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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3962-3966 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The submillimeter optical properties of hot-pressed polycrystalline boron nitride with a predominantly hexagonal crystal structure were studied at room temperature from ∼20 to 120 cm−1 (λ=500–84 μm) with a Fourier-transform spectrometer. Several grades were studied and probed both parallel and perpendicular to the material's optic axis. The material was found to behave as a negatively uniaxial birefringent crystal. The birefringence, defined as the difference between the real part of the extraordinary and ordinary indices of refraction (ne–no), was quite large in one case with a value of −0.152. The material's absorption properties were also studied. For certain grades, a modest dichroism was observed. The low absorption (α〈1 cm−1) for grade A at frequencies below 38 cm−1 suggests the possibility for millimeter/submillimeter wave applications. Results are compared with data obtained by other researchers on related materials.
    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 65 (1994), S. 438-444 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Instrumentation for making localized, precise relative reflection measurements of metals and superconductors in the terahertz frequency range is demonstrated. The results can be used to determine the surface resistivity of these materials which is of particular importance to development of high-temperature superconductors. Emission from a commerically available 1000 °C blackbody source was reflected from the materials under test and a reference reflector. The reflected signals were detected by a Schottky diode heterodyne receiver using a CO2-laser-pumped 214.5 μm CH2F2 laser as the local oscillator. Double-sideband bandwidth and receiver noise temperature were 2 GHz and 30 000 K, respectively. The use of a broadband incoherent diagnostic source minimizes instrumentation sensitivity to coherent interference effects. The heterodyne receiver provides for sensitive detection with good spatial and frequency resolution. Unoptimized spatial resolution of four times the diffraction limit was achieved. The potential for relative reflectivity measurement accuracy of better than 0.1% was demonstrated with 30 min measurement times though systematic errors limited actual measurement accuracy to about 0.3%.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 24 (1993), S. 21-37 
    ISSN: 1572-9680
    Keywords: paradigm ; agroforestry ; science ; epistemology ; economics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Because people need improved agroforestry and because there are perceived limitations in a largely ‘scientific approach’ to agroforestry research and development in the past, an alternative paradigm to gaining knowledge for use in this area is suggested. It is an encompassing approach to gaining knowledge which we call the rationally robust paradigm, RRP. The paradigm has 11 components: 1. Concentrating on site-specific knowledge, often in a geographic information system; 2. being aware of the limited funds to achieve agroforestry objectives; 3. de-emphasizing induction and deduction, and their replacement by or addition of other epistemological bases; 4. accepting lower confidence levels for conclusions and subsequent action; 5. using estimates of median values; 6. using knowledge of the range limits of agroforestry phenomena and factors; 7. giving attention to the system's phenomenon of equifinality and its consequences; 8. de-emphasizing ‘time’ as a factor in system analysis, and replacing it with other system phenomena; 9. using statistical regression techniques but simultaneously seeking to identify and use independent factors (e.g., solar radiation) that function significantly in many models; 10. appropriately using regression techniques emphasizing the use of hypothesized, often-non-linear relationships; and 11. operating in a conceptual clinical milieu. The paradigm is proposed for use throughout agroforestry.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9605
    Keywords: Submillimeter wave ; laser ; reflection ; surface resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Submillimeter wave laser reflection measurements of surface resistance can provide improved capability in the combination of sensitivity, spatial resolution, and frequency range. We have made reflectivity measurements on metals at 1630 GHz with an uncertainty of less than 0.3%. This sensitivity corresponds to a measurement sensitivity for surface resistance of 0.3 Ω. Assuming anf 2 frequency scaling of high-temperature superconductor surface resistance from the microwave to the terahertz frequency range, this sensitivity corresponds to about 1 ×10−5 Ω at 10 GHz. Capability for 10−7 Ω sensitivity could eventually be possible. Preliminary submillimeter wave reflection measurements of a YBCO thin film have been made with a sensitivity of 1%. Submillimeter wave reflectometry can make it possible to determine the spatial dependence of surface resistance in a wide range of material sizes and shapes. The spatial resolution could be on the order of 0.3–0.5 mm.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Environmental management 6 (1982), S. 452-452 
    ISSN: 1432-1009
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International journal of infrared and millimeter waves 11 (1990), S. 1299-1302 
    ISSN: 1572-9559
    Keywords: Terahertz ; far-infrared ; submillimeter ; spectroscopy ; refractive index ; extinction coefficient ; dielectric constant ; absorption ; Rexolite™
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The far-infrared optical properties of Rexolite™ 1422 were characterized at the University of Lowell Research Foundation using Fourier transform spectroscopy. The spectroscopic transmission measurements were performed on a 0.0236″ thick sample of material over the submillimeter wavelength region from 10 cm−1 to 360 cm−1. Using multiple reflection theory for transmission through an etalon, the frequency dependent complex refractive index of Rexolite™ is reported.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Wetlands ecology and management 4 (1996), S. 15-30 
    ISSN: 1572-9834
    Keywords: production systems ; agroecology ; hydroecology ; hydroperiod ; wetland policy ; sustainable agriculture ; Nigeria ; Sahel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The composition and complex interrelationships among the components of a Sahelian wetland community in Nigeria are described. The hydrology of the wetland is perceived to be the major determinant of the ecological integrity of the area. Ongoing ecological changes started by periodic meteorological droughts and sustained by the effects of large-scale hydro-agricultural projects are described along with their impacts on wildlife habitats and other valuable wetland resources. Establishing national wetland policies that recognize present and potential future values of various wetland types is recommended as an important step toward sustainable conservation of wetland resources in countries of the Sahel.
    Type of Medium: Electronic Resource
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