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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4737-4740 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Selectively red shifting the photoresponse of intersubband GaAs/Al0.25Ga0.75As multiple-quantum-well (MQW) infrared photodetectors (QWIPs) by furnace and rapid thermal annealing is explored. Selective interdiffusion of the MQW is achieved by dielectric encapsulating (SiO2 or Si3N4) the surface. The high dark current of annealed QWIPs is attributed to dopant out-diffusion from the QWs into the barriers. Declining responsivities result from reduced carrier density in the QW and a red shift of the intersubband transition energy. In this work, the intersubband energy is determined by the Fourier synthesis model and compared with experimental results (further confirming the interdiffusion mechanism). Minimal dark current and responsivity degradation is observed for Si3N4-encapsulated QWIPs red shifted by 1 μm © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2427-2429 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A very long wavelength broadband infrared detector, sensitive over a 10–16 μm spectral range, based on GaAs/AlxGa1−xAs quantum wells grown by molecular beam epitaxy, has been demonstrated. Wavelength broadening of Δλ/λp∼42% is observed to be about a 400% increase compared to a typical bound-to-quasibound quantum well infrared photodetector (QWIP). In this device structure, which is different from typical QWIP device structures, two different gain mechanisms associated with photocurrent electrons and dark current electrons were observed and explained. Even with broader response, D*∼1×1010 cmHz/W at T=55 K is comparable to regular QWIPs with similar cutoff wavelengths. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 78-80 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter, we describe the characteristics of molecular beam epitaxy GaAs/AlGaAs quantum-well infrared photodetectors (QWIP's) grown on a GaAs substrate, and on a GaAs-on-Si substrate produced by metalorganic chemical-vapor deposition. Important issues for QWIP applications such as dark current, spectral response, and absolute responsivity are studied. We find that compared to a similar detector structure grown on a GaAs substrate, the detector grown on a GaAs-on-Si substrate exhibits similar dark current and absolute responsivity while displaying a small blueshift in the spectral response. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lattice-matched InGaAs/InP quantum well intersubband photodetectors (QWIPs) have been grown on an InP substrate by gas source molecular beam epitaxy. Detection at 4.55 μm was observed for a narrow well p-type InGaAs QWIP which, when complimented by a high responsivity 8.93 μm n-type InGaAs/InP QWIP, demonstrates the possibility of dual band, monolithically integrated QWIPs on the same InP substrate. Theoretical calculations of the photocurrent spectra are in excellent agreement with the experimental data. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3573-3575 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of laser annealing on important detector characteristics such as dark current, spectral response, and absolute responsivity is investigated for bound-to-continuum GaAs/AlGaAs quantum-well infrared photodetectors (QWIPs) operating in the 8–12 μm wavelength regime. A set of experiments was conducted on QWIPs fabricated from both as-grown and laser-annealed multiple-quantum-well structures. Compared to the as-grown structure, the peak spectral response of the laser-annealed structure was shifted to longer wavelengths, though absolute responsivity was decreased by about a factor of two. In addition, over a wide range of bias levels, the laser-annealed QWIPs exhibited a slightly lower dark current compared to the as-grown QWIPs. Thus, the postgrowth control of GaAs/AlGaAs quantum-well composition profiles by laser annealing offers unique opportunities to fine tune various aspects of a QWIP's response. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0932
    Keywords: Key words Cervical disc disease ; MRI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this study is to assess the accuracy of MRI alone in the differentiation of soft cervical disc protrusion from osteophytic compression in cervical disc disease. In a retrospective study, the MRI scans of 41 patients with cervical disc disease, who had previously undergone surgery, were presented to three independent observers, randomly on two different occasions, to identify the accuracy of the diagnosis of the presence of hard or soft disc or both as a cause of compression. The observers (two neurosurgeons and one neuroradiologist) were not involved with the treatment of the cases at any stage and were unaware of the surgical findings. Their observations were compared with those of the surgeon recorded at operation. The intra-observer agreement was poor for diagnosis into three categories as hard or soft disc or both. In distinguishing between the presence or absence of hard disc, there was moderate to good (Kappa = 0.6) intra observer and fair to moderate (Kappa = 0.4) interobserver agreement. The sensitivity of diagnosis of a hard disc was high (87%) but specificity was low (44%), due to the overestimation of the presence of hard disc. There was a significantly higher incidence of hard disc in the elderly age group (76% over the fifth decade, P = 0.0073). It is concluded that MRI alone is not a very efficient diagnostic tool in distinguishing between hard and soft disc in the cervical disc disease.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 8 (1999), S. 78-80 
    ISSN: 1432-0932
    Keywords: Key words Cervical spine ; Surgery ; Neurologic complication ; Hypoglossal nerve
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Injury to the hypoglossal nerve is a recognised complication after soft tissue surgery in the upper part of the anterior aspect of the neck, e.g. branchial cyst or carotid body tumour excision. However, this complication has been rarely reported following surgery of the upper cervical spine. We report the case of a 35-year-old woman with tuberculosis of C2–3. She underwent corpectomy and fusion from C2 to C5 using iliac crest bone graft, through a left anterior oblique incision. She developed hypoglossal nerve palsy in the immediate postoperative period, with dysphagia and dysarthria. It was thought to be due to traction neurapraxia with possible spontaneous recovery. At 18 months’ follow-up, she had a solid fusion and tuberculosis was controlled. The hypoglossal palsy persisted, although with minimal functional disability. The only other reported case of hypoglossal lesion after anterior cervical spine surgery in the literature also failed to recover. It is concluded that hypoglossal nerve palsy following anterior cervical spine surgery is unlikely to recover spontaneously and it should be carefully identified.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 61 (1999), S. 179-186 
    ISSN: 1572-879X
    Keywords: CO oxidation ; Cu‐ZSM‐5 ; zeolites ; DFT
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic oxidation of CO by Cu‐exchanged high‐silica zeolites (e.g., ZSM‐5) has been investigated theoretically using density functional theory. Calculations reveal two distinct, parallel pathways for oxidation of CO: (i) adsorption of O2= on a reduced Cu site followed by O atom abstraction by CO, and (ii) adsorption of CO followed by its reaction with O2= to form a cyclic compound which decomposes to form CO2=. The reduced site is regenerated via two different pathways, both of which involve oxidation of one or more CO molecules: (i) abstraction of atomic oxygen by CO from the oxidized active site, and (ii) formation of a carbonate species followed by its reaction with a molecule of CO. The relevance of these reactions to the reduction of NO is discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Biotechnology letters 17 (1995), S. 567-570 
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Mutants of Escherichia coli K-12 resistant to a threonine analogue (α-amino-β-hydroxy valeric acid) were predominantly resistant to ethionine and overproduced both threonine and methionine (2 mg/ml each). Novelty of the mutants is discussed.
    Type of Medium: Electronic Resource
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