Downbeat nystagmus: aetiology and comorbidity in 117 patients

Objectives: Downbeat nystagmus (DBN) is the most common form of acquired involuntary ocular oscillation overriding fixation. According to previous studies, the cause of DBN is unsolved in up to 44% of cases. We reviewed 117 patients to establish whether analysis of a large collective and improved diagnostic means would reduce the number of cases with ``idiopathic DBN'' and thus change the aetiological spectrum.Methods: The medical records of all patients diagnosed with DBN in our Neurological Dizziness Unit between 1992 and 2006 were reviewed. In the final analysis, only those with documented cranial MRI were included. Their workup comprised a detailed history, standardised neurological, neuro-otological and neuro-ophthalmological examination, and further laboratory tests.Results: In 62% (n = 72) of patients the aetiology was identified (``secondary DBN''), the most frequent causes being cerebellar degeneration (n = 23) and cerebellar ischaemia (n = 10). In 38% (n = 45), no cause was found (``idiopathic DBN''). A major finding was the high comorbidity of both idiopathic and secondary DBN with bilateral vestibulopathy (36%) and the association with polyneuropathy and cerebellar ataxia even without cerebellar pathology on MRI.Conclusions: Idiopathic DBN remains common despite improved diagnostic techniques. Our findings allow the classification of ``idiopathic DBN'' into three subgroups: ``pure'' DBN (n = 17); ``cerebellar'' DBN (ie, DBN plus further cerebellar signs in the absence of cerebellar pathology on MRI; n = 6); and a ``syndromatic'' form of DBN associated with at least two of the following: bilateral vestibulopathy, cerebellar signs and peripheral neuropathy (n = 16). The latter may be caused by multisystem neurodegeneration

Structures of K0.05Na0.95NbO3 (50–300 K) and K0.30Na0.70NbO3 (100–200 K)

Rietveld refinement using neutron powder diffraction data is reported for the potential lead-free piezoelectric material KxNa1 - xNbO3 (x = 0.05, x = 0.3) at low temperatures. The structures were determined to be of rhombohedral symmetry, space group R3c, with the tilt system a-a-a- for both compositions. It was found that some of the structural parameters differ significantly in the two structures, and particularly the NbO6 octahedral strains as a function of temperature. The 300 K profile for K0.05Na0.95NbO3 shows the coexistence of rhombohedral and monoclinic phases, which indicates that the phase boundary is close to room temperature; the phase boundary for K0.30Na0.70NbO3 is found to be at approximately 180 K

Downfront winds over buoyant coastal plumes

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3139-3154, doi:10.1175/JPO-D-16-0042.1.Downfront, or downwelling favorable, winds are commonly found over buoyant coastal plumes. It is known that these winds can result in mixing of the plume with the ambient water and that the winds influence the transport, spatial extent, and stability of the plumes. In the present study, the interaction of the Ekman velocity in the surface layer and baroclinic instability supported by the strong horizontal density gradient of the plume is explored with the objective of understanding the potential vorticity and buoyancy budgets. The approach makes use of an idealized numerical model and scaling theory. It is shown that when winds are present the weak stratification resulting from vertical mixing and the strong baroclinicity of the front results in near-zero average potential vorticity q. For weak to moderate winds, the reduction of q by diapycnal mixing is balanced by the generation of q through the geostrophic stress term in the regions of strong horizontal density gradients and stable stratification. However, for very strong winds the wind stress overwhelms the geostrophic stress and leads to a reduction in q, which is balanced by the vertical mixing term. In the absence of winds, the geostrophic stress dominates mixing and the flow rapidly restratifies. Nonlinearity, extremes of relative vorticity and vertical velocity, and mixing are all enhanced by the presence of a coast. Scaling estimates developed for the eddy buoyancy flux, the surface potential vorticity flux, and the diapycnal mixing rate compare well with results diagnosed from a series of numerical model calculations.This study was supported by NSF Grants OCE-1433170 (MAS) and OCE-1459677 (LNT).2017-04-0