title: Resistive and viscous dynamics of finite-amplitude shear waves at a magnetic X-point

authors: Craig, Ian J.D.

subjects: mathematics

abstract: The dynamics and dissipation of axial shear waves, superposed on a planar magnetic X-point in a resistive viscous incompressible plasma, are analyzed numerically and analytically. The interplay of viscous and resistive effects is demonstrated by deriving solutions for various values of the scalar coefficients of viscosity and resistivity. These solutions show that viscous-resistive coupling can dramatically affect the global energy dissipation. When either viscosity or resistivity vanishes, the solutions are characterized by oscillatory decaying eigenmodes that maintain equipartition between the magnetic and kinetic energies. This behavior persists when resistivity is the dominant dissipation mechanism. When viscosity is the dominant dissipation mechanism, initial oscillations are followed by exponential decay at sufficiently long times. The applicability of the results to flares in solar active regions, where the viscous Reynolds number can be much smaller than the resistive one, is discussed.

text: Resistive and viscous dynamics of finite-amplitude shear waves at a magnetic X-point The dynamics and dissipation of axial shear waves, superposed on a planar magnetic X-point in a resistive viscous incompressible plasma, are analyzed numerically and analytically. The interplay of viscous and resistive effects is demonstrated by deriving solutions for various values of the scalar coefficients of viscosity and resistivity. These solutions show that viscous-resistive coupling can dramatically affect the global energy dissipation. When either viscosity or resistivity vanishes, the solutions are characterized by oscillatory decaying eigenmodes that maintain equipartition between the magnetic and kinetic energies. This behavior persists when resistivity is the dominant dissipation mechanism. When viscosity is the dominant dissipation mechanism, initial oscillations are followed by exponential decay at sufficiently long times. The applicability of the results to flares in solar active regions, where the viscous Reynolds number can be much smaller than the resistive one, is discussed.

year: 2005-11-22

title: The potential placebo effect of advanced footwear technology on running economy and comfort in female recreational runners

authors: Pfister, Ashlynne

abstract: Since the release of advanced footwear technology (AFT) in 2017, the running landscape has changed forever. However, researchers are unable to decisively conclude what part of AFT contributes the most to running economy (RE) improvements, with some eluding to a potential placebo effect of AFT shoes. Therefore, this study aimed to investigate the presence of a potential placebo effect of AFT on RE and perceptual measures in female recreational runners.

Chapter One provides a brief overview of the origins of AFT, the properties of AFT proposed to contribute to RE improvements, shoe comfort, and placebo effects in sports and footwear research. Features of AFT shoes typically are a curved geometry, a rigid plate embedded in the midsole, and a resilient and compliant energy-returning foam midsole. AFT shoes are also typically lightweight, linked with improved RE. Research generally reports an average improvement in RE of runners when wearing AFT; however, responses are variable and there are responders and non-responders to AFT.

In Chapter Two, 26 female recreational runners (age: 34.7 ± 10.1 y, VO2peak: 45.19 ± 4.65 mL/kg/min) completed one session at the University of Waikato Adams Centre for High Performance Laboratory to assess RE and perceptual measures in two pairs of women’s Nike Vaporfly NEXT% 2. Participants completed 4 x 6-minute RE trials in these two pairs of shoes. One pair was described as a performance-enhancing super shoe (SS) with AFT worn by elite athletes, and the other pair was spray-painted black and described as a “knock-off” (KO) of the performance-enhancing shoe without AFT. Data from 24 participants were analysed (age: 33.3 ± 8.9 y, VO2peak: 45.58 ± 4.17 mL/kg/min) as physiological data from two participants suggested running above their aerobic threshold. Oxygen consumption was not significantly different between SS and KO (mean difference: 0.24 ± 0.64 mL/kg/min, p = 0.077, d = 0.11 [-0.01, 0.23]). Overall comfort on a 100 mm visual analogue scale (VAS) was significantly greater in SS than KO (mean difference: 14.6 ± 15.0 mm, p < 0.001, d = 0.94 [0.46, 1.40]), with 87.5% of runners preferring the SS over the KO. Runners perceived running as more enjoyable and less difficult, and perceived an improved running performance and lower injury risk in SS when compared to KO based on visual analogue scale scores (p ≤ 0.009, d = 0.72 to 1.16). While no significant physiological difference was observed between shoes, a significant difference in perceived comfort and performance was observed favouring the performance-enhancing SS, suggesting a perceptual placebo effect based on shoe description alone.

Chapter Three summarises the findings and provides avenues for future research. Overall, this thesis provides evidence that product descriptions can influence the perception of shoe comfort, performance, and injury risk. The improvements in RE reported for AFT shoes appear underpinned by how runners interact with the shoe properties, rather than by a placebo effect – at least in female recreational runners. Investigating a potential placebo effect in AFT during maximal running performances may provide further insight into the performance enhancements associated with shoes containing AFT.

text: The potential placebo effect of advanced footwear technology on running economy and comfort in female recreational runners Since the release of advanced footwear technology (AFT) in 2017, the running landscape has changed forever. However, researchers are unable to decisively conclude what part of AFT contributes the most to running economy (RE) improvements, with some eluding to a potential placebo effect of AFT shoes. Therefore, this study aimed to investigate the presence of a potential placebo effect of AFT on RE and perceptual measures in female recreational runners.

Chapter One provides a brief overview of the origins of AFT, the properties of AFT proposed to contribute to RE improvements, shoe comfort, and placebo effects in sports and footwear research. Features of AFT shoes typically are a curved geometry, a rigid plate embedded in the midsole, and a resilient and compliant energy-returning foam midsole. AFT shoes are also typically lightweight, linked with improved RE. Research generally reports an average improvement in RE of runners when wearing AFT; however, responses are variable and there are responders and non-responders to AFT.

In Chapter Two, 26 female recreational runners (age: 34.7 ± 10.1 y, VO2peak: 45.19 ± 4.65 mL/kg/min) completed one session at the University of Waikato Adams Centre for High Performance Laboratory to assess RE and perceptual measures in two pairs of women’s Nike Vaporfly NEXT% 2. Participants completed 4 x 6-minute RE trials in these two pairs of shoes. One pair was described as a performance-enhancing super shoe (SS) with AFT worn by elite athletes, and the other pair was spray-painted black and described as a “knock-off” (KO) of the performance-enhancing shoe without AFT. Data from 24 participants were analysed (age: 33.3 ± 8.9 y, VO2peak: 45.58 ± 4.17 mL/kg/min) as physiological data from two participants suggested running above their aerobic threshold. Oxygen consumption was not significantly different between SS and KO (mean difference: 0.24 ± 0.64 mL/kg/min, p = 0.077, d = 0.11 [-0.01, 0.23]). Overall comfort on a 100 mm visual analogue scale (VAS) was significantly greater in SS than KO (mean difference: 14.6 ± 15.0 mm, p < 0.001, d = 0.94 [0.46, 1.40]), with 87.5% of runners preferring the SS over the KO. Runners perceived running as more enjoyable and less difficult, and perceived an improved running performance and lower injury risk in SS when compared to KO based on visual analogue scale scores (p ≤ 0.009, d = 0.72 to 1.16). While no significant physiological difference was observed between shoes, a significant difference in perceived comfort and performance was observed favouring the performance-enhancing SS, suggesting a perceptual placebo effect based on shoe description alone.

Chapter Three summarises the findings and provides avenues for future research. Overall, this thesis provides evidence that product descriptions can influence the perception of shoe comfort, performance, and injury risk. The improvements in RE reported for AFT shoes appear underpinned by how runners interact with the shoe properties, rather than by a placebo effect – at least in female recreational runners. Investigating a potential placebo effect in AFT during maximal running performances may provide further insight into the performance enhancements associated with shoes containing AFT.

year: 2024

title: Spat survival of Paphies ventricosa (Toheroa) in an aquaculture setting

authors: Chew, Martyn Andrew

abstract: The toheroa (Papris ventracosta) is a large intertidal surf cam endemic to New Zealand. This species has a long history with the people of New Zealand in both cultural and economic sense. Exploitation and environmental change have greatly diminished the wild stocks of these animals making a sustainable fishery no longer feasible. Aquaculture has been widely discussed as a potentially profitable option for this species due to its large size, esteemed taste and its social and cultural significance. Aquaculture of toheroa could generate many benefits for the people of the toheroa beaches, as aquaculture has done in other regions of New Zealand. However, the suitability of toheroa for aquaculture is largely unknown, with many questions needing to be answered before that can become a reality. The purpose of this research is to gain a better understanding of the environmental conditions which will support the successful cultivation of wild caught toheroa spat in recirculating aquaculture systems (RAS). This is done by answering questions around knowledge gaps in the biology of the animal. Three experiments were conducted on aspects of the animal’s environment and biology. The first experiment sought to identify the presence of microphytobenthos’s within the wild population beds of the toheroa. As evidence suggests from research conducted on other species, microphytobenthos is an essential part of the animal’s ecosystem which might be a necessary component of a successful spat rearing operation. The experiment showed elevated chlorophyll levels (a proxy for microphytobenthos) within toheroa beds relative to other areas of the beach. The second experiment compared survival and growth rates in sediment vs. non-sediment holding systems. The results of this study indicated the benefits of housing spat in sediments, as demonstrated by differences in measured growth and mortality. A third experiment sought to test for size dependent mortality rates within the RAS. Somewhat surprisingly, it was found that smaller toheroa (0-10mm) performed better within a system compared to larger ones (20-30). Larger toheroa tended to eject themselves from the sediment constantly, an act which may have compromised their growth and survivorship. The result of these experiments answered questions and raise many more.  Potentially through understanding these questions we can create tools which industry and conservation can use. This research show that successful toheroa spat can be successfully integrated into an aquaculture system. With mortality settling the animals feeding and showing healthy condition. However, the next stage would be to optimize this. Toheroa aquaculture being in its infancy requires a wide variety of research before considered feasible. However, results and observations made from this research can help in identifying and specializing future research objectives.

text: Spat survival of Paphies ventricosa (Toheroa) in an aquaculture setting The toheroa (Papris ventracosta) is a large intertidal surf cam endemic to New Zealand. This species has a long history with the people of New Zealand in both cultural and economic sense. Exploitation and environmental change have greatly diminished the wild stocks of these animals making a sustainable fishery no longer feasible. Aquaculture has been widely discussed as a potentially profitable option for this species due to its large size, esteemed taste and its social and cultural significance. Aquaculture of toheroa could generate many benefits for the people of the toheroa beaches, as aquaculture has done in other regions of New Zealand. However, the suitability of toheroa for aquaculture is largely unknown, with many questions needing to be answered before that can become a reality. The purpose of this research is to gain a better understanding of the environmental conditions which will support the successful cultivation of wild caught toheroa spat in recirculating aquaculture systems (RAS). This is done by answering questions around knowledge gaps in the biology of the animal. Three experiments were conducted on aspects of the animal’s environment and biology. The first experiment sought to identify the presence of microphytobenthos’s within the wild population beds of the toheroa. As evidence suggests from research conducted on other species, microphytobenthos is an essential part of the animal’s ecosystem which might be a necessary component of a successful spat rearing operation. The experiment showed elevated chlorophyll levels (a proxy for microphytobenthos) within toheroa beds relative to other areas of the beach. The second experiment compared survival and growth rates in sediment vs. non-sediment holding systems. The results of this study indicated the benefits of housing spat in sediments, as demonstrated by differences in measured growth and mortality. A third experiment sought to test for size dependent mortality rates within the RAS. Somewhat surprisingly, it was found that smaller toheroa (0-10mm) performed better within a system compared to larger ones (20-30). Larger toheroa tended to eject themselves from the sediment constantly, an act which may have compromised their growth and survivorship. The result of these experiments answered questions and raise many more.  Potentially through understanding these questions we can create tools which industry and conservation can use. This research show that successful toheroa spat can be successfully integrated into an aquaculture system. With mortality settling the animals feeding and showing healthy condition. However, the next stage would be to optimize this. Toheroa aquaculture being in its infancy requires a wide variety of research before considered feasible. However, results and observations made from this research can help in identifying and specializing future research objectives.

year: 2022