High-speed optical bit-pattern recognition employing fibre Bragg grating and Opto-VLSI processing

We propose a novel optical bit-pattern recognition employing an Opto-VLSI processor in conjunction with an array of fibre Bragg gratings (FBGs) with different Bragg wavelengths and a coherent-to-incoherent light converter. The FBG array slices the spectrum of the incoherent optical header and provides wavelength-dependent time delays, whereas the Opto-VLSI processor generates wavelength intensity profiles that match specific bit patterns. The recognition of 8-bit optical patterns is experimentally demonstrated at 2.2 Gb/s by showing that the correlator produces an autocorrelation waveform of high peak whenever the input bit pattern matches the wavelength intensity profile.     

Mesoporous aluminosilicate ropes with improved stability from protozeolitic nanoclusters

Mesoporous aluminosilicate ropes with improved hydrothermal stability have been prepared through S⁺X⁻I⁺ route via self-assembly of protozeolitic nanoclusters with cetyltrimethylammonium bromides (CTAB) template micelles in HNO₃ solution. SEM observation confirmed that high-yield aluminosilicate ropes could be produced under proper HNO₃ concentration. NO₃⁻ ions had strong binding strength to the CTA⁺ ions and tended to form more elongated surfactant micelles, thus fibrous products were fabricated under the direction of these long rod micelles in shearing flow. At the same time, the NO₃⁻ ions combining with CTA⁺ ions generated more active (CTA⁺NO₃⁻) assembly, which effectively catalysed the polymerization of protozeolitic nanoclusters with large volume into highly ordered mesostructures. Compared with normal MCM-41 silica synthesized through S⁺X⁻I⁺ route in acidic media, the hydrothermal stability was improved considerably. These protozeolitic nanoclusters survived strongly acidic media and entered into mesostructured framework, which contributed to the improvement of hydrothermal stability.     

The Role of Interfacial Layers in the Enhanced Thermal Conductivity of Nanofluids: A Renovated Maxwell Model

Nanofluids, a new class of solid/liquid suspensions, offer scientific challenges because their measured thermal conductivity is one order of magnitude greater than predictions. It has long been known that liquid molecules close to a solid surface form layered solid-like structures, but little is known about the connection between this nanolayer and the thermal properties of the suspensions. Here, we have modified the Maxwell equation for the effective thermal conductivity of solid/liquid suspensions to include the effect of this ordered nanolayer. Because this ordered nanolayer has a major impact on nanofluid thermal conductivity when the particle diameter is less than 10 nm, a new direction is indicated for development of next-generation coolants.     

Frequency and time transfer for metrology and beyond using telecommunication network fibres

The distribution and the comparison of an ultra-stable optical frequency and accurate time using optical fibres have been greatly improved in the last ten years. The frequency stability and accuracy of optical links surpass well-established methods using the global navigation satellite system and geostationary satellites. In this paper, we present a review of the methods and the results obtained. We show that public telecommunication network carrying Internet data can be used to compare and distribute ultra-stable metrological signals over long distances. This novel technique paves the way for the deployment of a national and continental ultra-stable metrological optical network.     

Rheology and Structure of Cornstarch Suspensions in Water-Poly(propylene glycol) Mixtures

Concentrated aqueous cornstarch (CS) suspensions are often used to demonstrate an extreme example of shear thickening rheological behavior. Here, we describe the increased rheological complexity that occurs on the addition of poly(propylene glycol) (PPG) to an aqueous CS suspension. The appearance of shear thickening/jamming, shear thinning, yield stress and near-Newtonian behaviors is dependent on the PPG:water ratio. Rheological measurements have been complemented by dielectric measurements and optical microscopy. The complex behavior is interpreted in terms of reduced electrostatic stabilization of the CS particles with increased poly(propylene glycol) concentration. The analysis also suggests why cornstarch suspensions in water exhibit particularly good shear thickening characteristics.     

Quantitative X-RAy Diffraction Analysis of Four Types of Amphibolic Asbestos by the Silver Membrane Filter Method

Abstract

In this paper, the method that utilizes the X-ray diffraction technique combined with a procedure for X-ray absorption correction, already applied to chrysotile, was extended to the quantitative determination of microgram quantities of four types of amphibolic asbestos. These are: crocidolite, amosite, tremolite and anthophyllite. The effectiveness of the absorption correction procedure, based on the use of a silver membrane filter, was tested for crocidolite by preparing standards of this substance in three different matrices and comparing their diffractometric responses with those of pure analyte standards. These experimental data were also used to calculate the mass absorption coefficients of the matrices, which were compared with both the theoretical values and the values obtained in previous experiments where chrysotile was used as the analyte. The limits of detection of the four pure amphiboles, and crocidolite in matrix were established, and a detailed study of the most common interferences that disturb the analytical peaks of the four amphiboles, was performed.     

Effect of Rotary Inertia on the Orientational Behavior of Dilute Brownian and Non-Brownian Fiber Suspensions

The orientational behavior of a dilute suspension of slender Brownian and non-Brownian fibers with rotary inertia in simple shear and turbulent channel flows is numerically investigated. The translational inertia of fibers is neglected. The equations describing the evolution of fibers orientation are integrated along the Lagrangian paths of the fluid elements. The fully developed turbulent channel flow at Re _τ = 180 is provided by a direct numerical simulation (DNS). The coupling between the flow field and the fiber dynamics is one way. The Brownian motion is modeled by a stochastic Wiener process. The results are compared with those of inertia-free particles. In simple shear flow, the inertial non-Brownian fibers align slower than the inertia-free fibers to the shear direction while they tend to the same steady state orientation. For Brownian fibers, the steady state orientation of inertial and inertia-free fibers differ. In turbulent channel flow, the second moment of the orientation distribution function shows an oscillatory behavior at high values of inertia for non-Brownian fibers while the oscillations disappear at lower inertia. For Brownian fibers, the oscillations are weaker due to the damping effect of the Brownian diffusivity.     

Dynamic Viscoelastic and Multiple Scattering Effects in Fiber Suspensions

This study considers the most fundamental problem of 2‐D acoustic scattering in fiber suspensions. It treats the interaction of a plane compressional sound wave with a cluster of two flexible fibers submerged in a boundless viscous fluid medium. The dynamic viscoelastic properties of the fibers and the viscosity of the surrounding fluid are rigorously taken into account in the solution of the problem. The translational addition theorem for cylindrical wave functions, the Havriliak‐Negami model for viscoelastic material behaviors and the appropriate wave field expansions and the pertinent boundary conditions are employed to develop a closed‐form solution in the form of an infinite series. The prime objectives are to investigate the influence of dynamic viscoelastic properties of fiber material as well as multiple scattering interaction effects on acoustic scattering and its associated quantities. The analytical results are illustrated with a numerical example in which two identical viscoelastic fibers are insonified by a plane sound wave at broadside/end‐on incidence. The backscattering form function amplitude and the spatial distribution of the total acoustic pressure are numerically evaluated and discussed for representative values of the parameters characterizing the system. The effects of incident wave frequency, angle of incidence, material properties, and proximity of the two fibers are examined. A limiting case involving a pair of rigid cylinders in an ideal fluid is considered, and fair agreement with a well‐known solution is established.     

Rheological Characterization of Alumina Ceramic Suspensions in Presence of a Dispersant and a Binder

The rheological responses of aqueous alumina suspensions, stabilized with an organic polyvalent salt dispersant called “Aluminon,” and including a poly(vinyl) alcohol (PVA) binder, are described in this study. It is observed that the addition of PVA, without any dispersant does not significantly influence the rheology. However, in the presence of the dispersant the rheology is affected significantly. At a given concentration of the dispersant, the viscosity, the storage and loss modulii all increase with the PVA concentration. Also, for a given concentration of the PVA, the viscosity, the storage and loss modulii values increases as the concentration of the dispersant is increased. At relatively low PVA concentrations, an excess concentration of the dispersant, causes flocculation of the particles in the suspension by a reduction of the electrostatic (double layer) effect. On the contrary, at higher concentrations of the PVA the flocculation of the suspension occurs via a depletion mechanism.     

Use of a Cross-Sectional Model for Determining Rheology in Settling Slurries: Effect of Solvent,Particle Size,and Density

Transport models for partially settling slurries need accurate rheology correlations, particularly describing viscosity relationship to the particle concentration. A method is needed to untangle the effects of settling on apparent viscosity and the real effects of particle concentration on viscosity during rheology measurements. Our approach is based on model inversion of a cross-section model for the vertical particle concentration gradient and the local rheologies in the gap of a Couette type rheometer, established by a balance between gravitational particle settling and shear induced migration of the particles. The Krieger-Dougherty rheology correlation with adjustable parameters has been applied, where the parameters are determined by minimizing the difference between the measured viscosity data and those calculated by the model. Fairly mono-disperse silver coated polystyrene particles with two sizes and densities were used in both the aqueous and oil phase. In the raw data an apparent shear thinning tendency is observed. Through the model inversion process, this is accounted for by the shear dependent settling and the steep increase of viscosity with particle concentration. Maximum packing fraction was obtained through settling experiments. The difference between this value and the maximum packing fraction from the model inversion was less than 3% for oil-based suspensions. The larger difference was found for smaller particle size in water which is attributed to the larger effect of interparticle forces.