Young-Wook Lee

Relationship between postural instability and subcortical volume loss in Alzheimer's disease

Abstract The relationship between postural instability and subcortical structure in AD has received less attention. The aims of this study were to assess whether there are differences in the ability to control balance between Alzheimers disease (AD) and controls, and to investigate the association between subcortical gray matter volumes and postural instability in AD. We enrolled 107 consecutive AD patients and 37 controls. All participants underwent detailed neuropsychological evaluations, T1-weighted MRI at 3 T, and posture assessment using computerized dynamic posturography. We segmented the volumes of 6 subcortical structures of the amygdala, thalamus, caudate nucleus, putamen, globus pallidus and nucleus accumbens, and of hippocampus, using the FMRIBs integrated registration and segmentation tool. All subcortical structures, except for the globus pallidus, were smaller in AD compared with controls on adjusting for age and gender. Falling frequencies in unilateral stance test (UST) and composite scores in sensory organization test (SOT) were worse in AD than in controls. The motor control test did not reveal any differences between groups. On subgroup analyses in AD, the groups with poor performance in UST or SOT exhibited significantly reduced nucleus accumbens and putamen volumes, and nucleus accumbens volume, respectively. The smaller volume of the nucleus accumbens was associated with postural instability in AD (OR [95% CI] 17.847 [2.59–122.80] for UST, 42.827[6.06–302.47] for SOT, all P < .05). AD patients exhibited reduced ability to control balance compared with controls, and this postural instability was associated with nucleus accumbens volume loss. Furthermore, cognitive dysfunction was more prominent in the group with severe postural instability.

YONSEI NEARBY SUPERNOVA EVOLUTION INVESTIGATION (YONSEI) SUPERNOVA CATALOGUE

We use light-curve fitting models (MLCS2k2, SALT2, and SNooPy) as implemented in SNANA to make the YOnsei Nearby Supernova Evolution Investigation (YONSEI) Supernova Catalogue. The catalogue consists of several hundred Type Ia supernovae (SNe Ia) in the redshift range from 0.01 to 1.35, and provides distance moduli, light-curve shape parameters, and color or extinction values for each supernova. This data set will be used to study the dependence of SNe Ia luminosities on the host galaxy morphologies. In this paper, we present the YONSEI Supernova Catalogue and preliminary systematic tests for the catalogue.

THE OOSTERHOFF PERIOD GROUPS AND MULTIPLE POPULATIONS IN GLOBULAR CLUSTERS

One of the long-standing problems in modern astronomy is the curious division of globular clusters (GCs) into two groups, according to the mean period (〈Pab〉) of type ab RR Lyrae variables. In light of the recent discovery of multiple populations in GCs, we suggest a new model explaining the origin of the Sandage period-shift and the difference in mean period of type ab RR Lyrae variables between the two Oosterhoff groups. In our models, the instability strip in the metal-poor group II clusters, such as M15, is populated by second generation stars (G2) with enhanced helium and CNO abundances, while the RR Lyraes in the relatively metal-rich group I clusters like M3 are mostly produced by first generation stars (G1) without these enhancements. This population shift within the instability strip with metallicity can create the observed period-shift between the two groups, since both helium and CNO abundances play a role in increasing the period of RR Lyrae variables. The presence of more metal-rich clusters having Oosterhoff-intermediate characteristics, such as NGC 1851, as well as of most metal-rich clusters having RR Lyraes with the longest periods (group III) can also be reproduced, as more helium-rich third and later generations of stars (G3) penetrate into the instability strip with further increase in metallicity. Therefore, although there are systems where the suggested population shift cannot be a viable explanation, for the most general cases, our models predict that RR Lyraes are produced mostly by G1, G2, and G3, respectively, for the Oosterhoff groups I, II, and III.