Modeling the short-circuit current density of polymer solar cells based on P3HT:PCBM blend

We have investigated the short-circuit current density of organic solar cells based on poly (3-hexylthiophene)(P3HT)/6,6-phenyl C61-butyric acid methyl ester (PCBM) blend. In order to model charge collection efficiencies with respect to short circuit density in such blends, a full optical modeling of the cell is performed. From the distribution of the electromagnetic field, we compute the rate of exciton generation. This exciton generation rate is used as input in the transport equations of holes and electrons. Charge densities at steady state are obtained as solutions are used for computing short-circuit current densities generated in the cell. The dependence of short-circuit current densities versus the thickness of the blend is analyzed and compared with our experimental data and with data extracted from the literature.     

Electroactive biofilms: new means for electrochemistry

This work demonstrates that electrochemical reactions can be catalysed by the natural biofilms that form on electrode surfaces dipping into drinking water or compost. In drinking water, oxygen reduction was monitored with stainless steel ultra-microelectrodes under constant potential electrolysis at −0.30 V/SCE for 13 days. 16 independent experiments were conducted in drinking water, either pure or with the addition of acetate or dextrose. In most cases, the current increased and reached 1.5–9.5 times the initial current. The current increase was attributed to biofilm forming on the electrode in a similar way to that has been observed in seawater. Epifluorescence microscopy showed that the bacteria size and the biofilm morphology depended on the nutrients added, but no quantitative correlation between biofilm morphology and current was established. In compost, the oxidation process was investigated using a titanium based electrode under constant polarisation in the range 0.10–0.70 V/SCE. It was demonstrated that the indigenous micro-organisms were responsible for the current increase observed after a few days, up to 60 mA m⁻². Adding 10 mm acetate to the compost amplified the current density to 145 mA m⁻² at 0.50 V/SCE. The study suggests that many natural environments, other than marine sediments, waste waters and seawaters that have been predominantly investigated until now, may be able to produce electrochemically active biofilms.     

ITER safety and licensing update

Safety files were submitted by the ITER Organization to the French nuclear safety authorities in March 2010 as a part of the licensing process. These included the preliminary safety report (RPrS) which presents the extensive safety analyses performed for ITER. The report has been the subject of examination by the authorities and their advisors, and discussions with them have been held on many topics. In the light of this process, this paper discusses some of the topics that remain prominent in the safety analysis of ITER. In particular, the provision of the two safety functions, confinement of radioactive material and limitation of exposure to radiation, is explained and some of the potential challenges to them are identified. Amongst these are the risks of fire and explosion, and external events such as earthquake and loss of all electric power. Provisions in the ITER design, together with the characteristics of fusion, ensure that a very good safety performance will be achieved.     

Investigation of aging mechanisms of high power Li-ion cells used for hybrid electric vehicles

High power lithium-ion batteries need to exhibit long service life to meet targets of automotive applications. This article describes the deep investigation of the so-called VL6P cells, high power lithium-ion cells mass produced by Johnson Controls - Saft (JC-S), in order to understand the root causes of their aging. Cells aged by calendar and cycle life are investigated here compared to fresh cells. Among the results of the different analyses, the most significant is that more active lithium is detected in negative electrode after aging. This tends to indicate that effect of aging is due to increase of positive electrode limitation. Results of this investigation will allow JC-S to continue to improve life of the lithium-ion cells.     

Fabrication of reducing atmosphere electrodes (fuel electrodes) by electroless plating of copper on BaZr0.9−xCexY0.1O3−δ – A proton-conducting ceramic

Copper appears to be an interesting fuel electrode material for proton-conducting ceramic electrolytes (such as BaZr_0.9?xCe_xY_0.1O_3?δ) because it is stable at high temperatures in reducing and hydrocarbon-containing atmospheres. However, when deposited using organometallic Cu pastes/inks, these electrodes suffer from poor performance due to delamination issues and coating thickness (10–20 μm). Alternatively, electroless plating (ELP) is a method of depositing metal films – without utilizing electric power – that can achieve much thinner coatings than with pastes. In this work ELP of Cu was shown to be an alternative to Cu pastes for electrode fabrication on the non-electrically conductive, proton-conducting ceramic BaZr_0.8Ce_0.1Y_0.1O_3?δ. Pd, Ru, and Cu were investigated as activation catalysts, on which Cu was then plated. All three were found to produce thin electrodes (～1 μm) with good electrode/electrolyte adhesion. Scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, x-ray fluorescence and x-ray diffraction were used to characterize the Cu-based ELP electrodes. Additionally, the ELP process was shown to be transferable to tubular substrates without significant modification to the procedure.     

Microbubbles for optofluidics: controlled defects in bubble crystals

We use liquid–gas microfluidics as a low-cost, tunable microstructuring tool, for which applications can be envisioned in optics. In order to obtain relevant geometries for photonics, beyond simple self-assembled crystals, we propose an original approach that excludes bubbles from chosen zones thanks to tiny pillars. To assess the strength of the exclusion mechanism, we predict the behaviour of a single flattened bubble in front of a thin cylindrical pillar located in a rectangular microchannel. The model compares the hydrodynamic force F _fluid that pushes the bubble and the force F _s, due to surface tension, resulting from the surface augmentation when the bubble rises over the pillar. The resulting predictions have been confirmed by experimental results which showed that the bubble passes over the pillar if F _s < F _fluid and goes around it in other cases. Consistently with this model, dynamic bubble crystals with controlled lacuna defects of one, two, or a line of bubbles have been successfully produced. Defects can be switched on or off by changing the flow. Using a photosensitive polymer as a carrier liquid, static bubble crystals have also been produced.     

The Lack of Cytotoxic Effect and Radioadaptive Response in Splenocytes of Mice Exposed to Low Level Internal β-Particle Irradiation through Tritiated Drinking Water in Vivo

Health effects of tritium, a β-emitter and a by-product of the nuclear industry, is a subject of significant controversy. This mouse in vivo study was undertaken to monitor biological effects of low level tritium exposure. Mice were exposed to tritiated drinking water (HTO) at 10 KBq/L, 1 MBq/L and 20 MBq/L concentrations for one month. The treatment did not result in a significant increase of apoptosis in splenocytes. To examine if this low level tritium exposure alters radiosensitivity, the extracted splenocytes were challenged in vitro with 2 Gy γ-radiation, and apoptotic responses at 1 and 24 h were measured. No alterations in the radiosensitivity were detected in cells from mice exposed to tritium compared to sham-treated mice. In contrast, low dose γ-irradiation at 20 or 100 mGy, resulted in a significant increase in resistance to apoptotic cell death after 2 Gy irradiation; an indication of the radioadaptive response. Overall, our data suggest that low concentrations of tritium given to mice as HTO in drinking water do not exert cytotoxic effect in splenocytes, nor do they change cellular sensitivity to additional high dose γ-radiation. The latter may be considered as the lack of a radioadaptive response, typically observed after low dose γ-irradiation.     

Position estimation and object collision detection of a tendon-driven actuator based on a polytopic observer synthesis

This paper proposes a multi-model based approach that estimates joint position and collision detection of a lightweight electric actuator dedicated to manipulation tasks. Taking advantage of an optimized back-drivable mechatronic design, the use of proprioceptive measures at the motor level enables the estimation of the unmeasured terminal position of the mechanical motor-to-joint transmission and force contact disturbance. A polytopic formulation is introduced based on an accurate model of the mechatronic transmission. Then, a multi-model observer-based estimator is synthesized using root-clustering for exteroceptive variables estimation without additional position/force sensor. The approach is experimentally validated with a single degree-of-freedom manipulator.     

Specifying and Automatically Generating a Specialization Tool for Fortran 90

Partial evaluation is an optimization technique traditionally used in compilation. We have adapted this technique to the understanding of scientific application programs during their maintenance. We have implemented a tool that analyzes Fortran 90 application programs and performs an interprocedural pointer analysis. This paper presents a dynamic semantics of Fortran 90 and manually derives a partial evaluator from this semantics. The tool implementing the specifications is also detailed. The partial evaluator has been implemented in a generic programming environment and a graphical interface has been developed to visualize the information computed during the partial evaluation (values of variables, already analyzed procedures, scope of variables, removed statements, etc.).