Fitting sinusoids to observations of rotating spotted stars     

Chris Koen 《Monthly notices of the Royal Astronomical Society》2007,376(1):233-247

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Large area forest inventory using Landsat ETM+: A geostatistical approach     

Qingmin Meng  Chris Cieszewski  Marguerite Madden 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):27-36

Large area forest inventory is important for understanding and managing forest resources and ecosystems. Remote sensing, the Global Positioning System (GPS), and geographic information systems (GIS) provide new opportunities for forest inventory. This paper develops a new systematic geostatistical approach for predicting forest parameters, using integrated Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images, GPS, and GIS. Forest parameters, such as basal area, height, health conditions, biomass, or carbon, can be incorporated as a response variable, and the geostatistical approach can be used to predict parameter values for uninventoried points. Using basal area as the response and Landsat ETM+ images of pine stands in Georgia as auxiliary data, this approach includes univariate kriging (ordinary kriging and universal kriging) and multivariable kriging (co-kriging and regression kriging). The combination of bands 4, 3, and 2, as well as the combination of bands 5, 4, and 3, normalized difference vegetation index (NDVI), and principal components (PCs) were used in this study with co-kriging and regression kriging. Validation based on 200 randomly sampling points withheld field inventory was computed to evaluate the kriging performance and demonstrated that band combination 543 performed better than band combination 432, NDVI, and PCs. Regression kriging resulted in the smallest errors and the highest R-squared indicating the best geostatistical method for spatial predictions of pine basal area.  相似文献   

Major changes in ice stream dynamics during deglaciation of the north-western margin of the Laurentide Ice Sheet     

Chris R. Stokes  Chris D. Clark  Robert Storrar 《Quaternary Science Reviews》2009,28(7-8):721-738

Victoria Island lies at the north-western limit of the former North American (Laurentide) Ice Sheet in the Canadian Arctic Archipelago and displays numerous cross-cutting glacial lineations. Previous work suggests that several ice streams operated in this region during the last (Wisconsinan) glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the Arctic Ocean. This paper produces the first detailed synthesis of their behaviour from the Last Glacial Maximum through to deglaciation (～21–9.5 cal ka BP) based on new mapping and a previously published radiocarbon-constrained ice sheet margin chronology. Over 70 discrete ice flow events (flow-sets) are ‘fitted’ to the ice margin configuration to allow identification of several ice streams ranging in size from large and long-lived (thousands of years) to much smaller and short-lived (hundreds of years). The reconstruction depicts major ice streams in M'Clure Strait and Amundsen Gulf which underwent relatively rapid retreat from the continental shelf edge at some time between ～15.2 and 14.1 cal ka BP: a period which encompasses climatic warming and rapid sea level rise (meltwater pulse-1a). Following this, overall retreat was slower and the ice streams exhibited asynchronous behaviour. The Amundsen Gulf Ice Stream continued to operate during ice margin retreat, whereas the M'Clure Strait Ice Stream ceased operating and was replaced by an ice divide within ～1000 years. This ice divide was subsequently obliterated by another short-lived phase of ice streaming in M'Clintock Channel ～13 cal ka BP. The timing of this large ice discharge event coincides with the onset of the Younger Dryas. Subsequently, a minor ice divide developed once again in M'Clintock Channel, before final deglaciation of the island shortly after 9.5 cal ka BP. It is concluded that large ice streams at the NW margin of the Laurentide Ice Sheet, equivalent in size to the Hudson Strait Ice Stream, underwent major changes during deglaciation, resulting in punctuated delivery of icebergs into the Arctic Ocean. Published radiocarbon dates constrain this punctuated delivery, as far as is possible within the limits imposed by their precision, and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores.  相似文献   

What is the origin of the soft excess in active galactic nuclei?   总被引：1，自引：0，他引：1  

Ma&#;gorzata A. Sobolewska  Chris Done 《Monthly notices of the Royal Astronomical Society》2007,374(1):150-158

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The environments and clustering properties of 2dF Galaxy Redshift Survey selected starburst galaxies     

Matt S. Owers  Chris Blake  Warrick J. Couch  Michael B. Pracy  Kenji Bekki 《Monthly notices of the Royal Astronomical Society》2007,381(2):494-510

We investigate the environments and clustering properties of starburst galaxies selected from the 2dF Galaxy Redshift Survey (2dFGRS) in order to determine which, if any, environmental factors play a role in triggering a starburst. We quantify the local environments, clustering properties and luminosity functions of our starburst galaxies and compare to random control samples. The starburst galaxies are also classified morphologically in terms of their broad Hubble type and evidence of tidal merger/interaction signatures. We find the starburst galaxies to be much less clustered on large (5–15 Mpc) scales compared to the overall 2dFGRS galaxy population. In terms of their environments, we find just over half of the starburst galaxies to reside in low to intermediate luminosity groups, and a further ∼30 per cent residing in the outskirts and infall regions of rich clusters. Their luminosity functions also differ significantly from that of the overall 2dFGRS galaxy population, with the sense of the difference being critically dependent on the way their star formation rates are measured. In terms of pin-pointing what might trigger the starburst, it would appear that factors relating to their local environment are most germane. Specifically, we find clear evidence that the presence of a near neighbour of comparable luminosity/mass within 20 kpc is likely to be important in triggering a starburst. We also find that a significant fraction (20–30 per cent) of the galaxies in our starburst samples have morphologies indicative of either an ongoing or a recent tidal interaction and/or merger. These findings notwithstanding, there remain a significant portion of starburst galaxies where such local environmental influences are not in any obvious way playing a triggering role, leading us to conclude that starbursts can also be internally driven.  相似文献   

Altering intertidal sediment topography: effects on biodiversity and ecosystem functioning     

Diane Jones  & Chris L. J. Frid 《Marine Ecology》2009,30(S1):83-96

Sedimentary marine systems are often highly productive and perform important nutrient regeneration functions as they efficiently decompose organic material. In recent years the role of habitat effects and of species composition in ecosystem functioning has become of interest. Estuarine environments are frequently subject to considerable anthropogenic pressures whilst supporting a variety of habitats ranging from well sorted soft muds through biogenically stable sediments to highly mobile coarse sands. There is therefore considerable spatial complexity in habitat type and faunal composition. This study set out to observe the effects of altering the topographical habitat features of an estuarine mudflat on a range of porewater nutrient concentrations (NH₄⁺, NO₃⁻, NO₂⁻, PO₄³⁻ and SiO) collected from four depths (3, 5, 9, and 12 cm) and on faunal composition. Two treatments (Shelled Nets and Net Controls) were used to alter the topography from simple mud to a mussel shell crumble and were compared to un-manipulated Control areas. Sediment granulometry and organic matter content analyses alongside biological traits analysis of the fauna were also conducted.
Differences were observed in porewater nutrient concentrations between the Control and both netted treatments at 5 cm depth only; the species diversity and abundance were also different in the netted treatments compared to the Controls, although no difference between the two manipulated treatments were observed. The changes in faunal composition were attributed solely to the altered topography and the observed nutrient changes were attributed to the faunal alteration rather than the topographical manipulation.  相似文献   

Second-order wave maker theory using force-feedback control. Part I: A new theory for regular wave generation     

Johannes Spinneken  Chris Swan 《Ocean Engineering》2009,36(8):539-548

Second-order wave maker theory has long been established; the most extensive and detailed approach given by Schäffer [1996. Second-order wave maker theory for irregular waves. Ocean Engineering 23, 47–88]. However, all existing theories assume the wave paddle is driven by a position-feedback motion controller. Early research in the wave power field led to the design of a force-controlled absorbing wave machine [Salter, S., 1982. Absorbing wave-makers and wide tanks. In: Directional Wave Spectra Applications, pp. 185–200]. In addition to operating as an excellent absorber, this machine seemed to introduce very little spurious harmonic content when driven with a first-order command signal. The present paper provides a mathematical model for the operation of wave makers using force-feedback control and seeks to explain this apparent advantage. The model is developed to second-order so that a command signal compensating for the remaining spurious wave is also provided. Due to the complexity of the problem, the model has been limited to flap-type wave machines and the generation of regular waves. A variety of numerical tests in force-control mode have been conducted, indicating that the spurious wave content is greatly reduced when compared to the position-control mode. A separate experimental study validating the theory is presented in a part II paper by the same authors.  相似文献   

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth,retreat and dynamics     

Sarah L. Greenwood  Chris D. Clark 《Quaternary Science Reviews》2009,28(27-28):3101-3123

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel – Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.  相似文献   

The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey     

Russell Cannon  Michael Drinkwater  Alastair Edge  Daniel Eisenstein  Robert Nichol  Phillip Outram  Kevin Pimbblet  Roberto De Propris  Isaac Roseboom  David Wake  Paul Allen  Joss Bland-Hawthorn  Terry Bridges  Daniel Carson  Kuenley Chiu  Matthew Colless  Warrick Couch  Scott Croom  Simon Driver  Stephen Fine  Paul Hewett  Jon Loveday  Nicholas Ross  Elaine M. Sadler  Tom Shanks  Robert Sharp  J. Allyn Smith  Chris Stoughton  Peter Weilbacher  Robert J. Brunner  Avery Meiksin  Donald P. Schneider 《Monthly notices of the Royal Astronomical Society》2006,372(1):425-442

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Genetic structure of the tall sea pen Funiculina quadrangularis in NW Scottish sea lochs          下载免费PDF全文

Erin P. Wright  Kirsty Kemp  Alex D. Rogers  Chris Yesson 《Marine Ecology》2015,36(3):659-667

The tall sea pen Funiculina quadrangularis has a patchy distribution around the UK, being found in sheltered waters below 20 m depth on the northwest coast of Scotland and Ireland. The limited distribution and sensitivity to bottom fishing activities make F. quadrangularis vulnerable to reduction in population numbers that may lead to genetic isolation and reduced diversity. Because of this vulnerability and low resilience to physical disturbance, the tall sea pen is recognised as a Species of Principle Importance under the Natural Environment and Rural Communities Act, 2006, UK. ( http://www.legislation.gov.uk/ukpga/2006/16/contents ) and is also on the Biodiversity Action Plan list of Priority Species for the UK. In the Mediterranean it is recognised as a sensitive and essential fish habitat because it forms habitat for several commercially important crustaceans. The aim of this study was to understand the current state of the genetic structure and gene flow of F. quadrangularis in areas of NW Scotland. We developed 10 microsatellite markers and used them to genotype 176 samples from four populations. Overall, our results suggest that there is high genetic diversity and high gene flow between colonies of F. quadrangularis in and among locations in Loch Linnhe and Loch Duich. As a result of the high rates of gene flow, genetic differentiation between sites was low. This may provide resilience to human impacts if distant populations have a high connectivity. However, care must be taken, as small but significant isolation by distance was found between the most geographically distant sites and only a small part of the species range was examined in this study. The genetic tools developed here will provide a foundation for wider studies of this vulnerable species.  相似文献