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  • 2000-2004
  • 1995-1999  (22)
  • 1999  (22)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1460-1462 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report that the quasibound states at the above-barrier region in AlGaAs–GaAs superlattices can be clearly observed at room temperature by photoconductivity as well as photoreflectance measurements. We provide concrete evidence to confirm that free-carrier confinement at barrier layer does exist. It is also found that the barrier-width dependence of the above-barrier transition energies can be described quite well by the modified Messiah's calculation. However, the simple calculation using the constructive interference condition can only explain the transitions at lower energies, and fails with increasing transition energy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3951-3953 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial layers of GaNxAs1−x were grown on (001) GaAs substrates by pulsed laser ablation of a GaAs target in an ammonia (NH3) atmosphere. High-resolution x-ray diffraction indicates the existence of a threshold NH3 pressure, above which the incorporated N content x increases linearly with increasing NH3 pressure. The band-gap dependence of GaNxAs1−x on x for x≤2.9% is examined by optical absorption and photoconductivity measurements at room temperature. We found that the band-gap energy reduces with higher N composition, and our results agree approximately with the prediction based on the dielectric model. © 1999 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1463-1465 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that hydrogen passivation by the photochemical vapor deposition method can have a significant influence on GaInP/GaAs heterostructures. The effect has been investigated by low-temperature photoluminescence and current–voltage and capacitance–voltage experiments. The photoluminescence measurement shows a strong increase in the luminescence intensity after hydrogenation. It is interpreted in terms of the passivation of nonradiative recombination defect centers by atomic hydrogen. The effect is also accompanied by a simultaneous decrease in the carrier concentration as shown from the capacitance–voltage measurements. In addition, the effect of hydrogenation is confirmed by the improvement of the Schottky-diode properties. These results provide concrete evidence to support the passivation of impurities and defects by atomic hydrogen in GaInP/GaAs heterostructures. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3152-3158 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a detailed investigation of the "positive" persistent photoconductivity (PPC) and "negative" persistent photoconductivity (NPPC) in semimetallic AlxGa1−xSb/InAs quantum wells. The studies of the NPPC and PPC effects have been performed under various conditions, such as different photon energy of excitation, different temperature, different Al composition x, and different well width. It is found that all the previously proposed mechanisms fail to explain several of our observations. We suggest that the NPPC and PPC effects are produced principally by two competing processes. At a high temperature, the photoconduction is dominated by the photogenerated electrons in the InAs well, in which the relaxation of the excess electrons is prohibited by an energy barrier due to the trapping of photoexcited holes by deep defects in the InAs well. As a result, the PPC is observed. At low temperature, electrons in the InAs layer are photoexcited into the local potential minima induced by compositional fluctuations at the AlGaSb and InAs interface, the number of electrons in the InAs well decreases, thus the NPPC occurs. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2978-2980 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoconductivity spectra have been investigated in InGaP/GaAs heterostructures, and persistent photoconductivity (PPC) has been observed. Through a detailed study of the dependence on excitation wavelengths and the decay kinetics, we identify that the separation of electrons and holes due to the macroscopic potential barrier between the heterointerface and the substrate is the origin of the PPC effect. In addition, we found that the PPC effect can be reduced and the photosensitivity can be enhanced after hydrogenation. We suggest that this behavior can be interpreted by the fact that the incorporation of atomic hydrogen produces donor neutralization and passivates the activity of defective bonds, thus reducing the potential barrier for the recombination of electrons and holes and enhances the photoresponse. © 1999 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Bingley : Emerald
    International journal of clothing science & technology 11 (1999), S. 151-160 
    ISSN: 0955-6222
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: As a first step towards objective evaluation of garment appearance, the present work considered seams on three-dimensional surfaces which simulate actual garment surfaces. The geometric profiles of the 3-D seams were scanned using a laser scanner. 1-D and 2-D digital filters were applied to obtain pucker signals from the geometric profiles by removing "high frequency" components due to fabric surface texture and "low frequency" components due to garment silhouette and drape. The advantages and disadvantages of the 1-D and 2-D digital filters are compared. Four physical parameters are examined to see their relevance to the subjective pucker grade. It was found that log(s2), i.e. the logarithm of the variance of the heights of pucker signals, is the best set of physical parameters for the objective evaluation of seam pucker. In addition, latest attempts at capturing and analyzing 3D garment image using a Cyberware laser scanner and Surfacer software are reported.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Heat and mass transfer 35 (1999), S. 191-196 
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In the present study, free convection and heat transfer behavior of electrically conducting fluid in the boundary layer over a vertical continuously stretching surface is investigated. The effects of free convection, magnetic field, suction/blowing at the surface and the stretching speed of the surface on the flow and heat transfer characteristics are considered. By applying one-parametric group theory to analysis of the problem, a similarity solution is found. The governing equations of continuity, momentum and energy are solved numerically by a fourth-order Runge-Kutta scheme. The numerical results, which are obtained for the flow and heat transfer characteristics, reveal the influences of the parameters.
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  • 8
    ISSN: 1432-0878
    Keywords: Key words Atherosclerosis ; Culture model ; Endothelial cell ; Endothelin-1 ; Oxidized LDL ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We investigated the structural and functional properties of human umbilical vein endothelial cells (HUVECs) cultured on a two-chamber culture model system using an amnion membrane. Compared to HUVECs cultured on a plastic dish, HUVECs cultured on the model system exhibited several features similar to those of in vivo vessels, including formation of the intercellular junctional devices and expression of tight junction-associated protein ZO-1 and adherence junction-associated protein α-catenin. Furthermore, we found that HUVECs had a property of polar secretion of endothelin-1 (ET-1). About 90% of the total amount of synthesized ET-1 was found in the lower well, designated as the basal side. When HUVECs were incubated with either native low-density lipoproteins (nLDLs) or oxidized LDLs (oxLDLs) at a concentration of 100 μg/ml, ET-1 secretion was significantly increased, dependent on the cell side (apical vs basal) on which the nLDLs or oxLDLs were loaded. When the LDLs were loaded on the apical side, the secretion of ET-1 from HUVECs on the apical side was increased by 48% (nLDL) and 61% (oxLDL), whereas it was accompanied by a concomitant decrease of ET-1 on the basal side (45% by nLDLs and 38% by oxLDLs). When loaded on the basal side, however, ET-1 was increased by 23% (nLDLs) and 53% (oxLDLs) on the basal side, with a 26% simultaneous decrease of ET-1 on the opposite side for both nLDLs and oxLDLs. On the contrary, high-density lipoproteins (HDLs) inhibited ET-1 secretion from HUVECs on the opposite side of the well on which HDLs were loaded; there was a 57% decrease on the basal side when HDLs were loaded on the apical side, and a 46% decrease on the apical side when loaded on the basal side. These results indicate that modulation of ET-1 secretion from ECs by lipoproteins is virtually dependent on the place (apical vs basal) where these proteins are present. The finding that nLDLs and oxLDLs enhance ET-1 secretion by ECs in a polarized pattern suggests that ET-1 may be involved in pathophysiological processes such as atherogenesis.
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  • 9
    Publication Date: 1999-06-28
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 10
    Publication Date: 1999-09-15
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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