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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 4 (1988), S. 1096-1100 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1907-1918 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The continuous inversion from a water-in-oil (w/o) microemulsion at low temperatures to an oil-in-water (o/w) microemulsion at higher temperatures within the one-phase channel of water (0.6% NaCl)–n-decane–AOT microemulsion system is investigated by small angle neutron scattering (SANS). At constant AOT (surfactant) weight fraction γ of 12%, the structural evolution as a function of temperature takes place in different forms as the oil-to-water weight fraction α is varied from 15 to 90 %. At low o-w weight fractions (α=15 and 20 %) the microemulsions transform from a water-internal, oil-continuous structure at lower temperatures to an oil-internal, water-continuous droplet structure at higher temperatures jumping across an intermediate region of a lamellar phase (Lα). However, at higher o-w weight fractions (α=80 and 90 %) the evolution goes through a stage of percolation of the water droplets first into extended water clusters, then the structural inversion takes place probably through a transition of these water clusters into an entangled tubular structure. At equal oil-to-water volume ration (α=40%), the structure can be described as bicontinuous at both low and high temperatures. In this case we are able to extract two lengths characterizing the structure from SANS data using different models for the scattering length density fluctuation correlation function of a bicontinuous microemulsion.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2071-2082 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the temperature and coverage-dependent transformations of the ordered structures of oxygen on Pd(100). The four ordered structures are the chemisorbed c(2×2) and p(2×2) lattices, and the reconstructed p(5×5) and ((5)1/2×(5)1/2)R27° lattices. We present evidence that the p(5×5) reconstruction forms in an activated stepfrom c(2×2) regions. The onset of p(5×5) formation is associated with an increase in oxygen sticking coefficient. In thermal desorption, there are three states which can be correlated directly with the structure of the adsorbed phase during desorption: At lowest coverage, the α state shows the traits of second-order kinetics and is due to desorption from a disordered adlayer. At higher coverage, the β state appears and is due to desorption from a layer with c(2×2) order. There is a lower barrier to desorption in the β state than in the α state because of the repulsive second-nearest-neighbor interactions in the c(2×2). At highest coverage, the sharp and narrow γ state emerges. This is accompanied by decomposition of the ((5)1/2×(5)1/2)R27° reconstruction, in which cooperative stabilization of the reconstruction by oxygen atoms effectively creates strong quasiattractive oxygen–oxygen interactions. There are interesting similarities between the oxygen-stabilized reconstructions of Pd(100) and the initial stages of oxidation of Ni(100), as well as the oxygen-stabilized reconstructions of Pt(100). The data are obtained from low-energy electron diffraction coupled with a computer-interfaced Video camera, Auger electron spectroscopy, and thermal desorption spectroscopy.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 825-826 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In the course of a discussion of the nature of an ambiguity in the indexing of Renninger peaks the possibility was discovered of distinguishing some opposite directions in a cubic crystal without recourse to anomalous scattering. A multiple-diffraction experiment performed on a (111) Ge plate rotated about [222] enabled distinction between the [1{\bar 1}0] and [0{\bar 1}1] directions to be made. The azimuthal angles counted from alternative zero meridians containing [1{\bar 1}0] or [0{\bar 1}1] are the same, but give rise to peaks indexed hkl and 2 - l,2 - h,2 - k respectively. However, dynamically equivalent situations 222, hkl/(2 - h,2 - k,2 - l) and 222, (2 - l,2 - h,2 - k)/lhk are geometrically different, being distinguished as Bragg-Laue and Bragg-Bragg, respectively, or vice versa.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 876-889 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Multiple simultaneous Bragg diffraction effects of X-rays in quaternary III-V liquid-phase epitaxial thin layers are investigated with both photographic and counter detection methods. For the photographic investigation, a divergent source is used. The geometric aspects of this type of diffraction, affected by lattice mismatch between epitaxial layers and substrates, are discussed for cases involving five-, six- and eight-beam reflections. The lattice mismatches in directions parallel and perpendicular to the interface normal of InGaAsP/ InP, determined from a single divergent-beam photograph, are obtained. For the counter detection study, a collimated incident beam and several single and double heterojunction samples, with large lattice mismatches are used. A kinematical treatment for a general n-beam diffraction, from double- and triple-layer systems, is derived to account for the measured intensities.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 41-48 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The use of exponential functions as an approximation for reflection powers leads the intensity problem of n-beam kinematical diffraction to an eigenvalue problem. It is solved in the way similar to an n-beam Borrmann dynamical diffraction problem. Besides the intensities of Bragg-reflected beams, the excitation of modes concerning the intensity attenuation is also calculated for highly absorbing infinitely thick crystals. Experiments of multiple reflection from GaAs, InAs and InP single crystals for Cu Kα radiation were carried out. Comparison between the experimental and calculated reflected intensities for several 2-, 3-, 4-, 5- and 8-beam cases are given and discussed.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 45 (1989), S. 870-878 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The method proposed by Chang & Tang [Acta Cryst. (1988), A44, 1065-1072] for quantitative determination of phases of X-ray reflection from three-beam diffraction profiles is applied to an organic crystal of (2R, 3 R)-3-acetoxy-5,7-dihydroxy-6-methylflavanone, with a mosaic spread of 0.08°. The expression for the kinematical diffraction intensities is modified according to the kinematical theory of X-ray diffraction in the multibeam regime. Three-beam Umweganregung and Aufhellung diffraction profiles are analyzed. With the help of the modified intensity expression, the crystal symmetry imposed by the space group and the three-beam diffraction geometry, four acentric phases and fourteen centric phases of structure-factor triplets are determined.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 98-101 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The relation Sp = SL SR between the signs of the triplet phase products Sp, the multiple diffraction line profiles SL and the crystal lattice rotations SR is applied to the structure determination of a centrosymmetric Cs10Ga6Se14 crystal [space group C2/m, a = 18.233 (7), b = 12.889 (5), c = 9.668 (3) Å, β = 108.2°, z = 2]. This structure could not be solved by the ordinary MULTAN program, including MUL TAN-80. From the profile analysis of the multiple diffraction pattern of 311 using a four-circle single-crystal diffractometer with Cu Kα radiation, 12 phase relations among closely linked reflections are determined. Four possible sets of 14 reflection phases are deduced. Using these four sets as the starting phases for MULTAN-74, 225 correct phases are developed. The final E map shows all the atomic positions of Cs, Ga and Se. The structure refinement gives R = 0.047, Rw = 0.053 [1907 reflections with I 〉 2σ(I)]. Details about the procedure are given.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 1073-1078 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The method proposed by Chang & Tang [Acta Cryst. (1988). A44, 1065-1072] of quantitative determination of X-ray reflection phases from multiple diffraction profiles is applied to nearly perfect crystals of gallium arsenide. The detailed intensity-profile-analysis procedures are given. Multiple diffraction profiles obtained with a conventional X-ray source and synchrotron radiation are subjected to this analysis. It is found that, for this particular diffraction example, errors as small as 15° in phase determination are achieved. Errors due to the theoretical approximation, peak position measurement and scaling factor are also discussed.
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