Analysis of principal gas products during combustion of polyether polyurethane foam at different irradiance levels

This paper studies the release of the principal gas species produced during the combustion of a non-flame-retarded Polyether Polyurethane Foam (PPUF) of density of 20.9 kg m⁻³ in the cone calorimeter. Five irradiance levels are studied: 10, 20, 30, 40 and 50 kW m⁻². Heat release rate, mass-loss rate and bulk gas mass flow are measured. The mass flow and yields of gas species are measured as well. The analysis of release of gas species relative to time allowed the study of the different stages of PPUF kinetics and to quantify the gas composition. Of the twenty-two different gas species that were monitored simultaneously, the principal species found were CO₂, CO, H₂O, NO and total hydrocarbons. According to species release, two decomposition stages for PPUF are identified. In the first stage, the solid structure breaks down carrying the decomposition of isocyanate, and in the second stage the polyol decomposes. These two stages are in agreement with the decomposition mechanism proposed in the literature. However, the data presented here is the first experimental study of burning behavior of PPUF taking into account the release of gas species too. An elemental analysis was performed and the chemical formula of the virgin material was determined. This allows the mass balance of the elements in the virgin foam content with the gaseous product content. The effective heat of combustion and the ratio between heat release rate and CO₂ mass flow are calculated at each of the irradiance levels.     

Laser ablation threshold dependence on pulse duration for fused silica and corneal tissues: experiments and modeling

The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent. Our model predicts that the ablation threshold will decrease rapidly for pulse durations in the low end of the femtosecond regime.     

High‐efficiency black silicon interdigitated back contacted solar cells on p‐type and n‐type c‐Si substrates

This work demonstrates the high potential of Al₂O₃ passivated black silicon in high‐efficiency interdigitated back contacted (IBC) solar cells by reducing surface reflectance without jeopardizing surface passivation. Very low reflectance values, below 0.7% in the 300–1000 nm wavelength range, together with striking surface recombination velocities values of 17 and 5 cm/s on p‐type and n‐type crystalline silicon substrates, respectively, are reached. The simultaneous fulfillment of requirements, low reflectance and low surface recombination, paves the way for the fabrication of high‐efficiency IBC Si solar cells using black silicon at their front surface. Outstanding photovoltaic efficiencies over 22% have been achieved both in p‐type and n‐type 9‐cm² cells. 3D simulations suggest that efficiencies of up to 24% can be obtained in the future with minor modifications in the baseline fabrication process. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal multichannel estimation of the location of a target with nonoverlapping noise

We propose a new algorithm for estimating the location of an object in multichannel images when the noise is spatially disjointed from (nonoverlapping with) the target. This algorithm is optimal for nonoverlapping noise and for multichannel images in the maximum-likelihood sense. We consider the case in which the statistical parameters of the input scene are unknown and are estimated by observation. We assess the results for simulated images with white and Gaussian background, for a large scale of variances of the background noise, and different values of the contrast in the scene. We compare the results of this algorithm with the results obtained with two other algorithms, the optimal algorithm for monochannel nonoverlapping noise and the optimal algorithm for multichannel additive noise, and we show that in both cases improvement can be obtained. We show the efficiency of the estimation for real input scenes when the background noise is correlated clutter noise. This algorithm has the same complexity as correlation, and the improvement is obtained with no more calculation cost than with classic methods.     

Construction and evaluation of a humic acid column: implication for pesticide risk assessment

In this paper, humic acid (HA), known to play a large role in the binding and transport of pesticides in soil, was immobilized on a chromatographic support. Then, the association of some herbicides and rodenticides with the main soil component HA was examined using this novel chromatographic column. It appeared that HA has a lower affinity for neutral than for charged pesticides. Moreover, the influence of various parameters was investigated on the pesticide retention in order to providevaluable information about both the binding mechanism and the utilization conditions of the HA column. For all the pesticides studied, a change was clearly vizualized in the HA-pesticide association mechanism at a critical value of the Na+ concentration in the bulk solvent, x(c), equal to 0.6 M. Around this value, the HA structure balanced between a flexible linear conformation for x < x(c) and a random coil form for x > x(c). This work confirmed the conformation change on HA immobilized on silica. As well, only for the charged pesticides, it was clearly pointed out that below a Na+ concentration equal to 0.3 M, the pesticide binding to HA decreased when the salt concentration was enhanced due to an ion pair formation and a competition effect between the sodium cation and pesticide to bind to the HA molecule. Furthermore, it was established that the HA column was stable during an extended period of time, indicating that the HA column could soon become very attractive to determine the risk assessment of pesticides.     

Special Issue on Content Based Multimedia Indexing

Multimedia Tools and Applications -     

Complete study of a millifluidic flow battery using iodide and ferricyanide ions: modeling,effect of the flow and kinetics

In this work, we present a comprehensive study dealing with the modeling of the conversion process occurring in a redox flow cell. Experiments are carried out on an original millifluidic flow battery with ferrocyanide and iodide as electrolytes. A simulation model supports the experimental data. In flow, intensity recovery is limited by the mass transfer. Thanks to diffusion, at low Peclet, the conversion is complete. On the contrary, at high Peclet, the convection prevents the diffusion of species and induces a conversion drop. A quantitative agreement is found between theoretic model and experiment both on current and on power curves. The originality of our work is to take into account the kinetics of the redox reaction at the electrodes. We evidence a new regime where the current intensity is constant as a function of the Peclet number. The maximal recovered power is obtained at a given flow rate and not at very high flow rate. This work paves the road for the optimization of the conversion process and for the measurements of the thermodynamic parameters involved in the redox process such as kinetic parameters at the electrodes.     

Synthesis of 3′‐Fluoro‐tRNA Analogues for Exploring Non‐ribosomal Peptide Synthesis in Bacteria

Aminoacyl‐tRNAs (aa‐tRNAs) participate in a vast repertoire of metabolic pathways, including the synthesis of the peptidoglycan network in the cell walls of bacterial pathogens. Synthesis of aminoacyl‐tRNA analogues is critical for further understanding the mechanisms of these reactions. Here we report the semi‐synthesis of 3′‐fluoro analogues of Ala‐tRNA^Ala. The presence of fluorine in the 3′‐position blocks Ala at the 2′‐position by preventing spontaneous migration of the residue between positions 2′ and 3′. NMR analyses showed that substitution of the 3′‐hydroxy group by fluorine in the ribo configuration favours the S‐type conformation of the furanose ring of terminal adenosine A76. In contrast, the N‐type conformation is favoured by the presence of fluorine in the xylo configuration. Thus, introduction of fluorine in the ribo and xylo configurations affects the conformation of the furanose ring in reciprocal ways. These compounds should provide insight into substrate recognition by Fem transferases and the Ala‐tRNA synthetases.