677 resultados para Sands
Resumo:
Biological soil crusts (BSCs) are formed by aggregates of soil particles and communities of microbial organisms and are common in all drylands. The role of BSCs on infiltration remains uncertain due to the lack of data on their role in affecting soil physical properties such as porosity and structure. Quantitative assessment of these properties is primarily hindered by the fragile nature of the crusts. Here we show how the use of a combination of non-destructive imaging X-ray microtomography (XMT) and Lattice Boltzmann method (LBM) enables quantification of key soil physical parameters and the modeling of water flow through BSCs samples from Kalahari Sands, Botswana. We quantify porosity and flow changes as a result of mechanical disturbance of such a fragile cyanobacteria-dominated crust. Results show significant variations in porosity between different types of crusts and how they affect the flow and that disturbance of a cyanobacteria-dominated crust results in the breakdown of larger pore spaces and reduces flow rates through the surface layer. We conclude that the XMT–LBM approach is well suited for study of fragile surface crust samples where physical and hydraulic properties cannot be easily quantified using conventional methods.
Resumo:
Full Text: August 2001 saw the birth of the British Journal of Diabetes & Vascular Disease (Figure 1): an open-access peer review journal.1 Free to publish and free to read. The founding editorial board and publisher (MediNews Diabetes) aimed to deliver a free journal to the diabetes team and vascular professionals with a special interest in diabetes. Despite the shifting sands of time and a change of publisher (SAGE) the journal has remained true to its founding philosophy - publication is on merit, not on ability to pay and free online access remains available worldwide (www.bjdvd.com) plus an extensive – mainly UK - print circulation. Evolution- The journal attracted much attention and was soon receiving good quality experimental and clinical science manuscripts. However it was felt that these articles, especially experimental and pre-clinical studies, were not within the focus of the British Journal of Diabetes & Vascular Disease, thus Diabetes & Vascular Disease Research was conceived –and is now also a SAGE journal and has an impact factor of 2.59. Over the years the organisation of topics has changed, for example the Healthcare management, The diabetes care team and Trans-cultural medicine sections have been absorbed into the Achieving Best Practice and Current Topics sections which better reflect the broader-based content of submitted material. Landmark Studies was a regular highly popular section – but how many truly Landmark Studies are undertaken? Not enough to warrant special attention 6 times a year for 12 years. Interestingly one of the studies reviewed is consistently amongst the top ten of our most read online articles.2 The British Journal of Diabetes & Vascular Disease has also challenged convention with the production of two Jubilee issues.3,4 The celebrations for the golden and diamond jubilees of Her Majesty Queen Elizabeth II afforded opportunities to reflect on changes in the understanding and treatment of diabetes during her reign. Most of the articles in these issues were written by authors who had first hand experience of the changing face of diabetes and vascular disease care. The increased costs of print and post – both financially and environmentally mean that digital communications are likely to become more popular (assuming that these approaches have a smaller ecological footprint). The British Journal of Diabetes & Vascular Disease is pleased to be able to celebrate its 12th birthday as an original open-access journal, with an ongoing commitment to support authors to publish free of charge whilst providing free reader access. As for what the future holds: tomorrow is another day. References 1.British Journal of Diabetes & Vascular Disease 2001; 1: 1-92. 2.Levy J. Impotence and its medical and psychosocial correlates: results of the Massachusetts Male Aging Study. Br J Diabetes Vasc Dis 2002; 2: 278-80. 3.British Journal of Diabetes & Vascular Disease. (Golden Jubilee Issue) 2002; 2: 415-480. 4.British Journal of Diabetes & Vascular Disease. (Diamond Jubilee Issue) 2012; 12: 266-380.
Resumo:
The natural and anthropogenic changes that are occurring at the coastal zone around the world represent the greatest problem to society in this century. This problem becomes more evident due to high density of coastal cities, to growing tourist-estate speculation of those areas and to climate change that tend to trigger and accelerate the erosive processes that operating in the littoral. In this context, it‟s possible perceive ever more a significant increase of problems associated to the coastal erosion and retreat of cliffs in the state of Rio Grande do Norte, where this study area of this search is located. The area is located in the coastal zone of the city of Baía Formosa/RN, in south-eastern coast of Rio Grande do Norte, and has a extension of about 1200 meters along the Porto beach. The main objective of this study is to analyze the stability of these cliffs in this region. Through field investigations, testings and computational analysis using the Finite Element Method and Equilibrium Limit Methods. The area was divided into four sections, and were applied checklists, and also realized characterization tests and direct shear tests with materials obtained along these sections. In this manner, it was found that the segments of cliff in this coastal zone have heights around 4 meters to 14 meters and inclinations of approximately 40° to 90°.However the constituents soils of the cliffs were classified, in general terms in accordance to Unified Soil Classification System (USCS), as clayey sands or silty sands, clays of low plasticity, clayey gravels and poorly graduaded sands. The most variegated and clayey soils belong to base of the cliff. The stability analysis showed that the safety factors ranged in section 01, from 1.92 to 4.93, in the section 02, from 1.00 to 1.43, in the section 03, from 1.36 to 1.75 , and section 04, from 1.00 to 3.64. Thus, the sections 02 and 03 were considered more unstable. However, the section 03 can be considered as the most critical section due to the absence of coastal protection structures and the narrow strip of beach.
Resumo:
In the shallow continental shelf in Northeastern Rio Grande do Norte - Brazil, important underwater geomorphological features can be found 6km from the coastline. They are coral reefs, locally known as “parrachos”. The present study aims to characterize and analyze the geomorphological feature as well as the ones of the benthic surface, and the distribution of biogenic sediments found in parrachos at Rio do Fogo and associated shallow platforms, by using remote sensing products and in situ data collections. This was made possible due to sedimentological, bathymetric and geomorphological maps elaborated from composite bands of images from the satellite sensors ETM+/Landsat-7, OLI/Landsat-8, MS/GeoEye and PAN/WordView-1, and analysis of bottom sediments samples. These maps were analyzed, integrally interpreted and validated in fieldwork, thus permitting the generation of a new geomorphological zoning of the shallow shelf in study and a geoenvironmental map of the Parrachos in Rio do Fogo. The images used were subject to Digital Image Processing techniques. All obtained data and information were stored in a Geographic Information System (GIS) and can become available to the scientific community. This shallow platform has a carbonate bottom composed mostly by algae. Collected and analyzed sediment samples can be classified as biogenic carbonatic sands, as they are composed 75% by calcareous algae, according to the found samples. The most abundant classes are green algae, red algae, nonbiogenic sediments (mineral grains), ancient algae and molluscs. At the parrachos the following was mapped: Barreta Channel, intertidal reefs, submerged reefs, the spur and grooves, the pools, the sandy bank, the bank of algae, sea grass, submerged roads and Rio do Fogo Channel. This work presents new information about geomorphology and evolution in the study area, and will be guiding future decision making in the handling and environmental management of the region
Resumo:
With the depletion of conventional oil and gas sources, the world is turning to what Urry terms “tough oil,” such as oil from the Alberta oil sands and Arctic. Fracking is a prominent example of this. Situated within an environmental justice framework, I analyze community interpretations and responses to proposed fracking development near Gros Morne National Park, Newfoundland, Canada. Based on data generated from interviews, field observations and content analysis of texts, my findings suggest that how residents view rural place is highly significant in influencing supportive or oppositional positions on fracking. Proponents picture place as a resource extraction landscape, whereas opponents understand place as a restorative landscape for leisure/tourism activities. Through debates about fracking, place is contested and re-imagined. In many ways, fracking is a struggle over who has the power to define the meanings and characteristics of rural community in an era of tough oil and significant rural change.
Resumo:
Density and diversity of bottom fauna population as dependent on sediment types and water depth is largely well known in Kiel Bay. This is in contrast to structures and processes of bioturbation, although generally it has a big influence on the benthic boundary layer and its processes, e.g., the metabolism of the bottom fauna, the mechanical properties, the age dating, and the large field of chemical processes. In the densely inhabited sands and muddy sands of the shallower waters with sediment thicknesses of some decimeters only, bioturbation is usually ubiquitous, and most of the structures left are monotonously of "biodeformational" character. At greater water depths, however, where a sedimentary column of several meters of Holocene is developed, the X-ray radiographs of numerous sediment cores show heterogeneous biogenic structures with regional and stratigraphical differentiation. They are described in terms of ichnofabrics and are interpreted on ethological knowledge of the related macrobenthos species. lmportant organisms creating specific traces include the bivalve Arctica (Cyprina) islandica and the polychaete worm Pectinaria koreni. These species are abundant in Kiel Bay and produce by their crawling-plowing mode of locomotion, a characteristic biogenic stratification, the "plow-sole structure". Other typical biogenic structures are tube traces, which are left by a number of different polychaetes occurring either singly, or as U-pairs mainly in mud sediments. Although sea urchins are rare to absent in Kiel Bay, layers of their characteristic traces Scolicia occur as witness of paleohydrographic events in channel sediments of the central bay. Plow-sole traces, polychaete-tube ichnofabric, Scolicia layers and alternations of laminated and bioturbated layers are considered as building blocks of a future "ichnostratigraphy" of Kiel Bay.
Resumo:
Geologie cores on two profiles oriented normaly to the continental shelf and slope, have been investigated to reconstruct the Quaternary sedimentary history of the southeast continental border of South Orkney (NW Weddell Sea). The sediments were described macroscopically and their fabric investigated by use of X-radiographs. Laboratory work comprised detailed grain-size analysis, determination of the watercontent, carbonate, organic carbon and sand fraction.composition. Stable oxygen and carbon isotopes have been measured On planktonic foraminifera. Palaeomagnetism, analysis of 230Th-content and detailed comparison of the lithlogic Parameters with the oxygen isotope stages (Martinson curve) were used for stratigraphic classification of the sediments. The sediment cores from the continental slope comprise a maximum age of 300,000 years B. P.. Bottom currents, ice rafting and biogenic input are the main sources of sediment. Based on lithologic parameters a distinction between glacial and interglacial facies is possible. Silty clays without microfossils and few bioturbation characterise the sediments of the glacial facies. Only small amounts of icerafted debris can be recognized. This type of sediment was accumulated during times of lower sea-level and drastically reduced rate of bottom water production. Based on grain-size distribution, bottom current velocities of 0.01 cmls were calculated. Thick sea-ice coverage reduced biogenic production in the surface water, and as consequence benthic communities were depleted. Because of the reduced benthic life, sediments are only slithly bioturbated. At the beginning of the interglacial Stage, the sea-level rised rapidly, and calving rate of icebergs, combined with input of ice-rafted material, increased considerably. Sediments of this transition facies are silty cliiys with a high proportion of coarse ice-rafted debris, but without microfossils. With the onset of bottom water production in connection with shelf ice water, sediments of interglacial facies were formed. They consist of silty clays to clayey silts with considerable content of sand and gravel. Sediments are strongly bioturbated. Based On the sediment caracteristics, current velocities of the bottom water were calculated to be of 0.96 cmls for interglacials. At the southern slope of a NW/SE-striking ridge, bottom water current is channelized, resulting in a drastic increase of current velocities. Current velocities up to 7.5 cm/s lead to formation of residual sediments. While the continental slope has predominantly fine sediments, the South Orkney shelf are mainly sandy silts and silty sands with a high proportion of gravel. These sediments were formed dominantly by ice-rafting during Brunhes- and Matuyama-Epoch. Currents removed the fine fraction of the sediments. Based on microfossil contents it was not possible to differentiate sediments from glacial to interglacial. In the upper Parts of the cores graded sequences truncated by erosion were observed. These sequences were formed during Brunhes-Epoch by strong currents with velocities decreasing periodically from about 7.5 cm/s to about 1 cm/s. Sediments with a high proportion of siliceous microfossils but barren of foraminifera compose the lower part of the shelf cores. These sediments have formed during the warmer Matuyama-Epoch.
Resumo:
Timothy Bata is thankful to the Petroleum Technology Development Fund of Nigeria (PTDF) (PTDF/E/OSS/PHD/BTP/359/11) for sponsoring his PhD research at the University of Aberdeen, and the management of Abubakar Tafawa Balewa University, Bauchi, Nigeria, for permitting him to proceed on study leave. We are grateful to Colin Taylor for his help during laboratory work and S. Bowden for advice on the interpretation of the gas chromatographic data.
Resumo:
Peer reviewed
Resumo:
Peer reviewed
Resumo:
Timothy Bata is thankful to the Petroleum Technology Development Fund of Nigeria (PTDF) (PTDF/E/OSS/PHD/BTP/359/11) for sponsoring his PhD research at the University of Aberdeen, and the management of Abubakar Tafawa Balewa University, Bauchi, Nigeria, for permitting him to proceed on study leave. We are grateful to Colin Taylor for his help during laboratory work and S. Bowden for advice on the interpretation of the gas chromatographic data.
Resumo:
Peer reviewed