内啮合弧面凸轮机构及其CAD

根据内啮合弧面凸轮机构的特点 ,基于齐次坐标变换和空间机构的共轭啮合原理 ,推导了内啮合弧面凸轮的轮廓曲面方程和压力角方程 ,利用UG软件的二次开发模块开发了内啮合弧面凸轮的三维CAD软件 ,最后通过实例对软件进行了验证。内啮合弧面凸轮机构可用作高效大转矩的减速装置 ,有很好的应用前景与推广价值。     

Dynamic behavior of cracked pipe conveying fluid with moving mass based on timoshenko beam theory

In this paper we studied about the effect of the open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments i.e. the crack is modeled as a rotational spring. The influences of the crack severity, the position of the crack, the moving mass and its velocity, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the mid-span displacement of the simply supported pipe are depicted.     

啤酒瓶装箱机的运动分析

啤酒瓶装箱机是由平面连杆机构组成 ,为了使其工作可靠和运动平稳 ,采用矩阵法进行运动分析 ,这对装箱机的设计是非常必要的     

Impact of correlation and induced correlation on the estimation of project cost of buildings

Treatment of correlation between variables is necessary for deriving any theoretical distribution of the project cost of buildings. This paper highlights some often ignored theoretical requirements necessary for a rigorous treatment of correlations. The condition for a positive definite correlation matrix is described, along with an analytical procedure and a computer program developed to verify the positive definite condition when correlation coefficients between input variables are estimated using historical data. The analytical procedure and the developed computer program can be used in any application that obtains correlation information from historical data or as subjective judgements to be used in a functional relationship. A new concept called induced correlation is suggested to define and to treat correlation between derived variables that arise from the common (shared) primary variables in their functional forms. A published numerical example is used to highlight the stages where correlation between variables can have an impact on the estimation of moments (estimated expected value and estimated standard deviation) for the project cost of buildings, and to demonstrate the improvement in the estimation of the standard deviation of project cost as a result of treating correlations in risk analysis.     

A functional matrix metalloproteinase (MMP)-9 polymorphism modifies plasma MMP-9 levels in subjects environmentally exposed to mercury

Mercury (Hg) exposure causes health problems including cardiovascular diseases. Although precise mechanisms have not been precisely defined yet, matrix metalloproteinases (MMPs) may be involved. The gene encoding MMP-9 presents genetic polymorphisms which affect the expression and activity level of this enzyme. Two polymorphisms in the promoter region [C^− 1562T and (CA)_n] are functionally relevant, and are implicated in several diseases. This study aimed at examining how these polymorphisms affect the circulating MMP-9 levels and its endogenous inhibitor, the tissue inhibitor of metalloproteinase-1 (TIMP-1) in 266 subjects environmentally exposed to Hg. Blood and plasma Hg concentrations were determined by inductively coupled plasma-mass spectrometry (ICP-MS). MMP-9 and TIMP-1 concentrations were measured in plasma samples by gelatin zymography and ELISA, respectively. Genotypes for the C^− 1562T and the microsatellite (CA)_n polymorphisms were determined. We found a positive association (P < 0.05) between plasma Hg concentrations and MMP-9/TIMP-1 ratio (an index of net MMP-9 activity). When the subjects were divided into tertiles with basis on their plasma Hg concentrations, we found that the (CA)_n polymorphism modified MMP-9 concentrations and MMP-9/TIMP-1 ratio in subjects with the lowest Hg concentrations (first tertile), with the highest MMP-9 levels being found in subjects with genotypes including alleles with 21 or more CA repeats (H alleles) (P < 0.05). Conversely, this polymorphism had no effects on subjects with intermediate or high plasma Hg levels (second and third tertiles, respectively). The C^− 1562T polymorphism had no effects on MMP-9 levels. These findings suggest a significant interaction between the (CA)_n polymorphism and low levels of Hg exposure, possibly increasing the risk of developing diseases in subjects with H alleles.     

低速冲击下复合材料板损伤预测

采用有限元分析方法,对低速冲击下碳纤维复合材料板进行研究。有限元方法中应用了Mind-lin’s薄板理论,采用9结点拉格朗日单元,同时采用无损复合梁本构方程进行动态应力分析。参数分析表明:90°铺层百分比的增加将提高接触压力,即层压板刚度减弱。对每个接触面每个单元的9个高斯点进行应力计算并取平均值。首先,对不同铺层顺序进行阈流速评价以预测基体开裂的起点;然后,通过破坏准则,对高速冲击下产生的破坏,包括基体开裂进行预测。结果显示,基体开裂出现在横向剪应力较大的90°铺层上部。     

土木工程中应用的纤维增强塑料的特性研究

虽然纤维增强塑料(FRP)的性能早已被认识,但本身的一些缺点限制了它作为一种建材的广泛应用。通过近年来广泛的研究,纤维增强塑料在不同的条件下的特性被进一步的了解。介绍了纤维增强塑料(FRP)的应用及组成,总结了常用几种类型的纤维材料和基体材料的力学性能及物理特性。还简要介绍了 FRP 筋的特性,为其工程应用提供一定的借鉴。     

约翰·丹顿的无锡“阳光100”光矩阵会所

澳大利亚DCM建筑设计事务所的约翰丹顿为无锡阳光100国际新城所设计的光矩阵会所以其简洁的形体、纯净的表面材质赋予会所建筑以现代的美感,隐含地方特色与城市个性,矩阵的几何造型体现出设计师对秩序的掌控,反映出建筑师所想表达的建筑必须表现结构,建筑的构造能反映出组成的材料以及它们的组成方式的观点。     

Fluorescence as a potential monitoring tool for recycled water systems: A review

A rapid, highly sensitive and selective detector is urgently required to detect contamination events in recycled water systems - for example, cross-connection events in dual reticulation pipes that recycle advanced treated sewage effluent - as existing technologies, including total organic carbon and conductivity monitoring, cannot always provide the sensitivity required. Fluorescence spectroscopy has been suggested as a potential monitoring tool given its high sensitivity and selectivity. A review of recent literature demonstrates that by monitoring the fluorescence of dissolved organic matter (DOM), the ratios of humic-like (Peak C) and protein-like (Peak T) fluorescence peaks can be used to identify trace sewage contamination in river waters and estuaries, a situation analogous to contamination detection in recycled water systems. Additionally, strong correlations have been shown between Peak T and biochemical oxygen demand (BOD) in rivers, which is indicative of water impacted by microbial activity and therefore of sewage impacted systems. Hence, this review concludes that the sensitive detection of contamination events in recycled water systems may be achieved by monitoring Peak T and/or Peak C fluorescence. However, in such systems, effluent is treated to a high standard resulting in much lower DOM concentrations and the impact of these advanced treatment processes on Peaks T and C fluorescence is largely unknown and requires investigation. This review has highlighted that further work is also required to determine (a) the stability and distinctiveness of recycled water fluorescence in relation to the treatment processes utilised, (b) the impact of matrix effects, particularly the impact of oxidation, (c) calibration issues for online monitoring, and (d) the advanced data analytical techniques required, if any, to improve detection of contamination events.     

寻找环境压力下的有序疏解黄土高原典型生态基质下的城镇化发展模式

黄土高原的环境压力是人类生存的压力, 小流域人居生态单元和生态基质是承载和反映黄土高原人居建设发展和水土流失变化双重压力的载体。压力的疏解是人居建设寻找符合多样的承载空间生态基质秩序的有机疏散或集中的建设模式。并由此提出山地末梢型的生态环抱先决、山地川道型的人居生态串珠和台塬型人居岛状自然环绕三种脆弱自然条件下疏解环境压力的城镇化发展模式。