324 research outputs found
Ideal free streamline flow over a curved obstacle
AbstractIn the classical two-dimensional model the description of Helmholtz's (Kirchhoff) flow is a problem of complex analysis which can be solved analytically only for a few simple bodies or polygonal contours, using the Schwarz-Christoffel map. This paper presents a practical method for computing flows over arbitrary obstacles whose boundaries may be piecewise smooth curves, while the impinging flow may be an unbounded flow, a jet, or a semi-infinite stream, i.e. the ocean
Commentaries on Viewpoint: Distinct modalities of eccentric exercise: different recipes, not the same dish
The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise
Purpose
This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions.
Methods
Ten male amateur football players completed a 120 min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response.
Results
At HT, FT, and ET, reductions in maximal voluntary force (MVC; −11, −20 and −27%, respectively, P ≤ 0.01), potentiated twitch force (−15, −23 and −23%, respectively, P < 0.05), voluntary activation (FT, −15 and ET, −18%, P ≤ 0.01), and voluntary activation measured with TMS (−11, −15 and −17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6–11%; ICC2,1 0.83–0.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5–18%; ICC2,1 0.63–0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3–6%; ICC2,1 0.90–0.98).
Conclusion
Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanisms
Resveratrol Acts Not through Anti-Aggregative Pathways but Mainly via Its Scavenging Properties against Aβ and Aβ-Metal Complexes Toxicity
It has been recently suggested that resveratrol can be effective in slowing down Alzheimer's disease (AD) development. As reported in many biochemical studies, resveratrol seems to exert its neuro-protective role through inhibition of β-amyloid aggregation (Aβ), by scavenging oxidants and exerting anti-inflammatory activities. In this paper, we demonstrate that resveratrol is cytoprotective in human neuroblastoma cells exposed to Aβ and or to Aβ-metal complex. Our findings suggest that resveratrol acts not through anti-aggregative pathways but mainly via its scavenging properties
The population biology of the living coelacanth studied over 21Â years
Between 1986 and 2009 nine submersible and
remote-operated vehicle expeditions were carried out to
study the population biology of the coelacanth Latimeria
chalumnae in the Comoro Islands, located in the western
Indian Ocean. Latimeria live in large overlapping home
ranges that can be occupied for as long as 21 years. Most
individuals are confined to relatively small home ranges,
resting in the same caves during the day. One hundred and
forty five coelacanths are individually known, and we
estimate the total population size of Grande Comore as
approximately 300–400 adult individuals. The local population
inhabiting a census area along an 8-km section of
coastline remained stable for at least 18 years. Using
LASER-assisted observations, we recorded length frequencies
between 100 and 200 cm total length and did not
encounter smaller-bodied individuals (\100 cm total
length). It appears that coelacanth recruitment in the
observation areas occur mainly by immigrating adults. We
estimate that the mean numbers of deaths and newcomers
are 3–4 individuals per year, suggesting that longevity may
exceed 100 years. The domestic fishery represents a threat
to the long-term survival of coelacanths in the study area.
Recent changes in the local fishery include a decrease in
the abundance of the un-motorized canoes associated with
exploitation of coelacanths and an increase in motorized
canoes. Exploitation rates have fallen in recent years, and
by 2000, had fallen to lowest ever reported. Finally, future
fishery developments are discussed
Muscle pain induced by hypertonic saline in the knee extensors decreases single-limb isometric time to task failure
Purpose: Increased nociceptive activity and the experience of exercise-induced pain (EIP) may contribute to fatigue during endurance exercise. To investigate this, a pain model that produces pain similar to EIP and decouples its’ relationship to exercise intensity is required. This study 1) compared the quality of pain caused by a hypertonic saline injection into the vastus lateralis in resting and exercise conditions, and 2) investigated whether this pain contributes to changes in time to task failure. Methods: On separate days, eighteen participants completed a time to task failure at 20% maximal voluntary torque (MVT), a resting hypertonic saline intramuscular injection, and in a further three visits a time to task failure at 10% MVT following injection of isotonic saline, hypertonic saline or a control (no injection). Results: In a subset of eligible participants (n = 12), the hypertonic saline combined with 10% MVT produced a qualitative experience of pain (assessed by the McGill Pain Questionnaire) that felt similar to EIP. 10% MVT with hypertonic saline significantly elevated pain intensity in the first 20% of the time to task failure and caused a significantly (P < 0.05) shorter time to task failure (448 ± 240 s) compared with the isotonic saline (605 ± 285 s) and control (514 ± 197 s) conditions. Conclusion: These findings demonstrate that hypertonic saline increases the intensity of pain during exercise, which results in a faster occurrence of exercise-induced fatigue. These results provide important evidence supporting pain as a limiting factor in endurance performance
Trophic niche partitioning of littoral fish species from the rocky intertidal of Helgoland, Germany
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