Moderate Power Output Research Articles

A Repeated-measures Case Series of Physiological Responses to a Transoceanic Rowing Race.

This repeated-measures case series describes the changes in cardiorespiratory fitness, body composition and systemic inflammation in 4 well-trained athletes pre- and post-completion of an unsupported transatlantic rowing race. The acute effects of endurance exercise have been well described previously, but the enduring consequences of ultra-endurance on the cardiorespiratory, metabolic and immune systems are largely unknown. This study explores these physiological adaptations following 2 weeks of recovery. Cardiorespiratory fitness testing, body composition analysis, and blood sampling for inflammatory cytokines were recorded immediately before race departure and repeated 14 days following race completion. Mean VO2max (ml/kg/min) was similar pre- (48.2±2.8) and post-race (46.7±1.5). Heart rate responses were equivalent at incremental workloads. Mean blood lactate (mmol/L) was higher at low to moderate power outputs and lower at maximal effort (14.6±1.85 vs. 13.1±2.5). Percentage body fat (17.7 ± 7.9 vs. 16.2±7.4) was analogous to pre-race analysis. Low-grade inflammation persisted, indicated by an increase in IL-1β (69%), IL-8 (10%), TNF-α (8%), IL-6 (5.4%), and C-reactive protein (22.4%). VO2max and heart rate responses were similar pre- and post-race, but sub-maximal efficiency measures of cardiorespiratory fitness were consistent with persistent fatigue. Body composition had returned to baseline but low-grade systemic inflammation persisted. Persistent pro-inflammatory cytokinaemia is known to exert deleterious consequences on immune, metabolic, and psychological function. Adequate recovery is necessary to re-establish inflammatory homeostasis, and the results of this study may inform these decisions.

Flexible hydrogen fuel cell fabricated on paper with embedded aluminium foil

Direct hydrogen fuel cells are generally heavy and rigid systems based on metal or plastic materials, which are not suitable for various miniwatt and flexible devices. In this study, we have developed a lightweight and flexible fuel cell based on paper substrate embedded with an Al foil inside, which is used as an in-situ hydrogen source by reaction with an electrolyte solution during operation. Benefited from the inhibited hydroxyl transportation by the porous cellulose network, the vigorous Al corrosion reaction is well controlled even though strong alkaline electrolyte is adopted, so that the fuel cell can be discharged for more than 5 hours at 1 mA cm-2 (0.83 V) with only 3.5 mg Al foil. The corresponding faradaic and energy efficiencies are as high as 72% and 18.3%, respectively. The fuel cell flexibility is also quite good when facing different bending angles. Considering its moderate power output, this flexible paper-based hydrogen fuel cell is especially suitable for powering various miniwatt and flexible devices, such as wearable electronics, biosensors, RFID tags, etc. However, higher power can be obtained by suitable stacking of the fuel cell.

Exercise efficiency of low power output cycling

Exercise efficiency at low power outputs, energetically comparable to daily living activities, can be influenced by homeostatic perturbations (e.g., weight gain/loss). However, an appropriate efficiency calculation for low power outputs used in these studies has not been determined. Fifteen active subjects (seven females, eight males) performed 14, 5-min cycling trials: two types of seated rest (cranks vertical and horizontal), passive (motor-driven) cycling, no-chain cycling, no-load cycling, cycling at low (10, 20, 30, 40 W), and moderate (50, 60, 80, 100, 120 W) power outputs. Mean delta efficiency was 57% for low power outputs compared to 41.3% for moderate power outputs. Means for gross (3.6%) and net (5.7%) efficiencies were low at the lowest power output. At low power outputs, delta and work efficiency values exceeded theoretical values. In conclusion, at low power outputs, none of the common exercise efficiency calculations gave values comparable to theoretical muscle efficiency. However, gross efficiency and the slope and intercept of the metabolic power vs mechanical power output regression provide insights that are still valuable when studying homeostatic perturbations.

Seated versus standing position for maximization of performance during intense uphill cycling

It is not known whether the seated or standing position favours performance during intensive bouts of uphill cycling. The following hypotheses were therefore tested: (1) the standing position results in better performance at a high power output, while (2) the seated position is best at a moderate power output. We also assessed the seated–standing transition intensity, above which seated cycling should be superseded by standing cycling for maximization of performance. Ten male cyclists (mean age 27 years, s = 3; height 1.82 m, s = 0.07; body mass 75.2 kg, s = 7.0; [Vdot]O2max 70.0 ml · kg−1 · min−1, s = 5.2) performed seated and standing treadmill cycling to exhaustion at 10% grade and at four power outputs ranging from 86% to 165% of their power output at maximal oxygen uptake (Wmax). Power output at maximal oxygen uptake was obtained during determination of [Vdot]O2max. There was no difference in time to exhaustion between the two cycling positions at 86% of Wmax (P = 0.29). All participants performed best at the highest power output (165% of Wmax) when standing (P = 0.002). An overall seated–standing transition intensity of 94% of Wmax was identified. Thus, in general, cyclists may choose either the standing or seated position for maximization of performance at a submaximal intensity of 86% of Wmax, while the standing position should be used at intensities above 94% of Wmax and approaching 165% of Wmax.

An Investigation of Power Stabilization and Space-Dependent Dynamics of a Nuclear Fluidized-Bed Reactor

Previous work into the space-dependent kinetics of the conceptual nuclear fluidized bed has highlighted the sensitivity of fission power to particle movements within the bed. The work presented in this paper investigates a method of stabilizing the fission power by making it less sensitive to fuel particle movement. Steady-state neutronic calculations are performed to obtain a suitable design that is stable to radial and axial fuel particle movements in the bed. Detailed spatial/temporal simulations performed using the finite element transient criticality (FETCH) code investigate the dynamics of the new reactor design. A dual requirement of the design is that it has a moderate power output of ˜300 MW(thermal).

Effect of cardiac-locomotor coupling on the metabolic efficiency of pedalling.

Coupling between cardiac and locomotor rhythms (CLC) has been reported while subjects exercise at cadences that are natural to them. The hypothesis that oxygen consumption (VO2) would be lower when subjects pedalled at the rate producing 1:1 coupling of heart and pedalling rates than when they pedalled at noncoupled rates was tested with 12 men on a cycle ergometer. At a moderate power output based on their VO2max, subjects pedalled at six different pedalling rates while VO2 and heart rate were measured. The pedalling rates were the preferred frequency, frequencies 15 and 30% above and below the preferred frequency, and the 1:1 coupled frequency. In 8 of the 12 subjects it was possible to fit their data with significant regression equations relating VO2 to pedalling rate, but in no subject was the 1:1 coupled state energetically beneficial, suggesting that any functional significance of CLC is unrelated to metabolic efficiency.

Ultrasonic energy. Effects on vascular function and integrity.

Ultrasonic energy transmitted via flexible wire probes provides a new means of ablating atherosclerotic plaque. We studied the effects of ultrasonic energy (20 kHz) delivered via a ball-tipped wire probe on arterial vasomotor behavior in rabbit thoracic aortas in a perfused whole-vessel model. After precontraction with phenylephrine (10(-5) M) or KCl (60 mM), the effects of ultrasonic energy (0.7-5.5 W x 60 seconds, 42-330 J) on arterial vasomotor behavior were measured using long-axis ultrasonic vessel imaging of the proximal (ultrasonic probe-treated) and distal (untreated) control segments. The efficacy of plaque ablation at these same probe-tip power outputs was evaluated in atherosclerotic, human cadaver iliofemoral arteries. Ultrasonic energy caused dose (energy)-dependent relaxation in rabbit aortas after precontraction with phenylephrine in arteries with endothelium (n = 8) and without endothelium (n = 8) (p less than 0.001 versus ultrasound treated at power outputs of 2.9 and 5.5 W). There was no difference in the relaxation dose responses between endothelialized and endothelially denuded segments (p = NS). Ultrasonic energy also caused significant relaxation (67 +/- 8%) after voltage-dependent precontraction with 60 mM KCl. Temperature measurements revealed less than 1 degrees C warming of the vessel wall during as long as 2 minutes of treatment at a power output of 5.5 W. Pathological examination showed no smooth muscle injury at (moderate) power outputs that caused arterial relaxation. At probe-tip power outputs of 2.9-5.5 W, ultrasonic energy recanalized two of two totally occluded cadaveric iliofemoral vessel segments. The ultrasonic ablation catheter was also demonstrated to cause arterial relaxation in a recanalized canine femoral artery in vivo. Ultrasonic energy delivered via a flexible-wire probe produces dose-dependent, endothelium-independent smooth muscle relaxation capable of reversing both receptor-mediated and voltage-dependent vasoconstriction in vitro. At moderate power outputs, this relaxation response does not appear to be due to thermal effects or irreversible smooth muscle cell injury. This vasorelaxant effect of ultrasonic energy is also apparent in vivo, at doses that effectively ablate atherosclerotic plaque, and may improve the safety of arterial recanalization using ultrasonic energy.

A 125-260-GHz Gyrotron

The second gyrotron constructed at the University of Sydney has produced continuous microwave output at more than 60 frequencies in the range 125-260 GHz at power levels approaching 10 W. A gyrotron Iike this, with broad frequency coverage and moderate power output, has a wide range of possible applications, from spectroscopy to scattering from waves and fluctuations in plasmas. In this paper, the results of detailed measurements of frequency, magnetic field, frequency pulling, and starting current are compared with theory. Agreement is excellent. We find that mode conversion at the output end of the cavity determines the level of output power.

Properties of an Argon Laser in the Schlieren Study of Gas Flow within an Electric Arc or Plasma

AbstractA diagnostic technique is suggested which will permit studies of gas (law within power arcs or plasmas by the use of a Schlieren system. Experimental evidence is given showing that High Speed (107 P.P.S.) Kine Schlieren photography can be undertaken with a gas laser of moderate power output. Both multiphase and uniphase modes of operation are considered, and a simple form of exposure assessment is given which relates spectral sensitivity (Sλ) of a photographic material with the laser beam in use. A possible method of obtaining pulsed amplification by the opplicotion of a solenoid is discussed.

The O-Type Carcinotron Tube

This paper is devoted to O-type Carcinotron tubes, which are backward wave oscillators particularly suitable in applications requiring a tube with a very wide electronic tuning range and moderate power output. A survey of backward-wave operation is given. Theoretical results on the starting conditions are shown to compare favorably with experimental values. The effects of reflections are discussed and are shown to be very small only when the delay line has properly matched terminals. Approximate expressions for efficiency and frequencypushing are derived. Design and performance data are given for a series of tubes now in production, each of which covers about one octave in frequency, providing total frequency coverage from 1,000 to 12,000 mc. The maximum beam voltage of any of the tubes in the series is 1,500 volts. The rf power output of the series is 100 to 1,000 milliwatts. Data on delay lines, gun structures and focusing are given, and results of tests on 100 tubes are tabulated.