XMM–Newton X-ray observations of the Wolf–Rayet binary system WR 147     

S. L. Skinner  S. A. Zhekov  M. Güdel  W. Schmutz 《Monthly notices of the Royal Astronomical Society》2007,378(4):1491-1498

We present results of an ≈20-ks X-ray observation of the Wolf–Rayet (WR) binary system WR 147 obtained with XMM–Newton . Previous studies have shown that this system consists of a nitrogen-type WN8 star plus an OB companion whose winds are interacting to produce a colliding wind shock. X-ray spectra from the pn and MOS detectors confirm the high extinction reported from infrared studies and reveal hot plasma including the first detection of the Fe Kα line complex at 6.67 keV. Spectral fits with a constant-temperature plane-parallel shock model give a shock temperature   kT _shock= 2.7  keV (   T _shock≈ 31  MK), close to but slightly hotter than the maximum temperature predicted for a colliding wind shock. Optically thin plasma models suggest even higher temperatures, which are not yet ruled out. The X-ray spectra are harder than can be accounted for using 2D numerical colliding wind shock models based on nominal mass-loss parameters. Possible explanations include: (i) underestimates of the terminal wind speeds or wind abundances, (ii) overly simplistic colliding wind models or (iii) the presence of other X-ray emission mechanisms besides colliding wind shocks. Further improvement of the numerical models to include potentially important physics such as non-equilibrium ionization will be needed to rigorously test the colliding wind interpretation.  相似文献   

Surface sediments pollution due to shipwreck s/s “Stuttgart”: a multidisciplinary approach     

Justyna Rogowska  Błażej Kudłak  Stefan Tsakovski  Agnieszka Gałuszka  Gabriela Bajger-Nowak  Vasil Simeonov  Piotr Konieczka  Lidia Wolska  Jacek Namieśnik 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(7):1797-1807

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Evaluation of the boundary layer morning transition using the CL-31 ceilometer signals     

Paulina Sokół  Iwona S. Stachlewska  Ioana Ungureanu  Sabina Stefan 《Acta Geophysica》2014,62(2):367-380

The morning transition of the atmospheric boundary layer from nighttime to daytime conditions was investigated using the Vaisala’s CL-31 ceilometer, located at Magurele, Romania (44.35°N, 26.03°E). Based on the 5-days backward trajectories, we rejected those measurements which were related to the intrusions of long-range transported particles. In the several discussed cases, which are representative for the morning transition in spring and summer seasons over Magurele, the increasing depth of the boundary layer related to the local aerosol load was well discernible. The dynamic change of its depth was estimated with errors using a simple method based on finding the minimum of the first derivative of the ceilometer signal. In the summer, the increase of the boundary layer depth due to the morning transition from the nighttime to daytime conditions starts on average of about 80 min earlier and the growth rate of this depth is 143 ± 6 m/h and about 37% slower than in the spring case.  相似文献   

Perspectives in Modelling Climate–Hydrology Interactions     

Stefan Hagemann  Tanja Blome  Fahad Saeed  Tobias Stacke 《Surveys in Geophysics》2014,35(3):739-764

Various land–atmosphere coupling mechanisms exist that may lead to large-scale impacts on climate and hydrology. Some of them are still less understood and not adequately represented in state-of-the-art climate modelling. But, as the current generation of climate models enables consideration and implementation of important coupling processes, the present study provides perspectives for the modelling of relevant climate–hydrology interactions. On a more short-term perspective, these comprise anthropogenic land use and especially irrigation, which has been shown that it may even affect remote regions. On a long-term perspective, the coupling of hydrology to carbon cycle and vegetation becomes important, specifically the dynamics of permafrost and wetlands. Here, we present a review of current knowledge combined with some exemplary studies from a large-scale point of view. Therefore, we focus on climate–hydrology interactions that are relevant on scales utilized in the current or forthcoming global and regional climate modelling exercises.  相似文献   

Strong-lensing optical depths in a ΛCDM universe – II. The influence of the stellar mass in galaxies     

Stefan Hilbert  Simon D. M. White  Jan Hartlap  Peter Schneider 《Monthly notices of the Royal Astronomical Society》2008,386(4):1845-1854

We investigate how strong gravitational lensing in the concordance ΛCDM cosmology is affected by the stellar mass in galaxies. We extend our previous studies, based on ray tracing through the Millennium Simulation, by including the stellar components predicted by galaxy formation models. We find that the inclusion of these components greatly enhances the probability for strong lensing compared to a 'dark matter only' universe. The identification of the 'lenses' associated with strong-lensing events reveals that the stellar mass of galaxies (i) significantly enhances the strong-lensing cross-sections of group and cluster haloes and (ii) gives rise to strong lensing in smaller haloes, which would not produce noticeable effects in the absence of the stars. Even if we consider only image splittings ≳10 arcsec, the luminous matter can enhance the strong-lensing optical depths by up to a factor of 2.  相似文献   

Revised palaeoclimatic significance of Mueller Glacier moraines,Southern Alps,New Zealand          下载免费PDF全文

Natalya V. Reznichenko  Tim R. H. Davies  Stefan Winkler 《地球表面变化过程与地形》2016,41(2):196-207

A sequence of Late Holocene moraines on the foreland of the Mueller Glacier, Southern Alps, New Zealand, forms part of a local moraine‐age database used to establish a regional glacier chronology and subsequently to investigate potential intra‐hemispheric and global climate forcing mechanisms. We present new sedimentological and geomorphological evidence that a set of these moraine ridges, previously considered to represent individual advances, constitutes a single moraine complex (the ‘Mueller Memorial Moraine’) formed by supraglacial transport of a large volume of landslide debris to the glacier terminus. Because a moraine formed in this way is not necessarily associated with an advance triggered by a climate event, we question the palaeoclimatic significance of the Mueller Memorial Moraine, as well as that of other moraines in comparable settings. Our findings suggest that the mode of formation and glacio‐dynamical context of moraines whose ages contribute to existing palaeoclimate reconstructions need to be re‐examined in order to assess the reliability of these reconstructions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Fate of Point‐Source Pesticide Spill in Clayey Till after 15 Years          下载免费PDF全文

Peter R. Jørgensen  Niels H. Spliid  Troels Laier  Stefan Outzen 《Ground Water Monitoring & Remediation》2016,36(3):33-42

This study investigated the development of pesticide pollution two, three, and 17 years after spills of the herbicides dichlorprop, mecoprop (MCPP), MCPA, 2,4‐D (phenoxy acids), simazine, and terbutylazine (triazines) in a former orchard machinery service yard. The spills had occurred over several decades on a 23‐m thick, mainly anaerobic fractured clayey till aquitard. Angled monitoring wells were installed in the aquitard 3 years after the spills ceased in 1989. In 1993, monitoring revealed that high groundwater concentrations of dichlorprop (677 µg/L) and MCPP (139 µg/L) were accumulated as a zone of maximum pollution in anaerobic and largely immobile pore water at 5 to 6 m depth in the aquitard profile. In contrast, 2,4‐D was determined in only one water sample, and MCPA and simazine and terbutylazine were determined only in low concentrations (below10 µg/L), although these pesticides had been handled at the site in greater amounts than dichlorprop and MCPP according to detailed historic information obtained for the site. Repeated monitoring in the same wells after a further 14 years in 2007 revealed that no identifiable degradation of MCPP had occurred, while dichlorprop had degraded by 75% to 80% (estimated half‐life of approximately 5 years). Furthermore, degradation products related to the phenoxy acids had accumulated, especially 4‐CPP with a maximum concentration of 218 µg/L. In the same zone, MCPA and simazine had almost disappeared. As the pollution was mainly accumulated in largely immobile pore water of the aquitard clayey matrix, and the groundwater recharge was low (30 to 60 mm/year), only minor vertical displacement of the zone with maximum pollution zone had occurred during the 15 years of monitoring. However, concentrations of dichlorprop (0.01 to 0.02 µg/L), MCPP (0.1 to 0.2 µg/L), and 4‐CPP (0.6 to 0.7 µg/L) had spread along textural heterogeneities in the aquitard into the underlying sandy aquifer at 23‐m depth.  相似文献   

Monitoring and volumetric estimation of injected CO2 using 4D seismic,petrophysical data,core measurements and well logging: a case study at Ketzin,Germany     

Alexandra Ivanova  Artem Kashubin  Niklas Juhojuntti  Juliane Kummerow  Jan Henninges  Christopher Juhlin  Stefan Lüth  Monika Ivandic 《Geophysical Prospecting》2012,60(5):957-973

More than 50 000 tons of CO₂ have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1^st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO₂ had been injected. We show here that rather complex time‐lapse signatures of this CO₂ can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO₂ saturation levels allow an estimate of the total amount of CO₂ visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO₂ injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO₂ storage site using seismic methods.  相似文献   

Prevalence and composition of fishing gear debris in the nests of northern gannets (Morus bassanus) are related to fishing effort     

Bond AL  Montevecchi WA  Guse N  Regular PM  Garthe S  Rail JF 《Marine pollution bulletin》2012,64(5):907-911

Bycatch and indirect mortality associated with global fishing operations affect non-target species. Northern gannets (Morus bassanus) and other seabirds incorporate marine debris, much of it originating in fisheries, into their nests, at times resulting in entanglement. We compared the prevalence and composition of marine debris in nests at two gannet colonies in Newfoundland before and after a basin-wide ground fish closure in 1992, and at the species' largest colony in the Gulf of St. Lawrence, where fishing effort is low. The proportion of nests with marine debris decreased following the fishery closure, and the proportion of nests with fishing gear was related exponentially to the number of gillnets set around breeding colonies. Assessing the composition of gannet nests could provide a useful index of the prevalence of fishing debris and could be used to assess entanglement risk of other animals in the marine environment over decadal scales.  相似文献   

Correlation equation for the marine drag coefficient and wave steepness     

Richard J. Foreman  Stefan Emeis 《Ocean Dynamics》2012,62(9):1323-1333

This work questions, starting from dimensional considerations, the generality of the belief that the marine drag coefficient levels off with increasing wind speed. Dimensional analysis shows that the drag coefficient scales with the wave steepness as opposed to a wave-age scaling. A correlation equation is employed here that uses wave steepness scaling at low aspect ratios (inverse wave steepnesses) and a constant drag coefficient at high aspect ratios. Invoked in support of the correlation are measurements sourced from the literature and at the FINO1 platform in the North Sea. The correlation equation is then applied to measurements recorded from buoys during the passage of hurricanes Rita, Katrina (2005) and Ike (2008). Results show that the correlation equation anticipates the expected levelling off in deeper water, but a drag coefficient more consistent with a Charnock type relation is also possible in more shallower water. Some suggestions are made for proceeding with a higher-order analysis than that conducted here.  相似文献