Yule-Nielsen based recto-verso color halftone transmittance prediction model

The transmittance spectrum of halftone prints on paper is predicted thanks to a model inspired by the Yule-Nielsen modified spectral Neugebauer model used for reflectance predictions. This model is well adapted for strongly scattering printing supports and applicable to recto-verso prints. Model parameters are obtained by a few transmittance measurements of calibration patches printed on one side of the paper. The model was verified with recto-verso specimens printed by inkjet with classical and custom inks, at different halftone frequencies and on various types of paper. Predictions are as accurate as those obtained with a previously developed reflectance and transmittance prediction model relying on the multiple reflections of light between the paper and the print-air interfaces. Optimal n values are smaller in transmission mode compared with the reflection model. This indicates a smaller amount of lateral light propagation in the transmission mode.     

An extension of Gurson model incorporating interface stresses effects

The classical Gurson model for ductile porous media is extended to incorporate the surface/interface stresses effect at the nano-scale. For capillary forces, the yield surface is shown to be obtained by a mere translation of Gurson one. For interface stresses obeying a von Mises criterion, the parametric equations of the yield surface are derived. The magnitude of the interface effect is proved to be controlled by a non dimensional parameter depending on the voids characteristic size.     

Sizing of disbonds at a thin-layer substrate interface from spectral peaks

An ultrasonic through transmission technique is used to inspect the interface of a thin layer and a substrate. An experiment is performed using a specimen constructed of a 0.040 inch (1.02 mm) polycarbonate layer bonded by an adhesive film to an aluminum plate. Circular flaws are induced with paper placed between the adhesive film and the polycarbonate layer to create disbonds. The flaws range in size from 0.5 inches (12.7 mm) to 0.067 inches (1.70 mm) in diameter. A through transmission ultrasonic inspection technique, which uses a flat transducer as a transmitter and a focused transducer as a receiver, is employed. Time signals from the receiving transducer are recorded for each flaw, transformed to the frequency domain by use of a fast Fourier transform (FFT), and are linearly deconvolved with the FFT of the time signals of the aluminum plate alone. The peaks of the resulting frequency response functions for each flaw predict the resonant frequencies of the flaws. The area of the thin layer above a disbond is modeled as a thin plate which is excited by the incident ultrasonic wave motion at its edges. The resonance peaks at the center of the plate are related to the size of the flaw. The principal result of the paper is that, based on the theory presented here, the size of the disbond can be obtained from measurements of the resonance peaks.     

Spectral model of a fluorescent ink halftone

A model is presented of a fluorescent ink halftone. Unlike a nonfluorescent ink, which only absorbs, a fluorescent ink absorbs higher-energy photons and emits lower-energy photons. The amount of fluorescent light produced depends on the percent absorption of the incident light. For fluorescent ink printed on paper, both photon scattering within the paper substrate and multiple internal reflections between the ink layer and the paper substrate significantly increase the percent absorption, so a realistic model must include these effects. The model presented here utilizes the generalized Clapper-Yule theory, which accounts for photon diffusion that is due to both scatter and internal reflection. It is shown that while multiple internal reflections alone only marginally increase the percent absorption, when there are both scattering and internal reflection, the percent absorption is increased significantly. The current study is a theoretical model and does not present experimental results.     

Reflectance and transmittance model for recto-verso halftone prints

We propose a spectral prediction model for predicting the reflectance and transmittance of recto-verso halftone prints. A recto-verso halftone print is modeled as a diffusing substrate surrounded by two inked interfaces in contact with air (or with another medium). The interaction of light with the print comprises three components: (a) the attenuation of the incident light penetrating the print across the inked interface, (b) the internal reflectance and internal transmittance that accounts for the substrate's intrinsic reflectance and transmittance and for the multiple Fresnel internal reflections at the inked interfaces, and (c) the attenuation of light exiting the print across the inked interfaces. Both the classical Williams-Clapper and Clapper-Yule spectral prediction models are special cases of the proposed recto-verso reflectance and transmittance model. We also extend the Kubelka-Munk model to predict the reflectance and transmittance of recto-verso halftone prints. The extended Kubelka-Munk model is compatible with the proposed recto-verso reflectance and transmittance model. In the case of a homogeneous substrate, the recto-verso model's internal reflectance and transmittance can be expressed as a function Kubelka-Munk's scattering and absorption parameters, or the Kubelka-Munk's scattering and absorption parameters can be inferred from the recto-verso model's internal reflectance and transmittance, deduced from spectral measurements. The proposed model offers new perspectives both for spectral transmission and reflection predictions and for characterizing the properties of printed diffuse substrates.     

Weighted compression of spectral color information

Spectral color information is used nowadays in many different applications. Accurate spectral images are usually very large files, but a proper compression method can reduce needed storage space remarkably with a minimum loss of information. In this paper we introduce a principal component analysis (PCA) -based compression method of spectral color information. In this approach spectral data is weighted with a proper weight function before forming the correlation matrix and calculating the eigenvector basis. First we give a general framework for how to use weight functions in compression of relevant color information. Then we compare the weighted compression method with the traditional PCA compression method by compressing and reconstructing the Munsell data set consisting of 1,269 reflectance spectra and the Pantone data set consisting of 922 reflectance spectra. Two different weight functions are proposed and tested. We show that weighting clearly improves retention of color information in the PCA-based compression process.     

Oceanic radiance model development and validation: application of airborne active-passive ocean color spectral measurements

It is shown that airborne active-passive (laser-solar) ocean color data can be used to develop and validate oceanic radiance models. The two principal inputs to the oceanic radiance model, chlorophyll pigment and incident solar irradiance, are obtained from a nadir-viewing laser-induced fluorescence spectrometer and a zenith-viewing radiometer, respectively. The computed water-leaving radiances are validated by comparison with the calibrated output of a separate nadir-viewing radiometer subsystem. In the North Atlantic Ocean, the calculated and the observed airborne radiances are found to compare very favorably for the 443-, 520-, and 550-nm wavelengths over an ～ 170-km flight track east of St. John's, Newfoundland. The results further suggest that the semianalytical radiance model of ocean color, the airborne active (laser) fluorescence spectrometer, and the passive (solar) radiometric instrumentation are all remarkably precise.     

Simultaneous two-photon spectral and lifetime fluorescence microscopy

When a fluorescence photon is emitted from a molecule within a living cell it carries a signature that can potentially identify the molecule and provide information on the microenvironment in which it resides, thereby providing insights into the physiology of the cell. To unambiguously identify fluorescent probes and monitor their physiological environment within living specimens by their fluorescent signatures, one must exploit as much of this information as possible. We describe the development and implementation of a combined two-photon spectral and lifetime microscope. Fluorescence lifetime images from 16 individual wavelength components of the emission spectrum can be acquired with 10-nm resolution on a pixel-by-pixel basis. The instrument provides a unique visualization of cellular structures and processes through spectrally and temporally resolved information and may ultimately find applications in live cell and tissue imaging.     

Maximum a posteriori estimation of spectral reflectance from color image and multipoint spectral measurements

Accurate color image reproduction under arbitrary illumination can be realized if the spectral reflectance functions in a scene are obtained. Although multispectral imaging is one of the promising methods to obtain the reflectance of a scene, it is expected to reduce the number of color channels without significant loss of accuracy. This paper presents what we believe to be a new method for estimating spectral reflectance functions from color image and multipoint spectral measurements based on maximum a posteriori (MAP) estimation. Multipoint spectral measurements are utilized as auxiliary information to improve the accuracy of spectral reflectance estimated from image data. Through simulations, it is confirmed that the proposed method improves the estimation accuracy, particularly when a scene includes subjects that belong to various categories.     

Improvement of color reproduction in color digital holography by using spectral estimation technique

We propose a color digital holography by using spectral estimation technique to improve the color reproduction of objects. In conventional color digital holography, there is insufficient spectral information in holograms, and the color of the reconstructed images depend on only reflectances at three discrete wavelengths used in the recording of holograms. Therefore the color-composite image of the three reconstructed images is not accurate in color reproduction. However, in our proposed method, the spectral estimation technique was applied, which has been reported in multispectral imaging. According to the spectral estimation technique, the continuous spectrum of object can be estimated and the color reproduction is improved. The effectiveness of the proposed method was confirmed by a numerical simulation and an experiment, and, in the results, the average color differences are decreased from 35.81 to 7.88 and from 43.60 to 25.28, respectively.     

An interface crack between an orthotropic thin film and substrate

This work is concerned with a semi-infinite interface crack between a thin film and a substrate. The two materials are assumed to be linearly elastic and orthotropic. A solution is presented for the stress field due to an edge dislocation on the interface which is valid for any combinations of material parameters. It is found that the behavior of such a bi-material system is governed by 6 independent material parameters. The stress intensity factor is computed for general edge loadings by solving integral equations numerically, and the size of the K-dominant zone is also studied for a residually stressed thin film. The situations in which the K-field zone of dominance is very small are identified and discussed.     

Probabilistic model of early fatigue crack growth

A model is developed in this paper to describe the nucleation and early growth of fatigue cracks. Polycrystalline materials are modelled as a set of elements (grains) with random properties. It is assumed that the resistance to damage of neighboring elements is mutually independent and follows the same probability distribution, except for the elements situated near the surface whose resistance is lower and which are subjected to higher scattering. Damage accumulation in each element due to cyclic loading is considered, and an element is treated as ruptured when a critical damage level is attained; then the ruptured element is included in the cracked domain. The finite element technique is applied to realize the modelling. Numerical results exhibit all the principal features of early fatigue crack growth such as nonmonotonous change of crack growth rates, statistical scatter of crack dimensions and growth rates, and stabilization of the process when a considerable number of grains enter the cracked domain.     

Dominant wavelength sensitivity of thin-film color filters to spectral centering

The dominant wavelength shift of 16 color filters is presented for a ±1% theoretical change in spectral centering and compared with the threshold-perceived color difference (dominant wavelength). The resulting change in dominant wavelength exceeds a threshold limit of a just-noticed color difference for some filters. Spectral-centering tolerance limits are given for the dominant wavelength to be at the threshold limit. The change in dominant wavelength is also presented from normal incidence to 60° angle of incidence, with incidence-angle limits and corresponding f-numbers for optical systems. For comparison, the color difference Δ E*(uv), from the L*u*v* color space, is calculated for each filter for ±1% spectral centering.     

Analytic model of ocean color

Ocean color is determined by spectral variations in reflectance at the sea surface. In the analytic model presented here, reflectance at the sea surface is estimated with the quasi-single-scattering approximation that ignores transspectral processes. The analytic solutions we obtained are valid for a vertically homogeneous water column. The solution provides a theoretical expression for the dimensionless, quasi-stable parameter (r), with a value of ~0.33, that appears in many models in which reflectance at the sea surface is expressed as a function of absorption coefficient (a) and backscattering coefficient (b(b)). In the solution this parameter is represented as a function of the mean cosines for downwelling and upwelling irradiances and as the ratio of the upward-scattering coefficient to the backscattering coefficient. Implementation of the model is discussed for two cases: (1) that in which molecular scattering is the main source of upwelling light, and (2) that in which particle scattering is responsible for all the upwelled light. Computations for the two cases are compared with Monte Carlo simulations, which accounts for processes not considered in the analytic model (multiple scattering, and consequent depth-dependent changes in apparent optical properties). The Monte Carlo models show variations in reflectance with the zenith angle of the incident light. The analytic model can be used to reproduce these variations fairly well for the case of molecular scattering. For the particle-scattering case also, the analytic and Monte Carlo models show similar variations in r with zenith angle. However, the analytic model (as implemented here) appears to underestimate r when the value of the backscattering coefficient b(b) increases relative to the absorption coefficient a. The errors also vary with the zenith angle of the incident light field, with the maximum underestimate being approximately 0.06 (equivalent to relative errors from 12 to 17%) for the range of b(b)/a studied here. One implication of this result is that the model could also be used to obtain approximate solutions for the Q factor, defined for a given look angle as the ratio of the upwelling irradiance at the surface to the upwelling radiance at the surface at that angle. This is a quantity that is important in remote-sensing applications of ocean-color models. An advantage of the model discussed here is that its implementation requires inputs that are in principle accessible only in a remote-sensing context.     

Probabilistic model of fatigue fracture of carbon nanostructures

Presented evaluation of risk of fatigue fracture of carbon nanostructures (CN) is based on: (a) the criterion of the threshold of the dissipated energy of tensile stresses, and (b) simulation of stochastic character of fracture by the failures in queueing system. The assessments of probability of fatigue fracture of CN in conditions of uniaxial tension, plane torsion and uniaxial compression are done.     

Effects of interface roughness on the spectral properties of thin films and multilayers

We introduce two parameters, large-scale and small-scale rms roughness, to take into account the interface properties of thin films and multilayers in the calculation of their specular reflectance and transmittance. A theoretical motivation for the introduction of these two parameters instead of a standard single rms roughness is provided. Experimental power spectral density functions of several samples are used to illustrate ways in which the parameters introduced can be evaluated.     

金属陶瓷覆层-钢基体界面结合状态的研究

为提高钢基材料的耐磨性和耐腐蚀性,以金属Mo粉、Fe粉和B-Fe合金粉末为原料,采用原位反应真空液相烧结技术,在钢基体表面制备三元硼化物金属陶瓷覆层.测定了覆层-钢基体界面结合强度及界面结合区的显微硬度变化,研究了界面微观结构和界面区元素分布,并对覆层-钢基体界面层形成的机理进行了分析.结果表明,覆层与钢基体之间的断裂破坏发生于界面附近的钢基体和覆层内,而不是覆层与钢基体之间结合界面的剥离;在覆层-钢基体结合界面处,存在由高硬度覆层到低硬度钢基体的狭窄过渡区,合金元素的分布形成具有一定厚度的过渡层.     

Crack initiation strength of an interface between a submicron-thick film and a substrate

The focus of this study was to evaluate the fracture initiation criteria of the interface between a thin film and a substrate by Bogy’s, Kitamura’s and Griffth’s methods. The critical stress intensity parameter K_ijC in Bogy’s method and the concentrated stress parameter σ_ijC in Kitamura’s method were calculated based on the singular stress field near the interface edge. The work of separation per unit area Γ_ο in Griffth’s method was calculated based on the work of fracture process. The results obtained show that in comparison among interface strengths, the fracture toughness K_θθC and the concentrated stress parameter σ_θθC were respectively applied to material combinations with specific edge geometry and with weak stress singularity, while the work of separation per unit area Γ_ο was applied in all cases.     

镍基喷焊涂层与钛合金基体界面特征的研究

考察了三种工艺制备的镍基喷焊涂层与钛合金基体结合界面的组织形貌、涂层横切面上合金元素的扩散和显微硬度的变化,分析了它们的界面特征及影响因素.结果表明:镍基喷焊涂层与基体钛合金的结合是基于合金元素扩散的冶金结合,合金元素的扩散对涂层与基体能否形成冶金结合具有决定性的影响,钛合金表面的活化处理、涂层合金重熔时液态停留时间以及喷焊后进行时效处理是影响合金元素扩散的主要因素.