A dynamic model to predict the occurrence of skidding in wind-turbine bearings

Despite use of the best in current design practices, high-speed shaft (HSS) bearings, in a wind-turbine gearbox, continue to exhibit a high rate of premature failure. As HSS bearings operate under low loads and high speeds, these bearings are prone to skidding. However, most of the existing methods for analyzing skidding are quasi-static in nature and cannot be used to study dynamic operating conditions. This paper proposes a dynamic model, which includes gyroscopic and centrifugal effects, to study the skidding characteristics of angular-contact ball-bearings. Traction forces between rolling-elements and raceways are obtained using elastohydrodynamic (EHD) lubrication theory. Underlying gross-sliding mechanisms for pure axial loads, and combined radial and axial loads are also studied. The proposed model will enable engineers to improve bearing reliability at the design stage, by estimating the amount of skidding. © 2011 Published under licence by IOP Publishing Ltd.

沼泽水牛与摩拉水牛杂种一代精母细胞联合复合体分析

在减数分裂粗线期, 杂种水牛精母细胞中形成22条正常的常染色体SC, 一个 中着丝粒/亚中着丝粒/端着丝粒三价体和XY双价体。表明沼泽水牛和摩拉水牛 的染色体具有高度的同源性, 沼泽水牛1号染色体是由摩拉水牛4号、9 号染色体 串联易位而形成。图版2参12

三种叶猴脊神经丛的比较研究

该文首次报道3种叶猴脊神经丛的组成, 并与其他灵长类作了比较研究. 结果表明: 颈丛由C_(1-4)组成, 多数标本不存在枕小神经和多数标本存在舌下袢; 臂丛由C_(4)-T_(2)组成,形成典型的三干三索结构, 后索形成两个神经袢; 腰骶丛由L_(2-7)和S_(1-2)组成, 存在屈股神经和耻坐股神经, 与猴超科共同特征相一致。

蓝氏贾第虫组蛋白的初步研究

贾第虫存在5种组蛋白, 其在两种不同性质电泳系统中的电泳行为与相应的小牛胸腺组蛋白有近似的对应关系。说明贾第虫的组蛋白已发生了分化, 并已初步形成了性质不同的几个组分, 从而在一定程度上支持核小体组蛋白在真核生物的原核祖先阶段就已产生了分化的假说。

Design methodology for composite structures: A small low air-speed wind turbine blade case study

A small low air-speed wind turbine blade case study is used to demonstrate the effectiveness of a materials and design selection methodology described by Monroy Aceves et al. (2008) [24] for composite structures. The blade structure comprises a shell of uniform thickness and a unidirectional reinforcement. The shell outer geometry is fixed by aerodynamic considerations. A wide range of lay-ups are considered for the shell and reinforcement. Structural analysis is undertaken using the finite element method. Results are incorporated into a database for analysis using material selection software. A graphical selection stage is used to identify the lightest blade meeting appropriate design constraints. The proposed solution satisfies the design requirements and improves on the prototype benchmark by reducing the mass by almost 50%. The flexibility of the selection software in allowing identification of trends in the results and modifications to the selection criteria is demonstrated. Introducing a safety factor of two on the material failure stresses increases the mass by only 11%. The case study demonstrates that the proposed design methodology is useful in preliminary design where a very wide range of cases should be considered using relatively simple analysis. © 2011 Elsevier Ltd.

Gated three-terminal device architecture to eliminate persistent photoconductivity in oxide semiconductor photosensor arrays

The composition of amorphous oxide semiconductors, which are well known for their optical transparency, can be tailored to enhance their absorption and induce photoconductivity for irradiation with green, and shorter wavelength light. In principle, amorphous oxide semiconductor-based thin-film photoconductors could hence be applied as photosensors. However, their photoconductivity persists for hours after illumination has been removed, which severely degrades the response time and the frame rate of oxide-based sensor arrays. We have solved the problem of persistent photoconductivity (PPC) by developing a gated amorphous oxide semiconductor photo thin-film transistor (photo-TFT) that can provide direct control over the position of the Fermi level in the active layer. Applying a short-duration (10 ns) voltage pulse to these devices induces electron accumulation and accelerates their recombination with ionized oxygen vacancy sites, which are thought to cause PPC. We have integrated these photo-TFTs in a transparent active-matrix photosensor array that can be operated at high frame rates and that has potential applications in contact-free interactive displays. © 2012 Macmillan Publishers Limited. All rights reserved.