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Strain-tuning of domain walls in multilayer graphene probed in the quantum Hall regime

Physical Review B 2022年第8期105卷 L081408-L081408页

作者： Paul Anderson Yifan Huang Yuanjun Fan Sara Qubbaj Sinisa Coh Qin Zhou Claudia Ojeda-Aristizabal Department of Physics and Astronomy California State University Long Beach Long Beach California 90840 USA Department of Mechanical and Materials Engineering University of Nebraska Lincoln Nebraska 68588-0526 USA Department of Mechanical Engineering and Materials Science and Engineering Program University of California Riverside Riverside California 92521 USA

Domain walls, topological defects that define the frontier between regions of different stacking order in multilayer graphene, have proved to host exciting physics. The ability to tune these topological defects in situ in an electronic transport experiment brings a wealth of possibilities in terms of fundamental understanding of domain walls as well as for electronic applications. Here, we demonstrate, through a MEMS (microelectromechanical system) actuator and magnetoresistance measurements, the effect of domain walls in multilayer graphene quantum Hall effect. Reversible and controlled uniaxial strain triggers the topological defects, manifested as addtional quantum Hall effect plateaus as well as a discrete and reversible modulation of the current across the device. Our findings are supported by theoretical calculations and constitute indication of the in situ tuning of topological defects in multilayer graphene probed through electronic transport, opening the way for the use of reversible topological defects in electronic applications.

关键词： Domain walls Transport phenomena Graphene Resistivity measurements Tight-binding model

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Study on structural and photoluminescence properties of CS/r-GO polymer nanocomposite

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Materials Today: Proceedings 2023年

作者： Dhayal, Vimala Hashmi, S.Z. Leel, N.S. Quraishi, A.M. Singh, Jasgurpreet Kumar, Kuldeep Alvi, P.A. Department of Physics Banasthali Vidyapith 304022 Rajasthan India Department of Chemistry Banasthali Vidyapith 304022 Rajasthan India Department of Pure & Applied Physics University of Kota Rajasthan Kota324005 India Department of Electrical Engineering College of Engineering Qassim University Unaizah Saudi Arabia University Centre for Research & Development Department of Mechanical Engineering Chandigarh University Punjab Gharuan India Department of Physics Government Degree College Akhnoor J&K Jammu181201 India

In this article, we reports the structural and photoluminescence properties of biodegradable CS/r-GO polymer nanocomposites (PNCs) prepared by simple solution mixing/casting technique. The details of sample preparation along with the characterization results are discussed and analyzed. The structural property of the prepared nanocomposite has been analyzed by XRD (X-ray diffraction) technique which confirms the crystalline size of the order of ∼37 nm with micro-strain ∼2.50 × 10-3. The optical properties (Photoluminescence and optical bandgap) have also been studied. The peak intensity in PL spectrum was found at ∼380 nm (near visible region) and optical bandgap has the order of ∼3.19 eV. The Raman spectra of the samples have also been studied which show the characteristic peaks of pure CS and r-GO nanofiller at 1548 /cm and 1581 /cm, respectively. © 2023

关键词： Structural properties

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Enhancement of bacterial rheotaxis in non-Newtonian fluids

arXiv

引用

arXiv 2024年

作者： Torres Maldonado, Bryan O. Théry, Albane Tao, Ran Brosseau, Quentin Mathijssen, Arnold J.T.M. Arratia, Paulo E. Department of Mechanical Engineering & Applied Mechanics University of Pennsylvania PhiladelphiaPA19104 United States Department of Mathematics University of Pennsylvania PhiladelphiaPA19104 United States Department of Physics & Astronomy University of Pennsylvania PhiladelphiaPA19104 United States

Bacteria often exhibit upstream swimming, which can cause the contamination of biomedical devices and the infection of organs including the urethra or lungs. This process, called rheotaxis, has been studied extensively in Newtonian fluids. However, most microorganisms thrive in non-Newtonian fluids that contain suspended polymers such as mucus and biofilms. Here, we investigate the rheotatic behavior of E. coli near walls in non-Newtonian fluids. Our experiments demonstrate that bacterial upstream swimming is enhanced by an order of magnitude in shear-thinning polymeric fluids relative to Newtonian fluids. This result is explained by direct numerical simulations, revealing a torque that promotes the alignment of bacteria against the flow. From this analysis, we develop a theoretical model that accurately describes experimental rheotatic data in both Newtonian and shear-thinning fluids. © 2024, CC BY.

关键词： Shear thinning

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Efficient modeling of organic adsorbates on oxygen-intercalated graphene on Ir(111)

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Physical Review B 2022年第19期105卷 195304-195304页

作者： Jari Järvi Milica Todorović Patrick Rinke Department of Applied Physics Aalto University P.O. Box 11100 FI-00076 AALTO Finland Department of Mechanical and Materials Engineering University of Turku FI-20014 Turku Finland

Organic charge transfer complexes (CTCs) can be grown as thin films on intercalated graphene (Gr). Deciphering their precise film morphologies requires global ab initio structure search, where configurational sampling is computationally intractable unless we reconsider the model for the complex substrate. In this study, we employ charged freestanding Gr to approximate an intercalated Gr/O/Ir(111) substrate, without altering the adsoption properties of deposited molecules. We compare different methods of charging Gr and select the most appropriate substitute model for Gr/O/Ir(111) that maintains the adsorption properties of fluorinated tetracyanoquinodimethane (F4TCNQ) and tetrathiafulvalene (TTF), prototypical electron acceptor/donor molecules in CTCs. Next, we apply our model in the Bayesian optimization structure search method and density-functional theory to identify the stable structures of F4TCNQ and TTF on supported Gr. We find that both molecules physisorb to Gr in various configurations. The narrow range of adsorption energies indicates that the molecules may diffuse easily on the surface and molecule-molecule interactions likely have a central role in film formation. Our study shows that complex intercalated substrates may be approximated with charged freestanding Gr, which can facilitate exhaustive structure search of CTCs.

关键词： Physisorption Graphene Surfaces Density functional theory Machine learning

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Challenges of measuring spin Seebeck noise

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Physical Review B 2024年第10期109卷 104429-104429页

作者： Renjie Luo Xuanhan Zhao Tanner J. Legvold Liyang Chen Changjiang Liu Deshun Hong Anand Bhattacharya Douglas Natelson Department of Physics and Astronomy Rice University Houston Texas 77005 USA Applied Physics Program Smalley-Curl Institute Rice University Houston Texas 77005 USA Materials Science Division Argonne National Laboratory Lemont Illinois 60439 USA Department of Electrical and Computer Engineering Rice University Houston Texas 77005 USA Department of Materials Science and NanoEngineering Rice University Houston Texas 77005 USA

Just as electronic shot noise in driven conductors results from the granularity of charge and the statistical variation in the arrival times of charge carriers, there are predictions for fundamental noise in magnon currents due to angular momentum being carried by discrete excitations. The inverse spin Hall effect as a transduction mechanism to convert spin current into charge current raises the prospect of experimental investigations of such magnon shot noise. Spin Seebeck effect measurements have demonstrated the electrical detection of thermally driven magnon currents and have been suggested as an avenue for accessing spin current fluctuations. Using spin Seebeck structures made from yttrium iron garnet on gadolinium gallium garnet, we demonstrate the technical challenges inherent in such noise measurements. While there is a small increase in voltage noise in the inverse spin Hall detector at low temperatures associated with adding a magnetic field, the dependence on field orientation implies that this is not due to magnon shot noise. We describe theoretical predictions for the expected magnitude of magnon shot noise, highlighting ambiguities that exist. Further, we show that magnon shot noise detection through the standard inverse spin Hall approach is likely impossible due to geometric factors. Implications for future attempts to measure magnon shot noise are discussed.

关键词： Spin Seebeck effect Spin current Magnetic insulators Noise measurements

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Unified Variational Approach Description of Ground-State Phases of the Two-Dimensional Electron Gas

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Physical Review Letters 2024年第26期133卷 266504-266504页

作者： Conor Smith Yixiao Chen (陈一潇) Ryan Levy Yubo Yang (杨煜波) Miguel A. Morales Shiwei Zhang Center for Computational Quantum Physics Flatiron Institute New York New York 10010 USA Department of Electrical and Computer Engineering University of New Mexico Albuquerque New Mexico 87131 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

The two-dimensional electron gas (2DEG) is a fundamental model, which is drawing increasing interest because of recent advances in experimental and theoretical studies of 2D materials. Current understanding of the ground state of the 2DEG relies on quantum Monte Carlo calculations, based on variational comparisons of different Ansätze for different phases. We use a single variational ansatz, a general backflow-type wave function using a message-passing neural quantum state architecture, for a unified description across the entire density range. The variational optimization consistently leads to lower ground-state energies than previous best results. Transition into a Wigner crystal (WC) phase occurs automatically at rs=37±1, a density lower than currently believed. Between the liquid and WC phases, the same ansatz and variational search strongly suggest the existence of intermediate states in a broad range of densities, with enhanced short-range nematic spin correlations.

关键词： Wave functions

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Plasmonic BICs as Biosensors with Better Detectivity

Plasmonic BICs as Biosensors with Better Detectivity

引用

Conference on Lasers and Electro-Optics (CLEO)

作者： Zhichao Li Ciril S. Prasad Xielin Wang Gururaj V. Naik Applied Physics Graduate Program Smalley-Curl Institute Rice University Houston TX USA Department of Electrical and Computer Engineering Rice University Houston TX USA

Plasmonic sensors exhibit high sensitivity due to enhanced local fields. But, their detectivity is poor because of their poor Q-factors. Using a plasmonic BIC, we experimentally demonstrate enhanced Q-factors in a pla... 详细信息

ISBN: (纸本)9781957171258

关键词： Absorption spectroscopy Field enhancement Optical sensing Plasmonic sensors Q factor Sensor performance

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Learning to write with the fluid rope trick

arXiv

引用

arXiv 2023年

作者： Chaudhary, Gaurav Christ, Stephanie Hart, A. John Mahadevan, L. School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States Department of Mechanical Engineering Massachusetts Institute of Technology CambridgeMA02139 United States School of Engineering and Applied Sciences Department of Physics Department of Organismic and Evolutionary Biology Harvard University CambridgeMA02138 United States

The range and speed of direct ink writing, the workhorse of 3d and 4d printing, is limited by the practice of liquid extrusion from a nozzle just above the surface to prevent instabilities to cause deviations from the required print path. But what if could harness the "fluid rope trick", whence a thin stream of viscous fluid falling from a height spontaneously folds or coils, to write specified patterns on a substrate? Using Deep Reinforcement Learning we control the motion of the extruding nozzle and thence the fluid patterns that are deposited on the surface. The learner (nozzle) repeatedly interacts with the environment (a viscous filament simulator), and improves its strategy using the results of this experience. We demonstrate the results in an experimental setting where the learned motion control instructions are used to drive a viscous jet to accomplish complex tasks such as cursive writing and Pollockian paintings. © 2023, CC BY.

关键词： Nozzles

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Inferring System and Optimal Control Parameters of Closed-Loop Systems from Partial Observations

arXiv

引用

arXiv 2025年

作者： Geadah, Victor Arbelaiz, Juncal Ritz, Harrison Daw, Nathaniel D. Cohen, Jonathan D. Pillow, Jonathan W. Program in Applied and Computational Mathematics Princeton University PrincetonNJ United States Department of Mechanical and Aerospace Engineering Princeton University PrincetonNJ United States Princeton Neuroscience Institute Princeton University PrincetonNJ United States

We consider the joint problem of system identification and inverse optimal control for discrete-time stochastic Linear Quadratic Regulators. We analyze finite and infinite time horizons in a partially observed setting, where the state is observed noisily. To recover closed-loop system parameters, we develop inference methods based on probabilistic state-space model (SSM) techniques. First, we show that the system parameters exhibit non-identifiability in the infinite-horizon from closed-loop measurements, and we provide exact and numerical methods to disentangle the parameters. Second, to improve parameter identifiability, we show that we can further enhance recovery by either (1) incorporating additional partial measurements of the control signals or (2) moving to the finite-horizon setting. We further illustrate the performance of our methodology through numerical examples. © 2025, CC BY.

关键词： Stochastic systems

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Exploiting Circular Shifts for Efficient Chaotic Image Encryption

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IEEE Access 2025年 13卷 92997-93016页

作者： Moysis, Lazaros Lawnik, Marcin Alexan, Wassim Goudos, Sotirios K. Baptista, Murilo S. Fragulis, George F. University of Western Macedonia Department of Electrical and Computer Engineering Kozani Greece University of Western Macedonia Department of Mechanical Engineering Kozani Greece Silesian University of Technology Faculty of Applied Mathematics Department of Mathematical Methods in Technics and Informatics Kaszubska 23 Gliwice44-100 Poland German University Faculty of Information Engineering and Technology Communications Department Cairo Egypt Aristotle University of Thessaloniki School of Physics Thessaloniki54124 Greece University of Aberdeen Institute for Complex Systems and Mathematical Biology SUPA Department of Physics AberdeenAB24 3UX United Kingdom

This work presents a chaotic image encryption algorithm that acts on the binary level of the image for effective permutation, and on the byte level for substitution. The permutation step combines actions of bit level rearranging, and bit shuffling. Circular shift operations are used for bit shuffling, to reduce the execution time. Circular shifts are also applied to shuffle the permutation and substitution rules, effectively increasing security at a very low execution cost. The encryption keys are plaintext dependent, and a key mixing step in included, so that each part of the key affects all the subsequent encryption operations. For the encryption, a new Soboleva hyperbolic tangent based map is first designed. The dynamical behavior of the map is studied and shows robust chaos, and an absence of equilibria, meaning that it can generate hidden attractors. This map is used as an entropy source, along with a chaotic pseudo random number generator. The encryption process shows a good performance under a collection of tests, and has also a low execution time, 0.0134 sec for a 256x256 image, 0.0530 sec for a 512x512 image, and 0.2050 sec for a 1024x1024 image. © 2013 IEEE.

关键词： Random number generation

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