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.     

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.     

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.     

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.     

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.     

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.     

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.     

Calculation of the statistical characteristics of the light reflected by a rough random cylindrical homogeneous Gaussian surface

Statistical characteristics of light reflected by a rough random cylindrical homogeneous Gaussian surface are investigated using a modified method of specular points, as developed by Gardashov. In this proposed method, a special procedure for determining the light intensity near the caustics has been formulated. The probability distribution of the intensity of reflected light is expressed in terms of a special function, which is determined by the characteristic function of distribution of radii of curvature at the specular points and the distribution density of the number of specular points. The distribution of radii of curvature, derived by Gardashov, and expressed in terms of dimensionless radii of curvature, has a simple expression which does not contain any parameter of the surface (as a surface rms deviation, etc.). Consequently, it is universally valid and applicable to any cylindrical homogeneous Gaussian surface. After modification, the infinite dispersion of the reflected light intensity turns into a finite. The relationship between the distributions of reflected light intensity and the number of specular points, in the form of a Fredholm integral equation of the first kind is obtained. The kernel of the integral equation is expressed in terms of a characteristic function of the radii of curvature at specular points. The validity of formulae and relationships, thus derived, is tested by numerical simulations.     

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.     

Optical properties of non-stoichiometric SiO2 as a function of excess silicon content and thermal treatments

The infrared (IR) absorption spectra and the behavior of the refraction index of a two-phase non-stoichiometric SiO₂ film with excess Si have been studied as a function of the excess of Si and post-deposition thermal treatment. The oxides were deposited by low-pressure chemical vapor deposition using SiH₄ and N₂O as reactant gases at a substrate temperature in the range of 650 to 750 °C. Some of the films were given a final annealing treatment at temperatures ranging from 700 to 1100 °C in N₂ for 30 min. Both annealed and as-deposited oxides have IR absorption peaks associated with the bending, rocking and stretching modes of the Si-O-Si bonds in SiO₂, although the exact location of these peaks is different for different contents of excess silicon and it also depend on the post-deposition thermal treatment given to the oxides. Unannealed samples present a shift of the stretching peak towards low wavenumbers as the excess of Si is increased. The samples annealed at 1000 °C on the other hand do not present this shift. Unannealed samples with large content of Si also present an absorption peak at 890 cm⁻¹ that could be associated with partially oxidized Si. It is suggested that at least part of the excess Si in the as-deposited samples is present in the form of an SiO_x phase while in the annealed samples a clear separation occurs between a Si and a SiO₂ phase. The behavior of the refraction index is similar for both types of sample, increasing as the excess silicon is increased.     

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.     

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.     

Role of ZnO-CeO2 Nanostructures as a Photo-catalyst and Chemi-sensor

ZnO-CeO2 nanostructures were synthesized by simple and effcient low temperature method. The structure and morphology of the ZnO-CeO2 nanostructures were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM), which revealed elongated shaped CeO2 nanoparticles with diameters of 40-90 nm distributed on the surface of elongated ZnO nanostructures with diameters of 50-200 nm (edge-centre). Further the structure of the synthesized ZnO-CeO2 nanostructure was supported by Raman spectra and Fourier transform infrared spectroscopy (FTIR). UV-vis absorption spectrum was used to confirm the optical properties of the CeO2 doped ZnO nanostructures. Photo-catalytic activity of CeO2 doped ZnO nanostructure was evaluated by degradation of acridine orange and methylene blue which degraded 84.55% and 48.65% in 170 min, respectively. ZnO-CeO2 nanostructures also showed good sensitivity (0.8331 μA·cm-2·(mol/l)-1) in short response time (10 s) by applying to chemical sensing using ethanol as a target compound by I-V technique. These degradation and chemical sensing properties of ZnO-CeO2 nanostructures are of great importance for the application of ZnO-CeO2 system as a photo-catalyst and chemical sensor.     

Postbuckling of functionally graded fiber reinforced composite laminated cylindrical shells, Part I: Theory and solutions

Buckling and postbuckling behavior are presented for fiber reinforced composite (FRC) laminated cylindrical shells subjected to axial compression or a uniform external pressure in thermal environments. Two kinds of fiber reinforced composite laminated shells, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The governing equations are based on a higher order shear deformation shell theory with von Kármán-type of kinematic non-linearity and including the extension-twist, extension-flexural and flexural-twist couplings. The thermal effects are also included, and the material properties of FRC laminated cylindrical shells are estimated through a micromechanical model and are assumed to be temperature dependent. The non-linear prebuckling deformations and the initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths of FRC laminated cylindrical shells.     

Electron beam surface treatment. Part I: surface hardening of AISI D3 tool steel

The effects of electron beam surface hardening treatment on the microstructure and hardness of AISI D3 tool steel have been investigated in this paper. The results showed that the microstructure of the hardened layer consisted of martensite, a dispersion of fine carbides and retained austensite while the transition area mainly consisted of tempered sorbite. Also, the microhardness of the hardened layer on the surface increased dramatically compared to that of base material. Finally, the hardening response of AISI D3 tool steel to electron beam surface treatment is closely related to the scanning speed of the electron beam.