 22, 2012
Conference Paper
Published in:
7th LCN Workshop on Security in Communications, 22 October 2012, pp. 1006-13.
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In this paper, we present a novel paradigm for studying the problem of group key distribution, use it to analyze existing key distribution schemes, and then present a novel scheme for group key distribution which we call "Dynamic Set Key Encryption," or DSKE. DSKE meets the demands of a tactical environment while relying only on standard cryptographic primitives. Our "set key" paradigm allows us to focus on the underlying problem of establishing a confidential communication channel shared by a group of users, without concern for related security factors like authenticity and integrity, and without the need to consider any properties of the group beyond a list of its members. This separation of concerns is vital to our development and analysis of DSKE, and can be applied elsewhere to simplify the analyses of other group key distribution schemes.
Summary
In this paper, we present a novel paradigm for studying the problem of group key distribution, use it to analyze existing key distribution schemes, and then present a novel scheme for group key distribution which we call "Dynamic Set Key Encryption," or DSKE. DSKE meets the demands of a tactical...
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