The evolution of clay rock/cement interfaces in a cementitious repository for low- and intermediate level radioactive waste     

《Physics and Chemistry of the Earth》2013

In Switzerland, deep geological storage in clay rich host rocks is the preferred option for low- and intermediate-level radioactive waste. For these waste types cementitious materials are used for tunnel support and backfill, waste containers and waste matrixes. The different geochemical characteristics of clay and cementitious materials may induce mineralogical and pore water changes which might affect the barrier functionality of host rocks and concretes.We present numerical reactive transport calculations that systematically compare the geochemical evolution at cement/clay interfaces for the proposed host rocks in Switzerland for different transport scenarios. We developed a consistent set of thermodynamic data, simultaneously valid for cementitious (concrete) and clay materials. With our setup we successfully reproduced mineralogies, water contents and pore water compositions of the proposed host rocks and of a reference concrete.Our calculations show that the effects of geochemical gradients between concrete and clay materials are very similar for all investigated host rocks. The mineralogical changes at material interfaces are restricted to narrow zones for all host rocks. The extent of strong pH increase in the host rocks is limited, although a slight increase of pH over greater distances seems possible in advective transport scenarios. Our diffusive and partially also the advective calculations show massive porosity changes due to precipitation/dissolution of mineral phases near the interface, in line with many other reported transport calculations on cement/clay interactions. For all investigated transport scenarios the degradation of concrete materials in emplacement caverns due to diffusive and advective transport of clay pore water into the caverns is limited to narrow zones.A specific effort has been made to improve the geochemical setup and the extensive use of solid solution phases demonstrated the successful application of a thermodynamically consistent union of very different materials like hydrated cement and clay phases. A reactive system utilizing a novel solid-solution approach is used, where cation exchange is an intrinsic property of the mineral phase definition. Although such features were not the primary aim of the study, they offer a large potential for studies where ion exchange and changing sorption properties are of interest.  相似文献   

High body temperatures in an arid,winter-rainfall environment: Thermal biology of the smallest tortoise     

《Journal of Arid Environments》2012

Herbivorous tortoises in arid, winter-rainfall regions need to forage in seasons that provide relatively little heat for their ectothermic metabolism. To help understand how tortoises exploit resources in winter-rainfall areas, I recorded ambient, soil, and body temperatures for Homopus signatus in four spring seasons, and in one summer, autumn, and winter. The spring thermal environment enabled H. signatus to maintain body temperatures that were high compared to other small tortoise species. Mature females had higher spring body temperatures than males and immature individuals, probably because mature females were developing eggs. In summer, autumn, and winter, body temperatures differed between males and females, relating to sexually different activities and retreat uses. The relatively high body temperatures of H. signatus in winter and spring, along with a non-isometric relationship between body temperature and soil temperature, suggest that tortoises thermoregulated and may need considerable time to gain heat. Additional studies should compare body temperatures of H. signatus to operative temperatures, and determine the vulnerability of the taxon to human interferences that affect behavioural time budgets and body temperatures.  相似文献   

Formal subdivision of the Holocene Series/Epoch: a Discussion Paper by a Working Group of INTIMATE (Integration of ice‐core,marine and terrestrial records) and the Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy)     

M. J. C. Walker  M. Berkelhammer  S. Björck  L. C. Cwynar  D. A. Fisher  A. J. Long  J. J. Lowe  R. M. Newnham  S. O. Rasmussen  H. Weiss 《第四纪科学杂志》2012,27(7):649-659

This discussion paper, by a Working Group of INTIMATE (Integration of ice‐core, marine and terrestrial records) and the Subcommision on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS), considers the prospects for a formal subdivision of the Holocene Series/Epoch. Although previous attempts to subdivide the Holocene have proved inconclusive, recent developments in Quaternary stratigraphy, notably the definition of the Pleistocene–Holocene boundary and the emergence of formal subdivisions of the Pleistocene Series/Epoch, mean that it may be timely to revisit this matter. The Quaternary literature reveals a widespread but variable informal usage of a tripartite division of the Holocene (‘early’, ‘middle’ or ‘mid’, and ‘late’), and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology. We propose an Early–Middle Holocene Boundary at 8200 a BP and a Middle–Late Holocene Boundary at 4200 a BP, each of which is linked to a Global Stratotype Section and Point (GSSP). Should the proposal find a broad measure of support from the Quaternary community, a submission will be made to the International Union of Geological Sciences (IUGS), via the SQS and the ICS, for formal ratification of this subdivision of the Holocene Series/Epoch. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Spatial and temporal variations in food web structure from newly-opened habitat at hydrothermal vents     

《Marine environmental research》2012

To highlight the spatio-temporal variability of the food web structure of hydrothermal vent fauna from newly-opened habitat, a series of Titanium Ring for Alvinellid Colonization devices (TRACs) was deployed at TICA site on the East Pacific Rise in 2006. This experiment was conducted for periods of 4 days, 13 days and one month and deployments were aligned along a gradient from the basaltic bottom to the vent openings. δ¹³C values of colonists revealed a narrower range of carbon sources in proximity to vent openings in Alvinella pompejana habitat than in Tevnia jerichonana habitat, separated by a distance of four meters. This was possibly due to a spatial change in available food sources with a possible higher contribution of particulate organic matter (POM) to the siboglinid habitat compared to a higher contribution of microbial primary producers such as Epsilonproteobacteria in the alvinellid habitat. Temporal variability was also observed during experimentation in the form of a shift in either δ¹³C and/or δ¹⁵N values for A. pompejana, Lepetodrilus elevatus, dirivultid copepods and polynoid polychaetes within a one-month window showing first of all, fast tissues turnover and secondly, a possible switch in feeding strategy or food sources. Lepidonotopodium riftense and Branchinotogluma sandersi may have to alternate between detritivorous and predatory feeding strategies. In addition, through the analysis of stable isotope composition of A. pompejana and its episymbionts, we provided evidence that these attached bacteria formed part of the worms’ diet during the course of these colonization experiments.  相似文献   

A real-time,event-triggered storm surge forecasting system for the state of North Carolina     

《Ocean Modelling》2009,26(3-4):95-119

A new real-time, event-triggered storm surge prediction system has been developed for the State of North Carolina to assist emergency managers, policy-makers and other government officials with evacuation planning, decision-making and resource deployment during tropical storm landfall and flood inundation events. The North Carolina Forecast System (NCFS) was designed and built to provide a rapid response assessment of hurricane threat, accomplished by driving a high-resolution, two-dimensional, depth-integrated version of the ADCIRC (Advanced Circulation) coastal ocean model with winds from a synthetic asymmetric gradient wind vortex. These parametric winds, calculated at exact finite-element mesh node locations and directly coupled to the ocean model at every time step, are generated from National Hurricane Center (NHC) forecast advisories the moment they are inserted into the real-time weather data stream, maximizing the number of hours of forecast utility. Tidal harmonic constituents are prescribed at the open water boundaries and applied as tidal potentials in the interior of the ocean model domain. A directional surface roughness parameterization that modulates the wind speed at a given location based on the types of land cover encountered upwind, a forest canopy sheltering effect, and a spatially varying distribution of Manning’s–n friction coefficient used for computing the bottom/channel bed friction are also included in the storm surge model. Comparisons of the simulated wind speeds and phases against their real meteorological counterparts, of model elevations against actual sea surface elevations measured by NOAA tide gauges along the NC coast, and of simulated depth-averaged current velocities against Acoustic Doppler Current Profiler (ADCP) data, indicate that this new system produces remarkably realistic predictions of winds and storm surge.  相似文献   

Seismic diffraction tomography technique using very fast simulated annealing method for delineating small subsurface features     

Mahasweta Mahapatra  Samiran Mahapatra 《Journal of Applied Geophysics》2009,67(2):125-129

Diffraction, once considered noise rather than signal in seismic tomography, has recently been successfully used for delineating smaller objects whose size is comparable to or less than the wavelength of the incident seismic wave. But Most of the seismic diffraction tomography works are based on Born's and Rytov's approximation of weak scattering to linearize the expression for the scattered field due to an object and this is the basis of Fourier Diffraction Theorem. However, In this paper, we used the amplitude of the total scattered wave field without considering any approximation of weak scattering to obtain the synthetic scattered field data for forward modeling. These synthetic data are then inversed by Very Fast Simulated Annealing method which is a nonlinear inversion technique to obtain the unknown model parameters. This algorithm is applicable to both weak as well as strong scatterers. The simulated results give fairly good estimate for unknown model parameters of the scattering object within acceptable error limits.  相似文献   

Deep-water and fluvial sinuous channels—Characteristics,similarities and dissimilarities,and modes of formation     

《Marine and Petroleum Geology》2007,24(6-9):388-405

High-resolution 3D seismic data of several subsurface examples reveal significant differences in internal architecture and evolution of fluvial and deep-water sinuous channel systems, although there are many similarities in external morphologies of both systems. Channel migrations or shifts in fluvial systems, with point-bar scrolls, are relatively continuous laterally and show a downstream component; they are commonly a single seismic phase thick, with flat tops. In deep-water systems, channel migrations or shifts, with or without point-bar scroll-like features, may be lateral, either continuous or discrete, and laterally to vertically aggrading, again either continuous or discrete; they are single to multiple seismic phases thick, with or without a downstream component. Even the most laterally migrated channel complex commonly aggrades, to varying degrees, from the inside to the outside of sinuous loops. Similarities between fluvial and deep-water sinuous channel systems discussed here imply that sinuosity enhancements in both cases are the result of gradual processes, involving interaction of flows, sediments and alluvial plain or seafloor in attempts to build equilibrium profiles. Flat gradients, high width to depth ratios of valleys/channel belts, fine sediment grain sizes, a certain degree of bank cohesiveness, and presence of secondary circulations in flows were pre-requisites in both systems. However, a number of factors appear to have caused major differences in the internal architecture and modes of evolution of fluvial and deep-water channels. These include differences in (1) density contrasts of flows relative to ambient fluids, (2) entrainments of ambient fluids into flows, (3) effects of centrifugal and Coriolis forces on flows, (4) frequency, volume and duration of steady vs. catastrophic flows, (5) modes of sediment transport, and (6) effects of sea level changes on deposition. Furthermore, within deep-water systems, changes in flow parameters and sediment grain size can cause erosion, bypassing or deposition in space and time and result, through cuts and fills, in sinuous channels with lateral migrations, vertical aggradations and combinations thereof.  相似文献   

Data errors and hydrological modelling: The role of model structure to propagate observation uncertainty     

《Advances in water resources》2013

  相似文献   

Temporal distributions of anthropogenic Al,Zn and Pb in Hong Kong Porites coral during the last two centuries     

《Marine pollution bulletin》2012,64(5-12):508-515

A 182-year long record of trace metal concentrations of aluminum, zinc and lead was reconstructed from a massive Porites coral skeleton from southeastern Hong Kong to evaluate the impacts of anthropogenic activity on the marine environment. Zn/Ca and Pb/Ca ratios fluctuate synchronously from the early 19th century to the present, indicating that the marine environment has been anthropogenically influenced since industrialization. Additionally, land reclamation, mining, and ship building activities are recorded by elevated Al/Ca ratios from 1900 to 1950. The coral record indicates that high levels of Zn, Pb and Al occur coincidentally with local wars, and may have contributed to partial colony mortality. Pb/Ca does not correlate well with hemispheric proxy records after 1950, indicating that coastal corals may be recording local rather than hemispheric contamination. Pb/Ca levels in Hong Kong, Guangdong and Hainan corals imply a continuous supply of Pb-based contamination to southern China not reflected in hemispheric signals.  相似文献   

Factors influencing the mesoscale variations in marine stratocumulus albedo     

D. A. HEGG  K. NIELSEN  D. S. COVERT  H. H. JONSSON  P. A. DURKEE 《Tellus. Series B, Chemical and physical meteorology》2007,59(1):66-76

  相似文献