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The shear response of a model polymer–clay gel is measured using small-angle neutron and light scattering, optical microscopy, and rheometry. As the flow disrupts the transient network that forms between clay and polymer, coupling between composition and stress leads to the formation of a macroscopic domain pattern, while the clay platelets orient with their surface normal parallel to the direction of vorticity. We discuss similarities with shear-induced structural transitions observed in other complex fluids, and we offer a physical explanation for the orientation of the clay platelets. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Non-linear analysis of a gyrotron using an axially grooved rectangular waveguide operating at the high harmonic I of the cyclotron frequency Ω[sub c] is given. We use 120 electrons in the simulation of the electron beam. The growth rate, electric field, relativistic factor γ and phase factor are calculated as functions of the slip parameter χ = lΩ[sub o]/ωγ[sub o] for the chosen optimized operating parameters of the gyrotron. Efficiency of ∼20% in the electron-beam frame is possible for the sixth harmonic of the cylotron frequency which increases to 58% in the second harmonic. [ABSTRACT FROM AUTHOR]

Describes developments in methods for characterizing chemical structure and molecular motion in polymers in the United States. Use of two-dimensional nuclear magnetic resonance; Properties of liquid-crystalline polymers; Effects of isotope in polymer melts.

Studies the development of a thermally stable, nonspiking ohmic contact to p-GaAs based on the solid-phase regrowth mechanism. Contact resistivity as a function of annealing temperature; Planar interface between the metallization and the GaAs substrate after annealing; Proposed reaction that leads to the formation of the ohmic contact.

Discusses the use of the principle of solid phase regrowth (SPR) to induce compositional disordering in superlattice structures compared to the conventional diffusion method. Requirement of SPR of thin film deposition and annealing; Improvement of the crystal quality and the photoluminescence signals emerging from the disordered region with increasing processing temperature.

We have studied the chain conformations of fullerenol-derived star polymers in two organic solvents using small-angle neutron scattering (SANS). The SANS results indicate that the six poly(urethane-ether) arms, chemically bonded on the fullerenol of the C[sub 60]-based star polymer, have a Gaussian chain conformation in toluene. However, these arms exhibit a pronounced excluded-volume effect in dimethylformamide solutions. We use a scattering model, with the polydispersity of the polymer taken into account, and a fractal model to extract the radius of gyration R[sub g] values and the persistence lengths of the C[sub 60]-star polymers in these two organic solutions. [ABSTRACT FROM AUTHOR]