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Fundamental bounds on the operation of Fano nonlinear isolators

Physical Review B 2018年第11期97卷 115431-115431页

作者： Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York 10031 USA Physics Program Graduate Center City University of New York New York 10016 USA Department of Electrical Engineering City College of The City University of New York New York 10031 USA

Nonlinear isolators have attracted significant attention for their ability to break reciprocity and provide isolation without the need of an external bias. A popular approach for the design of such devices is based on Fano resonators, which, due to their sharp frequency response, can lead to very large isolation for moderate input intensities. Here, we show that, independent of their specific implementation, these devices are subject to fundamental bounds on the transmission coefficient in the forward direction versus their quality factor, input power, and nonreciprocal intensity range. Our analysis quantifies a general tradeoff between forward transmission and these metrics, stemming directly from time-reversal symmetry, and that unitary transmission is only possible for vanishing nonreciprocity. Our results also shed light on the operation of resonant nonlinear isolators, reveal their fundamental limitations, and provide indications on how it is possible to design nonlinear isolators with optimal performance.

关键词： Electromagnetism Metamaterials Nonlinear optics

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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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Consistency of surface electromyography assessment at lower limb selected muscles during vertical countermovement 39

Consistency of surface electromyography assessment at lower ...

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39th Annual International Conference of the IEEE engineering in Medicine and Biology Society, EMBC 2017

作者： Rodrigues, Carlos Correia, Miguel Abrantes, Joao M. C. S. Nadal, Jurandir Rodrigues, Marco A. Benedetti Centre for Biomedical Engineering Research INESC TEC Porto4200 - 465 Portugal Department of Electrical and Computer Engineering Faculty of Engineering University of Porto 4200-465 Portugal MovLab Interactions and Interfaces Lab Lusófona University of Humanities and Technologies Lisboa1749-024 Portugal Biomedical Engineering Program Federal University of Rio de Janeiro 21941-972 Brazil Graduate Program in Electrical Engineering Federal University of Pernambuco Recife50740-550 Brazil

ISBN: (纸本)9781509028092

Given the difficulty of invasive methods to assess muscle action during natural human movement, surface electromyography (sEMG) has been increasingly used to capture muscle activity in relation to kinesiological analysis of specific tasks. Isolated isometric, concentric and eccentric forms of muscle action have been receiving the most attention for research purposes. Nevertheless natural muscle action frequently involves the use of a preceding eccentric muscle action as a form of potentiation of immediate muscle concentric action, in what is designated as muscle stretch-shortening cycle (SSC). The most frequently applied protocols for the evaluation of SSC on vertical jumps are by virtue of their reproducibility and control of experimental conditions, squat jump (SJ) without countermovement (CM), countermovement jump (CMJ) with long CM and drop jump (DJ) with short CM. The methods used to extract information and relationship of the captured signals also present a high diversity, with the question about the consistency of the methods and obtained results. The objective of this study is to evaluate the consistency of the analysis and results by applying different EMGs signal analysis techniques related to strategic muscle groups of the lower limbs at different countermovement evaluated in vertical jumps. Raw sEMG signals of 5 lower limb muscles of 6 subjects during SJ, CMJ and DJ were rectified, filtered and obtained their envelope, and then correlated (CR) for detection of synergistic, agonist and antagonist activity, applied principal component analysis (PCA) for the detection of uncorrelated components explaining maximum variability and normalized cross-correlation (CCRN) for detection of maximum correlations and time lag. CR of EMG envelopes presented higher coactivities (CoA) in DJ relative to SJ and these CoA superior to CMJ with greater synergy in DJ relative to SJ and CMJ that present several loop cycles corresponding to time lag of activity. CCRN of the EMG e

关键词： Muscles Correlation Electromyography Principal component analysis Eigenvalues and eigenfunctions Electronic mail Radio frequency

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Is deep learning better than kernel regression for functional connectivity prediction of fluid intelligence?

Is deep learning better than kernel regression for functiona...

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2018 International Workshop on Pattern Recognition in Neuroimaging, PRNI 2018

作者： He, Tong Kong, Ru Holmes, Avram J. Sabuncu, Mert R. Eickhoff, Simon B. Bzdok, Danilo Feng, Jiashi Yeo, B.T. Thomas Clinical Imaging Research Centre Singapore Institute for Neurotechnology National University of Singapore Singapore Singapore Department of Electrical and Computer Engineering National University of Singapore Singapore Singapore Department of Psychology Yale University New HavenCT United States School of Electrical and Computer Engineering Cornell University IthacaNY United States Department of Psychiatry Psychotherapy and Psychosomatics RWTH Aachen University Germany Institute of Systems Neuroscience Medical Faculty Heinrich Heine University Dösseldorf Dösseldorf Germany Research Centre Jölich Jölich Germany Martinos Center for Biomedical Imaging Massachusetts General Hospital CharlestownMA United States Centre for Cognitive Neuroscience Duke-NUS Medical School Singapore Singapore NUS Graduate School for Integrative Sciences and Engineering National University of Singapore Singapore Singapore

ISBN: (纸本)9781538668597

In recent years, deep learning has transformed the field of machine learning. In the field of neuroimaging, there are increasing interests in adopting deep learning techniques. However, deep neural networks (DNNs) usually need large quantity of data to perform well, which is often lacking in neuroimaging. In this work, we evaluated three different DNNs (fully-connected neural network, BrainNetCNN [1], and graph convolutional neural network [2]) for functional connectivity (FC)-based prediction of fluid intelligence using the Human Connectome Project. These DNNs were compared with kernel regression, a classical machine learning algorithm. Our results suggested that the DNNs did not outperform kernel regression. However, we do not preclude the possibility that with more participants or different FC features, DNNs might eventually outperform their classical counterpart. © 2018 IEEE.

关键词： Deep neural networks

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Signatures of electronic nematicity in (111) LaAlO3/SrTiO3 interfaces

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Physical Review B 2018年第4期97卷 041408(R)-041408(R)页

作者： S. Davis Z. Huang K. Han Ariando T. Venkatesan V. Chandrasekhar Graduate Program in Applied Physics and Department of Physics and Astronomy Northwestern University 2145 Sheridan Road Evanston Illinois 60208 USA NUSNNI-Nanocore National University of Singapore 117411 Singapore Department of Physics National University of Singapore 117551 Singapore NUS Graduate School for Integrative Sciences & Engineering National University of Singapore 117456 Singapore Department of Electrical and Computer Engineering National University of Singapore 117576 Singapore Department of Material Science and Engineering National University of Singapore 117575 Singapore

The two-dimensional conducting gas (2DCG) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has been widely studied due to the multitude of in situ tunable phenomena that exist at the interface. Recently it has been shown that nearly every property of the 2DEG that forms at the interface of (111) oriented LAO/STO is strongly anisotropic with respect to the in-plane crystal direction. This in-plane rotational symmetry breaking points to the existence of an electronic nematic phase at the interface that can be modified by an in situ electrostatic back-gate potential. Here we show that the onset temperature of the anisotropy in the longitudinal resistance is T≈22K, which does not match up with any known structural transition, and coincides with the onset of anisotropy in the Hall response of the system. Furthermore, below 22 K, charge transport is activated in nature with different activation energies along the two in-plane crystal directions. Such a response implies that the band edges along the two directions are different and provides further evidence of an electronic nematic state at the interface.

关键词： electrical properties Hall effect Nematic order Transport phenomena Hall bar Resistivity measurements Transport techniques

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Corrigendum: Functional vagotopy in the cervical vagus nerve of the domestic pig: implications for the study of vagus nerve stimulation (2020 J. Neural Eng. 17 026022)

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Journal of neural engineering 2021年第4期18卷

作者： Megan L Settell Nicole A Pelot Bruce E Knudsen Aaron M Dingle Andrea L McConico Evan N Nicolai James K Trevathan J Ashley Ezzell Erika K Ross Kenneth J Gustafson Andrew J Shoffstall Justin C Williams Weifeng Zeng Samuel O Poore Luis C Populin Aaron J Suminski Warren M Grill Kip A Ludwig Department of Biomedical Engineering University of Wisconsin-Madison Madison WI United States of America. Mayo Clinic Mayo Clinic Graduate School of Biomedical Sciences Rochester MN United States of America. Department of Biomedical Engineering Duke University Durham NC United States of America. Department of Neurologic Surgery Mayo Clinic Rochester MN United States of America. Division of Plastic Surgery Department of Surgery University of Wisconsin-Madison Madison WI United States of America. Histology Research Core University of North Carolina School of Medicine Chapel Hill NC United States of America. Department of Cell Biology and Physiology University of North Carolina School of Medicine Chapel Hill NC United States of America. Abbott Neuromodulation Plano TX United States of America. Department of Biomedical Engineering Case Western Reserve University Cleveland OH United States of America. Louis Stokes Cleveland VA Medical Center Cleveland OH United States of America. Department of Neurosurgery University of Wisconsin-Madison Madison WI United States of America. Department of Surgery University of Wisconsin-Madison Madison WI United States of America. University of Wisconsin School of Medicine and Public Health Madison WI United States of America. Department of Neuroscience University of Wisconsin-Madison Madison WI United States of America. Department of Electrical and Computer Engineering Duke University Durham NC United States of America. Department of Neurobiology Duke University Durham NC United States of America. Department of Neurosurgery Duke University Durham NC United States of America.

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Broadband Cyclic-Symmetric Magnet-less Circulatorsand Theoretical Bounds on their Bandwidth

arXiv

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arXiv 2018年

作者： Kord, Ahmed Sounas, Dimitrios L. Xiao, Zhicheng Alù, Andrea Department of Electrical and Computer Engineering University of Texas at Austin AustinTX78712 United States Advanced Science Research Center Physics Program Graduate Center Photonics Initiative Department of Electrical Engineering City College of New York City University of New York New York NY10031 United States

In this paper, we explore theoretically and experimentally broadband spatiotemporally modulated (STM) magnet-less circulators realized by combining three-port non-reciprocal junctions with three identical bandpass filters. We develop a rigorous theory for the proposed circuit, which allows to optimize its design and to derive a global bound on the maximum possible bandwidth (BW). We verify our theory with simulations and measurements of a printed circuit board (PCB) prototype based on a differential wye junction and second-order Chebyshev bandpass filters, resulting in a measured fractional BW of 13.9% at a center frequency of 1 GHz. Copyright © 2018, The Authors. All rights reserved.

关键词： Bandwidth

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Maximum Willis Coupling in Acoustic Scatterers

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Physical Review Letters 2018年第25期120卷 254301-254301页

作者： Li Quan Younes Ra’di Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

Willis coupling in acoustic materials defines the cross-coupling between strain and velocity, analogous to bianisotropic phenomena in electromagnetics. While these phenomena have been garnering significant attention in recent years, to date their effects have been considered mostly perturbative. Here, we derive general bounds on the Willis response of acoustic scatterers, show that these bounds can be reached in suitably designed scatterers, and outline a systematic venue for the realistic implementation of maximally bianisotropic acoustic inclusions. We then employ these inclusions to realize acoustic metasurfaces for bending and steering of sound with unitary efficiency.

关键词： Acoustic metamaterials Acoustic wave phenomena Acoustics Mechanical & acoustical properties

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Active Microwave Cloaking Using Parity-Time-Symmetric Satellites

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Physical Review Applied 2018年第5期10卷 054040-054040页

作者： Ahmed Kord Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering the University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

In this paper, we present and study the dynamics of an active microwave cloaking technique that alleviates the trade-offs between loss, bandwidth, and size inherent in passive approaches. The presented cloak consists of a finite number of satellite antennas loaded with parity-time-symmetric lumped admittances, which, without external control, can track in real time the amplitude, frequency, and phase variations of the impinging signals and generate the required current distributions at the antennas to totally suppress the scattered waves, including reflections and shadows. We analytically derive the optimal density and frequency dispersion of the antenna satellites surrounding the object in order to achieve substantial reduction in the scattering crosssection over a wide bandwidth. We also investigate the conditions necessary to maintain the cloak stability and study its transient response for excitation with pulsed signals.

关键词： Cloaking Metamaterials Optical cloaking PT-symmetry Microwave techniques

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Cytocompatible magnetostrictive microstructures for nano- A nd microparticle manipulation on linear strain response piezoelectrics

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Multifunctional Materials 2018年第1期1卷

作者： Xiao, Zhuyun Khojah, Reem Chooljian, Marc Conte, Roberto Lo Schneider, Joseph D. Fitzell, Kevin Chopdekar, Rajesh V. Wang, Yilian Scholl, Andreas Chang, Jane Carman, Gregory P. Bokor, Jeffrey Carlo, Dino Di Candler, Rob N. Department of Electrical and Computer Engineering University of California Los Angeles United States Department of Bioengineering University of California Los Angeles United States University of California Berkeley UCSF Graduate Program in Bioengineering Berkeley United States Department of Electrical Engineering and Computer Sciences University of California Berkeley United States Department of Mechanical and Aerospace Engineering University of California Los Angeles United States Department of Chemical and Biomolecular Engineering University of California Los Angeles United States Advanced Light Source Lawrence Berkeley National Laboratory Berkeley United States California Nanosystems Institute Los Angeles United States

In this work, we investigate polycrystalline Ni and FeGamagnetostrictivemicrostructures on prepoled (011)-cut single crystal [Pb(Mg1/3Nb2/3)O3]1-x-[PbTiO3]x (PMN-PT, x ≈ 0.31) with linear strain profile versus applied electric field. Magnetostrictive microstructure arrays with various geometries are patterned on PMN-PT. Functionalizedmagnetic beads are trapped by localized stray fields originating fromthe microstructures. With an applied electric field, themagnetic domains are actuated, inducing the motion of the coupled particles with sub-micrometer precision. This work shows promise of using energy-efficient electric-field-controlled magnetostrictivemicro- A nd nanostructures formanipulatingmagnetic beads via a linear strain response. The work also demonstrates the viability of cells suspended in solution on these structures when subject to applied electric fields, proving the cytocompatibility of the platform for live cell sorting applications. © 2018 IOP Publishing Ltd.

关键词： Electric fields

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