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71.
72.
A. Smith I. A. Crawford R. A. Gowen A. J. Ball S. J. Barber P. Church A. J. Coates Y. Gao A. D. Griffiths A. Hagermann K. H. Joy A. Phipps W. T. Pike R. Scott S. Sheridan M. Sweeting D. Talboys V. Tong N. Wells J. Biele J. Chela-Flores B. Dabrowski J. Flannagan M. Grande J. Grygorczuk G. Kargl O. B. Khavroshkin G. Klingelhoefer M. Knapmeyer W. Marczewski S. McKenna-Lawlor L. Richter D. A. Rothery K. Seweryn S. Ulamec R. Wawrzaszek M. Wieczorek I. P. Wright M. Sims 《Experimental Astronomy》2009,23(3):711-740
While the surface missions to the Moon of the 1970s achieved a great deal, scientifically much was also left unresolved. The
recent plethora of lunar missions (flown or proposed) reflects a resurgence in interest in the Moon, not only in its own right,
but also as a record of the early solar system including the formation of the Earth. Results from recent orbiter missions
have shown evidence of ice or at least hydrogen within shadowed craters at the lunar poles. 相似文献
73.
Edward L. Chapin Alexandra Pope † Douglas Scott Itziar Aretxaga Jason E. Austermann Ranga-Ram Chary Kristen Coppin Mark Halpern David H. Hughes James D. Lowenthal Glenn E. Morrison Thushara A. Perera Kimberly S. Scott Grant W. Wilson Min S. Yun 《Monthly notices of the Royal Astronomical Society》2009,398(4):1793-1808
We present results from a multiwavelength study of 29 sources (false detection probabilities <5 per cent) from a survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field at 1.1 mm using the Astronomical Thermal Emission Camera (AzTEC). Comparing with existing 850 μm Submillimetre Common-User Bolometer Array (SCUBA) studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1σ depth of ∼1 mJy. Searching deep 1.4 GHz Very Large Array (VLA) and Spitzer 3–24 μm catalogues, we identify robust counterparts for 21 1.1 mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of z = 2.7 , somewhat higher than z = 2.0 for 850 μm selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift z = 1.1460 . We measure the 850 μm to 1.1 mm colour of our sources and do not find evidence for '850 μm dropouts', which can be explained by the low signal-to-noise ratio of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T , and dust emissivity indices β for the sample, concluding that existing estimates T ∼ 30 K and β∼ 1.75 are consistent with these new data. 相似文献
74.
Scott F. Korom Michael J. McFarland Ronald C. Sims 《Ground Water Monitoring & Remediation》1996,16(1):100-105
A preliminary field performance evaluation of in situ bioremediation of a contaminated aquifer at the Libby, Montana, Superfund site, a former wood preserving site, was conducted for the Bioremediation Field Initiative sponsored by the U.S. Environmental Protection Agency (U.S. EPA). The current approach for site remediation involves injecting oxygen and nutrients into the aquifer to stimulate microbial degradation of target compounds that include polycyclic aromatic hydrocarbons and pentachlorophenol. The preliminary field evaluation determined that, in addition to the oxygen demand associated with the microbial oxidation of the organic contamination, uncontaminated aquifer sediments at the site are naturally reduced and also exert a significant oxygen demand. This conclusion is supported by three types of information: (1) analyses of ground water samples; (2) results from a field-scale tracer test; and (3) results of laboratory evaluations of oxygen use by reduced aquifer sediment samples. An estimate of the cost of supplying hydrogen peroxide to satisfy the oxygen demand of the uncontaminated reduced sediments is provided to demonstrate that the additional cost of oxidizing the reduced sediments could be significant. The presence of naturally occurring reduced sediments at a contamination site should be considered in the design of subsurface oxidant delivery systems. 相似文献
75.
Summary The atmospheric balance of the kinetic energy of the zonally averaged zonal motion is investigated from five years of daily data at 800 stations for the northern hemisphere. The basic equation for such energy is used, together with the simplifying assumption that the frictional destruction is due in the main to stresses acting across horizontal surfaces, being thus presumably related to the vertical shear of the mean zonal wind, although no further details are needed in the analysis. The five-year averages of various terms as well as their seasonal means appear to give reasonable results.The research reported in this paper was sponsored by the U.S. National Science Foundation under Grant No. GA-1310X. 相似文献
76.
77.
S. J. Mazzullo Chellie S. Teal William D. Bischoff Kimberly Dimmick-Wells Brian W. Wilhite 《Sedimentology》2003,50(4):743-770
Abstract Cangrejo and Bulkhead Shoals are areally extensive, Holocene biodetrital mud‐mounds in northern Belize. They encompass areas of 20 km2 and 35 km2 in distal and proximal positions, respectively, on a wide and shallow‐water, microtidal carbonate shelf where storms are the major process affecting sediment dynamics. Sediments at each mound are primarily biodetrital and comprise part of a eustatically forced, dominantly subtidal cycle with a recognizable deepening‐upward transgressive systems tract, condensed section and shallowing‐upward highstand systems tract. Antecedent topographic relief on Pleistocene limestone bedrock also provided marine accommodation space for deposition of sediments that are a maximum of 7·6 m thick at Cangrejo and 4·5 m thick at Bulkhead. Despite differences in energy levels and location, facies and internal sedimentological architectures of the mud‐mounds are similar. On top of Pleistocene limestone or buried soil developed on it are mangrove peat and overlying to laterally correlative shelly gravels. Deposition of these basal transgressive, premound facies tracked the rapid rate of sea‐level rise from about 6400–6500 years BP to 4500 years BP, and the thin basal sedimentation unit of the overlying mound‐core appears to be a condensed section. Following this, the thick and complex facies mosaic comprising mound‐cores represents highstand systems tract sediments deposited in the last ≈ 4500 years during slow and decelerating sea‐level rise. Within these sections, there is an early phase of progradationally offlapping catch‐up deposition and a later (and current) phase of aggradational keep‐up deposition. The mound‐cores comprise stacked storm‐deposited autogenic sedimentation units, the upper bounding surfaces of which are mostly eroded former sediment–water interfaces below which depositional textures have largely been overprinted by biogenic processes associated with Thalassia‐colonized surfaces. Vertical stacking of these units imparts a quasi‐cyclic architecture to the section that superficially mimics metre‐scale parasequences in ancient rocks. The locations of the mud‐mounds and the tidal channels transecting them have apparently been stable over the last 50 years. Characteristics that might distinguish these mud‐mounds and those mudbanks deposited in more restricted settings such as Florida Bay are their broad areal extent, high proportion of sand‐size sediment fractions and relatively abundant biotic particles derived from adjoining open shelf areas. 相似文献
78.
79.
Sensitivity of Mesoscale Surface Dynamics to Surface Soil and Vegetation Contrasts over the Carolina Sandhills 总被引:1,自引:0,他引:1
A region of contrasting soils exists over the Carolinas region of the southeastern United States. Previous research has shown
an increase in mesoscale summertime precipitation over this region. Numerical simulations are analyzed to investigate the
relationships between mesoscale surface dynamics and the transition from clay to sandy soils over this region. Numerical modeling
experiments using four different soil and vegetation patterns suggest that the presence of the clay-to-sand transition zone
produces a surface heat flux gradient and enhanced convergence. The soil contrasts appear to dominate over vegetation contrasts
in affecting local surface heating and convergence in the model atmosphere. 相似文献
80.
Candace A. Oviatt Kimberly J. W. Hyde Aimee A. Keller Jefferson T. Turner 《Estuaries and Coasts》2007,30(1):35-46
On September 6, 2000, the sewage outfall at the mouth of Boston Harbor was relocated 15 km offshore to alleviate pollution
in Boston Harbor. The expected responses for nutrients and water column productivity parameters were for values to decrease
at Boston Harbor, to increase at the outfall location, and to remain unchanged at the boundary of the near field region within
5 km of the outfall. Average values ofr water column measurements from 1992 to 2004 indicated these general responses with
some exceptions. At the Harbor, nutrients decreased and chlorophyll increased but14C primary productivity remained statistically unchanged. At the new outfall location and at the boundary of the near field,
nutrients increased and chlorophyll increased but primary productivity remained unchanged. Physical factors affecting primary
production, such as pring water temperature, stratification, and wind, had more affects on productivity patters than nutrients
from outfall relocation in the near field. A decrease in summer zooplankton after outfall relocation appeared to be due to
a region-wide rather than outfall effluents. 相似文献