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861.
In general, biological organisms have the ability to absorb a specific element selectively. Holcombe and his co-workers reported that copper, nickel and cobalt could be separated from riverine and sea-water samples and cadmium from river water samples by unicellular green algae and were determined by slurry GFAAS. Dar- 相似文献
862.
Joung Sook Hong Yong Kyung Kim Kyung Hyun Ahn Seung Jong Lee Chongyoup Kim 《Rheologica Acta》2007,46(4):469-478
We investigated the effect of organically modified nanoclay (organoclay) on immiscible polymer blends [polybutylene terephthalate
(PBT)/polyethylene (PE)] with a special focus on the role of clay as a compatibilizer. When organoclay (Nanofil 919; Sud-Chemie,
Inc.) is added to the blend, the clay first locates at the interface and then selectively locates in the PBT phase due to
its affinity with PBT. This results in effective size reduction and narrowed size distribution of the dispersed phase. However,
with a small amount of organoclay, it is observed that the clay locates at the interface regardless of its affinity for a
specific component to minimize the chemical potential. The interfacial tension change of the blend with the addition of organoclay
was quantitatively predicted from extensional force measurement. When the blend is subjected to an extension, the interfacial
tension functions as a resistance against drop deformation. When we added organoclay to the blend, the extensional force was
significantly reduced, which means that the contribution of the interfacial tension to the total force is reduced. For a 10/90
PBT/PE blend, the interfacial tension was reduced from 5.76 to 0.14 cN m−1 when 1 wt% of organoclay was added. This interfacial tension reduction arises from the localization of the organoclay at
the interface and its nonhomogeneous distribution along the interface, suppressing the coalescence between the droplets, which
is a role of a compatibilizer. Conclusively, the immiscible polymer blends can be compatibilized with organoclay. The organoclay
changes the blend morphology by interfacial tension reduction due to the localization of the organoclay at the interface and
by the viscosity ratio change due to the selective localization by its affinity to a specific component in the blend. 相似文献
863.
864.
阵列天线是77 GHz毫米波雷达的核心硬件之一,其天线性能决定着雷达的探测能力。由于工作频率的升高以及毫米波雷达小型化、集成化的发展趋势,使得雷达阵列天线阵元间距过密,从而相互干扰出现强互耦效应,严重恶化雷达阵列天线的性能。为了解决上述问题,本文提出了一种基于77 GHz毫米波雷达接收天线的周期性条形阵列解耦结构优化方法。该方法通过优化周期性条形阵列解耦结构单元的条形厚度和间距,在保证阵列天线辐射性能的基础上,来抑制毫米波雷达接收天线阵元间的互耦并提高其阵元间的隔离度。仿真结果表明,相比于无解耦结构的阵列天线,提出的解耦结构能够有效地降低毫米波雷达接收天线间的耦合,尤其在中心频率77.75 GHz处互耦减少了13.29 dB。在施加周期性条形阵列解耦结构前后,阵列天线均在77.5 GHz~78.5 GHz指定频段内正常工作,且合成辐射方向图的最大增益几乎保持不变,从而保证了毫米波雷达阵列天线的辐射性能。典型的数值算例能够很好地验证所提方法的有效性。 相似文献