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41.
近几年,大学生就业难的问题日益凸显,用人单位对毕业生工作经验的要求是谋职的重要环节之一,特别是对测绘工程专业毕业生来讲是必不可少的.在简要分析国内外就业见习现状的基础上,详细分析测绘工程专业就业见习的现状.最后从政府、用人单位、学校及毕业生四个方面分别阐述了目前存在的问题与思考. 相似文献
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Solute and runoff time-series at Finsterwalderbreen, Svalbard, provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments. The hydrochemistry of a subglacial upwelling provides evidence for a snowmelt-fed subglacial reservoir that dominates bulk runoff during recession flow. High concentrations of Cl− and crustal ions, high pCO2 and ratios of [*SO2−4/(*SO2−4+HCO−3)] close to 0·5 indicate the passage of snowmelt through a subglacial weathering environment characterized by high rock:water ratios, prolonged residence times and restricted access to the atmosphere. At higher discharges, bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conveyed through a chemical weathering environment characterized by low rock:water ratios, short residence times and free contact with atmospheric gases. These observations suggest that icemelt is routed via a hydrological system composed of basal/ice-marginal, englacial and supraglacial components and is directed to the glacier margins by the ice surface slope. Upwelling water flows relatively independently of icemelt to the terminus via a subglacial drainage system, possibly constituting flow through a sediment layer. Cold basal ice at the terminus forces it to take a subterranean routing in its latter stages. The existence of spatially discrete flow paths conveying icemelt and subglacial snowmelt to the terminus may be the norm for polythermal-based glaciers on Svalbard. Proglacial mixing of these components to form the bulk meltwaters gives rise to hydrochemical trends that resemble those of warm-based glaciers. These hydrochemical characteristics of bulk runoff have not been documented on any other glacier on Svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology. © 1998 John Wiley & Sons, Ltd. 相似文献
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Daniel L. R. Hodson Sarah P. E. Keeley Alex West Jeff Ridley Ed Hawkins Helene T. Hewitt 《Climate Dynamics》2013,40(11-12):2849-2865
Wide ranging climate changes are expected in the Arctic by the end of the 21st century, but projections of the size of these changes vary widely across current global climate models. This variation represents a large source of uncertainty in our understanding of the evolution of Arctic climate. Here we systematically quantify and assess the model uncertainty in Arctic climate changes in two CO2 doubling experiments: a multimodel ensemble (CMIP3) and an ensemble constructed using a single model (HadCM3) with multiple parameter perturbations (THC-QUMP). These two ensembles allow us to assess the contribution that both structural and parameter variations across models make to the total uncertainty and to begin to attribute sources of uncertainty in projected changes. We find that parameter uncertainty is an major source of uncertainty in certain aspects of Arctic climate. But also that uncertainties in the mean climate state in the 20th century, most notably in the northward Atlantic ocean heat transport and Arctic sea ice volume, are a significant source of uncertainty for projections of future Arctic change. We suggest that better observational constraints on these quantities will lead to significant improvements in the precision of projections of future Arctic climate change. 相似文献
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The dissolution of CaCO3 granules secreted by earthworms in soil leaching columns was governed by soil pH and exchange sites available for Ca. Results indicate that granules could last for significant periods of time in soils and that, therefore, granules could be an important source of soil calcite. 相似文献
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Laboratory simulation of terrestrial meteorite weathering using the Bensour (LL6) ordinary chondrite
Martin R. Lee Caroline L. Smith Sarah H. Gordon Mark E. Hodson 《Meteoritics & planetary science》2006,41(8):1123-1138
Abstract— Laboratory dissolution experiments using the LL6 ordinary chondrite Bensour demonstrate that meteoritic minerals readily react with distilled water at low temperatures, liberating ions into solution and forming reaction products. Three experiments were performed, all for 68 days and at atmospheric fO2 but using a range of water/rock ratios and different temperatures. Experiments 1 and 2 were batch experiments and undertaken at room temperature, whereas in experiment 3, condensed boiling water was dripped onto meteorite subsamples within a Soxhlet extractor. Solutions from experiment 1 were chemically analyzed at the end of the experiment, whereas aliquots were extracted from experiments 2 and 3 for analysis at regular intervals. In all three experiments, a very significant proportion of the Na, Cl, and K within the Bensour subsamples entered solution, demonstrating that chlorapatite and feldspar were especially susceptible to dissolution. Concentrations of Mg, Al, Si, Ca, and Fe in solution were strongly affected by the precipitation of reaction products and Mg and Ca may also have been removed by sorption. Calculations predict saturation of experimental solutions with respect to Al hydroxides, Fe oxides, and Fe (oxy)hydroxides, which would have frequently been accompanied by hydrous aluminosilicates. Some reaction products were identified and include silica, a Mg‐rich silicate, Fe oxides, and Fe (oxy)hydroxides. The implications of these results are that even very short periods of subaerial exposure of ordinary chondrites will lead to dissolution of primary minerals and crystallization of weathering products that are likely to include aluminosilicates and silicates, Mg‐Ca carbonates, and sulfates in addition to the ubiquitous Fe oxides and (oxy)hydroxides. 相似文献
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M. Tranter P. Huybrechts G. Munhoven M. J. Sharp G. H. Brown I. W. Jones A. J. Hodson R. Hodgkins J. L. Wadham 《Chemical Geology》2002,190(1-4):33-44
Chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates. Solute fluxes from small valley glaciers are usually a linear function of discharge. Representative glacial solute concentrations can be derived from the linear association of solute flux with discharge. These representative glacial concentrations of the major ions are 25% of those in global river water. A 3-D thermomechanically coupled model of the growth and decay of the Northern Hemisphere ice sheets was used to simulate glacial runoff at 100-year time steps during the last glacial cycle (130 ka to the present). The glacially derived fluxes of major cations, anions and Si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration. A second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations. The fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans. The glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric CO2. The potential change in atmospheric CO2 concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant, being <1 ppm. 相似文献
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Recently there has been growing interest in, and use of, the PROFILE model, principally through the role of weathering rates in determining critical loads. In many cases the accuracy of the data used to run the model is not quoted. A simple sensitivity analysis of the model has been carried out by varying the input data one at a time in a systematic fashion. The variation in weathering rate that this generates for monomineralic soil profiles and for a soil profile from an acid sensitive forested catchment in Scotland has been recorded. Variations in weathering rates of over 100% can be generated using ranges of input parameters measured in field studies. The model broadly predicts the relative ease of weathering of the different minerals. Minerals which are particularly sensitive to input variations have been identified, e.g. Kfeldspar. Some input parameters exert a larger influence on the weathering rate as calculated by the model than others. The most sensitive input data are soil temperature, moisture content and exposed mineral surface area. The least sensitive input data are cation load and precipitation rate. 相似文献