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131.
J. Berg J. Mann A. Bechmann M. S. Courtney H. E. Jørgensen 《Boundary-Layer Meteorology》2011,141(2):219-243
132.
Kyle R. Murphy Ian R. Mann I. Jonathan Rae David K. Milling 《Journal of Atmospheric and Solar》2011,73(11-12):1500-1510
Utilising fifteen (1990–2005) years of ground-based magnetometer data from four magnetometer stations, we characterise the statistical dependence of the Pc5 ULF wave power spectra on variations in F10.7 solar radio flux and on solar cycle phase. We show that the median Pc5 ULF wave power spectra can be characterised as a power-law with a localised Gaussian centred at a specific frequency superimposed on the power-law spectrum. Further, we demonstrate that the location of the Gaussian in frequency systematically varies with both solar cycle phase and F10.7 and is more pronounced during high-speed solar wind intervals. We postulate that the localised power spectrum enhancement (or Gaussian) is a manifestation of the local eigenfrequency of field line resonances in the Earth's magnetosphere and that the variation in the location of the Gaussian occurs as a result of increased ionospheric outflow during periods of enhanced F10.7 and active solar activity. 相似文献
133.
The Cariaco basin, located ∼40 km off the central part of the coast of Venezuela, is the largest (∼4000 km2) and bathymetrically deepest (1400 m BSL) Neogene fault-bounded basin within the right-lateral strike-slip plate boundary zone that separates the Caribbean and South American plates. Using subsurface geophysical data, we test two previously proposed tectonic models for the age, distribution and nature of east-west-striking, strike-slip faults, and basin-forming mechanism for the two main depocenters of the Cariaco basin. The earliest interpretation for the opening of the twin Cariaco depocenters by Schubert (1982) proposes that both depocenters formed synchronously by extension along transverse (north-south) normal faults at a ∼30-km-wide rhomboidally-shaped pull-apart basin between the right-lateral, east-west-striking, and parallel San Sebastian and El Pilar fault zones. A later model by Ben-Avraham and Zoback (1992) proposes that both depocenters formed synchronously by a process of ”transform-normal parallel extension”, or rifting in a north-south direction orthogonal to the east-west-striking and parallel strike-slip faults.We use more than 4000 km of 2D single- and multi-channel seismic data tied to 11 wells to map 5 tectono-stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both Cariaco depocenters evolved from Paleogene to the present. Comparison of fault and isopach maps for dated horizons from Paleogene to late Neogene in age show three main phases in basin development: 1) from middle Miocene to Pliocene, the West Cariaco basin formed as a rhomboidally-shaped pull-apart at a 30-km-wide stepover between the northern branch of the San Sebastian fault and the El Pilar fault zone; 2) during the early Pliocene, a new strike-slip fault transected the West Cariaco basin (southern branch of the San Sebastian fault) and caused extension to cease; and 3) during the early Pliocene to recent, a “lazy-Z” shaped pull-apart formed along the curving connection between the southern branch of the San Sebastian and El Pilar fault zones. 相似文献
134.
Robert G. Mann Seb Oliver Ruth Carballo Alberto Franceschini Michael Rowan-Robinson Alan F. Heavens Maria Kontizas David Elbaz Anastasios Dapergolas Evanghelos Kontizas Gian Luigi Granato Laura Silva Dimitra Rigopoulou J. Ignacio Gonzalez-Serrano Aprajita Verma Steve Serjeant reas Efstathiou Paul P. van der Werf 《Monthly notices of the Royal Astronomical Society》2002,332(3):549-574
135.
In this contribution we review the properties of Brightest Cluster Galaxies (BCGs) and discuss the impact that X-ray cluster
selection is having on their use as cosmological probes. BCGs form a unique galaxy population. They are located near the gravitational
centre of galaxy clusters and are the most massive galaxies in the universe, being some 10 times more luminous than L* systems.
Historically, BCGs have been credited with small intrinsic dispersion in their absolute magnitudes (Δ≃0.2–0.3 mag) and used
as standard candles to constrain the cosmological parameters. Although indirect signs of mass accretion out to z≃1 have been observed, uncovering their full evolutionary picture has remained an elusive goal. Studies of BCGs based on serendipitiously
discovered X-ray cluster samples, particularly from ROSAT, provide large numbers of unbiased clusters at z≤1. Furthermore X-ray emission guarantees the presence of a large gravitationally bound potential well and the X-ray information
can be used to locate the centroids of clusters, aiding the identification of the BCG. We show that this has important consequences
for studies of distance determination and large-scale streaming flows based on the optical properties of BCGs. Recent results
based on X-ray selected clusters show large differences in near-IR BCG properties with their cluster environment; such that
those in clusters with L
x≥1.9×1044erg s-1 are brighter and more uniform than those in their low-L
x counterparts. The BCGs in highL
x systems show no evidence of having undergone mass growth, whereas those in low L
x systems show a widerrange of evolution, with evidence that some have grown by a factor of 4 ormore since z≃1. These results are a direct indication of howa single homogeneous population of galaxies evolves and are a challenge to
simple semi-analytical hierarchical models. If future observations at high redshift are to seriously challenge theory then
better predictions of the evolutionary process are required.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
136.
137.
M. J.Fox A.Efstathiou M.Rowan-Robinson J. S.Dunlop S.Scott S.Serjeant R. G.Mann S.Oliver R. J.Ivison A.Blain O.Almaini D.Hughes C. J.Willott M.Longair A.Lawrence J. A.Peacock 《Monthly notices of the Royal Astronomical Society》2002,331(4):839-852
We present the results of a multiwavelength study of the 19 most significant submillimetre (submm) sources detected in the SCUBA 8-mJy survey. As described in Scott et al. , this survey covers ≃260 arcmin2 using the submillimetre camera SCUBA, to a limiting source detection limit S 850 μm ≃8 mJy . One advantage of this relatively bright flux-density limit is that accurate astrometric positions are potentially achievable for every source using existing radio and/or millimetre-wave interferometers. However, an associated advantage is that spectral energy distribution (SED) based redshift constraints should be more powerful than in fainter submm surveys. Here we therefore exploit the parallel SCUBA 450-μm data, in combination with existing radio and Infrared Space Observatory ( ISO ) data at longer and shorter wavelengths to set constraints on the redshift of each source. We also analyse new and existing optical and near-infrared imaging of our SCUBA survey fields to select potential identifications consistent with these constraints. Our derived SED-based redshift constraints, and the lack of statistically significant associations with even moderately bright galaxies allow us to conclude that all 19 sources lie at z >1 , and at least half of them apparently lie at z >2 . 相似文献
138.
The problem of electromagnetic radiation from electric and magnetic line sources interacting with a moving uniaxially anisotropic dielectric or plasma half-space is treated. The anisotropy of the plasma is due to an infinitely strong magnetizing field impressedparallel to the motion of plasma. The line source is oriented normal to the direction of medium motion. TheE and theH modes are excited independently in the medium by the magnetic and the electric line sources, respectively. Invoking the saddle-point method of integration, the far-zone radiation field and the radiation pattern are obtained for both line sources. It is found that the radiation from an electric line source is not affected by the anisotropy of the moving medium and that a magnetic line source invacuum has finite components of radiation in directions which are parallel and antiparallel to the direction of motion, for the case of a uniaxial plasma in contrast to the results for a uniaxial dielectric. Numerical results for the far-zone radiation pattern, referring to a magnetic line source, are presented for several values of parameters characterizing the non-dimensional velocity, the anisotropy of the medium, the electron-plasma density and the location of the line source. 相似文献
139.
140.
Ashley R. Smyth Anna E. Murphy Iris C. Anderson Bongkeun Song 《Estuaries and Coasts》2018,41(4):1147-1163
In coastal ecosystems, suspension-feeding bivalves can remove nitrogen though uptake and assimilation or enhanced denitrification. Bivalves may also retain nitrogen through increased mineralization and dissimilatory nitrate reduction to ammonium (DNRA). This study investigated the effects of oyster reefs and clam aquaculture on denitrification, DNRA, and nutrient fluxes (NO x , NH4 +, O2). Core incubations were conducted seasonally on sediments adjacent to restored oyster reefs (Crassostrea virginica), clam aquaculture beds (Mercenaria mercenaria) which contained live clams, and bare sediments from Smith Island Bay, Virginia, USA. Denitrification was significantly higher at oyster reef sediments and clam aquaculture site than bare sediment in the summer; however, DNRA was not enhanced. The clam aquaculture site had the highest ammonium production due to clam excretion. While oyster reef and bare sediments exhibited seasonal differences in rate processes, there was no effect of season on denitrification, or dissimilatory nitrate reduction to ammonium (DNRA) or ammonium flux at the clam aquaculture site. This suggests that farm management practices or bivalve metabolism and excretion may override seasonal differences. When water column nitrate concentration was elevated, denitrification increased in clam aquaculture site and oyster reef sediments but not in bare sediment; DNRA was only stimulated at the clam aquaculture site. This, along with a significant and positive relationship between denitrification and sediment organic matter, suggests that labile carbon limited nitrate reduction at the bare sediment site. Bivalve systems can serve as either net sinks or sources of nitrogen to coastal ecosystems, depending mainly on the type of bivalve, location, and management practices. 相似文献