How 'do's' and 'dont's' can be of significant importance in radiation protection: a case report

The Norwegian Radiation Protection Authority (NRPA) was contacted by a cardiology department because of a suspicious radiation burn on a patient. The patient had undergone two bi-ventricular pacemaker implantations and the lesion was recognised as radiation dermatitis. The NRPA sent sets of thermoluminescense dosemeters to the department to measure the skin dose on eight successive patients undergoing bi-ventricular pacemaker implantations. The average maximum entrance surface dose for the eight patients was 5.3 Gy, ranging from 2.0 to 13.1 Gy. A site audit was performed during a procedure, with the aim to observe the general skills in radiation protection. Based on the findings in the audit, a few very simple 'Do's' and 'Don'ts' were highlighted in a meeting directly after the audit. After the audit, dose measurements were performed on six new patients showing an average maximum entrance surface dose of 0.4 Gy, ranging from 0.2 to 0.8 Gy. The aim of this work was to illustrate the dose reductions that are possible to achieve with a very few basic advices, especially when the operator has suboptimal competence.     

Limitations of codon adaptation index and other coding DNA-based features for prediction of protein expression in Saccharomyces cerevisiae

The relationship between codon usage and protein/mRNA expression in S. cerevisiae has been extensively studied. Recently, protein expression data for the whole yeast genome was published. We investigate which properties of coding DNA sequences can be used to predict expression levels. The new algorithm by Carbone et al. for computing dominating codon bias in a genome is evaluated. It is concluded that it works at least as well as existing methods, and eliminates the need to arbitrarily choose a set of highly expressed genes. Also, the hypothesis that information on codon pair frequencies can be used to predict expression is investigated. Our conclusion is that codon pairs do not contribute more information than do single codon frequencies. Overall correlation between predicted and actual expression data using properties of coding DNA sequences is around 0.65. Hence, while being a useful source of information, the expression levels predicted by these methods should only be used as a rule of thumb.     

A liquid crystal lubricant with partial polymerisation

Lamellar lyotropic liquid crystals were evaluated as lubricants in a slow sliding ball-on-disk friction rig. The liquid crystalline structure was modified by addition of a monomer and the influence of polymerisation on lubrication properties was studied. The results showed that partial polymerisation of a monomer located close to the polar group layer in the liquid crystal, followed by addition of a small amount of long-chain aliphatic hydrocarbon, gives low friction coefficient and enhances load-carrying capacity.     

Physical habitat structure in Danish lowland streams

Dredging or channelization has physically modified the majority (90%) of the 64 000 km of Danish stream network with substantial habitat degradation as a result. Analyses of physical habitat structure in streams, biota, catchment features and regional differences in hydrology, topography and geology have never been carried out in Denmark. Therefore, there is little knowledge of processes, interactions and patterns across the different scales. Physical habitats, catchment parameters and macroinvertebrates were sampled at 39 sites in three major river systems during summer and winter 1993. In‐stream physical conditions and catchment attributes affect the physical habitat structure in Danish lowland streams. Local differences in hydrology, land use, catchment topography and soil types correlated to the in‐stream physical habitat parameters. Local differences in hydrology and topography resulted in a separation of the Suså streams with respect to physical habitats. Mud deposition was pronounced at sites with low discharge and low near‐bed current velocity. Low mud cover was primarily associated with streams with high discharge located in pristine catchments. Stability in the streams was therefore closely linked to in‐stream deposition of fine sediment. Generally, macroinvertebrate community diversity increased as discharge increased. Mud cover negatively affected macroinvertebrate diversity and EPT taxon richness. Regional physical habitat structure and macroinvertebrate community structure were primarily associated with local variations in hydrology, geology and topography. Low‐energy streams were primarily located in the Suså river system and the high‐energy streams in the Gudenå and Storå river systems, leading to extensive deposition of mud during summer. Streams in the Suså river system generally had lower diversity and species richness compared to the streams in the Gudenå and Storå river systems. Hydraulic conditions and substratum dynamics in streams are important when managing lowland streams. This study therefore analysed interactions and parameter correlations between physical habitats, stream stability and catchment attributes as well as macroinvertebrate community structure across multiple scales. Copyright © 2004 John Wiley & Sons, Ltd.     

Fragrance compounds and amphiphilic association structures

Fragrance formulations have traditionally been based on alcohol as the solvent, but the recent legal restrictions on volatile organic solvents have prompted the industry to change to aqueous solubilized systems. The article reviews the fundamental factors in the application of such systems evaluating the influence by different amphiphilic association structures on the vapor pressure of fragrance compounds. This information is subsequently used to estimate the variation of fragrance compound vapor pressures during evaporation. The results reveal that the vapor pressure versus time variation is improved compared to solvent-based formulations.     

Surfactant/cosurfactant association and emulsion stability

The stability of emulsions with an anionic surfactant combined with dodecanol and ethylene glycol dodecyl ether, respectively, was studied. The stability of the emulsion with the nonionic compound as cosurfactant was superior. The results are discussed, with the phase diagrams of water and the cosurfactant as a basis. The phase diagram of the nonionic compound shows a lamellar liquid crystal of superior stability against high water contents.     

Thermodynamic analysis of two‐step solar water splitting with mixed iron oxides

A two‐step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of process conditions and at the evaluation of the theoretical potential of the process. In order to evaluate the maximum hydrogen production potential of a coating material, theoretical considerations based on thermodynamic laws and properties are useful and faster than actual tests. Through thermodynamic calculations it is possible to predict the theoretical maximum output of H₂ from a specific redox‐material under certain conditions. Calculations were focussed on the two mixed iron oxides nickel–iron‐oxide and zinc–iron‐oxide. In the simulation the amount of oxygen in the redox‐material is calculated before and after the water‐splitting step on the basis of laws of thermodynamics and available material properties for the chosen mixed iron oxides. For the simulation the commercial Software FactSage and available databases for the required material properties were used. The analysis showed that a maximum hydrogen yield is achieved if the reduction temperature is raised to the limits of the operation range, if the temperature for the water splitting is lowered below 800°C and if the partial pressure of oxygen during reduction is decreased to the lower limits of the operational range. The predicted effects of reduction temperature and partial pressure of oxygen could be confirmed in experimental studies. The increased hydrogen yield at lower splitting temperatures of about 800°C could not be confirmed in experimental results, where a higher splitting temperature led to a higher hydrogen yield. As a consequence it can be stated that kinetics must play an important role especially in the splitting step. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental study on sulfur trioxide decomposition in a volumetric solar receiver–reactor

Process conditions for the direct solar decomposition of sulfur trioxide have been investigated and optimized by using a receiver–reactor in a solar furnace. This decomposition reaction is a key step to couple concentrated solar radiation or solar high‐temperature heat into promising sulfur‐based thermochemical cycles for solar production of hydrogen from water. After proof‐of‐principle a modified design of the reactor was applied. A separated chamber for the evaporation of the sulfuric acid, which is the precursor of sulfur trioxide in the mentioned thermochemical cycles, a higher mass flow of reactants, an independent control and optimization of the decomposition reactor were possible. Higher mass flows of the reactants improve the reactor efficiency because energy losses are almost independent of the mass flow due to the predominant contribution of re‐radiation losses. The influence of absorber temperature, mass flow, reactant initial concentration, acid concentration, and residence time on sulfur trioxide conversion and reactor efficiency has been investigated systematically. The experimental investigation was accompanied by energy balancing of the reactor for typical operational points. The absorber temperature turned out to be the most important parameter with respect to both conversion and efficiency. When the reactor was applied for solar sulfur trioxide decomposition only, reactor efficiencies of up to 40% were achieved at average absorber temperature well below 1000°C. High conversions almost up to the maximum achievable conversion determined by thermodynamic equilibrium were achieved. As the re‐radiation of the absorber is the main contribution to energy losses of the reactor, a cavity design is predicted to be the preferable way to further raise the efficiency. Copyright © 2009 John Wiley & Sons, Ltd.     

Modeling of a solar receiver–reactor for sulfur‐based thermochemical cycles for hydrogen generation

Sulfur‐based thermochemical cycles for hydrogen generation from water have one reaction step in common, which is the decomposition of sulfuric acid, which is one of the most energy‐consuming steps. The present work deals with the development of a dynamic mathematical model of a solar reactor for this key step. One of the core parts of the model is a partial model of the reaction kinetics of the decomposition of sulfur trioxide, which is based on experiments investigating the kinetics of the used catalyst platinum coated on a ceramic solar absorber. Other partial models describe, e.g. the absorption of solar radiation, heat conduction in the absorber, convection between gas and the absorber walls and energy losses due to heat radiation. A comprehensive validation of the reactor model is performed using measured data, which is gained in experiments with a prototype reactor. The operating behavior of the real reactor is compared with the results of the numerical simulation with the model. The validation is, in particular, performed by reproducing the influences of individual parameters on the chemical conversion and the reactor efficiency. The relative deviations between the experimental data and the simulation results are mostly within the range of measurement accuracy. In particular, the good agreement of calculated values of the derived parameters, SO₃ conversion and reactor efficiency with those determined from the experiments qualifies the model for optimization purposes. Copyright © 2010 John Wiley & Sons, Ltd.