The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform

William K. Milsom - One of the best experts on this subject based on the ideXlab platform.

  • the paradox of extreme high altitude migration in bar headed geese anser indicus
    Proceedings of The Royal Society B: Biological Sciences, 2013
    Co-Authors: Lucy A Hawkes, William K. Milsom, Sivananinthaperumal Balachandran, Nyambayar Batbayar, P J Butler, Beverly Chua, David C Douglas, Peter B Frappell, Yuansheng Hou, Scott H Newman
    Abstract:

    Bar-headed geese are renowned for migratory Flights at extremely high altitudes over the world's tallest mountains, the Himalayas, where partial pressure of oxygen is dramatically reduced while Flight costs, in terms of rate of oxygen consumption, are greatly increased. Such a mismatch is paradoxical, and it is not clear why geese might fly higher than is absolutely necessary. In addition, direct empirical measurements of High-Altitude Flight are lacking. We test whether migrating bar-headed geese actually minimize Flight altitude and make use of favourable winds to reduce Flight costs. By tracking 91 geese, we show that these birds typically travel through the valleys of the Himalayas and not over the summits. We report maximum Flight altitudes of 7290 m and 6540 m for southbound and northbound geese, respectively, but with 95 per cent of locations received from less than 5489 m. Geese travelled along a route that was 112 km longer than the great circle (shortest distance) route, with transit ground speeds suggesting that they rarely profited from tailwinds. Bar-headed geese from these eastern populations generally travel only as high as the terrain beneath them dictates and rarely in profitable winds. Nevertheless, their migration represents an enormous challenge in conditions where humans and other mammals are only able to operate at levels well below their sea-level maxima.

  • evolution of muscle phenotype for extreme high altitude Flight in the bar headed goose
    Proceedings of The Royal Society B: Biological Sciences, 2009
    Co-Authors: Graham R. Scott, Stuart Egginton, Jeffrey G Richards, William K. Milsom
    Abstract:

    Bar-headed geese migrate over the Himalayas at up to 9000 m elevation, but it is unclear how they sustain the high metabolic rates needed for Flight in the severe hypoxia at these altitudes. To better understand the basis for this physiological feat, we compared the Flight muscle phenotype of bar-headed geese with that of low altitude birds (barnacle geese, pink-footed geese, greylag geese and mallard ducks). Bar-headed goose muscle had a higher proportion of oxidative fibres. This increased muscle aerobic capacity, because the mitochondrial volume densities of each fibre type were similar between species. However, bar-headed geese had more capillaries per muscle fibre than expected from this increase in aerobic capacity, as well as higher capillary densities and more homogeneous capillary spacing. Their mitochondria were also redistributed towards the subsarcolemma (cell membrane) and adjacent to capillaries. These alterations should improve O2 diffusion capacity from the blood and reduce intracellular O2 diffusion distances, respectively. The unique differences in bar-headed geese were much greater than the minor variation between low altitude species and existed without prior exercise or hypoxia exposure, and the correlation of these traits to Flight altitude was independent of phylogeny. In contrast, isolated mitochondria had similar respiratory capacities, O2 kinetics and phosphorylation efficiencies across species. Bar-headed geese have therefore evolved for exercise in hypoxia by enhancing the O2 supply to Flight muscle.

  • Control of Breathing in Birds: Implications for High-Altitude Flight
    Cardio-Respiratory Control in Vertebrates, 2009
    Co-Authors: Graham R. Scott, William K. Milsom
    Abstract:

    For birds that fly at high altitude, breathing must increase substantially to accommodate the dual oxygen transport requirements of exercise and hypoxia. Here we review the literature on control of breathing in birds, with particular emphasis on the adaptive trends seen in High-Altitude flying species. Increases in breathing during High-Altitude Flight result from neurally mediated reflexes arising from multiple sites. The locomotor system stimulates breathing directly during exercise via both feedforward stimulation from brainstem locomotor centers and feedback stimulation from exercising muscles. O2-sensitive chemoreceptors in the carotid body also stimulate breathing during hypoxia, whereas CO2/pH-sensitive chemoreceptors can restrain breathing if the hypoxic ventilatory response produces a secondary hypocapnia. Theoretical modeling suggests that an enhanced capacity to increase breathing should be adaptive for high altitude Flight. Empirical research suggests that the High-Altitude flying bar-headed goose can indeed increase breathing significantly more than low-altitude birds during hypoxia at rest, loading more oxygen into the blood. This is probably caused by a reduction in the sensitivity of CO2/pH-sensitive chemoreceptors to hypocapnia, and/or a reduction in hypoxic metabolic suppression and its depressive effects on breathing. Although this suggests that alterations in respiration control are an important component of the suite of adaptations to high altitude in birds, future studies are needed on control of breathing during Flight, especially at altitude. A greater appreciation of the genetic basis for differences in the oxygen transport pathway that occur in High-Altitude species will lead to a greater understanding of the evolution of physiological performance.

  • Flying high: A theoretical analysis of the factors limiting exercise performance in birds at altitude
    Respiratory Physiology & Neurobiology, 2006
    Co-Authors: Graham R. Scott, William K. Milsom
    Abstract:

    Abstract The ability of some bird species to fly at extreme altitude has fascinated comparative respiratory physiologists for decades, yet there is still no consensus about what adaptations enable high altitude Flight. Using a theoretical model of O2 transport, we performed a sensitivity analysis of the factors that might limit exercise performance in birds. We found that the influence of individual physiological traits on oxygen consumption ( V ˙ O 2 ) during exercise differed between sea level, moderate altitude, and extreme altitude. At extreme altitude, haemoglobin (Hb) O2 affinity, total ventilation, and tissue diffusion capacity for O2 ( D T O 2 ) had the greatest influences on V ˙ O 2 ; increasing these variables should therefore have the greatest adaptive benefit for high altitude Flight. There was a beneficial interaction between D T O 2 and the P50 of Hb, such that increasing D T O 2 had a greater influence on V ˙ O 2 when P50 was low. Increases in the temperature effect on P50 could also be beneficial for high flying birds, provided that cold inspired air at extreme altitude causes a substantial difference in temperature between blood in the lungs and in the tissues. Changes in lung diffusion capacity for O2, cardiac output, blood Hb concentration, the Bohr coefficient, or the Hill coefficient likely have less adaptive significance at high altitude. Our sensitivity analysis provides theoretical suggestions of the adaptations most likely to promote high altitude Flight in birds and provides direction for future in vivo studies.

Chao Wang - One of the best experts on this subject based on the ideXlab platform.

  • a heat transient model for the thermal behavior prediction of stratospheric airships
    Applied Thermal Engineering, 2014
    Co-Authors: Xiaochen Lu, Chao Wang
    Abstract:

    The gas temperature of a stratospheric airship plays an important role in its Flight dynamics. A multi-nodes heat transient model is proposed and evaluated by the theoretical solutions of the adiabatic processes and the high altitude Flight test data. A thermodynamic analysis code for stratospheric airships (TACSA) is developed to investigate the ascent subcooling induced by the thermodynamic expansion and the descent superheating induced by the thermodynamic compression. The simulation results show that the airship volume, vertical speed and the solar radiation have evident influence on the ascent subcooling descent superheating effects.

Xiaochen Lu - One of the best experts on this subject based on the ideXlab platform.

  • a heat transient model for the thermal behavior prediction of stratospheric airships
    Applied Thermal Engineering, 2014
    Co-Authors: Xiaochen Lu, Chao Wang
    Abstract:

    The gas temperature of a stratospheric airship plays an important role in its Flight dynamics. A multi-nodes heat transient model is proposed and evaluated by the theoretical solutions of the adiabatic processes and the high altitude Flight test data. A thermodynamic analysis code for stratospheric airships (TACSA) is developed to investigate the ascent subcooling induced by the thermodynamic expansion and the descent superheating induced by the thermodynamic compression. The simulation results show that the airship volume, vertical speed and the solar radiation have evident influence on the ascent subcooling descent superheating effects.

Graham R. Scott - One of the best experts on this subject based on the ideXlab platform.

  • evolution of muscle phenotype for extreme high altitude Flight in the bar headed goose
    Proceedings of The Royal Society B: Biological Sciences, 2009
    Co-Authors: Graham R. Scott, Stuart Egginton, Jeffrey G Richards, William K. Milsom
    Abstract:

    Bar-headed geese migrate over the Himalayas at up to 9000 m elevation, but it is unclear how they sustain the high metabolic rates needed for Flight in the severe hypoxia at these altitudes. To better understand the basis for this physiological feat, we compared the Flight muscle phenotype of bar-headed geese with that of low altitude birds (barnacle geese, pink-footed geese, greylag geese and mallard ducks). Bar-headed goose muscle had a higher proportion of oxidative fibres. This increased muscle aerobic capacity, because the mitochondrial volume densities of each fibre type were similar between species. However, bar-headed geese had more capillaries per muscle fibre than expected from this increase in aerobic capacity, as well as higher capillary densities and more homogeneous capillary spacing. Their mitochondria were also redistributed towards the subsarcolemma (cell membrane) and adjacent to capillaries. These alterations should improve O2 diffusion capacity from the blood and reduce intracellular O2 diffusion distances, respectively. The unique differences in bar-headed geese were much greater than the minor variation between low altitude species and existed without prior exercise or hypoxia exposure, and the correlation of these traits to Flight altitude was independent of phylogeny. In contrast, isolated mitochondria had similar respiratory capacities, O2 kinetics and phosphorylation efficiencies across species. Bar-headed geese have therefore evolved for exercise in hypoxia by enhancing the O2 supply to Flight muscle.

  • Control of Breathing in Birds: Implications for High-Altitude Flight
    Cardio-Respiratory Control in Vertebrates, 2009
    Co-Authors: Graham R. Scott, William K. Milsom
    Abstract:

    For birds that fly at high altitude, breathing must increase substantially to accommodate the dual oxygen transport requirements of exercise and hypoxia. Here we review the literature on control of breathing in birds, with particular emphasis on the adaptive trends seen in High-Altitude flying species. Increases in breathing during High-Altitude Flight result from neurally mediated reflexes arising from multiple sites. The locomotor system stimulates breathing directly during exercise via both feedforward stimulation from brainstem locomotor centers and feedback stimulation from exercising muscles. O2-sensitive chemoreceptors in the carotid body also stimulate breathing during hypoxia, whereas CO2/pH-sensitive chemoreceptors can restrain breathing if the hypoxic ventilatory response produces a secondary hypocapnia. Theoretical modeling suggests that an enhanced capacity to increase breathing should be adaptive for high altitude Flight. Empirical research suggests that the High-Altitude flying bar-headed goose can indeed increase breathing significantly more than low-altitude birds during hypoxia at rest, loading more oxygen into the blood. This is probably caused by a reduction in the sensitivity of CO2/pH-sensitive chemoreceptors to hypocapnia, and/or a reduction in hypoxic metabolic suppression and its depressive effects on breathing. Although this suggests that alterations in respiration control are an important component of the suite of adaptations to high altitude in birds, future studies are needed on control of breathing during Flight, especially at altitude. A greater appreciation of the genetic basis for differences in the oxygen transport pathway that occur in High-Altitude species will lead to a greater understanding of the evolution of physiological performance.

  • Flying high: A theoretical analysis of the factors limiting exercise performance in birds at altitude
    Respiratory Physiology & Neurobiology, 2006
    Co-Authors: Graham R. Scott, William K. Milsom
    Abstract:

    Abstract The ability of some bird species to fly at extreme altitude has fascinated comparative respiratory physiologists for decades, yet there is still no consensus about what adaptations enable high altitude Flight. Using a theoretical model of O2 transport, we performed a sensitivity analysis of the factors that might limit exercise performance in birds. We found that the influence of individual physiological traits on oxygen consumption ( V ˙ O 2 ) during exercise differed between sea level, moderate altitude, and extreme altitude. At extreme altitude, haemoglobin (Hb) O2 affinity, total ventilation, and tissue diffusion capacity for O2 ( D T O 2 ) had the greatest influences on V ˙ O 2 ; increasing these variables should therefore have the greatest adaptive benefit for high altitude Flight. There was a beneficial interaction between D T O 2 and the P50 of Hb, such that increasing D T O 2 had a greater influence on V ˙ O 2 when P50 was low. Increases in the temperature effect on P50 could also be beneficial for high flying birds, provided that cold inspired air at extreme altitude causes a substantial difference in temperature between blood in the lungs and in the tissues. Changes in lung diffusion capacity for O2, cardiac output, blood Hb concentration, the Bohr coefficient, or the Hill coefficient likely have less adaptive significance at high altitude. Our sensitivity analysis provides theoretical suggestions of the adaptations most likely to promote high altitude Flight in birds and provides direction for future in vivo studies.

Rolf Sondergaard - One of the best experts on this subject based on the ideXlab platform.

  • Toward the Expansion of Low-Pressure-Turbine Airfoil Design Space
    Journal of Turbomachinery, 2013
    Co-Authors: T. J. Praisner, E. A. Grover, D. C. Knezevici, I. Popovic, S. A. Sjolander, J. P. Clark, Rolf Sondergaard
    Abstract:

    Future engine requirements, including High-Altitude Flight of unmanned air vehicles as well as an impetus to reduce engine cost and weight, are challenging the current state of the art in low-pressure-turbine airfoil design. These new requirements present low-Reynolds number challenges as well as the need for high-performance, high-lift design concepts. Here, we report on an effort to expand the relatively well established aerodynamic design space for low-pressure turbine airfoils through the application of recent developments in transition modeling to airfoil design. Analytical and experimental midspan performance data and predicted loadings are presented for four high-lift airfoil designs based on the Pack B velocity triangles. The new designs represent a systematic expansion of low-pressure turbine airfoil design space through the application of high-lift design concepts for front- and aft-loaded airfoils. All four designs performed as predicted across a range of operationally representative Reynolds numbers. Full-span loss data for the new high-lift designs reveal increased endwall losses, which, with the application of nonaxisymmetric endwall contouring, have been substantially reduced. Taken holistically, the results presented here demonstrate that accurate transition modeling provides a reliable method to develop optimized, very high-lift airfoil designs. However, further improvements in endwall-loss mitigation technologies are required to enable the implementation of the very high-lift technology presented here in engine systems.

  • Toward the Expansion of Low-Pressure-Turbine Airfoil Design Space (Postprint)
    2008
    Co-Authors: T. J. Praisner, Rolf Sondergaard, E. A. Grover, D. C. Knezevici, I. Popovic, S. A. Sjolander, J. P. Clark, P. J. Koch
    Abstract:

    Abstract : Future engine requirements, including High-Altitude Flight of unmanned air vehicles as well as a movement to reduce engine cost and weight, are challenging the current state of the art in low-pressure-turbine airfoil design. These new requirements present low-Reynolds number challenges as well as the need for high-performance high-lift design concepts. Here we report on an effort to expand the relatively well established design space for low-pressure turbine airfoils. Analytical and experimental mid-span performance data and loadings are presented for four new airfoil designs based on the Pack B velocity triangles. The new designs represent a systematic expansion of low-pressure turbine airfoil design space through the application of high-lift design concepts for front- and aft-loaded airfoils. Taken holistically, the results presented here demonstrate accurate transition modeling provides a reliable method to develop optimized, very high-lift airfoil designs.

  • toward the expansion of low pressure turbine airfoil design space
    ASME Turbo Expo 2008: Power for Land Sea and Air, 2008
    Co-Authors: T. J. Praisner, E. A. Grover, D. C. Knezevici, I. Popovic, S. A. Sjolander, J. P. Clark, Rolf Sondergaard
    Abstract:

    Future engine requirements, including High-Altitude Flight of unmanned air vehicles, as well as an impetus to reduce engine cost and weight, are challenging the current state of the art in low-pressure-turbine airfoil design. These new requirements present low-Reynolds number challenges as well as the need for high-performance, high-lift design concepts. Here we report on an effort to expand the relatively well established aerodynamic design space for low-pressure turbine airfoils through the application of recent developments in transition modeling to airfoil design. Analytical and experimental mid-span performance data and predicted loadings are presented for four high-lift airfoil designs based on the Pack B velocity triangles. The new designs represent a systematic expansion of low-pressure turbine airfoil design space through the application of high-lift design concepts for front- and aft-loaded airfoils. All four designs performed as predicted across a range of operationally representative Reynolds numbers. Full-span loss data for the new high-lift designs reveal increased endwall losses, which, with the application of non-axisymmetric endwall contouring, have been substantially reduced. Taken holistically, the results presented here demonstrate that accurate transition modeling provides a reliable method to develop optimized, very high-lift airfoil designs. However, further improvements in endwall-loss mitigation technologies are required to enable the implementation of the very high-lift technology presented here in engine systems.© 2008 ASME