6,910 research outputs found
Spectroscopy of Giant Stars in the Pyxis Globular Cluster
The Pyxis globular cluster is a recently discovered globular cluster that
lies in the outer halo (R_{gc} ~ 40 kpc) of the Milky Way. Pyxis lies along one
of the proposed orbital planes of the Large Magellanic Cloud (LMC), and it has
been proposed to be a detached LMC globular cluster captured by the Milky Way.
We present the first measurement of the radial velocity of the Pyxis globular
cluster based on spectra of six Pyxis giant stars. The mean heliocentric radial
velocity is ~ 36 km/sec, and the corresponding velocity of Pyxis with respect
to a stationary observer at the position of the Sun is ~ -191 km/sec. This
radial velocity is a large enough fraction of the cluster's expected total
space velocity, assuming that it is bound to the Milky Way, that it allows
strict limits to be placed on the range of permissible transverse velocities
that Pyxis could have in the case that it still shares or nearly shares an
orbital pole with the LMC. We can rule out that Pyxis is on a near circular
orbit if it is Magellanic debris, but we cannot rule out an eccentric orbit
associated with the LMC. We have calculated the range of allowed proper motions
for the Pyxis globular cluster that result in the cluster having an orbital
pole within 15 degrees of the present orbital pole of the LMC and that are
consistent with our measured radial velocity, but verification of the tidal
capture hypothesis must await proper motion measurement from the Space
Interferometry Mission or HST. A spectroscopic metallicity estimate of [Fe/H] =
-1.4 +/- 0.1 is determined for Pyxis from several spectra of its brightest
giant; this is consistent with photometric determinations of the cluster
metallicity from isochrone fitting.Comment: 22 pages, 5 figures, aaspp4 style, accepted for publication in
October, 2000 issue of the PAS
Leadership considerations for executive vice chairs, new chairs, and chairs in the 21st century.
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Toward decoupling the selection of compression algorithms from quality constraints
Data intense scientific domains use data compression to reduce the storage space needed. Lossless data compression preserves the original information accurately but on the domain of climate data usually yields a compression factor of only 2:1. Lossy data compression can achieve much higher compression rates depending on the tolerable error/precision needed. Therefore, the field of lossy compression is still subject to active research. From the perspective of a scientist, the compression algorithm does not matter but the qualitative information about the implied loss of precision of data is a concern.
With the Scientific Compression Library (SCIL), we are developing a meta-compressor that allows users to set various quantities that define the acceptable error and the expected performance behavior. The ongoing work a preliminary stage for the design of an automatic compression algorithm selector. The task of this missing key component is the construction of appropriate chains of algorithms to yield the users requirements. This approach is a crucial step towards a scientifically safe use of much-needed lossy data compression, because it disentangles the tasks of determining scientific ground characteristics of tolerable noise, from the task of determining an optimal compression strategy given target noise levels and constraints. Future algorithms are used without change in the application code, once they are integrated into SCIL.
In this paper, we describe the user interfaces and quantities, two compression algorithms and evaluate SCIL’s ability for compressing climate data. This will show that the novel algorithms are competitive with state-of-the-art compressors ZFP and SZ and illustrate that the best algorithm depends on user settings and data properties
The Developing Methodology for Analyzing Privacy Torts
The authors assert the need for a common method of analyzing privacy situations that can be applied consistently by practitioners, juries and courts. They contend that confusion exists as to the legal basis of privacy torts because the right of privacy, as originally conceived by Warren and Brandeis, was never adequately defined. Prosser\u27s analysis of privacy torts departs from the Warren and Brandeis formulation and, according to the authors, also can be criticized for lack of definition. The authors present a new methodology that analyzes privacy torts based upon the scope of consent standard. They maintain that the result will be the protection of the right of privacy as originally conceived by Warren and Brandeis
Plasmid-based lacZalpha assay for DNA polymerase fidelity: application to archaeal family-B DNA polymerase
The preparation of a gapped pUC18 derivative, containing the lacZalpha reporter gene in the single-stranded region, is described. Gapping is achieved by flanking the lacZalpha gene with sites for two related nicking endonucleases, enabling the excision of either the coding or non-coding strand. However, the excised strand remains annealed to the plasmid through non-covalent Watson-Crick base-pairing; its removal, therefore, requires a heat-cool cycle in the presence of an exactly complementary competitor DNA. The gapped plasmids can be used to assess DNA polymerase fidelity using in vitro replication, followed by transformation into Escherichia coli and scoring the blue/white colony ratio. Results found with plasmids are similar to the well established method based on gapped M13, in terms of background ( approximately 0.08% in both cases) and the mutation frequencies observed with a number of DNA polymerases, providing validation for this straightforward and technically uncomplicated approach. Several error prone variants of the archaeal family-B DNA polymerase from Pyrococcus furiosus have been investigated, illuminating the potential of the method
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