检索结果-内蒙古大学图书馆

Learning to continuously optimize wireless resource in episodically dynamic environment

学校读者我要写书评

暂无评论

arXiv 2020年

作者： Sun, Haoran Pu, Wenqiang Zhu, Minghe Fu, Xiao Chang, Tsung-Hui Hong, Mingyi Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States The Shenzhen Research Institute of Big Data Shenzhen China Shenzhen Research Institute of Big Data The Chinese University of Hong Kong Shenzhen China The School of Electrical Engineering and Computer Science Oregon State University CorvallisOR97331 United States

There has been a growing interest in developing data-driven and in particular deep neural network (DNN) based methods for modern communication tasks. For a few popular tasks such as power control, beamforming, and MIMO detection, these methods achieve state-of-the-art performance while requiring less computational efforts, less channel state information (CSI), etc. However, it is often challenging for these approaches to learn in a dynamic environment where parameters such as CSIs keep changing. This work develops a methodology that enables data-driven methods to continuously learn and optimize in a dynamic environment. Specifically, we consider an "episodically dynamic" setting where the environment changes in "episodes", and in each episode the environment is stationary. We propose to build the notion of continual learning (CL) into the modeling process of learning wireless systems, so that the learning model can incrementally adapt to the new episodes, without forgetting knowledge learned from the previous episodes. Our design is based on a novel min-max formulation which ensures certain "fairness" across different data samples. We demonstrate the effectiveness of the CL approach by customizing it to two popular DNN based models (one for power control and one for beamforming), and testing using both synthetic and real data sets. These numerical results show that the proposed CL approach is not only able to adapt to the new scenarios quickly and seamlessly, but importantly, it maintains high performance over the previously encountered scenarios as well. Copyright © 2020, The Authors. All rights reserved.

关键词： Deep neural networks

Spin and Charge Interconversion in Dirac-Semimetal Thin Films

学校读者我要写书评

暂无评论

Physical Review Applied 2021年第5期16卷 054031-054031页

作者： Wilson Yanez Yongxi Ou Run Xiao Jahyun Koo Jacob T. Held Supriya Ghosh Jeffrey Rable Timothy Pillsbury Enrique González Delgado Kezhou Yang Juan Chamorro Alexander J. Grutter Patrick Quarterman Anthony Richardella Abhronil Sengupta Tyrel McQueen Julie A. Borchers K. Andre Mkhoyan Binghai Yan Nitin Samarth Department of Physics Pennsylvania State University University Park Pennsylvania 16802 USA Department of Condensed Matter Physics Weizmann Institute of Science Rehovot 7610001 Israel Department of Chemical Engineering and Materials Science University of Minnesota Minneapolis Minnesota 55455 USA Department of Physics and Electronics Humacao Campus of the University of Puerto Rico 100 Tejas Avenue Humacao 00791-4300 Puerto Rico Department of Materials Science and Engineering Pennsylvania State University University Park Pennsylvania 16802 USA Department of Chemistry Johns Hopkins University Baltimore Maryland USA NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg Maryland 20899 USA School of Electrical Engineering and Computer Science Pennsylvania State University University Park Pennsylvania 16802 USA

We use spin torque ferromagnetic resonance and ferromagnetic-resonance-driven spin pumping to detect spin-charge interconversion at room temperature in heterostructure devices that interface an archetypal Dirac semimetal, Cd3As2, with a metallic ferromagnet, Ni0.80Fe0.20 (permalloy). Angle-resolved photoemission directly reveals the Dirac-semimetal nature of the samples prior to device fabrication and high-resolution transmission electron microscopy is used to characterize the crystalline structure and the relevant heterointerfaces. We find that the spin-charge interconversion efficiency in Cd3As2/permalloy heterostructures is comparable to that in heavy metals and that it is enhanced by the presence of an interfacial oxide. Spin torque ferromagnetic resonance measurements reveal an in-plane spin polarization regardless of an oxidized or pristine interface. We discuss the underlying mechanisms for spin-charge interconversion by comparing our results with first principles calculations and conclude that extrinsic mechanisms dominate the observed phenomena. Our results indicate a need for caution in interpretations of spin-transport and spin-charge conversion experiments in Cd3As2 devices that seek to invoke the role of topological Dirac and Fermi arc states.

关键词： Spin pumping Spin transfer torque Surface & interfacial phenomena Surface states Topological materials Dirac semimetal Magnetic multilayers Ferromagnetic resonance

Understanding viscoelastic flow instabilities: Oldroyd-B and beyond

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Sánchez, Hugo A. Castillo Jovanović, Mihailo R. Kumar, Satish Morozov, Alexander Shankar, V. Subramanian, Ganesh Wilson, Helen J. Department Of Applied Mathematics And Statistics Institute Of Mathematics And Computational Sciences University Of Sao Paulo Brazil Ming Hsieh Department Of Electrical And Computer Engineering University Of Southern California Los AngelesCA90089 United States Department Of Chemical Engineering And Materials Science University Of Minnesota MinneapolisMN55455 United States SUPA School Of Physics And Astronomy The University Of Edinburgh EdinburghEH9 3FD United Kingdom Department Of Chemical Engineering Indian Institute Of Technology Kanpur208016 India Engineering Mechanics Unit Jawaharlal Nehru Center For Advanced Scientific Research Bangalore560064 India Mathematics Department University College London Gower Street LondonWC1E 6BT United Kingdom

The Oldroyd-B model has been used extensively to predict a host of instabilities in shearing flows of viscoelastic fluids, often realized experimentally using polymer solutions. The present review, written on the occasion of the birth centenary of James Oldroyd, provides an overview of instabilities found across major classes of shearing flows. These comprise (i) the canonical rectilinear shearing flows including plane Couette, plane and pipe Poiseuille flows;(ii) viscometric shearing flows with curved streamlines such as those in the TaylorCouette, cone-and-plate and parallel-plate geometries;(iii) non-viscometric shearing flows with an underlying extensional flow topology such as the flow in a cross-slot device;and (iv) multilayer shearing flows. While the underlying focus in all these cases is on results obtained using the Oldroyd-B model, we also discuss their relation to the actual instability, and as to how the shortcomings of the Oldroyd-B model may be overcome by the use of more realistic constitutive models. All the three commonly used tools of stability analysis, viz., modal linear stability, nonmodal stability, and weakly nonlinear stability analyses are discussed, with supporting evidence from experiments and numerical simulations as appropriate. Despite only accounting for a shear-rate-independent viscosity and first normal stress coefficient, the Oldroyd-B model is able to qualitatively predict the majority of instabilities in the aforementioned shearing flows. The review also highlights, where appropriate, open questions in the area of viscoelastic stability. © 2022, CC BY.

关键词： Stability

Broadband focusing of acoustic plasmons in graphene with an applied current

学校读者我要写书评

暂无评论

arXiv 2021年

作者： Sammon, Michael Margetis, Dionisios Mele, E.J. Low, Tony Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States Institute for Physical Science and Technology Department of Mathematics Center for Scientific Computation and Mathematical Modeling University of Maryland College ParkMD20742 United States Dept. of Physics and Astronomy University of Pennsylvania PhiladelphiaPA19104 United States

Non-reciprocal plasmons in current-driven, isotropic, and homogenous graphene with proximal metallic gates is theoretically explored. Nearby metallic gates screen the Coulomb interactions, leading to linearly dispersive acoustic plasmons residing close to its particle-hole continuum counterpart. We show that the applied bias leads to spectral broadband focused plasmons whose resonance linewidth is dependent on the angular direction relative to the current flow due to Landau damping. We predict that forward focused non-reciprocal plasmons are possible with accessible experimental parameters and setup. © 2021, CC BY.

关键词： Plasmons

Charge-to-spin conversion in twisted graphene/WSe2 heterostructures

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Lee, Seungjun de Sousa, D.J.P. Kwon, Young-Kyun de Juan, Fernando Chi, Zhendong Casanova, Fèlix Low, Tony Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States Department of Physics Department of Information Display Research Institute for Basic Sciences Kyung Hee University Seoul02447 Korea Republic of Donostia International Physics Center P. Manuel de Lardizabal 4 Donostia-San Sebastian20018 Spain IKERBASQUE Basque Foundation for Science Maria Diaz de Haro 3 Bilbao48013 Spain CIC nanoGUNE Basque Country Donostia-San Sebastián20018 Spain Department of Physics University of Minnesota MinneapolisMN55455 United States

We investigate the twist angle dependence of spin-orbit coupling (SOC) proximity effects and charge-to-spin conversion (CSC) in graphene/WSe2 heterostructures from first principles. The CSC is shown to strongly depend on the twist angle, with both the spin Hall and standard Rashba-Edelstein efficiencies optimized at or near 30° twisting. Symmetry breaking due to twisting also gives rise to an unconventional Rashba-Edelstein effect, with electrically generated non-equilibrium spin densities possessing spins collinear to the applied electric field. We further discuss how the carrier doping concentration and band broadening control the crossover between the Fermi-sea and -surface spin response, which reconciles the seemingly disparate experimental observations of different CSC phenomena. © 2022, CC BY.

关键词： Selenium compounds

Comparative Assessment and Outlook on Methods for Imputing Proteomics Data

学校读者我要写书评

暂无评论

Research Square

Research Square 2021年

作者： Shen, Minjie Chang, Yi-Tan Wu, Chiung-Ting Parker, Sarah J. Saylor, Georgia Wang, Yizhi Yu, Guoqiang Van Eyk, Jennifer E. Clarke, Robert Herrington, David M. Wang, Yue Department of Electrical and Computer Engineering Virginia Polytechnic Institute State University ArlingtonVA22203 United States Advanced Clinical Biosystems Research Institute Cedars Sinai Medical Center Los AngelesCA90048 United States Department of Internal Medicine Wake Forest University Winston-SalemNC27157 United States The Hormel Institute University of Minnesota AustinMN55912 United States

Background: Missing values are a major issue in quantitative proteomics data analysis. While many methods have been developed for imputing missing values in high-throughput proteomics data, comparative assessment on the accuracy of existing methods remains inconclusive, mainly because the true missing mechanisms are complex and the existing evaluation methodologies are imperfect. Moreover, few studies have provided an outlook of current and future development. Results: We first report an assessment of eight representative methods collectively targeting three typical missing mechanisms. The selected methods are compared on both realistic simulation and real proteomics datasets, and the performance is evaluated using three quantitative measures. We then discuss fused regularization matrix factorization, a popular low-rank matrix factorization framework with similarity and/or biological regularization, which is extendable to integrating multi-omics data such as gene expressions or clinical variables. We further explore the potential application of convex analysis of mixtures, a biologically-inspired latent variable modeling strategy, to missing value imputation. The preliminary results on proteomics data are provided together with an outlook into future development directions. Conclusion: While a few winners emerged from our comparative assessment, data-driven evaluation of imputation methods is imperfect because performance is evaluated indirectly on artificial missing or masked values not authentic missing values. Imputation accuracy may vary with signal intensity. Fused regularization matrix factorization provides a possibility of incorporating external information. Convex analysis of mixtures presents a biologically plausible new approach. © 2021, CC BY.

关键词： Mixtures

Comparative Assessment and Novel Strategy on Methods for Imputing Proteomics Data

学校读者我要写书评

暂无评论

Research Square

Research Square 2021年

作者： Shen, Minjie Chang, Yi-Tan Wu, Chiung-Ting Parker, Sarah J. Saylor, Georgia Wang, Yizhi Yu, Guoqiang van Eyk, Jennifer E. Clarke, Robert Herrington, David M. Wang, Yue Department of Electrical and Computer Engineering Virginia Polytechnic Institute State University ArlingtonVA22203 United States Advanced Clinical Biosystems Research Institute Cedars Sinai Medical Center Los AngelesCA90048 United States Department of Internal Medicine Wake Forest University Winston-SalemNC27157 United States The Hormel Institute University of Minnesota AustinMN55912 United States

Missing values are a major issue in quantitative proteomics analysis. While many methods have been developed for imputing missing values in high-throughput proteomics data, a comparative assessment of imputation accuracy remains inconclusive, mainly because mechanisms contributing to true missing values are complex and existing evaluation methodologies are imperfect. Moreover, few studies have provided an outlook of future methodological development. We first re-evaluate the performance of eight representative methods targeting three typical missing mechanisms. These methods are compared on both simulated and masked missing values embedded within real proteomics datasets, and performance is evaluated using three quantitative measures. We then introduce fused regularization matrix factorization, a low-rank global matrix factorization framework, capable of integrating local similarity derived from additional data types. We also explore a biologically-inspired latent variable modeling strategy - convex analysis of mixtures - for missing value imputation and present preliminary experimental results. While some winners emerged from our comparative assessment, the evaluation is intrinsically imperfect because performance is evaluated indirectly on artificial missing or masked values not authentic missing values. Nevertheless, we show that our fused regularization matrix factorization provides a novel incorporation of external and local information, and the exploratory implementation of convex analysis of mixtures presents a biologically plausible new approach. © 2021, CC BY.

关键词： Mixtures

Near-field probing of image phonon-polaritons in hexagonal boron nitride on gold crystals

学校读者我要写书评

暂无评论

arXiv 2021年

作者： Menabde, Sergey G. Boroviks, Sergejs Ahn, Jongtae Heiden, Jacob T. Watanabe, Kenji Taniguchi, Takashi Low, Tony Hwang, Do Kyung Mortensen, N. Asger Jang, Min Seok School of Electrical Engineering Korea Advanced Institute of Science and Technology Daejeon Korea Republic of Center for Nano Optics University of Southern Denmark Odense Denmark Center for Opto-Electronic Materials and Devices Korea Institute of Science and Technology Seoul Korea Republic of Research Center for Functional Materials National Institute for Materials Science Ibaraki Japan International Center for Materials Nanoarchitectonics National Institute for Materials Science Ibaraki Japan Department of Electrical and Computer Engineering University of Minnesota Minneapolis United States Division of Nano & Information Technology University of Science and Technology Daejeon Korea Republic of Danish Institute for Advanced Study University of Southern Denmark Odense Denmark

Near-field mapping has been widely used to study hyperbolic phonon-polaritons in van der Waals crystals. However, an accurate measurement of the polaritonic loss remains challenging because of the inherent complexity of the near-field signal and the substrate-mediated loss. Here we demonstrate that large-area monocrystalline gold flakes, an atomically-flat low-loss substrate for image polaritons, provide a platform for precise near-field measurement of the complex propagation constant of polaritons in van der Waals crystals. As a topical example, we measure propagation loss of the image phonon-polaritons in hexagonal boron nitride, revealing that their normalized propagation length exhibits a parabolic spectral dependency. Further, we show that image phonon-polaritons exhibit up to a twice lower normalized propagation loss, while being 2.4 times more compressed compared to the case of dielectric substrate. We conclude that the monocrystalline gold flakes provide a unique nanophotonic platform for probing and exploitation of the image modes in low-dimensional materials. © 2021, CC BY.

关键词： Van der Waals forces

A nested hybridizable discontinuous Galerkin method for computing second-harmonic generation in three-dimensional metallic nanostructures

学校读者我要写书评

暂无评论

arXiv 2020年

作者： Vidal-Codina, F. Nguyen, N.-C. Ciracì, C. Oh, S.-H. Peraire, J. Department of Aeronautics and Astronautics Massachusetts Institute of Technology CambridgeMA02139 United States 73010 Italy Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States

We develop a nested hybridizable discontinuous Galerkin (HDG) method to numerically solve the Maxwell's equations coupled with a hydrodynamic model for the conduction-band electrons in metals. The HDG method leverages static condensation to eliminate the degrees of freedom of the approximate solution defined in the elements, yielding a linear system in terms of the degrees of freedom of the approximate trace defined on the element boundaries. This article presents a computational method that relies on a degree-of-freedom reordering such that the HDG linear system accommodates an additional static condensation step to eliminate a large portion of the degrees of freedom of the approximate trace, thereby yielding a much smaller linear system. For the particular metallic structures considered in this article, the resulting linear system obtained by means of nested static condensations is a block tridiagonal system, which can be solved efficiently. We apply the nested HDG method to compute second harmonic generation on a triangular coaxial periodic nanogap structure. This nonlinear optics phenomenon features rapid field variations and extreme boundary-layer structures that span a wide range of length scales. Numerical results show that the ability to identify structures which exhibit resonances at ω and 2ω is essential to excite the second harmonic response. Copyright © 2020, The Authors. All rights reserved.

关键词： Harmonic generation