检索结果-内蒙古大学图书馆

Adsorption and dissociation of O2 at Be(0001): First-principles prediction of an energy barrier on the adiabatic potential energy surface

引用

Physical Review B 2009年第16期79卷 165416-165416页

作者： Ping Zhang Bo Sun Yu Yang LCP Institute of Applied Physics and Computational Mathematics P.O. Box 8009 Beijing 100088 People’s Republic of China Center for Applied Physics and Technology Peking University Beijing 100871 People’s Republic of China Department of Physics and Center for Advanced Study Tsinghua University Beijing 100084 People’s Republic of China

The adsorption and dissociation of O2 molecules at the Be(0001) surface is studied by using density-functional theory within the generalized gradient approximation and a supercell approach. The physisorbed and chemisorbed molecular precursor states are identified to be along the parallel and vertical channels, respectively. It is shown that the vertical channel with O2 being at the hcp hollow sites of the Be(0001) surface is the most stable channel for the molecular chemisorption. The electronic and magnetic properties of this most stable chemisorbed molecular state are studied, which show that the electrons transfer forth and back between the spin-resolved antibonding π∗ molecular orbitals and surface Be sp states. A distinct covalent weight in the molecule-metal bond is also shown. The dissociation of O2 is determined by calculating the adiabatic potential energy surfaces, wherein the T-Y channel is found to be the most stable and favorable for dissociative adsorption of O2. Remarkably, we predict that unlike other simple sp metal surfaces such as Al(111) and Mg(0001), the adiabatic dissociation process of O2 at Be(0001) is an activated type with a sizeable energy barrier.

关键词： adsorption aluminium beryllium charge exchange chemisorption density functional theory dissociation magnesium oxygen potential energy surfaces reaction kinetics theory surface chemistry

来源：评论

学校读者我要写书评

暂无评论

A new approach in image registration

A new approach in image registration

引用

IEEE International Workshop on Imaging Systems and Techniques (IST)

作者： Constantinos Spanakis Emmanuel Mathioudakis Nikos Kampanis Manolis Tsiknakis Kostas Marias Institute of Computer Science Foundation for Research and Technology Greece Technical University of Crete Chania Greece School of Mineral Resources Engineering Technical University of Crete Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology Greece Department of Applied Informatics and Multimedia Technological Educational Institute of Crete

ISBN: (纸本)9781509018185

Evolutionary algorithms are metaheuristic algorithms that mimic biological mechanisms for the solution of optimization problems. They are widely used in many problems of engineering, including image analysis and pattern recognition. Such methods had shown added value in overcoming certain problems and limitations of more traditional methods and approaches. This is particularly interesting in Computer for designing faster and more accurate optimization methods. Despite recent advances in image registration, there is still room for improvement especially with the use of metaheuristic algorithms. In this paper, we present a novel method for solving the automated rigid registration problem by introducing a variant of the relatively new metaheuristic method called harmony search which shows promising results in difficult rigid registration cases.

关键词： Image registration Search problems Radiation detectors Mutual information Electronic mail Standards Optimization

来源：评论

学校读者我要写书评

暂无评论

Hard convex lens-shaped particles: Characterization of dense disordered packings

引用

Physical Review E 2019年第6期100卷 062902-062902页

作者： Giorgio Cinacchi Salvatore Torquato Departamento de Física Teórica de la Materia Condensada Instituto de Física de la Materia Condensada (IFIMAC) Instituto de Ciencias de Materiales “Nicolás Cabrera” Universidad Autónoma de Madrid Ciudad Universitaria de Cantoblanco E-28049 Madrid Spain Department of Chemistry and Department of Physics Institute for the Science and Technology of Materials Program for Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

Among the family of hard convex lens-shaped particles (lenses), the one with aspect ratio equal to 2/3 is “optimal” in the sense that the maximally random jammed (MRJ) packings of such lenses achieve the highest packing fraction ϕMRJ≃0.73 [G. Cinacchi and S. Torquato, Soft Matter 14, 8205 (2018)]. This value is only a few percent lower than ϕDKP=0.76210⋯, the packing fraction of the corresponding densest-known crystalline (degenerate) packings [G. Cinacchi and S. Torquato, J. Chem. Phys. 143, 224506 (2015)]. By exploiting the appreciably reduced propensity that a system of such optimal lenses has to positionally and orientationally order, disordered packings of them are progressively generated by a Monte Carlo method–based procedure from the dilute equilibrium isotropic fluid phase to the dense nonequilibrium MRJ state. This allows us to closely monitor how the (micro)structure of these packings changes in the process of formation of the MRJ state. The gradual changes undergone by the many structural descriptors calculated here can coherently and consistently be traced back to the gradual increase in contacts between the hard particles until the isostatic mean value of ten contact neighbors per lens is reached at the effectively hyperuniform MRJ state. Compared to the MRJ state of hard spheres, the MRJ state of such optimal lenses is denser (less porous), more disordered, and rattler-free. This set of characteristics makes them good glass formers. It is possible that this conclusion may also hold for other hard convex uniaxial particles with a correspondingly similar aspect ratio, be they oblate or prolate, and that, by using suitable biaxial variants of them, that set of characteristics might further improve.

关键词： Granular packing Jamming Colloids Disordered systems Granular materials Lyotropic liquid crystals Monte Carlo methods

来源：评论

学校读者我要写书评

暂无评论

Solving Constrained Optimization Problems by an Improved Particle Swarm Optimization

Solving Constrained Optimization Problems by an Improved Par...

引用

International Conference on Innovations in Bio-inspired Computing and Applications (IBICA)

作者： Chaoli Sun Jianchao Zeng Shuchuan Chu John F. Roddick Jengshyang Pan Complex System and Computational Intelligence Laboratory Taiyuan University of Science and Technology Taiyuan Shanxi China School of Computer Science Engineering and Mathematics Flinders University Australia Department of Electronic Engineering National Kaohsiung University of Applied Sciences Kaohsiung Taiwan

Constrained optimization problems compose a large part of real-world applications. More and more attentions have gradually been paid to solve this kind of problems. An improved particle swarm optimization (IPSO) algorithm based on feasibility rules is presented in this paper to solve constrained optimization problems. The average velocity of the swarm and the best history position in the particle's neighborhood are introduced as two turbulence factors, which are considered to influence the fly directions of particles, into the algorithm so as not to converge prematurely. The performance of IPSO algorithm is tested on 13 well-known benchmark functions. The experimental results show that the proposed IPSO algorithm is simple, effective and highly competitive.

关键词： Optimization Particle swarm optimization Algorithm design and analysis Convergence History Educational institutions

来源：评论

学校读者我要写书评

暂无评论

Can AI weather models predict out-of-distribution gray swan tropical cyclones?

arXiv

引用

arXiv 2024年

作者： Sun, Y. Qiang Hassanzadeh, Pedram Zand, Mohsen Chattopadhyay, Ashesh Weare, Jonathan Abbot, Dorian S. University of Chicago Department of the Geophysical Sciences ChicagoIL60637 United States University of Chicago Committee on Computational and Applied Mathematics ChicagoIL60637 United States University of Chicago Research Computing Center ChicagoIL60637 United States University of California Department of Applied Mathematics Santa CruzCA95064 United States New York University Courant Institute of Mathematical Sciences New YorkNY10012 United States

Predicting gray swan weather extremes, which are possible but so rare that they are absent from the training dataset, is a major concern for AI weather/climate models. An important open question is whether AI models can extrapolate from weaker weather events present in the training set to stronger, unseen weather extremes. To test this, we train independent versions of the AI model FourCastNet on the 1979-2015 ERA5 dataset with all data, or with Category 3-5 tropical cyclones (TCs) removed, either globally or only over the North Atlantic or Western Pacific basin. We then test these versions of FourCastNet on 2018-2023 Category 5 TCs (gray swans). All versions yield similar accuracy for global weather, but the one trained without Category 3-5 TCs cannot accurately forecast Category 5 TCs, indicating that these models cannot extrapolate from weaker storms. The versions trained without Category 3-5 TCs in one basin show some skill forecasting Category 5 TCs in that basin, suggesting that FourCastNet can generalize across tropical basins. This is encouraging and surprising because regional information is implicitly encoded in inputs. No version satisfies gradient-wind balance, implying that enforcing such physical constraints may not improve generalizability to gray swans. Given that current state-of-the-art AI weather/climate models have similar learning strategies, we expect our findings to apply to other models and extreme events. Our work demonstrates that novel learning strategies are needed for AI weather/climate models to provide early warning or estimated statistics for the rarest, most impactful weather extremes. © 2024, CC BY-NC-SA.

关键词： Tropical cyclone

来源：评论

学校读者我要写书评

暂无评论

ERROR ANALYSIS FOR DISCONTINUOUS GALERKIN TIME-STEPPING METHODS FOR NONLINEAR PARABOLIC EQUATIONS VIA MAXIMAL REGULARITY

arXiv

引用

arXiv 2024年

作者： Akrivis, Georgios Larsson, Stig Department of Computer Science and Engineering University of Ioannina Ioannina451 10 Greece Institute of Applied and Computational Mathematics FORTH Heraklion Crete700 13 Greece Department of Mathematical Sciences Chalmers University of Technology University of Gothenburg GothenburgSE–412 96 Sweden

We consider the discretization of a class of nonlinear parabolic equations by discontinuous Galerkin time-stepping methods and establish a priori as well as conditional a posteriori error estimates. Our approach is motivated by the error analysis in [9] for Runge–Kutta methods for nonlinear parabolic equations;in analogy to [9], the proofs are based on maximal regularity properties of discontinuous Galerkin methods for nonautonomous linear parabolic *** Codes 65M12, 65M15, 65M60 © 2024, CC BY.

关键词： Galerkin methods

来源：评论

学校读者我要写书评

暂无评论

Improving hp-Variational Physics-Informed Neural Networks for Steady-State Convection-Dominated Problems

arXiv

引用

arXiv 2024年

作者： Anandh, Thivin Ghose, Divij Jain, Himanshu Sunkad, Pratham Ganesan, Sashikumaar John, Volker Department of Computational and Data Sciences Indian Institute of Science Karnataka Bangalore India Department of Mechanical Engineering Indian Institute of Technology Tamil Nadu Madras India Weierstrass Institute for Applied Analysis and Stochastics Berlin Germany Department of Mathematics and Computer Science Freie University Berlin Germany

This paper proposes and studies two extensions of applying hp-variational physics-informed neural networks, more precisely the FastVPINNs framework, to convection-dominated convection-diffusion-reaction problems. First, a term in the spirit of a SUPG stabilization is included in the loss functional and a network architecture is proposed that predicts spatially varying stabilization parameters. Having observed that the selection of the indicator function in hard-constrained Dirichlet boundary conditions has a big impact on the accuracy of the computed solutions, the second novelty is the proposal of a network architecture that learns good parameters for a class of indicator functions. Numerical studies show that both proposals lead to noticeably more accurate results than approaches that can be found in the literature. © 2024, CC BY-NC-SA.

关键词： Stabilization

来源：评论

学校读者我要写书评

暂无评论

Dynamic model of a hyper-redundant, octopus-like manipulator for underwater applications

Dynamic model of a hyper-redundant, octopus-like manipulator...

引用

2011 IEEE/RSJ International Conference on Intelligent Robots and Systems

作者： Rongjie Kang Asimina Kazakidi Emanuele Guglielmino David T. Branson Dimitris P. Tsakiris John A. Ekaterinaris Darwin G. Caldwell Department of Advanced Robotics Istituto Italiano di Tecnologia Genova Italy Institute of Computer Science Foundation for Research and Technology Hellas FORTH Heraklion Greece Institute of Applied and Computational Mathematics Foundation for Research and Technology Hellas FORTH Heraklion Greece

The octopus arm is a unique tool that combines strength and flexibility. It can shorten, elongate and bend at any point along its length. To model this behavior, a hyper-redundant manipulator composed of multiple segments is proposed. Each segment is a parallel robotic mechanism with redundant actuation. The kinematics and dynamics of this manipulator are analyzed and simulated utilizing a modular computational modeling method. Simulation results for some primitive movements are presented, and the effect of hydrodynamic forces is included.

关键词： Mathematical model Force Manipulator dynamics Joints Equations Pistons

来源：评论

学校读者我要写书评

暂无评论

Reliable Extrapolation of Deep Neural Operators Informed by Physics or Sparse Observations

SSRN

引用

SSRN 2023年

作者： Zhu, Min Zhang, Handi Jiao, Anran Karniadakis, George Em Lu, Lu Department of Chemical and Biomolecular Engineering University of Pennsylvania PhiladelphiaPA19104 United States Graduate Group in Applied Mathematics and Computational Science University of Pennsylvania PhiladelphiaPA19104 United States Department of Computer and Information Science University of Pennsylvania PhiladelphiaPA19104 United States Division of Applied Mathematics Brown University ProvidenceRI02912 United States School of Engineering Brown University ProvidenceRI02912 United States

Deep neural operators can learn nonlinear mappings between infinite-dimensional function spaces via deep neural networks. As promising surrogate solvers of partial differential equations (PDEs) for real-time prediction, deep neural operators such as deep operator networks (DeepONets) provide a new simulation paradigm in science and engineering. Pure data-driven neural operators and deep learning models, in general, are usually limited to interpolation scenarios, where new predictions utilize inputs within the support of the training set. However, in the inference stage of real-world applications, the input may lie outside the support, i.e., extrapolation is required, which may result to large errors and unavoidable failure of deep learning models. Here, we address this challenge of extrapolation for deep neural operators. First, we systematically investigate the extrapolation behavior of DeepONets by quantifying the extrapolation complexity via the 2-Wasserstein distance between two function spaces and propose a new strategy of bias-variance trade-off for extrapolation with respect to model capacity. Subsequently, we develop a complete workflow, including extrapolation determination, and we propose five reliable learning methods that guarantee a safe prediction under extrapolation by requiring additional information-the governing PDEs of the system or sparse new observations. The proposed methods are based on either fine-tuning a pre-trained DeepONet or multifidelity learning. We demonstrate the effectiveness of the proposed framework for various types of parametric PDEs. Our systematic comparisons provide practical guidelines for selecting a proper extrapolation method depending on the available information, desired accuracy, and required inference speed. © 2023, The Authors. All rights reserved.

关键词： Extrapolation

来源：评论

学校读者我要写书评

暂无评论

Testing viable f(R) models with the angular-diameter distance to compact quasar cores

引用

Physical Review D 2019年第10期99卷 103505-103505页

作者： Joseph Sultana Fulvio Melia Demosthenes Kazanas Department of Mathematics Faculty of Science University of Malta Msida MSD2080 Malta Department of Physics The Applied Math Program and Department of Astronomy The University of Arizona Tucson Arizona 85721 USA Astrophysics Science Division NASA/Goddard Space Flight Center Greenbelt Maryland 20771 USA

We consider here some popular f(R) models generally viewed as possible alternatives to the existence of dark energy in General Relativity. For each of these, we compute the redshift zmax at which the angular diameter distance dA(z) is expected to reach its maximum value. This turning point in dA(z) was recently measured in a model-independent way using compact quasar cores and was found to occur at zmax=1.70±0.20. We compare the predictions of zmax for the f(R) models with this observed value to test their viability at a deeper level than has been attempted thus far, thereby quantifying an important observational difference between such modified gravity scenarios and standard Lambda Cold Dark Matter (ΛCDM) cosmology. Our results show that, while the most popular f(R) models today are consistent with this measurement to within 1σ, the turning point zmax will allow us to prioritize these alternative gravity theories as the measurement precision continues to improve, particularly with regard to how well they mitigate the tension between the predictions of ΛCDM and the observations. For example, while the Hu-Sawicki version of f(R) increases this tension, the Starobinky model reduces it.

关键词： Alternative gravity theories Cosmological parameters Relativistic aspects of cosmology

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：