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| 2. |
- Fulle, M., et al.
(author)
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Evolution Of The Dust Size Distribution Of Comet 67P/Churyumov-Gerasimenko From 2.2 Au To Perihelion
- 2016
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 821:1
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Journal article (peer-reviewed)abstract
- The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, has been detecting individual dust particles of mass larger than 10(-10) kg by means of the GIADA dust collector and the OSIRIS Wide Angle Camera and Narrow Angle Camera since 2014 August and will continue until 2016 September. Detections of single dust particles allow us to estimate the anisotropic dust flux from 67P, infer the dust loss rate and size distribution at the surface of the sunlit nucleus, and see whether the dust size distribution of 67P evolves in time. The velocity of the Rosetta orbiter, relative to 67P, is much lower than the dust velocity measured by GIADA, thus dust counts when GIADA is nadir-pointing will directly provide the dust flux. In OSIRIS observations, the dust flux is derived from the measurement of the dust space density close to the spacecraft. Under the assumption of radial expansion of the dust, observations in the nadir direction provide the distance of the particles by measuring their trail length, with a parallax baseline determined by the motion of the spacecraft. The dust size distribution at sizes > 1 mm observed by OSIRIS is consistent with a differential power index of -4, which was derived from models of 67P's trail. At sizes <1 mm, the size distribution observed by GIADA shows a strong time evolution, with a differential power index drifting from -2 beyond 2 au to -3.7 at perihelion, in agreement with the evolution derived from coma and tail models based on ground-based data. The refractory-to-water mass ratio of the nucleus is close to six during the entire inbound orbit and at perihelion.
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| 3. |
- McDonnell, A.C., et al.
(author)
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Circadian rhythm of peripheral perfusion during 10-day hypoxic confinement and bed rest
- 2014
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In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 114:10, s. 2093-2104
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Journal article (peer-reviewed)abstract
- Future planetary habitats will be hypobaric and hypoxic to reduce the risk of decompression sickness during preparation for extra-vehicular activities. This study was part of a research programme investigating the combined effects of hypoxia and microgravity on physiological systems. We tested the hypothesis that hypoxia-induced peripheral vasoconstriction persists at night and is aggravated by bed rest. Since sleep onset has been causally linked to nocturnal vasodilatation, we reasoned that hypoxia-induced vasoconstriction at night may explain sleep disturbances at altitude. Peripheral perfusion alterations as a consequence of bed rest may explain poor sleep quality reported during sojourns on the International Space Station. Eleven males underwent three 10-day interventions in a randomised order: (1) hypoxic ambulatory confinement; (2) hypoxic bed rest; (3) normoxic bed rest. During each intervention we conducted 22-h monitoring of peripheral perfusion, as reflected by the skin temperature gradient. Measurements were conducted on the first (D 1) and last day (D 10) of each intervention. All interventions resulted in a decrease in daytime toe perfusion from D 1 to D 10. There was no difference in the magnitude of the daytime reduction in toe perfusion between the three interventions. There was a significant vasodilatation of the toes in all interventions by 11 pm. The fingertips remained well perfused throughout. Daytime vasoconstriction induced by hypoxia and/or bed rest is abolished at night, lending further support to the theory that changes in peripheral skin temperature may be functionally linked to sleep onset.
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| 4. |
- McDonnell, A. C., et al.
(author)
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Effect of hypoxia and bedrest on peripheral vasoconstriction
- 2013
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In: Proceedings of Life in space for life on earth, 18-22 June 2012, Aberdeen. - : ESA Communications. - 9789290922704 ; , s. 1-2
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Conference paper (peer-reviewed)abstract
- Future planetary habitats may expose astronauts to both microgravity and hypobaric hypoxia, both inducing a reduction in peripheral perfusion. Peripheral temperature changes have been linked to sleep onset and quality [5]. However, it is still unknown what effect combining hypoxia and bedrest has on this relationship. Eleven male participants underwent three 10-day campaigns in a randomized manner: 1) normobaric hypoxic ambulatory confinement (HAmb); 2) normobaric hypoxic bed rest (HBR); 3) normobaric normoxic bed rest (NBR). There was no change in skin temperature gradient between the calf and toes, an index of peripheral perfusion (ΔTc-t), over the 10-d period in the HAmb trial. However, there was a significant increase (p< 0.001) in daytime (9am-9pm) ΔTc-t on day 10 of the inactivity/unloading periods (HBR and NBR trials). This reduction in the perfusion of the toes during the daytime was augmented during the HBR trial compared to NBR (p< 0.001). Before and on day 10 of the interventions we conducted polysomnographic assessment, which revealed no changes in sleep onset and/or architecture. These data support the theory that circadian changes in temperature are functionally linked to sleepiness [1].
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| 6. |
- Mekjavic, I. B., et al.
(author)
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Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest?
- 2020
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In: Experimental Physiology. - : Blackwell Publishing Ltd. - 0958-0670 .- 1469-445X.
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Journal article (peer-reviewed)abstract
- New Findings: What is the central question of this study? Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest? What is the main finding and its importance? During 10-day bed rest, exposure to a simulated (normobaric hypoxia) altitude of ∼4000 m does not exert additional significant structural or functional effect on the weight-bearing muscles in females compared to those noted under normoxic conditions. Whereas males and females exhibit decrements in muscle cross-sectional area and mass during normoxic and hypoxic bed rest, a concomitant strength decrement was only observed in males. Abstract: This study investigated the effects of hypoxia on the known processes of adaptation of body composition and muscle function to normoxic inactivity. Females (n = 12) and males (n = 11) took part in the following interventions: hypoxic ambulation (HAMB; ∼4000 m); hypoxic bed rest (HBR; ∼4000 m) and normoxic bed rest (NBR). Prior to and immediately following each intervention, body composition, thigh and lower leg cross-sectional area (CSA) and isometric muscular strength were recorded. Participants lost body mass (HAMB: male −1.5 ± 0.9 kg, female −1.9 ± 0.7 kg; HBR: male −2.0 ± 1.8 kg, female −2.4 ± 0.8 kg; NBR: male −1.4 ± 1.3 kg, female −1.4 ± 0.9 kg) and lean mass (HAMB: male −3.9 ± 3.0%, female −3.4 ± 2.0%; HBR: male −4.0 ± 4.4%, female −4.1 ± 2.0%; NBR: male −4.0 ± 3.4%, female −2.2 ± 2.7%) with no between-condition or sex differences. Knee extension decreased for males in NBR compared to HAMB (HAMB: male −0.2 ± 9.1%, female 1.3 ± 4.9%; HBR: male −7.8 ± 10.3%, female −3.3 ± 10.9%; NBR: male −14.5 ± 11%, female −3.4 ± 6.9%). Loss of force during maximal voluntary contraction (MVC) in the knee extensors was significantly different between males and females following NBR. There were no other significant changes noted following the experimental interventions. There were no differences recorded between sexes in maximal MVC for elbow or ankle joints. Female lower leg CSA decreased following bed rest (HAMB: -4.5 ± 2.0%; HBR: -9.9 ± 2.6%; NBR: -8.0 ± 1.6%). These findings indicate that a 10-day hypoxic bed rest does not exert any significant additional effect on muscle atrophy when compared to NBR, except for female thigh CSA. In contrast to males, who exhibited a significant loss of muscle strength, no such decrement in strength was observed in the female participants.
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| 7. |
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| 8. |
- Stavrou, N. A., et al.
(author)
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Indices of psychological strain during hypoxic bedrest and confinement
- 2013
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In: Proceedings of Life in space for life on earth, 18-22 June 2012, Aberdeen. - : European Space Agency. - 9789290922704
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Conference paper (peer-reviewed)abstract
- Much attention has been devoted to the physiological changes that occur during bed rest. However, there has been a lack of focus on the psychological aspects per se. We investigated indices of psychological strain during three 10-d interventions, designed to assess the combined effects of inactivity/unloading and normobaric hypoxia on several physiological systems. Eleven male participants underwent three 10-d campaigns in a randomized manner: 1) normobaric hypoxic ambulatory confinement (HAMB), 2) normobaric hypoxic bed rest (HBR) and 3) normoxic bed rest (NBR). The most negative psychological profile appeared on BR10 of HBR and HAmb conditions (hypoxic conditions). Concomitantly a decrease in positive emotions was observed from BR-2 to BR10. Bed rest and exposure to hypoxic environments seems to exert a negative effect on person's psychological mood.
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| 9. |
- Stavrou, N., et al.
(author)
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The effect of moderate exercise on emotional state during hypoxic confinement
- 2014
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Conference paper (peer-reviewed)abstract
- Normobaric hypoxic training is routinely used by athletes to improve their altitude and sea level performance. A multitude of schedules are being used, combining inactive and active exposure to hypoxic environments. The live high – train low regimen, in particular, requires athletes to spend a majority of time confined to a normobaric hypoxic environment. Despite the known positive effects of hypoxic training on physical performance, there is a lack of information regarding the influence of hypoxia and physical activity on emotional state. This was the principal aim of the current study. Specifically, we tested the hypothesis that physical activity alleviates the hypoxia-induced increases in negative feelings. Fourteen male subjects were confined to 10-day continuous hypoxia (fraction of inspired O2=0.139±0.003; 4000m simulated altitude). Subjects were assigned to either the Hypoxic Confinement: Exercise group (HCE: N=8, two 1 hour training sessions/day at 50% hypoxic peak power output) or the Hypoxic Confinement: Sedentary group (HCS: N=6, no exercise). Subjects were administered the Profile of Mood States (POMS) and the Positive and Negative Affect Schedule (PANAS) tests two days prior to hypoxic confinement (D-2), on days 3 (D3), 7 (D7) and 10 (D10) of hypoxic confinement and on the first day of recovery following the confinement period (R+1). The ANOVA repeated measure of the PANAS determined that positive affect differed significantly across the five time measures between HCS and HCE. Bonferroni post hoc analysis revealed that the HCS group elicited a reduction of positive emotion from D-2 to D7 and to D10 with a concomitant increase of negative emotion from D-2 to D10. In addition, an increase of tension from D-2 to D7 and to D10 was revealed in HCS, whereas an increase in tension on D10 was indicated in HCE. Based on the POMS, an increase of depression from D-2 to D7 was found in HCS, whereas no differences were revealed in HCE, among the five time measures. Finally, no significant differences revealed between D10 and R+1 in the PANAS or POMS in either HCS or HCE. The results indicate that in sedentary subjects hypoxic confinement increases tension and negative emotions, and decreases vigor and positive emotions. It is concluded that hypoxia negatively affects the emotional state, but that increasing the level of physical activity ameliorates such feelings.
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