Radially truncated galactic discs     

Richard de Grijs  Michiel Kregel  Karen H. Wesson † 《Monthly notices of the Royal Astronomical Society》2001,324(4):1074-1086

We present the first results of a systematic analysis of radially truncated exponential discs for four galaxies of a complete sample of disc-dominated edge-on spiral galaxies.
The discs of our sample galaxies are truncated at similar radii on either side of their centres. With the possible exception of the disc of ESO 416-G25, it appears that the truncations in our sample galaxies are closely symmetric, in terms of both their sharpness and the truncation length. However, the truncations occur over a larger region and not as abruptly as found in previous studies.
We show that the truncated luminosity distributions of our sample galaxies, if also present in the mass distributions, comfortably meet the requirements for longevity. The formation and maintenance of disc truncations are probably closely related to stability requirements for galactic discs.  相似文献   

Vertical zonation and distributions of calanoid copepods through the lower oxycline of the Arabian Sea oxygen minimum zone     

Karen F. Wishner  Celia Gelfman  Marcia M. Gowing  Dawn M. Outram  Mary Rapien  Rebecca L. Williams 《Progress in Oceanography》2008,78(2):163-191

This paper provides the first comprehensive analysis of calanoid copepod vertical zonation and community structure at midwater depths (300–1000 m) through the lower oxygen gradient (oxycline) (0.02 to 0.3 ml/L) of an oxygen minimum zone (OMZ). Feeding ecology was also analyzed. Zooplankton were collected with a double 1 m² MOCNESS plankton net in day and night vertically-stratified oblique tows from 1000 m to the surface at six stations during four seasons as part of the 1995 US Joint Global Ocean Flux Study (JGOFS) Arabian Sea project. The geographic comparison between a eutrophic more oxygenated onshore station and an offshore station with a strong OMZ served as a natural experiment to elucidate the influence of depth, oxygen concentration, season, food resources, and predators on the copepod distributions.Copepod species and species assemblages of the Arabian Sea OMZ differed in their spatial and vertical distributions relative to environmental and ecological characteristics of the water column and region. The extent and intensity of the oxycline at the lower boundary of the OMZ, and its spatial and temporal variability over the year of sampling, was an important factor affecting distributional patterns. Calanoid copepod species showed vertical zonation through the lower OMZ oxycline. Clustering analyses defined sample groups with similar copepod assemblages and species groups with similar distributions. No apparent diel vertical migration for either calanoid or non-calanoid copepods at these midwater depths was observed, but some species had age-related differences in vertical distributions. Subzones of the OMZ, termed the OMZ Core, the Lower Oxycline, and the Sub-Oxycline, had different copepod communities and ecological interactions. Major distributional and ecological changes were associated with surprisingly small oxygen gradients at low oxygen concentrations. The calanoid copepod community was most diverse in the most oxygenated environments (oxygen >0.14 ml/L), but the rank order of abundance of species was similar in the Lower Oxycline and Sub-Oxycline. Some species were absent or much scarcer in the OMZ Core. Two copepod species common in the Lower Oxycline were primarily detritivorous but showed dietary differences suggesting feeding specialization. The copepod Spinocalanus antarcticus fed primarily on components of the vertical particulate flux and suspended material, a less versatile diet than the co-occurring copepod Lucicutia grandis. Vertical zonation of copepod species through the lower OMZ oxycline is probably a complex interplay between physiological limitation by low oxygen, potential predator control, and potential food resources. Pelagic OMZ and oxycline communities, and their ecological interactions in the water column and with the benthos, may become even more widespread and significant in the future ocean, if global warming increases the extent and intensity of OMZs as predicted.  相似文献   

A search for low surface brightness dwarf galaxies in different environments     

Sarah Roberts  Jonathan Davies  Sabina Sabatini  Wim van Driel  Karen O'Neil  Maarten Baes  Suzanne Linder  Rodney Smith  Rhodri Evans 《Monthly notices of the Royal Astronomical Society》2004,352(2):478-492

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Improved method for modelling sediment transport on unpaved roads using KINEROS2 and dynamic erodibility     

Alan D. Ziegler  Thomas W. Giambelluca  Ross A. Sutherland 《水文研究》2002,16(15):3079-3089

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Long-range transport of Asian emissions to the West Pacific tropical tropopause layer     

Treadaway  Victoria  Atlas  Elliot  Schauffler  Sue  Navarro  Maria  Ueyama  Rei  Pfister  Leonhard  Thornberry  Troy  Rollins  Andrew  Elkins  James  Moore  Fred  Rosenlof  Karen 《Journal of Atmospheric Chemistry》2022,79(2):81-100

Journal of Atmospheric Chemistry - Rapid transport by deep convection is an important mechanism for delivering surface emissions of reactive halocarbons and other trace species to the tropical...  相似文献   

A Study of Governance Arrangements for Land Use and Natural Resource Management Planning in Cape York Peninsula     

Ruth Potts  Karen Vella  Allan Dale  Neil Sipe 《The Australian geographer》2015,46(3):389-409

Complex intersecting social, economic and environmental dilemmas in Australia's Cape York Peninsula present a number of challenges for planners seeking to develop and implement land use and natural resource management (NRM) plans. There have been five different attempts at land use and NRM planning in Cape York Peninsula over the last 20 years. These processes have (to greater or lesser extents) failed to deliver community-owned and government-supported plans to guide development and/or the management of the region's natural resources. The region is remote, sparsely populated, and home to a significant Indigenous population. Much of the contestation within the region surrounds the access, use and ownership of the region's internationally valuable natural resources. This paper reviews, from the literature, the relevancy and applicability of criteria for best practice planning and governance. A range of identified best practice governance and planning principles are applied to assess the governance arrangements for planning in the Peninsula. The paper finds that decision-making arrangements for land use and NRM planning in the Peninsula are still in their infancy and are inadequate to support effective outcomes. The paper concludes that broader attention to best practice principles in governance for planning is needed to improve planning outcomes.  相似文献   

Writing difference differently          下载免费PDF全文

Karen Fisher  Miriam Williams  Stephen FitzHerbert  Lesley Instone  Michelle Duffy  Sarah Wright  Sandie Suchet‐Pearson  Kate Lloyd  Laklak Burarrwanga  Ritjilili Ganambarr  Merrkiyawuy Ganambarr‐Stubbs  Banbapuy Ganambarr  Djawundil Maymuru  Bawaka Country 《New Zealand geographer》2015,71(1):18-33

This paper investigates the writing of situated knowledge and explores the possibilities of enacting difference by writing differently. We present a selection of research stories in which carrier bags, sounds, baskets, gardens and potatoes are interpreted less as objects of research or metaphors to aid in analysing phenomena, than as mediators of the stories. Our stories emphasise the ontological politics of engaging with and representing the relational, the messy, the spontaneous, the unpredictable, the non‐human and bodily experiences. These stories demonstrate how writing is performative and how it is integral to the production of knowledge.  相似文献   

Erratum to: Quantifying and monetizing potential climate change policy impacts on terrestrial ecosystem carbon storage and wildfires in the United States     

David Mills  Russell Jones  Karen Carney  Alexis St. Juliana  Richard Ready  Allison Crimmins  Jeremy Martinich  Kate Shouse  Benjamin DeAngelo  Erwan Monier 《Climatic change》2015,131(1):179-181

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Mussel fishery affects diet and reduces body condition of Eiders Somateria mollissima in the Wadden Sea     

Karsten Laursen  Karen S. Asferg  John Frikke  Peter Sunde 《Journal of Sea Research》2009,62(1):22-30

Although the Danish Wadden Sea is of international importance for several bird species, large-scale blue mussel Mytilus edulis fishing took place from 1984–1987, ceasing thereafter due to low mussel stocks. Mussel fishing removes much of the blue mussel biomass, especially larger individuals. Hence we predict that intensive mussel fishing will affect their predators, such as the Eider Somateria mollissima, which is predominantly a blue mussel feeder by, 1) reducing the amount of blue mussels in their diet relative to alternative prey items, 2) exploitation of smaller blue mussel shell classes, 3) loss of body condition, 4) changing feeding distribution to aggregate to the remaining mussel stocks, and 5) decreasing numbers. Before winter 1986/87 blue mussel biomass was estimated at 40,600 tons, decreasing to 15,400 tons in 1987/88 due to mussel fishery. We collected Eiders in both periods to monitor their diet and body mass and used aerial surveys to determine changes in numbers and distribution. Between the two periods, blue mussels declined in the Eiders diet, numbers of Eiders with empty stomachs increased and the mean length of blue mussel taken by Eiders decreased. Eider body condition declined from 1986/87 to 1987/88, mostly the result of the reduction in numbers of individuals with blue mussel remains in their gizzards and in better body condition compared to those taking alternative food items or having empty gizzards. Eiders shifted their distribution from the southern part of the Danish Wadden Sea to the northern part, where the remaining blue mussel stocks were situated. Eider numbers were lowest in 1987/88, the year of lowest blue mussel stocks. We conclude that intensive mussel fishery affected the Eider's diet, reduced their body condition and affected distribution and abundance. The results also showed that availability of blue mussels may have a key role in building up and maintaining body condition in Eiders during winter.  相似文献   

Assessing the effects of post‐pine beetle forest litter on snow albedo     

Rita Winkler  Sarah Boon  Barbara Zimonick  Karen Baleshta 《水文研究》2010,24(6):803-812

The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood‐dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south‐central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007–2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献