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微尺寸梁存在明显尺寸效应,应变梯度理论可以描述这种尺寸效应。该文基于修正偶应力理论,应用双层梁与单层梁的等效关系,给出了双层微梁的动力学模型,具体求解了简支双层微梁的固有频率,并分析了微梁特征尺寸及双材料参数对双层微梁固有特性的影响规律。结果表明,当双层微梁的厚度接近材料内秉特征尺寸参数时,其固有频率值明显大于传统理论下的值;当双层微梁的厚度远大于材料内秉特征尺寸时,其固有频率值与传统理论下的值基本一致。双层微梁无量纲固有频率表现出明显尺寸效应,并随双材料参数的改变表现出一定的差异。当一层梁厚度远大于另一层厚度时,双层微梁可简化为单层微梁。 相似文献
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回顾茅台酒的发展历史,作为一个具有悠久历史的品牌,作为民族酒业的杰出代表,国酒茅台几十年的辉煌业绩让每一个国人为她而骄傲。但它的巨大品牌优势同时也吸引了众多制假、售假者的目光。这些不法之徒大肆制售假茅台,严重侵害了企业和消费者的合法权益。对此,茅台酒厂投入了大量人力、物力、财力,在打假、防伪方面取得了很大的成效。据茅台打假办提供的信息表明,他们每年花在防伪打假上的各种费用达上亿元。总结茅台打假防伪的经验无疑对保护知名品牌是有益的。 相似文献
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Developing an electrically conductive and corrosion-resistant coating is essential for metal bipolar plates of polymer electrolyte membrane fuel cells(PEMFCs). Although enhanced corrosion resistance was seen for Cr coated stainless steel(Cr/SS) bipolar plates, they experience a quick decrease of through-plane electrical conductivity due to the formation of a porous and low-conductive corrosion product layer at the plate surface, thus leading to an increase in interfacial contact resistance(ICR). To tackle this issue, the multilayer Cr coatings were deposited using the magnetron sputtering with a remote inductively coupled oxygen plasma(O-ICP) in the present study. After the O-ICP treatment, a Cr oxide layer(Cr O*) is formed on the specimen surface. The Cr O*/Cr/SS has a remarkably lower stable corrosion rate(iss) than that of the native Cr oxides(Cr On/Cr/SS). Compared with Cr On/Cr/SS, the excellent performance of Cr O*/Cr/SS is attributed to a denser and thicker surface layer of Cr O* with Cr being oxidized to its highest valence state,Cr(VI). More importantly, the through-plane electrical conductivity of the specimens treated by the optimized O-ICP decreases much slowly than Cr On/Cr/SS and thus, the increament of ICR of Cr O*/Cr/SS after the potentiostatic polarization test is considerably smaller than that of Cr On/Cr/SS, which is benefited from the reduced issthat mitigates the deposition of corrosion products and hinders further oxidation of Cr coating. Therefore, Cr O*/Cr/SS proves to be a well balanced trade-off between corrosion resistance and through-plane electrical conductivity. The results of this study demonstrate that O-ICP treatment on a conductive metal coating is an effective strategy to improve the corrosion resistance and suppress the increase of ICR over the long-term polarization. The technique reported herein exhibits its promising potential application in preparing corrosion resistant and electrically conductive coatings on metal bipolar plates to be used in PEMFCs. 相似文献
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公共交通优先发展,不仅体现落实科学发展观的客观要求,也是建设资源节约型、环境友好型社会的重要举措。但孝感市公共交发展存在公交车辆总量不足、公交车辆道路运行难、公交车辆运营调度技术手段和票务方式落后等问题。于是,研究深入调查分析产生这些问题的原因并提出相应的对策与建议,这有其一定的现实指导意义。 相似文献
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食物,是指能够满足人体正常生理和生化能量需求,并能延续正常寿命的物质.食物和水是人每天的必需品品.在满足这个基本需求之后,人类对食物有了更多的需求.除了果脯,美味的食品在人的一生中扮演着越来越重要的作用,例如医疗、社交、改善心情等等.同时,对"美味"生活的追求也衍生出很多与美食有关的趣味话题和知识.
8种改善心情的彩色食物
不同色彩的食物对情绪的影响有所不同,一些颜色食物具有调节和改善心情的作用.例如红色菜肴使人们感到亢奋;面对白色菜肴时,人们会感觉轻松;而黄色能产生令人振奋的效果,刺激大脑活动,让人感受到温暖与舒适等.所以,当你心情不好时,可以尝试吃些有助于调节心情的食物. 相似文献