No abstract

No abstract

Superconducting states with "extended s-wave" symmetry have been suggested in connection with recent ARPES experiments on BSCCO. In the presence of impurities, thermodynamic properties of such states re ect a residual density of states N (0) for a range of concentrations. While properties re ecting N (!) alone will be similar to those of d-wave states, transport measurements may be shown to qualitatively distinguish between the two. In contrast to the d-wave case with unitarity limit scattering, limiting low-temperature residual conductivities in the s-wave state are large and scale inversely with impurity concentration.

We study the response of a Hodgkin-Huxley neuron stimulated by a periodic sequence of conductance pulses arriving through the synapse in the high frequency regime. In addition to the usual excitation threshold there is a smooth crossover from the firing to the silent regime for increasing pulse amplitude gsyn. The amplitude of the voltage spikes decreases approximately linearly with gsyn.In some regions of parameter space the response is irregular, probably chaotic. In the chaotic regime between the mode-locked regions 3:1 and 2:1 near the lower excitation threshold the output interspike interval histogram (ISIH) undergoes a sharp transition. If the driving period is below the critical value, Ti < T * , the output histogram contains only odd multiples of Ti. For Ti > T * even multiples of Ti also appear in the histogram, starting from the largest values. Near T * the ISIH scales logarithmically on both sides of the transition. The coefficient of variation of ISIH has a cusp singularity at T * . The average response period has a maximum slightly above T * . Near the excitation threshold in the chaotic regime the average firing rate rises sublinearly from frequencies of order 1 Hz.

A very important reference was inadvertently omitted from the list of references in this paper. Paydarfar et al.[1] studied squid giant axons in a bistable regime, where the stable states are in close proximity of each other. They found that noise was capable of annihilating the spiking action. When noise amplitude exceeded a certain threshold, the transition from quiescence to sporadic bursts was induced. The switching between quiescence and sporadic bursts was more frequent for stronger stimuli. They found their experimental results to be qualitatively reproduced in the Hodgkin-Huxley model. The annihilation of repetitive spiking by noise and a transition to sporadic bursts upon an increase of noise level, shown in Fig. 13 of this paper, is an illustration of the same effect.