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21.
McElwee K Donohue MJ Courtney CA Morishige C Rivera-Vicente A 《Marine pollution bulletin》2012,65(1-3):7-15
Derelict fishing gear (DFG) is a highly persistent form of marine pollution known to cause environmental and economic damage. At-sea detection of DFG would support pelagic removal of this gear to prevent and minimize impacts on marine environments and species. In 2008, experts in marine debris, oceanography, remote sensing, and marine policy outlined a strategy to develop the capability to detect and ultimately remove DFG from the open ocean. The strategy includes three interrelated components: understanding the characteristics of the targeted DFG, indirectly detecting DFG by modeling likely locations, and directly detecting pelagic DFG using remote sensing. Together, these components aim to refine the search area, increase the likelihood of detection, and decrease mitigation response time, thereby providing guidance for removal operations. Here, we present this at-sea detection strategy, relate it to relevant extant research and technology, and identify gaps that currently prevent successful at-sea detection and removal of DFG. 相似文献
22.
Abstract— The characterization of comet and asteroid interiors will eventually require in situ exploration with drills, penetrators/penetrometers, hypervelocity impactors, excavators or other devices. Because they offer desirable scientific capabilities and relative mechanical simplicity, penetrators and penetrometers, which use only axial force to push beneath the surface, are a good choice for near‐term missions. Penetrometers are instruments, generally deployed from a larger vehicle, that measure subsurface mechanical properties and may also contain additional scientific instruments. There are three basic types: “fast” penetrometers are released from above and plunge into the surface. Static and dynamic (collectively referred to as “slow”) penetrometers use, respectively, a constant slow penetration speed and periodic hammering impulses. The low gravity environment of asteroids and comets presents a key challenge to instrument deployment and also greatly affects the mechanical properties of surface materials, and in turn penetrometer performance. The Rosetta mission, currently en route to comet 67P/Churyumov‐Gerasimenko, will be the next mission to try both fast and slow, dynamic penetrometry, when it arrives in 2014. We present some new concepts of static penetrometers for small body exploration that are adapted to the low gravity environment. The low gravity environment also presents challenges for the testing of penetrometers on Earth and a number of previous solutions are described and new methods suggested. In the next generation of missions to study comets and asteroids, penetrometers could provide important data on their mechanical, seismic, thermal, electromagnetic, and chemical characteristics, as well as sample collection. 相似文献
23.
The relevant data for the known 147 pulsars are presented in graphical and tabular forms. Various data correlations are discussed, and a detailed analysis of pulsar dispersion measures and distances is given. The range of the electron densities in the diffuse interstellar medium is found to be 0.01 cm–3n
e0.1 cm–3, and n
e0.03 cm–3. The dispersion scale height for pulsars is found to be 5.9±0.7 pc cm–3 implying a linear scale height of 200 pc, which is much smaller than the electron scale height of our Galaxy.Astrophysics and Space Science Review Paper. 相似文献
24.
25.
The current paradigm of high energy spectroscopy tells us that light emitted from a wide variety of objects has its origin
close to the black hole event horizon. As such, these photons are subject to general relativistic effects such as light-bending,
gravitational lensing and redshift, time-dilation, etc. These gravitational effects are well-understood from a theoretical
standpoint and therefore, provide a natural mechanism to test the properties of strong gravitational fields. To this end,
we have developed a new (semi-analytic) strong gravity code, capable of describing the contribution of photons that perform
multiple orbits of the hole. We apply this code to a simple Keplerian accretion disk in order to understand the role played
by the angular emissivity, black hole spin and higher order images in forming the line profile. 相似文献
26.
Jan Inge Faleide Anders Solheim Anne Fiedler Berit O. Hjelstuen Espen S. Andersen Kris Vanneste 《Global and Planetary Change》1996,12(1-4)
Seven regionally correlatable reflectors, named R7 (oldest) to R1, have been identified in the Upper Cenozoic sedimentary succession along the western continental margin of Svalbard and the Barents Sea. Regional seismic profiles have been used to correlate between submarine fans that comprise major depocentres in this region. Glacial sediment thicknesses reach up to 3 seconds two-way time, corresponding to 3.5–4 km. Despite limited chronostratigraphic control, ages have been assigned to the major sequence boundaries based on ties both to exploration wells and to shallow boreholes, and by paleoenvironmental interpretations and correlations with other regions. Lateral and vertical variations in seismic facies, between stratified and chaotic with slump structures, have major implications for the interpretation of the depositional regime along the margin. The main phases of erosion and deposition at different segments of the margin are discussed in the paper, which also provides a regional seismic stratigraphic framework for two complementary papers in the present volume. Reflector R7 marks the onset of extensive continental shelf glaciations, but whereas the outer Svalbard shelf has been heavily and frequently glaciated since R7 time, this did not occur, or occurred to a much less extent, until R5 time in the southern Barents Sea. The present study provides the background for a quantification of the late Cenozoic glacial erosion of Svalbard and the Barents Sea. The rates of erosion and deposition exhibit large temporal and spatial variations reflecting the importance of glacial processes in the Late Cenozoic development of this nearly 1000 km long margin. 相似文献
27.
Kris Davidson 《Astrophysics and Space Science》1970,6(3):422-435
A newly-formed massive star is likely to be surrounded by dense gas and dust as it approaches the main sequence. Radiation pressure must push some of the inner material outward before the star begins to produce ionizing radiation; this affects the formation of theHii region. A remarkably dense dust front may precede the ionization front.The observable radio and infrared spectra are discussed. If the dust cloud is composed of small graphite grains, extraordinarily large far-infrared fluxes are possible. 相似文献
28.
Jonas Schoelynck Dieter Meire Kris Bal Kerst Buis Peter Troch Tjeerd Bouma Patrick Meire Stijn Temmerman 《Limnologica》2013,43(5):371-380
In most aquatic ecosystems, hydrodynamic conditions are a key abiotic factor determining species distribution and aquatic plant abundance. Recently, local differences in hydrodynamic conditions have been shown to be an explanatory mechanism for the patchy pattern of Callitriche platycarpa Kütz. vegetation in lowland rivers. These local conditions consists of specific areas of increased shear zones, resulting in additional plant stress and erosion of the sediment on the one hand and local decreased shear zones resulting in zones favourable to plant growth and sedimentation of bed material on the other hand. In this study, the process of this spatial plant-flow-sedimentation interaction has been illustrated quantitatively by in situ flume measurements. By disturbing the incoming discharge on a single patch in such flume, we have quantified the behaviour and influence of a C. platycarpa patch under normal field conditions (base flow). Additionally, the behaviour of a C. platycarpa patch under different conditions of hydrodynamic stress has been examined in a laboratory flume. Indeed, flexible, submerged macrophytes are capable to adapt patch dimensions with changing stream velocities. At times of modest hydrodynamic stress, the species takes a position near the water surface and optimises its leaf stand, thereby maximising its photosynthetic capacity. At times of peak discharge, the patch will bend down towards the river bed and become more confined and streamlined, as such averting the stream velocity and diminishing the risk of breaking or being uprooted.In this paper, the processes of local hydrodynamic conditions on the patch and the patch’ intriguing life strategy of avoiding negative feedback was shown. 相似文献
29.
Lucille Le Corre Vishnu Reddy Nico Schmedemann Kris J. Becker David P. O’Brien Naoyuki Yamashita Patrick N. Peplowski Thomas H. Prettyman Jian-Yang Li Edward A. Cloutis Brett W. Denevi Thomas Kneissl Eric Palmer Robert W. Gaskell Andreas Nathues Michael J. Gaffey David W. Mittlefehldt William B. Garry Holger Sierks Christopher T. Russell Carol A. Raymond Maria C. De Sanctis Eleonora Ammanito 《Icarus》2013
NASA’s Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types: (a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), (b) lobate patches with well-defined edges (nicknamed “pumpkin patches”), and (c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed “Leslie feature” first identified by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Several possible options for the composition of the orange material are investigated including, cumulate eucrite layer exposed during impact, metal delivered by impactor, olivine–orthopyroxene mixture and impact melt. Based on our analysis, the orange material on Vesta is unlikely to be metal or olivine (originally proposed by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157)). Analysis of the elemental composition of Oppia ejecta blanket with GRaND suggests that its orange material has ∼25% cumulate eucrite component in a howarditic mixture, whereas two other craters with orange material in their ejecta, Octavia and Arruntia, show no sign of cumulate eucrites. Morphology and topography of the orange material in Oppia and Octavia ejecta and orange patches suggests an impact melt origin. A majority of the orange patches appear to be related to the formation of the Rheasilvia basin. Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt. 相似文献
30.
The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field mapping, GIS analysis, statistical associations between landslides and terrain attributes, and a comparison between Neoglaciated and non-Neoglaciated terrain within each basin.The bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the LIA trimline. Valleys carved in weak Quaternary volcanics show significant erosional oversteepening and contain deep-seated slope movement features, active rock fall, rock slides, and rock avalanches near glacial trimlines. Basins in stronger granitic rock rarely show increased bedrock instability resulting from post-LIA retreat, except for shallow-seated rock slides along some trimlines and failures on previously unstable slopes. In surficial materials, landslides associated with post-LIA retreat originate in till or colluvium, as debris slides or debris avalanches, and are concentrated along lateral moraines or glacial trimlines.Significant spatial association was also observed between recent catastrophic failures, gravitational slope deformation, and slopes that were oversteepened then debuttressed by glacial erosion. Eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep-seated gravitational slope movement, implying that this type of deformation is a precursor to catastrophic detachment. 相似文献