5,496 research outputs found
Shifts in ownership toward high-powered motorcycles and its effects on public health
Objectives. We assessed whether policies designed to safeguard young motorcyclists would be effective given shifts in ownership toward high-powered motorcycles. Methods. We investigated population-wide motor vehicle driver and motorcyclist casualties (excluding passengers) recorded in Britain between 2002 and 2009. To adjust for exposure and measure individual risk, we used the estimated number of trips of motorcyclists and drivers, which had been collected as part of a national travel survey. Results. Motorcyclists were 76 times more likely to be killed than were drivers for every trip. Older motorcyclist age—strongly linked to experience, skill set,and riding behavior—did not abate the risks of high-powered motorcycles. Older motorcyclists made more trips on high-powered motorcycles. Conclusions: Tighter engine size restrictions would help reduce the use of high-powered motorcycles. Policymakers should introduce health warnings on the risks of high-powered motorcycles and the benefits of safety equipment
Glueball Spin
The spin of a glueball is usually taken as coming from the spin (and possibly
the orbital angular momentum) of its constituent gluons. In light of the
difficulties in accounting for the spin of the proton from its constituent
quarks, the spin of glueballs is reexamined. The starting point is the
fundamental QCD field angular momentum operator written in terms of the
chromoelectric and chromomagnetic fields. First, we look at the restrictions
placed on the structure of glueballs from the requirement that the QCD field
angular momentum operator should satisfy the standard commutation
relationships. This can be compared to the electromagnetic charge/monopole
system, where the quantization of the field angular momentum places
restrictions (i.e. the Dirac condition) on the system. Second, we look at the
expectation value of this operator under some simplifying assumptions.Comment: 11 pages, 0 figures; added references and some discussio
Efcacy of sodium bicarbonate ingestion strategies for protecting blinding
Sodium bicarbonate (NaHCO3) is a widely researched ergogenic aid, but the optimal blinding strategy during randomised placebo-controlled trials is unknown. In this multi-study project, we aimed to determine the most efficacious ingestion strategy for blinding NaHCO3 research. During study one, 16 physically active adults tasted 0.3 g·kg-1 body mass NaHCO3 or 0.03 g·kg-1 body mass sodium chloride placebo treatments given in different flavour (orange, blackcurrant) and temperature (chilled, room temperature) solutions. They were required to guess which treatment they had received. During study two, 12 recreational athletes performed time-to-exhaustion (TTE) cycling trials (familiarisation, four experimental). Using a randomised, double-blind design, participants consumed 0.3 g·kg-1 body mass NaHCO3 or a placebo in 5 mL·kg-1 body mass chilled orange squash/water solutions or capsules and indicated what they believed they had received immediately after consumption, pre-TTE and post-TTE. In study one, NaHCO3 prepared in chilled orange squash resulted in the most unsure ratings (44%). In study two, NaHCO3 administered in capsules resulted in more unsure ratings (% here) than NaHCO3 (% here) given in solution, with differences in treatment assignment after consumption, epre-TTE, and post-TTE (all p<0.05). Administering NaHCO3 in capsules was the most efficacious blinding strategy which provides important implications for researchers conducting randomised placebo-controlled trials
Effect of significant data loss on identifying electric signals that precede rupture by detrended fluctuation analysis in natural time
Electric field variations that appear before rupture have been recently
studied by employing the detrended fluctuation analysis (DFA) as a scaling
method to quantify long-range temporal correlations. These studies revealed
that seismic electric signals (SES) activities exhibit a scale invariant
feature with an exponent over all scales investigated
(around five orders of magnitude). Here, we study what happens upon significant
data loss, which is a question of primary practical importance, and show that
the DFA applied to the natural time representation of the remaining data still
reveals for SES activities an exponent close to 1.0, which markedly exceeds the
exponent found in artificial (man-made) noises. This, in combination with
natural time analysis, enables the identification of a SES activity with
probability 75% even after a significant (70%) data loss. The probability
increases to 90% or larger for 50% data loss.Comment: 12 Pages, 11 Figure
Improved 1000-m running performance and pacing strategy with caffeine and placebo effect: a balanced placebo design study
Purpose: To investigate the placebo effect of caffeine on pacing strategy and performance over 1000-m running time-trials using a balanced placebo design.
Methods: Eleven well-trained male middle-distance athletes performed seven 1000-m time-trials (one familiarisation, two baseline and four experimental). Experimental trials consisted of the administration of four treatments: informed caffeine/received caffeine (CC), informed caffeine/received placebo (CP), informed placebo/received caffeine (PC), and informed placebo/received placebo (PP). Treatments were randomized. Split times were recorded at 200-, 400-, 600-, 800- and 1000-m and peak heart rate (HRpeak) and rating of perceived exertion (RPE) were recorded at the completion of the trial.
Results: Relative to baseline, participants ran faster during CC (d = 0.42) and CP (d = 0.43). These changes were associated with an increased pace during the first half of the trial. No differences were shown in pacing or performance between baseline and the PC (d = 0.21) and open administration of placebo (d = 0.10). No differences were reported between treatments for HRpeak (η2 = 0.084) and RPE (η2 = 0.009).
Conclusions: Our results indicate that the effect of believing to have ingested caffeine improved performance to the same magnitude as actually receiving caffeine. These improvements were associated with an increase in pace during the first half of the time-trial
Sodium bicarbonate and time-to-exhaustion cycling performance: a retrospective analysis exploring the mediating role of expectancy
Background: A body of evidence has shown that ingesting 0.3 g·kg-1 body mass sodium bicarbonate (NaHCO3) can improve time-to-exhaustion (TTE) cycling performance, but the influence of psychophysiological mechanisms on ergogenic effects is not yet understood.
Objective: This study retrospectively examined whether changes in TTE cycling performance are mediated by positive expectations of receiving NaHCO3 and/or decline in blood bicarbonate.
Methods: In a randomised, crossover, counterbalanced, double-blind, placebo-controlled design, 12 recreationally trained cyclists (maximal oxygen consumption, 54.4 ± 5.7 mL·kg·min-1) performed four TTE cycling tests 90 min after consuming: i) 0.3 g·kg-1 body mass NaHCO3 in 5 mL·kg-1 body mass solution, ii) 0.03 g·kg-1 body mass sodium chloride in solution (placebo), iii) 0.3 g·kg-1 body mass NaHCO3 in capsules and iv) cornflour in capsules (placebo). Prior to exercise, participants rated on 1 – 5 Likert type scales how much they expected the treatment they believe had been given would improve performance. Capillary blood samples were measured for acid-base balance at baseline, pre-exercise and post-exercise.
Results: Administering NaHCO3 in solution and capsules improved TTE compared with their respective placebos (solution: 27.0 ± 21.9 s, p = 0.001; capsules: 23.0 ± 28.1 s, p = 0.016). Compared to capsules, NaHCO3 administered via solution resulted in a higher expectancy about the benefits on TTE cycling performance (Median: 3.5 vs. 2.5, Z = 2.135, p = 0.033). Decline in blood bicarbonate during exercise was higher for NaHCO3 given in solution compared to capsules (2.7 ± 2.1 mmol·L-1, p = 0.001). Mediation analyses showed that improvements in TTE cycling were indirectly related to expectancy and decline in blood bicarbonate when NaHCO3 was administered in solution but not capsules
Entropy of the Nordic electricity market: anomalous scaling, spikes, and mean-reversion
The electricity market is a very peculiar market due to the large variety of
phenomena that can affect the spot price. However, this market still shows many
typical features of other speculative (commodity) markets like, for instance,
data clustering and mean reversion. We apply the diffusion entropy analysis
(DEA) to the Nordic spot electricity market (Nord Pool). We study the waiting
time statistics between consecutive spot price spikes and find it to show
anomalous scaling characterized by a decaying power-law. The exponent observed
in data follows a quite robust relationship with the one implied by the DEA
analysis. We also in terms of the DEA revisit topics like clustering,
mean-reversion and periodicities. We finally propose a GARCH inspired model but
for the price itself. Models in the context of stochastic volatility processes
appear under this scope to have a feasible description.Comment: 16 pages, 7 figure
Spectral fluctuation characterization of random matrix ensembles through wavelets
A recently developed wavelet based approach is employed to characterize the
scaling behavior of spectral fluctuations of random matrix ensembles, as well
as complex atomic systems. Our study clearly reveals anti-persistent behavior
and supports the Fourier power spectral analysis. It also finds evidence for
multi-fractal nature in the atomic spectra. The multi-resolution and
localization nature of the discrete wavelets ideally characterizes the
fluctuations in these time series, some of which are not stationary.Comment: 7 pages, 2 eps figure
Possibility between earthquake and explosion seismogram differentiation by discrete stochastic non-Markov processes and local Hurst exponent analysis
The basic purpose of the paper is to draw the attention of researchers to new
possibilities of differentiation of similar signals having different nature.
One of examples of such kind of signals is presented by seismograms containing
recordings of earthquakes (EQ's) and technogenic explosions (TE's). We propose
here a discrete stochastic model for possible solution of a problem of strong
EQ's forecasting and differentiation of TE's from the weak EQ's. Theoretical
analysis is performed by two independent methods: with the use of statistical
theory of discrete non-Markov stochastic processes (Phys. Rev. E62,6178 (2000))
and the local Hurst exponent. Time recordings of seismic signals of the first
four dynamic orthogonal collective variables, six various plane of phase
portrait of four dimensional phase space of orthogonal variables and the local
Hurst exponent have been calculated for the dynamic analysis of the earth
states. The approaches, permitting to obtain an algorithm of strong EQ's
forecasting and to differentiate TE's from weak EQ's, have been developed.Comment: REVTEX +12 ps and jpg figures. Accepted for publication in Phys. Rev.
E, December 200
Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings
Granular packings slowly driven towards their instability threshold are
studied using a digital imaging technique as well as a nonlinear acoustic
method. The former method allows us to study grain rearrangements on the
surface during the tilting and the latter enables to selectively probe the
modifications of the weak-contact fraction in the material bulk. Gradual ageing
of both the surface activity and the weak-contact reconfigurations is observed
as a result of repeated tilt cycles up to a given angle smaller than the angle
of avalanche. For an aged configuration reached after several consecutive tilt
cycles, abrupt resumption of the on-surface activity and of the weak-contact
rearrangements occurs when the packing is subsequently inclined beyond the
previous maximal tilting angle. This behavior is compared with literature
results from numerical simulations of inclined 2D packings. It is also found
that the aged weak-contact configurations exhibit spontaneous restoration
towards the initial state if the packing remains at rest for tens of minutes.
When the packing is titled forth and back between zero and near-critical
angles, instead of ageing, the weak-contact configuration exhibits "internal
weak-contact avalanches" in the vicinity of both the near-critical and zero
angles. By contrast, the stronger-contact skeleton remains stable
- …