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  • 2000-2004  (3)
  • 2001  (3)
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  • 2000-2004  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of the orientation of active and passive scalars in two-dimensional turbulence (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 251-264 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The active nature of vorticity is investigated in order to understand its difference with a passive scalar. The direct cascade down to small scales is examined through both classical and new diagnostics (based on tracer gradient properties) in numerical simulations of freely decaying two-dimensional (2D) turbulence. During the transient evolution of turbulence, the passive scalar possesses a stronger cascade due to different alignment properties with the equilibrium orientations obtained in the adiabatic approximation by Lapeyre et al. [Phys. Fluids 11, 3729 (1999)] and Klein et al. [Physica D 146, 246 (2000)]. In strain-dominated regions, the passive scalar gradient aligns better with the equilibrium orientation than the vorticity gradient does, while the opposite is true in effective-rotation-dominated regions. A study of the kinematic alignment properties shows that this is due to structures with closed streamlines in the latter regions. However, in the final evolutionary stage of turbulence, both active and passive tracer gradients have identical orientations (i.e., there is a perfect alignment between the two gradients, all the more so when they are stronger). The effect of diffusion on the cascade is also studied. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1324705
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  • 2
    Electronic Resource
    Electronic Resource
    Current collapse and the role of carbon in AlGaN/GaN high electron mobility transistors grown by metalorganic vapor-phase epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3527-3529 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The two deep traps responsible for current collapse in AlGaN/GaN high electron mobility transistors grown by metalorganic vapor-phase epitaxy have been studied by photoionization spectroscopy. Varying the growth pressure of the high resistivity GaN buffer layer results in a change in the deep trap incorporation that is reflected in the observed current collapse. Variations in the measured trap concentrations with growth pressure and carbon incorporation indicate that the deepest trap is a carbon-related defect, while the mid-gap trap may be associated with grain boundaries or dislocations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1418452
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  • 3
    Electronic Resource
    Electronic Resource
    Citric acid-enhanced Helicobacter pylori urease activity in vivo is unrelated to gastric emptying (2001)
    Oxford UK : Blackwell Science Ltd
    Alimentary pharmacology & therapeutics 15 (2001), S. 0 
    Details
    ISSN: 1365-2036
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In a previous study, the use of a citric acid test meal produced a rapid dose-dependent increase in urease activity that was significantly greater than that resulting from a pudding meal, ascorbic acid or sodium citrate. The mechanism was hypothesized to be related to the ability of citric acid to delay gastric emptying and possibly to enhance intragastric distribution of the urea.〈section xml:id="abs1-2"〉〈title type="main"〉Objective:To compare the effects of sodium citrate, two doses of citric acid and a pudding meal on gastric motor function.〈section xml:id="abs1-3"〉〈title type="main"〉Method:Eleven normal healthy volunteers were investigated using non-invasive techniques to measure gastric emptying and gastric motility. We evaluated gastric emptying using the Meretek 13Ceebiscuit solid phase gastric emptying breath test, which employs a 340-calorie biscuit containing 200 mg of the edible 13C-blue–green alga Spirulina platensis, after the administration of test meals of pudding, 2 g and 4 g of citric acid and 2 g of sodium citrate. Electrogastrograms (Digitrapper EGG) were also recorded for 30 min before and 180 min after the test meal.〈section xml:id="abs1-4"〉〈title type="main"〉Results:Gastric emptying, as assessed by the half-time (T1/2), was delayed similarly with the pudding (136.8 ± 9 min) and with 4 g of citric acid (144.5 ± 7 min) (P 〉 0.7). Sodium citrate (108.7 ± 6 min) and 2 g of citric acid (110.1 ± 6 min) had similar effects on gastric emptying (P=0.986), and were significantly less effective in delaying gastric emptying (P 〈 0.01) compared to pudding or 4 g of citric acid. The electrogastrograms remained normal and there were no differences among meals and no relation with the gastric emptying results.〈section xml:id="abs1-5"〉〈title type="main"〉Conclusions:The increased intragastric urea hydrolysis associated with citric acid test meals cannot be attributed to delayed gastric emptying. Changes in the intragastric distribution of urea or a direct effect of citric acid on the bacteria (e.g. via the cytoplasmic protein, UreI) are more likely to be responsible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2036.2001.01096.x
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