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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms of electroluminescence during aging of polyethylene (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4346-4353 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The study of electrical aging of polyethylene subjected to a 50 Hz ac voltage has shown that electroluminescence occured in the bulk of the polymer. These light emissions (detected in the visible range of wavelength) were due to the buildup of space charge around the electrodes. In a previous paper [J. Appl. Phys. 54, 1532 (1983)] results concerning the role of dissolved gases in polyethylene were presented, where particular attention was paid to electroluminescence effects. The present work aims to answer the two following questions: (1) what are the mechanisms causing the electroluminescence? (2) what is the nature of the luminescent centers? Study of the light emission with respect to the applied voltage form, the frequency, (when ac voltage is applied) and the voltage amplitude, shows that the light emission is due to radiative recombinations of carriers injected through the metal-dielectric interface following the Fowler–Nordheim effect. This process requires a double injection of carriers. The influence of electrode material on the light emission intensity is then shown, which is in good agreement with the injection mechanism proposed. The luminescent centers are carriers stabilized by deep traps in the polyethylene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335523
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  • 2
    Electronic Resource
    Electronic Resource
    Transforming growth factor-β1 and ultraviolet A1 radiation increase production of vascular endothelial growth factor but not endothelin-1 in human dermal fibroblasts (2000)
    Oxford, UK : Blackwell Publishing Ltd
    British journal of dermatology 143 (2000), S. 0 
    Details
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background  Normal and dysregulated wound healing involves fibroblast activation and angiogenesis, in which polypeptide factors such as transforming growth factor (TGF)-β, vascular endothelial growth factor (VEGF) and endothelin-1 (ET-1) play an important part. Ultraviolet (UV) A1 (365 nm) has recently received attention as a possible treatment for some dermal fibrotic disorders. Objectives The aim of this study was to evaluate the effects of TGF-β1 and UVA1 radiation, as well as that of cobalt chloride, reported to mimic hypoxia both in vivo and in vitro, on the expression of VEGF and ET-1 by cultured human dermal fibroblasts. Methods Levels of VEGF and ET-1 were measured by enzyme-linked immunosorbent assay and expression of neutral endopeptidase (NEP, CD10), known to degrade ET-1, was quantified by flow cytometric analysis after cell trypsinization. Results Our results showed that the cells released minor amounts of VEGF and ET-1. Both TGF-β1 and UVA1 strongly increased VEGF secretion in a dose- and time-dependent manner, without significantly affecting ET-1 release. Irradiation of TGF-β1-stimulated fibroblasts resulted in a synergistic effect on increasing levels of VEGF but not ET-1 after 48 h. Cobalt chloride stimulated the secretion of VEGF by fibroblasts; the effects of TGF-β1 and cobalt were additive. However, no significant effect of cobalt chloride on ET-1 secretion was observed, suggesting that ET-1 production in fibroblasts is not oxygen-sensitive. The expression of NEP was not modified by TGF-β1 or UVA1 radiation. Addition of a neutralizing anti-CD10 antibody to fibroblast cultures downregulated CD10 expression at the cell surface without changing ET-1 levels in cell supernatants after 24 or 48 h. This suggests that membrane-bound NEP has minimal or no activity against secreted ET-1. Conclusions Taken together, these results underline the major role played by TGF-β1 in increasing VEGF secretion by fibroblasts. This, as well as the documented effect of UVA1 on increasing VEGF production, may have implications for wound healing in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2133.2000.03707.x
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  • 3
    Electronic Resource
    Electronic Resource
    Modulation of endothelin-1 in normal human keratinocytes by UVA1/B radiations, prostaglandin E2 and peptidase inhibitors (2000)
    Copenhagen : Munksgaard International Publishers
    Experimental dermatology 9 (2000), S. 0 
    Details
    ISSN: 1600-0625
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: In the skin, keratinocytes synthesize and secrete endothelin-1 (ET-1), a potent vasoconstrictor peptide which acts also as a growth factor for most skin cells. The aim of the study was to test the effects of UVA1 and the associations UVA1/B on the expression of ET-1 in normal human keratinocytes and to determine whether exogenously added prostaglandin E2 (PGE2) regulated ET-1 expression. As ET-1 is susceptible to degradation, we also evaluated whether ET-1 secretion was modulated by peptidase inhibitors. Our results showed that UVA1 (365 nm) did not modify the levels of preproET-1 mRNA and protein. Moreover, the associations UVA1+UVB or UVB+UVA1 down-regulated the overexpression of secreted ET-1 induced by UVB alone. PGE2 at 10−5 M reduced the expression of ET-1 at the mRNA and protein levels but did not exert any significant modification at lower concentrations from 10−10 to 10−6 M. Phosphoramidon, an endothelin converting enzyme (ECE) inhibitor, drastically decreased the amount of ET-1 accumulating in the culture medium in basal conditions or after UVB irradiation. Conversely, thiorphan, a specific inhibitor of neutral endopeptidase (NEP), rather increased the levels of ET-1 secretion mainly after UVB irradiation. Taken together, the results showed that normal human keratinocytes secrete and partly degrade ET-1 through ECE and NEP pathways and pointed out a differential regulation of ET-1 by UVB and UVA1 radiations without any noticeable role for PGE2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-0625.2000.009006401.x
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  • 4
    Electronic Resource
    Electronic Resource
    Fine structure of defects in polyethylene used for power cable insulation observed by fluorescence microscopy (1993)
    Springer
    Journal of materials science 28 (1993), S. 161-169 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The growth of defects called watertrees in cross-linked polyethylene power-insulated cables is poorly understood. We characterized the watertree structure on artificially aged samples. The resolution of the observations was improved by contrasting watertrees with rhodamine, a fluorescent probe and using epifluorescence microscopy. Both video-enhanced microscopy and confocal laser scanning microscopy provided evidence that watertrees are constituted of continuous microchannels. Their diameter is irregular and ranges between 0.6 and 0.2 μm, and maybe less. They form a complex three-dimensional array that is accurately depicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349047
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison Between Air Filamentary and Helium Glow Dielectric Barrier Discharges for the Polypropylene Surface Treatment (1998)
    Springer
    Plasmas and polymers 3 (1998), S. 43-59 
    Details
    ISSN: 1572-8978
    Keywords: Atmospheric pressure glow discharge ; dielectric controlled barrier discharge ; silent discharge ; corona treatment ; polymer surface activation ; surface energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Recently, a glow like dielectric controlled barrier discharge (GDBD) working at atmospheric pressure has been observed. Such a discharge could replace a filamentary dielectric controlled barrier discharge (FDBD) used in corona treatment systems to improve the wettability or the adhesion of polymers. So it is of interest to compare these two types of discharges and their respective effect on a polymer surface. This is the aim of an extensive study we have undertaken. The first step presented here is the comparison of a filamentary discharge in air with a glow discharge in helium. Helium is the most appropriate gas to realize a glow discharge at atmospheric pressure. Air is the usual atmosphere for a corona treatment. The plasma was characterized by emission spectroscopy and current measurements. The surface transformations were indicated by the water contact angle, the leakage current measurement and the X-ray photoelectron spectroscopy. Results show that the helium GDBD is better than air FDBD to increase polypropylene wettability without decreasing the bulk electrical properties below a certain level. Contact angle scattering as well as leakage current measurements confirm that the GDBD clearly results in more reproducible and homogeneous treatment than the FDBD.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022582017499
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  • 6
    Electronic Resource
    Electronic Resource
    Some observations on wool, paper, and polypropylene treated in a corona discharge (1978)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 66 (1978), S. 155-167 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es werden Untersuchungen über die Umwandlung einiger Isolierstoffe bei Einwirkung von Korona-Entladungen beschrieben, unter Berücksichtigung der Rolle, die die Atmosphäre spielt, in der die Entladungen erfolgen. Die sich ergebenden Veränderungen werden unter einem Rastermikroskop beobachtel, und die Veränderugen chemischer Art werden durch Infrarotspektroskopie untersucht.Im allgemeinen sind lange Einwirkungszeiten erforderlich. Das Auftreten einer charakteristischen Infrarotabsorption im Isolierstoff unter der Wirkung der Entladungen wurde in Abhängigkeit von der Zeit untersucht. Die Oberflächenwirkung dieser Entladung ist sowohl mechanischer als auch chemischer Natur.
    Notes: A study has been made of the transformation of some insulating materials exposed to corona discharges, including the role played by the atmosphere in which discharges are initiated. The resulting modifications are observed through a scanning electron microscope and the chemical changes are studied by means of infrared spectroscopy. In general, long exposure times were needed and the minimum time necessary to produce characteristic infrared absorption due to the effect of the discharges was selected. The action of the discharges on the bulk material has been studied as a function of time; the surface action of this discharge is both mechanical and chemical in nature.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1978.050660115
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  • 7
    Electronic Resource
    Electronic Resource
    Initiation and growth of fracture in electrical treeing development (1981)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 100 (1981), S. 117-127 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Basierend auf früheren Ergebnissen zur Ausbreitungsphase des elektrischen „Treeing“ wurden verschiedene Möglichkeiten für das Wachstum neuer Defekte untersucht. Es wird vermutet, daß zwischen den Elektroden in zwei unterschiedlichen Gebieten elektromechanisches Versagen bzw. rein mechanisches Versagen auftritt. Das elektromechanisches Versagen wird bestimmt durch die lokale Feldstärke in einem Abstand von der Elektrode, der durch die Spitze der ersten Risse festgelegt wird. Der rein mechanische Versagensprozeß läßt sich auf den Druck zurückführen, der durch den Abbau des Polymeren infolge einer partiellen Entladung erzeugt wird.
    Notes: From their previous results concerning the propagation phase of electrical treeing, the authors studied different possibilities for the growth of new defects. The space between electrodes is divided into two regions in which the influence of electromechanical and purely mechanical failure are envisaged, respectively. The electromechanical effect being due to the local intensity of the field as near the high voltage electrode as at the tip of the first cracks. The purely mechanical effect is the result of a pressure. This pressure is created by the polymer decomposition under the impinging of partial discharges.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1981.051000107
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