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Multi-scale analysis of subgrid stress and energy dissipation in turbulent channel flow

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Acta Mechanica Sinica 2010年第1期26卷 81-90页

作者： chun-Xiao xu School of Aerospace Tsinghua University 100084 Beijing China

In present study, the subgrid scale （SGS） stress and dissipation for multiscale formulation of large eddy simulation are analyzed using the data of turbulent channel flow at Ret = 180 obtained by direct numerical simulation. It is found that the small scale SGS stress is much smaller than the large scale SGS stress for all the stress components. The dominant contributor to large scale SGS stress is the cross stress between small scale and subgrid scale motions, while the cross stress between large scale and subgrid scale motions make major contributions to small scale SGS stress. The energy transfer from resolved large scales to subgrid scales is mainly caused by SGS Reynolds stress, while that between resolved small scales and subgrid scales are mainly due to the cross stress. The multiscale formulation of SGS models are evaluated a priori, and it is found that the small- small model is superior to other variants in terms of SGS dissipation.

关键词： SGS stress SGS dissipation - Multi-scale energy transfer Multi-scale SGS model - Turbulent channel flow

ECC-Based RFID Authentication Protocol

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Journal of Electronic Science and Technology 2020年第4期18卷 320-329页

作者： Xing-chun Yang chun-Xiang xu Chao-Rong Li Department of Computer Science and Technology Sichuan Police CollegeLuzhou 646000 School of Computer Science and Engineering University of Electronic Science and Technology of ChinaChengdu 611731 Department of Computer Science and Information Engineering Yibin UniversityYibin 644000

The radio frequency identification(RFID)technology has been widely used so far in industrial and commercial *** develop the RFID tags that support elliptic curve cryptography(ECC),we propose a scalable and mutual authentication protocol based on *** also suggest a tag privacy model that provides adversaries exhibiting strong abilities to attack a tag’s *** prove that the proposed protocol preserves privacy under the privacy model and that it meets general security *** with other recent ECCbased RFID authentication protocols,our protocol provides tag privacy and performs the best under comprehensive evaluation of tag privacy,tag computation cost,and communications cost.

关键词： Elliptic curve cryptography radio frequency identification(RFID) authentication protocol privacy

In-situ evaluation for corrosion process at fusion boundary of stainless steel strip overlay joints in H2S containing solution

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中国有色金属学会会刊：英文版 2004年第Z1期14卷 413-419页

作者： ZOU Yang PAN chun-xu FU Qiang Department of Physics & Center for Electron Microscopy Wuhan University Wuhan 430063 China Department of Physics & Center for Electron Microscopy Wuhan University Wuhan 430063 China Department of Physics & Center for Nano-Science and Technology Wuhan University Wuhan 430063 China

The present work studied the corrosion properties around the fusion boundaries of 2.25Cr-1Mo steel with stainless steel strip overlay joints under as welded condition and after post-weld heat treatment (PWHT) in H2 S containing solution (NACE TM-01-77 standard) with different time. An in-situ observation method was introduced for evaluating corrosive progress in the fusion boundary in H2 S containing solution, that is, the samples were marked firstly at the boundary and then treated in the solution for variant time. Each time after the corrosion treatment, the observations were kept to focus at the same marked area by using scanning electron microscopy (SEM) to observe the corrosion progress. The results reveal that the fusion boundary is the worst region for corrosion resistance when comparing with other boundaries, and a broad fusion boundary has a stronger resistance for "hydrogen induced disbonding" than a narrow one.

关键词： dissimilar steel welding fusion boundary H2S corrosion post-weld heat treatment

Crystal structure determination of a chimeric FabF by XRD

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Nuclear Science and Techniques 2017年第9期28卷 63-68页

作者： Ke Li Li Li Ye-chun xu College of Science Shanghai University CAS Key Laboratory of Receptor Research Drug Discovery and Design Center Shanghai Institute of Materia MedicaChinese Academy of Sciences (CAS)

Beta-ketoacyl-acyl-carrier-protein synthase Ⅱ,an important enzyme in biosynthesis of bacterial fatty acid,is an attractive target in antibacterial drug design. Platensimycin(PTM), produced by Streptomyces platensis, has a strong, broad-spectrum Gram-positive antibacterial activity by selectively targeting to Fab F but exhibits no inhibition to the Fab F from Streptomyces platensis(spFabF). To study the self-resistance mechanism within the PTM-producing strain and provide hint for development of novel antibiotics, it is imperative to solve the structure of spFabF and elucidate the difference between spFabF and other Fab Fs which are not resistant to PTM. To this end, we constructed four chimeric Fab Fs based on the sequence of spFabF and its homologous protein after the expression of wide-type spFabF was failed. The crystal structure of one chimera, js_(200)FabF, of 91.2% sequence identity to spFabF,was solved. A structure comparison of js_(200)FabF with a PTM-bound Fab F suggested that three loops nearby the catalytic site might play key roles in preventing the binding of PTM to spFabF. The results provide an encouraging basis for further studies on the self-resistance mechanismand structure-based design of novel antibiotics targeting FabFs.

关键词：晶体结构嵌合体 XRD 广谱抗菌活性测定药物设计生产菌株 PTM

Block dual Toeplitz Operators on the Orthogonal Complements of Fock Spaces

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Acta Mathematica Sinica,English Series 2024年第8期40卷 1967-1988页

作者： Jian Xiang DONG chun xu xu Yu Feng LU School of Mathematical Sciences Dalian University of TechnologyDalian 116024P.R.China School of Mathematics and Information Science Guangzhou UniversityGuangzhou 510006P.R.China

In this paper,we characterize the boundedness and compactness of the block dual Toeplitz operators acting on the orthogonal complement of the Fock spaces,and the compactness of the finite sum of two dual Toeplitz oper... 详细信息

关键词： Block dual Toeplitz operators boundedness compactness Fock space (semi)-commutator

Effect of Tube Spinning With Subsequent Heat-Treatment on Performance and Microstructure Evolution of T250 Maraging Steel

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Journal of Iron and Steel Research International 2012年第5期19卷 63-68页

作者： HU Zheng-fei WANG chun-xu School of Material Science and Engineering Tongji UniversityShanghai 200092China China Iron and Steel Institute Group Beijing 100081China

The effects of spinning deformation and subsequent heat treatments on the mechanical properties and microstructure of 18Ni Co-free Maraging steel （T250） tube were evaluated comparatively with the perform. An obvious radial shrinkage is detected in spun tubes after heat treatment and the magnitude of the shrinkage induced by solution treatment is almost the same as that by aging. Plastic deformation during spinning elongated the grains severely in the direction of metal flow. The solution treatment resulted in a drastically refined grain and recrystallised microstructure, removing the effect of plastic deformation, relieving the tangential residual stress and strain and improving hardness. Subsequent aging obtained a tempered microstructure, enhancing hardness values strikingly for precipitation strengthening. XRD （X-ray diffraction） analysis indicated that the reversed austenite formed in a plate-like along the grain boundaries and the volume fraction of austenite in spun tube was more than double that in the preform. These results imply that the residual stress and stain induced by spinning process and reversed austenite forming during aging might have the similar contribution to the radical shrinkage.

关键词： maraging steel spinning process plastic deformation heat-treatment microstructure reversed austenite

Loss of fragile histidine triad protein expression in inflammatory bowel disease

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World Journal of Gastroenterology 2006年第45期12卷 7355-7360页

作者： chun-Mei xu Chuan-Hu Qiao Department of Gastrocnterology Xiangfan No.1 Hospital 75 Jiefang Road Xiangfan 441000 Hubei Province China

AIM： To investigate the expression of fragile histidine triad （FHIT） protein in 64 patients with ulcerative colitis （UC） and Crohn＇s disease （CD）, and its relation with clinicopathological data. METHODS： Rabbit-anti-FHIT antibody was used to detect FHIT protein expression in 64 formalin-fixed, paraffin-embedded tissue specimens of inflammatory bowel disease （IBD） by citrate-microwave-streptavidin （SP）-HRP immunohistochemical method. RESULTS： The positive FHIT protein expression was 22.79% ± 16.16%, 42.14% ± 16.82% in active and remittent phases of UC, 36.07% ± 19.23% in CD, and 57.05% ±8.86% in normal colon mucosa. Statistically significant differences in FHIT protein expression were observed between the active and remittent phases of UC, between the active phase of UC and normal colon mucosa, as well as between the remittent phase of UC and normal colon mucosa, and between CD and normal colon mucosa. CONCLUSION： Our results show that FHIT protein expression is completely absent or reduced in IBD, suggesting that the FHIT gene might be associated with the oncogenesis and progression of IBD, an early event from inflammatory conditions to carcinoma in IBD.

关键词： Fragile histidine triad protein expression Ulcerative colitis Crohn's disease Inflammatory bowel disease

Numerical Analysis of Nd:YAG Pulsed Laser Polishing CVD Self-standing Diamond Film

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Chinese Journal of Mechanical Engineering 2013年第1期26卷 121-127页

作者： xu Feng HU Haifeng ZUO Dunwen xu chun QING Zhenghua WANG Min College of Mechanical and Electrical Engineering Nanjing University of Aeronautics and Astronautics Jiangsu Key Laboratory of Precision and Micro Machining Nanjing University of Aeronautics and Astronautics

Chemical vapor deposited （CVD） diamond film has broad application foreground in high-tech fields. But polycrystalline CVD self-standing diamond thick film has rough surface and non-uniform thickness that adversely affect its extensive applications. Laser polishing is a useful method to smooth self-standing diamond film. At present, attentions have been focused on experimental research on laser polishing, but the revealing of theoretical model and the forecast of polishing process are vacant. The paper presents a finite element model to simulate and analyze the mechanism of laser polishing diamond based on laser thermal conduction theory. The experimental investigation is also carried out on Nd：YAG pulsed laser smoothing diamond thick film. The simulation results have good accordance with the results of experimental results. The temperature and thermal stress fields are investigated at different incidence angles and parameters of Nd：YAG pulsed laser. The pyramidal-like roughness of diamond thick film leads to the non-homogeneous temperature fields. The temperature at the peak of diamond film is much higher than that in the valley, which leads to the smoothing of diamond thick film. The effect of laser parameters on the surface roughness and thickness of graphite transition layer is also carried out. The results show that high power density laser makes the diamond surface rapid heating, evaporation and sublimation after its graphitization. It is also found that the good polish quality of diamond thick film can be obtained by a combination of large incident angle, moderate laser pulsed energy, large repetition rate and moderate laser pulse width. The results obtained here provide the theoretical basis for laser polishing diamond film with high efficiency and high quality.

关键词： chemical vapor deposition self-standing diamond film polishing pulsed laser finite element surface roughness

Context Processing in Contextual and Cued Fear Extinction

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Neuroscience Bulletin 2024年第6期40卷 835-839页

作者： Yimu Zhang chun xu Yu Gu State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science Institutes of Brain ScienceFudan UniversityShanghai200032China Institute of Neuroscience State Key Laboratory of NeuroscienceCenter for Excellence in Brain Science and Intelligence TechnologyChinese Academy of SciencesShanghai200031China

Anxiety disorders such as post-traumatic stress disorder(PTSD)are prevalent mental disorders that disturb millions *** disorders often manifest as excessive fear,anxiety,and distress,significantly impacting daily *** fear extinction paradigms in animals were established decades ago and have been widely used in research,providing a scientific basis for exposure therapies for anxiety disorders in humans.

关键词： distress disorders traumatic