Natural convection in a vertical porous cavity filled with a non‐newtonian binary fluid

Numerical and analytical study of natural convection in a vertical porous cavity filled with a non‐Newtonian binary fluid is presented. The density variation is taken into account by the Boussinesq approximation. A power‐law model is used to characterize the non‐Newtonian fluid behavior. Neumann boundary conditions for temperature are applied to the vertical walls of the enclosure, while the two horizontal ones are assumed impermeable and insulated. Both double‐diffusive convection (a = 0) and Soret‐induced convection (a = 1) are considered. Scale analysis is presented for the two extreme cases of heat‐driven and solute‐driven natural convection. For convection in a thin vertical layer (A ? 1), a semianalytical solution for the stream function, temperature, and solute fields, Nusselt and Sherwood numbers are obtained using a parallel flow approximation in the core region of the cavity and an integral form of the energy and constituent equations. Numerical results of the full governing equations show the effects of the governing parameters, namely the thermal Rayleigh number, R_T, the Lewis number, Le, the buoyancy ratio, φ, the power‐law index, n, and the integer number a. A good agreement between the analytical predictions and the numerical simulations is obtained. © 2012 American Institute of Chemical Engineers AIChE J, 58: 1704–1716, 2012     

Modelling the surface adsorption of methane on carbon nanostructures

Methane (CH₄) adsorption is investigated on both graphite and in the region between two aligned single-walled carbon nanotubes, which we refer to as the groove site. We exploit the Lennard–Jones potential function and the continuous approximation to determine surface binding energies between a single CH₄ molecule and graphite and between a single CH₄ and two aligned single-walled carbon nanotubes. Our modelling indicates that for a CH₄ molecule interacting with graphite, the binding energy of the system is minimized when the CH₄ carbon is 3.83 Å above the surface of the graphitic carbon, while the binding energy of the CH₄–groove site system is minimized when the CH₄ carbon is 5.17 Å away from the common axis shared by the two aligned single-walled carbon nanotubes. Our results confirm the current view that for larger groove sites, CH₄ molecules in grooves are likely to move towards the outer surfaces of one of the single-walled carbon nanotubes. Our results are computationally efficient and are in good agreement with experiments and molecular dynamics simulations, and show that CH₄ adsorption on graphite and groove surfaces is more favourable at lower temperatures and higher pressures.     

Statistical mechanical model of sorption and diffusion of simple penetrants in polymers

Amorphous polymers are assumed to possess a quasicrystalline structure with chain bundles that are locally parallel over distances ～1 nm. Two possible types of random motion for a spherical penetrant in such a substrate are described, one type determining the jump frequency and activation energy of diffusion, the other type determining the jump length. The former quantities may be calculated from the model, but not the latter. Sorption of simple gases at low penetrant pressures is assumed to occur mostly in pre-existing holes, both above and below T_g, and the same penetrant diffusion mechanism is assumed to hold in the two regions. The changes in apparent heat of solution and activation energy of diffusion observed at T_g are explained in terms of additional hole formation with increase in temperature above T_g. The theory is shown to be consistent with experimental diffusion data for several glassy and rubbery systems. Evidence is given that hole formation in simple polymers such as polyethylene may occur by chain “kinking”. For polymers possessing articulated side groups, however, it appears that hole formation arises principally from motions within these groups.     

Application of the parallel Avrami model to crystallization of poly(etheretherketone)

We have reexamined the parallel Avrami model recently proposed by Velisaris and Seferis (1) to describe the non-Isothermal crystallization of poly(etheretherketone), PEEK. We show that, based on considerations of morphology development, the crystallization process with the larger Avrami exponent has the higher melting point, whereas the process with the smaller Avrami exponent has the lower melting point. This assignment differs from that of Velisaris and Seferis. In addition, we have used the infinite crystal melting point, as required by crystallization theory, to determine the Avrami rate parameters for the two processes. With this revision of the parallel Avrami model, we have applied the model to non-isothermal crystallization of APC-2 PEEK composite. Under the assumption that the linear growth rate determines the Avrami rate parameter, both the transport activation energy, U, and the kinetic parameter, K_g, are found to compare favorably with the values previously determined from isothermal crystallization of neat resin PEEK.     

Effects of anisotropic scattering of radiation in laminar forced convection in a parallel-plate duct

Effects of anisotropic scattering to heat transfer in hydrodynamically-developed, thermally-developing steady laminar forced flow of a gray fluid between two infinite parallel plates are investigated for the case when the inlet temperature of the fluid is less than the wall temperature. An implicit finite difference scheme is applied to solve the energy equation, while the high order P_N method is used to solve the radiation part of this problem. The effects of the anisotropy, the conduction-to-radiation parameter, the optical thickness, the reflectivity of the plates and the inlet temperature on the local Nusselt number are studied.     

On the Chemical Origin of the Gap Bowing in (GaAs)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys: A Combined DFT–QS<Emphasis Type="Italic">GW</Emphasis> Study

Motivated by the research and analysis of new materials for photovoltaics and by the possibility of tailoring their optical properties for improved solar energy conversion, we have focused our attention on the (GaAs)_{1− x} Ge_2x series of alloys. We have investigated the structural properties of some (GaAs)_{1− x} Ge_2x compounds within the local-density approximation to density-functional theory, and their optical properties within the Quasiparticle Self-consistent GW approximation. The QSGW results confirm the experimental evidence of asymmetric bandgap bowing. It is explained in terms of violations of the octet rule, as well as in terms of the order–disorder phase transition.     

Influence of scattering processes on electron quantum states in nanowires

In the framework of quantum perturbation theory the self-consistent method of calculation of electron scattering rates in nanowires with the one-dimensional electron gas in the quantum limit is worked out. The developed method allows both the collisional broadening and the quantum correlations between scattering events to be taken into account. It is an alternative per se to the Fock approximation for the self-energy approach based on Green’s function formalism. However this approach is free of mathematical difficulties typical to the Fock approximation. Moreover, the developed method is simpler than the Fock approximation from the computational point of view. Using the approximation of stable one-particle quantum states it is proved that the electron scattering processes determine the dependence of electron energy versus its wave vector.     

The Use of AFM and Surface Energy Measurements to Investigate Drug-Canister Material Interactions in a Model Pressurized Metered Dose Inhaler Formulation

The aim of the project was to investigate the interactions between micronized salbutamol sulphate, budesonide, and formoterol fumarate dihydrate and different canister surfaces materials (Aluminium, anodized aluminium, perfluoroalkoxy, fluorinated ethylene propylene—polyether sulphone, and polytetrafluoroethylene) used in pressurized metered dose inhalers (pMDIs).

The surface component approach for polar and apolar interfacial interactions was used to predict the adhesion behavior of micronized drugs with the inner surfaces of pMDI canisters. This was achieved using a combination of in situ colloid probe atomic force microscopy (AFM) measurements and theoretical treatment of the surface free energy measurements, via a contact angle–based technique of the interacting surfaces.

All three drugs exhibited similar dispersive surface energy free values. A greater variation was, however, found in the polar component of the surface free energy measurements. These results were also reflected in the dispersive and polar components of the canister materials. Moreover, the linear relationship between the work of adhesion and AFM measured adhesion was shown to be correlated on the polar contributions of the surface free energies of the interacting materials. AFM measurements indicated that salbutamol sulphate was found to have the strongest adhesive forces with respect to the canister surface materials while budesonide and formoterol fumarate dihydrate appeared to have similar adhesive characteristics. The present study suggests that investigations into the design and characterization of pMDI formulations would benefit from considerations of the polar contribution of the surface free energy and relative work of adhesion of the drug and various components of a pMDI system.     

Field Dependence of the Spin Relaxation Within a Film of Iron Oxide Nanocrystals Formed via Electrophoretic Deposition

The thermal relaxation of macrospins in a strongly interacting thin film of spinel-phase iron oxide nanocrystals (NCs) is probed by vibrating sample magnetometry (VSM). Thin films are fabricated by depositing FeO/Fe₃O₄ core–shell NCs by electrophoretic deposition (EPD), followed by sintering at 400°C. Sintering transforms the core–shell structure to a uniform spinel phase, which effectively increases the magnetic moment per NC. Atomic force microscopy (AFM) confirms a large packing density and a reduced inter-particle separation in comparison with colloidal assemblies. At an applied field of 25 Oe, the superparamagnetic blocking temperature is T _B^SP ≈ 348 K, which is much larger than the Néel-Brown approximation of T _B^SP ≈ 210 K. The enhanced value of T _B^SP is attributed to strong dipole–dipole interactions and local exchange coupling between NCs. The field dependence of the blocking temperature, T _B^SP(H), is characterized by a monotonically decreasing function, which is in agreement with recent theoretical models of interacting macrospins.     

Optimization of the Composition of High-Temperature Coatings Using a <Emphasis Type="Italic">B</Emphasis>-Spline Approximation Method

The operational characteristics (fracture energy, apparent density, and open porosity) of multicomponent phosphate-hardened coatings are studied as a function of the component concentration using a B-spline approximation method and optimum compositions for the coating material are obtained.__________Translated from Novye Ogneupory, No. 2, pp. 50 – 54, February, 2005.     

First Exit Times of Compound Poisson Processes with Parallel Boundaries

Abstract

We consider distributions of several first exit times of compound Poisson processes (CPPs) with positive jumps from a region that is bounded by two parallel boundaries. Recursive formulas of exact distributions are given for a CPP with absolutely continuous jumps. Non-recursive formulas are given for a CPP with discrete jumps, and are used as a numerical approximation for the absolutely continuous case. The problem has applications in queueing and risk theory as well as sequential testing.     

Steered molecular dynamics simulation of the detaching process of two parallel surfaces glued together by a single polyethylene chain

The detaching process of two parallel surfaces glued together by a single polyethylene chain in vacuo was investigated with a steered molecular dynamics method. Various statistical properties were analyzed in detail, including the mean‐square end‐to‐end distance; parallel and perpendicular mean‐square radii of gyration; shape factor; segment density distribution; average percentages of the microstructure of the chain of the tail, train, bridge, and loop; average surface adsorption energy; average total energy; and average pulling force (〈f〉). All these properties depended strongly on the pulling velocity (v). There existed a peak in the curve of 〈f〉 as a function of the detaching distance. Further, the relation between the maximum value of 〈f〉 and v showed three distinctive regions: a region of weak dependence at v < 10^?2 Å/ps, a region of strong dependence at 10^?2 Å/ps < v < 6.50 Å/ps, and a region of weak dependence at v > 6.50 Å/ps. These investigations may provide some insight into the microcosmic principle of the failure process of polymeric adhesives. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effects of urine and temperature on the physicochemical surface properties and adhesion behaviour of uropathogenic bacteria

Bacterial adhesion in relation to urinary-tract infections has gained importance in the last years because of the increasing catheterization in hospitals to assist post-surgery flow of urine. Since the initial adhesion of bacteria to biomaterials is governed by physicochemical forces emerging from the physicochemical properties of both interacting phases, we have investigated the physicochemical surface changes of uropathogen Enterococcus faecalis ATCC29212 bacteria due to the presence of urine in its growth medium and to the differences in the environmental temperature. Urine-grown cells were found to be less hydrophobic based on water contact angles at 22°C, while no changes were detected at 37°C. In addition, they exhibited higher acid-base surface energy component than urine-free cultured cells. These changes in surface properties were also reflected in thermodynamic predictions of the adhesion to glass and silicone, which were experimentally compared with the in vitro adhesion curves obtained in a parallel plate flow chamber. The shapes of the adhesion graphs indicated that interaction free energies should be used to describe only the initial adhesion stages. Adhesion to silicone was always enhanced by urine-grown cells, while the adhesion to glass did not seem to be affected by the urine constituents. Despite the fact that the interaction free energies were not able to explain the adhesion process in some cases, changes in the electron-donor and electron-acceptor parameters of their surface free energy due to urine addition seemed to have a relation with initial adhesion rates.     

Influence of an epoxy reactive diluent on the thermal degradation process of the system DGEBA n = 0/1,2 DCH

The thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (DGEBA n = 0)/1,2‐diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent, vinylcyclohexene dioxide (VCHD), was studied by thermogravimetric analysis to determine the reaction mechanism of the degradation process for these two systems. Values of the activation energy, necessary for this study, were calculated by using various integral and differential methods. Values obtained by using the different methods were compared to the value obtained by Kissinger's method, which does not require a knowledge of the reaction mechanism. All the experimental results were compared to master curves in the range of Doyle's approximation (20–35% of conversion). Analysis of the results suggests that the two reaction mechanisms are R_n and F_n deceleratory type in contrast with the sigmoidal A₂ type of the system with filler and the sigmoidal A₄ type of the system without additives. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1199–1207, 2004     

Titration of Apparent In-Cellula Affinities of Protein-Protein Interactions**

A genetic assay permits simultaneous quantification of two interacting proteins and their bound fraction at the single-cell level using flow cytometry. Apparent in-cellula affinities of protein-protein interactions can be extracted from the acquired data through a titration-like analysis. The applicability of this approach is demonstrated on a diverse set of interactions with proteins from different families and organisms and with in-vitro dissociation constants ranging from picomolar to micromolar.     

Phase Stability and Phase Structure of Ru–Ti–O Complex Oxide Electrocatalyst

Phase stability of (Ru_1?x,Ti_x)O₂ solid solution was investigated via materials computation and X‐ray diffraction phase analyses. The unit cell volume of (Ru_1?x,Ti_x)O₂ was found not increasing monotonously with the fraction of TiO₂, making the volume–composition relationship no longer suitable for the quantitative phase analysis. A monotonous nonlinear c/a–x relation obtained from the ab initio density functional theory (DFT) computation was proved critical to achieving accurate phase analysis results. Gibbs free energy of mixing and its derivatives were determined for (Ru_1?x,Ti_x)O₂ by a combination of DFT and thermodynamic calculations, where approximation of the temperature dependence of the interaction parameter (Ω) played a critical role. It was found that the conventional approximation method of arbitrarily choosing a value & [10,25] kJ (mole of atoms)^?1 for Ω near a critical temperature of a solid solution structure failed to predict the correct symmetry and span of the miscibility gap for (Ru_1?x,Ti_x)O₂. In comparison, Ω calculated from disordered (Ru_1?x,Ti_x)O₂ was found a good approximation at the critical temperature. The calculated miscibility gap for (Ru_1?x,Ti_x)O₂, therefore, showed good agreement with the accurate quantitative phase analysis results for the samples prepared by a sol–gel method.     

Temporal Aggregation of Lognormal AR processes

We consider temporal aggregation of lognormal autoregressive (AR) processes. More specifically, we develop a novel moment‐matching approximation for temporally aggregated lognormal AR processes. In addition, we show that our approximation provides the closest lognormal AR process in terms of Kullback–Leibler divergence. Moreover, we perform a simulation study to compare our proposed approximation with two competing approximations. This study shows that in terms of L¹‐ and L²‐norm distances our approximation provides superior results. Our results have an important practical application and one main practical implication. In terms of practical application, our approximation can provide possible candidate solutions for simulation‐based algorithms such as the Metropolis–Hastings algorithm. The practical implication gives support to common practice: when the original fine‐level process follows a lognormal AR process but only aggregated data are available, then instead of assuming a Gaussian process it is better to assume a lognormal AR process at the aggregated level. Finally, we illustrate the utility of our results with two applications. The first example considers a simulated dataset whereas the second example examines the number of yearly sunspots in the period 1700–1984.     

Design of a dome-shaped aluminium water battery

Aluminium/water batteries using hydrogen evolving cathodes are one of the candidate batteries for sub-sea application. However, it is impractical to use parallel plate construction because the significant increase in the anode-cathode gap during long term anodic discharge leads to unacceptable iR losses. A conceptual design, using a dome-shaped configuration, is presented and preliminary tests on a prototype show that such a battery can ensure constant anode-cathode gap and uniform anode dissolution. The energy density of such a battery for a two year period is estimated to be 855 Wh kg^–1.     

The majority of minerals present in natural rubber are associated with the macrogel: An ICP‐MS and SEM/EDX investigation

The mineral composition of the insoluble (macrogel) and soluble fractions of two natural rubber (NR) samples made from the latex of two different clones (RRIM600 from Thailand and GT1 from Côte d'Ivoire) was determined using inductively coupled plasma mass spectrometry (ICP‐MS). The ICP‐MS results showed that mineral elements were concentrated in the macrogel. The major mineral elements found in macrogel were phosphorus, magnesium, potassium, and sulfur. Some mineral elements were mostly concentrated in micron‐sized mineral aggregates, visible at the surface of the samples using scanning electron microscopy coupled with an energy dispersive X‐ray microanalyzer (SEM/EDX). The nature of these mineral aggregates was found to be highly variable. Their inhomogeneous distribution in the macrogel indicates that these aggregates do not have a major influence on macrogel structure. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43062.