Random phase mask as a model of a rough surface: Part II. Experiment

Artificial roughness was created on sample surfaces by etching through a two-dimensional orthogonal grating with a stochastic distribution of square "defects" of size. "Defects" depth was varied from 0.02 μm up to 1.005 μm. The experimental dependences of the scattering of polarized light were studied on four types of surface roughness for two materials: quartz and aluminum. The defect sizes of the random phase mask were 25 × 25 μm and 2.5 × 2.5 μm. The impacts of the sizes and density of artificial defects of rough surfaces on the polarization of reflected light were investigated by multiple-angle-of-incidence (MAI) ellipsometry at a wavelength of 0.63 μm.     

Investigation of surface roughness on etched glass surfaces

Roughening the surface of solar cells is a common practice within the photovoltaic industry as it reduces reflectance, and thus enhances the performance of devices. In this work the relationship between reflectance characterized by the haze parameter, surface roughness and optical properties was investigated. To achieve this goal, model samples were prepared by hydrofluoric acid etching of glass for various times and measured by optical microscopy, spectroscopic ellipsometry, scanning electron microscopy, and atomic force microscopy. Our investigation showed that the surface reflectance was decreased not only by the roughening of the surface but also by the modification of the depth profile and lowering of the refractive index of the surface domain of the samples.     

Effect of a spoke surface error on a phase mask in a computational imaging system

The effect of a spoke surface error on a phase mask in a computational imaging system was analyzed by combining the similarity of the point spread function (PSF) and the peak signal-to-noise ratio (PSNR) of de-convoluted images. The spoke surface error was applied on a phase mask with different peak-to-valley (P-V) values with various numbers of spoke rings in simulation. The minimum requirement of PSF similarity will be determined by a given PSNR threshold, which relates the defocus aberration. Finally, it can be concluded that a low-spatial frequency surface error is critical for a cubic phase mask in a computational imaging system with lower P-V error.     

First-principles calculations of a corrugated anatase TiO2 surface

The structural, electronic and optical properties of a corrugated anatase TiO₂ surface are studied using the pseudopotential density-functional theory (DFT). The calculation of the electronic and optical properties provides the electronic and optical band gaps. The optical band gap is calculated using the photon energy dependent imaginary part of the dielectric function that indicates the exact optical transitions from occupied valence bands to unoccupied conduction bands. The estimated optical band gap is higher than the electronic band gap at the Γ point and shows consistency with the experimental band gap of an anatase TiO₂ thin-film. This result also shows the significant optical anisotropy in directions normal and parallel to the corrugated surface.     

Analytical model for the optical functions of indium gallium nitride with application to thin film solar photovoltaic cells

This paper presents the preliminary results of optical characterization using spectroscopic ellipsometry of wurtzite indium gallium nitride (In_xGa_1−xN) thin films with medium indium content (0.38 < x < 0.68) that were deposited on silicon dioxide using plasma-enhanced evaporation. A Kramers-Kronig consistent parametric analytical model using Gaussian oscillators to describe the absorption spectra has been developed to extract the real and imaginary components of the dielectric function (?₁, ?₂) of In_xGa_1−xN films. Scanning electron microscope (SEM) images are presented to examine film microstructure and verify film thicknesses determined from ellipsometry modeling. This fitting procedure, model, and parameters can be employed in the future to extract physical parameters from ellipsometric data from other In_xGa_1−xN films.     

On the influence of silicon oxide nanoparticles on the optical and surface properties of hybrid (inorganic–organic) barrier materials

One of the major scientific and technological challenges for the production of flexible organic electronic devices is the device protection against atmospheric molecule permeation, which causes corrosion reducing its operation and lifetime. In this work, Spectroscopic Ellipsometry has been implemented to investigate the influence of silicon dioxide nanoparticles on the optical properties of hybrid polymers. The spectra analysis revealed valuable information about the electronic and vibrational response as well as the cross-linking mechanisms of these materials. The correlation of the optical properties with the synthesis parameters and the barrier response will contribute towards their optimization in order to be used as high barrier coatings for flexible organic electronics applications.     

Modeling of coalescence of dispersed surface cracks. Part 2. Simulation model for multiple fracture

Abstarct A simulation model for multiple fracture has been developed that reproduces random processes of initiation, growth, and coalescence of dispersed surface cracks. The model is based on the method of statistical simulation (Monte Carlo method) and on the fracture regularities determined experimentally. The main factor responsible for fracture is found to be the coalescence of dispersed cracks, especially at the final stage, which accounts for about 30% of the total life. The ultimate state of a structure is defined by the condition according to which the length of the largest of the available damages is bigger than the calculated value of the maximum crack length.Translated from Problemy Prochnosti, No. 1, pp. 108–117, January–February, 2005.     

CFD simulation of particle segregation in a rotating drum. Part I: Eulerian solid phase kinetic viscosity

Although the Eulerian approach coupling the kinetic theory of granular flow is usually used to study granular flows with relative lower solid fractions, it can be used to study relative denser granular flows if appropriate solid phase kinetic viscosity values were adopted. A granular bed surface fitting (BSF) method is proposed to determine the appropriate solid phase kinetic viscosities of the granular flows in a rotating drum. The specularity coefficient is also used to address the interaction between particles and the drum wall. The BSF solid phase kinetic viscosity increases with decreasing of particle sizes and drum rotational speeds. The BSF solid phase kinetic viscosity and the specularity coefficient follow a power-law relationship with 0.6–1.1 as the exponent of the specularity coefficient. The BSF solid phase kinetic viscosities for the particles of two different sizes are used to study particle segregation in a rotating drum. The core thickening segregation mechanism and the segregation band formations are well predicted.     

Direct patterning of polymer-based photo luminescent structures with a mask

We report a simple method to directly pattern polymer-based photo luminescent material, i.e. a prepatterned mask is placed a close distance above it. The final structure is a positive replica of the lateral structures in the mask with submicrometer resolution. The comparison of luminescence efficiency before and after patterning indicates almost no degradation in optical property of the material during the experiments. The mechanism of pattern formation is also discussed.     

Scattering of the electromagnetic waves from a rough surface

The electromagnetic field scattered by a rough surface of a semi-infinite body is computed up to the second order of a perturbation scheme with the surface roughness as a perturbation parameter. The calculations are based on the equation of motion of the polarization within the Lorentz–Drude (plasma) model of polarizable, non-magnetic, homogeneous matter. The surface roughness contributes both to the main (specularly) reflected and refracted fields and diffuse scattering, or gives rise to secondary (second-order) diffraction peaks for a regular grating. The calculations are performed both for the s- and p-waves. Two-dimensional modes, resonant at certain frequencies, are identified, confined to and propagating only on the surface, as a consequence of the surface roughness.     

On the overall elastic moduli of polymer-clay nanocomposite materials using a self-consistent approach. Part I: Theory

Although few investigations recently proposed to describe the overall elastic response of polymer-clay nanocomposite materials using micromechanical-based models, the applicability of such models for nanocomposites is far from being fully established. The main point of criticism to mention is the shelving of crucial physical phenomena, such as interactions and length scale effects, generally associated by material scientists, in addition to the nanofiller aspect ratio, to the remarkable mechanical property enhancement of polymer-clay nanocomposites. In this Part I of two-part paper, we present a micromechanical approach for the prediction of the overall moduli of polymer-clay nanocomposites using a self-consistent scheme based on the double-inclusion model. This approach is used to account for the inter-inclusion and inclusion-matrix interactions. Although neglected in the models presented in the literature, the active interaction between the nanofillers should play a key role in the reinforcing effect of nano-objects dispersed in a polymer matrix. The present micromechanical model incorporates the nanostructure of clay stacks, modeled as transversely isotropic spheroids, and the so-called constrained region, modeled as an interphase around reinforcements. This latter is linked to the interfacial interaction between matrix and reinforcements that forms a region where the polymer chain mobility is reduced. To account for length scale effects, interphase thickness and particle dimensions are taken as explicit model parameters. Instead of solving iteratively the basic homogenization equation of the self-consistent scheme, our formulation yields to a pair of equations that can be solved simultaneously for the overall elastic moduli of composite materials. When the interphase is disregarded for spheroids with zero aspect ratio, our formulation coincides with the Walpole solution (J Mech Phys Solids 1969;17:235-251). Using the proposed general form, a parametric study is presented to analyze the respective influence of aspect ratio, number of silicate layers, interlayer spacing and nanoscopic size of the transversely isotropic spheroids on the overall elastic moduli of nanocomposite materials.     

Automatic metric 3D surface mesh generation using subdivision surface geometrical model. Part 2: Mesh generation algorithm and examples

In this paper, a new metric advancing front surface mesh generation scheme is suggested. This new surface mesh generator is based on a new geometrical model employing the interpolating subdivision surface concept. The target surfaces to be meshed are represented implicitly by interpolating subdivision surfaces which allow the presence of various sharp and discontinuous features in the underlying geometrical model. While the main generation steps of the new generator are based on a robust metric surface triangulation kernel developed previously, a number of specially designed algorithms are developed in order to combine the existing metric advancing front algorithm with the new geometrical model. As a result, the application areas of the new mesh generator are largely extended and can be used to handle problems involving extensive changes in domain geometry. Numerical experience indicates that, by using the proposed mesh generation scheme, high quality surface meshes with rapid varying element size and anisotropic characteristics can be generated in a short time by using a low‐end PC. Finally, by using the pseudo‐curvature element‐size controlling metric to impose the curvature element‐size requirement in an implicit manner, the new mesh generation procedure can also generate finite element meshes with high fidelity to approximate the target surfaces accurately. Copyright © 2003 John Wiley & Sons, Ltd.     

A bidirectional ring fiber laser with a 90° Faraday rotator as the nonreciprocal phase element. I. Theory

The scheme of a bidirectional ring fiber laser with a 90° Faraday rotator in the cavity has been theoretically studied. The Faraday rotator is employed as a nonreciprocal phase element producing splitting of natural frequencies of the laser cavity modes propagating in opposite directions. The theory predicts two possible regimes of bidirectional operation. According to this, the laser generates a pair of modes propagating in opposite directions with either complex-conjugate or orthoconjugate polarization states. In the former case, the frequency shift between the modes propagating in opposite directions is independent of the reciprocal birefringence of the laser cavity and amounts to half of the free spectral band of this cavity.     

Damage characterization in non-isothermal stretching of acrylics. Part I: Theory

An improved version of dual-mechanism constitutive model was proposed to describe thermo-mechanical response of amorphous polymers below and above glass transition temperature (θ_g). Material property definitions and plastic flow rules were revisited to provide a smooth and continuous transition in material response around θ_g. The elastic-viscoplastic constitutive model was developed based on thermodynamics framework and was implemented in a fully coupled thermo-mechanical simulation of non-isothermal testing of PMMA in Part II [Gunel, E. M., Basaran, C., 2010. Damage characterization in non-isothermal stretching of acrylics. Part II: Experimental validation. Mechanics of Materials]. For damage evolution in complex thermo-mechanical problems such as polymer processing operation, irreversible entropy production was considered as the measure of damage.     

Dynamic behavior of a direct expansion evaporator under frosting condition. Part I. Distributed model

A general distributed model with two-phase flow for refrigerant coupled with a frost model is developed for studying the dynamic behavior of an evaporator. The equations are derived in non-steady-state manner for the refrigerant and a quasi-steady state model with permeation for the frost. The complex flow and geometry of the finned tube evaporator lead to uneven wall and air temperature distributions, which in turn affect the rate of frost growth and densification along the coil depth. Results include frost accumulation and its effect on energy transfer, air off-coil temperature, refrigerant liquid dry-out position and propagation of frost formation along the coil.     

Evaluation of Defatted Soybean Flakes as a Tablet Excipient Part I. As a Disintegrant

Abstract

Oriental people have been using soybeans as a protein foodstuff for centuries. At present soybeans have become a major source of edible oil, and the meal provides an important source of protein for animal feeds. In the present study, the dehulled, and defatted soybean flakes were investigated as a possible tablet excipient.

Four different samples (sieve fraction 150-180 um), namely samples A, B, C, and D were prepared from dehulled, defatted soybean flakes and their physical characteristics were determined subsequently. Compacts of these four substances and their binary mixtures with dicalcium phosphate dihydrate in four different ratios were also prepared at seven different compression pressures.

The changes in density of the compacts under compression were 1 2 interpreted using the Heckel plots ^{1, 2} The crushing strength and disintegration time of the subsequent compacts were also determined. Great differences in the disintegrating properties between the four soybean samples were noticed.

Samples A, B, C, and D, corn starch, microcrystalline cellulose and starch 1500 were added to dicalcium phosphate dihydrate either as intragranular, extragranular or both intra- and extragranular disintegrants respectively; the compacts of these substances were prepared at two compression pressures and the disintegration time of the compacts determined. In general the disintegrating efficiencies are in the rank order corn starch>starch 1500>sample Osample D>sample B>sample A>microcrystalline cellulose.     

Self-assembly of cadmium metasilicate nanowires as a broadband optical limiter

Cadmium metasilicate nanowires (CdSiO₃ NWs) have been synthesized through a facile, eco-friendly, low-cost water–ethanol mixed-solution hydrothermal route. The transmission electron microscopy measurements of as-prepared samples indicate that the CdSiO₃ NWs with diameters in the range of 10–60 nm and lengths of more than 1 μm were constructed by self-assembly of 5–10-nm CdSiO₃ nanoparticles with good crystallinity. The monoclinic phase formation of the sample is studied in detail by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermo gravimetric analysis. The results indicate that a pure monoclinic phase of CdSiO₃ can be obtained by a hydrothermal route without further calcinations and SiO₄ tetrahedra were the main constituents of the CdSiO₃ NWs. The nanosecond optical limiting (OL) effects were characterized by using an open-aperture (OA) Z-scan technique with 4-ns laser pulses at both 532 and 1064 nm. Theses CdSiO₃ NWs displayed an excellent OL performance at 532 and 1064 nm, which was better than carbon nanotubes, a benchmark optical limiter. Input-fluence dependent scattering measurements suggested than nonlinear scattering played an important role in the observed optical limiting behavior in CdSiO₃ NWs at 532 and 1064 nm. More significantly, the NLO performance in CdSiO₃ NWs incorporated solid silica gel glass has been improved in comparison to those dispersed in water. The unique structure and excellent OL property render these CdSiO₃ NWs competitors in the realms of optical limiting applications.