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  • 1
    Electronic Resource
    Electronic Resource
    As desorption from GaAs and AlAs surfaces studied by improved high-energy electron reflectivity measurements (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1753-1759 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The desorption of As from GaAs (001), (111)B, and AlAs(001) is studied in detail by measuring the electron-beam current reflected from these surfaces. When the As supply to the surface was terminated, the electron specular reflectivity decreases exponentially with time due to the As desorption. The decay rate was much smaller for AlAs (001) than for GaAs (001) and (111)B, which indicates stronger atomic bonding for AlAs than for GaAs. For the GaAs (001) surface, the decay rate and the activation energy for the decay in specular reflectivity change discontinuously at the transition between (2×4) and (3×1) reconstructions. This shows the As desorption process is sensitive to the transition of surface reconstruction. The dependence of the As desorption rate on the thickness of the top GaAs layer in GaAs/AlAs heterostructures indicates an abrupt change of bond strength near the interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351209
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  • 2
    Electronic Resource
    Electronic Resource
    Replacement of group-III atoms on the growing surface during migration-enhanced epitaxy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1610-1615 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An InAs monolayer is grown between GaAs layers using migration-enhanced epitaxy. The surface chemical characteristics during growth are investigated by reflection high-energy electron diffraction. With low As4 pressure and with a substrate temperature of 500 °C, the oscillation amplitude of the reflected electron beam after growth of one monolayer of InAs vanishes during the growth of GaAs over more than 20 atomic layers. High-resolution secondary-ion-mass spectroscopic analysis and photoluminescence characteristics of fabricated structures indicate an anomalous distribution of In atoms with a gradual slope toward the growth direction only when the substrate temperature is 500 °C. Numerical calculation shows that the experimental results are explained by the In atoms in the InAs monolayer being replaced by subsequently deposited Ga atoms. The comparison between experimental results and calculated ones indicates that replacement occurs with a probability of 98% at 500 °C. An InGaAs layer was also grown on an InP substrate using migration-enhanced epitaxy with the deposition of two monolayer metallic atoms per one cycle. X-ray diffraction analysis shows that the composition is modulated with a period of two monolayers in the grown InGaAs layer. This phenomenon is also explained in terms of metallic atom replacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346640
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  • 3
    Electronic Resource
    Electronic Resource
    Circadian Variation of Vasovagal Syncope (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 11 (2000), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Circadian Variation of Vasovagal Syncope. Introduction. Circadian patterns have been demonstrated for several cardiovascular catastrophes. Chronobiologic factors play a role in the emergence of vasovagal syncope (VVS); however, diurnal variation of syncopal episodes in VVS has not been reported previously.Methods and Results. We assessed daily distribution of the time of syncopal episodes in VVS. Time of syncope could be determined in 80 episodes in 54 patients (32 men and 22 women; mean age 37 years, range 12 to 67). Patients who were prescribed beta blockers or vasodilators, and who had syncopes related to alcohol intake, were excluded from the study. Head-up tilt testing was performed in 53 patients. The distribution of the episodes of VVS in 3-hour intervals differed significantly from uniform occurrence (P 〈 0.0001). with a peak frequency between 6 A.M. and noon (67.5% of total episodes). In patients who had experienced the initial syncope in the morning, most (78%) of the next syncopal episodes also occurred in the morning. There was no significant correlation between the time of last syncopes and tilt testing results.Conclusion. We demonstrated a prominent circadian variation in the frequency of VVS, with a peak in the morning. Recognition of the daily distribution of VVS is useful for patient education and therapeutic strategy. (J Cardiovasc Eleciroptiysiol. Vol. 11. pp. 1078-1080, October 2000)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.2000.tb01751.x
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  • 4
    Electronic Resource
    Electronic Resource
    Normal Values for Time-Domain, Frequency-Domain, and Spectral Turbulence Analyses of Signal-Averaged Electrocardiograms in Healthy Subjects (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of noninvasive electrocardiology 5 (2000), S. 0 
    Details
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Signal-averaged electrocardiograms (SAE) have mainly been studied in high risk patients with ischemic heart disease. A systemic study of the normal values and the comparative results using analytical methods has not been reported.Methods: We recorded SAE results in 200 apparently healthy subjects (100 males and 100 females, average age 28.9 years). The obtained signals were analyzed by for the time-domain (TD), frequencydomain (fast Fourier transform [FFT]), and spectral turbulence (ST) analyses. The normal values for these parameters, including differences according to gender, were evaluated. The correlation between body characteristics and individual measurements was also evaluated for each analytical method. Results were compared using previously reported criteria and gender-specific criteria.Results: The normal values for TD and FFT analyses, but not ST analysis, showed differences related to gender. A significant correlation was observed between the body characteristics noted in the TD and the FFT analyses, but this correlation was not seen for all parameters in the ST analysis. According to the conventional criteria, the rate of positive diagnosis was 9% for TD analysis, 4.5% for FFT analysis, and 2% for ST analysis. When gender-specific criteria were applied, it was 1% for TD analysis, 3.5% for FFT analysis, and 0.5% for ST analysis. However, the positive results for subjects that were found using TD analysis were discordant with the results found using FFT and ST analyses in those subjects.Conclusions: The normal values for TD and FFT analyses showed gender-related differences that were not seen using ST analysis. Gender-specific criteria are recommended when using TD analysis because it decreased positive results for healthy subjects. However, as discordant results were obtained among the various analyses, the selection of the method for analyzing the SAE and interpretation of the results should be performed with caution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1542-474X.2000.tb00379.x
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  • 5
    Electronic Resource
    Electronic Resource
    Structural analysis of erbium sheet-doped GaAs grown by molecular-beam epitaxy, with ion channeling followed by Monte Carlo simulation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3095-3103 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The detailed structure of erbium (Er) sheet-doped GaAs grown by molecular-beam epitaxy is directly determined by analysis of the ion-channeling spectra in the [100], [110], and [111] directions with 2.0 MeV He+ beams followed by a recently developed Monte Carlo simulation. It is shown that Er atoms form NaCl-type crystalline ErAs clusters in the GaAs epitaxial layer at 500 and 580 °C. The clusters grow in the [100] direction with the common three principal axes of the cubic unit cell; the lattice constant of the clusters coincides exactly with that of the zinc-blende-type crystalline GaAs epitaxial layer. The shape and size of the clusters can be roughly deduced in the simulation from the dependence of the visible Er fraction on the cluster size for various cluster shapes. These results are consistent with those obtained by cross-sectional transmission electron microscopy. Almost all Er atoms are located precisely in tetrahedral interstitial sites with 0.1 A(ring) standard deviation; only 2% of the Er atoms occupy random sites. These results mean that the lattice constant of the crystalline ErAs clusters is compressed to that for the crystalline GaAs host during the cluster formation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358660
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  • 6
    Electronic Resource
    Electronic Resource
    Flexible Loop That Is Novel Catalytic Machinery in a Ligase. Atomic Structure and Function of the Loopless Glutathione Synthetase (1994)
    s.l. : American Chemical Society
    Biochemistry 33 (1994), S. 4995-4999 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00183a001
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  • 7
    Electronic Resource
    Electronic Resource
    Chemistry of .alpha.,.beta.-unsaturated thione dimers. 3. Reactions of thiochalcones and 2-arylidene-1-thiotetralones with cumulenes containing a carbon-carbon double bond (1980)
    s.l. : American Chemical Society
    The @journal of organic chemistry 45 (1980), S. 927-930 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo01294a001
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  • 8
    Electronic Resource
    Electronic Resource
    Imaging of layer by layer growth processes during molecular beam epitaxy of GaAs on (111)A substrates by scanning electron microscopy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3079-3081 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When we use a scanning electron microscope-molecular beam epitaxy system with a GaAs (111)A substrate that dramatically improves the flatness of the growing surface, it makes possible detailed observations of the near-equilibrium growth processes of island nucleation, coalescence, and step motion. These observations allow the quantitative analysis of the growth processes based on the standard model of crystal growth. As an example, the Ga adatom surface diffusion length is directly determined from the dependence of measured step velocity on the Ga arrival rate. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122678
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  • 9
    Electronic Resource
    Electronic Resource
    Direct comparison of GaAs surface morphology between migration enhanced epitaxy and molecular beam epitaxy using in situ scanning electron microscopy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 63-65 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used scanning electron microscopy (SEM) for real-time-observation to compare the surface evolution during the early stage growth of GaAs with molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE), at the substrate temperature of 500 °C. Surface roughness during MEE growth is about 1 ML and much smaller than during MBE growth. Immediately after growth termination, monolayer steps can be seen and the surface recovers to initial smoothness in MEE, while islands do not disappear without higher temperature annealing in MBE. Present results confirm high surface atom mobility in MEE growth. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116758
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  • 10
    Electronic Resource
    Electronic Resource
    In situ observation of phase transition and the transition-induced step bunching on InAs(001) surfaces by scanning electron microscopy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1626-1628 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reconstruction and the step structure change during the phase transition on an InAs(001) surface under As pressure is observed directly by using scanning electron microscopy. The domain formation corresponding to the first-order phase transition is clearly seen as predicted by Monte Carlo simulation with a lattice gas model. It is also seen that the step structure largely depends on the surface reconstruction and the misorientation direction. This gives the first observation of phase-transition-induced step bunching on a compound semiconductor surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113873
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