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Fast Implementation of Iterative Reconstruction with Exact Ray-Driven Projector on GPUs

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Tsinghua Science and Technology 2010年第1期15卷 30-35页

作者： Fang Xu Siemens Corporate Research Princeton NJ 08540 USA

Iterative methods are popular choices in image reconstruction fields due to their capability of recovering object information from incomplete acquisition data. However, the computation process involves frequent uses of forward and backward projections that are computationally expensive. Past research has proved that a forward projector that can produce high quality images is crucial to achieve a good convergence rate. In this paper a high performance iterative reconstruction framework is introduced, where two most popular iterative algorithms： Simultaneous Algebraic Reconstruction Technique （SART） and Ordered-subsets Expectation Maximization （OSEM） are supported. The framework utilizes Siddon＇s ray-driven method to generate forward projected images. Benefited from functionalities offered by current generation of graphics processing units （GPUs）, it achieves better performance when compared to previous GPU implementations that use grid-interpolated methods, on top of the significant speedups over CPU-based solutions.

关键词： image reconstruction tomography graphics processing units

Efficient hedging under ambiguity in continuous time

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Probability, Uncertainty and Quantitative Risk 2020年第1期5卷 135-153页

作者： Ludovic Tangpi princeton university Department of Operations Research and Financial EngineeringPrinceton 08540NJUSA

It is well known that the minimal superhedging price of a contingent claim is too high for practical *** a continuous-time model uncertainty framework,we consider a relaxed hedging criterion based on acceptable shortfall *** existing aggregation and convex dual representation theorems,we derive duality results for the minimal price on the set of upper semicontinuous discounted claims.

关键词： Superhedging model ambiguity Acceptance set Risk measure Optimized certainty equivalent Volatility uncertainty

A review of stochastic algorithms with continuous value function approximation and some new approximate policy iteration algorithms for multidimensional continuous applications

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控制理论与应用（英文版） 2011年第3期9卷 336-352页

作者： Warren B.POWELL Department of Operations Research and Financial Engineering Princeton University

We review the literature on approximate dynamic programming,with the goal of better understanding the theory behind practical algorithms for solving dynamic programs with continuous and vector-valued states and actions and complex information *** build on the literature that has addressed the well-known problem of multidimensional(and possibly continuous) states,and the extensive literature on model-free dynamic programming,which also assumes that the expectation in Bellman’s equation cannot be ***,we point out complications that arise when the actions/controls are vector-valued and possibly *** then describe some recent research by the authors on approximate policy iteration algorithms that offer convergence guarantees(with technical assumptions) for both parametric and nonparametric architectures for the value function.

关键词： Approximate dynamic programming Reinforcement learning Optimal control Approximation algorithms

Electromagnetic High Frequency Gyrokinetic Particle-in-Cell Simulation

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Communications in Computational Physics 2008年第8期4卷 575-591页

作者： R.A.Kolesnikov W.W.Lee H.Qin Plasma Physics Laboratory Princeton UniversityP.O.Box 451PrincetonNew Jersey 08543USA

Using the gyrocenter-gauge kinetic theory,an electromagnetic version of the high frequency gyrokinetic numerical algorithm for particle-in-cell simulation has been *** new algorithm,being an alternative to a direct Lorentz-force simulation,offers an efficient way to simulate the dynamics of plasma heating and current drive with radio frequency *** formalism enables separation of gyrocenter and gyrophase motions of a particle in a strong magnetic *** this point of view,a particlemay be viewed as a combination of a slow gyrocenter and a quickly changing Kruskal *** this approach,the nonlinear dynamics of high frequency waves is described by the evolution of Kruskal rings based on first principles *** efficiency of the algorithm is due to the fact that the simulation particles are advanced along the slow gyrocenter orbits,while the Kruskal rings capture fast gyrophase ***,the gyrokinetic formalism allows separation of the cold response from kinetic effects in the current,which allows one to use much smaller number of particles than what is required by a direct Lorentz-force ***,the new algorithm offers the possibility to have particle refinement together with mesh refinement,when *** illustrate the new algorithm,a simulation of the electromagnetic low-hybrid wave propagating in inhomogeneous magnetic field is presented.

关键词： Gyrokinetics magnetized plasmas plasma kinetic equations

Partial Order in Potts Models on the Generalized Decorated Square Lattice

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Chinese Physics Letters 2013年第7期30卷 152-156页

作者： QIN Ming-Pu CHEN Jing CHEN Qiao-Ni XIE Zhi-Yuan KONG Xin ZHAO Hui-Hai Bruce Normand XIANG Tao Institute of Physics Chinese Academy of SciencesBeijing 100190 Department of Chemistry Frick LaboratoryPrinceton UniversityPrincetonNew Jersey 08544USA Department of Physics Renmin University of ChinaBeijing 100872

We explore the Potts model on the generalized decorated square lattice,with both nearest(J1)and next-nearest(J2)neighbor *** the tensor renormalization-group method augmented by higher order singular value decompositions,we calculate the spontaneous magnetization of the Potts model with q=2,3,and *** results for q=2 allow us to benchmark our numerics using the exact *** q=3,we find a highly degenerate ground state with partial order on a single sublattice,but with vanishing entropy per site,and we obtain the phase diagram as a function of the ratio J2/*** is no finite-temperature transition for the q=4 case when J1=J2,whereas the magnetic susceptibility diverges as the temperature goes to zero,showing that the model is critical at T=0.

关键词： solution. degenerate magnetization

A New Semi-Lagrangian Finite Volume Advection Scheme Combines the Best of Both Worlds

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Advances in Atmospheric Sciences 2021年第9期38卷 1608-1609页

作者： Lucas HARRIS NOAA/Geophysical Fluid Dynamics Laboratory Princeton University Forrestal Campus201 Forrestal RoadPrincetonNJ 08540-6649USA

Advection,or transport by wind,is fundamental to numerical weather and climate *** is especially important to solve the equations governing the distribution of heat,moisture,pollutants,and so *** classes of advection schemes have become dominant in recent ***-Lagrangian (SL;Diamantakis,2013) methods form the advection equation in its"Lagrangian"or flow-following form and use the winds (either prescribed or predicted) to trace trajectories backwards from a grid point to their original location on the previous time step.

关键词： prescribed backward Finite

Ultrathin coating of particles in fluidized bed using submicron droplet aerosol

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Particuology 2020年第6期18卷 23-29页

作者： Maksim Mezhericher Christian Rieck Nikolay Razorenov Evangelos Tsotsas Mechanical and Aerospace Engineering Princeton UniversityPrincetonNJ 08544USA Thermal Process Engineering Otto-von-Guericke University39106 MagdeburgGermany Mechanical Engineering Shamoon College of EngineeringBeer Sheva84100Israel

In this work,we demonstrate that particles can be coated in a fluidized bed w让h coating solution provided by a novel aerosol *** droplets are smaller than 1 pim in volume-based diameter,hence they are very much smaller than droplets in conventional spray fluidized bed processes(around 40μm).A proof-of-principle experiment with 30%aqueous coating solution of sodium benzoate and γ-Al2O3 core particles in 150 mm fluidized bed fed with droplet aerosol supplied from the chamber side is *** simultaneously coat and dry the particles,inlet of fluidization air was at 50℃ .Moreover,Monte Carlo simulations of coating with small aerosol and large spray droplets were *** to dramatically smaller building blocks,ultrathin particle coating of high-resolution(very small layer thickness)can be attained with the new aerosol process,with the potential of even going *** coverage of particles is reached substantially faster than in the conv entional process,so that material dema nd is much lower and sensitive materials can be processed in short reside nee *** yield of around 30%was much higher than expected,that is considered to be technically viable and may be enhanced by the recycling of entrained solids or better equipment design.

关键词： Aerosol Fluidized bed Particle Submicron droplet Ultrathin coating

Global sources, emissions, transport and deposition of dust and sand and their effects on the climate and environment： a review

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Frontiers of Environmental Science & Engineering 2017年第1期11卷 35-43页

作者： Feng Wang Xueqiu Zhao Cynthia Gerlein-Safdi Yue Mu Dongfang Wang Qi Lu Institute of Desertification Studies Chinese Academy of Forestry Beijing 100091 China School of Resources and Environment Anhui Agricultural University Hefei 230036 China Department of Civil and Environmental Engineering Princeton University Princeton NJ 08544 USA

Dust and Sand Storms （DSS） originating in deserts in arid and semi-arid regions are events raising global public concern. An important component of atmospheric aerosols, dust aerosols play a key role in climatic and environmental changes at the regional and the global scale. Deserts and semi-deserts are the main source of dust and sand, but regions that undergo vegetation deterioration and desertification due to climate change and human activities also contribute significantly to DSS. Dust aerosols are mainly composed of dust particles with an average diameter of 2 ***, which can be transported over thousands of kilometers. Dust aerosols influence the radiation budget of the earth- atmosphere system by scattering solar short-wave radiation and absorbing surface long-wave radiation. They can also change albedo and rainfall patterns because they can act as cloud condensation nuclei （CCN） or ice nuclei （IN）. Dust deposition is an important source of both marine nutrients and contaminants. Dust aerosols that enter marine ecosystems after long-distance transport influence phytoplankton biomass in the oceans, and thus global climate by altering the amount of CO2 absorbed by phytoplankton. In addition, the carbonates carried by dust aerosols are an important source of carbon for the alkaline carbon pool, which can buffer atmospheric acidity and increase the alkalinity of seawater. DSS have both positive and negative impacts on human society： they can exert adverse impacts on human＇s living environment, but can also contribute to the mitigation of global warming and the reduction of atmospheric acidity.

关键词： Dust and sand storm Climate effects Radiative forcing Cloud condensation nuclei Precipitation Iron fertilizer

NUMERICAL MODELING OF 3-D TURBULENT TWO-PHASE FLOW AND COAL COMBUSTION IN A PULVERIZED-COAL COMBUSTOR

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Acta Mechanica Sinica 1997年第3期13卷 193-202页

作者：周彪吴承康 Department of Mechanical and Aerospace Engineering Princeton UniversityPrincetonNJ 08544USA Combustion Laboratory Institute of MechanicsChinese Academy of SciencesBeijing 100080China

In the present paper, a multifluid model of two-phase flows with pulverized-coal combustion, based on a continuum-trajectory model with reacting particle phase, is developed and employed to simulate the 3-D turbulent two-phase hows and combustion in a new type of pulverized-coal combustor with one primary-air jet placed along the wall of the combustor. The results show that: (1) this continuum-trajectory model with reacting particle phase can be used in practical engineering to qualitatively predict the flame stability, concentrations of gas species, possibilities of slag formation and soot deposition, etc.; (2) large recirculation zones can be created in the combustor, which is favorable to the ignition and flame stabilization.

关键词： numerical simulation pulverized-coal combustor two-phase flow