The window layers effect on the hardness improvement of space solar cells exposed to the 1 MeV electron irradiations

Because of their state of art technology, GaAs solar cells are generally preferred for spatial applications. Exposure to proton and electron irradiations, solar cells suffer significant degradation in their performance such as short circuit current and open circuit voltage. Adding a window layer helps in effectively reducing the surface recombination at the emitter surface of the solar cell without absorbing the useful light required for the device. It remains to study the physics of the window-emitter hetero-interface in order to understand how the window layer presence increases the minority carrier lifetime of the solar cell exposed to particles irradiation. In this work Numerical simulation has been used to study the AlxGa1-xAs window composition effect on the current–voltage characteristics of a GaAs solar cell under AM0 illumination and exposed to 1 MeV electron irradiation. To predict the effect of window layers on solar cells degradation, the current voltage characteristic are evaluated for different electron irradiation fluences. The findings are supported by experimental data. They lead us to get to know how the window layer improves resistance to electron irradiation through its own parameters.     

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.     

On the fiber orientation in steady recirculating flows involving short fibers suspensions

In this work we present a new numerical strategy to treat the 3D Fokker–Planck equation in steady recirculating flows. This strategy combines some ideas of the method of particles, with a more original treatment of the periodicity condition, which characterizes the steady solution of the FP equation in steady recirculating flows, as usually encountered in some rheometric devices. Using this numerical technique the fiber orientation distribution can be computed accurately in any steady recirculating flow. The simulation results can be used to identify some rheological parameters of the suspension, using an inverse technique, as well as to analyze the validity of some simplified models widely used, which require a closure relation. Thus, in this paper several closure relations of the fourth-order orientation tensor will be discussed in the context of a numerical example involving a steady recirculating flow.     

Part I: A comparative study of bismuth-modified screen-printed electrodes for lead detection

Lead determination was carried out in the frame of the European Union project Biocop (www.biocop.org) using a bismuth-modified screen-printed electrode (Bi-SPE) and the stripping analysis technique. In order to choose a sensitive Bi-SPE for lead detection, an analytical comparative study of electrodes modified by Bi using "in situ", "ex situ" and "bulk" procedures was carried out. On the basis of the results obtained, we confirmed that the "in situ" procedure resulted in better analytical performances with respect to not only "ex situ" but also to "Bi(2)O(3) bulk" modified electrodes, allowing for a linear range of lead ion concentration from 0.5 to 100 μg L(-1) and a detection limit of 0.15 μg L(-1). We demonstrated that, before the Bi film deposition, an oxidative electrochemical pre-treatment of the working electrode could be useful because it eliminates traces of lead in the graphite-ink, as shown with stripping measurements. It also improves the electrochemical performance of the electrodes as demonstrated with Electrochemical Impedance Spectroscopy (EIS) measurements. The influence of different analytical parameters, such as the electrolyte solution composition (acetate buffer, chloridric acid, nitric acid, perchloric acid) and the ionic strength was investigated in order to evaluate how to treat the sample before the analysis. The morphology of prepared "in situ" Bi-SPEs was also characterized by Atomic Force Microscopy (AFM). Finally, the Bi-SPEs were used to determine the concentration of lead ions in tap and commercial water samples obtaining satisfactory values of the recovery percentage (81% and 98%).     

Dual lithium insertion and conversion mechanisms in a titanium-based mixed-anion nanocomposite

The electrochemical reaction of lithium with a vacancy-containing titanium hydroxyfluoride was studied. On the basis of pair distribution function analysis, NMR, and X-ray photoelectron spectroscopy, we propose that the material undergoes partitioning upon initial discharge to form a nanostructured composite containing crystalline Li(x)TiO(2), surrounded by a Ti(0) and LiF layer. The Ti(0) is reoxidized upon reversible charging to an amorphous TiF(3) phase via a conversion reaction. The crystalline Li(x)TiO(2) is involved in an insertion reaction. The resulting composite electrode, Ti(0)-LiF/Li(x)TiO(2) ? TiF(3)/ Li(y)TiO(2), allows reaction of more than one Li per Ti, providing a route to higher capacities while improving the energy efficiency compared to pure conversion chemistries.     

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.     

Electrochemical Characterization of Carbon Solidlike Paste Electrode Assembled Using Different Carbon Nanoparticles

Solid like carbon paste electrodes (SCPEs) are built using different carbon materials namely carbon black N110, N220, N375, N772 and acetylene black. The electrochemical behavior of these electrodes and the influence of carbon black/paraffin ratio were studied and the results were discussed and compared to other electrodes prepared with graphite, mesoporous carbon and nanopowder carbon. Cyclic voltammetry, amperometry and electrochemical impedance spectroscopy were employed for their electrochemical and analytical characterizations. Amperometric measurements using N110, N220, N375 SCPEs with solid paraffin, showed a linear response of benzoquinone concentration with a detection limit of 75, 32 and 171 nM respectively.     

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.