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33.
Designing future underwater vehicles: principles and mechanisms of the weakly electric fish 总被引：1，自引：0，他引：1
Future underwater vehicles will be increasingly called upon to work in cluttered environments and to interact with their surroundings. These vehicles will need sensors that work efficiently at short range and be highly maneuverable at low speed. To obtain insights into principles and mechanisms of low-speed operation in cluttered environments, we examine a fish that excels in this regime, the black ghost knifefish Apteronotus albifrons. This fish hunts in dark or turbid water using a short-range self-generated electric field to sense its surroundings. Coupled with this unique mode of sensing is an unusual ribbon fin propulsion system that confers high multidirectional maneuverability at low speeds. To better understand the relationship between body morphology and common maneuvers of this fish, we utilized an idealized ellipsoidal body model, Kirchhoff's equations, and an optimal control algorithm for generating trajectories. We present evidence that common fish trajectories are optimal, and that these trajectories complement the sensory abilities of the fish. We also discuss prototypes of the sensing and propulsion systems of the fish with a view to providing alternative approaches for underwater vehicle design where high maneuverability in geometrically complex environments is needed. 相似文献
34.
Charles A. Ogunbode Gisela Böhm Stuart B. Capstick Christina Demski Alexa Spence Nicole Tausch 《Climate Policy》2019,19(6):703-715
Climate change is projected to increase the frequency, intensity and unpredictability of extreme weather events across the globe and these events are likely to have significant mental health implications. The mental health literature broadly characterises negative emotional reactions to extreme weather experiences as undesirable impacts on wellbeing. Yet, other research in psychology suggests that negative emotional responses to extreme weather are an important motivation for personal action on climate change. This article addresses the intersection of mental health and functional perspectives on negative emotions, with a specific focus on the potential that reduced negative emotional responses to extreme weather may also translate to diminished motivation to undertake climate change mitigation actions – which we term the ‘resilience paradox’. Using survey data gathered in the aftermath of severe flooding across the UK in winter 2013/2014, we present new evidence indicating that self-appraised coping ability moderates the link between flooding experience and negative emotions and thereby attenuates the indirect link between flooding experience and climate change mitigation intentions. We conclude that support for flood victims should extend beyond addressing emotional, physical and financial stresses to include acknowledgement of the involvement of climate change and communication of the need for action to combat future climate risks.
Key policy insights
Psychological resilience to flooding and other extreme weather events can translate to diminished motivation to mitigate climate change
Negative emotional reactions need to occur at an optimal level to enable people to respond appropriately to climate risks.
Flood victims’ subjective appraisal of their ability to cope does not necessarily encompass consideration of the role played by climate change. Therefore, support for victims of extreme weather should include explicit acknowledgement of the involvement of climate change and the need for action to mitigate future climate risks.
35.
Joseph J. Fontaine Karie L. Decker Susan K. Skagen Charles van Riper III 《Climatic change》2009,97(1-2):305-311
Recent changes in global climate have dramatically altered worldwide temperatures and the corresponding timing of seasonal climate conditions. Recognizing the degree to which species respond to changing climates is therefore an area of increasing conservation concern as species that are unable to respond face increased risk of extinction. Here we examine spatial and temporal heterogeneity in the rate of climate change across western North America and discuss the potential for conditions to arise that may limit the ability of western migratory birds to adapt to changing climates. Based on 52 years of climate data, we show that changes in temperature and precipitation differ significantly between spring migration habitats in the desert southwest and breeding habitats throughout western North America. Such differences may ultimately increase costs to individual birds and thereby threaten the long-term population viability of many species. 相似文献
36.
V. Van Grootel S. Charpinet G. Fontaine P. Brassard 《Astrophysics and Space Science》2010,329(1-2):217-224
The hot pulsating sdB star PG 1605+072 exhibits uncommon spectroscopic and pulsation properties, and is one of the biggest challenge in the field of sdB star modeling. Two hypotheses have been proposed to explain its unusually rich pulsation spectrum. The first is the natural explanation of a fast-rotating pulsator, which lifts the (2l+1)-fold degeneracy of the frequency components. Another approach, where PG 1605+072 can be seen as a slow rotator, considers that the numerous low amplitude frequency components are second- and third-order harmonics and nonlinear combinations of the highest amplitude frequencies. We investigated the two hypotheses in the light of asteroseismology, using our latest tools—including pulsation codes that incorporate star rotation and new generation complete sdB models. The results of both approaches are presented, showing interesting results and raising new questions for our understanding of this mysterious sdB star. 相似文献
37.
Xuan Thanh Pham Bernard Fontaine Nathalie Philippon 《Theoretical and Applied Climatology》2010,99(1-2):105-113
The summer monsoon onset over southern Vietnam is determined through a new criterion based on both in situ daily rainfall at six selected stations provided by the Institute of Meteorology and Hydrology, Vietnam, and the zonal component of the wind at 1,000 hPa from the National Center for Environmental Prediction/Department of Energy Reanalysis 2. Over the period 1979–2004, the summer monsoon onset mean date is on 12 May, with a standard deviation of 11.6 days. The temporal and spatial structures of the atmospheric conditions prevailing during the onset period are detailed. Clear changes are seen in the zonal wind (strengthened over the Bay of Bengal and changed from negative to positive over South Vietnam) and in convection (deeper), in association with an intensification of the meridional gradients of sea level pressure at 1,000 hPa and of moist static energy at 2 m over Southeast Asia. The predictability of onset dates is then assessed. Cross-validated hindcasts based upon four predictors linked to robust signals in the atmospheric dynamics are then provided. They are highly significant when compared to observations (56% of common variance). Basically, late (early) onsets are preceded in March–April by higher (lower) sea level pressure over the East China Sea, stronger (weaker) southeasterly winds over southern Vietnam, decreasing (increasing) deep convection over the Bay of Bengal, and the reverse situation over Indonesia (120–140°E, 0–10°S). 相似文献
38.
Fluid theories explain the origin of region-2 field-aligned currents as the closure of the ring current, driven itself by the azimuthal pressure gradients generated in the magnetospheric ring plasma by the sunward convection. Although the structure of pressure gradients appears experimentally complex, observations confirm that a close connection exists between the region-2 field-aligned currents and the ring current. The fluid linear theory of the adiabatic transport by convection of the ring plasma gives a first estimate of this process, and leads ultimately to phase quadrature (in terms of magnetic local time) between the region-2 field-aligned currents and the convection potential. When significant non-adiabatic processes are taken into account, such as precipitations at auroral latitudes, the theoretical phase difference rotates toward opposition. We determine experimentally the phase relationship between the region-2 field-aligned currents and the convection potential from recent statistics, depending on the magnetic activity index Kp, and performed from the EISCAT data base. For geometrical reasons of sufficient probing of region 2, it is only computed in the case of a moderate magnetic activity corresponding to 2\leqKp<4. Region-2 field-aligned currents are found to be in phase opposition with the convection electrostatic potential at auroral latitudes. This confirms the importance of non adiabatic processes, especially ion losses, in the generation of region-2 field-aligned currents, as theoretically suggested. 相似文献
39.
Free amino acid concentrations were determined in sea-water at three stations in the Tahiti area. At each station, sampling was done both offshore and in the lagoon. Comparison of results from two stations suggests a relationship between free amino acid levels in lagoon waters and organic man-made pollution. 相似文献
40.
Bernhard?SchulzEmail author Klaus?Bombach Sabine?Pawlig Helene?Br?tz 《International Journal of Earth Sciences》2004,93(5):824-843
In the Austroalpine Basement to the south of the Tauern Window, distinct suites of metabasites occur with orthogneisses in pre-Early-Ordovician units. Tholeiitic and alkaline within-plate basalt-type metabasites are associated with acid meta-porphyroids in the post-Early-Ordovician Thurntaler Phyllite Group. According to their correlated trace element abundances, metabasite zircons crystallized with their host rocks. Protolith Pb–Pb zircon ages, whole-rock Ta/Yb–Th/Yb and oxygen, Sr, Nd isotope data define two principal evolution lines. An older evolution at elevated Th/Yb typical of subduction-related magmatism, started by 590-Ma N-MORB-type and 550–530 Ma volcanic arc basalt type basic suites, which mainly involved depleted mantle sources. It finished with mainly crustal-source 470–450-Ma acid magmatites. An other evolution line by tholeiitic and 430-Ma alkaline within-plate basalt-type suites in both pre- and post-Early-Ordovician units is characterized by an intraplate mantle metasomatism and enrichment trend along multicomponent sources. These magmatic evolution lines can be related to a plate tectonic scenario that involved terranes in a progressively mature Neoproterozoic to Ordovician active margin, and a subsequent Palaeo-Tethys passive margin along the north Gondwanan periphery. 相似文献