检索结果-内蒙古大学图书馆

Computer Modeling in Engineering & Sciences 2016年第5期111卷 395-419页

作者： Hao Dong Yufeng Nie Zihao Yang Yang Zhang YataoWu Department of Applied Mathematics School of ScienceNorthwestern Polytechnical UniversityXi’an 710129PR China Research Center for Computational Science Northwestern Polytechnical UniversityXi’an 710129PR China

In this paper,we discuss the numerical accuracy of asymptotic homogenization method(AHM)and multiscale finite element method(MsFEM)for periodic composite *** numerical calculation of the model problems for four kinds of typical periodic composite materials,the main factors to determine the accuracy of first-order AHM and second-order AHM are found,and the physical interpretation of these factors is ***,the way to recover multiscale solutions of first-order AHM and MsFEM is theoretically analyzed,and it is found that first-order AHM and MsFEM provide similar multiscale solutions under some ***,numerical experiments verify that MsFEM is essentially a first-order multiscale method for periodic composite materials.

关键词： Asymptotic homogenization method Multiscale finite element method First-order AHM Slight fluctuations Second-order AHM Severe fluctuations

A Framework for Directional and Higher-Order Reconstruction in Photoacoustic Tomography

学校读者我要写书评

暂无评论

arXiv 2017年

作者： Boink, Yoeri E. Lagerwerf, Marinus J. Steenbergen, Wiendelt van Gils, Stephan A. Manohar, Srirang Brune, Christoph Department of Applied Mathematics University of Twente Netherlands Biomedical Photonic Imaging Group University of Twente Netherlands Computational Imaging Group Centrum Wiskunde & Informatica Netherlands

Photoacoustic tomography is a hybrid imaging technique that combines high optical tissue contrast with high ultrasound resolution. Direct reconstruction methods such as filtered backprojection, time reversal and least squares suffer from curved line artefacts and blurring, especially in case of limited angles or strong noise. In recent years, there has been great interest in regularised iterative methods. These methods employ prior knowledge on the image to provide higher quality reconstructions. However, easy comparisons between regularisers and their properties are limited, since many tomography implementations heavily rely on the specific regulariser chosen. To overcome this bottleneck, we present a modular reconstruction framework for photoacoustic tomography. It enables easy comparisons between regularisers with different properties, e.g. nonlinear, higher-order or directional. We solve the underlying minimisation problem with an efficient first-order primal-dual algorithm. Convergence rates are optimised by choosing an operator dependent preconditioning strategy. Our reconstruction methods are tested on challenging 2D synthetic and experimental data sets. They outperform direct reconstruction approaches for strong noise levels and limited angle measurements, offering immediate benefits in terms of acquisition time and quality. This work provides a basic platform for the investigation of future advanced regularisation methods in photoacoustic tomography. Copyright © 2017, The Authors. All rights reserved.

关键词： Image reconstruction

Robust spatial memory maps encoded in networks with transient connections

学校读者我要写书评

暂无评论

arXiv 2017年

作者： Babichev, Andrey Morozov, Dmitriy Dabaghian, Yuri Department of Computational and Applied Mathematics Rice University HoustonTX77005 United States Lawrence Berkeley National Laboratory BerkeleyCA94720 United States

The spiking activity of principal cells in mammalian hippocampus encodes an internalized neuronal representation of the ambient space-a cognitive map. Once learned, such a map enables the animal to navigate a given environment for a long period. However, the neuronal substrate that produces this map remains transient: the synaptic connections in the hippocampus and in the downstream neuronal networks never cease to form and to deteriorate at a rapid rate. How can the brain maintain a robust, reliable representation of space using a network that constantly changes its architecture? Here, we demonstrate, using novel Algebraic Topology techniques, that cognitive maps stability is a generic, emergent phenomenon. The model allows evaluating the effect produced by specific physiological parameters, e.g., the distribution of connections' decay times, on the properties of the cognitive map as a whole. It also points out that spatial memory deterioration caused by weakening or excessive loss of the synaptic connections may be compensated by simulating the neuronal activity. Lastly, the model explicates functional importance of the complementary learning systems for processing spatial information at different levels of spatiotemporal granularity, by establishing three complementary timescales at which spatial information unfolds. Thus, the model provides a principal insight into how can the brain develop a reliable representation of the world, learn and retain memories despite complex plasticity of the underlying networks and allows studying how instabilities and memory deterioration mechanisms may affect learning process. Copyright © 2017, The Authors. All rights reserved.

关键词： Learning systems

The Automatic Learning for the Rapid Classification of Events (ALeRCE) alert broker

学校读者我要写书评

暂无评论

arXiv 2020年

作者： Förster, Francisco Cabrera-Vives, G. Castillo-Navarrete, E. Estévez, P.A. Sánchez-Sáez, P. Arredondo, J. Bauer, F.E. Carrasco-Davis, R. Catelan, M. Elorrieta, F. Eyheramendy, S. Huijse, P. Pignata, G. Reyes, E. Reyes, I. Rodríguez-Mancini, D. Ruz-Mieres, D. Valenzuela, C. Álvarez-Maldonado, I. Astorga, N. Borissova, J. Clocchiatti, A. de Cicco, D. Donoso-Oliva, C. Graham, M.J. Kurtev, R. Mahabal, A. Maureira, J.C. Molina-Ferreiro, R. Moya, A. Palma, W. Prez-Carrasco, M. Protopapas, P. Romero, M. Sabatini-Gacitua, L. Snchez, A. San Martín, J. Sepúlveda-Cobo, C. Vera, E. Vergara, J.R. Center for Mathematical Modeling University of Chile AFB170001 Chile Millennium Institute of Astrophysics Nuncio Monseñor Sótero Sanz 100 Providencia Santiago Chile Departamento de Astronomía Universidad de Chile Casilla 36D Santiago Chile Department of Computer Science University of Concepcin Chile Department of Electrical Engineering Universidad de Chile Av. Tupper 2007 Santiago8320000 Chile Instituto de Astrofísica Facultad de Física Pontificia Universidad Católica de Chile Av. Vicuña Mackenna 4860 Macul Santiago7820436 Chile Department of Engineering and Science Universidad Adolfo Ibaez Av. Diagonal Las Torres 2700 Santiago Chile Centro de Astroingeniería Pontificia Universidad Católica de Chile Av. Vicuña Mackenna 4860 Macul Santiago7820436 Chile Space Science Institute 4750 Walnut Street Suite 205 BoulderCO80301 United States Department of Mathematics and Computer Science Universidad de Santiago de Chile Av. Libertador Bernardo OHiggins 3663 Estación Central Santiago Chile Instituto de Informática Universidad Austral de Chile General Lagos 2086 Valdivia Chile Departamento de Ciencias Físicas Universidad Andres Bello Avda. Republica 252 Santiago Chile Institute of Astronomy University of Cambridge Madingley Road CambridgeCB3 0HA United Kingdom Instituto de Física y Astronomía Universidad de Valparaíso Av. Gran Bretaña 1111 Playa Ancha Casilla5030 Chile Division of Physics Mathematics and Astronomy California Institute of Technology PasadenaCA91125 United States Center for Data Driven Discovery California Institute of Technology PasadenaCA91125 United States Institute for Applied Computational Science Harvard University CambridgeMA United States Departmento de Informática y Computación Universidad Tecnológica Metropolitana Santiago Chile

We introduce the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker, an astronomical alert broker designed to provide a rapid and self–consistent classification of large etendue telescope alert streams, such as that provided by the Zwicky Transient Facility (ZTF) and, in the future, the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). ALeRCE is a Chilean–led broker run by an interdisciplinary team of astronomers and engineers, working to become intermediaries between survey and follow–up facilities. ALeRCE uses a pipeline which includes the real–time ingestion, aggregation, cross–matching, machine learning (ML) classification, and visualization of the ZTF alert stream. We use two classifiers: a stamp–based classifier, designed for rapid classification, and a light–curve–based classifier, which uses the multi–band flux evolution to achieve a more refined classification. We describe in detail our pipeline, data products, tools and services, which are made public for the community (see https://***). Since we began operating our real–time ML classification of the ZTF alert stream in early 2019, we have grown a large community of active users around the globe. We describe our results to date, including the real–time processing of 9.7×107 alerts, the stamp classification of 1.9 × 107 objects, the light curve classification of 8.5 × 105 objects, the report of 3088 supernova candidates, and different experiments using LSST-like alert streams. Finally, we discuss the challenges ahead to go from a single-stream of alerts such as ZTF to a multi–stream ecosystem dominated by LSST. Copyright © 2020, The Authors. All rights reserved.

关键词： Surveys

The Kinematic Effects of the Defects in Liquid Crystal Dynamics

学校读者我要写书评

暂无评论

Communications in computational Physics 2016年第6期20卷 234-249页

作者： Rui Chen Weizhu Bao Hui Zhang Institute of Applied Physics and Computational Mathematics Beijing 100088P.R.China Department of Mathematics National University of SingaporeSingapore119076 School of Mathematical Sciences Beijing Normal UniversityLaboratory of Mathematics and Complex SystemsMinistry of EducationBeijing 100875P.R.China

Here we investigate the kinematic transports of the defects in the nematic liquid crystal system by numerical *** model is a shear flow case of the viscoelastic continuummodel simplified fromthe Ericksen-Leslie *** numerical experiments are carried out by using a *** on these numerical experiments we find some interesting and important relationships between the kinematic transports and the characteristics of the *** present the development and interaction of the *** results are partly consistent with the observation from the *** this scheme illustrates,to some extent,the kinematic effects of the defects.

关键词： Nematic liquid crystals kinematic effects finite differencemethod defects

Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study (vol 2, pg 144, 2021)

学校读者我要写书评

暂无评论

LANCET GLOBAL HEALTH 2021年第4期9卷 E408-E408页

作者： Steinmetz, Jaimie D. Vision and Eye Research Institute Anglia Ruskin University Cambridge United Kingdom Biomedical Informatics Seoul National University Hospital Seoul South Korea Institute for Health Metrics and Evaluation University of Washington Seattle WA United States Department of Health Metrics Sciences School of Medicine University of Washington Seattle WA United States Institute of Health Services Research Yonsei University Seoul South Korea Department of Ophthalmology University of Washington Seattle WA United States Department of Mathematics Imperial College London London United Kingdom WHO Collaborating Centre for Public Health Education and Training Imperial College London London United Kingdom Department of Primary Care and Public Health Imperial College London London United Kingdom School of Population and Global Health University of Melbourne Carlton VIC Australia School of Optometry and Vision Science UNSW Sydney NSW Australia Brien Holden Vision Institute Sydney Australia Department of Ophthalmology University of Adelaide Adelaide SA Australia Department of Parasitology and Mycology Jahrom University of Medical Sciences Jahrom Iran Department of Clinical Sciences University of Sharjah Sharjah United Arab Emirates Ophthalmic Research Center Shahid Beheshti University of Medical Sciences Tehran Iran Department of Ophthalmology Shahid Beheshti University of Medical Sciences Tehran Iran Research Institute for Endocrine Sciences Shahid Beheshti University of Medical Sciences Tehran Iran Ophthalmic Epidemiology Research Center Shahid Beheshti University of Medical Sciences Tehran Iran Health Services Management Department Qazvin University of Medical Sciences Qazvin Iran Department of Systems Populations and Leadership University of Michigan Ann Arbor MI United States Department of Medicine Sofia Ismail Memorial Medical Centre Bogura Bangladesh The Fred Hollows Foundation Sydney NSW Australia Berhan Public Health & Eye Care Consultancy Addis A

Hospital El Salvador: a novel paradigm of intensive care in response to COVID-19 in central America. Lancet Glob Health 2021;9: e241?42?In this Comment, the conflict of interest statement should have included the following: ?By virtue of their roles within a public hospital or the Ministry of Health, MB, LC, WH, and XS are government employees. The findings and conclusions in the Comment are only those of the authors.? This correction has been made as of Feb 26, 2021.

关键词：

The Multifractal Formalism for Measures, Review and Extension to Mixed Cases

学校读者我要写书评

暂无评论

Analysis in Theory and Applications 2016年第4期32卷 303-332页

作者： Mohamed Menceur Anouar Ben Mabrouk Kamel Betina Algerba and Number Theory Laboratory Faculty of Mathematics University of Sciences and Technology Houari Boumediene Computational Mathematics Laboratory Department of Mathematics Faculty of Sciences Department of Mathematics HIgher Institute of Applied Mathematics and Informatics Street of Assad Ibn Alfourat Kairouan University

The multifractal formalism for single measure is reviewed. Next, a mixed generalized multifractal formalism is introduced which extends the multifractal formalism of a single measure based on generalizations of the Hausdorff and packing measures to a vector of simultaneously many measures. Borel-Cantelli and Large deviations Theorems are extended to higher orders and thus applied for the validity of the new variant of the multifractal formalism for some special cases of multi-doubling type measures.

关键词： Hausdorff measures packing measures Hausdorff dimension packing dimension renyi dimension multifractal formalism vector valued measures mixed cases Holderian measures doubling measures Borel-Cantelli large deviations

Sea-ice distribution and mixed-layer depths in fram strait

学校读者我要写书评

暂无评论

arXiv 2017年

作者： Agarwal, Sahil Grae Worster, M. Program in Applied Mathematics Yale University New Haven United States Institute of Theoretical Geophysics Department of Applied Mathematics and Theoretical Physics University of Cambridge Wilberforce Road CambridgeCB3 0WA United Kingdom

In an effort to understand the dynamics of the Arctic sea-ice edge, we present a simple model of heat and mass transfer in the Fram Strait that reveals some fundamental mechanisms controlling sea-ice extent in the marginal seas and the depth and properties of the Arctic mixed layer. We identify and study key mechanisms relating to the sea-ice wedge described by Untersteiner, a boundary-layer structure near the ice edge, demonstrating how ice thickness and extent depend on ice-export rates, atmospheric forcing and the properties of incoming warm and salty Atlantic water in the West Spitsbergen Current. Our time-dependent results demonstrate a seasonal asymmetry between the rates of ice advance and retreat and explain the significant variations in the Southerly extent of sea ice across the Fram Strait, with a long ice tongue corresponding with the East Greenland Current. Our simple model indicates that thinning of the Arctic sea-ice cover will lead to warming and freshening of the North Atlantic, which would give a de-stabilizing feedback to the Arctic ice cover, leading to a slowdown of the Atlantic Meridional Overturning Circulation. Copyright © 2017, The Authors. All rights reserved.

关键词： Sea ice

Partial Differential Equations — Spectral gaps and non-Bragg resonances in a water channel

学校读者我要写书评

暂无评论

Atti della Accademia Nazionale dei Lincei, Classe di Scienze Fisiche, Matematiche e Naturali, Rendiconti Lincei Matematica e Applicazioni 2018年第2期29卷 321-342页

作者： Piat, Valeria Chiadò Nazarov, Sergey A. Ruotsalainen, Keijo M. DISMA Department of Mathematical Sciences Politecnico di Torino Corso Duca degli Abruzzi 24 Torino10129 Italy St. Petersburg State University Universitetskaya nab. 7–9 St. Petersburg199034 Russia Institute of Problems of Mechanical Engineering V.O. Bolshoj pr. 61 St. Petersburg199178 Russia Applied and Computational Mathematics Research Group University of Oulu Box 4500 Oulu90014 Finland

In this paper the essential spectrum of the linear problem of water-waves on a 3d-channel with gently periodic bottom will be studied. We show that under a certain geometric condition on the bottom profile the essential spectrum has spectral gaps. In classical analysis of waveguides it is known that the Bragg resonances at the edges of the Brillouin zones create band gaps in the spectrum. Here we demonstrate that the band gaps can be opened also in the frequency range far from the Bragg resonances. The position and the length of the gaps are found out by applying an asymptotic analysis to the model problem in the periodicity cell. © 2018 European Mathematical Society Publishing House. All rights reserved.

关键词： Water waves

An algorithm for computing Lipschitz inner functions in Kolmogorov's superposition theorem

学校读者我要写书评

暂无评论

arXiv 2017年

作者： Actor, Jonas Knepley, Matthew G. Department of Computational and Applied Mathematics Rice University HoustonTX77005 United States Department of Computer Science and Engineering University of Buffalo BuffaloNY14260 United States

Kolmogorov famously proved in [6] that multivariate continuous functions can be represented as a superposition of a small number of univariate continuous functions, (Equation Presented) Fridman [4] posed the best smoothness bound for the functions ψpq, that such functions can be constructed to be Lipschitz continuous with constant 1. Previous algorithms to describe these inner functions have only been Hölder continuous, such as those proposed by Köppen in [7] and Braun and Griebel in [2]. This is problematic, as pointed out by Griebel [5], in that non-smooth functions have very high storage/evaluation complexity, and this makes Kolmogorov's representation (KR) impractical using the standard definition of the inner functions. To date, no one has presented a method to compute a Lipschitz continuous inner function. In this paper, we revisit Kolmogorov's theorem along with Fridman's result. We examine a simple Lipschitz function which appear to satisfy the necessary criteria for Kolmogorov's representation, but fails in the limit. We then present a full solution to the problem, including an algorithm that computes such a Lipschitz function. Copyright © 2017, The Authors. All rights reserved.

关键词： Functions