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151.
Kristen Coppin Mark Halpern Douglas Scott Colin Borys James Dunlop Loretta Dunne Rob Ivison Jeff Wagg Itziar Aretxaga Elia Battistelli rew Benson rew Blain Scott Chapman Dave Clements Simon Dye Duncan Farrah David Hughes Tim Jenness Eelco van Kampen Cedric Lacey Angela Mortier Alexandra Pope Robert Priddey Stephen Serjeant Ian Smail Jason Stevens Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2008,384(4):1597-1610
A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 μm has been carried out to map the regions around several 850-μm-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared (IR) luminosities and hence star formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350-μm flux densities for 24 850-μm sources, seven of which are detected at ≥2.5σ within a 10 arcsec search radius of the 850-μm positions. When results from the literature are included the total number of 350-μm flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-IR (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich ( M dust ≃ 9 × 108 M⊙ ) , luminous ( L FIR ≃ 2 × 1012 L⊙ ) star-forming galaxies with intrinsic dust temperatures of ≃35 K and star formation rates of ≃400 M⊙ yr−1 . We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350-μm source counts, N 350 (>25 mJy) ∼ 200–500 deg−2 . 相似文献
152.
W. G. Hartley L. Gazzola F. R. Pearce S. T. Kay P. A. Thomas 《Monthly notices of the Royal Astronomical Society》2008,386(4):2015-2021
The physical processes that define the spine of the galaxy cluster X-ray luminosity–temperature ( L – T ) relation are investigated using a large hydrodynamical simulation of the universe. This simulation models the same volume and phases as the millennium simulation and has a linear extent of 500 h −1 Mpc . We demonstrate that mergers typically boost a cluster along but also slightly below the L – T relation. Due to this boost, we expect that all of the very brightest clusters will be near the peak of a merger. Objects from near the top of the L – T relation tend to have assembled much of their mass earlier than an average halo of similar final mass. Conversely, objects from the bottom of the relation are often experiencing an ongoing or recent merger. 相似文献
153.
Biological damage to plants is commonly found from the Devonian but occurs most commonly from the Cretaceous. Damage inflicted on plants whilst they were alive may trigger a pathological response involving the growth of abnormal tissues. Much of the damage is caused by arthropods, particularly insects. Whilst some damage is non-taxon specific, such as simple feeding traces, other damage, such as leaf mines, galls or bark boring, may reveal the co-evolution of host specific taxa and the timing of such interactions. Damaged plants, particularly from the Cretaceous and Tertiary are described and illustrated. The geological history of the evolution of insect-related plant damage is briefly reviewed. Increased variety in the pathological response of plants is seen from the Cretaceous with the evolution of the angiosperms and diversification of numerous insect groups. 相似文献
154.
155.
The Gamtoos is a shallow flood-tidal estuary located on the south coast of South Africa. Even though it has an extensive catchment area, dams limit runoff and mean freshwater inflow is estimated at less than 1 m3 s?1, and the flood tidal deltas constrict and at times even close the mouth. The results presented here derive from an intensive measurement program carried out over a 3-wk period at the end of 1992, immediately after good rains in the Gamtoos catchment region. Freshwater inflow increased to more than 10 m3 s?1, driving the salt wedge downstream and resulting in intense haloclines in the mid-estuary region. The program monitored the return to more average estuarine structures, and even though tidal exchange was restricted, marked differences occurred in stratification at neap and spring tides; tidal exchanges provided the dominant mixing forces. It is found that the shallower upper reaches of the estuary are flushed with relatively small increases in freshwater inflow, though a balance exists with the tidal exchanges through the constricted mouth. The variation in the position of the salt wedge and in the salinity stratification can have substantial implications for biota. 相似文献
156.
The hydrodynamic and sedimentary setting of nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a case study 总被引:4,自引:0,他引:4
The Great Barrier Reef (GBR) shelf contains a range of coral reefs on the highly turbid shallow inner shelf, where interaction occurs with terrigenous sediments. The modern hydrodynamic and sedimentation regimes at Paluma Shoals, a shore‐attached ‘turbid‐zone’ coral reef, and at Phillips Reef, a fringing reef located 20 km offshore, have been studied to document the mechanisms controlling turbidity. At each reef, waves, currents and near‐bed turbidity were measured for a period of ≈1 month. Bed sediments were sampled at 135 sites. On the inner shelf, muddy sands are widespread, with admixed terrigenous and carbonate gravel components close to the reefs and islands, except on their relatively sheltered SW side, where sandy silty clays occur. At Paluma Shoals, the coral assemblage is characteristic of inner‐shelf or sheltered habitats on the GBR shelf (dominated by Galaxea fascicularis, up to >50% coral cover) and is broadly similar to that at Phillips Reef, further offshore and in deeper water. The sediments of the Paluma Shoals reef flats consist of mixed terrigenous and calcareous gravels and sands, with intermixed silts and clays, whereas the reef slope is dominated by gravelly quartz sands. The main turbidity‐generating process is wave‐driven resuspension, and turbidity ranges up to 175 nephelometric turbidity units (NTU). In contrast, at Phillips Reef, turbidity is <15 NTU and varies little. At Paluma Shoals, turbidity of >40 NTU probably occurs for a total of >40 days each year, and relatively little time is spent at intermediate turbidities (15–50 NTU). The extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning (autotrophy and heterotrophy) in response to different levels of turbidity. Sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux (BTF) of sediment to the sea floor, i.e. 10 000 BTF, over three orders of magnitude greater than the Holocene average for Halifax Bay of <3 BTF. As elsewhere along the nearshore zone of the central GBR, dry‐season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments. The location of modern nearshore coral reefs is controlled by the presence of suitable substrates, which in Halifax Bay are Pleistocene and early Holocene coarse‐grained (and relatively stable) alluvial deposits. 相似文献
157.
158.
The deepest part of the Canary Basin, the Madeira Abyssal Plain, receives allochthonous sediments derived from a large drainage basin which, if its subaerial continuation is included, covers an area of 3.36 times 106 km2. An international research effort over the last 10 years has recovered over 160 sediment cores from the plain, and the development of a high-resolution stratigraphy has enabled individual turbidites to be correlated layer by layer. Sedimentation on the Madeira Abyssal Plain during the late Quaternary is dominated by thick turbidite muds separated by thin pelagic intervals. The core density has allowed the mapping of each sedimentary unit throughout the abyssal plain, thus building up a layer by layer picture of sediment accumulation. Over the last 300 kyr, 600 km3 of turbidites compared to 60 km3 of pelagic sediments have been deposited on the plain. Sedimentary structures developed in the coarse basal facies of the larger turbidites are more complex than simple models predict due to surging flows, fluctuating flow velocities and reflection from adjacent high ground. Over the last 300 kyr, there has been a switching of entry points for turbidity currents entering the abyssal plain. From 300 ka to 200 ka, organic-rich turbidites were emplaced predominantly from the south but around 200 ka this source switched off and subsequent organic- and volcanic-rich turbidites, which included units deposited by giant, possibly hyperconcentrated flows, were emplaced from northern or eastern sources. Although restricted to the late Quaternary, the data presented provides a detailed case study of the evolution of an oceanic basin fill. 相似文献
159.
Twenty six samples from seven hand specimens, collected from the station 6 boulder at the Apollo 17 landing site, were studied magnetically. The boulder is a breccia consisting of three lithologic units distinguished by their clast population. The direction of magnetization of samples from unit B which is almost devoid of large clasts cluster fairly well after alternating field demagnetization. Samples from unit C which is characterized by abundant large clasts up to 1 m in size do not contain a uniform direction of magnetization but the distribution is not random. Based on these data we propose that the natural remanent magnetization (NRM) in these breccias is the vector sum of two magnetizations, a pre-impact magnetization and a partial thermoremanence acquired during breccia formation. The relative contribution of the two components is controlled by the thermal history of the ejecta, which in turn is determined by its clast population. Depending on the clast population, the NRM can be a total thermoremanence, a partial thermoremanence plus a pre-impact magnetization, or a pre-impact magnetization. This model of thermal overprinting might be applicable to all lunar breccias of medium and higher metamorphic grade. 相似文献
160.
The TiO2–K2O–P2O5 ternary diagram is proposed as a method of discriminating between oceanic and non-oceanic (continental) basalts. This diagram is effective for non-alkaline “primitive” basalts: fractionated rocks cannot be adequately discriminated. Suitable analyses are those which have total alkalies ≤ 20% in an (Fe2O3 + FeO)–MgO–(Na2O + K2O) diagram. The proposed dividing line separates 93% of 222 ocean-floor and ocean-ridge basalts into the oceanic field and > 80% of continental basalt analyses into the non-oceanic field. Two exceptions are the Tertiary basalts of Greenland and the Deccan Traps which have oceanic affinities. “Continental” suites displaying an oceanic affinity in the TiO2–K2O–P2O5 diagram may be a result of abortive attempts to generate new sea floor. Preliminary results for dike swarms and Archean basalts suggest preponderant oceanic affinities. Alteration and metamorphism of oceanic basalts generally occasion enrichment of K2O relative to TiO2 and P2O5. 相似文献