Condensed Matter Theory

Abstract:

Regional cooling of human sensory nerves increases the amplitude and surface area of an evoked sensory compound action potential (SCAP). It has been proposed that these changes are due to cold-induced slowing of Na+ inactivation. Na+ inactivation is also the main voltage-dependent event that underlies the refractory period in myelinated nerve. Therefore, if slowed Na+ inactivation causes the increased SCAP amplitude and area seen in focal cooling, a parallel temperature-dependent change should also occur in the SCAP refractory period. We compared the duration and magnitude of the relative refractory period to the total surface of a median nerve SCAP at 5 intervals of increasing temperature, from 24 degrees C to 36 degrees C. In 5 control subjects, the SCAP surface area and the relative refractory period increased 4-5-fold in parallel and revealed a non-linear relation to temperature change. Prolongation of the duration of individual nerve fiber potentials from slowed Na+ inactivation is proposed as one explanation of these temperature-related changes.

Abstract:

The structures and phases developed in a variety of polysomatic series (e.g. the biopyriboles (M.A. 78-4032) and the sheet silicates) are shown to be similar to those predicted by a simple spin model, the axial next-nearest-neighbour Ising (ANNNI) model, in a magnetic field. The authors argue that the different polysomatic structures can be considered as thermodynamically stable phases composed of ordered sequences of chemically distinct structural modules. It is suggested that the key factors determining their stability are: 1) the chemical potential, which controls the proportion of the different modules and 2) the competing interactions between first and second neighbour modules within the structures.-R.A.H.