Structure and clumping in the fast wind of NGC6543

Far-UV spectroscopy from the FUSE satellite is analysed to uniquely probe spatial structure and clumping in the fast wind of the central star of the H-rich planetary nebula NGC6543 (HD164963). Time-series data of the unsaturated PV 1118, 1128 resonance line P Cygni profiles provide a very sensitive diagnostic of variable wind conditions in the outflow. We report on the discovery of episodic and recurrent optical depth enhancements in the PV absorption troughs, with some evidence for a 0.17-day modulation time-scale. SEI line-synthesis modelling is used to derive physical properties, including the optical depth evolution of individual `events'. The characteristics of these features are essentially identical to the `discrete absorption components' (DACs) commonly seen in the UV lines of massive OB stars. We have also employed the unified model atmosphere code CMFGEN to explore spectroscopic signatures of clumping, and report in particular on the clear sensitivity of the PV lines to the clump volume filling factor. The results presented here have implications for the downward revision of mass-loss rates in PN central stars. We conclude that the temporal structures seen in the PV lines of NGC6543 likely have a physical origin that is similar to that operating in massive, luminous stars, and may be related to near-surface perturbations caused by stellar pulsation and/or magnetic fields.Comment: 11 pages, 11 figures. Accepted for publication in MNRA

Physiological Evidence that the Critical Torque Is a Phase Transition Not a Threshold

Introduction: Distinct physiological responses to exercise occur in the heavy and severe-intensity domains, which are separated by the critical power or critical torque (CT). However, how the transition between these intensity domains actually occurs is not known. We tested the hypothesis that CT is a sudden threshold, with no gradual transition from heavy- to severe-intensity behavior within the confidence limits associated with the CT. Methods: Twelve healthy participants performed four exhaustive severe-intensity trials for the determination of CT, and four 30-minute trials in close proximity to CT (one or two standard errors above or below each participant’s CT estimate; CT–2, CT–1, CT+1, CT+2). Muscle O2 uptake (mV[Combining Dot Above]O2), rectified EMG and torque variability and complexity were monitored throughout each trial, and maximal voluntary contractions with femoral nerve stimulation were performed before and after each trial to determine central and peripheral fatigue responses. Results: The rates of change in fatigue-related variables, mV[Combining Dot Above]O2, EMG amplitude and torque complexity were significantly faster in the severe trials compared to CT–2. For example, the fall in maximal voluntary contraction (MVC) torque was –1.5 ± 0.8 N.m.min-1 in CT–2 vs. –7.9 ± 2.5 N.m.min-1 in the lowest severe-intensity trial (S1; P < 0.05). Individual analyses showed a low frequency of severe responses even in the circa-CT trials ostensibly above the CT, but also the rare appearance of severe-intensity responses in all circa-CT trials. Conclusion: These data demonstrate that the transition between heavy- and severe-intensity exercise occurs gradually rather than suddenly

Ischemic Preconditioning Blunts Loss of Knee Extensor Torque Complexity with Fatigue

Introduction: Neuromuscular fatigue reduces the temporal structure, or complexity, of muscle torque output, purportedly through an effect on motor unit behaviour. Ischaemic pre-conditioning (IPC), an emerging ergogenic aid, has been demonstrated to have a potent effect on muscular output and endurance. We therefore tested the hypothesis that IPC would attenuate the fatigueinduced loss of muscle torque complexity. Methods: Ten healthy participants (6 male/4 female) performed intermittent isometric knee extension contractions (6 s contraction, 4 s rest) to task failure at 40% maximal voluntary contraction (MVC). Contractions were preceded by either IPC (three bouts of 5 minutes proximal thigh occlusion at 225 mmHg, interspersed with 5 minutes rest) or SHAM (as IPC, but occlusion at only 20 mmHg) treatments. Torque and EMG signals were sampled continuously. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Muscle oxygen consumption (mV̇O$_2$) was determined using near-infrared spectroscopy. Results: IPC increased time to task failure by 43 ± 13% (mean ± SEM, P = 0.047). Complexity decreased in both trials (decreased ApEn, increased DFA α; both P < 0.001), though the rate of decrease was significantly lower following IPC (ApEn, –0.2 ± 0.1 vs. –0.4 ± 0.1, P = 0.013; DFA α, 0.2 ± 0.1 vs. 0.3 ± 0.1, P = 0.037). Similarly, the rates of increase in EMG amplitude (P = 0.022) and mV̇O$_2$ (P = 0.043) were significantly slower following IPC. Conclusion: These results suggest the ergogenic effect of IPC observed here is of neural origin and accounts for the slowing of the rates of change in torque complexity, EMG amplitude and muscle oxygen consumption as fatigue develops

Initial Acoustoelastic Measurements in Olivine: Investigating the Effect of Stress on P- and S-Wave Velocities

It is well known that elasticity is a key physical property in the determination of the structure and composition of the Earth and provides critical information for the interpretation of seismic data. This study investigates the stress-induced variation in elastic wave velocities, known as the acoustoelastic effect, in San Carlos olivine. A recently developed experimental ultrasonic acoustic system, the Directly Integrated Acoustic System Combined with Pressure Experiments (DIASCoPE), was used with the D-DIA multi-anvil apparatus to transmit ultrasonic sound waves and collect the reflections. We use the DIASCoPE to obtain longitudinal (P) and shear (S) elastic wave velocities from San Carlos olivine at pressures ranging from 3.2–10.5 GPa and temperatures from 450–950°C which we compare to the stress state in the D-DIA derived from synchrotron X-ray diffraction. We use elastic-plastic self-consistent (EPSC) numerical modeling to forward model X-ray diffraction data collected in D-DIA experiments to obtain the macroscopic stress on our sample. We can observe the relationship between the relative elastic wave velocity change (ΔV/V) and macroscopic stress to determine the acoustoelastic constants, and interpret our observations using the linearized first-order equation based on the model proposed by Hughes and Kelly (1953), https://doi.org/10.1103/physrev.92.1145. This work supports the presence of the acoustoelastic effect in San Carlos olivine, which can be measured as a function of pressure and temperature. This study will aid in our understanding of the acoustoelastic effect and provide a new experimental technique to measure the stress state in elastically deformed geologic materials at high pressure conditions

Did you know? Using entropy and fractal geometry to quantify fluctuations in physiological outputs

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Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle

Abstract Purpose Joint angle is a significant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate ($${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 ) would be conserved at reduced joint angles (i.e. shorter muscle lengths). Methods Eleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30º, 60º and 90º of flexion (0º = extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 was determined using near-infrared spectroscopy. Results Time to task failure/end increased as joint angle decreased (P &lt; 0.001). Over time, complexity decreased at 90º and 60º (decreased ApEn, increased DFA α, both P &lt; 0.001), but not 30º. $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 increased at all joint angles (P &lt; 0.001), though the magnitude of this increase was lower at 30º compared to 60º and 90º (both P &lt; 0.01). There were significant correlations between torque complexity and $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 at 90º (ApEn, r =  − 0.60, P = 0.049) and 60º (ApEn, r =  − 0.64, P = 0.035; DFA α, ρ = 0.68, P = 0.015). Conclusion The lack of correlation between $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and complexity at 30º was likely due to low relative task demands, given the similar kinetics of $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and torque complexity. An inverse correlation between $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths. </jats:sec

Dialogue to address the roots of resource competition: Lessons for policy and practice

Conflict management is an intrinsic element of natural resource management, and becomes increasingly important amid growing pressure on natural resources from local uses, as well as from external drivers such as climate change and international investment. If policymakers and practitioners aim to truly improve livelihood resilience and reduce vulnerabilities of poor rural households, issues of resource competition and conflict management cannot be ignored. This synthesis report summarizes outcomes and lessons from three ecoregions: Lake Victoria, with a focus on Uganda; Lake Kariba, with a focus on Zambia; and Tonle Sap Lake in Cambodia. Partners used a common approach to stakeholder engagement and action research that we call “Collaborating for Resilience”. In each region, partners assisted local stakeholders in developing a shared understanding of risks and opportunities, weighing alternative actions, developing action plans, and evaluating and learning from the outcomes. These experiences demonstrate that investing in capacities for conflict management is practical and can contribute to broader improvements in resource governance

Caffeine Ingestion Attenuates Fatigue-induced Loss of Muscle Torque Complexity

Purpose: We tested the hypothesis that caffeine administration would attenuate the fatigue-induced loss of torque complexity. Methods: Eleven healthy participants performed intermittent isometric contractions of the knee extensors to task failure at a target torque of 50% maximal voluntary contraction (MVC), with a 60% duty factor (6 s contraction, 4 s rest), 60 min after ingesting 6 mg·kg?1 caffeine or a placebo. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) ? scaling exponent. Global, central and peripheral fatigue were quantified using MVCs with femoral nerve stimulation. Results: Caffeine ingestion increased endurance by 30 ± 16% (mean ± SD, P = 0.019). Complexity decreased in both trials (decreased ApEn, increased DFA ?; both P < 0.01), as global, central and peripheral fatigue developed (all P < 0.01). Complexity decreased significantly more slowly following caffeine ingestion (ApEn, -0.04 ± 0.02 vs. –0.06 ± 0.01, P = 0.004; DFA ?, 0.03 ± 0.02 vs. 0.04 ± 0.03, P = 0.024), as did the rates of global (-18.2 ± 14.1 vs. –23.0 ± 17.4 N.m.min?1, P = 0.004) and central (-3.5 ± 3.4 vs. –5.7 ± 3.9 %·min?1, P = 0.02) but not peripheral (-6.1 ± 4.1 vs. –7.9 ± 6.3 N.m.min?1, P = 0.06) fatigue. Conclusion: Caffeine ingestion slowed the fatigue-induced loss of torque complexity and increased the time to task failure during intermittent isometric contractions, most likely through central mechanisms