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  • 1
    ISSN: 1741-0444
    Keywords: Accelerometry ; Gait analysis ; Walking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1741-0444
    Keywords: Accelerometers ; Body movement ; Elderly ; Gait ; Rehabilitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0749-1581
    Keywords: Carbon-13 relaxation ; Molecular motion ; Rotational barriers ; Dicyclohexyl compounds ; Traction fluids ; Molecular modelling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four dicyclohexyl compounds were studied, one of which is a traction fluid and the remainder have related structures in which the cyclohexane rings are separated by two or three carbon atoms. Carbon-13 NMR T1 and NOE data were obtained for the four compounds at 22.50 and 100.62 MHz over a wide temperature range. The data were fitted simultaneously to either a reduced Lorentzian spectral density or to a ‘model-free’ two-correlation time spectral density. For the first time it has been possible to observe the tracking from the full ‘model-free’ two-correlation time spectral density to the reduced Lorentzian spectral density. From the correlation times and activation energies derived from these fittings, it can be concluded that all the compounds have semi-rigid structures. Computer modelling of the structures and molecular mechanics calculations of the rotational barriers gave results in agreement with those from the NMR data. Similarly, it was found that the friction coefficients of the compounds correlate with the NMR and molecular mechanics conclusions, namely that the increased rigidity produced by the introduction of methyl groups into the linkage between the cyclohexane rings leads to a more effective traction fluids. Hence it seems to be feasible to design new traction fluids in the laboratory.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0749-1581
    Keywords: Dicyclohexyl derivatives ; 13C spin-lattice relaxation times ; High-pressure NMR ; Rotational-translational coupling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four dicyclohexyl compounds were investigated, one of which is a traction fluid and the remainder have related structures in which the cyclohexyl rings are separated by two or three carbon atoms. Carbon-13 spin-lattice relaxation times have been measured at 25.16 MHz at pressures up to 200 MPa over the temperature range 280-329 K. High-pressure relaxation data have been successfully interpreted in terms of the ‘model-free’ approximation. A pressure-dependent rotational coupling parameter, κ, was evaluated from a modified Stokes-Einstein-Debye relationship using experimentally determined pressure-dependent rotational correlation times. The smallest value of κ was found to be associated with the most rigid and least-extended molecule, showing that molecular shape has a significant effect on the rotational-translational coupling. The values obtained for the activation volumes derived from methyl group data suggest that barriers to internal motion are governed by intramolecular effects. It has been demonstrated that high-pressure 13C relaxation measurements can provide a powerful means of studying the relationship between molecular rigidity and the macroscopic behaviour of functional fluids.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0749-1581
    Keywords: High pressure ; Molecular motion ; Carbon-13 relaxation ; Octyl chains ; Tetraoctyltin ; Polydecene ; Model lubricants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR spin-lattice relaxation times, T1, and nuclear Overhauser effect data were obtained for neat tetra-n-octyltin at 22.5 and 100.6 MHz over a wide temperature range. T1 values were also measured at 25.16 MHz at pressures up to 211 MPa. The ambient-pressure data were fitted to the ‘model-free’ two-correlation time spectral density with a temperature-dependent order parameter, S2. The pressure data were interpreted by assuming that internal motions of the octyl chain are independent of pressure while the overall (tumbling) motion and S2 are pressure dependent. The values of the motional parameters for tetra-n-octyltin lie in the ranges expected for compounds containing long n-alkyl chains. The results show that this approach is applicable to complex liquids such as synthetic lubricants of the polydecene type.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0749-1581
    Keywords: NMR relaxation ; Carbon-13 ; Deuterium ; ESR ; Micelles ; Surfactants ; Spin probes ; Alkyl chains ; Molecular dynamics ; ‘Two-step’ model ; ‘Three-step’ model ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multi-frequency relaxation studies combined with the ‘two-step’ and ‘three-step’ models for molecular motion have been applied to a range of anionic surfactant molecules. From the internal dynamic parameters (τf and S) conclusions have been drawn about the dependence of surfactant molecular dynamics inside micelles on molecular structure, and two unusual conformations have been identified. Slow correlation time (τs) data have also been obtained for these compounds. Three deuteriated surfactant molecules were subjected to the ‘three-step’ model and data are presented showing how the dimensions of the non-spherical micelles vary with temperature. An ESR spin probe study has been carried out on the compounds giving probe rotational correlation times at various temperatures. Information on alkyl chain packing at or near the water/micelle interface can be obtained from the derived thermodynamic parameters.
    Additional Material: 8 Ill.
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  • 7
    ISSN: 1573-5117
    Keywords: long-term changes ; benthos ; organic enrichment ; temperature anomalies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Population fluctuations over a twenty year period in the macrobenthic communities of Loch Linnhe and Loch Eil, on the western coast of Scotland, are related to changing organic inputs to the area and to long-term temperature changes. It is suggested that the carrying capacity of sedimentary benthos is dependent on organic input, but that the species composition of the communities may be modified by climatic fluctuations acting on the spawning success and subsequent recruitment of particular species. Confirmation of such hypotheses generated from field time-series data should be obtained by experimentation.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract There is considerable debate about the methodologies used to estimate VNTR (Variable Number of Tandem Repeats) multi-locus genotype frequencies or odds of inclusion in forensic cases. To compare two of the methods in use, allele frequency distributions among six populations were compared and the effect of population heterogeneity on VNTR multi-locus genotype frequency estimation was examined. Genotype frequencies estimated from single population data were one or two orders of magnitude smaller than those estimated by picking the highest allele frequency in a group of subpopulations to estimate genotype frequencies using a ceiling principle. The average change does not appear to be very sensitive to the set of subpopulations used; four locus frequencies still give inclusion odds of one in a million or less. We think that use of the ceiling principle solves both the statistical problem engendered by subpopulation heterogeneity and the legal problem of assuming that the prepetrator and suspect belong to the same subpopulation. The counterintuitive fact of human genetic polymorphism is that it is easier to identify an individual than it is to identify the subpopulation, ethnic group or race to which that individual belongs.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1301-1303 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present measurements of differential transmission and four-wave mixing in GaAs quantum well structures at 1.8 K near the inhomogeneously broadened lowest heavy-hole (hh1) exciton resonance using narrow band cw excitation. The data show an increase in absorption and an excitation lifetime of order 1–10 μs outside the spectral hole produced by the pump. The long lifetime and the experimentally determined absence of excitation spatial diffusion in this region suggests that optical absorption produces electron-hole pairs that are correlated but separately localized due to disorder. A phenomenological model is proposed to explain the nonlinear response based on two-photon absorption.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 63 (1941), S. 1361-1362 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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