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  • Articles  (25)
  • 1990-1994  (25)
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  • Articles  (25)
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  • 1
    Electronic Resource
    Electronic Resource
    Comparative Fine Structural Investigations of Interphase and Mitotic Nuclei of Vampyrellid Filose Amoebae (1994)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 41 (1994), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The nuclei of trophozoites and digestive cysts as well as mitotic nuclei of several species of the vampyrellids Vampyrella, Gobiella, Hyalodiscus, Arachnula, and Leptophrys were investigated by electron microscopy. Except for some species of the genus Hyalodiscus, the vampyrellids are generally multinucleate. The nuclei of the trophozoite stage are in interphase. These nuclei are spherical, except for the genus Arachnula, which reveals elongated nuclei. In digestive cysts of all vampyrellids the nuclei enlarge and the pars granulosa of the nucleoli becomes prominent. Karyokineses take place synchronously in older digestive cysts, which transform into reproductive cysts. The nuclei divide by closed intranuclear orthomitosis. In telophase the old nuclear envelope disintegrates and a new one is rearranged. Only in the genus Leptophrys the nuclear envelope decomposes before telophase. Neither centrioles nor MTOC-plaques have been found in any stage of mitosis. After karyokinesis the cell divides inside the cyst or when leaving the cyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1994.tb05930.x
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  • 2
    Electronic Resource
    Electronic Resource
    Picosecond pulse response characteristics of GaAs metal-semiconductor-metal photodetectors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2435-2448 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a comprehensive theoretical and experimental analysis of the current response of GaAs metal-semiconductor-metal Schottky photodiodes exposed to 70 fs optical pulses. Theoretical simulations of the carrier transport in these structures by a self-consistent two-dimensional Monte Carlo calculation reveal the strong influence of the distance between the finger electrodes, the external voltage, the GaAs layer thickness and the excitation intensity on the response time and the corresponding frequency bandwidth of these photodetectors. For many experimental conditions, the model demonstrates a clear temporal separation of the electron and hole contributions to the output current due to the different mobilities of the two carrier types. For a diode with an electrode separation of 0.5 μm, an electric-field strength above 10 kV/cm and low intensity of the incident light the theory predicts a pulse rise time below 2 ps, an initial rapid decay as short as 5 ps associated with the electron sweep out and a subsequent slower tail attributed to the hole current. For weaker electric fields and/or higher light intensities a significant slowing down of the detector speed is predicted because of effective screening of the electric field by the photoexcited carriers. Heterostructure layer-based devices are shown to provide superior performance compared to diodes manufactured on bulk substrates. Experimental data obtained by photoconductive or electro-optic sampling on diodes with electrode separation between 0.5 and 1.2 μm agree fairly well with the theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349395
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  • 3
    Electronic Resource
    Electronic Resource
    Subpicosecond characterization of carrier transport in GaAs-metal-semiconductor-metal photodiodes (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1410-1412 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal evolution of the photocurrent in interdigitated GaAs metal-semiconductor- metal Schottky photodiodes is directly measured in the time domain by photoconductive and electro-optic sampling with subpicosecond resolution. Excellent agreement is found between experiment and theoretical data obtained by two-dimensional self-consistent Monte Carlo calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105208
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  • 4
    Electronic Resource
    Electronic Resource
    Time-resolved photocurrent response of metal-semiconductor-metal photodetectors to double-pulse excitation (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2780-2782 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photocurrent response of a GaAs metal-semiconductor-metal (MSM) photodetector was measured after excitation with two femtosecond pulses having a variable delay Δt of 0 ps≤Δt≤100 ps. At low excitation densities the influence of the first pulse on the pulse shape of the second is negligible for Δt≥20 ps. This corresponds to a resolvable pulse train of 50 GHz repetition rate for the detectors used in our experiments. The influence of space charge effects at higher excitation density and/or lower bias could be shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110332
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrafast metal-semiconductor-metal photodiodes fabricated on low-temperature GaAs (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 627-629 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs metal-semiconductor-metal photodiodes fabricated on GaAs grown at low substrate temperatures (200 °C) have been investigated in the time domain by electro-optic sampling. It could be shown that these diodes have a faster response, a considerably reduced long time tail, and can be used at larger bias than comparable diodes produced on GaAs grown at 700 °C. Temperature-dependent measurements show that the tail can be described by hopping conductivity and disappears below 50 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106574
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  • 6
    Electronic Resource
    Electronic Resource
    Lateromyxa gallica N. G., N. Sp. (Vampyrellidae): A Filopodial Amoeboid Protist With A Novel Life Cycle and Conspicuous Ultrastructural Characters (1993)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 40 (1993), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . A large, uni- or multinucleate vampyrellid rhizopod, Lateromyxa gallica n. g., n. sp., has been isolated several times from two lakes in central France between September 1973 and August 1989 and cultivated for several months or years under laboratory conditions. No essential variations of feeding behaviour were found over the time; all isolated strains invade the trichomes of the green alga Oedogonium and move, divide and encyst inside the vanished plant cells. Penetration is performed by attacking the cross walls and only primary attacks are directed against the lateral cell walls of the algae. These findings contrast with the behaviour, life cycles and fine structure of all known species of the genera Vampyrella, Hyalodiscus, Arachnula and Gobiella. The establishment of a new genus, Lateromyxa, with the type species Lateromyxa gallica is therefore proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1993.tb04894.x
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  • 7
    Electronic Resource
    Electronic Resource
    Carnitine requirement of vascular endothelial and smooth muscle cells in imminent ischemia (1992)
    Springer
    Molecular and cellular biochemistry 116 (1992), S. 125-129 
    Details
    ISSN: 1573-4919
    Keywords: fatty acid ; carnitine ; smooth muscle ; endothelium ; ischemia ; heart ; skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Vascular endothelial and -smooth muscle cells have been shown to use fatty acids as substrates for oxidative phosphorylation. Endothelial cells are more vulnerable to oxidative stress than muscle cells and are prone to loose carnitine early during hypoperfusion. This has been suggested by two observations. The first is that incubation of isolated endothelial cells in a low carnitine medium leads to oleate oxidation, dependent upon carnitine addition, whereas smooth muscle cells do not depend on carnitine addition duringin vitro incubation, although aminocarnitine, a specific inner-membrane carnitine palmitoyltransferase inhibitor, inhibits fatty acid oxidation. The second observation is that rat hearts labeledin vivo with14C-carnitine loose, as paced Langendorff heart, only 4% of their carnitine in 20 min perfusion, following 60 min global ischemia. The carnitine released had a much higher specific radioactivity than the carnitine that was not released. It indicates compartmentation of carnitine in heart. As earlier and presently discussed work shows endothelial vulnerability, it is to be expected that this cell type may become carnitine deficient during pacing and ischemia. Endothelial incompetence in flow regulation could be delaved by the presence of carnitine and fatty acids in pre-ischemia. It is speculated how activated fatty acids could protect endothelium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01270579
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical foundations of handling large substitution sets in temporal integrity monitoring (1992)
    Springer
    International journal of biometeorology 36 (1992), S. 365-407 
    Details
    ISSN: 1432-1254
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Temporal integrity constraints describe long-term data dependencies in databases to be satisfied by each correct database evolution. They can be formulated in a temporal logic. For a runtime monitoring of temporal integrity the problem arises to handle the historical information necessary to monitor the long-term dependencies. This paper extends the already known techniques for minimizing the stored information for a single substitution of the free constraint variables using transition graph construction. Our extension allows to decrease also the amount of handled substitutions for constraint monitoring. For this purpose, the notion of substitution descriptions is formally introduced allowing to monitor simultaneously whole substitution sets. The notions of formula validity and of stepwise monitoring potential validity of temporal constraints are redefined for descriptions. Based on these notions an algorithm for monitoring temporal integrity by handling descriptions is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212961
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  • 9
    Electronic Resource
    Electronic Resource
    Materials and device properties of pseudomorphic In x Ga1−x As/Al0.3Ga0.7As/GaAs high electron mobility transistors (0〈x〈0.5) (1991)
    Springer
    Applied physics 53 (1991), S. 109-113 
    Details
    ISSN: 1432-0630
    Keywords: 6855 ; 7280E ; 7340L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Modulation doped Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures for device application have been grown using molecular beam epitaxy. Initially the critical layer thickness for InAs mole fractions up to 0.5 was investigated. For InAs mole fractions up to 0.35 good agreement with theoretical considerations was observed. For higher InAs mole fractions disagreement occurred due to a strong decrease of the critical layer thickness. The carrier concentration for Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures with a constant In x Ga1−x As quantum well width was investigated as a function of InAs mole fraction. If the In x Ga1−x As quantum well width is grown at the critical layer thickness the maximum carrier concentration is obtained for an InAs mole fraction of 0.37. A considerable higher carrier concentration in comparison to single-sided δ-doped structures was obtained for the structures with δ-doping on both sides of the In x Ga1−x As quantum well. Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures with InAs mole fractions in the range 0–0.35 were fabricated for device application. For the presented field effect transistors best device performance was obtained for InAs mole fractions in the range 0.25–0.3. For the field effect transistors with an InAs mole fraction of 0.25 and a gate length of 0.15 μm a f T of 115 GHz was measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323868
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  • 10
    Electronic Resource
    Electronic Resource
    Theoretical foundations of handling large substitution sets in temporal integrity monitoring (1991)
    Springer
    Acta informatica 28 (1991), S. 365-407 
    Details
    ISSN: 1432-0525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Summary Temporal integrity constraints describe long-term data dependencies in databases to be satisfied by each correct database evolution. They can be formulated in a temporal logic. For a runtime monitoring of temporal integrity the problem arises to handle the historical information necessary to monitor the long-term dependencies. This paper extends the already known techniques for minimizing the stored information for a single substitution of the free constraint variables using transition graph construction. Our extension allows to decrease also the amount of handled substitutions for constraint monitoring. For this purpose, the notion of substitution descriptions is formally introduced allowing to monitor simultaneously whole substitution sets. The notions of formula validity and of stepwise monitoring potential validity of temporal constraints are redefined for descriptions. Based on these notions an algorithm for monitoring temporal integrity by handling descriptions is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01893887
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