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  • 2005-2009  (1)
  • 1985-1989  (4)
  • 1950-1954  (1)
  • 1
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract the general problem of pairing correlations within a many-fermion system of identical particles is discussed at some length. We show in this first work in a series how the ground-state version of the [exp(S) or] coupled-cluster formalism (CCF) of quantum many-body theory may be rather generally applied to this problem, and how it thereby provides a very powerful and unifying approach to it. At the so-called SUB2 level of truncation, which is the lowest natural level of approximation for homogeneous systems, the CCF may be cast as a nonlinear integral equation for a four-point correlation function,S 2, which provides a measure of the two-particle/two-hole component in the true “ground-state” wavefunction. This approximation couples the particle-particle, hole-hole and particle-hole correlations simultaneously, and treats them all on an equal footing. In the present work we concentrate particular attention on particle-particle and hole-hole correlations by focussing on the formulation of generalised ladder approximations within the CCF. These are therefore likely to be physically applicable in the low-density regime. In particular, we show that the well-known Galitskii approximation may be formulated within the CCF as that drastic sub-approximation to the full SUB2 equation which keeps only the so-called complete ladder (CLAD) terms, which we describe. A second paper applies the CCF to the particular case of a general (non-local) separable potential, and obtains exact analytic solutions within the CLAD approximation for the corresponding wavefunctions of the simultaneous particle-particle and hole-hole substructures within the many-fermion system.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this series of papers, the so-called ground-state version of the [exp(S) or] coupled-cluster formalism (CCF) of quantum many-body theory is applied to the general problem of pairing correlations within a many-body system of identical fermions. In this second work in the series we restrict ourselves to exact calculations and concentrate on analytic solutions to the generalised ladder approximations formulated in the first paper. We focus attention on the particular model case of a general (non-local) separable potential, and work within the so-called complete ladder (CLAD) approximation which was shown in the earlier paper to be the CCF formulation of the well-known Galitskii approximation. We show how the CLAD approximation reduces in this case to a highly non-trivial pair of coupled nonlinear integral equations for the four-point correlation function,S 2, which provides a measure of the two-particle/two-hole component in the true “ground-state” wave-function. In the further derivation of exact analytic solutions for bothS 2 and the corresponding “ground-state” energy, we also see how various types of composite pairs within the many-body medium manifest themselves as “virtual (de-)excitations”. We thus show how our CCF provides an efficient and unified framework in which to describe all aspects of pairing, such as: (i) a possible free bound pair and its gradual approach to “dissolution” as the density is increased; (ii) the possible appearance of a second bound pair of predominantly hole-like quasi-particles above some lower critical density (which depends on the total momentum of the pair); (iii) the unstable but bound resonant pairs that can exist for densities above a comparable upper critical density at which the two previous types of real bound pairs have “dissolved”; and (iv) Cooper pairs. Even though each of these composite pairs leads to a new “condensed-pair phase” of lower energy, we further show that our so-called ground-state CCF leads only to the fluid-like state of uncondensed particles. In a third paper in this series we use the solutions obtained here as input to the analogous excited-state version of the CCF, and show how these various composite pairs materialise as “negative energy (de-)excitations”.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 174 (1954), S. 178-179 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Table 1 Relative silver Relative radioactivities (and hence silver masses) determined Autoradiography Autoradiography and by Geiger and density visual estimation chemical counter measurement analysis Observer 1 Observer 2 16-1 13-9 15 1 17 17 38-6 37 0 39-5 42 35 ...
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  • 4
    ISSN: 1524-475X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Introduction:  Negative pressure wound therapy (NPWT) is an established treatment of chronic wounds. There is limited understanding of the molecular biological mechanisms of NPWT. The purpose of this study was to characterize changes in the biochemical composition of wound fluid collected from chronic pressure ulcer wounds in adults treated with NPWT.Methods:  Nine stage III or IV pressure ulcer patients scheduled for NPWT (V.A.C.® Therapy, KCI, San Antonio, TX) were recruited. Their ages ranged between 30 and 99. Concentrations of cytokines (IL-1β, TNF-α), metalloproteinases (MMP-2, MMP-3), and tissue inhibitor of metalloproteinase (TIMP)-1 in wound fluids were measured at baseline and after 1 day, 3 days, and 7 days of continuous NPWT.Results:  At days 1, 3, and 7, TNF-α levels were significantly and comparably lower than baseline (p 〈 0.05). MMP- 3 levels significantly decreased from baseline at days 1 and 3 (p 〈 0.05) and significantly increased from baseline at day 7 (p 〈 0.05) with continuous NPWT. IL-1β levels significantly increased at day 3 (p 〈 0.05). There were no significant differences in TIMP-1 or MMP-2 levels at any of the time points when compared to baseline.Discussions and Conclusions:  A key finding of this study is that with NWPT, reductions in levels of the proinflammatory cytokine, TNF-α, from baseline levels were observed and this effect was sustained for at least 1 week. This, together with effects on IL-1 and MMP-3, may be an indication that the NPWT has a rapid and sustained effect on the inflammatory state of chronic wounds. Further studies are being conducted to expand sample size and to analyze other wound healing indicators.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 32 (1986), S. 2079-2082 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fast flow reactor technique, by which thin silicon dioxide layers can be grown, is described in detail. Wafers 3 in. in diameter are treated in the afterglow of a microwave-induced plasma in oxygen/argon mixtures. This method allowed us to produce SiO2 layers of a uniform thickness up to 300 A(ring). It is shown that the oxide growth rate initially follows a parabolic dependence on the oxidation time while at thicknesses from about 170 A(ring) on, a linear relationship is observed. Various physicochemical parameters affecting the oxidation rate are investigated, such as the flow velocity, the wafer position, the microwave power, and the temperature. It is also shown by chemical titration techniques that oxygen atoms in their electronic ground state are the major oxidizing species under the experimental conditions used.
    Type of Medium: Electronic Resource
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