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  • 1
    Electronic Resource
    Electronic Resource
    Heteroepitaxy of Group III Nitrides for Device Applications (1998)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 264-268 (Feb. 1998), p. 1115-1120 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/03/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.264-268.1115.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Optical band gap in Ga1−xInxN (0〈x〈0.2) on GaN by photoreflection spectroscopy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1994-1996 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical band gap in 40 nm Ga1−xInxN/GaN single heterostructures is investigated in the composition range 0〈x〈0.2 by photoreflection spectroscopy (PR) at room temperature and compared with photoluminescence (PL) data. Clear PR oscillations at the GaInN band gap are observed as originating in the large piezoelectric field. Effective band gap bowing parameters b are derived for pseudomorphically stressed GaInN on GaN: b=2.6 eV (PR) and b=3.2 eV (PL in localized states). Using experimental deformation potentials of GaN, b=3.8 eV is extrapolated for the optical band gap in relaxed GaInN material. Previously reported smaller values are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122346
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1691-1693 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122247
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  • 4
    Electronic Resource
    Electronic Resource
    Observation of photoluminescence from Al1−xInxN heteroepitaxial films grown by metalorganic vapor phase epitaxy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 830-831 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed photoluminescence of Al1−xInxN films. The films were grown on GaN by atmospheric pressure metalorganic vapor phase epitaxy. GaN was grown on a c-plane sapphire substrate with a low-temperature deposited AlN buffer layer. Photoluminescence, absorption, and x-ray diffraction measurements have shown that each spectral peak shifts with alloy composition x and that Al1−xInxN heteroepitaxial films are not macroscopically in phase separation and are constituted in the wurzite structure. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122015
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  • 5
    Electronic Resource
    Electronic Resource
    Inhibition of phosphatase activity by dissolved humic substances and hydrolytic reactivation by natural ultraviolet light (1998)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 40 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Phosphatases released extracellularly by aquatic micro-organisms often complex with humic compounds that are released from decomposing tissues of plants and imported in dissolved and colloidal forms to lakes and rivers.2. Dissolved humic substances from several natural sources formed complexes with phosphatases of bacterial and algal origin and reduced hydrolytic activity by non-competitive inhibition. Restoration of the hydrolytic enzyme activities from the humic substances–enzyme complexes increased progressively over time when exposed experimentally to natural and artificial ultraviolet (UV) irradiance.3. Greater phosphatase restoration occurred from humic acid–phosphatase complexes when humic acids were extracted from dissolved organic matter (DOM) of mixed natural plant sources, than when humic acids were isolated from a decomposing single plant species.4. The data support a previously suggested hypothesis that phosphatases and other enzymes in aquatic ecosystems can complex with humic substances that dominate the DOM pool. These humic substances–enzyme complexes, in which the enzyme is temporarily inactivated, can be transported with water movements and displaced to other sites within the ecosystem. Upon exposure to UV irradiance in the photic zone, functional enzymes can be released. The potential for inactivation and storage of enzyme activity, relocation within the ecosystem, and subsequent reactivation holds important implications for regulation of nutrient cycling in fresh waters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00349.x
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  • 6
    Electronic Resource
    Electronic Resource
    A quantitative infrared spectral database of hazardous air pollutants (1998)
    Springer
    Fresenius' journal of analytical chemistry 360 (1998), S. 426-429 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Open-path monitoring of the atmosphere using Fourier transform infrared spectrometry has recently become a useful real-time in situ analytical technique. The U.S. Environmental Protection Agency (EPA) is currently formulating Method TO-16, a protocol for infrared remote sensing of the hazardous air pollutants (HAPs) identified in EPA’s Clean Air Act of 1990. To support infrared based sensing technologies, the National Institute of Standards and Technology (NIST) is currently developing a standard quantitative spectral database of the HAPs based on gravimetrically prepared samples. This paper presents the protocol used to prepare the gravimetric mixtures and initial results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160050728
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  • 7
    Electronic Resource
    Electronic Resource
    Expanding the applications of holographic interferometry to the quantitative visualization of oscillatory thermofluid processes using temperature as tracer (1998)
    Springer
    Experiments in fluids 24 (1998), S. 431-446 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  In this paper we discuss a novel application of holographic interferometry in the simultaneous quantitative visualization of high-speed, oscillatory flow and temperature fields in complex flow geometries. We consider cases of (i) self-sustained oscillatory flows with main flow imposed in grooved and communicating channels as well as (ii) oscillating thermofluid processes with zero mean velocity in a thermoacoustic refrigerator model. Examples showing unsteady temperature distributions obtained by real-time holographic interferometry combined with high-speed cinematography illustrate the possibilities of the approach introduced in the paper. Our study shows that temperature distributions accurately mirror flow structures in certain types of complex, unsteady flows, thus allowing, apart from the measurement of temperature profiles and heat transfer, also the measurement of oscillatory amplitudes, frequencies, wavelengths as well as the speed of propagation of traveling waves by applying digital image processing techniques. In the grooved and communicating channels it is possible to visualize the structure of the Tollmien–Schlichting waves through isotherms by using the infinite fringe field alignment of holographic interferometry. In the thermoacoustic refrigerator model, small amplitude temperature oscillations generated by the acoustic standing wave are visualized and measured. Image processing as well as data reduction procedures used in the analysis of these flow fields are discussed in the paper. Experimental data obtained by applying the techniques introduced in the paper show good agreement with theory and results of numerical simulations. Our study suggests that using temperature as tracer offers numerous advantages in the study of certain types of complex, unsteady flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050193
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  • 8
    Electronic Resource
    Electronic Resource
    Interferometric measurement and tomography of the density field of supersonic jets (1998)
    Springer
    Experiments in fluids 25 (1998), S. 375-387 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The density field of cylindrical supersonic jets is investigated by Mach-Zehnder interferometry. The optical phase shift is extracted from the interferograms by digital image processing. Disturbing turbulence effects in the free shear layer are eliminated by sequential averaging of the phase shifts of several experimental images. The resulting steady state phase shift is used to calculate time-averaged interferograms and to reconstruct the density field by computerized tomography. The obtained results are compared with theoretical predictions and good quantitative agreement is found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050244
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  • 9
    Electronic Resource
    Electronic Resource
    Regulation of phytoene desaturase expression is independent of leaf pigment content in Arabidopsis thaliana (1998)
    Springer
    Plant molecular biology 37 (1998), S. 1045-1053 
    Details
    ISSN: 1573-5028
    Keywords: carotenoid ; chloroplast ; immutans ; norflurazon ; photooxidation ; phytoene desaturase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Synthesis of carotenoids in higher plants occurs in the plastids, but all of the required enzymes are coded for in the nuclear genome and are post-transcriptionally imported into the plastid compartment. Regulation of the synthesis of the enzymes is poorly understood. The two-step desaturation of phytoene to zeta-carotene, carried out by the enzyme phytoene desaturase (PDS), is one of the earliest steps in the pathway and has been studied in several systems. Previous analyses of phytoene-accumulating tissue suggested that there may be feedback regulation of PDS gene transcription, with higher expression in white tissue. To investigate this regulation further, we examined phytoene-accumulating tissue in Arabidopsis thaliana (L.) Heynh. Two types of phytoene-accumulating tissue were studied: Norflurazon-bleached plants and white sectors from the immutans variegation mutant. Based on competitive RT-PCR measurements of PDS mRNA and immunochemical detection of PDS protein, we determined that there is no significant induction of PDS gene expression specific to white tissue, indicating that PDS expression is independent of the pigment status of the cells. Reasons why our results differ from those in other systems are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006021522259
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of nutrient and soil moisture on competition between shape Carex stricta, shape Phalaris arundinacea, and shape Typha latifolia (1998)
    Springer
    Plant ecology 138 (1998), S. 179-190 
    Details
    ISSN: 1573-5052
    Keywords: Biomass ; Foliar nitrogen ; Foliar phosphorus ; Interspecific competition ; Resource allocation ; Shoot: Root ratio ; Wetland plants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We investigated the importance of nutrients, soil moisture, arbuscular mycorrhizal fungi (AMF), and interspecific competition levels on the biomass allocation patterns of three wetland perennial plant species, Carex stricta Lam., Phalaris arundinacea L., and Typha latifolia L. A factorial experiment was conducted with high-low nutrient levels, high-low soil moisture levels, and with and without AMF inoculation. Under the experimental conditions, plant inoculation by AMF was too low to create a treatment and the AMF treatment was dropped from the total analysis. P. arundinacea and T. latifolia biomass were 73% and 77% higher, respectively, in the high nutrient treatment compared to the low nutrient treatment. Biomass allocation between shoots and roots remained relatively constant between environmental treatments, although shoot:root ratios of P. arundinacea declined in the low nutrient treatment. For C. stricta, the high nutrient and soil moisture treatments resulted in an increase in biomass of 50% and 15%, respectively. Shoot:root ratios were nearly constant among all environmental conditions. Biomass of T. latifolia and C. stricta was greatly decreased when grown with P. arundinacea. The rapid, initial height growth of P. arundinacea produced a spreading, horizontal canopy that overshadowed the vertical leaves of T. latifolia and C. stricta throughout the study. This pattern was repeated in both high and low nutrient and soil moisture treatments. When grown with P. arundinacea, C. stricta and T. latifolia significantly increased their mean shoot height, regardless of the nutrient or soil moisture level. The results of this experiment suggest that C. stricta and T. latifolia were light limited when growing with P. arundinacea and that canopy architecture is more important for biomass allocation than the other environmental conditions tested. The results also suggest that Phalaris arundinacea is an inherently better competitor (sensu Grime 1979) than C. stricta or T. latifolia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009751703827
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