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  • 1
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Many interesting tasks in technology need the solution of complex boundary value problems within the mathematical theory of elastoplasticity. Error controlled adaptive strategies should be used in order to achieve a prescribed accuracy of the computed solutions at minimum cost. Local error indicators in the primal form of the finite-element-method for Hencky- and Prandtl–Reußplasticity without and with nonlinear hardening are presented, controlling global errors of equilibrium, plastic strain rates, the yield condition and the numerical integration of the flow rule. A 2D finite element code was extended for the transfer of physical parameters between meshes and for a combined space and time adaptive strategy. All error indicators are tested with the benchmark example of a rectangular plane strain problem with a hole.
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  • 2
    ISSN: 1432-1017
    Keywords: Iron superoxide dismutase ; SOD ; X-ray absorption ; XAS ; Extended X-ray absorption fine structure ; EXAFS ; P. shermanii ; E. coli ; Metalloproteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The local structure of the iron site in ferric superoxide dismutase from P. shermanii was analyzed by X-ray absorption spectroscopy. The metal-ligand cluster of the enzyme is found to be similar to the crystallographically investigated ferric superoxide dismutase from E. coli. At pH 6.4 the enzyme is five-fold coordinated with three histidines, an aspartate and a water molecule. The average bond lengths between the metal and the histidines are about 2.10 Å, between metal and aspartate they are about 1.86 Å and between metal and water 1.96 Å. With an increase in pH a change in the coordination number from five to six is observed both in pre-edge peak and EXAFS spectra analysis. However, the bond lengths of the ligands do not change dramatically, they are conserved for the aspartate and increase slightly to 2.13 Å for the average metal - histidine distance at pH 9.3. The observation of the increase in coordination number is correlated with a decrease in enzymatic activity which occurs in the high pH range. The zinc EXAFS spectra of P. shermanii superoxide dismutase have shown that zinc can be incorporated in the active center instead of the iron.
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  • 3
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Die Verweilzeitverteilung des Gases in mehrstufigen Wirbelschichtanlagen wurde untersucht. Als Spurengas diente Helium. Bei den Versuchen wurden die Partikelkonzentration, die Zahl der Wirbelschichtstufen und deren bezogene Höhe verändert. Ein Vergleich mit den Ergebnissen von Untersuchungen an absatzweise betriebenen Wirbelschichtanlagen ergaben, daß bei kontinuierlichem Durchfluß der fluiden und der partikelförmigen Phase durch die mehrstufige Anlage das Gas die engere Verweilzeitverteilung aufweist und daher zu günstigeren Betriebsbedingungen beiträgt.
    Notes: Abstract The residence time distribution of the gas in multistage fluidised beds is studied, using Helium as tracer, for different conditions of the solids concentration, the number of stages and the height-to-diameter ratio of the stage. The results are compared with that of batch fluidisation with and without baffles and it is found that continuous fluidisation gives better flow characteristics of the gas and possesses a wider range of operation than batch fluidisation.
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  • 4
    ISSN: 1432-1017
    Keywords: Monte Carlo ; Crystal water ; Structure refinement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The space in the unit cell of a metmyoglobin crystal not occupied by myoglobin atoms was filled with water using Monte Carlo calculations. Independent calculations with different amounts of water have been performed. Structure factors were calculated using the water coordinates thus obtained and the known coordinates of the myoglobin atoms. A comparison with experimental structure factors showed that both the low and the high resolution regime could be well reproduced with 814 Monte Carlo water molecules per unit cell with a B-value of 50 Å2. The Monte Carlo water molecules yield a smaller standard R-value (0.166) than using a homogeneous electron density for the simulation of the crystal water (R = 0.212). A reciprocal space refinement of the water and the protein coordinates has been performed. Monte Carlo calculations can be used to obtain information for crystallographically invisible parts of the unit cell and yield better coordinates for the visible part in the refinement.
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  • 5
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Digital Particle-Image-Velocimetry was applied to investigate particle trajectories in a gas flow past a sphere. The particle displacement was determined by autocorrelation analysis of image sections. To enhance the signal/noise ratio a synthetic image with idealized particle pictures was generated from the real image. The autocorrelation function (ACF) was calculated using the Fast Hartley Transformation (FHT). The desired secondary maximum of this function was detected by an algorithm with subpixel resolution. A data validation step testing the plausibility of the velocity vectors completes the image analysis. Particle trajectories are traced with help of the particles' velocity vectors. The particle deposition on a sphere can be deduced from the course of these trajectories.
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  • 6
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  We present a measurement technique designed to accurately measure small flow rates near atmospheric pressure, and demonstrate the ability to measure flows on the order of 10-10 mol/sec. The technique is based upon a modification of a constant-volume mass accumulation scheme where the flow rate is measured by monitoring the change in pressure of a known volume of gas. We identify two phenomena, thermally-induced fluctuations and thermodynamically-induced fluctuations, which will affect the resolution and dynamic range of the instrumentation and discuss how the problems associated with them can be mitigated. We estimate the resolution to be approximately 2.0×10-13 mol/s, and the maximum measurable flow rate to be to the order 2×10-9 mol/s.
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  • 7
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An optical bench study has been carried out to assess the effects of both beam alignment and nonconical disturbances in the application of conical shadowgraphy for flow visualization. Conical and quasiconical plastic test models were immersed in a refractive index matching fluid and then examined by shadowgraphy with a conical light beam. The results show that problems of interpretation may arise due to both axial and transverse beam misalignment. Among these difficulties, axial misalignment with positive vertex displacement is the least serious. Also, the effect of a particular nonconical disturbance field was found to introduce fewer difficulties of interpretation than that of beam misalignment.
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  • 8
    ISSN: 1432-1041
    Keywords: frusemide ; piretanide ; variance comparison ; regularity of effect ; activity comparison ; drug excretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Comparison of variances can be useful in assessing the regularity of drug effects. In order to compare the variances of the saluretic effects of piretanide and frusemide, two loop diuretics with different bioavailabilities, a double-blind cross-over study was carried out in 34 normal volunteers. The diuretics were given in randomized order, with an interval of 7 days, in single equipotent doses (frusemide 6.25 mg and piretanide 1.0 mg chosen from previous results) adjusted by body weight. The dispersion of individual values (comparison of variances from paired measures) for Na+, Cl− and Ca++ excretion, urine osmolality and excretion of the drugs, was significantly smaller for piretanide than for frusemide. It is concluded that the saluretic effect of a single dose of piretanide varies less than that of an equipotent dose of frusemide. The methodology may be useful in trials of drugs for which regularity of effect is important.
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  • 9
    ISSN: 1432-2242
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2242
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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