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Imaging the spin chirality of ferrimagnetic Néel skyrmions stabilized on topological antiferromagnetic Mn3Sn

Physical Review Materials 2021年第8期5卷 084406-084406页

作者： Teng Xu Zhen Chen Heng-An Zhou Zidong Wang Yiqing Dong Lucia Aballe Michael Foerster Pierluigi Gargiani Manuel Valvidares David M. Bracher Tatiana Savchenko Armin Kleibert Riccardo Tomasello Giovanni Finocchio Soong-Guen Je Mi-Young Im David A. Muller Wanjun Jiang State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics and Tsinghua University Beijing 100084 China Frontier Science Center for Quantum Information Tsinghua University Beijing 100084 China School of Applied and Engineering Physics Cornell University Ithaca New York 14853 USA ALBA Synchrotron Light Source Cerdanyola del Vallès 08290 Barcelona Spain Paul Scherrer Institut 5232 Villigen PSI Switzerland Institute of Applied and Computational Mathematics Foundation for Research and Technology—Hellas (FORTH) GR-70013 Heraklion Crete Greece Department of Mathematical and Computer Sciences Physical Sciences and Earth Sciences University of Messina Messina 98166 Italy Center for X-ray Optics Materials Science Division Lawrence Berkeley National Laboratory Cyclotron Road Berkeley California 94720 USA Kavli Institute at Cornell for Nanoscale Science Cornell University Ithaca New York 14853 USA

Néel skyrmions are generally realized in asymmetric multilayers made of heavy metals (HMs) and ultrathin ferromagnets possessing strong interfacial Dzyaloshinskii-Moriya interactions (iDMIs). Depending on the relative strengths of iDMIs at the interfaces, various types of Néel skyrmions have been suggested, which are typified with characteristically different topological properties and current-driven dynamics. This suggests the importance of a precise quantification of their spin chiralities. In this paper, we explore the possibility of realizing Néel skyrmions in magnetic multilayers without the direct usage of standard HMs. Specifically, through depositing a thin layer of ferrimagnetic (FIM) CoTb layer on top of an antiferromagnetic (AFM) quantum material of composition Mn3Sn, the AFM exchange interaction at the asymmetric interface provides an equivalent iDMI for stabilizing FIM Néel skyrmions. Secondly, through using advanced four-dimensional Lorentz scanning transmission electron microscopy (4D LSTEM), in combination with x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM), we can directly determine the spin chirality of FIM Néel skyrmions. The present findings not only broaden the phase space for chiral interfacial magnetism but also provide a possibility for future applications of heavy-metal-free skyrmionic devices.

关键词： Magnetic texture Magnetism Spintronics

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Handling time-dependent exposures and confounders when estimating attributable fractions — bridging the gap between multistate and counterfactual modeling

arXiv

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arXiv 2020年

作者： Steen, Johan Morzywolek, Pawel Van Biesen, Wim Decruyenaere, Johan Vansteelandt, Stijn Department of Internal Medicine and Pediatrics Ghent University Belgium Renal Division Ghent University Hospital Belgium Department of Intensive Care Medicine Ghent University Hospital Belgium Department of Applied Mathematics Computer Science and Statistics Ghent University Belgium Department of Medical Statistics London School of Hygiene and Tropical Medicine United Kingdom

The population-attributable fraction (PAF) expresses the proportion of events that can be ascribed to a certain exposure in a certain population. It can be strongly time-dependent because either exposure incidence or excess risk may change over time. Competing events may moreover hinder the outcome of interest from being observed. Occurrence of either of these events may, in turn, prevent the exposure of interest. Estimation approaches therefore need to carefully account for the timing of events in such highly dynamic settings. The use of multistate models has been widely encouraged to eliminate preventable yet common types of time-dependent bias. Even so, it has been pointed out that proposed multistate modeling approaches for PAF estimation fail to fully eliminate such bias. In addition, assessing whether patients die from rather than with a certain exposure not only requires adequate modeling of the timing of events but also of their confounding factors. While proposed multistate modeling approaches for confounding adjustment may adequately accommodate baseline imbalances, unlike g-methods, these proposals are not generally equipped to handle time-dependent confounding. However, the connection between multistate modeling and g-methods (e.g. inverse probability of censoring weighting) for PAF estimation is not readily apparent. In this paper, we provide a weighting-based characterization of both approaches to illustrate this connection, to pinpoint current shortcomings of multistate modeling, and to enhance intuition into simple modifications to overcome these. R code is made available to foster the uptake of g-methods for PAF estimation. Copyright © 2020, The Authors. All rights reserved.

关键词： Inverse problems

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Critical Imaginaries and Reflections on Artificial Intelligence and Robots in Postdigital K-12 Education

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Postdigital science and Education 2019年第2期1卷 427-445页

作者： Hrastinski, Stefan Olofsson, Anders D. Arkenback, Charlotte Ekström, Sara Ericsson, Elin Fransson, Göran Jaldemark, Jimmy Ryberg, Thomas Öberg, Lena-Maria Fuentes, Ana Gustafsson, Ulrika Humble, Niklas Mozelius, Peter Sundgren, Marcus Utterberg, Marie Division of Digital Learning KTH Royal Institute of Technology Stockholm Sweden Department of Applied Educational Science Umeå University Umeå Sweden Department of Applied IT University of Gothenburg Gothenburg Sweden Department of Economics and IT University West Trollhättan Sweden Faculty of Education and Business Studies University of Gävle Gävle Sweden Department of Education Mid Sweden University Sundsvall Sweden Department of Communication and Psychology Aalborg University Aalborg Denmark Department of Computer and System Science Mid Sweden University Östersund Sweden

It is commonly suggested that emerging technologies will revolutionize education. In this paper, two such emerging technologies, artificial intelligence (AI) and educational robots (ER), are in focus. The aim of the paper is to explore how teachers, researchers and pedagogical developers critically imagine and reflect upon how AI and robots could be used in education. The empirical data were collected from discussion groups that were part of a symposium. For both AI and ERs, the need for more knowledge about these technologies, how they could preferably be used, and how the emergence of these technologies might affect the role of the teacher and the relationship between teachers and students, were outlined. Many participants saw more potential to use AI for individualization as compared with ERs. However, there were also more concerns, such as ethical issues and economic interests, when discussing AI. While the researchers/developers to a greater extent imagined ideal future technology-rich educational practices, the practitioners were more focused on imaginaries grounded in current practice. © 2019, The Author(s).

关键词： Artificial intelligence Automation Educational robots K-12 education Postdigital education Symposium

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Spectral/hp element methods:Recent developments, applications, and perspectives

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Journal of Hydrodynamics 2018年第1期30卷 1-22页

作者： Hui Xu Chris D.Cantwell Carlos Monteserin Claes Eskilsson Allan P.Engsig-Karup Spencer J.Sherwin Department of Aeronautics Imperial College London Department of Applied Mathematics and Computer Science Technical University of Denmark Department of Civil Engineering Aalborg University Division Safety and Transport Research Institutes of Sweden (RISE) Center for Energy Resources Engineering (CERE) Technical University of Denmark

The spectral/hp element method combines the geometric flexibility of the classical h-type finite element technique with the desirable numerical properties of spectral methods, employing high-degree piecewise polynomial basis functions on coarse finite element-type meshes. The spatial approximation is based upon orthogonal polynomials, such as Legendre or Chebychev polynomials,modified to accommodate a C~0-continuous expansion. Computationally and theoretically, by increasing the polynomial order p,high-precision solutions and fast convergence can be obtained and, in particular, under certain regularity assumptions an exponential reduction in approximation error between numerical and exact solutions can be achieved. This method has now been applied in many simulation studies of both fundamental and practical engineering flows. This paper briefly describes the formulation of the spectral/hp element method and provides an overview of its application to computational fluid dynamics. In particular, it focuses on the use of the spectral/hp element method in transitional flows and ocean engineering. Finally, some of the major challenges to be overcome in order to use the spectral/hp element method in more complex science and engineering applications are discussed.

关键词： High-precision spectral/hp elements continuous Galerkin method discontinuous Galerkin method implicit large eddy simulation

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Corrigendum to “ICACIA: An Intelligent Context-Aware framework for COBOT in defense industry using ontological and deep learning models” [Robotics and Autonomous Systems Volume 157, November 2022, 104234]

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Robotics and Autonomous Systems 2024年 178卷

作者： Arodh Lal Karn Sudhakar Sengan Ketan Kotecha Irina V Pustokhina Denis A Pustokhin V Subramaniyaswamy Dharam Buddhi Department of Financial and Actuarial Mathematics School of Science Xi'an Jiaotong-Liverpool University China Department of Computer Science and Engineering PSN College of Engineering and Technology Tirunelveli Tamil Nadu India Symbiosis Centre for Applied Artificial Intelligence Symbiosis International (Deemed University) Pune Maharashtra 412115 India Department of Entrepreneurship and Logistics Plekhanov Russian University of Economics 117997 Moscow Russia Department of Logistics State University of Management 109542 Moscow Russia School of Computing SASTRA Deemed University Thanjavur 613401 Tamil Nadu India Division of Research & Innovation Uttaranchal University Uttarakhand 248007 Dehradun India

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Unbiased Estimation of the Gradient of the Log-Likelihood in Inverse Problems

arXiv

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arXiv 2020年

作者： Jasra, B.Y. Ajay Law, Kody J.H. Deng, L.U. Computer Electrical and Mathematical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal23955 Saudi Arabia Department of Mathematics University of Manchester ManchesterM13 9PL United Kingdom Department of Statistics & Applied Probability National University of Singapore Singapore117546 Singapore

We consider the problem of estimating a parameter θ ∈ Θ ⊆ Rdθ associated to a Bayesian inverse problem. Treating the unknown initial condition as a nuisance parameter, typically one must resort to a numerical approximation of gradient of the log-likelihood and also adopt a discretization of the problem in space and/or time. We develop a new methodology to unbiasedly estimate the gradient of the log-likelihood with respect to the unknown parameter, i.e. the expectation of the estimate has no discretization bias. Such a property is not only useful for estimation in terms of the original stochastic model of interest, but can be used in stochastic gradient algorithms which benefit from unbiased estimates. Under appropriate assumptions, we prove that our estimator is not only unbiased but of finite variance. In addition, when implemented on a single processor, we show that the cost to achieve a given level of error is comparable to multilevel Monte Carlo methods, both practically and theoretically. However, the new algorithm provides the possibility for parallel computation on arbitrarily many processors without any loss of efficiency, asymptotically. In practice, this means any precision can be achieved in a fixed, finite constant time, provided that enough processors are available. Copyright © 2020, The Authors. All rights reserved.

关键词： Parameter estimation

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Quantum Circuits for Exact Unitary t-Designs and Applications to Higher-Order Randomized Benchmarking

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PRX Quantum 2021年第3期2卷 030339-030339页

作者： Yoshifumi Nakata Da Zhao Takayuki Okuda Eiichi Bannai Yasunari Suzuki Shiro Tamiya Kentaro Heya Zhiguang Yan Kun Zuo Shuhei Tamate Yutaka Tabuchi Yasunobu Nakamura Photon Science Center Graduate School of Engineering The University of Tokyo Bunkyo-ku Tokyo 113–8656 Japan JST PRESTO 4–1–8 Honcho Kawaguchi Saitama 332–0012 Japan School of Mathematical Sciences Shanghai Jiao Tong University Shanghai 400240 China Department of Mathematics Hiroshima University 1-3-1 Kagamiyama Higashihiroshima 739-8562 Japan Faculty of Mathematics Kyushu University (emeritus) Fukuoka 819-0385 Japan Mathematics Division National Center for Theoretical Sciences National Taiwan University Taipei 10617 Taiwan NTT Computer and Data Science Laboratories NTT Corporation Musashino 180-8585 Japan Department of Applied Physics Graduate School of Engineering The University of Tokyo 7-3-1 Hongo Bynkyo-ku Tokyo 113-8656 Japan Research Center for Advanced Science and Technology (RCAST) The University of Tokyo Meguro-ku Tokyo 153-8904 Japan RIKEN Center for Quantum Computing (RQC) Wako Saitama 351-0198 Japan

A unitary t-design is a powerful tool in quantum information science and fundamental physics. Despite its usefulness, only approximate implementations were known for general t. In this paper, we provide quantum circuits that generate exact unitary t-designs for any t on an arbitrary number of qubits. Our construction is inductive and is of practical use in small systems. We then introduce a tth-order generalization of randomized benchmarking (t-RB) as an application of exact 2t-designs. We particularly study the 2-RB in detail and show that it reveals self-adjointness of quantum noise, a metric related to the feasibility of quantum error correction (QEC). We numerically demonstrate that the 2-RB in one- and two-qubit systems is feasible, and experimentally characterize background noise of a superconducting qubit by the 2-RB. It is shown from the experiment that interactions with adjacent qubits induce the noise that may result in an obstacle toward a realization of QEC.

关键词： Quantum algorithms Quantum benchmarking Quantum gates Quantum protocols

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Optimizing beat-wise input for arrhythmia detection using 1-D convolutional neural networks: A real-world ECG study

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computer Methods and Programs in Biomedicine 2025年 269卷

作者： Sunghan Lee Guangyao Zheng Jeonghwan Koh Haoran Li Zicheng Xu Sung Pil Cho Sung Il Im Vladimir Braverman In cheol Jeong Cerebrovascular Disease Research Center Hallym University Chuncheon 24252 Republic of Korea Department of Computer Science Rice University Houston TX 77005 USA Department of Artificial Intelligence Convergence Hallym University Chuncheon 24252 Republic of Korea MEZOO Co. Ltd. Wonju 26354 Republic of Korea Division of Cardiology Department of Internal Medicine Kosin University Gospel Hospital Kosin University College of Medicine Busan 49267 Republic of Korea Department of Applied Mathematics and Statistics Johns Hopkins University Baltimore MD 21218 USA Department of Population Health Science and Policy Icahn School of Medicine at Mount Sinai New York NY 10029 USA

Backgrounds and objectives: Cardiac arrhythmias, characterized by irregular heartbeats, are difficult to diagnose in real-world scenarios. Machine learning has advanced arrhythmia detection; however, the optimal number of heartbeats for precise classification remains understudied. This study addresses this using machine learning while assessing the performance of arrhythmia detection across inter-patient and intra-patient conditions. Furthermore, the performance–resource trade-offs are evaluated for practical deployment in mobile health (mHealth) applications. Methods: Beat-wise segmentation and resampling techniques were utilized for preprocessing electrocardiography (ECG) signals to ensure consistent input lengths. A 1-D convolutional neural network was used to classify the eight multi-labeled arrhythmias. The dataset comprised real-world ECG recordings from the HiCardi wireless device alongside data from the MIT-BIH Arrhythmia database. Model performance was assessed through fivefold cross-validation under both inter-patient and intra-patient conditions. Results: The proposed model demonstrated peak accuracy at four beats under inter-patient conditions, with minimal improvements beyond this point. This configuration achieved a balance between performance (94.82% accuracy) and resource consumption (training time: 72.27 s per epoch; prediction time: 155 μ s per segment). Real-world simulations validated the feasibility of real-time arrhythmia detection for approximately 5000 patients. Conclusion: Utilizing four heartbeats as the input size for arrhythmia classification results in a trade-off between accuracy and computational efficiency. This discovery has significant implications for real-time wearable ECG devices, where both performance and resource constraints are crucial considerations. This insight is expected to serve as a valuable reference for enhancing the design and implementation of arrhythmia detection systems for scalable and efficient mHealth applicat

关键词： Arrhythmia detection Convolutional neural network (CNN) Electrocardiography (ECG) Biosignal Beat-wise processing

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Interactive Protocols for Classically-Verifiable Quantum Advantage

arXiv

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arXiv 2021年

作者： Zhu, Daiwei Kahanamoku-Meyer, Gregory D. Lewis, Laura Noel, Crystal Katz, Or Harraz, Bahaa Wang, Qingfeng Risinger, Andrew Feng, Lei Biswas, Debopriyo Egan, Laird Gheorghiu, Alexandru Nam, Yunseong Vidick, Thomas Vazirani, Umesh Yao, Norman Y. Cetina, Marko Monroe, Christopher Joint Quantum Institute Departments of Physics and Electrical and Computer Engineering University of Maryland College ParkMD20742 United States Joint Center for Quantum Information and Computer Science NIST University of Maryland College ParkMD20742 United States Department of Physics University of California BerkeleyCA94720 United States Materials Sciences Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Computing and Mathematical Sciences California Institute of Technology CA91125 United States Division of Physics Mathematics and Astronomy California Institute of Technology CA91125-0001 United States Duke Quantum Center Department of Physics Duke University DurhamNC27708 United States Department of Electrical and Computer Engineering Duke University DurhamNC27708 United States IonQ Inc. College ParkMD20740 United States Institute for Theoretical Studies ETH Zürich CH 8001 Switzerland Chemical Physics Program Institute for Physical Science and Technology University of Maryland College ParkMD20742 United States Departments of Electrical and Computer Engineering University of Maryland College ParkMD20742 United States

Interaction is a powerful resource for quantum computation. It can be utilized in applications ranging from the verification of quantum algorithms all the way to verifying quantum mechanics itself. Here, we present the first implementation of interactive protocols for proofs of quantumness — which when suitably scaled promise the efficient verification of quantum computational advantage. The key feature that distinguishes these protocols from existing demonstrations of quantum advantage is that the classical verification is efficient and scales polynomially rather than exponentially with the number of qubits. The experimental implementation of such interactive protocols requires the ability to independently measure subsets of qubits in the middle of a quantum circuit and to continue coherent evolution afterwards. This is achieved by spatially isolating target qubits via shuttling, and opens the door to a range of quantum interactive protocols as well as new information processing architectures. Copyright © 2021, The Authors. All rights reserved.

关键词： Qubits

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A Dibenzo[g,p]chrysene-Based Organic Semiconductor with Small Exciton Binding Energy via Molecular Aggregation

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Angewandte Chemie 2024年第42期136卷

作者： Hiroki Mori Dr. Seihou Jinnai Yasushi Hosoda Prof. Azusa Muraoka Prof. Ken-ichi Nakayama Prof. Akinori Saeki Prof. Yutaka Ie The Institute of Scientific and Industrial Research (SANKEN) Osaka University 8-1 Mihogaoka Ibaraki Osaka 567-0047 Japan Innovative Catalysis Science Division Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI) Osaka University 2-1 Yamadaoka Suita Osaka 565-0871 Japan Department of Mathematics Physics and Computer Science Japan Women's University 2-8-1 Mejirodai Bunkyo-ku Tokyo 112-8681 Japan Department of Applied Chemistry Graduate School of Engineering Osaka University 2-1 Yamadaoka Suita Osaka 565-0871 Japan

Exciton binding energy ( E b ) is understood as the energy required to dissociate an exciton in free-charge carriers, and is known to be an important parameter in determining the performance of organic opto-electronic devices. However, the development of a molecular design to achieve a small level of E b in the solid state continues to lag behind. Here, to investigate the relationship between aggregation and E b , star-shaped π-conjugated compounds DBC-RD and TPE-RD were developed using dibenzo[ g , p ]chrysene (DBC) and tetraphenylethylene (TPE). Theoretical calculations and physical measurements in solution showed no apparent differences between DBC-RD and TPE-RD, indicating that these molecules possess similar properties on a single-molecule level. By contrast, pristine films incorporating these molecules showed significantly different levels of electron affinity, ionization potential, and optical gap. Also, DBC-RD had a smaller E b value of 0.24 eV compared with that of TPE-RD (0.42 eV). However, these molecules showed similar E b values under dispersed conditions, which suggested that the decreased E b of DBC-RD in pristine film is induced by molecular aggregation. By comparison with TPE-RD, DBC-RD showed superior performances in single-component organic solar cells and organic photocatalysts. These results indicate that a molecular design suitable for aggregation is important to decrease the E b in films.

关键词： organic semiconductors organic solar cells organic photocatalysts exciton binding energies dielectric constants

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