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71.
Elaine M. FitzGerald Christopher J. Bean & Ronan Reilly 《Geophysical Prospecting》1999,47(6):1031-1044
Borehole-wall imaging is currently the most reliable means of mapping discontinuities within boreholes. As these imaging techniques are expensive and thus not always included in a logging run, a method of predicting fracture frequency directly from traditional logging tool responses would be very useful and cost effective. Artificial neural networks (ANNs) show great potential in this area. ANNs are computational systems that attempt to mimic natural biological neural networks. They have the ability to recognize patterns and develop their own generalizations about a given data set. Neural networks are trained on data sets for which the solution is known and tested on data not previously seen in order to validate the network result. We show that artificial neural networks, due to their pattern recognition capabilities, are able to assess the signal strength of fracture-related heterogeneity in a borehole log and thus fracture frequency within a borehole. A combination of wireline logs (neutron porosity, bulk density, P-sonic, S-sonic, deep resistivity and shallow resistivity) were used as input parameters to the ANN. Fracture frequency calculated from borehole televiewer data was used as the single output parameter. The ANN was trained using a back-propagation algorithm with a momentum learning function. In addition to fracture frequency within a single borehole, an ANN trained on a subset of boreholes in an area could be used for prediction over the entire set of boreholes, thus allowing the lateral correlation of fracture zones. 相似文献
72.
Deon E. Barnes Peter J. Wright Sandra M. Graham Elaine A. Jones-Watson 《Geostandards and Geoanalytical Research》2000,24(2):183-195
The determination of cyanide in various forms is important for industrial processes as well as for environmental investigations and monitoring associated with these processes. The accurate determination of cyanide is difficult for various reasons. Depending on the pH of the solution, cyanide is present both in molecular form (HCN) and ionic form (CN). Furthermore, cyanide is a good complexing reagent and reacts with almost all cations resulting in complexes with widely varying properties, such as stabilities, solubilities and rates of reaction. Cyanide also breaks down in sunlight and air, so that sampling and sample treatment become very important aspects to consider in the methodologies. During the last fifty years the determination of cyanide has been approached from various angles and a myriad of methods has been developed for its determination. This study represents a survey of methods commonly used in industrial laboratories for the analysis of cyanide-containing solutions. An overview of the nomenclature often used for the various forms of cyanides is discussed and the values resulting from a particular analysis will be interpreted. Most common interferences in samples originating from gold processing plants will be discussed. 相似文献
73.
Helen M. Johnston Elaine M. Sadler Russell Cannon Scott M. Croom Nicholas P. Ross Donald P. Schneider 《Monthly notices of the Royal Astronomical Society》2008,384(2):692-700
We present an analysis of the optical spectra of a volume-limited sample of 375 radio galaxies at redshift 0.4 < z < 0.7 from the 2dF-SDSS (Sloan Digital Sky Survey) Luminous Red Galaxy (LRG) and QSO (quasi-stellar object) (2SLAQ) redshift survey. We investigate the evolution of the stellar populations and emission-line properties of these galaxies. By constructing composite spectra and comparing with a matched sample of radio-quiet sources from the same survey, we also investigate the effect on the galaxy of the presence of an active nucleus.
The composite spectra, binned by redshift and radio luminosity, all require two components to describe them, which we interpret as an old and a younger population. We found no evolution with redshift of the age of the younger population in radio galaxies, nor were they different from the radio-quiet comparison sample. Similarly, there is no correlation with radio power, with the exception that the most powerful radio sources ( P1.4 > 1026 W Hz−1 ) have younger stars and stronger emission lines than the less powerful sources. This suggests that we have located the threshold in radio power where strong emission lines 'switch on', at radio powers of around 1026 W Hz−1 . Except for the very powerful radio galaxies, the presence of a currently active radio active galactic nucleus (AGN) does not appear to be correlated with any change in the observed stellar population of a luminous red galaxy at z ∼ 0.5 . 相似文献
The composite spectra, binned by redshift and radio luminosity, all require two components to describe them, which we interpret as an old and a younger population. We found no evolution with redshift of the age of the younger population in radio galaxies, nor were they different from the radio-quiet comparison sample. Similarly, there is no correlation with radio power, with the exception that the most powerful radio sources ( P
74.
Robinson CD Craft JA Moffat CF Davies IM Brown ES Megginson C 《Marine environmental research》2004,58(2-5):147-150
Understanding the ecological significance of oestrogenic biomarker responses, seen in field surveys of some UK estuarine fish, requires a suitable model to link biochemical and reproductive effects. The sand goby (Pomatoschistus minutus) is a common inshore fish that has been successfully bred in laboratory aquaria. Juvenile sand goby were continuously exposed to 17beta-oestradiol (E2) during gonadal maturation, and their subsequent reproductive success investigated. Exposure endpoints included hepatic vitellogenin (VTG) mRNA expression and maturation (male nuptial colouration, sperm duct gland- and gonado-somatic indices (SDGSI, GSI)). Reproductive endpoints included spawning behaviour, brood size, fertility and population-level fertile egg production. Measured E2 exposure concentrations were <5 (controls), 17, 71 and 530 ngl(-1). Male maturation decreased with increasing E2 concentration. VTG mRNA expression increased with E2 concentration, but not with duration of exposure. Reproductive endpoints showed progressive impairment with increasing E2 concentration. For most endpoints, the lowest observed effect concentration (LOEC) was 71 ngl(-1), and EC50s were in the range 87-165 ngl(-1). Pre-breeding male colouration, VTG expression and SDGSI were good predictors of subsequent population-level fertile egg production, but GSI was not. The sensitivity of oestrogenic markers in sand goby are comparable to those used in other species, and feral fish populations exhibiting such oestrogenic responses at molecular and organ levels are likely to have reduced fertile egg production. 相似文献
75.
Today’s forests are largely viewed as a natural asset, growing in a climate envelope, which favors natural regeneration of
species that have adapted and survived the variability’s of past climates. However, human-induced climate change, variability
and extremes are no longer a theoretical concept. It is a real issue affecting all biological systems. Atmospheric scientists,
using global climate models, have developed scenarios of the future climate that far exceed the traditional climate envelope
and their associated forest management practices. Not all forests are alike, nor do they share the same adaptive life cycles,
feedbacks and threats. Much of tomorrow’s forests will become farmed forests, managed in a pro-active, designed and adaptive
envelope, to sustain multiple products, values and services. Given the life cycle of most forest species, forest management
systems will need to radically adjust their limits of knowledge and adaptive strategies to initiate, enhance and plan forests
in relative harmony with the future climate. Protected Areas (IUCN), Global Biosphere Reserves (UNESCO) and Smithsonian Institution
sites provide an effective community-based platform to monitor changes in forest species, ecosystems and biodiversity under
changing climatic conditions. 相似文献
76.
77.
Ross MS Pulster EL Ejsmont MB Chow EA Hessel CM Maruya KA Wong CS 《Marine pollution bulletin》2011,63(5-12):548-555
To investigate the potential for enantioselective transformation and accumulation, the enantiomer distributions of seven polychlorinated biphenyl (PCB) atropisomers were measured in the sediment and biota from a sub-tropical estuary heavily contaminated with Aroclor 1268, a technical mixture of highly chlorinated PCB congeners. Enantiomer fractions (EFs) of PCBs 91, 95, 136, 149, 174, 176, and 183 in marsh sediment, invertebrate, forage and predatory fish species, and bottlenose dolphins were determined. Non-racemic EFs greater than 0.75 were found in sediments for PCBs 136 and 174, likely the result of microbial dechlorination. Although enantiomer fractions in grass shrimp (Palaemonetes spp.) mirrored those of sediment, fish species had EFs that differed significantly from sediment or grass shrimp. Similarly, bottlenose dolphins were also found to contain non-racemic quantities of PCBs 91, 136, 174, 176, and 183. Non-racemic EFs in these biota were likely a result of both uptake of non-racemic proportions of PCBs from the diet and enantioselective biotransformation. 相似文献
78.
Elaine J. Hallisey 《The Professional geographer》2005,57(3):350-364
This article examines the concept of cartographic visualization. The value of cartographic visualization as an essential component in the study of geographic phenomena is discussed. Ontological and epistemological perspectives are addressed, with examinations of positivist, realist, postmodern, feminist, and anarchist approaches to visualization. Critiques of cartographic visualization from social theorists and quantitative positivists are presented. The author asserts that cartographic visualization is not restricted to any one particular epistemological framework but may combine methods of knowledge production. For comprehensive analysis of spatial data, cartographic visualization must be included along with other qualitative and quantitative analysis. 相似文献
79.
Annette Spies Elaine D. Nutbrown Timothy R. Parsons 《Estuarine, Coastal and Shelf Science》1983,17(1):97-105
An experimental approach was used in determining which factors, natural or man made, had the greatest impact on estuarine microplankton ecology. In microcosms, filled with natural water of <5‰, 10‰, 18‰ and > 26‰ salinity, the impact of high organic load (glucose), shading, Cu and a heavy metal mixture on the microplankton populations was monitored. Naturally occurring perturbations were of much greater impact to estuarine ecology than the addition of heavy metals in concentrations five to ten times that which are known to occur in moderately polluted estuaries. 相似文献
80.
E. E. Wheaton 《Natural Hazards》1984,5(1):53-63
Dust storms are quite frequent in the Canadian Prairies, but few scientific studies of prairie dust storms exist. The droughts of the 1980s have resulted in many dust storms, even in the winter. Dust storms can no longer be considered just phenomena of the past. Dust storms are defined and examples are provided. The effects of dust storms are numerous, costly and severe. They include soil degradation, crop damage, water and air quality deterioration, and health problems. The climatological analysis of prairie dust storms is in its infancy. Much more information about prairie dust storms is needed in order to control or avoid their impacts. 相似文献