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

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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

Implications of Delayed Reopening in Controlling the COVID-19 Surge in Southern and West-Central USA

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健康数据科学（英文）

健康数据科学（英文） 2022年第2期 25-34页

作者： Raj Dandekar Emma Wang George Barbastathis Chris Rackauckas Department of Computational Science and Engineering Massachusetts Institute of TechnologyCambridgeUSA MA 02139 Department of Electrical Engineering and Computer Sciences Massachusetts Institute of TechnologyCambridgeMA 02139USA Department of Mechanical Engineering Massachusetts Institute of TechnologyCambridgeMA 02139USA Singapore-MIT Alliance for Research and Technology(SMART)Centre Singapore 138602 Department of Applied Mathematics Massachusetts Institute of TechnologyCambridgeMA 02139USA

In the wake of the rapid surge in the COVID-19-infected cases seen in Southern and West-Central USA in the period of June-July 2020,there is an urgent need to develop robust,data-driven models to quantify the effect which early reopening had on the infected case count *** particular,it is imperative to address the question:How many infected cases could have been prevented,had the worst affected states not reopened early?To address this question,we have developed a novel COVID-19 model by augmenting the classical SIR epidemiological model with a neural network *** model decomposes the contribution of quarantine strength to the infection time series,allowing us to quantify the role of quarantine control and the associated reopening policies in the US states which showed a major surge in *** show that the upsurge in the infected cases seen in these states is strongly corelated with a drop in the quarantine/lockdown strength diagnosed by our ***,our results demonstrate that in the event of a stricter lockdown without early reopening,the number of active infected cases recorded on 14 July could have been reduced by more than 40％in all states considered,with the actual number of infections reduced being more than 100,000 for the states of Florida and *** we continue our fight against COVID-19,our proposed model can be used as a valuable asset to simulate the effect of several reopening strategies on the infected count evolution,for any region under consideration.

关键词： covid-19 southern controlling delayed implications reopening surge west-central

UO2/BeO interfacial thermal resistance and its effect on fuel thermal conductivity

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arXiv 2020年

作者： Zhu, Xueyan Gao, Rui Gong, Hengfeng Liu, Tong De-Ye Lin Song, Haifeng CAEP Software Center for High Performance Numerical Simulation Beijing100088 China Institute of Applied Physics and Computational Mathematics Beijing100088 China Institute of Materials China Academy of Engineering Physics JiangyouSichuan621908 China China Nuclear Power Technology Research Institute Shenzhen518031 China

UO2/BeO interfacial thermal resistance (ITR) is calculated by diffuse mismatch model (DMM) and the effects of ITR on UO2-BeO thermal conductivity are investigated. ITR predicted by DMM is on the order of 10-9 m2K/W. Using this ITR, UO2-BeO thermal conductivities are calculated by theoretical models and compared with experimental data. The results of this comparison indicate that DMM prediction is applicable to the interface between UO2 and dispersed BeO, while not applicable to the interface between UO2 and continuous BeO. If the thermal conductivity of UO2 containing continuous BeO was to be in agreement with experimental data, its ITR should be on the order of 10-6 ̶ 10-5 m2K/W. Therefore, the vibrational mismatch between UO2 and BeO considered by DMM is the major mechanism for attenuating the heat flux through UO2/dispersed-BeO interface, but not for UO2/continuousBeO interface. Furthermore, it is found that the presence of ITR leads to the dependence of the thermal conductivity of UO2 containing dispersed BeO on BeO size. With the decrease in BeO size, UO2-BeO thermal conductivity decreases. When BeO size is smaller than a critical value, UO2-BeO thermal conductivity becomes even smaller than UO2 thermal conductivity. For UO2 containing continuous BeO, the thermal conductivity decreases with the decrease in the size of UO2 granule surrounded by BeO, but not necessarily smaller than UO2 thermal conductivity. Under a critical temperature, UO2-BeO thermal conductivity is always larger than UO2 thermal conductivity. Above the critical temperature, UO2-BeO thermal conductivity is larger than UO2 thermal conductivity only when UO2 granule size is large enough. The conditions for achieving the targeted enhancement of UO2 thermal conductivity by doping with BeO are derived. These conditions can be used to design and optimize the distribution, content, size of BeO, and the size of UO2 granule. Copyright © 2020, The Authors. All rights reserved.

关键词： Uranium dioxide

PKS J0805−0111: A Second Owens Valley Radio Observatory Blazar Showing Highly Significant Sinusoidal Radio Variability - The Tip of the Iceberg

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arXiv 2024年

作者： de la Parra, P.V. Kiehlmann, S. Mróz, P. Readhead, A.C.S. Synani, A. Begelman, M.C. Blandford, R.D. Ding, Y. Harrison, F. Liodakis, I. Max-Moerbeck, W. Pavlidou, V. Reeves, R. Vallisneri, M. Aller, M.F. Graham, M.J. Hovatta, T. Lawrence, C.R. Lazio, T.J.W. Mahabal, A.A. Molina, B. O’Neill, S. Pearson, T.J. Ravi, V. Tassis, K. Zensus, J.A. CePIA Astronomy Department Universidad de Concepción Casilla 160-C Concepción Chile Department of Physics Institute of Theoretical and Computational Physics University of Crete Heraklion71003 Greece Astronomical Observatory University of Warsaw Al. Ujazdowskie 4 Warszawa00-478 Poland Owens Valley Radio Observatory California Institute of Technology PasadenaCA91125 United States Institute of Astrophysics Foundation for Research and Technology-Hellas HeraklionGR-70013 Greece JILA University of Colorado National Institute of Standards and Technology 440 UCB BoulderCO80309-0440 United States Department of Astrophysical and Planetary Sciences University of Colorado 391 UCB BoulderCO80309-0391 United States Kavli Institute for Particle Astrophysics and Cosmology Department of Physics 20 Stanford University StanfordCA94305 United States Cahill Center for Astronomy and Astrophysics California Institute of Technology PasadenaCA91125 United States NASA Marshall Space Flight Center HuntsvilleAL35812 United States Finnish Center for Astronomy with ESO University of Turku Vesilinnantie 5 FI-20014 Finland Departamento de Astronomía Universidad de Chile Camino El Observatorio 1515 Las Condes Santiago Chile Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive PasadenaCA91109 United States Department of Astronomy University of Michigan 323 West Hall 1085 S. University Avenue Ann ArborMI48109 United States Division of Physics Mathematics and Astronomy California Institute of Technology PasadenaCA91125 United States University of Turku University of Turku FI-20014 Finland Aalto University Metsähovi Radio Observatory Metsähovintie 114 Kylmälä02540 Finland Center for Data Driven Discovery California Institute of Technology PasadenaCA91125 United States Department of Physics Princeton University Jadwin Hall PrincetonNJ08540 United States Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 BonnD-5312

Owens Valley Radio Observatory (OVRO) observations of supermassive black hole binary (SMBHB) candidate PKS 2131−021 revealed, for the first time, six likely characteristics of the phenomenology exhibited by SMBHB in blazars, of which the most unexpected and critical is sinusoidal flux density variations. We have now identified a second blazar, PKS J0805−0111, showing significant sinusoidal variations, with an observed period that translates to 1.422 ± 0.005 yr in the rest frame of the z = 1.388 object. We generate 106 simulated light curves to reproduce the radio variability characteristics of PKS J0805−0111, and show that the global probability, considering the look-elsewhere effect, indicates that the observed periodicity can be attributed to the red noise tail of the power spectral density, with a p0 value of 7.8 × 10−5 (i.e. 3.78σ). PKS J0805−0111 displays all six characteristics observed in PKS 2131−021. Taking into account the well-defined OVRO sample size, the false positive probability ∼ 0.22, but the rare behavior makes this a strong SMBHB candidate. The discovery of a second SMBHB candidate exhibiting these rare characteristics reveals that PKS 2131−021 is not a unique, isolated case. With these two strong cases we are clearly seeing only the tip of the iceberg. We estimate that the number of SMBHB candidates amongst blazars ∼ 1 in 100. © 2024, CC BY.

关键词： Landforms

Equivalence of f ( Q ) cosmology with quintom-like scenario: The phantom field as effective realization of the non-trivial connection

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Physics Letters B 2025年 868卷

作者： Spyros Basilakos Andronikos Paliathanasis Emmanuel N. Saridakis National Observatory of Athens Lofos Nymfon 11852 Athens Greece Academy of Athens Research Center for Astronomy and Applied Mathematics Soranou Efesiou 4 11527 Athens Greece School of Sciences European University Cyprus Diogenes Street Engomi 1516 Nicosia Cyprus Department of Mathematics Faculty of Applied Sciences Durban University of Technology Durban 4000 South Africa School for Data Science and Computational Thinking Stellenbosch University 44 Banghoek Rd Stellenbosch 7600 South Africa Departamento de Matemáticas Universidad Católica del Norte Avda. Angamos 0610 Casilla 1280 Antofagasta Chile National Institute for Theoretical and Computational Sciences (NITheCS) Stellenbosch South Africa CAS Key Laboratory for Researches in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei Anhui 230026 PR China

We show that f ( Q ) cosmology with a non-trivial connection, namely the Connection II of the literature, is dynamically equivalent with a quintom-like model. In particular, we show that the scalar field arising from the non-linear f ( Q ) form, and the scalar field associated to the non-trivial connection, are combined to provide one canonical and one phantom field in the minisuperspace Lagrangian. Hence, the combination of two well-behaved fields appears effectively as a phantom field. This is fundamentally different from the usual approach in phantom and quintom cosmology, in which the phantom field is introduced ad hoc, and thus it may open a new way to handle the phantom fields, namely as effective realizations of the connection-related canonical fields.

关键词：

Nonuniform 3D finite difference elastic wave simulation on staggered grids

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arXiv 2020年

作者： Gao, Longfei Ghattas, Omar Keyes, David Oden Institute for Computational Engineering and Sciences The University of Texas at Austin AustinTX78712 United States Oden Institute for Computational Engineering and Sciences Jackson School of Geosciences Department of Mechanical Engineering The University of Texas at Austin AustinTX78712 United States Applied Mathematics and Computational Science Program Extreme Computing Research Center King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia

We present an approach to simulate the 3D isotropic elastic wave propagation using nonuniform finite difference discretization on staggered grids. Specifically, we consider simulation domains composed of layers of uniform grids with different grid spacings, separated by nonconforming interfaces. We demonstrate that this layer-wise finite difference discretization has the potential to significantly reduce the simulation cost, compared to its fully uniform counterpart. Stability of such a discretization is achieved by using specially designed difference operators, which are variants of the standard difference operators with adaptations near boundaries or interfaces, and penalty terms, which are appended to the discretized wave system to weakly impose boundary or interface conditions. Combined with specially designed interpolation operators, the discretized wave system is shown to preserve the energy conserving property of the continuous elastic wave equation, and a fortiori ensure the stability of the simulation. Numerical examples are presented to demonstrate the efficacy of the proposed simulation approach. © 2020, CC BY.

关键词： Elastic waves

Decoding electron tunnelling delay time by embracing wave-particle duality

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arXiv 2021年

作者： Wang, Chuncheng Li, Xiaokai Liu, Xiwang Li, Jie Zhou, Shengpeng Yang, Yizhang Song, Xiaohong Chen, Jing Yang, Weifeng Ding, Dajun Institute of Atomic and Molecular Physics Advanced Light Field and Modern Medical Treatment Science and Technology Innovation Center of Jilin Province Jilin University Changchun130012 China Research Center for Advanced Optics and Photoelectronics Department of Physics College of Science Shantou University Guangdong515063 China Institute of Mathematics Shantou University Shantou Guangdong515063 China MOE Key Laboratory of Intelligent Manufacturing Technology Shantou University Shantou Guangdong515063 China Institute of Applied Physics and Computational Mathematics P.O. Box 8009 Beijing100088 China Laboratory for Physical Chemistry ETH Zürich Vladimir-Prelog-Weg 2 Zürich8093 Switzerland

Tunnelling lies at the heart of quantum mechanics and is a fundamental process in attosecond science, molecular biology, and quantum devices. Whether tunnelling takes time and how a microscopic particle transits through a barrier have been debated since the early days of quantum mechanics 1-9. The time required for an electron to tunnel through an atomic potential barrier has been measured with attosecond angular streaking (attoclock), and a recent work on the hydrogen atom claimed that electron tunnelling is instantaneous 10. However, the time required for Rb atoms to tunnel through an optical potential barrier has been measured to be on the order of milliseconds with a recent Larmor clock measurement 11. The essence of electron and atom tunnelling is identical, but the reason for the contradictory conclusions remains unknown. Here, we demonstrate that the sub-barrier potential interaction is the root of the nonzero tunnelling delay time. We reveal that the wave-particle duality of a tunnelling electron must be fully taken into account when decoding the tunnelling delay time from the attoclock measurements. Based on energy-resolved attoclock measurements, we show that the tunnelling delay time of an electron ranges from 24 to 58 attoseconds, and the counterintuitive result that an electron with a lower energy may spend less time in the barrier is consistent with the velocity-dependent tunnelling time of atoms in Larmor clock measurements 11. Our results unify the tunnelling time of microscopic particles by highlighting the classically forbidden sub-barrier potential interactions of matter waves. © 2021, CC BY-NC-ND.

关键词： Electrons

Phase stabilities of Cmcm and Pnma SnSe studied by phonon quasiparticle approach

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Physical Review B 2019年第5期100卷 054304-054304页

作者： Yong Lu Fa-wei Zheng Yu Yang Ping Zhang Dong-Bo Zhang Beijing University of Chemical Technology College of Mathematics and Physics Beijing 100029 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China College of Nuclear Science and Technology Beijing Normal University Beijing 100875 China Beijing Computational Science Research Center Beijing 100193 China

We investigated the structural stability of SnSe from 0 to 800 K by the phonon quasiparticle approach combining first-principles molecular-dynamics (MD) simulations and lattice dynamics. At high temperature, we witness the dynamic stability of the Cmcm phase and reveal the coupling of the polarization of phonon modes and the phase transition between the Cmcm and Pnma phases. Specifically, in real space, the probability distribution of atomic displacements from first-principles MD simulations successfully captures the structural instability at low temperature and the structural stability at high temperature for Cmcm SnSe. An analysis of phonon power spectra of several modes also delivers the dynamic stabilization of Cmcm at high temperature. Particularly, the soft modes of the Y1 mode at the q=Y(12,12,0) point and the Γ1 mode at the q=Γ(0,0,0) point of the Cmcm phase in the harmonic approximation become relatively rigid at elevated temperature, in agreement with experimental and previous theoretical results. The calculated anharmonic phonon dispersions and density of states are strongly temperature-dependent, and some phonon modes adopt giant frequency shifts. These aspects demonstrate the heavy anharmonicity in SnSe. At low temperature, the transition from the Cmcm to the Pnma phase induces a symmetry breaking of structure. Consequently, the degeneracy of associated electronic states (mainly p states) is lifted, thus lowering the energy of the Pnma phase.

关键词： First-principles calculations Phase transitions Phonons

Causes of evolutionary divergence in prostate cancer

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arXiv 2025年

作者： Esentürk, Emre Sahli, Atef Haberland, Valeriia Ziuboniewicz, Aleksandra Wirth, Christopher Bova, G. Steven Bristow, Robert G. Brook, Mark N. Brors, Benedikt Butler, Adam Cancel-Tassin, Géraldine Cheng, Kevin C.L. Cooper, Colin S. Corcoran, Niall M. Cussenot, Olivier Eeles, Ros A. Favero, Francesco Gerhauser, Clarissa Gihawi, Abraham Girma, Etsehiwot G. Gnanapragasam, Vincent J. Gruber, Andreas J. Hamid, Anis Hayes, Vanessa M. He, Housheng Hansen Hovens, Christopher M. Imada, Eddie Luidy Jakobsdottir, G. Maria Jung, Chol-Hee Khani, Francesca Kote-Jarai, Zsofia Lamy, Philippe Leeman, Gregory Loda, Massimo Lutsik, Pavlo Marchionni, Luigi Molania, Ramyar Papenfuss, Anthony T. Pellegrina, Diogo Pope, Bernard Queiroz, Lucio R. Rausch, Tobias Reimand, Jüri Robinson, Brian Schlomm, Thorsten Sørensen, Karina D. Uhrig, Sebastian Weischenfeldt, Joachim Xu, Yaobo Yamaguchi, Takafumi N. Zanettini, Claudio Lynch, Andy G. Wedge, David C. Brewer, Daniel S. Woodcock, Dan J. Nuffield Department of Medicine University of Oxford United Kingdom Manchester Cancer Research Centre The University of Manchester United Kingdom Norwich Medical School University of East Anglia United Kingdom Nuffield Department of Surgical Sciences University of Oxford United Kingdom Prostate Cancer Research Center Faculty of Medicine and Health Technology Tampere University Finland Manchester Cancer Research Centre Cancer Research UK Manchester Institute The University of Manchester United Kingdom Christie NHS Foundation Trust United Kingdom Div Cancer Sciences Faculty of Biology Medicine & Health University of Manchester United Kingdom The Institute of Cancer Research United Kingdom Germany Germany Medical Faculty Heidelberg Faculty of Biosciences Heidelberg University Germany Wellcome Sanger Institute United Kingdom France Sorbonne Université GRC n°5 Predictive Onco-Urology APHP Tenon Hospital France Computational Biology Program Ontario Institute for Cancer Research Canada Department of Medical Biophysics University of Toronto Canada Department of Urology Royal Melbourne Hospital Australia Department of Surgery The University of Melbourne Australia Department of Urology Western Health Australia The Royal Marsden NHS Foundation Trust London United Kingdom University of Copenhagen Denmark Finsen Laboratory Copenhagen University Hospital - Rigshospitalet Denmark Germany Cambridge Biomedical Campus Addenbrooke's Hospital Site S Wards Building United Kingdom University of Konstanz Germany School of Medical Sciences University of Sydney Faculty of Medicine & Health Australia School of Health Systems & Public Health University of Pretoria South Africa Manchester Cancer Research Centre University of Manchester United Kingdom Princess Margaret Cancer Centre University Health Network Department of Medical Biophysics University of Toronto Canada Department of Surgery The Collaborative Centre for Genomic Cancer Medicine The University of Melbourne

Cancer progression involves the sequential accumulation of genetic alterations that cumulatively shape the tumour phenotype. In prostate cancer, tumours can follow divergent evolutionary trajectories that lead to distinct subtypes, but the causes of this divergence remain unclear. While causal inference could elucidate the factors involved, conventional methods are unsuitable due to the possibility of unobserved confounders and ambiguity in the direction of causality. Here, we propose a method that circumvents these issues and apply it to genomic data from 829 prostate cancer patients. We identify several genetic alterations that drive divergence as well as others that prevent this transition, locking tumours into one trajectory. Further analysis reveals that these genetic alterations may cause each other, implying a positive-feedback loop that accelerates divergence. Our findings provide insights into how cancer subtypes emerge and offer a foundation for genomic surveillance strategies aimed at monitoring the progression of prostate cancer. © 2025, CC BY-NC-SA.

关键词： Lung cancer