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971.
We investigate Bianchi type V cosmological models with bulk viscous fluid source. Exact solutions of the Einstein field equations
are presented via a suitable power law assumption for the Hubble parameter. We show that the corresponding solutions retain
the well established features of the standard cosmology and in addition, are in accordance with recent type Ia supernovae
observations. Some observational parameters for the models have also been discussed. 相似文献
972.
David K. Anthony 《Applied Acoustics》2009,70(9):1219-1225
For a single degree of freedom system, especially with non-light damping, the use of the real spectral part of either the displacement or velocity responses (or the transfer functions based on them) has the advantages of determining the natural frequency (fn) directly, independent of the response parameter, and providing an accurate measurement for damping (ζ). However, this method is sensitive to spectral phase errors due to temporal misalignment of the signal or due to net inter-channel delay differences caused by signal filtering. Two techniques are presented to correct for these errors; one based on the correct temporal alignment of the impulsive part, and the other on the infimum of the imaginary spectral part. These are first demonstrated using a numerical model, and are shown to facilitate the correct measurement of fn and bring ζ within the expected error limits due to quantisation. Secondly, they are applied to an experimental system and are seen to greatly improve the consistency between measurements using different methods. 相似文献
973.
报道了一种高精度测量光纤连接器端面几何参量的自动测量仪。叙述了光纤连接器的端面几何参量的测量原理。由光纤连接器端面形貌和纤芯中心坐标,可以高精度得到曲率半径、顶点偏移量、端面倾斜角和光纤高度等影响连接器性能的关键端面几何参量。该仪器体积小,自动化程度高,用户界面友好,使用方便,可测量物理接触、角度式物理接触等类型的光纤连接器端面几何参量。实际测量证明,该测量仪有很好的重复测量精度。该测量仪与美国Dorc公司ZX-1 mini PMS测量仪和Norland公司NC3000测量仪相比,测量精度水平相当。该仪器样机已通过华东国家计量测试中心的测试。 相似文献
974.
操作参数对PEM燃料电池中水迁移的影响 总被引:4,自引:1,他引:3
质子膜内水分和阴极多孔电极中液态水含量是PEM燃料电池正常运行的控制因素。本文给出了一个用于研究PEM燃料电池内水迁移的稳态、等温、两相流模型。模型耦合了连续方程、动量守恒方程和物质守恒方程,以及水在质子膜中传递方程。运用试验结果验证了模型的有效性。分析模拟结果表明,增大系统操作压力、升高电池操作温度和降低加湿温度将会使质子膜中水的净迁移通量增大;增大操作压力、降低操作温度和升高加湿温度会增加阴极CTL与GDL界面上液态水含量。 相似文献
975.
新型聚合物固体电解质的红外光谱研究 总被引:1,自引:0,他引:1
采用微波热交联技术制备出了多孔状的聚偏氟乙烯 /聚甲基丙烯酸甲酯 (PVDF PMMA)共混的聚合物固体电解质薄膜材料 ,电性能测试表明该固体电解质薄膜在室温下的电导率可达到 2 0 5× 10 - 3S·cm- 1 ,并具有良好的机械性能。用红外光谱对该膜进行了分析 ,结果表明在聚合物固态电解质中的PVDF ,PMMA ,LiClO4 和γ 丁内指 (BL)之间并不是简单的混合 ,而是存在着某种相互作用 ,并且这种作用只有在生成聚合物固态电解质时 ,才明显地得到了加强。 相似文献
976.
977.
978.
979.
Sarmimala Hore Dr. Robert Dinnebier Dr. Wen Wen Johnathan Hanson Joachim Maier 《无机化学与普通化学杂志》2009,635(1):88-93
The temperature dependent (150–290 K) crystal structure of the low‐temperature α‐phase, and high temperature β‐phase, of succinonitrile has been determined by high resolution in situ powder diffraction. The α‐phase has a monoclinic unit cell that contains four gauche molecules and belongs to the P21/a space group. The crystal undergoes a reversible first‐order phase transition at 233 K into the high temperature β‐phase. The lattice parameters increase with temperature and the phase transition leads to an abrupt 6.7 % increase in volume. The β‐phase crystallizes into a bcc‐structure that belongs to the space group. The high temperature phase; however, is a highly disordered plastic crystal at room temperature that contains both gauche and trans molecules. The non‐linearity in the overall isotropic temperature‐factor indicates other possible phase transitions in the temperature range of 233–250 K. 相似文献
980.
A mixture of post-consumer plastic waste (PE/PP/PS/PVC) was pyrolyzed over various catalysts using a fluid catalytic cracking (FCC) process operating isothermally at ambient pressure. Experiments with various catalysts gave good yields of valuable hydrocarbons with differing selectivity in the final products dependent on reaction conditions. A model based on kinetic and mechanistic schemes for the observed products associated with chemical reactions and catalyst deactivation has been developed. The model gives a good representation of experimental results. It is also an improvement on the currently available empirical “lumping” techniques which are usually severely restricted in terms of product definitions. Additionally, this model represents the benefits of product selectivity for the chemical composition in relation to the effect of structurally different catalyst types, and the performance of the reaction temperature used as well as the particle size of the catalyst selected. 相似文献