The reaction e+e~e+e m. m has been analyzed using 97 pb ' of data taken with the Crystal Ball detector at the DESY e e+ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for yy~m. m. for n m invariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for 8'=m 0 0 (0.8 GeV, which is below 0.6 GeV, in good agreement with a theoretical prediction 'tr n' based on an unitarized Born-term model. At higher invariant masses we observe formation of the ft(1270) resonance and a hint of the fo(975). We deduce the following two-photon widths: I rr(f, (1270)) =3.19+0. 1620 z, keV and I "(fo( 975)) (0.53 keV at 90% CL. The decayangular distributions show the m~system to be dominantly spin 0 for W &0.7 GeV and spin 2, helicity 2 in the f, (1270) region, with helicity 0 contributing at most 22% (90% C.L.).

On a set of strips of ultraoriented polyethylene of ultrahigh molecular weight the thermal diffusivity has been measured at room temperature. The draw ratio was between 12 and 250. The diffusivity increases with draw ratio and begins to level off at about X = 50. The maximum diffusivity a ~1.9 X 10~5 m2/s corresponding to a thermal conductivity of k = 37.5 W/mK obtained in the stretching direction is 4 times that of steel. In the perpendicular direction the diffusivity decreased to a = 10'7 m2/s (i.e., half its initial value). The plot of conductivity versus modulus enables an extrapolation to the ultimate modulus (300 GPa), yielding k" < 80 W/mK. This value being higher than that of many metals corresponds to a crystal in the impurity-governed range, i.e., the lower limit of crystal thermal conductivity.

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An analysis of micro-hardness and elastic modulus data for different iamellar systems in the light of both eutectoid copolymer and chain folded Iamellar microphases is presented. A novel thermodynamically derived expression offering a fair description of hardness (stress required to plastically deform a crystal) of autonomous non-homogeneous microphases in terms of the average crystal thickness, including a defective surface boundary is developed. The present results characterize the mechansim of plastic deformation as primarily governed by the initial mosaic-block structure controlling the "solid state" mechanism underlined. The average dimensions of the remaining blocks after crystal destruction are thus related to the original block dimensions before plastic deformation. Within this context it is shown that the dissipated energy for crystal destruction increases very rapidly with the molar mass-function of crystalline material.The elastic deformation of these lamellar systems at small strains is correlated to the rubber-like behaviour of the cluster-network. Finally, the role of the average thickness of the non-homogeneous microcrystallites is stressed as describing concurrently the elastic and plastics properties of the polymer allowing a quantitative description of the correlation found between micro-hardness and elastic modulus.