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  • 1
    Electronic Resource
    Electronic Resource
    PRS1 is a key member of the gene family encoding phosphoribosylpyrophosphate synthetase in Saccharomyces cerevisiae (1997)
    Springer
    Molecular genetics and genomics 254 (1997), S. 148-156 
    Details
    ISSN: 1617-4623
    Keywords: Key words Phosphoribosylpyrophosphate synthetase  ;  Gene family  ;  Nucleotide metabolism  ;  Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Saccharomyces cerevisiae the metabolite phosphoribosyl-pyrophosphate (PRPP) is required for purine, pyrimidine, tryptophan and histidine biosynthesis. Enzymes that can synthesize PRPP can be encoded by at least four genes. We have studied 5-phospho-ribosyl-1(α)-pyrophosphate synthetases (PRS) genetically and biochemically. Each of the four genes, all of which are transcribed, has been disrupted in haploid yeast strains of each mating type and although all disruptants are able to grow on complete medium, differences in growth rate and enzyme activity suggest that disruption of PRS1 or PRS3 has a significant effect on cell metabolism, whereas disruption of PRS2 or PRS4 has little measurable effect. Using Western blot analysis with antisera raised against peptides derived from the non-homology region (NHR) and the N-terminal half of the PRS1 gene product it has been shown that the NHR is not removed by protein splicing. However, the fact that disruption of this gene causes the most dramatic decrease in cell growth rate and enzyme activity suggests that Prs1p may have a key structural or regulatory role in the production of PRPP in the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050402
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  • 2
    Electronic Resource
    Electronic Resource
    High precision mechanical approach mechanism for a low temperature scanning tunneling microscope (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 129-132 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel mechanical micropositioner has been developed for producing exact linear displacements in the nm range. Incorporated in a low temperature scanning tunneling microscope (STM), it is used as a coarse approach mechanism for the tunneling tip. The advantage of the design is the high accuracy of the linear motion and the absence of backlash. The design principle is discussed and its positioning accuracy and stability for STM imaging are demonstrated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147846
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  • 3
    Electronic Resource
    Electronic Resource
    Electron traps in Ca2+- or Sr2+-doped BaFBr:Eu2+ x-ray storage phosphors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4157-4165 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The x-ray storage phosphor BaFBr:Eu2+ may be made sensitive to stimulation further into the infrared by doping with Ca2+ or Sr2+. This enables the use of light-emitting diodes instead of gas lasers for photostimulation. It is shown by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and optically detected EPR and ENDOR that upon x irradiation FA(Br−, Ca2+) centers are formed as photostimulable electron traps in Ca2+-doped BaFBr, in which one of the two nearest Ba2+ neighbors along the c axis is replaced by Ca2+. The FA(Br−, Ca2+) center has tetragonal symmetry as has the F(Br−) center. The optical absorption band of those FA(Br−, Ca2+) centers is red shifted. No FA(Br−, Ca2+) centers have been detected upon additive coloration only. The red shift of the photostimulation spectrum is caused by formation of the FA(Br−, Ca2+, or Sr2+) centers as electron traps. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361782
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of domain size on optical properties of ordered GaInP2 (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2633-2639 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using dark-field transmission electron microscopy images of ordered GaInP samples, we show how the ordering domain size depends on the growth temperature. Samples with different average domain sizes are compared with regard to their photoluminescence (PL) and excitation spectra. We find a close correlation between the size of the ordered domains and the relative intensity of the PL peak from band–band recombination compared with the rapidly shifting, below-band-gap luminescence emission. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361099
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  • 5
    Electronic Resource
    Electronic Resource
    Optical transitions and carrier relaxation in self assembled InAs/GaAs quantum dots (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4019-4026 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present experimental results concerning optical transitions and carrier dynamics (capture and relaxation) in self assembled InAs/GaAs quantum dot structures grown by metalorganic vapor phase epitaxy. Photoluminescence (PL) measurements at high excitation level reveal optical transitions above the ground state emission. These transitions are found to originate from occupied hole states by solving the quantum dot eigenvalue problem. Time-resolved studies after non-resonant pulse excitation exhibit a relaxation ladder of the excited carriers from the GaAs barrier down to the ground state of the quantum dots. From both the continuous-wave measurements and the PL-decay curves we conclude that the carrier relaxation at non-resonant excitation is mediated by Coulomb interaction (Auger effect). PL-decay curves after resonant pulse excitation reveal a longer rise time compared to non-resonant excitation which is a clear indication of a relaxation bottleneck inside the quantum dots. We interpret the rise time (≈ 400 ps) in this case to originate from relaxation via scattering by acoustic phonons. The PL-decay time of the ground state emission ≈700 ps is interpreted as the excitonic lifetime of the quantum dot. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363361
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  • 6
    Electronic Resource
    Electronic Resource
    Growth twins in nanocrystalline SnO2 thin films by high-resolution transmission electron microscopy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7688-7694 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Growth twins in nanocrystalline SnO2 thin films with grain size 5–50 nm have been investigated by high-resolution transmission electron microscopy. They show the {101}〈101〉 geometry, metal atom mirror symmetry, and slight distortion of oxygen atoms. Multiple twins and step twin boundaries with a density about 1015 m−2 were frequently observed in the films. It appears there are tin interstitials at step twin boundaries and, hence, electronic donors associated with the interstitials. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362434
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  • 7
    Electronic Resource
    Electronic Resource
    Interdiffusion behavior in n-doped and undoped GaInAs/AlGaInAs multiple-quantum-well structures grown by molecular-beam epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3534-3536 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present investigations on the interdiffusion behavior and thermal stability of n-doped and undoped GaInAs/AlGaInAs multiple-quantum-well structures, grown lattice matched on InP by molecular-beam epitaxy. The activation energy of the main interdiffusion process is determined to Ean doped=2.5 eV and Eaundoped=2.9 eV. The different interdiffusion processes are monitored mainly by photoluminescence spectroscopy at T=8 K after rapid thermal annealing of the samples. The influence of doping is studied by comparing the results of n-doped and undoped structures. Additionally photoluminescence excitation spectroscopy at T=2 K was carried out to verify the different interdiffusion processes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359992
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  • 8
    Electronic Resource
    Electronic Resource
    Auger carrier relaxation in self-assembled quantum dots by collisions with two-dimensional carriers (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 7895-7899 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carrier relaxation in self-assembled quantum dots due to Coulomb interaction with two dimensional (2D) carriers is studied theoretically. Auger coefficients for carrier relaxation rates are calculated in the dipole approximation for Coulomb interaction. The dipole approximation allows one to derive selection rules for Auger relaxation in a cylindrical quantum dot, and to describe a general picture of Auger relaxation via energy levels in self-assembled quantum dots. A numerical example for InAs/GaAs self-assembled quantum dots demonstrates that the Auger effect may lead to relaxation times in the order of 1–10 ps at 2D carrier densities of 1011–1012 cm−2. This result demonstrates the possibility of fast carrier relaxation in quantum dots if the carrier density in the surrounding barrier is sufficiently high. Analytical formulas for Auger coefficients are derived for moderate temperatures of the 2D carriers. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365363
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  • 9
    Electronic Resource
    Electronic Resource
    Deep-level defects and n-type-carrier concentration in nitrogen implanted GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2525-2527 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyzed the intrinsic defects and the n-type-carrier concentration generated by nitrogen ion implantation in n-type GaN by deep-level-transient spectroscopy and by capacitance–voltage measurements, respectively. The samples were grown on sapphire by metalorganic vapor-phase epitaxy. Nitrogen implantation with different ion doses and postimplantation rapid-thermal annealing (RTA) were investigated. We observed a growing n-type-carrier concentration and increasing defect concentration with increasing nitrogen ion implantation doses. After RTA the concentration of free carriers and deep levels as found in the as-grown state are restored. We also address contrarily seeming results from measurements of sheet resistance after N implantation published recently. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117727
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  • 10
    Electronic Resource
    Electronic Resource
    Direct determination of carrier capture times in low-dimensional semiconductor lasers: The role of quantum capture in high speed modulation (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1585-1587 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effective carrier capture time, which limits the maximum modulation bandwidth of low-dimensional semiconductor lasers, can be determined by a simple technique as shown in this letter. For demonstration, the technique is applied to InGaAs/InGaAsP multi-quantum well, InGaAs/GaAs single quantum well and InGaAs/InGaAsP wire lasers, respectively, at low temperature (2 K). Moreover, by comparing quantum-well lasers with wire lasers, which have different packing densities of the active regions but approximately the same carrier diffusion length before capture, we found that the effective carrier capture times for these two laser types are quite different. This shows the significant role of the scale-up factor in the contribution of quantum capture time to the total effective carrier capture time, as discussed by S. C. Kan et al. [Appl. Phys. Lett. 62, 2307 (1993)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117038
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