Collapse of dome cup ends under external hydrostatic pressure     

Carl T. F. Ross  Angela Gill-Carson 《Ocean Engineering》2000,27(9):933

An experimental investigation was carried out in which four dome cup ends were tested to failure under external hydrostatic pressure. The collapse pressures of the dome cup ends were compared with that of a conventional dome cap end. The investigation revealed that the dome cup ends were structurally more efficient than the conventional dome cap ends. All the vessels were made from the same batch of glass fibre matting and associated material.  相似文献   

Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil   总被引：1，自引：0，他引：1  

Wagener Ade L  Carreira RS  Hamacher C  Scofield Ade L  Farias CO  Cordeiro LG  Luz LG  Baêta AP  Kalas FA 《Marine pollution bulletin》2011,62(8):1877-1882

Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total dispersed/dissolved concentrations in the water column ranged from 10-50 ng L⁻¹ for ∑16PAH and 5-10 μg L⁻¹ for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low (0.5-10 ng g⁻¹for ∑16PAH and 0.01-5.0 μg g⁻¹ for total aliphatic hydrocarbons) and were consistent with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin.  相似文献   

The degassing behavior of Au, Tl, As, Pb, Re, Cd and Bi from silicate liquids: Experiments and applications     

Angela Johnson 《Geochimica et cosmochimica acta》2011,75(7):1773-1784

We investigate the degassing of volatile heavy metals from natural basalt and dacite and synthetic rhyolite melts doped with Bi, Pb, Tl, Au, Re, Sb, Sn, Cd, Mo, As, Cu in Pt capsules over a range of temperatures (1200-1430 °C) exposed to air at 0.1 MPa. We also investigated the effects of ligands on degassing by adding known concentrations of Cl and S. During the experiments concentration gradients normal to the melt/gas interface arose for the trace metals Au, Tl, As, Cd, Re, Bi and Pb, as shown by measurements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on the quenched glasses. In contrast, erratic concentration gradients occurred for Cu, Mo, Sn, Sb due to the development of compositional cords in the glass for those elements. The diffusivities for Au, Tl, As, Cd, Re, Bi and Pb (in decreasing order of volatility) followed an Arrhenius relationship with log D at 1260 °C varying from −12 to −17. The addition of Cl and S were shown to increase by two-to five-fold the volatilities of all metals, with S having a more profound effect. Diffusivities from the experiments were applied in a bubble growth model to examine the behavior of Tl and Pb in volcanic gases. The Tl/Pb ratio in gases shows much greater variation than can be explained by partitioning and magma composition alone, with diffusion serving to drastically enrich or deplete the Tl/Pb of gases to values significantly different from that of the melt.  相似文献   

A depositional history of particulate organic carbon in a floodplain lake from the lower Ob’ River, Siberia     

Angela F. Dickens  Jeff Baldock  Timothy I. Eglinton 《Geochimica et cosmochimica acta》2011,75(17):4796-4815

Northern, high latitude soils have stored vast amounts of organic carbon (OC) in permafrost and peats for many millennia, however, climate change may mobilize and release this particulate OC (POC) to arctic rivers. Deltaic and floodplain lakes that receive fluvial sediments, primarily during the spring freshet, may provide records of such changes in riverine POC. Here, we examine properties of OC in a sediment core from a lake in the lower floodplain of the Ob’ River, west Siberia, to determine how the properties of OC deposited in this lake varied over many decades and to evaluate use of this sedimentary OC as a recorder of riverine POC load and properties. The core predates the most recent, dramatic changes in arctic climate and hence may serve as a benchmark against which to contrast future variations in fluvial POC discharge. Elemental, stable carbon and radiocarbon isotopic analyses, along with nuclear magnetic resonance (NMR) spectroscopy and molecular-level information (lignin phenol composition), indicate two major sources of OC to most of the sediments in this lake: plant-derived OC and algal-derived OC. However, a mixing model indicates that the nature and ¹⁴C content of these two sources change with depth in the sediment, resulting in three distinct layers: surface horizons, a “high-OC” layer and “mixing” horizons found above and below the high-OC layer. The plant-derived component is significantly aged throughout the core (¹⁴C ages of 1300-3900 years) and appears to derive from primarily local, tundra sources, whereas the algal component is modern. Our analysis suggests that the usual mode of OC deposition, as exemplified by the “mixing” and surface horizons, involved mixing of varying amounts of new algal production (35-65%) with aged permafrost- or peat-derived OC. This deposition was interrupted by an event, such as the collapse of a riverbank, which laid down the compositionally distinct “high-OC” layer in which plant-derived OC mixes with aged mineral-soil-derived OC without clear input from algae. The relative amounts of the plant and algal components in the lake sediments appear to be controlled primarily by local hydrological conditions rather than by river-wide processes, suggesting that comparison of sediment records from multiple lakes within a floodplain will be important to assess changes in POC export by arctic rivers. However, the flux and nature of the higher plant-derived OC may carry important information on the sources and dynamics of OC stored within the drainage basin.  相似文献   

“I Still Have the Old Tradition”: The co-production of sweetgrass basketry and coastal development     

Brian Grabbatin  Patrick T. Hurley  Angela Halfacre 《Geoforum》2011,42(6):638-649

Scholars working around the world have drawn attention to the physical and social changes associated with rural gentrification. Case studies from the United States have focused on how these patterns lead to the cultural displacement and replacement of land-based livelihoods, including non-timber forest product (NTFP) practices. Scholars have also documented the persistence of culturally and economically important NTFP practices in urban and suburban areas. We reconcile these disparate outcomes, displacement on the one hand and persistence on the other, by focusing on the social relationships that co-produce land use and livelihood change. Our case investigates how African American sweetgrass basketmakers in Mount Pleasant South Carolina negotiate the complex terrain of a rapidly urbanizing and gentrifying landscape.Analysis of interviews with basketmakers and participant observation at public meetings suggests that gathering materials and selling baskets occur across spaces not typically considered important for NTFP practices. Access to these sites depends upon continually reinforced and negotiated social relationships between a variety of actors. Findings illustrate that, by themselves, development and gentrification are insufficient for explaining livelihood and land use patterns that emerge in places experiencing intensive development. Using a co-production framework, we acknowledge the wide variety of complex trajectories and local power dynamics shaping land use and livelihoods. Findings also have implications for connecting global research on housing, employment, and demographic transitions associated with rural gentrification, to international NTFP research, which is increasingly turning to rural–urban interfaces for insights on how livelihoods are linked to land development and migration.  相似文献   

High-temperature vesuvianite: crystal chemistry and surface considerations     

Chiara Elmi  Maria Franca Brigatti  Luca Pasquali  Monica Montecchi  Angela Laurora  Daniele Malferrari  Stefano Nannarone 《Physics and Chemistry of Minerals》2011,38(6):459-468

A multi-methodical approach has been applied for characterizing the bulk and surface crystal chemical features of a high-temperature vesuvianite crystal from skarns of Mount Somma-Vesuvius Volcano (Naples, Italy). Vesuvianite belongs to the space group P4/nnc with unit cell parameters a = 15.633(1) Å, c = 11.834(1) Å and chemical formula (Ca_18.858 Na_0.028 Ba_0.004 K_0.006 Sr_0.005 □_0.098)_19.000 (Al_8.813 Ti_0.037 Mg_2.954 Mn_0.008 Fe_0.114²⁺ Fe_1.375³⁺ Cr_0.008 B_0.202)_13.511 Si_18.000(O_0.261 F_0.940 OH_7.799)_9.000. Structure refinement, which converges at R = 0.0328, demonstrates a strong positional disorder down the fourfold axes, indicating that the Y1 site is split into two positions (Y1A and Y1B) alternatively occupied. However, because of X4 proximity to Y1B and Y1A, X4 cannot be occupied if Y1B or Y1A are. Overall Y1 occupancy (Y1A + Y1B) reaches approximately 0.5, as common in vesuvianite and occupancy of Y1B site is extremely limited. Moreover, T1 position, limitedly occupied, accommodates the excess of cations generally related to Y position. A small quantity (0.202 apfu) of boron is sited at the T2 site that, like T1, is poorly occupied. The determination of the amount of each element on the (100) vesuvianite surface, obtained through X-ray photoelectron spectroscopy high-resolution spectra in the region of the Si_2p, Al_2p, Mg_1s, and Ca_2p core levels, evidences that a greater amount of aluminum and a smaller amount of calcium characterize the surface with respect to the bulk. Although both of these features require further investigation, we may consider the Al increase can be related to preferential orientation of Al-rich sites on the (100) plane. Furthermore, the surface structure of vesuvianite suggests that Al, Ca, and Mg cations maintain coordination features at the surface similar to the bulk. Silica, however, while presenting fourfold coordination, shows also a [1]-fold small coordinated component at binding energy 99.85 eV, due to broken Si–O bonds at the surface. The presence of eight- and nine-coordinated Ca cations is suggested by a large XPS feature resulting from the merging of Ca_2p3/2 and Ca_2p1/2 peaks at 348.45 and 352.05 eV, respectively.  相似文献   

Morphological features of the Apennines foreland/accretionary-wedge boundary in the Ionian Sea     

Valentina Volpi  Daniela Accettella  Angela Cuppari 《Marine Geophysical Researches》2011,32(4):481-492

A detailed reconstruction of the morphology and recent tectonic activity of the Northern Ionian basin is provided on the basis of newly acquired high-resolution swath bathymetric and single and multichannel seismic profiles. The tectonic domains in this area are the Calabrian accretionary wedge and the Apulian foreland. The contact between the two domains, oriented NW–SE, morphologically coincides with a sea-bottom erosional channel (Taranto canyon) characterized on both sides by mass movements induced by slope instability. Along the accretionary wedge/Apulian foreland boundary three different morphological sectors have been recognized whose main characters are represented by a southward stepped increase of erosional canyon activity resulting in a pronounced slope acclivity and a superficial sediment instability. By means of seismic data we correlate the morphology of the sea-bottom to different contractional and flexural processes of the accretionary wedge/foreland system. The interaction between the different rheological domains in the subduction/collision processes could have also induced horizontal stress represented by areas of tectonic release. In an area like this, where very few detailed surveys have been carried out, this study represents the first attempt in correlating the recent tectonic activity to the morphological features and in locating possible slope instability that has to be evaluated for the positioning of offshore infrastructures.  相似文献   

Use of radon isotopes,gamma radiation and dye tracers to study water interactions in a small stream in Brazil   总被引：1，自引：0，他引：1  

Vinícius V. M. Ferreira  Rubens M. Moreira  Zildete Rocha  Cláudio J. Chagas  Raquel L. M. Fonseca  Talita O. Santos  Paulo C. H. Rodrigues  Maria Angela B. C. Menezes 《Environmental Earth Sciences》2018,77(19):699

In this study, natural (²²²Rn) and fluorescent (uranin) tracers were used to investigate the interactions between surface and subsurface waters in a small hydrographical basin located in the southeast region of Brazil. Levels of ²²²Rn were measured in 117 water samples with the use of an alpha solid-state detector. After the identification of the probable discharge sections along the stream, a measurement of the natural flows, upstream and downstream of these sections, was done with the use of a fluorimeter and fluorescent tracers. Also, scanning was done to verify a correlation between the natural gamma radiation and the ²²²Rn in the areas where its activity was higher. The results showed some sections where the ²²²Rn activity is more significant and contributed to the growth of the flows along the stream. It was possible to confirm a correlation between the discharge sections and the natural gamma radiation, what can be used as a preliminary approach to finding these sections in scenarios similar to the one studied here.  相似文献   

The legacy of river channel modification in wadeable,lowland rivers: Exploring overdeep rivers in England     

Angela M. Gurnell  Peter W. Downs 《地球表面变化过程与地形》2021,46(15):3016-3025

Many lowland fluvial systems are suspected to possess a morphological legacy from a long history of channel modifications as a consequence of limited energy and sediment supply to facilitate recovery. We explore the extent of such modifications using a regionally extensive dataset of physical habitat surveys compiled by non-specialist surveyors. Representative photographs for each surveyed site were used to quality check channel width, depth and bed grain size information derived from Modular River Physical (MoRPh) surveys. Following checking, 1659 surveys were retained for analysis from alluvial sites, almost entirely in England. The photographs were also inspected for evidence of clear ‘overdeepening’ that would preclude frequent overtopping of the lower bank top. Results indicated that almost one-third of the sites were overdeepened, that width-to-depth ratios defined using the active bed width showed stronger discrimination of overdeepening than bankfull width, that highly statistically significant identification of overdeepened channels was possible in channels up to 10 m wide and with only minimal differences attributable to channel bed materials. Stepwise regression analysis estimated relationships between channel width-to-depth ratios and channel size for overdeepened and non-overdeepened channels. We demonstrate that large data sets collected by numerous non-specialist surveyors can, with careful filtering, generate statistically robust results of geomorphological value over areas larger than is otherwise practicable. Furthermore, we reveal a notable legacy of overdeepening in the analysed lowland rivers, which presents a significant ‘hydromorphological’ management challenge.  相似文献   

The geomorphological context and impact of the linear emergent macrophyte,Sparganium erectum L.: a statistical analysis of observations from British rivers     

Angela M. Gurnell  Matthew T. O'Hare  Judith M. O'Hare  Peter Scarlett  Thomas M.R. Liffen 《地球表面变化过程与地形》2013,38(15):1869-1880

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