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Experimental observation of the topological structure of exceptional points in an ultrathin hybridized metamaterial

Physical Review A 2017年第6期96卷 063823-063823页

作者： Ming Kang Weiren Zhu Ivan D. Rukhlenko College of Physics and Materials Science Tianjin Normal University Tianjin 300387 China Department of Electronic Engineering Shanghai Jiao Tong University Shanghai 200240 China Modeling and Design of Nanostructures Laboratory ITMO University Saint Petersburg 197101 Russia Department of Electrical and Computer Systems Engineering Monash University Clayton Victoria 3800 Australia

The exceptional point (EP), which is one of the most important branch-type singularities exclusive to non-Hermitian systems, has been observed recently in various synthetic materials, giving rise to counterintuitive phenomena due to the nontrivial topology of the EP. Here, we present a direct experimental observation of the topological structure of the EPs via the angle-resolved transmission measurement of a hybridized metamaterial. Both eigenvalues and eigenvectors show branch-point singularities in the investigated biparametric space of frequency and incident angle. Importantly, the angle-resolved transmission coefficients provide all the information about the eigenvalues as well as the corresponding eigenvectors in the biparametric space, revealing the nontrivial topological structure of the EP, such as mode switching and the topological phase for a parameter loop encircling the EP. It is shown that the appearance of the EP in the scattering matrix is related directly to the perfect unidirectional transmission and the chirality of the EP corresponds to the maximum or minimum value of the asymmetric factor. Our investigation uncovers the capabilities of metamaterials for exploring the physics of EPs and their potential for having extreme optical properties, which provide potential applications in the spectral band ranging from microwaves to visible frequencies.

关键词： Metamaterials

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A Supervised Constructive Neuro-Immune Network for Pattern Classification

A Supervised Constructive Neuro-Immune Network for Pattern C...

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International Joint Conference on Neural Networks (IJCNN)

作者： H. Knidel L. Nunes de Castro F.J. Von Zuben Laboratory of Bioinformatics and Bioinspired Computing-LBiC Department of Computer Engineering and Industrial Automation-DCA School of Electrical and Computer Engineering-FEEC State University of Campinas-UNICAMP Sao Paulo Brazil Graduate Program in Computer Science Catholic University of Santos Sao Paulo Brazil

This paper proposes a supervised version of a learning algorithm for a constructive neuro-immune network. The proposed methodology is developed by taking ideas from the immune system and learning vector quantization. The resulting classification algorithm is characterized by high-performance, similar to the ones produced by alternative methods in the literature, and parsimonious solutions, with a much smaller set of prototypes per class when compared with the other approaches. The number of prototypes is automatically defined by the convergence criterion. The algorithm requires a single user-defined parameter for training, associated with the convergence criterion, and the computational cost is sufficiently reduced to support applications involving large data sets.

关键词： Pattern classification Immune system Neurons Supervised learning Vector quantization Classification algorithms Prototypes Clustering algorithms Unsupervised learning Artificial neural networks

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Transistor characteristics of thermal CVD carbon nanotubes field emission triode

Transistor characteristics of thermal CVD carbon nanotubes f...

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International Conference on Vacuum Nanoelectronics (IVNC)

作者： Y.M. Wong W.P. Kang J.L. Davidson W. Hofmeister S. Wei J.H. Huang Dept. of Electrical Engineering and Computer Science Vanderbilt Univ. Nashville TN USA Interdisciplinary Graduate Program in Material Science Vanderbilt Univ. Nashville TN USA Dept. of Materials Science and Engineering National Tsing Hua Univ. Hsinchu Taiwan ROC

In this paper, the study of thermal CVD grown CNT field emitters in a triode amplifier configuration is reported. The DC characteristics of the CNT triode are investigated, including I/sub a/ vs. V/sub a/ for different V/sub g/. Moreover, DC parameters such as transconductance, amplification factor and anode resistance of the triode amplifier are determined. It was shown that a higher amplification factor can be achieved with optimum gate-anode-cathode spacing such that the cathode is effectively shielded from the anode by the gate but the anode still collects all electrons emitted from the cathode. High emission current at low gate voltage is key to achieving high transconductance. This can be obtained by optimum configuration of high-density CNTs array in a triode structure with a common gate.

关键词： Carbon nanotubes Voltage Anodes materials science and technology Current measurement Palladium Silicon Furnaces Temperature Cathodes

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Multi-level Electro-thermal Switching of Optical Phase-Change materials Using Graphene

arXiv

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arXiv 2020年

作者： Ríos, Carlos Zhang, Yifei Shalaginov, Mikhail Deckoff-Jones, Skylar Wang, Haozhe An, Sensong Zhang, Hualiang Kang, Myungkoo Richardson, Kathleen A. Roberts, Christopher Chou, Jeffrey Liberman, Vladimir Vitale, Steven A. Kong, Jing Gu, Tian Hu, Juejun Department of Materials Science & Engineering Massachusetts Institute of Technology CambridgeMA United States Department of Electrical & Computer Engineering University of Massachusetts Lowell LowellMA United States College of Optics & Photonics Department of Materials Science and Engineering University of Central Florida OrlandoFL United States Lincoln Laboratory Massachusetts Institute of Technology LexingtonMA United States

Reconfigurable photonic systems featuring minimal power consumption are crucial for integrated optical devices in real-world technology. Current active devices available in foundries, however, use volatile methods to modulate light, requiring a constant supply of power and significant form factors. Essential aspects to overcoming these issues are the development of nonvolatile optical reconfiguration techniques which are compatible with on-chip integration with different photonic platforms and do not disrupt their optical performances. In this paper, a solution is demonstrated using an optoelectronic framework for nonvolatile tunable photonics that employs undoped-graphene microheaters to thermally and reversibly switch the optical phase-change material Ge2Sb2Se4Te1 (GSST). An in-situ Raman spectroscopy method is utilized to demonstrate, in real-time, reversible switching between four different levels of crystallinity. Moreover, a 3D computational model is developed to precisely interpret the switching characteristics, and to quantify the impact of current saturation on power dissipation, thermal diffusion, and switching speed. This model is used to inform the design of nonvolatile active photonic devices;namely, broadband Si3N4 integrated photonic circuits with small form-factor modulators and reconfigurable metasurfaces displaying 2π phase coverage through neural-network-designed GSST meta-atoms. This framework will enable scalable, low-loss nonvolatile applications across a diverse range of photonics platforms. Copyright © 2020, The Authors. All rights reserved.

关键词： Graphene

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Molecular Beam Epitaxy Growth of High Crystalline Quality LiNbO3

arXiv

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arXiv 2019年

作者： Brooks Tellekamp, M. Shank, Joshua C. Goorsky, Mark S. Alan Doolittle, W. Department of Electrical and Computer Engineering Georgia Institute of Technology 777 Atlantic Drive Atlanta Ga30332 United States Department of Materials Science and Engineering University of California Engineering V 410 Westwood Plaza 3111 Los AngelesCa90095 United States

Lithium niobate is a multi-functional material with wide reaching applications in acoustics, optics, and electronics. Commercial applications for lithium niobate require high crystalline quality currently limited to bulk and ion sliced material. Thin film lithium niobate is an attractive option for a variety of integrated devices, but the research effort has been stagnant due to poor material quality. Both lattice matched and mismatched lithium niobate are grown by molecular beam epitaxy (MBE) and studied to understand the role of substrate and temperature on nucleation conditions and material quality. Growth on sapphire produces partially coalesced columnar grains with atomically flat plateaus and no twin planes. A symmetric rocking curve shows a narrow linewidth with a full width at half-maximum (FWHM) of 8.6 arcsec (0.0024°) which is comparable to the 5.8 arcsec rocking curve FWHM of the substrate, while the film asymmetric rocking curve is 510 arcsec FWHM. These values indicate that the individual grains are relatively free of long-range disorder detectable by x-ray diffraction (XRD) with minimal measurable tilt and twist and represents the highest structural quality epitaxial material grown on lattice mismatched sapphire without twin planes. Lithium niobate is also grown on lithium tantalate producing high quality coalesced material without twin planes and with a symmetric rocking curve of 193 arcsec, which is nearly equal to the substrate rocking curve of 194 arcsec. The surface morphology of lithium niobate on lithium tantalate is shown to be atomically flat by atomic force microscopy (AFM). Copyright © 2019, The Authors. All rights reserved.

关键词： Thin films

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Simple and strong: Twisted silver painted nylon artificial muscle actuated by Joule heating

Simple and strong: Twisted silver painted nylon artificial m...

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Electroactive Polymer Actuators and Devices, EAPAD 2014

作者： Mirvakili, Seyed M. Ravandi, Ali Rafie Hunter, Ian W. Haines, Carter S. Li, Na Foroughi, Javad Naficy, Sina Spinks, Geoffrey M. Baughman, Ray H. Madden, John D. W. Department of Electrical and Computer Engineering Advanced Materials and Process Engineering Laboratory University of British Columbia Vancouver BC V6T 1Z4 Canada Department of Mechanical Engineering BioInstrumentation Laboratory Massachusetts Institute of Technology Cambridge MA 02139 United States Alan G. MacDiarmid NanoTech Institute University of Texas at Dallas Richardson TX 75083 United States Intelligent Polymer Research Institute ARC Centre of Excellence for Electromaterials Science University of Wollongong Wollongong NSW 2522 Australia

ISBN: (纸本)9780819499820

Highly oriented nylon and polyethylene fibres shrink in length when heated and expand in diameter. By twisting and then coiling monofilaments of these materials to form helical springs, the anisotropic thermal expansion has recently been shown to enable tensile actuation of up to 49% upon heating. Joule heating, by passing a current through a conductive coating on the surface of the filament, is a convenient method of controlling actuation. In previously reported work this has been done using highly flexible carbon nanotube sheets or commercially available silver coated fibres. In this work silver paint is used as the Joule heating element at the surface of the muscle. Up to 29% linear actuation is observed with energy and power densities reaching 840 kJ m -3 (528 J kg-1) and 1.1 kW kg-1 (operating at 0.1 Hz, 4% strain, 1.4 kg load). This simple coating method is readily accessible and can be applied to any polymer filament. Effective use of this technique relies on uniform coating to avoid temperature gradients. © 2014 SPIE.

关键词： Yarn

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Exploring the Potential of Tesla Valve for Filtering and Sorting Microscale Active Swimmers: A Computational Study

SSRN

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SSRN 2023年

作者： Rogers, Ariel He, Zhiyao Wang, Yong Department of Physics University of Arkansas FayettevilleAR72701 United States Department of Computer Science and Computer Engineering University of Arkansas FayettevilleAR72701 United States Materials Science & Engineering Program University of Arkansas FayettevilleAR72701 United States Cell & Molecular Biology Program University of Arkansas FayettevilleAR72701 United States

An interesting connection between shark spiral intestines and the Tesla valve was proposed recently;however, how Tesla valves interact with active matters and the potential applications of Tesla valves in biology remain largely unexplored. Here, we present a computational study on the potential use of Tesla valves for filtering and sorting microscale active swimmers such as bacteria. We investigated the behavior of microswimmers passing through the Tesla valve at different linear and angular velocities using numerical simulations, and quantified the diodicity of the Tesla valve for active swimmers. Our results demonstrate that the Tesla valve can effectively filter and sort microscale swimmers based on their swimming behavior. The findings of this study suggest that Tesla valves could have potential applications in microscale sorting and chromatography, with significant implications for biomedical and environmental engineering. © 2023, The Authors. All rights reserved.

关键词： Bacteria

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Tunable Asymmetric Transmission via Lossy Acoustic Metasurfaces

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Physical Review Letters 2017年第3期119卷 035501-035501页

作者： Yong Li Chen Shen Yangbo Xie Junfei Li Wenqi Wang Steven A. Cummer Yun Jing Institute of Acoustics School of Physics Science and Engineering Tongji University Shanghai 200092 People’s Republic of China Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology School of Physics Science and Engineering Tongji University Shanghai 200092 People’s Republic of China Department of Electrical and Computer Engineering Duke University Durham North Carolina 27708 USA Department of Mechanical and Aerospace Engineering North Carolina State University Raleigh North Carolina 27695 USA

In this study, we show that robust and tunable acoustic asymmetric transmission can be achieved through gradient-index metasurfaces by harnessing judiciously tailored losses. We theoretically prove that the asymmetric wave behavior stems from loss-induced suppression of high order diffraction. We further experimentally demonstrate this novel phenomenon. Our findings could provide new routes to broaden applications for lossy acoustic metamaterials and metasurfaces.

关键词： Acoustics

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A model for the current-voltage characteristic of membrane/electrolyte junctions

arXiv

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arXiv 2024年

作者： Mele, L.J. Alam, M.A. Palestri, P. Department of Materials Science and Engineering Stanford University StanfordCA94305 United States School of Electrical and Computer Engineering Purdue University West LafayetteIN47907 United States Engineering Department "Enzo Ferrari" University of Modena and Reggio Emilia Modena41125 Italy

A model for the current-voltage characteristic of the junction between an Ion- Sensitive-Membrane and an electrolyte solution is derived and compared with numerical simulations of the Poisson-Nernst-Planck model for ion transport. The expression resembles that of a semiconductor pn junction with a non-ideality factor of 2. The non-ideality correlated to the voltage drop in the electrolyte induced by the re-arrangement of the counter-ions. © 2024, CC BY-NC-ND.

关键词： Semiconductor junctions

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Fast Communication-efficient Spectral Clustering Over Distributed Data

arXiv

引用

arXiv 2019年

作者： Yan, Donghui Wang, Yingjie Wang, Jin Wu, Guodong Wang, Honggang Department of Mathematics and Program in Data Science Department of Electrical and Computer Engineering University of Massachusetts DartmouthMA United States Lovelace Respiratory Research Institute AlbuquerqueNM United States

The last decades have seen a surge of interests in distributed computing thanks to advances in clustered computing and big data technology. Existing distributed algorithms typically assume all the data are already in one place, and divide the data and conquer on multiple machines. However, it is increasingly often that the data are located at a number of distributed sites, and one wishes to compute over all the data with low communication overhead. For spectral clustering, we propose a novel framework that enables its computation over such distributed data, with "minimal" communications while a major speedup in computation. The loss in accuracy is negligible compared to the non-distributed setting. Our approach allows local parallel computing at where the data are located, thus turns the distributed nature of the data into a blessing;the speedup is most substantial when the data are evenly distributed across sites. Experiments on synthetic and large UC Irvine datasets show almost no loss in accuracy with our approach while about 2x speedup under various settings with two distributed sites. As the transmitted data need not be in their original form, our framework readily addresses the privacy concern for data sharing in distributed computing. Copyright © 2019, The Authors. All rights reserved.

关键词： Large dataset

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