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  • 1
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    A Novel Way to Induce Erythroid Progenitor Self Renewal: Cooperation of c-Kit with the Erythropoietin Receptor (1999)
    De Gruyter
    Details
    Publication Date: 1999-01-01
    Description: Red blood cells are of vital importance for oxygen transport in vertebrates. Thus, their formation during development and homeostasis requires tight control of both progenitor proliferation and terminal red cell differentiation. Self renewal (i.e. long-term proliferation without differentiation) of committed erythroid progenitors has recently been shown to contribute to this regulation. Avian erythroid progenitors expressing the EGF receptor/c-ErbB (SCF/TGFα progenitors) can be induced to long-term proliferation by the c-ErbB ligand transforming growth factor α and the steroids estradiol and dexamethasone. These progenitors have not yet been described in mammals and their factor requirements are untypical for adult erythroid progenitors. Here we describe a second, distinct type of erythroid progenitor (EpoR progenitors) which can be established from freshly isolated bone marrow and is induced to self renew by ligands relevant for erythropoiesis, i.e. erythropoietin, stem cell factor, the ligand for c-Kit and the glucocorticoid receptor ligand dexamethasone. Limiting dilution cloning indicates that these EpoR progenitors are derived from normal BFU-E/CFU-E. For a detailed study, mEpoR progenitors were generated by retroviral expression of the murine Epo receptor in bone marrow erythroblasts. These progenitors carry out the normal erythroid differentiation program in recombinant differentiation factors only. We show that mEpoR progenitors are more mature than SCF/TGFα progenitors and also do no longer respond to transforming growth factor α and estradiol. In contrast they are now highly sensitive to low levels of thyroid hormone, facilitating their terminal maturation into erythrocytes.
    Print ISSN: 1431-6730
    Electronic ISSN: 1437-4315
    Topics: Biology , Chemistry and Pharmacology
    Published by De Gruyter
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  • 2
    Electronic Resource
    Electronic Resource
    Inductively coupled plasma etching of GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1119-1121 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inductively coupled plasma (ICP) etch rates for GaN are reported as a function of plasma pressure, plasma chemistry, rf power, and ICP power. Using a Cl2/H2/Ar plasma chemistry, GaN etch rates as high as 6875 A(ring)/min are reported. The GaN surface morphology remains smooth over a wide range of plasma conditions as quantified using atomic force microscopy. Several etch conditions yield highly anisotropic profiles with smooth sidewalls. These results have direct application to the fabrication of group-III nitride etched laser facets. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117077
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  • 3
    Electronic Resource
    Electronic Resource
    High mobility InAs grown on GaAs substrates using tertiarybutylarsine and trimethylindium (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 882-884 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report transport measurements on a series of high purity InAs epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using tertiarybutylarsine and trimethylindium. Perfectly specular surfaces were obtained by a two step growth method consisting of a 400 °C prelayer followed by deposition of the thick bulk layer at higher growth temperatures. Temperature dependent Hall measurements between 1.8 and 293 K showed a competition between bulk and surface conduction, with average Hall mobilities of up to 1.2×105 cm2/V s at 50 K. Large changes in the temperature dependent transport data are observed several hours after Hall contact formation and appear to be due to passivation of the surface accumulation layer by native oxide formation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113419
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  • 4
    Electronic Resource
    Electronic Resource
    In situ observation of indium segregation by reflectance difference spectroscopy in single monolayer heterostructures grown by atomic layer epitaxy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1576-1578 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single monolayers of InAs in GaAs and GaAs in InAs have been grown by atomic layer epitaxy (ALE) at 50 Torr. In situ reflectance difference spectroscopy monitoring of the surface during each stage of the growth showed a strong asymmetry in the surface behavior between the two systems. Following insertion of an InAs monolayer in GaAs, approximately 20 ML of GaAs are required to recover an In-free, As-stabilized GaAs surface at 390 °C. On the other hand, following the insertion of 1 ML of GaAs in InAs, the spectrum returns to a Ga-free, As-stabilized InAs surface after only 1 ML of InAs deposition. This behavior shows clear evidence of the presence of segregation caused by thermodynamic factors even at the very low growth temperatures used for ALE. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114944
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  • 5
    Electronic Resource
    Electronic Resource
    Competition between band gap and yellow luminescence in GaN and its relevance for optoelectronic devices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4615-4620 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The competition between band gap and the 2.2 eV (yellow) luminescence of epitaxial GaN is studied for excitation densities ranging from 5×10−6 to 50 W/cm2. The ratio of the peak intensities of the band gap-to-yellow luminescence changes from 4:1 to 3000:1 as the excitation density is increased by 7 orders of magnitude. At room temperature, the band gap luminescence linewidth is 2.3kT, close to the theoretical minimum of 1.8kT. A model is developed describing the intensity of the two radiative transitions as a function of the excitation density. This model is based on bimolecular rate equations and takes into account shallow impurities, deep levels, and continuum states. The theoretically predicted dependences of the two different luminescence channels follow power laws with exponents of 1/2, 1 and 3/2. Thus the intensity of the yellow luminescence does not saturate at high excitation densities. These dependences are in excellent agreement with experimental results. The relevance of the results for optoelectronic GaN devices is discussed. It is shown that the peak intensity of the yellow luminescence line is negligibly small at typical injection currents of light-emitting diodes and lasers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363443
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  • 6
    Electronic Resource
    Electronic Resource
    Low-temperature photoluminescence of epitaxial InAs (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6416-6424 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence studies as well as reflectance and transmittance measurements were performed on high-purity epitaxial InAs grown by metal-organic chemical-vapor deposition. We report the optical identification of excitonic, donor, and acceptor impurity related transitions at a temperature of 1.4 K. Measurements at higher temperature and in the presence of magnetic fields up to 7 T support these identifications. We find the excitonic band gap at 415.65±0.01 meV according to the minimum in the polariton reflectance feature. The donor–acceptor-pair and acceptor-bound exciton transitions for three different acceptors are observed by photoluminescence, and we tentatively associate one of them to a double acceptor formed by a Ga impurity on an As lattice site. A donor-bound exciton transition is observed with a binding energy of 0.42 meV. The magnetic field dependence yields values of the electron effective mass and g factor of (0.026±0.002)m0 and −15.3±0.2, respectively, in good agreement with values obtained by other techniques. Furthermore, we report a deep luminescence band of unknown origin at ∼375 meV, related to drastic temporal changes in the band-edge photoluminescence intensity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363660
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of 3C–SiC crystals grown by thermal decomposition of methyltrichlorosilane (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3824-3826 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystal 3C–SiC platelets, formed by thermal decomposition of methyltrichlorosilane at 1650–1750 °C, have been characterized in terms of structure and morphology. The platelets are ∼3–5 mm in length and 1–1.5 mm in thickness. The (111) C face of the crystal, which has an effective zero growth rate, presents a large, mirrorlike surface in the as-grown 3C crystals. Atomic force microscopy indicates that these as-grown surfaces are extraordinarily flat and uniform, with a mean surface roughness of 1–2 A(ring). This value is comparable with the roughness of state-of-art polished Si wafers. X-ray rocking curves of the 〈111〉 peak were obtained with a linewidth of 12.3 arcsec. This is the smallest value reported to date for any polytype of SiC. Raman spectroscopy at 300 K reveals a very sharp TO–phonon peak at 797.8 cm−1, with a linewidth of 2.1 cm−1. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117117
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  • 8
    Electronic Resource
    Electronic Resource
    Sharp excitonic photoluminescence from epitaxial InAs (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1101-1103 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optically excited luminescence of epitaxial InAs has been studied at 1.4 K, revealing well-resolved emission lines identified as the exciton–polariton, neutral–acceptor–bound exciton principal and two-hole transitions, donor–acceptor pair band, and phonon assisted transitions. These features are seen in samples of high purity InAs grown by metalorganic chemical vapor deposition on InAs substrates using tertiarybutylarsine and trimethylindium. Only one acceptor species is observed, having a 1 S3/2–2 S3/2 transition energy of 13.39±0.01 meV, and an acceptor–bound exciton binding energy of 2.11±0.03 meV. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113825
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  • 9
    Electronic Resource
    Electronic Resource
    SiC rapid thermal carbonization of the (111)Si semiconductor-on-insulator structure and subsequent metalorganic chemical vapor deposition of GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2264-2266 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si (111) semiconductor-on-insulator (SOI) structures have been converted to SiC by carbonization of the thin (〈100 nm) Si layer using rapid thermal chemical vapor deposition with mixtures of propane and H2 at atmospheric pressure. Carbonization temperatures around 1225–1250 °C produced SiC films with optimum structural properties. X-ray diffraction (XRD) reveals a single SiC peak at 2θ=35.7° corresponding to the (111) reflection, with an uncorrected full width at half-maximum (FWHM) of ∼0.24°. Infrared spectroscopy of SiC SOI structures obtained under optimum carbonization conditions exhibited a sharp absorbtion peak produced by the Si–C bond at 795 cm−1, with FWHM=22–25 cm−1. Metalorganic chemical vapor deposition growth of GaN on the (111) SiC SOI was carried out with trimethylgallium and NH3 precursors at 1000 °C. XRD indicates highly oriented hexagonal GaN, with FWHM of the (0002) peak of ∼0.15°. The 300 °K photoluminescence (PL) spectrum of GaN films exhibits a strong near band-edge peak (at λp∼371 nm, with FWHM=100–150 meV) and weak yellow emission. Under low power excitation, the 370 nm PL emission from the GaN/SiC SOI structure displays an emission intensity ∼10× higher than that of equivalent GaN films grown on sapphire. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117528
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  • 10
    Electronic Resource
    Electronic Resource
    Precision X-ray optics for fundamental interactions in atomic physics, resolving discrepancies in the X-ray regime (1999)
    Springer
    Optical and quantum electronics 31 (1999), S. 495-505 
    Details
    ISSN: 1572-817X
    Keywords: accuracy ; complex form factor f ; X-ray optics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Reliable knowledge of the complex X-ray form factor (Re(f) and f″) is required for many fields including crystallography, medical diagnosis and XAFS studies. However, there are discrepancies between theory and theory, experiment and experiment and theory and experiment of 10% and more, over central X-ray energies. Discrepancies exist for most elements, despite claimed experimental accuracies of 1%. This paper summarises the current variation between experimental and theoretical results, and outlines key issues for obtaining experimental accuracies of 1% in critical wavelength ranges for selected elements to address these issues. This paper critically surveys available experimental data for attenuation coefficients and suggests a procedure for obtaining significantly higher accuracy measurements in the future.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006923329884
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