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771.
Marcella Massardi Ronald D. Ekers Tara Murphy Roberto Ricci Elaine M. Sadler Sarah Burke Gianfranco De Zotti Philip G. Edwards Paul J. Hancock Carole A. Jackson Michael J. Kesteven Elizabeth Mahony Christopher J. Phillips Lister Staveley-Smith Ravi Subrahmanyan Mark A. Walker Warwick E. Wilson 《Monthly notices of the Royal Astronomical Society》2008,384(2):775-802
The Australia Telescope 20-GHz (AT20G) Survey is a blind survey of the whole southern sky at 20 GHz (with follow-up observations at 4.8 and 8.6 GHz) carried out with the Australia Telescope Compact Array from 2004 to 2007.
The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic ) radio sources south of δ=−15° with Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz.
In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index α, assuming S ∝να , decreases from α8.6 4.8 = 0.11 between 4.8 and 8.6 GHz to α20 8.6 =−0.16 between 8.6 and 20 GHz), even if the sample is dominated by flat spectra sources (85 per cent of the sample has α20 8.6 > −0.5) . The almost simultaneous spectra in total intensity and polarization allowed us a comparison of the polarized and total intensity spectra: polarized fraction slightly increases with frequency, but the shapes of the spectra have little correlation. Optical identifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13, respectively, for QSO and galaxies. 相似文献
The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic ) radio sources south of δ=−15° with Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz.
In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index α, assuming S ∝ν
772.
The early-type galaxies NGC 1407 and NGC 1400 – II. Star formation and chemical evolutionary history
Max Spolaor Duncan A. Forbes Robert N. Proctor George K. T. Hau Sarah Brough 《Monthly notices of the Royal Astronomical Society》2008,385(2):675-686
We present a possible star formation and chemical evolutionary history for two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study.
Our analysis is based on new high signal-to-noise ratio spatially resolved integrated spectra obtained at the ESO 3.6-m telescope, out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. Using Lick/IDS indices, we estimate luminosity-weighted ages, metallicities and α-element abundance ratios. Colour radial distributions from HST /ACS and Subaru Suprime-Cam multiband wide-field imaging are compared to colours predicted from spectroscopically determined ages and metallicities using single stellar population (SSP) models. The galaxies formed over half of their mass in a single short-lived burst of star formation (≥100 M⊙ yr−1 ) at redshift z ≥ 5. This likely involved an outside–in mechanism with supernova-driven galactic winds, as suggested by the flatness of the α-element radial profiles and the strong negative metallicity gradients. Our results support the predictions of the revised version of the monolithic collapse model for galaxy formation and evolution. We speculate that, since formation, the galaxies have evolved quiescently and that we are witnessing the first infall of NGC 1400 in the group. 相似文献
Our analysis is based on new high signal-to-noise ratio spatially resolved integrated spectra obtained at the ESO 3.6-m telescope, out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. Using Lick/IDS indices, we estimate luminosity-weighted ages, metallicities and α-element abundance ratios. Colour radial distributions from HST /ACS and Subaru Suprime-Cam multiband wide-field imaging are compared to colours predicted from spectroscopically determined ages and metallicities using single stellar population (SSP) models. The galaxies formed over half of their mass in a single short-lived burst of star formation (≥100 M
773.
Sarah E. Zedler Guido Kanschat Robert Korty Ibrahim Hoteit 《Journal of Oceanography》2012,68(2):227-241
We seek to determine if a small number of measurements of upper ocean temperature and currents can be used to make estimates
of the drag coefficient that have a smaller range of uncertainty than previously found. We adopt a numerical approach using
forward models of the ocean’s response to a tropical cyclone, whereby the probability density function of drag coefficient
values as a function of wind speed that results from adding realistic levels of noise to the simulated ocean response variables
is sought. Allowing the drag coefficient two parameters of freedom, namely the values at 35 and at 45 m/s, we found that the
uncertainty in the optimal value is about 20% for levels of instrument noise up to 1 K for a misfit function based on temperature,
or 1.0 m/s for a misfit function based on 15 m velocity components. This is within tolerable limits considering the spread
of measurement-based drag coefficient estimates. The results are robust for several different instrument arrays; the noise
levels do not decrease by much for arrays with more than 40 sensors when the sensor positions are random. Our results suggest
that for an ideal case, having a small number of sensors (20–40) in a data assimilation problem would provide sufficient accuracy
in the estimated drag coefficient. 相似文献
774.
Cetacean mass stranding events associated with naval mid-frequency sonar use have raised considerable conservation concerns. These strandings have mostly involved beaked whales, with common pathologies, including "bubble lesions" similar to decompression sickness symptoms and acoustic traumas. However, other cetacean species have also stranded coincident with naval exercises. Possible mechanisms for the strandings include a behavioral response that causes deep divers to alter their diving behavior, which then results in decompression sickness-like impacts. Current mitigation measures during military exercises are focused on preventing auditory damage (hearing loss), but there are significant flaws with this approach. Behavioral responses, which occur at lower sound levels than those that cause hearing loss, may be more critical. Thus, mitigation measures should be revised. A growing number of international bodies recognize this issue and have urged increasing scrutiny of sound-producing activities, but many national jurisdictions have resisted calls for increased protection. 相似文献
775.
Influence of rural land use on streamwater nutrients and their ecological significance 总被引:1,自引:0,他引:1
Helen P. Jarvie Paul J.A. Withers Robin Hodgkinson Adam Bates Margaret Neal Heather D. Wickham Sarah A. Harman Linda Armstrong 《Journal of Hydrology》2008,350(3-4):166-186
Concentrations and loads of N and P fractions were examined for lowland rivers, the Wye and Avon, draining a range of representative agricultural land-use types in two major UK river basins. Data collected over a 2-year period demonstrated important diffuse agricultural source contributions to N and P loads in these rivers. Ground water provided a major source of total dissolved nitrogen (TDN) loads, whereas near-surface sources provided a major contribution to total phosphorus (TP) loads. In terms of aquatic ecology, concentrations of nutrients, at times of eutrophication risk (spring and summer low flows) were of key environmental and management significance. Agricultural diffuse sources provided the major source of long-term P loads across the two basins. However, the results demonstrated the dominance of point-source contributions to TP and SRP concentrations at times of ecological risk. Point sources typically ‘tip the balance’ of dissolved inorganic P (soluble reactive P, SRP) above the 100 μg l−1 guideline value indicative of eutrophication risk. The significance of point sources for TP and SRP concentrations was shown by (a) the strong correlations between TP, SRP and B concentrations, using B as a tracer of sewage effluent, (b) the dominant contribution of SRP to TP concentrations and (c) the predominant pattern of dilution of SRP and B with flow. The clean Chalk streams draining low intensity grassland in areas of the Avon with sparse human settlement were oligotrophic and P limited with low SRP concentrations under spring and summer baseflows attributable to groundwater sources. The data provide important insights into the ecological functioning of different lowland stream systems. There was evidence of greater SRP losses and N-limitation in a stream which drains a pond system, demonstrating the importance of longer water residence times for biological nutrient uptake. 相似文献
776.
Sarah E. M. Gain Yoann Grau Hadrien Henry Elena Belousova Ivars Dainis William L. Griffin Suzanne Y. O'Reilly 《Geostandards and Geoanalytical Research》2019,43(3):339-354
Zircon megacrysts from the Mud Tank carbonatite, Australia, are being used in many laboratories as a reference material for LA‐ICP‐MS U‐Pb dating and trace element measurement, and LA‐MC‐ICP‐MS determination of Hf isotopes. We summarise a database of > 10000 analyses of Mud Tank zircon (MTZ), collected from 2000 to 2018 during its use as a secondary reference material for simultaneous U‐Pb and trace element analysis, and for Hf‐isotope analysis. Trace element mass fractions are highest in dark red‐brown stones and lowest in colourless and gem‐quality ones. Individual unzoned grains can be chemically homogeneous, while significant variations in trace element mass fraction are associated with oscillatory zoning. Chondrite‐normalised trace element patterns are essentially parallel over large mass fraction ranges. A Concordia age of 731.0 ± 0.2 Ma (2s, n = 2272) is taken as the age of crystallisation. Some grains show lower concordant to mildly discordant ages, probably reflecting minor Pb loss associated with cooling and the Alice Springs Orogeny (450–300 Ma). Our weighted mean 176Hf/177Hf is 0.282523 ± 10 (2s, n = 9350); the uncertainties on this ratio reflect some heterogeneity, mainly between grains. A few analyses suggest that colourless grains have generally lower 176Hf/177Hf. MTZ is a useful secondary reference material for U‐Pb and Hf‐isotope analysis, but individual grains need to be carefully selected using CL imaging and tested for homogeneity, and ideally should be standardised by solution analysis. 相似文献
777.
778.
Sarah Marie Hall 《Area》2009,41(3):263-272
This paper addresses the difficulties and dilemmas that may occur when friendships are formed with participants during an ethnographic research project. The ongoing, reciprocal relationships developed with participants are considered essential in the data collection of ethnography, as an avenue through which research can be carried out. However, while friendships in the field may open new doors to research, they can also create new (ethical) challenges. This paper revisits these issues, alongside research ethics guidelines, using three different scenarios: the negotiation of methods of contact, the maintenance of contact with participants and the sharing of research diaries with participants. From these discussions, two issues arise that may have implications for future ethnographic research: the obstacle of social networking websites and the negotiation of appropriate research ethics when participants become our friends. 相似文献
779.
Since the end of the commercial fur seal hunt in 1984, the economy of the Pribilof Islands, Alaska, has lacked a stable, lasting basis. As a contribution to the effort to understand and promote the effective management of the Pribilof Islands as a social–ecological system, we examined current and recent conditions on the islands to assess local perceptions of, and prospects for, economic, social and environmental well-being. We found few correlations between environmental conditions and socio-economic indicators. The lack of apparent connection between population levels and economic or environmental stimuli is likely attributable to one or more of several factors: (a) modest economic dependence on the environment; (b) predominance of other economic inputs to the economies of the islands; (c) islanders basing residence choices largely on non-economic factors; and (d) the islanders' tolerance for economic fluctuations and uncertainty. These results suggest economic analysis alone is insufficient to explain the dynamics of this social–ecological system, contrary to many other case studies and an expectation of tight coupling and clear connections between society and ecology in the Pribilofs. 相似文献
780.
E.C.M. Parsons Sarah J. Dolman Michael Jasny Mark P. Simmonds 《Marine pollution bulletin》2009,58(5):643-651
The United Kingdom’s statutory conservation agency, the Joint Nature Conservation Committee (JNCC), developed guidelines in 1995 to minimise acoustic disturbance of marine mammals by oil and gas industry seismic surveys. These were the first national guidelines to be developed and have subsequently become the standard, or basis, of international mitigation measures for noise pollution during seismic surveys. However, relatively few aspects of these measures have a firm scientific basis or proven efficacy. Existing guidelines do not offer adequate protection to marine mammals, given the complex propagation of airgun pulses; the difficulty of monitoring in particular the smaller, cryptic, and/or deep-diving species, such as beaked whales and porpoises; limitations in monitoring requirements; lack of baseline data; and other biological and acoustical complications or unknowns. Current guidelines offer a ‘common sense’ approach to noise mitigation, but in light of recent research and ongoing concerns, they should be updated, with broader measures needed to ensure adequate species protection and to address data gaps. 相似文献