正方空气柱结构二维三角晶格光子晶体及其禁带特征

基于平面波展开法比较研究了空气圆柱三角晶格光子晶体和正方介质柱三角晶格光子晶体的禁带特征,提出了正方空气柱三角晶格光子晶体结构,并分析了相对介电常数对其禁带宽度的影响.结果表明:空气圆柱三角晶格光子晶体要比由同种介质材料构成的正方介质柱三角晶格光子晶体的完全禁带要大得多;对于正方空气柱三角晶格光子晶体,当相对介电常数ε_r>12.0时将出现双禁带,且当ε_r=19.0时两条禁带均达到最大值.     

超宽带隙一维光子晶体的设计与优化

一维光子晶体结构简单,不难制备,成本低廉,有一定的研发应用潜力.为了获得在可见光频段内具有超宽带隙的一维光子晶体,以Al2O3和TiO2为组分材料,将缺陷结构光子晶体与周期结构光子晶体进行组合,研究含有缺陷结构一维光子晶体(多层膜)的带隙性能.结果表明:在周期性一维光子晶体结构中插入缺陷层,带隙中出现缺陷模态的同时,原来的光子能带的区域宽度也随着增宽,利用这一性质,可将周期结构与含缺陷的结构组合成"异质结构",利用周期结构的带隙来补偿缺陷层引起的缺陷模,从而实现带隙的增宽.此外,对"异质结构"进行了优化,结果表明,优化可以大大减少总层数、简化结构,但基本不影响展宽的光子带隙性能.     

大直径钨镧合金锻造棒材性能研究

采用纳米掺杂方法制备了大直径钨镧合金棒坯,通过与纯钨对比,研究了不同氧化镧质量分数的钨镧合金棒坯烧结性能以及含质量分数1.0%纳米氧化镧粉掺杂的钨镧合金锻造棒材的室温性能和高温再结晶性能。结果表明:采用质量分数1.0%、1.5%和2.0%三种含量的纳米氧化镧粉掺杂烧结后,合金掺杂分布和晶粒组织均匀,随着氧化镧含量的增高,棒坯密度逐渐降低、晶粒数逐渐越多;1.0%氧化镧粉掺杂钨镧合金棒坯经过78.7%锻造变形量后,较纯钨棒材硬度值更高,金相组织更细、更均匀,车加工后车削较长,表面光洁度较高,再结晶温度比纯钨高约150℃。     

Assessing the functionality of a membrane protein in a three-dimensional crystal

Hexagonal microcrystals of bacteriorhodopsin embedded in a lipidic cubic phase have been investigated by time-resolved FT-IR and resonance Raman spectroscopy. Retinal isomerization, conformational changes in the protein backbone and proton translocation are virtually indistinguishable from those in the native membrane. The protein is thus fully active in three-dimensional crystals.     

Polyhedral assembly of a membrane protein in its three-dimensional crystal

A novel ordered assemblage of bacteriorhodopsin, a transmembrane protein functioning as a light-driven proton pump, is found in its three-dimensional crystal. Atomic force microscope images of the crystal surface reveal that spherical protein clusters with a diameter of approximately 50 nm are hexagonally close-packed. Electron micrographs of mechanically disintegrated crystals show that the inside of the protein cluster is filled with the mother liquor. The crystal is made up of hollow protein clusters. When disintegrated crystals are illuminated in the presence of a lipophilic anion, a significant alkalization of the external medium occurs. This result indicates that the protein cluster contains native lipids and that the cytoplasmic side of the protein faces the external medium. X-ray diffraction patterns and the observed diameter of the spherical shell suggest that approximately 200 bacteriorhodopsin trimers are aligned on a polyhedral surface lattice. Another remarkable feature of the spherical assemblies of bacteriorhodopsin is that they fuse with each other at low ionic strength and occasionally form a tubular or doughnut-like structure. The concept of membrane protein polymorphism is introduced on the basis of these observations, and it is used to describe the dynamic structure of some other biological membranes.