Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 4 Articles
A novel method which is a combination of wavelet packet transform (WPT),\r\nuninformative variable elimination by partial least squares (UVE-PLS) and simulated\r\nannealing (SA) to extract best variance information among different varieties of lubricants\r\nis presented. A total of 180 samples (60 for each variety) were characterized on the basis of\r\nvisible and short-wave infrared spectroscopy (VIS-SWNIR), and 90 samples (30 for each\r\nvariety) were randomly selected for the calibration set, whereas, the remaining 90 samples\r\n(30 for each variety) were used for the validation set. The spectral data was split into\r\ndifferent frequency bands by WPT, and different frequency bands were obtained. SA was\r\nemployed to look for the best variance band (BVB) among different varieties of lubricants.\r\nIn order to improve prediction precision further, BVB was processed by UVE-PLS and the\r\noptimal cutoff threshold of UVE was found by SA. Finally, five variables were mined, and\r\nwere set as inputs for a least square-support vector machine (LS-SVM) to build the\r\nrecognition model. An optimal model with a correlation coefficient (R) of 0.9850 and root\r\nmean square error of prediction (RMSEP) of 0.0827 was obtained. The overall results\r\nindicated that the method of combining WPT, UVE-PLS and SA was a powerful way to\r\nselect diagnostic information for discrimination among different varieties of lubricating oil,\r\nfurthermore, a more parsimonious and efficient LS-SVM model could be obtained...
Background: Material wear testing is an important technique in the development and\r\nevaluation of materials for use in implant for total knee arthroplasty. Since a knee joint\r\ninduces a complex rolling-gliding movement, standardised material wear testing devices\r\nsuch as Pin-on-Disc or Ring-on-Disc testers are suitable to only a limited extent because\r\nthey generate pure gliding motion only.\r\nMethods: A rolling-gliding wear simulator was thus designed, constructed and\r\nimplemented, which simulates and reproduces the rolling-gliding movement and loading\r\nof the knee joint on specimens of simplified geometry. The technical concept was to run a\r\nbase-plate, representing the tibia plateau, against a pivoted cylindrical counter-body,\r\nrepresenting one femur condyle under an axial load. A rolling movement occurs as a result\r\nof the friction and pure gliding is induced by limiting the rotation of the cylindrical\r\ncounter-body. The set up also enables simplified specimens handling and removal for\r\ngravimetrical wear measurements. Long-term wear tests and gravimetrical wear\r\nmeasurements were carried out on the well known material pairings: cobalt chromepolyethylene,\r\nceramic-polyethylene and ceramic-ceramic, over three million motion cycles\r\nto allow material comparisons to be made.\r\nResults: The observed differences in wear rates between cobalt-chrome on polyethylene\r\nand ceramic on polyethylene pairings were similar to the differences of published data for\r\nexisting material-pairings. Test results on ceramic-ceramic pairings of different frontalplane\r\ngeometry and surface roughness displayed low wear rates and no fracture failures.\r\nConclusions: The presented set up is able to simulate the rolling-gliding movement of the\r\nknee joint, is easy to use, and requires a minimum of user intervention or monitoring. It is\r\nsuitable for long-term testing, and therefore a useful tool for the investigation of new and\r\npromising materials which are of interest for application in knee joint replacement\r\nimplants....
Bio-oil from fast pyrolysis of biomass is a low-grade liquid fuel, which can be\r\nupgraded through the emulsification with diesel oil. In this study, we prepared two rice\r\nhusk bio-oil samples with different solid char contents and three bio-oil/diesel-oil emulsion\r\nsamples with the bio-oil content of 10 wt%, 30 wt% and 50 wt%, respectively. The\r\nlubrication properties of these oil samples were evaluated by a four-ball tester. The\r\nmorphologies of the worn ball surface were observed by scanning electron microscope\r\n(SEM). The chemical states of the elements on the worn surface and non-worn surface\r\nwere analyzed by X-ray photoelectron spectroscope (XPS). The results showed that the\r\nbio-oil possessed better extreme-pressure, anti-wear and friction-reducing properties than\r\nthe commercial diesel oil (number zero). The solid char particles in the bio-oil could\r\nimprove its lubrication performance. Moreover, the lubrication ability of the emulsions\r\nwould be enhanced with the increasing of the bio-oil content in the emulsions...
Impact and friction model of nanofluid for molecular dynamics simulation was built which consists of two Cu\r\nplates and Cu-Ar nanofluid. The Cu-Ar nanofluid model consisted of eight spherical copper nanoparticles with each\r\nparticle diameter of 4 nm and argon atoms as base liquid. The Lennard-Jones potential function was adopted to\r\ndeal with the interactions between atoms. Thus motion states and interaction of nanoparticles at different time\r\nthrough impact and friction process could be obtained and friction mechanism of nanofluids could be analyzed. In\r\nthe friction process, nanoparticles showed motions of rotation and translation, but effected by the interactions of\r\nnanoparticles, the rotation of nanoparticles was trapped during the compression process. In this process,\r\nagglomeration of nanoparticles was very apparent, with the pressure increasing, the phenomenon became more\r\nprominent. The reunited nanoparticles would provide supporting efforts for the whole channel, and in the\r\nmeantime reduced the contact between two friction surfaces, therefore, strengthened lubrication and decreased\r\nfriction. In the condition of overlarge positive pressure, the nanoparticles would be crashed and formed particles\r\non atomic level and strayed in base liquid....
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