X-ray observations of the edge-on star-forming galaxy NGC 891 and its supernova SN1986J     

Rowan F. Temple  Somak Raychaudhury  Ian R. Stevens 《Monthly notices of the Royal Astronomical Society》2005,362(2):581-591

We present XMM–Newton observations of NGC 891, a nearby edge-on spiral galaxy. We analyse the extent of the diffuse emission emitted from the disc of the galaxy, and find that it has a single-temperature profile with best-fitting temperature of 0.26 keV, though the fit of a dual-temperature plasma with temperatures of 0.08 and 0.30 keV is also acceptable. There is a considerable amount of diffuse X-ray emission protruding from the disc in the north-west direction out to approximately 6 kpc. We analyse the point-source population using a Chandra observation, using a maximum-likelihood method to find that the slope of the cumulative luminosity function of point sources in the galaxy is  −0.77^+0.13_−0.1  . Using a sample of other local galaxies, we compare the X-ray and infrared properties of NGC 891 with those of 'normal' and starburst spiral galaxies, and conclude that NGC 891 is most likely a starburst galaxy in a quiescent state. We establish that the diffuse X-ray luminosity of spirals scales with the far-infrared luminosity as   L _X∝ L ^0.87±0.07_FIR  , except for extreme starbursts, and NGC 891 does not fall in the latter category. We study the supernova SN1986J in both XMM–Newton and Chandra observations, and find that the X-ray luminosity has been declining with time more steeply than expected  ( L _X∝ t ⁻³)  .  相似文献   

Interpretation of Na–Cl–Br Systematics in Sedimentary Basin Brines: Comparison of Concentration, Element Ratio, and Isometric Log-ratio Approaches     

Mark A. Engle  Elisabeth L. Rowan 《Mathematical Geosciences》2013,45(1):87-101

Mathematicians and geochemists have long realized that compositional data intrinsically exhibit a structure prone to spurious and induced correlations. This paper demonstrates, using the Na–Cl–Br system, that these mathematical problems are exacerbated in the study of sedimentary basin brines by such processes as the evaporation or dissolution of salts owing to their high salinities. Using two published datasets of Na–Cl–Br data for fluids from the Appalachian Basin, it is shown that log concentration and Na/Br versus Cl/Br methods for displaying solute chemistry may lead to misinterpretation of mixing trends between meteoric waters (for example shallow drinking water aquifers) and basinal brines, partially due to spurious mathematical relationships. An alternative approach, based on the isometric log-ratio transformation of molar concentration data, is developed and presented as an alternative method, free from potential numerical problems of the traditional methods. The utility, intuitiveness, and potential for mathematical problems of the three methods are compared and contrasted. Because the Na–Cl–Br system is a useful tool for sourcing solutes and investigating the evolution of basinal brines, results from this research may impact such critical topics as evaluating sources of brine contamination in the environment (possibly related to oil and gas production), evaluating the behavior of fluids in the reservoir during hydraulic fracturing, and tracking movement of fluids as a result of geologic CO₂ sequestration.  相似文献   

Case studies in interannual to decadal climate predictability   总被引：1，自引：0，他引：1  

Leon Hermanson  Rowan T. Sutton 《Climate Dynamics》2010,35(7-8):1169-1189

The predictability of ocean and climate variables is investigated, using a perfect model-based case study approach that recognises that predictability is dependent on the initial climate state. In line with previous studies, large scale ocean variables show predictability for several years or more; by contrast, the predictability of climate variables is generally limited to 2 years at most. That predictability shows high sensitivity to the initial state is demonstrated by predictable climate signals arising in different regions, variables and seasons for different initial conditions. The predictability of climate variables in the second year is of particular interest, because this is beyond the timescale that is usually considered to be the limit of seasonal predictability. For different initial conditions, second year predictability is found in: temperatures in southeastern North America (winter) and western Europe (winter and summer), and precipitation in India (summer monsoon) and in the tropical South Atlantic. Second year predictability arises either from persistence of large-scale sea surface temperature (SST) and related ocean heat content anomalies, particularly in regions such as the North Atlantic and Southern Ocean, or from mechanisms that involve El Niño Southern Oscillation (ENSO) dynamics.  相似文献   

Grain-size sensitive deformation of a stretched conglomerate from Plymouth, Vermont     

B. Evans  M. Rowan  W.F. Brace 《Journal of Structural Geology》1980,2(4):411-424

The finite strain of clasts (maximum aspect ratio varying from 2 to 40) in a deformed conglomerate from Dry Hill, Plymouth, Vermont, correlates inversely with the average grain size (300-150 μm) in the clast, suggesting that the operative deformation mechanism was grain-size sensitive. In a general way, the average quartz grain size appeared to be smaller in those clasts with higher volume of minerals other than quartz. Dislocation densities varied by as much as a factor of 10 from grain to grain within a clast, but the average dislocation density was relatively constant from clast to clast. If grain-size sensitivity of strength is accepted as a working hypothesis, other elements of the microstructure, such as grain flattening, grain morphology, and dislocation structure can be reconciled as happening either through a late, low strain, high stress pulse—if the current palaeostress indicators are correct to within a factor of 10 or as happening concurrently with the grain-size sensitive mechanism if the current palaeostress estimates are in error. The evidence from this study agrees with several previously published suggestions that grain-size sensitive deformation occurs in the crust for quartzose rocks with grain size of 100 to 300 μm at temperatures of 350 to 420°C.  相似文献   

LNAPL in fine-grained soils: Conceptualization of saturation, distribution, recovery, and their modeling     

Mark Adamski  Victor Kremesec  Ravi Kolhatkar  Chris Pearson  Beth Rowan 《Ground Water Monitoring & Remediation》2005,25(1):100-112

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Ocean acidification and photic‐zone anoxia at the Toarcian Oceanic Anoxic Event: Insights from the Adriatic Carbonate Platform     

Nicholas P. Ettinger  Toti E. Larson  Charles Kerans  Alyson M. Thibodeau  Kelly E. Hattori  Sean M. Kacur  Rowan C. Martindale 《Sedimentology》2021,68(1):63-107

Severe global climate change led to the deterioration of environmental conditions in the oceans during the Toarcian Stage of the Jurassic. Carbonate platforms of the Western Tethys Ocean exposed in Alpine Tethyan mountain ranges today offer insight into this period of environmental upheaval. In addition to informing understanding of climate change in deep time, the effect of ancient carbon cycle perturbations on carbonate platforms has important implications for anthropogenic climate change; the patterns of early Toarcian environmental deterioration are similar to those occurring in modern oceans. This study focuses on the record of the early Toarcian Oceanic Anoxic Event (ca 183.1 Ma) in outcrops of the north‐west Adriatic Carbonate Platform in Slovenia. Amidst environmental deterioration, the north‐west Adriatic Platform abruptly transitioned from a healthy, shallow‐water environment with diverse metazoan ecosystems to a partially drowned setting with low diversity biota and diminished sedimentation. An organic carbon‐isotope excursion of ?2.2‰ reflects the massive injection of CO₂ into the ocean‐atmosphere system and marks the stratigraphic position of the Toarcian Oceanic Anoxic Event. A prominent dissolution horizon and suppressed carbonate deposition on the platform are interpreted to reflect transient shoaling of the carbonate compensation depth to unprecedentedly shallow levels as the dramatic influx of CO₂ overwhelmed the ocean’s buffering capacity, causing ocean acidification. Trace metal geochemistry and palaeoecology highlight water column deoxygenation, including the development of photic‐zone anoxia, preceding and during the Toarcian Oceanic Anoxic Event. Ocean acidification and reduced oxygen levels likely had a profoundly negative effect on carbonate‐producing biota and growth of the Adriatic Platform. These effects are consistent with the approximate doubling of the concentration of CO₂ in the ocean‐atmosphere system from pre‐event levels, which has previously been linked to a volcanic triggering mechanism. Mercury enrichments discovered in this study support a temporal and genetic link between volcanism, the Toarcian Oceanic Anoxic Event and the carbonate crisis.  相似文献   

Equifinality and uncertainty in physically based soil erosion models: application of the GLUE methodology to WEPP–the Water Erosion Prediction Project–for sites in the UK and USA     

Richard E. Brazier  Keith J. Beven  Jim Freer  John S. Rowan 《地球表面变化过程与地形》2000,25(8):825-845

Despite the wealth of soil erosion models available for the prediction of both runoff and soil loss at a variety of scales, little quantification is made of uncertainty and error associated with model output. This in part reflects the need to produce unequivocal or optimal results for the end user, which will often be an unrealistic goal. This paper presents a conceptually simple methodology, Generalized Likelihood Uncertainty Estimation (GLUE), for assessing the degree of uncertainty surrounding output from a physically based soil erosion model, the Water Erosion Prediction Project (WEPP). The ability not only to be explicit about model error but also to evaluate future improvements in parameter estimation, observed data or scientific understanding is demonstrated. This approach is applied to two sets of soil loss/runoff plot replicates, one in the UK and one in the USA. Although it is demonstrated that observations can be largely captured within uncertainty bounds, results indicate that these uncertainty bounds are often wide, reflecting the need to qualify results that derive from ‘optimum’ parameter sets, and to accept the concept of equifinality within soil erosion models. Attention is brought to the problem of under‐prediction of large events/over‐prediction of small events, as an area where model improvements could be made, specifically in the case of relatively dry years. Finally it is proposed that such a technique of model evaluation be employed more widely within the discipline so as to aid the interpretation and understanding of complex model output. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Heterogeneous water storage and thermal regime of supraglacial ponds on debris‐covered glaciers          下载免费PDF全文

Cameron Scott Watson  Duncan J. Quincey  Jonathan L. Carrivick  Mark W. Smith  Ann V. Rowan  Robert Richardson 《地球表面变化过程与地形》2018,43(1):229-241

The water storage and energy transfer roles of supraglacial ponds are poorly constrained, yet they are thought to be important components of debris‐covered glacier ablation budgets. We used an unmanned surface vessel (USV) to collect sonar depth measurements for 24 ponds to derive the first empirical relationship between their area and volume applicable to the size distribution of ponds commonly encountered on debris‐covered glaciers. Additionally, we instrumented nine ponds with thermistors and three with pressure transducers, characterizing their thermal regime and capturing three pond drainage events. The deepest and most irregularly‐shaped ponds were those associated with ice cliffs, which were connected to the surface or englacial hydrology network (maximum depth = 45.6 m), whereas hydrologically‐isolated ponds without ice cliffs were both more circular and shallower (maximum depth = 9.9 m). The englacial drainage of three ponds had the potential to melt ~100 ± 20 × 10³ kg to ~470 ± 90 × 10³ kg of glacier ice owing to the large volumes of stored water. Our observations of seasonal pond growth and drainage with their associated calculations of stored thermal energy have implications for glacier ice flow, the progressive enlargement and sudden collapse of englacial conduits, and the location of glacier ablation hot‐spots where ponds and ice cliffs interact. Additionally, the evolutionary trajectory of these ponds controls large proglacial lake formation in deglaciating environments. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

揭开水星的秘密     

Karen Rowan  胡德良 《海洋地质前沿》2008,24(10):41-41

1975年,“水手”10号太空船曾首次飞临并造访水星。此后,“信使”号太空船拍下了1213张水星的新图片。有关这颗太阳系最里面的行星,该太空飞行任务的首席研究员肖恩·所罗门（Sean Solomon）解释了其中几张独特的图片。  相似文献   

Generating probabilistic estimates of hydrological response for Irish catchments using a weather generator and probabilistic climate change scenarios     

Satish Bastola  Conor Murphy  Rowan Fealy 《水文研究》2012,26(15):2307-2321

In accounting for uncertainties in future simulations of hydrological response of a catchment, two approaches have come to the fore: deterministic scenario‐based approaches and stochastic probabilistic approaches. As scenario‐based approaches result in a wide range of outcomes, the role of probabilistic‐based estimates of climate change impacts for policy formulation has been increasingly advocated by researchers and policy makers. This study evaluates the impact of climate change on seasonal river flows by propagating daily climate time series, derived from probabilistic‐based climate scenarios using a weather generator (WGEN), through a set of conceptual hydrological models. Probabilistic scenarios are generated using two different techniques. The first technique used probabilistic climate scenarios developed from statistically downscaled scenarios for Ireland, hereafter called SDprob. The second technique used output from 17 global climate models (GCMs), all of which participated in CMIP3, to generate change factors (hereafter called CF). Outputs from both the SDprob and the CF approach were then used in combination with WGEN to generate daily climate scenarios for use in the hydrological models. The range of simulated flow derived with the CF method is in general larger than those estimated with the SDprob method in winter and vice versa because of the strong seasonality in the precipitation signal for the 17 GCMs. Despite this, the simulated probability density function of seasonal mean streamflow estimated with both methods is similar. This indicates the usefulness of the SDprob or probabilistic approach derived from regional scenarios compared with the CF method that relies on sampling a diversity of response from the GCMs. Irrespective of technique used, the probability density functions of seasonal mean flow produced for four selected basins is wide indicating considerable modelling uncertainties. Such a finding has important implications for developing adaptation strategies at the catchment level in Ireland. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献