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151.
152.
The inner parts of many of the western world's metropolitan areas are currently suffering such drastic decline that many governments are attempting to rejuvenate their economic fortunes This is the context in which the present study is set, focusing attention on five major English cities — London, Manchester, Birmingham, Nottingham and Leicester — and using census employment and worktravel data for small areas. The study first reports on the relationships between the skills offered by residents, both male and female, and those demanded by employers in inner city areas. In addition to the consideration of the detailed variety of manufacturing and servicing activities taking place, an examination of the office and non-office components of both is undertaken. The second main aspect of the study considers the patterns of worktravel movement linking the places of residence and workplaces so described. The research concludes with a view on the policy implications of the results in the light of the overall context of the rejuvenation of inner city areas.  相似文献   
153.
The giant East China Mesozoic metallogenic province hosts some of the World’s largest resources of tungsten, tin, molybdenum, antimony and bismuth. Ores of gold, silver, mercury, lead, zinc, copper, uranium and iron are also of major importance. The province and its constituent metallogenic belts or regions (South China; Middle–Lower Yangtze River Valley; East Qinling–Dabie; Interior of North China Craton; Yan-Liao and North-east China) are the products of several pulses of igneous activity and mineralisation between ~240 and ~80 Ma. Each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the Mesozoic. This geodynamic evolution is linked to a complex series of tectonic events, involving far-field-subduction, plate collisions, crustal thickening, post-collision collapse and rifting.  相似文献   
154.
Mortality in longline fisheries is one of the most critical global threats to some seabird species. Underwater setting technology may offer an effective and commercially viable solution. The underwater setting chute for pelagic longline fisheries releases baited hooks underwater, out of sight and reach of diving seabirds. Results from a study in the Hawaii pelagic longline tuna fishery indicate that the underwater setting chute is the most effective technology tested to date to minimize seabird capture in this fishery. The chute eliminated seabird capture during this short-term trial. During control replicates, the capture rate was 4.24 captures per 1000 hooks and when normalized for albatross abundance, the rate was 0.114 captures per 1000 hooks per albatross. Expressed as contacts per 1000 hooks per albatross, the chute was 95% effective at reducing albatross contacts with fishing gear compared to a control.The chute was practical for use and design and installation improvements are likely possible to make the chute more palatable for uptake by industry. The chute has the added benefit of increasing fishing efficiency. The cost for purchasing and installing the chute would be recouped after only a maximum of two fishing trips. Based on an assessment of bait retention and hook setting interval when using the chute versus setting conventionally, vessels would experience a gain in efficiency of between 14.7% and 29.6% when albatrosses are abundant. Economic incentives are essential to abate global seabird mortality in longline fisheries.  相似文献   
155.
156.
The impacts of climate change on river flood risk at the global scale   总被引:6,自引:0,他引:6  
This paper presents an assessment of the implications of climate change for global river flood risk. It is based on the estimation of flood frequency relationships at a grid resolution of 0.5?×?0.5°, using a global hydrological model with climate scenarios derived from 21 climate models, together with projections of future population. Four indicators of the flood hazard are calculated; change in the magnitude and return period of flood peaks, flood-prone population and cropland exposed to substantial change in flood frequency, and a generalised measure of regional flood risk based on combining frequency curves with generic flood damage functions. Under one climate model, emissions and socioeconomic scenario (HadCM3 and SRES A1b), in 2050 the current 100-year flood would occur at least twice as frequently across 40 % of the globe, approximately 450 million flood-prone people and 430 thousand km2 of flood-prone cropland would be exposed to a doubling of flood frequency, and global flood risk would increase by approximately 187 % over the risk in 2050 in the absence of climate change. There is strong regional variability (most adverse impacts would be in Asia), and considerable variability between climate models. In 2050, the range in increased exposure across 21 climate models under SRES A1b is 31–450 million people and 59 to 430 thousand km2 of cropland, and the change in risk varies between ?9 and +376 %. The paper presents impacts by region, and also presents relationships between change in global mean surface temperature and impacts on the global flood hazard. There are a number of caveats with the analysis; it is based on one global hydrological model only, the climate scenarios are constructed using pattern-scaling, and the precise impacts are sensitive to some of the assumptions in the definition and application.  相似文献   
157.
A hydrological investigation was conducted in a small headwater peatland located in the Experimental Lakes Area, north-western Ontario, Canada, to determine the subsurface and surface flow paths within the peatland, and between the peatland and an adjacent forested upland during baseflow and storm flow conditions. Distinct zones of groundwater recharge and discharge were observed within the peatland. These zones are similar to those found in much larger flow systems even though the peatland was only influenced by local groundwater flow. Groundwater emerging in seeps and flowing beneath the peatland sustained the surface wetness of the peatland and maintained a constant baseflow. The response of the peatland stream to summer rain events was controlled by peatland water table position when the basin was dry and antecedent moisture storage on the uplands when the basin was wet. The magnitude and timing of peak runoff during wet conditions were controlled by the degree of hydrological connectivity between the surrounding upland terrain and the peatland. © 1998 John Wiley & Sons, Ltd.  相似文献   
158.
Lunar seismic data from three Apollo seismometers are interpreted to determine the structure of the Moon's interior to a depth of about 100 km. The travel times and amplitudes ofP arrivals from Saturn IV B and LM impacts are interpreted in terms of a compressional velocity profile. The most outstanding feature of the model is that, in the Fra Mauro region of Oceanus Procellarum, the Moon has a 65 km thick layered crust. Other features of the model are: (i) rapid increase of velocity near the surface due to pressure effects on dry rocks, (ii) a discontinuity at a depth of about 25 km, (iii) near constant velocity (6.8 km/s) between 25 and 65 km deep, (iv) a major discontinuity at 65 km marking the base of the lunar crust, and (v) very high velocity (about 9 km/s) in the lunar mantle below the crust. Velocities in the upper layer of the crust match those of lunar basalts while those in the lower layer fall in the range of terrestrial gabbroic and anorthositic rocks.Lamant-Doherty Geological Observatory Contribution No. 1768.  相似文献   
159.
160.
ABSTRACT Mixed‐sand‐and‐gravel beaches are a distinctive type of coarse‐clastic beach. Ground‐penetrating radar (GPR) and photographic records of previous excavations are used to investigate the stratigraphy and internal sedimentary structure of mixed‐beach deposits at Aldeburgh in Suffolk, south‐east England. The principles of radar stratigraphy are used to describe and interpret migrated radar reflection profiles obtained from the study site. The application of radar stratigraphy allows the delineation of both bounding surfaces (radar surfaces) and the intervening beds or bed sets (radar facies). The deposits of the main backshore berm ridge consist of seaward‐dipping bounding surfaces that are gently onlapped by seaward‐dipping bed sets. Good correspondence is observed between a sequence of beach profiles, which record development of the berm ridge on the backshore, and the berm ridge's internal structure. The beach‐profile data also indicate that backshore berm ridges at Aldeburgh owe their origin to discrete depositional episodes related to storm‐wave activity. Beach‐ridge plain deposits at the study site consist of a complex, progradational sequence of foreshore, berm‐ridge, overtop and overwash deposits. Relict berm‐ridge deposits, separated by seaward‐dipping bounding surfaces, form the main depositional element beneath the beach‐ridge plain. However, the beach ridges themselves are formed predominantly of vertically stacked overtop/overwash units, which lie above the berm‐ridge deposits. Consequently, beach‐ridge development in this progradational, mixed‐beach setting must have occurred when conditions favoured overtopping and overwashing of the upper beachface. Interannual to decadal variations in wave climate, antecedent beach morphology, shoreline progradation rate and sea level are identified as the likely controlling factors in the development of such suitable conditions.  相似文献   
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