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  • Articles  (18)
  • Polymer and Materials Science  (9)
  • Computational Chemistry and Molecular Modeling  (7)
  • Porous medium  (2)
  • 1
    Electronic Resource
    Electronic Resource
    The effect of anisotropic permeability on free convective boundary layer flow in porous media (1995)
    Springer
    Transport in porous media 19 (1995), S. 79-92 
    Details
    ISSN: 1573-1634
    Keywords: Porous medium ; convection ; boundary layer ; anisotropy ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The effect of an anisotropic permeability on thermal boundary layer flow in porous media is studied. The convective flow is induced by a vertical, uniformly heated surface embedded in a fluid-saturated medium. A leading-order boundary layer theory is presented. It is shown that the thickness of the resulting boundary layer flow is different from that obtained in an isotropic porous medium. In general, an anisotropic permeability induces a fluid drift in the spanwise direction, the strength of which depends on the precise nature of the anisotropy. Conditions are found which determine whether or not the boundary layer flow is three-dimensional.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00716050
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  • 2
    Electronic Resource
    Electronic Resource
    Non-Darcy natural convection from a vertical wavy surface in a porous medium (1995)
    Springer
    Transport in porous media 20 (1995), S. 223-234 
    Details
    ISSN: 1573-1634
    Keywords: Porous medium ; convection ; boundary layer ; nonsimilarity ; inertia ; surface waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We examine the combined effect of spatially stationary surface waves and the presence of fluid inertia on the free convection induced by a vertical heated surface embedded in a fluid-saturated porous medium. We consider the boundary-layer regime where the Darcy-Rayleigh number, Ra, is very large, and assume that the surface waves have O(1) amplitude and wavelength. The resulting boundary-layer equations are found to be nonsimilar only when the surface is nonuniform and inertia effects are present; self-similarity results when either or both effects are absent. Detailed results for the local and global rates of heat transfer are presented for a range of values of the inertia parameter and the surface wave amplitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073173
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  • 3
    Electronic Resource
    Electronic Resource
    Localized functions on a circle (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 54 (1995), S. 351-359 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The derivation of hybrids as localized equivalent functions in the plane is discussed using the simultaneous eigenfunctions of the x and y position operators, as represented in a finite basis. It proves helpful, initially, to use complex exponentials as basis functions, but the transformation to a real basis is made later. The introduction of alias functions to produce commuting matrices is described. Full results are obtained for any number of functions in the plane. © 1995 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560540604
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  • 4
    Electronic Resource
    Electronic Resource
    A discrete look at localization (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 53 (1995), S. 189-205 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article introduces a set of localized orthonormal functions to serve as basis functions for quantum calculations. They are defined to be eigenfunctions of the position operator in a function space. Their properties, including their variances, for a one-dimensional system are developed. The application to simple harmonic motion is considered as an example and, in particular, the time evolution of an initially localized function is calculated and shown to be periodic. The theory can be interpreted as producing a discrete quantization of space with Hamiltonian interactions that are predominantly between nearest neighbors. These functions can also be used in approximate calculations. To illustrate their accuracy, the example of a Morse oscillator treated as a perturbation of a harmonic oscillator is reconsidered. It is shown that the localized functions in a variational calculation lead to a result that is a good approximation for the lowest states. Furthermore, the use of a wave function that is defined only at discrete points can be justified as the first approximation to this, so that its accuracy can also be discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560530206
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  • 5
    Electronic Resource
    Electronic Resource
    Localized planar atomic hybrids (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 54 (1995), S. 361-368 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The derivation of localized atomic hybrids in the plane is discussed using their definition as simultaneous eigenfunctions of the x and y position operators, when these are represented by commuting matrices in a finite basis. The use of alias functions, as introduced in the preceding paper, to produce commuting matrices is described and illustrated. Full results are obtained for any regular polygon. The extension to three dimensions allows the sp2 trigonal, sp2d square, and sp2d2 pentagonal hybrids to be derived. The theory also allows the radial factors to differ so that several shells of hybrids can be found at once. The double trigonal configuration is described as an example. The implications for any calculation of a molecular dipole moment are discussed. © 1995 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560540605
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  • 6
    Electronic Resource
    Electronic Resource
    Localized functions on a sphere (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 99-108 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article provides a fully consistent group theoretical procedure for finding atomic hybrids on a sphere and for relating them to the matrices representing the operators x, y, and z with respect to given basis functions. The tetrahedral, octahedral, and cubic hybrids based on the cube are derived. These functions are localized and directional. They can be used to describe valence aspects of atoms. © 1996 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of molecular organization in agarose sulphate (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1009-1029 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nongelling solutions of structurally regular chain segments of agarose sulphate show disorder-order and order-disorder transitions (as monitored by the temperature dependence of optical rotation) that are closely similar to the conformational changes that accompany the sol-gel and gel-sol transitions of the unsegmented polymer. The transition midpoint temperature (Tm) for formation of the ordered structure on cooling is ∼25 K lower than Tm for melting. Salt-induced conformational ordering, monitored by polarimetric stopped-flow, occurs on a millisecond time scale, and follows the dynamics expected for the process 2 coil ⇌ helix. The equilibrium constant for helix growth (s) was calculated as a function of temperature from the calorimetric enthalpy change for helix formation (ΔHcal = -3.0 ± 0.3 kJ per mole of disaccharide pairs in the ordered state), measured by differential scanning calorimetry. The temperature dependence of the nucleation rate constant (knuc), calculated from the observed second-order rate constant (kobs) by the relationship kobs = knuc(1 - 1/s) gave the following activation parameters for nucleation of the ordered structure of agarose sulphate (1 mg mL-1; 0.5M Me4NCl or KCl): ΔH* = 112 ± 5 kJ mol-1; ΔS* = 262 ± 20 J mol-1 K-1; ΔG*298 = 34 ± 6 kJ mol-1; (knuc)298 = (7.5 ± 0.5) × 106 dm3 mol-1 s-1. The endpoint of the fast relaxation process corresponds to the metastable optical rotation values observed on cooling from the fully disordered form. Subsequent slow relaxation to the true equilibrium values (i.e., coincident with those observed on heating from the fully ordered state) was monitored by conventional optical rotation measurements over several weeks and follows second-order kinetics, with rate constants of (2.25 ± 0.07) × 10-4 and (3.10 ± 0.10) × 10-4 dm3 mol-1 s-1 at 293.7 and 296.2 K, respectively. This relaxation is attributed to the sequential aggregation processes helix + helix → dimer, helix + dimer → trimer, etc., with depletion of isolated helix driving the much faster coil-helix equilibrium to completion. Light-scattering measurements above and below the temperature range of the conformational transitions indicate an average aggregate size of 2-3 helices.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250604
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic origin of conformation-sensitive contributions to polysaccharide optical activity: Vacuum-ultraviolet circular dichroism of agarose (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 327-333 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vacuum-uv CD of agarose solid films has been measured to 145 nm and shows a positive band near 180 nm and a larger negative band at around 152 nm. The positive band remains accessible in aqueous solution and has been used to characterize changes in molecular conformation and interaction during the sol-gel transition. The temperature profile of vacuum-uv CD shows sharp, discontinuous changes around the melting and setting points of the gel, which are interpreted in terms of cooperative intermolecular association through double helices, and pronounced hysteresis, which is discussed in terms of helix-helix aggregation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1979.360180209
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  • 9
    Electronic Resource
    Electronic Resource
    Peptide-bond distortions and the curvature of α-helices (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1087-1093 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent accessible peptide bonds in proteins exhibit a 1-3° compression of the OCN bond angle and a corresponding expansion of the NCCa bond angle, relative to buried peptide bonds. These changes are consistent with an increase in hydrogen bonding to the carbonyl oxygen accompanying solvent exposure (J. D. Dunitz and F. K. Winkler, (1975) Acta Cryst. B31, 251-263). For amphiphilic structures such as α-helices, systematic differences in peptide-bond geometry between solvent-exposed and buried residues will generate significant curvature. A decrease of 4° in the OCN bond angle between hydrophilic and hydrophobic sides of an amphiphilic helix will lead to smooth bending, with a radius of curvature of about 70 Å. This curvature is in the range observed for α-helices in proteins. Helix curvature is estimated to have only a small effect on the magnitude and direction of the helical dipole moment.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250609
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  • 10
    Electronic Resource
    Electronic Resource
    Total optical activity of agarose: Relation to observable transitions in the vacuum ultraviolet (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 959-973 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The changes in optical activity that accompany and characterize the coil-helix and helix-coil transitions of agarose in aqueous solutions and gels have been investigated by combined quantitative analysis of data from vacuum ultraviolet circular dichroism (VUCD) and optical rotary dispersion (ORD). VUCD of agarose in the high-temperature coil state shows a single accessible Gaussian band centered at ∼183 nm. In the helix state this band is blue-shifted by ∼9 nm, and the intensity is increased by a factor of ∼2.6. Spectra at intermediate temperatures can be fitted to within experimental error by linear combination of coil and helix spectra, the relative proportions required providing an index of the extent of conformational ordering. ORD spectra throughout the conformational transition have a common form and differ only in absolute magnitude. The temperature course of conformational ordering derived from ORD intensity is in close agreement with the values obtained from VUCD. In both the coil and helix states the accessible VUCD band is positive, while the overall ORD is negative, indicating strong negative CD activity at lower wavelength. The ORD contribution corresponding to the positive VUCD band was calculated by Kronig-Kramers transform, and it was subtracted from the total ORD to give the residual ORD from all other optically active transitions of the molecule. In both the coil and helix states, this residual ORD could be fitted to within experimental error by a single Gaussian CD band at ∼149 nm. A negative band at this wavelength has been reported previously for agarose films, but the observed intensity, relative to that of the lower energy positive band, is substantially smaller than the fitted value under hydrated conditions. In both the coil and helix states the total optical activity of agarose, characterized by observed ORD spectra, can be matched to within experimental error by Kronig-Kramers transform of the 149-nm negative band and the smaller positive band at higher wavelength, with no necessary involvement of deeper-lying transitions. The significance of this conclusion for fundamental understanding of carbohydrate optical activity is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250514
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