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Collision avoidance for unmanned aircraft using Markov Decision Processes

Summary

Before unmanned aircraft can fly safely in civil airspace, robust airborne collision avoidance systems must be developed. Instead of hand-crafting a collision avoidance algorithm for every combination of sensor and aircraft configuration, we investigate the automatic generation of collision avoidance algorithms given models of aircraft dynamics, sensor performance, and intruder behavior. By formulating the problem of collision avoidance as a Markov Decision Process (MDP) for sensors that provide precise localization of the intruder aircraft, or a Partially Observable Markov Decision Process (POMDP) for sensors that have positional uncertainty or limited field-of-view constraints, generic MDP/POMDP solvers can be used to generate avoidance strategies that optimize a cost function that balances flight-plan deviation with collision. Experimental results demonstrate the suitability of such an approach using four different sensor modalities and a parametric aircraft performance model.
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Summary

Before unmanned aircraft can fly safely in civil airspace, robust airborne collision avoidance systems must be developed. Instead of hand-crafting a collision avoidance algorithm for every combination of sensor and aircraft configuration, we investigate the automatic generation of collision avoidance algorithms given models of aircraft dynamics, sensor performance, and intruder...

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Wind-shear system cost-benefit analysis

Author:
Published in:
Lincoln Laboratory Journal, Vol. 18, No. 2, August 20, pp. 47-68.

Summary

Mitigating thunderstorm wind-shear threats for aircraft near the ground has been an important issue since the 1970s, when several fatal commercial aviation accidents were attributed to wind shear. Updating the knowledge base for airport wind-shear exposure and effectiveness of detection systems has become critical to the Federal Aviation Administration as they consider options for aging systems and evaluations of new systems.
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Summary

Mitigating thunderstorm wind-shear threats for aircraft near the ground has been an important issue since the 1970s, when several fatal commercial aviation accidents were attributed to wind shear. Updating the knowledge base for airport wind-shear exposure and effectiveness of detection systems has become critical to the Federal Aviation Administration as...

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GROK: a practical system for securing group communications

Published in:
NCA 2010, 9th IEEE Int. Symp. on Network Computing and Applications, 15 July 2010, pp. 100-107.

Summary

We have designed and implemented a general-purpose cryptographic building block, called GROK, for securing communication among groups of entities in networks composed of high-latency, low-bandwidth, intermittently connected links. During the process, we solved a number of non-trivial system problems. This paper describes these problems and our solutions, and motivates and justifies these solutions from three viewpoints: usability, efficiency, and security. The solutions described in this paper have been tempered by securing a widely-used group-oriented application, group text chat. We implemented a prototype extension to a popular text chat client called Pidgin and evaluated it in a real-world scenario. Based on our experiences, these solutions are useful to designers of group-oriented systems specifically, and secure systems in general.
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Summary

We have designed and implemented a general-purpose cryptographic building block, called GROK, for securing communication among groups of entities in networks composed of high-latency, low-bandwidth, intermittently connected links. During the process, we solved a number of non-trivial system problems. This paper describes these problems and our solutions, and motivates and...

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Predictive modeling of forecast uncertainty in the Route Availability Planning Tool (RAPT)

Published in:
2010 Intl. Conf. on Scientific Computing, CSC, 12-15 July 2010.

Summary

MIT Lincoln Laboratory has developed the Route Availability Planning Tool (RAPT), which provides automated convective weather guidance to air traffic managers of the NYC metro region. Prior studies of RAPT have shown high-accuracy guidance from forecast weather, but further refinements to prevent forecast misclassification is still desirable. An attribute set of highly correlated predictors for forecast misclassification is identified. Using this attribute set, a variety of prediction models for forecast misclassification are generated and evaluated. Rule-based models, decision trees, multi-layer perceptrons, and Bayesian prediction model techniques are used. Filtering, resampling, and attribute selection methods are applied to refine model generation. Our results show promising accuracy rates for multi-layer perceptrons trained on full attribute sets.
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Summary

MIT Lincoln Laboratory has developed the Route Availability Planning Tool (RAPT), which provides automated convective weather guidance to air traffic managers of the NYC metro region. Prior studies of RAPT have shown high-accuracy guidance from forecast weather, but further refinements to prevent forecast misclassification is still desirable. An attribute set...

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Weighted nuisance attribute projection

Published in:
Odyssey 2010, the Speaker and Language Recognition Workshop, 28 June - 1 July 2010.

Summary

Nuisance attribute projection (NAP) has become a common method for compensation of channel effects, session variation, speaker variation, and general mismatch in speaker recognition. NAP uses an orthogonal projection to remove a nuisance subspace from a larger expansion space that contains the speaker information. Training the NAP subspace is based on optimizing pairwise distances to reduce intraspeaker variability and retain interspeaker variability. In this paper, we introduce a novel form of NAP called weighted NAP (WNAP) which significantly extends the current methodology. For WNAP, we propose a training criterion that incorporates two critical extensions to NAP variable metrics and instance-weighted training. Both an eigenvector and iterative method are proposed for solving the resulting optimization problem. The effectiveness of WNAP is shown on a NIST speaker recognition evaluation task where error rates are reduced by over 20%.
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Summary

Nuisance attribute projection (NAP) has become a common method for compensation of channel effects, session variation, speaker variation, and general mismatch in speaker recognition. NAP uses an orthogonal projection to remove a nuisance subspace from a larger expansion space that contains the speaker information. Training the NAP subspace is based...

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Adaptive optics wavefront sensors based on photon-counting detector arrays

Published in:
Proc. SPIE Vol. 7736, Adaptive Optics Systems II, 27 June 2010, 773610.

Summary

For adaptive optics systems, there is a growing demand for wavefront sensors that operate at higher frame rates and with more pixels while maintaining low readout noise. Lincoln Laboratory has been investigating Geiger·mode avalanche photodiode arrays integrated with CMOS readout circuits as a potential solution. This type of sensor counts photons digitally within the pixel, enabling data to be read out at high rates without the penalty of readout noise. After a brief overview of adaptive optics sensor development at Lincoln Laboratory, we will present the status of silicon Geiger· mode·APD technology along with future plans to improve performance.
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Summary

For adaptive optics systems, there is a growing demand for wavefront sensors that operate at higher frame rates and with more pixels while maintaining low readout noise. Lincoln Laboratory has been investigating Geiger·mode avalanche photodiode arrays integrated with CMOS readout circuits as a potential solution. This type of sensor counts...

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Voice production mechanisms following phonosurgical treatment of early glottic cancer

Published in:
Ann. Ontol., Rhinol. Laryngol., Vol. 119, No. 1, 2010, pp. 1-9.

Summary

Although near-normal conversational voices can be achieved with the phonosurgical management of early glottic cancer, there are still acoustic and aerodynamic deficits in vocal function that must be better understood to help further optimize phonosurgical interventions. Stroboscopic assessment is inadequate for this purpose. A newly discovered color high-speed videoendoscopy (HSV) system that included time-synchronized recordings of the acoustic signal was used to perform a detailed examination of voice production mechanisms in 14 subjects. Digital image processing techniques were used to quantify glottal phonatory function and to delineate relationships between vocal fold vibratory properties and acoustic perturbation measures. [not complete]
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Summary

Although near-normal conversational voices can be achieved with the phonosurgical management of early glottic cancer, there are still acoustic and aerodynamic deficits in vocal function that must be better understood to help further optimize phonosurgical interventions. Stroboscopic assessment is inadequate for this purpose. A newly discovered color high-speed videoendoscopy (HSV)...

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A roadmap for optical lithography

Published in:
Optics & Photonics News, Vol. 21, No. 6, June 2010, pp. 26-31.

Summary

The International Technology Roadmap for Semiconductors is the go-to standard for predicting future technology requirements and driving global research and development in the semiconductor industry. This article serves as your roadmap to what it all means for optical lithography over the next 10 to 15 years.
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Summary

The International Technology Roadmap for Semiconductors is the go-to standard for predicting future technology requirements and driving global research and development in the semiconductor industry. This article serves as your roadmap to what it all means for optical lithography over the next 10 to 15 years.

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Optical limiting with complex plasmonic nanoparticles

Published in:
J. Optics, Vol. 12, No. 6, 2010, 065001.

Summary

Optical limiting by suspensions of Au nanoparticles is enhanced by several orders of magnitude with the use of complex plasmonic shapes, such as spined "nanourchins," instead of nanospheres. Similar enhancements are observed by changing the material of nanospheres from Au to Ag. The experiments, measuring intensity-dependent transmission over a wavelength range from 450 to 650 nm for a 6 ns pulsed laser, are analyzed in terms of an effective nonlinear extinction coefficient, which we relate to the local, plasmonically enhanced electric field. FDTD simulations reveal a large electric field enhancement inside the nanospined structures and qualitatively confirm the plasmonic trends, where Ag nanospheres and Au nanourchins are more effective than Au nanospheres. These results suggest that designing nanostructures for the maximum plasmonic enhancement provides a roadmap to materials and geometries with optimized optical limiting behavior.
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Summary

Optical limiting by suspensions of Au nanoparticles is enhanced by several orders of magnitude with the use of complex plasmonic shapes, such as spined "nanourchins," instead of nanospheres. Similar enhancements are observed by changing the material of nanospheres from Au to Ag. The experiments, measuring intensity-dependent transmission over a wavelength...

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Advanced architecture for a low cost multifunction phased array radar

Summary

MIT Lincoln Laboratory and MIA-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.
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Summary

MIT Lincoln Laboratory and MIA-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit...

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