Numerical simulations of line-profile variation beyond a single-surface approximation for oscillations in roAp stars

Prior to the last decade, most observations of roAp stars have concerned the light variations. Recently some new, striking results of spectroscopic observations with high time resolution, high spectral dispersion, and a high signal-to-noise ratio became available. Since the oscillations found in roAp stars are high overtones, the vertical wavelengths of the oscillations are so short that the amplitude and phase of the variation of each spectroscopic line are highly dependent on the level of the line profile. Hence, analyses of the variation of the spectroscopic lines of roAp stars potentially provide us with new information about the vertical structure of the atmosphere of these stars. In order to extract such information, a numerical simulation of the line-profile variation beyond a single-surface approximation is necessary. We carried out a numerical simulation of line-profile variation by taking account of the finite thickness of the line forming layer. We demonstrated how effective this treatment is, by comparing the simulation with the observed line profiles.Comment: PASJ, 64, 9 (2012), in press. 18 pages, 16 figure

Radial Symmetry of Self-Similar Solutions for Semilinear Heat Equations

AbstractThe symmetry properties of positive solutions of the equationΔu+12x·∇u+1p−1u+up=0inRn,where n⩾2, p>(n+2)/n, was studied. It was proved that u must be radially symmetric about the origin provided u(x)=o(|x|−2/(p−1)) as |x|→∞, and that there exist non-radial solutions u satisfying limsup|x|→∞|x|2/(p−1)u(x)>0

Characterizing and Modeling Arctic Shrub Expansion on the North Slope of Alaska, USA

Shrub expansion is one of the most recognized components of terrestrial Arctic change and has been documented in studies involving fine-scale experimental manipulations or broad-scale satellite remote sensing. The characteristics and drivers of this phenomenon at the landscape scale, however, are understudied. The motivation of this dissertation was to develop an improved understanding of the historic spatial characteristics of shrub expansion on the North Slope of Alaska and its environmental drivers at this landscape scale. This work has three objectives, which include: 1) mapping and quantifying historic shrub expansion patterns; 2) examining a relationship between shrub expansion and its hydrological controls; and 3) designing and implementing a spatially-explicit simulation model to develop hypotheses regarding the landscape-scale drivers of shrub expansion (i.e., modes of reproduction, hydrological constraints, and their interactions). Shrubs maps were generated from semi-automated classification of historic vertical aerial photographs and contemporary high-resolution satellite imagery within a GIS. The spatial patterns of historic shrub expansion were quantified using FRAGSTATS and the multi-scale information fractal dimension. Relationships between shrub expansion and local hydrology was determined statistically through associations between areas that gained shrub cover and topographic wetness index values derived from a digital elevation model. The contribution of shrub reproductive characteristics was determined by developing a C#-based spatially-explicit simulation model that simulates clonal and sexual reproduction of shrubs. The reproductive mode(s) producing spatial patterns most similar to the observed patterns was determined through principal components analyses. Results from this work suggest that: 1) the shrub-tundra ecotone within river valleys on the North Slope is has either initiated or completed a phase transition from tundra to shrubland; 2) shrub development is promoted in areas where the potential for water accumulation or throughflow is higher; and 3) vegetative reproduction appears to have been dominant mode of reproduction . Considering our current understanding of the fine-scale relationships between shrub expansion and hydrology, surface energy balances, and C and nutrient cycling, continued expansion may have considerable implications for circumpolar tundra ecosystems. These findings will facilitate the development of improved projections of the structure and function of these ecosystems and their feedbacks to climate change