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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5137-5149 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We consider front formation and steady-state front motion in a one-dimensional polymer system undergoing case-II diffusion. The polymer system approximates a polymer sheet whose thickness is very small compared with its lateral dimensions. The osmotic pressure of Thomas and Windle (TW) is used in the theoretical analysis. The transient problem of front formation is formulated. It is found that the original coupled system of partial differential equations proposed by TW can be reduced to one equation. An exact solution of this equation for a diffusion front moving with a velocity V is presented. The solution allows us to predict the dependence of the steady-state velocity on material parameters and the equilibrium concentration of penetrant outside the sheet. The concentration and pressure profile ahead of the moving front is obtained. We also show that the TW Model predicts the existence of a Fickian tail ahead of the steadily moving front. Conditions for the dominance of the Fickian tail are determined. The predicitions of our theoretical analysis are then compared with concentration profiles of iodohexane diffusing into polystyrene determined from Rutherford backscattering spectrometry.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5129-5136 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The swelling of a polymer glass by sorption of a small molecule penetrant is considered in a regime characterized by so-called case-II diffusion. Attention is focused on the polymer so that the swelling process can be investigated apart from diffusion. The model of Thomas and Windle (TW) is used to predict the surface swelling as a function of exposure time. This model assumes that the swelling is driven by the osmotic pressure which relaxes to zero as the surface penetrant volume fraction φs approaches its equilibrium value φe. The rate-controlling factor of the swelling process is the viscosity of the polymer η, which decreases with increasing surface sorption according to η=η0 exp(−mφ) where η0 is the viscosity of the unswollen polymer. For large values of M=mφe, φs is very small until a time τ is reached beyond which the swelling then accelerates rapidly towards its equilibrium value. This feature is absent if M〈e. The time τ is estimated by asymptotic analysis. Rutherford backscattering spectrometry is used to investigate the surface swelling kinetics of polystyrene by iodohexane. The TW model tends to underestimate the swelling rate when φs is low and to overestimate it when φs is high. Nevertheless, the time for φs to approach its equilibrium value φe is approximated well by the TW model.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 3046-3062 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Direct numerical simulations using high-resolution total variation diminishing (TVD) scheme are performed for studying the shock enhancement of two-dimensional confined (spatially growing) supersonic mixing flows. Several specially designed mixing enhancement schemes are examined with emphasis placed on the study of the fundamental aspects involved in the shock-induced mixing enhancement process. The merits associated with these mixing enhancement schemes are evaluated based on a cost/effectiveness criterion, in which the cost paid for the total pressure loss encountered and the improvement in mixing gained are considered together. The results suggest that mixing enhancement using shock waves can only be effective if the stimulation is spatially persistent, and begins from the very upstream. Being motivated by this observation, an idea of using wavy-wall configuration to generate the desirable periodic shock stimulation is proposed and investigated. The computed results show that, by an appropriate manipulation of the parameters including wall wavelength, relative phase shift between the top and bottom walls, as well as the amplitude of the waviness, considerable improvement in mixing efficiency can be achieved.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 3063-3079 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Direct numerical simulations using the high-resolution TVD scheme are performed for the study of two-dimensional confined spatially growing supersonic mixing layers. Numerical simulations, being forced by the linear instability wall modes, are justified by comparing the calculated results with both theoretical and experimental data. The numerically visualized downstream compression/expansion wave system explains the so-called "strange waves'' observed in experiments and are found to be responsible for the rapid growth of the mixing layer in that region. The existence of shock waves would lead to mixing enhancement by accelerating the process of extracting turbulent kinetic energy from the mean stream. However, the phenomenon of shock-induced mixing improvement is found quite local around the shock impingement area, and often is followed by a saturation in turbulent energy absorption which impedes the further growth of the shear layer in the immediate downstream region. For the present cases considered, the subharmonic instability modes are not dominant, and the baroclinic-torque effect is comparatively less important for the vorticity development. These observations suggest that compressibility effects may behave in a considerably different manner as the underlying instability mechanism changes from the subsonic Kelvin–Helmholtz type to the present supersonic wall instability type.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 82 (1978), S. 1827-1830 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Oxford, UK : Munksgaard International Publishers
    Allergy 59 (2004), S. 0 
    ISSN: 1398-9995
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Background:  A polymorphism in the monocyte chemoattractant protein 1 (MCP-1) gene regulatory region has been associated with asthma in Caucasians. This polymorphism is possibly endemic to the Asian region, but its impact on Asian populations is unclear. In addition, the relationship of this marker with life-threatening asthma has not been clarified. The aim of this study was to test the genetic association between the MCP-1 –2518A/G polymorphism and asthma/atopy in a cohort of Chinese children, with particular emphasis on those patients who had experienced life-threatening asthma attacks.Methods:  Forty-eight children with near-fatal asthma, 134 mild-to-moderate asthmatics, 69 allergic-disorder cases without asthma, and 107 nonasthmatic, nonatopic control children were genotyped by a polymerase chain reaction-based assay.Results:  Comparison of the four groups of children (n = 358) revealed no detectable differences in genotype or allele frequencies of the MCP-1 –2518A/G polymorphism. There was no evidence of association between the polymorphism and any of the outcomes of interest including clinical severity, blood eosinophil count, atopy, total serum IgE levels, and degree of bronchial hyper-responsiveness.Conclusion:  These results suggest that the MCP-1 –2518A/G polymorphism is not a risk factor for near-fatal asthma. Furthermore, this polymorphism seems to play no role in the development of asthma or atopy in Chinese subjects, possibly as a result of the genetic heterogeneity between Asian and Caucasian populations with respect to regulation of MCP-1 expression. Our results underscore the necessity of accounting for ethnic background in the investigation of asthma-predisposition genes.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 83 (1979), S. 3180-3183 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 83 (1979), S. 2823-2826 
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    ISSN: 1573-2568
    Schlagwort(e): ulcerative colitis ; Crohn's disease ; lymphocytes ; flow cytometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract By using two-color immunofluorescence with fluorescein isothiocyanate (FITC) and phycoerythrin (PE)-labelled monoclonal antibodies and multiparameter flow cytometry, we investigated lamina propria lymphocyte subsets of patients with ulcerative colitis (UC) and Crohn's disease (CD). Leu-3/Leu-2 (CD4/CD8) ratio of lamina propria lymphocytes (LPL) of CD (mean±sd: 1.9±0.8,P〈0.01) was significantly decreased compared with controls (3.3±1.1), because of an increased number of CD8+lymphocytes. The majority of lamina propria CD4+cells were CD4+, Leu-8-and CD4+, CD45R-both in controls and IBD tissue. Many lamina propria T lymphocytes were activated, expressing HLA-DR antigen not only in IBD but also in controls. NK cells defined by CD16 and CD 56 (3.0±1.4%,P〈0.01) were significantly decreased in patients with UC compared with controls (6.5±3.0%). A low proportion of B cells in the intestinal mucosa expressed Leu-8 antigen and CD23 antigen. The proportion of activated B cells of LPL was high in IBD mucosa as well as normal mucosa. These findings suggest that local activation of B cells leads to the loss of the expression of Leu-8 antigen and CD23.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    International journal of fracture 106 (2000), S. 1-12 
    ISSN: 1573-2673
    Schlagwort(e): Dynamic crack growth ; anisotropic material.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Dynamic propagation of a crack in an anisotropic material under uniform stress is studied. The crack is assumed to nucleate from an infinitesimal micro-crack and expands with a constant velocity. Explicit expressions for the stress intensity factor and the energy release rate are derived.
    Materialart: Digitale Medien
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