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  • Wiley-Blackwell  (10)
  • American Institute of Physics (AIP)  (5)
  • Institute of Physics  (3)
  • Springer Nature
  • 2000-2004
  • 1995-1999
  • 1990-1994  (18)
  • 1990  (18)
  • 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
    Kinetic and thermodynamic parameters for Schiff-rase formation between 5′-deoxypyridoxal and hexylamineSupported by the CICYT and the universidad de Alcalá de Henares (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1991-1998 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermodynamic parameters involved in the formation of Schiff bases between 5′-deoxypyridoxal and hexylamine were determined at different pH values and a constant ionic strength (0.1 M). The overall and individual rale constants of formation and hydrolysis at 10, 15, 20, 25, and 30° were also determined. The enthalpy of the overall formation process was found to be negative at all the pH values assayed except the neutral, while its entropy was always positive. The results obtained show the great relevance of the phosphate group at C(5′) to the stabilization of the Schiff bases of pyridoxal 5′-phosphate.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730723
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  • 7
    Electronic Resource
    Electronic Resource
    Ordered odd-number terpolyamides, 2.Part 1: cf4 Crystal structure (1990)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 2587-2597 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A combined X-ray diffraction and electron microscopy study was carried out on both the solution-grown crystals and oriented films of nylons 3/5/7 and 7/5/3. These regular odd-odd-odd terpolyamides have such sequence of amide groups along the chain that they have to be aligned parallel in order to form every hydrogen bond without strain. It was found that a layered α-structure with hydrogen-bonded sheets made up of parallel chains in fully extended conformation is adopted in both cases. These results are not necessarily generalized to odd-numbered nylons where an antiparallel alignement of chains is compatible with the formation of hydrogen bonds. Chain-folded lamellar crystals obtained from solution were investigated by electron diffraction and their surface topology examined by polymer decoration with polyethylene. A bimodal orientation of hydrogen-bonded sheets within the lamella is assumed to occur in order to account for the obtained decorating patterns. Either way, chain foldings are not contained in such sheets but intersect them at an angle of about 60°.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1990.021911107
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  • 8
    Electronic Resource
    Electronic Resource
    Changes in the activity of the general amino acid permease from Saccharomyces cerevisiae var. ellipsoideus during fermentation (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 36 (1990), S. 808-810 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The evolution of the activity of the general amino acid permease and ethanol and glucose concentrations in the medium were studied in a mild fermentation process carried out by a wine strain of Saccharomyces cerevisiae var. ellipsoideus isolated from grape musts in spontaneous fermentation. The cells displayed a reduction in the activity of the general amino acid permease parallel to the increase of ethanol in the medium. This ethanol increase was not enough to promote a substantial inhibition on the total polypeptide synthesis measured as polyuridylic-acid-directed polyphenylalanine synthesis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260360808
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  • 9
    Electronic Resource
    Electronic Resource
    Rheological and thermal properties of a commercial liquid-crystalline polyesteramide (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 1533-1550 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A commercial main-chain liquid-crystalline, naphthalene-based polyesteramide, was studied by three experimental techniques: extrusion capillary rheometry, dynamic viscoelasticity, and differential scanning calorimetry (DSC). From capillary rheometry a maximum at 360°C was observed in viscosity temperature curve. This result is compared with literature data for other thermotropics, and the possibility of a transition from a nematic to an isotropic phase is considered. The results obtained from dynamic viscoelasticity and DSC agree, and reveal the existence of a glass transition at 128°C (by DSC) and 137-147°C (by viscoelastic measurements, depending on frequency) as well as melting at 282°C. Annealing below 230°C produces two types of crystals, whereas annealing above this temperature gives rise to only one type of crystal, the melting temperature of which can be, depending on annealing time, as high as 340°C. The results are compiled in a phase diagram with six regions, four of them corresponding to the solid state, one to a liquid mesophase, and one to an isotropic phase.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090280909
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  • 10
    Electronic Resource
    Electronic Resource
    Zymographic screening of plant peroxidase isoenzymes oxidizing 4-hydroxystilbenes (1990)
    Weinheim : Wiley-Blackwell
    Electrophoresis 11 (1990), S. 507-508 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A zymographic assay is described for the detection of peroxidase isoenzymes oxidizing 4-hydroxystilbene following isoelectric focusing. The assay is based on coupling intermediate products of the oxidation of 4-hydroxystilbene with 4-aminoantipyrine, with resultant formation of dye complexes. Control experiments in the absence of 4-hydroxystilbene and hydrogen peroxide demonstrate the peroxidative nature of the 4-hydroxystilbene-dependent dye reaction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150110614
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