Publications

Refine Results

(Filters Applied) Clear All

Data-driven evaluation of a flight re-route air traffic management decision-support tool

Published in:
Applied Human Factors and Ergonomics Conf., 21 July 2012.

Summary

Air traffic delays in the U.S. are problematic and often attributable to convective (thunderstorms) weather. Air traffic management is complex, dynamic, and influenced by many factors such as projected high volume of departures and uncertain forecast convective weather at airports and in the airspace. To support the complexities of making a re-route decision, which is one solution to mitigate airspace congestion, a display integrating convective weather information with departure demand predictions was prototyped jointly by MIT Lincoln Laboratory and the MITRE Corporation. The tool was deployed to twelve air traffic facilities involved in handling New York area flights for operational evaluation during the summer of 2011. Field observations, data mining and analyses were conducted under both fair and convective weather conditions. The system performance metrics chosen to evaluate the tool's effectiveness in supporting re-route decisions include predicted wheels-off error, predicted wheels-off forecast spread, and hourly departure fix demand forecast spread. The wheels-off prediction errors were near zero for half the flights across all days, but the highest 10% errors exceeded 30 minutes on convective weather days. The wheels-off forecast spread exceeded 30 minutes for 25% of forecasts on convective weather days. The hourly departure demand forecast spread was 9 flights or less for 50% of departures across all days except one. Six out of the seven days having the highest hourly departure demand forecast spreads occurred in the presence of long-lived weather impacts.
READ LESS

Summary

Air traffic delays in the U.S. are problematic and often attributable to convective (thunderstorms) weather. Air traffic management is complex, dynamic, and influenced by many factors such as projected high volume of departures and uncertain forecast convective weather at airports and in the airspace. To support the complexities of making...

READ MORE

Loading of a surface-electrode ion trap from a remote, precooled source

Published in:
Phys. Rev. A, At. Mol. Opt. Phys., Vol. 86, No. 1, 20 July 2012, 013417.

Summary

We demonstrate loading of ions into a surface-electrode trap (SET) from a remote, laser-cooled source of neutral atoms. We first cool and load ~10^6 neutral 88Sr atoms into a magneto-optical trap from an oven that has no line of sight with the SET. The cold atoms are then pushed with a resonant laser into the trap region where they are subsequently photoionized and trapped in an SET operated at a cryogenic temperature of 4.6 K. We present studies of the loading process and show that our technique achieves ion loading into a shallow (15 meV depth) trap at rates as high as 125 ions/s while drastically reducing the amount of metal deposition on the trap surface as compared with direct loading from a hot vapor. Furthermore, we note that due to multiple stages of isotopic filtering in our loading process, this technique has the potential for enhanced isotopic selectivity over other loading methods. Rapid loading from a clean, isotopically pure, and precooled source may enable scalable quantum-information processing with trapped ions in large, low-depth surface-trap arrays that are not amenable to loading from a hot atomic beam.
READ LESS

Summary

We demonstrate loading of ions into a surface-electrode trap (SET) from a remote, laser-cooled source of neutral atoms. We first cool and load ~10^6 neutral 88Sr atoms into a magneto-optical trap from an oven that has no line of sight with the SET. The cold atoms are then pushed with...

READ MORE

Ring array antenna with optimized beamformer for simultaneous transmit and receive

Published in:
2012 IEEE Antennas and Propagation Society International Symp. and USNC/URSI National Radio Sci. Mtg., 8-14 July 2012.

Summary

In order to avoid self-interference, Simultaneous Transmit And Receive (STAR) systems require low mutual coupling between their respective transmit and receive antennas. This paper discusses the development of an 8-element transmit ring array antenna on a circular ground plane with a raised receive element. When combined with a beamformer that supplies linear progressive phase shifts to the array with opposing elements phased 180-degrees apart, the receive and transmit antennas are measured to exhibit 55 dB of isolation and omni-directional patterns in the 2.4 to 2.5 GHz band.
READ LESS

Summary

In order to avoid self-interference, Simultaneous Transmit And Receive (STAR) systems require low mutual coupling between their respective transmit and receive antennas. This paper discusses the development of an 8-element transmit ring array antenna on a circular ground plane with a raised receive element. When combined with a beamformer that...

READ MORE

Sub-picosecond pulses at 100 W average power from a Yb:YLF chirped-pulse amplification system

Published in:
Opt. Lett., Vol. 37, No. 13, 1 July 2012, pp. 2700-2702.

Summary

We present a high-repetition-frequency, diode-pumped, and chirped-pulse amplification system operating at 106 W average output with excellent beam quality (M^2 = 1.3), based on cryogenically cooled Yb:YLF. 1 nJ seed pulses, derived from a mode-locked Ti:sapphire laser, are first amplified to 1 mJ pulse energy at 10 kHz repetition frequency in a regenerative amplifier. The second-stage, multipass amplifier increases the pulse energy to 10.6 mJ, resulting in a spectral width of 2.2 nm. The pulses are compressed to 865 fs in duration, which is 1.26 times the transform limit.
READ LESS

Summary

We present a high-repetition-frequency, diode-pumped, and chirped-pulse amplification system operating at 106 W average output with excellent beam quality (M^2 = 1.3), based on cryogenically cooled Yb:YLF. 1 nJ seed pulses, derived from a mode-locked Ti:sapphire laser, are first amplified to 1 mJ pulse energy at 10 kHz repetition frequency...

READ MORE

Measurement of the third-order nonlinear optical susceptibility chi^(3) for the 1002-cm^-1 mode of benzenethiol using coherent anti-Stokes Raman scattering with continuous-wave diode lasers

Published in:
J. Raman Spectrosc., Vol. 43, No. 7, July 2012, pp. 911-916.

Summary

The components of the third-order nonlinear optical susceptibility x^(3) for the 1002-cm^?1 mode of neat benzenethiol have been measured using coherent anti-Stokes Raman scattering with continuous-wave diode pump and Stokes lasers at 785.0 and 852.0 nm, respectively. Values of 2.8±0.3 X 10^-12, 2.0±0.2 X 10^-12, and 0.8±0.1 X 10^-12 cmg^-1 s^2 were measured for the xxxx, xxyy, and xyyx components of |3x^(3)|, respectively. We have calculated these quantities using a microscopic model, reproducing the same qualitative trend. The Raman cross-section sigma RS for the 1002-cm^-1 mode of neat benzenethiol has been determined to be 3.1±0.6 X 10^-29 cm^2 per molecule. The polarization of the anti-Stokes Raman scattering was found to be parallel to that of the pump laser, which implies negligible depolarization. The Raman linewidth (full-width at half-maximum) Gamma was determined to be 2.4±0.3 cm^-1 using normal Stokes Raman scattering. The measured values of sigma RS and Gamma yield a value of 2.1±0.4 X 10^-12 cmg^-1 s^2 for the resonant component of 3x^(3). A value of 1.9±0.9 X 10^-12 cmg^-1 s^2 has been deduced for the nonresonant component of 3x^(3).
READ LESS

Summary

The components of the third-order nonlinear optical susceptibility x^(3) for the 1002-cm^?1 mode of neat benzenethiol have been measured using coherent anti-Stokes Raman scattering with continuous-wave diode pump and Stokes lasers at 785.0 and 852.0 nm, respectively. Values of 2.8±0.3 X 10^-12, 2.0±0.2 X 10^-12, and 0.8±0.1 X 10^-12 cmg^-1...

READ MORE

Establishing wind information needs for four dimensional trajectory-based operations

Published in:
1st Int. Conf. on Interdisciplinary Science for Innovative Air Traffic Management, ISIATM, 26 June 2012.

Summary

Accurate wind information is of fundamental importance to the delivery of benefits from future air traffic concepts. A Wind Information Analysis Framework is described in this paper and its utility for assessing wind information needs for a four-dimensional trajectory based operations application is demonstrated.
READ LESS

Summary

Accurate wind information is of fundamental importance to the delivery of benefits from future air traffic concepts. A Wind Information Analysis Framework is described in this paper and its utility for assessing wind information needs for a four-dimensional trajectory based operations application is demonstrated.

READ MORE

Towards the detection of aircraft icing conditions using operational dual-polarimetric radar

Published in:
7th European Conf. on Radar in Meteorology and Hydrology, ERAD, 25-29 June 2012.

Summary

In anticipation of the dual-polarimetric upgrade to the National Weather Service operational radar network (WSR-88D) research is being conducted to utilize this extensive new data source for remote aircraft icing detection. The first challenge is to accurately locate the melting layer. A new image-processing-based algorithm is proposed and demonstrated. The next challenge is to use the dual-polarimetric data above the melting level to distinguish regions containing super-cooled liquid water, which constitutes an aviation icing hazard, from regions of pure ice and snow. It has been well documented that the S-band dual-polarimetric radar signatures at individual range gates of super-cooled liquid water and ice crystals overlap significantly, complicating the identification of icing conditions using individual radar measurements. Recently several investigators have found that the aggregate characteristics of dual-polarimetric radar measurements over regions on the order of several kilometers show distinguishing features between regions containing super-cooled liquid and those with ice only. In this study, the features found in the literature are evaluated, extended and combined using a fuzzy-logic framework to provide an icing threat likelihood. The results of this new algorithm are computed using data collected in Colorado from the Colorado State University CHILL radar and the National Center for Atmospheric Research S-Pol radar (collectively called FRONT – The Front Range Observational Testbed) collected in the winter of 2010/2011 in coordination with the NASA Icing Remote Sensing System (NIRSS) and compared to pilot reports on approach or departure from nearby airports. The preliminary results look encouraging and will be presented. The ultimate goal is to produce an end-to-end algorithm to produce a reliable icing threat product that can then be combined with existing icing detection systems to improve their performance.
READ LESS

Summary

In anticipation of the dual-polarimetric upgrade to the National Weather Service operational radar network (WSR-88D) research is being conducted to utilize this extensive new data source for remote aircraft icing detection. The first challenge is to accurately locate the melting layer. A new image-processing-based algorithm is proposed and demonstrated. The...

READ MORE

Exploring the impact of advanced front-end processing on NIST speaker recognition microphone tasks

Summary

The NIST speaker recognition evaluation (SRE) featured microphone data in the 2005-2010 evaluations. The preprocessing and use of this data has typically been performed with telephone bandwidth and quantization. Although this approach is viable, it ignores the richer properties of the microphone data-multiple channels, high-rate sampling, linear encoding, ambient noise properties, etc. In this paper, we explore alternate choices of preprocessing and examine their effects on speaker recognition performance. Specifically, we consider the effects of quantization, sampling rate, enhancement, and two-channel speech activity detection. Experiments on the NIST 2010 SRE interview microphone corpus demonstrate that performance can be dramatically improved with a different preprocessing chain.
READ LESS

Summary

The NIST speaker recognition evaluation (SRE) featured microphone data in the 2005-2010 evaluations. The preprocessing and use of this data has typically been performed with telephone bandwidth and quantization. Although this approach is viable, it ignores the richer properties of the microphone data-multiple channels, high-rate sampling, linear encoding, ambient noise...

READ MORE

Linear prediction modulation filtering for speaker recognition of reverberant speech

Published in:
Odyssey 2012, The Speaker and Language Recognition Workshop, 25-28 June 2012.

Summary

This paper proposes a framework for spectral enhancement of reverberant speech based on inversion of the modulation transfer function. All-pole modeling of modulation spectra of clean and degraded speech are utilized to derive the linear prediction inverse modulation transfer function (LP-IMTF) solution as a low-order IIR filter in the modulation envelope domain. By considering spectral estimation under speech presence uncertainty, speech presence probabilities are derived for the case of reverberation. Aside from enhancement, the LP-IMTF framework allows for blind estimation of reverberation time by extracting a minimum phase approximation of the short-time spectral channel impulse response. The proposed speech enhancement method is used as a front-end processing step for speaker recognition. When applied to the microphone condition of the NISTSRE 2010 with artificially added reverberation, the proposed spectral enhancement method yields significant improvements across a variety of performance metrics.
READ LESS

Summary

This paper proposes a framework for spectral enhancement of reverberant speech based on inversion of the modulation transfer function. All-pole modeling of modulation spectra of clean and degraded speech are utilized to derive the linear prediction inverse modulation transfer function (LP-IMTF) solution as a low-order IIR filter in the modulation...

READ MORE

The MITLL NIST LRE 2011 language recognition system

Summary

This paper presents a description of the MIT Lincoln Laboratory (MITLL) language recognition system developed for the NIST 2011 Language Recognition Evaluation (LRE). The submitted system consisted of a fusion of four core classifiers, three based on spectral similarity and one based on tokenization. Additional system improvements were achieved following the submission deadline. In a major departure from previous evaluations, the 2011 LRE task focused on closed-set pairwise performance so as to emphasize a system's ability to distinguish confusable language pairs. Results are presented for the 24-language confusable pair task at test utterance durations of 30, 10, and 3 seconds. Results are also shown using the standard detection metrics (DET, minDCF) and it is demonstrated the previous metrics adequately cover difficult pair performance. On the 30 s 24-language confusable pair task, the submitted and post-evaluation systems achieved average costs of 0.079 and 0.070 and standard detection costs of 0.038 and 0.033.
READ LESS

Summary

This paper presents a description of the MIT Lincoln Laboratory (MITLL) language recognition system developed for the NIST 2011 Language Recognition Evaluation (LRE). The submitted system consisted of a fusion of four core classifiers, three based on spectral similarity and one based on tokenization. Additional system improvements were achieved following...

READ MORE