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arXiv 2020年

作者： Gulde, Max Rissanou, Anastassia N. Harmandaris, Vagelis Müller, Marcus Schäfer, Sascha Ropers, Claus 4th Physical Institute - Solids and Nanostructures University of Göttingen Göttingen37077 Germany Institute of Applied and Computational Mathematics Foundation for Research and Technology Hellas HeraklionCrete71110 Greece Department of Mathematics and Applied Mathematics University of Crete HeraklionCrete71409 Greece Institute for Theoretical Physics University of Göttingen Göttingen37077 Germany Fraunhofer Institute for High-Speed Dynamics Ernst-Mach-Institut Freiburg79104 Germany

Graphene-based nanostructured systems and van-der-Waals heterostructures comprise a material class of growing technological and scientific importance. Joining materials with vastly different properties, polymer-graphene heterosystems promise diverse applications in surface- and nanotechnology, including photovoltaics or nanotribology. Fundamentally, molecular adsorbates are prototypical systems to study confinement-induced phase transitions exhibiting intricate dynamics, which require a comprehensive understanding of the dynamical and static properties on molecular time and length scales. Here, we investigate the dynamics and the structure of a single polyethylene chain on free-standing graphene by means of molecular dynamics simulations. In equilibrium, the adsorbed polymer is orientationally linked to the graphene as two-dimensional folded-chain crystallites or, at elevated temperatures, as a floating solid. The associated superstructure can be reversibly melted on a picosecond time scale upon quasi-instantaneous substrate heating, involving ultrafast heterogeneous melting via a transient floating phase. Our findings elucidate time-resolved molecular-scale ordering and disordering phenomena in individual polymers interacting with solids, yielding complementary information to collective friction and viscosity, and linking to recent experimental observables from ultrafast electron diffraction. We anticipate that the approach will help in resolving non-equilibrium phenomena of hybrid polymeric systems over a broad range of time and length scales. Copyright © 2020, The Authors. All rights reserved.

关键词： Graphene

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Approximations of energy minimization in cell-induced phase transitions of fibrous biomaterials: Γ-convergence analysis

arXiv

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arXiv 2019年

作者： Grekas, Georgios Koumatos, Konstantinos Makridakis, Charalambos Rosakis, Phoebus Aerospace Engineering and Mechanics University of Minnesota Minneapolis United States Department of Mathematics University of Sussex Department of Mathematics and Applied Mathematics University of Crete Institute of Applied & Computational Mathematics Foundation for Research & Technology-Hellas

We consider a model of energy minimization arising in the study of the mechanical behavior caused by cell contraction within a fibrous biological medium. The macroscopic model is based on the theory of non rank-one convex nonlinear elasticity for phase transitions. We study appropriate numerical approximations based on the discontinuous Galerkin treatment of higher gradients and used succesfully in numerical simulations of experiments. We show that the discrete minimizers converge in the limit to minimizers of the continuous problem. This is achieved by employing the theory of Γ-convergence of the approximate energy functionals to the continuous model when the discretization parameter tends to zero. The analysis is involved due to the structure of numerical approximations which are defined in spaces with lower regularity than the space where the minimizers of the continuous variational problem are sought. This fact leads to the development of a new approach to Γ-convergence, appropriate for discontinuous finite element discretizations, which can be applied to quite general energy minimization problems. Furthermore, the adoption of exponential terms penalising the interpenetration of matter requires a new framework based on Orlicz spaces for discontinuous Galerkin methods which is developed in this paper as well. Copyright © 2019, The Authors. All rights reserved.

关键词： Galerkin methods

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Generalized Young measures and the hydrodynamic limit of condensing zero range processes

arXiv

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arXiv 2019年

作者： Loulakis, Michail Stamatakis, Marios G. School of Applied Mathematical and Physical Sciences National Technical University of Athens Polytechnioulopis Zographou Athens15780 Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology Hellas Greece

Condensing zero range processes (ZRPs) are stochastic interacting particle systems that exhibit phase separation with the emergence of a condensate. Standard approaches for deriving a hydrodynamic limit of the density fail in these models, and an effective macroscopic description has not been rigorously established, yet. In this article we prove that the limiting triple (π, W, σ) of the empirical density, the empirical current, and the empirical jump rate of the ZRP satisfies the continuity equation ∂tπ = −divW in the sense of distributions. Here (πt)t≥0 is a w∗continuous curve of finite non-negative measures on the torus Td, σt ∈ H1(Td) and Wt = −∇σt is a vector-valued measure that is absolutely continuous with respect to the Lebesgue measure, for all almost all t ≥ 0. In order to obtain a closed equation we propose a generalization of Young measures and we prove that for symmetric ZRPs on the torus, the hydrodynamic limit of the density is a generalized Young-measure-valued weak solution π = (πt)t≥0 to a saturated filtration equation ∂tπ = ∆Φ(π). Furthermore we prove a one-sided two-blocks estimate and we give an equivalent criterion for its validity. Assuming the validity of the two-blocks estimate one obtains the equation ∂tπ = ∆Φ(πac) for the empirical density, where π = πac + π is the Radon-Nikodym decomposition.60K35, 82C22, 35K65, 46S50 Copyright © 2019, The Authors. All rights reserved.

关键词： Phase separation

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A posteriori error estimate for the IPDGFEM of a general problem of the strain gradient elasticity theory in 2D

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AIP Conference Proceedings 2021年第1期2343卷

作者： Konstantinos G. Eptaimeros Institute of Applied and Computational Mathematics Foundation for Research and Technology 100 N. Plastira Str. Vassilika Vouton Heraklion Crete Greece 70013

The strain gradient elasticity theory (SGET) introduces the microstructure to the constitutive equations to explain the material size effects. The constitutive equations of the SGET appear a boundary layer [1, 2]. The interior penalty discontinuous Galerkin finite element method (IPDGFEM) is suitable to handle the boundary layer and the mesh design as well as vary the polynomial degree in the local basis functions. This research objective centers on carrying out an a posteriori error analysis for the (symmetric) IPDGFEM of a general problem of the SGET in 2D.

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Evolutionary convergence of sensory circuits in the pallium of amniotes

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Science (New York, N.Y.) 2025年第6735期387卷 eadp3411页

作者： Rueda-Alaña, Eneritz Senovilla-Ganzo, Rodrigo Grillo, Marco Vázquez, Enrique Marco-Salas, Sergio Gallego-Flores, Tatiana Ordeñana-Manso, Aitor Ftara, Artemis Escobar, Laura Benguría, Alberto Quintas, Ana Dopazo, Ana Rábano, Miriam Vivanco, María dM Aransay, Ana María Garrigos, Daniel Toval, Ángel Ferrán, José Luis Nilsson, Mats Encinas-Pérez, Juan Manuel De Pittà, Maurizio García-Moreno, Fernando Achucarro Basque Center for Neuroscience Scientific Park of the University of the Basque Country (UPV/EHU) Leioa Spain Department of Neuroscience Faculty of Medicine and Odontology UPV/EHU Barrio Sarriena s/n Leioa Bizkaia Spain Science for Life Laboratory Department of Biophysics and Biochemistry Stockholm University Solna Sweden Genomics Unit Centro Nacional de Investigaciones Cardiovasculares (CNIC) Madrid Spain Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares (CIBERCV) Madrid Spain Center for Cooperative Research in Biosciences (CIC bioGUNE) Basque Research and Technology Alliance (BRTA) Bizkaia Technology Park Derio Spain Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd) Madrid Spain Department of Human Anatomy Medical School University of Murcia and Murcia Arrixaca Institute for Biomedical Research Murcia Spain IKERBASQUE Foundation Bilbao Spain Basque Center for Applied Mathematics Bilbao Spain Computational Neuroscience Hub Krembil Research Institute University Health Network Toronto ON Canada Department of Physiology Temerty Faculty of Medicine University of Toronto Toronto ON Canada

The amniote pallium contains sensory circuits that are structurally and functionally equivalent, yet their evolutionary relationship remains unresolved. We used birthdating analysis, single-cell RNA and spatial transcriptomics, and mathematical modeling to compare the development and evolution of known pallial circuits across birds (chick), lizards (gecko), and mammals (mouse). We reveal that neurons within these circuits' stations are generated at varying developmental times and brain regions across species and found an early developmental divergence in the transcriptomic progression of glutamatergic neurons. Our research highlights developmental distinctions and functional similarities in the sensory circuit between birds and mammals, suggesting the convergence of high-order sensory processing across amniote lineages.

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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

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Unprivileged groups are less served by green cooling services in major European urban areas

Nature Cities

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Nature Cities 2024年 424-435页

作者： Alby Duarte Rocha Stenka Vulova Michael Förster Birgit Kleinschmit Beniamino Gioli Bradley Matthews Carole Helfter Fred Meier Gert-Jan Steeneveld Janet F. Barlow Leena Järvi Nektarios Chrysoulakis Giacomo Nicolini Geoinformation in Environmental Planning Lab Technische Universität Berlin Berlin Germany Department of Environmental Meteorology University of Kassel Kassel Germany Institute of BioEconomy National Research Council (IBE-CNR) Florence Italy Department of Forest- and Soil Sciences Institute of Forest Ecology University of Natural Resources and Life Sciences Vienna Austria Environment Agency Austria Vienna Austria UK Center for Ecology and Hydrology Penicuik UK Chair of Climatology Institute of Ecology Technische Universität Berlin Berlin Germany Meteorology and Air Quality Section Wageningen University Wageningen the Netherlands Department of Meteorology University of Reading Reading UK Institute for Atmospheric and Earth System Research/Physics Helsinki Institute of Sustainability Science University of Helsinki Helsinki Finland Remote Sensing Lab Institute of Applied and Computational Mathematics Foundation for Research and Technology Hellas Heraklion Greece CMCC Foundation Euro-Mediterranean Center on Climate Change Viterbo Italy

Heat stress is the leading climate-related cause of premature deaths in Europe. Major heatwaves have struck Europe recently and are expected to increase in magnitude and length. Large cities are particularly threatened due to the urban morphology and imperviousness. Green spaces mitigate heat, providing cooling services through shade provision and evapotranspiration. However, the distribution of green cooling and the population most affected are often unknown. Here we reveal environmental injustice regarding green cooling in 14 major European urban areas. Vulnerable residents in Europe are not concentrated in the suburbs but in run-down central areas that coincide with low-cooling regions. In all studied areas, lower-income residents, tenants, immigrants and unemployed citizens receive below-average green cooling, while upper-income residents, nationals and homeowners experience above-average cooling provision. The fatality risk during extreme heatwaves may increase as vulnerable residents are unable to afford passive or active cooling mitigation.

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Towards a Robust and Accurate Screening Tool for Dyslexia with Data Augmentation using GANs

Towards a Robust and Accurate Screening Tool for Dyslexia wi...

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IEEE Symposium on Bioinformatics and Bioengineering (BIBE)

作者： Thomais Asvestopoulou Victoria Manousaki Antonis Psistakis Erjona Nikolli Vassilios Andreadakis Ioannis M. Aslanides Yannis Pantazis Ioannis Smyrnakis Maria Papadopouli Department of Computer Science University of Crete Heraklion Greece Institute of Computer Science Foundation for Research and Technology-Hellas Heraklion Greece Optotech Ltd. Heraklion Greece Emmetropia Eye Institute Heraklion Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology-Hellas Heraklion Greece University of Crete Heraklion Greece

Eye movements during text reading can provide insights about reading disorders. We developed the DysLexML, a screening tool for developmental dyslexia, based on various ML algorithms that analyze gaze points recorded via eye-tracking during silent reading of children. We comparatively evaluated its performance using measurements collected from two systematic field studies with 221 participants in total. This work presents DysLexML and its performance. It identifies the features with prominent predictive power and performs dimensionality reduction. Specifically, it achieves its best performance using linear SVM, with an accuracy of 97% and 84% respectively, using a small feature set. We show that DysLexML is also robust in the presence of noise. These encouraging results set the basis for developing screening tools in less controlled, larger-scale environments, with inexpensive eye-trackers, potentially reaching a larger population for early intervention. Unlike other related studies, DysLexML achieves the aforementioned performance by employing only a small number of selected features, that have been identified with prominent predictive power. Finally, we developed a new data augmentation/substitution technique based on GANs for generating synthetic data similar to the original distributions.

关键词： Support vector machines Feature extraction Sociology Statistics Tools Training Cameras

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LINEAR NON-DEGENERACY OF THE 1-D BLOW-UP LIMIT IN THE PHASE SEGREGATION OF BOSE-EINSTEIN CONDENSATES

arXiv

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arXiv 2018年

作者： Sourdis, Christos Institute of Applied and Computational Mathematics Foundation of Research and Technology of Hellas

We show that the kernel of the linearization of the blow-up problem at the regular part of the interface that separates segregated BECs is one-dimensional, generated by translations in the normal direction to the interface. This useful non-degeneracy property was previously known only in one and two dimensions. Copyright © 2018, The Authors. All rights reserved.

关键词： Bose-Einstein condensation

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Staggered explicit-implicit time-discretization for elastodynamics with dissipative internal variables

arXiv

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arXiv 2020年

作者： Roubíček, Tomáš Tsogka, Chrysoula Charles University Mathematical Institute Sokolovská 83 Praha 8CZ-186 75 Czech Republic Institute of Thermomechanics of the Czech Acad. Sci. Dolejškova 5 Praha 8CZ–182 08 Czech Republic Department of Applied Mathematics University of California Merced 5200 North Lake road MercedCA95343 United States Institute of Applied and Computational Mathematics Foundation for Research and Technology - Hellas Nikolaou Plastira 100 Vassilika Vouton Heraklion CreteGR-700 13 Greece

An extension of the two-step staggered time discretization of linear elastodynamics in stress-velocity form to systems involving internal variables subjected to a possibly non-linear dissipative evolution is proposed. The original scheme is thus enhanced by another step for the internal variables which, in general, is implicit, although even this step might be explicit if no spatial gradients of the internal variables are involved. Using an abstract Banach-space formulation, a-priori estimates and convergence are proved under a CFL condition. The developed three-step scheme finds applications in various problems of continuum mechanics at small strain. Here, we consider in particular plasticity, viscoelasticity (creep), diffusion in poroelastic media, and damage. Copyright © 2020, The Authors. All rights reserved.

关键词： Non Newtonian flow

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