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  • 1
    Electronic Resource
    Electronic Resource
    Raman study under resonant conditions of defects near the interface in a GaAs/Si heterostructure (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4777-4781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Raman study has been performed, under resonant conditions, on a GaAs bevelled-edge layer grown on a Si substrate to characterize the optical and crystalline properties of the epilayer near the interface. According to the geometrical characteristics of the sample, a theoretical expression for the Raman intensities profile has been established and compared to the experimental data. This fitting procedure enables us to investigate the absorption coefficient of the GaAs layer due to the disorder-induced softening of the E1 edge. A quantitative analysis of the lattice disorder has been carried out on both longitudinal and transverse optical modes by studying the Raman line-shape evolution versus the laser spot position on the bevel edge. From this study, we have followed the recovery of the crystalline quality of the epilayer while going away from the interface, and evaluated the "Raman thickness'' of the dislocated layer. Using the spatial correlation model as a relationship between the disorder amount and the outcoming effects on the Raman line peaks, we have estimated the dislocation density at the heterostructure interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346133
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  • 2
    Electronic Resource
    Electronic Resource
    Tin diffusion and segregation in GaAs processed with a pulsed ruby laser (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3832-3837 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tin-diffused GaAs layer samples, with mean concentrations larger than 1019 cm−3, were obtained by irradiating with a ruby laser GaAs substrates covered with thin tin layers. Mobilities between 100 and 200 cm2/V s were obtained. Both carrier concentration and mobility decrease with increasing energy density. Strong segregation effects were observed in the samples processed with large energy densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346267
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  • 3
    Electronic Resource
    Electronic Resource
    Generalization of Bragg reflector geometry: Application to (Ga,Al)As-(Ca,Sr)F2 reflectors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5366-5368 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bragg reflectors based on (Ca,Sr)F2 and (Ga,Al)As are studied. Modeling and fabrication of these structures by molecular-beam epitaxy were performed. Quarter-wave Bragg reflectors were found to present an excellent reflectance around the wavelength of interest, 870 nm, for only three periods of bilayers. However, the structures grown exhibited cracks after epitaxy due to thermal stress between both materials. To alleviate this problem, other reflector geometries were investigated consisting of deviations from the classical Bragg reflector. The new geometries enable one to reduce the absolute or relative fluoride thickness within the structure. The results obtained show that the use of adequate geometries allows one to overcome the stress problem, and good heteroepitaxial reflectors with a crack-free surface morphology were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347034
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of the local environment on the properties of DX centers in Si-doped GaAs and dilute AlxGa1−xAs alloys (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 934-936 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si-doped GaAs and dilute AlxGa1−xAs alloys under hydrostatic pressure have been studied using deep level transient spectroscopy (DLTS). In GaAs the DLTS spectrum of the DX center is a single peak. In AlGaAs however, multiple peaks, resulting from different thermal emission rates from donors having different numbers of Al atoms as near neighbors, are observed. The pressure dependence of the electron occupation of individual DX levels shows that the larger the number of Al atoms near the Si donor, the lower the energy position of the DX level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102630
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  • 5
    Electronic Resource
    Electronic Resource
    Exponential critical-state model for magnetization of hard superconductors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3430-3437 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have calculated the initial magnetization curves and hysteresis loops for hard type-II superconductors based on the exponential-law model, Jc(Hi) =k exp(−||Hi||/H0), where k and H0 are constants. After discussing the general behavior of penetrated supercurrents in an infinitely long column specimen, we define a general cross-sectional shape based on two equal circles of radius a, which can be rendered into a circle, a rectangle, or many other shapes. With increasing parameter p (=ka/H0), the computed M-H curves show obvious differences with those computed from Kim's model and approach the results of a simple infinitely narrow square pulse Jc(Hi). For high-Tc superconductors, our results can be applied to the study of the magnetic properties and the critical-current density of single crystals, as well as to the determination of the intergranular critical-current density from magnetic measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345355
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  • 6
    Electronic Resource
    Electronic Resource
    TiO2 catalysed reduction of Cr(VI) in aqueous solutions under ultraviolet illumination (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 518-521 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The photoassisted reduction of Cr(VI) to Cr(III) in aqueous suspensions of TiO2 under ultraviolet (UV) illumination has been studied by determining the amount of Cr(VI) photoreduced at different irradiation times, the mass of catalyst in suspension, the Cr(VI) initial concentration and the pH. Samples of wastes from metal-surface treatment industries have been used to test this photocatalytic procedure for Cr(VI) elimination in a real ease. It has been observed that the presence in these samples of certain species such as Fe(III) and Cr(III) at low concentrations can increase significantly the yield of Cr(VI) photoreduction. It is assumed that these cations act by maintaining the pH during the photoreduction process, preventing the alkalization by hydrolysis of the solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01076066
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  • 7
    Electronic Resource
    Electronic Resource
    Indole-3-methanol is the main product of the oxidation of indole-3-acetic acid catalyzed by two cytosolic basic isoperoxidases from Lupinus (1990)
    Springer
    Planta 181 (1990), S. 448-450 
    Details
    ISSN: 1432-2048
    Keywords: Auxin catabolism ; Cytosol (isoperoxidase) ; Indole-3-methanol ; Isoperoxidase, basic ; Lupinus (auxin, isoperoxidase) ; Parenchyma (auxin, isoperoxidase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The nature of the products of the auxin catabolism mediated by both basic and acidic isoperoxidases has been studied. While indole-3-methanol is only a minor product of the oxidation of indole-3-acetic acid catalyzed by extracellular acidic isoperoxidases, it is the only product of the oxidation of indole-3-acetic acid catalyzed by two cytosolic basic isoperoxidases (EC 1.11.1.7) from lupin (Lupinus albus L.) hypocotyls. The putative indole-3-methanol formed by these latter isoperoxidases was isolated and then characterized by mass spectrometry and 1H-nuclear magnetic resonance spectrometry. These results are discussed with respect to the diversity and compartmentation of the catabolism of indole-3-acetic acid in plant tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195900
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  • 8
    Electronic Resource
    Electronic Resource
    Extracellular deamination of l-amino acids by Chlamydomonas reinhardtii cells (1990)
    Springer
    Planta 182 (1990), S. 194-198 
    Details
    ISSN: 1432-2048
    Keywords: L-amino acids (utilization) ; Chlamydomonas ; Deaminase (extracellular)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When grown in the light and in a Tris-acetate phosphate medium, cells of Chlamydomonas reinhardtii Dang. can use the following l-amino acids as a sole nitrogen source: asparagine, glutamine, arginine, lysine, alanine, valine, leucine, isoleucine, serine, methionine, histidine, and phenylalanine, whereas, in the absence of acetate, the cells only used l-arginine. The utilization system in the acetate medium consisted of an extracellular deaminating activity induced by l-amino acids; it took between 10 to 30 h before the system appeared in cells previously grown with ammonium. This deaminase activity was nonspecific, required an organic carbon source for its de-novo synthesis, and was sensitive to high ammonium concentration and light deprivation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197110
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  • 9
    Electronic Resource
    Electronic Resource
    Thermal degradation of chalcogenides containing poly(methacrylates) (1990)
    Springer
    Journal of thermal analysis and calorimetry 36 (1990), S. 121-127 
    Details
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurden TG-Untersuchungen an aromatischen Polymethacrylaten mit heterocyclischen Seitenketten durchgefürt. Dabei wurde der Einfluß des Substituenten der Seitenkette auf die termische Stabilität der Polymere untersucht. Die kinetischen Parameter des thermischen Zersetzungsprozesses wurden untersucht. In Abhängigkeit von der Struktur der Seitenkette des Polymeres konnten verschiedene TG-Profile erhalten werden.
    Notes: Abstract Thermogravimetric analysis of aromatic poly(methacrylates) containing heterocyclic side chains were carried out. The effect of the substituent introduced into the side chain on the thermal stability of the polymer was investigated. The kinetic parameters of thermal degradation process were analysed. Different thermogravimetric profiles were obtained depending on the structure of the side chain of the polymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01912075
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  • 10
    Electronic Resource
    Electronic Resource
    Photometric separation of the bulge and disc components of spirals using CCD imaging (1990)
    Springer
    Astrophysics and space science 170 (1990), S. 225-229 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present high-resolution CCD images of a sample of spiral galaxies, in infrared photometric bands, obtained at the Cassegrain focus of the 1 m Jacobus Kapteyn Telescope, La Palma. A decisive advantage of the linearity in these images is that we can effect a reliable separation of the light from bulge and disc. We describe possible applications of the results to determine the structure of the bulges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652672
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