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  • 2000-2004  (52)
  • 1995-1999  (102)
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  • 1
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    Genome sequence of an obligate intracellular pathogen of humans: Chlamydia trachomatis (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1998-10-23
    Description: Analysis of the 1,042,519-base pair Chlamydia trachomatis genome revealed unexpected features related to the complex biology of chlamydiae. Although chlamydiae lack many biosynthetic capabilities, they retain functions for performing key steps and interconversions of metabolites obtained from their mammalian host cells. Numerous potential virulence-associated proteins also were characterized. Several eukaryotic chromatin-associated domain proteins were identified, suggesting a eukaryotic-like mechanism for chlamydial nucleoid condensation and decondensation. The phylogenetic mosaic of chlamydial genes, including a large number of genes with phylogenetic origins from eukaryotes, implies a complex evolution for adaptation to obligate intracellular parasitism.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stephens, R S -- Kalman, S -- Lammel, C -- Fan, J -- Marathe, R -- Aravind, L -- Mitchell, W -- Olinger, L -- Tatusov, R L -- Zhao, Q -- Koonin, E V -- Davis, R W -- AI 39258/AI/NIAID NIH HHS/ -- New York, N.Y. -- Science. 1998 Oct 23;282(5389):754-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Program in Infectious Diseases, University of California, Berkeley, CA 94720, USA. ctgenome@socrates.berkeley.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9784136" target="_blank"〉PubMed〈/a〉
    Keywords: Aerobiosis ; Amino Acid Sequence ; Amino Acids/biosynthesis ; Bacterial Outer Membrane Proteins/genetics ; Bacterial Proteins/chemistry/genetics ; Biological Evolution ; Chlamydia trachomatis/classification/*genetics/metabolism/physiology ; DNA Repair ; Energy Metabolism ; Enzymes/chemistry/genetics ; *Genome, Bacterial ; Humans ; Lipids/biosynthesis ; Molecular Sequence Data ; Peptidoglycan/biosynthesis/genetics ; Phylogeny ; Protein Biosynthesis ; Recombination, Genetic ; *Sequence Analysis, DNA ; Transcription, Genetic ; Transformation, Bacterial ; Virulence
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    Above-barrier states in GaAs–AlGaAs superlattices studied by photoconductivity and photoreflectance (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1460-1462 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.370965
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  • 3
    Electronic Resource
    Electronic Resource
    Compositional disordering of InGaAs/GaAs heterostructures by low-temperature-grown GaAs layers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 664-670 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Compositional disordering of InGaAs/GaAs superlattices using a low-temperature-grown GaAs cap layer (LT-GaAs) by molecular beam epitaxy has been studied. The disordering of the superlattice was verified by photoluminescence and double-crystal x-ray rocking curve measurements. The Ga-vacancy-enhanced interdiffusion due to the presence of LT-GaAs was found to be the disordering mechanism. Diffusion equations and the Schrödinger's equation were solved numerically to obtain the composition profile and the transition energies in the disordered quantum well, respectively. The simulated energy shifts for samples under different annealing conditions agreed very well with the experimental results. The calculated effective diffusivity for the In–Ga interdiffusion has an activation energy of 1.63 eV, which is smaller than the activation energy 1.93 eV, for intrinsic interdiffusion. The diffusivity for the enhanced In–Ga interdiffusion due to the presence of LT-GaAs is about two orders of magnitude larger than the intrinsic In–Ga diffusivity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360810
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal reactions of Pd/AlxGa1−xAs contacts (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2891-2895 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pd/AlxGa1−xAs Schottky contacts and their thermal reactions are studied by capacitance–voltage measurements, current–voltage measurements, and x-ray diffraction. The thickness of AlxGa1−xAs consumed by the Pd/AlxGa1−xAs reaction during annealing was calculated. For annealing temperatures below 300 °C the Schottky characteristics of the diodes were good but the electrical junction moves into AlxGa1−xAs after annealing. The amount of junction movement was calculated directly from our measurements. The diffusion coefficients of Pd in AlxGa1−xAs and the activation energy were estimated. The activation energy was found to be larger for higher Al concentration. PdAl, PdAs2, PdGa5, and Pd5Ga2 were detected in the compounds formed by the Pd/AlxGa1−xAs reaction after annealing. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363141
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  • 5
    Electronic Resource
    Electronic Resource
    Enhancement of conduction-band effective mass in III–V semiconductor alloys induced by chemical disorder (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6761-6765 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conduction-band effective masses in InxGa1−xAs with a complete range of composition, and InAlGaAs and InGaAsP alloys covering the complete range of lattice matched to InP have been determined by far-infrared optically detected cyclotron resonance and magnetophotoconductivity measurements. It is found that the measured effective masses as a function of alloy composition are heavier than the values predicted from the five-band k⋅p theory. We show that this discrepancy can be resolved by including the effect of disorder-induced potential fluctuations that causes the wave function mixing between conduction and valence bands. We find that the strength of the potential fluctuations can be well described in terms of the Phillips electronegativity difference related to chemical disorder. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363804
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of disorder-induced band mixing on the conduction-band effective mass of InAlGaAs alloys lattice matched to InP (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1239-1241 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is found that the calculation of the effective mass for InAlGaAs alloys obtained from the five-band k⋅p theory is smaller than the measured value from the optically detected cyclotron resonance reported recently. We point out that the effect of disorder-induced conduction valence band mixing must be considered. This disorder effect which creates potential fluctuations is to reduce the matrix element P2 for the conduction valence band coupling in the k⋅p theoretical expression. The strength of the potential fluctuations can be described in terms of the electronegativity difference related to chemical disorder. The inclusion of the disorder effect in the (In0.53Al0.47As)x(In0.53Ga0.47As)1−x quaternary system gives a very good fit to the measured data. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362862
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  • 7
    Electronic Resource
    Electronic Resource
    Pulsed laser deposition of epitaxial GaNxAs1−x on GaAs (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3951-3953 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124234
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  • 8
    Electronic Resource
    Electronic Resource
    The optical and electrical studies of hydrogen passivation in GaInP/GaAs heterostructures (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1463-1465 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123582
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  • 9
    Electronic Resource
    Electronic Resource
    Observation of persistent photoluminescence in porous silicon: Evidence of surface emission (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1605-1607 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the observation of persistent photoluminescence (PPL) in oxidized porous silicon. The PPL decay can be well described by a stretched-exponential function, and its decay rate is not sensitive to the change of temperature. We point out that the PPL behavior can be interpreted in terms of the picture that the emission arises from the excited surface complexes, which is produced by capture of photocarriers tunneling from the nearest shallow trap in the nanocrystalline silicon. To explore the microscopic origin of the surface compounds, we performed infrared absorption, and found that the PPL intensity correlates well with Si–OH vibration mode. Further evidence is provided by the recent theoretical calculation showing that the Si–OH complex can emit the photon energy in the range observed here. We thus provide concrete evidence to support the fact that the PL signal of porous silicon does contain surface emission. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121128
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  • 10
    Electronic Resource
    Electronic Resource
    Dependence of electron effective mass on alloy composition of InAlGaAs lattice matched to InP studied by optically detected cyclotron resonance (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1256-1258 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron effective mass of InAlGaAs lattice matched to InP has been determined as a function of Al content. The electron effective mass is obtained from far-infrared optically detected cyclotron resonance (ODCR). In ODCR, the carriers are provided by optical pumping, and hence no doping is necessary. Unlike previous reports, we are able to detect the cyclotron resonance signal of a thin intrinsic epilayer at low temperature. Thus corrections of nonparabolicity are not required. In addition, from photoluminescence measurement, we determine the band-gap energy. Both the effective mass and band-gap energy show a nonlinear variation with Al composition. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114389
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