Thermal convection around obstacles: the case of Sierpinski carpets

Measurements of free convection velocity profiles by laser Doppler velocimetry in a cavity containing Plexiglas reconstructed Sierpinski carpets are compared with computed profiles using the SIMPLER numerical code applied to the Navier–Stokes equations. This first step validates the numerical code into which two thermal conductivities are used (that of the liquid and that of the solid), together with two viscosities (that of the liquid and a fictitious high viscosity of the order of 10³⁰ for the solid). Next, the code is used for a network of Sierpinski carpets, allowing the evaluation of a seepage velocity from the Navier–Stokes equations.     

Random walks on highly symmetric graphs

We consider uniform random walks on finite graphs withn nodes. When the hitting times are symmetric, the expected covering time is at least 1/2n logn-O(n log logn) uniformly over all such graphs. We also obtain bounds for the covering times in terms of the eigenvalues of the transition matrix of the Markov chain. For distance-regular graphs, a general lower bound of (n-1) logn is obtained. For hypercubes and binomial coefficient graphs, the limit law of the covering time is obtained as well.     

Electrochemical Sensing of Paracetamol Using 3D Porous Laser Scribed Graphene Platform

This work presents a novel disposable electrochemical sensor for paracetamol (PCM). The sensing platform is based on graphene, manufactured via laser-scribing technology (LSG) to produce a 3D-porous structure that offers a large surface area. The analytical performances of LSG electrodes were greatly enhanced due to the high catalytic activity of graphene produced by LSG technology compared to conventional carbon electrodes. Moreover, the results showed an outstanding adsorption feature towards PCM, allowing its detection at nanomolar level from 5 nM to 100 nM through pre-concentration. The proposed sensing strategy was successfully applied for the determination of PCM in human urine samples.     

Optimization of Bioethanol Production from Enzymatic Treatment of Argan Pulp Feedstock

Argan pulp is an abundant byproduct from the argan oil process. It was investigated to study the feasibility of second-generation bioethanol production using, for the first time, enzymatic hydrolysis pretreatment. Argan pulp was subjected to an industrial grinding process before enzymatic hydrolysis using Viscozyme L and Celluclast 1.5 L, followed by fermentation of the resulting sugar solution by Saccharomyces cerevisiae. The argan pulp, as a biomass rich on carbohydrates, presented high saccharification yields (up to 91% and 88%) and an optimal ethanol bioconversion of 44.82% and 47.16% using 30 FBGU/g and 30 U/g of Viscozyme L and Celluclast 1.5 L, respectively, at 10%_w/v of argan biomass.     

Geometric representation of the mean–variance–skewness portfolio frontier based upon the shortage function

The literature suggests that investors prefer portfolios based on mean, variance and skewness rather than portfolios based on mean–variance (MV) criteria solely. Furthermore, a small variety of methods have been proposed to determine mean–variance–skewness (MVS) optimal portfolios. Recently, the shortage function has been introduced as a measure of efficiency, allowing to characterize MVS optimal portfolios using non-parametric mathematical programming tools. While tracing the MV portfolio frontier has become trivial, the geometric representation of the MVS frontier is an open challenge. A hitherto unnoticed advantage of the shortage function is that it allows to geometrically represent the MVS portfolio frontier. The purpose of this contribution is to systematically develop geometric representations of the MVS portfolio frontier using the shortage function and related approaches.     

Combining the pair distribution function and computational methods to understand lithium insertion in Brookite (TiO2)

X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO(2) Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO(2) framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li(+) ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li(+) sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO(2) lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior.     

Sorption efficiency of a new sorbent towards uranyl: phosphonic acid grafted Merrifield resin

A novel sorbent resin consisting of a Phosphonic Acid grafted on Merrifield Resin (PA-MR) for the extraction of uranyl from nitrate media is described. The sorption behaviour of uranyl cation on PA-MR was investigated using batch equilibrium technique. The effects of parameters such as shaking speed, pH levels, contact time, metal concentrations, ionic strength and temperature were reported. The results show that the sorption capacity increases with increasing both initial uranyl ion concentration and temperature and decreases with increasing ionic strength. Therefore, the optimum condition for the present study should be using 6.6 mg adsorbent per 1.0 mg uranyl in solution with pH 3.6 and shaking at 250 rpm for 180 min. The adsorption behavior of the system was also investigated and found to be in line with Langmuir isotherm. The kinetic data was well described by the pseudo second-order. Thermodynamics data leads to endothermic process ∆H = + 31.03 kJ⁻¹ mol⁻¹, ∆S = + 146.64 J mol⁻¹ K⁻¹ and ∆G = −11.96 kJ mol⁻¹ at 20 K. ∆G decreased to negatives values with increasing temperature indicating that the process was more favoured at high temperature.     

Inequalities and bounds for the eigenvalues of the sub-Laplacian on a strictly pseudoconvex CR manifold

We establish inequalities for the eigenvalues of the sub-Laplace operator associated with a pseudo-Hermitian structure on a strictly pseudoconvex CR manifold. Our inequalities extend those obtained by Niu and Zhang (Pac J Math 208(2):325–345, 2003 [26]) for the Dirichlet eigenvalues of the sub-Laplacian on a bounded domain in the Heisenberg group and are in the spirit of the well known Payne–Pólya–Weinberger and Yang universal inequalities.     

A new class of lithium and sodium rechargeable batteries based on selenium and selenium-sulfur as a positive electrode

A new class of selenium and selenium-sulfur (Se(x)S(y))-based cathode materials for room temperature lithium and sodium batteries is reported. The structural mechanisms for Li/Na insertion in these electrodes were investigated using pair distribution function (PDF) analysis. Not only does the Se electrode show promising electrochemical performance with both Li and Na anodes, but the additional potential for mixed Se(x)S(y) systems allows for tunable electrodes, combining the high capacities of S-rich systems with the high electrical conductivity of the d-electron containing Se. Unlike the widely studied Li/S system, both Se and Se(x)S(y) can be cycled to high voltages (up to 4.6 V) without failure. Their high densities and voltage output offer greater volumetric energy densities than S-based batteries, opening possibilities for new energy storage systems that can enable electric vehicles and smart grids.