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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3792-3794 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality ultraviolet photoconductive detectors have been fabricated using GaN layers grown by low-pressure metalorganic chemical vapor deposition on (11⋅0) sapphire substrates. The spectral responsivity remained nearly constant for wavelengths from 200 to 365 nm and dropped sharply by almost three orders of magnitude for wavelengths longer than 365 nm. The kinetics of the photoconductivity have been studied by the measurements of the frequency-dependent photoresponse and photoconductivity decay. Strongly sublinear response and excitation-dependent response time have been observed even at relatively low excitation levels. This can be attributed to redistribution of the charge carriers with increased excitation level. © 1995 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 67 (1995), S. 22-24 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Background limited infrared photodetection has been achieved up to 100 K at normal incidence with p-type GaAs/Ga0.71In0.29As0.39P0.61 quantum well intersubband photodetectors grown by low-pressure metalorganic chemical vapor deposition. Photoresponse covers the wavelength range from 2.5 μm up to 7 μm. The device shows photovoltaic response, the cutoff wavelength increases slightly with bias, and the responsivity increases nonlinearly with bias. These effects are attributed to an asymmetric quantum well profile. © 1995 American Institute of Physics.
    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 80 (1996), S. 2542-2544 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three papers published recently [P. M. Young, C. H. Grein, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 74, 4774 (1993); G. M. Williams, J. Appl. Phys. 77, 4153 (1995); C. H. Grein, M. E. Flatte, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 77, 4156 (1995)] concerning the comparison of theoretically predicted performance of HgCdTe photodiodes with InAs/InGaSb superlattice photovoltaic detectors are obscure with respect to optimal selection of HgCdTe photodiode structures. Both Comments [G. M. Williams, J. Appl. Phys. 77, 4153 (1995); C. H. Grein, M. E. Flatte, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 77, 4156 (1995)] have not noticed the important results of papers published by Humpreys [Infrared Phys. 23, 171 (1983); Infrared Phys. 26, 337 (1986)], who critically reexamined the role of a radiative mechanism in the detection of infrared radiation. To explain our point of view on competition between InAs/InGaSb SLs and "bulk'' HgCdTe detectors, we present a generalized model of an infrared photodetector and derive the figure merit of any material for infrared photodetector as the ratio of absorption coefficient to the thermal generation rate. This determines the detectivity of infrared photodetectors. Using that model for the most common n+-p and p+-n long wavelength HgCdTe photodiodes, it is shown that the highest performance can be obtained with a low doping of the base photodiode regions. This means that the previously assumed (Young et al.) highly doped HgCdTe photodiode structure with a thick base region is far from optimal. Our calculations carried out for optimal device structures indicate that the ultimate detectivities of long wavelength HgCdTe photodiodes operating at 77 K are higher than those for InAs/InGaSb SLs. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2645-2647 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: p+-InSb/π-InAs1−xSbx/n+-InSb heterojunction photodiodes operating at near room temperature in the 8–13 μm region of infrared (IR) spectrum are reported. A room-temperature photovoltaic response of up to 13 μm has been observed at 300 K with an x≈0.85 sample. The voltage responsivity-area product of 3×10−5 V cm2/W has been obtained at 300 K for the λ=10.6 μm optimized device. This was close to the theoretical limit set by the Auger mechanism, with a detectivity at room temperature of ≈1.5×108 cm Hz1/2/W. © 1995 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 67 (1995), S. 2028-2030 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Large-area GaN photovoltaic structures with p-n junctions have been fabricated using atmospheric pressure metalorganic chemical vapor deposition. The photovoltaic devices typically exhibit selective spectral characteristics with two narrow peaks of opposite polarity. This can be related to p-n junction connected back-to-back with a Schottky barrier. The shape of the spectral characteristic is dependent on the thickness of the n- and p-type regions. The diffusion length of holes in the n-type GaN region, estimated by theoretical modeling of the spectral response shape, was about 0.1 μm. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 99-101 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Long-wavelength InAs1−xSbx photoconductors operated without cryogenic cooling are reported. The devices are based on p-InAs1−xSbx/p-InSb heterostructures grown on (100) semi-insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Photoreponse up to 14 μm has been obtained in a sample with x=0.77 at 300 K, which is in good agreement with the measured infrared absorption spectra. The corresponding effective lifetime of ≈0.14 ns at 300 K has been derived from stationary photoconductivity. The Johnson noise limited detectivity at λ=10.6 μm is estimated to be about 3.27×107 cm Hz1/2/W at 300 K. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of environmental contamination and toxicology 61 (1998), S. 22-30 
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Surgical endoscopy and other interventional techniques 11 (1997), S. 113 -115 
    ISSN: 1432-2218
    Keywords: Key words: Ruptured abdominal aortic aneurysm — Ischemic colitis — Flexible sigmoidoscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Background: The development of colonic ischemia following repair of ruptured abdominal aortic aneurysm (AAA) is associated with significant morbidity and timely diagnosis is essential. The purpose of this study was to determine the efficacy of endoscopy in the diagnosis of colonic ischemia and in prediction of need for resection. Methods: Patients who underwent postoperative lower endoscopy after ruptured AAA from 1986 to 1995 were reviewed for endoscopic findings, clinical course, and patient outcome. Results: A total of 80 patients had ruptured AAA during the study period, of which 56 survived for longer than 24 h postoperatively. Flexible lower endoscopy was done in 18 patients (32%) on an average of 4.4 days following AAA repair (range 1–16). Indications for initial endoscopy included early or bloody stools in 12 (67%), hemodynamic instability or sepsis in eight (44%), and acidosis in four (22%). The extent of the examination was sigmoid or descending colon in 13, cecum in four, and transverse colon in one. Endoscopic findings were normal in four patients. Five examinations showed only areas of hemorrhagic mucosa. Absence of full-thickness ischemia was confirmed by clinical course or autopsy in these nine patients. Two examinations demonstrated full-thickness necrosis which was confirmed at subsequent laparotomy. In six examinations, ischemia was noted but judged to be limited to mucosa only. Absence of full-thickness disease was demonstrated by laparotomy in three and subsequent course in three. Eight patients (57%) with initial abnormal examinations underwent repeat endoscopy showing improved interval appearance in seven cases and progression to full-thickness ischemia in one patient. Conclusions: Flexible sigmoidoscopy reliably predicts full-thickness colonic ischemia following repair of ruptured aortic aneurysms. Patients with non-confluent ischemia limited to the mucosa can be safely followed by serial endoscopic examinations.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-8868
    Keywords: geostatistics ; regionalization ; fuzzy ; kriging ; hydrogeology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract In many instances hydrogeological parameters obtained by conventional methods for selected localities within an aquifer or an aquitard are not sufficient for adequate regionalization at the scale of the entire layer. Here, we demonstrate an application of the fuzzy kriging method in regionalization of hydrogeological data, in which the set of conventional, crisp values is supplemented by imprecise information subjectively estimated by an expert. It is believed that such an approach eventually may reflect the real-world conditions more closely than a traditional crisp-value approach, because the former does not impose exactness artificially on phenomena which are diffuse by their nature. Spatial interpolation was done for the thickness of one of the major aquitards (till and glaciolacustrine clay) in northwestern Germany. The dataset consists of 329 crisp values from boreholes supplemented by 172 imprecise values defined as fuzzy numbers. It is demonstrated that the reliability of regionalization was higher, compared to regionalization performed with the crisp dataset only. Fuzzy kriging was performed with FUZZEKS (Fuzzy Evaluation and Kriging System) developed at the Ecosystem Research Center at the University of Kiel.
    Type of Medium: Electronic Resource
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