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At least 325 records · Page 18

Hard tissue as a composite material. I - Bounds on the elastic behavior.

Recent determination of the elastic moduli of hydroxyapatite by ultrasonic methods permits a re-examination of the Voigt or parallel model of the elastic behavior of bone, as a two phase composite material. It is shown that such a model alone cannot be used to describe the behavior of bone. Correlative data on the elastic moduli of dentin, enamel and various bone samples indicate the existence of a nonlinear dependence of elastic moduli on composition of hard tissue. Several composite models are used to calculate the bounds on the elastic behavior of these tissues. The limitations of these models are described, and experiments to obtain additional critical data are discussed.

Katz, J. L.↗

Upper bound on compression ratio for run-length encoding.

Run-length encoding is a scheme which has been used to remove redundancy from video signals. Based upon a first-order Markov model of video data, an upper bound on compression ratio is found for run-length encoding. It is shown that at best run-length encoding will give a compression ratio which is approximately 60% of the maximum attainable value. This percentage is fairly independent of the particular picture involved.

Gray, K. G.↗

Curved space cosmological bounds on the time variation of G.

Additional quantitative and revealing arguments are given in favor of author's previous suggestion (1971) that the introduction of pressure results in a decrease in the theoretical upper bound on the time variation of G, as predicted by the Brans-Dicke theory (1961) for Friedmann-type expanding cosmologies in flat space, and that this suggestion holds in curved spaces as well. Moreover, it is shown that the curvature contribution to G is of the same order of magnitude as the flat space contribution and adds to it or subtracts from it for positive or negative curvatures respectively.

Morganstern, R. E.↗