273 research outputs found
Test-retest reliability of ski-specific aerobic, sprint, and neuromuscular performance tests in highly trained cross-country skiers.
Laboratory tests are commonly performed by cross-country (XC) skiers due to the challenges of obtaining reliable performance indicators on snow. However, only a few studies have reported reliability data for ski-specific test protocols. Therefore, this study examined the test-retest reliability of ski-specific aerobic, sprint, and neuromuscular performance tests.
Thirty-nine highly trained XC skiers (26 men and 13 women, age: 22 ± 4 years, V̇O <sub>2max</sub> : 70.1 ± 4.5 and 58.8 ± 4.4 mL·kg <sup>-1</sup> ·min <sup>-1</sup> , respectively) performed two test trials within 6 days of a diagonal V̇O <sub>2max</sub> test, n = 27; skating graded exercise test to assess the second lactate threshold (LT <sub>2</sub> ), n = 27; 24-min double poling time trial (24-min DP, n = 25), double poling sprint test (Sprint <sub>DP1</sub> , n = 27), and 1-min self-paced skating sprint test (Sprint <sub>1-min</sub> , n = 26) using roller skis on a treadmill, and an upper-body strength test (UB-ST, n = 27) to assess peak power (P <sub>peak</sub> ) with light, medium, and heavy loads. For each test, the coefficient of variation (CV), intraclass correlation coefficient (ICC), and minimal detectable change (MDC) were calculated.
V̇O <sub>2max</sub> demonstrated good-to-excellent reliability (CV = 1.4%; ICC = 0.99; MDC = 112 mL·min <sup>-1</sup> ), whereas moderate-to-excellent reliability was found for LT <sub>2</sub> (CV = 3.1%; ICC = 0.95). Performance during 24-min DP, Sprint <sub>DP1</sub> , and Sprint <sub>1-min</sub> showed good-to-excellent reliability (CV = 1.0%-2.3%; ICC = 0.96-0.99). Absolute reliability for UB-ST P <sub>peak</sub> was poor (CV = 4.9%-7.8%), while relative reliability was excellent (ICC = 0.93-0.97) across the loads.
In highly trained XC skiers, sport-specific aerobic and sprint performance tests demonstrated high test-retest reliability, while neuromuscular performance for the upper body was less reliable. Using the presented protocols, practitioners can assess within- and between-season changes in relevant performance indicators
Relaxation of the cosmological constant at inflation?
We suggest that the cosmological constant has been relaxed to its present,
very small value during the inflationary stage of the evolution of the
Universe. This requires relatively low scale, very long duration and
unconventional source of inflation. We present a concrete mechanism of the
cosmological constant relaxation at the inflationary epoch.Comment: 11 page
Reconciling inflation with openness
It is already understood that the increasing observational evidence for an
open Universe can be reconciled with inflation if our horizon is contained
inside one single huge bubble nucleated during the inflationary phase
transition. In this frame of ideas, we show here that the probability of living
in a bubble with the right (now the observations require ) can be comparable with unity, rather than infinitesimally small.
For this purpose we modify both quantitatively and qualitatively an intuitive
toy model based upon fourth order gravity. As this scheme can be implemented in
canonical General Relativity as well (although then the inflation driving
potential must be designed entirely ad hoc), inferring from the observations
that not only does not conflict with the inflationary paradigm,
but rather supports therein the occurrence of a primordial phase transition.Comment: 4 pages, one postscript figure, to be published on Physical Review D
PACS: 98.80. C
Supergravity pp-wave solutions with 28 and 24 supercharges
We conduct an exhaustive search for solutions of IIA and IIB supergravity
with augmented supersymmetry. We find a two-parameter family of IIB solutions
preserving 28 supercharges, as well as several other IIA and IIB families of
solutions with 24 supercharges. Given the simplicity of the pp-wave solution,
the algorithm described here represents a systematic way of classifying all
such solutions with augmented supersymmetry. By T-dualizing some of these
solutions we obtain exact non-pp wave supergravity solutions (with 8 or 16
supercharges), which can be interpreted as perturbations of the AdS-CFT
correspondence with irrelevant operators
Transition Radiation Spectra of Electrons from 1 to 10 GeV/c in Regular and Irregular Radiators
We present measurements of the spectral distribution of transition radiation
generated by electrons of momentum 1 to 10 GeV/c in different radiator types.
We investigate periodic foil radiators and irregular foam and fiber materials.
The transition radiation photons are detected by prototypes of the drift
chambers to be used in the Transition Radiation Detector (TRD) of the ALICE
experiment at CERN, which are filled with a Xe, CO2 (15 %) mixture. The
measurements are compared to simulations in order to enhance the quantitative
understanding of transition radiation production, in particular the momentum
dependence of the transition radiation yield.Comment: 18 pages, 15 figures, submitted to Nucl. Instr. Meth. Phys. Res.
Energy loss of pions and electrons of 1 to 6 GeV/c in drift chambers operated with Xe,CO2(15%)
We present measurements of the energy loss of pions and electrons in drift
chambers operated with a Xe,CO2(15%) mixture. The measurements are carried out
for particle momenta from 1 to 6 GeV/c using prototype drift chambers for the
ALICE TRD. Microscopic calculations are performed using input parameters
calculated with GEANT3. These calculations reproduce well the measured average
and most probable values for pions, but a higher Fermi plateau is required in
order to reproduce our electron data. The widths of the measured distributions
are smaller for data compared to the calculations. The electron/pion
identification performance using the energy loss is also presented.Comment: 15 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth.
Space charge in drift chambers operated with the Xe,CO2(15%) mixture
Using prototype modules of the ALICE Transition Radiation Detector we
investigate space charge effects and the dependence of the pion rejection
performance on the incident angle of the ionizing particle. The average pulse
height distributions in the drift chambers operated with the Xe,CO2(15%)
mixture provide quantitative information on the gas gain reduction due to space
charge accumulating during the drift of the primary ionization. Our results
demonstrate that the pion rejection performance of a TRD is better for tracks
which are not at normal incidence to the anode wires. We present detailed
simulations of detector signals, which reproduce the measurements and lend
strong support to our interpretation of the measurements in terms of space
charge effects.Comment: 18 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth.
A. Data files available at http://www-alice.gsi.de/tr
Sequential design of computer experiments for the estimation of a probability of failure
This paper deals with the problem of estimating the volume of the excursion
set of a function above a given threshold,
under a probability measure on that is assumed to be known. In
the industrial world, this corresponds to the problem of estimating a
probability of failure of a system. When only an expensive-to-simulate model of
the system is available, the budget for simulations is usually severely limited
and therefore classical Monte Carlo methods ought to be avoided. One of the
main contributions of this article is to derive SUR (stepwise uncertainty
reduction) strategies from a Bayesian-theoretic formulation of the problem of
estimating a probability of failure. These sequential strategies use a Gaussian
process model of and aim at performing evaluations of as efficiently as
possible to infer the value of the probability of failure. We compare these
strategies to other strategies also based on a Gaussian process model for
estimating a probability of failure.Comment: This is an author-generated postprint version. The published version
is available at http://www.springerlink.co
Position Reconstruction in Drift Chambers operated with Xe, CO2 (15%)
We present measurements of position and angular resolution of drift chambers
operated with a Xe,CO(15%) mixture. The results are compared to Monte Carlo
simulations and important systematic effects, in particular the dispersive
nature of the absorption of transition radiation and non-linearities, are
discussed. The measurements were carried out with prototype drift chambers of
the ALICE Transition Radiation Detector, but our findings can be generalized to
other drift chambers with similar geometry, where the electron drift is
perpendicular to the wire planes.Comment: 30 pages, 18 figure
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