13,235 research outputs found
A Hubble Space Telescope Survey of X-ray Luminous Galaxy Clusters: Gravitationally Lensed Arcs and EROs
We are conducting a systematic lensing survey of X-ray luminous galaxy
clusters at z~0.2 using the Hubble Space Telescope and large ground-based
telescopes. We summarize initial results from our survey, including a
measurement of the inner slope of the mass profile of A383, and a search for
gravitationally lensed Extremely Red Objects.Comment: 4 pages, 2 figures. To appear in "A New Era in Cosmology" (ASP
Conference Proceedings), eds. T. Shanks and N. Metcalf
Hubble, chandra and keck constraints on massive galaxy clusters at z=0.2 and z=0.5
I present recent observations from two Hubble Space Telescope(HST)/ACS programs
that target the most X–ray luminous and thus (presumably) most massive galaxy clusters at
z=0.5 – the highest redshift at which complete, well–defined samples of such rare systems
are available. The first program (GO:9836, PI: R.S. Ellis) exploits a huge mosaic of 41 ACS
pointings spanning a 10 Mpc region centered on MS0451-03. This is the largest contiguous
space–based image of a cluster to date. I describe a preliminary weak–lensing analysis and a new
Keck/DEIMOS redshift catalog of 1000 galaxies in this field. The second program (GO:9722,
PI: H. Ebeling) studies the core regions of the twelve most luminous clusters at z≥0.5 from
the MAssive Cluster Survey (MACS; Ebeling et al. 2001). Multi–color ACS observations in
combination with recent Keck/LRIS spectroscopy of gravitational arcs constrain the distribution
of mass in the cluster cores, thus laying the foundation for detailed multi–diagnostic (lensing,
X–ray, near–infrared, SZE) investigation of this sample. For example, it is of particular interest
to explore how the structure and state of relaxation of massive clusters evolved between this
sample at z≥0.5 that measured by Smith et al. (2004, astro–ph/0403588) at z=0.2
LoCuSS: Weak-lensing mass calibration of galaxy clusters
We present weak-lensing mass measurements of 50 X-ray luminous galaxy
clusters at , based on uniform high quality observations with
Suprime-Cam mounted on the 8.2-m Subaru telescope. We pay close attention to
possible systematic biases, aiming to control them at the per cent
level. The dominant source of systematic bias in weak-lensing measurements of
the mass of individual galaxy clusters is contamination of background galaxy
catalogues by faint cluster and foreground galaxies. We extend our conservative
method for selecting background galaxies with colours redder than the
red sequence of cluster members to use a colour-cut that depends on
cluster-centric radius. This allows us to define background galaxy samples that
suffer per cent contamination, and comprise galaxies per square
arcminute. Thanks to the purity of our background galaxy catalogue, the largest
systematic that we identify in our analysis is a shape measurement bias of
per cent, that we measure using simulations that probe weak shears upto
. Our individual cluster mass and concentration measurements are in
excellent agreement with predictions of the mass-concentration relation.
Equally, our stacked shear profile is in excellent agreement with the Navarro
Frenk and White profile. Our new LoCuSS mass measurements are consistent with
the CCCP and CLASH surveys, and in tension with the Weighing the Giants at
significance. Overall, the consensus at that is
emerging from these complementary surveys represents important progress for
cluster mass calibration, and augurs well for cluster cosmology.Comment: 30 pages, 14 figures, 7 tables : accepted for the publication in
MNRAS : mass table update
Statistics and implications of substructure detected in a representative sample of X-ray clusters
We present a morphological study of 35 X-ray luminous galaxy clusters at
0.15<z<0.3, selected in a similar manner to the Local Cluster Substructure
Survey (LoCuSS), for which deep XMM-Newton observations are available. We
characterise the structure of the X-ray surface brightness distribution of each
cluster by measuring both their power ratios and centroid shift, and thus rank
the clusters by the degree of substructure. These complementary probes give a
consistent description of the cluster morphologies with some well understood
exceptions. We find a remarkably tight correlation of regular morphology with
the occurrence of cool cores in clusters. We also compare our measurements of
X-ray morphology with measurements of the luminosity gap statistics and
ellipticity of the brightest cluster galaxy (BCG). We check how our new X-ray
morphological analysis maps onto cluster scaling relations, finding that (i)
clusters with relatively undisturbed X-ray morphologies are on average more
luminous at fixed X-ray temperature than those with disturbed morphologies, and
(ii) disturbed clusters have larger X-ray masses than regular clusters for a
given temperature in the M-T relation. We also show that the scatter in the
ratio of X-ray and weak lensing based cluster mass measurements is larger for
disturbed clusters than for those of more regular morphology. Overall, our
results demonstrate the feasibility of assembling a self-consistent picture of
the physical structure of clusters from X-ray and optical data, and the
potential to apply this in the measurement of cosmological cluster scaling
relations.Comment: 12 pages, 13 figures, A&A accepte
Variation in pelvic morphology may prevent the identification of anterior pelvic tilt
Pelvic tilt is often quantified using the angle between the horizontal and a line connecting the anterior superior iliac spine (ASIS) and the posterior superior iliac spine (PSIS). Although this angle is determined by the balance of muscular and ligamentous forces acting between the pelvis and adjacent segments, it could also be influenced by variations in pelvic morphology. The primary objective of this anatomical study was to establish how such variation may affect the ASIS-PSIS measure of pelvic tilt. In addition, we also investigated how variability in pelvic landmarks may influence measures of innominate rotational asymmetry and measures of pelvic height. Thirty cadaver pelves were used for the study. Each specimen was positioned in a fixed anatomical reference position and the angle between the ASIS and PSIS measured bilaterally. In addition, side-to-side differences in the height of the innominate bone were recorded. The study found a range of values for the ASIS-PSIS of 0–23 degrees, with a mean of 13 and standard deviation of 5 degrees. Asymmetry of pelvic landmarks resulted in side-to-side differences of up to 11 degrees in ASISPSIS tilt and 16 millimeters in innominate height. These results suggest that variations in pelvic morphology may significantly influence measures of pelvic tilt and innominate rotational asymmetry
A model of ant route navigation driven by scene familiarity
In this paper we propose a model of visually guided route navigation in ants that captures the known properties of real behaviour whilst retaining mechanistic simplicity and thus biological plausibility. For an ant, the coupling of movement and viewing direction means that a familiar view specifies a familiar direction of movement. Since the views experienced along a habitual route will be more familiar, route navigation can be re-cast as a search for familiar views. This search can be performed with a simple scanning routine, a behaviour that ants have been observed to perform. We test this proposed route navigation strategy in simulation, by learning a series of routes through visually cluttered environments consisting of objects that are only distinguishable as silhouettes against the sky. In the first instance we determine view familiarity by exhaustive comparison with the set of views experienced during training. In further experiments we train an artificial neural network to perform familiarity discrimination using the training views. Our results indicate that, not only is the approach successful, but also that the routes that are learnt show many of the characteristics of the routes of desert ants. As such, we believe the model represents the only detailed and complete model of insect route guidance to date. What is more, the model provides a general demonstration that visually guided routes can be produced with parsimonious mechanisms that do not specify when or what to learn, nor separate routes into sequences of waypoints
SPEED, STRENGTH & POWER CHARACTERISITCS OF HORIZONTAL JUMPERS
It is well established that approach speed on the long and triple jump runways is the single-most important determinant of performance across a wide range of ability levels (Hay, 1986; Hay, 1992). However, the relationship between speed and jump distance decreases when the range of performances is reduced.
At an elite level speed is regarded as a pre-requisite, the differentiating factor between performances relates more to how well athlete control their speed when they make contact with the take-off board (and subsequent take-offs in the triple jump). In the take-off athletes typically experience vertical impact forces in the range of 7.9 to 12.6 x BW (Ramey and Williams, 1985), with ground contact times ranging from 120 to 180 ms (the higher values relating to the step and jump take-offs). It is therefore imperative that horizontal jumpers are conditioned appropriately to accept such high loading forces, be powerful and reactive, in order to generate vertical speed in such a small timescale. Graham-Smith and Lees (2002) suggested that performance is made up of three main interacting factors; speed, strength and technique (with power being a derivative of speed and strength). They added that optimal performance can only be achieved when all three factors are in ‘balance’.
The aim of this study was to develop a battery of tests to monitor speed, strength and power for horizontal jumpers in as functional a way as possible. The relationship between strength and power variables with speed and controlled functional performance was also investigated
Biomechanical comparison of the track start and the modified one-handed track start in competitive swimming: an intervention study
This study compared the conventional track and a new one-handed track start in elite age group swimmers to determine if the new technique had biomechanical implications on dive performance. Five male and seven female GB national qualifiers participated (mean ± SD:
age 16.7 ± 1.9 years, stretched stature 1.76 ± 0.8 m, body mass 67.4 ± 7.9 kg) and were assigned to a control group (n = 6) or an intervention group (n = 6) that learned the new onehanded dive technique. All swimmers underwent a 4-week intervention comprising 12 ± 3 thirty-minute training sessions. Video cameras synchronized with an audible signal and timing suite captured temporal and kinematic data. A
portable force plate and load cell handrail mounted to a swim starting block collected force data over 3 trials of each technique. A MANCOVA identified Block Time (BT),
Flight Time (FT), Peak Horizontal Force of the lower limbs (PHF) and Horizontal Velocity at Take-off (Vx) as covariates. During the 10-m swim trial, significant differences were found in Time to 10 m (TT10m), Total Time (TT), Peak Vertical Force (PVF), Flight Distance (FD), and Horizontal Velocity at Take-off (Vx) (p < .05). Results indicated that the conventional track start method was faster over 10 m, and therefore may be seen as a superior start after a short intervention. During training, swimmers and coaches should focus on the most statistically significant dive performance variables: peak horizontal force and velocity at take-off, block and flight time
A combined HST/CFH12k/XMM survey of X-ray luminous clusters of galaxies at z~0.2
We describe a project to study a sample of X-ray luminous clusters of
galaxies at redshift z~0.2 at several scales (with HST/WFPC2 and CFHT/CFH12k)
and wavebands (optical and X-ray). The main aims of the project are (i) to
determine the mass profiles of the clusters on scales ranging from ~10 kpc/h to
>1.5 Mpc/h using weak and strong lensing, thereby testing theoretical
predictions of a ``universal mass profile'', and (ii) to calibrate the M_tot -
T_X relation in view of future application in the study of the evolution of the
cluster mass function at higher redshift.Comment: 4 pages, 2 figures, Proceedings of the XXth Moriond Astrophysics
Meeting ``Cosmological Physics with Gravitational Lensing'', J.-P. Kneib, Y.
Mellier, M. Moniez and J. Tran Thanh Van eds., 200
LoCuSS: Exploring the selection of faint blue background galaxies for cluster weak-lensing
Cosmological constraints from galaxy clusters rely on accurate measurements
of the mass and internal structure of clusters. An important source of
systematic uncertainty in cluster mass and structure measurements is the secure
selection of background galaxies that are gravitationally lensed by clusters.
This issue has been shown to be particular severe for faint blue galaxies. We
therefore explore the selection of faint blue background galaxies, by reference
to photometric redshift catalogs derived from the COSMOS survey and our own
observations of massive galaxy clusters at z~0.2. We show that methods relying
on photometric redshifts of galaxies in/behind clusters based on observations
through five filters, and on deep 30-band COSMOS photometric redshifts are both
inadequate to identify safely faint blue background galaxies. This is due to
the small number of filters used by the former, and absence of massive galaxy
clusters at redshifts of interest in the latter. We therefore develop a
pragmatic method to combine both sets of photometric redshifts to select a
population of blue galaxies based purely on photometric analysis. This sample
yields stacked weak-lensing results consistent with our previously published
results based on red galaxies. We also show that the stacked clustercentric
number density profile of these faint blue galaxies is consistent with
expectations from consideration of the lens magnification signal of the
clusters. Indeed, the observed number density of blue background galaxies
changes by ~10-30 per cent across the radial range over which other surveys
assume it to be flat.Comment: submitted to MNRA
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