Open-Circuit Voltage in Inverted Polycarbazole:Fullerene Bulk Heterojunction Solar Cells

The correlation between cathode work function and open-circuit voltages (Voc) in inverted polycarbazole:fullerene (PCDTBT:PC70BM) bulk-heterojunction solar cells has been investigated by postannealing of indium tin oxide (ITO) electrodes. The ITO function is seen to change from 4.2 to 4.5 eV without the need to insert additional interfacial layers with annealing temperature up to 400 °C. The best device performance was obtained at room temperature with the ITO work function of 4.2 eV with a Voc of 0.89 eV, a Jsc of 8.06 mA·cm-2, a fill factor (FF) of 64.70%, and a power conversion efficiency of 4.62%. Together with previously published results, we are able to extract two regimes of Voc dependence on the cathode work function: first, a linear relationship when the cathode work function exceeds the lowest unoccupied molecular orbital (LUMO) of PCBM and, second, a constant Voc regime when the ITO work function reduces below the LUMO level. These results provide general guidelines for the cathode contact design in inverted polymer solar cells

Flow-cytometric quantification of microbial cells on sand from water biofilters

Rapid quantification of absolute microbial cell abundances is important for a comprehensive interpretation of microbiome surveys and crucial to support theoretical modelling and the design of engineered systems. In this paper, we propose a protocol specifically optimised for the quantification of microbial abundances in water biofilters using flow cytometry (FCM). We optimised cell detachment from sand biofilter particles for FCM quantification through the evaluation of five chemical dispersants (NaCl, Triton-X100, CaCl2, sodium pyrophosphate (PP), Tween 80 combined with PP), different mechanical pre-treatments (low and high energy sonication and shaking) and two fixation methods (glutaraldehyde and ethanol). The developed protocol was cross-compared using other established and commonly employed methods for biomass quantification in water filter samples (adenosine triphosphate (ATP) quantification, real-time quantitative PCR (qPCR) and volatile solids (VS)). The highest microbial count was obtained by detaching the biofilm from biofilter grains and dispersing clusters into singles cells using Tween 80 and sodium pyrophosphate combined with four steps of high energy sonication (27W, for 80 s each step); glutaraldehyde was shown to be the best fixative solution. The developed protocol was reliable and highly reproducible and produced results that are comparable to data from alternative quantification methods. Indeed, high correlations were found with trends obtained through ATP and qPCR (ρ = 0.98 and ρ = 0.91) measurements. The VS content was confirmed as an inaccurate method to express biomass in sand samples since it correlated poorly with all the other three methods (ρ = 0.005 with FCM, 0.002 with ATP and 0.177 with qPCR). FCM and ATP showed the strongest agreement between absolute counts with a slope of the correlation equal to 0.7, while qPCR seemed to overestimate cell counts by a factor of ten. The rapidity and reproducibility of the method developed make its application ideal for routine quantification of microbial cell abundances on sand from water biofilters and thus useful in revealing the ecological patterns and quantifying the metabolic kinetics involved in such systems

Mise au point d'un nouveau modèle de comportement élasto-viscoplastique. Application au dimensionnement à la fatigue d'un collecteur d'échappement de moteur Diesel en fonte

National audienceFatigue design of structures for high temperature service resorts to modelling based on elasto-viscoplasticity constitutive laws. The new model describes complex anisothermal cyclic loadings, accounting for viscosity on a large range of strain. The new constitutive law that has been developed for nodular cast iron, is intended for the design of automotive parts for high temperature service

Détermination d'une nouvelle loi de comportement élasto-viscoplastique pour une fonte à graphite sphéroidal. Application au dimensionnement à la fatigue oligocyclique d'un collecteur d'échappement de moteur diesel automobile

National audienceLe travail présenté ici porte sur le développement d'une nouvelle loi de comportement mécanique élastoviscoplastique. Cette dernière est développée dans le but de dimensionner à la fatigue thermomécanique des structures de l'industrie automobile travaillant à hautes températures en décrivant au mieux la viscosité sur une large gamme de sollicitation. Ce nouveau modèle a été implémenté dans le code Abaqus en se basant sur l'algorithme du retour radial. Des simulations thermomécaniques ont été ensuite réalisées sur des collecteurs d'échappement et ont permis de prédire la tenue dimensionnelle ainsi que les zones à risque du point de vue fissuration

Pupils’ Conception of Organic Foods and Healthy Eating in School. Qualitative insights from focus group interviews with 5th and 7th grade pupils in a Copenhagen elementary school

Adult habits, including unhealthy eating patterns, are largely established during a person´s childhood and early youth. In this connection, public schools are important health promoting platforms due to their potential for encouraging interest, knowledge and learning about health related issues. The main aim of the study was to shed light on primary and lower secondary school pupils´ everyday experience with food, nutrition, ecology and health in connection to public organic school food, using the municipality of Copenhagen as a case. We have examined how a procurement and provision strategy that primarily originates from “backstage agents” such as engaged politicians and civil servants and governed by administrative priorities, is perceived among agents at the front stage arena - the school. Furthermore we have investigated to which degree the pupils experience a connection between the “organicness” of the food program and the underlying organic supply chain principles, and to which degree the pupils experience a connection between the “organicness” of the food program and classroom initiatives in subjects related to ecology and health. In February 2008, we approached a public school which proved willing to participate in our study. Subsequently, over a period of four weeks, we designed an interview guide used to conduct focus group interviews with pupils from grades 5 and 7, which were then transcribed. In general, pupils were very interested in ecology as a subject. However it seems that they do not see a very strong connection between the healthy, organic meals offered at school and class room activities related to health and ecology. The pupils did not feel that they had been involved in the decision to establish organic and healthy food procurement. As a result they held that they did not feel very committed or engaged in the school provision initiative, and the organic and healthy food procurement was not highly sought after on the part of the pupils. This appears to justify a distinction between the perspective that front stage actors have, including pupils, and the perspective of politicians and planners that operate back stage. The distance between these two stages, which tends to increase in large scale municipal school food systems, is an important challenge to address when planning school food interventions. There seems to be a potential for linking organic school food service more closely with curricular activities, and for linking issues of healthier eating and organic food supply. There is also a need for greater involvement of the pupils and other front stage actors when the food service system and food related curricular activities are planned