Cellulose: refutation of a folded-chain structure.

Calculations of modulus of elasticity for extended-and folded-chain configurations have been compared with the experimental observations of mechanical properties of native cellulosic fibers. A recent folded-chain proposal is incompatible with the experimental evidence.

Convective instability of magnetic fluids under alternating magnetic fields.

A theoretical investigation of the convective instability problem in the thin horizontal layer of a magnetic fluid heated from below and under alternating magnetic fields is carried out. Both the quasistationary model and the model with internal rotation with vortex viscosity are considered. Floquet theory is used for discussing the existence and stability boundaries of the differential equations with periodic coefficients. The Chebyshev pseudospectral method is employed to discretize the partial differential equation, and QZ algorithm is used for solving the eigenvalue problem. For quasistationary model, both free-free and rigid-rigid boundary cases are considered, whereas for the model with internal rotation only rigid-rigid boundary condition is studied. The effect of frequency variations on the stability are considered in all the cases.

Convective instability of magnetic fluids.

A theoretical investigation of the convective instability problem in the thin horizontal layer of a magnetic fluid heated from below is carried out. The effects of the relaxation time tau and the vortex (rotational) viscosity xi are considered and discussed. The Chebyshev pseudospectral method is employed to solve the eigenvalue problems and numerical calculations are carried out for a number of magnetic fluids and in full range of the magnetic field. A variety of results under gravity-free conditions are also presented and the critical temperature gradient are determined for a variety of situations. It is shown that the consideration of (xi,tau), in the stability analysis, is most effective in the thin layer of the fluid and at low values of Langevin parameter alpha(L).

Generalized dispersion in a synovial fluid of human joints.

An unsteady convective diffusion in a synovial fluid of human joints modeled as a power-law fluid is studied using the generalized dispersion model of Gill and Sankara-subramanian [12]. The contributions of convection and diffusion, and pure convection on the dispersion of nutrient are investigated in detail. It is shown that the effect of decrease in non-Newtonian parameter is to decrease the dispersion coefficient. The mean concentration distribution appears to increase as the non-Newtonian parameter decreases upto a certain value of the axial distance. Beyond this point, however, the reverse pattern is observed.