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Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects

Physical Review E 2017年第1期96卷 013201-013201页

作者： W.-M. Wang P. Gibbon Z.-M. Sheng Y.-T. Li J. Zhang Beijing National Laboratory for Condensed Matter Physics Institute of Physics CAS Beijing 100190 China Beijing Advanced Innovation Center for Imaging Technology Department of Physics Capital Normal University Beijing 100048 China IFSA Collaborative Innovation Center Shanghai Jiao Tong University Shanghai 200240 China Forschungzentrum Jülich GmbH Institute for Advanced Simulation Jülich Supercomputing Centre D-52425 Jülich Germany Centre for Mathematical Plasma Astrophysics Katholieke Universiteit Leuven B-3000 Leuven Belgium SUPA Department of Physics University of Strathclyde Glasgow G4 0NG United Kingdom Key Laboratory for Laser Plasmas (MoE) and Department of Physics and Astronomy Shanghai Jiao Tong University Shanghai 200240 China School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 China

We investigate how next-generation laser pulses at 10–200PW interact with a solid target in the presence of a relativistically underdense preplasma produced by amplified spontaneous emission (ASE). Laser hole boring and relativistic transparency are strongly restrained due to the generation of electron-positron pairs and γ-ray photons via quantum electrodynamics (QED) processes. A pair plasma with a density above the initial preplasma density is formed, counteracting the electron-free channel produced by hole boring. This pair-dominated plasma can block laser transport and trigger an avalanchelike QED cascade, efficiently transferring the laser energy to the photons. This renders a 1−μm scale-length, underdense preplasma completely opaque to laser pulses at this power level. The QED-induced opacity therefore sets much higher contrast requirements for such a pulse in solid-target experiments than expected by classical plasma physics. Our simulations show, for example, that proton acceleration from the rear of a solid with a preplasma would be strongly impaired.

关键词： High intensity laser-plasma interactions laboratory plasma Near-critical & underdense plasmas Particle-in-cell methods

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Anti-controlling pitchfork bifurcation on Poincaré map of a three-degree-of-freedom vibro-impact system

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Zhendong yu Chongji/Journal of Vibration and Shock 2016年第20期35卷 24-29页

作者： Wu, Xin Xu, Huidong Wen, Guilin Wei, Kexiang School of Mechanical Engineering Hunan Institute of Engineering Xiangtan411104 China Key Laboratory of Advanced Design and Simulation Techniques for Special Equipment of Education Ministry Hunan University Changsha410082 China College of Mechanics Taiyuan University of Technology Taiyuan030024 China

In the premise of not changing periodic solutions of the original system and with considering the difficulties that are given by the implicit Poincaré map of the vibro-impact system, anti-control of Pitchfork bifurcation on Poincaré map of a three-degree-of-freedom vibro-impact system was studied by using the linear feedback control method. Firstly, the six-dimensional Poincaré map of a close-loop system was established. To overcome the difficulty that the numerical computing method can only be used to determine control gains on the basis of the classical critical criteria of Pitchfork bifurcation described by the properties of eigenvalues in the six-dimensional map, an explicit pitchfork critical criterion without using eigenvalues was used to obtain the controlling parameters area of two parameters. Then, the stability of the pitchfork bifurcation was further analyzed by utilizing the center manifold and normal formal theory. Finally, the numerical experiments verify that the stable pitchfork bifurcation solutions can be generated at arbitrary specified parameters. © 2016, Editorial Office of Journal of Vibration and Shock. All right reserved.

关键词： Degrees of freedom (mechanics)

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GPS Nonstationary Interference Suppression based on Sparse Representation

GPS Nonstationary Interference Suppression based on Sparse R...

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2016 IEEE 13th International Conference on Signal Processing（ICSP2016）

作者： Yanlei Zhao Shupeng Wang Baoguo Yu Wenyi Wang Qingrong Du Renbiao Wu State Key Laboratory of Satellite Navigation System and Equipment Technology The 54th research institute of CETC Tianjin Key Lab for Advanced Signal Processing Civil Aviation University of China

For GPS(Global Position System) receivers, the nonstationary interferences may result from rapid relative motion between interference and GPS receiver, a change in the number of interferences and impulse interference, etc. The conventional interference suppression algorithms based on covariance matrix are ineffective with nonstationary interferences. By utilizing the sparse representation, a new kind of nonstationary interference suppression algorithm is proposed in this letter. In particular,a greedy sparse interference space reconstruction algorithm is utilized to directly estimate the received interferences instead of DOA(Direction of Arrival) estimation. The interferences are suppressed by subtracting the estimated interferences for every snapshot without covariance matrix estimation. There are two typical advantages:(1) the proposed algorithms do not require the number of interferences;(2) the proposed algorithms are robust for both DOA separation of interferences and grid mismatch of sparse representation. The simulated results demonstrate the effectiveness of the proposed algorithms.

关键词： Global Position System nonstationary interference sparse representation covariance matrix estimation

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Robust superhydrophobic surface on Al substrate with durability, corrosion resistance and ice-phobicity

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Scientific reports 2016年第1期6卷 20933页

作者： Guoyong Wang Shuai Liu Sufeng Wei Yan Liu Jianshe Lian Qing Jiang Key Laboratory of Automobile Materials Department of Materials Science and Engineering Jilin University No. 5988 Renmin Street Changchun 130025 PR China. Key Laboratory of Advanced Structural Materials Changchun University of Technology Changchun 130012 P.R. China. Key Laboratory of Bionic Engineering (Ministry of Education) and State Key Laboratory of Automotive Simulation and Control Jilin University Changchun 130022 China.

Practical application of superhydrophobic surfaces is limited by the fragility of nanoscale asperities. Combining chemical etching and anodization, microscale pits and nanoscale pores, instead of the micro and nano protrusions on traditional superhydrophobic surfaces mimicking Lutos leaves, were fabricated on commercially pure aluminum surfaces. After modified by FDTS, the surfaces were superhydrophobic and self-cleaning. The ultrahigh hardness and electrochemical stability of Al2O3 coating endowed the surface excellent mechanical durability and good corrosion resistance. Because the method is scalable, it may find practical application on body panels of automobiles and aircrafts and so on.

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Grain Refinement of CrCoNi Multi-principal-element Alloy

Grain Refinement of CrCoNi Multi-principal-element Alloy

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第十三届全国铸造年会暨2016中国铸造活动周

作者： Liu Xinwang Guillaume Laplanche AleksANDer Kostka Suzana G.Fries Janine Pfetzing-Micklich Liu Gang Fan Zitian Easo P.George Department of Materials Design Ruhr-University Bochum State Key Laboratory of Materials Processing and Die & Mould Technology Huazhong University of Science and Technology Interdisciplinary Centre for Advanced Materials Simulation Ruhr-University Bochum

The equiatomic multi-principal-element alloy, CrCoNi, as a single-phase FCC solid solution, displays excellent strength-toughness properties that exceed those of all high entropy alloys, which is considered as a promising engineering alloy at cryogenic temperatures. Cast, as a common-used method to form complex-shaped components, is a necessary technique for engineering alloys, whereas the cast multi-principal-element alloys have not be systematically investigated previously. Here we study the grain refinement of cast CrCoNi alloy and their corresponding mechanical properties. The alloys were produced by arc melting and drop casting, which are much simpler than the preparation procedures of deformed alloys by cold deformation and recrystallization in the previous studies. The cast CrCoNi alloy consists with anisotropic coarse columnar grains with the average width of more than 210 m. Their microstructures, however, become equiaxed grains after grain modification which exhibit uniform fine equiaxed grains with the size of 76 m nearly throughout the entire ingots. The tensile tests at an engineering strain rate of 10-3 s-1 reveals that yield strength, ultimate tensile strength and elongation to fracture are all improved by grain refinement both at 293 and 77 K. Meanwhile, the cast alloy shows the comparable mechanical properties with the alloys after cold working and recrystallization. The corresponding mechanism was also discussed related to the constitutional supercooling.

关键词： multi-principal-element alloy grain refinement microstructures tensile properties

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Mold-Filling Ability of Aluminum Alloy Melt during the Two-Step Foaming Process

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Journal of Materials Science & technology 2016年第6期32卷 509-514页

作者： Wang H Zhang M Zhou B C Yang D H Wu Y Liu X J Lu Z P University of Science and Technology Beijing State Key Laboratory for Advanced Metals and Materials Beijing 100083 Department of Aviation and Military Transportation Airforce Logistics College of PLA Xuzhou 221000 College of Mechanics and Materials Hohai University Nanjing 210098

For the two-step foaming method, one of the most cost-effective ways to fabricate three-dimensional shaped aluminum alloy foams with dense outer surface skin, it is crucial to describe and predict the moldfilling behavior of the shaped aluminum alloy foams with a favorable pore-distribution accurately. In this paper, a mold-filling model for semi-solid aluminum alloy foams was initially established and subsequently employed to predict the filling height, which represents the mold-filling ability of semi-solid aluminum alloy foams in a specially designed tube-like mold. Our results indicate that the proposed model can be applied to characterize the mold-filling property of aluminum alloy melts in a quantitative manner. Theoretically, our findings actually provide a guideline for mass-production of the shaped aluminum alloy foams by using the two-step foaming process.

关键词： Mould-filling Aluminum alloy Semi-solid metal forming

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Irradiation treatment of pharmaceutical and personal care products (PPCPs) in water and wastewater: An overview

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Radiation Physics and Chemistry 2016年 125卷 56-64页

作者： Jianlong Wang Libing Chu Collaborative Innovation Center for Advanced Nuclear Energy Technology INET Tsinghua University Beijing 100084 PR China Beijing Key Laboratory of Radioactive Waste Treatment Tsinghua University Beijing 100084 PR China State Key Joint Laboratory of Environment Simulation and Pollution Control Tsinghua University Beijing 100084 PR China

Pharmaceutical and personal care products (PPCPs), especially the pharmaceutically active compounds (PhACs) such as antibiotics and hormones have attracted great concerns worldwide for their persistence and potential threat to ecosystem and public health. This paper presents an overview on the ionizing irradiation-induced degradation of PPCPs in aqueous solution. Parameters that affect PPCPs degradation, such as the absorbed dose, solution pH, dose rate, water matrices and the presence of some inorganic ions and humic acid are evaluated. The mechanism and pathways of radiolytic degradation of PPCPs are reviewed. In many cases, PPCPs such as antibiotics and X-ray contrast agent could be removed completely by radiation, but a higher absorbed dose was needed for their mineralization and toxicity reduction. The combination of ionizing irradiation with other methods such as H 2 O 2 , ozonation and TiO 2 nanoparticles could improve the degradation efficacy and reduce the cost. Ionizing irradiation is a promising alternative for degradation of PPCPs in aqueous solution.

关键词： Irradiation Radiolysis PPCPs PhACs Pharmaceutical Antibiotics

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Characteristic of Electron Density of Coaxial Dielectric Barrier Discharge of CH4/Air Mixture

Characteristic of Electron Density of Coaxial Dielectric Bar...

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2016 4th International Conference on Machinery,Materials and Information technology Applications(ICMMITA 2016)

作者： CHEN Lei FENG Chao LONG Wuqiang SONG Peng WU Qianqian Institute of Internal Combustion Engine Dalian University of Technology Liaoning Key Laboratory of Advanced Measurement and Test Technology for Aviation Propulsion System Shenyang Aerospace University College of Mechanical and Electronic Engineering Dalian Nationalities University

Numerical study of dielectric barrier discharge of CH4/air mixture were carried out by employing a coaxial cylindrical electrode with diameter of 10 mm under the condition of the discharge voltage of 6000 V. The influence of electrode structure parameter and equivalence ratio on electron density were analyzed. The result shows that the electron density which increases with the decrease of the distance from the cathode has a quick increase at the small position near the cathode(0.05～0.4mm), and the maximum value of electron density appears at the position of 0.1mm. The electron density has no obvious change with the equivalence ratio, it is benefit to the lean combustion of natural gas application.

关键词： Non-equilibrium plasma Dielectric barrier discharge Electron density

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Effect of Equivalence Ratio on Particle Variation of CH4/Air Mixture of Coaxial Dielectric Barrier Discharge

Effect of Equivalence Ratio on Particle Variation of CH4/Air...

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2016 4th International Conference on Machinery,Materials and Information technology Applications(ICMMITA 2016)

The effect of equivalence ratio on particle components of dielectric barrier discharge of CH/air mixture were carried out by employing a coaxial cylindrical electrode. The result shows that molar fraction of active particles such as H, O, CH and NO decrease slightly with the equivalence ratio, however, enough active particles could be obtained even at the smallest equivalence ratio conditions;no obvious change in the electron density with the equivalence ratio has been obtained, which has a very beneficial effect on the methane-air combustion reaction under the conditions of low equivalence ratio.

关键词： Dielectric barrier discharge Non equilibrium plasma Active particles Equivalence ratio

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Space-charge effect of the time-varying electron injection in a diode: classical and relativistic regimes

arXiv

引用

arXiv 2017年

作者： Liu, Yangjié Tang, Qi Wu, Biyi Faculty of Physics and Electronic Science Hubei University Hubei Collaboration Innovation Centre for Advanced Organic Chemical Materials Hubei Key Laboratory of Ferro & Piezoelectric Materials and Devices WuhanHubei Province430062 China Antennas Group School of Electrical Engineering and Computer Science Queen Mary University of London E1 4NS Mile End East London United Kingdom Department of Mathematical Sciences Rensselaer Polytechnic Institute United States Center for Electromagnetic Simulation Beijing Institute of Technology Haidian District Beijing China

Conventionally, space-charge (SC) limited current density is defined as the maximal current density allowed to traverse a diode under a DC voltage when a time-invariant flow is injected from the cathode. In this work, we study the SC limited current density under a time-varying injection for both classical and relativistic regimes and determine the maximal amount of limited current density under certain conditions. Our simulations show that it is unlikely that a time-varying injection emitted from cathode exceeds the known SC limits, in either classical or relativistic regime. Copyright © 2017, The Authors. All rights reserved.

关键词： Current density

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