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Tapping mode atomic force microscope has been applied to observe single-chain PMMAparticles which were stored for six months at room temperature after sprayed from verydilute solutions in good solvents, good/poor mixed solvents, and a theta solvent. Monodis-perse PMMA standards of molecular weights ranging from 7.90×10~4 to 1.3×10~6 wereused to investigate the effect of molecular weight oh the size of the single-chain PMMAparticles. These single-chain particles showed close to spherical shapes. The morphologyof single-chain PMMA particles of a given molecular weight was found to be identical inspite of different solvents used for solution spraying. Molecular weigh dependence of theparticle dimension was also found. The diameters of single-chain PMMA particles aftercorrection of tlp-geometry effect were compared to the values estimated from molecularweight and density. 相似文献
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改进了有限差分格子Boltzmann方法(FDLBM),以直接数值模拟气动噪声.基于LB求解器特性,采用动力学方程中的恒定对流速度以实施高阶迎风差分,提高了声波和湍流的分辨率.通过建立一个新的三维粒子模型,计算得到了任意比热容的三维可压缩Navier-Stokes系统.此外,利用Bhatnagar-Gross-Krook (BGK)碰撞算子,通过引入热流量修正,实现了Prandtl数的可变性.在激波管内弱声波以及伴随有温度梯度的Taylor-Couette层流的验证计算中,提出的新方法结果良好.此外也对NACA0012翼型绕流进行了三维模拟.其中,Reynolds数、Mach数和攻角分别取2× 105,8.75×10-2以及9°.计算发现,在机翼前缘附近的分离气流位置,以及表面压力波动强度的Maeh数依赖性方面,数值计算结果与实验结果相吻合. 相似文献
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The PVC/EBBA ultrathin composite membranes with thickness of about 100 nm were prepared by spreading the solution on water surface. The overlapped composite membrane showed a characteristic aggregation structure in which the polymer matrix exists as a three-dimensional spongy network and the liquid crystal domains werc observed. Tne surface modification for the overlapped membranes was carried out by means of plasma-polymerization with the monomers of fluorocarbon compounds. Both Arrhenius plots of permeability coefficients for oxygen ((?)_O_2) in the membrane samples before and after modification showed significant increase in the vicinity of the T_(KN) of EBBA. 相似文献
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针对高功率微波对毫米波引信的前门耦合效应问题,利用电磁仿真软件对某型毫米波调频连续波引信模型进行辐照试验,并与引信前端限幅电路结合进行联合仿真。在此基础上,继续设计正交试验,对信号参数影响水平进行分析。通过仿真试验发现,在高功率微波信号频率和引信工作频率对准的情况下,辐照场强峰值为60 kV/m时,天线末端耦合电压最大可达188 V;当辐照场强峰值为40 kV/m时,改变辐照信号特征参数,发现长脉宽信号更容易导致限幅器的热击穿效应;信号上升时间会影响天线末端耦合电压波形复杂程度,当信号峰值、脉宽一定时,上升时间为5 ns的输入信号导致的尖峰泄漏电压约为5.94 V,而当上升时间为0.1 ns时,尖峰泄漏电压为18.4 V,并且限幅电路更快达到饱和状态;通过正交试验发现,信号上升时间对尖峰泄漏峰值电压的影响最大,信号峰值对其的影响次之。 相似文献
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Ce3+—高分子络合物发光的激发过程 总被引:1,自引:0,他引:1
本文研究了Ce3+-PMMA及Ce3+—PMA18·C·6两个高分子络合物发光材料的荧光激发过程以及激发过程与高分子结构的关系。通过荧光寿命、荧光光谱以及时间分辨光谱分析表明,在Ce3+—PMMA络合物体系中,Ce3+的荧光发射主要是来自高分子配体的能量传递,而对于Ce3+—PMA18·C·6粉末络合物体系,Ce3+发光的能量主要是来自入射光的直接激发。文章对上述两个稀土高分子络合物的激发机制的差异也做了较为详细地描述。 相似文献
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