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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultrafine cobalt particles have been reproducibly synthesized by decomposition of an organometallic precursor in the presence of a stabilizing polymer. The size of the stable monodisperse colloids thus obtained is seen to strongly depend on the nature of the polymer: around 4.2 nm diameter in polyphenylenoxide (PPO) and around 1.4 nm diameter in polyvinylpyrrolidone (PVP). Investigations by wide angle x-ray scattering (WAXS) and high-resolution transmission electron microscopy (HRTEM) give evidence for a size dependence of the structural organization, and hence for a close relationship between structure and synthesis conditions. Co/PPO particles exhibit a hexagonal compact structure with the metal–metal bond length of the bulk material while Co/PVP ones display an original structure. We show that the unusual features of the experimental data in Co/PVP clearly point to a nonperiodic polytetrahedral structure. Successful simulations of the HRTEM and WAXS results have been obtained using models built on the basis of a polytetrahedral arrangement. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The chemical educator 5 (2000), S. 296-305 
    ISSN: 1430-4171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using mathematics from the method of the exponential scale, crystals inner and outer structures are given. A number of fundamental crystal structures are described as mathematical functions. Plotting the equations gives the classical ball representation of the structures. In the case of intricate structures, the pedagogical interest lies in the possibility of describing the whole structure as the sum of very simple partial structures, each corresponding to a part of the equation. Structures given are primitive cubic packing, primitive hexagonal packing, face-centered-cubic close-packing, hexagonal close-packing, body-centered packing, CsCl, diamond, zinc blende, CaF2, ReO3, perovskite, NaCl, Mg3NF3, SiO2, Cu3Au, NiAs, wurtzite, and graphite. A crystal-structure dynamics is described. Varying a constant in the equation, it is possible to modify the representation of the structure from small ball-shaped atoms to packing of interconnected polyhedrons and finally to minima-like surfaces. This last description gives a much deeper understanding of the actual structure in term of forces and open spaces. The final, and maybe the main, interest of this concept of surfaces is the possibility of shedding light on the difficult problems of structure-property relationships.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6079
    Keywords: PACS. 41.85.Ew Beam profile, beam intensity – 42.50.Ar Photon statistics and coherence theory – 42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps – 42.79.-e Optical elements, devices, and systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The pixel by pixel calibration of a scientific CCD camera allows Poissonian statistics of the spatial fluctuations of an uniform enlightening to be retrieved in the full range of the camera dynamic. The procedure works efficiently for thermal as well as for laser sources, provided that the wavelength and the coherence properties of the source are chosen in order to avoid the formation of equal thickness fringes in the chip (etaloning effect). Calibration allows also the comparison at the shot noise level of images recorded at different places on the chip.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present, to the best of our knowledge, the first experimental demonstration by direct detection of the Bose-Einstein photon-number distribution of highly spatially multi-mode but temporally single mode spontaneous parametric down-conversion.
    Type of Medium: Electronic Resource
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