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  • Articles  (334)
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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Experimental investigation of the helical magnetic instability of an arc discharge in an axial magnetic field and comparison with theory (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2274-2279 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The helical magnetic instability of arcs is investigated experimentally at a long low current H2 arc in a tube of 20 mm diam. The measurements are compared with theoretical results given in a preceding paper [Phys. Fluids 30, XXXX (1987)] in which a first order homogeneous differential equation for the helix amplitude was derived from the basic differential equations. Confirmation is achieved for the critical external axial magnetic field which just destabilizes the arc. It amounts to only a few gauss. Agreement is also found for the growth rate of the instability in both cases of destabilization by an external magnetic field and by the self-magnetic field. The measured growth rates have an order of magnitude of 1000 sec−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866162
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  • 8
    Electronic Resource
    Electronic Resource
    A comparative study of microsporogenesis and anther wall development in different types of genic and cytoplasmic male sterilities in chives (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 121 (2002), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A new cytoplasmic and two genic male sterilities in chives are compared with male-fertile counterparts for anther development and microsporogenesis. The genic male sterilities (wi and st1) fail to produce viable pollen, since microsporogenesis is stopped around the stage of tetrads. Compared with a previously described cytoplasmic male sterility, CMS1, which also shows alterations during this stage, wi- and st1-sterile plants fail to produce pollen walls. The last two male sterilities are very similar in development but can be distinguished by the missing breakdown of callose in st1-sterile plants. In contrast to the sterilities described above, the second cytoplasmic male sterility, CMS2, is caused by functional damages to sporophytic tissues, such as no degeneration of mesothecium cells and no thickening of the endothecial cell walls. These alterations prevent the release of pollen, although they are normally developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1439-0523.2002.00704.x
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  • 9
    Electronic Resource
    Electronic Resource
    The helical magnetic instability of arcs in an axial magnetic field treated by a linear time dependent perturbation theory (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2266-2273 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A straight arc column operated in a cylindrical tube changes its shape into a helical form if the strength of the arc current, the gas pressure, or a superimposed axial magnetic field exceed marginal values. The helical arc is described by the electromagnetic equations in an electrostatic approximation and by the balances of mass, momentum, and energy. The critical nonlinear term is the Lorentz force. The equations are solved by linear perturbation theory. A first order differential equation is deduced for the helix amplitude from which the stability limit of the cylindrical arc and the growth rate of the helical instability can be evaluated. The ratio of the destabilizing and stabilizing terms in the equation is determined by a dimensionless number, the Maecker number, which comprises integral properties of the arc and properties of the gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866161
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  • 10
    Electronic Resource
    Electronic Resource
    Predation by underyearling perch (Perca fluviatilis) on a Daphnia galeata population in a short-term enclosure experiment (1997)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 38 (1997), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The predation impact of underyearling perch (20 mm total length) on the dynamics of Daphnia galeata was studied in three 6.5-m3 enclosures during a 17-day experiment in June 1995. These data were compared with zooplankton succession in three fish-free control enclosures and in the pelagic zone of Bautzen reservoir, Germany.2. Due to individual growth during the experiment, fish biomass in the enclosures increased from 210 mg wet body mass (w.b.m.) m–3 to 830 mg w.b.m. m–3, equivalent to an increase from 20 kg ha–1 to 75 kg ha–1.3. In the enclosures with fish, biomass of daphnids decreased steadily to values below 1 mg wet weight (w.w.) l–1 within 17 days, whereas in the fish-free controls and in Bautzen reservoir the Daphnia biomass fluctuated around 8 mg w.w. l–1. Other zooplankton species exhibited little or no change. Approximately 60 kg ha–1 was calculated as the critical underyearling perch biomass which may induce a drastic decline of the Daphnia galeata population in Bautzen reservoir. Comparison with values from other lakes is difficult due to differences in water depths and Daphnia biomasses.4. Mean individual biomass of daphnids, egg ratio and proportion of adult daphnids were significantly lower in the enclosures with fish compared with the control enclosures at the end of the experiment. This may be explained partly by preferential predation of the large, egg-carrying daphnids by fish. However, no difference was found in clutch size and size at first reproduction, possibly due to the short duration of the experiment.5. It must be assumed that the ‘summer depression’ of daphnids observed in many waters is not the exclusive effect of direct reduction of daphnids by fish predation. Even the high biomass of underyearling perch stocked in the enclosures did not completely account for Daphnia mortality. Instead, the selective loss of large size classes, combined with low food resources and reduced reproduction rates, may induce the marked declines in daphnids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1997.00208.x
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