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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 3319-3324 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 88 (1966), S. 4203-4211 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Summary The FeSII protein of Azotobacter vinelandii has been proposed to mediate the ‘conformational protection’ of the molybdenum-dependent nitrogenase components against oxygen inactivation. We have cloned and characterized the structural gene for the FeSII protein (the fesII Iocus). Hybridization studies did not reveal the presence of fesII-like genes in a number of diverse species of well-studied nitrogen-fixing bacteria, with the exception of Azotobacter chroococcum. The fesll locus is transcriptionally expressed during both nitrogen fixing and non-nitrogen fixing conditions, although the level of its message is up-regulated by approximately 2.5-fold during nitrogen fixation. The promoter region was identified by primer extension analysis, and is similar to other σ70-type promoters. Mutants devoid of the FeSII protein were constructed. These mutants possessed growth characteristics on a variety of carbon substrates during non-diazotrophic as well as diazotrophic growth that were essentially indistinguishable from the wild-type strain. Nevertheless, the nitrogenase activity in cell-free extracts is significantly more sensitive to irreversible oxygen inactivation in the mutants as compared with the wild type. When treated with 250 mM NaCI (a condition known to dissociate FeSII from nitrogenase components), the wild-type and mutant extracts were equally hypersensitive to oxygen Inactivation. Upon energy starvation, conditions in which ‘respiratory protection’ is inoperable, the MoFe and Fe proteins of nitrogenase are degraded much more rapidly in vivo in the deletion mutants, compared to the wild type. Strains relying on either the vanadium or the ‘iron-only’ alternative nitrogenases exhibited similar growth rates irrespective of the presence of absence of the FeSII protein, and the in vitro inactivation of the vanadium nitrogenase components was not affected by the lack of the FeSII protein. All in all, these results are consistent with a model whereby ‘respiratory protection’ is the major physiological mechanism responsible for the protection of all three nitrogenases during energy supplemented growth. Upon energy starvation, however, ‘conformational protection’ mediated by the FeSII protein is capable of temporarily protecting the conventional molybdenum nitrogenase components from inactivation and subsequent degradation.
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bacterial exopolysaccharide (EPS) and lipopolysaccharide (LPS) molecules have been shown to play important roles in plant-bacterium interactions. Here we have demonstrated that the fix-23 loci, which compensate for exo mutations during symbiotic nodule development, are involved in the production of a novel polysaccharide that is rich in 3-deoxy-D manno-2-octulosonic acid (Kdo) but is not the classical LPS. This molecule is likely to be a surface antigen since antiserum to whole Rhizobium meliloti cells reacts strongly with it, and since mutations in fix-23 result in an inability to produce this polysaccharide and to bind bacteriophage 16-3. It is likely that this Kdo-rich polysaccharide is analogous to certain Escherichia coli K-antigens which are anchored to the membrane via a phospholipid moiety. DNA sequence analysis of one gene cluster of this region revealed that the predicted protein products of six genes exhibit a high degree of homology and similar organization to those of the rat fatty acid synthase multifunctional enzyme domains.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 695-706 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A database obtained from direct numerical simulation of a turbulent channel flow is analyzed to extract the streamwise component of the propagation velocity V of velocity, vorticity, and pressure fluctuations from their space-time correlations. A surprising result is that V is approximately the same as the local mean velocity for most of the channel, except for the near-wall region. For y+≤15, V is virtually constant, implying that perturbations of all flow variables propagate like waves near the wall. In this region, V is 55% of the centerline velocity Uc for velocity and vorticity perturbations and 75% of Uc for pressure perturbations. This is equal to U at y+=15 for velocity and vorticity perturbations, and equal to U at y+=20 for pressure perturbations, indicating that the dynamics of the near-wall turbulence is controlled by turbulence structures present near y+(approximately-equal-to)15–20. Scale dependence of V is also examined by analyzing the bandpass-filtered flow fields. This paper contains comprehensive documentation on the propagation velocities, which should prove useful in the evaluation of Taylor's hypothesis. An attempt has been made to explain some of the data in terms of the current understanding of organized structures.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 633-641 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Instability and transition in plane Poiseuille flow with spanwise system rotation is studied via direct numerical simulations with initial small-amplitude random disturbances. The results confirm and clarify the recent experimental findings of Alfredsson and Persson [J. Fluid Mech. 202, 543 (1989)]. A large computational domain is used to allow natural selection of the dominant spanwise wavelength of the observed streamwise vortices, and also the streamwise wavelength of the dominant secondary modes which subsequently develop in the presence of the streamwise vortices. Temporal evolutions of these vortices for several different cases are studied in detail. It is found that the spanwise wavelength of the streamwise vortices can be significantly different from that obtained from linear stability analysis. In all cases examined, the unstable primary three-dimensional waves, which develop during the linear stage, are still persistent in the nonlinear stage. It is also found that for the cases in which the primary three-dimensional waves decay, the finite-amplitude streamwise vortices can become unstable to two different three-dimensional secondary modes of instability, depending on the range of Reynolds number (Re) and rotation number (Ro). The first mode has a streamwise wavelength an order of magnitude longer than the spanwise wavelength; the other, referred to by Alfredsson and Persson as the "twisting mode'' because of its visual appearance, has a streamwise wavelength comparable to the spanwise wavelength, and is shown to consist of counter-rotating streamwise vortices whose centers oscillate mostly in the vertical direction. It is shown that these modes are nondispersive traveling waves.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 3326-3328 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequency of occurrence of the bursting process near a wall is studied by examining turbulent velocity fields obtained from numerical simulations of a flat-plate boundary layer at three different Reynolds numbers. It is found that the frequency scaled by the inner variables is essentially independent of the Reynolds number.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 1885-1888 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear process in wall-bounded turbulent shear flows has been investigated through numerical experiments. It is shown that the linear coupling term, which enhances non-normality of the linearized Navier–Stokes system, plays an important role in fully turbulent—and hence, nonlinear —flows. Near-wall turbulence is shown to decay without the linear coupling term. It is also shown that near-wall turbulence structures are not formed in their proper scales without the nonlinear terms in the Navier–Stokes equations, thus indicating that the formation of the commonly observed near-wall turbulence structures are essentially nonlinear, but the maintenance relies on the linear process. Other implications of the linear process are also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 764-766 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Turbulence-producing events in turbulent channel flow were found to be predominantly associated with asymmetric vortical structures rather than pairs of counter-rotating structures. An asymmetry-preserving averaging scheme was devised, allowing a picture of the "average'' structure that more closely resembles the instantaneous one to be obtained. In addition, these structures were found to persist for long distances with little change while convecting downstream.
    Type of Medium: Electronic Resource
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