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  • 1995-1999  (8)
  • 1955-1959
  • 1915-1919
  • 1999  (8)
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  • 1995-1999  (8)
  • 1955-1959
  • 1915-1919
Year
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  • 1
    Electronic Resource
    Electronic Resource
    Improved device performance using a semi-transparent p-contact AlGaN/GaN heterojunction positive-intrinsic-negative photodiode (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2138-2140 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the improved device performance of GaN-based ultraviolet heterojunction photodiodes using a semi-transparent p-contact device structure. At a reverse bias of 10 V, these photodiodes exhibit a low dark current density of 0.3 nA/cm2. The external quantum efficiency is 38% at the band edge, with only a slight decrease at the shorter wavelengths. The forward current is 〉10 mA at Vf=5 V. Fitting of the forward current–voltage data to the diode equation yields a very low series resistance (Rs=62Ω), which results in a very fast decay of the time response. The improved performance afforded by the thin, semi-transparent, p-contact layer is due to an increase in the uniformity of the lateral field distribution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124942
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Improved ultraviolet quantum efficiency using a semitransparent recessed window AlGaN/GaN heterojunction p-i-n photodiode (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2421-2423 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the improved quantum efficiency of GaN-based ultraviolet heterojunction photodiodes using a semitransparent recessed window device structure. At a reverse bias of −5 V the quantum efficiency was ∼57% at the band edge, and remained relatively flat down to ∼330 nm after which some absorption in the p-AlGaN layer became evident. The quantum efficiency only gradually declines after this point, remaining 〉20% at 280 nm. We attribute these results to avoidance of the optical dead space at the surface of GaN homojunction p-i-ns. The semitransparent p-AlGaN layer was comparatively resistive, causing an electric field crowding effect which resulted in a spatially nonuniform temporal behavior. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125034
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The chemokine receptor CCR4 in vascular recognition by cutaneous but not intestinal memory T cells (1999)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 400 (1999), S. 776-780 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Lymphocytes that are responsible for regional (tissue-specific) immunity home from the blood to the intestines, inflamed skin or other sites through a multistep process involving recognition of vascular endothelial cells and extravasation. Chemoattractant cytokine molecules known as chemokines ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/23495
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  • 4
    Electronic Resource
    Electronic Resource
    Accurate and highly complete synchrotron protein crystal Laue diffraction data using the ESRF CCD and the Daresbury Laue software (1999)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 6 (1999), S. 995-1006 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Developments in electronic area detectors such as CCDs and image plates have transformed the capability of the synchrotron Laue protein crystallography technique compared with film. The rapid readout of CCDs makes practical the use of rather fine angular interval settings of the crystal between each Laue exposure and a large overall angle coverage. The use of the ESRF CCD (image intensifier type) presented here in the Laue data collection on ESRF ID09 (the `Laue beamline') from a single crystal of the 34 kDa wild-type hydroxymethylbilane synthase (HMBS), space group P21212 a = 88.06, b = 75.73, c = 50.35 Å, yielded 47 Laue exposures in 2.5° angle intervals from a single crystal. The data processed by the Daresbury Laue software is highly complete (∞–2dmin = 77.5%; 2dmin–dmin= 91.7%) to 2.3 Å with high redundancy (11.2). Comparison with calculated structure factors and careful analysis of the Laue geometry shows that between ∞ and 5dmin better completeness still should be possible, which can ideally be realized from CCD detector dynamic range hardware improvements and/or software algorithms to integrate saturated spot profiles. Prospects for Laue diffraction data collection using yet faster detectors such as the `pixel detector' to study irreversible catalytic structural processes in a crystal, the most challenging of all time-resolved experiments, are bright.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049599006342
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  • 5
    Electronic Resource
    Electronic Resource
    Green-fluorescent protein facilitates rapid in vivo detection of genetically transformed plant cells (1999)
    Springer
    Plant cell reports 18 (1999), S. 707-714 
    Details
    ISSN: 1432-203X
    Keywords: Key words Green-fluorescent protein ; Transformation ; Particle bombardment ; Agrobacterium ; Sugarcane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Early detection of plant transformation events is necessary for the rapid establishment and optimization of plant transformation protocols. We have assessed modified versions of the green fluorescent protein (GFP) from Aequorea victoria as early reporters of plant transformation using a dissecting fluorescence microscope with appropriate filters. Gfp-expressing cells from four different plant species (sugarcane, maize, lettuce, and tobacco) were readily distinguished, following either Agrobacterium-mediated or particle bombardment-mediated transformation. The identification of gfp-expressing sugarcane cells allowed for the elimination of a high proportion of non-expressing explants and also enabled visual selection of dividing transgenic cells, an early step in the generation of transgenic organisms. The recovery of transgenic cell clusters was streamlined by the ability to visualize gfp-expressing tissues in vitro.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002990050647
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of phosphate-related components in Hanford tank wastes (1999)
    Springer
    Journal of radioanalytical and nuclear chemistry 241 (1999), S. 297-306 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Several organophosphorus compounds including tributyl phosphate (TBP), bis-2-(ethylhexyl) phosphate (D2EHP), and dibutyl butyl phosphonate (DBBP) were used as extractants at the Hanford site. The mass spectral fragmentation patterns of various organosphosphorus compounds have been interpreted and used to predict the identity of phosphate-related components and their degradation products in tank waste.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02347465
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Model-based reasoning in a year 10 classroom (1999)
    Springer
    Research in science education 29 (1999), S. 189-208 
    Details
    ISSN: 1573-1898
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General
    Notes: Abstract Studies have shown that secondary school students experience difficulties making scientific models meaningful, yet explanatory models are central to the development of scientific understanding. This study investigated the extent and nature of students' model-based reasoning in a laboratory investigation. It was an interpretive study involving a single Year 10 Science class investigating the influence of six factors on electrical resistance. Before commencing their practical investigations students were re-familiarised with the “electron drift” model of metals. Data sources included videotapes of classroom interactions, audiotaped interviews with students, student workbooks showing their experimental procedures and results, and explanations of those results. The research suggests that spontaneous use of the model in explanations increased over the duration of the task but that the explanations were restricted mainly to model-based reasoning with lower order relational mapping. Even after further formal instruction on the model after the initial experimental investigations, many students were still unable to use the model effectively, displaying mainly the same level of reasoning. As model-based reasoning is an important part of learning some aspects of science, it is imperative that science educators take appropriate steps to facilitate the development of such reasoning in appropriate contexts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461768
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    The proliferation-associated nuclear protein Ki-67 in the bovine system: partial characterisation and its application for determination of the proliferation of Theileria-infected bovine cells (1999)
    Springer
    Parasitology research 85 (1999), S. 613-620 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Theileria annulata-infected bovine cells as well as mitogen-stimulated bovine peripheral blood mononuclear cells (PBMC) express a proliferation-associated nuclear protein equivalent to the human Ki-67 protein. In analogy to the human system, the expression of the bovine Ki-67 protein is restricted to proliferating cells only, since (a) Ki-67 expression paralleled [3H]-thymidine incorporation in concanavalin A (Con A)-stimulated bovine PBMC, (b) Ki-67 was not detectable in quiescent bovine cells, and (c) Ki-67 expression in Theileria-infected cells is related to the presence of the parasites within the cytoplasm of the host cells; upon treatment with the theilericidal drug buparvaquone the parasites are destroyed and the cells cease to proliferate and to express the Ki-67 protein. Western-blot analysis of lysates of proliferating bovine cells revealed that the prototype monoclonal antibody Ki-67 and the new equivalent antibody MIB-1 detected one prominent protein band with an apparent molecular weight of 430 kDa. Two cDNA clones (pUC18.B1.Ki-67 and pUC18.B2.Ki-67) were isolated from a λgt11 cDNA library of T. annulata-infected bovine cells by immunoscreening with the monoclonal antibody MIB-1. Comparison of these cDNA sequences with those of the human Ki-67 protein revealed 60–70% identity. Within the “Ki-67 motif”, identity proved to be 80% at the amino acid level. The remarkable identity between bovine and human Ki-67 proteins suggests that MIB-1 can be used as a marker for cell proliferation in animal research. In this context we could identify proliferating cells in lymph nodes of Theileria-infected animals and, furthermore, we could distinguish between infected and uninfected proliferating cells using MIB-1 and an antiserum against a recombinant parasite protein designated SA288.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004360050605
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