Characteristics of selenium in marine animals     

W.A. Maher 《Marine pollution bulletin》1985,16(1):33-34

The biochemical association and chemical form of selenium in the muscle tissues of four marine animals has been examined. Selenium was predominantly associated with soluble proteins (72–80%), and not present as characterizable inorganic selenium species (SeO₃^2?, SeO₄^2?).  相似文献   

Developing artificial neural network models to predict allowable bearing capacity and elastic settlement of shallow foundation in Sharjah,United Arab Emirates     

Maher Omar  Khaled Hamad  Mey Al Suwaidi  Abdallah Shanableh 《Arabian Journal of Geosciences》2018,11(16):464

This research proposes the use of artificial neural network to predict the allowable bearing capacity and elastic settlement of shallow foundation on granular soils in Sharjah, United Arab Emirates. Data obtained from existing soil reports of 600 boreholes were used to train and validate the model. Three parameters (footing width, effective unit weight, and SPT blow count) are considered to have the most significant impact on the magnitude of allowable bearing capacity and elastic settlement of shallow foundations, and thus were used as the model inputs. Throughout the study, depth of footing was limited to 1.5 m below existing ground level and water table depth taken at the level of the footing. Performance comparison of the developed models (in terms of coefficient of determination, root mean square error, and mean absolute error) revealed that the developed artificial neural network models could be effectively used for predicting the allowable bearing capacity and elastic settlement. As such, the developed models can be used at the preliminary stage of estimating the allowable bearing capacity and settlements of shallow foundations on granular soils, instead of the conventional methods.  相似文献   

First identification and characterization of Borrobol‐type tephra in the Greenland ice cores: new deposits and improved age estimates          下载免费PDF全文

Eliza Cook  Siwan M. Davies  Esther R. Guðmundsdóttir  Nicholas J. G. Pearce 《第四纪科学杂志》2018,33(2):212-224

Contiguous sampling of ice spanning key intervals of the deglaciation from the Greenland ice cores of NGRIP, GRIP and NEEM has revealed three new silicic cryptotephra deposits that are geochemically similar to the well‐known Borrobol Tephra (BT). The BT is complex and confounded by the younger closely timed and compositionally similar Penifiler Tephra (PT). Two of the deposits found in the ice are in Greenland Interstadial 1e (GI‐1e) and an older deposit is found in Greenland Stadial 2.1 (GS‐2.1). Until now, the BT was confined to GI‐1‐equivalent lacustrine sequences in the British Isles, Sweden and Germany, and our discovery in Greenland ice extends its distribution and geochemical composition. However, the two cryptotephras that fall within GI‐1e ice cannot be separated on the basis of geochemistry and are dated to 14358 ± 177 a b2k and 14252 ± 173 a b2k, just 106 ± 3 years apart. The older deposit is consistent with BT age estimates derived from Scottish sites, while the younger deposit overlaps with both BT and PT age estimates. We suggest that either the BT in Northern European terrestrial sequences represents an amalgamation of tephra from both of the GI‐1e events identified in the ice‐cores or that it relates to just one of the ice‐core events. A firm correlation cannot be established at present due to their strong geochemical similarities. The older tephra horizon, found within all three ice‐cores and dated to 17326 ± 319 a b2k, can be correlated to a known layer within marine sediment cores from the North Iceland Shelf (ca. 17179‐16754 cal a BP). Despite showing similarities to the BT, this deposit can be distinguished on the basis of lower CaO and TiO₂ and is a valuable new tie‐point that could eventually be used in high‐resolution marine records to compare the climate signals from the ocean and atmosphere.  相似文献   

Prediction of Resilient Modulus from Post-compaction Moisture Content and Physical Properties Using Support Vector Regression     

Naji Khoury  Maher Maalouf 《Geotechnical and Geological Engineering》2018,36(5):2881-2892

The present study assesses the use of support vector machine regression to predict the variation of resilient modulus with post-compaction moisture content of soils commonly encountered in Oklahoma, Pennsylvania and Wisconsin. Results show the prediction model using the support vector regression (SVR) approach is a function of degree of saturation, moisture content and plasticity index. The developed model is compared to current models in the literature. Results indicate the proposed SVR model gives more accurate values than current regression models. This model will better predict changes in the bearing capacity of pavements due to seasonal variations of moisture content.  相似文献   

Simulation of subcritical flow at open-channel junction     

Georges Kesserwani  Rabih Ghostine  José Vazquez  Robert Mosé  Maher Abdallah  Abdellah Ghenaim 《Advances in water resources》2008

The spectrum of this survey turns on the evaluation of various existing theoretical combining models, when invoked within the internal boundary condition management at a junction. Based on the assumption that: when the Froude number is low (i.e. the flow is subcritical), the energy equation at the junction can be approximated by the stages heads equality. Actual literature and many commercial packages rather use this concept for the treatment of the junction’s internal boundary handling because it is easy to implement and it avoids the solving of nonlinear equations. In the last decade, many nonlinear combining models, based on the momentum conservation through the junction, have been reported. However, using them to operate within the internal boundary condition treatment of an open-channel confluence has not yet been investigated. Hence, this research focuses on studying the practical aspect of several combining models, once applied within the junction’s internal boundary management. Therefore, the recent nonlinear models of Gurram, Hsu and Shabayek have been briefly detailed together with the traditional concept of assuming water stages equality at the junction. Subsequently, an experimental examination was performed according to available experiments as mean to pre-evaluate (separately at the junction) the four junction models in the steady state. Moreover, according to the latter inspection the attention was constrained to study the effect of high/low subcritical Froude number at the junction. Finally, two hypothetical hydraulic problems were defined and computed in order to exhibit the performance of these junction models when used to contend the junction’s internal boundary handling. The problems involved: (a) steady and transient flows; (b) high and low (subcritical) Froude number at the junction. Supported by the experimental and numerical investigations, it can be concluded that even while the Froude number spectrum is subcritical, precautions have to be taken when dealing with the concept of energy heads equality, notably for a Froude higher than 0.35 at the junction.  相似文献   

Growing new generations of critical zone scientists          下载免费PDF全文

Adam S. Wymore  Nicole R. West  Kate Maher  Pamela L. Sullivan  Adrian Harpold  Diana Karwan  Jill A. Marshall  Julia Perdrial  Daniella M. Rempe  Lin Ma 《地球表面变化过程与地形》2017,42(14):2498-2502

Critical zone (CZ) science is entering its second decade. A new generation of scientists is emerging trained specifically in CZ science and are contributing to advances in environmental science across disciplines. Concurrently, the global scope of CZ science is being elevated as new countries invest in CZ observatories. Global CZ science has great potential to address a diverse array of questions beyond any single discipline. In this commentary we discuss a series of CZ science grand challenges that should be targeted by early‐career researchers: understanding water availability in the CZ; expanding CZ science into new environments; communicating the societal relevance of CZ science including earthcasting to the public; seamlessly integrating biological sciences within the CZ framework; and scaling CZ processes over large spatial and temporal gradients. Targeting these grand challenges will push CZ science well into the future. We also highlight mechanisms for increased leadership within the CZ community. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A hybrid approach to compute seismic travel times in three-dimensional tetrahedral meshes     

Maher Nasr  Bernard Giroux  J. Christian Dupuis 《Geophysical Prospecting》2020,68(4):1291-1313

We propose an optimized method to compute travel times for seismic inversion problems. It is a hybrid method combining several approaches to deal with travel time computation accuracy in unstructured meshes based on tetrahedral elementary cells. As in the linear travel time interpolation method, the proposed approach computes travel times using seismic ray paths. The method operates in two sequential steps: At a first stage, travel times are computed for all nodes of the mesh using a modified version of the shortest path method. The difference with the standard version is that additional secondary nodes (called tertiary nodes) are added temporarily around seismic sources in order to improve accuracy with a reasonable increase in computational cost. During the second step, the steepest travel time gradient method is used to trace back ray paths for each source–receiver pair. Travel times at each receiver are then recomputed using slowness values at the intersection points between the ray path and the traversed cells. A number of numerical tests with an array of different velocity models, mesh resolutions and mesh topologies have been carried out. These tests showed that an average relative error in the order of 0.1% can be achieved at a computational cost that is suitable for travel time inversion.  相似文献   

Petaloid Organs Preserved in an Arctic Plant Macrofossil Assemblage from Full-Glacial Sediments in Southeastern Minnesota     

R. G. Baker  J. A. Mason  L. J. Maher  Jr. 《Quaternary Research》1999,52(3):388

A small suite of plant macrofossils indicates that southeastern Minnesota supported subarctic to arctic vegetation 18,700 yr B.P. Fossil tepals of Polygonum viviparum are exceptionally well preserved; they occur with more fragmentary remains of Dryas integrifolia, Vaccinium uliginosum var. alpinum, and probable species of arctic Salix, S. cf. herbacea, and S. cf. arctica. The pollen spectrum from this site is dominated by Picea, Pinus, and Cyperaceae, which are typical of midwestern full-glacial sequences. Tundra-like conditions with permafrost were present in southeastern Minnesota during full-glacial time. Local environments 18,700 yr B.P. reconstructed from both physical and paleobotanical evidence include wind-swept ridge tops with thin loess, outcrops of dolostone and sandstone on valley walls, colluvial slopes, sandy to gravelly floodplains, shallow floodplain pools, wet meadows, and peaty turfs, all in a treeless or nearly treeless environment.  相似文献   

Selenium in sediments, pore waters and benthic infauna of Lake Macquarie, New South Wales, Australia   总被引：1，自引：0，他引：1  

G. M. Peters  W. A. Maher  F. Krikowa  A. C. Roach  H. K. Jeswani  J. P. Barford  V. G. Gomes  D. D. Reible 《Marine environmental research》1999,47(5):2518

Measurements of selenium in sediments and benthic infauna of Lake Macquarie, an estuary on the east coast of Australia, indicate that sediments are a significant source of selenium in the lake's food web. Analysis of surficial sediment samples indicated higher selenium concentrations near what are believed to be the main industrial sources of selenium to the lake: a smelter and a power station. Sediment cores taken from sediments in Mannering Bay, near a power station at Vales Point, contained an average of 12 times more selenium in surficial sections than sediment cores from Nord's Wharf, a part of the lake remote from direct inputs of selenium. The highest selenium concentration found in Mannering Bay sediments (17.2 μg/g) was 69 times the apparent background concentration at Nord's Wharf (0.25 μg/g). Pore water concentrations in Mannering Bay were also high, up to 5 μg/l compared to those at Nord's Wharf which were below detection limits (0.2 μg/l). Selenium concentrations in muscle tissues of three benthic-feeding fish species (Mugil cephalus, Platycephalus fuscus, Acanthopagrus australis) were significantly correlated (p<0.05) with surficial sediment selenium concentration. Selenium concentrations in polychaetes and molluscs of Mannering Bay were up to 58 times higher than those from Nord's Wharf. Two benthic organisms, the eunicid polychaete Marphysa sanguinea and the bivalve mollusc Spisula trigonella, were maintained at different densities in selenium-spiked sediments. Both animals accumulated selenium from the spiked sediment, confirming that bioaccumulation from contaminated sediments occurs. Collectively, these data suggest that benthic food webs are important sources of selenium to the fish of Lake Macquarie.  相似文献   

The accumulation of Zn, Se, Cd, and Pb and physiological condition of Anadara trapezia transplanted to a contamination gradient in Lake Macquarie, New South Wales, Australia     

Burt A  Maher W  Roach A  Krikowa F  Honkoop P  Bayne B 《Marine environmental research》2007,64(1):54-78

The benthic bivalve, Anadara trapezia, was collected from a 'clean' reference site and transplanted along a suspected trace metal contamination gradient in Lake Macquarie, NSW. At monthly intervals, Zn, Se, Cd and Pb concentrations were measured in the surficial sediments and whole tissues of the cockle as well as their physiological condition (Scope for Growth). Zinc, Cd and Pb concentrations in sediments decreased together, southward, with the highest concentrations in the Cockle Bay area, suggesting that this is the main source of contamination. Zinc, Cd and Pb concentrations were near or above [ANZECC/ARMCANZ, 2000. National water quality management strategy paper 4. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand. pp. 3.5.-1-3.5-10] sediment quality guidelines at Cockle Creek, Warners Bay and Koorooa Bay. Significant differences in trace metal concentrations could not be attributed to grain size or Fe concentration differences. Se concentrations were highest in fine grain Fe rich sediments of Whiteheads Lagoon, and likely to be associated with power generation operations. Trace metal concentrations did not vary significantly over time. Zinc, Cd and Pb concentrations in the tissues of A. trapezia followed a similar pattern to that of sediments. Zinc and Pb concentrations in cockles and sediments were highly correlated, indicating significant exposure-dose relationships. Selenium concentrations in the tissues of A. trapezia were higher after transplantation to the lake, however, Se concentrations were similar in all transplanted cockles, indicating that Se in contaminated sediments is not the major source of Se to organisms. There was a decline in the physiological condition of A. trapezia transplanted to Lake Macquarie after a 90-day-period with marked differences in clearance rates and respiration rates at some locations and absorption efficiencies at all locations. The mean Scope for Growth value at the most contaminated location, Cockle Bay, was markedly lower than at other locations. A significant Zn exposure-dose response relationship indicates that Zn bioaccumulation is occurring in response to sediment contamination. A significant Cd exposure-response relationship indicates that Cd may be influencing the health of cockles. Significant Pb exposure-dose, exposure-response and dose-response relationships indicate that Pb probably is affecting the health of cockles in Lake Macquarie. Therefore, Zn, Cd and Pb concentrations in sediments are likely to be affecting the health of cockles in Lake Macquarie.  相似文献