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  • 1
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    Oxygen as a control on seafloor biological communities and their roles in sedimentary carbon cycling (2007)
    In:  EPIC3Limnology and oceanography, 52(4), pp. 1698-1709
    Details
    Publication Date: 2019-07-17
    Description: 13C tracer experiments were conducted at sites spanning the steep oxygen, organic matter, and biological community gradients across the Arabian Sea oxygen minimum zone, in order to quantify the role that benthic fauna play in the short-term processing of organic matter (OM) and to determine how this varies among different environments. Metazoan macrofauna and macrofauna-sized foraminiferans took up as much as 56 +/- 13 mg of added C m**-2 (685 mg C m**-2 added) over 25 d, and at some sites this uptake was similar in magnitude to bacterial uptake and/or total respiration. Bottom-water dissolved oxygen concentrations exerted a strong control over metazoan macrofaunal OM processing. At oxygen concentrations 〉7 µmol/L (0.16 ml/L), metazoan macrofauna were able to take advantage of abundant OM and to dominate OM uptake, while OM processing at O2 concentrations of 5.0 µmol/L (0.11 ml/L) was dominated instead by (macrofaunal) foraminiferans. This led us to propose the hypothesis that oxygen controls the relative dominance of metazoan macrofauna and foraminifera in a threshold manner, with the threshold lying between 5 and 7 µmol/L (0.11 to 0.16 ml/L). Large metazoan macrofaunal biomass and high natural concentrations of OM were also associated with rapid processing of fresh OM by the benthic community. Where they were present, the polychaete Linopherus sp. and the calcareous foraminiferan Uvigerina ex gr. semiornata, dominated the uptake of OM above and below, respectively, the proposed threshold concentrations of bottom-water oxygen.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    Electronic Resource
    Electronic Resource
    Grating-coupled quantum-well infrared detectors: Theory and performance (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3600-3610 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of the grating-coupled quantum-well infrared detector, based on the modal expansion method (MEM) is presented together with numerical simulation results. MEM is a near-exact way of determining the electromagnetic-field pattern in a reflection grating-coupled quantum-well infrared detector, and is suitable for the calculation of absorption quantum efficiencies. Both lamellar gratings and crossed (doubly periodic) gratings are dealt with. Numerical simulations show that quantum efficiencies integrated with respect to wavelength ηint equal to 1 μm may be obtained in a detector equipped with a crossed grating of square symmetry, and a waveguide. The waveguide is defined by the metal grating on one side of the infrared absorbing quantum wells, and a thick aluminum arsenide layer on the other. This implies a factor of 4 higher ηint than in a 45° polished edge detector with the corresponding quantum-well characteristics. Finally, a sensitivity analysis shows that a change in grating dimensions of the order of 0.1 μm results in relative changes of ηint of about 1%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350916
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  • 3
    Electronic Resource
    Electronic Resource
    Dark current mechanisms and conditions of background radiation limitation of n-doped AlGaAs/GaAs quantum-well infrared detectors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6298-6304 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The most important mechanism of dark current in n-doped quantum-well infrared photodetectors (QWIPs) is due to interaction of electrons with longitudinal optical phonons. Theoretical expressions are derived for the carrier lifetime, and for generation currents originating from both photoexcitation as well as from thermal excitation in a single quantum well. Detector gain is discussed briefly. Calculated values of thermal generation currents and the ratio of photocurrent to thermal current are found to accord well with experimental data. Finally the conditions of background radiation limitation of QWIPs are investigated and the theory gives a temperature of background radiation limitation TBLIP=81 K for a 9 μm cutoff detector with a two-dimensional grating and optical cavity, for 300 K background temperature, optics f number=1 with 100% optical transmission, provided that a photocurrent to dark current ratio of 1 criterion is used. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360510
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  • 4
    Electronic Resource
    Electronic Resource
    Optimization of two dimensional gratings for very long wavelength quantum well infrared photodetectors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4989-4994 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed a detailed study of two-dimensional grating coupling for quantum well infrared photodetectors in the very long wavelength spectral region λ∼16–17 μm. Using calculations based on the modal expansion method we quantitatively explain the double peaked responsivity spectrum. By optimizing the grating parameters we achieve a normal incidence responsivity and detectivity which are three times larger than the 45° angle of incidence geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357209
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum efficiency enhancement of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a grating coupler (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2264-2266 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Long wavelength quantum well detectors with very high quantum efficiency, based on the coupling of radiation into an optical resonant cavity or waveguide defined by a reflection grating coupler on one side of the infrared absorbing multiquantum well stack, and an aluminum arsenide cladding layer on the other, have been fabricated and the results compared with theory. Theory shows that quantum efficiencies up to 90% may be obtained (for polarized radiation). However, experimental results indicate that the response peak becomes broadened due to spread in the grating period and therefore the maximum quantum efficiency is in practice limited to 60%, corresponding to a current responsivity of 2.1 A/W. This is 2.7 times larger than for a 45° polished edge detector with the same quantum well characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104917
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  • 6
    Electronic Resource
    Electronic Resource
    Intersubband transitions in single AlGaAs/GaAs quantum wells studied by Fourier transform infrared spectroscopy (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4123-4127 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Infrared intersubband absorption in modulation-doped MOVPE-grown AlxGa1−xAs/GaAs single-quantum wells have been studied by Fourier transform infrared spectroscopy. High signal to noise ratio was obtained by utilizing the multiple internal reflection (MIR) technique and a quantitative model of the absorption for this geometry was developed. Overlapping from multiphonon absorption was eliminated by using radiation polarized in two orthogonal directions and taking the difference between the resulting spectra, only one of them exhibiting the intersubband peak. The absorption wavelengths and intensities were fitted to theoretical expressions and the dimensions of the quantum wells were compared with independent determinations by photoluminescence, double crystal x-ray diffraction, and Hall-effect measurements. A narrow linewidth of about 6 meV was measured, corresponding to a 0.1-ps lifetime of electrons in the excited state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341322
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  • 7
    Electronic Resource
    Electronic Resource
    Near-unity quantum efficiency of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a doubly periodic grating coupler (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 857-859 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantum well infrared detectors based on a waveguide with a doubly periodic grating coupler are shown to provide quantum efficiencies of nearly unity with respect to unpolarized polarization. This is a factor of six larger than for a conventional 45° polished edge detector with the same quantum well characteristics. As a further advantage the detector response becomes nearly insensitive to the polarization direction of the incident radiation. Detectors have been fabricated and tested. Measurements lead to a maximum quantum efficiency of 92% with respect to unpolarized radiation, with a response linewidth =0.8 μm, thus confirming theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105259
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  • 8
    Electronic Resource
    Electronic Resource
    Efficiency of grating coupled AlGaAs/GaAs quantum well infrared detectors (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3361-3363 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The efficiency of grating coupling of radiation into the quantum well infrared detector is studied experimentally, with special emphasis on the influence of detector mesa size. It is found that compared to a 45° polished edge detector, the integrated quantum efficiency for crossed grating detectors of mesa size as small as 45 μm is about four times larger with a waveguide included, and two times larger without a waveguide. Furthermore, the importance of a high conductivity grating metal, the use of crossed gratings instead of lamellar gratings, as well as of a dielectric reflector is demonstrated. To show the superior coupling efficiency, the detectivity is measured for a detector with a crossed grating and a waveguide, and of mesa size 500 μm, resulting in D*=1.4×1011 cm Hz1/2 W−1 at 77 K operating temperature with the detector shielded from background radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110145
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  • 9
    Electronic Resource
    Electronic Resource
    Factors Controlling the B-Cell Cycle (1986)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Immunology 4 (1986), S. 13-34 
    Details
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.iy.04.040186.000305
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  • 10
    Electronic Resource
    Electronic Resource
    The effects of thermal effluent exposure on the gametogenesis of female fish (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 56 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: High temperature in Swedish and Lithuanian thermal effluent areas influenced gametogenesis of female perch Perca fluviatilis, roach Rutilus rutilus and pike Esox lucius negatively, indicating reduced reproductive capacity. Oocyte atresia started during vitellogenesis in autumn, and was often followed by asynchronous egg cell development. Among other anomalies, multi-nucleus oocytes and hermaphroditism were observed. No significant impact was seen in silver bream Blicca bjoerkna. Ruffe Gymnocephalus cernuus reacted by a tendency to produce an additional mature oocyte generation during the spawning period. Ovaries in roach from coastal areas were often infected by a microsporidian parasite Pleistophora mirandellae, causing severe damage to the gonad. Parasites were also detected in pike, but neither in perch nor in lake populations of roach. Fish living in open coastal environments did not avoid impact by moving out of the heated areas. There seems to be a conflict in some temperate fish between temperature preference behaviour and safeguarding normal reproduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb02085.x
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