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Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene(pTFE)

Friction 2024年第5期12卷 997-1015页

作者： pontus JOHANSSON p.MARKLUND M.BJORLING y.SHI Division of Machine Element LuleåUniversity of TechnologyLuleåSE-97187Sweden

Carbon fiber reinforced polytetrafluoroethylene (CF/pTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/pTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/pTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/pTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/pTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm coul

关键词： polymer composite tribofilm tribochemistry atmosphere

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LOCAL MEDIAN ESTIMATION OF VARIANCE FUNCTION

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Acta Mathematica Scientia 2004年第1期24卷 28-38页

作者：杨瑛 W.C.Ip y.K.Kwan p.y.K.Kwan School of Mathematical Sciences Peking University Beijing 100871 China Department of Applied Mathematics The Hong Kong Polgytechnic University Hung Hom Kowloon Hongkong China

This paper considers local median estimation in fixed design regression problems. The proposed method is employed to estimate the median function and the variance function of a heteroscedastic regression model. Strong convergence rates of the proposed estimators are obtained. Simulation results are given to show the performance of the proposed methods.

关键词： Heteroscedasticity nonparametric median regression strong convergence rate variance function local median estimation

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NUMERICAL STUDy ON CREEp DAMAGE OF COMpOSITES AT HIGH TEMpERATURE

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Acta Metallurgica Sinica(English Letters) 2004年第4期17卷 493-497页

作者： y.p.Jiang Z.F.yue School of Mechanics Civil Engineering and Architecture Northwestern Polytechnic University Xi'an710072 ChinaSchool of Mechanics Civil Engineering and Architecture Northwestern Polytechnic University Xi'an710072 China

A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEp has been programmed for ABAQUS. The fiber breakage results in a new crack. The results show that the stress concentration factor resulted from the fiber breakage increases with the creep time. The creep damage takes place near the crack, and then grows in the matrix along a certain angle, up to the total failure. The influences of the ratio of modulus of the fiber to the matrix (Ef/Em) on the creep deformation, damage and stress distributions have been studied. With the increasing Ef/Em, the damage in the matrix increases. Analysis on the different ductility of matrix shows that the creep damage of low ductile matrix composites is higher than high ductile matrix composites.

关键词： composites creep damage unit cell finite element method

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Growth-temperature-dependent optical and acetone detection properties of ZnO thin films

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Journal of Semiconductors 2015年第7期36卷 17-21页

作者： p.S.Shewale y.S.yu Convergence of IT Devices Institute Dong-Eui University Department of Radiological Science Dong-Eui University

Zinc oxide （ZnO） thin films were prepared onto glass substrates at moderately low growth tempera- ture by two-stage spray pyrolysis technique. The effects of growth temperature on structural, optical and acetone detection properties were investigated with X-ray diffractometry, a UV-visible spectrophotometer, photoluminescence （pL） spectroscopy and a homemade gas sensor testing unit, respectively. All the films are polycrystalline with a hexagonal wurtzite phase and exhibit a preferential orientation along [002] direction. The film crystallinity is gradually enhanced with an increase in growth temperature. The optical measurements show that all the films are physically highly transparent with a transmittance greater than 82% in the visible range. The band gap of the film is observed to exhibit a slight red shift with an increasing growth temperature. The pL studies on the films show UV/violet pL band at - 395 nm. Among all the films investigated, the film deposited at 250℃ demonstrates a maximum sensitivity of 13% towards 20 ppm of acetone vapors at 300℃ operating temperature.

关键词： ZnO thin film growth temperature optical acetone sensing properties

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Expression of inducible nitric oxide synthase in human gastric cancer

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World Journal of Gastroenterology 1999年第5期5卷 430-431页

作者： Jun y Fei G Ebert Mp Malfertheiner p Department of Gastroenterology Hepatology and Infectious Diseases University Hospital of Magdeburg Germany

INTRODUCTIONInducible nitric oxide synthase (iNOS) is an enzyme that catalyzes the formation of nitric oxide (NO) from L-arginine. iNOS expression and activity results in the production of high levels of NO[1]. The generation of physiological levels of NO is important for mucosal function and it also exerts a cytoprotective effect on the gastrointestinal mucosa. However, increased iNOS expression has been observed in patients with chronic inflammatory diseases of the gastrointestinal tract, such as ulcerative colitis[2,3], and gastritis[4] and it has been speculated that increased NO may induce DNA damage[5,6] and angiogenesis[7]. Nonetheless, the role of iNOS in human GI neoplasia is largely unkown. previous studies have demonstrated increased iNOS expression in breast cancer[8,9], and increased iNOS activity and protein levels have been demonstrated in colorectal cancer[10] and adenocarcinoma of the esophagus[11]. However, to date, the role of iNOS in gastric carcinogenesis has not been elucidated.

关键词： stomach neoplasms nitric oxide synthase nitric oxide

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Evaluation of carbon-based nanosorbents synthesised by ethylene decomposition on stainless steel substrates as potential sequestrating materials for nickel ions in aqueous solution

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Journal of Environmental Sciences 2012年第9期24卷 1559-1568页

作者： X.J.Lee L.y.Lee L.p.y.Foo D.G.Hassell Department of Chemical and Environmental Engineering University of Nottingham Malaysia CampusJalan Broga43500 SemenyihSelangor Darul EhsanMalaysia.

The present work covers the preparation of carbon-based nanosorbents by ethylene decomposition on stainless steel mesh without the use of external catalyst for the treatment of water containing nickel ions （Ni2＋）. The reaction temperature was varied from 650 to 850℃, while reaction time and ethylene to nitrogen flow ratio were maintained at 30 rain and 1：1 cma/min, respectively. Results show that nanosorbents synthesised at a reaction temperature of 650℃ had the smallest average diameter （75 nm）, largest BET surface area （68.95 m2/g） and least amount of impurity （0.98 wt.% Fe）. A series of batch sorption tests were performed to evaluate the effects of initial pH, initial metal concentration and contact time on Ni2~ removal by the nanosorbents. The equilibrium data fitted well to Freundlich isotherm. The kinetic data were best correlated to a pseudo second-order model indicating that the process was of chemisorption type. Further analysis by the Boyd kinetic model revealed that boundary layer diffusion was the controlling step. This primary study suggests that the prepared material with Freundiich constants compared well with those in the literature, is a promising sorbent for the sequestration of Ni2＋ in aqueous solutions.

关键词： adsorption nanosorbent nickel ions isotherms kinetics

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Assessing temporal variation of coloured dissolved organic matter in the coastal waters of South Eastern Arabian Sea

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Acta Oceanologica Sinica 2020年第1期39卷 102-109页

作者： p Minu V p Souda S K Baliarsingh R M Dwivedi y Ali p M Ashraf ICAR-Central Institute of Fisheries Technology Matsyapuri P.O.Cochin 682029India Indian National Centre for Ocean Information Services(INCOIS) Hyderabad 500090India Department of Geology Aligarh Muslim UniversityAligarh 202001India

Coloured dissolved organic matter(CDOM) plays a major role in marine photochemical and biological processes and its optical properties are known to affect the underwater light penetration. This paper highlights in situ optical estimation and satellite retrieval of CDOM in deciphering its temporal variations in coastal waters of the South Eastern Arabian Sea. The study accentuated the source of CDOM as terrigenous origin during monsoon, of in situ productions during pre-monsoon and during post-monsoon of autochthonous-allocthonous origin. The matchup analysis for in situ and MODIS Aqua retrieved Adg443 exhibited bias which decreased by incorporating the seasonal component. The study also identified degrading bloom of Noctiluca scintillans as the source for exceptionally high CDOM in the area during January and February. The study demands to incorporate seasonal components and phytoplankton abundance while assessing the performance of CDOM algorithms in optically complex coastal waters.

关键词： CDOM absorption chlorophyll MODIS Arabian Sea

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Solving generalized lattice Boltzmann model for 3-D cavity flows using CUDA-GpU

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Science China(physics,Mechanics & Astronomy) 2012年第10期55卷 1894-1904页

作者： LI ChengGong MAA Jerome p.-y KANG HaiGui State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116023China Virginia Institute of'Marine Science College of William and MaryGloucester PointVA 23062USA

The generalized lattice Boltzmann equation(GLBE),with the addition of the standard Smagorinsky subgrid-stress(SGS) model,has been proved that it is more suitable for simulating high Reynolds number turbulent flows when compared with the lattice BGK Boltzmann equation(LBGK).However,the computing efficiency of lattice Boltzmann method(LBM) is too low to make it for practical applications,unless using a massive parallel computing clusters *** this study,the massive parallel computing power from an inexpensive graphic processor unit(GpU) and a typical personal computer has been developed for improving the computing efficiency,more than 100 *** developed three-dimensional(3-D) GLBE-SGS model,with the D3Q19 scheme for simplifying collision and streaming courses,has been successfully used to study 3-D rectangular cavity flows with Reynolds number up to 10000.

关键词： generalized lattice Boltzmann equation (GLBE) subgrid-stress (SGS) D3Q19 3-D rectangular cavity flows GpU

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processing and performance of Alumina Fiber Reinforced Alumina Composites

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Journal of Materials Science & Technology 2003年第4期19卷 337-340页

作者： p.y.Leet T.Uchijima T.yano Research Laboratory for Nuclear Reactors Tokyo Institute of Technology2-12-1O-okayamaMeguro-kuTokyo152-8550JapanResearch Laboratory for Nuclear ReactorsTokyo Institute of Technology2-12-1O-okayamaMeguro-kuTokyo152-8550JapanResearch Laboratory for Nuclear ReactorsTokyo Institute of Technology2-12-1O-okayamaMeguro-kuTokyo152-8550Japan

processing of alumina fiber-reinforced alumina matrix composites by hot-pressing was described. The mechanical properties of the composites fabricated by different sintering conditions including temperature and pressure have been investigated. The results indicated that the higher sintering temperature and pressure corresponded to the higher bulk density and higher maximum strength of the composite, whereas the pseudo-ductility of the composite was lower. The preliminary results of the composite with monazite-coated fibers showed that maximum strength could be improved up to 35% compared with the noncoated fiber composite in the same sintering condition. Moreover, the fracture behavior of the composite changed from completely brittle fracture to non-brittle fracture under the suitable sintering conditions. SEM observation of the fracture surface indicated that the coating worked as a protective barrier and avoided sintering of the fibers together even at high temperature and pressure during densification process.

关键词： Al2O3/Al2O3 composites Mechanical properties Hot-pressing Fiber reinforced composites

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phytotoxicity of cadmium on protein, proline and antioxidant enzyme activities in growing Arachis hypogaea L. seedlings

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Journal of Environmental Sciences 2008年第2期20卷 199-206页

作者： N Dinakar p C Nagajyothi S Suresh y Udaykiran T Damodharam Department of Environmental Sciences Sri Venkateswara UniversityTirupatiAndhra Pradesh-517 502India.

phytotoxicity of cadmium on growing Arachis hypogaea L. seedlings was studied. Seeds were exposed to 25, 50, and 100 μmol/L CdCl2 concentrations, for a period of 10, 15, 20 and 25 d. The extent of damage to chlorophyll, protein, proline, nitrate and nitrite reductase, antioxidant enzyme activity in leaves and roots were evaluated after 10 d of cadmium stress. The higher concentration of cadmium （100 μmol/L） resulted （leaves and roots） total chlorophyll 91.01%, protein 79.51%, 83.61%, nitrate reductase 79.39%, 80.72% and nitrite reductase 77.07%, 75.88% activity decreased with increase in cadmium concentrations and exposure periods. Cadmium caused significant changes in the activity of antioxidative enzymes. Contrastingly Cd treated plant tissues showed an increase in proline 159.87%, 239.6%, gluthion reductase （GR） 337.72%, 306.14%, superoxide disumutase （SOD） 688.56%, 381.72%, ascorbate peroxidase （ApX） 226.47%, 252.14%, peroxidase （pOD） 72.19%, 60.29% and catalase （CAT） 228.96%, 214.74% as compared to control. Cadmium stress caused a significant increase in the rate of SOD activity in leaves and roots of plant species. Results show the crop A. hypogaea is highly sensitive even at very low cadmium concentrations.

关键词： toxicological effects cadmium protein proline antioxidant enzymes

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