Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Tropical climate imposes a high level of physiological stress, which could modify the target heart rate in training load prescription, as the recommendations are often determined by maximal oxygen uptake testing in temperature-neutral laboratories. To test this hypothesis, 7 highlevel cyclists performed two randomised maximal tests in neutral (19.2±0.9 ◦C; 51.7±1.3% RH) and Tropical environment (25.8±1.1 ◦C; 63.7±2.3% RH). Neither maximal oxygen uptake nor ventilatory threshold was influenced by the environmental conditions. However, ventilation (p < 0.005) and the respiratory equivalent in O2 (p < 0.05) were significantly higher in the Tropical environment, whereas maximal power output and the time to attain maximal oxygen uptake were significantly lower (p < 0.05 for both). Moreover, the ventilatory cost of cycling (expressed in LW−1) was significantly greater in the Tropical condition (0.40±0.03 LW−1 vs. 0.32±0.05 LW−1, in Tropical vs. Neutral; condition effect: p < 0.005; condition×time: p < 0.001). Rectal temperature was influenced by neither the environmental conditions nor exercise (36.7±0.1 and 37.0±0.1 ◦Cvs. 36.8±0.1 and 37.1±0.2 ◦C, in Tropical vs. Neutral, before and after exercise) but was influenced by condition×time (p < 0.05). The heart rate (HR) values usually used for training prescription were not significantly different (154±5 bpm vs. 156±4 bpm and 172±4 bpm vs. 167±4 bpm in Tropical vs. Neutral climate, for the first and second thresholds, respectively). We concluded that the usual parameters measured during maximal exercise to establish training programs are not impaired in moderate Tropical environment. Nevertheless, the thermal stress attested by the increased ventilatory cost of cycling could have prevented the cyclists from performing a true maximal test in Tropical conditions.
ISSN: 1440-2440

hal-00703461
https://hal.univ-antilles.fr/hal-00703461
DOI : 10.1016/j.jsams.2009.11.004

Éditeur(s) : HAL CCSD Institute of Electrical and Electronics Engineers
Résumé : International audience
: A new set-up for exposure of human cells in vitro at 37°C to pulse-modulated 300 MHz and 500 MHz signals of future magnetic resonance imaging (MRI) systems is designed, built up, and characterized. Two dipole antennas, specifically designed for ultra high field MRI, are used as radiating structures. The electromagnetic (EM) field distribution inside the incubator containing the cells is computed, and it is shown to be in a good agreement with measurements. The electric field at the cell level is quantified numerically. Local, 1g average, and averaged over the culture medium volume SAR are provided along with the standard deviation values for each well. Temperature increments are measured inside the culture medium during the exposure using an optical fiber thermometer. Then we identify the pulse parameters corresponding to the thermal threshold of 1°C, usually considered as a threshold for thermally-induced biological effects. For these parameters, the induction of heat shock proteins is assessed to biologically verify a potential thermal response of cells. The data demonstrate that, under the considered experimental conditions, exposure to pulsemodulated radiations emulating typical ultra high field MRI signals, corresponding to temperature increments below 1°C, does not trigger any heat shock response in human brain cells.
ISSN: 0018-9294

hal-00874329
https://hal.archives-ouvertes.fr/hal-00874329
DOI : 10.1109/TBME.2013.2270371
PUBMED : 23799680

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We explore the use of seismic noise produced by rivers to monitor the bed load transport in the case of a low-discharge braided river in the French Alps: the "torrent de St Pierre". For this purpose, we deployed two dedicated seismic networks during summers 2007 and 2008, for which the characteristics of the recorded continuous signal are similar despite changes in the sensor locations. For dry weather conditions, only melting of nearby glaciers controls the supply of water to the stream. In these conditions, the river hydrology and the seismic energy in the 2-80 Hz frequency band both follow a diurnal fluctuation similar to the thermal amplitude. In contrast during rainfall episodes, the temperature variation fails to explain the hydrodynamic changes. Dense cloud covers reduce glacier melting and the recorded seismic energy denotes bursts of high-frequency seismic noise well correlated with water level data. Comparisons between the recorded seismic signals and the collected hydrological and sediment load data indicate that a frequency band of 3-9 Hz best explains the water level changes and thus the seismic waves coming from the flow turbulence. These analyses also reveal the presence of a seismic noise threshold that might be linked to the water shear stress exerted by the flowing water. Using the seismic energy in this frequency band as a proxy of the fluvial shear stress, the seismic-hydrologic relationship may be sensitive to variations in bed load transport. The spectral content of the seismic energy shows patterns consistent with the mobilization of sediment particles. From the interpretations of the seismic wave attenuation of river sources, we finally propose that stations at a distance from the stream less than 50 m are able to record most sediment particles. Farther stations are still useful during extreme events when largest grain sizes are mobilized. More generally this study demonstrates the feasibility of using the river seismic signal to survey bed load transport in various river types from small braided mountain rivers like the "torrent de St Pierre" to the large entrenched Himalayan rivers.
ISSN: 0022-1694

hal-00644789
https://hal.archives-ouvertes.fr/hal-00644789
DOI : 10.1016/j.jhydrol.2011.07.014

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
The only symbiotic Mediterranean gorgonian, Eunicella singularis, has faced several mortality events connected to abnormal high temperatures. Since thermotolerance data remain scarce, heat-induced necrosis was monitored in aquarium by morphometric analysis. Gorgonian tips were sampled at two sites: Medes (Spain) and Riou (France) Islands, and at two depths: 15 m and-35 m. Although coming from contrasting thermal regimes, seawater above 28 degrees C led to rapid and complete tissue necrosis for all four populations. However, at 27 degrees C, the time length leading to 50% tissue necrosis allowed us to classify samples within three classes of thermal sensitivity. Irrespectively of the depth, Medes specimens were either very sensitive or resistant, while Riou fragments presented a medium sensitivity. Microsatellite analysis revealed that host and symbiont were genetically differentiated between sites, but not between depths. Finally, these genetic differentiations were not directly correlated to a specific thermal sensitivity whose molecular bases remain to be discovered.
ISSN: 1631-0691

hal-01546168
https://hal.archives-ouvertes.fr/hal-01546168
DOI : 10.1016/j.crvi.2013.06.008