Surface specific asperity model for prediction of friction in boundary and mixed regimes of lubrication

Machine downsizing, increased loading and better sealing performance have progressively led to thinner lubricant films and an increased chance of direct surface interaction. Consequently, mixed and boundary regimes of lubrication are prevalent with ubiquitous asperity interactions, leading to increased parasitic losses and poor energy inefficiency. Surface topography has become an important consideration as it influences the prevailing regime of lubrication. As a result a plethora of machining processes and surface finishing techniques have emerged. The stochastic nature of the resulting topography determines the separation at which asperity interactions are initiated and ultimately affect the conjunctional load carrying capacity and operational efficiency. The paper presents a procedure for modelling of asperity interactions of real rough surfaces, from measured data, which do not conform to the usually assumed Gaussian distributions. The model is validated experimentally using a bench top reciprocating sliding test rig. The method demonstrates accurate determination of the onset of mixed regime of lubrication. In this manner, realistic predictions are made for load carrying and frictional performance in real applications where commonly used Gaussian distributions can lead to anomalous predictions

A flexible capacitive micromachined ultrasonic transducer (CMUT) array with increased effective capacitance from concave bottom electrodes for ultrasonic imaging applications

2009 IEEE International Ultrasonics Symposium, IUS 2009, Rome, 20-23 September 2009A flexible capacitive micromachined ultrasonic transducer (CMUT) array with increased effective capacitance from concave bottom electrodes is proposed for ultrasonic imaging. A CMUT can transmit and receive ultrasound by vibrating its membrane like a drum. DC bias is applied to bring the membrane closer to the bottom electrode for increasing its sensitivity. However, most of the developed CMUTs have flat bottom electrode, which can not comply with the deflected membrane in a concave surface. Since the capacitance is inverse-proportional to the gap distance between the electrodes, this makes only the 25% central area more sensitive to the capacitance change and the other 75% of the area is considered as parasitic capacitance without coverage of the top electrode. Based on the theoretical analysis, when using concave bottom electrode to reduce the gap distance around the membrane edge, the effective capacitance can increase 10 times comparing with using the flat bottom electrode. The concave bottom electrode is formed on top of the reflowed photoresist in convex spherical shape using over-plating technique. By using the concave bottom electrode to increase the effective area of the membrane, it can increase the effective capacitance to improve the fill factor, output pressure, bandwidth, and sensitivity of the transducer.Department of Mechanical Engineerin

An analysis of Taiwan's energy ecological efficiency and the effectiveness of the Kyoto Protocol

This paper examines and discusses core issues relating to ecological pressure and climate policy performance in Taiwan, given Taiwan's status as a non-signer of the Kyoto Protocol. Taiwan's CO 2 emissions account for 0.9 percent of the world's total, making it the 23rd largest producer of global CO 2 emissions. To better understand Taiwan's performance in energy efficiency, this study calculates Taiwan's energy ecological footprint (EEF) and its ecological debt and eco-energy efficiency (EEE) from 1990 to 2005. These measures are then used in cross-national comparisons of EEF and EEE between Taiwan and Annex 1 and non-Annex-1 countries that have ratified the Kyoto Protocol. In addition, a regional comparison of the same indices is made between Taiwan, Japan and the Republic of Korea. The results suggest that Taiwan would experience a decline in its EEF and an increase in its eco-energy efficiency if it were to sign the Kyoto Protocol and to implement policies for better management of energy resources. Copyright © 2009 John Wiley & Sons, Ltd and ERP Environment.