1,797 research outputs found
SOUSA: the Swift Optical/Ultraviolet Supernova Archive
The Ultra-Violet Optical Telescope on the Swift spacecraft has observed
hundreds of supernovae, covering all major types and most subtypes. Here we
introduce the Swift Optical/Ultraviolet Supernova Archive (SOUSA), which will
contain all of the supernova images and photometry. We describe the observation
and reduction procedures and how they impact the final data. We show photometry
from well-observed examples of most supernova classes, whose absolute
magnitudes and colors may be used to infer supernova types in the absence of a
spectrum. A full understanding of the variety within classes and a robust
photometric separation of the groups requires a larger sample, which will be
provided by the final archive. The data from the existing Swift supernovae are
also useful for planning future observations with Swift as well as future UV
observatories.Comment: Accepted for publication in the UV issue of Astrophysics and Space
Science 10 pages, 6 figures SOUSA is an archive in progress with data being
posted to the Swift SN website:
http://swift.gsfc.nasa.gov/docs/swift/sne/swift_sn.htm
Effects of Backtracking on PageRank
In this paper, we consider three variations on standard PageRank:
Non-backtracking PageRank, -PageRank, and -PageRank, all of which
alter the standard formula by adjusting the likelihood of backtracking in the
algorithm's random walk. We show that in the case of regular and bipartite
biregular graphs, standard PageRank and its variants are equivalent. We also
compare each centrality measure and investigate their clustering capabilities
Concentration Dependence of the Size and Symmetry of a Bottlebrush Polymer in a Good Solvent
Bottlebrush polymers consist of a linear backbone with densely grafted side chains which impact the rigidity of the molecule. The persistence length of the bottlebrush backbone in solution is influenced by both the intrinsic structure of the polymer and the local environment, such as the solvent quality and concentration. Increasing the concentration reduces the overall size of the molecule because of the reduction in backbone stiffness. In this study, we map out the size of a bottlebrush polymer as a function of concentration for a single backbone length. Small-angle neutron scattering measurements are conducted on a polynorbornene-based bottlebrush with polystyrene side chains in a good solvent. The data are fit using a model which provides both the long and short axis radius of gyration (R_(g,2) and R_(g,1), respectively), providing a measure for how the conformation changes as a function of concentration. At low concentrations, a highly anisotropic structure is observed (R_(g,2)/R_(g,1) ≈ 4), becoming more isotropic at higher concentrations (R_(g,2)/R_(g,1) ≈ 1.5). The concentration scaling for both R_(g,2) and the overall Rg is evaluated and compared with predictions in the literature. Coarse-grained molecular dynamics simulations were also conducted to probe the impact of concentration on bottlebrush conformation, showing qualitative agreement with the experimental results
Concentration Dependence of the Size and Symmetry of a Bottlebrush Polymer in a Good Solvent
Bottlebrush polymers consist of a linear backbone with densely grafted side chains which impact the rigidity of the molecule. The persistence length of the bottlebrush backbone in solution is influenced by both the intrinsic structure of the polymer and the local environment, such as the solvent quality and concentration. Increasing the concentration reduces the overall size of the molecule because of the reduction in backbone stiffness. In this study, we map out the size of a bottlebrush polymer as a function of concentration for a single backbone length. Small-angle neutron scattering measurements are conducted on a polynorbornene-based bottlebrush with polystyrene side chains in a good solvent. The data are fit using a model which provides both the long and short axis radius of gyration (R_(g,2) and R_(g,1), respectively), providing a measure for how the conformation changes as a function of concentration. At low concentrations, a highly anisotropic structure is observed (R_(g,2)/R_(g,1) ≈ 4), becoming more isotropic at higher concentrations (R_(g,2)/R_(g,1) ≈ 1.5). The concentration scaling for both R_(g,2) and the overall Rg is evaluated and compared with predictions in the literature. Coarse-grained molecular dynamics simulations were also conducted to probe the impact of concentration on bottlebrush conformation, showing qualitative agreement with the experimental results
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