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Three-dimensional nanoscale reduced-angle ptycho-tomographic imaging with deep learning(RAPID)

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eLight 2023年第1期3卷 198-210页

作者： Ziling Wu Iksung Kang Yudong Yao Yi Jiang Junjing Deng Jeffrey Klug Stefan Vogt George Barbastathis Department of Mechanical Engineering Massachusetts Institute of TechnologyCambridgeMA 02139USA Department of Electrical Engineering and Computer Science Massachusetts Institute of TechnologyCambridgeMA 02139USA Argonne National Laboratory LemontIL 60439USA singapore-MIT alliance for research and Technology(SMART)Centre Singapore 138602Singapore Present Address:singapore-MIT alliance for research and Technology(SMART)Centre Singapore 138602Singapore Present Address:University of California BerkeleyCA 94720USA

X-ray ptychographic tomography is a nondestructive method for three dimensional(3D)imaging with nanometer-sized resolvable *** size of the volume that can be imaged is almost arbitrary,limited only by the penetration depth and the available scanning *** we present a method that rapidly accelerates the imaging operation over a given volume through acquiring a limited set of data via large angular reduction and compensating for the resulting ill-posedness through deeply learned *** proposed 3D reconstruction method“RAPID”relies initially on a subset of the object measured with the nominal number of required illumination angles and treats the reconstructions from the conventional two-step approach as ground *** is then trained to reproduce equal fidelity from much fewer *** training,it performs with similar fidelity on the hitherto unexamined portions of the object,previously not shown during training,with a limited set of *** our experimental demonstration,the nominal number of angles was 349 and the reduced number of angles was 21,resulting in a×140 aggregate speedup over a volume of 4.48×93.18×3.92μm^(3) and with(14 nm)^(3) feature size,i.e.10^(8) ***’s key distinguishing feature over earlier attempts is the incorporation of atrous spatial pyramid pooling modules into the deep neural network framework in an anisotropic *** found that adjusting the atrous rate improves reconstruction fidelity because it expands the convolutional kernels’range to match the physics of multi-slice ptychography without significantly increasing the number of parameters.

关键词： X-ray ptychographic tomography Deep learning Reduced-angle Rapid imaging Atrous spatial pyramid pooling Anisotropic

Road Pricing Design Based on Game Theory and Multi-agent Consensus

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IEEE/CAA Journal of Automatica Sinica 2014年第1期1卷 31-39页

作者： Nan Xiao Xuehe Wang Lihua Xie Tichakorn Wongpiromsarn Emilio Frazzoli Daniela Rus the singapore-MIT alliance for research and Technology Centre the EXQUISITUS Centre for ECity School of Electrical and Electronic Engineering Nanyang Technological University the Ministry of Science and Technology the Massachusetts Institute of Technology

Consensus theory and noncooperative game theory respectively deal with cooperative and noncooperative interactions among multiple players/agents. They provide a natural framework for road pricing design, since each motorist may myopically optimize his or her own utility as a function of road price and collectively communicate with his or her friends and neighbors on traffic situation at the same time. This paper considers the road pricing design by using game theory and consensus theory. For the case where a system supervisor broadcasts information on the overall system to each agent, we present a variant of standard fictitious play called average strategy fictitious play(ASFP) for large-scale repeated congestion *** a weighted running average of all other players actions is assumed to be available to each player. The ASFP reduces the burden of both information gathering and information processing for each player. Compared to the joint strategy fictitious play(JSFP) studied in the literature, the updating process of utility functions for each player is avoided. We prove that there exists at least one pure strategy Nash equilibrium for the congestion game under investigation, and the players actions generated by the ASFP with inertia(players reluctance to change their previous actions) converge to a Nash equilibrium almost surely. For the case without broadcasting, a consensus protocol is introduced for individual agents to estimate the percentage of players choosing each resource, and the convergence property of players action profile is still ensured. The results are applied to road pricing design to achieve socially local optimal trip timing. Simulation results are provided based on the real traffic data for the singapore case study.

关键词： Average strategy fictitious play(ASFP) gametheory multi-agent consensus road pricing

Numerical Studies of Turbulent Flows in Channels with Abrupt Cross-sectional Changes

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南水北调与水利科技 2013年第1期11卷 J0007-J0015页

作者： CHEN Hao-liang LIN Quan-hong Cheong Hin Fatt LIN Peng-zhi singapore-MIT alliance for research and Technology Singapore 138602 Department of Civil & Environmental Engineering National University of Singapore Singapore 117576 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Chengdu 610065 China

The turbulent flows through the channels with abrupt cross-sectional changes are common and importantphysical process in *** a better prediction of the mean flow and turbulent characteristics for this problem,atwo-dimensional depth-averaged numerical model is *** model is robust and accurate in reproducing therecirculation flow behind a groyne and turbulent flows in channels with abrupt cross-sectional changes,when com-pared to the available experimental data of mean velocities and turbulence kinetic *** results reveal that theabrupt cross-sectional change of a channel can affect the flow pattern significantly and introduces the complex turbu-lence *** particular,when the channel has an abrupt expansion,the mean flow pattern is mainly in lon-gitudinal direction with rather small transverse ***,a recirculating region forms behind the expan-sion position and the turbulence has very strong intensity within this *** the flow in the channel with an ab-rupt contraction,the longitudinal component of the flow is decreased by the obstruction on one side and accelerated onthe other side,whereas the transverse velocity is *** turbulence is extraordinarily strong in the regions adja-cent to the contraction wall in the narrow *** both cases of abrupt cross-sectional changes,the TKE is genera-ted dominantly by the shear of the longitudinal velocities.

关键词： turbulent flow open channel abrupt expansion abrupt contraction shallow water equation

An Implementation ofMAC Grid-Based IIM-Stokes Solver for Incompressible Two-Phase Flows

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Communications in Computational Physics 2011年第10期10卷 1333-1362页

作者： Zhijun Tan K.M.Lim B.C.Khoo Guangdong Province Key Laboratory of Computational Science and School of Mathematics and Computational Science Sun Yat-sen UniversityGuangzhou 510275China singapore-MIT alliance 4 Engineering Drive 3National University of SingaporeSingapore 117576Singapore Department ofMechanical Engineering National University of Singapore10 Kent Ridge CrescentSingapore 119260Singapore

*** this paper,a novel implementation of immersed interface method combined with Stokes solver on a MAC staggered grid for solving the steady two-fluid Stokes equations with *** velocity components along the interface are introduced as two augmented variables and the resulting augmented equation is then solved by the GMRES *** augmented variables and/or the forces are related to the jumps in pressure and the jumps in the derivatives of both pressure and velocity,and are interpolated using cubic splines and are then applied to the fluid through the jump *** Stokes equations are discretized on a staggered Cartesian grid via a second order finite difference method and solved by the conjugate gradient *** numerical results show that the overall scheme is second order *** major advantages of the present IIM-Stokes solver are the efficiency and flexibility in terms of types of fluid flow and different boundary *** proposed method avoids solution of the pressure Poisson equation,and comparisons are made to show the advantages of time savings by the present *** generalized two-phase Stokes solver with correction terms has also been applied to incompressible two-phase Navier-Stokes flow.

关键词： Incompressible two-phase Stokes equations two-phaseNavier-Stokes equations discontinuous viscosity singular force immersed interface method Uzawa method front tracking method.

Thermal energy dependent transient permittivity of epsilon-near-zero material

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Science China(Physics,Mechanics & Astronomy) 2022年第8期65卷 96-101页

作者： Heng Wang Lixun Sun Kang Du Wending Zhang SooJin Chua Guixin Li Ting Mei MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions and Shaanxi Key Laboratory of Optical Information TechnologySchool of Physical Science and TechnologyNorthwestern Polytechnical UniversityXi’an710129China Department of Materials Science and Engineering Southern University of Science and TechnologyShenzhen518055China Shenzhen Institute for Quantum Science and Engineering Southern University of Science and TechnologyShenzhen518055China Department of Electrical and Computer Engineering National University of SingaporeSingapore117583Singapore LEES Program Singapore-MIT Alliance for Research&Technology(SMART)Singapore138602Singapore

Transparent conductive oxides exhibit attractive optical nonlinearity with ultrafast response and giant refractive index change near the epsilon-near-zero(ENZ) wavelength, originating from the intraband dynamics of conduction electrons. The optical nonlinearity of ENZ materials has been explained by using the overall-effective-mass and the overall-scattering-time of electrons in the extended Drude model. However, their response to optical excitation is yet the last building block to complete the theory. In this paper, the concept of thermal energy is theoretically proposed to account for the total energy of conduction electrons exceeding their thermal equilibrium value. The time-varying thermal energy is adopted to describe the transient optical response of indium-tin-oxide(ITO), a typical ENZ material. A spectrally-resolved femtosecond pump-probe experiment was conducted to verify our theory. By correlating the thermal energy with the pumping density, both the giant change and the transient response of the permittivity of ITO can be predicted. The results in this work provide a new methodology to describe the transient permittivities of ENZ materials, which will benefit the design of ENZ-based nonlinear photonic devices.

关键词： epsilon-near-zero optical nonlinearity transient response thermal energy hot electron indium tin oxide

Effect of sintering time on the electrochemical properties of spinel LiMn_2O_4 synthesized by solid-state reaction

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Journal of University of Science and Technology Beijing 2008年第1期15卷 74-78页

作者： Tao Li Weihua Qiu Renhua Zhao Hui Xia Hailei Zhao Jingjing Liu Department of Inorganic Nonmetallic Materials School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083. China General research Institute for Nonferrous Metals Beijing 100088 China Advanced Materials for Micro- and Nano- System Singapore-MIT Alliance 4 Engineering Drive 3 Singapore 117576

LiMn2O4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from LitCO3 and electrolytic MnOz at different sintering periods （2, 6, 18, and 32 h）. X-ray diffraction （XRD） patterns of the prepared samples are identified as the spinel structure with a space group of Fd3 m. The lattice parameters almost remain the same as the sintering periods increase. The sample with a sintering period of 32 h shows good cycling performance at both low and nigh current densities, and also elevated temperature. It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples. Different electrochemical measurements were conducted to investigate the electrochemical properties of spinel LiMn204. 2008 University of Science and Technology Beijing. All rights reserved.

关键词： cathode material spinel LiMn204 sintering period microstructure electrochemical properties

Effects of catalyst mass loading on electrocatalytic activity:An example of oxygen evolution reaction

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Fundamental research 2021年第4期1卷 448-452页

作者： Linghui Yu Shengnan Suna Haiyan Li Zhichuan JXu School of Materials Science and Engineering Nanyang Technological UniversityBlock N4.150 Nanyang Avenue639798Singapore singapore-huj alliance for research and Enterprise Campus for Research Excellence and Technological Enterprise(CREATE)NEW-CREATE Phase II138602Singapore Beijing Innovation Center for Engineering Science and Advanced Technology(BIC-ESAT) Beijing Key Laboratory for Magnetoelectric Materials and Devices(BKL-MMD)School of Materials Science and EngineeringCollege of EngineeringPeking UniversityBeijing 100871China Energy research Institute@NTU ERI@NInterdisciplinary Graduate SchoolNanyang Technological University639798Singapore

The evaluation of the intrinsic activity of catalysts is the most basic in searching energy-and cost-efficient catalyst materials for various *** accurate determination of the intrinsic activity is essential for identifying efficient *** a huge number of studies of electrocatalysis for various applications have been reported,the effects of electrode loading on the apparent intrinsic activity obtained experimentally have been rarely *** a high mass loading on the electrode,not all the catalyst surfaces can be electrochemically active because not all the surfaces can be wetted by the *** loading also affects the transport of electrons over the electrode as well as the transport of ions in the electrolyte,and thus affects the *** lead to the derivations of the apparent intrinsic activity from the real intrinsic ***,for better understanding the derivations,we evaluate and discuss the effects of electrode mass loading using oxygen evolution reaction as an example.

关键词： Electrocatalysis Water splitting Oxygen reduction reaction Electrode loading

Simulations of Compressible Two-Medium Flow by Runge-Kutta Discontinuous Galerkin Methods with the Ghost Fluid Method

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Communications in Computational Physics 2008年第2期3卷 479-504页

作者： Jianxian Qiu Tiegang Liu Boo Cheong Khoo Department of Mathematics Nanjing UniversityNanjingJiangsu 210093China Institute of High Performance Computing ♯01−01 The CapricornSingapore Science Park IISingapore 117528Singapore Department of Mathematics Beijing University of Aeronautics and AstronauticsBeijingChina Department of Mechanical Engineering National University of SingaporeSingapore 119260Singapore./Singapore-MIT Alliance4 Engineering Drive 3National University of SingaporeSingapore 117576Singapore.

The original ghost fluid method (GFM) developed in [13] and the modifiedGFM (MGFM) in [26] have provided a simple and yet flexible way to treat twomediumflow problems. The original GFM and MGFM make the material interface"invisible" during computations and the calculations are carried out as for a singlemedium such that its extension to multi-dimensions becomes fairly *** Runge-Kutta discontinuous Galerkin (RKDG) method for solving hyperbolic conservationlaws is a high order accurate finite element method employing the usefulfeatures from high resolution finite volume schemes, such as the exact or approximateRiemann solvers, TVD Runge-Kutta time discretizations, and limiters. In this paper,we investigate using RKDG finite element methods for two-medium flow simulationsin one and two dimensions in which the moving material interfaces is treated via nonconservativemethods based on the original GFM and MGFM. Numerical results forboth gas-gas and gas-water flows are provided to show the characteristic behaviors ofthese combinations.

关键词： Runge-Kutta discontinuous Galerkin method WENO scheme ghost fluid method approximate Riemann problem solver.

Bimetallic MOF derived nickel nanoclusters supported by nitrogendoped carbon for efficient electrocatalytic CO_(2)reduction

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Nano research 2023年第4期16卷 4546-4553页

作者： Haojing Wang Xiaodong Wu Guanyu Liu Shuyang Wu Rong Xu School of Chemical and Biomedical Engineering Nanyang Technological UniversitySingapore 637459Singapore College of Materials Science and Engineering Nanjing Tech UniversityNanjing 210009China Cambridge Centre for Advanced research and Education in singapore(CARES) Singapore 138602Singapore

Utilizing electrocatalytic CO_(2)reduction(ECR)to decrease the carbon footprint has been regarded as a promising ***,we report the synthesis of Ni nanoclusters(NCs)of below 2 nm highly dispersed on N-doped carbon using a Ni/Zn bimetallic metal-organic framework(MOF)*** size and the content of the Ni catalyst can be effectively controlled by varying the Ni:Zn ratio in MOF ***-NH2 group in MOF ligand critically influences the size of Ni catalyst,as well as the property of the carbon *** the optimum ratio of 1:150,Ni NCs with an average size of 1.9 nm anchored on pyridinic N-rich carbon were obtained after MOF *** resultant catalyst exhibits a high Faradaic efficiency for CO(FECO,98.7%)and considerable partial current density for CO(JCO,−40.4 mA·cm^(−2))at−0.88 V versus reversible hydrogen electrode(RHE).Benefiting from the synergistic effect of small Ni clusters and their optimal interaction with the carbon support,the catalyst displays exceptional long-term *** functional theory(DFT)calculations carried out for the three model structures confirm that Ni NCs anchored on N-doped carbon facilitate the easier formation of*COOH intermediate and faster electron transfer rate compared with the large-sized Ni particles represented by Ni(111)and the N-doped carbon without Ni.

关键词： electrochemical CO_(2)reduction metal-organic framework N-doped carbon nanocluster