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Lubrication of contacting and sliding surfaces in MEMS (microelectromechanical systems) is particularly challenging because of the predominance of suiface forces at the microscale. The current paper explores the possibility of using liquid lubrication in this application. Measurements of friction and lubricant film thickness have been made for liquid lubricants of different viscosities, including low viscosity silicone oil, hexadecane, squalane, and water. Testing was carried out using a newly developed MEMS trihometer in which a rotating silicon disk is loaded against a stationary silicon disk. Two different test setups were used: one where both disks are flat, and the other where the stationary disk is structured as in a thrust pad hearing. In all tests the disks were fully submerged in the lubricant. With the flat-on-patterned disk combination, the variation of friction with rotation speed was found to follow classical Sin beck curves for all the lubricants tested. The friction at high speeds also decreased with increasing normal load, in accordance with hydrodynamic lubrication theory. For the least viscous lub;~icants, it was found that the hydrodynamic friction coefficients remained relatively low even at higher speeds. In particular, for water the friction coefficient for water was around 0.1 at 10,000 rpnl. However, houndaiy friction was found to be unacceptably high at low speeds where there was insufficient lubricant entrainment. The experimental results have been compared with a finite difference solution of Reynolds equation and reasonable agreement is seen between theory and experiment. The results indicate that liquid lubrication is potentially an effective means of lubricating MEMS components with high levels of sliding. [ABSTRACT FROM AUTHOR]

A broad-line region (BLR) disc model is derived and fitted to 121 published broad emission-line profiles from quasistellar objects (QSOs) and Seyfert I galaxies. Keplerian rotation of material in calm circular orbits, plus stimulated non-isotropic emission is best suited to explain the observed profiles. BLR discs in QSOs are, within the framework of the model, found to be tapered and extensive, whereas Seyfert I discs are usually fanned out but equally extensive. The material density in each disc appears to be constant with radius. In QSO emission-line profiles, the peak relative to adjacent continuum intensity increases with increasing logarithm of disc mass or maximum radius, on average. [ABSTRACT FROM AUTHOR]