New assembly route for three-dimensional metamaterials obtained through effective medium theory

In this study, we illustrate the effective medium theories in the designs of three-dimensional composite metama- terials of both negative permittivity and negative permeability. The proposed metamaterial consists of random coated spheres with sizes smaller compared to the wavelength embedded in a dielectric host. Simple design rules and formulas following the effective medium models are numerically and analytically presented. We demonstrate that the revised Maxwell-Garnett effective medium theory enables us to design three-dimensional composite metamaterials through the assembly of coated spheres which are random and much smaller than the wavelength of the light. The proposed ap- proach allows for the precise control of the permittivity and the permeability and guides a facile, flexible, and versatile way for the fabrication of composite metamaterials.

Factors influencing pore-pressure prediction in complex carbonates based on effective medium theory

A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential method.All types of pores are simultaneously introduced to the composite during the differential iteration process according to the ratio of their volume fractions.Based on this model,the effects of pore structures on predicted pore-pressure in carbonates were analyzed.Calculation results indicate that cracks with low pore aspect ratios lead to pore-pressure overestimation which results in lost circulation and reservoir damage.However,moldic pores and vugs with high pore aspect ratios lead to pore-pressure underestimation which results in well kick and even blowout.The pore-pressure deviation due to cracks and moldic pores increases with an increase in porosity.For carbonates with complex pore structures,adopting conventional pore-pressure prediction methods and casing program designs will expose the well drilling engineering to high uncertainties.Velocity prediction models considering the influence of pore structure need to be built to improve the reliability and accuracy of pore-pressure prediction in carbonates.

Optimal design of sub-wavelength metal rectangular gratings for polarizing beam splitter based on effective medium theory

A novel optimal design of sub-wavelength metal rectangular gratings for the polarizing beam splitter （PBS） is proposed. The method is based on effective medium theory and the method of designing single layer antireflection coating. The polarization performance of PBS is discussed by rigorous couple-wave analysis （RCWA） method at a wavelength of 1550 nm. The result shows that sub-wavelength metal rectangular grating is characterized by a high reflectivity, like metal films for TE polarization, and high transmissivity, like dielectric films for TM polarization. The optimal design accords well with the results simulated by RCWA method.

High color saturation and angle-insensitive ultrathin color filter based on effective medium theory

An ultrathin angle-insensitive color filter enabling high color saturation and a wide color gamut is proposed by relying on magnesium hydride-hydrogenated amorphous silicon[MgH2-a-Si:H]lossy dielectric layer.Based on effective medium theory,the MgH2-a-Si:H layer with an ultrathin thickness can be equivalent to a quasi-homogeneous dielectric layer wit an effective complex refractive index,which can be tuned by altering the thickness of MgH2to obtain the targeted value o the imaginary part,corresponding to the realization of high color saturation.It is verified that the proposed color filte offers highly enhanced color saturation in conjunction with a wide color gamut by introducing a few-nanometer thic MgH2layer.As the MgH2-a-Si:H layer retains the advantages of high refractive index and tiny thickness,the proposed colo filter exhibits large angular tolerance up to±60°.In addition,MgH2with an unstable property can interconvert with Mg unde a dehydrogenation/hydrogenation reaction,which empowers the proposed color filter with dynamically tunable outpu color.The proposed scheme shows great promise in color printing and ultracompact display devices with high color sat uration,wide gamut,large angular tolerance,and dynamic tunability.

A novel binary effective medium model to describe the prepeak stressstrain relationship of combined bodies of rock-like material and rock

Combined bodies of rock-like material and rock are widely encountered in geotechnical engineering,such as tunnels and mines.The existing theoretical models describing the stress-strain relationship of a combined body lack a binary feature.Based on effective medium theory,this paper presents the governing equation of the“elastic modulus”for combined and single bodies under triaxial compressive tests.A binary effective medium model is then established.Based on the compressive experiment of concretegranite combined bodies,the feasibility of determining the stress threshold based on crack axial strain is discussed,and the model is verified.The model is further extended to coal-rock combined bodies of more diverse types,and the variation laws of the compressive mechanical parameters are then discussed.The results show that the fitting accuracy of the model with the experimental curves of the concretegranite combined bodies and various types of coal-rock combined bodies are over 95%.The crack axial strain method can replace the crack volumetric strain method,which clarifies the physical meanings of the model parameters.The variation laws of matrix parameters and crack parameters are discussed in depth and are expected to be more widely used in geotechnical engineering.

多孔中药固体片剂孔隙率的太赫兹有效介质模型研究

目前对中药片剂的孔隙测量,一般采用的是具有破坏性的密度测量方法,缺乏无损量化方法。太赫兹辐射能用于无损的提取药物若干光学信息。针对直压型中药片剂,通过太赫兹时域和频域信号处理等不同方法分别计算各种片剂的有效折射率,发现两种方法得到的有效折射率和片剂的孔隙率均呈良好的线性关系。根据有效折射率特性,利用四种有效介质模型提取了中药片剂的孔隙率并进行量化回归,通过交叉验证与相对分析误差(RPD)发现通过时域信号处理的有效折射率得到的孔隙率回归模型解释性与验证准确性更高,其中最佳模型是Bruggeman模型(RPD=11.3325)。为中药多孔粉体制剂工艺优化提供支持。

Designing nonlinear thermal devices and metamaterials under the Fourier law: A route to nonlinear thermotics

Nonlinear heat transfer can be exploited to reveal novel transport phenomena and thus enhance people’s ability to manipulate heat flux at will.However,there has not been a mature discipline called nonlinear thermotics like its counterpart in optics or acoustics to make a systematic summary of relevant researches.In the current review,we focus on recent progress in an important part of nonlinear heat transfer,i.e.,tailoring nonlinear thermal devices and metamaterials under the Fourier law,especially with temperature-dependent thermal conductivities.We will present the basic designing techniques including solving the equation directly and the transformation theory.Tuning nonlinearity coming from multi-physical effects,and how to calculate effective properties of nonlinear conductive composites using the effective medium theory are also included.Based on these theories,researchers have successfully designed various functional materials and devices such as the thermal diodes,thermal transistors,thermal memory elements,energy-free thermostats,and intelligent thermal materials,and some of them have also been realized in experiments.Further,these phenomenological works can provide a feasible route for the development of nonlinear thermotics.

纳米金属粒子梯度掺杂的硅基近红外吸收增强结构

硅基光电子与CMOS工艺兼容,借助成熟的微电子加工工艺平台可以实现大规模批量生产,具有低成本、高集成度、高可靠性的优势。其中,硅基半导体探测器是目前应用最为广泛的可见光波段探测设备,将其工作频段拓展到近红外波段具有重要意义。由于硅的禁带宽度,硅基材料在近红外波段电磁波吸收存在明显限制,硅基探测器在近红外波段的应用受到挑战。根据纳米金属粒子发生局域表面等离子共振时产生的近场增强效应,提出了一种纳米金属粒子梯度掺杂的硅基结构。通过应用等效介质理论,模拟了复合硅基结构在可见光与近红外波段的吸收特性。结果表明:该结构在近红外波段具有电磁波吸收提升效果,并且当选择纳米金粒子梯度递增掺杂时,可以在610~1 450 nm波段提升吸收性能,最高提升可达到10.7 dB。所提出的结构可以有效增强硅基材料在近红外波段的吸收效率,研究结果为硅基半导体探测器在近红外波段的应用提供了重要参考。

Microwave metamaterials: from exotic physics to novel information systems

Metamaterials and metasurfaces have attracted much attention due to their powerful ability to control electromagnetic(EM)waves.In this paper,we review the recent developments in the field of EM metamaterials,starting from their exotic physics to their applications in novel information systems.First,we show the fundamental understanding on traditional metamaterials based on the effective medium theory and related applications,such as invisibility cloaks and meta-lenses.Second,we review the two-dimensional versions of metamaterials,i.e.,metasurfaces,for controlling spatial waves and surface waves and thereafter present their typical designs.In particular,we briefly introduce spoof surface plasmon polaritons and their applications in microwave frequencies.Following the above approach,we emphatically present the concepts of digital coding metamaterials,programmable metamaterials,and information metamaterials.By extending the principles of information science to metamaterial designs,several functional devices and information systems are presented,which enable digital and EM-wave manipulations simultaneously.Finally,we give a brief summary of the development prospects for microwave metamaterials.

促进科技型中小企业研发人员创新行为的组态研究

在创新驱动背景下,如何有效激发科技型中小企业研发人员的创新活力和创造力是亟待解决的重要问题。从多维理论出发,以科技型中小企业研发人员为研究样本,采用模糊集定性比较分析方法,探究个体层面、组织层面和社会层面对企业研发人员创新行为的多因素影响机制。研究发现:创新自我效能感、心理韧性、组织创新氛围、组织创新奖酬、政府创新政策和社会网络关系强度均不是研发人员积极或非积极创新行为产生的必要条件;科技型中小企业研发人员积极创新行为驱动模式有4种,分别为社会关系—主导型、创新政策—驱动型、个体—社会均衡型、个体—组织协同型;企业研发人员非积极创新行为驱动模式为创新动力—缺乏型,且与研发人员积极创新行为之间是非对称关系。研究结论丰富了研发人员创新行为相关理论研究,为促进科技型中小企业研发人员创新行为提供启示。

Effective medium theory of checkboard structures in the long-wavelength limit

Effective medium theory is a powerful tool to solve various problems for achieving multifarious functionalities and applications. In this article, we present a concise empirical formula about effective permittivity of checkboard structures for different directions. To verify our empirical formula, we perform simulations of checkboard periodic structures in squares, rectangles, and sectors in two dimensions. Our results show that the formula is valid in a large range of parameters. This work provides a new way to understand and design composite materials, which might lead to further optical applications in transformation optics.

从博弈论视角探讨中小股东的参与对提升高管薪酬契约有效性

本文从中小股东对高管监督过程中互动博弈出发,通过构建利益双方的博弈模型,利用双方的期望效用函数对博弈局中人的行为选择进行了动态分析。研究发现中小股东积极参与公司治理可以有效降低信息不对称,弥补大股东对高管监督激励不足的部分,充分发挥其监督作用,进而能够提升高管薪酬契约有效性。在中小股东对高管采取监督策略且该策略有效的条件下,最终促使博弈双方达到利益均衡;同时,提高对高管的监督效率、加大对高管在职谋私事件后的处罚力度可以降低中小股东对其监督的需求。本文研究从博弈论视角,拓展了对中小股东积极参与公司治理,进一步提升企业内部治理效率作用的认知,为完善公司内部治理提供了理论参考依据。

还原论视角下的时变超构材料构建与等效媒质理论研究

等效媒质理论是从微观角度出发,根据复合材料的结构特点,研究其宏观意义上材料参数的方法。将空间等效媒质理论推广到时间等效媒质理论,以时变声学超构材料为例,从理论上推导超构材料的材料参数在时间上以高频率调制时,其等效参数形式。基于还原论思想,在COMSOL Multiphysics数值仿真软件中设计时变人工原子进而构建时变超构材料,从数值上验证时间等效媒介公式的正确性,进而扩展等效媒质理论体系。

沈阳市科技型中小企业集群机理、效应分析与创新建议

本文以沈阳市科技型中小企业为研究对象,利用博弈理论模型,对沈阳市科技型中小企业集群创新的产生机理进行剖析,并在实证研究基础上,从拓宽科技型中小企业融资渠道、加强科技型中小企业集群合作、完善科技型中小企业服务平台、加大科技型中小企业资金扶持的角度,提出了沈阳市科技型中小企业创新效应途径。对提高广大科技型中小企业的产业竞争力、充分挖掘企业内部的创新能力、合理利用外部环境中的有利因素,促进区域经济协同发展、扩大就业,加强高新技术开发区的建设等方面都具有良好的促进作用。

聚合物基导电复合材料几种导电理论的评述

近年来,有关聚合物基导电复合材料的研究已受到普遍的重视,但对导电复合材料导电机理研究的不足制约了其应用和发展。导电复合材料的导电机理相当复杂,通常可分为导电通路如何形成和材料形成导电通路后如何导电这两个方面来研究。人们提出了许多导电机理模型,详细介绍了渗滤理论、有效介质理论、量子力学隧道效应理论等几种具有代表性的导电理论,对其适用范围、优缺点等进行了评述。通过对这些导电机理的探讨,有助于加深对复合型导电塑料以及其它导电复合材料导电行为的了解。

导电胶粘剂的导电机理研究进展

综述了导电胶的导电机理。导电胶作为无铅焊焊料的替代品,相关研究已受到普遍的重视,但对导电胶导电机理研究的不足在一定程度上制约了其应用与发展。导电胶的导电机理相当复杂,通常可以分为导电通路如何形成与材料形成导电通路后如何导电这两个方面的内容来研究。对此,人们提出了许多阐述导电胶导电机理的理论和模型。本文详细介绍了渗流理论、界面热力学理论、有效介质理论、量子力学隧道效应理论等几种具有代表性的导电理论,对其适应范围、优缺点等进行了评述。

岩石裂纹闭合效应及其定量模型研究

岩石的裂纹闭合效应对于岩石的变形以及强度性质具有重要影响。主要研究了岩石内部微裂纹的闭合压密效应及其定量评价方法。首先,基于有效介质理论将岩石的轴向应变分为基质轴向应变和裂纹轴向应变两部分;然后通过3组岩石压缩试验资料,建立裂纹轴向应变随轴向应力变化的负指数模型。分析发现,负指数模型可以较好地描述岩石裂纹闭合压密阶段的非线性。裂纹闭合应变可以在一定程度上反映岩石内部的微裂纹数量(密度),能够描述微裂纹密度在单轴、三轴压缩条件下的变化规律。

微粒子复合体介电特性有效媒质理论的形状修正

本文从平均极化场出发，根据平均场理论建立有效媒质理论的形状修正模型，并就微粒的实际分布形态，讨论了两种理论的具体形式，以及微粒形状对有效介电函数的影响。

利用有效媒质理论对纳米金属薄膜介电函数的初步分析

利用有效媒质理论描述了纳米金属薄膜形成过程中介电函数的变化规律．与实验获得的纳米 Ａｌ和 Ｔｉ薄膜形成过程中

金属薄膜形成过程中电导特性变化的有效媒质理论

利用有效媒质理论描述了金属薄膜形成过程中电导率变化规律，与实验测得的Ａｌ薄膜形成过程中电导率变化结果比较接近．分析和讨论了一些影响计算结果准确性的因素．