Planar elastic laminates and their homogenization

Summary The state of stress and deformation of a planar elastic-homogeneous transversely isotropic thick layer in the case of plane and axisymmetric strain respectively is determined in a systematic and uniform manner using integral transforms and transfer matrices. Next, a laminate with an arbitrary number of different layers is considered without any simplifying assumptions. Then we analyze a periodic structure consisting of many thin and identical layer groups by means of a suitable homogenization, where a layer group contains two or more different transversely isotropic homogeneous basic layers. As an example exact closed form solutions for a periodically layered half space are evaluated. The well known result, that a medium which is composed of alternating thin layers of two different elastic-isotropic substances is elastostatically equivalent to a homogeneous transversely isotropic medium is extended to the above mentioned more general case. Further, the in-plane normal stresses which are discontinuous for a finite layering are evaluated in addition to the smeared ones which are continuous and correct only in the limit of a vanishing thickness of the individual layers. The explicit knowledge of the resultant elastic constants (called effective ones) turns out to be dispensable; rather, the effective material parameters (defined in this paper) which are the weighted sums of the material parameters of the basic layers are proved to be relevant. Nevertheless, for the purpose of comparison with some published results the effective elastic constants, especially for a layer group consisting of two different elastic-isotropic substances, are evaluated additionally.Dedicated to Prof. Gallus Rehm on the occasion of his 75th birthday     

Composite load models based on field measurements and their applications in dynamic analysis

The composite load model with an induction motor in parallel with a static load has been studied and applied in analysis of dynamics of power systems for a long time. However, the load parameters from field tests are still very limited. Based on the theoretical results of identifiability and estimation methodology of load parameters that have been achieved in the previous work, a project of load modelling based on field measurements is described. Eight sets of equipment for load modelling were installed in HeNan Electric Power Grid (HNEPG) Corporation, and the dynamics of the load were recorded and a dynamic index is proposed to evaluate the dynamic characteristics of the data measured. The load models derived from the field measurements are applied to stability analysis of HNEPG. The critical clearing time and power transfer capability analyses illustrate the enhancement of the stability analysis of the power grid using the load parameters derived from the field measurements and show the benefits of application of such model parameters in power system dynamic analysis.     

Robust solutions to conic quadratic problems and their applications

This paper deals with uncertain conic quadratic constraints. An approximate robust counterpart is formulated for the case where both sides of the constraint depend on the same perturbations, and the perturbations belong to an uncertainty set which is an intersection of ellipsoids. Examples to problems in which such constraints occur are presented and solved. The research was supported by BSF grant no. 729/04.     

Composite materials for aerospace applications

Fibre-reinforced polymer composite materials are fast gaining ground as preferred materials for construction of aircraft and spacecraft. In particular, their use as primary structural materials in recent years in several technology-demonstrator front-line aerospace projects world-wide has provided confidence leading to their acceptance as prime materials for aerospace vehicles. This paper gives a review of some of these developments with a discussion of the problems with the present generation composites and prospects for further developments. Although several applications in the aerospace sector are mentioned, the emphasis of the review is on applications of composites as structural materials where they have seen a significant growth in usage. The focus of the paper is especially on the developments on the Indian aerospace scene. A brief review of composites usage in aerospace sector is first given. The nature of composite materials behaviour and special problems in designing and working with them are then highlighted. The issues discussed relate to the impact damage and damage tolerance in general, environmental degradation and long-term durability. Current solutions are briefly described and the scope for new developments is outlined. In the end, some directions for future work are given.     

Woven fabric composites—developments in engineering bounds,homogenization and applications

Various approaches for approximating upper and lower bounds for the elastic stiffness tensor for general woven fabric composites are first described. Well accepted minimum energy principles are briefly presented to establish the foundation for practical finite element procedures for determining these bounds. Secondly, comparisons of four common homogenization procedures are shown: the strain energy balance method, the plate approximation method, a direct approach via area averaging, and asymptotic expansion homogenization. As a limiting case, all of the methods obtain the well‐known Rule of Mixtures for a unidirectional uniaxial specimen. In attempting to consolidate much of the existing knowledge of structural constitutive models for woven fabric composites, this research seeks to summarize and compare various homogenization methods via finite element analyses. Finally, some illustrative applications are presented. Copyright © 1999 John Wiley & Sons, Ltd.     

EKF和PF算法及其在目标跟踪中的应用

基于贝叶斯滤波的目标跟踪原理,介绍了扩展卡尔曼滤波(Extended Kalman Filter,EKF)和粒子滤波(ParticleFilter,PF)的基本思想和算法实现步骤。在非线性环境下对比分析了EKF算法和PF算法的估计精度,并给出两种方法的适用条件。EKF算法采用Taylor展开的线性变换来近似非线性模型,而PF算法采用一些带有权值的随机样本来表示所需要的后验概率密度。仿真结果表明,在强非线性非高斯环境下,PF算法的跟踪性能远优于EKF算法,当系统非线性强度不大时,EKF算法和PF算法的估计精度相差不大,但PF算法计算复杂,跟踪时间长,实时性差。     

Magnetic sensors and their applications

Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented.     

Nanofluidic devices and their applications

Recent developments in micro- and nanotechnologies made possible the fabrication of devices integrating a deterministic network of nanochannels, i.e., with at least one dimension in a range from 1 to 100 nm. The proximity of this dimension and the Debye length, the size of biomolecules such as DNA or proteins, or even the slip length, added to the excellent control on the geometry gives unique features to nanofluidic devices. This new class of devices not only finds applications wherever less well-defined porous media, such as electrophoresis gels, have been traditionally used but also give a new insight into the sieving mechanisms of biomolecules and the fluid flow at the nanoscale. Beyond this, the control on the geometry allows smarter design resulting, among others, in new separation principles by taking advantage of the anisotropy. This perspective gives an overview on the fabrication technologies of nanofluidic devices and their applications. In the first part, the current state of the art of nanofluidic fabrication is presented. The second part first discusses the key transport phenomena in nanochannels. Current applications of nanofluidic devices are next discussed. Finally, future challenges and possible applications are highlighted.     

化学气相沉积反应研究的量子化学方法及应用

量子化学方法在研究化学气相沉积反应体系的反应机理、动力学计算方面有很大的潜力.本文分析了化学气相沉积过程的特点,并对量子化学计算的主要方法进行介绍.在此基础上,针对气相和表面基元过程的量子化学研究现状进行总结和评述.     

Low-resistance ohmic contacts to SiC nanowires and their applications to field-effect transistors

We report on the electrical characterization of two ohmic contacts (Ti/Au and Ni/Au) to unintentionally doped silicon carbide nanowires (SiCNWs) using the modified transmission line model (TLM) method. Our results indicate that subsequently deposited Ni/Au ohmic contacts on SiCNWs had ～40 times lower specific contact resistances (SCRs) of 5.9 × 10(-6) ± 8.8 × 10(-6)?Ω?cm(2) compared to the values of Ti/Au ohmic contacts (2.6 × 10(-4) ± 3.4 × 10(-4)?Ω?cm(2)). We also conducted a comparison study of the electrical characteristics of top-gated SiCNW field-effect transistors (FETs) with two different ohmic contacts as used for ohmic contact studies. The electrical transport measurements on the SiCNW FET with Ni/Au ohmic contacts show much lower resistance contacts to SiC NWs and better FET performances than those for Ti/Au ohmic contact-based FETs.     

Introduction to the feature on spatial light modulators and their applications

The special issue of Applied Optics on spatial light modulators presents a collection of papers that describe improvements in basic devices, smart pixels, and system applications.     

Acoustic properties of plasma-sprayed coatings and their applications to non-destructive evaluation

Measurements were made of the attenuation in thin samples of plasma-sprayed molybdenum, nickel aluminide and aluminium in the frequency range 2.5–15 MHz. It was shown that the attenuation is dependent on the structure and thickness of the coating. A simple system to produce C scans of sprayed coatings is described and its ability to detect adhesion defects is demonstrated. Preliminary studies of the acoustic emission of sprayed samples in bending suggests that the pattern of the emission reflects the integrity of the coatings.     

Lithium solid electrolytes and their applications

The preparation, characterisation and applications of two systems of lithium ion conductors, lithium zinc germanate (Lisicon) and lithium germanate vanadate are described. Ionic conductivity studies include ac conductivity, thermopower andnmr which provide complementary information. High pressure studies and fabrication of a solid-state cell are also reported. An erratum to this article is available at .     

Soluble carbon nanotubes and their applications

Carbon nanotubes (CNTs) have been the forefront of nanoscience and nanotechnology due to their unique electrical and mechanical properties and specific functions. However, due to their poor solubility in solvents, the applications using the materials have been limited. Therefore, strategic approaches toward the solubilization of CNTs are important in wide fields including chemistry, physics, biochemistry, biology, pharmaceuticals, and medical sciences. In this article, we summarize: (i) the strategic approaches toward the solubilization of CNTs using chemical and physical modifications, (ii) nanocomposites of CNTs and biological molecules including DNA, (iii) formation of CNTs with topological structures, (iv) separation of metallic and semiconducting nanotubes, (v) the preparations of films and fibers of CNTs and hybrid materials of CNTs and organic and inorganic molecules.     

Ferroelectric films and their device applications

Recent reseach on ferroelectric films is discussed, with emphasis on preparative problems, optimization of film structure and of electrical properties and application in devices. Rapid progress has been made in each of these research areas and this fact, together with the emergence of certain new materials such as polyvinylidene fluoride (PVF₂), is increasing the variety of possible applications to solid state devices. Typical examples considered here include microwave capacitors, thermistor bolometers, pyroelectrics, piezoelectric transducers, memories and optical display devices. The present state of the art for these applications and materials development needed for further progress are reviewed.     

Nanocellulose-stabilized Pickering emulsions and their applications

Abstract

Pickering emulsion, which is an emulsion stabilized by solid particles, offers a wide range of potential applications because it generally provides a more stable system than surfactant-stabilized emulsion. Among various solid stabilizers, nanocellulose may open up new opportunities for future Pickering emulsions owing to its unique nanosizes, amphiphilicity, and other favorable properties (e.g. chemical stability, biodegradability, biocompatibility, and renewability). In this review, the preparation and properties of nanocellulose-stabilized Pickering emulsions are summarized. We also provide future perspectives on their applications, such as drug delivery, food, and composite materials.     

Nanocellulose-based films and their emerging applications

Extensive research has been directed towards the reinvention of paper for advanced applications. Nanocellulose-based films, a novel class of specialty paper primarily made of nanocellulose, demonstrate an ideal combination of sustainability and enhanced or novel properties. Enormous efforts have been devoted to enhancing these intrinsic properties and/or creating novel functions to expedite and expand the use of these materials in high-end fields such as touchscreen, solar cells, and nanogenerators. We review state-of-the-art advances in nanocellulose-based films and their utilization in several emerging and promising fields. We begin with an introduction of four types of nanocellulose-based films distinguished by their functional material loads (e.g., synthetic macromolecular polymers, 0D, 1D, and 2D nanomaterials), which involves their manufacturing techniques, structure design, properties, novel functions, and underlying principles. Additionally, we summarize the value-added applications of nanocellulose-based films in flexible electronics, energy converting or harvesting devices, and water treatment. Finally, we provide a critical viewpoint on the remaining challenges and future opportunities in this field.