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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of antennas for personal wireless communications applications (1994)
    Springer
    International journal of wireless information networks 1 (1994), S. 165-176 
    Details
    ISSN: 1572-8129
    Keywords: Wireless ; FDTD ; PIFA ; monopole ; loop antenna ; diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The advancement of antenna technology in personal wireless communication systems has been encouraged by the increasingly stringent demands placed upon these systems to provide low-power and highly reliable information transfer. The antenna designer must not only consider the cost, manufacturability, compactness, and system integrability of the radiator but also generate a product which satisfies rigid specifications concerning return loss, bandwidth, and gain while operating in a complex radiating environment. Successful, cost-effective approaches to the design of antennas for communication devices rely upon the implementation of sophisticated analysis tools, such as the finite-difference time-domain (FDTD) method, capable of predicting the electromagnetic behavior of complicated topologies. In this work, the behavior of planar inverted F, monopole, and loop antennas is investigated using tools based upon the FDTD approach. Such factors as the effects of the conducting chassis, plastic casing, and biological tissue on the antenna performance are investigated. Experimental measurements are used to validate the results obtained from computations and to provide further insight into the behavior of the different geometries. The use of antenna diversity to reduce the effects of multipath fading is discussed, and several examples of antenna diversity configurations are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02107416
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    In situ mineralization of nitorgen and phosphorus of arctic soils after perturbations simulating climate change (1993)
    Springer
    Oecologia 95 (1993), S. 179-186 
    Details
    ISSN: 1432-1939
    Keywords: Arctic-Alpine ; Climate change ; N and P mineralization ; Nutrient immobilization ; Soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seasonal net nitrogen (N) and phosphorus (P) mineralization was investigated at Abisko, Swedish Lapland in soils of a subarctic heath and in soils of a colder (by about 4° C), high altitude fellfield by (a) using in situ soil incubation in soils which had been shaded or subjected to two levels of increased temperature, combined with (b) reciprocal transplantation of soils between the two sites. Proportionally large and significant net seasonal mineralization of N, in contrast to non-significant P mineralization, was found in untransplanted and transplanted fellfield soil. In contrast, P was mineralized in proportionally large amounts, in contrast to low N mineralization, in the transplanted and untransplanted heath soil. The differences indicate that P was strongly immobilized in relation to N at the fellfield and that N was more strongly immobilized than P in the heath soil. The immobilization in both soils remained high even after a temperature change of 4–5° C experienced by transplanted soils. Air temperature increases of up to 4–5° C in greenhouses resulted in a soil temperature increase of 1–2° C and did not cause any extra increase of net N and P mineralization. The results suggest that soil temperature increases of up to 2° C, which are likely to occur by the end of the next century as an effect of a predicted 4–5° C rise in air temperature, have only small effects on net mineralization in at least two characteristic tundra soils. These effects are probably smaller than the natural fluctuation of plant available nutrients from site to site, even within the same plant community. A further soil temperature increase of up to 4–5° C may enhance decomposition and gross mineralization, but the rate of net mineralization, and hence the change of nutrient availability to the plants, depends on the extent of microbial immobilization of the extra nutrients released.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323488
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    Paper (German National Licenses)
    Fulltext
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