This thesis contains the following papers:
1) A new class of g-modes in neutron stars (Astrophys. J., 395, 240 (1992)):In the fluid core of a neutron star, the ratio of the number densities of chargedparticles (protons and electrons) to neutrons is an increasing function of the massdensity. This composition gradient stably stratifies the matter, giving rise to g-modeswith periods ranging upward from a few milliseconds. Some of these modesare computed and their damping mechanisms are discussed.
2) Magnetic field decay in isolated neutron stars (Astrophys. J., 395, 250(1992)): We investigate mechanisms that promote the loss of magnetic flux froman isolated neutron star. Ambipolar diffusion involves a drift of the magnetic fieldand charged particles relative to the neutrons, opposed by frictional drag. Variantsof it include both the buoyant rise and the dragging by superfluid neutron vorticesof magnetic flux tubes. The charged particle flux decomposes into a solenoidaland an irrotational component. The irrotational component perturbs the chemicalequilibrium, generating pressure gradients that effectively choke it. The solenoidalcomponent can transport magnetic flux from the outer core to the crust on a shorttimescale. Flux that threads the inner core is permanently trapped unless particleinteractions can rapidly smooth departures from chemical equilibrium. We speculatethat Hall drift may lead to a turbulent cascade of the magnetic field in thesolid crust, terminated by ohmic dissipation at small scales.
3) The spin-up problem in helium II (To appear, J. Low Temp. Phys., 92 (1/2)(July 1993)): The laminar spin-up of helium II is studied by solving the linearizedtwo-fluid equations in a simple case. No direct interactions between vortex linesand container walls are included. Two mechanisms are identified for the transferof angular momentum from the container to the interior fluid. Both involve apoloidal secondary flow. An analytic expression for the spin-up time is found.
