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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4237-4239 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intrinsic short carrier lifetime (∼5 ps) makes the quantum-well infrared photodetector (QWIP) well suited for high speed and high frequency applications. In such cases, since lasers are commonly used, a high dark current can be tolerated. The most important parameter is then the absorption efficiency. For system simplicity and potential wide use, room temperature operation is desirable. Using GaAs/AlGaAs QWIPs, high absorption (∼100%) and up to room temperature operation are achieved in devices having high doping densities and 100 quantum wells. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Microsystem technologies 1 (1994), S. 14-22 
    ISSN: 1432-1858
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Technology
    Notes: Abstract Reliability and functionality of microsystems, i.e. of small scale integrated electronic, mechanical and optical components, largely depend on their mechanical and thermal constitution. Thermo-mechanical aspects of component and system reliability become more and more important with growing miniaturization as the local physical parameters and field quantities show an increase in sensitivity due to inhomogeneities in local stresses, strains and temperature fields. Since there is usually a lack of information about the local material parameters, a pure field simulation cannot, as a rule, solve the problem. The state of the art of microsystem design more and more requires direct “coupling” between simulation tools (including e.g. FE modelling) and advanced physical experiments. The authors have combined various laser technique, scanning microscopy, and X-ray diffraction with numerical field simulation. The investigations have been directed towards current problems of mechanical and thermal reliability in electronic packaging, crack and fracture behaviour within the interconnected regions and life time estimation. Special problems of mechanical behaviour in solder joints are discussed taking into account local plasticity as well as creep effects.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4919
    Keywords: endothelin ; prostacyclin ; endothelium-derived relaxing factor ; freshly harvested cells ; monocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Cultured endothelial cells have been used in the past as a source of endothelium-derived relaxing factor (EDRF) and of prostacyclin (PGI2). Although cell cultures are essential for observation of prolonged exposure to media or when there is delayed response, they are time consuming and sterile conditions are essential. In the present study, we report that endothelial cells, freshly harvested from bovine aortas, readily attached themselves to cytodex-3 microcarrier beads and released an endothelium-derived relaxing factor (EDRF), prostacyclin (PGI2) and increased the amount of cyclic GMP in vascular smooth muscle. Attachment to microcarrier beads was essential since it increased the surface area and the number of attached cells and permited collection of cell free filtrates because of the formation of dense networks of cells and beads. As a result superfusion of cells and beads on the filter did not dislodge bound cells which remain on the filter. Conditioned filtrates from freshly harvested endothelial cells attached to microcarrier beads caused marked relaxation of endothelium-deprived bovine pulmonary artery strips. The degree of relaxation depended on the number of cells; maximal relaxation occurred with 50 million cells at ED50 of 14 million. High values of cyclic GMP were found in vascular smooth muscle exposed to conditioned filtrate. The calcium ionophore A23187 further increased the amount of cyclic GMP. Large amounts of PGI2 were released by freshly harvested endothelial cells particularly after stimulation with the calcium ionophore. In contrast, endothelin production by freshly harvested cells attached to microcarrier beads was barely detectable after 30 min incubation and was beyond the limit of detection by bioassay procedures. Freshly harvested endothelial cells attached to microcarrier beads appear to be a useful adjunct to tissue cultures under specific experimental conditions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 13 (1993), S. 61-67 
    ISSN: 1573-4935
    Keywords: Nitric oxide ; membrane function ; lysophosphatidylcholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract This communication examines the possibility that nitric oxide (NO) production by endothelial cells results from changes in cell membrane fluidity. Lysophosphatidylcholine (LPC) alters fluidity of the endothelial cell membranes causing vascular relaxation. Through membrane alterations LPC influences function of a number of membrane receptors and modulates enzyme activity. As a result of detergent action, lysophosphatidylcholine (LPC) causes activation of guanylate cyclase, stimulates syalytransferase and regulates protein kinase C activity. It has already been demonstrated that ionic detergents, such as Triton X-100 also cause vascular relaxation, possibly induced by NO production from endothelial cells. It is postulated that production of nitric oxide results from changes in membrane viscosity; this may represent a mechanism for its regulation in biological systems.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 175 (1986), S. 217-243 
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this article we have presented a philosophical and historical perspective on quick freezing, freeze-drying, freeze-substitution, and immunocytochemical localization of pancreatic islet hormones. A compilation of our findings indicates that (1) quick-freezing does not produce any gross distortion of islet tissue; (2) the amount of usable islet tissue for ultrastructural analysis is approximately 13 μm deep from the frozen edge; (3) three different cell types can be identified in quick-frozen tissue based on general morphological characteristics; (4) freeze-substitution with tetrahydrofuran produces a unique ultrastructural appearance in which ribosomes are particularly striking; (5) with the use of protein A-gold, insulin and glucagon can be localized immunocytochemically on silver-gray (50-nm-thick) sections treated with 1% ovalbumin at room temperature overnight; (6) secretory granules of quick-frozen alpha and beta cells may exist in either a swollen or condensed state; (7) swollen beta cell secretory granules contain a filamentous material that demonstrates immunogold labeling for insulin; (8) insulin and glucagon can be localized within the cisternae of endoplasmic reticulum; (9) our methods provide not only discrete immunocytochemical localization of hormone, but also well-preserved cellular compartments; (10) energy electron loss spectroscopy (EELS) has shown that quantifiable nitrogen maps can be used as an index of hormone packaging in secretory granules; and (11) the sectioning properties of secretory granules at the ultramicrotome change when islet tissue is unosmicated and sectioned on glycerol.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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