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  • 1
    Electronic Resource
    Electronic Resource
    Zeeman studies of the first excited states of palladium and metal free phthalocyanines in Shpol'skii matrix (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8210-8215 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Phthalocyanines (Pcs) are planar molecules of relatively high symmetry and exhibit magneto-optic effects in many ways. We report the Zeeman effect of the first excited states of palladium (Pd–) and free-base (H2–) Pcs in a 5 K Shpol'skii matrix by direct observation of their fluorescence position shifts. From the experimental data an apparent angular momentum integral, coupling the lowest two Jahn–Teller stabilized crystal field split first excited states, Λ′, was found to be 2.7±0.1 (h-dash-bar) for PdPc. No conclusive Λ′ was deduced for H2Pc but its value can be estimated to be around the theoretical value of 3 (h-dash-bar). The experimental data of H2Pc revealed a complex structure in the fluorescence band examined, which complicated the analysis of Λ′ but helped unravel the biexponential decay problem of the structure. We infer one narrower band in the structure has the previously reported lifetime of τ 6.3 ns, and the other broader band being ∼1.8 cm−1 higher, has τ 3.7 ns. We believe this composite situation also exists for the other tautomeric structure since it also exhibited biexponential decay. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471574
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  • 2
    Electronic Resource
    Electronic Resource
    Optimal crystal cuts and propagation directions for excitation of acoustic waves in LiNbO3 (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 49-54 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Acoustic power flow in a LiNbO3 single crystal was calculated to find the optimal crystal cutting orientation and the wave propagation direction for the efficient excitation of acoustic waves in the crystal. By solving the stiffened Christoffel equations and calculating the acoustic Poynting vectors with piezoelectric effect included, maximum longitudinal acoustic power flow in a 30° Z-rotated, Y-cut LiNbO3 crystal was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336837
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  • 3
    Electronic Resource
    Electronic Resource
    Transport critical current density and microstructure in extruded YBa2Cu3O7−x wires processed by zone melting (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 228-232 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: YBa2Cu3O7−x compounds were extruded into long wires with the diameter of 1 mm after sintering. The sintered wires were subsequently zone melted to develop a highly textured microstructure. Magnetization experiments at 77 K indicated a Jc value of 1×105 A/cm2 at 1 T. Transport measurements at 77 K showed a greatly enhanced field dependence of the critical current density. Transmission electron microscopy revealed an important grain-boundary feature which eliminated the weak-link behavior. Large amounts of dislocations have also been found in the zone-melted sample which may contribute to flux pinning in the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347122
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal stability study of Ni/Ta n-GaN Schottky contacts (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 595-597 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Schottky behavior of Ni/Ta and Ni contacts on n-GaN was investigated under various annealing conditions by current–voltage measurements. It is found that with the addition of Ta between the Ni layer and the GaN substrate the thermal stability properties of devices can be significantly improved. Experimental results indicate that a high quality Ni/Ta n-GaN Schottky diode with an ideality factor and barrier height of 1.16 and 1.24 eV, respectively, can be obtained under 1 h annealing, at 700 °C. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1425455
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  • 5
    Electronic Resource
    Electronic Resource
    Gallium K-edge x-ray absorption study on Mg-doped GaN (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 31-33 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ga K-edge x-ray absorption measurements were employed to investigate Mg-doping effects in GaN samples. Strong polarization-dependent x-ray absorption near-edge structures become less pronounced with increasing doping concentration, indicating the formation of a mixing-phase structure of cubic and hexagonal phases. Analysis of the extended x-ray absorption region of the spectra revealed doping-related defects such as vacancies, substitutions, and interstitial occupations. They were formed anisotropically in the crystal c axis direction and its perpendiculars. Disorderliness arising from phase mix and defects is believed to have lowered the Debye temperature of the doped GaN films and caused the destructive interference of the absorption fine-structure oscillation functions. These effects were taken into account for the observed large coordination number reductions in our samples. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337636
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  • 6
    Electronic Resource
    Electronic Resource
    Photoluminescence and photoluminescence excitation studies of as-grown and P-implanted GaN: On the nature of yellow luminescence (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 3349-3351 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied optical and electronic properties of isoelectronic P-implanted GaN films grown by metalorganic chemical vapor phase epitaxy. After rapid thermal annealing, a strong emission band around 430 nm was observed, which is attributed to the recombination of exciton bound to isoelectronic P-hole traps. From the Arrhenius plot, the hole binding energy of ∼180 meV and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, the implantation process likely introduced NI and P-related defects. By using photoluminescence excitation technique, we found that the P-implantation-induced localized states not only increase the yellow luminescence but also suppress the transitions from the free carriers to deep levels. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1476400
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  • 7
    Electronic Resource
    Electronic Resource
    Isoelectronic As doping effects on the optical characteristics of GaN films grown by metalorganic chemical-vapor deposition (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2819-2821 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor–acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I2) transition in undoped GaN increases with temperature as T1.5. However, the I2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316075
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  • 8
    Electronic Resource
    Electronic Resource
    Electrical characterization of isoelectronic In-doping effects in GaN films grown by metalorganic vapor phase epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 897-899 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Indium isoelectronic doping was found to have profound effects on electrical properties of GaN films grown by metalorganic chemical vapor deposition. When a small amount of In atoms was introduced into the epilayer, the ideality factor of n-GaN Schottky diode was improved from 1.20 to 1.06, and its calculated saturation current could be reduced by 2 orders of magnitude as compared to that of the undoped sample. Moreover, it is interesting to note that In isodoping can effectively suppress the formation of deep levels at 0.149 and 0.601 eV below the conduction band, with the 0.149 eV trap concentration even reduced to an undetected level. Our result indicates that the isoelectronic In-doping technique is a viable way to improve the GaN film quality. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125622
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  • 9
    Electronic Resource
    Electronic Resource
    Flux creep and pinning potential distribution in zone-melted YBa2Cu3Ox (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 225-227 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic relaxation data have been taken on zone-melted and sintered YBa2Cu3Ox samples over wide temperature and magnetic field ranges. We have found that magnetic relaxation varies greatly in the samples with different microstructures and crystallographic orientations. Flux-creep rates have been found to be reduced in the zone-melted samples owing to large amounts of intragranular crystal defects such as edge dislocations and stacking faults. An important flux-pinning behavior related to the pinning potential distributions has been observed in the samples. The relationship between microstructural orientation and pinning potential distributions in YBa2Cu3Ox is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105973
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  • 10
    Electronic Resource
    Electronic Resource
    High incidence of clopidogrel-associated gastrointestinal bleeding in patients with previous peptic ulcer disease (2003)
    Oxford, UK : Blackwell Science Ltd
    Alimentary pharmacology & therapeutics 18 (2003), S. 0 
    Details
    ISSN: 1365-2036
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background:  In average-risk patients, the new anti-platelet agent, clopidogrel, causes less upper gastrointestinal adverse events than aspirin. However, there are no safety data on the use of clopidogrel in high-risk patients.Aim:  To evaluate the safety of clopidogrel in patients with peptic ulcer disease in a retrospective cohort longitudinal study.Methods:  During the period from January 2000 to May 2002, 70 patients who were prescribed clopidogrel (75 mg/day) for a previous history of non-aspirin-related peptic ulcer disease or a history of aspirin-related gastrointestinal complications (dyspepsia or peptic ulcer) were recruited. The occurrence of ulcer complications (bleeding/perforation/obstruction) was the primary end-point.Results:  After a median follow-up of 1 year, nine patients (12%) developed gastrointestinal bleeding and one had a perforated peptic ulcer. Clopidogrel-associated gastrointestinal bleeding was significantly more common in patients with a history of gastrointestinal bleeding than in those without (22% vs. 0%; P = 0.007; odds ratio, 1.3; 95% confidence interval, 1.1–1.5).Conclusions:  Clopidogrel is associated with a high incidence of upper gastrointestinal bleeding in high-risk patients. A previous history of gastrointestinal bleeding appears to be a predictor of adverse gastrointestinal events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2036.2003.01693.x
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