超材料宽带圆偏振器的研究进展

超材料因其独特的性质可以作为选择圆偏振光的器件,即圆偏振器。随着偏振分辨成像系统的重要性日益增强,圆偏振器已被用于增强对比度、圆偏振显微镜以及生物分子的检测,如氨基酸、DNA和具有固有手性结构的葡萄糖,尤其是在可见光波长下工作的圆偏振器已经引起了人们广泛的关注,已被用作控制复杂显示系统中光的偏振态的关键光学元件。然而通过传统方法获取圆偏振器有很大的局限性,如体积庞大、工作带宽窄等,极大地限制了它们的发展。近几年来,超材料中螺旋结构和堆叠结构的提出,促进了宽带圆偏振器的发展。本文简述了超材料中螺旋结构和堆叠结构形成宽带圆偏振器的偏振原理,详述了两种结构作为宽带圆偏振器的数值模拟和实验研究进展。     

PMI Foam Cored Sandwich Components Produced by Means of Different Manufacturing Methods

Thepaperwillintroducestructuralapplications withPMI(Polymethacrylimide)foamsinsandwich componentsforrotorcraftandcivilaircraftanddis cusssometypicallyusedmanufacturingmethods,suchase.g.in mouldpressing,autoclavecuringand resininfusion.Theadvantagesoffoam coredsand wichdesignversushoneycomb coreddesignwillbe discussed,focussingonmanufacturingcosts.1PropertiesofRigidFoamPlastics1.1MechanicalPropertiesatRoomTemperature Logically,thesuitabilityoffoamcorematerials foraparticularsandwichapplicat…     

梯度结构Al_2O_3-(W,Ti)C-TiN-Mo-Ni纳米金属陶瓷刀具材料的设计及制备

基于对高速硬切削时刀具应力和温度分布,以及刀具内部疲劳裂纹扩展仿真分析,提出一个组分含量分布和微观结构具有梯度特征的设计模型。通过韧性相的添加和梯度结构的引入,实现疲劳裂纹扩展速率的减缓,从而提高刀具寿命。采用二阶段热压烧结工艺制备出具有梯度结构的Al_2O_3-(W,Ti)C-TiN-Mo-Ni纳米复合刀具材料,并对其微观结构和力学性能进行研究。结果表明:所制备的梯度结构金属陶瓷材料表层硬度、内层的断裂韧度和抗弯强度分别达到19.258GPa,10.015MPa·m~(1/2)和1017.475MPa,满足高速硬切削刀具的性能要求。材料的断口出现韧窝和黏结相撕裂形成的断裂棱,有利于断裂韧度和抗弯强度的增强,从而提高刀具抗疲劳裂纹扩展能力。     

JH机载雷达天线的研制EI

通过结构、材料和工艺选择，研制出一种目前国内最大的机载雷达天线。该天线综合技术性能优良，现已通过各项性能检测和试飞，并投入小批量生产。     

Freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors

Nanocellulose is a sustainable and eco-friendly nanomaterial derived from renewable biomass.In this study,we utilized the structural advantages of two types of nanocellulose and fabricated freestanding carbonized hybrid nanocellulose films as electrode materials for supercapacitors.The long cellulose nanofibrils (CNFs) formed a macroporous framework,and the short cellulose nanocrystals were assembled around the CNF framework and generated micro/mesopores.This two-level hierarchical porous structure was successfully preserved during carbonization because of a thin atomic layer deposited (ALD) Al2O3 conformal coating,which effectively prevented the aggregation of nanocellulose.These carbonized,partially graphitized nanocellulose fibers were interconnected,forming an integrated and highly conductive network with a large specific surface area of 1,244 m2·g-1.The two-level hierarchical porous structure facilitated fast ion transport in the film.When tested as an electrode material with a high mass loading of 4 mg·cm-2 for supercapacitors,the hierarchical porous carbon film derived from hybrid nanocellulose exhibited a specific capacitance of 170 F.g-1and extraordinary performance at high current densities.Even at a very high current of 50 A·g-1,it retained 65％ of its original specific capacitance,which makes it a promising electrode material for high-power applications.     

浙江硅藻土吸附性能的研究

测定了25℃时浙江硅藻土对苯的吸附等温线及吸附回线,硅藻土的孔径分布、硅藻土表面硅羟基SiOH数目,并讨论了吸附等温线及吸附回线与孔结构、表面SiOH数目之间的关系.     

核壳型铂基燃料电池催化剂制备方法与微结构控制综述

目前催化剂是制约燃料电池走向市场的关键,限制了燃料电池发展及大规模商业应用,寻求能够同时降低催化剂成本和提高催化剂性能的有效方法十分迫切.具有核壳结构的Pt-M催化剂不仅可以降低贵金属铂的用量,而且能显著提高催化活性.本文总结了近20年来核壳型Pt-M催化剂的主要制备方法,包括晶种法、去合金法、电化学沉积法等;重点分析非贵金属-铂核壳结构(M@Pt,M = Ni、Co、Cu、Fe等)的制备途径,总结了每种方法的特点.另外,还讨论了核壳结构在纳米层次上的精细控制和设计方案,这有助于理解核壳结构对电化学催化动力学的作用规律,更好地设计开发新型催化剂.     

氟橡胶在碱性环境中脱氟化氢反应机理及其结构

为了研究26型氟橡胶(偏氟乙烯-六氟丙烯二元共聚物)和246型氟橡胶(偏氟乙烯-四氟乙烯-六氟丙烯三元共聚物)在碱性环境中所发生的反应,本文对其反应机理进行了系统的讨论。采用红外(FTIR)、氢谱(1 H-NMR)和氟谱核磁(19 F-NMR)对氟橡胶反应前、后的分子链结构进行了分析,并对不同序列结构双键及羟基含量进行了计算。结果表明,26型和246型氟橡胶在碱性环境中发生脱氟化氢反应时,会伴随着双键重排及氧化反应的发生。其中,26型氟橡胶遵循以Zaitsev规则消除反应为主、Hofmann规则消除反应为辅的脱氟化氢反应,在分子链中5个位置出现了双键;而246型氟橡胶则与之相反,遵循以Hofmann规则消除反应为主、Zaitsev规则消除反应为辅的脱氟化氢反应,在分子链中7个位置出现了双键;两种氟橡胶中遵循Hofmann规则进行消除反应所产生的双键会被氧化为羟基;相同条件下,反应后246型氟橡胶的双键和羟基含量均高于26型氟橡胶。     

Pb(Zn1/3Nb2/3)O3-Ba(Zn1/3Nb2/3)O3铁电陶瓷结构与性能的研究

采用固相反应的方法系统地研究了BZN稳定PZN基陶瓷的相结构与介电性能.随着BZN含量的增加,PZN-BZN陶瓷中钙钛矿相的稳定性增强,居里温度近似呈线性下降,室温介电常数和介质损耗随也显著降低,最小值分别为380和0.002.为获得100%钙钛矿结构的PZN基陶瓷所需BZN的最小用量为8mol%～10mol%,当BZN的mol%超过15mol%时,PZN基陶瓷中钙钛矿相所占的百分比不再受烧结工艺的影响,基本保持100%.1kHz时Pb0.9Ba0.1Zn1/3Nb2/3O3陶瓷的最大介电常数Kmax=8680,tgδ=0.02,相应的居里温度Tm为24℃.     

High Pressure Behavior of 4-Amino-3,7-dinitrotriazolo-［5,1,c］ ［1,2,4］triazine Crystal: a DFT Investigation

The effect of external pressure on 4-amino-3,7-dinitrotriazolo-［5,1,c］［1,2,4］ triazine (ADT) crystal in the pressure range of 0-130 GPa was investigated by the density functional theory (DFT) periodic calculation with LDA/CA-PZ function. With the increasing pressure, the volume of ADT crystal decreases while the energy increases. The topological analysis shows that the energy of hydrogen bonds increases as the pressure increases. At 81 GPa, hydrogen bonding between atoms O2 and H5 converts into covalent interaction. And the covalent interaction is formed between atoms N4 and H6. At 82 GPa, the interaction between atoms O2 and H5, N4 and H6 become hydrogen bonding. At 92 GPa, H6…N4 turns into a covalent bond, and there is s covalence interaction between the two atoms. The band gap decreases first and then increases with the increasing pressure.     

Ti(C,N)基金属陶瓷中添加成分的研究现状

简要介绍了Ti(C,N)基金属陶瓷的基本结构和组成,重点阐述了各种添加成分的加入方法和加入量对材料组织和性能的影响。     

双重抗震结构及其设计参数的分析研究

本文根据多道抗震设防概念,对双重抗震结构的设防目标进行了探讨,明确了主、 次结构的功能．文中利用单自由度双重结构分析模型,对主、次结构的合理参数关系进行了 计算分析,提出了有关抗震设计建议。有关结果同样也适用于滞迟型减震控制结构。     

Electronic structure of YBa2Cu3O7 and YBa2Cu3O6—charge-self-consistent band structure calculations

Charge self-consistent LCAO band structure (CSCBS) calculations are reported for orthorhombic YBa₂Cu₃O₇ and tetragonal YBa₂Cu₃O₆ assuming ordered vacancy models. The effective atomic charges are used to study the charge transfer. In YBa₂Cu(1)₁Cu(2)₂O₇, the two types of copper atoms have their energy bands almost overlapping with effective valency of each copper as 7/3 (or effective valency of each oxygen as approximately — 13/7), so that electron hopping can take place without any loss or gain of energy while in YBa₂Cu(1)₁Cu(2)₂O₆, Cu(1)₁ is monovalent and Cu(2)₂ are divalent with significant difference in their bands. Therefore, YBa₂Cu₃O₇ should conduct much better compared to YBa₂Cu₃O₆. This corroborates the experimental observations that YBa₂Cu₃O₇ is a (super)conductor while YBa₂Cu₃O₆ is not. The calculated effective charges and DOS support the above view.     

Mechanism of arsenate coprecipitation at the solid/liquid interface of ferrihydrite: A perspective review

Arsenate (As(V)) is a toxic element in acid mine drainage and has to be removed during the neutralization process. Coprecipitation with ferrihydrite is the main mechanism for As(V) removal from acid mine drainage. To improve treatment efficiency, a quantitative understanding of the coprecipitation mechanism is required. Coprecipitation can incorporate more As(V) into ferrihydrite than adsorption. The results of XRD (X-ray Diffraction) and XANES (X-ray Adsorption Near Edge Structure) analysis confirmed that the formation of poorly crystalline ferric arsenate increased when the initial As/Fe molar ratio increased in the coprecipitation with ferrihydrite. EXAFS (Extended X-ray Adsorption Fine Structure) analysis at the iron K-edge showed that the proportion of octahedral structures in ferrihydrite increased when the initial As/Fe molar ratio increased. Moreover, EXAFS analysis at the arsenic K-edge, assuming three kinds of surface complexes for the AsFe bond, revealed that the coordination number for AsFe with an atomic distance of 2.85 × 10⁻¹⁰ m increased and that for As-Fe with an atomic distance of 3.24 × 10⁻¹⁰ m decreased as the initial As/Fe molar ratio increased. Thus, for more efficient wastewater treatment, active control of coprecipitation phenomena according to mechanistic details is essential.     

粉末X射线衍射法对酰胺酸-酰亚胺共聚物晶体结构的研究

通过粉末X射线衍射仪对不同工艺条件获得的PMDA-ODA型酰胺酸-酰亚胺共聚物(PA-I)粉末的XRD图谱进行分析表明,PA-I粉末为半晶粉末,使用消除无定型鼓包的XRD图谱指标化,计算出晶体结构为三斜晶系,空间群为P1。采用Pawley全谱精修晶体结构,结果表明,随着酰亚胺化时间的延长和酰亚胺化温度的提高,PMDA-ODA的晶胞参数、微晶尺寸和晶格畸变都呈现规律性变化。     

Recent progress in the design and fabrication of multifunctional structures based on metamaterials

Metamaterials, with unconventional properties realized through various ingenious designs of micro-architectures, have become a recent research hotspot in the fields of electromagnetics, acoustics, mechanics, and physics. Since the integration of mechanical features and specific functions is still a challenge, the application of metamaterials has so far been limited. The research in relevant areas has shown a clear trend of incorporating the multifunctional design into a single integrated structure. Here, we review the latest advances in the design and fabrication of multifunctional structures based on metamaterials, covering three main aspects, i.e., the direct design of mechanical metamaterials and their multifunctional structures, the intelligent multifunctional structures with shape-shifting capabilities, the metamaterials-based design to achieve both the load bearing capability and other specific functions. We emphasize the important roles that the mechanics-driven designs play, as well as the mechanisms and other key aspects behind the multifunctional structures. The structure-level innovations could not only improve multifunctional features, but also pave the way to function fusion structures that allow the incorporation of ‘conflicting’ functions into a single structure.     

基于补偿器结构的LTR结构振动控制方法

针对传统观测器结构LQG/LTR控制器的问题,该文提出了一种基于补偿器结构的LTR控制器设计方法。设计出的补偿器结构控制器的有如下特点:是开闭环稳定的控制器;对给定的回路传函恢复度,该控制器需要的增益和带宽要小于LQG/LTR控制器;对于相同的控制器增益,该控制器的回路传函恢复效果要好于LQG/LTR控制器;低增益和小带宽控制器能较好地摆脱控制力易饱和与控制过程易受噪声污染的困扰,这对结构控制的实际应用和推广有着非常重要的现实意义。最后,数值算例验证了该方法的有效性。     

粘弹性阻尼器控制的框架结构弹塑性地震响应分析

针对框架结构，采用粘弹性阻尼器来控制其地震响应，提出了粘弹性阻尼器的等效刚度矩阵和等效附加粘弹性力向量的概念，推导了子结构平面内的粘弹性阻尼器的有限元计算公式，在此基础上，提出了结构等效附加粘弹性力荷载的概念，采用拟外荷载法对安装了粘弹性阻尼器的框架结构的弹塑性地震响应进行了计算分析，开发了计算受粘弹性阻尼器控制的框架结构的动力特性、受控框架结构的地震弹性响应、受控框架结构的地震弹塑性响应的计算机程序。应用所开发的计算程序对一框架结构在粘弹性阻尼器控制下的地震响应进行了计算，计算表明，粘弹性阻尼器可以有效地控制框架结构的地震响应、采用拟外荷载法可以有效地求解受控结构的运动方程。     

地震工程:从抗震、减隔震到可恢复性

近年我国地震工程研究的发展呈现从抗震、减隔震走向可恢复功能的趋势。地震可恢复功能可定义为:受到地震动输入扰动后,结构、系统、城市具有可恢复功能的能力。对于工程结构而言,地震可恢复功能结构不仅要求结构在地震作用下保护生命,而且要求结构在震后快速恢复,减少对正常使用的影响。该文首先介绍了地震可恢复功能的基本概念,围绕地震可恢复功能结构,从设防目标、规范标准、结构体系、设计方法、性能指标以及工程应用等方面阐述了可恢复功能结构的特点及其与传统抗震结构的区别,最后对可恢复功能结构的未来进行了展望。     

现代晶界几何结构理论及其在工程材料中的应用

现代晶界结构理论是70年代以来所发展起来的新理论。它在解释与晶界有关的物理现象(晶界扩散、晶界偏聚和析出、晶界腐蚀、晶界破断)方面有不少十分新颖的结论.本文介绍晶界几何结构理论,着重评述该理论在工程材料中的应用及发展前景,并指出了这种理论在解释晶界能方面所面临的困难。