Star formation in the circumnuclear environment of NGC 1068     

Richard I. Davies  Hajime Sugai  & Martin J. Ward 《Monthly notices of the Royal Astronomical Society》1998,300(2):388-396

We present near-infrared emission-line images of the circumnuclear ring in NGC 1068. We have measured the Brγ fluxes in a number of star-forming complexes and derived the extinction for each of these by comparison with Hα. We investigate the star-forming histories of these regions and find that a short burst of star formation occurred coevally throughout the ring within the last 30–40 Myr, and perhaps as recently as 4–7 Myr ago. The 1–0 S(1) flux and S(1)/Brγ ratios indicate that as well as fluorescence, shock-excited H₂ emission contributes to the total flux. There is excess H₂ flux to the north-west where the ionization cone crosses the ring, and we show that it is possible that the non-stellar continuum from the Seyfert nucleus which produces the high-excitation lines could also be causing fluorescence at the edges of molecular clouds in the ring. The nuclear 1–0 S(1) is more extended than previously realized but only along the bar's major axis, and we consider mechanisms for its excitation.  相似文献   

ROSAT ASCA observations of X-ray luminous starburst galaxies: NGC 3310 and 3690     

A. L. Zezas    I. Georgantopoulos  & M. J. Ward 《Monthly notices of the Royal Astronomical Society》1998,301(4):915-925

We present ROSAT [High Resolution Imager (HRI) and Position Sensitive Proportional Counter (PSPC)] and ASCA observations of the two luminous ( L _x ∼ 10⁴¹⁻⁴² erg s⁻¹) star-forming galaxies NGC 3310 and 3690. The HRI shows clearly that the sources are extended with the X-ray emission in NGC 3690 coming from at least three regions. The combined 0.1–10 keV spectrum of NGC 3310 can be described by two components, a Raymond–Smith plasma with temperature kT  = 0.81^+0.09_−0.12 keV and a hard power law, Γ = 1.44^−0.20_−0.11 (or alternatively a harder Raymond–Smith plasma with kT  ∼ 15 keV), while there is no substantial excess absorption above the Galactic column value. The soft component emission is probably a super wind while the nature of the hard emission is more uncertain with the likely origins being X-ray binaries, inverse Compton scattering of infrared photons, an active galactic nucleus or a very hot gas component (∼10⁸ K). The spectrum of NGC 3690 is similar, with kT  = 0.83^+0.02_−0.04 keV and Γ = 1.56^+0.11_−0.11. We also employ more complicated models such as a multi-temperature thermal plasma, a non-equilibrium ionization code or the addition of a third softer component, which improve the fit but not at a statistically significant level (2σ). These results are similar to recent results on the archetypal star-forming galaxies M82 and NGC 253.  相似文献   

Land degradation is not a necessary outcome of communal pastoralism in arid Namibia   总被引：1，自引：0，他引：1  

David Ward    Ben T. Ngairorue  Johannes Kathena  Rana Samuels  Yanay Ofran 《Journal of Arid Environments》1998,40(4):357-371

In Otjimbingwe, a region of arid south-central Namibia, human population densities are high and these communal pastoralists own large numbers of livestock. Such situations are commonly perceived to lead to the ‘tragedy of the commons'. This region lends itself to a comparison of the effects of communal and commercial farming (with private land ownership) because the communal area is completely surrounded by commercial farms. In spite of far higher stocking densities on the communal areas and the absence of an overall grazing strategy, we found no evidence of the ‘tragedy of the commons' on Otjimbingwe. Indeed, the communal areas did not differ in a number of soil and vegetation parameters from the commercial farms. These results point both to the resilience of arid environments to high stocking levels and the over-riding influence of abiotic variables on environmental quality.  相似文献   

On the consistency of earthquake moment rates, geological fault data, and space geodetic strain: the United States   总被引：7，自引：0，他引：7  

Steven N. Ward 《Geophysical Journal International》1998,134(1):172-186

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CENSUS OF GREY SEALS BY AERIAL PHOTOGRAPHY   总被引：1，自引：0，他引：1  

A. R. Hiby  D. Thompson  A. J. Ward 《The Photogrammetric Record》1988,12(71):589-594

The factors determining resolution in aerial photography of wildlife concentrations are considered and two developments that improve resolution with inexpensive equipment are described. Firstly, a rocking camera mount has been constructed that compensates for apparent image motion resulting from forward movement of the aircraft. The mount allows slower shutter speeds to be used so that aerial surveys can be conducted using high resolution colour film under poor light conditions. Secondly, critical prefocusing to the survey flying height is carried out, even for lenses of short focal length. Aerial photography of grey seal breeding colonies is used to illustrate these developments.  相似文献   

Editorial: Symposium on Cretaceous Stage Boundaries, Copenhagen 18–21 October 1983     

Malcolm Hart  Editor  Peter Ward  Editor 《Cretaceous Research》1984,5(4):301

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Chemical characteristics of laboratory produced tarballs     

M Savage  C.H Ward 《Marine pollution bulletin》1984,15(5):174-178

Artificial tarballs were made in the laboratory from four crude petroleums. Relative to the parent petroleum, a decrease in aromatic hydrocarbon content for all samples was observed, as was a decrease in saturate content for three of four samples and an increase in compounds containing nitrogen, sulphur and oxygen for three samples. The asphaltene content also increased for three samples. The saturate, aromatic and asphaltic content of the artificial tarballs was compared to values for natural tarballs reported in the literature.  相似文献   

Editorial     

Kevin Ward 《Urban geography》2018,39(1):1-2

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Ecohydrologic separation alters interpreted hydrologic stores and fluxes in a headwater mountain catchment   总被引：1，自引：0，他引：1  

Molly R. Cain  Adam S. Ward  Markus Hrachowitz 《水文研究》2019,33(20):2658-2675

Recent studies have demonstrated that compartmentalized pools of water preferentially supply either plant transpiration (poorly mobile water) or streamflow and groundwater (highly mobile water) in some catchments, a phenomenon referred to as ecohydrologic separation. The omission of processes accounting for ecohydrologic separation in standard applications of hydrological models is expected to influence estimates of water residence times and plant water availability. However, few studies have tested this expectation or investigated how ecohydrologic separation alters interpretations of stores and fluxes of water within a catchment. In this study, we compare two rainfall‐runoff models that integrate catchment‐scale representations of transport, one that incorporates ecohydrologic separation and one that does not. The models were developed for a second‐order watershed at the H.J. Andrews Experimental Forest (Oregon, USA), the site where ecohydrologic separation was first observed, and calibrated against multiple years of stream discharge and chloride concentration. Model structural variations caused mixed results for differences in calibrated parameters and differences in storage between reservoirs. However, large differences in catchment storage volumes and fluxes arise when considering only mobile water. These changes influence interpreted residence times for streamflow‐generating water, demonstrating the importance of ecohydrologic separation in catchment‐scale water and solute transport.  相似文献   

Geomorphic controls on floodplain sediment and soil organic carbon storage in a Scottish mountain river     

Ward Swinnen  Teun Daniëls  Eline Maurer  Nils Broothaerts  Gert Verstraeten 《地球表面变化过程与地形》2020,45(1):207-223

River floodplains constitute an important element in the terrestrial sediment and organic carbon cycle and store variable amounts of carbon and sediment depending on a complex interplay of internal and external driving forces. Quantifying the storage in floodplains is crucial to understand their role in the sediment and carbon cascades. Unfortunately, quantitative data on floodplain storage are limited, especially at larger spatial scales. Rivers in the Scottish Highlands can provide a special case to study alluvial sediment and carbon dynamics because of the dominance of peatlands throughout the landscape, but the alluvial history of the region remains poorly understood. In this study, the floodplain sediment and soil organic carbon storage is quantified for the mountainous headwaters of the River Dee in eastern Scotland (663 km²), based on a coring dataset of 78 floodplain cross-sections. Whereas the mineral sediment storage is dominated by wandering gravel-bed river sections, most of the soil organic carbon storage can be found in anastomosing and meandering sections. The total storage for the Upper Dee catchment can be estimated at 5.2 Mt or 2306.5 Mg ha^-1 of mineral sediment and 0.7 Mt or 323.3 Mg C ha^-1 of soil organic carbon, which is in line with other studies on temperate river systems. Statistical analysis indicates that the storage is mostly related to the floodplain slope and the geomorphic floodplain type, which incorporates the characteristic stream power, channel morphology and the deposit type. Mapping of the geomorphic floodplain type using a simple classification scheme shows to be a powerful tool in studying the total storage and local variability of mineral sediment and soil organic carbon in floodplains. © 2019 John Wiley & Sons, Ltd.  相似文献