Experimental studies and thermodynamic assessment of the Ba-Mo-O system by the CALPHAD method

Thermodynamic measurements on BaMoO₄, BaMoO₃ and BaMo₃O₁₀ are reported, that served as input for the development of a thermodynamic model of the Ba-Mo-O system using the CALPHAD methodology. The valence states of molybdenum in BaMoO₄ and BaMoO₃ were confirmed to be VI and IV, respectively, from X-ray Absorption Near Edge Structure Spectroscopy measurements at the Mo K-edge. The heat capacity at low temperatures of these compounds was obtained from thermal-relaxation calorimetry. Phase equilibrium data in the BaMoO₄-MoO₃ section were also measured, and the transition enthalpy associated with the peritectic decomposition of BaMo₃O₁₀ was determined using Differential Scanning Calorimetry. The developed thermodynamic model used the compound energy formalism for intermediate compounds, and an ionic two-sublattice model for the liquid phase. The optimized Gibbs energies were assessed with respect to the known thermodynamic and phase equilibrium data. A good agreement is generally obtained, but a number of ill-defined data were also identified.     

Kinetic studies of the α-β phase transition in the Zr1%Nb cladding for nuclear reactors

The α-β phase transition of a zirconium alloy doped with 1 mol% of niobium (E110 alloy) is investigated using differential scanning calorimetry. The onset and endpoints of the transition are identified from the measured heat flow signal and from the integration of the observed peak the extent of the α-β phase change is calculated as a function of temperature. The experiment has been performed at different heating rates and a shift of the onset temperature with increasing heating rate was observed. From the dataset the equilibrium transition curve has been extrapolated and compared with other types of zirconium-based cladding materials.     

Modelling and calculation of the phase diagrams of the LiF–NaF–RbF–LaF3 system

Four ternary phase diagrams of the quaternary system LiF–NaF–RbF–LaF₃ were calculated from the data of LiF–NaF, LiF–RbF, LiF–LaF₃, NaF–RbF, NaF–LaF₃ and RbF–LaF₃ binary phase diagrams using the Kohler symmetric and Kohler–Toop asymmetric approximation. Excess Gibbs parameters of all six mentioned binaries were optimized using the experimental results taken from the literature. For the LiF–RbF system our own data were used. In all cases very good agreement between the experimental data and our optimized values was achieved. Excess Gibbs functions for the liquid phases were obtained using the modified quasi-chemical method based on quadruplet interactions and the excess Gibbs function for the solid solution was calculated by a sublattice model. The quaternary eutectic was determined and a set of pseudo-ternary systems with fixed ratio of LaF₃ was calculated in order to find the optimal composition for a molten salt fuel.     

Categorisation and priorities for future research on inert matrix fuels: An extended synthesis of the panel discussions

There are three categories of basic fuel cycle needs, which are being addressed by the different types of inert matrix fuel (IMF) concepts currently under development. These are: plutonium burning in existing LWRs, plutonium burning in fast reactors and minor actinide transmutation — corresponding to three distinct timescales for perceived IMF implementation, viz. short, medium and long term, respectively. The current paper, based partly on the two panel discussions organised at the 6^th IMF workshop, presents viewpoints and priorities for each of the three categories of IMF applications, both in terms of the fuel concepts to be pursued and the corresponding R&D requirements.     

Mechanism of the citrate transporters in carbohydrate and citrate cometabolism in Lactococcus and Leuconostoc species

Citrate metabolism in the lactic acid bacterium Leuconostoc mesenteroides generates an electrochemical proton gradient across the membrane by a secondary mechanism (C. Marty-Teysset, C. Posthuma, J. S. Lolkema, P. Schmitt, C. Divies, and W. N. Konings, J. Bacteriol. 178:2178-2185, 1996). Reports on the energetics of citrate metabolism in the related organism Lactococcus lactis are contradictory, and this study was performed to clarify this issue. Cloning of the membrane potential-generating citrate transporter (CitP) of Leuconostoc mesenteroides revealed an amino acid sequence that is almost identical to the known sequence of the CitP of Lactococcus lactis. The cloned gene was expressed in a Lactococcus lactis Cit- strain, and the gene product was functionally characterized in membrane vesicles. Uptake of citrate was counteracted by the membrane potential, and the transporter efficiently catalyzed heterologous citrate-lactate exchange. These properties are essential for generation of a membrane potential under physiological conditions and show that the Leuconostoc CitP retains its properties when it is embedded in the cytoplasmic membrane of Lactococcus lactis. Furthermore, using the same criteria and experimental approach, we demonstrated that the endogenous CitP of Lactococcus lactis has the same properties, showing that the few differences in the amino acid sequences of the CitPs of members of the two genera do not result in different catalytic mechanisms. The results strongly suggest that the energetics of citrate degradation in Lactococcus lactis and Leuconostoc mesenteroides are the same; i.e., citrate metabolism in Lactococcus lactis is a proton motive force-generating process.     

Coastal Oil Spill: Apollo Sea Shipping Disaster — June 1994

The sinking of the Apollo Sea bulk ore carrier off the west coast of South Africa, in June 1994, resulted in an oil spill which had a great impact on the endangered African Penguin bird populations nesting on islands in the vicinity. Due to the relatively rare occurrence of this type of disaster in this region, the media focused much attention on the plight of these birds, the efforts taken to rehabilitate them, as well as the oil pollution inflicted on many of Cape Town's prime tourist beaches. The Major Coastal Oil Spill Contingency Plan was seriously tested in all aspects. Severe storms battered the whole area at the same time, which made the tasks of participating relief organizations all the more difficult. Good co-operation and co-ordination minimized the effects to a great extent; nevertheless, many lessons were learnt.     

Artemisinin-derived sesquiterpene lactones as potential antitumour compounds: cytotoxic action against bone marrow and tumour cells

Epidemiologic and public health researchers frequently include several dependent variables, repeated assessments, or subgroup analyses in their investigations. These factors result in multiple tests of statistical significance and may produce type 1 experimental errors. This study examined the type 1 error rate in a sample of public health and epidemiologic research. A total of 173 articles chosen at random from 1996 issues of the American Journal of Public Health and the American Journal of Epidemiology were examined to determine the incidence of type 1 errors. Three different methods of computing type 1 error rates were used: experiment-wise error rate, error rate per experiment, and percent error rate. The results indicate a type 1 error rate substantially higher than the traditionally assumed level of 5% (p < 0.05). No practical or statistically significant difference was found between type 1 error rates across the two journals. Methods to determine and correct type 1 errors should be reported in epidemiologic and public health research investigations that include multiple statistical tests.     

In vitro pore-forming activity of the lantibiotic nisin. Role of protonmotive force and lipid composition

Human prostate cancer displays a high degree of variability in its rate of spread, which could be due largely to differences in the invasive potential of the tumor cells. The degradation of the basal lamina and stromal extracellular matrix is mediated in part by the secretion of matrix metalloproteinases (MMPs). Matrilysin (PUMP-1, MMP-7) and gelatinase A (M(r) 72,000 type IV collagenase, MMP-2) have been shown to be overexpressed in prostate carcinoma. We have expressed the single MMP matrilysin in the tumorigenic but nonmetastatic human prostate tumor cell line DU-145 to determine if matrilysin has a functional role in prostate tumor cell invasion. DU-145 cells expressing matrilysin were significantly more invasive than vector-only transfected cell lines as assayed by a severe combined immunodeficient mouse model of tumor cell invasion. Vector-only transfected DU-145 cells injected i.p. into severe combined immunodeficient mice invaded the diaphragm in only 1 of 9 mice (11%), whereas matrilysin-transfected DU-145 cells invaded the diaphragm in 12 of 18 mice (66%). The difference between the controls and matrilysin-transfected cells was statistically significant (P < 0.006). These results suggest a functional role for matrilysin in the initial invasion of prostate cancer through the epithelial basal lamina and into the surrounding stroma.