252 research outputs found
Test-retest reliability of segment kinetic energy measures in the golf swing
Analyses of segment kinetic energy (KE) can provide the most appropriate means of exploring sequential movements. As the reliability associated with its measurement has not been reported, the aim of this study was to examine the test-retest reliability of segment KE measures in the golf swing. On two occasions, seven male golfers hit five shots with three different clubs. Body segment inertia parameters were estimated for 17 rigid bodies and 3D kinematic data were collected during each swing. The magnitude and timing of peak total, linear and angular kinetic energies were then calculated for each rigid body and for four segment groups. Regardless of club type, KE was measured with high reliability for almost all rigid bodies and segment groups. However, significantly larger magnitudes of peak total (p = 0.039) and linear (p = 0.021) lower body KE were reported in test 2 than in test 1. The high reliability reported in this study provides support for the use of analyses of segment kinetic energy. However, practitioners should pay careful attention to the identification of anatomical landmarks which define the thigh, pelvis and thorax as this was the main cause of variability in repeated measures of segment kinetic energy
The 2dF QSO Redshift Survey - 10K@2K!
With ~10000 QSO redshifts, the 2dF QSO Redshift Survey (2QZ) is already the
biggest individual QSO survey. The aim for the survey is to have ~25000 QSO
redshifts, providing an order of magnitude increase in QSO clustering
statistics. We first describe the observational parameters of the 2dF QSO
survey. We then describe several highlights of the survey so far; we present
new estimates of the QSO luminosity function and the QSO correlation function.
We also present the first estimate of the QSO power spectrum from the 2QZ
catalogue, probing the form of the fluctuation power-spectrum out to the
\~1000h-1Mpc scales only previously probed by COBE. We find a power spectrum
which is steeper than the prediction of standard CDM and more consistent with
the prediction of Lambda-CDM. The best-fit value for the power spectrum shape
parameter for a range of cosmologies is Gamma=0.1+-0.1. Finally, we discuss how
the complete QSO survey will be able to constrain the value of Omega_Lambda by
combining results from the evolution of QSO clustering and from a geometric
test of clustering isotropy.Comment: 11 pages, 6 figures, latex, eso and springer sty files included. To
appear in the proceedings of the MPA/ESO/MPA conference "Mining the Sky",
Garching, July 31 - August 4 2000, eds. A.J. Banday et a
First Results from the 2dF QSO redshift survey
We present some initial results from the 2dF QSO redshift survey. The aim of
the survey is to produce an optically-selected catalogue of 25000 QSOs over the
redshift range 0<z<3 using the 2-degree field at the Anglo-Australian
Telescope.Comment: 7 pages, 6 figures, submitted to proceedings of ESO Deep Fields
conferenc
Clustering in the 2dF QSO Redshift Survey
We present clustering results from the 2dF QSO Redshift Survey (2QZ) which
currently contains over 20,000 QSOs at z<3. The two-point correlation function
of QSOs averaged over the entire survey (~1.5) is found to be similar to
that of local galaxies. When sub-dividing the sample as a function of redshift,
we find that for an Einstein-de Sitter universe QSO clustering is constant (in
comoving coordinates) over the entire redshift range probed by the 2QZ, while
in a universe with Omega_0=0.3 and Lambda_0=0.7 there is a marginal increase in
clustering with redshift. Sub-dividing the 2QZ on the basis of apparent
magnitude we find only a slight difference between the clustering of QSOs of
different apparent brightness, with the brightest QSOs having marginally
stronger clustering. We have made a first measurement of the redshift space
distortion of QSO clustering, with the goal of determining the value of
cosmological parameters (in partcular Lambda_0) from geometric distortions. The
current data do not allow us to discriminate between models, however, in
combination with constraints from the evolution of mass clustering we find
Omega_0=1-Lambda_0=0.23 +0.44-0.13 and beta(z~1.4)=0.39 +0.18-0.17. The full
2QZ data set will provide further cosmological constraints.Comment: 5 pages, 7 figures. Contributed to the 'Where's the Matter'
conference in Marseille 25-29 June 200
Probing 3-D matter distribution at z~2 with QSO multiple lines of sight
We investigate the 3-D matter distribution at z~2 with high resolution (R ~
40000) spectra of QSO pairs and groups obtained with the UVES spectrograph at
ESO VLT. Our sample is unique for the number density of objects and the variety
of separations, between 0.5 and 7 proper Mpc. We compute the real space
cross-correlation function of the Lyman-alpha forest transmitted fluxes. There
is a significant clustering signal up to ~2 proper Mpc, which is still present
when absorption lines with high column density (log N > 13.8) are excluded.Comment: Poster paper presented at the IAU Colloquium #199 on "Probing
Galaxies through Quasar Absorption Lines" held in Shanghai, China from March
14th to 18th, 200
Tomography of the intergalactic medium with Ly-alpha forests in close QSO pairs
We study the three-dimensional distribution of non virialised matter at z~2
using high resolution spectra of QSO pairs and simulated spectra drawn from
cosmological hydrodynamical simulations. We have collected the largest sample
of QSO pairs ever observed with UVES at the ESO-VLT, with angular separations
between ~1 and 14 arcmin. The observed correlation functions of the transmitted
flux in the HI Lyman alpha forest along and transverse to the lines of sight
are in good agreement implying that the distortions in redshift space due to
peculiar velocities are small. The clustering signal is significant up to
velocity separations of ~200 km/s, or about 3 h^{-1} comoving Mpc. The regions
at lower overdensity (rho/ < 6.5) are still clustered but on smaller
scales (Delta v < 100 km/s). The observed and simulated correlation functions
are compatible at the 3 sigma level. A better concordance is obtained when only
the low overdensity regions are selected for the analysis or when the effective
optical depth of the simulated spectra is increased artificially, suggesting a
deficiency of strong lines in the simulated spectra. We found that also a lower
value of the power-law index of the temperature-density relation for the Lyman
alpha forest gas improves the agreement between observed and simulated results.
If confirmed, this would be consistent with other observations favouring a late
HeII reionization epoch (at z~3). We remark the detection of a significant
clustering signal in the cross correlation coefficient at a transverse velocity
separation Delta v_{\perp} ~500 km/s whose origin needs further investigation.Comment: Accepted for publication in MNRAS, revised version matching the
accepted on
High-frequency monitoring of nitrogen and phosphorus response in three rural catchments to the end of the 2011â2012 drought in England
This paper uses high-frequency bankside measurements from three catchments selected as part of the UK government-funded Demonstration Test Catchments (DTC) project. We compare the hydrological and hydrochemical patterns during the water year 2011â2012 from the Wylye tributary of the River Avon with mixed land use, the Blackwater tributary of the River Wensum with arable land use and the Newby Beck tributary of the River Eden with grassland land use. The beginning of the hydrological year was unusually dry and all three catchments were in states of drought. A sudden change to a wet summer occurred in April 2012 when a heavy rainfall event affected all three catchments. The year-long time series and the individual storm responses captured by in situ nutrient measurements of nitrate and phosphorus (total phosphorus and total reactive phosphorus) concentrations at each site reveal different pollutant sources and pathways operating in each catchment. Large storm-induced nutrient transfers of nitrogen and or phosphorus to each stream were recorded at all three sites during the late April rainfall event. Hysteresis loops suggested transport-limited delivery of nitrate in the Blackwater and of total phosphorus in the Wylye and Newby Beck, which was thought to be exacerbated by the dry antecedent conditions prior to the storm. The high rate of nutrient transport in each system highlights the scale of the challenges faced by environmental managers when designing mitigation measures to reduce the flux of nutrients to rivers from diffuse agricultural sources. It also highlights the scale of the challenge in adapting to future extreme weather events under a changing climate
Ice Age megafauna rock art in the Colombian Amazon?
Megafauna paintings have accompanied the earliest archaeological contexts across the continents, revealing a fundamental inter-relationship between early humans and megafauna during the global human expansion as unfamiliar landscapes were humanized and identities built into new territories. However, the identification of extinct megafauna from rock art is controversial. Here, we examine potential megafauna depictions in the rock art of SerranĂa de la Lindosa, Colombian Amazon, that includes a giant sloth, a gomphothere, a camelid, horses and three-toed ungulates with trunks. We argue that they are Ice Age rock art based on the (i) naturalistic appearance and diagnostic morphological features of the animal images, (ii) late Pleistocene archaeological dates from La Lindosa confirming the contemporaneity of humans and megafauna, (iii) recovery of ochre pigments in late Pleistocene archaeological strata, (iv) the presence of most megafauna identified in the region during the late Pleistocene as attested by archaeological and palaeontological records, and (v) widespread depiction of extinct megafauna in rock art across the Americas. Our findings contribute to the emerging picture of considerable geographical and stylistic variation of geometric and figurative rock art from early human occupations across South America. Lastly, we discuss the implications of our findings for understanding the early human history of tropical South America. This article is part of the theme issue âTropical forests in the deep human pastâ.1. Introduction 2. Early rock art in the Americas, study region and brief archaeological background 3. The La Lindosa rock art 4. The megafauna paintings (a) Giant ground sloth (Megatheriidae) (b) Proboscidean (Gomphotheriidae) (c) Horse (Equidae) (d) Camelid (Camelidae) (e) Macraucheniid (Macraucheniidae) 5. Concluding remark
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