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Theory of differential approximations of radiative transfer equation 1

作者： Han, Weimin Eichholz, Joseph A. Sheng, Qiwei Department of Mathematics and Program in Applied Mathematical and Computational Sciences University of Iowa Iowa City IA 52242 United States Department of Mathematics Rose-Hulman Institute of Technology Terre Haute IN 47803 United States

ISBN: (数字)9781461463931

ISBN: (纸本)9781461463924

The radiative transfer equation (RTE) arises in a variety of applications. The equation is challenging to solve numerically for a couple of reasons: high dimensionality, integro-differential form, highly forward-peaked scattering in application. In the literature, various approximations of RTE have been proposed in the literature. In an earlier publication, we explored a family of differential approximations to RTE, to be called RT/DA equations. In this paper, we study the RT/DA equations and investigate numerically the closeness of solutions of the RT/DA equations to that of the RTE. © Springer Science+Business Media New York 2013.

关键词： Radiative transfer

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Chirality-selective transparency induced by lattice resonance in bilayer metasurfaces

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Photonics Research 2021年第4期9卷 484-493页

作者： Shuxia Zhao Lei Shao Jianfang Wang Hai-Qing Lin Wei Zhang Institute of Applied Physics and Computational Mathematics Beijing 100088China Beijing Computational Science Research Center Beijing 100193China Department of Physics The Chinese University of Hong KongShatinHong Kong SARChina

Chiral optical responses of bilayer metasurfaces made of twisted metallic nanorods are investigated in detail with focus on the collective effect due to lattice resonance(LR).Using an analytical approach based on the coupled dipole method(supported by full wave simulation),we find optical chirality is dramatically increased by the coupling between localized surface plasmon resonances and *** collective effect results in significant chiral signal even for metasurfaces made of achiral unit *** interlayer coupling generally destroys the Wood’s anomaly and the associated *** making use of Pancharatnam–Berry(PB)phase and propagation phase,one can modulate the optical activity effectively and achieve chirality-selective transparency induced by LR in a designed structure with a g-factor of absorption as high as 1.99(close to the upper limit of 2).Our studies not only reveal a new mechanism of modulating chiral optical response by combination effects from PB phase,propagation phase,and LR,but also give a quantitative relationship between the geometry configuration and chiral optical properties,thus providing helpful guidance for device design.

关键词： transparency chiral lattice

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Load balancing for multi-physics simulations 21

Load balancing for multi-physics simulations

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21st IEEE International Conference on High Performance Computing and Communications, 17th IEEE International Conference on Smart City and 5th IEEE International Conference on Data Science and Systems, HPCC/SmartCity/DSS 2019

作者： Chen, Chunsen Li, Kenli Liu, Xu Li, Keqin College of Information Science and Engineering Hunan University Changsha China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing China Department of Computer Science State University of New York New York United States

ISBN: (纸本)9781728120584

Multi-physics simulations are usually essential to simplify researches on complex physical phenomena. In this paper, we extend the rectangular partitioning from single-physics simulations to multi-physics simulations. This work presents the Single-rectangle Tightly-coupled algorithm (ST) and Multirectangle Tightly-coupled algorithm (MT) based on rectangular partitioning. The MT algorithm is more flexible and achieves higher load balancing efficiency than the ST algorithm by greedily assigning the remaining unallocated most loaded rectangle to the least loaded processor and assigning k rectangles to each of the processors. To study the effect of machine characteristics on load balancing, the experiments use two types of machine parameters based on Tianhe-2 supercomputer. Inspired by the roofline model, this paper analyzes the relationship among the choice of the load balancing algorithms, the load characteristics of multi-physics application and the features of high performance parallel computer through the comparison experiment of looselycoupled algorithm and tightly-coupled algorithm. In the case of LARED-P, MT algorithm can further reduce the total simulation time compared with the ST algorithm. Through experiments, we show that whether the load balancing algorithm is effective depends on both the load characteristics of multi-physics simulation and the features of high performance parallel computer. © 2019 IEEE.

关键词： Supercomputers

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A new note on spectra of optimal and superoptimal preconditioned matrices

A new note on spectra of optimal and superoptimal preconditi...

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2010 International Conference on Computer Application and System Modeling, ICCASM 2010

作者： Zhang, Li-Tao Huang, Ting-Zhu Cheng, Shao-Hua Gu, Tong-Xiang Department of Mathematics and Physics Zhengzhou Institute of Aeronautical Industry Management Henan China School of Mathematical Sciences University of Electronic Science Technology of China Chengdu China Laboratory of Computationary Physics Institute of Applied Physics and Computational Mathematics Beijing China

ISBN: (纸本)9781424472369

Recently, Cheng et al. [Lin. Alg. Appl. 422 (2007): 482-485] proposed the spectral comparison of optimal preconditioner in Chan [SIAM J. Sci. Statist. Com put. 9 (1988): 766-771] and superoptimal preconditioner in Tyrtyshnikov [SIAM J. Matrix Anal. Appl. 13 (1992): 459-473]. In this paper, based on the work of Cheng et al., we further compare the spectra of optimal and superoptimal preconditioned matrices. © 2010 IEEE.

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Ordering image set to reconstruct 3d models

Ordering image set to reconstruct 3d models

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19th International Conference on Computer Graphics and Vision, GraphiCon'2009

作者： Volegov, Dmitriy B. Yurin, Dmitry V. Moscow Institute of Physics and Technology Department of General and Applied Physics Russia Laboratory of Mathematical Methods of Image Processing Faculty of Computational Mathematics and Cybernetics Moscow Lomonosov State University Russia

The problem of reconstruction of 3d models from unordered image set is considered. To begin a small number of images is processed and initial model is built, then other images are processed and the model is refined. Firstly the problem of image ordering is considered. Secondly the original measure "determinacy of fundamental matrix" is introduced. This measure allows easily to estimate the precision of reconstruction without actually doing it. The results for real and synthetic sequences are presented.

关键词： Image reconstruction

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Performance Optimization of Ratchet Upconversion Devices 5th

Performance Optimization of Ratchet Upconversion Devices

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5th China and International Young Scientist Terahertz Conference, YTHZ 2024

作者： Han, Shangjie Yan, Jieyun Bai, Peng Yang, Ning Chu, Weidong Xie, Yan Wang, Yingxin Meng, Chen Zhao, Ziran Beijing University of Posts and Telecommunications Beijing100876 China Institute of Applied Physics and Computational Mathematics Beijing100088 China Department of Engineering Physics Tsinghua University Beijing100084 China

ISBN: (纸本)9789819739127

Semiconductor upconversion devices have important applications in biological imaging, solar photovoltaic efficiency enhancement, and future interstellar travel. Existing semiconductor upconversion devices face problems such as limited detection range and low upconversion efficiency. We propose a novel upconversion device based on ratchet detectors, achieving ultra-wideband semiconductor upconversion (4–200 THz to NIR), but the upconversion efficiency needs further improvement. In this paper, we use an optimized LED structure to optimize the performance of the ratchet upconversion device. We focus on studying the electroluminescence efficiency, emission spectrum, and emission uniformity of the LED. This work clarifies the principles of performance optimization and provides a direction for future improvement of upconversion devices. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.

关键词： Emission spectroscopy

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An Iterative Thresholding Method for the Minimum Compliance Problem

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Communications in computational physics 2023年第4期33卷 1189-1216页

作者： Luyu Cen Wei Hu Dong Wang Xiaoping Wang Department of Mathematics Hong Kong University of Science and TechnologyClear Water BayKowloonHong KongChina The Program in Applied and Computational Mathematics Princeton UniversityPrincetonNew JerseyUSA School of Science and Engineering The Chinese University of Hong KongShenzhenGuangdong 518172China Shenzhen International Center for Industrial and Applied Mathematics Shenzhen Research Institute of Big DataGuangdong 518172China

In this paper,we propose a simple energy decaying iterative thresholding algorithm to solve the two-phase minimum compliance *** material domain is implicitly represented by its characteristic function,and the problem is formulated into a minimization problem by the principle of minimum complementary *** prove that the energy is decreasing in each *** effective continuation schemes are proposed to avoid trapping into the local *** results on 2D isotropic linear material demonstrate the effectiveness of the proposed methods.

关键词： Minimum compliance convolution thresholding linear elasticity

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Comparative study on atomic ionization in bicircular laser fields by length and velocity gauges S-matrix theory

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Chinese physics B 2020年第2期29卷 254-261页

作者： Hong Xia Xin-Yan Jia Xiao-Lei Hao Li Guo Dai-He Fan Gen-Bai Chu Jing Chen School of Physical Science and Technology Southwest Jiaotong UniversityChengdu 610031China Institute of Theoretical Physics and Department of Physics Shanxi UniversityTaiyuan 030006China State Key Laboratory for Quantum Optics and Center for Cold Atom Physics Shanghai Institute of Optics and Fine MechanicsChinese Academy of SciencesShanghai 201800China Science and Technology on Plasma Physics Laboratory Laser Fusion Research CenterChina Academy of Engineering PhysicsMianyang 621900China HEDPS Center for Applied Physics and TechnologyPeking UniversityBeijing 100871China Institute of Applied Physics and Computational Mathematics Beijing 100088China

Ionization of atoms in counter-rotating and co-rotating bicircular laser fields is studied using the S-matrix theory in both length and velocity *** show that for both the bicircular fields,ionization rates are enhanced when the two circularly polarized lights have comparable *** addition,the curves of ionization rate versus the field amplitude ratio of the two colors for counter-rotating and co-rotating fields coincide with each other in the length gauge case at the total laser intensity 5×10^14 W/cm^2,which agrees with the experimental ***,the degree of the coincidence between the ionization rate curves of the two bicircular fields decreases with the increasing field amplitude ratio and decreasing total laser *** the help of the ADK theory,the above characteristics of the ionization rate curves can be well interpreted,which is related to the transition from the tunneling to multiphoton ionization mechanism.

关键词： above-threshold ionization(ATI) bicircular laser fields length gauge velocity gauge S-matrix theory

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Elasticity and acoustic velocities of δ−AlOOH at extreme conditions: A methodology assessment

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Physical Review Materials 2024年第10期8卷 103601页

作者： Chenxing Luo (罗晨星) Yang Sun (孙阳) Renata M. Wentzcovitch Department of Applied Physics and Applied Mathematics Department of Physics Department of Earth and Environmental Sciences Lamont–Doherty Earth Observatory Data Science Institute Center for Computational Quantum Physics

Hydrous phases play a fundamental role in the deep-water cycle on Earth. Understanding their stability and thermoelastic properties is essential for constraining their abundance using seismic tomography. However, determining their elastic properties at extreme conditions is notoriously challenging. The challenges stem from the complex behavior of hydrogen bonds under high pressures and temperatures (P,Ts). In this study, we evaluate how advanced molecular dynamics simulation techniques can address these challenges by investigating the adiabatic elasticity and acoustic velocities of δ−AlOOH, a critical and prototypical high-pressure hydrous phase. We compared the performances of three methods to assess their viability and accuracy. The thermoelastic tensor was computed up to 140 GPa and temperatures up to 2700 K using molecular dynamics with a DeePMD machine-learning interatomic potential based on the SCAN meta-GGA functional. The excellent agreement with ambient condition single-crystal ultrasound measurements and the correct description of velocity changes induced by H-bond disorder-symmetrization transition observed at 10 GPa in Brillouin scattering measurements underscores the accuracy and efficacy of our approach.

关键词： Elasticity Geophysics High-pressure studies Hydrogen bonds Disordered systems Minerals Molecular dynamics

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Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime

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Particuology 2022年第8期20卷 8-17页

作者： Kaiyuan Wang Pei Wang Suyuan Yu Institute of Applied Physics and Computational Mathematics Bejing 100094.China Center forCombustionEergy.Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energyand PowerEngineeringTsinghua UniversityBejing 100084.China Smoore International Holdings Ltd.Shenzhen 518102 China

In many energy and combustion *** experience large temperature gradients,which can affect the coagulation process due to *** study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size *** theoretical derivations are based on the kinetictheory forthe free-molecular regime and the harmonic mean method for the transition *** coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor,The enhancement factor represents the coagulationrate enhancement induced by thermophoresis and is a function of specific dimensionless *** on the enhancement factor,the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle *** results show that thermophoretic enhancement effects are ignorable in the free-molecular regime,but need to be considered in the continuum regime and the transition *** addition,the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas *** present study can improve understanding ofthermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

关键词： Thermophoresis Brownian coagulation Enhancement factor Knudsen number

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