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Aqueous and mechanical exfoliation, unique properties, and theoretical understanding of MoO3 nanosheets made from free-standing a-MoO3 crystals： Raman mode softening and absorption edge blue shift

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Nano Research 2018年第3期11卷 1193-1203页

作者： Hongfei Liu Yongqing Cai Mingyong Han Shifeng Guo Ming Lin Meng Zhao Yongwei Zhang Dongzhi Chi institute of Materials Research and Engineering (IMRE) A＊STAR (Agency for Science Technology and Research) 2 Eusionopolis Way Singapore 138634 Singapore institute of high performance computing (IHPC) A ＊STAR (Agency for Science Technology and Research) 1 Fusionopolis Way Singapore 138632 Singapore

Crystalline α-MoO3 belts consisting of nanosheets stacked along their [010] axes were synthesized via thermal vapor transport of MoO3 powders at elevated temperatures. The MoO3 belts were millimeters in length along their [001] axes and tens to hundreds of micrometers in width along their [100] axes. Mechanical and aqueous exfoliations of the belts to form two-dimensional （2D） nanosheets were processed via the scotch-tape and bovine serum albumin （BSA） assisted methods, respectively. Upon scotch-tape exfoliation, the Raman features of MoO3 exhibited monotonic decreases in intensity as the thickness was gradually fell to approach that of a 2D nanosheet. Most Raman features eventually disappeared when a monolayer nanosheet was produced, except for the Mo-O-Mo stretching mode （Ag） at - 818 cm^-1, which was accompanied by mode-softening of up to 5 cm^-1 This mode softening, hitherto not reported for 2D α-MoO3 nanosheets, can be attributed to lattice relaxations that are validated here via theoretical density functional perturbation theory calculations. The BSA-assisted exfoliation products exhibited a blueshift in the α-MoO3 nanosheet absorption edge; they also revealed an absorption peak at 3.98 eV that can be attributed to their intrinsic exciton absorptions. These observations, together with the facile synthesis of high-purity α-MoO3 crystals, illuminate the possibility of further 2D α-MoO3 nanosheet production and lattice dynamic studies.

关键词： α-MoO3 two-dimensionalmaterials exfoliations lattice vibrationaldynamics micro-Raman scattering

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Graphene-based thermal modulators

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Nano Research 2015年第8期8卷 2755-2762页

作者： Xiangjun Liu Gang Zhang Yong-Wei Zhang institute of high performance computing A＊STAR Singapore 138632 Singapore

The quest for materials and devices that are capable of controlling heat flux continues to fuel research on thermal controlling devices. In this letter, using molecular dynamics simulations, we demonstrate that a partially clamped singlelayer graphene can serve as a thermal modulator. The mismatch in phonon dispersion between the unclamped and clamped graphene sections results in phonon interface scattering, and the strength of interface scattering is tunable by controlling the clamp-graphene distance via applying the external pressure. Owing to the ultra-thin structure of graphene and its highly sensitive phonon dispersion to external physical interaction, the modulation efficiency--which is defined as the ratio of the highest to lowest heat flux-can reach as high as 150% at a moderate pressure of 50 GPa. This modulation efficiency can be further enhanced by arranging a number of clamps in series along the direction of the heat flux.

关键词： graphene thermal modulator molecular dynamics thermal conductivity phonon dispersion

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Filling the gap: thermal properties and device applications of graphene

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science China(Information sciences) 2021年第4期64卷 103-119页

作者： Rui WU Rui-Zhi ZHU Shi-Hui ZHAO Gang ZHANG He TIAN Tian-Ling REN institute of Microelectronics and Beijing National Research Center for Information science and Technology (BNRist) Tsinghua University institute of high performance computing A*STAR

With the miniaturization and integration of electronic devices, the heat dissipation problems caused by higher power density are getting more serious, limiting the development of integrated circuits industry. Graphene, as a representative of two-dimensional materials, has attracted extensive attention for its excellent thermal properties. Ever since it has been discovered, researches have been carried out and achievements have been made both theoretically and practically. Here, we review the established theories and simulation system for 2D heat conduction, different measurement methods for thermal conductivity and graphene’s device applications. We propose two gaps between different scales and between theoretical prediction and practical effect. Owing to the higher heat dissipation requirements and the endless pursuit of better thermal performance, it is challenging but critical to continue studying and further understand the thermal properties of graphene. Challenges and opportunities are both emphasized. It is hoped that the diversification and progress in morphology and manufacturing technology can bring new development and that graphene can eventually be widely used and make huge changes to micoelectronic industry.

关键词： graphene thermal properties device application thermal conductivity 2D material

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Parallelization of Lattice Boltzmann method using MPI domain decomposition technology for a drop impact on a wetted solid wall

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International Journal of Modeling, Simulation, and Scientific computing 2014年第2期5卷 40-52页

作者： Zhi Shang Ming Cheng Jing Lou institute of high performance computing agency for science Technology and Research(A*STAR)1 Fusionopolis Way#16-16 ConnexisSingapore 138632

Lattice Boltzmann method(LBM)is a new attractive computational approach for simulating isothermal multi-phase flows in computational fluid dynamics(CFD).It is based on the kinetic theory and easy to be *** study aims to analyze the performance of parallel LBM programming for the incompressible two-phase flows at high density and viscosity *** this purpose,a liquid drop impact on a wetted wall with a pre-existing thin film of the same liquid is simulated by using the parallel LBM *** the simulations,the domain decomposition,data communication and parallelization of the LBM code using the message passing interface(MPI)library have been *** computational results show that the parallel LBM code exhibits a good high performance computing(HPC)on the parallel speed-up.

关键词： Dropimpact two-phaseflow Lattice Boltzmann method MPI domain decomposition HPC

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Customisable sound absorption properties of functionally graded metallic foams

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Journal of Materials science & Technology 2022年第13期108卷 196-207页

作者： Jun Wei Chua Xinwei Li Tao Li Beng Wah Chua Xiang Yu Wei Zhai Department of Mechanical Engineering National University of Singapore117575Singapore agency for science Technology and Research(A^(*)STAR)Singapore Institute of Manufacturing Technology138634Singapore agency for science Technology and Research(A^(*)STAR)Engineering MechanicsInstitute of High-Performance Computing1 Fusionopolis Way138632Singapore

In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a *** products have a similar pore morphology as the templates and adjacent layers were successfully sintered together by particle *** absorption experiments on graded metallic foams reveal that the sound absorption at particular frequency ranges can be improved by various permutations of foam *** graded foam of two distinct pore sizes,a mathematical equation was proposed to predict the location of the intersection point of the sound absorption curves,thereby aiding in graded foam *** increase in sound absorption coefficients by resonance-like effects can be introduced before the intersection points by placing the foam layer of smaller pore size nearer to the sound *** sound absorption performances can be further customized when the thickness proportion of the pore sizes is changed and when the number of distinct pore sizes used is *** sound absorption performance at lower frequencies is generally boosted by resonance-like effects when the layer of foam with the largest pore size is placed furthest from the sound *** the same composition of foam with a fixed thickness proportion of pore sizes,one can introduce resonance-like effects to improve the sound absorption performance compared to other permutations while possibly satisfying weight requirements in practical *** study provides valuable insights and mathematical guidelines in the design and manufacturing of functionally graded metallic foam for specific applications.

关键词： Template replication method Functionally graded foam Sound absorption Transfer matrix method Composite metal foam

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Timing-Sequence Testing of Parallel Programs

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Journal of Computer science & Technology 2000年第1期15卷 84-95页

作者：梁煜李舒张辉韩承德 Center of high-performance computing Institute of Computing Technology Chinese Academy of Sciences Beijing P.R. China

Testing of parallel programs involves two parts-testing of controlflow within the processes and testing of timing-sequence. This paper focuses on thelatter, particularly on the timing-sequence of message-passing paradigms. Firstlythe coarse-grained SYN-sequence model is built up to describe the execution of distributed programs. All of the topics discussed in this paper are based on it. Themost direct way to test a program is to run it. A fault-free parallel program shouldbe of both correct computing results and proper SYN-sequence. In order to analyzethe validity of observed SYN-sequence, this paper presents the formal specification(Backus Normal Form) of the valid SYN-sequence. Till now there is little workabout the testing coverage for distributed programs. Calculating the number of thevalid SYN-sequences is the key to coverage problem, while the number of the validSYN-sequences is terribly large and it is very hard to obtain the combination lawamong SYN-events. In order to resolve this problem, this paper proposes an efficienttesting strategy- atomic SYN-event testing, which is to linearize the SYN-sequence(making it only consist of serial atomic SYN-events) first and then test each atomicSYN-event independently. This paper particularly provides the calculating formulaabout the number of the valid SYN-sequences for tree-topology atomic SYN-event(broadcast and combine). Furthermore, the number of valid SYN-sequences also,to some degree, mirrors the testability of parallel programs. Taking tree-topologyatomic SYN-event as an example, this paper demonstrates the testability and communication speed of the tree-topology atomic SYN-event under different numbersof branches in order to achieve a more satisfactory tradeoff between testability andcommunication efficiency.

关键词： timing-sequence testing SYN-sequence atomic SYN-event linearization coverage

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Quantum algorithm and experimental demonstration for the subset sum problem

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science China(Information sciences) 2022年第8期65卷 261-274页

作者： Qilin ZHENG Pingyu ZHU Shichuan XUE Yang WANG Chao WU Xinyao YU Miaomiao YU Yingwen LIU Mingtang DENG Junjie WU Ping XU institute for Quantum Information and State Key Laboratory of high performance computing College of Computer Science and TechnologyNational University of Defense Technology

To solve the subset sum problem, a well-known nondeterministic polynomial-time complete problem that is widely used in encryption and resource scheduling, we propose a feasible quantum algorithm that utilizes fewer qubits to encode and achieves quadratic speedup. Specifically, this algorithm combines an amplitude amplification algorithm with quantum phase estimation, and requires n + t + 1 qubits and O(2(0.5+o(1))n) operations to obtain the solution, where n is the number of elements, and t is the number of qubits used to store the eigenvalues. To verify the performance of the algorithm, we simulate the algorithm with the online quantum simulator of IBM named ibmq simulator using Qiskit and then run it on two IBM quantum computers called ibmq santiago and ibmq bogota. The experimental results indicate that compared with the brute force algorithm, the proposed algorithm results in quadratic acceleration for the problem of a set S with four elements and two subsets whose sum equals target w. Using the iterator twice, we obtain success probabilities of 0.940 ± 0.004, 0.751 ± 0.040, and 0.665 ± 0.060 on the simulator, ibmq santiago, and ibmq bogota, respectively, and the fidelity between the theoretical and experimental quantum states is calculated to be 0.944 ± 0.002, 0.753 ± 0.017, and 0.657 ± 0.028, respectively. If the error rates of the experimental quantum logic gates can be reduced, the success probabilities of the proposed algorithm on real quantum devices can be further improved.

关键词： quantum algorithm subset sum quadratic speedup encryption algorithm complexity

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Unravelling the metal borides evolution in the transient liquid phase bonding of Ni-based alloys via high-throughput transmission electron microscopy and first-principles thermo-kinetic calculations

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Journal of Materials science & Technology 2021年第26期85卷 118-128页

作者： Kewu Bai Ming Lin institute of high performance computing Agency for ScienceTechnology and ResearchFusionopolis Way#16-16 ConnexisSingapore 138632Singapore institute of Materials Research and Engineering(IMRE) Fusionopolis WayInnovis#08-03Singapore 138634Singapore

The understanding of temperature and time-dependent metal borides precipitation/dissolution is crucial for the design of the transient liquid phase(TLP)bonding process of Ni-based *** however remains elusive despite substantial research efforts for many years mainly owing to the uncertainty on the precipitated metal borides and the complex thermo-kinetics in the *** this paper,we have unambiguously constructed the micro/nano scale map of the precipitated metal borides in the TLP bonded Ni-based Inconel 718 superalloy via a high-throughput transmission electron microscopy(TEM)*** types of metal borides were found to precipitate in the diffusion affected zone(DAZ)when the isothermal solidification is *** are the M_(5)B_(3)with stacking faults,Ti-rich M_(3)B4,and Nb-rich M_(3)B4 at the grain boundaries as well as single-crystalline M_(5)B_(3)and M_(3)B2 inside the ***,the crystal structure of the faulted M_(5)B_(3)was rationalized by a hybrid modelling approach integrating firstprinciples calculation and TEM *** sublattice model,with the optimized thermodynamic model parameters,was used to reproduce the metal borides precipitation map in the TLP process using DICTRA *** with multiscale simulation and experimental data,the present work built a modified thermo-kinetic model,which enables the design of the TLP bonding process of Ni-based alloys that often involves complicated time-tempe rature schedules and the precipitation/dissolution of a variety of diffe rent *** strategy can be applied to the design of the brazing process of other alloys or hybrid materials such as ceramics and metal.

关键词： Ni-based superalloy Transmission electron microscopy Transient liquid bonding Precipitation Kinetics

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Resources Allocation Schemas for Web Information Monitoring

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Tsinghua science and Technology 2005年第3期10卷 309-315页

作者：陈康沈美明郑纬民 institute of high performance computing Department of Computer Science and Technology Tsinghua University Beijing 100084 China

The web is an extremely dynamic world where information is updated even every second. A web information monitoring system fetches information from the web continuously and finds changes by compar- ing two versions of the same page. The updating of a specific web page is modeled as a Poisson process with parameter to indicate the change frequency. As the amount of computing resources is limited, it is nec- essary to find some policies for reducing the overall change-detection time. Different allocation schemas are evaluated experimentally to find out which one is the most suitable for the web information monitoring prob- lem. The experimental data shows the runtime characteristics of the overall system performance and the re- lationship to the total amount of resources.

关键词： web information monitoring resources allocation Poisson process response time

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Representation of performance Data in Grid Systems

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Tsinghua science and Technology 2004年第4期9卷 410-415页

作者：时培植李三立 high performance computing institute Department of Computer Science and TechnologyTsinghua University Beijing 100084 China

The increasingly frequent exchange of performance data in grid systems across heterogeneous platforms requires a uniform 搑epresentation?of various types of performance data. This paper reviews the current related research, considers the defect of existing methods, and proposes a new portable description method: grid performance data description (GPDD) using an extensible markup language (XML)-based grid performance data representation language (XGPDRL). GPDD describes the abstract structure, which has excellent extensibility (all types of performance data can be described in one format), efficiency, and flexibil-ity. XGPDRL defines the grammar of the GPDD performance data representation, and is both extensible and portable. For benchmarking purposes, performance data can be collected during runtime, represented in XGPDRL, and analyzed visually using a browser across heterogeneous platforms. GPDD and XGPDRL can conveniently ensure data comprehension across various platforms, and are very suitable for grid per-formance data representation.

关键词： performance tool performance data representation grid

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