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ABSTRACT:The effects of microstructural rearrangements during the stretching of semicrystalline polymers and the resultant inhomogeneous strains are modeled by rigid spheres embedded in a polymer network. This results in strain concentrations in the network, which is then caused to yield at realistic overall strains. To simulate the collapse of the original spherulitic morphology, the radii of the spheres decrease at a rate dependent on the shear stress imposed on them by the surrounding network. This results in time-dependent behavior. The resultant large strain viscoelastic model is implemented in a commercial finite element code and used to predict shapes of necking polypropylene sheet specimens at 150°C. Rate dependence of stress and stress relaxation are also predicted, and the model is shown to be generally effective in its predictions of shapes and forces up to large deformations.

We have measured the state-to-state differential scattering cross section (DCS) for a rotationally inelastic process using an entirely spectroscopic method. The system studied was Li2(A 1 Sj)-Xe and the method utilizes two color sub-Doppler double resonance. Analysis of the shape of the double resonance line yields the final distribution of relative velocity vectors. This represents the first measurement of a state-to-state DCS using thermal cell spectroscopy In addition we have determined, also for the first time, the dependence of the state-to-state DCS on initial relative velocity. Results are presented for the Aj = 6 rotationally inelastic process.PACS numbers: 34.50.Ez, 33.70.Jg Scattering cross sections differential in angle are generally measured by molecular beam methods. In molecular scattering, quantum state selection and detection are an essential prerequisite to meaningful analysis of the data and such enhancements add greatly to the cost and complexity of the experiment. An alternative approach is through Doppler-resolved double resonance spectroscopy [1,2] which may be performed in simple collision cells.Here we demonstrate that velocity selected double resonance (VSDR) may be used to give state-to-state cross sections for atom-molecule rotationally inelastic collisions that are differential in angle and relative velocity. These are the first purely spectroscopic measurements of such quantities for inelastic processes in molecules.That information on angular distributions is contained in double resonance line shapes of atoms in thermal cells was first pointed out by Berman [3]. Gottscho et al.[4] extended this to rotationally inelastic collisions of molecules and determined energy averaged, most probable scattering angles for BaO colliding with argon. Of relevance are the experiments of Kinsey, Pritchard, and coworkers [5,6] who developed laser methods to determine velocity distributions, the velocity selection by Doppler shift method of Smith et al [7,8], and most recently, a fully polarization-resolved, four-vector experiment by Collins, McCaffery, and Wynn [9]. Alternative treat-Coherent 699-29 Coherent Innova 100 PC i Control 3392 LZJ FIG. 1. Velocity selected double resonance experimental setup.

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