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arXiv 2018年

作者： Ho, V.X. Al tahtamouni, T.M. Jiang, H.X. Lin, J.Y. Zavada, J.M. Vinh, N.Q. Department of Physics Center for Soft Matter and Biological Physics Virginia Tech BlacksburgVA24061 United States Materials Science & Technology Program College of Arts & Sciences Qatar University Doha2713 Qatar Department of Electrical and Computer Engineering Texas Tech University LubbockTX79409 United States Department of Electrical and Computer Engineering New York University BrooklynNY11201 United States

Large-scale optoelectronics integration is strongly limited by the lack of efficient light sources, which could be integrated with the silicon complementary metal-oxide-semiconductor (CMOS) technology. Persistent efforts continue to achieve efficient light emission from silicon in the extending the silicon technology into fully integrated optoelectronic circuits. Here, we report the realization of room-temperature stimulated emission in the technologically crucial 1.5 µm wavelength range from Er-doped GaN multiple-quantum wells on silicon and sapphire. Employing the well-acknowledged variable stripe technique, we have demonstrated an optical gain up to 170 cm-1 in the multiple-quantum well structures. The observation of the stimulated emission is accompanied by the characteristic threshold behavior of emission intensity as a function of pump fluence, spectral linewidth narrowing and excitation length. The demonstration of room-temperature lasing at the minimum loss window of optical fibers and in the eye-safe wavelength region of 1.5 µm are highly sought-after for use in many applications including defense, industrial processing, communication, medicine, spectroscopy and imaging. As the synthesis of Er-doped GaN epitaxial layers on silicon and sapphire has been successfully demonstrated, the results laid the foundation for achieving hybrid GaN-Si lasers providing a new pathway towards full photonic integration for silicon optoelectronics. Driven by the strong need for cheap and integrable Si-based optoelectronic devices for a wide range of applications, continuing endeavors have been made to develop structures for light emission, modulation, and detection in this material system. Recent breakthroughs including the demonstration of a high-speed optical modulator in Si,1-2 photodetectors3, and waveguides4 have brought the concept of transition from electrical to optical interconnects closer to realization. However, the base for silicon photonics, namely, a group IV la

关键词： Semiconductor quantum wells

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Superiorization of preconditioned conjugate gradient algorithms for tomographic image reconstruction

arXiv

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arXiv 2018年

作者： Helou, Elias S. Herman, Gabor T. Lin, Chuan Zibetti, Marcelo V.W. Institute of Mathematical Science and Computation University of São Paulo SP Brazil Department of Computer Science Graduate Center City University of New York NY United States School of Electrical Engineering Southwest Jiaotong University Chengdu China Program in Electrical and Computer Engineering Federal University of Technology PR Brazil

Properties of Superiorized Preconditioned Conjugate Gradient (SupPCG) algorithms in image reconstruction from projections are examined. Least squares (LS) is usually chosen for measuring data-inconsistency in these inverse problems. Preconditioned Conjugate Gradient algorithms are fast methods for finding an LS solution. However, for ill-posed problems, such as image reconstruction, an LS solution may not provide good image quality. This can be taken care of by superiorization. A superiorized algorithm leads to images with the value of a secondary criterion (a merit function such as the total variation) improved as compared to images with similar data-inconsistency obtained by the algorithm without superiorization. Numerical experimentation shows that SupPCG can lead to high-quality reconstructions within a remarkably short time. A theoretical analysis is also provided.15A29, 65F22, 65F10, 94A08 Copyright © 2018, The Authors. All rights reserved.

关键词： Image reconstruction

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The spontaneous symmetry breaking in Ta2NiSe5 is structural in nature

arXiv

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arXiv 2020年

作者： Baldini, Edoardo Zong, Alfred Choi, Dongsung Lee, Changmin Michael, Marios H. Windgaetter, Lukas Mazin, Igor I. Latini, Simone Azoury, Doron Lv, Baiqing Kogar, Anshul Wang, Yao Lu, Yangfan Takayama, Tomohiro Takagi, Hidenori Millis, Andrew J. Rubio, Angel Demler, Eugene Gedik, Nuh Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Electrical Engineering & Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States Department of Physics Harvard University CambridgeMA02138 United States Max Planck Institute for the Structure and Dynamics of Matter Hamburg Germany Department of Physics and Astronomy Center for Quantum Materials George Mason University FairfaxVA22030 United States Department of Physics University of Tokyo Bunkyo-ku Tokyo113-0033 Japan Max Planck Institute for Solid State Research Stuttgart70569 Germany Department of Physics Columbia University New YorkNY10027 United States Center for Computational Quantum Physics Flatiron Institute 162 Fifth Avenue New YorkNY10010 United States Nano-Bio Spectroscopy Group Departamento de Física de Materiales Universidad del País Vasco San Sebastían20018 Spain

The excitonic insulator is an electronically-driven phase of matter that emerges upon the spontaneous formation and Bose condensation of excitons. Detecting this exotic order in candidate materials is a subject of paramount importance, as the size of the excitonic gap in the band structure establishes the potential of this collective state for superfluid energy transport. However, the identification of this phase in real solids is hindered by the coexistence of a structural order parameter with the same symmetry as the excitonic order. Only a few materials are currently believed to host a dominant excitonic phase, Ta2NiSe5 being the most promising. Here, we test this scenario by using an ultrashort laser pulse to quench the broken-symmetry phase of this transition metal chalcogenide. Tracking the dynamics of the materials electronic and crystal structure after light excitation reveals surprising spectroscopic fingerprints that are only compatible with a primary order parameter of phononic nature. We rationalize our findings through state-of-the-art calculations, confirming that the structural order accounts for most of the electronic gap opening. Not only do our results uncover the long-sought mechanism driving the phase transition of Ta2NiSe5, but they also conclusively rule out any substantial excitonic character in this instability. Copyright © 2020, The Authors. All rights reserved.

关键词： Crystal structure

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Meta-Learning Related Tasks with Recurrent Networks: Optimization and Generalization

Meta-Learning Related Tasks with Recurrent Networks: Optimiz...

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International Joint Conference on Neural Networks

作者： Thy Nguyen Emmett Redd A. Steven Younger Tayo Obafemi-Ajayi Computer Science Dept. Missouri State University Springfield MO Department of Physics Astronomy and Materials Science Missouri State University Springfield MO Engineering Program Missouri State University Springfield MO

There have been recent interest in meta-learning systems: i.e. networks that are trained to learn across multiple tasks. This paper focuses on optimization and generalization of a meta-learning system based on recurrent networks. The optimization investigates the influence of diverse structures and parameters on its performance. We demonstrate the generalization (robustness) of our meta-learning system to learn across multiple tasks including tasks unseen during the metatraining phase. We introduce a meta-cost function (Mean Squared Fair Error) that enhances the performance of the system by not penalizing it during transitions to learning a new task. Evaluation results are presented for Boolean and quadratic functions datasets. The best performance is obtained using a Long Short-Term Memory (LSTM) topology without a forget gate and with a clipped memory cell. The results demonstrate i) the impact of different LSTM architectures, parameters, and error functions on the meta-learning process;ii) that the mean squared fair error function does improve performance for best learning;and iii) the robustness of our meta-learning framework as it generalizes well when tested on tasks unseen during metatraining. Comparison between No-Forget-Gate LSTM and Gated Recurrent Unit also suggest that absence of a memory cell tends to degrade performance.

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Observation of Narrow-Band Terahertz Gain in Two-Dimensional Magnetoexcitons

Observation of Narrow-Band Terahertz Gain in Two-Dimensional...

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2019 Conference on Lasers and Electro-Optics, CLEO 2019

作者： Li, Xinwei Yoshioka, Katsumasa Zhang, Qi Katsutani, Fumiya Gao, Weilu Marquez, Nicolas Timothy Noe, G. Watson, John D. Manfra, Michael J. Katayama, Ikufumi Takeda, Jun Kono, Junichiro Deparment of Electrical and Computer Engineering Rice University HoustonTX77005 United States Department of Physics Graduate School of Engineering Yokohama National University Yokohama240-8501 Japan Argonne National Laboratories LemontIL60439 United States Deparment of Physics and Astronomy Rice University HoustonTX77005 United States Department of Physics and Astronomy Purdue University West LafayetteIN47907 United States Deparment of Materials Science and NanoEngineering Rice University HoustonTX77005 United States

We have performed time- and polarization-resolved optical-pump-terahertz-probe magnetospectroscopy measurements on a GaAs quantum well and observed narrow-band, polarization-selective THz gain, whose center frequency ... 详细信息

ISBN: (纸本)9781943580576

关键词： Magnetic fields Conductivity Probes Gallium arsenide Excitons Magnetic field measurement Time-frequency analysis"

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Nonretarded edge plasmon-polaritons in anisotropic two-dimensional materials

arXiv

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arXiv 2019年

作者： Margetis, Dionisios Maier, Matthias Stauber, Tobias Low, Tony Luskin, Mitchell Institute for Physical Science and Technology Department of Mathematics Center for Scientific Computation and Mathematical Modeling University of Maryland College ParkMD20742 United States Department of Mathematics Texas A&M University College StationTX77843 United States Materials Science Factory Instituto de Ciencia de Materiales de Madrid CSIC MadridE-28049 Spain Department of Electrical & Computer Engineering University of Minnesota MinneapolisMN55455 United States School of Mathematics University of Minnesota MinneapolisMN55455 United States

By an integral equation approach to the time-harmonic classical Maxwell equations, we describe the dispersion in the nonretarded frequency regime of the edge plasmon-polariton (EPP) on a semi-infinite flat sheet. The sheet has an arbitrary, physically admissible, tensor valued and spatially homogeneous conductivity, and serves as a model for a family of two-dimensional conducting materials. We formulate a system of integral equations for the electric field tangential to the sheet in a homogeneous and isotropic ambient medium. We show how this system is simplified via a length scale separation. This view entails the quasi-electrostatic approximation, by which the tangential electric field is replaced by the gradient of a scalar potential, . By the Wiener-Hopf method, we solve an integral equation for in some generality. The EPP dispersion relation comes from the elimination of a divergent limiting Fourier integral for at the edge. We connect the existence, or lack thereof, of the EPP dispersion relation to the index for Wiener-Hopf integral equations, an integer of topological character. We indicate that the values of this index may express an asymmetry due to the material anisotropy in the number of wave modes propagating on the sheet away from the edge with respect to the EPP direction of propagation. We discuss extensions such as the setting of two semi-infinite, coplanar sheets. Our theory forms a generalization of the treatment by Volkov and Mikhailov (1988 Sov. Phys. JETP 67 1639). Copyright © 2019, The Authors. All rights reserved.

关键词： Integral equations

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Emerging Photoluminescence from the Dark-Exciton Phonon Replica in Monolayer WSe2

arXiv

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arXiv 2019年

作者： Li, Zhipeng Wang, Tianmeng Jin, Chenhao Lu, Zhengguang Lian, Zhen Meng, Yuze Blei, Mark Gao, Shiyuan Taniguchi, Takashi Watanabe, Kenji Ren, Tianhui Tongay, Sefaattin Yang, Li Smirnov, Dmitry Cao, Ting Shi, Su-Fei Department of Chemical and Biological Engineering Rensselaer Polytechnic Institute TroyNY12180 United States School of Chemistry and Chemical Engineering Shanghai Jiao Tong University Shanghai200240 China Kavli Institute at Cornell for Nanoscale Science IthacaNY14853 National High Magnetic Field Lab TallahasseeFL32310 United States Department of Physics Florida State University TallahasseeFL32306 United States College of Physics Nanjing University Nanjing210093 China National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan School for Engineering of Matter Transport and Energy Arizona State University TempeAZ85287 United States Department of Physics Washington University in St. Louis St. LouisMO63136 United States Geballe Laboratory for Advanced Materials Stanford University StanfordCA94305 United States Department of Materials Science and Engineering University of Washington SeattleWA98195 United States Department of Electrical Computer & Systems Engineering Rensselaer Polytechnic Institute TroyNY12180 United States

Tungsten-based monolayer transition metal dichalcogenides host a long-lived "dark" exciton, an electron-hole pair in a spin-triplet configuration. The long lifetime and unique spin properties of the dark exciton provide exciting opportunities to explore light-matter interactions beyond electric dipole transitions. Here we demonstrate that the coupling of the dark exciton and an optically silent chiral phonon enables the intrinsic photoluminescence of the dark-exciton replica in monolayer WSe2. Gate and magnetic-field dependent PL measurements unveil a circularly-polarized replica peak located below the dark exciton by 21.6 meV, equal to E′′ phonon energy from Se vibrations. First-principles calculations show that the exciton-phonon interaction selectively couples the spin-forbidden dark exciton to the intravalley spin-allowed bright exciton, permitting the simultaneous emission of a chiral phonon and a circularly-polarized photon. Our discovery and understanding of the phonon replica reveals a chirality dictated emission channel of the phonons and photons, unveiling a new route of manipulating valley-spin. Copyright © 2019, The Authors. All rights reserved.

关键词： Monolayers

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Self-Awareness for Autonomous Systems

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PROCEEDINGS OF THE IEEE 2020年第7期108卷 971-975页

作者： Dutt, Nikil Regazzoni, Carlo S. Rinner, Bernhard Yao, Xin Nikil Dutt (Fellow IEEE) received the Ph.D. degree from the University of Illinois at Urbana–Champaign Champaign IL USA in 1989.""He is currently a Distinguished Professor of computer science (CS) cognitive sciences and electrical engineering and computer sciences (EECS) with the University of California at Irvine Irvine CA USA. He is a coauthor of seven books. His research interests include embedded systems electronic design automation (EDA) computer architecture distributed systems healthcare Internet of Things (IoT) and brain-inspired architectures and computing.""Dr. Dutt is a Fellow of ACM. He was a recipient of the IFIP Silver Core Award. He has received numerous best paper awards. He serves as the Steering Committee Chair of the IEEE/ACM Embedded Systems Week (ESWEEK). He is also on the steering organizing and program committees of several premier EDA and embedded system design conferences and workshops. He has served on the Editorial Boards for the IEEE Transactions on Very Large Scale Integration (VLSI) Systems and the ACM Transactions on Embedded Computing Systems and also previously served as the Editor-in-Chief (EiC) for the ACM Transactions on Design Automation of Electronic Systems. He served on the Advisory Boards of the IEEE Embedded Systems Letters the ACM Special Interest Group on Embedded Systems the ACM Special Interest Group on Design Automationt and the ACM Transactions on Embedded Computing Systems. Carlo S. Regazzoni (Senior Member IEEE) received the M.S. and Ph.D. degrees in electronic and telecommunications engineering from the University of Genoa Genoa Italy in 1987 and 1992 respectively.""He is currently a Full Professor of cognitive telecommunications systems with the Department of Electrical Electronics and Telecommunication Engineering and Naval Architecture (DITEN) University of Genoa and a Co-Ordinator of the Joint Doctorate on Interactive and Cognitive Environments (JDICE) international Ph.D. course started initially as EU Erasmus Mundus Project and

Autonomous systems are able to make decisions and potentially take actions without direct human intervention, which requires some knowledge about the system and its environment as well as goal-oriented reasoning. In computer systems, one can derive such behavior from the concept of a rational agent with autonomy (“control over its own actions”), reactivity (“react to events from the environment”), proactivity (“act on its own initiative”), and sociality (“interact with other agents”) as fundamental properties \n[1]\n. Autonomous systems will undoubtedly pervade into our everyday lives, and we will find them in a variety of domains and applications including robotics, transportation, health care, communications, and entertainment to name a few. \nThe articles in this month’s special issue cover concepts and fundamentals, architectures and techniques, and applications and case studies in the exciting area of self-awareness in autonomous systems.

关键词： Special issues and sections Autonomous systems Self-aware Robot sensing systems Computational modeling

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Analysis of “Dose Accuracy, Injection Force, and Usability Assessment of a New Half-Unit, Prefilled Insulin Pen”

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Journal of Diabetes science and Technology 2018年第2期12卷 373-375页

作者： Bariya, Mallika Nayberg, Irina Department of Electrical Engineering and Computer Science University of California Berkeley Berkeley CA United States Berkeley Sensor and Actuator Center University of California Berkeley Berkeley CA United States Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA United States Mills-Peninsula Medical Center Diabetes Research Institute San Mateo CA United States

Half-unit insulin pens (HUPs) offer finer gradation of insulin dosing than their integer-unit counterparts, tackling the inaccuracies of dose rounding that make it difficult for insulin-sensitive populations to achieve tight glycemic control. This article analyzes the first prefilled HUP, the Humalog Junior KwikPen, in the context of other, similar devices and the developing landscape of smart insulin pens. The Junior KwikPen’s suitability for pediatric patients is assessed in reference to a recent study surveying its accuracy and usability under varying conditions intended to simulate real-world use. © 2017, © 2017 Diabetes Technology Society.

关键词： dose accuracy half-unit insulin pen Humalog Junior KwikPen prefilled

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Size effect on memristive properties of nanocrystalline ZnO film for resistive synaptic devices

Size effect on memristive properties of nanocrystalline ZnO ...

引用

5th International School and Conference on Optoelectronics, Photonics, engineering and Nanostructures, Saint Petersburg OPEN 2018

作者： Shandyba, N.A. Panchenko, I.V. Tominov, R.V. Smirnov, V.A. Pelipenko, M.I. Zamburg, E.G. Chu, Y.H. Department of Nanotechnology and Microsystems Southern Federal University Taganrog347928 Russia UAC Company BERIEV Taganrog347923 Russia Department of Electrical and Computer Engineering National University of Singapore Singapore117582 Singapore Department of Materials Science and Engineering National Chiao Tung University Hsinchu1001 Taiwan Department of Electrophysics National Chiao Tung University Hsinchu1001 Taiwan Institute of Physics Academia Sinica Taipei11529 Taiwan Material and Chemical Research Laboratories Industrial Technology Research Institute Hsinchu31040 Taiwan

Size effect on memristive properties of nanocrystalline ZnO film was investigated. It was shown, ZnO film thickness increase from 6.23±1.54 nm to 47.60±8.12 nm leads to high-resistance state (HRS) increase from 3.26±2.14 M to 700.32±300.83 M and low-resistance state (LRS) from 0.03±0.02 M to 0.09±0.03 M, respectively. The HRS/LRS ratio increases from 108 to 7742. The results can be useful for based on nanocrystalline ZnO films resistive synaptic devices manufacturing. © Published under licence by IOP Publishing Ltd.

关键词： II-VI semiconductors

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