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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Europhysics news 28 (1997), S. 129-132 
    ISSN: 1432-1092
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 11 (1985), S. 225-237 
    ISSN: 1432-1017
    Keywords: Solvent structure ; hydrogen bond networks ; computer simulation ; B12 coenzyme crystals ; probability density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Both the ordered and disordered solvent networks of vitamin B12 coenzyme crystal hydrate have been generated by Monte Carlo simulation techniques. Several different potential functions have been use to model both water-water and water-solute (i.e., water-coenzyme) interactions. The results have been analysed in terms of the structural properties of the water networks, such as mean water oxygen and hydrogen positions, coordination of each water molecule, and maxima of probability density maps in all four asymmetric units of this crystal. The following results were found: (I) Within each asymmetric unit only one hydrogen bonding network was predicted although there were several hydrogen atom positions for any one solvent molecule (defined as maxima in probability density). (II) Reasonable agreement was obtained between predicted and experimental positions in the ordered solvent region, independent of the potential function used. (III) The positions of the calculated probability density maxima for the disordered channel region were different in different asymmetric units; this led to different simulated hydrogen bond networks which were not always consistent with the experimentally determined alternative (lower occupancy) sites. The results suggest that it is advisable to simulate more than one asymmetric unit if one wishes to look at disorder in the solvent regions. Probability density maps were qualitatively very useful for picturing these disordered regions. However, there were no significant differences between quantitative results predicted using either average atomic positions or maxima of the probability density distributions. Problems in quantifying agreement between experimental and predicted disordered solvent networks are discussed. The potential which included hydrogen atoms explicitly (EMPWI) seemed to give the best overall agreement, mainly because it was successful in predicting the unusually short hydrogen bonds which are found in this crystal.
    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 94 (1991), S. 6770-6775 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Inelastic incoherent neutron scattering (IINS) cross sections have been measured for the recovered high-pressure phases of ice, ices II, V, VI, and IX (H2O) and ices II and IX (D2O) in the energy range from 2 to 150 meV at 20 K using the TFXA (time-focused crystal analyzer) neutron spectrometer on the ISIS pulsed neutron source at the Rutherford-Appleton Laboratory. The excellent resolution of the TFXA (less than 2%) covers the whole range of translational and librational modes for the ices investigated and enables us to identify the fine structures in their spectra. Hence a direct comparison between the amplitude-weighted phonon density of states derived from the experimental spectrum and from a lattice dynamic calculation is possible [E. Whalley and J. E. Bertie, J. Chem. Phys. 46, 1271 (1967); J. E. Bertie and E. Whalley, ibid. 40, 1646 (1964)]. The spectra from these polymorphic ices show many new features in the translational region, which are not visible using infared and Raman techniques. In the librational band region, the general features vary remarkably between phases. Thus, for instance, ice II, in which the protons are ordered, shows more structure in this region and has a sharper low-energy cutoff than do the other phases examined. The most significant observation is that the low-energy cutoff is characteristic of the phase. Relative to ice Ih, there is a shift of 4.3 meV for ice IX, of 8.8 meV for ice II, 8.6 meV for ice V, and 12.2 meV for ice VI.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 3928-3934 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: No reliable structural data have been reported on ice II under pressure, earlier work in the literature relating either to samples recovered to ambient pressure or the helium hydrate that is formed when helium is used as the pressurizing medium. We report structural refinements of helium-free ice II at three points in the phase's region of stability. The structural differences from the helium-affected structure are significant, and can be related to the mainly repulsive interaction between the helium and both the oxygen and hydrogen atoms of the ice framework. These repulsions explain, among other changes, the different behaviors of the a (expansion) and c (contraction) lattice parameters, and the change in compressibility on the inclusion of helium. © 2002 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 98-100 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A table is given of putative solutions to the Fejes problem: to find the maximum value of the smallest angular distance between any two of N points movable on the surface of a sphere. Values of N run without omission up to 27 with six sporadic cases thereafter. Some applications of this system as a model are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 213 (1967), S. 1079-1082 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Heats of fusion of inert gases can be calculated using a random close packed model of the liquid and intermolecular potential functions of the Lennard-Jones 6–12 type. Experimental agreement is improved by allowing small decreases in the nearest neighbour distances on melting. This might be ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 214 (1967), S. 265-266 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We cannot agree that wall effects are eliminated by using a flexible balloon: a glance at Fig. 1 of their article in fact shows very clearly the existence of large areas of highly ordered regular packing. Previous work on this wall effect2,3 has shown that regular crystalline patches are induced on ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 257 (1975), S. 120-122 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We thought it worthwhile to 'relax1 the '1968' (ref. 10) Bernal sphere-packing model under a realistic interatomic potential function to observe which of the resultant geometrical changes can occur fairly easily in an intially dense packing, as distinct from those which may need to be induced in ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 256 (1975), S. 522-522 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] GOTOH AND FINNEY REPLY-We are aware of the numerical closeness of 2/n and 0.6366, but until now had no good nonnumerological reason for asserting its significance. We are grateful to Gamba for pointing out the possible use of integral geometry, and will follow up the The average volume of the ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 215 (1967), S. 269-270 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] For a change of state, using the second law U=-pV+TS where U is the initial energy change of 1 mole, p is the external pressure, T the temperature, and S the entropy change. For triple point calculations1 the term p V is negligible; for pressures an order of magnitude higher, it is not. Using ...
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