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991.
Plasma electrolytic oxidation (PEO) is a specialised but well-developed process which has found applications in aerospace, oil/gas, textile, chemical, electrical and biomedical sectors. A novel range of coatings having technologically attractive physical and chemical properties (e.g. wear- and corrosion-resistance) can be produced by suitable control of the electrolyte as well as electrical parameters of the PEO process. Oxide ceramic films, 3 to 40 μm thick, were produced on 6082 aluminium alloy by DC PEO using 5 to 20 A/dm2 current density in KOH electrolyte with varied concentration (0.5 to 2.0 g/l). Phase analysis (composition and crystallite size) was carried out using X-ray diffraction and TEM techniques. Residual stresses associated with the crystalline coating phase (α-Al2O3) were evaluated using the X-ray diffraction Sin2ψ method. Nanoindentation studies were conducted to evaluate the hardness and elastic modulus. SEM, SPM and TEM techniques were utilised to study surface as well as cross-sectional morphology and nano features of the PEO coatings. Correlations between internal stress and coating thickness, surface morphology and phase composition are discussed. It was found that, depending on the current density and electrolyte concentration used, internal direct and shear stresses in DC PEO alumina coatings ranged from − 302 ± 19 MPa to − 714 ± 22 MPa and − 25 ± 12 MPa to − 345 ± 27 MPa, respectively. Regimes of PEO treatment favourable for the production of thicker coatings with minimal stress level, dense morphology and relatively high content of α-Al2O3 phase are identified. 相似文献
992.
Tamar Opher 《The Science of the total environment》2009,407(15):4490-4496
Pollutants accumulated on road pavement during dry periods are washed off the surface with runoff water during rainfall events, presenting a potentially hazardous non-point source of pollution. Estimation of pollutant loads in these runoff waters is required for developing mitigation and management strategies, yet the numerous factors involved and their complex interconnected influences make straightforward assessment impossible. Data-driven models (DDMs) have lately been used in water and environmental research and have shown very good prediction ability. The proposed methodology of a coupled MT-GA (model tree-genetic algorithm) model provides an effective, accurate and easily calibrated predictive model for EMC (event mean concentration) of highway runoff pollutants. The models were trained and verified using a comprehensive data set of runoff events monitored in various highways in California, USA. EMCs of Cr, Pb, Zn, TOC and TSS were modeled, using different combinations of explanatory variables. The models' prediction ability in terms of correlation between predicted and actual values of both training and verification data was mostly higher than previously reported values. Sensitivity analysis was performed to examine the relative significance of each explanatory variable and the models' response to changes in input values. 相似文献
993.
994.
995.
A fabrication process to produce graded porous and skin-core structure propellants via supercritical CO2 concentration profile is reported in this article. It utilizes a partial gas saturation technique to obtain nonequilibrium gas concentration profiles in propellants. Once foamed, the propellant obtains a graded porous or skin-pore structure. This fabrication method was studied with RDX(Hexogen)-based propellant under an SC-CO2 saturation condition. The principle was analyzed and the one-dimensional diffusion model was employed to estimate the gas diffusion coefficient and to predict the gas concentration profiles inside the propellant. Scanning electron microscopy images were used to analyze the effects of partial saturation on the inner structure. The results also suggested that the sorption time and desorption time played an important role in gas profile generation and controlled the inner structure of propellants. 相似文献
996.
界面可移动圆柱形刚性夹杂对SH波散射及动应力集中 总被引:3,自引:0,他引:3
利用Green函数方法求解界面可移动圆柱形刚性夹杂对SH波的散射问题。首先给出了带有半圆柱形刚性夹杂的弹性半空间水平上任一点承受时间谐和的出平面线源荷载作用时的位移解。其次,将此移解答为Green函数,推导界面可移动圆柱形刚性夹杂对SH波散射问题定解积分方程。最后,给出不同介质参数对界面可移动圆柱形刚性夹杂的动应力集中系数的影响。 相似文献
997.
Three types of foam concentration measurement techniques are examined: total fluorine content, optical absorption, and specific conductivity. Specific conductivity was found to be the most useful for field measurements and was therefore compared with the traditional refractive index approach. It was found that electrical conductance provides a more accurate method of estimating the concentration of AFFF solution than does the refractive index technique described in NFPA 11. 相似文献
998.
Elettaria cardamomum is one of the most broadly used spices in Moroccan gastronomy. Its antimicrobial activity against both Gram-positive and Gram-negative bacterial species was demonstrated. Likewise, its toxicity was investigated on Swiss albinos mice. Daily, mice were treated orally with 0.003 and 0.3 mg during 7 days. Plasmatic markers and antioxidant defence systems were assessed and histological alterations were evaluated. A significant increase in creatine phosphokinase level was observed. The microscopic evaluation shows that E. cardamomum induce morphological perturbation in mice’s heart. The results show also an inhibitory effect of glyceraldehyde 3-phosphate dehydrogenase and an important increase in the level of thiobarbituric acid reactive substances, succinate dehydrogenase and catalase activities. Results show that E. cardamomum induces toxicity at 0.3 mg/g mouse and affect energy metabolism and oxidative stress. 相似文献
999.
抽油杆扳手方缺陷应力集中系数和容限 总被引:1,自引:1,他引:0
针对抽油杆扳手方部位经常出现引发断裂的各种缺陷的情况,建立了横向凹槽、平面凹坑和边棱凹坑三组有代表性的缺陷模型,利用平面模型有限元法计算结果及受拉伸无限体和半无限体旋转椭球面空洞和凹坑应力集中系数,求得近、远边界影响修正系数以及三组不同缺陷模型应力集中系数近似表达式。用三维趋势面图描述了这些应力集中系数的变化规律,求得各组缺陷容限方程,绘制了典型的容限图,为带缺陷抽油杆的修复使用和判废提供了理论依据。 相似文献
1000.