9,178 research outputs found
Provenance and geochemistry of exotic clasts in conglomerates of the Oligocene Torehina Formation, Coromandel Peninsula, New Zealand
Non-marine pebble to cobble conglomerates of the lower Torehina Formation (Oligocene) crop out along western Coromandel Peninsula and overlie, with strong angular discordance, continental-margin metasedimentary rocks (Manaia Hill Group) of Mesozoic (Late Jurassic to ?Early Cretaceous) age. The conglomerates contain provenance information that identifies a pre-Oligocene depositional history obscured by the unconformable juxtaposition of these Tertiary and Mesozoic strata. Most clasts in the lower Torehina Formation are visually similar to local bedrock lithologies, including metamorphosed sandstones and argillites, but are kaolinitic and contain more detrital and authigenic chert, quartz, and potash feldspar. Local derivation of these clasts seems unlikely. By comparing geochemical ratios with those defined for continental margin sandstones, and well characterised New Zealand tectonic terranes, we interpret the majority of clasts in the lower Torehina Formation to have been derived from a dissected orogen, with mixtures of felsic and volcanogenic-derived sediment. The most likely sources are the Waipapa and Torlesse Terranes. The remaining 20â30% of the clasts in the lower Torehina Formation were originally friable, are coarse grained, and appear to be lithologically exotic relative to known metamorphosed sandstones in basement terrane sources on North Island. Some clasts contain coal laminae and particles, and all contain detrital kaolinite as lithic fragments and matrix. Such characteristics imply a non-marine to marginal-marine source containing sediment derived from strongly weathered granite or granodiorite. Mechanical fragility implies a likely proximal, easily erodible source. We propose that this group of clasts was derived from an Upper Cretaceous sedimentary cover, either part of a locally developed basin fill or part of a once regionally extensive cover on North Island. Either case defines a more widely distributed Cretaceous source than found today
Observations of the 5âday wave in the mesosphere and lower thermosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94851/1/grl7954.pd
The Chandra X-ray Spectrum of the 10.6 s Pulsar in Westerlund 1: Testing the Magnetar Hypothesis
Two sensitive Chandra X-ray observations of the heavily-reddened galactic
starburst cluster Westerlund 1 in May and June 2005 detected a previously
unknown X-ray pulsar (CXO J164710.20-455217). Its slow 10.6 s pulsations,
moderate X-ray temperature kT 0.5 keV, and apparent lack of a massive
companion tentatively suggest that it is an Anomalous X-ray Pulsar (AXP). An
isothermal blackbody model yields an acceptable spectral fit but the inferred
source radius is much less than that of a neutron star, a result that has also
been found for other AXPs. We analyze the X-ray spectra with more complex
models including a model that assumes the pulsar is a strongly magnetized
neutron star (``magnetar'') with a light element atmosphere. We conclude that
the observed X-ray emission cannot be explained as global surface emission
arising from the surface of a cooling neutron star or magnetar. The emission
likely arises in one or more localized regions (``hot spots'') covering a small
fraction of the surface. We discuss these new results in the context of both
accretion and magnetar interpretations for the X-ray emission.Comment: 14 pages, 5 figures; to appear in Ap
The Delphi Method Research Strategy in Studies of Information Systems
In this paper, we discuss the nature and use of the Delphi methodology in information systems research. More specifically, we explore how and why it may be used. We discuss criteria for evaluating Delphi research and define characteristics useful for categorizing the studies. We review Delphi application use in IS research over the last 23 years, summarize lessons learned from prior studies, offer suggestions for improvement, and present guidelines for employing this distinctly useful qualitative method in future information systems research studies
A Single Circumbinary Disk in the HD 98800 Quadruple System
We present sub-arcsecond thermal infrared imaging of HD 98800, a young
quadruple system composed of a pair of low-mass spectroscopic binaries
separated by 0.8'' (38 AU), each with a K-dwarf primary. Images at wavelengths
ranging from 5 to 24.5 microns show unequivocally that the optically fainter
binary, HD 98800B, is the sole source of a comparatively large infrared excess
upon which a silicate emission feature is superposed. The excess is detected
only at wavelengths of 7.9 microns and longer, peaks at 25 microns, and has a
best-fit black-body temperature of 150 K, indicating that most of the dust lies
at distances greater than the orbital separation of the spectroscopic binary.
We estimate the radial extent of the dust with a disk model that approximates
radiation from the spectroscopic binary as a single source of equivalent
luminosity. Given the data, the most-likely values of disk properties in the
ranges considered are R_in = 5.0 +/- 2.5 AU, DeltaR = 13+/-8 AU, lambda_0 =
2(+4/-1.5) microns, gamma = 0+/-2.5, and sigma_total = 16+/-3 AU^2, where R_in
is the inner radius, DeltaR is the radial extent of the disk, lambda_0 is the
effective grain size, gamma is the radial power-law exponent of the optical
depth, tau, and sigma_total is the total cross-section of the grains. The range
of implied disk masses is 0.001--0.1 times that of the moon. These results show
that, for a wide range of possible disk properties, a circumbinary disk is far
more likely than a narrow ring.Comment: 11 page Latex manuscript with 3 postscript figures. Accepted for
publication in Astrophysical Journal Letters. Postscript version of complete
paper also available at
http://www.hep.upenn.edu/PORG/web/papers/koerner00a.p
Swift BAT Survey of AGN
We present the results of the analysis of the first 9 months of data of the
Swift BAT survey of AGN in the 14-195 keV band. Using archival X-ray data or
follow-up Swift XRT observations, we have identified 129 (103 AGN) of 130
objects detected at |b|> 15 deg and with significance >4.8 sigma. One source
remains unidentified. These same X-ray data have allowed measurement of the
X-ray properties of the objects. We fit a power law to the log N - log S
distribution, and find the slope to be 1.42+/-0.14. Characterizing the
differential luminosity function data as a broken power law, we find a break
luminosity log L_*(erg/s) = 43.85+/-0.26, a low luminosity power law slope
a=0.84^{+0.16}_{-0.22}, and a high luminosity power law slope
b=2.55^{+0.43}_{-0.30}, similar to the values that have been reported based on
INTEGRAL data. We obtain a mean photon index 1.98 in the 14-195 keV band, with
an rms spread of 0.27. Integration of our luminosity function gives a local
volume density of AGN above 10^{41} erg/s of 2.4x10^{-3}/Mpc^3, which is about
10% of the total luminous local galaxy density above M_*=-19.75. We have
obtained X-ray spectra from the literature and from Swift XRT follow-up
observations. These show that the distribution of log n_H is essentially flat
from n_H=10^{20}/cm^{2} to 10^{24}/cm^2, with 50% of the objects having column
densities of less than 10^{22}/cm^{2}. BAT Seyfert galaxies have a median
redshift of 0.03, a maximum log luminosity of 45.1, and approximately half have
log n_H > 22.Comment: 15 pages, 15 figures, 2 tables; to appear in the Astrophysical
Journal, July 10, 2008, v. 68
The effect of homogenization at different pressures on the physical properties of an ice cream mixture and the resulting ice cream
The data presented in this bulletin were taken from a thesis submitted by the junior author in partial fulfillment of the requirements for the degree of Master of Arts in the Graduate School of the University of Missouri, 1927--P. [3].Includes bibliographical references (page 24)
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