In situ X-ray diffraction of CaO based CO2 sorbents

In situ X-ray diffraction coupled with Rietveld refinement has been used to study CO2 capture by CaO, Ca(OH)2 and partially hydrated CaO, as a function of temperature. Phase quantification by Rietveld refinement was performed to monitor the conversion to CaCO3 and the results were compared to those derived using thermogravimetric analysis (TGA). It was found that Ca(OH)2 converted directly to 100% CaCO3 without the formation of a CaO intermediate, at ca. 600 °C. Both pure CaO and partially hydrated CaO (33.6 wt% Ca(OH)2) reached the same capture capacity, containing approximately 65 wt% CaCO3 at 800 °C. It was possible to provide direct evidence of the capture mechanism. The stresses in the Ca(OH)2 phase of the partially hydrated CaO were found to be more than 20 times higher than its strength, leading to disintegration and the generation of nano-sized crystallites. The crystallite size determined using diffraction (75 × 16 nm) was in good agreement with the average crystallite size observed using TEM (of 83 × 16 nm). Electron diffraction patterns confirmed coexistence of CaO and Ca(OH)2. The analysis provides an explanation of the enhanced capture/disintegration observed in CaO in the presence of steam

Hydrogen production by sorption-enhanced steam reforming of glycerol

Catalytic steam reforming of glycerol for H(2) production has been evaluated experimentally in a continuous flow fixed-bed reactor. The experiments were carried out under atmospheric pressure within a temperature range of 400-700 degrees C. A commercial Ni-based catalyst and a dolomite sorbent were used for the steam reforming reactions and in situ CO(2) removal. The product gases were measured by on-line gas analysers. The results show that H(2) productivity is greatly increased with increasing temperature and the formation of methane by-product becomes negligible above 500 degrees C. The results suggest an optimal temperature of approximately 500 degrees C for the glycerol steam reforming with in situ CO(2) removal using calcined dolomite as the sorbent, at which the CO(2) breakthrough time is longest and the H(2) purity is highest. The shrinking core model and the 1D-diffusion model describe well the CO(2) removal under the conditions of this work

Sea hare <i>Aplysia punctata</i> (Mollusca: Gastropoda) can maintain shell calcification under extreme ocean acidification

Ocean acidification is expected to cause energetic constraints upon marine calcifying organisms such as molluscs and echinoderms, because of the increased costs of building or maintaining shell material in lower pH. We examined metabolic rate, shell morphometry, and calcification in the sea hare Aplysia punctata under short-term exposure (19 days) to an extreme ocean acidification scenario (pH 7.3, ∼2800 μatm pCO2), along with a group held in control conditions (pH 8.1, ∼344 μatm pCO2). This gastropod and its congeners are broadly distributed and locally abundant grazers, and have an internal shell that protects the internal organs. Specimens were examined for metabolic rate via closed-chamber respirometry, followed by removal and examination of the shell under confocal microscopy. Staining using calcein determined the amount of new calcification that occurred over 6 days at the end of the acclimation period. The width of new, pre-calcified shell on the distal shell margin was also quantified as a proxy for overall shell growth. Aplysia punctata showed a 30% reduction in metabolic rate under low pH, but calcification was not affected. This species is apparently able to maintain calcification rate even under extreme low pH, and even when under the energetic constraints of lower metabolism. This finding adds to the evidence that calcification is a largely autonomous process of crystallization that occurs as long as suitable haeomocoel conditions are preserved. There was, however, evidence that the accretion of new, noncalcified shell material may have been reduced, which would lead to overall reduced shell growth under longer-term exposures to low pH independent of calcification. Our findings highlight that the chief impact of ocean acidification upon the ability of marine invertebrates to maintain their shell under low pH may be energetic constraints that hinder growth of supporting structure, rather than maintenance of calcification

The problem with medical research on tissue and organ samples taken in connection with forensic autopsies in France

Currently, in France, it is legally impossible to conduct scientific research on tissue and organ samples taken from forensic autopsies. In fact, the law schedules the destruction of such samples at the end of the judicial investigation, and the common law rules governing cadaver research cannot be applied to the forensic context. However, nothing seems in itself to stand in the way of such research since, despite their specific nature, these samples from forensic autopsies could be subject, following legislative amendments, to common law relating to medical research on samples taken from deceased persons. But an essential legislative amendment, firstly to allow the Biomedicine Agency to become authorized to issue a research permit and secondly, to change the research conditions in terms of the non-opposition of the deceased to said research. Such an amendment would be a true breakthrough because it would allow teams to continue to move forward calmly in research, and allow this research to be placed within a legal framework, which would promote international exchanges

Application of the Hess-Brezowsky classification to the identification of weather patterns causing heavy winter rainfall in Brittany (France)

An accurate knowledge of the weather patterns causing winter rainfall over the Scorff watershed in western Brittany (W. France) was developed prior to studies of the impact of the climate factor on land use management, and of the hydrological reponses to rain-producing weather patterns. These two studies are carried out in the context of the climate change. The identification of rainy air-circulation types was realized using the objective computational version of the 29-type Hess and Brezowsky Grosswetterlagen system of classifying European synoptic regimes, for the cold season (November-March) of the 1958–2005 period at the reference weather station of Lorient, and 13 other stations located in western and southern Brittany, including a more detailed study for the wet 2000–2001 cold season for three reference stations of the Scorff watershed (Lorient, Plouay and Plouray). The precipitation proportion (including the days with rainfall &amp;ge;20 mm) was calculated by major air-circulation type (GWT: see Appendix A) and by individual air-circulation subtype (GWL: see Appendix A) for the studied time-period. The most frequently occurrence of rainy days associated with westerly and southerly GWL confirmed well-known observations in western Europe and so justify the use of the Hess-Brezowsky classification in other areas outside Central Europe. The southern or south-western exposure of the watershed with a hilly inland area enhanced the heavy rainfall generated by the SW and S circulation types, and increased the difference between the rainfall amounts of coastal and inland stations during the wettest days

Simulation of optically conditioned retention and mass occurrences of Periphylla periphylla

Jellyfish blooms are of increasing concern in many parts of the world, and in Norwegian fjords an apparent increase in mass occurrences of the deep water jellyfish Periphylla periphylla has attracted attention. Here we investigate the hypothesis that changes in the water column light attenuation might cause local retention and thereby facilitate mass occurrences. We use a previously tested individual-based model of light-mediated vertical migration in P. periphylla to simulate how retention is affected by changes in light attenuation. Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined. In category 1, increased light attenuation turns fjords into dark “deep-sea” environments which increase the habitat and retention of P. periphylla. In category 2, an optimal light attenuation facilitates the maximum retention and likelihood for mass occurrences. In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention. This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection

Remarks on the tight-binding model of graphene

We address a simple but fundamental issue arising in the study of graphene, as well as of other systems that have a crystalline structure with more than one atom per unit cell. For these systems, the choice of the tight-binding basis is not unique. For monolayer graphene two bases are widely used in the literature. While the expectation values of operators describing physical quantities should be independent of basis, the form of the operators may depend on the basis, especially in the presence of disorder or of an applied magnetic field. Using the inappropriate form of certain operators may lead to erroneous physical predictions. We discuss the two bases used to describe monolayer graphene, as well as the form of the most commonly used operators in the two bases. We repeat our analysis for the case of bilayer graphene.Comment: 15 pages, 4 figure