The energetics and mass loss of the dwarf starburst Markarian 33     

Lesley K. Summers  Ian R. Stevens  David K. Strickland † 《Monthly notices of the Royal Astronomical Society》2001,327(2):385-396

We present ROSAT HRI X-ray data and optical imaging of the important dwarf starburst Markarian 33. We find an extended, complex, shell-like morphology in the X-ray emission, with an extent of ∼     , coincident with the bright star-forming regions at the centre of the galaxy. The physical extent of this X-ray emission from Mrk 33 is very similar to the observed H α emission, and suggests that the bulk of the X-ray emission is coming from an expanding superbubble.
We estimate the age and mass of Mrk 33's starburst to be 5.8 Myr and     respectively, with the energy injection rate in the central regions of the galaxy being ∼10⁴¹ erg s⁻¹, while the associated mass-loss rate from the star-forming regions is estimated to be ∼0.2 M_⊙ yr⁻¹. We suggest that the X-ray emission is predominantly powered by starburst-type activity, and argue that a blow-out in the form of a galactic wind is the most likely fate for Mrk 33, resulting in the loss of most of the galaxy's metal-enriched material and a small fraction (<1 per cent) of the ISM.  相似文献   

Book Review: Mathematica® in the Laboratory By Samuel Dick,Alfred Riddle,and Douglas Stein Cambridge University Press,Cambridge, 1997, 320 p., $74.95/$29.95 (U.S.), ISBN 0-521-58137-0 hardback, 0-521-49906-2 paperback     

Underwood  Robert 《Mathematical Geosciences》2001,33(4):539-540

Mathematical Geosciences -  相似文献   

Porphyry Copper Deposit Tract Definition – A Global Analysis Comparing Geologic Map Scales     

Gary L. Raines  Katherine A. Connors  Lesley B. Chorlton 《Natural Resources Research》2007,16(2):191-198

Geologic maps are a fundamental data source used to define mineral-resource potential tracts for the first step of a mineral resource assessment. Further, it is generally believed that the scale of the geologic map is a critical consideration. Previously published research has demonstrated that the U.S. Geological Survey porphyry tracts identified for the United States, which are based on 1:500,000-scale geology and larger scale data and published at 1:1,000,000 scale, can be approximated using a more generalized 1:2,500,000-scale geologic map. Comparison of the USGS porphyry tracts for the United States with weights-of-evidence models made using a 1:10,000,000-scale geologic map, which was made for petroleum applications, and a 1:35,000,000-scale geologic map, which was created as context for the distribution of porphyry deposits, demonstrates that, again, the USGS US porphyry tracts identified are similar to tracts defined on features from these small scale maps. In fact, the results using the 1:35,000,000-scale map show a slightly higher correlation with the USGS US tract definition, probably because the conceptual context for this small-scale map is more appropriate for porphyry tract definition than either of the other maps. This finding demonstrates that geologic maps are conceptual maps. The map information shown in each map is selected and generalized for the map to display the concepts deemed important for the map maker’s purpose. Some geologic maps of small scale prove to be useful for regional mineral-resource tract definition, despite the decrease in spatial accuracy with decreasing scale. The utility of a particular geologic map for a particular application is critically dependent on the alignment of the intention of the map maker with the application.  相似文献   

Hydrological Research and the Status of Physical Geography Journals: Increasing the Impact of Physical Geography in the Academy     

Delphis F. Levia  S. Jeffrey Underwood 《The Professional geographer》2004,56(3):345-349

Physical geographers are often confronted with the decision of whether to publish in geography or nongeography journals. The present study seeks to quantify the number of articles with a significant hydrology content published in geography versus hydrology journals by physical geographers from 1997 to 2002 using the ISI Web of Knowledge electronic database. Of 690 articles published in the 10 selected geography and hydrology journals during the period of study, over four‐fifths were published in hydrology journals. Based on our interpretation of the data, the comparatively smaller audience in geography and the risk of acquiring fewer citations compels physical geographers to publish in hydrology journals for increased visibility. A critical mass of physical geographers should consider publishing some of their work in physical geography journals to elevate the status of geography in the academy.  相似文献   

Character of sediments entering the Costa Rica subduction zone: Implications for partitioning of water along the plate interface     

Glenn A.  Spinelli  Michael B.  Underwood 《Island Arc》2004,13(3):432-451

Abstract   Sediments deposited off the Nicoya Peninsula advect large volumes of water as they enter the Costa Rica subduction zone. Seismic reflection data, together with results from Ocean Drilling Program Leg 170, show that hemipelagic mud comprises the upper ∼135 m of the sediment column (ranging from 0 to 210 m). The lower ∼215 m of the sediment column (ranging from 0 to 470 m) is pelagic carbonate ooze. We analyzed samples from 60 shallow (<7 m) cores to characterize the spatial variability of sediment composition on the incoming Cocos Plate. The bulk hemipelagic sediment is 10 wt% opal and 60 wt% smectite on average, with no significant variations along strike; the pelagic chalk contains approximately 2 wt% opal and <1 wt% smectite. Initially, most of the water (96%) in the subducting sediment is stored in pore spaces, but the pore water is expelled during the early stages of subduction by compaction and tectonic consolidation. Approximately 3.6% of the sediment's total water volume enters the subduction zone as interlayer water in smectite; only 0.4% of the water is bound in opal. Once subducting strata reach depths greater than 6 km (more than 30 km inboard of the subduction front), porosity drops to less than 15%, and temperature rises to greater than 60°C. Under those conditions, discrete pulses of opal and smectite dehydration should create local compartments of fluid overpressure, which probably influence fluid flow patterns and reduce effective stress along the plate boundary fault.  相似文献   

Palaeontology,stratigraphy and sedimentology of Woodeaton Quarry (Oxfordshire) and a new microvertebrate site from the White Limestone Formation (Bathonian,Jurassic)     

Simon Wills  Emma Louise Bernard  Philippa Brewer  Charlie J. Underwood  David J. Ward 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(2):170-186

Woodeaton Quarry in Oxfordshire has previously yielded a number of large sauropod vertebrae and other (unpublished) dinosaur remains from a horizon in the Rutland Formation. No review of the wider terrestrial fauna from Woodeaton has been published to date. Here we present an overview of new material recovered from a microvertebrate site at the top of the White Limestone Formation (Middle Jurassic, Bathonian, Great Oolite Group, Retrocostatum Zone) and review the stratigraphy to provide a comprehensive local stratigraphic framework and place the quarry in the correct regional context. The terrestrial fauna is similar to that found from other UK Bathonian microvertebrate sites and includes probable dromaeosaurid theropods, ornithischians, tritylodontids and mammaliaforms such as amphitheriids, docodonts, ‘eutriconodonts’, ‘haramyids’ and multituberculates. Placement of the White Limestone Formation boundaries are clarified with respect to the Rutland and Forest Marble Formations. This indicates that the microvertebrate bed from Woodeaton is slightly older than that of the well-known mammal bed from nearby Kirtlington Quarry.  相似文献   

Situating nature: On doing cultural geographies of Australian nature     

Lesley Instone 《The Australian geographer》2004,35(2):131-140

This paper concentrates on the practices and possibilities of doing poststructural cultural geographies of nature. The paper begins with an overview of the ways in which nature is being reconceptualised in social thought. It charts a middle territory between strong social constructivism and realist approaches, arguing for a relational understanding of nature and culture, and the extension of agency to non-humans--organic and artificial. These 'more than human worlds' (&lt;citeref rid="b51"&gt;Whatmore, 'Hybrid geographies'&lt;/citeref&gt;, Sage, London, 2002) pose considerable challenges for researchers. They open spaces for new subjects and new subjectivities, decentre human agency, and challenge more conventional methodological approaches that rely on a separation between subject and object. The paper considers the sorts of methodological shifts required for relational analysis, arguing for a multilayered, multivalent, embodied and situated approach. The practices of situatedness are emphasised in the Australian context, especially in relation to cross-cultural and postcolonial understandings. The paper concludes with a brief comment on the politics of doing such cultural geographies.  相似文献   

Trends and variability in column-integrated atmospheric water vapor   总被引：4，自引：0，他引：4  

Kevin E. Trenberth  John Fasullo  Lesley Smith 《Climate Dynamics》2005,24(7-8):741-758

An analysis and evaluation has been performed of global datasets on column-integrated water vapor (precipitable water). For years before 1996, the Ross and Elliott radiosonde dataset is used for validation of European Centre for Medium-range Weather Forecasts (ECMWF) reanalyses ERA-40. Only the special sensor microwave imager (SSM/I) dataset from remote sensing systems (RSS) has credible means, variability and trends for the oceans, but it is available only for the post-1988 period. Major problems are found in the means, variability and trends from 1988 to 2001 for both reanalyses from National Centers for Environmental Prediction (NCEP) and the ERA-40 reanalysis over the oceans, and for the NASA water vapor project (NVAP) dataset more generally. NCEP and ERA-40 values are reasonable over land where constrained by radiosondes. Accordingly, users of these data should take great care in accepting results as real. The problems highlight the need for reprocessing of data, as has been done by RSS, and reanalyses that adequately take account of the changing observing system. Precipitable water variability for 1988–2001 is dominated by the evolution of ENSO and especially the structures that occurred during and following the 1997–98 El Niño event. The evidence from SSM/I for the global ocean suggests that recent trends in precipitable water are generally positive and, for 1988 through 2003, average 0.40±0.09 mm per decade or 1.3±0.3% per decade for the ocean as a whole, where the error bars are 95% confidence intervals. Over the oceans, the precipitable water variability relates very strongly to changes in SSTs, both in terms of spatial structure of trends and temporal variability (with a regression coefficient for 30°N–30°S of 7.8% K^?1) and is consistent with the assumption of fairly constant relative humidity. In the tropics, the trends are also influenced by changes in rainfall which, in turn, are closely associated with the mean flow and convergence of moisture by the trade winds. The main region where positive trends are not very evident is over Europe, in spite of large and positive trends over the North Atlantic since 1988. A much longer time series is probably required to obtain stable patterns of trends over the oceans, although the main variability could probably be deduced from past SST and associated precipitation variations.  相似文献   

Oil spillages affecting seabirds in the United Kingdom, 1966–1983     

T.J Stowe  L.A Underwood 《Marine pollution bulletin》1984,15(4):147-152

Oil spillages have affected large numbers of seabirds, principally auks, in the United Kingdom waters between 1966 and 1983. The annual scale of mortality has varied widely, although the worst kills are substantially less than some recorded elsewhere in N.W. Europe. Regional variations in the occurrence of mortality incidents are recorded, which in general reflect the distribution at sea of both birds and marine traffic. Oil pollution incidents affecting birds are essentially a winter phenomenon in UK waters and some reasons for this are discussed.  相似文献   

A late Ordovician (Hirnantian) karstic surface in a submarine channel,recording glacio‐eustatic sea‐level changes: Meifod,central Wales     

Patrick J. Brenchley  Jim D. Marshall  David A. T. Harper  Caroline J. Buttler  Charlie J. Underwood 《Geological Journal》2006,41(1):1-22

The growth and decay of the end‐Ordovician Gondwanan glaciation is globally reflected by facies changes in sedimentary sequences, which record a major eustatic fall and subsequent rise in the Hirnantian Stage at the end of the Ordovician. However, there are different reported estimates of the magnitude and pattern of sea‐level change. Particularly good evidence for end‐Ordovician sea‐level change comes from a sequence at Meifod in central Wales, which has a karstified limestone unit within a channel incised into marine shelf sediments. Pre‐glacial (Rawtheyan) mudstones have a diverse fauna suggesting a mid‐to‐deep‐shelf water depth of c. 60 m. The channel, 20 m deep, was incised into these mudstones and partially filled with a mixture of fine sand and detrital carbonate. The taphonomy of bioclasts and intraclasts indicates that many had a long residence time on the sea floor or suffered diagenesis after shallow burial before being resedimented into the channel. The presence of carbonates on the Welsh shelf is atypical and they are interpreted as having accumulated as patches during a minor regression prior to the main glacio‐eustatic fall. Comparison of the carbon stable‐isotopic values of the bioclast material with the global isotopic record confirms that most of the material is of Rawtheyan age, but that some is Hirnantian. The resedimented carbonates lithified rapidly and formed a limestone, several metres thick, in the deepest parts of the channel. As sea‐level fell, this limestone was exposed and eroded into karstic domes and pillars with a relief of over 2 m. The overall, glacio‐eustatic, sea‐level fall is estimated to be in excess of 80 m. A succeeding sea‐level rise estimated to be 40–50 m is recorded in the laminated crust that mantles the karstic domes and pillars. The crust is formed of encrusting bryozoans, associated cystoids, crinoid holdfasts and clusters of the brachiopod Paromalomena, which is normally associated with mid‐shelf environments. Fine sands buried the karst topography and accumulated to fill the channel. In the sandstones at the base of the channel there is a Hirnantia fauna, while in the sandstones high in the channel‐sequence there is cross‐stratification characteristic of mid‐shoreface environments. This would indicate a fall of sea‐level of c. 30 m. The subsequent major transgression marking the end of the glaciation is not recorded at the Meifod locality, but nearby exposures of mudstones suggest a return to mid‐to‐deep‐shelf environments, similar to those that prevailed before the Hirnantian regression. The Meifod sequence provides strong evidence for the magnitude of the Hirnantian sea‐level changes and by implication confirm larger estimates for the size of the ice sheets. Smaller oscillations in relative sea‐level seen at Meifod may be local phenomena or may reflect eustatic changes that have not been widely reported elsewhere. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献