Thermochemical hydrogen production from a two-step solar-driven water-splitting cycle based on cerium oxides

A new thermochemical cycle for H₂ production based on CeO₂/Ce₂O₃ oxides has been successfully demonstrated. It consists of two chemical steps: (1) reduction, 2CeO₂ → Ce₂O₃ + 0.5O₂; (2) hydrolysis, Ce₂O₃ + H₂O → 2CeO₂ + H₂. The thermal reduction of Ce(IV) to Ce(III) (endothermic step) is performed in a solar reactor featuring a controlled inert atmosphere. The feasibility of this first step has been demonstrated and the operating conditions have been defined (T = 2000 °C, P = 100–200 mbar). The hydrogen generation step (water-splitting with Ce(III) oxide) is studied in a fixed bed reactor and the reaction is complete with a fast kinetic in the studied temperature range 400–600 °C. The recovered Ce(IV) oxide is then recycled in first step. In this process, water is the only material input and heat is the only energy input. The only outputs are hydrogen and oxygen, and these two gases are obtained in different steps avoiding a high temperature energy consuming gas-phase separation. Furthermore, pure hydrogen is produced (it is not contaminated by carbon products like CO, CO₂), thus it can be used directly in fuel cells. The results have shown that the cerium oxide two-step thermochemical cycle is a promising process for hydrogen production.     

Identifying a Threshold Impurity Level for Organic Solar Cells: Enhanced First‐Order Recombination Via Well‐Defined PC84BM Traps in Organic Bulk Heterojunction Solar Cells

Small amounts of impurity, even one part in one thousand, in polymer bulk heterojunction solar cells can alter the electronic properties of the device, including reducing the open circuit voltage, the short circuit current and the fill factor. Steady state studies show a dramatic increase in the trap‐assisted recombination rate when [6,6]‐phenyl C₈₄ butyric acid methyl ester (PC₈₄BM) is introduced as a trap site in polymer bulk heterojunction solar cells made of a blend of the copolymer poly[N‐9″‐hepta‐decanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PCDTBT) and the fullerene derivative [6,6]‐phenyl C₆₁ butyric acid methyl ester (PC₆₀BM). The trap density dependent recombination studied here can be described as a combination of bimolecular and Shockley–Read–Hall recombination; the latter is dramatically enhanced by the addition of the PC₈₄BM traps. This study reveals the importance of impurities in limiting the efficiency of organic solar cell devices and gives insight into the mechanism of the trap‐induced recombination loss.     

Design of a 10 PW (150 J/15 fs) peak power laser system with Ti:sapphire medium through spectral control

We designed a 10 PW (150 J-15 fs) laser system based on the use of titanium-doped sapphire power amplifiers. The solution is to provide an overall compensating spectral gain narrowing and shifting technique for obtaining a controlled output spectrum.     

Use of a pulsed column contactor as a continuous oxalate precipitation reactor

The current objective of coprecipitating uranium, and minor actinides in order to fabricate a new nuclear fuel by direct (co)precipitation for further transmutation, requires to develop specific technology in order to meet the following requirements: nuclear maintenance, criticity, and potentially high flowrates due to global coprecipitation. A new type of device designed and patented by the CEA was then tested in 2007 under inactive conditions and with uranium. The patent is for organic confinement in a pulsed column (PC). Actually, pulsed columns have been working for a long time in a nuclear environment, as they allow high capacity, sub-critical design (annular geometry) and easy high activity maintenance. The precipitation reaction between the oxalate complexing agent and a surrogate nitrate - cerium(III) or neodymium(III) alone, or coprecipitated uranium(IV) and cerium(III) - occurs within an emulsion created in the device by these two phases flowing with a counter-current chemically inert organic phase (for example tetrapropylene hydrogen—TPH) produced by the stirring action of the column pulsator. The precipitate is confined and thus does not form deposits on the vessel walls (which are also water-repellent); it flows downward by gravity and exits the column continuously into a settling tank.The results obtained for precipitation of cerium or neodymium alone in a short column of small diameter have demonstrated that high throughputs are feasible without system malfunctions. The measured particle size of the precipitates ranges from 20 to 40 μm on average, and the measured device outflow indicates that the precipitation reaction is complete. These results suggest that this laboratory design can be extrapolated to an industrial column. Moreover, a recent test campaign demonstrated that a uranium-cerium coprecipitate easily forms when the two nitrates are mixed in a pulsed column of the same size operating under very similar process conditions. Qualitatively, the coprecipitate meets the process requirements to filter, calcine and fabricate the new nuclear fuel in the downstream steps.     

Simplified J estimation methods for cracked cylinders under combined thermal and mechanical loading

In the field of non-linear fracture mechanics, a lot of work has been done on structures submitted to mechanical loadings. However, for thermal loadings and particularly for thermal shocks, only few results are available. The aim of this paper is to present the main results of a complete set of finite element (FE) computations, conducted by CEA, EDF and FRAMATOME, on cracked cylinders submitted to combined mechanical and thermal loads. The interaction between these two types of loads is analysed in the cases of austenitic and ferritic structures. Moreover, these results are compared to the predictions obtained by simplified engineering methods (R6 procedure and two French approaches) in order to improve them. Their domain of validity is also discussed.     

Les phases SrLa2Al2O7 et SrGd2Al2O7

SrLa₂Al₂O₇ and SrGd₂Al₂O₇ belong to the structural type Sr₃Ti₂O₇. In SrGd₂Al₂O₇ strontium and gadolinium occupy respectively the 12 and 9 coordinated sites, whereas in SrLa₂Al₂O₇ the homologous cations are statistically distributed. The fluorescence spectra of both phases activated by Eu³⁺ ions show that the only possible position of Eu³⁺ is the 9 coordinated site.     

Long-Term Measures of Dyslipidemia,Inflammation, and Oxidative Stress in Rats Fed a High-Fat/High-Fructose Diet

Inflammation and oxidative stress are thought to be involved in, or associated with, the development of obesity, dyslipidemia, hepatic steatosis, and insulin resistance. This work was designed to determine the evolution of inflammation and oxidative stress during onset and progression of hepatic steatosis and glucose intolerance. Seventy-five male Wistar rats were divided to control and high-fat high-fructose (HFHFr) groups. A subgroup of each group was sacrificed at 4, 8, 12, 16, and 20 weeks. HFHFr-fed rats exhibited overweight, glucose intolerance, and hepatic steatosis with increased contents of hepatic diacylglycerols and ceramides. The HFHFr diet increased hepatic interleukin 6 (IL-6) protein and adipose tissue CCL5 gene expression and hepatic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity but not mitochondrial reactive oxygen species (ROS) production. The HFHFr diet decreased plasma and liver levels of isoprostanoid metabolites as well as plasma thiobarbituric acid-reactive substance (TBARS) levels. Hepatic glutathione content was decreased with a moderate decrease in superoxide dismutase (SOD) and glutathione peroxidase (GPx) with the HFHFr diet. Overall, HFHFr diet led to hepatic lipid accumulation and glucose intolerance, which were accompanied by only moderate inflammation and oxidative stress. Most of these changes occurred at the same time and as early as 8 or 12 weeks of diet treatment. This implies that oxidative stress may be the result, not the cause, of these metabolic alterations, and suggests that marked hepatic oxidative stress should probably occur at the end of the steatotic stage to result in frank insulin resistance and steatohepatitis. These findings need to be further evaluated in other animal species as well as in human studies.     

Large scale multiple sequence alignment with simultaneous phylogeny inference

Multiple sequence alignment (MSA) and phylogenetic tree reconstruction are one of the most important problems in the computational biology. While both these problems are of great practical significance, in most cases they are very computationally demanding. In this paper we propose a new approach to the MSA problem which simultaneously infers an underlying phylogenetic tree. To process large data sets we provide parallel implementation of our method, which is based on the distributed caching of intermediate results. Finally, we show a parallel server designed for grid environments, and we report results of experiments performed with actual biological data, e.g. 1000 ribosomal RNA sequences.     

一种基于Kirchhoff积分的快速三维非均匀弹性介质地震波场模拟方法

提出了一种基于Kirchhoff积分的快速地震波场数值模拟算法。在地下弹性介质的速度、反射界面的空间位置及反射率均已知的情况下，可以利川该算法计算三维非均匀弹性介质模型中的反射地震波场。讨论了算法的计算效率和计算精度。针对基丁Kirchhoff积分的二维地震波场模拟计算量巨大这一问题，采用了两种尺度网格单元和限制积分区域等手段，不仅降低了计算量，节省了内存，同时还保待了足够的计算精度。利用数值模拟对算法的有效性进行了验证。