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  • Springer  (383)
  • American Institute of Physics (AIP)  (55)
  • 2020-2024  (2)
  • 1995-1999  (428)
  • 1930-1934  (8)
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  • 1
    ISSN: 1420-9071
    Keywords: Glutathione ; free radicals ; antioxidants ; oxidant stressors ; buthionine ; menadione
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Using a prokaryote (Escherichia coli) and a metazoa-resembling eukaryote (Ochromonas danica), we surveyed antioxidants which might overcome redox stress imposed by menadione sodium bisulphite (MD) and buthionine sulphoximine (BSO). BSO oxidant stress was evident only inO. danica; MD oxidant stress was evident in both organisms. Glutathione, its precursors, e.g. cysteine, homocysteine, and 2-oxo-4-thiazolidine carboxylic acid, and red blood cells, emerged as prime antioxidants for relieving BSO and MD oxidant stress. BSO and MD oxidant activity and antioxidant-annulling effect inO. danica were judged comparable to those found in animal cells whereas the resultsE. coli were not entirely equivalent. TheO. danica system emerged as a practical, rapid, and useful system for pinpointing oxidant stressors and antioxidants, and shows promise for studies with mammalian systems.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Growth hormone (GH) exerts its regulatory functions in controlling metabolism, balanced growth and differentiated cell expression by acting on specific receptors which trigger a phosphorylation cascade, resulting in the modulation of numerous signalling pathways dictating gene expression. A panel of five monoclonal antibodies was used in mapping the presence and somatic distribution of the GH receptor by immunohistochemistry in normal and neoplastic tissues and cultured cells of human, rat and rabbit origin. A wide distribution of the receptor was observed in many cell types. Not all cells expressing cytoplasmic GH receptors displayed nuclear immunoreactivity. In general, the relative proportion of positive cells and intensity of staining was higher in neoplastic cells than in normal tissue cells. Immunoreactivity showed subcellular localisation of the GH receptor in cell membranes and was predominantly cytoplasmic, but strong nuclear immunoreaction was also apparent in many instances. Intense immunoreactivity was also observed in the cellular Golgi area of established cell lines and cultured tissue-derived cells in exponential growth phase, indicating cells are capable of GH receptor synthesis. The presence of intracellular GH receptor, previously documented in normal tissues of mostly animal origin, is the result of endoplasmic reticulum and Golgi localisation. Heterogeneity of immunoreactivity was found in normal and neoplastic tissue with a variable range of positive cells. The nuclear localisation of immunoreactivity is the result of nuclear GH receptor/binding protein, identically to the cytosolic and plasma GH-binding protein, using a panel of five monoclonal antibodies against the GH receptor extracellular region. The expression of GH receptors, not only on small proliferating tumour cells such as lymphocytes, but also on well differentiated cells including keratinocytes, suggests that GH is necessary not only for differentiation of progenitor cells, but also for their subsequent clonal expansion, differentiation and maintenance.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1327
    Keywords: Key words Superoxide dismutase ; Manganese enzyme ; Crystal structure ; Metalloprotein ; DNA binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The three-dimensional structure of the manganese-dependent superoxide dismutase (MnSOD) from Escherichia coli has been determined by X-ray crystallography at 2.1 Å resolution. The protein crystallizes with two homodimers in the asymmetric unit, and a model comprising 6528 protein atoms (residues 1–205 of all four monomers), four manganese ions and 415 water molecules has been refined to an R factor of 0.188 (R free 0.218). The structure shows a high degree of similarity with other MnSOD and FeSOD enzymes. The Mn centres are 5-coordinate, trigonal bipyramidal, with His26 and a solvent molecule, probably a hydroxide ion, as apical ligands, and His81, Asp167 and His171 as equatorial ligands. The coordinated solvent molecule is linked to a network of hydrogen bonds involving the non-coordinated carboxylate oxygen of Asp167 and a conserved glutamine residue, Gln146. The MnSOD dimer is notable for the way in which the two active sites are interconnected and a "bridge" comprising His171 of one monomer and Glu170 of the other offers a route for inter-site communication. Comparison of E. coli MnSOD and FeSOD (a) reveals some differences in the dimer interface, (b) yields no obvious explanation for their metal specificities, and (c) provides a structural basis for differences in DNA binding, where for MnSOD the groove formed by dimerization is complementary in charge and surface contour to B-DNA.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 1996-06-01
    Print ISSN: 0014-4754
    Topics: Biology , Medicine
    Published by Springer
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  • 5
    Publication Date: 1998-01-28
    Print ISSN: 0018-2222
    Electronic ISSN: 1432-119X
    Topics: Biology , Medicine
    Published by Springer
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2651-2654 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe particles with sizes in the range 1–5 nm, formed by a gas-aggregation method and deposited onto graphite and C60 supports, were studied by x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and magnetic linear dichroism. Clusters deposited onto a C60 coated graphite substrate become embedded within the fullerene film, and have an increased resistance to oxidation compared to exposed clusters supported on a graphite surface. No evidence for hybridization between the electronic states of Fe and C60 is seen. The magnetic dichroism signal of the exposed clusters increases sharply with the film thickness because of the increased cluster interactions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The scalings of heat transport with safety factor (q), normalized collisionality (ν), plasma beta (β), and relative gyroradius (ρ*) have been measured on the DIII-D tokamak [Fusion Technol. 8, 441 (1985)]. The measured ρ*, β and ν scalings of heat transport indicate that E×B transport from drift wave turbulence is a plausible basis for anomalous transport. For high confinement (H) mode plasmas where the safety factor was varied at fixed magnetic shear, the effective (or one-fluid) thermal diffusivity was found to scale like χeff∝q2.3±0.64 , with the ion and electron fluids having the same q scaling to within the experimental errors except near the plasma edge. The scaling of the thermal confinement time with safety factor was in good agreement with this local transport dependence, τth∝q−2.42±0.31 ; however, when the magnetic shear was allowed to vary to keep q0 fixed during the (edge) safety factor scan, a weaker global dependence was observed, τth∝q95−1.43±0.23. This weaker dependence was mainly due to the change in the local value of q between the two types of scans. The combined ρ*, β , ν and q scalings of heat transport for H-mode plasmas on DIII-D reproduce the empirical confinement scaling using physical (dimensional) parameters with the exception of weaker power degradation. © 1998 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 101-112 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Most studies of a gravitationally unstable interface between a liquid and a gas by boundary integral techniques prescribe the motion of the liquid in the far field. The mean gas pressure at the interface is then irrelevant in its motion. On the other hand, when a pressure jump is applied to a liquid column in a vertical duct, its acceleration is determined by the pressure jump no matter how tall the column. Previous studies of accelerating liquid layers [G. R. Baker, R. L. McCrory, C. P. Verdon, and S. A. Orszag, "Rayleigh–Taylor instability of fluid layers," J. Fluid Mech. 178, 161 (1987)] show that the motion of the gravitationally unstable interface depends on the reciprocal of the mean layer thickness H. In this paper, we derive an asymptotic boundary integral method that captures the O(1/H) effects on the motion of the unstable interface with a correction that is exponentially small in H. The validity of the asymptotic approach is confirmed by comparison with numerical simulations of the liquid layer. The success of the approach relies on expansions of the kernels in the boundary integrals, indicating that the procedure for deriving the asymptotic equations is more general than just for vertical ducts or periodic geometry. In a subsequent paper, we use our approach to derive the equations for the formation of a bubble at a submerged orifice that is driven by an increase in gas pressure. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2936-2941 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A formal expression for the canonical steady-state density profile in a tokamak can be obtained from the Fokker–Planck-type diffusion equation derived from the Vlasov equation in the limit of anomalous diffusion due to strong turbulence. Here we derive an explicit expression for this canonical profile for a tokamak with arbitrary cross section and aspect ratio. The resulting profile is independent of the spatial dependence of the diffusion coefficient, but does depend on the relative diffusion of trapped versus passing particles. Under conditions where only the trapped particles transport due to interactions with the turbulence the profiles are considerably flatter than if both the trapped and passing transport the same. The steepness of the calculated profile depends on the ratio of the diffusion coefficients for passing and trapped particles. The calculated profiles are compared with measured profiles from the tokamak known as DIII-D [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. Density profiles for a typical International Thermonuclear Experimental Reactor (ITER) [R. Aymar, Fusion Eng. Design 24, 977 (1984)] plasma are also derived. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3012-3020 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering was used to measure the Langmuir wave spectrum driven by stimulated Raman scattering. The Thomson scattering signals measured in the experiment showed Langmuir waves with components both parallel and antiparallel to the incident laser's wave vector, k0. The parallel component was attributed to stimulated Raman scattering. However, the Langmuir waves with components antiparallel to k0, which cannot be explained by stimulated Raman scattering, were attributed to the Langmuir decay instability (LDI). The relative amplitude of the two Langmuir wave features and their angular width supported the conclusion that the Langmuir waves traveling antiparallel to the incident laser's wave vector were driven by the Langmuir decay instability. © 1997 American Institute of Physics.
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