127 research outputs found
IRAS versus POTENT Density Fields on Large Scales: Biasing and Omega
The galaxy density field as extracted from the IRAS 1.2 Jy redshift survey is
compared to the mass density field as reconstructed by the POTENT method from
the Mark III catalog of peculiar velocities. The reconstruction is done with
Gaussian smoothing of radius 12 h^{-1}Mpc, and the comparison is carried out
within volumes of effective radii 31-46 h^{-1}Mpc, containing approximately
10-26 independent samples. Random and systematic errors are estimated from
multiple realizations of mock catalogs drawn from a simulation that mimics the
observed density field in the local universe. The relationship between the two
density fields is found to be consistent with gravitational instability theory
in the mildly nonlinear regime and a linear biasing relation between galaxies
and mass. We measure beta = Omega^{0.6}/b_I = 0.89 \pm 0.12 within a volume of
effective radius 40 h^{-1}Mpc, where b_I is the IRAS galaxy biasing parameter
at 12 h^{-1}Mpc. This result is only weakly dependent on the comparison volume,
suggesting that cosmic scatter is no greater than \pm 0.1. These data are thus
consistent with Omega=1 and b_I\approx 1. If b_I>0.75, as theoretical models of
biasing indicate, then Omega>0.33 at 95% confidence. A comparison with other
estimates of beta suggests scale-dependence in the biasing relation for IRAS
galaxies.Comment: 35 pages including 10 figures, AAS Latex, Submitted to The
Astrophysical Journa
Nonlinearity and stochasticity in the density--velocity relation
We present results of the investigations of the statistical properties of a
joint density and velocity divergence probability distribution function (PDF)
in the mildly non-linear regime. For that purpose we use both perturbation
theory results, extended here for a top-hat filter, and numerical simulations.
In particular we derive the quantitative (complete as possible up to third
order terms) and qualitative predictions for constrained averages and
constrained dispersions -- which describe the nonlinearities and the
stochasticity properties beyond the linear regime -- and compare them against
numerical simulations. We find overall a good agreement for constrained
averages; however, the agreement for constrained dispersions is only
qualitative. Scaling relations for the Omega-dependence of these quantities are
satisfactory reproduced.
Guided by our analytical and numerical results, we finally construct a robust
phenomenological description of the joint PDF in a closed analytic form. The
good agreement of our formula with results of N-body simulations for a number
of cosmological parameters provides a sound validation of the presented
approach.
Our results provide a basis for a potentially powerful tool with which it is
possible to analyze galaxy survey data in order to test the gravitational
instability paradigm beyond the linear regime and put useful constraints on
cosmological parameters. In particular we show how the nonlinearity in the
density--velocity relation can be used to break the so-called Omega-bias
degeneracy in cosmic density-velocity comparisons.Comment: 12 pages, 11 figures; revised version with minor changes in the
presentation, accepted for publication in MNRA
The X-ray Cluster Dipole
We estimate the dipole of the whole sky X-ray flux-limited sample of
Abell/ACO clusters (XBACs) and compare it to the optical Abell/ACO cluster
dipole. The X-ray cluster dipole is well aligned () with the
CMB dipole, while it follows closely the radial profile of its optical cluster
counterpart although its amplitude is per cent lower. In view of
the fact that the the XBACs sample is not affected by the volume incompleteness
and the projection effects that are known to exist at some level in the optical
parent Abell/ACO cluster catalogue, our present results confirm the previous
optical cluster dipole analysis that there are significant contributions to the
Local Group motion from large distances (Mpc). In order to
assess the expected contribution to the X-ray cluster dipole from a purely
X-ray selected sample we compare the dipoles of the XBACs and the Brightest
Cluster Sample (Ebeling et al. 1997a) in their overlap region. The resulting
dipoles are in mutual good aggreement with an indication that the XBACs sample
slightly underestimates the full X-ray dipole (by per cent) while the
Virgo cluster contributes about 10 - 15 per cent to the overall X-ray cluster
dipole. Using linear perturbation theory to relate the X-ray cluster dipole to
the Local group peculiar velocity we estimate the density parameter to be
.Comment: 16 pages, latex, + 4 ps figures, submitted to Ap
Research and Client-Based Projects
This chapter will:; ; ; Show how to develop a needs analysis based on sound research principles;; ; ; Examine a number of different client-based projects that have taken a business discourse approach to teaching;; ; ; Discuss different ways in which business discourse research can be used in the classroom;; ; ; Present a case study that illustrates how business discourse projects can be incorporated into teaching practices together with a set of tasks related to the use of business discourse research in the classroom and a set of further readings
Invasive Predators Deplete Genetic Diversity of Island Lizards
Invasive species can dramatically impact natural populations, especially those living on islands. Though numerous examples illustrate the ecological impact of invasive predators, no study has examined the genetic consequences for native populations subject to invasion. Here we capitalize on a natural experiment in which a long-term study of the brown anole lizard (Anolis sagrei) was interrupted by rat invasion. An island population that was devastated by rats recovered numerically following rat extermination. However, population genetic analyses at six microsatellite loci suggested a possible loss of genetic diversity due to invasion when compared to an uninvaded island studied over the same time frame. Our results provide partial support for the hypothesis that invasive predators can impact the genetic diversity of resident island populations
CFHTLenS: Improving the quality of photometric redshifts with precision photometry
Here we present the results of various approaches to measure accurate colours
and photometric redshifts (photo-z's) from wide-field imaging data. We use data
from the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS) which have been
re- processed by the CFHT Lensing Survey (CFHTLenS) team in order to carry out
a number of weak gravitational lensing studies. An emphasis is put on the
correction of systematic effects in the photo-z's arising from the different
Point Spread Functions (PSF) in the five optical bands. Different ways of
correcting these effects are discussed and the resulting photo-z accuracies are
quantified by comparing the photo-z's to large spectroscopic redshift (spec-z)
data sets. Careful homogenisation of the PSF between bands leads to increased
overall accuracy of photo-z's. The gain is particularly pronounced at fainter
magnitudes where galaxies are smaller and flux measurements are affected more
by PSF-effects. We also study possible re- calibrations of the photometric
zeropoints (ZPs) with the help of galaxies with known spec-z's. We find that if
PSF-effects are properly taken into account, a re-calibration of the ZPs
becomes much less important suggesting that previous such re-calibrations
described in the literature could in fact be mostly corrections for PSF-effects
rather than corrections for real inaccuracies in the ZPs. The implications of
this finding for future surveys like KiDS, DES, LSST, or Euclid are mixed. On
the one hand, ZP re-calibrations with spec-z's might not be as accurate as
previously thought. On the other hand, careful PSF homogenisation might provide
a way out and yield accurate, homogeneous photometry without the need for full
spectroscopic coverage. This is the first paper in a series describing the
technical aspects of CFHTLenS. (abridged)Comment: 15 pages, 10 figures, accepted by MNRAS, minor revision
Evasion of anti-growth signaling: a key step in tumorigenesis and potential target for treatment and prophylaxis by natural compounds
The evasion of anti-growth signaling is an important characteristic of cancer cells. In order to continue to proliferate, cancer cells must somehow uncouple themselves from the many signals that exist to slow down cell growth. Here, we define the anti-growth signaling process, and review several important pathways involved in growth signaling: p53, phosphatase and tensin homolog (PTEN), retinoblastoma protein (Rb), Hippo, growth differentiation factor 15 (GDF15), AT-rich interactive domain 1A (ARID1A), Notch, insulin-like growth factor (IGF), and Krüppel-like factor 5 (KLF5) pathways. Aberrations in these processes in cancer cells involve mutations and thus the suppression of genes that prevent growth, as well as mutation and activation of genes involved in driving cell growth. Using these pathways as examples, we prioritize molecular targets that might be leveraged to promote anti-growth signaling in cancer cells. Interestingly, naturally-occurring phytochemicals found in human diets (either singly or as mixtures) may promote anti-growth signaling, and do so without the potentially adverse effects associated with synthetic chemicals. We review examples of naturally-occurring phytochemicals that may be applied to prevent cancer by antagonizing growth signaling, and propose one phytochemical for each pathway. These are: epigallocatechin-3-gallate (EGCG) for the Rb pathway, luteolin for p53, curcumin for PTEN, porphyrins for Hippo, genistein for GDF15, resveratrol for ARID1A, withaferin A for Notch and diguelin for the IGF1-receptor pathway. The coordination of anti-growth signaling and natural compound studies will provide insight into the future application of these compounds in the clinical setting
KiDS+GAMA:The weak lensing calibrated stellar-to-halo mass relation of central and satellite galaxies
We simultaneously present constraints on the stellar-to-halo mass relation
for central and satellite galaxies through a weak lensing analysis of
spectroscopically classified galaxies. Using overlapping data from the fourth
data release of the Kilo-Degree Survey (KiDS), and the Galaxy And Mass Assembly
survey (GAMA), we find that satellite galaxies are hosted by halo masses that
are dex (68\% confidence, detection) smaller than
those of central galaxies of the same stellar mass (for a stellar mass of
). This is consistent with galaxy formation
models, whereby infalling satellite galaxies are preferentially stripped of
their dark matter. We find consistent results with similar uncertainties when
comparing constraints from a standard azimuthally averaged galaxy-galaxy
lensing analysis and a two-dimensional likelihood analysis of the full shear
field. As the latter approach is somewhat biased due to the lens incompleteness
and as it does not provide any improvement to the precision when applied to
actual data, we conclude that stacked tangential shear measurements are
best-suited for studies of the galaxy-halo connection.Comment: 12 pages, 10 figures, accepted for publication in A&
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