基于二维材料的压电光电子学器件

二维(2D)材料由于原子级超薄、可调带隙和优异的光电性质,在柔性光电子学领域有着巨大的潜力.利用应变诱导的压电势或压电极化电荷可以调控二维材料界面载流子的传输和光电过程,这种将压电、半导体特性、光激发三者耦合产生的压电光电子学效应推动了新型二维材料光电器件的开发,特别是压电光电子学增强的光电探测、光电化学、气体传感和太阳能电池等方向.本文简要综述了近年来二维材料在压电光电子学领域取得的研究进展,并对这一新兴领域未来的挑战和科学突破进行了展望.     

压电光子学效应及其应用

近年来,压电光子学作为一个新兴的研究领域吸引了学者们的广泛关注.压电光子学效应是压电半导体的压电极化和光激发的耦合,是利用应变诱导的压电极化调控材料能带结构进而控制电子-空穴的复合发光过程.压电光子学效应为新光源、智能触觉传感和机械光子学等重要技术提供了研究基础,尤其结合第三代、第四代半导体材料同时具有压电效应和半导体特性的优势,有望实现高性能的力-致发光器件.本文简要介绍了压电光子学效应的基本原理、材料体系以及压电光子学器件的研究进展,并对这一学科的未来发展进行了展望.     

压电驱动的载荷比拟方法

随着压电材料与结构大量进入航空航天结构控制领域，针对大型复杂结构的压电驱动计算与优化对计算方法提出更高的要求．本文提出并验证了压电驱动载荷比拟方法．使用该方法可以大大降低有限元模型规模，避免多压电铺层面内电压定义困难、简化材料参数在材料主向与单元主向之间的复杂转换，特别适合于结构强度工程人员进行压电驱动的振动与形状控制设计．     

压电电子学及其仿生智能传感

在低维压电半导体材料(比如ZnO和GaN)中,压电极化和半导体电子传输特性的耦合可以给器件带来预想不到的性能.这大大提高了研究人员对压电电子学这一新兴领域的兴趣.另外低维压电半导体材料拥有优异的机械特性,可以被集成到能够应对巨大应力的柔性器件中,外部的机械刺激为柔性器件运行中的电荷-载流子传输,载流子的产生、复合以及分离提供了新的调制方法.本综述回顾了压电电子学的基础理论,不同维度材料体系中的压电电子学,压电电子学晶体管的分类,及广义压电电子学晶体管的应用方面的最新研究进展,并对将来的研究方向进行了深入讨论.     

有限元法在电机温度场仿真中的运用

运行的超声电机会产生温升,过高的温升对超声电机的机械特性及使用寿命都有较大影响。本文首先通过实验证明压电陶瓷元件发热和摩擦层摩擦发热是超声电机温升的主要热源;然后,分别以压电陶瓷元件发热和摩擦层摩擦发热为热源,建立其相应的温度场热分布模型。并用有限元软件分别对压电陶瓷元件发热场和接触摩擦发热场进行仿真计算。计算结果表明,压电陶瓷片发热源部分,热量最大处为压电陶瓷片粘贴面的内圈;接触摩擦发热中,摩擦产生的热量集中在接触表面。     

杂交应力实壳单元对压电结构的非线性分析

给出8节点实壳单元对压电结构的几何非线性分析. 为了克服剪切、梯形和厚度锁定, 采用了假设自然应变方法, 特别是修正广义层合刚度矩阵. 由修正广义层合刚度矩阵得到的广义应力被单独假设, 导出了推广的Hellinger-Reissner 泛函, 通过选择广义应力假设实体单元的应力假设, 导出了杂交应力实壳单元的表达式. 非线性数值算例说明给出的单元模型对分析非线性压电结构的有效性.     

轴对称层合横观各向同性压电圆板的精确解：I.压电圆 …

从压电材料的三维弹性方程出发，导出压电圆板在轴对称变形下的状态方程，对其应用有限Ｈａｎｋｅｌ变换并使变换产生的边界自由项等于零，得到一常系数常微分方程组和相应的边界条件，进而求得对应于广义刚性滑动和广义弹性简支２种边界条件的２个精确解。     

用PVDF压电传感器对高强度聚焦超声声功率实时监测的实验研究

本实验研究旨在探索一种实时监测高强度聚焦超声(HIFU)声功率的方法.用PVDF压电膜制成传感器,安装在HIFU换能器声场中某一固定位置.换能器工作过程中用示波器检测PVDF压电传感器的电压输出信号.结果显示示波器可稳定检测出PVDF压电传感器的输出电压,该电压正比于换能器的驱动电压.这表明换能器的声功率输出与PVDF压电传感器的电压输出呈正相关关系,证明PVDF压电传感器可用于实时监测HIFU治疗过程中换能器的声功率输出,从而保证HIFU治疗的安全性和有效性.     

2—2结构压电复合材料的机电耦合系数研究

对２－２结构的压电复合材料提出一种动态模型，求解沿界面传播的平面波，获得这平面波传播的色散曲线。取换能器厚度为半波长或其奇数倍，换能器的谐振，反谐振频率及高次谐振频率的实验值与理论色散曲线相吻合。由动态模型可求得压电复合材料厚度振动的机电耦合系数随两仃材料的宽厚比和体积比的变化。     

抑制宽带双激励换能器发射响应起伏的电学方法

针对双激励宽带换能器发射响应起伏较大的问题,本文提出了在前后压电陶瓷堆分别串联电阻来降低换能器工作频带内的发射电压响应起伏,拓展换能器工作频带的方法.推导了双激励换能器的等效电路,计算了在前后压电陶瓷堆分别串联不同电阻时换能器发射电压响应起伏随频率的变化关系,并通过有限元数值仿真证明,在前后压电陶瓷堆上串联合适的电阻,可以有效降低换能器发射电压响应在工作频带内的起伏.最后制作了工作频带在14~34 kHz的双激励超声换能器,测试了该换能器在串联不同电阻时的发射电压响应随频率的变化关系.实验测试结果表明在前后压电陶瓷堆串联电阻,可以有效地降低换能器的发射响应起伏,换能器在14~34 kHz的工作频带内发射电压响应的起伏由原来的12 dB降低到7.3 dB,换能器工作频带内的发射响应起伏得到明显的改善.研究结果对双激励宽带换能器的设计具有一定的意义.     

基于贝叶斯网络的变压器故障诊断及重要度分析

以云南电网公司提供的500 kV变压器历史运行数据为依据,利用贝叶斯网络和数据挖掘技术,结合变压器油中溶解气体分析的改良三比值法,针对500 kV变压器建立故障诊断模型,并对引起变压器故障的各影响因素进行重要度分析。最后,利用变压器实时运行数据进行试验,验证了模型的有效性和实用性。     

Periodic and chaotic dynamics of composite laminated piezoelectric rectangular plate with one-to-two internal resonance

The bifurcations and chaotic dynamics of a simply supported symmetric cross-ply composite laminated piezoelectric rectangular plate are studied for the first time,which are simultaneously forced by the transverse,in-plane excitations and the excitation loaded by piezoelectric layers.Based on the Reddy's third-order shear deformation plate theory,the nonlinear governing equations of motion for the composite laminated piezoelectric rectangular plate are derived by using the Hamilton's principle.The Galerkin's...     

Dynamic substructure model for multiple impact responses of micro/nano piezoelectric precision drive system

A dynamic substructure technique which considers the electromechanical coupling effect of the PZT and the inertial effect of flexible components is presented to study the multiple impact dynamic behavior of micro/nano piezoelectric impact drive systems.It can investigate the step-like motion of object body and the multiple impacts behaviors reasonably by the comparison of the experimental data and the numerical solution of the spring-mass model.It is expected to have higher accuracy in the numerical simulat...     

壳聚糖磁性光敏剂血卟啉衍生物微球的制备及其体外表征研究

目的制备壳聚糖包覆的磁性光敏剂血卟啉衍生物微球并考察其体外表征。方法以五羰基铁为原料制备羰基铁粉纳米颗粒,非溶剂法将羰基铁粉纳米颗粒与光敏剂血卟啉衍生物HPD复合,并用壳聚糖包覆制备成壳聚糖包覆磁性血卟啉衍生物微球(CS-M-HPD)。使用电子显微镜、激光粒度仪、X-射线衍射仪和磁力测定仪考察微球的表征。结果检测结果表明该微球为球形,分散性良好,粒径大多集中在290～300 nm。微球羰基铁粉纯度高,呈现优良磁性。结论本研究实现了壳聚糖对磁性HPD的包覆,得到了单分散性磁性HPD微球,为进一步研究该微球靶向光动力治疗肿瘤的生物活性奠定了实验基础。     

A hybrid-stress solid-shell element for non-linear analysis of piezoelectric structures

This paper presents eight-node solid-shell elements for geometric non-linear analyze of piezoelectric structures.To subdue shear,trapezoidal and thickness locking,the assumed natural strain method and an ad hoc modified generalized laminate stiffness matrix are employed.With the generalized stresses arising from the modified generalized laminate stiffness matrix assumed to be independent from the ones obtained from the displacement,an extended Hellinger-Reissner functional can be derived.By choosing the ass...     

From ultrasonic to frequency standards: Walter Cady’s discovery of the sharp resonance of crystals

In 1918–1919 Walter G. Cady was the first to recognize the significant electrical consequences of the fact that piezoelectric crystals resonate at very sharp, precise and stable frequencies. Cady was also the first to suggest the employment of these properties, first as frequency standards and then to control frequencies of electric circuits—an essential component in electronic technology. Cady’s discovery originated in the course of research on piezoelectric ultrasonic devices for submarine detection (sonar) during World War I. However, for the discovery Cady had to change his research programme to crystal resonance. This change followed Cady’s experimental findings and the scientific curiosity that they raised, and was helped by the termination of the war. Cady’s transition was also a move from “applied” research, aimed at improving a specific technology, to “pure” research lacking a clear practical aim. This article examines how Cady reached the discovery and his early ideas for its use. It shows that the discovery was not an instantaneous but a gradual achievement. It further suggests that disinterested “scientific” research (rather than “engineering” research) was needed in this process, while research aimed at design was required for the subsequent development of technological devices. I am very grateful to Chris McGahey for providing me with his research notes taken from Walter Cady’s diaries kept by the Rhode Island Historical Society, henceforth Diaries. I would like to thank Aharon (Arkee) Eviatar for linguistic comments, Ido Yavetz for our helpful discussion and Jed Buchwald for his thoughtful comments and editorial work. I thank the Lemelson Center in the National Museum for American History for a grant that enabled me to study Walter Guyton Cady Papers, 1903–1974, Archives Center, National Museum of American History (henceforth, ACNMAH) and the staff of the center, especially Alison Oswald, for their help. The following abbreviations are used: NB—Cady’s research notebooks kept at ACNMAH, AIP - Niels Bohr Library, American Institute of Physics, Cady’s dossier.     

可再生能源互联网中的微电子技术

可再生能源互联网对电子系统提出了五大要求:高效性、安全性、可靠性、便利性、宽泛性.为了实现上述要求,可再生能源互联网需要多学科、多方面、多层次的创新.微电子技术将会渗透到可再生能源互联网的各个层级,是可再生能源互联网的重要支撑性技术之一.文章重点围绕固态变压器、分布式储能技术、信息采集芯片技术、通信芯片技术四个方面,阐述了可再生能源互联网中的微电子技术所面临的特殊要求、技术挑战及未来可能的发展趋势.     

The natural selection of conservative science

Social epistemologists have argued that high risk, high reward science has an important role to play in scientific communities. Recently, though, it has also been argued that various scientific fields seem to be trending towards conservatism—the increasing production of what Kuhn (1962) might have called ‘normal science’. This paper will explore a possible explanation for this sort of trend: that the process by which scientific research groups form, grow, and dissolve might be inherently hostile to such science. In particular, I employ a paradigm developed by Smaldino and McElreath (2016) that treats a scientific community as a population undergoing selection. As will become clear, perhaps counter-intuitively this sort of process in some ways promotes high risk, high reward science. But, as I will point out, risky science is, in general, the sort of thing that is hard to repeat. While more conservative scientists will be able to train students capable of continuing their successful projects, and so create thriving lineages, successful risky science may not be the sort of thing one can easily pass on. In such cases, the structure of scientific communities selects against high risk, high rewards projects. More generally, this project makes clear that there are at least two processes to consider in thinking about how incentives shape scientific communities—the process by which individual scientists make choices about their careers and research, and the selective process governing the formation of new research groups.     

Bau und Funktion der Nukleolen

Summary In previous years the composition and function of chromosomes have been analyzed to a considerable extent, in contrast to the small number of investigations that have been made on nucleoli. There exist at present many conflicting opinions about the structure and function of the nucleolus, and therefore a critical survey of the facts and theories about the nucleolar substance appears necessary.The structure, chemical composition and metabolism of the nucleoli of various cells are described in this publication. The regulation of the size and function of the nucleolus is also discussed.It is concluded that the size and structure of the nucleolus is organ- and species-specific. A rapid synthesis of RNA and proteins occurs in the nucleolus. After a short interval, this disappears; and it is therefore concluded that the nucleolus must have a high turnover of these substances. The size and function of the nucleoli depends on the energy state of the cytoplasm.It appears that the nucleolus can synthesize proteins which can be utilized by the chromosomes during their genetic function.