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  • 1
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The purpose of this study was to examine the effects of a bleaching agent (30% hydrogen peroxide) on the surface of bovine enamel using a scanning electron microscope and a UV-VIS-NIR spectrophotometer. Five non-carious bovine incisors were bleached for 0, 1, 2 and 3 days using 30% hydrogen peroxide. The light reflectance spectrum was measured using a spectrophotometer with diffuse reflectance mode. Colour values and colour differences in the teeth were evaluated from the reflectance measurements with the CIE L*a*b* colour coordinate system. Surface alterations in the bleached and unbleached teeth were studied using a scanning electron microscope. The change of reflectance in the teeth was related to the change of colour. Most reflectance change occurred within a 1-day bleaching, and this result was confirmed by a CIE L*a*b* colour coordinate system. The colour differences in the bleached teeth were significant enough to be perceived by the observer's eye. The comparison of bleached to unbleached bovine enamel revealed that the bleached surface showed non-uniform slight morphological alterations, and it developed varying degrees of surface porosity. This study indicates that the bleached bovine teeth showed apparent colour differences as well as slight morphological alterations after bleaching.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Bean rust fungus ; F-actin ; Laser scanning confocal microscopy ; Microtubules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Formation of appressoria inUromyces appendiculatus is triggered by external physical features of host stomata as well as artifical surfaces bearing inductive topographies. Microtubule and F-actin microfilament cytoskeletons were examined for their involvement in the process of appressorium formation in this fungus, using laser scanning confocal and electron microscopy. In germlings not stimulated to form appressoria the microtubule and microfilament cytoskeletons were organized as filaments mostly oriented parallel to the longitudinal axis of the cell. Following contact of the germling apex with an inductive topographical signal, e.g., 0.5 μm high ridge, the microtubules and F-actin filaments in the cell apex nearest the substrate appeared randomly oriented. Microtubules farther from the substrate remained oriented parallel to the longitudinal axis of the cell. In later stages of appressorium development, many cytoskeletal elements became oriented parallel to the inductive ridge, especially near the substrate. In regions farther from the substrate in these same cells, the microtubules and microfilaments were arranged in a reticulate pattern. Changes in the distribution and organization of the microtubule and F-actin microfilament cytoskeletons reflect a change in cell function following signal reception for appressorium. The reorientation of the cytoskeleton likely dictates the change in cell morphology.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 600-603 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of hydrogenation on electrical properties of InGaP epitaxy layers grown on GaAs has been investigated. It is found that hydrogenation using an infrared lamp heating at 200 °C can give rise to good rectifying characteristics on the Au/n-InGaP Schottky diode as well as to the passivation of defects. For the hydrogenated sample, the breakdown voltage increases to 35 from 4 V, the leakage current decreases by three orders of magnitude, and the saturation current increases about 100 times, relative to those for the untreated one. This characteristic is thought to result from the increase of the diode barrier height during hydrogenation. That is, the atomic hydrogen which diffuses into InGaP neutralizes the Si donor dopant as well as deep levels near the surface, resulting in the increase of the barrier height and the reduction of recombination centers. © 1999 American Institute of Physics.
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN metal–oxide–semiconductor (MOS) capacitors were fabricated by using Ga oxide formed by photoelectrochemical oxidation of GaN. The electrical properties of the MOS structures as characterized by capacitance–voltage measurement were found to be dependent on the oxidation time and posttreatment. Positive flatband voltage was observed in devices with thin oxide layers indicating the existence of negative oxide charge. Very thin oxide exhibits high capacitance and reverse leakage, which can be reduced by rapid thermal annealing (RTA). Passivation of the interface by RTA is partially responsible for the improvement. Thicker oxide layers exhibit improved electrical properties. Low density of interface states (∼1011 eV−1 cm−2) was obtained in the Ga-oxide/GaN structure grown under optimized conditions. © 2002 American Institute of Physics.
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low-pressure metalorganic chemical vapor deposition. The SCH wells are unstrained and lattice-matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3905-3907 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results of an experimental study on efficient laser action in an optically pumped GaN/AlGaN separate-confinement heterostructure (SCH) in the temperature range of 10–300 K. The lasing threshold was measured to be as low as 15 kW/cm2 at 10 K and 105 kW/cm2 at room temperature. Strongly polarized (TE:TM≥300:1) lasing peaks were observed over the wavelength range of 358–367 nm. We found high-finesse lasing modes that originate from self-formed microcavities in the AlGaN and GaN layers. Through analysis of the relative shift between spontaneous emission and lasing peaks, combined with the temperature dependence of the lasing threshold, we conclude that exciton–exciton scattering is the dominant gain mechanism leading to low-threshold ultraviolet lasing in the GaN/AlGaN SCH over the entire temperature range studied. Based on our results, we discuss possibilities for the development of ultraviolet laser diodes with a GaN active medium. © 1999 American Institute of Physics.
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  • 7
    ISSN: 1438-2199
    Keywords: Keywords: Amino acids – Cysteine – Cysteine dioxygenase – Glutathione –γ-Glutamylcysteine synthetase – Hepatocytes – Taurine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary. Hepatocytes were cultured for 3 days as spheroids (aggregates) or as monolayers in basal medium and in sulfur amino acid-supplemented media. Cultured hepatocytes had low levels of cysteine dioxygenase (CDO) activity and normal levels of γ-glutamylcysteine synthetase (GCS) and cysteinesulfinate decarboxylase (CSDC) activities compared to freshly isolated cells. CDO activity increased and GCS activity decreased in a dose-response manner in cells cultured in either methionine- or cysteine-supplemented media. CSDC activity was not significantly affected by methionine supplementation. Changes in CDO and GCS were associated with changes in cysteine catabolism to taurine plus sulfate and in synthesis of glutathione, respectively. These responses are similar to those observed in liver of intact rats fed diets supplemented with sulfur amino acids. A near-maximal response of CDO or GCS activity was observed when the medium contained 1.0 mmol/L of methionine plus cyst(e)ine. Changes in CDO and GCS activities did not appear to be mediated by changes in the intracellular glutathione concentration. Cultured hepatocytes offer a useful model for further studies of cysteine metabolism and its regulation in response to sulfur amino acid availability.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The enhanced positive magnetoresistance effect has been observed in GaAs containing nanoscale magnetic clusters. The ferromagnetic metallic clusters were embedded into GaAs by Mn ion implantation and rapid thermal annealing. Positive magnetoresistance in these structures has been observed and attributed to the enhanced geometric magnetoresistance effect in inhomogeneous semiconductors with metallic inclusions. The additional enhancement of positive magnetoresistance under light illumination is due to the higher mobility of photoexcited electrons in comparison with the mobility of holes in p-type GaAs prepared by Mn ion implantation. © 2001 American Institute of Physics.
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