Application of a dual variational formulation to finite element reactor calculations

A number of improvements have been made to the nodal collocation method in order to obtain a high-order nodal technique capable of solving the neutron diffusion equation over full-core three-dimensional pressurized water reactors. First, the nodal collocation method is derived formally from a dual variational principle, using Gauss-Lobatto quadratures. Analytical integration and Gauss-Legendre quadratures are next applied to the same dual functional in order to obtain more accurate discretizations. An efficient ADI numerical technique with a supervectorization procedure was set up to solve the resulting matrix system. Validation results are given for the IAEA 2-D, Biblis and IAEA 3-D benchmarks and for a typical full-core 3-D representation of a pressurized water reactor at the beginning of the second cycle.     

The cytomegalovirus-encoded chemokine receptor US28 can enhance cell-cell fusion mediated by different viral proteins

The human cytomegalovirus (CMV) US28 gene encodes a functional CC chemokine receptor. However, this activity was observed in cells transfected to express US28 and might not correspond to the actual role of the protein in the CMV life cycle. Expression of US28 allows human immunodeficiency virus type 1 (HIV-1) entry into certain CD4(+) cells and their fusion with cells expressing HIV-1 envelope (Env) proteins. Such properties were initially reported for the cellular chemokine receptors CCR5 and CXCR4, which behave as CD4-associated HIV-1 coreceptors. We found that coexpression of US28 and either CXCR4 or CCR5 in CD4(+) cells resulted in enhanced synctium formation with HIV-1 Env+ cells. This positive effect of US28 on cell fusion seems to be distinct from its HIV-1 coreceptor activity. Indeed, enhancement of cell fusion was also observed when US28 was expressed on the HIV-1 Env+ cells instead of an CD4(+) target cells. Furthermore, US28 could enhance cell fusion mediated by other viral proteins, in particular, the G protein of vesicular stomatitis virus (VSV-G). The HIV-1 coreceptor and fusion-enhancing activities could be affected by mutations in different domains of US28. The fusion-enhancing activity of US28 seems to be cell type dependent. Indeed, cells coexpressing VSV-G and US28 fused more efficiently with human, simian, or feline target cells, while US28 had no apparent effect on fusion with the three mouse or rat cell lines tested. The positive effect of US28 on cell fusion might therefore require its interaction with a cell-specific factor. We discuss a possible role for US28 in the fusion of the CMV envelope with target cells and CMV entry.     

Agrobiodiversität und Pflanzenschutz – ein ambivalentes Verhältnis

No Abstract. .      

Investigation of the stability of tablets prepared from sucrose and citric acid anhydride utilizing response surface methodology

Inversion of sucrose is a stability problem particularly of candies with acidic taste that contain sucrose and small amounts of organic acids such as citric acid, since the free d-fructose produced by hydrolysis is hygroscopic. The following possibilities were investigated for preventing the hydrolysis of sucrose in tablets containing sucrose and citric acid: Adding various amounts of tri-sodium citrate to the formulation to neutralize the citric acid, (Hot) melt coating of citric acid and tri-sodium citrate with a vegetable fat at different coating ratios, variation of the ratio of coated citric acid and tri-sodium citrate in formulations, and compressing the formulations with different compression forces. After tablet processing and storage of tablets, the concentration of d-fructose was determined on the basis of enzymatic reactions. A response surface central composite design was used. The above-mentioned variations were chosen as independent variables and the amount of d-fructose was chosen as response variable. The lowest rates of inversion could be achieved by increasing the content of tri-sodium citrate and the ratio of coating material and decreasing the ratio of coated citric acid and tri-sodium citrate in the tablet formulations. The compression force had no significant effect on the inversion of sucrose.     

Energetics of Plastic Deformation of Metastable Austenitic Stainless Steel

The change in the internal energy during uniaxial tensile deformation of austenitic stainless steels EN 1.4301 (AISI 304) and EN 1.4318 (AISI 301LN) was determined by measuring the extent of γ→α'‐martensite transformation and the temperature increase of the samples. From the results the fraction of the stored energy of cold work and the free energy change related to the strain‐induced γ→α'‐martensite transformation were determined. The fraction of stored energy varied around 0.4. With the metastable steel grades the free energy change related to the γ→α'‐martensite transformation was found to vary between ‐98 MJ/m³ and ‐206 MJ/m³ depending on the austenite stability of the steel. Furthermore, the magnitude of the mechanical driving force was estimated by comparing the results with the free energy change of thermally induced transformation.     

Some Notes on the Formal Properties of Bidirectional Optimality Theory

In this paper, we discuss some formal properties of the model ofbidirectional Optimality Theory that was developed inBlutner (2000). We investigate the conditions under whichbidirectional optimization is a well-defined notion, and we give aconceptually simpler reformulation of Blutner's definition. In thesecond part of the paper, we show that bidirectional optimization can bemodeled by means of finite state techniques. There we rely heavily onthe related work of Frank and Satta (1998) about unidirectionaloptimization.     

Validation of the three-dimensional acquisition mode in positron emission tomography for the quantitation of [18F]fluoro-DOPA uptake in the human striata

Three-dimensional (3D) positron emission tomography (PET) is attractive for [18F]fluoro-DOPA studies, since the sensitivity improvement is maximal for radioactive sources located in central planes, which is usually the case for the human striata. However, the image quantitation in that mode must be assessed because of the nearly threefold increase in scattered coincidences. We report the results of [18F]fluoro-DOPA studies performed on six normal volunteers. Each one was scanned in the 3D and two-dimensional (2D) modes on the same tomograph. The quantitation in the 3D and 2D modes was compared for a Patlak graphical analysis with the occipital counts as the input function (Ki) and a striatooccipital ratio analysis. We find that, in 3D PET, a scatter correction is required to preserve the same quantitation as in 2D PET. When the 3D data sets are corrected for scatter, the quantitation of the [18F]fluoro-DOPA uptake, using the Patlak analysis, is similar in the 2D and 3D acquisition modes. Conversely, analysis of the striatooccipital ratio leads to higher values in 3D PET because of a better in-plane resolution. Finally, using the 3D mode, the dose injected to the subjects can be reduced by a factor greater than 1.5 without any loss in accuracy compared to the 2D mode.     

Thermophysical Properties of W–Re Alloys Above the Melting Region

In earlier experiments we have studied pure elements with a fast pulse heating technique to obtain thermophysical properties of the liquid state. We report here results for thermophysical properties such as specific heat and dependences among enthalpy, electrical resistivity, and temperature, for four W–Re alloys (3.95, 21.03, 23.84, and 30.82 at % of Re) in a wide temperature range covering solid and liquid states. Thermal conductivity is calculated using the Wiedemann–Franz law for the liquid alloy, as.well as data for thermal diffusivity for the beginning of the liquid phase. Additionally, data for the entire temperature range studied have been analyzed in comparison with those of the constituent elements, tungsten and rhenium, since both metals have been studied previously with the same experimental technique. Such information is of interest in the field of metallurgy since W–Re alloys of low Re content in the region of mutual component solubility in the solid state are widely used as thermocouple materials for the purposes of high-temperature thermometry.     

PilT mutations lead to simultaneous defects in competence for natural transformation and twitching motility in piliated Neisseria gonorrhoeae

Neisseria gonorrhoeae, the Gram-negative aetiological agent of gonorrhoeae, is one of many mucosal pathogens of man that expresses competence for natural transformation. Expression of this phenotype by gonococci appears to rely on the expression of type IV pili (Tfp), but the mechanistic basis for this relationship remains unknown. During studies of gonococcal pilus biogenesis, a homologue of the PilT family of proteins, required for Tfp-dependent twitching motility in Pseudomonas aeruginosa and social gliding motility in Myxococcus xanthus, was discovered. Like the findings in these other species, we show here that gonococcal PilT mutants constructed in vitro no longer display twitching motility. In addition, we demonstrate that they have concurrently lost the ability to undergo natural transformation, despite the expression of structurally and morphologically normal Tpf. These results were confirmed by the findings that two classes of spontaneous mutants that failed to express twitching motility and transformability carried mutations in PilT. Piliated PilT mutants and a panel of pilus assembly mutants were found to be deficient in sequence-specific DNA uptake into the cell, the earliest demonstrable step in neisserial competence. The PilT-deficient strains represent the first genetically defined mutants that are defective in DNA uptake but retain Tfp expression.     

Morphologic image processing operators: reduction of partial volume effects for improved 3D visualization of CT data

AIM: The quality of segmentation and three-dimensional reconstruction of anatomical structures in tomographic slices is often impaired by disturbances due to partial volume effects (PVE). The potential for artefact reduction by use of the morphological image processing operators (MO) erosion and dilation is investigated. DESIGN: The CT examinations of 31 patients with pathological alterations in lung or brain were segmented using automatic region growing and the MO were applied in a different number of iterations. The processed regions were 3D-reconstructed (shaded surface display, MIP, volume rendering) and the occurrence of PVE-related artefacts using the signal-to-background ratio (SBR) prior to and after MO application was compared. RESULTS: For all patients under review, the artefacts caused by PVE were significantly reduced by erosion (lung: mean SBRpre = 1.67, SBRpost = 4.83; brain: SBRpre = 1.06, SBRpost = 1.29) even with only a small number of iterations. Region dilation was applied to integrate further structures (e.g. at tumor borders) into a configurable neighbourhood for segmentation and quantitative analysis. CONCLUSIONS: The MO represent an efficient approach for the reduction of PVE artefacts in 3D-CT reconstructions and allow optimized visualization of individual objects.