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人教版数学七上第三单元第一节是《从算式到方程》,这是学生们比较系统的学习方程的开始.在此之前,学生们已经对方程有初步的认识:会解最简单的方程,会用方程表示简单情境中的数量关系.但当学生遇到实际问题时,学生还是习惯于用他们比较熟悉的算式法来解决,不善于运用方程.因此人教版教材编写者在编写这一部分时,把引导学生认识到方程是更方便、更有力的数学工具,从算式到方程是数学的进步作为教学目标之一. 相似文献
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Microphase Separation of Star-diblock Copolymer Films: a Dissipative Particle Dynamics Simulation 下载免费PDF全文
The microphase-separating behaviors of two types of star-diblock copolymers (Ax)4(By)4 and (AxBy)4 in thin films are studied using the simulation technique of dissipative particle dynamics. A variety of ordered mesostructures have been observed and the simulated phase diagrams show obvious symmetries for the (Ax)4(By)4 films and asymmetries for the (AxBy)4 films, besides, it is easier for the (Ax)4(By)4 than for the (AxBy)4 to carry out microphase separation under the same conditions, which has been recognized in bulk and can be ascribed to the structural difference between the two types of star copolymers. There are some correspondences between the mesostructures formed in the film and those formed in bulk at the same composition fraction. Decreasing the thickness of film and strengthening the A-B repulsion both help the mesostructures enhance the degree of order. Composition fraction dependences of the mean-square radius of gyration in the two types of star copolymer films are almost contrary, which can be attributed to the differences in their respective structures.These findings can provide a guide to designing novel microstructures involving star-diblock copolymers via geometrical confinement. 相似文献
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两性聚电解质溶液的分子热力学模型和分子动力学模拟 总被引:3,自引:3,他引:0
从带电硬球混合物出发采用化学缔合理论建立了聚电解质和两性聚电解质溶液的分子热力学模型.用考虑溶剂的粘滞力和热浴随机力作用的分子动力学(MD)方法模拟了聚电解质和两性聚电解质溶液的渗透系数.对模型预测结果和MD模拟结果进行了比较,表明基于化学缔合理论的分子热力学模型可以用于聚电解质溶液和两性聚电解质溶液热力学性质的预测,对于均聚电解质溶液效果令人满意,对由直径不同的离子构成的聚电解质溶液,模型的预测效果变差,有待进一步改进.该模型对两性聚电解质溶液渗透系数的预测效果比对聚电解质溶液的预测效果更好. 相似文献
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用分子动力学模拟研究了铆接于带电固体壁面上的两性无规共聚电解质链的构型及其随溶剂的介电常数、系统温度和带电壁面电场的变化。结果表明,聚离子链的构型取决于外电场对链节的作用、链内各链节间的静电作用和链节的热运动(温度)三者的综合作用结果。电场强度较低时,铆接聚离子链与非铆接聚离子链的构型变化类似。电场强度较高时,两性聚离子链构型更为舒展。溶剂介电常数减小,链节间静电作用增强,净电荷比较小的中性或非中性两性聚电解质链倾向于收缩,净电荷比较多的链则膨胀。温度的升高一般总是抵消电场和分子内静电作用的影响,当它占主导地位时将使聚离子链膨胀。 相似文献
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