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排序方式: 共有141条查询结果,搜索用时 15 毫秒
1.
John Logan 《Ground water》1986,24(3):382-382
Abstract. Execution time of many programs can be markedly shortened by (a) defining frequently used constants in assignment statements or placing them in arrays and by (b) avoiding or minimizing the use of exponentials. 相似文献
2.
With recent changes in the ways that state agencies are implementing their environmental policies, the line between public and private is becoming increasingly blurred. This includes shifts from state-led implementation of environmental policies to conservation plans that are implemented and managed by multi-sectoral networks of governments, the private sector and environmental non-governmental organizations (ENGOs). This paper examines land trusts as private conservation initiatives that become part of neoliberal governance arrangements and partnerships that challenge our conceptions of environmental preservation and democratic participation. The paper starts with an examination of the concept of neoliberalized environmental governance. Next, it addresses the shifting social constructions of property and land in the context of protecting large scale ecosystems. Through a case study of the extension of new environmental governance arrangements on the Oak Ridges Moraine in Ontario, we examine the relationships that have formed between different levels of the state and environmental non-governmental organizations. Finally, we analyze the expansion of land trusts and private conservation initiatives that are predicated on private land ownership and the commodification of nature, the emerging discourses and practices of private conservation, and how these are implicated in the privatization and neoliberalization of nature. 相似文献
3.
4.
A New Genus and Species of Rhynchonellid (Brachiopoda, Recent) from Submarine Caves in the Mediterranean Sea 总被引:1,自引:0,他引:1
Abstract. A new rhynchonellid brachiopod genus Tethyrhynchia , with type species Tethyrhynchia mediterranea n. sp., is described from specimens discovered in dark zones of submarine caves along the Mediterranean coast of France between Marseille and La Ciotat, and also at Zembra Island, off the Gulf of Tunis, Tunisia. Other brachiopods occurring with this diminutive rhynchonellid are also small and include the megathyridids Argyrotheca cistellula and Megathiris detruncata . This is the first recorded occurrence of a rhynchonellid from the Mediterranean Sea. The new form is apparently neotenous, in that the lophophore in adults never develops beyond the trocholophous stage. A new type of rhynchonellid crus, crescentic in profile and here named the lunifer type, is described. The new genus is assigned to the new family Tethyrhynchiidae , and comparisons are made with other extant rhynchonellid genera. 相似文献
5.
ABSTRACT This study investigated the impact of pastoral land use and nutrient and fine sediment inputs on Microcoleus autumnalis and filamentous algae-dominated mats, and benthic chlorophyll-a in streams (lower North Island, New Zealand). Surveying and sampling was undertaken monthly at 61 sites spanning a wide gradient in catchment cover and environmental conditions. Two boosted regression tree models were built. The first models included pastoral land cover and five environmental variables as predictors. In the second model pastoral land cover was replaced by nutrient/sediment data. The abundance of the two mat types and chlorophyll-a increased when pastoral land cover was between 20% and 70% (model 1). Replacement of pastoral land cover by nutrient/sediment data (model 2) slightly improved the model fit for all three periphyton variables. Microcoleus autumnalis-dominant mats increased with dissolved inorganic nitrogen concentrations up to ca. 0.6?mg?L?1, and in streams with more frequent flushes. In contrast, filamentous algal-dominated mats increased with turbidity, and in streams with less frequent flushes. Chlorophyll-a generally followed the response of the dominant periphyton type. Increased knowledge on responses of specific periphyton types, rather than total biomass, to environmental variables is essential to guide effective management strategies. 相似文献
6.
W. R. Skinner M. D. Flannigan B. J. Stocks D. L. Martell B. M. Wotton J. B. Todd J. A. Mason K. A. Logan E. M. Bosch 《Theoretical and Applied Climatology》2002,71(3-4):157-169
Summary
In Canada, the average annual area of burned forest has increased from around 1 million ha in the 1970’s to over 2.5 million
ha in the 1990’s. A previous study has identified the link between anomalous mid-tropospheric circulation at 500 hPa over
northern North America and wildland fire severity activity in various large regions of Canada over the entire May to August
fire season. In this study, a northern North American study region of the hemispheric gridded 5° latitude by 10° longitude
500 hPa dataset is identified and analysed from 1959 to 1996 for a sequence of six monthly periods through the fire season,
beginning in April and ending in September. Synoptic types, or modes of upper air behavior, are determined objectively by
the eigenvector method employing K-means cluster analysis. Monthly burned areas from the Canadian Large Fire Database (LFDB)
for the same period, 1959 to 1996, are analysed in conjunction with the classified monthly 500 hPa synoptic types. Relationships
between common monthly patterns of anomalous upper flow and spatial patterns of large fire occurrence are examined at the
ecozone level. Average occurrence of a monthly synoptic type associated with very large area burned is approximately 18% of
the years from 1959 to 1996. The largest areas burned during the main fire (May to August) season occur in the western Boreal
and Taiga ecozones – the Taiga Plains, Taiga Shield, Boreal West Shield and Boreal Plains. Monthly burned areas are also analysed
temporally in conjunction with a calculated monthly zonal index (Zim) for two separate areas defined to cover western and eastern Canada. In both western and eastern Canada, high area burned
is associated with synoptic types with mid-tropospheric ridging in the proximity of the affected region and low Zim with weak westerlies and strong meridional flow over western Canada.
Received April 3, 2001 Revised July 13, 2001 相似文献
7.
Bitumens extracted from 2.7 to 2.5 billion-year-old (Ga) shales of the Fortescue and Hamersley Groups in the Pilbara Craton, Western Australia, contain traces of molecular fossils. Based on a combination of molecular characteristics typical of many Precambrian bitumens, their consistently and unusually high thermal maturities, and their widespread distribution throughout the Hamersley Basin, the bitumens can be characterized as ‘probably of Archean age’. Accepting this interpretation, the biomarkers open a new window on Archean biodiversity. The presence of hopanes in the Archean rocks confirms the antiquity of the domain Bacteria, and high relative concentrations of 2α-methylhopanes indicate that cyanobacteria were important primary producers. Oxygenic photosynthesis therefore evolved > 2.7 Ga ago, and well before independent evidence suggests significant levels of oxygen accumulated in the atmosphere. Moreover, the abundance of cyanobacterial biomarkers in shales interbedded with oxide-facies banded iron formations (BIF) indicates that although some Archean BIF might have been formed by abiotic photochemical processes or anoxygenic phototrophic bacteria, those in the Hamersley Group formed as a direct consequence of biological oxygen production. Biomarkers of the 3β-methylhopane series suggest that microaerophilic heterotrophic bacteria, probably methanotrophs or methylotrophs, were active in late Archean environments. The presence of steranes in a wide range of structures with relative abundances like those from late Paleoproterozoic to Phanerozoic sediments is convincing evidence for the existence of eukaryotes in the late Archean, 900 Ma before visible fossil evidence indicates that the lineage arose. Sterol biosynthesis in extant eukaryotes requires molecular oxygen. The presence of steranes together with biomarkers of oxygenic photosynthetic cyanobacteria suggests that the concentration of dissolved oxygen in some regions of the upper water column was equivalent to at least ∼1% of the present atmospheric level (PAL) and may have been sufficient to support aerobic respiration. 相似文献
8.
Arid karst landscapes that have been degraded by human activities provide a challenge for rehabilitation and an opportunity
to test ideas about the stability and resilience of limestone ecosystems. The Nullarbor Plain is the largest arid karst area
in Australia (220 000 km2) and is divided into extensive closed karstic depressions separated by low rocky ridges, while the dominant vegetation is
chenopod shrubland. Since European settlement there has been considerable change in the vegetation, with significant reduction
in shrub and grass cover over large areas of the plain. These changes are related to a state and transition model of vegetation
dynamics which incorporates climatic variability, fire history and grazing pressure from sheep, kangaroos and rabbits. A partial
sediment budget using 137Cs inventories reveals local and regional patterns of soil redistribution within this arid karst landscape. Rehabilitation
of eroded soil in pastoral lands has been accomplished at several sites but is labour intensive and vulnerable to climatic
fluctuations. Given the low stock numbers, limited number of people involved, and poor economic returns, it would be sensible
to make pastoral activities on the Nullarbor secondary to conservation priorities. This would necessitate a change in land
ethic to stewardship, with emphasis on rehabilitation and control of feral animals. Management of increased numbers of visitors
to the caves and karst also requires that resource inventories and management plans for each area be drawn up and used.
Received: 1 June 1995 · Accepted: 4 December 1995 相似文献
9.
John M. Logan 《Environmental Geology》2004,46(3-4):456-467
Studies of marble panels from the exterior of two buildings document the processes leading to bowing of the material. Bowing of panels is most extensive in those areas that are exposed to direct or reflected thermal energy. The thermal anisotropic behavior of calcite results in grain-boundary separation, grain sliding and microfracturing. The resulting loss of strength is one factor leading to bowing. The development of bows further reduces the panel strength as the outer portions elongate by inelastic deformation mechanisms. Laboratory experiments cycling marble samples for over 200 cycles at three temperatures up to 107°C above room conditions show similar strength losses as the natural situation. The second factor contributing to the bowing process is the release of residual elastic strain. The strain is in part stored in the marble from its geologic history, but may also be accumulated during thermal cycling due to the properties of calcite. Marble panels have been found to bow when stored outside, but not attached to any framework, indicating that the release of residual strain is a critical factor in producing the bows. 相似文献
10.
Sabine K.J. Cochrane Stanislav G. Denisenko Paul E. Renaud Christopher S. Emblow William G. Ambrose Jr. Ingrid H. Ellingsen Jofrid Skarhamar 《Journal of Sea Research》2009,61(4):222-233
Benthic faunal assemblages were analysed from 47 stations in the central and southern parts of the Barents Sea, together with sedimentary and water column parameters, daily ice records and modelled integrated primary productivity. Sampling spanned areas influenced by Atlantic Water (AW) to those lying under Arctic Water (ArW), and included stations with mixed water masses. Ice cover suppressed water column productivity in the northern areas. Three main faunal groups were identified, based on similarity of numerical faunal composition. The northern and southern faunal groups were separated by the northernmost penetration of AW in the bottom water and the third group, the Hopen group, was influenced by modified bank water. Faunal abundances were significantly higher within the southern faunal group relative to the northern group, but the numbers of taxa present were similar. The particularly rich fauna of the Hopen group reflected sediment heterogeneity and tight pelagic–benthic coupling. These results suggest that a retreat and thinning of the ice cover in the Barents Sea likely will result in the northern parts of the Barents Sea becoming more Atlantic in character, with a higher productivity at the sea floor. 相似文献