Vapor liquid equilibrium modeling of alkane systems with Equations of State: “Simplicity versus complexity”

Two types of Equations of State (EoS), which are characterized here as “simple” and “complex” EoS, are evaluated in this study. The “simple” type involves two versions of the Peng–Robinson (PR) EoS: the traditional one that utilizes the experimental critical properties and the acentric factor and the other, referred to as PR-fitted (PR-f), where these parameters are determined by fitting pure compound vapor pressure and saturated liquid volume data. As “complex” EoS in this study are characterized the EoS derived from statistical mechanics considerations and involve the Sanchez–Lacombe (SL) EoS and two versions of the Statistical Associating Fluid Theory (SAFT) EoS, the original and the Perturbed-Chain SAFT (PC-SAFT).

The evaluation of these two types of EoS is carried out with respect to their performance in the prediction and correlation of vapor liquid equilibria in binary and multicomponent mixtures of methane or ethane with alkanes of various degree of asymmetry. It is concluded that for this kind of systems complexity offers no significant advantages over simplicity. Furthermore, the results obtained with the PR-f EoS, especially those for multicomponent systems that are encountered in practice, even with the use of zero binary interaction parameters, indicate that this EoS may become a powerful tool for reservoir fluid phase equilibria modeling.     

Prediction Helps Analytical Experimental Work for Environmental Purposes

 Analytical work, especially for environmental purposes, involves in the typical case determination of organic compounds in compartments, where their presence is very small. Identification of the appropriate experimental technique, whose range of applicability covers the concentration value involved, requires an estimate of this value. To this purpose, we present in this study a methodology for the prediction of the concentration of organic pollutants in the various environmental compartments (aquatic biota, air, sediment and soil) from the knowledge of the concentration in one of them. In case where the pollutant’s concentration is not available for any of the compartments, the proposed methodology can be used to estimate the maximum expected concentration in each one of them assuming that the water phase is saturated with the pollutant. The latter value can be obtained from a simple correlation presented here. The methodology is based on the correlation of the partition coefficients of pollutants among the various environmental compartments with two important thermodynamic quantities of pollutants: the octanol/water partition coefficient and the Henry’s law coefficient, which can be easily predicted by simple models presented here. Application of the methodology to field experimental data gives very satisfactory results at least for identifying the appropriate experimental technique.     

Layer potential techniques for the narrow escape problem

The narrow escape problem consists in deriving the asymptotic expansion of the solution of a drift-diffusion equation with the Dirichlet boundary condition on a small absorbing part of the boundary and the Neumann boundary condition on the remaining reflecting boundaries. Using layer potential techniques, we rigorously find high-order asymptotic expansions of such solutions. The asymptotic formula explicitly exhibits the nonlinear interaction of many small absorbing targets. Based on the asymptotic theory for eigenvalue problems developed in Ammari et al. (2009) [3], we also construct high-order asymptotic formulas for the perturbation of eigenvalues of the Laplace and the drifted Laplace operators for mixed boundary conditions on large and small pieces of the boundary.     

Microfluidic device to investigate factors affecting performance in biosensors designed for transdermal applications

In this work we demonstrate a novel microfluidic based platform to investigate the performance of 3D out-of-plane microspike array based glucose and lactate biosensors. The microspike array was bonded with a glass slide and modified with glucose oxidase or lactate oxidase using covalent coupling chemistry. An epoxy-polyurethane based membrane was used to extend the linear working range (from 0 to 25 mM of substrate) of these biosensors. Both lactate and glucose sensors performed well in the clinically relevant substrate concentration range. Glucose microspikes were further investigated with respect to the effects of substrate transfer by incorporation into a microfluidic system. Data from the microfluidic system revealed that the sensor response is mainly dependent on enzyme kinetics rather than membrane permeability to glucose. The robustness of the sensors was demonstrated by its consistency in performance extending over 48 h.     

Omnidirectional antireflective properties of porous tungsten oxide films with in-depth variation of void fraction and stoichiometry

We report on the fabrication of porous hot-wire deposited WO_x (hwWO_x) films with omnidirectional antireflective properties coming from in-depth variation of both (i) void fraction from 0% at the Si substrate/hwWO_x interface to 30% within less than 7 nm and to higher than 50% at the hwWO_x/air interface, and (ii) x, namely hwWO_x stoichiometry, from 2.5 at the Si/hwWO_x to 3 within less than 7 nm. hwWO_x films were deposited by means of hw deposition at rough vacuum and controlled chamber environment. The films were analyzed by Spectroscopic Ellipsometry to extract the graded refractive index profile, which was then used in a rigorous coupled wave analysis (RCWA) model to simulate the antireflective properties. RCWA followed reasonably the experimental reflection measurements. Void fraction and x in-depth variation, controlled by the hw process, greatly affect the antireflective properties, and improve the omnidirectional and broadband characteristics. The reflection suppression below 10% within the range of 500-1000 nm for angles of incidence up to more than 60° is demonstrated.     

Experimental Design and Optimization of Recovering Bioactive Compounds from Chlorella vulgaris through Conventional Extraction

Microalgae contain an abundance of valuable bioactive compounds such as chlorophylls, carotenoids, and phenolics and, consequently, present great commercial interest. The aim of this work is the study and optimization of recovering the aforementioned components from the microalgae species Chlorella vulgaris through conventional extraction in a laboratory-scale apparatus using a “green” mixture of ethanol/water 90/10 v/v. The effect of three operational conditions—namely, temperature (30–60 °C), duration (6–24 h) and solvent-to-biomass ratio (20–90 mL_solv/g_biom), was examined regarding the extracts’ yield (gravimetrically), antioxidant activity, phenolic, chlorophyll, and carotenoid contents (spectrophotometric assays), as well as concentration in key carotenoids, i.e., astaxanthin, lutein, and β-carotene (reversed-phase–high-performance liquid chromatography (RP–HPLC)). For this purpose, a face-centered central composite design (FC-CCD) was employed. Data analysis resulted in the optimal extraction conditions of 30 °C, for 24 h with 37 mL_solv/g_biom and validation of the predicted models led to 15.39% w/w yield, 52.58 mg_extr/mg_DPPH (IC50) antioxidant activity, total phenolic, chlorophyll, and carotenoid content of 18.23, 53.47 and 9.92 mg/g_extr, respectively, and the total sum of key carotenoids equal to 4.12 mg/g_extr. The experimental data and predicted results were considered comparable, and consequently, the corresponding regression models were sufficiently reliable for prediction.     

The Heat Equation in the Interior of an Equilateral Triangle

We present the solution of the classical problem of the heat equation formulated in the interior of an equilateral triangle with Dirichlet boundary conditions. This solution is expressed as an integral in the complex Fourier space, i.e., the complex k₁ and k₂ planes, involving appropriate integral transforms of the Dirichlet boundary conditions. By choosing Dirichlet data so that their integral transforms can be computed explicitly, we show that the solution is expressed in terms of an integral whose integrand decays exponentially as . Hence, it is possible to evaluate this integral numerically in an efficient and straightforward manner. Other types of boundary value problems, including the Neumman and Robin problems, can be solved similarly.     

Photoacoustic imaging in attenuating acoustic media based on strongly causal models

In this paper, we derive time reversal imaging functionals for two strongly causal acoustic attenuation models, which have been proposed recently. The time reversal techniques are based on recently proposed ideas of Ammari et al. for the thermo‐viscous wave equation. Here and there, an asymptotic analysis provides reconstruction functionals from first order corrections for the attenuating effect. In addition, we present a novel approach for higher order corrections. Copyright © 2013 John Wiley & Sons, Ltd.