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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 3 (1971), S. 69-86 
    ISSN: 1572-9613
    Schlagwort(e): Protein ; helix-coil transition ; thermoelastic properties ; statistical mechanics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The effect of stress on the helix-coil transition in a protein or polypeptide is investigated using the methods of statistical mechanics. A case is treated in which the helical sections are regarded as flexible chains withvery long, freely “orienting” segments and another in which they are considered to be rigid rods. Thermoelastic relations are derived; and it turns out that, depending upon conditions, stress can induce the helix-coil transition in one or another direction or do nothing at all. The most probable situations either involve stress applied to a molecule initially helical, in which case the helix is stabilized, or stress applied to the coil form, in which case transformation to the helical form is induced. The helical form exhibits a very low modulus of elasticity (which we also compute), and it is speculated that preservation of, or transition to, the helical form under stress aids in the protection of living tissue from disruption when subjected to large applied strain. Real tissues involve highly organized or quasirandom networks of protein chains. The results of this analysis suggest that, insofar as the mechanical properties of the networks are concerned, the chains can be treated as quasiharmonic strings whose configurations (weighted by potential energy) can be enumerated in order to include entropy effects in the calculation of the network modulus.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 3 (1971), S. 191-210 
    ISSN: 1572-9613
    Schlagwort(e): Information theory ; coding ; statistical mechanics ; ensembles ; thermodynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This is the first of several papers dealing with the application of statistical thermodynamic methodology to the solution of coding and communication theory problems. Emphasis is placed on the various “ensemble techniques” of statistical mechanics, the words or “samples” of a message taking the place of molecules in the prototype physical system. Analogs of temperature, internal energy, pressure, chemical potential, volume, entropy, etc., are developed. The isomorphism with thermodynamics is complete and these quantities transform (for example, by partial differentiation) in exactly the same way as the prototype physical quantities. The methods are nicely applicable to coding cases involving sources with memory, in which case, correlation can be discussed in terms of analog “coupling energies” between signals or words so that the store of “many-body-problem” techniques can be used. In addition, the manipulative freedom stemming from the possibility of choosing from a multiplicity of ensembles constrained by “intensive” parameters proves a distinct advantage. A concrete example dealing with the choice of a compact code for a nonextended source with memory is presented. The compact code is derived, and some discussion is given concerning the breadth of its power spectrum. In a following paper, its autocorrelation function within the framework of “pulse code modulation” is derived and transformed by Wiener theory so that the power spectrum is directly exhibited (along with the spectra for several other cases).
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 3 (1971), S. 261-289 
    ISSN: 1572-9613
    Schlagwort(e): Pulse code modulation ; transmission time ; bandwidth ; statistical mechanics ; power spectrum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Employing the “statistical thermodynamic formalism” developed in an earlier paper, it is possible to determine “compact” sets of transmission times for the words of PCM (pulse code modulation) messages. In particular, we deal with pulses of zero or unit heights. These compact signals, which lead to shorter message times and eliminate redundancy even when successive words are correlated (Markov source), may, however, require additional bandwidth. We examine two simple cases where autocorrelation functions, and therefore power spectra, can be evaluated. In one case, that of the Markov source, it proves possible to accomplishboth shorter transmission time and narrower bandwidth (half-width of the power spectrum), showing that optimization of transmission times can be very worthwhile. Techniques for deriving autocorrelation functions are discussed at length.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 7 (1973), S. 143-159 
    ISSN: 1572-9613
    Schlagwort(e): Statistical thermodynamics of curved boundary layers ; scaledparticle theory ; equation of state ; cycle equation ; fluid-solid phase transition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The thermodynamics of curved boundary layers is combined with scaled particle theory to determine the rigid-sphere equation of state. In particular, the boundary analog of the Gibbs-Tolman-Koenig-Buff equation is solved for a rigid-sphere fluid, using the approximation that the distance between the surface of a cavity and its surface of tension is a function of the density only (the first-order approximation). This, in conjunction with several exact conditions onG, the central function of scaled particle theory, leads to an approximate rigid-sphere fluid equation of state and a qualitatively correct rigid-sphere solid equation of state. The fluid isotherm compares favorably with previous results (2.9 % error in the fourth virial coefficient), but due to the inaccuracy of the solid isotherm, no phase transition is obtained. The theory described here is to be contrasted with previous approaches in that a less arbitrary functional form forG is assumed, and the surface of tension and cavity surface are not assumed to be coincident. The “cycle equation” of Reiss and Tully-Smith is rederived by a simpler route and shown to be correct to all orders of cavity curvature, rather than only first order as was originally thought. A new exact condition, obtained from the compressibility equation of state, is used as a boundary condition for the “cycle equation” to determine the location of the equimolecular surface. This molecular calculation compares favorably (discrepancy of 〈2 %) with a thermodynamic calculation based on the boundary analog of the Gibbs adsorption equation and indicates the accuracy and consistency of the first-order approximation.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 8 (1973), S. 299-307 
    ISSN: 1572-9613
    Schlagwort(e): Statistical thermodynamics of curved boundary layers ; scaled particle theory ; equation of state ; cycle equation ; fluid-solid phase transition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The thermodynamics of curved boundary layers, with the assumption that the distance between the surface of a fluid cavity and its surface of tension is a quadratic function of the cavity radius, is applied to the exact thermo-dynamic expression forG, the central function of scaled particle theory. The coefficients in the quadratic representation are determined so as to satisfyall five of the known exact conditions onG valid for cavity radii between one-half and one molecular diameter. The results of the calculation are displayed as the hard-sphere equation of state, the boundary tension associated with the surface of tension, and the distance between the cavity surface and the surface of tension. Although the hard-sphere equation of state obtained by this method using all five conditions onG is more accurate than in the case where only two or three conditions are used, the original scaled particle theory, in whichG itself was represented simply by a quadratic function of inverse powers of cavity radius, still yields the more accurate equation of state. Nevertheless, the present approach limits approximations to the distance between the cavity surface and the surface of tension, a small quantity in itself. The path to a still more improved theory remains well defined, contingent upon the discovery of additional exact conditions, and does not depend, as in the original scaled particle theory, on a form forG arrived at in a somewhat ad hoc manner.
    Materialart: Digitale Medien
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