4,078 research outputs found
Review of meteoroid-bumper interaction studies at McGill University
Experimental investigation of meteoroid-bumper impact, debris cloud expansion, and second surface pressure loadin
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
Quantum Stochastic Processes and the Modelling of Quantum Noise
This brief article gives an overview of quantum mechanics as a {\em quantum
probability theory}. It begins with a review of the basic operator-algebraic
elements that connect probability theory with quantum probability theory. Then
quantum stochastic processes is formulated as a generalization of stochastic
processes within the framework of quantum probability theory. Quantum Markov
models from quantum optics are used to explicitly illustrate the underlying
abstract concepts and their connections to the quantum regression theorem from
quantum optics.Comment: 14 pages, invited article for the second edition of Springer's
Encyclopedia of Systems and Control (to appear). Comments welcom
Probing Solar Convection
In the solar convection zone acoustic waves are scattered by turbulent sound
speed fluctuations. In this paper the scattering of waves by convective cells
is treated using Rytov's technique. Particular care is taken to include
diffraction effects which are important especially for high-degree modes that
are confined to the surface layers of the Sun. The scattering leads to damping
of the waves and causes a phase shift. Damping manifests itself in the width of
the spectral peak of p-mode eigenfrequencies. The contribution of scattering to
the line widths is estimated and the sensitivity of the results on the assumed
spectrum of the turbulence is studied. Finally the theoretical predictions are
compared with recently measured line widths of high-degree modes.Comment: 26 pages, 7 figures, accepted by MNRA
Quantifying the effects of acute hypoxic exposure on exercise performance and capacity: A systematic review and meta-regression
Objective: To quantify the effects of acute hypoxic exposure on exercise capacity and performance, which includes continuous and intermittent forms of exercise. Design: A systematic review was conducted with a three-level mixed effects meta-regression. The ratio of means method was used to evaluate main effects and moderators providing practical interpretations with percentage change. Data Sources: A systemic search was performed using 3 databases (Google scholar, PubMed and SPORTDiscus). Eligibility criteria for selecting studies: Inclusion was restricted to investigations that assessed exercise performance (time trials, sprint, and intermittent exercise tests) and capacity (time to exhaustion test (TTE)) with acute hypoxic (< 24 hrs) exposure and a normoxic comparator. Results: Eighty-two outcomes from 53 studies (N = 798) were included in this review. The results show an overall reduction in exercise performance/capacity -17.8 ± 3.9% (95% CI -22.8% to -11.0%), which was significantly moderated by -6.5 ± 0.9% per 1000 m altitude elevation (95% CI -8.2% to -4.8%) and oxygen saturation (-2.0 ± 0.4% 95% CI -2.9% to -1.2%). Time trial (-16.2 ± 4.3%; 95% CI -22.9% to -9%) and TTE (-44.5 ± 6.9%; 95% CI -51.3% to -36.7%) elicited a negative effect, whilst indicating a quadratic relationship between hypoxic magnitude and both TTE and TT performance. Furthermore, exercise < 2-min exhibited no ergolytic effect from acute hypoxia. Summary/ Conclusion: This review highlights the ergolytic effect of acute hypoxic exposure; which is curvilinear for TTE and TT performance with increasing hypoxic levels, but short-duration intermittent and sprint exercise seem to be unaffected
Contemplations on Dirac's equation in quaternionic coordinates
A formulation of Dirac's equation using complex-quaternionic coordinates
appears to yield an enormous gain in formal elegance, as there is no longer any
need to invoke Dirac matrices. This formulation, however, entails several
peculiarities, which we investigate and attempt to interpret
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
Asteroseismic Theory of Rapidly Oscillating Ap Stars
This paper reviews some of the important advances made over the last decade
concerning theory of roAp stars.Comment: 9 pages, 5 figure
On the Penetration of Meridional Circulation below the Solar Convection Zone II: Models with Convection Zone, the Taylor-Proudman constraint and Applications to Other Stars
The solar convection zone exhibits a strong level of differential rotation,
whereby the rotation period of the polar regions is about 25-30% longer than
the equatorial regions. The Coriolis force associated with these zonal flows
perpetually "pumps" the convection zone fluid, and maintains a quasi-steady
circulation, poleward near the surface. What is the influence of this
meridional circulation on the underlying radiative zone, and in particular,
does it provide a significant source of mixing between the two regions? In
Paper I, we began to study this question by assuming a fixed meridional flow
pattern in the convection zone and calculating its penetration depth into the
radiative zone. We found that the amount of mixing caused depends very
sensitively on the assumed flow structure near the radiative--convective
interface. We continue this study here by including a simple model for the
convection zone "pump", and calculating in a self-consistent manner the
meridional flows generated in the whole Sun. We find that the global
circulation timescale depends in a crucial way on two factors: the overall
stratification of the radiative zone as measured by the Rossby number times the
square root of the Prandtl number, and, for weakly stratified systems, the
presence or absence of stresses within the radiative zone capable of breaking
the Taylor-Proudman constraint. We conclude by discussing the consequences of
our findings for the solar interior and argue that a potentially important
mechanism for mixing in Main Sequence stars has so far been neglected.Comment: 42 pages, 13 figures. Submitted to Ap
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