An exact threshold for separator bifurcation

Reconnection involving magnetic separators is known to lead to the spontaneous generation of new separator pairs. In this work, we explore the bifurcation process for a system composed of a pair of null points with a joining separator. We begin with a simplified analytical model to derive the basic principles of bifurcation in this system and then consider models with more general separator curve geometry and generic localised null structure. We demonstrate that the maximum pairwise linking (net-winding) of the separator and the local fan plane always approaches a multiple of 0.25 just before bifurcation. Additionally, we show the integrated twisting along the separator (the field strength normalised parallel current) can be used to determine when this limit will definitely lead to bifurcation. We present step-by-step algorithms to assess how close such systems are to bifurcation

A study of the pathology of a bovine primary peripheral myelinopathy with features of tomaculous neuropathy

Cases of a bovine neuropathy are reported in which peripheral nerves show “sausage-shaped” thickenings of the myelin sheaths at different sites of the internode. Clinical signs of dysphagia and chronic rumenal bloat developed after weaning which were attributable to bilateral vagus nerve degeneration. Trunks of the sciatic nerves and brachial plexuses were similarly affected with the animal adopting a weak shuffling gait. Affected animals were the progeny of sire-daughter matings. The lesions are similar to those seen in the tomaculous neuropathies of man. The present study is believed to be the first report of this lesion occurring in domestic animals