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Publisher’s Note: “Correlation of a generation-recombination center with a deep level trap in GaN” [Appl. Phys. Lett. 106, 102101 (2015)]

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Applied Physics Letters 2015年第15期106卷

作者： X. S. Nguyen K. Lin Z. Zhang B. McSkimming A. R. Arehart J. S. Speck S. A. Ringel E. A. Fitzgerald S. J. Chua 1Low energy electronic system IRG Singapore MIT Alliance for Research and Technology Center 1 CREATE way Singapore 138602 2Institute of Materials Research and Engineering 3 Research Link Singapore 117602 3Department of Electrical and Computer Engineering The Ohio State University Columbus Ohio 43210 USA 4Materials Department University of California Santa Barbara California 93106-5050 USA 5Department of Materials Science and Engineering Massachusetts Institute of Technology Room 13-5153 77 Mass. Ave. Cambridge Massachusetts 02139 USA 6Department of Electrical and Computer Engineering National University of Singapore Block E4 Engineering Drive 3 Singapore 117583

This article was originally published online on 9 March 2015. As originally published, several co-authors were missing from the byline. The authors' names and a

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A 4.7 THz HEB/QCL heterodyne receiver for STO-2

A 4.7 THz HEB/QCL heterodyne receiver for STO-2

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International Conference on Infrared and Millimeter Waves

作者： Darren J. Hayton Jenna L. Kloosterman Jian-rong Gao Nathan Vercruyssen Chris K. Walker Qing Hu Tsung-Yu Kao SRON Netherlands Institute for Space Research Utrecht Utrecht NL Department of Electrical and Computer Engineering University of Arizona Tucson Arizona USA SRON Netherlands Institute for Space Research Groningen AD Netherlands Delft University of Technology Delft CJ Netherlands Technische Universiteit Delft Delft Zuid-Holland NL Steward Observatory University of Arizona Tucson Arizona USA Dept. of Electrical Engineering and Computer Science MIT Cambridge Massachusetts USA

We report on a 4.7 THz heterodyne receiver being developed to fly on the Stratospheric Terahertz Observatory (STO-2) balloon platform. The receiver is based on a single pixel hot electron bolometer (HEB) mixer pumped by a 4.7 THz 3 rd order distributed feedback quantum cascade laser (QCL) as local oscillator and is designed for high resolution spectroscopy of the astronomically important neutral oxygen (OI) line at 4.745 THz. We describe the expected receiver performance and outline novel approaches to QCL amplitude and frequency/phase stabilization.

关键词： Quantum cascade lasers Receivers Noise Mixers Observatories Bolometers Distributed feedback devices

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Group theory analysis of phonons in two-dimensional transition metal dichalcogenides

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Physical Review B 2014年第11期90卷 115438-115438页

作者： J. Ribeiro-Soares R. M. Almeida E. B. Barros P. T. Araujo M. S. Dresselhaus L. G. Cançado A. Jorio Departamento de Física Universidade Federal de Minas Gerais Belo Horizonte Minas Gerais 30123-970 Brazil Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology (MIT) Cambridge Massachusetts 02139 USA Departamento de Física Universidade Federal do Ceará Fortaleza Ceará 60455-900 Brazil Department of Physics and Astronomy University of Alabama Tuscaloosa Alabama 35487 USA Department of Physics Massachusetts Institute of Technology (MIT) Cambridge Massachusetts 02139 USA

Transition metal dichalcogenides (TMDCs) have emerged as a new two-dimensional material's field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers N (N even or odd) drives changes in space-group symmetry that are reflected in the optical properties. The understanding of the space-group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e., 2Ha, 2Hc and 1T, as a function of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical activity, and Raman tensors are discussed.

关键词： GROUP theory PHONONS RAMAN effect BULK solids RAMAN spectroscopy OPTICAL spectroscopy

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Dynamic reduction of query result sets for interactive visualizaton

Dynamic reduction of query result sets for interactive visua...

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IEEE International Conference on Big Data

作者： Leilani Battle Michael Stonebraker Remco Chang Electrical Engineering and Computer Science Department MIT Department of Computer Science Tufts University

ISBN: (纸本)9781479912940

Modern database management systems (DBMS) have been designed to efficiently store, manage and perform computations on massive amounts of data. In contrast, many existing visualization systems do not scale seamlessly from small data sets to enormous ones. We have designed a three-tiered visualization system called ScalaR to deal with this issue. ScalaR dynamically performs resolution reduction when the expected result of a DBMS query is too large to be effectively rendered on existing screen real estate. Instead of running the original query, ScalaR inserts aggregation, sampling or filtering operations to reduce the size of the result. This paper presents the design and implementation of ScalaR, and shows results for an example application, displaying satellite imagery data stored in SciDB as the back-end DBMS.

关键词： Data visualization Arrays Earthquakes Database systems Satellites Information management

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Experimental Study of the Interplay of Channel and Network Coding in Low Power Sensor Applications

Experimental Study of the Interplay of Channel and Network C...

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IEEE International Conference on Communications

作者： Georgios Angelopoulos Arun Paidimarri Anantha P. Chandrakasan Muriel Médard Department of Electrical Engineering and Computer Science MIT Cambridge MA USA

In this paper, we evaluate the performance of random linear network coding (RLNC) in low data rate indoor sensor applications operating in the ISM frequency band. We also investigate the results of its synergy with forward error correction (FEC) codes at the PHY-layer in a joint channel-network coding (JCNC) scheme. RLNC is an emerging coding technique which can be used as a packet-level erasure code, usually implemented at the network layer, which increases data reliability against channel fading and severe interference, while FEC codes are mainly used for correction of random bit errors within a received packet. The hostile wireless environment that low power sensors usually operate in, with significant interference from nearby networks, motivates us to consider a joint coding scheme and examine the applicability of RLNC as an erasure code in such a coding structure. Our analysis and experiments are performed using a custom low power sensor node, which integrates on-chip a low-power 2.4 GHz transmitter and an accelerator implementing a multi-rate convolutional code and RLNC, in a typical office environment. According to measurement results, RLNC of code rate 4/8 can provide an effective SNR improvement of about 3.4 dB, outperforming a PHY-layer FEC code of the same code rate, at a PER of 10~(-2). In addition, RLNC performs very well when used in conjunction with a PHY-layer FEC code as a JCNC scheme, offering an overall coding gain of 5.6 dB.

关键词： Forward error correction Encoding Signal to noise ratio Wireless communication Wireless sensor networks Network coding Gain

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Energy consumption optimisation in classrooms using lighting energy audit

Energy consumption optimisation in classrooms using lighting...

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National Conference on Challenges in Research & Technology in the Coming Decades (CRT 2013)

作者： K. R. Shailesh S. Tanuja Manish Kumar Rai Aseem Krishna Department of Electrical & Electronics Engineering MIT Manipal University Department of Computer Science & Engineering MIT Manipal University

Good quality lighting promotes better learning. Good quality classroom illumination improves mood, behavior and concentration of students. Lighting contributes to around 20% - 30% of electricity consumption in an academic institute. It is important to cut energy costs as availability of energy is a matter of concern. There should be greater effort to optimize the usage of energy in lighting installations. Energy efficiency in an academic institution does not mean compromising the comfort level of staff and students. The objective of this work is to conduct a lighting energy audit in a class room of academic institution. The results of the audit suggest that there is ample scope for improvement. Lighting energy audit was useful in understanding the lighting level distribution throughout the classroom. It is important to create awareness to optimally use energy in an educational institute. Using energy efficient equipment and use of appropriate controls is the best way to improve the lighting and efficiency in the academic institution. The paybacks of implementing the energy efficiency measures in academic institution are significant both in terms of savings energy and cost.

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Phase locking a 4.7 THz quantum cascade laser using a super-lattice diode as harmonic mixer

Phase locking a 4.7 THz quantum cascade laser using a super-...

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International Conference on Infrared and Millimeter Waves

作者： A. V. Khudchenko D. J. Hayton D. G. Pavelyev A. M. Baryshev J. R. Gao T-Y. Kao Q. Hu J. L. Reno V. L. Vaks SRON The Netherlands Institute for Space Research Radiophysics department of Nizhny Novgorod State University Russia NOVA/Kapteyn Astronomical Institute The Netherlands Kavli Institute of NanoScience Delft University of Technology The Netherlands Department of Electrical Engineering and Computer Science MIT Cambridge MA USA Sandia National Laboratories Albuquerque NM USA Institute for Physics of Microstructures Russian Academy of Sciences Nizhniy Novgorod Russia

We have phase locked a 4.7 THz Quantum Cascade Laser (QCL) to a stable microwave reference signal. The QCL is a 3 rd order distributed feedback (DFB) laser with a low power consumption of 0.5 W and radiation power of about 0.25 mW. One of the key elements in our experimental setup is a superlattice diode operating as a harmonic mixer and providing the beat signal between the QCL and the 24 th harmonic of a 198 GHz reference signal. A phase locked beat signal is about 20 dB above the noise level for a 30 KHz resolution bandwidth.

关键词： Quantum cascade lasers Harmonic analysis Mixers Bandwidth Masers Signal resolution Microwave oscillators

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Distributed approximation of joint measurement distributions using mixtures of gaussians

Distributed approximation of joint measurement distributions...

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International Conference on Robotics science and Systems, RSS 2012

作者： Julian, Brian J. Smith, Stephen L. Rus, Daniela Computer Science and Artificial Intelligence Laboratory MIT CambridgeMA02139 United States MIT Lincoln Laboratory 244 Wood Street LexingtonMA02420 United States Department of Electrical and Computer Engineering University of Waterloo WaterlooONN2L 3G1 Canada

ISBN: (纸本)9780262519687

This paper presents algorithms to distributively approximate the continuous probability distribution that describes the fusion of sensor measurements from many networked robots. Each robot forms a weighted mixture of scaled Gaussians to represent the continuous measurement distribution (i.e., likelihood) of its local observation. From this mixture set, each robot then draws samples of Gaussian elements to enable the use of a consensus-based algorithm that evolves the corresponding canonical parameters. We show that these evolved parameters form a distribution that converges weakly to the joint of all the robots' unweighted mixture distributions, which itself converges weakly to the joint measurement distribution as more system resources are allocated. The innovation of this work is the combination of sample-based sensor fusion with the notion of pre-convergence termination without the risk of 'double-counting' any single observation. We also derive bounds and convergence rates for the approximated joint measurement distribution, specifically the elements of its information vectors and the eigenvalues of its information matrices. Most importantly, these performance guarantees do not come at a significant cost of complexity, since computational and communication complexity of the canonical parameters scales quadratically with respect to the Gaussian dimension, linearly with respect to the number of samples, and constant with respect to the number of robots. Results from numerical simulations for object localization are discussed using both Gaussians and mixtures of Gaussians. © 2013 Massachusetts Institute of Technology.

关键词： Robots

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Optimization of a z-source DC circuit breaker

Optimization of a z-source DC circuit breaker

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2013 5th IEEE Electric Ship Technologies Symposium, ESTS 2013

作者： Prempraneerach, P. Angle, M.G. Kirtley Jr., J.L. Karniadakis, G.E. Chryssostomidis, C. Mechanical Engineering Department Rajamangala University of Technology Thunyaburi Pathumthani 12110 Thailand Electrical Engineering and Computer Science Department Research Laboratory for Electronics MIT Cambridge MA 02139 United States Division of Applied Mathematics Brown University Providence RI 02912 United States MIT Sea Grant College Program Department of Mechanical Engineering MIT Cambridge MA 02138 United States

ISBN: (纸本)9781467352437

DC faults may cause severe disruptions in continuity of service to vital loads in a shipboard integrated power system, hence detection, isolation, and protection against such faults must be incorporated in both medium-voltage DC (MVDC) and low-voltage DC (LVDC) systems. Here we consider the effectiveness of existing z-source breakers and propose several new designs more appropriate for fault detection in MVDC and LVDC systems. In particular, we perform an optimization study that aims to minimize dissipation and weight and we identify the key parameters for use in MVDC and LVDC systems. Preliminary verification and validation studies are also included. © 2013 IEEE.

关键词： Electric circuit breakers

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Advances on matroid secretary problems: Free order model and laminar case

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16th Conference on Integer Programming and Combinatorial Optimization, IPCO 2013

作者： Jaillet, Patrick Soto, José A. Zenklusen, Rico Dept. of Electrical Engineering and Computer Science MIT United States DIM-CMM University of Chile Chile Technische Universität Berlin Germany Dept. of Applied Mathematics and Statistics Johns Hopkins University United States

ISBN: (纸本)9783642366932

The best-known conjecture in the context of matroid secretary problems claims the existence of an O(1)-approximation applicable to any matroid. Whereas this conjecture remains open, modified forms of it were shown to be true, when assuming that the assignment of weights to the secretaries is not adversarial but uniformly at random [20,18]. However, so far, no variant of the matroid secretary problem with adversarial weight assignment is known that admits an O(1)-approximation. We address this point by presenting a 9-approximation for the free order model, a model suggested shortly after the introduction of the matroid secretary problem, and for which no O(1)-approximation was known so far. The free order model is a relaxed version of the original matroid secretary problem, with the only difference that one can choose the order in which secretaries are interviewed. Furthermore, we consider the classical matroid secretary problem for the special case of laminar matroids. Only recently, a O(1)-approximation has been found for this case, using a clever but rather involved method and analysis [12] that leads to a 16000/3-approximation. This is arguably the most involved special case of the matroid secretary problem for which an O(1)-approximation is known. We present a considerably simpler and stronger 3√3e ≈ 14.12-approximation, based on reducing the problem to a matroid secretary problem on a partition matroid. © 2013 Springer-Verlag.

关键词： Artificial intelligence

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