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  • Springer  (374)
  • American Geophysical Union  (90)
  • Wiley-Blackwell  (77)
  • American Institute of Physics (AIP)  (49)
  • Molecular Diversity Preservation International
  • 1990-1994  (590)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Ecological and evolutionary implications of digestive processes: Bird preferences and the sugar constituents of floral nectar and fruit pulp (1992)
    Springer
    Cellular and molecular life sciences 48 (1992), S. 544-551 
    Details
    ISSN: 1420-9071
    Keywords: Bird feeding preferences ; digestion ; intestinal enzymes ; sucrase ; fruit ; nectar
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Plants pollinated and dispersed by different groups of birds offer different kinds of sugars in nectar and fruit pulp. The preferences and physiological traits of avian pollinators and seed dispersers are broadly correlated with the sugar composition of the nectar and fruit that they feed on and appear to have influenced the evolution of the sugar composition of the rewards that plants offer. Hummingbirds prefer sucrose whereas many nectar- and fruit-eating passerines prefer glucose and fructose. Preference for hexoses in passerines seems to be associated with poor sucrose assimilation resulting from two physiological mechanisms: lack of intestinal sucrase activity and fast passage rates. Sucrase activity absence appears to be restricted to a single phylogenetic group (the sturnid-muscicapid lineage). Fast passage rates seem to be characteristic of many small frugivores and to hinder the assimilation of complex nutrients that require hydrolysis before absorption. Hummingbirds have extremely specialized digestive traits that allow them to assimilate sucrose at high rates and with extremely high efficiency. These specialized digestive traits appear not to be present in many nectar-feeding passerines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01920237
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  • 2
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    Ecological and evolutionary implications of digestive processes: Bird preferences and the sugar constituents of floral nectar and fruit pulp (1992)
    Springer
    Details
    Publication Date: 1992-06-01
    Print ISSN: 0014-4754
    Topics: Biology , Medicine
    Published by Springer
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    PAPER CURRENT
  • 3
    Electronic Resource
    Electronic Resource
    Magnetic measurements with a SQUID magnetometer: Possible artifacts induced by sample-holder off-centering : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5088-5090 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Asymmetries in sample holders used for magnetic measurements on magnetometers based on induction methods, such as those equipped with SQUID sensors, can lead to substantial errors and/or important artifacts which resemble phase transitions. They occur under the conditions for which sample and/holder have signals of opposite sign, but are nearly equal in magnitude. The most serious errors can occur often, but not exclusively, for compounds having intermediate magnetic dilution. We present here a general discussion of the problem illustrated by measurements of a polyoxometallate with the known Keggin structure K6[Fe(III)W12O40]⋅nH2O, done on a SHE VTS model 905. While one of the obvious solutions to this problem is the use of holders with a signal much smaller than that of the sample, it would be preferable if, in addition, the holder had a response of the same sign as that of the sample, for all temperatures and fields measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348132
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  • 4
    Electronic Resource
    Electronic Resource
    Si impurity-induced layer disordering of Alx Ga1−x -GaAs quantum-well heterostructures by As-free open-tube rapid thermal annealing (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6199-6206 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented describing Si impurity-induced layer disordering (IILD) and Al-Ga interdiffusion in AlxGa1−x As-GaAs quantum-well heterostructures (QWHs) using open-tube rapid thermal annealing (900–1000 °C) in a flowing N2/H2 ambient. The data show that Al-Ga interdiffusion is enhanced by n-type crystal doping and suppressed by p-type doping. By surrounding the active layers of the heterostructure with layers of opposite doping, we show that the surrounding layers modify the interdiffusion by controlling the diffusion of point defects to the active layers of the heterostructure. Data are presented showing the effects of dielectric encapsulation (SiO2, Si3N4 ) on Al-Ga interdiffusion. The data show that regardless of doping SiO2 enhances interdiffusion as compared to Si3N4. To achieve more thorough layer intermixing of AlxGa1−x As-GaAs QWHs, Si IILD is also investigated in the high-temperature As-poor regime. The experimental data show that in a high-temperature As-poor annealing ambient, little or no Si diffusion occurs from an elemental Si source in contact with a p-type GaAs QWH cap layer. To achieve Si diffusion under these conditions requires removal of the GaAs cap and the use of Al-reduced SiO2 or Si3N4 as a Si diffusion source. Based on secondary-ion mass spectroscopic measurements, direct comparison of Si diffusion from closed-tube (825 °C, 48 h) and open tube (1000 °C, 10 min) anneals shows increased Si incorporation and layer disordering at higher temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346911
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  • 5
    Electronic Resource
    Electronic Resource
    Fracture and spall ejecta mass distribution: Lognormal and multifractal distributions (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2724-2731 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerous distributions (Mott, exponential, bimodal) have been proposed on the basis of geometrical or semi-empirical grounds as suitable for characterizing the mass distribution from fracture or spallation. It is argued here that the lognormal distribution is particularly suitable on the basis of a number of considerations: empirical fits, the fractal character of fracture, and the geometrical arguments when carried to their logical conclusion. We explain the deviations from the lognormal distribution as due to the finite thickness of the shell, which violates the scale-independence requirement for exact fractal behavior and introduces multifractal character to the spallation process. A plausiblity argument for the observed relationship between ductility and the shape of the distribution is offered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351522
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  • 6
    Electronic Resource
    Electronic Resource
    Generation of high-energy x-radiation using a plasma flow switch (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1999-2007 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments with coaxial plasma guns at currents in excess of ten megamperes have resulted in the production of high-voltage pulses (0.5 MV) and hard x radiation (10–200 keV). The x-radiation pulse occurs substantially after the high-voltage pulse suggesting that high-energy electrons are generated by dynamic processes in a very high speed ((approximately-greater-than)106 m/s), magnetized plasma flow. Such flows, which result from acceleration of relatively low-density plasma (10−4 vs 1.0 kg/m3) by magnetic fields of 20–30 T, support high voltages by the back electromotive force-u×B during the opening switch phase of the plasma flow switch. A simple model of classical ion slowing down and subsequent heating of background electrons can explain spectral evidence of 30-keV electron temperatures in fully stripped aluminum plasma formed from plasma flows of 1–2 × 106 m/s. Similar modeling and spectral evidence indicates tungsten ion kinetic energies of 4.5 MeV and 46 keV electron temperatures of a highly stripped tungsten plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348773
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  • 7
    Electronic Resource
    Electronic Resource
    Si incorporation in laser-melted AlxGa1−xAs-GaAs quantum well heterostructures from a dielectric source (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6174-6178 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented describing the incorporation of Si in locally laser-melted AlxGa1−xAs-GaAs quantum well heterostructures from a thin-film dielectric source. The composition of the melted material, the effects of the Si source (SiO2 or Si3N4) on impurity incorporation, and the doping behavior are examined via secondary-ion mass spectroscopy, electron dispersion x-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. The data indicate that upon melting, a (Si)y(AlxGa1−xAs)1−y alloy is formed from which impurity-induced layer disordering may be effected. After annealing the melt region is found to contain crystalline segregates, which are attributed to rapid thermal quenching of the melt. Applications of these results to the fabrication of buried-heterostructure lasers by laser-assisted disordering are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346907
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  • 8
    Electronic Resource
    Electronic Resource
    Design and performance of a focused beam line for surface x-ray diffraction : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 1083-1086 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Focusing optics have been installed on the 5.0 T Wiggler beam line of the SRS at Daresbury Laboratory for use with x-ray diffraction measurements of surfaces and interfaces. A significant increase in the flux has been achieved without excessive degradation of the resolution in the vertical plane. The full width at half-maximum of the focused image compares well with the predictions of ray tracing analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143207
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  • 9
    Electronic Resource
    Electronic Resource
    Two-point quasifractional approximant in physics. Truncation error (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 1470-1477 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The quasifractional approximation method is developed in a systematic manner. This method uses simultaneously the power series, and at a second point, the asymptotic expansion. The usual form of the approximants is two or more rational fractions, in terms of a suitable variable, combined with auxiliary nonfractional functions. Coincidence in the singularities in the region of interest is pursued. Equal denominators in the rational fractions is required so that the solution of only linear algebraic equations is needed to determine the parameters of the approximant. An upper bound is obtained for the truncation error for a certain class of functions, which contains most of the functions for which this method has been applied so far. It is shown that quasifractional approximants can be derived as a mixed German and Latin polynomial problem in the context of Hermite–Padé approximation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529304
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  • 10
    Electronic Resource
    Electronic Resource
    Series operation of power MOSFETs for high-speed, high-voltage switching applications (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1655-1656 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Series operation of power metal-oxide semiconductor field-effect transistors (MOSFETs) to increase their effective hold off voltage is described. The design procedure presented is a modification of a recently reported [Baker and Johnson, Rev. Sci. Instrum. 63, 5799 (1992)] method. Comments are made on implementing MOSFET stacks in various types of instrumentation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144043
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