PACS. 62.20.Qp -Tribology and hardness. PACS. 68.35.Ct -Interface structure and roughness. PACS. 91.60.Ba -Elasticity, fracture, and flow.Abstract. -We model numerically the partial normal contact of two elastic rough surfaces with highly correlated asperities. Facing surfaces are unmated and described as self-affine with a Hurst exponent H. The numerical algorithm is based on Fourier acceleration and allows for numerous and large system computations. We find that for H = 0.6 and H = 0.8, the force F scales as A 1.1 , where A is the contact area. This is in contrast to the law F ∼ A (1+H)/2 , predicting an exponent of 0.8 and 0.9, respectively, which was suggested by Roux et al. (Europhys. Lett., 23 (1993) 277). We propose an explanation for this discrepancy.
Two -wavelength laser ranging experiments with subpicosecond temporal resolution are described. To provide these experiments a reliable passively mode -locked Nd:YAP laser with two saturable dyes in the same laser cavity was specially designed. For laser pulses recording the commercial anglo-soviet Imacon 500 streak camera fitted with the PV -001 tube and matched with SIT -vidicon and computer data handling system were employed.The possibilities for further increasing of resolution and other recording characteristics of the developed installation are briefly discussed.
A brief review of established methods shows that only with the Berthelot technique is it possible to see a finite volume of liquid in sustained mechanical tension. A short discussion of the practice and theory reveals two uncertainties with the conventional technique : that of the determination of a true filling temperature, and the influence of compliance by the glass on the tension developed. A description is then given of a modified apparatus with which these difficulties do not arise. The tube is formed into a coil which deflects sufficiently to indicate internal pressure or tension, and by monitoring these deflections with a distance meter a record of pressure/ tension against temperature can be made. The course of a typical run is shown from which the excess pressure, filling temperature and limiting tension may all be estimated with much greater precision than befoie. The orders of magnitude of the results obtained are indicated, and a possible influence of non-uniform gaseous supersaturation is suggested.
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