3,343 research outputs found
Atomic spectrometry update. Clinical and biological materials, foods and beverages
This review discusses developments in elemental mass spectrometry, atomic absorption, emission and fluorescence, XRF and LIBS, as applied to the analysis of specimens of clinical interest, foods and beverages. Sample preparation procedures and quality assurance are also included.</p
The Multi-Component Nature of the Vela Pulsar Nonthermal X-ray Spectrum
We report on our analysis of a 274 ks observation of the Vela pulsar with the
Rossi X-Ray Timing Explorer (RXTE). The double-peaked, pulsed emission at 2 -
30 keV, which we had previously detected during a 93 ks observation, is
confirmed with much improved statistics. There is now clear evidence, both in
the spectrum and the light curve, that the emission in the RXTE band is a blend
of two separate non-thermal components. The spectrum of the harder component
connects smoothly with the OSSE, COMPTEL and EGRET spectrum and the peaks in
the light curve are in phase coincidence with those of the high-energy light
curve. The spectrum of the softer component is consistent with an extrapolation
to the pulsed optical flux, and the second RXTE pulse is in phase coincidence
with the second optical peak. In addition, we see a peak in the 2-8 keV RXTE
pulse profile at the radio phase.Comment: 12 pages, 3 figures, accepted for publication in Astrophysical
Journa
A catalog of Nearby Poor Clusters of Galaxies
A catalog of 732 optically selected, nearby poor clusters of galaxies
covering the entire sky north of declination is presented. The
poor clusters, called WBL clusters, were identified as concentrations of 3 or
more galaxies with photographic magnitudes brighter than 15.7, possessing a
galaxy surface overdensity of . These criteria are consistent with
those used in the identification of the original Yerkes poor clusters, and this
new catalog substantially increases the sample size of such objects. These poor
clusters cover the entire range of galaxy associations up to and including
Abell clusters, systematically including poor and rich galaxy systems spanning
over three orders of magnitude in the cluster mass function. As a result, this
new catalog contains a greater diversity of richness and structures than other
group catalogs, such as the Hickson or Yerkes catalogs. The information on
individual galaxies includes redshifts and cross-references to other galaxy
catalogs. The entries for the clusters include redshift (where available) and
cross-references to other group and cluster catalogs.Comment: 27 pages, 7 figures, + one 20-page landscape table, accepted for
publication in A
Highly Purified Micro- and Macronuclei from Tetrahymena thermophila Isolated by Percoll Gradients 1
A new procedure is described that utilizes Percoll gradients for purifying micronuclei (MIC) and macronuclei (MAC) from Tetrahymena thermophila . Separation of MIC from MAC during certrifugation in Percoll gradients occurs as a result of their difference in size rather than density. Three kinds of tests were used to evaluate the purity of the nuclei: visualization of the nuclei by light microscopy; examination of the nuclei by electron microscopy; and Southern blots of MIC and MAC DNA probed with the 5s rRNA genes or a fragment from the MAC extrachromosomal rDNA molecule. When examined under the light microscope, the isolated MIC and MAC have much lower nuclear cross contamination levels than previous methods have reported. MIC's contaminated with less than 1 MAC in 1000 MIC and MAC's contaminated with less than 1 MIC in 500 MAC can be routinely prepared. Quantitative analyses of electron micrographs gave higher estimates of cross contamination in our purified nuclei, which may, in part, be explained by the difficulty in identifying small MIC or MAC fragments. Southern blots of MIC and MAC DNA probed with 5s rDNA confirmed the level of MAC contamination in the MIC estimated by light microscopy during purification of the nuclei. The level of nucleolar contamination in the MIC was estimated at 10% by Southern blots of MIC and MAC DNA, derived from a heterokaryon with distinctive MIC and MAC Bam HI sites, using an rDNA probe.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75629/1/j.1550-7408.1983.tb01027.x.pd
Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey
We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical
spectrum shows unambiguous broad absorption features while its double-lobed
radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type
II radio source. Its radio luminosity places it at the extreme of the recently
established class of radio-loud broad absorption line quasars (Becker et al.
1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate
that FIRST J101614.3+520916 is a typical FR-II quasar which has been
rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep
Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be
estimated from its radio structure and optical brightness, indicating that we
are viewing the system at a viewing angle of > 40 degrees. The position angles
of the radio jet and optical polarization are not well-aligned, differing by 20
to 30 degrees. When combined with the evidence presented by Becker et al.
(2000) for a sample of 29 BAL quasars showing that at least some BAL quasars
are viewed along the jet axis, the implication is that no preferred viewing
orientation is necessary to observe BAL systems in a quasar's spectrum. This,
and the probable young nature of compact steep spectrum sources, leads
naturally to the alternate hypothesis that BALs are an early stage in the lives
of quasars.Comment: 14 pages, 6 postscript figures; accepted for publication in the
Astrophysical Journa
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Shoot yield drives phosphorus use efficiency in Brassica oleracea and correlates with root architecture traits
The environmental and financial costs of using inorganic phosphate fertilizers to maintain crop yield and quality are high. Breeding crops that acquire and use phosphorus (P) more efficiently could reduce these costs. The variation in shoot P concentration (shoot-P) and various measures of P use efficiency (PUE) were quantified among 355 Brassica oleracea L. accessions, 74 current commercial cultivars, and 90 doubled haploid (DH) mapping lines from a reference genetic mapping population. Accessions were grown at two or more external P concentrations in glasshouse experiments; commercial and DH accessions were also grown in replicated field experiments. Within the substantial species-wide diversity observed for shoot-P and various measures of PUE in B. oleracea, current commercial cultivars have greater PUE than would be expected by chance. This may be a consequence of breeding for increased yield, which is a significant component of most measures of PUE, or early establishment. Root development and architecture correlate with PUE; in particular, lateral root number, length, and growth rate. Significant quantitative trait loci associated with shoot-P and PUE occur on chromosomes C3 and C7. These data provide information to initiate breeding programmes to improve PUE in B. oleracea
Development of an Ultraflex-Based Thin Film Solar Array for Space Applications
As flexible thin film photovoltaic (FTFPV) cell technology is developed for space applications, integration into a viable solar array structure that optimizes the attributes of this cell technology is critical. An advanced version of ABLE'sS UltraFlex solar array platform represents a near-term, low-risk approach to demonstrating outstanding array performance with the implementation of FTFPV technology. Recent studies indicate that an advanced UltraFlex solar array populated with 15% efficient thin film cells can achieve over 200 W/kg EOL. An overview on the status of hardware development and the future potential of this technology is presented
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