The physiological and biomechanical requirements of flight at high altitude have been the subject of much interest. Here, we uncover a steep relation between heart rate and wingbeat frequency (raised ...to the exponent 3.5) and estimated metabolic power and wingbeat frequency (exponent 7) of migratory bar-headed geese. Flight costs increase more rapidly than anticipated as air density declines, which overturns prevailing expectations that this species should maintain high-altitude flight when traversing the Himalayas. Instead, a "roller coaster" strategy, of tracking the underlying terrain and discarding large altitude gains only to recoup them later in the flight with occasional benefits from orographic lift, is shown to be energetically advantageous for flights over the Himalayas.
A process model has been developed to evaluate the potential performance of a large-scale high-temperature co-electrolysis plant for the production of syngas from steam and carbon dioxide. The ...co-electrolysis process allows for direct electrochemical reduction of the steam/carbon dioxide gas mixture, yielding hydrogen and carbon monoxide, or syngas. The process model has been developed using the UniSim system-analysis code. Using this code, a detailed process flow sheet has been defined that includes all the components that would be present in an actual plant such as pumps, compressors, heat exchangers, turbines, and the electrolyzer. Since the electrolyzer is not a standard UniSim component, a custom integral co-electrolysis model was developed for incorporation into the overall UniSim process flow sheet. The integral co-electrolysis model assumes local chemical equilibrium among the four process-gas species via the water-gas shift reaction. The electrolyzer model allows for the determination of co-electrolysis outlet temperature, composition (anode and cathode sides); mean Nernst potential, operating voltage and electrolyzer power based on specified inlet gas flow rates, heat loss or gain, current density, and cell area-specific resistance. The integral electrolyzer model was validated by comparison with results obtained from a fully three-dimensional computational fluid dynamics model developed using FLUENT, and by comparison with experimental data. This paper provides representative results obtained from the UniSim flow sheet model for a 300
MW
e co-electrolysis plant, coupled to a high-temperature gas-cooled nuclear reactor. The co-electrolysis process, coupled to a nuclear reactor, provides a means of recycling carbon dioxide back into a useful liquid fuel. If the carbon dioxide source is based on biomass, the overall process, from production through utilization, would be climate-neutral.
Sexual selection is responsible for the evolution of many elaborate traits, but sexual trait evolution could be influenced by opposing natural selection as well as genetic constraints. As such, the ...evolution of sexual traits could depend heavily on the environment if trait expression and attractiveness vary between environments. Here, male Drosophila simulans were reared across a range of diets and temperatures, and we examined differences between these environments in terms of (i) the expression of male cuticular hydrocarbons (CHCs) and (ii) which male CHC profiles were most attractive to females. Temperature had a strong effect on male CHC expression, whereas the effect of diet was weaker. Male CHCs were subject to complex patterns of directional, quadratic and correlational sexual selection, and we found differences between environments in the combination of male CHCs that were most attractive to females, with clearer differences between diets than between temperatures. We also show that genetic covariance between environments is likely to cause a constraint on independent CHC evolution between environments. Our results demonstrate that even across the narrow range of environmental variation studied here, predicting the outcome of sexual selection can be extremely complicated, suggesting that studies ignoring multiple traits or environments may provide an over‐simplified view of the evolution of sexual traits.
During the mid-first millennium AD, new kingdoms and states emerged across South Asia. At this time, land grants made to Hindu temples are thought to have led to wide-ranging societal ...transformations. To date, however, neither the land-grant charters nor the changes they are said to have driven have been studied archaeologically. Here, the authors present the results of the first archaeological investigation of the charters and their landscape context. Bringing together the textual record with a survey of 268 religious and residential sites, the results establish historical baselines against which the longue durée developments of South Asian social, political and economic formation can be profitably re-posed.
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.
Ruddy shelduck migrate from wintering grounds in lowland India and Myanmar to breeding grounds in central China and Mongolia, sustaining flight over the Himalayas, where oxygen availability is ...greatly reduced. We compared phenotypes of the pectoralis muscle and the ventricle of the heart from ruddy shelduck and common shelduck (a closely related low-altitude congener) that were raised in common conditions at sea level, predicting that oxidative capacity would be greater in ruddy shelduck to support high-altitude migration. Fibre-type composition of the pectoralis and the maximal activity of eight enzymes involved in mitochondrial energy metabolism in the pectoralis and heart, were compared between species. Few differences distinguished ruddy shelduck from common shelduck in the flight muscle, with the exception that ruddy shelduck had higher activities of complex II and higher ratios of complex IV (cytochrome
c
oxidase) and complex II when expressed relative to citrate synthase activity. There were no species differences in fibre-type composition, so these changes in enzyme activity may reflect an evolved modification in the functional properties of muscle mitochondria, potentially influencing mitochondrial respiratory capacity and/or oxygen affinity. Ruddy shelduck also had higher lactate dehydrogenase activity concurrent with lower pyruvate kinase and hexokinase activity in the left ventricle, which likely reflects an increased capacity for lactate oxidation by the heart. We conclude that changes in pathways of mitochondrial energy metabolism in the muscle and heart may contribute to the ability of ruddy shelduck to fly at high altitude.
The generation of GeV-scale electron beams in a gas-filled capillary discharge waveguide with good reproducibility is discussed. Beams of electrons with energies above 900 MeV, and with ...root-mean-square divergences of 3.5 mrad, are observed for a plasma density of 2.2 × 1018 cm−3 and a peak input laser power of 55 TW. The variation of the maximum electron energy with the plasma density is measured and found to agree well with simple models. Injection and acceleration of electrons at the to date lowest plasma density of 3.2 × 1017 cm−3 are reported. The energy spectra of the generated electron beams exhibit good shot-to-shot reproducibility, with the observed variations attributable to the measured shot-to-shot jitter of the laser parameters. Two methods for correcting the effect of beam pointing variations on the measured energy spectrum are described.
Background
Hepatocyte nuclear factor 4 alpha (HNF4A) gene mutations have a well‐recognized role in maturity‐onset diabetes of the young and have recently been described in congenital hyperinsulinism. ...A biphasic phenotype has been postulated, with macrosomia and congenital hyperinsulinism in infancy, and diabetes in young adulthood. In this case series, we report three children with HNF4A mutations (two de novo) and diazoxide‐responsive congenital hyperinsulinism, highlighting the potential for ongoing diazoxide requirement and the importance of screening for these mutations even in the absence of family history.
Case reports
All patients presented with macrosomia (mean birthweight 4.26 kg) and hyperinsulinaemic hypoglycaemia soon after birth (median age 1 day). All three (age range 7 months to 11 years 10 months) remain on diazoxide therapy, with dose requirements increasing in one patient. There was no prior family history of diabetes, neonatal hypoglycaemia or macrosomia. Parents were screened for HNF4A mutations post‐diagnosis and one father was subsequently found to have maturity‐onset diabetes of the young.
Conclusions
This case series follows the evolving course of three patients with confirmed HNF4A‐mediated congenital hyperinsulinism, highlighting (1) the variable natural history of these mutations, (2) the potential for prolonged diazoxide requirement, even into adolescence, and (3) the need for screening, regardless of family history.
Control of ionic polymer metal composites Richardson, R.C.; Levesley, M.C.; Brown, M.D. ...
IEEE/ASME transactions on mechatronics,
06/2003, Letnik:
8, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Robotic devices are traditionally actuated by hydraulic systems or electric motors. However, with the desire to make robotic systems more compact and versatile, new actuator technologies are ...required. In this paper, the control of ionic polymer metal composite actuators is investigated from a practical perspective. The actuator characteristics are examined through the unblocked maximum displacement and blocked force output. An open-loop position control and closed-loop position proportional-integral-derivative (PID) control are then applied to a strip of actuators. Finally, the performance of the polymer is investigated when implementing an impedance controller (force/position control).
PDF
