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程守洙等编写的“普通物理学”对运动叠加原理是这样叙述的: “根据类似的无数的客观事实,可以得到这样一个结论:任何一个方向的运动,都不会因为任何另外一个方向的运动是否存在而受到影响,也就是说,一个运动可以看成几个各自独立进行的运动叠加而成。这个结论称为运动的独立性原理,或运动叠加原理。这一原理是物理学中普遍原理之一。”(1) 这段话的含意是:在同样力场的条件下,各个方向的运动是互相独立的。例如在水平抛体抛出后,垂直方向的下落不会受到水平方向的运动的影响。实验证明了水平抛体和自由落体同一时刻从同一高度抛出则同时落… 相似文献
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The high deposition of microcrystalline silicon thin film by very high frequency plasma enhanced
chemical vapour deposition and the fabrication of solar cells 下载免费PDF全文
This paper reports that the intrinsic microcrystalline silicon ($\mu
$c-Si:H) films are prepared with plasma enhanced chemical vapour
deposition from silane/hydrogen mixtures at 200\du\ with the aim to
increase the deposition rate. An increase of the deposition rate to
0.88\,nm/s is obtained by using a plasma excitation frequency of
75\,MHz. This increase is obtained by the combination of a higher
deposition pressure, an increased silane concentration, and higher
discharge powers. In addition, the transient behaviour, which can
decrease the film crystallinity, could be prevented by filling the
background gas with Hchemical vapour deposition,
plasma deposition, solar cells, crystallinity Program supported by the State Key
Development Program for Basic Research of China (Grant No
2006CB202601), and Basic Research Project of Henan Province in China
(Grant No 072300410140). 7280N, 7830G, 8115H This paper reports that the intrinsic microcrystalline silicon ($\mu
$c-Si:H) films are prepared with plasma enhanced chemical vapour
deposition from silane/hydrogen mixtures at 200\du\ with the aim to
increase the deposition rate. An increase of the deposition rate to
0.88\,nm/s is obtained by using a plasma excitation frequency of
75\,MHz. This increase is obtained by the combination of a higher
deposition pressure, an increased silane concentration, and higher
discharge powers. In addition, the transient behaviour, which can
decrease the film crystallinity, could be prevented by filling the
background gas with Hchemical vapour deposition,
plasma deposition, solar cells, crystallinity Program supported by the State Key
Development Program for Basic Research of China (Grant No
2006CB202601), and Basic Research Project of Henan Province in China
(Grant No 072300410140). 7280N, 7830G, 8115H This paper reports that the intrinsic microcrystalline silicon ($\mu
$c-Si:H) films are prepared with plasma enhanced chemical vapour
deposition from silane/hydrogen mixtures at 200\du\ with the aim to
increase the deposition rate. An increase of the deposition rate to
0.88\,nm/s is obtained by using a plasma excitation frequency of
75\,MHz. This increase is obtained by the combination of a higher
deposition pressure, an increased silane concentration, and higher
discharge powers. In addition, the transient behaviour, which can
decrease the film crystallinity, could be prevented by filling the
background gas with Hchemical vapour deposition,
plasma deposition, solar cells, crystallinity Program supported by the State Key
Development Program for Basic Research of China (Grant No
2006CB202601), and Basic Research Project of Henan Province in China
(Grant No 072300410140). 7280N, 7830G, 8115H This paper reports that the intrinsic microcrystalline silicon ($\mu
$c-Si:H) films are prepared with plasma enhanced chemical vapour
deposition from silane/hydrogen mixtures at 200\du\ with the aim to
increase the deposition rate. An increase of the deposition rate to
0.88\,nm/s is obtained by using a plasma excitation frequency of
75\,MHz. This increase is obtained by the combination of a higher
deposition pressure, an increased silane concentration, and higher
discharge powers. In addition, the transient behaviour, which can
decrease the film crystallinity, could be prevented by filling the
background gas with Hchemical vapour deposition,
plasma deposition, solar cells, crystallinity Program supported by the State Key
Development Program for Basic Research of China (Grant No
2006CB202601), and Basic Research Project of Henan Province in China
(Grant No 072300410140). 7280N, 7830G, 8115H This paper reports that the intrinsic microcrystalline silicon ($\mu
$c-Si:H) films are prepared with plasma enhanced chemical vapour
deposition from silane/hydrogen mixtures at 200\du\ with the aim to
increase the deposition rate. An increase of the deposition rate to
0.88\,nm/s is obtained by using a plasma excitation frequency of
75\,MHz. This increase is obtained by the combination of a higher
deposition pressure, an increased silane concentration, and higher
discharge powers. In addition, the transient behaviour, which can
decrease the film crystallinity, could be prevented by filling the
background gas with H$_{2}$ prior to plasma ignition, and selecting
proper discharging time after silane flow injection. Material
prepared under these conditions at a deposition rate of 0.78\,nm/s
maintains higher crystallinity and fine electronic properties. By
H-plasma treatment before i-layer deposition, single junction $\mu
$c-Si:H solar cells with 5.5{\%} efficiency are fabricated. 相似文献
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针对太阳能甲醇重整制氢系统的数值研究,以往受限于网格划分和计算资源,多采用假设均匀的多孔介质模型,但难以准确描述微观结构下的多组分热-质传输和化学反应过程。本文结合催化剂颗粒床模型和多孔介质模型各自优势,建立了基于实际催化剂颗粒床孔隙率分布的太阳能甲醇重整制氢系统三维综合数值模型,并将计算结果与传统模型进行对比,发现孔隙率分布对系统性能有着较大的影响,而本文所建的基于实际孔隙率分布的模型更接近于系统真实情况。基于此,本文进一步考察了催化剂颗粒尺寸和运行参数对整个系统流动传热和化学反应综合性能的影响规律。 相似文献
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甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注. 贵金属 Pt 是甲醇燃料电池阳极催化剂不可缺少的活性组分, 但 Pt 价格昂贵, 易与 CO 等中间体强相互作用而中毒失活, 从而限制了甲醇燃料电池的广泛应用. 因此, 如何提高Pt 的利用率成为一个关键问题. 研究表明, 在碳材料载体中掺杂氮元素, 改变了载体本身的表面结构和电子性质, 有利于Pt 颗粒的成核和生长, 可获得尺寸小、分布均匀的 Pt 纳米颗粒, 能显著提升催化反应活性和 Pt 利用率. 然而, 传统的氮掺杂方法需要在高温、高压及氨气条件下进行, 增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术, 能够在原子级别精确控制膜的厚度, 既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰. 本课题组利用原子层沉积技术优势, 首先在碳纳米管表面沉积了直径 2 nm 左右的 Pt纳米颗粒, 然后在 Pt 纳米颗粒外表面超薄修饰聚酰亚胺膜, 通过后处理得到多孔掺氮碳膜修饰的 Pt/CNTs 催化剂. 碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制. 结果表明, 适当厚度的碳膜修饰 Pt/CNTs 催化剂可显著提升其甲醇电氧化性能, 电流密度可达商业 20% Pt/C 的 2.7 倍, 催化剂稳定性也显著改善. 然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现, 超薄修饰碳膜后催化剂活性表面积有所降低, 这是由于碳膜的覆盖导致表面 Pt原子数减少. 修饰前后催化剂颗粒尺度变化不大, 推测催化剂活性的提高与形成了有利于催化反应的 Pt-碳膜界面有关.然而, 当碳膜修饰层过厚时, 会导致反应物分子难以扩散到 Pt 颗粒表面, 使催化剂活性降低. 预吸附单层 CO 溶出实验结果表明, 多孔掺氮碳膜超薄修饰 Pt/CNTs 催化剂后, CO 氧化峰的起始电位和峰值电位都向低电位处偏移, 这表明 Pt 表面吸附的 CO 在较低电位下即可被氧化, CO 更容易从 Pt 表面移除, 从而提高了催化剂的抗 CO 毒化能力. X 射线光电子能谱实验结果进一步表明, 经多孔掺氮碳膜修饰后, Pt 的 4f 电子向高结合能处偏移, 表明 Pt 原子周围的电子密度减小, 从而弱化了 Pt 对 CO 吸附的σ-π键反馈作用, 即减弱了 Pt 原子对 CO 的吸附, 这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因. 相似文献
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用磁控溅射法在玻璃衬底上制备了掺铝氧化锌(AZO)薄膜,然后用脉冲式快速光热处火(PRTP)法对样品进行了600~800℃的退火处理.采用X射线衍射仪(XRD)、分光光度计、四探针等测试手段对AZO薄膜的结晶性能、透光率和导电性能进行了表征.结果表明:(1)薄膜退火后透光率基本维持在退火前(82~92;)的水平,而电阻率则由10-4Ω·cm 上升了1到6个数量级,已丧失了"导电膜"意义;(2)样品具有好的结构性能有利于提高样品的导电性能.对此现象进行了理论分析. 相似文献
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纺织结构复合材料冲击拉伸研究进展 总被引:2,自引:0,他引:2
纺织结构复合材料是以纺织结构作为增强体的一类复合材料, 其在一系列实际应用时往往要承受着高速冲击拉伸、冲击压缩等冲击载荷(冲击加载) 的作用. 因为纺织结构的整体性能, 纺织结构复合材料具有优异的抗冲击、抗分层与高损伤容限性能. 研究复合材料的冲击性能对于纺织结构复合材料的设计与应用具有指导作用. 本文详细介绍了纺织结构复合材料的发展, 纺织结构的种类及纺织结构复合材料的冲击拉伸性能实验与有限元分析研究情况, 同时也分析了纺织结构复合材料冲击拉伸破坏下的破坏机理研究进展, 并对纺织结构复合材料冲击拉伸性能研究的发展进行了展望. 相似文献
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本文建立了线性菲涅尔式太阳能吸热/反应器光热–化学反应过程三维数值模型,并对其缩小模型进行了研究,探究了典型的外部因素(太阳能热流分布)和内部因素(催化剂颗粒半径)对系统流动换热与热化学反应综合性能的影响。首先,基于离散元法建立了催化剂颗粒随机堆积床模型。其次,基于蒙特卡罗光线追迹法与多目标优化遗传算法获得了太阳能热流分布。然后,对比了优化前的、优化后的以及理想情况下的系统综合性能,进一步分析了催化剂颗粒半径的影响。研究发现,热流优化后的系统化学反应性能接近于理想,而减小颗粒半径也可促进化学反应,但会增加流动阻力。催化剂颗粒大小的优选或可综合考虑反应程度、流动阻力和烧结温度限制等进行权衡选取。 相似文献