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31.
Abstract. Two sediment cores were collected in the southern Baltic Sea and sliced into 1.0cm-thick layers. Sediments of each layer were analysed for activities of 210Pb, 137Cs, 134Cs and for the density of meiobenthic organisms (meiofauna). Zones with the rapid mixing occur in the uppermost layers (0–3 cm) of the cores based on I34Cs profiles. The extent and density of meiofauna confirmed the rapid mixing and revealed layers with slow mixing (4–8 cm). Sedimentation rates were derived from 210Pb profiles below the mixing zones (1.21 and 1.72 mm a-I) and were confumed by 137Cs distribution. Of twenty-one major meiofauna taxa commonly found in the Baltic sediments, three were present in the cores. 相似文献
32.
某港口堆场地基上部5.0m系吹填而成,地表下18m范围均属软土,经真空预压初级加固后地基承载力仅在80—90kPa,局部区域上部淤泥土层土性指标较差,含水量大于50%,地基承载力不足60kPa。为了使地基达到230kPa的承载要求,设计采用深层搅拌法加固超软弱地基。通过现场成桩工艺试验和检测表明,桩身水泥土强度在90d龄期时大于1.80MPa,单桩承载力标准值大于150kN,以φ600桩径、桩长13.5m、置换率为0.308和φ500桩径、桩长13.5m、置换率为0.267两种方案布置的复合地基承载力标准值均超过了230kPa的设计要求。试验结果表明,深层搅拌法在港口超软弱地基土应用只要施工工艺适当,完全可以使地基承载力提高2—3.5倍以土,从而节省大量的工程投资。 相似文献
33.
34.
In this contribution, we present a virtual voyage through 3D structures generated by chaotic mixing of magmas and numerical
simulations with the aim to highlight the power of 3D representations in the understanding of this geological phenomenon.
In particular, samples of mixed juveniles from Salina island (Southern Italy) are reconstructed in 3D by serial lapping and
digital montage and numerical simulations are performed by using a 3D chaotic dynamical system. Natural and simulated magma
mixing structures are visualized by using several multimedia tools including animations and “virtual reality” models. It is
shown that magma interaction processes can generate large spatial and temporal compositional heterogeneities in magmatic systems.
The same topological structures are observed in both 3D reconstructed rock samples and chaotic numerical simulations, indicating
that the mixing of magmas is governed by chaotic dynamics. The use of 3D multimedia models gives the opportunity to penetrate
into magma mixing structures and to understand their significance in the context of magma dynamics. Such an approach is very
powerful since multimedia tools can strongly capture the attention of the reader bringing him/her into an interactive and
memorable geological experience.
Electronic supplementary material enclosed: 相似文献
35.
场地回填土与搅拌桩施工顺序将直接影响软土地坪复合地基的处理效果,其中沉降控制是影响地坪安全运行的关键。以近海软土地区工业厂房水泥土搅拌桩复合地基工程为例,探讨了复合地基水泥土搅拌桩、回填土两种不同施工顺序的影响因素及相应处理效果;通过数值模拟试验,计算分析了不同填土厚度下两种工况的地基固结总沉降、施工沉降、工后沉降。结果表明,采用“先土后桩”的施工顺序的施工期沉降大于“先桩后土”,但工后沉降大大减小,提高了软土地坪地基处理效果,有利于处理后地坪的安全运行,验证了前述分析结论,为合理设计方案的确定提供了重要的参考依据。 相似文献
36.
Reconstructing recent limnological history often relies on lead-210 dating to accurately ascribe a chronology to a sediment
profile. In Lake Okeechobee, Florida, a large, shallow subtropical lake that may experience severe mixing, multiple dating
methods are required to confirm that conformable sedimentation has been preserved and that the assumptions of the 210Pb method are satisfied. This study uses stratigraphic profiles of heavy metals, 137Cs, PCBs and pollen as independent dating markers to validate the sediment chronology as determined by 210Pb for three cores from the central mud zone of the lake. Unsupported 210Pb and most dating markers show distinct concentration/depth profiles, suggesting that the sediments have not been severely
mixed for at least the last 75 years. Onset and maximum activity of the radioisotope 137Cs in the cores coincides with the 210Pb-dated interval of 1945–1970. This agrees well with the known timing of atmospheric deposition of 137Cs that resulted from above-ground nuclear testing during late 1940s until 1963. Sediment core profiles of atmospherically
deposited metals such as Zn and Pb, which reflect regional increases during industrialization and decreases after regulation
in the 1970s, exhibit expected concentration increases and peaks coinciding within 5–15 years of the predicted 210Pb dates. Uranium, a contaminant in some phosphate fertilizers, shows large concentration increases at core depths dated to
be about 1950 by 210Pb, matching the intensification of agriculture after WWII. PCBs, which are expected to peak in the early 1970s, were measured
in one core, and the observed peak corresponds to a 210Pb date of about 1960. Pollen makers were unable to verify specific events, but increases in disturbance taxa and declines
in native types correspond generally with the expected dates assigned by 210Pb dating. Conformity between the 210Pb defined dates and independent markers of < ±15 years confirm that Lake Okeechobee sediments do preserve a sequential and
reliable stratigraphic history of the lake, useful for reconstructing past limnological conditions. 相似文献
37.
Tackling social exclusion in European neighbourhoods: experiences and lessons from the NEHOM project
Anneli Kährik 《GeoJournal》2006,67(1):9-25
Disadvantaged urban neighbourhoods with their complex social, economic and physical situations have increasingly become the focus of governmental policies in the EU. The emphasis has shifted from improving physical qualities to building opportunities for social groups in these areas. While physical upgrade is easier to achieve, at least in the short run, initiatives often fail in outcomes on communities and local participation. This paper aims to improve understanding on how to tackle area-based social exclusion and create socially coherent communities. Building on the results of the NEHOM project, the focus is on examining how various interventions have impacted local communities and their opportunities for better inclusion. A comparison between neighbourhoods shows that mixing social groups to a certain degree is likely to be a necessary step towards opening long-term opportunities for a disadvantaged neighbourhood. The planned initiatives should at the same time directly benefit local communities, and the involvement of local groups in the planning and implementation process helps to guarantee that the overall changes are accepted by the local community. However, the proposed guidelines do not provide a universal recipe for a successful renewal suiting each neighbourhood—the contextual matters should always be a starting point when planning an initiative. 相似文献
38.
39.
Fluid mixing as the mechanism of formation of the Dajing Cu-Sn-Ag-Pb-Zn ore deposit,Inner Mongolia ——Fluid inclusion and stable isotope evidence 总被引:2,自引:0,他引:2
Since the 1990s, interest in the magmatic fluids and their relation to mineralization has been re-aroused[1—6]. Studies on stable isotopes of low-sulfidation deposits commonly show the predominance of meteoric water[7]. Paradoxically, the evidence for me… 相似文献
40.
Tidal mixing plays an important role in the modification of dense water masses around the Antarctic continent. In addition to the vertical (diapycnal) mixing in the near-bottom layers, lateral mixing can also be of relevance in some areas. A numerical tide simulation shows that lateral tidal mixing is not uniformly distributed along the shelf break. In particular, strong mixing occurs all along the Ross Sea and Southern Weddell Sea shelf breaks, while other regions (e.g., the western Weddell Sea) are relatively quiet. The latter regions correspond surprisingly well to areas where indications for cross-shelf exchange of dense water masses have been found. The results suggest that lateral tidal mixing may account for the relatively small contribution of Ross Sea dense water masses to Antarctic Bottom Water. 相似文献