Bandwidth optimization of a Planar Inverted-F Antenna using binary and real coded genetic algorithms

With the exponential development of mobile communications and the miniaturization of radio frequency transceivers, the need for small and low profile antennas at mobile frequencies is constantly growing. Therefore, new antennas should be developed to provide larger bandwidth and at the same time small dimensions. Although the gain in bandwidth performances of an antenna are directly related to its dimensions in relation to the wavelength, the aim is to keep the overall size of the antenna constant and from ...     

腾冲嗜酸两性菌硫氧化还原酶分子结构中铁原子结合位点的新特征

前期研究表明, 铁原子对于嗜酸两性菌中硫氧化还原酶(SOR)的活性至关重要. 本研究表明, 2,2′-联吡啶、1,2-二羟基苯-3,5-二磺酸钠、8-羟基喹啉等特异性铁离子螯合剂强烈抑制腾冲嗜酸两性菌SOR酶活性, 进一步表明铁原子是SOR酶活必需. 对目前基因组数据库中的SOR基因或者SOR类似基因进行序列比对, 发现了一个潜在的铁原子结合模体(H⁸⁶-X₃- H⁹⁰-X_n-E¹¹⁴-X_n-E¹²⁹). 据此, 本研究采用定点突变技术, 将氨基酸残基H⁸⁶, H⁹⁰和E¹²⁹分别突变为苯丙氨酸或者丙氨酸, 圆二色光谱测定发现突变体(H⁸⁶F, H⁹⁰F和E¹²⁹A)的二级结构没有明显改变, 但是这3个突变体全部丧失了酶活性. 突变体蛋白中铁原子含量测定结果表明, 3个突变体全部或者部分丢失了铁原子, 而之前研究中获得的3个半胱氨酸突变体(完全丧失了酶活)铁原子含量没有变化. 根据本研究并结合前期实验结果可知, SOR分子中模体C³¹-X_n-C¹⁰¹-X₂-C¹⁰⁴是底物硫分子活化区域; 而模体H⁸⁶-X₃-H⁹⁰-X₂₃-E¹¹⁴-X_¹⁴-(E/D)¹²⁹是SOR分子中铁原子的结合区域, 与铁原子结合形成一个非卟啉铁中心, 是SOR的氧化还原中心; 这两个区域均是SOR酶活性的必需部分.     

南京栖霞山铅锌矿山中的现代钙华:一种高度富锌和锰的方解石

金属硫化物矿山开发引发的重金属污染已成为当前急需解决的环境问题. 以南京栖霞山铅锌矿采矿巷道壁上的现代钙华为研究对象, 利用电子探针、扫描电子显微镜和X射线粉末衍射分析等矿物学手段, 分析了钙华中的矿物组成及其重金属元素的赋存形态和分布状况. 结果表明钙华的主要矿物成分为方解石. 尽管地层水的重金属含量较低, 但是钙华中碳酸盐矿物的微量元素含量却较高, 最高含量分别为: Mn 23.65%, Zn 9.60%, Mg 0.76%, Fe 4.44%和Pb 0.66%. 钙华在电子探针背散射电子像中呈现出复杂的韵律壳层构造, 成分分析表明这种韵律壳层构造与重金属的分布有关. 另外, 在钙华中见有螺旋状及团絮状物质可能表明微生物参与了钙华的形成过程, 并与重金属的富集存在关联. 所报道的高度富锌-锰方解石对矿山环境中的重金属污染治理具有可借鉴意义.     

东方龙虱鞘翅:形态学及力学性能研究

研究了东方龙虱鞘翅的拓扑结构及其鞘翅生物材料的力学性能. SEM观测表明鞘翅横向截面和纵向截面结构相同, 是一种具 “桥墩” 状连接的空腔轻质结构, 由致密的黑色外表皮层和其下数十层几丁质纤维层平行、螺旋交织构成的内表皮层组成; 纳米压痕仪测得新鲜鞘翅外侧区域的硬度和弹性模量分别为0.31和6.13 GPa; 拉伸实验得到新鲜鞘翅横向和纵向的强度极限分别为169.2和194.5 MPa; 干燥鞘翅对应的强度极限为85.38和90.91 MPa, 新鲜鞘翅的强度是干燥鞘翅值的2倍; 结果表明甲虫鞘翅是一种力学性能呈现拓扑分布规律的轻质生物复合材料, 该研究为航空航天材料的轻质结构的设计提供了生物学的参考.     

大气降水中低分子有机酸的季节变化及对酸雨形成的贡献(以贵阳市和尚重镇为例)

低分子有机酸是大气中普遍存在的一种化学成分, 对酸雨的形成有重要的贡献. 西南地区是酸雨污染重灾区, 2006年4月到2007年4月用离子色谱法测定了贵阳市和尚重镇大气降水中的7种低分子有机酸. 实验结果表明: 两地大气降水中, 甲酸、乙酸和草酸是最主要的有机酸, 贵阳市其雨量加权平均值分别为14.24, 9.35和2.79 μmol/L, 而尚重镇则分别为4.95, 1.35和2.31 μmol/L. 尚重镇大气降水中低分子有机酸生长季节浓度高于非生长季节浓度, 说明植物或土壤的释放可能是尚重镇大气有机酸的主要来源; 与之相反, 贵阳市大气降水中有机酸非生长季节浓度高于生长季节浓度, 可能与该地区冬季降水次数少, 每次雨量小以及降水同时易伴随颗粒物沉降有关. 贵阳市有机酸对自由酸贡献分别为: 甲酸?7.9%, 乙酸?4.7%, 草酸?6.1%, 3种主要有机酸贡献了18.7%的自由酸; 尚重镇分别为: 甲酸?25.1%, 乙酸?7.5%, 草酸?25.5%, 有机酸对自由酸贡献为58.1%. 贵阳市降水中有机酸根占阴离子总和的1.7%~19.2%, 平均值为6.6%. 尚重镇降水中有机酸根对总阴离子的贡献为0.5%~92.2%, 平均贡献为13.2%. 由此可见, 低分子有机酸, 尤其是边远地区, 对大气降水酸化的影响不可忽视.     

On-chip natural assembly of silicon photonic bandgap crystals.

Photonic bandgap crystals can reflect light for any direction of propagation in specific wavelength ranges. This property, which can be used to confine, manipulate and guide photons, should allow the creation of all-optical integrated circuits. To achieve this goal, conventional semiconductor nanofabrication techniques have been adapted to make photonic crystals. A potentially simpler and cheaper approach for creating three-dimensional periodic structures is the natural assembly of colloidal microspheres. However, this approach yields irregular, polycrystalline photonic crystals that are difficult to incorporate into a device. More importantly, it leads to many structural defects that can destroy the photonic bandgap. Here we show that by assembling a thin layer of colloidal spheres on a silicon substrate, we can obtain planar, single-crystalline silicon photonic crystals that have defect densities sufficiently low that the bandgap survives. As expected from theory, we observe unity reflectance in two crystalline directions of our photonic crystals around a wavelength of 1.3 micrometres. We also show that additional fabrication steps, intentional doping and patterning, can be performed, so demonstrating the potential for specific device applications.     

Water capture by a desert beetle.

Some beetles in the Namib Desert collect drinking water from fog-laden wind on their backs. We show here that these large droplets form by virtue of the insect's bumpy surface, which consists of alternating hydrophobic, wax-coated and hydrophilic, non-waxy regions. The design of this fog-collecting structure can be reproduced cheaply on a commercial scale and may find application in water-trapping tent and building coverings, for example, or in water condensers and engines.     

Superconductivity in CaCuO2 as a result of field-effect doping.

Understanding the doping mechanisms in the simplest superconducting copper oxide-the infinite-layer compound ACuO2 (where A is an alkaline earth metal)-is an excellent way of investigating the pairing mechanism in high-transition-temperature (high-Tc) superconductors more generally. Gate-induced modulation of the carrier concentration to obtain superconductivity is a powerful means of achieving such understanding: it minimizes the effects of potential scattering by impurities, and of structural modifications arising from chemical dopants. Here we report the transport properties of thin films of the infinite-layer compound CaCuO2 using field-effect doping. At high hole- and electron-doping levels, superconductivity is induced in the nominally insulating material. Maximum values of Tc of 89 K and 34 K are observed respectively for hole- and electron-type doping of around 0.15 charge carriers per CuO2. We can explore the whole doping diagram of the CuO2 plane while changing only a single electric parameter, the gate voltage.