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K G Pearson - One of the best experts on this subject based on the ideXlab platform.
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contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat Step Cycle
Journal of Neurophysiology, 1996Co-Authors: Gordon W Hiebert, Arthur Prochazka, Patrick J Whelan, K G PearsonAbstract:1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion during walking. The hip flexor muscle iliopsoas (IP) and the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) were stretched or vibrated at various phases of the Step Cycle in spontaneously walking decerebrate cats. Changes in electromyogram amplitude, duration, and timing were then examined. The effects of electrically stimulating group I and II afferents in the nerves to TA and EDL also were examined. 2. Stretch of the individual flexor muscles (IP, TA, or EDL) during the stance phase reduced the duration of extensor activity and promoted the onset of flexor burst activity. The contralateral Step Cycle also was affected by the stretch, the duration of flexor activity being shortened and extensor activity occurring earlier. Therefore, stretch of the flexor muscles during the stance phase reset the locomotor rhythm to flexion ipsilaterally and extension contralaterally. 3. Results of electrically stimulating the afferents from the TA and EDL muscles suggested that different groups of afferents were responsible for the resetting of the Step Cycle. Stimulation of the TA nerve reset the locomotor Step Cycle when the stimulus intensity was in the group II range (2-5 xT). By contrast, stimulation of the EDL nerve generated strong resetting of the Step Cycle in the range of 1.2-1.4 xT, where primarily the group Ia afferents from the muscle spindles would be activated. 4. Vibration of IP or EDL during stance reduced the duration of the extensor activity by similar amounts to that produced by muscle stretch or by electrical stimulation of EDL at group Ia strengths. This suggests that the group Ia afferents from IP and EDL are capable of resetting the locomotor pattern generator. Vibration of TA did not affect the locomotor rhythm. 5. Stretch of IP or electrical stimulation of TA afferents (5 xT) during the flexion phase did not change the duration of the flexor activity. Stimulation of the EDL nerve at 1.8-5 xT during flexion increased the duration of the flexor activity. In none of our preparations did we observe resetting to extension when the flexor afferents were activated during flexion. 6. We conclude that as the flexor muscles lengthen during the stance phase of gait, their spindle afferents (group Ia afferents for EDL and IP, group II afferents for TA) act to inhibit the spinal center generating extensor activity thus facilitating the initiation of swing.
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contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat Step Cycle
Journal of Neurophysiology, 1996Co-Authors: Gordon W Hiebert, Arthur Prochazka, Patrick J Whelan, K G PearsonAbstract:1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion...
Arthur Prochazka - One of the best experts on this subject based on the ideXlab platform.
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sensory systems in the control of movement
Comprehensive Physiology, 2012Co-Authors: Arthur Prochazka, P H EllawayAbstract:Animal movement is immensely varied, from the simplest reflexive responses to the most complex, dexterous voluntary tasks. Here, we focus on the control of movement in mammals, including humans. First, the sensory inputs most closely implicated in controlling movement are reviewed, with a focus on somatosensory receptors. The response properties of the large muscle receptors are examined in detail. The role of sensory input in the control of movement is then discussed, with an emphasis on the control of locomotion. The interaction between central pattern generators and sensory input, in particular in relation to stretch reflexes, timing, and pattern forming neuronal networks is examined. It is proposed that neural signals related to bodily velocity form the basic descending command that controls locomotion through specific and well-characterized relationships between muscle activation, Step Cycle phase durations, and biomechanical outcomes. Sensory input is crucial in modulating both the timing and pattern forming parts of this mechanism. C � 2012 American Physiological Society. Compr Physiol 2:2615-2627, 2012.
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spatiotemporal activation of lumbosacral motoneurons in the locomotor Step Cycle
Journal of Neurophysiology, 2002Co-Authors: Sergiy Yakovenko, Vivian K Mushahwar, Veronique G J M Vanderhorst, Gert Holstege, Arthur ProchazkaAbstract:The aim of this study was to produce a dynamic model of the spatiotemporal activation of ensembles of alpha motoneurons (MNs) in the cat lumbosacral spinal cord during the locomotor Step Cycle. The...
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contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat Step Cycle
Journal of Neurophysiology, 1996Co-Authors: Gordon W Hiebert, Arthur Prochazka, Patrick J Whelan, K G PearsonAbstract:1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion during walking. The hip flexor muscle iliopsoas (IP) and the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) were stretched or vibrated at various phases of the Step Cycle in spontaneously walking decerebrate cats. Changes in electromyogram amplitude, duration, and timing were then examined. The effects of electrically stimulating group I and II afferents in the nerves to TA and EDL also were examined. 2. Stretch of the individual flexor muscles (IP, TA, or EDL) during the stance phase reduced the duration of extensor activity and promoted the onset of flexor burst activity. The contralateral Step Cycle also was affected by the stretch, the duration of flexor activity being shortened and extensor activity occurring earlier. Therefore, stretch of the flexor muscles during the stance phase reset the locomotor rhythm to flexion ipsilaterally and extension contralaterally. 3. Results of electrically stimulating the afferents from the TA and EDL muscles suggested that different groups of afferents were responsible for the resetting of the Step Cycle. Stimulation of the TA nerve reset the locomotor Step Cycle when the stimulus intensity was in the group II range (2-5 xT). By contrast, stimulation of the EDL nerve generated strong resetting of the Step Cycle in the range of 1.2-1.4 xT, where primarily the group Ia afferents from the muscle spindles would be activated. 4. Vibration of IP or EDL during stance reduced the duration of the extensor activity by similar amounts to that produced by muscle stretch or by electrical stimulation of EDL at group Ia strengths. This suggests that the group Ia afferents from IP and EDL are capable of resetting the locomotor pattern generator. Vibration of TA did not affect the locomotor rhythm. 5. Stretch of IP or electrical stimulation of TA afferents (5 xT) during the flexion phase did not change the duration of the flexor activity. Stimulation of the EDL nerve at 1.8-5 xT during flexion increased the duration of the flexor activity. In none of our preparations did we observe resetting to extension when the flexor afferents were activated during flexion. 6. We conclude that as the flexor muscles lengthen during the stance phase of gait, their spindle afferents (group Ia afferents for EDL and IP, group II afferents for TA) act to inhibit the spinal center generating extensor activity thus facilitating the initiation of swing.
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contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat Step Cycle
Journal of Neurophysiology, 1996Co-Authors: Gordon W Hiebert, Arthur Prochazka, Patrick J Whelan, K G PearsonAbstract:1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion...
Bruno Antonny - One of the best experts on this subject based on the ideXlab platform.
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a four Step Cycle driven by pi 4 p hydrolysis directs sterol pi 4 p exchange by the er golgi tether osbp
Cell, 2013Co-Authors: Bruno Mesmin, Joelle Bigay, Joachim Moser Von Filseck, Sandra Lacasgervais, Guillaume Drin, Bruno AntonnyAbstract:Several proteins at endoplasmic reticulum (ER)-Golgi membrane contact sites contain a PH domain that interacts with the Golgi phosphoinositide PI(4)P, a FFAT motif that interacts with the ER protein VAP-A, and a lipid transfer domain. This architecture suggests the ability to both tether organelles and transport lipids between them. We show that in oxysterol binding protein (OSBP) these two activities are coupled by a four-Step Cycle. Membrane tethering by the PH domain and the FFAT motif enables sterol transfer by the lipid transfer domain (ORD), followed by back transfer of PI(4)P by the ORD. Finally, PI(4)P is hydrolyzed in cis by the ER protein Sac1. The energy provided by PI(4)P hydrolysis drives sterol transfer and allows negative feedback when PI(4)P becomes limiting. Other lipid transfer proteins are tethered by the same mechanism. Thus, OSBP-mediated back transfer of PI(4)P might coordinate the transfer of other lipid species at the ER-Golgi interface.
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a four Step Cycle driven by pi 4 p hydrolysis directs sterol pi 4 p exchange by the er golgi tether osbp
Cell, 2013Co-Authors: Bruno Mesmin, Joelle Bigay, Sandra Lacasgervais, Guillaume Drin, Joachim Moser Von Filseck, Bruno AntonnyAbstract:Several proteins at endoplasmic reticulum (ER)-Golgi membrane contact sites contain a PH domain that interacts with the Golgi phosphoinositide PI(4)P, a FFAT motif that interacts with the ER protein VAP-A, and a lipid transfer domain. This architecture suggests the ability to both tether organelles and transport lipids between them. We show that in oxysterol binding protein (OSBP) these two activities are coupled by a four-Step Cycle. Membrane tethering by the PH domain and the FFAT motif enables sterol transfer by the lipid transfer domain (ORD), followed by back transfer of PI(4)P by the ORD. Finally, PI(4)P is hydrolyzed in cis by the ER protein Sac1. The energy provided by PI(4)P hydrolysis drives sterol transfer and allows negative feedback when PI(4)P becomes limiting. Other lipid transfer proteins are tethered by the same mechanism. Thus, OSBP-mediated back transfer of PI(4)P might coordinate the transfer of other lipid species at the ER-Golgi interface.
Peter G. Loutzenhiser - One of the best experts on this subject based on the ideXlab platform.
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aluminum doped calcium manganite particles for solar thermochemical energy storage reactor design particle characterization and heat and mass transfer modeling
International Journal of Heat and Mass Transfer, 2020Co-Authors: Andrew J Schrader, Evan H Bush, Devesh Ranjan, Peter G. LoutzenhiserAbstract:Abstract A two-Step Cycle was considered for solar thermochemical energy storage based on particulate aluminum-doped calcium manganite reduction/oxidation reactions for direct integration into Air-Brayton Cycles. The two Steps encompass (1) the storage of concentrated solar irradiation within endothermic reduction of aluminum-doped calcium manganite and (2) the delivery of heat to an Air-Brayton Cycle via exothermic re-oxidation of oxygen-deficient aluminum-doped calcium magnanite. A 5 kWth scale solar thermochemical reactor operating under vacuum was designed, modeled, and optimized to thermally reduce a continuous, gravity-driven flow of aluminum-doped calcium manganite particles. The granular flows were characterized in a tilt-flow rig, and particle image velocimetry was used to determine flow properties via frictional and velocity scaling relationships. Flow properties were integrated into a detailed heat and mass transfer model of the solar thermochemical reactor. A reactor design with 31° inclination angle, 230 g/min of particles, and 5.2 kWth radiative input from the high-flux solar simulator was found to produce an outlet flow temperature of 1158 K, with stoichiometric deviations of 0.076 and a storage efficiency of 0.628 while avoiding particle overheating and promoting longer particle residence times.
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h2o splitting via a two Step solar thermoelectrolytic Cycle based on non stoichiometric ceria redox reactions thermodynamic analysis
International Journal of Hydrogen Energy, 2017Co-Authors: Garrett L Schieber, Ellen B Stechel, Andrea Ambrosini, James E Miller, Peter G. LoutzenhiserAbstract:Abstract H2 production via a novel two-Step solar thermoelectrolytic Cycle based on non-stoichiometric ceria reduction/oxidation reactions is thermodynamically analyzed. The two-Step Cycle encompasses (1) the solar thermoelectrolytic reduction of ceria using a combination of concentrated solar irradiation, reduced partial pressure, and electricity from a photovoltaic array to increase the oxygen vacancy concentration in the sublattice and (2) the non-solar oxidation of non-stoichiometric ceria with H2O to produce H2, or CO2 to produce CO. The re-oxidized ceria is returned to the first Step to complete the Cycle. A thermodynamic analysis that imposes first and second law constraints to determine optimal performance predicts a solar-to-fuel efficiency of 31.1% for a reduction temperature of 1424 K and a maximum oxygen vacancy concentration of 0.229.
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solar electricity via an air brayton Cycle with an integrated two Step thermochemical Cycle for heat storage based on co 3 o 4 coo redox reactions iii solar thermochemical reactor design and modeling
Solar Energy, 2017Co-Authors: Andrew J Schrader, Gretchen L Schieber, Gianmarco De Dominicis, Peter G. LoutzenhiserAbstract:Abstract A two-Step solar thermochemical Cycle based on Co3O4/CoO redox reactions integrated into an Air Brayton Cycle is considered for thermochemical heat storage. The two-Step Cycle encompasses (1) the thermal reduction of Co3O4 to CoO and O2 driven by concentrated solar irradiation and (2) the re-oxidation of CoO with O2 to Co3O4, releasing heat and completing the Cycle. An evacuated horizontal solar thermochemical reactor is proposed with an inclined slope and quartz window for promoting direct irradiation of dense, granular Co3O4/CoO flows. Mechanical analysis of flat and spherical quartz window designs for a 5 kWth scale prototype was performed to ensure window stability. Detailed mass and heat transfer analysis for a 5 kWth scale prototype was performed coupling Monte Carlo ray tracing for radiative heat exchange to the energy balances for the bed and the reactor. A parametric study of the reactor design was performed with varying cavity depth, particle inlet temperature, and solar concentration ratio. The optimal solar reactor design maximized conversion of Co3O4 to CoO and particle outlet temperature while preventing particle overheating and achieved a Co3O4 to CoO conversion of 0.91, particle outlet temperature of 1385 K, maximum flow temperature of 1572 K, and absorption efficiency of 0.76.
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review of the two Step h2o co2 splitting solar thermochemical Cycle based on zn zno redox reactions
Materials, 2010Co-Authors: Peter G. Loutzenhiser, Anton Meier, Aldo SteinfeldAbstract:This article provides a comprehensive overview of the work to date on the two‑Step solar H2O and/or CO2 splitting thermochemical Cycles with Zn/ZnO redox reactions to produce H2 and/or CO, i.e., synthesis gas—the precursor to renewable liquid hydrocarbon fuels. The two-Step Cycle encompasses: (1) The endothermic dissociation of ZnO to Zn and O2 using concentrated solar energy as the source for high-temperature process heat; and (2) the non-solar exothermic oxidation of Zn with H2O/CO2 to generate H2/CO, respectively; the resulting ZnO is then reCycled to the first Step. An outline of the underlying science and the technological advances in solar reactor engineering is provided along with life Cycle and economic analyses.
Gordon W Hiebert - One of the best experts on this subject based on the ideXlab platform.
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contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat Step Cycle
Journal of Neurophysiology, 1996Co-Authors: Gordon W Hiebert, Arthur Prochazka, Patrick J Whelan, K G PearsonAbstract:1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion during walking. The hip flexor muscle iliopsoas (IP) and the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) were stretched or vibrated at various phases of the Step Cycle in spontaneously walking decerebrate cats. Changes in electromyogram amplitude, duration, and timing were then examined. The effects of electrically stimulating group I and II afferents in the nerves to TA and EDL also were examined. 2. Stretch of the individual flexor muscles (IP, TA, or EDL) during the stance phase reduced the duration of extensor activity and promoted the onset of flexor burst activity. The contralateral Step Cycle also was affected by the stretch, the duration of flexor activity being shortened and extensor activity occurring earlier. Therefore, stretch of the flexor muscles during the stance phase reset the locomotor rhythm to flexion ipsilaterally and extension contralaterally. 3. Results of electrically stimulating the afferents from the TA and EDL muscles suggested that different groups of afferents were responsible for the resetting of the Step Cycle. Stimulation of the TA nerve reset the locomotor Step Cycle when the stimulus intensity was in the group II range (2-5 xT). By contrast, stimulation of the EDL nerve generated strong resetting of the Step Cycle in the range of 1.2-1.4 xT, where primarily the group Ia afferents from the muscle spindles would be activated. 4. Vibration of IP or EDL during stance reduced the duration of the extensor activity by similar amounts to that produced by muscle stretch or by electrical stimulation of EDL at group Ia strengths. This suggests that the group Ia afferents from IP and EDL are capable of resetting the locomotor pattern generator. Vibration of TA did not affect the locomotor rhythm. 5. Stretch of IP or electrical stimulation of TA afferents (5 xT) during the flexion phase did not change the duration of the flexor activity. Stimulation of the EDL nerve at 1.8-5 xT during flexion increased the duration of the flexor activity. In none of our preparations did we observe resetting to extension when the flexor afferents were activated during flexion. 6. We conclude that as the flexor muscles lengthen during the stance phase of gait, their spindle afferents (group Ia afferents for EDL and IP, group II afferents for TA) act to inhibit the spinal center generating extensor activity thus facilitating the initiation of swing.
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contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat Step Cycle
Journal of Neurophysiology, 1996Co-Authors: Gordon W Hiebert, Arthur Prochazka, Patrick J Whelan, K G PearsonAbstract:1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion...
