9,378 research outputs found
UV observations of blue stragglers and population 2 K dwarfs
Blue stragglers are stars, found usually in either open or globular clusters, that appear to lie on the main sequence, but are brighter and bluer than the cluster turn-off. Currently, two rival models are invoked to explain this apparently pathological behavior: internal mixing (so that fresh fuel is brought into the stellar core); and mass transfer (by which a normal main sequence star acquires mass from an evolving nearby companion and so moves up the main sequence). The latter model predicts that in the absence of complete mass transfer (i.e., coalescence), blue stragglers should be binary systems with the fainter star in a post-main sequence evolutionary state. It is important to ascertain the cause of this phenomenon since stellar evolution models of main sequence stars play such a vital role in astronomy. If mass transfer is involved, one may easily exclude binaries from age determinations of clusters, but if mixing is the cause, our age determinations will be much less accurate unless we can determine whether all stars or only some mix, and what causes the mixing to occur at all
Identifying multiple detachment horizons and an evolving thrust history through cross-section restoration and appraisal in the Moine Thrust Belt, NW Scotland
Peer reviewedPublisher PD
Probing the Primordial Power Spectrum with Cluster Number Counts
We investigate how well galaxy cluster number counts can constrain the
primordial power spectrum. Measurements of the primary anisotropies in the
cosmic microwave background (CMB) may be limited, by the presence of
foregrounds from secondary sources, to probing the primordial power spectrum at
wave numbers less than about 0.30 h Mpc^{-1}. We break up the primordial power
spectrum into a number of nodes and interpolate linearly between each node.
This allows us to show that cluster number counts could then extend the
constraints on the form of the primordial power spectrum up to wave numbers of
about 0.45 h Mpc^{-1}. We estimate combinations of constraints from PLANCK and
SPT primary CMB and their respective SZ surveys. We find that their
constraining ability is limited by uncertainties in the mass scaling relations.
We also estimate the constraint from clusters detected from a SNAP like
gravitational lensing survey. As there is an unambiguous and simple
relationship between the filtered shear of the lensing survey and the cluster
mass, it may be possible to obtain much tighter constraints on the primordial
power spectrum in this case.Comment: Clarifications added and a few minor corrections made. Matches
version to appear in PR
Influence of structural position on fracture networks in the Torridon Group, Achnashellach fold and thrust belt, NW Scotland
Acknowledgements This research is funded by a NERC CASE studentship (NERC code NE/I018166/1) in partnership with Midland Valley. The authors thank Midland Valley for use of FieldMove Clino software for fracture data collection, and Move software for cross section construction, and strain modelling. 3D Field software is acknowledged for contour map creation. We also thank Toru Takeshita for overseeing the editorial process, and Catherine Hanks and Ole Petter Wennberg for constructive reviews.Peer reviewedPublisher PD
Comments on "The long-period Galactic Cepheid RS Puppis. I. A geometric distance from its light echoes"
The luminous Galactic Cepheid RS Puppis is unique in being surrounded by a
dust nebula illuminated by the variable light of the Cepheid. In a recent paper
in this journal, Kervella et al. (2008) report a very precise geometric
distance to RS Pup, based on measured phase lags of the light variations of
individual knots in the reflection nebula. In this commentary, we examine the
validity of the distance measurement, as well as the reality of the spatial
structure of the nebula determined by Feast (2008) based upon the phase lags of
the knots. {Kervella et al. assumed that the illuminated dust knots lie, on
average, in the plane of the sky (otherwise it is not possible to derive a
geometric distance from direct imaging of light echoes). We consider the
biasing introduced by the high efficiency of forward scattering. We conclude
that most of the knots are in fact likely to lie in front of the plane of the
sky, thus invalidating the Kervella et al. result. We also show that the flat
equatorial disk structure determined by Feast is unlikely; instead, the
morphology of the nebula is more probably bipolar, with a significant tilt of
its axis with respect to the plane of the sky. Although the Kervella et al.
distance result is invalidated, we show that high-resolution polarimetric
imaging has the potential to yield a valid geometric distance to this important
Cepheid.Comment: 10 pages, 5 figures, 1 table; accepted by Astronomy & Astrophysic
Analysis of recent type Ia supernova data based on evolving dark energy models
We study characters of recent type Ia supernova (SNIa) data using evolving
dark energy models with changing equation of state parameter w. We consider
sudden-jump approximation of w for some chosen redshift spans with double
transitions, and constrain these models based on Markov Chain Monte Carlo
(MCMC) method using the SNIa data (Constitution, Union, Union2) together with
baryon acoustic oscillation A parameter and cosmic microwave background shift
parameter in a flat background. In the double-transition model the Constitution
data shows deviation outside 1 sigma from LCDM model at low (z < 0.2) and
middle (0.2 < z < 0.4) redshift bins whereas no such deviations are noticeable
in the Union and Union2 data. By analyzing the Union members in the
Constitution set, however, we show that the same difference is actually due to
different calibration of the same Union sample in the Constitution set, and is
not due to new data added in the Constitution set. All detected deviations are
within 2 sigma from the LCDM world model. From the LCDM mock data analysis, we
quantify biases in the dark energy equation of state parameters induced by
insufficient data with inhomogeneous distribution of data points in the
redshift space and distance modulus errors. We demonstrate that location of
peak in the distribution of arithmetic means (computed from the MCMC chain for
each mock data) behaves as an unbiased estimator for the average bias, which is
valid even for non-symmetric likelihood distributions.Comment: 12 pages, 6 figures, published in the Phys. Rev.
Design guide for high pressure oxygen systems
A repository for critical and important detailed design data and information, hitherto unpublished, along with significant data on oxygen reactivity phenomena with metallic and nonmetallic materials in moderate to very high pressure environments is documented. This data and information provide a ready and easy to use reference for the guidance of designers of propulsion, power, and life support systems for use in space flight. The document is also applicable to designs for industrial and civilian uses of high pressure oxygen systems. The information presented herein are derived from data and design practices involving oxygen usage at pressures ranging from about 20 psia to 8000 psia equal with thermal conditions ranging from room temperatures up to 500 F
Using laterally compatible cross sections to infer fault growth and linkage models in foreland thrust belts
This research is partially funded by a CGG-financed pathfinder project, and formed part of a study by the Fold-Thrust Research Group at the University of Aberdeen, co-funded by InterOil, Oil Search and Santos. We also thank Nicolas Bellahsen and Stefano Tavani for constructive reviews.Peer reviewedPublisher PD
Structural validation as an input into seismic depth conversion to decrease assigned structural uncertainty
This study is based on PhD research project funded by INPEX CORPORATION at University of Aberdeen. Seismic images for this study were taken from the Higgins et al. (2009), through the courtesy of CGG (formerly CGG Veritas). Further examples are available through the Virtual Seismic Atlas (www.seismicatlas.org). Restoration and forward modelling and measurements for the area-depth-strain analysis were performed in Move 2016.1 by Midland Valley made available through academic partnership. Trishear inverse modelling was programmed referring to MATLAB scripts publicized on Allmendinger et al. (2012, chapter 11) and Nester Cardozo's website (http://www.ux.uis.no/∼nestor/work/programs.html) and implemented in MATLAB 2015b. Finally we thank Nester Cardozo and Richard Groshong for valuable comments that significantly improved this contribution.Peer reviewedPostprin
THE EFFECTS OF 2.0-Bev PROTONS IN MICE
The biological effects of proton beams of 2.0 to 2.2 Bev were studied in mice. Physical studies of particle distribution and depth dosimetry are described. Data are presented on lethal dosage measurements and studies of light element activation in tissues through proton reactions (p,pn) as determined by whole-body counting of gamma activity. (C.H.
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