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First-principles determination of the phonon-point defect scattering and thermal transport due to fission products in ThO2

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arXiv 2023年

作者： Malakkal, Linu Katre, Ankita Zhou, Shuxiang Jiang, Chao Hurley, David H. Marianetti, Chris A. Khafizov, Marat Computational Mechanics and Materials Department Idaho National Laboratory Idaho FallsID83415 United States Department of Scientific Computing Modeling and Simulation SP Pune University Pune411007 India Idaho National Laboratory Idaho FallsID83415 United States Department of Applied Physics and Applied Mathematics Columbia University 500 West 120th Street New YorkNY10027 United States Department of Mechanical and Aerospace Engineering The Ohio State University 201 West 19th Ave ColumbusOH43210 United States

This work presents the first-principles calculations of the lattice thermal conductivity degradation due to point defects in thorium dioxide using an iterative solution of the Peirels-Boltzmann transport equation. We have used the non-perturbative Green's function methodology to compute the phononpoint defect scattering rates that consider the local distortion around the point defect, including the mass difference changes, interatomic force constants, and structural relaxation near the point defects. The point defects considered in this work include the vacancy of thorium (VTh) and oxygen (VO), substitutions of helium (HeTh), krypton (KrTh), zirconium (ZrTh), iodine (ITh) and xenon (XeTh) in the thorium site, and the three different configurations of the Schottky defects. The results of the phonon-defect scattering rate reveal that, among all the considered intrinsic defects, the thorium vacancy and helium substitution in the thorium site scatter the phonon most due to the substantial changes in the force constant and structural distortions. The scattering of phonons due to the substitutional defects unveils that the zirconium atom scatters phonons the least, followed by xenon, iodine, krypton, and helium. This is contrary to the intuition that the scattering strength follows HeTh > KrTh > ZrTh > ITh > XeTh based on the mass difference. This striking difference in the zirconium phonon scattering is due to the local chemical environment changes. Zirconium is an electropositive element with valency similar to thorium and, therefore, can bond with the oxygen atoms, thus creating less force constant variance compared to iodine, an electronegative element, and the noble gases helium, xenon, and krypton. These results can serve as a benchmark for analytical models and help the engineering-scale modeling effort for nuclear design. © 2023, CC BY.

关键词： Boltzmann equation

Robotically Steered Needles: A Survey of Neurosurgical Applications and Technical Innovations

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Robotic surgery (Auckland)

Robotic surgery (Auckland) 2020年 7卷 1-23页

作者： Michel A Audette Stéphane P A Bordas Jason E Blatt Department of Computational Modeling and Simulation Engineering Old Dominion University Norfolk VA USA. Institute of Computational Engineering University of Luxembourg Faculty of Sciences Communication and Technology Esch-Sur-Alzette Luxembourg. Department of Neurosurgery University of Florida Gainesville FL USA.

This paper surveys both the clinical applications and main technical innovations related to steered needles, with an emphasis on neurosurgery. Technical innovations generally center on curvilinear robots that can adopt a complex path that circumvents critical structures and eloquent brain tissue. These advances include several needle-steering approaches, which consist of tip-based, lengthwise, base motion-driven, and tissue-centered steering strategies. This paper also describes foundational mathematical models for steering, where potential fields, nonholonomic bicycle-like models, spring models, and stochastic approaches are cited. In addition, practical path planning systems are also addressed, where we cite uncertainty modeling in path planning, intraoperative soft tissue shift estimation through imaging scans acquired during the procedure, and simulation-based prediction. Neurosurgical scenarios tend to emphasize straight needles so far, and span deep-brain stimulation (DBS), stereoelectroencephalography (SEEG), intracerebral drug delivery (IDD), stereotactic brain biopsy (SBB), stereotactic needle aspiration for hematoma, cysts and abscesses, and brachytherapy as well as thermal ablation of brain tumors and seizure-generating regions. We emphasize therapeutic considerations and complications that have been documented in conjunction with these applications.

关键词： brain biopsy brachytherapy deep-brain stimulation intracerebral drug delivery needle steering stereoelectroencephalography stereotactic needle aspiration

Fluorine intercalated graphene: Formation of a two-dimensional spin lattice through pseudoatomization

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Physical Review Materials 2020年第7期4卷 074411-074411页

作者： Shashi B. Mishra Satyesh K. Yadav D. G. Kanhere B. R. K. Nanda Condensed Matter Theory and Computational Lab Department of Physics IIT Madras Chennai 600036 India Department of Metallurgical and Materials Engineering IIT Madras Chennai 600036 India Centre for Modeling and Simulation Savitribai Phule Pune University Pune 411007 India

A suspended layer made up of ferromagnetically ordered spins could be created between two- monolayer or multilayer graphene through intercalation. Stability and electronic structure studies show that, when fluorine molecules are intercalated between two mono/multilayer graphene, their bonds get stretched enough (∼1.9–2.0Å) to weaken their molecular singlet eigenstate. Geometrically, these stretched molecules form a pseudoatomized fluorine layer by maintaining a van der Waals separation of ∼2.6Å from the adjacent carbon layers. As there is a significant charge transfer from the adjacent carbon layers to the fluorine layers, a mixture of triplet and doublet states stabilizes to induce local spin moments at each fluorine site and in turn form a suspended two-dimensional spin lattice. The spins of this lattice align ferromagnetically with nearest-neighbor coupling strength as large as ∼100meV. Our finite-temperature ab initio molecular dynamics study reveals that the intercalated system can be stabilized up to a temperature of 100 K with an average magnetic moment of ∼0.6μB/F. However, if the graphene layers can be held fixed, the room-temperature stability of such a system is feasible.

关键词： Electronic structure Magnetic interactions Magnetism Graphene Interfaces Two-dimensional electron system

Vesicle shape deformation using a discontinuous Galerkin method 6

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Vesicle shape deformation using a discontinuous Galerkin met...

6th ECCOMAS European Conference on computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th ECCOMAS European Conference on computational Fluid Dynamics, ECFD 2018

作者： Kim, Tae-Yeon Jiang, Wen Lee, Sung Mun Song, Jeong-Hoon Park, Eun-Jae Civil Infrastructure and Environmental Engineering Khalifa University of Science and Technology Abu Dhabi127788 United Arab Emirates Fuels Modeling and Simulation Idaho National Laboratory Idaho FallsID83415 United States Department of Biomedical Engineering Khalifa University of Science and Technology Abu Dhabi127788 United Arab Emirates Department of Civil Environmental and Architectural Engineering University of Colorado at Boulder BoulderCO80309 United States Department of Computational Science and Engineering Yonsei University Seoul03722 Korea Republic of

ISBN: (纸本)9788494731167

This work concerns the development of a finite-element algorithm to discretize the phase-field model for the shape deformation of a vesicle based on the idea of discontinuous Galerkin method. The phase-field model originated from minimization of Canham-Helfrich elastic bending energy involves fourth-order gradients and thus C1-basis functions are required for the standard conforming Galerkin formulation. We introduce a relatively inexpensive, nonconforming method based on C0-basis functions. We present the variational form of the method including additional terms to weakly enforce continuity of the derivatives across interelement boundaries and its stabilization is achieved via Nitsche's method. Numerical tests for the equilibrium shape of a single component vesicle are performed to demonstrate the performance of the proposed variational formulation. copyright © Crown copyright (2018).All right reserved.

关键词： Galerkin methods

Hopping-Transport Mechanism for Reconfigurable Logic in Disordered Dopant Networks

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Physical Review Applied 2022年第6期17卷 064025-064025页

作者： Henri Tertilt Jesse Bakker Marlon Becker Bram de Wilde Indrek Klanberg Bernard J. Geurts Wilfred G. van der Wiel Andreas Heuer Peter A. Bobbert Institut für physikalische Chemie Westfälische Wilhelms-Universität Münster Münster Germany NanoElectronics Group University of Twente Enschede Netherlands Multiscale Modeling and Simulation Group Faculty of Electrical Engineering Mathematics and Computer Science MESA+ Institute for Nanotechnology and Center for Brain-Inspired Nano Systems (BRAINS) University of Twente Enschede Netherlands Center for Computational Energy Research (CCER) Eindhoven University of Technology Netherlands Fachbereich Physik Westfälische Wilhelms-Universität Münster Münster Germany Department of Applied Physics Eindhoven University of Technology Netherlands

We present an atomic-scale mechanism based on variable-range hopping of interacting charges enabling reconfigurable logic in dopant network processing units. Kinetic Monte Carlo simulations of the hopping process show temperature-dependent current-voltage characteristics and artificially evolved basic Boolean logic gates in very good agreement with experiment. The simulations provide unique insights into the local electrostatic potential and current flow in the dopant network, showing subtle changes induced by control voltages that set the conditions for the logic operation. These insights will be crucial in the systematic further development of this burgeoning technology for unconventional computing. The establishment of the principles underlying the logic functionality of these devices encourages the exploration and utilization of the same principles in other materials and device geometries.

关键词： Doping effects Hopping transport Neuromorphic computing Devices for digital logic, storage & processing Disordered systems Doped semiconductors Genetic algorithm Monte Carlo methods

A BIM-Based Framework to Visually Evaluate Circularity and Life Cycle Cost of buildings.

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A BIM-Based Framework to Visually Evaluate Circularity and L...

Central Europe towards Sustainable Building 2019, CESB 2019

作者： Di Biccari, C. Abualdenien, J. Borrmann, A. Corallo, A. Department of Innovation Engineering University of Salento Edificio Aldo Romano Campus Ecotekne Lecce73100 Italy Department of Computational Modeling and Simulation Department of Civil Geo and Environmental Engineering Technical University of Munich Arcistrasse 21 Munich80333 Germany

The Circular Economy paradigm seeks to shift products and systems from linear to "closed loop" life cycles applying specific business models and strategies to their designs and lifelines. The implementation of the circular economy in buildings depends on the efforts made by all the stakeholder involved in the life cycle of a building, where it can draw most of the benefits if the application of a circular business model is planned during the design phases. Building Information Modelling is an approach that helps designers in creating and managing semantically rich 3D-models describing the status of the building over its life cycle. In this paper, a BIM-based framework for evaluating the application of circular business models of buildings from the circularity and the life cycle cost points of views is proposed. © Published under licence by IOP Publishing Ltd.

关键词： Life cycle

Polyconvex anisotropic hyperelasticity with neural networks

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arXiv 2021年

作者： Klein, Dominik K. Fernández, Mauricio Martin, Robert J. Neff, Patrizio Weeger, Oliver Cyber-Physical Simulation Group Department of Mechanical Engineering Centre for Computational Engineering Technical University of Darmstadt Dolivostr. 15 Darmstadt64293 Germany Access e.V. Intzestr. 5 Aachen52072 Germany Chair for Nonlinear Analysis and Modeling Faculty of Mathematics University of Duisburg-Essen Thea-Leymann-Str. 9 Essen45127 Germany

In the present work, two machine learning based constitutive models for finite deformations are proposed. Using input convex neural networks, the models are hyperelastic, anisotropic and fulfill the polyconvexity condition, which implies ellipticity and thus ensures material stability. The first constitutive model is based on a set of polyconvex, anisotropic and objective invariants. The second approach is formulated in terms of the deformation gradient, its cofactor and determinant, uses group symmetrization to fulfill the material symmetry condition, and data augmentation to fulfill objectivity approximately. The extension of the dataset for the data augmentation approach is based on mechanical considerations and does not require additional experimental or simulation data. The models are calibrated with highly challenging simulation data of cubic lattice metamaterials, including finite deformations and lattice instabilities. A moderate amount of calibration data is used, based on deformations which are commonly applied in experimental investigations. While the invariant-based model shows drawbacks for several deformation modes, the model based on the deformation gradient alone is able to reproduce and predict the effective material behavior very well and exhibits excellent generalization capabilities. In addition, the models are calibrated with transversely isotropic data, generated with an analytical polyconvex potential. For this case, both models show excellent results, demonstrating the straightforward applicability of the polyconvex neural network constitutive models to other symmetry groups. © 2021, CC BY-NC-ND.

关键词： Machine learning

Fluorine intercalated graphene: Formation of a 2D spin lattice through pseudoatomization

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arXiv 2020年

作者： Mishra, Shashi B. Yadav, Satyesh K. Kanhere, D.G. Nanda, B.R.K. Condensed Matter Theory and Computational Lab Department of Physics IIT Madras Chennai India Department of Metallurgy and Materials Engineering IIT Madras Chennai India Centre for Modeling and Simulation Savitribai Phule Pune University Pune India

A suspended layer made up of ferromagnetically ordered spins could be created between two mono/multilayer graphene through intercalation. Stability and electronic structure studies show that, when fluorine molecules are intercalated between two mono/multilayer graphene, their bonds get stretched enough (∼ 1.9−2.0 Å) to weaken their molecular singlet eigenstate. Geometrically, these stretched molecules form a pseudoatomized fluorine layer by maintaining a van der Waals separation of ∼ 2.6 Å from the adjacent carbon layers. As there is a significant charge transfer from the adjacent carbon layers to the fluorine layers, a mixture of triplet and doublet states stabilize to induce local spin-moments at each fluorine sites and in turn form a suspended 2D spin lattice. The spins of this lattice align ferromagnetically with nearest neighbour coupling strength as large as ∼ 100 meV. Our finite temperature ab initio molecular dynamics study reveals that the intercalated system can be stabilized up to a temperature of 100 K with an average magnetic moment of ∼ 0.6 µB/F. However, if the graphene layers can be held fixed, the room temperature stability of such a system is feasible. Copyright © 2020, The Authors. All rights reserved.

关键词： Fluorine

Theoretical insights into the chemical bonding, electronic structure, and spectroscopic properties of the lanarkite Pb2SO5 structure

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arXiv 2023年

作者： Fabris, Guilherme S.L. Ferrer, Mateus M. Sambrano, Julio R. Almeida, Cláudio R.R. Paskocimas, Carlos A. La Porta, Felipe A. Graduate Program in Materials Science and Engineering Technological Development Center Universidade Federal de Pelotas RS Pelotas96010-610 Brazil Modeling and Molecular Simulation Group São Paulo State University Bauru São Paulo17033-360 Brazil Department of Materials Engineering Federal University of Rio Grande do Norte RN Natal59078-970 Brazil Postgraduate Program in Science and Engineering of Materials Federal University of Rio Grande do Norte RN Natal59078-970 Brazil Federal University of Technology - Paraná Nanotechnology and Computational Chemistry Laboratory Avenida dos Pioneiros 3131 CEP PR Londrina86036-370 Brazil State University of Londrina Post-Graduation Program in Chemistry Rodovia Celso Garcia Cid 445 km 380 CEP PR Londrina86057-970 Brazil

Lanarkite is a mineral formed by a combination of lead, sulphur, and oxygen atoms arranged in the general chemical formula Pb2SO5 (PSO) that crystallises with monoclinic symmetry (belonging to the C2/m space group, No. 12). This mineral was first discovered in Lanarkshire, Scotland and was named after its location. PSO has a unique structure comprising alternating penta-coordinated lead [PbO5] and tetra-coordinated sulphur [SO4] clusters. This lanarkite-type structure has recently attracted significant scientific interest and has been the focus of the superconducting material research community. However, its chemistry needs to be explored further. This article presents a comprehensive investigation on the chemical bonding, electronic structure, and spectroscopic properties of the lanarkite-type PSO structure from a computational perspective. Thus, different functionals in the DFT (e.g., PBE, PBE0, PBESOL, PBESOL0, BLYP, WC1LYP37, and B3LYP) were assessed to accurately predict their fundamental properties. All the DFT calculations were performed using a triple-zeta valence plus polarisation basis set. Among all the DFT functionals tested in this study, PBE showed the best agreement with the experimental data available in the literature. Our results also reveal that the [PbO5] clusters are formed with three Pb–O bond lengths, with values of about 2.32, 2.59, and 2.84 Å, respectively, while the [SO4] clusters have the same S–O bond length of 1.57 Å. We performed a complete topological analysis of this system to comprehend these structural differences. Additionally, the PSO structure has an indirect band gap energy of 2.9 eV and an effective mass ratio (mℎ∗ /me∗) of about 0.415 (using PBE calculations) which may, in principle, indicate a low recombination of electron-hole pairs in the lanarkite structure. Therefore, we believe that a detailed understanding of their electronic structures, spectroscopic properties as well as their chemical bonding is critically important

关键词： Lead compounds