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排序方式: 共有655条查询结果,搜索用时 15 毫秒
81.
This paper offers an exploratory investigation of the effects of a child's age on three behavioral constructs (awareness space, activity space, and attitude) concerning a downtown shopping center in Bristol, England. The data are elicited from three samples of Bristol school children defined according to age and are analyzed using statistical inferential procedures. The results disclose that awareness space and activity space consistently increase with age. In addition, attitudinal responses to specific features of the shopping center exhibit a gradual change over a long-term period. 相似文献
82.
The proximity of the Great Barrier Reef (GBR) Marine Park to areas of intensive agriculture and increasing urbanisation places the park under potential threat of contamination by land-based pollutants. Passive samplers were deployed at inshore reef and river mouth sites in the Wet Tropics region of the GBR during a dry and a wet season to measure levels of land-based organic pollutants in this environment. Two types of passive sampling devices were deployed: (i) a polar sampler, which can be used to monitor polar herbicides and (ii) semipermeable membrane devices (SPMDs) which sequester more hydrophobic compounds (e.g. PAHs, chlorpyrifos). Herbicides (diuron, simazine, atrazine, hexazinone and/or flumeturon) were detected at low concentrations (ng L−1) at all sites sampled and in both seasons. Chlorpyrifos was not detected while PAHs were present in SPMDs at levels below limits of detection. The results show that the GBR environment does contain low levels of organic pollutants and that passive sampling provides a sensitive monitoring tool for measuring waterborne organic pollutants. 相似文献
83.
Melanie Krips Andreas Eckart Roberto Neri Joerg-Uwe Pott Jens Zuther Julia Scharwächter Thomas Bertram 《Astrophysics and Space Science》2005,295(1-2):95-100
We present new interferometric observations of the molecular gas distribution and kinematics in the nuclei of different active galaxies at high angular resolution and high sensitivity carried out with the IRAM Plateau de Bure interferometer (PdBI). The observations cover galaxies in a redshift range of 0.03–1.4. We have so far observed five different active galaxies: NGC3718, NGC1068, HE1029–1831, 3C48 and Q0957+561. The first two objects belong to the NUGA (NUclei of GAlaxies) project – an international collaboration mainly between Spain, France and Germany – containing about 30 Seyfert and LINER galaxies. Both are at the same distance of 14Mpc and show a warped gas and dust disk. The new mosaic map of NGC3718 corrected for short-spacing effects with IRAM 30 m observations well demonstrates the existence of the warped gas disk with several secondary maxima in the projected gas distribution caused by orbit crowding effects. Based on these new data we have improved recent simulations of the warped disk in NGC3718. HE1029–1831 and 3C48 are nearby QSOs. HE1029–1831 is taken out of the Cologne nearby QSO sample. The maps of the integrated CO(1–0) and CO(2–1) emission clearly show that the molecular gas is mostly related to the central bulge with a non-negligible fraction distributed along the bar known from optical observations. Our new CO data of 3C48 unveil new information about the kinematics of its molecular gas complementing and improving further studies based on previous infrared observations and detailed multi-particle simulations. Finally, new measurements of the CO(1–0) line in Q0957+561 – a highly-red-shifted, gravitationally lensed quasar – will be presented as a link to earlier evolutionary stages of active galaxies and their hosts. 相似文献
84.
Evaluation of an ensemble of Arctic regional climate models: spatiotemporal fields during the SHEBA year 总被引:1,自引:1,他引:0
A.?RinkeEmail author K.?Dethloff J.?J.?Cassano J.?H.?Christensen J.?A.?Curry P.?Du E.?Girard J.-E.?Haugen D.?Jacob C.?G.?Jones M.?K?ltzow R.?Laprise A.H.?Lynch S.?Pfeifer M.?C.?Serreze M.?J.?Shaw M.?Tjernstr?m K.?Wyser M.??agar 《Climate Dynamics》2006,26(5):459-472
Simulations of eight different regional climate models (RCMs) have been performed for the period September 1997–September
1998, which coincides with the Surface Heat Budget of the Arctic Ocean (SHEBA) project period. Each of the models employed
approximately the same domain covering the western Arctic, the same horizontal resolution of 50 km, and the same boundary
forcing. The models differ in their vertical resolution as well as in the treatments of dynamics and physical parameterizations.
Both the common features and differences of the simulated spatiotemporal patterns of geopotential, temperature, cloud cover,
and long-/shortwave downward radiation between the individual model simulations are investigated. With this work, we quantify
the scatter among the models and therefore the magnitude of disagreement and unreliability of current Arctic RCM simulations.
Even with the relatively constrained experimental design we notice a considerable scatter among the different RCMs. We found
the largest across-model scatter in the 2 m temperature over land, in the surface radiation fluxes, and in the cloud cover
which implies a reduced confidence level for these variables.
An erratum to this article can be found at 相似文献
85.
Although widely investigated in relation to acid mine drainage systems at pH > 1.0, we know little about the impact of sulfuric acid (H2SO4) on the geochemistry and mineralogy of clays at pH < 1.0 (including negative pH values). Thus, laboratory batch experiments were conducted on three mixed clay samples with different mass ratios of phyllosilicates (smectite, illite, and kaolinite) to investigate the impact of H2SO4 from pH 1.0 to −3.0 for exposure periods of 14, 90, 180, and 365 days. Si and Al K- and L2,3-edge X-ray absorption near edge structure (XANES) spectroscopy were employed on these samples to determine the chemical and structural changes that occur during acidic dissolution of phyllosilicates that cannot be distinguished using X-ray diffraction analyses. A series of silicate, phyllosilicate, and Al-bearing standard compounds were also studied to provide an explanation for the observed changes in the clay samples. The Si XANES results indicated the preferential dissolution of the phyllosilicates (pH ? 1.0, t ? 14 d), the persistence of quartz even at pH ? −3.0 and t ? 365 d, and the formation of an amorphous silica-like phase that was confined to the surface layer of the altered clay samples at pH ? 0.0 and t ? 90 d). Al XANES results demonstrated dissolution of Al-octahedral layers (pH ? 1.0, t ? 14 d), the persistence of four-fold relative to six-fold coordinated Al, and the precipitation of an Al-SO4-rich phase (pH ? −1.0, t ? 90 d). An existing conceptual model of phyllosilicate dissolution under extremely acidic conditions was modified to include the results of this study. 相似文献
86.
Zircon Hf Isotopic Evidence for Mixing of Crustal and Silicic Mantle-derived Magmas in a Zoned Granite Pluton, Eastern Australia 总被引:3,自引:0,他引:3
Zircon Hf isotopic data from a zoned pluton of the Moonbi supersuite,New England batholith, eastern Australia, are consistent withmagma mixing between two silicic melts, each derived from isotopicallydistinct sources. Although zircons from three zones within theWalcha Road pluton give a U–Pb crystallization age of249 ± 3 Ma, zircon populations from each zone have arange in Hf. Zircons from the mafic hornblende–biotitemonzogranite pluton margin and intermediate zones have Hf +5to +11, whereas those from the more felsic centre of the plutonhave Hf +7 to +16, representing a total variation of 11 Hfunits. The Lu–Hf depleted mantle model ages range from650 to 250 Ma, with the younger zircons present only in thefelsic pluton centre. The variation in Hf indicates the involvementof silicic melts from at least two sources, one a crustal componentwith a Neoproterozoic model age and the other a primitive mantle-derivedcomponent with model ages similar to the U–Pb crystallizationage of the pluton. The zircons reflect the isotopic compositionsof the different proportions of crustal-derived silicic melt,relative to mantle-derived silicic melt, between melt generationand final pluton construction. The Walcha Road pluton is consideredto have formed by incremental assembly of progressively morefelsic melt batches resulting from mixing, replenishment andcrystal–melt separation, with final pluton constructioninvolving mechanical concentration as zones of crystal mush.The zoned pluton and, more broadly, the Moonbi supersuite provideexamples of magma mixing by which the more silicic units havemore juvenile isotopic compositions as a result of increasingproportions of residual melt from basalt fractionation, relativeto crustal partial melt. KEY WORDS: Australia; granite magma mixing; zircon; zoned pluton; Hf isotopes 相似文献
87.
88.
89.
Flavia Burger Alvaro Ayala David Farias Thomas E. Shaw Shelley MacDonell Ben Brock James McPhee Francesca Pellicciotti 《水文研究》2019,33(2):214-229
We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response, and runoff generation from a high‐elevation catchment in central Chile over the period 2000–2015 to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000 and 2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years. 相似文献
90.
Bi Yu Chen Donggen Wang Shih-Lung Shaw Hui-Ping Chen 《International journal of geographical information science》2017,31(4):783-804
Travel time uncertainty has significant impacts on individual activity-travel scheduling, but at present these impacts have not been considered in most accessibility studies. In this paper, an accessibility evaluation framework is proposed for urban areas with uncertain travel times. A reliable space-time service region (RSTR) model is introduced to represent the space-time service region of a facility under travel time uncertainty. Based on the RSTR model, four reliable place-based accessibility measures are proposed to evaluate accessibility to urban services by incorporating the effects of travel time reliability. To demonstrate the applicability of the proposed framework, a case study using large-scale taxi tracking data is carried out. The results of the case study indicate that the proposed accessibility measures can evaluate large-scale place-based accessibility well in urban areas with uncertain travel times. Conventional place-based accessibility indicators ignoring travel time reliability can significantly overestimate the accessibility to urban services. 相似文献