Publications
Detection statistics in Geiger-mode avalanche photodiode quad-cell arrays with crosstalk and dead time
April 1, 2015
Journal Article
Published in:
IEEE Sens. J., Vol. 15, No. 4, April 2015, pp. 2133-43.
Summary
The detection statistics of Geiger-mode photodetector subarrays with a combination of reset-time blocking loss and optical crosstalk are investigated. Closed-form expressions are obtained for the means and covariances of the numbers of counts in 2 x 2 subarrays (quad cells) used in Shack-Hartmann wavefront sensors. The predicted wavefront sensing precision is compared with that obtained with a charge-coupled device-based wavefront sensor with readout noise. The results of the theory are also used to predict photon transfer curves for the Geiger-mode device and these are compared with experiment.
Summary
The detection statistics of Geiger-mode photodetector subarrays with a combination of reset-time blocking loss and optical crosstalk are investigated. Closed-form expressions are obtained for the means and covariances of the numbers of counts in 2 x 2 subarrays (quad cells) used in Shack-Hartmann wavefront sensors. The predicted wavefront sensing precision...
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Cryptographically secure computation
April 1, 2015
Journal Article
Published in:
Computer, Vol. 48, No. 4, April 2015, pp. 78-81.
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Summary
Researchers are making secure multiparty computation--a cryptographic technique that enables information sharing and analysis while keeping sensitive inputs secret--faster and easier to use for application software developers.
Summary
Researchers are making secure multiparty computation--a cryptographic technique that enables information sharing and analysis while keeping sensitive inputs secret--faster and easier to use for application software developers.
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Permittivity evaluation of multilayered hyperbolic metamaterials: ellipsometry vs. reflectometry
March 14, 2015
Journal Article
Published in:
J. Appl. Phys., Vol. 117, No. 10, 14 March 2015, 103104.
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Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectrometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered material as a uniaxial medium and compare the derived optical parameters to those expected from the effective medium approximation. We also experimentally compare the effect of varying the material outer layer on the homogenization of the composite. Additionally, we introduce a simple empirical method of extracting the epsilon-near-zero point of the nanolaminates from normal incidence reflectance. The results of this study are useful in accurate determination of the hyperbolic material permittivity and in the ability to tune its optical properties.
Summary
Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectrometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered...
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Hyperspectral Microwave Atmospheric Sounder (HyMAS) - new capability in the CoSMIR/CoSSIR scanhead
March 7, 2015
Conference Paper
Published in:
2015 IEEE Aerospace Conf., 7-14 March 2015.
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MIT Lincoln Laboratory and NASA's Goddard Space Flight Center have teamed to adapt an existing instrument platform, the CoSMIR/CoSSIR system for atmospheric sensing, to develop and demonstrate a new capability in a hyperspectral microwave atmospheric sounder (HyMAS). This new sensor comprises a highly innovative intermediate frequency processor (IFP), that provides the filtering and digitization of 52 radiometric channels and the interoperable remote component (IRC) adapted to CoSMIR, CoSSIR, and HyMAS that stores and archives the data with time tagged calibration and navigation data. The first element of the work is the demonstration of a hyperspectral microwave receiver subsystem that was recently shown using a comprehensive simulation study to yield performance that substantially exceeds current state-of-the-art. Hyperspectral microwave sounders with ~100 channels offer temperature and humidity sounding improvements similar to those obtained when infrared sensors became hyperspectral. Hyperspectral microwave operation is achieved using independent RF antenna/receiver arrays that sample the same area/volume of the Earth's surface/atmosphere at slightly different frequencies and therefore synthesize a set of dense, finely spaced vertical weighting functions. The second, enabling element is the development of a compact 52-channel Intermediate Frequency processor module. A principal challenge of a hyperspectral microwave system is the size of the IF filter bank required for channelization. Large bandwidths are simultaneously processed, thus complicating the use of digital back-ends with associated high complexities, costs, and power requirements. Our approach involves passive filters implemented using low-temperature co-fired ceramic (LTCC) technology to achieve an ultra-compact module that can be easily integrated with existing RF front-end technology. This IF processor is applicable to other microwave sensing missions requiring compact IF spectrometry. The unit produces 52 channels of spectral data in a highly compact volume (
Summary
MIT Lincoln Laboratory and NASA's Goddard Space Flight Center have teamed to adapt an existing instrument platform, the CoSMIR/CoSSIR system for atmospheric sensing, to develop and demonstrate a new capability in a hyperspectral microwave atmospheric sounder (HyMAS). This new sensor comprises a highly innovative intermediate frequency processor (IFP), that provides...
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The 2013 Buffalo Area Icing and Radar Study (BAIRS)
March 6, 2015
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-419
Summary
The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the radar-sensed thermodynamic phase of the hydrometeors (solid, liquid, mix) in the context of cloud microphysics and precipitation physics makes it possible to assess the icing hazard potential to aviation. That assessment for Federal Aviation Administration (FAA) purposes would necessarily be performed by automated algorithms based in hydrometeor classification terms. The truth as to the icing hazard aloft (where the radar scans) is required to ascertain the value of such algorithms. The Buffalo Area Icing and Radar Study (BAIRS) of 2013 was a partnership between MIT Lincoln Laboratory (LL) and the National Research Council of Canada (NRC) to perform in situ icing missions within the surveillance range of the dual polarization NEXRAD in Buffalo, NY. The goal of these 2013 missions, and the subject of this report, was to target specific winter weather scenarios known to exhibit an aviation icing hazard for the purpose of quantifying the microphysical properties of the target zones and verifying the presence of supercooled liquid water (SLW) to support validation of hydrometeor classification algorithms. These are the first such missions to execute in situ measurements within a NEXRAD's surveillance range running with the fielded, operational NEXRAD hydrometeor classifier. NRC's Convair-580 instrumented research plane was used for three icing missions covering 14 hours. Three distinctly different winter weather scenarios were encountered. This document details the analysis of in situ data such as particle type and liquid water content (LWC) with NEXRAD dual polarization parameters for the three missions. The BAIRS analysis identified these key findings: -NEXRAD radar returns are prevalent in conditions of supercooled water, -NEXRAD classification shows positive results based on particle imagery, -NEXRAD "dry snow" class masks the presence of mixed phase potential icing hazard, -NEXRAD "unknown" class contains diverse regions of icing hazard potential, and there are methods to classify some of these regions, and -In situ aircraft observations are an important tool to both verify algorithm performance and guide further development.
Summary
The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the radar-sensed thermodynamic phase of the...
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Nanochannel fabrication based on double patterning with hydrogen silsesquioxane
March 1, 2015
Journal Article
Published in:
J. Vac. Sci. Technol. B, Microelectron. Process. Phenon., Vol. 33, No. 2, March 2015, 020601.
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Summary
A double patterning process is presented to pattern sub-35 nm wide channels in hydrogen silsesquioxane with near 100% pattern densities. Using aligned electron beam lithography, each side of the nanochannel structure is patterned as a separate layer. A 50000 uC/cm^2 high-dose anneal is applied to the first layer after exposure. Channels with widths below ~60 nm are shown to exhibit footing with standard tetramethyl ammonium hydroxide developers. This problem is resolved by adding surfectant during the development of the final channel structure. The resulting process produced channels
Summary
A double patterning process is presented to pattern sub-35 nm wide channels in hydrogen silsesquioxane with near 100% pattern densities. Using aligned electron beam lithography, each side of the nanochannel structure is patterned as a separate layer. A 50000 uC/cm^2 high-dose anneal is applied to the first layer after exposure...
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Measurements of differential reflectivity in snowstorms and warm season stratiform systems
March 1, 2015
Journal Article
Published in:
J. Appl. Meteor. Climatol., Vol. 54, No. 3, 2015, pp. 573-95.
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The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion chambers in which humidity and temperature are both stringently controlled. The overriding operational interest here is in the identification of regions prone to icing hazards with long horizontal paths. Two predominant regimes are identified: category A, which is typified by moderate reflectivity (from 10 to 30 dBZ) and modest +ZDR values (from 0 to 13 dB) in which both supercooled water and dendritic ice crystals (and oriented aggregates of ice crystals) are present at a mean temperature of -13 degrees C, and category B, which is typified by small reflectivity (from -10 to +10 dBZ) and the largest +ZDR values (from +3 to +7 dB), in which supercooled water is dilute or absent and both flat-plate and dendritic crystals are likely. The predominant positive values for ZDR in many case studies suggest that the role of an electric field on ice particle orientation is small in comparison with gravity. The absence of robust +ZDR signatures in the trailing stratiform regions of vigorous summer squall lines may be due both to the infusion of noncrystalline ice particles (i.e., graupel and rimed aggregates) from the leading deep convection and to the effects of the stronger electric fields expected in these situations. These polarimetric measurements and their interpretations underscore the need for the accurate calibration of ZDR.
Summary
The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion...
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Advisory services for user composition tools
February 7, 2015
Conference Paper
Published in:
9th IEEE Int. Conf. on Semantic Computing, IEEE ICSC 2015, 7-9 February 2015.
Summary
We have developed an ontology based framework that evaluates compatibility between processing modules within an end user development framework, using MIT Lincoln Laboratory's Composable Analytics environment as a test case. In particular, we focus on inter-module semantic compatibility as well as compatibility between data and modules. Our framework includes a core ontology that provides an extendible vocabulary that can describe module attributes, module input and output requirements and preferences, and data characteristics that are pertinent to selecting appropriate modules in a given situation. Based on the ontological description of the modules and data, we first present a framework that takes a rule based approach in measuring semantic compatibility. Later, we extend the rule based approach to a flexible fuzzy logic based semantic compatibility evaluator. We have built an initial simulator to test module compatibility under varying situations. The simulator takes in the ontological description of the modules and data and calculates semantic compatibility. We believe the framework and simulation environment together will help both the developers test new modules they create as well as support end users in composing new capabilities. In this paper, we describe the details of the framework, the simulation environment, and our iterative process in developing the module ontology.
Summary
We have developed an ontology based framework that evaluates compatibility between processing modules within an end user development framework, using MIT Lincoln Laboratory's Composable Analytics environment as a test case. In particular, we focus on inter-module semantic compatibility as well as compatibility between data and modules. Our framework includes a...
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Terminal Flight Data Manager (TFDM) runway balancing capability assessment
February 6, 2015
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-421
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Under the Terminal Flight Data Manager program, new operational improvements are envisioned at a number of large airports. One operational improvement manifests through the Airport Resource Management tool, which seeks to balance departure demand at runways. Another related operational improvement is runway balancing, which is expected to provide greater flexibility in tactical runway assignments. Both improvements are expected to reduce surface delays for departing aircraft. This report provides a study into the potential delay-reduction benefits of both capabilities at three case-study airports (DFW, LAX, and MCO). Through a series of simulation studies, it is found that the benefits associated with each operational improvement are closely linked to departure demand and imbalances in demand across filed aircraft departure procedures. So, while large delay-reduction benefits are expected at LAX--which exhibits both large demand and departure imbalances--smaller benefits are expected at DFW where departure operations are already well-balanced. Meanwhile at MCO, the operational improvements are not expected to reduce delays due to limited departure demand at the airport.
Summary
Under the Terminal Flight Data Manager program, new operational improvements are envisioned at a number of large airports. One operational improvement manifests through the Airport Resource Management tool, which seeks to balance departure demand at runways. Another related operational improvement is runway balancing, which is expected to provide greater flexibility...
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Joint audio-visual mining of uncooperatively collected video: FY14 Line-Supported Information, Computation, and Exploitation Program
February 5, 2015
Project Report
Published in:
MIT Lincoln Laboratory Report LSP-116
Summary
The rate at which video is being created and gathered is rapidly accelerating as access to means of production and distribution expand. This rate of increase, however, is greatly outpacing the development of content-based tools to help users sift through this unstructured, multimedia data. The need for such technologies becomes more acute when considering their potential value in critical, media-rich government applications such as Seized Media Analysis, Social Media Forensics, and Foreign Media Monitoring. A fundamental challenge in developing technologies in these application areas is that they are typically in low-resource data domains. Low-resource domains are ones where the lack of ground-truth labels and statistical support prevent the direct application of traditional machine learning approaches. To help bridge this capability gap, the Joint Audio and Visual Mining of Uncooperatively Collected Video ICE Line Program (2236-1301) is developing new technologies for better content-based search, summarization, and browsing of large collections of unstructured, uncooperatively collected multimedia. In particular, this effort seeks to improve capabilities in video understanding by jointly exploiting time aligned audio, visual, and text information, an approach which has been underutilized in both the academic and commercial communities. Exploiting subtle connections between and across multiple modalities in low-resource multimedia data helps enable deeper video understanding, and in some cases provides new capability where it previously didn't exist. This report outlines work done in Fiscal Year 2014 (FY14) by the cross-divisional, interdisciplinary team tasked to meet these objectives. In the following sections, we highlight technologies developed in FY14 to support efficient Query-by-Example, Attribute, Keyword Search and Cross-Media Exploration and Summarization. Additionally, we preview work proposed for Fiscal Year 2015 as well as summarize our external sponsor interactions and publications/presentations.
Summary
The rate at which video is being created and gathered is rapidly accelerating as access to means of production and distribution expand. This rate of increase, however, is greatly outpacing the development of content-based tools to help users sift through this unstructured, multimedia data. The need for such technologies becomes...
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