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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 39 (2004), S. 491-498 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Silver nanoparticles embedded in ZnO matrix were deposited onto fused silica substrates using high pressure (~40 Pa) d.c. sputtering techniques. The particle size in the films was tailored by varying the system pressure and substrate temperature, while the metal volume fraction was controlled by adjusting the relative time of sputtering of the targets. Blue-shift of the surface plasmon resonance peak was observed with the reduction in size and volume fraction of metal particles. A surface plasmon peak in the absorption spectra was found to be absent in the films with particle size and metal concentration below a critical value. A sharp absorption edge in the absorbance spectra within the UV-VIS range indicated semiconducting behavior of the ultrafine silver particles. Films deposited at lower substrate temperature showed a narrow distribution of nanoparticles, nearly spherical in shape. Increase in substrate temperature resulted in a non-uniform size and shape in the films due to the agglomeration of the nanoparticles. These size and shape distributions have a profound effect on the optical absorbance spectra and result in a broad and asymmetric surface plasmon band. A shape distribution introduced in the Maxwell-Garnett or Bruggeman effective medium theory was found to give a reasonable description of the experimentally observed optical absorption spectra.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 34 (2003), S. 25-31 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Dielectric properties of silver/SiO2 nanocomposite thin films grown by high-pressure d.c. sputtering technique were studied by spectroscopic ellipsometry (300-800 nm). The dielectric behavior of the nanocomposite thin films largely depended on the particle size, its number density and the surrounding environments. The films showed semiconductor-like behavior up to a critical particle size and concentration, beyond which the films exhibited the typical surface plasmon resonance characteristics in their optical properties. The refractive index was also found to have a strong dependence on the particle size and its dispersion in the matrix. The results were found to be consistent with those obtained from UV-VIS optical absorbance data. Bruggeman effective medium theory was used to explain the experimental results.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1573-1561
    Keywords: Alkaloids ; coccinellines ; decahydroquinolines ; indolizidines ; pyrrolidines ; pyrrolizidines ; dendrobatid frogs ; myrmicine ants ; coccinellid beetles ; millipedes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Neotropical poison frogs (Dendrobatidae) contain a wide variety of lipophilic alkaloids, apparently accumulated unchanged into skin glands from dietary sources. Panamanian poison frogs (Dendrobates auratus) raised in a large, screened, outdoor cage and provided for six months with leaf-litter from the frog's natural habitat, accumulated a variety of alkaloids into the skin. These included two isomers of the ant pyrrolizidine 251K; two isomers of the 3,5-disubstituted indolizidine 195B; an alkaloid known to occur in myrmicine ants; another such indolizidine, 211E; two pyrrolidines, 197B and 223N, the former known to occur in myrmicine ants; two tricyclics, 193C and 219I, the former known to occur as precoccinelline in coccinellid beetles; and three spiropyrrolizidines, 222, 236, and 252A, representatives of an alkaloid class known to occur in millipedes. The alkaloids 211E, 197B, and 223N appear likely to derive in part from ants that entered the screened cage. In addition, the frog skin extracts contained trace amounts of four alkaloids, 205D, 207H, 219H, and 231H, of unknown structures and source. Wild-caught frogs from the leaf-litter site contained nearly 40 alkaloids, including most of the above alkaloids. Pumiliotoxins and histrionicotoxins were major alkaloids in wild-caught frogs, but were absent in captive-raised frogs. Ants microsympatric with the poison frog at the leaf-litter site and at an island site nearby in the Bay of Panamá were examined for alkaloids. The decahydroquinoline (−)-cis-195A and two isomers of the pyrrolizidine 251K were found to be shared by microsympatric myrmicine ants and poison frogs. The proportions of the two isomers of 251K were the same in ant and frog.
    Type of Medium: Electronic Resource
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