Uniform postglacial slip-rate along the central 600 km of the Kunlun Fault (Tibet), from ²⁶Al, ¹⁰Be, and ¹⁴C dating of riser offsets, and climatic origin of the regional morphology     

Jerome Van Der Woerd  Paul Tapponnier  Frederick J. Ryerson  Anne-Sophie Meriaux  Bertrand Meyer  Yves Gaudemer  Robert C. Finkel  Marc W. Caffee  Zhao Guoguang  Xu Zhiqin 《Geophysical Journal International》2002,148(3):356-388

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Controlled source apparent resistivity tensors and their relationship to the magnetotelluric impedance tensor   总被引：2，自引：0，他引：2  

T. Grant Caldwell  Hugh M. Bibby  Colin Brown 《Geophysical Journal International》2002,151(3):755-770

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Marine birds breeding in Penny Strait and Queens Channel, Nunavut, Canada     

Mark L. Mallory  H. Grant Gilchrist 《Polar research》2003,22(2):399-403

Surveys of breeding birds on small islands in Penny Strait and Queens Channel, Nunavut Territory, Canada, were conducted in July 2002 and 2003. Approximately 3600 marine birds were observed, with the most common species being Arctic terns ( Sterna paradisaea , N=2400) and common eiders ( Somateria mollissima borealis , N=620). We observed no Ross's gulls ( Rhodostethia rosed ) in either year, and we found ivory gulls ( Pagophila eburned ) only in 2003, even though these species commonly bred here in the 1970s. This previously unsurveyed region supports numerous breeding marine birds, but reproductive success on these small islands may be dependent on annual ice conditions and consequent movements of Arctic foxes ( Alopex lagopus ).  相似文献   

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment     

Thomas Backhaus  Rolf Altenburger  sa Arrhenius  Hans Blanck  Michael Faust  Antonio Finizio  Paola Gramatica  Matthias Grote  Marion Junghans  Wiebke Meyer  Manuela Pavan  Tobias Porsbring  Martin Scholze  Roberto Todeschini  Marco Vighi  Helge Walter  L. Horst Grimme 《Continental Shelf Research》2003,23(17-19):1757

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.  相似文献   

Tensor time domain electromagnetic resistivity measurements at Ngatamariki geothermal field, New Zealand     

George F. Risk  T. Grant Caldwell  Hugh M. Bibby 《Journal of Volcanology and Geothermal Research》2003,127(1-2):33-54

Experimental measurements in the Ngatamariki geothermal field, North Island, New Zealand were made to test the applicability of the time domain electromagnetic method for detailed investigation of the resistivity structure within a geothermal field. Low-frequency square wave signals were transmitted through three grounded bipole current sources sited about 8 km from the measurement lines. Despite high levels of electrical noise, transient electric field vectors could be determined reliably for times between 0.02 and 3.3 s after each step in the source current. Instantaneous apparent resistivity tensors were then calculated. Apparent resistivity pseudosections along the two measurement lines show smooth variations of resistivity from site to site. Over most of the field the images consistently show a three-layer resistivity structure with a conductive middle layer (3–10 Ωm) representing the conductive upper part of the thermal reservoir. A deep-seated region of low resistivity in the northwest of the field may indicate a conductive structure at about 1 km associated with a deeper diorite intrusion. Measurements sited closer than about 100 m to drillholes appear to have been disturbed by metallic casing in the holes. A change in resistivity structure in the east of the field may indicate a major geological or hydrothermal boundary.  相似文献   

Redetermination of the transformation enthalpies of the xanthoconite–proustite, pyrostilpnite–pyrargyrite and trechmannite–smithite phase transitions     

B. Meyer  F. Scholz 《Physics and Chemistry of Minerals》1997,24(1):50-52

 We report here refined values of the transformation enthalpy for xanthoconite to proustite (54.81 kJ/mol) and pyrostilpnite to pyrargyrite (40.32 kJ/mol). Additionally, the enthalpy for the transformation of trechmannite to smithite (5.82 kJ/mol) has been determined. The refinement was possible by taking into account a previously unknown dependence of electrochemical signals on the amount of substance undergoing the reduction process. Received December 21, 1995/Revised, accepted June 29, 1996  相似文献   

Solar modulation of cosmogenic nuclide production over the last millennium: comparison between C and Be records     

Edouard Bard  Grant M. Raisbeck  Franoise Yiou  Jean Jouzel 《Earth and Planetary Science Letters》1997,150(3-4):453-462

For about the last 30 years it has been recognized that the high frequency component of the tree rings ¹⁴C/¹²C record is dominated by the modulation of the cosmic ray flux by the solar wind. In particular, it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric ¹⁴C/¹²C. During the last millennium other periods of high ¹⁴C/¹²C values were observed but their solar origin is still debatable. In the present work we compare these fluctuations with an independent record of cosmogenic ¹⁰Be measured in ice from the South Pole to check the solar origin of the observed ¹⁴C/¹²C variations. In order to compare quantitatively the results obtained on ¹⁰Be and ¹⁴C, it is necessary to take into account the different behaviour of these two cosmogenic isotopes, and especially the damping effect of the carbon cycle in the case of ¹⁴C. As an input to a 12-box numerical model we used the relative fluctuations of the ¹⁰Be concentrations record measured in South Pole ice and converted it into a synthetic ¹⁴C record. We took into account the fact that ¹⁰Be modulation is enhanced in polar regions due to the orientation of the geomagnetic field. As expected, the fluctuations of the modelled ¹⁴C record are much smaller (a factor of 20) than those observed for the raw ¹⁰Be record. In addition, the variations are smoother and shifted in time by a few decades. The ¹⁰Be-based ¹⁴C variations closely resemble the ¹⁴C measurements obtained on tree rings (R = 0.81). In particular, it is easy to identify periods of maximal ¹⁴C/¹²C which correspond to solar activity minima centred at about 1060, 1320 (Wolf), 1500 (Spörer), 1690 (Maunder) and 1820 (Dalton) yr A.D. Cross-correlation calculations suggest that there is no significant lag between the ¹⁰Be-based ¹⁴C and the tree-ring ¹⁴C records. Our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium.  相似文献   

Effect of scallop shells and sediment grain size on phytoplankton flux to the bed     

C.A. Pilditch  C.W. Emerson  J. Grant 《Continental Shelf Research》1997,17(15):1869-1885

A flume study was made of bed skin friction and phytoplankton (Thalassiosira weissf ogii) deposition about a sea scallop (Placopecten magellanicus) mimic on a coarse (mean grain dia. =1200 μm), medium (615 μm) and fine (170 μm) quarry sand. Bed skin friction immediately upstream, and at one shell diameter downstream of the mimic was 1.2–2.4 times higher than ambient values (8.1 × 10⁻² Pa). Directly downstream of the mimic there was a region of near-zero skin friction. Bed diatom density was correlated with changes in skin friction; after 21 h, cell densities were 36–87% greater in the regions of high skin friction upstream and downstream of scallop than in control experiments. The pattern of bed diatom density about the scallop was similar in the coarse and medium sands, but deposition to the fine bed was not affected by the mimic. Diatom density was significantly correlated with grain diameter; deposition in the coarse bed was 2.3 times higher than in the medium sand, and 7.4 times higher than in the fine sand. A field experiment confirmed that the coarse sand was a greater sink of phytoplankton pigment than the fine sand. Previous studies and scaling arguments suggest that the differences in bed diatom density were controlled by the magnitude of interfacial solute fluxes. Regions of high skin friction about the mimic increased the porewater exchange, resulting in greater concentrations of diatoms retained within the bed. Similarly, the more permeable coarse sand would have a greater rate of porewater exchange than the fine sand, explaining the higher bed diatom density. Differences in the predicted volume of interstitial void space as a function of grain size closely matched the observed differences in bed diatom density. Results suggest that alteration of boundary layer flows by centimetre scale topography such as scallops, increases the flux of particulate organic matter toward the bed, but whether it is retained within the bed, and thus made available to the benthos is dependent on the sediment granularity.  相似文献   

Estimated N2O and CO2 Emissions as Influenced by Agricultural Practices in Canada   总被引：4，自引：0，他引：4  

B. Grant  W. N. Smith  R. Desjardins  R. Lemke  C. Li 《Climatic change》2004,65(3):315-332

The Denitrification-Decompostion (DNDC) model was used to estimate the impact of change in management practices on N₂O emissions in seven major soil regions in Canada, for the period 1970 to 2029. Conversion of cultivated land to permanent grassland would result in the greatest reduction in N₂O emissions, particularly in eastern Canada wherethe model estimated about 60% less N₂O emissions for thisconversion. About 33% less N₂O emissions were predicted for a changefrom conventional tillage to no-tillage in western Canada, however, a slight increase in N₂O emissions was predicted for eastern Canada. GreaterN₂O emissions in eastern Canada associated with the adoption of no-tillage were attributed to higher soil moisture causing denitrification, whereas the lower emissions in western Canada were attributed to less decomposition of soil organic matter in no-till versus conventional tilled soil. Elimination of summer fallow in a crop rotation resulted in a 9% decrease in N₂O emissions, with substantial emissions occurringduring the wetter fallow years when N had accumulated. Increasing N-fertilizer application rates by 50% increased average emissions by 32%,while a 50% decrease of N-fertilizer application decreased emissions by16%. In general, a small increase in N₂O emissions was predicted when N-fertilizer was applied in the fall rather than in the spring. Previous research on CO₂ emissions with the CENTURY model (Smith et al.,2001) allowed the quantification of the combined change in N₂O andCO₂ emissions in CO₂ equivalents for a wide range of managementpractices in the seven major soil regions in Canada. The management practices that have the greatest potential to reduce the combined N₂O andCO₂ emissions are conversion from conventional tillage to permanent grassland, reduced tillage, and reduction of summer fallow. The estimated net greenhouse gas (GHG) emission reduction when changing from cultivated land to permanent grassland ranged from 0.97 (Brown Chernozem) to 4.24 MgCO₂ equiv. ha^–1 y^–1 (BlackChernozem) for the seven soil regions examined. When changing from conventional tillage to no-tillage the net GHG emission reduction ranged from 0.33 (Brown Chernozem) to 0.80 Mg CO₂ equiv. ha^–1 y^–1 (Dark GrayLuvisol). Elimination of fallow in the crop rotation lead to an estimated net GHG emission reduction of 0.43 (Brown Chernozem) to 0.80 Mg CO₂ equiv.ha^–1 y^–1 (Dark Brown Chernozem). The addition of 50% more or 50% less N-fertilizer both resulted in slight increases in combined CO₂ and N₂O emissions. There was a tradeoff in GHG flux with greaterN₂O emissions and a comparable increase in carbon storage when 50% more N-fertilizer was added. The results from this work indicate that conversion of cultivated land to grassland, the conversion from conventional tillage to no-tillage, and the reduction of summerallow in crop rotations could substantially increase C sequestration and decrease net GHG emissions. Based on these results a simple scaling-up scenario to derive the possible impacts on Canada's Kyoto commitment has been calculated.  相似文献   

Analytical methods Of assessing the image quality associated with digital and photographic imaging systems     

Grant H. Thomson 《The Photogrammetric Record》2004,19(107):237-249

The introduction of digital cameras for aerial survey photography and use of scanners with processed aerial film present a number of technical questions concerning the way photography is to be acquired in the future. Among the questions to be addressed are the comparative metric properties of images acquired by each system and the associated image quality characteristics. The new digital camera systems will require very careful appraisal, using well-established methods of assessing metric quality already available to survey organisations. The questions concerning image quality are more difficult to answer, as they require very specialised instrumentation if measurements are to be made directly in practice. Over the course of the past several decades a more analytical approach to assessing image quality has emerged, and one that may be used by individuals. The method is particularly effective where information on the micro-image characteristics of products is made available by the manufacturers concerned. An outline is given of some considerations that need to be taken into account when using an analytical approach, with references given for further reading.  相似文献