In the last few years, a lot of publications suggested that disabling cerebellar ataxias may develop through immune-mediated mechanisms. In this consensus paper, we discuss the clinical features of the main described immune-mediated cerebellar ataxias and address their presumed pathogenesis. Immune-mediated cerebellar ataxias include cerebellar ataxia associated with anti-GAD antibodies, the cerebellar type of Hashimoto’s encephalopathy, primary autoimmune cerebellar ataxia, gluten ataxia, Miller Fisher syndrome, ataxia associated with systemic lupus erythematosus, and paraneoplastic cerebellar degeneration. Humoral mechanisms, cell-mediated immunity, inflammation, and vascular injuries contribute to the cerebellar deficits in immune-mediated cerebellar ataxias.

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This study reports a metastable hcp→fcc polymorphic transformation in elemental titanium induced by high-energy mechanical attrition in a planetary ball mill. The transformation is monitored and verified by x-ray and electron diffraction and high-resolution transmission electron microscopy. The grain size decreases and lattice parameter increases with continued milling. The phase change is gradual and accompanied by about 16% increase in volume per atom. The milling intensity and deformation mode seem crucial for the completion of the change in crystal structure. The extent and influence of both substitutional and interstitial impurities in this transformation have been assessed. It is suggested that structural instability due to negative (from core to boundary) hydrostatic pressure arising out of nanocrystallization or grain refinement, increasing lattice expansion, and plastic strain/strain rate is responsible for this hcp→fcc polymorphic transformation in titanium. Thus, the present transformation is similar in nature and genesis to those in elemental niobium and zirconium earlier reported by us.

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Positron lifetime and Doppler broadening measurements on nanocrystalline niobium over a wide range of grain sizes ͑5-35 nm͒ were performed. Significant changes in the structure and properties of grain boundaries and intercrystalline regions were observed when the grain size was reduced below 10 nm. While positron lifetime at the grain boundaries sharply increased owing to an increase in the excess free volume associated with the atoms, the atomic reordering brought in a remarkable redistribution of the electron momenta at the grain boundaries. A model-based calculation of the excess free volume of atoms at the grain boundaries supported these findings. The calculated bulk modulus and the negative hydrostatic pressure predicted a lower size limit of ϳ2 nm for the mechanical and thermodynamic stability of the grain boundaries. Quantum confinement of the electron energy levels can be expected only below 20 K for grains of size above this limit.