Characterization of an energy source for modeling hypothetical core disruptive accidents in nuclear reactors

The experimental methods for and results of determining the expansion characteristics of the detonation products of an energy source that simulates the pressure-volume change relationships for sodium vapor expansions during hypothetical core disruptive accidents in a fast test reactor are presented. Rigid cylinder-piston experiments performed at two scales (ratio 1:3) to determine a pressure-volume relationship as a function of source mass and expansion environment are described. Some of these measurements are compared with code calculations for the source. The results show: (1) that the pressure-volume relationship depends significantly on the presence of water in the cylinder and comparatively little on the timescale of the expansion, the presence of steel balls in the water, or a Mylar sheet on the water surface; and (2) the experiment's scale. A relationship between the measured work energy from the source and the charge mass is presented, and pressure-volume change measurements are compared with previous experimental measurements and with theoretical calculations for a 150 MWsec hypothetical core disruptive accident. The measurements and code calculations of the pressure-volume relationship for the source agree reasonably well.     

Genetics of heat-curability of killer virus of yeast

The cytoplasmically inherited M double-stranded (ds) RNA genome segment of killer virus of Saccharomyces cerevisiae is heat-curable in some yeast strains but not in others. Temperature sensitivity is conferred on both M₁ and M₂ dsRNA satellite virus segments by the L-A-HN allele of the killer helper virus genome, but not by the L-A-H allele. Both diploidy and mating type heterozygosity of the host cell are also correlated with increased virus curability.     

New Insight into the Residual Rate of Borosilicate Glasses: Effect of S/V and Glass Composition

We report and discuss initial and residual rate measurements performed on 6 borosilicate glasses to highlight (i) some glass composition effects (namely Zn and Fe), (ii) the role of dissolved silica, and (iii) the importance of the glass-surface-area-to-solution-volume (S/V) ratio. We show that there is no apparent relation between the initial and the residual rate. As an example, the well-known positive effect of Zn on short-term glass dissolution becomes adverse under residual rate conditions. Dissolved silica as well as S/V strongly impact the transient rate drop regime, but have no or minor effects on the magnitude of the residual rate of the SON68 glass. Increasing S/V is indeed a good mean to explore higher reaction progresses. Additional simulations performed with the GRAAL model show that, in the case of SON68 glass altered in deionized water, the residual rate continuously diminishes despite the formation of secondary crystalline phases. This result can be used to derive conservative rate values. More generally, it is shown that the residual rate can fluctuate depending on the relative importance of two coupled mechanisms: the formation of a passivating layer and the transformation of this layer into more stable compounds.     

Experimental determination of pesticide processing factors during extraction of seed oils

ABSTRACT

Processing Factors (PFs) reflect the concentration or dilution of pesticide residues resulting from food processing. PFs are key elements to demonstrate the compliance of processed foods with Maximum residue levels (MRLs) as set by Regulation 396/2005. While efforts have been made by the European Food Safety Authority (EFSA) and by national authorities to compile PFs from processing studies, such PFs are not available for all pesticides/processed product combinations. The EU vegetable oil and proteinmeal industry association (FEDIOL) has therefore developed a theoretical approach to approximate MRLs in crude vegetable oils and fats, based on the partition coefficient (log P_ow) of the pesticides and on the oil content of the raw materials. To substantiate this approach, a pilot-scale processing study was initiated with rapeseeds spiked with selected pesticides and the experimental PFs for these pesticides determined. The aims of this study were (i) to study the reliability of pilot-scale conditions for PF determination and (ii) to assess the experimental PFs obtained in comparison to the theoretical PFs proposed by FEDIOL. This study demonstrated that production yields obtained for crude oil and meal in this processing study are similar to those in industrial processes even if differences were observed in the individual production steps (mechanical or solvent extraction steps). The experimental PFs obtained confirmed that the chosen fat-soluble pesticides did concentrate in the oil fraction. For metalaxyl-M having a log P_ow lower than 3, a partitioning between the oil and the meal was observed, as expected. By comparing the experimental PFs and theoretical PFs, it can be concluded that the FEDIOL approach can be recommended as a suitable tool when PFs derived from specific processing studies are missing. Similar studies on pesticides with wider ranges of log P_ow are required in order to complete our conclusions on default PFs for vegetable oils.     

Intracellular Fate of Hydrophobic Nanocrystal Self‐Assemblies in Tumor Cells

Control of interactions between nanomaterials and cells remains a biomedical challenge. A strategy is proposed to modulate the intralysosomal distribution of nanoparticles through the design of 3D suprastructures built by hydrophilic nanocrystals (NCs) coated with alkyl chains. The intracellular fate of two water‐dispersible architectures of self‐assembled hydrophobic magnetic NCs: hollow deformable shells (colloidosomes) or solid fcc particles (supraballs) is compared. These two self‐assemblies display increased cellular uptake by tumor cells compared to dispersions of the water‐soluble NC building blocks. Moreover, the self‐assembly structures increase the NCs density in lysosomes and close to the lysosome membrane. Importantly, the structural organization of NCs in colloidosomes and supraballs are maintained in lysosomes up to 8 days after internalization, whereas initially dispersed hydrophilic NCs are randomly aggregated. Supraballs and colloidosomes are differently sensed by cells due to their different architectures and mechanical properties. Flexible and soft colloidosomes deform and spread along the biological membranes. In contrast, the more rigid supraballs remain spherical. By subjecting the internalized suprastructures to a magnetic field, they both align and form long chains. Overall, it is highlighted that the mechanical and topological properties of the self‐assemblies direct their intracellular fate allowing the control intralysosomal density, ordering, and localization of NCs.     

On the modification of photocatalysts for improving visible light and UV degradation of gas-phase toluene over TiO2

The photocatalytic behavior of different TiO₂-based photocatalysts was reported for gas-phase toluene removal under both UV and visible light illumination, and compared to that of commercial P25 (Degussa) TiO₂. Promotion by sulfates and the use of nanosized anatase TiO₂ were reported to strongly increase the toluene removal efficiency under UV illumination. Nanosized-anatase was prepared by a protecting group sol–gel synthesis using hexamethyldisilazane as crystallite growth inhibitor. Sulfates played a double positive role, with photogenerated electrons transfer effects limiting charge recombination and as repulsive species for strongly adsorbed aromatic intermediates that act as poisons. The decrease in particle size obtained on nanosized anatase TiO₂ (5 nm) yielded a considerable enhancement in the toluene removal efficiency. Pure high surface area rutile has been synthesized at low temperature by a polyethylenglycol-containing sol–gel method for visible light activation purposes. A two-way semiconductor coupling phenomenon, consisting of a reciprocal electron/hole transfer between two visible light-activated oxides, rutile TiO₂ and WO₃, was proposed to explain the large gain in efficiency when adding low amounts of WO₃ to rutile TiO₂.