Structural,optical and electrical properties of silicon nanocrystals embedded in SixC1−x/SiC multilayer systems for photovoltaic applications

In this work we present a structural, optical and electrical characterization of Si_xC_1?x/SiC multilayer systems with different silicon content. After the deposition process, an annealing treatment was carried out in order to induce the silicon nanocrystals formation. By means of energy-filtered transmission electron microscopy (EFTEM) we observed the structural morphology of the multilayers and the presence of crystallized silicon nanoprecipitates for samples annealed up to 1100 °C. We discuss the suitability of optical techniques such as Raman scattering and reflectance and transmittance (R&T) for the evaluation of the crystalline fraction of our samples at different silicon excess ranges. In addition, the combination of R&T measurements with simulation has proved to be a useful instrument to confirm the structural properties observed by EFTEM. Finally, we explore the origin of the extremely high current density revealed by electrical measurements, probably due to the presence of an undesired defective SiC_yO_z ternary compound layer, already supported by the structural and optical results. Nevertheless, the variation of the electrical measurements with the silicon amount indicates a small but significant contribution from the multilayers.     

Supercomputing and grid computing on the verification of covering arrays

The Covering Arrays (CAs) are mathematical objects with minimal coverage and maximum cardinality that are a good tool for the design of experiments. A?covering array is an N×k matrix over an alphabet v s.t. each N×k subset contains at least one time each combination from {0,1,??,v?1} ^t , given a positive integer value?t. The process of ensuring that a CA contains each of the v ^t combinations is called verification of CA. In this paper, we present an algorithm for CA verification and its implementation details in three different computation paradigms: (a)?sequential approach (SA); (b)?parallel approach (PA); and (c)?Grid approach (GA). Four different PAs were compared in their performance of verifying a matrix as a CA; the PA with the best performance was included in a different experimentation where the three paradigms, SA, PA, and GA were compared in a benchmark composed by 45 possible CA instances. The results showed the limitations of the different paradigms when solving the verification of CA problem, and points out the necessity of a Grid approach to solve the problem when the size of a CA grows.     

A multiobjective GRASP–VND algorithm to solve the waste collection problem

In this paper, the waste collection problem (WCP) of a city in the south of Spain is addressed as a multiobjective routing problem that considers three objectives. From the company's perspective, the minimization of the travel cost is desired as well as that of the total number of vehicles. Additionally, from the employee's point of view, a set of balanced routes is also sought. Four variants of a multiobjective hybrid algorithm are proposed. Specifically, a GRASP (greedy randomized adaptive search procedure) with a VND (variable neighborhood descent) is combined. The best GRASP–VND algorithm found is applied in order to solve the real‐world WCP of a city in the south of Spain.     

In-plane shear behaviour of thin low reinforced concrete panels for earthquake re-construction

Low reinforced thin concrete panels have been used for the re-construction of living buildings in the devastated zone of L’Aquila. A structural characterization of these types of panels is presented in this paper, paying particular attention to the fact that these panels are subjected mainly to shear forces. Refined compression-field theory (RCFT) has recently been proposed in order to better predict the behaviour of reinforced concrete members subjected to in-plane shear and axial stresses. This theory is based on continuum mechanics, i.e. satisfying compatibility, equilibrium and formulating the constitutive equations in terms of average (i.e. “smeared”) stresses and strains. The improvement of RCFT in comparison with the two most famous theories for reinforced concrete member subjected to shear [i.e. the modified compression-field theory (MCFT), and the rotating-angle softened-truss model (RA-STM)], deals with an embedded bar model based on the tension stiffening model in concrete. After an ad-hoc calibration procedure, the RCFT is employed in order to reproduce the envelope of the experimental load-deflection response of three full-scale thin low reinforced concrete panels subjected to cyclic loading. The predictions provided by RCFT are compared with the experimental data as well as with those provided by MCFT and RA-STM. This paper presents the necessary parameters for the design of thin low reinforced concrete panels using the RCFT. The preliminary numerical validations seem very promising. However, additional experimental data are required for calibrating and validating the parameters of the proposed RCFT theory.     

ZnO@Ni foam photoelectrode modified with heteroatom doped graphitic carbon for enhanced photoelectrochemical water splitting under solar light

In this study, an electrocatalyticaly inactive ZnO@Ni foam photoelectrode was modified with heteroatom doped graphitic carbon to achieve enhanced photoelectrochemical (PEC) water splitting performance. The O, S and N doped graphitic carbon was simultaneously deposited with ZnO on Ni foam substrate under hydrothermal deposition. One dimensional ZnO nanorods with flower-like graphitic carbon on their surface were obtained on the Ni foam substrate, which was directly used as photoelectrode to derive photoelectrochemical water splitting under solar light irradiation. The pristine ZnO@NF exhibit unattractive PEC performance evidenced by the high overpotential required for the oxygen evolution reaction (OER) couple of water splitting reaction (398 mV vs. RHE). The carbon modified ZnO–C@NF photoelectrode lowers the overpotential required to 317 mV. This enhancement was attributed to the carbon modification which serves as both active site and photoelectron reservoir; facilitating the sluggish kinetics of OER couple reaction and promoting separation of photogenerated charge carriers.     

A Box–Behnken Design-Based Model for Predicting Power Performance in Microbial Fuel Cells Using Wastewater

Although modeling is regarded as a useful tool to understand the performance of microbial fuel cells (MFCs), the number of MFC models remains very low compared with the number of experimental works available in the literature. Moreover, there are very few MFC modeling attempts dealing with the use of wastewater as fuel in these devices, which is essential for the practical implementation of MFCs since the potential of this technology lies in the two-fold benefit of wastewater treatment and bioenergy generation. In this work, a four-factor three-level Box–Behnken design was developed to model the electrochemical power generation in two-chamber MFCs using wastewater as fuel. The optimum values of temperature, external resistance, feed concentration and anodic pH that maximized power output were investigated. Optimum conditions were found at T = 35°C and R = 1 kΩ, corresponding to a maximum power density of 0.88 W·m^?3, while feed concentration and pH did not show statistical significance in the ranges studied. Thus, a Box–Behnken design-based model as empirical approach could provide an effective tool for the optimization study of MFC systems.