Porous space characterization of carbonate rocks is an important aid in petroleum exploration from carbonate reservoir. In this study, X-ray microtomography technique was applied to evaluate total ...porosity of a coquina sample extracted from pre-salt reservoir, in Brazil, before and after acid injection. Two image processing program were used in order to assess performance. The results showed that microtomography has potential to compute porosity of coquina samples and provides information about rock porous network.
•Porous space characterization is an important data of the carbonate reservoir.•Microtomography provides quantitative information about rock porous network.•Characterization of internal rock structures as wormhole formation.•Different image processing programs can be used to quantify the porous space.
The trend toward automation of today's power stations has prompted an increased demand for excitation systems having voltage regulators with the ability to automatically regulate generator reactive ...power (VAr) output or power factor (PF). While not really a new type of control, automatic VAr and PF controllers are appearing in the specifications of more and more power plants and generator voltage regulators. This paper provides a functional description of voltage, VAr, and PF controllers and regulators, along with an example demonstrating the superior steady-state voltage support performance on a transmission system by regulating voltage, rather than VArs or PF. The paper concludes that VAr/PF controllers or regulators should generally not be specified or utilized on excitation controls for voltage supporting generator applications.
The purpose of this study is to evaluate the pore space evolution of a rock sample from the coquina region of the subterranean Pre-Salt carbonate reservoir formation (later referred simply as coquina ...sample) subjected to hydrochloric acid flow through the whole sample. For that purpose, X-ray computed tomography with a microfocus source was used in order to evaluate the porous media space. The results show that the branches of the wormhole divert away from the areas near the main channel and the quartz volume decreases after acidification. From the porous space 3D model it could be verified that, although the acid reacts with the most porous part of the medium, the wormhole also crosses regions of lower porosity. Such a process leads to an increase in the total porosity of the carbonate rock.
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•The size and pattern of the wormhole also depends on factors like acid concentration and pumping rate.•Microtomography is employed to inspect porosity evolution and quartz distribution.•The branches of the wormhole divert away from the areas near the principal channel and the quartz volume decreases after acidification.
The increased sophistication of modern turbine and boiler control systems along with the emergence of a deregulated power industry have introduced new challenges in both the implementation of ...controls and the modeling of turbine response to power grid frequency excursions. Past modeling assumptions may no longer be valid when such aspects as steam supply pressure, coordinated boiler/turbine controls, and application (or nonapplication) of speed control loops are considered. This paper provides a summary of some of the discussion topics presented in this area regarding steam turbines, combustion turbines and combined cycle applications.
The repeatability of cognitive performance: a meta-analysis Cauchoix, M.; Chow, P. K. Y.; van Horik, J. O. ...
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
09/2018, Volume:
373, Issue:
1756
Journal Article
Peer reviewed
Open access
Behavioural and cognitive processes play important roles in mediating an individual's interactions with its environment. Yet, while there is a vast literature on repeatable individual differences in ...behaviour, relatively little is known about the repeatability of cognitive performance. To further our understanding of the evolution of cognition, we gathered 44 studies on individual performance of 25 species across six animal classes and used meta-analysis to assess whether cognitive performance is repeatable. We compared repeatability (R) in performance (1) on the same task presented at different times (temporal repeatability), and (2) on different tasks that measured the same putative cognitive ability (contextual repeatability). We also addressed whether R estimates were influenced by seven extrinsic factors (moderators): type of cognitive performance measurement, type of cognitive task, delay between tests, origin of the subjects, experimental context, taxonomic class and publication status. We found support for both temporal and contextual repeatability of cognitive performance, with mean R estimates ranging between 0.15 and 0.28. Repeatability estimates were mostly influenced by the type of cognitive performance measures and publication status. Our findings highlight the widespread occurrence of consistent inter-individual variation in cognition across a range of taxa which, like behaviour, may be associated with fitness outcomes.
This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.
We report on the first comparison of distant caesium fountain primary frequency standards (PFSs) via an optical fiber link. The 1415 km long optical link connects two PFSs at LNE-SYRTE (Laboratoire ...National de métrologie et d'Essais-SYstème de Références Temps-Espace) in Paris (France) with two at PTB (Physikalisch-Technische Bundesanstalt) in Braunschweig (Germany). For a long time, these PFSs have been major contributors to accuracy of the International Atomic Time (TAI), with stated accuracies of around 3×10−16. They have also been the references for a number of absolute measurements of clock transition frequencies in various optical frequency standards in view of a future redefinition of the second. The phase coherent optical frequency transfer via a stabilized telecom fiber link enables far better resolution than any other means of frequency transfer based on satellite links. The agreement for each pair of distant fountains compared is well within the combined uncertainty of a few 10−16 for all the comparisons, which fully supports the stated PFSs' uncertainties. The comparison also includes a rubidium fountain frequency standard participating in the steering of TAI and enables a new absolute determination of the 87Rb ground state hyperfine transition frequency with an uncertainty of 3.1×10−16. This paper is dedicated to the memory of André Clairon, who passed away on 24 December 2015, for his pioneering and long-lasting efforts in atomic fountains. He also pioneered optical links from as early as 1997.
The size and growth patterns of nestling birds are key determinants of their survival up to fledging and long‐term fitness. However, because traits such as feathers, skeleton and body mass can follow ...different developmental trajectories, our understanding of the impact of adverse weather on development requires insights into trait‐specific sensitive developmental windows. We analysed data from nestling Alpine swifts in Switzerland measured throughout growth up to the age of 50 days (i.e. fledging between 50 and 70 days), for wing length and body mass (2693 nestlings in 25 years) and sternum length (2447 nestlings in 22 years). We show that the sensitive developmental windows for wing and sternum length corresponded to the periods of trait‐specific peak growth, which span almost the whole developmental period for wings and the first half for the sternum. Adverse weather conditions during these periods slowed down growth and reduced size. Although nestling body mass at 50 days showed the greatest inter‐individual variation, this was explained by weather in the two days before measurement rather than during peak growth. Interestingly, the relationship between temperature and body mass was not linear, and the initial sharp increase in body mass associated with the increase in temperature was followed by a moderate drop on hot days, likely linked to heat stress. Nestlings experiencing adverse weather conditions during wing growth had lower survival rates up to fledging and fledged at later ages, presumably to compensate for slower wing growth. Overall, our results suggest that measures of feather growth and, to some extent, skeletal growth best capture the consequences of adverse weather conditions throughout the whole development of offspring, while body mass better reflects the short, instantaneous effects of weather conditions on their body reserves (i.e. energy depletion vs. storage in unfavourable vs. favourable conditions).
Using data from more than 2000 Alpine swift nestlings with measurements spanning more than 20 years, we show that adverse weather conditions during the sensitive developmental windows for wing and sternum length result in slower growth, reduced size at 50 days (i.e. close to fledging), delayed fledging and lowered fledging success. Variation in nestling body mass at 50 days was explained by the weather in the two days before measurement rather than during peak growth. Overall, our results suggest that measures of feather growth and, to some extent, skeletal growth best capture the consequences of adverse weather conditions throughout the whole development of offspring, while body mass better reflects the short, instantaneous effects of weather conditions on their body reserves.
We have remeasured the absolute 1S-2S transition frequency nu(H) in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (-29+/-57) Hz for the ...drift of nu(H) with respect to the ground state hyperfine splitting nu(Cs) in 133Cs. Combining this result with the recently published optical transition frequency in 199Hg+ against nu(Cs) and a microwave 87Rb and 133Cs clock comparison, we deduce separate limits on alpha/alpha=(-0.9+/-2.9) x 10(-15) yr(-1) and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments mu(Rb)/mu(Cs) equal to (-0.5+/-1.7) x 10(-15) yr(-1). The latter provides information on the temporal behavior of the constant of strong interaction.
In this paper we describe the cold atom clock PHARAO, designed for microgravity operation. All elements of the PHARAO engineering model have been manufactured and delivered to CNES, the French space ...agency. We present the clock design, its main characteristics, and initial science operation. PHARAO is one of the main components of the Atomic Clock Ensemble in Space payload that is scheduled to fly on board the International Space Station in 2010.
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