Biomimetic propulsion under random heaving conditions,using active pitch control

Marine mammals travel long distances by utilizing and transforming wave energy to thrust through proper control of their caudal fin. On the other hand, manmade ships traveling in a wavy sea store large amounts of wave energy in the form of kinetic energy for heaving, pitching, rolling and other ship motions. A natural way to extract this energy and transform it to useful propulsive thrust is by using a biomimetic wing. The aim of this paper is to show how an actively pitched biomimetic wing could achieve this goal when it performs a random heaving motion. More specifically, we consider a biomimetic wing traveling with a given translational velocity in an infinitely extended fluid and performing a random heaving motion with a given energy spectrum which corresponds to a given sea state. A formula is invented by which the instantaneous pitch angle of the wing is determined using the heaving data of the current and past time steps. Simulations are then performed for a biomimetic wing at different heave energy spectra, using an indirect Source-Doublet 3-D–BEM, together with a time stepping algorithm capable to track the random motion of the wing. A nonlinear pressure type Kutta condition is applied at the trailing edge of the wing. With a mollifier-based filtering technique, the 3-D unsteady rollup pattern created by the random motion of the wing is calculated without any simplifying assumptions regarding its geometry. Calculated unsteady forces, moments and useful power, show that the proposed active pitch control always results in thrust producing motions, with significant propulsive power production and considerable beneficial stabilizing action to ship motions. Calculation of the power required to set the pitch angle prove it to be a very small percentage of the useful power and thus making the practical application of the device very tractable.     

硫醇类配体修饰金纳米粒子在嵌段共聚物中自组装的研究进展

本文综述了不同类型硫醇配体修饰金纳米粒子的合成方法以及功能性金纳米粒子在嵌段共聚物薄膜中的自组装研究进展,重点介绍了硫醇类配体修饰金纳米粒子的合成方法,包括Brust合成法、原位合成法、grafting from合成法、配体置换法、单晶模板法等。总结了硫醇基小分子或聚合物配体修饰的金纳米粒子与嵌段共聚物之间自组装的调控方法,如利用配体与嵌段共聚物组分的隔离作用、配体与嵌段共聚物组分形成的氢键作用、溶剂蒸气退火或热退火等诱导嵌段共聚物/纳米粒子复合薄膜自组装。展望了功能性金纳米粒子以及嵌段共聚物/金纳米复合材料的发展方向。     

ZnO纳米线基MWNTs/PVDF复合热电材料的制备及特性研究

将不同比例的多壁碳管(MWNTs)与聚偏二氟乙烯(PVDF)聚合物混合后,喷涂于n型ZnO半导体纳米线阵列上,制备了一种新型ZnO纳米线基MWNTs/PVDF热电复合材料.与以往采用价格昂贵的p型与n型单壁碳纳米管(SWNTs)与聚合物混合制备的复合热电材料特性相比,这种新型热电复合材料在降低制造成本的同时,利用分散于聚合物中MWNTs的一维电子传输特性及形成的大量界面势垒,加上ZnO半导体纳米线具有的较高载流子密度与迁移率,提高了复合热电材料中电子的输运特性,增加了材料对声子的散射强度.测试发现,在一定的温度梯度下,随着MWNTs添加质量百分比的增加,热电材料的温差电动势和电导率也随之增加,但其Seebeck系数变化量不大.研究表明,这种热电材料有望替代采用p型与n型SWNTs构建的SWNTs/PVDF复合热电材料.研究结果对开发超轻、无毒、廉价、可应用于各种微纳电子领域的新型电源具有重要的参考价值.     

High-resolution transmission electron microscopy study on reversion of Al2CuMg precipitates in Al–Cu–Mg alloys under irradiation

Image deconvolution analyses showed that reversion of S-Al₂CuMg precipitates occurred in an Al–Cu–Mg alloy during high-resolution transmission electron microscopy observations. A fraction of Mg and Cu atoms in the precipitates diffused into Al matrix due to electron beam irradiation at 300 kV, resulting in structural/chemical reversion of the precipitates. The structural reversion of the S-Al₂CuMg precipitates is closely related with irradiation-induced displacement of atoms. The strong attraction between Cu and Mg atoms might assist the sub-threshold displacement of Cu atoms. One transitional structure is determined to be S′′-Al₁₀Cu₃Mg₃, a precursor of S-Al₂CuMg. Two other transitional structures, Al₃CuMg and Al₁₈Cu₅Mg₅ which have the same lattice parameters of a = c = 0.405 nm as that of S′′-Al₁₀Cu₃Mg₃, but different b values, are suggested.     

Monopoles connected by strings and the monopole problem

To clarify the status of proposed causality arguments limiting the annihilation rate of monopoles, we present a three-dimensional model for the formation of monopoles connected by strings. The length distribution of the strings has been found using a Monte carlo simulation of the phase transition. The result is that long strings connecting monopoles are exponentially suppressed in agreement with the theoretical predictions of Mitchell and Turok [1]. The implications of our results for the monopole problem are discussed.     

水硬性石灰合成及拉破坏特性试验研究

水硬性石灰在欧洲石质文物修复和加固中获得了很大成功。我国的石质文物主要是砂岩,水硬性石灰的修复效果不好。为满足我国石质文物修复和加固的需求,本文以石灰石和黏土为原料,在950℃煅烧不同时间,制备出水硬性石,对试样的成分、微观形貌、收缩率、抗拉强度和拉破坏过程等进行了研究。结果表明:(1)试样中含有水硬性成分2CaO·SiO2(C2S);煅烧8h时,成分与欧洲水硬性石灰NHL5接近;1.5CaO·SiO2·xH2O(C-S-H)和CaCO3的含量随龄期的增加逐渐增加。(2)龄期1~3d,收缩率较小;龄期4~6d,收缩率以线性规律增加;7d以后,收缩率趋于稳定。(3)局部变形区随拉应力的增加而变大,邻近局部变形区逐渐合并,形成面积更大的应变局部化带;载荷超过峰值后,产生微裂隙;随载荷进一步增加,微裂隙扩展,贯穿整个试件,发展成宏观裂隙,使试件破坏。(4)抗拉强度随龄期的增加而增加,水硬性石灰中C-S-H、CaCO3等相互交织,构成空间致密体,使试件力学强度提高。合成的水硬性石灰物理力学性能与欧洲水硬性石灰NHL5相近,并且成分均匀、可控,在石质文物修复和加固工程中具有良好应用前景。     

无标记型核酸适体荧光传感器检测氯霉素的含量

建立了DNA核酸适体检测氯霉素的荧光分析新方法。将前人筛选得到的80bp的氯霉素DNA核酸适体截短至40bp,实验发现截短并不影响核酸适体与氯霉素的结合能力。40bp的DNA核酸适体与另一条互补DNA链形成双链DNA,SYBR Green I荧光染料能插入双链并有强荧光发射,加入氯霉素后,氯霉素能和DNA核酸适体形成稳定的复合物,诱导DNA双链打开,SYBR Green I释放,荧光降低。实验结果显示:在10~200μmol/L范围内,荧光降低百分数和氯霉素之间有良好线性关系,检测限为6μmol/L。     

Ag/PANI/Fe_2O_3复合纳米粒子的合成与催化性能

借助于PANI的还原性质,PANI/Fe2O3复合载体与AgNO3发生表面氧化还原反应,合成了Ag/PANI/Fe2O3复合纳米粒子。TEM和XRD结果表明,立方晶系纳米银的平均粒径10nm。FTIR结果表明,Ag与PANI及Fe2O3复合载体之间不存在化学键合作用,但由于PANI与Ag之间的电子相互作用,Ag/PANI/Fe2O3复合纳米粒子的FTIR吸收峰发生蓝移。Ag/PANI/Fe2O3复合纳米粒子对于间硝基苯磺酸钠的硼氢化钠还原反应表现出良好的催化活性,30min内间硝基苯磺酸钠的转化率达到86.77%。     

水热法合成α-MnO2纳米棒及其电化学性能

以KMnO4、氧化石墨(GO)和硫酸为原料,在120℃水热条件下3 h成功合成了直径为10~20 nm,长度为300~400 nm的α-MnO2纳米棒。研究发现GO的引入降低了纳米棒的制备温度,缩短了反应时间。电化学测试结果表明,在1 mol.L-1Na2SO4中性水系电解液中,该纳米棒表现出良好的电容性能,当扫描速率分别为2 mV.s-1和5 mV.s-1时,比电容分别为276 F.g-1和240F.g-1;该纳米材料是一种潜在的电化学电容器电极材料。