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  • 2000-2004
  • 1990-1994  (20)
  • 1940-1944
  • 1993  (20)
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  • 2000-2004
  • 1990-1994  (20)
  • 1940-1944
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1803-1808 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this paper, we describe a new, entirely computer-controlled apparatus designed for degradation studies of photochromic compounds. Photodegradation can be performed in three different ways using, in addition to the usual flash mode, the cyclic and continuous modes which more closely simulate daylight exposure conditions. In each mode, the "fatigue resistance'' parameter is computed. Moreover, the spectrokinetic parameters of photomerocyanine species can be obtained from the kinetic mode. Due particularly to the fully computer-controlled experimental setup, the between-day reproducibility of the initial absorbance and fatigue resistance determinations are better than 4% and 6%, respectively. Owing to the modular design of the menu-driven software, written in C language, the apparatus is very flexible and easy to use.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 839-853 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Pulsed transverse electric (TE) glow discharges used to produce population inversions in gas lasers at 1–20 atm require high-speed, high-voltage, high-current capacitor banks. In this article we first review and compare the circuits in common use to produce the required fast, self-sustained glow discharges in CO2, excimer, and N2 lasers. The parameters and circuit types given will be useful to future designers of pulsed gas lasers to design and to optimize any proposed circuit in order to yield any desired operating conditions and parameters. The n-stage circuit types presented are capacitor-transfer (C-C), L-C inversion, Marx bank, and fourfold L-C inversion, with their double-sided counterparts, and also their transmission-line counterparts, such as the Blumlein circuit. A one-parameter differential equation is developed which describes the general series C-L-R circuit. Electrical pulses measured on various lasers are compared with the differential equation solutions for various bank impedances and load resistances. We then present the design and measurements of a new automatically preionized, double-sided, L-C inversion circuit for an 800-mJ, TE CO2 laser, and compare it to previous systems. Methods to lengthen the discharge pulse, and some novel active mode locking techniques are discussed. We compare the L-C inversion circuit, the fourfold L-C inversion circuit, the conventional Marx bank, and the "double Marx bank'' for lasers and other applications, such as pulsed particle accelerators. Finally, we discuss capacitor bank interconnections, electro-optic probe systems, and various triggering methods.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6676-6685 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a general theoretical treatment of ionized impurity scattering in semiconductor superlattices. Employing an extension of the quasi-two-dimensional calculations of Stern and Howard to multi-well structures, we explicitly account for nonuniformity of the wavefunction distribution function, arbitrary dispersion relations, scattering by impurities in neighboring periods, and screening by electrons in neighboring wells. Interperiod phenomena are found to be quite significant whenever the screening length is comparable to or longer than the distance between the quantum wells. Calculated results are compared with recent data for modulation-doped and setback-modulation-doped HgTe-CdTe superlattices. However, the discussion emphasizes general aspects of the problem rather than features specific to a particular system.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2810-2812 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretical investigations are presented of the electric-field dependence of normal-incidence interconduction subband absorption in Ga1−xAlxSb/AlSb L-valley quantum wells. Under an applied electric field of 50 kV/cm, a blue shift of the absorption peak from 4.94 to 4.82 μm was found in a Ga0.7Al0.3Sb/AlSb structure with well width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark shifts with bias makes the Ga1−xAlxSb/AlSb L-valley system an attractive choice for the 3–5 μm vertical optical modulators.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1195-1198 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose a new type of optical modulator employing two-step Ga1−xAlxSb/Ga1−yAlySb/Ga1−zAlzSb L-valley quantum wells to enhance the Stark shifts of the intersubband transition energy and therefore to achieve large absorption spectral changes with applied bias. Due to the effective-mass anisotropy of electrons in the L-valleys and the tilted growth direction with respect to the valleys, this novel structure can intrinsically absorb normal incidence light. Under an electric field of 50 kV/cm, a blue shift of the absorption peak from 10.9 to 9.8 μm was found from our calculations in a Ga0.7Al0.3Sb/Ga0.5Al0.5Sb/Ga0.4Al0.6Sb structure with a Ga0.7Al0.3Sb well width of 25 A(ring) and a Ga0.5Al0.5Sb step width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark effects with bias makes this structure an attractive choice for such high-speed optoelectronic devices as vertical infrared light modulators and voltage tunable photodetectors.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Heating in the Alfvén resonant regime has been demonstrated in the Phaedrus-T tokamak [Fusion Technol. 19, 1327 (1991)]. Electron heating during injection of radio-frequency (rf) power is indicated by a 30%–40% drop in loop voltage and modifications in sawtooth activity. Heating was observed at a frequency ωrf≈0.7Ωi on axis, using a two-strap fast wave antenna operated at 7 and 9.2 MHz with 180° phasing (N(parallel)∼100). Numerical modeling with the fast wave code fastwa [Plasma Phys. Controlled Fusion 33, 417 (1991)] indicates that for Phaedrus-T parameters the kinetic Alfvén wave is excited via mode conversion from a surface fast wave at the Alfvén resonance and is subsequently damped on electrons.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2362-2364 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fabrication of nanometer scale features in the narrow gap, compound semiconductor mercury cadmium telluride has been demonstrated through the application of e-beam lithography and reactive ion etching with an electron cyclotron resonance (ECR) microwave generated methane/hydrogen plasma. The effects of methane concentration, substrate bias, total pressure, and substrate position with respect to the ECR condition on etch rate, anisotropy, and overall etch performance have been examined. The optimized process resulting from these studies has produced the first mercury-based nanostructures consisting of 30–60 nm features with sidewall angles of 88°.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1098-1100 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have successfully synthesized heterojunctions and elementary multilayered structures of the semimetal-semiconductor system Sb/GaSb using molecular beam and migration enhanced epitaxies. The study is motivated in part by the potential for producing an indirect narrow-gap semiconductor, in which a confinement-induced positive energy gap in the Sb layers will lead to highly attractive properties for nonlinear optical switches operating in the infrared. One may also be able to exploit the long mean free path in Sb (up to 2 μm) in studying quantum transport phenomena. X-ray diffraction confirms the ordered growth of GaSb/Sb/GaSb multilayers, and field-dependent magnetotransport measurements yield electron and hole mobilities ≥3×104 cm2/V s in Sb thin films.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2210-2212 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of magnetotransport results for InAs-Ga1−xInxSb superlattices with a range of layer thicknesses demonstrates that interface roughness scattering dominates the electron mobility under most conditions of interest for infrared detector applications. However, the dependence on well thickness is much weaker than the d16 relation observed in other systems with thicker barriers, which is consistent with predictions based on the sensitivity of the energy levels to roughness fluctuations. Theory also correctly predicts an abrupt mobility decrease at the semiconductor-to-semimetal transition point, as well as the coexistence of two electron species in semimetallic samples.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    British journal of dermatology 129 (1993), S. 0 
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Iloprost, a stable prostacyclin analogue, is known to have beneficial effects on the disturbed microcirculation. To develop a topical application for venous leg ulcers it is necessary to know the extent to which iloprost might be absorbed through the ulcer base. The aim of this study was to measure the absorption kinetics of iloprost solutions in increasing concentrations and doses (0.004% [15 μg]-0.006% [30 μg] in 23 patients.There was considerable variation amongst the patients in the amount of iloprost absorbed. In 40% of patients no iloprost could be detected in the plasma, whereas in others up to 82% of the iloprost applied was absorbed through the ulcer base. High iloprost plasma levels provoked flushing in two patients. The highest plasma levels were always reached during the first hour after application. There was no direct relation between the ulcer size and the amount of iloprost absorbed. Iloprost concentrations up to the highest concentration applied (0.006%) were well tolerated locally.
    Type of Medium: Electronic Resource
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