Structural coloring in large scale core-shell nanowires

We demonstrated two complementary size-dependent structural coloring mechanisms, interference and scattering, in indefinitely long core-shell nanowire arrays. The unusual nanostructures are comprised of an amorphous semiconducting core and a polymer shell layer with disparate refractive indices but with similar thermomechanical properties. Core-shell nanowires are mass produced from a macroscopic semiconductor rod by using a new top-to-bottom fabrication approach based on thermal size reduction. Nanostructures with diameters from 30 to 200 nm result in coloration that spans the whole visible spectrum via resonant Mie scattering. Nanoshell coloration based on thin film interference is proposed as a structural coloration mechanism which becomes dominant for nanowires having 700-1200 nm diameter. Controlled color generation in any part of visible and infrared spectral regions can be achieved by the simple scaling down procedure. Spectral color generation in mass-produced uniform core-shell nanowire arrays paves the way for applications such as spectral authentication at nanoscale, light-scattering ingredients in paints and cosmetics, large-area devices, and infrared shielding.     

Evaluation of art subjects implemented in the marquetry technique by the optical coherence microscopy method

Evaluation of internal microstructure of decorative and applied art objects implemented in the intarsia and marquetry techniques by the optical coherence tomography method is considered. The high resolving optical coherence microscope with a radiation source with tunable wavelength in the range of 1305 ± 75 nm was applied. The ability to analyse layered microstructure of wood object surface layer in intarsia regions is demonstrated. The geometric features evaluation of the object's microstructure in the areas of interest was conducted. Systematisation of layers structure and typical defects inherent in intarsia regions was performed considering the structural features that may be important for restoration of such objects. Examples of experimentally obtained B‐scans and three‐dimensional representations of sample fragments of microstructure studied by the optical coherence microscopy method are given.     

Thin-film biological reflectors: optical characterization of the Chrysiridia croesus moth

The optical properties of colored wing scales of the Chrysiridia croesus moth were investigated experimentally and theoretically by reflection spectroscopy and ellipsometry. Transmission electron microscope micrographs show that the outer surfaces of these scales incorporate a fairly regular layered structure of alternating dense and less-dense material, which reflects light by the well-known thin-film interference process. A Monte Carlo-type simulation of the reflection process is discussed, which permits the determination of the complex index of refraction of the scale material.     

鲍鱼壳珍珠层无机文石片的层状微结构研究

贝壳珍珠层是软体动物壳的最内层,经过若干世纪的自然进化,贝壳珍珠层形成了优良的微结构,并使贝壳具有了相当高的强度、刚度及断裂韧性.本文利用扫描电镜(SEM)观察了鲍鱼贝壳珍珠层的主要微结构特征,发现其是由层状的无机文石片和有机胶原蛋白质组成的生物陶瓷复合材料.根据发现的贝壳珍珠层层状微结构特征,建立贝壳珍珠层三维有限元模型,并用此模型分析了珍珠层的拉伸屈服极限与无机文石片拉伸屈服极限及其厚度的关系,研究表明珍珠层的屈服极限随无机文石片屈服极限的增加和无机文石片厚度的减小而增加.     

The Optical Janus Effect: Asymmetric Structural Color Reflection Materials

Structurally colored materials are often used for their resistance to photobleaching and their complex viewing‐direction‐dependent optical properties. Frequently, absorption has been added to these types of materials in order to improve the color saturation by mitigating the effects of nonspecific scattering that is present in most samples due to imperfect manufacturing procedures. The combination of absorbing elements and structural coloration often yields emergent optical properties. Here, a new hybrid architecture is introduced that leads to an interesting, highly directional optical effect. By localizing absorption in a thin layer within a transparent, structurally colored multilayer material, an optical Janus effect is created, wherein the observed reflected color is different on one side of the sample than on the other. A systematic characterization of the optical properties of these structures as a function of their geometry and composition is performed. The experimental studies are coupled with a theoretical analysis that enables a precise, rational design of various optical Janus structures with highly controlled color, pattern, and fabrication approaches. These asymmetrically colored materials will open applications in art, architecture, semitransparent solar cells, and security features in anticounterfeiting materials.     

Case study of modeled aerosol optical properties during the SAFARI 2000 campaign

We present modeled aerosol optical properties (single scattering albedo, asymmetry parameter, and lidar ratio) in two layers with different aerosol loadings and particle sizes, observed during the Southern African Regional Science Initiative 2,000 (SAFARI 2,000) campaign. The optical properties were calculated from aerosol size distributions retrieved from aerosol layer optical thickness spectra, measured using the NASA Ames airborne tracking 14-channel sunphotometer (AATS-14) and the refractive index based on the available information on aerosol chemical composition. The study focuses on sensitivity of modeled optical properties in the 0.3-1.5 microm wavelength range to assumptions regarding the mixing scenario. We considered two models for the mixture of absorbing and nonabsorbing aerosol components commonly used to model optical properties of biomass burning aerosol: a layered sphere with absorbing core and nonabsorbing shell and the Maxwell-Garnett effective medium model. In addition, comparisons of modeled optical properties with the measurements are discussed. We also estimated the radiative effect of the difference in aerosol absorption implied by the large difference between the single scattering albedo values (approximately 0.1 at midvisible wavelengths) obtained from different measurement methods for the case with a high amount of biomass burning particles. For that purpose, the volume fraction of black carbon was varied to obtain a range of single scattering albedo values (0.81-0.91 at lambda=0.50 microm). The difference in absorption resulted in a significant difference in the instantaneous radiative forcing at the surface and the top of the atmosphere (TOA) and can result in a change of the sign of the aerosol forcing at TOA from negative to positive.     

The Influence of a Surface Coating on the High-rate Fragmentation of a Ductile Material

A bifurcation analysis of a layered ductile structural element undergoing homogeneous, high-rate extension is presented. Formation of multiple strain localization sites provides a precursor to ductile fragmentation, and the objective of the analysis is to investigate the effect of an added surface layer on resistance of the structural element to fragmentation. The analysis shows that, in addition to dissipating plastic work, the outer layer can increase the total energy dissipation prior to fragmentation by increasing bifurcation strain. The analysis also shows that the strain hardening exponent of the outer layer plays an important role in increasing the bifurcation strain; higher values of hardening exponent result in higher bifurcation strain. Strength and density of the outer layer play a secondary role in increasing bifurcation strain. Once a material with a high hardening exponent is chosen for the outer material, its strength plays an important role in increasing the total dissipated energy. The analysis also reveals that, for certain combinations of strength and hardening exponent of the outer layer, the sandwich structure can dissipate more energy than a homogeneous core structure of the same total thickness and length. This is so even when the outer layer is weaker than the core. Energy dissipated per unit mass can be significantly improved by choosing a softer outer layer which displays high-strain hardening. Thus, the bifurcation analysis presented here provides a quantitative guideline for material selection in designing layered structures optimized for resistance to fragmentation.     

Sensitivity studies for imaging a spherical object embedded in a spherically symmetric, two-layer turbid medium with photon-density waves

We present analytic expressions for the amplitude and phase of photon-density waves in strongly scattering, spherically symmetric, two-layer media containing a spherical object. This layered structure is a crude model of multilayered tissues whose absorption and scattering coefficients lie within a range reported in the literature for most tissue types. The embedded object simulates a pathology, such as a tumor. The normal-mode-series method is employed to solve the inhomogeneous Helmholtz equation in spherical coordinates, with suitable boundary conditions. By comparing the total field at points in the outer layer at a fixed distance from the origin when the object is present and when it is absent, we evaluate the potential sensitivity of an optical imaging system to inhomogeneities in absorption and scattering. For four types of background media with different absorption and scattering properties, we determine the modulation frequency that achieves an optimal compromise between signal-detection reliability and sensitivity to the presence of an object, the minimum detectable object radius, and the smallest detectable change in the absorption and scattering coefficients for a fixed object size. Our results indicate that (l) enhanced sensitivity to the object is achieved when the outer layer is more absorbing or scattering than the inner layer; (2) sensitivity to the object increases with the modulation frequency, except when the outer layer is the more absorbing; (3) amplitude measurements are proportionally more sensitive to a change in absorption, phase measurements are proportionally more sensitive to a change in scattering, and phase measurements exhibit a much greater capacity for distinguishing an absorption perturbation from a scattering perturbation.     

Structure-based color of natural petals discriminated by polymer replication

The optical appearance of many flowers in nature relies on their inherent pigments ("chemical color") as well as on the surface structure of the epidermis ("structural color"). The structural color is created by a combination of regular and irregular micro- and nanosized features. With a red rose petal as a biological template, we have separated the structural coloration from the chemical coloration by reproducing the petal's intricate surface structure in a pigment-free polymer. UV-vis reflectance measurements of the templates showed that the pigment-induced chemical coloration of the red-rose petal results in intense absorption and reflection in the green (～550 nm) and red (～700 nm) spectral region, respectively. The micro- and nanosized structural hierarchy on the petal surface, on the other hand, induced a modulation of the optical reflectivity and a filtering effect in specific wavelength ranges. More notably, we observed that a variation in the size of the micro/nanostructures on the petal surface leads to an effective modulation of the reflectance. These results could provide useful tips for the design of bioinspired optical devices, emulating natural petal structures.     

氧化锌/二氧化硅复合膜的结构色研究

采用静电自组装技术,以氧化锌（ZnO）和二氧化硅（SiO2）溶胶颗粒为前驱体,通过控制双组分膜层的不同厚度,制备出结构色鲜艳的ZnO/SiO2复合膜,并利用分光测色仪、多角度分光光度仪及扫描电子显微镜等研究复合膜的颜色、微观结构和形态特征。研究结果发现,ZnO/SiO2复合膜的亮度和色度均较单一组分薄膜的高,复合薄膜的颜色仍随厚度和观察角度的变化而变化。通过对薄膜的微观结构分析,结合其厚度随周期数的变化规律,发现复合薄膜的厚度随着自组装循环次数的增加而增加,薄膜中的纳米粒子并没有形成明显的高低折射率交替分布的双层结构,可能形成的是高折射率层（H层）、有效折射率层（eff层）和低折射率层（L层）的多层微观结构。这种特殊的多层结构与光作用发生干涉,形成了鲜亮度和饱和度更高的结构色。     

Effect of Microstructure and Sulfide on Corrosion of Cu-Ni Alloys in Seawater

1. IntroductionThe Cu-Ni alloys become an important category ofmaterials in marine engineering since they are highlyresistant to corrosion caused by seawater and biofouling. These alloys have been widely applied in marineengineering, such ajs condensing tubes in various ships,heat exchangers for electric plants near seashore, andtubes in chlorinating systems. However, early failureand even leakage can occasionally occur during theirservice though Cu-Ni alloys come to practical use fordecades…     

Hollow microspheres with binary colloidal and polymeric membrane: Effect of polymer and particle concentrations

We report here the preparation of hollow microspheres with a binary shell structure consisting of a precipitated polymer film with a layer of colloidal particles embedded on its outer surface. We recently demonstrated a method for the preparation of microspheres from solid-stabilised emulsion templates using various colloidal particle systems as emulsifiers. In the present work we use colloidal silica as an emulsifier for the preparation of the emulsion template for the microspheres and study the effect of polymer and particle concentrations on the obtained structures.Observations using optical microscopy showed that decreasing the polymer concentration led to a reduction in the capsule wall thickness and apparent strength of the microspheres when dried. Importantly, all microspheres preserved their integrity when in suspension. SEM studies confirmed the differences observed in the thickness of the precipitated film at the oil/water interface. In addition, we also demonstrate that a larger particle concentration leads to microspheres with a lower degree of porosity.     

Origin of Interference Colors on Austenitic Stainless Steel

Data are presented on the coloring conditions, colored layer parameters, and color characteristics of stainless steel 304 samples treated in an electrolytic cell (60 Hz, 100 mV) using a mixture of 5 M sulfuric acid and 2.5 M chromic acid. Reflectance spectra indicate that the samples have high-purity color mainly in the yellow region and that the color is due to interference oscillations in the visible range. In addition, reflectance data in conjunction with composition-depth profiles obtained using glow discharge spectrometry indicate that the coloration of the samples is due not only to reflectance oscillations but also to the subtraction effect. The reduced Fe content and significant oxygen content in the near-surface region attest to the formation of a mixed oxide layer. Atomic-force microscopy examination indicates that the sample surface has an island structure.     

Thermal transport in au-core polymer-shell nanoparticles

Thermal transport in aqueous suspensions of Au-core polymer-shell nanoparticles is investigated by time-resolved measurements of optical absorption. The addition of an organic cosolvent to the suspension causes the polystyrene component of the polymer shell to swell, and this change in the microstructure of the shell increases the effective thermal conductivity of the shell by a factor of approximately 2. The corresponding time scale for the cooling of the nanoparticle decreases from 200 ps to approximately 100 ps. The threshold concentration of cosolvent that creates the changes in thermal conductivity, 5 vol % tetrahydrofuran in water or 40 vol % N,N-dimethylformamide in water, is identical to the threshold concentrations for producing small shifts in the frequency of the plasmon resonance. Because the maximum fraction of solvent in the polymer shell is less than 20 vol %, the increase in the effective thermal conductivity of the shell cannot be easily explained by contributions to heat transport by the solvent or enhanced alignment of the polystyrene backbone along the radial direction.     

Modeling of optical properties of silver-doped nanocomposite glasses modified by electric-field-assisted dissolution of nanoparticles

It has been demonstrated recently that silver nanoparticles embedded in a glass matrix can be dissolved by the combination of an intense dc electric field and moderately elevated temperature. In an intermediate state of this process percolated silver layers inside the glass can also occur. These structural modifications significantly modify the optical behavior of the glass, suggesting an interesting perspective for the engineering of optical properties of this kind of metallodielectric materials. We present the optical characterization of silver-doped glasses subjected to the electric-field-assisted dissolution of nanoparticles. The characterization is performed by means of fitting spectrophotometric measurements. The optical properties of the investigated samples are described in terms of the interference between the light reflected from the glass surface and the light reflected from a buried silver-containing layer formed in the depths of the glass. The analysis of the data reveals a porosity of the glass in the region where the nanoparticles are dissolved that can be attributed to the presence of residual nanopores.     

Architecture and composite structure of hornet cuticle (Insecta, Hymenoptera)

The present study is devoted to the microstructure of the cuticle in the gastral segments of the Oriental hornet Vespa orientalis. In order to elucidate the architectural structure in the region of the abdominal strips endowed with yellow pigment, sections were prepared for viewing via scanning electron microscope (SEM) and these revealed that the cuticle in the named regions is of a layered nature, composed of duplex layers, each consisting of a thin double wall of chitin enclosing a filling of proteins as a matrix. There are 30 or more such layers which become progressively thinner as one proceeds from the outside interiorly. A statistical model that describes this decrease in layer thickness was accordingly developed. The semi-log plots obtained from the studied specimens show that the logarithm of layer thickness tends to decrease approximately as a linear function of the number of layers. The importance of such vespan type of architectonics is discussed in terms and is compared with similar structures both in nature and in industry.     

Skin layer of A380 aluminium alloy die castings and its blistering during solution treatment

Skin layer is a characteristic microstructure of aluminium die castings, which would effect the surface blistering during solution treatment. In this study, the microstructures of skin layer were investigated by the methods of optical microscope (OM), scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). High resolution X-ray CT was used to compare the skin layer with normal surface before and after solution treatment. With the aid of computational fluid dynamics (CFD), the formation mechanism of the skin layer was discussed based on microstructure distribution, solute segregation, porosity distribution and surface blistering. The results suggested that the skin layer is related to a succession of complex processes before the filling process finished. Pore clusters or laminar defects would be formed in skin layers during solution treatment and cause severe surface blistering.     

Bioinspired Photonic Pigments from Colloidal Self‐Assembly

The natural world is a colorful environment. Stunning displays of coloration have evolved throughout nature to optimize camouflage, warning, and communication. The resulting flamboyant visual effects and remarkable dynamic properties, often caused by an intricate structural design at the nano‐ and microscale, continue to inspire scientists to unravel the underlying physics and to recreate the observed effects. Here, the methodologies to create bioinspired photonic pigments using colloidal self‐assembly approaches are considered. The physics governing the interaction of light with structural features and natural examples of structural coloration are briefly introduced. It is then outlined how the self‐assembly of colloidal particles, acting as wavelength‐scale building blocks, can be particularly useful to replicate coloration from nature. Different coloration effects that result from the defined structure of the self‐assembled colloids are introduced and it is highlighted how these optical properties can be translated into photonic pigments by modifications of the assembly processes. The importance of absorbing elements, as well as the role of surface chemistry and wettability to control structural coloration is discussed. Finally, approaches to integrate dynamic control of coloration into such self‐assembled photonic pigments are outlined.     

N层过盈联接结合压力算法研究

过盈联接作为联接件间的传统配合方式,具有结构简单、承载能力高等优点,在机械工程领域有着广泛的应用,其研究大多数局限在单层或3层以内的联接.随着机械设备中多层过盈联接应用逐步增多,为进一步完善多层过盈联接设计理论,以厚壁圆筒理论为基础,通过分析过盈联接中各圆筒的几何关系,推导出过盈联接中过盈量与圆筒内、外表面径向位移的变化关系,得到了N层过盈联接结合压力与过盈量的矩阵表达式;用推导所得的解析法和Abaqus数值法,对比分析了过盈联接结合压力和过盈结合面两端存在的应力集中现象.结果表明:N层过盈联接中最内层过盈的结合压力随着过盈层数的增加而增加,结合压力由内到外依次减小;解析法和数值法的计算结果基本吻合,中点相对误差均在4%之内,说明该解析法可以为N层过盈联接设计提供可靠的理论指导.同时,数值法计算中显示在结合面两端存在应力集中,不同模型最内层过盈面的理论应力集中系数差别较小,且各模型中理论应力集中系数由内到外呈现依次增大的规律.提出的算法和所得规律对N层过盈联接的设计研究工作具有一定的指导和帮助.     

Enhancement of wear resistance of ductile iron surface alloyed by stellite 6

This paper deals with the improvement of the wear resistance of ductile iron surface alloyed by a hypoeutectic stellite 6 alloy. In this regard, the surface alloyed layer with 3 mm thickness deposited on ductile iron using tungsten inert gas (TIG) surface processing. The microstructure, hardness and wear resistance of surface alloyed layer were investigated using optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, Vickers hardness (HV0.3) and pin-on-plate tests. The results showed that the microstructure of the surface alloyed layer consisted of carbides dispersed in a Co-based solid solution matrix with dendritic structure. This microstructure was responsible for the improvement of the hardness and wear resistance of the coating. Further investigations showed that the dominant mechanism of the wear in the coated and uncoated samples was delamination wear.