3,625 research outputs found
Effect of plyometric training on swimming block start performance in adolescents
This study aimed to identify the effect of plyometric training (PT), when added to habitual training (HT) regimes, on swim start performance. After the completion of a baseline competitive swim start, 22 adolescent swimmers were randomly assigned to either a PT (n = 11, age: 13.1 ± 1.4 yr, mass: 50.6 ± 12.3 kg, stature: 162.9 ± 11.9 cm) or an HT group (n = 11, age: 12.6 ± 1.9 yr, mass: 43.3 ± 11.6 kg, stature: 157.6 ± 11.9 cm). Over an 8-week preseason period, the HT group continued with their normal training program, whereas the PT group added 2 additional 1-hour plyometric-specific sessions, incorporating prescribed exercises relating to the swimming block start (SBS). After completion of the training intervention, post-training swim start performance was reassessed. For both baseline and post-trials, swim performance was recorded using videography (50Hz Canon MVX460) in the sagital plane of motion. Through the use of Silicon Coach Pro analysis package, data revealed significantly greater change between baseline and post-trials for PT when compared with the HT group for swim performance time to 5.5 m (−0.59 s vs. −0.21 s; p < 0.01) and velocity of take-off to contact (0.19 ms−1 vs. −0.07 ms−1; p < 0.01). Considering the practical importance of a successful swim start to overall performance outcome, the current study has found that inclusion of suitable and safely implemented PT to adolescent performers, in addition to HT routines, can have a positive impact on swim start performance
A Multiwavelength Study on the Fate of Ionizing Radiation in Local Starbursts
The fate of ionizing radiation is vital for understanding cosmic ionization,
energy budgets in the interstellar and intergalactic medium, and star formation
rate indicators. The low observed escape fractions of ionizing radiation have
not been adequately explained, and there is evidence that some starbursts have
high escape fractions. We examine the spectral energy distributions of a sample
of local star-forming galaxies, containing thirteen local starburst galaxies
and ten of their ordinary star-forming counterparts, to determine if there
exist significant differences in the fate of ionizing radiation in these
galaxies. We find that the galaxy-to-galaxy variations in the SEDs is much
larger than any systematic differences between starbursts and non-starbursts.
For example, we find no significant differences in the total absorption of
ionizing radiation by dust, traced by the 24um, 70um, and 160um MIPS bands of
the Spitzer Space Telescope, although the dust in starburst galaxies appears to
be hotter than that of non-starburst galaxies. We also observe no excess
ultraviolet flux in the GALEX bands that could indicate a high escape fraction
of ionizing photons in starburst galaxies. The small H-alpha fractions of the
diffuse, warm ionized medium in starburst galaxies are apparently due to
temporarily boosted H-alpha luminosity within the star-forming regions
themselves, with an independent, constant WIM luminosity. This independence of
the WIM and starburst luminosities contrasts with WIM behavior in non-starburst
galaxies and underscores our poor understanding of radiation transfer in both
ordinary and starburst galaxies.Comment: 10 pages, 8 figures, accepted to ApJ 10/11/1
Improving measurements of SF6 for the study of atmospheric transport and emissions
Sulfur hexafluoride (SF6) is a potent greenhouse gas and useful atmospheric tracer. Measurements of SF6 on global and regional scales are necessary to estimate emissions and to verify or examine the performance of atmospheric transport models. Typical precision for common gas chromatographic methods with electron capture detection (GC-ECD) is 1–2%. We have modified a common GC-ECD method to achieve measurement precision of 0.5% or better. Global mean SF6 measurements were used to examine changes in the growth rate of SF6 and corresponding SF6 emissions. Global emissions and mixing ratios from 2000–2008 are consistent with recently published work. More recent observations show a 10% decline in SF6 emissions in 2008–2009, which seems to coincide with a decrease in world economic output. This decline was short-lived, as the global SF6 growth rate has recently increased to near its 2007–2008 maximum value of 0.30±0.03 pmol mol−1 (ppt) yr−1 (95% C.L.)
Estimation of trace gas fluxes with objectively determined basis functions using reversible-jump Markov chain Monte Carlo
Atmospheric trace gas inversions often attempt to attribute fluxes to a
high-dimensional grid using observations. To make this problem
computationally feasible, and to reduce the degree of under-determination,
some form of dimension reduction is usually performed. Here, we present an
objective method for reducing the spatial dimension of the parameter space in
atmospheric trace gas inversions. In addition to solving for a set of
unknowns that govern emissions of a trace gas, we set out a framework that
considers the number of unknowns to itself be an unknown. We rely on the
well-established reversible-jump Markov chain Monte Carlo algorithm to use
the data to determine the dimension of the parameter space. This framework
provides a single-step process that solves for both the resolution of the
inversion grid, as well as the magnitude of fluxes from this grid. Therefore,
the uncertainty that surrounds the choice of aggregation is accounted for in
the posterior parameter distribution. The posterior distribution of this
transdimensional Markov chain provides a naturally smoothed solution, formed
from an ensemble of coarser partitions of the spatial domain. We describe the
form of the reversible-jump algorithm and how it may be applied to trace gas
inversions. We build the system into a hierarchical Bayesian framework in
which other unknown factors, such as the magnitude of the model uncertainty,
can also be explored. A pseudo-data example is used to show the usefulness of
this approach when compared to a subjectively chosen partitioning of a
spatial domain. An inversion using real data is also shown to illustrate the
scales at which the data allow for methane emissions over north-west Europe
to be resolved
MgII absorption systems with W_0 > 0.1 \AA for a radio selected sample of 77 QSOs and their associated magnetic fields at high redshifts
We present a catalogue of MgII absorption systems obtained from high
resolution UVES/VLT data of 77 QSOs in the redshift range 0.6 < z < 2.0, and
down to an equivalent width W_0 > 0.1 \AA. The statistical properties of our
sample are found to be in agreement with those from previous work in the
literature. However, we point out that the previously observed increase with
redshift of dN/dz for weak absorbers, pertains exclusively to very weak
absorbers with W_0 < 0.1 \AA. Instead, dN/dz for absorbers with W_0 in the
range 0.1-0.3 \AA actually decreases with redshift, similarly to the case of
strong absorbers. We then use this catalogue to extend our earlier analysis of
the links between the Faraday Rotation Measure of the quasars and the presence
of intervening MgII absorbing systems in their spectra. In contrast to the case
with strong MgII absorption systems W_0 > 0.3 \AA, the weaker systems do not
contribute significantly to the observed Rotation Measure of the background
quasars. This is possibly due to the higher impact parameters of the weak
systems compared to strong ones, suggesting that the high column density
magnetized material that is responsible for the Faraday Rotation is located
within about 50 kpc of the galaxies. Finally, we show that this result also
rules out the possibility that some unexpected secondary correlation between
the quasar redshift and its intrinsic Rotation Measure is responsible for the
association of high Rotation Measure and strong intervening MgII absorption
that we have presented elsewhere, since this would have produced an equal
effect for the weak absorption line systems, which exhibit a very similar
distribution of quasar redshifts.Comment: Accepted for publication in ApJ. 12 pages, 8 figure
Species of ground beetle (Coleoptera: Carabidae) in organic apple orchards of British Columbia
In a two year study, 14 genera of Carabidae (Agonum Bonelli, Amara Bonelli, Anisodactylus Dejean, Bembidion Latreille, Carabus Linné, Harpalus Latreille, Lebia Latreille, Loricera Latreille, Poecilus Bonelli, Pterostichus Bonelli, Scaphinotus Dejean, Stenolophus Stephens, Syntomus Hope and Trechus Clairville) represented by 44 species were identified from six commercial organic apple orchards in the southern Similkameen valley in British Columbia, Canada; 13 of these species were not native to the area. The 4,299 specimens were caught in 'ramp' pitfall traps, with the genera Pterostichus and Harpalus comprising 56% and 43%, respectively. Numbers of Carabidae ranged from 11-21 species per orchard, with their presence detected throughout the collection period
Characterization of uncertainties in atmospheric trace gas inversions using hierarchical Bayesian methods
We present a hierarchical Bayesian method for atmospheric trace gas
inversions. This method is used to estimate emissions of trace gases as well
as "hyper-parameters" that characterize the probability density functions
(PDFs) of the a priori emissions and model-measurement covariances. By
exploring the space of "uncertainties in uncertainties", we show that the
hierarchical method results in a more complete estimation of emissions and
their uncertainties than traditional Bayesian inversions, which rely heavily
on expert judgment. We present an analysis that shows the effect of
including hyper-parameters, which are themselves informed by the data, and
show that this method can serve to reduce the effect of errors in assumptions
made about the a priori emissions and model-measurement uncertainties. We
then apply this method to the estimation of sulfur hexafluoride (SF6)
emissions over 2012 for the regions surrounding four Advanced Global
Atmospheric Gases Experiment (AGAGE) stations. We find that improper
accounting of model representation uncertainties, in particular, can lead to
the derivation of emissions and associated uncertainties that are unrealistic
and show that those derived using the hierarchical method are likely to be
more representative of the true uncertainties in the system. We demonstrate
through this SF6 case study that this method is less sensitive to
outliers in the data and to subjective assumptions about a priori emissions
and model-measurement uncertainties than traditional methods
Recent and future trends in synthetic greenhouse gas radiative forcing
Atmospheric measurements show that emissions of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons are now the primary drivers of the positive growth in synthetic greenhouse gas (SGHG) radiative forcing. We infer recent SGHG emissions and examine the impact of future emissions scenarios, with a particular focus on proposals to reduce HFC use under the Montreal Protocol. If these proposals are implemented, overall SGHG radiative forcing could peak at around 355 mW m[superscript −2] in 2020, before declining by approximately 26% by 2050, despite continued growth of fully fluorinated greenhouse gas emissions. Compared to “no HFC policy” projections, this amounts to a reduction in radiative forcing of between 50 and 240 mW m[superscript −2] by 2050 or a cumulative emissions saving equivalent to 0.5 to 2.8 years of CO2 emissions at current levels. However, more complete reporting of global HFC emissions is required, as less than half of global emissions are currently accounted for.Natural Environment Research Council (Great Britain) (Advanced Research Fellowship NE/I021365/1)United States. National Aeronautics and Space Administration (Upper Atmospheric Research Program Grant NNX11AF17G)United States. National Oceanic and Atmospheric Administratio
LBT and Spitzer Spectroscopy of Star-Forming Galaxies at 1 < z < 3: Extinction and Star Formation Rate Indicators
We present spectroscopic observations in the rest-frame optical and near- to
mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous
star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the
Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample
was selected to represent pure, actively star-forming systems, absent of active
galactic nuclei. The large lensing magnifications result in high
signal-to-noise spectra that can probe faint IR recombination lines, including
Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three
lensed galaxies with similar suites of unpublished data and observations from
the literature, resulting in the final sample of seven galaxies. We use the IR
recombination lines in conjunction with H-alpha observations to probe the
extinction, Av, of these systems, as well as testing star formation rate (SFR)
indicators against the SFR measured by fitting spectral energy distributions to
far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger
than previously known for a similar range of IR luminosities at these
redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of
extinction in the most IR luminous galaxies. We also measure extinction by
comparing SFR estimates from optical emission lines with those from far-IR
measurements. The comparison of results from these two independent methods
indicates a large variety of dust distribution scenarios at 1 < z < 3. Without
correcting for dust extinction, the H-alpha SFR indicator underestimates the
SFR; the size of the necessary correction depends on the IR luminosity and dust
distribution scenario. Individual SFR estimates based on the 6.2 micron PAH
emission line luminosity do not show a systematic discrepancy with extinction,
although a considerable, ~0.2 dex scatter is observed.Comment: Accepted for publication in The Astrophysical Journal; 14 pages, 8
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