The radio–optical correlation in steep-spectrum quasars     

Stephen Serjeant  Steve Rawlings  Stephen J. Maddox  Joanne C. Baker  Dave Clements  Mark Lacy  & Per B. Lilje 《Monthly notices of the Royal Astronomical Society》1998,294(3):494-504

Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation dependence (such as relativistic beaming), nor a by-product of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion on to a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio-luminous high-redshift galaxies.  相似文献   

Approaching four decades of forest watershed research at Upper Penticton Creek,British Columbia: A synthesis     

Rita D. Winkler  Diana M. Allen  Tim R. Giles  Brian A. Heise  R. Dan Moore  Todd E. Redding  Dave L. Spittlehouse  Xiaohua Wei 《水文研究》2021,35(5):e14123

Over the past 35 years, the Upper Penticton Creek (UPC) Watershed Experiment has supported forest hydrology research in south-central British Columbia (BC), Canada. This paper provides a synthesis of research results, highlights the challenges facing UPC and identifies new research directions. Clearcutting approximately 50% of two small, snow-dominated (Dfb Koppen classification) watersheds advanced the timing of snowmelt-generated high flows and decreased late-summer low flows, relative to predictions based on pre-treatment regressions. Changes in high flows did not have a significant effect on stream channels due to low stream power, coarse substrate, and limited riparian disturbance. Changes in summer low flows reduced modelled useable fish habitat by 20%–50%. Evaporation averaged 52% of the annual precipitation in the mature forest, was reduced to 30% in a clearcut, and recovered to 40% and 47% in a 10 and 25 year-old stand, respectively. Groundwater recharge to the bedrock was estimated at 19% of annual precipitation, indicating that, even with the large uncertainty associated with this estimate, deep groundwater should not be ignored in the water balance. Suspended sediment, turbidity, and colour increased post-logging; however, chemical surface water quality did not change. Aquatic community structure changed post-logging; and although this affected the processing of organic matter, the effects on habitat quality were considered minimal. The information gained at UPC has supported provincial policies, management guidelines, forest stewardship plans and watershed risk assessments. The undisturbed control watershed, re-growing treatment watersheds and ongoing long-term hydrometric monitoring continue to provide opportunities for future research addressing issues such as the effects of young forests on streamflow and hydrologic recovery, and the influence of climate change on the hydrologic regime.  相似文献   

High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table     

Colin Neal  Brian Reynolds  James W. Kirchner  Phil Rowland  Dave Norris  Darren Sleep  Alan Lawlor  Clive Woods  Sarah Thacker  Hayley Guyatt  Colin Vincent  Kathryn Lehto  Simon Grant  Jeremy Williams  Margaret Neal  Heather Wickham  Sarah Harman  Linda Armstrong 《水文研究》2013,27(17):2531-2539

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Sandy beach ecosystems: key features, sampling issues, management challenges and climate change impacts   总被引：4，自引：0，他引：4  

Thomas A. Schlacher  Dave S. Schoeman  Jenifer Dugan  Mariano Lastra  Alan Jones  Felicita Scapini  & Anton McLachlan 《Marine Ecology》2008,29(S1):70-90

Escalating pressures caused by the combined effects of population growth, demographic shifts, economic development and global climate change pose unprecedented threats to sandy beach ecosystems worldwide. Conservation of beaches as functional ecosystems and protection of their unique biodiversity requires management interventions that not only mitigate threats to physical properties of sandy shores, but also include ecological dimensions. Yet, beach management remains overwhelmingly focused on engineering interventions. Here we summarise the key outcomes of several workshops, held during the 2006 Sandy Beach Ecology Symposium in Vigo, Spain, that addressed issues of climate change, beach management and sampling methodology. Because efficient communication between managers and ecologists is critical, we summarise the salient features of sandy beaches as functional ecosystems in 50 'key statements'; these provide a succinct synopsis of the main structural and functional characteristics of these highly dynamic systems. Key outcomes of the workshops include a set of recommendations on designs and methods for sampling the benthic infaunal communities of beaches, the identification of the main ecological effects caused by direct and indirect human interventions, the predicted consequence of climate change for beach ecosystems, and priority areas for future research.  相似文献   

Modeling IR spectral energy distributions: a?pilot study of?starburst parameters and silicate absorption curves for some GOALS galaxies     

Michael A. Dopita  Lee Armus  Lisa J. Kewley  Jeff A. Rich  Dave Sanders  Phillip N. Appleton  Ben H. P. Chan  Vassilis Charmandaris  Aaron S. Evans  David T. Frayer  Justin H. Howell  Hanae Inami  Joseph A. Mazzarella  Andreea Petric  Sabrina Stierwalt  Jason Surace 《Astrophysics and Space Science》2011,333(1):225-239

This paper describes a pilot study into the spectral energy distribution (SED) fitting and the derivation of physical parameters for 19 galaxies observed as part of the Great Observatories All-sky LIRG Survey (GOALS) survey as observed with the Spitzer Space Telescope. For this we have used the pan-spectral fitting tools developed in a series of papers by Dopita and his co-workers. We show that the standard Lee and Draine ??astronomical silicate?? model cannot provide a good fit to the silicate absorption features as observed in the heavily dust-extinguished (A _V??50 mag.) starbursts. We have derived an empirical fit to the ??starburst silicate?? absorption in these objects. This absorption curve is consistent with the silicate grains being systematically larger in starburst environments than in the local Galactic interstellar medium. We demonstrate the sensitivity of the SED fitting to each of the fitted parameters, and derive these parameters for those galaxies which do not have an embedded AGN. This technique is simple and provides reasonably robust and uniform parameters for the starburst, especially as far as the star formation rate, population of old stars, compactness of the starburst region and total foreground extinction are concerned. However, the chemical abundances and the optical extinction cannot be reliably determined by this analysis, and optical SEDs will also be required to provide a complete characterization of the starburst region and of the surrounding galaxy.  相似文献   

Using field analogue soil column experiments to quantify radon-222 gas migration and transport through soils and bedrock of Halifax,Nova Scotia,Canada     

Kelsey E. O’Brien  Dave Risk  Daniel Rainham  Anne Marie O’Beirne-Ryan 《Environmental Earth Sciences》2014,72(7):2607-2620

Radon gas is a human health hazard; long-term exposure to high radon concentrations through inhalation is the second leading cause of lung cancer. Nova Scotia has been previously identified as a potential high risk region because of the geology. As such, the gas transport through Halifax’s fine grained leucomonzogranite (FGL) unit of the South Mountain Batholith needed to be quantified to further remediation efforts. Using controlled laboratory experiments, four different soil columns were created using the Halifax Regional Municipality’s (HRM) highest producing field tills and bedrock. Permeability, diffusivity, radon-222 gas concentrations, and gas transit time/speed were measured in both dry tills (field moisture) and wet tills (simulated rain event moisture). Columns with HRM till displayed the highest radon concentrations, and were less permeable with additional moisture. Radon diffusivity calculated from CO₂ was 7.52 × 10^?8 m² (dry), and 3.37 × 10^?8 m² (wet); diffusivity calculated from ²²²Rn was 7.30 × 10^?7 m² (dry), and 6.47 × 10^?7 m² (wet). The average FGL transit time in a 60 cm column was 3.57 days (dry), and 3.82 days (wet). Locally this study presents two different methods for diffusivity calculations, for a unit lacking previous diffusivity information. The radon gas concentrations and transport speeds quantified the transport mechanisms within the till. Globally, the correlation between soil moisture, and radon/permeability values was established using these results. The link between diffusivity and permeability was also confirmed using field tills. Implications were made for building foundations, as well as the depth and type of material necessary to reduce radon gas from reaching the surface.  相似文献   

Sleeping restlessly in Japan     

Dave Rothery 《Geology Today》2001,17(4):137-137

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Finding outlier light curves in catalogues of periodic variable stars   总被引：2，自引：0，他引：2  

P. Protopapas  J. M. Giammarco  L. Faccioli  M. F. Struble  R. Dave  C. Alcock 《Monthly notices of the Royal Astronomical Society》2006,369(2):677-696

We present a methodology to discover outliers in catalogues of periodic light curves. We use a cross-correlation as the measure of 'similarity' between two individual light curves, and then classify light curves with lowest average 'similarity' as outliers. We performed the analysis on catalogues of periodic variable stars of known type from the MACHO and OGLE projects. This analysis was carried out in Fourier space and we established that our method correctly identifies light curves that do not belong to those catalogues as outliers. We show how an approximation to this method, carried out in real space, can scale to large data sets that will be available in the near future such as those anticipated from the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) and Large Synoptic Survey Telescope (LSST).  相似文献   

The quest for Type 2 quasars: Chandra observations of luminous obscured quasars in the Sloan Digital Sky Survey     

Cristian Vignali  Dave M. Alexander  Andrea Comastri 《Monthly notices of the Royal Astronomical Society》2006,373(1):321-329

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Simulating zonal scale shifts in the partitioning of surface and subsurface freshwater flow in response to increasing pCO2     

Sascha Fl?gel  Geoffrey Parkin  Dave Pollard  Wolf-Christian Dullo  Thomas Wagner 《Climate Dynamics》2011,37(7-8):1565-1573

Freshwater discharge is one main element of the hydrological cycle that physically and biogeochemically connects the atmosphere, land surface, and ocean and directly responds to changes in pCO₂. Nevertheless, while the effect of near-future global warming on total river runoff has been intensively studied, little attention has been given to longer-term impacts and thresholds of increasing pCO₂ on changes in the partitioning of surface and subsurface flow paths across broad climate zones. These flow paths and their regional responses have a significant role for vegetation, soils, and nutrient leaching and transport. We present climate simulations for modern, near-future (850?ppm), far-future (1880?ppm), and past Late Cretaceous (1880?ppm) pCO₂ levels. The results show large zonal mean differences and the displacement of flows from the surface to the subsurface depending on the respective pCO₂ level. At modern levels the ratio of deeper subsurface to near-surface flows for tropical and high northern latitudes is 1:4.0 and 1:0.5, respectively, reflecting the contrast between permeable tropical soils and the areas of frozen ground in high latitudes. There is a trend toward increased total flow in both climate zones at 850?ppm, modeled to be increases in the total flow of 34 and 51%, respectively, with both zones also showing modest increases in the proportion of subsurface flow. Beyond 850?ppm the simulations show a distinct divergence of hydrological trends between mid- to high northern latitudes and tropical zones. While total wetting reverses in the tropics beyond 850?ppm due to reduced precipitation, with average zonal total runoff decreasing by 46% compared to the 850?ppm simulation, the high northern latitude zone becomes slightly wetter with the average zonal total runoff increasing by a further 3%. The ratio of subsurface to surface flows in the tropics remains at a level similar to the present day, but in the high northern latitude zone the ratio increases significantly to 1:1.6 due to the loss of frozen ground. The results for the high pCO₂ simulations with the same uniform soil and vegetation cover as the Cretaceous are comparable to the results for the Cretaceous simulation, with higher fractions of subsurface flow of 1:5.4 and 1:5.6, respectively for the tropics, and 1:2.2 and 1:1.6, respectively for the high northern latitudes. We suggest that these fundamental similarities between our far future and Late Cretaceous models provide a framework of possible analogous consequences for (far-) future climate change, within which the integrated human impact over the next centuries could be assessed. The results from this modeling study are consistent with climate information from the sedimentary record which highlights the crucial role of terrestrial-marine interactions during past climate change. This study points to profound consequences for soil biogeochemical cycling, with different latitudinal expressions, passing of climate thresholds at elevated pCO₂ levels, and enhanced export of nutrients to the ocean at higher pCO₂.  相似文献