Small-strain behaviour of unsaturated silty clay: experiments and model interpretation     

Mohyla  Tomáš  Boháč  Jan  Mašín  David 《Acta Geotechnica》2021,16(9):2837-2849

Acta Geotechnica - The experimental data dealing with the so-called small strain stiffness of soils are indispensable in developing and calibrating advanced numerical models. A literature review...  相似文献   

Human occupation of the northern Arabian interior during early Marine Isotope Stage 3          下载免费PDF全文

Richard P. Jennings  Ash Parton  Laine Clark‐Balzan  Tom S. White  Huw S. Groucutt  Paul S. Breeze  Adrian G. Parker  Nick A. Drake  Michael D. Petraglia 《第四纪科学杂志》2016,31(8):953-966

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Market access,population density,and socioeconomic development explain diversity and functional group biomass of coral reef fish assemblages     

Tom D. Brewer  Joshua E. Cinner  Rebecca Fisher  Alison Green  Shaun K. Wilson 《Global Environmental Change》2012,22(2):399-406

There is overwhelming evidence that many local-scale human activities (e.g. fishing) have a deleterious effect on coral reef fish assemblages. Our understanding of how broad social phenomena (e.g. socioeconomic development) affect the diversity and function of coral reef fish assemblages however, is still poor. Here, we use structural equation models to reveal how human population density, socioeconomic development, and market access affect fishing pressure and coral cover to, in turn, explain the diversity and biomass of key functional groups of reef fish assemblages within Solomon Islands. Fishing pressure is predominantly driven by both market access and local population density, and has a clear negative effect on the diversity and function of coral reef fishes. The strong positive effect of market access on fishing pressure makes clear the importance of understanding social-ecological linkages in the context of increasingly connected societies. This study highlights the need to address broad social phenomena rather than focusing on proximate threats such as fishing pressure, to ensure the continued flow of coral reef goods and services in this time of rapid global social and environmental change.  相似文献   

Modelling magnetization processes in single-and multi-domain rock samples using the preisach diagram     

Pavel Hejda  Vladimír Kropáček  Tomáš Zelinka 《Studia Geophysica et Geodaetica》1990,34(3):220-229

Summary The paper presents the results of identifying a model of the Preisach type for haematite grains of the single-domain as well as multi-domain size. Due to the phenomenological conception of the model, the relations between the parameters of the model and actual parameters are very complex, however, impressive accuracy and stability of the modified model indicate the need to resume studies of this problem. The model parameters also confirm the adequate properties of the vibrating-sample magnetometr (VSM) used and developed in our laboratories.  相似文献   

Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence     

Tom L. Phillips  Russel A. Peppers 《International Journal of Coal Geology》1984,3(3):205-255

Improved regional and interregional stratigraphic correlations of Pennsylvanian strata permit comparisons of vegetational changes in Euramerican coal swamps. The coal-swamp vegetation is known directly from in situ coal-ball peat deposits from more than 65 coals in the United States and Europe. Interpretations of coal-swamp floras on the basis of coal-ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology. Objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation. Morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps.Changes in composition of Pennsylvanian coal-swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate. Paleobotany and paleogeography of the Euramerican province indicate a moist tropical paleoclimate. Rainfall, runoff and evapotranspiration were the variable climatic controls in the distribution of coal-swamp vegetation, peat accumulation and coal resources. In relative terms of climatic wetness the Pennsylvanian Period is divisible into five intervals, which include two relatively drier intervals that developed during the Lower-Middle and Middle-Upper Pennsylvanian transitions. The climate during Early Pennsylvanian time was moderately wet and the median in moisture availability. Early Middle Pennsylvanian was drier, probably seasonally dry-wet; late Middle Pennsylvanian was the wettest in the Midcontinent; early Late Pennsylvanian was the driest; and late Late Pennsylvanian was probably the wettest in the Dunkard Basin. The five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation. Regional differences in basinal geology and climate were significant variables, but the synchronous control of paleoclimate was of primary importance.  相似文献   

Towards the detection and attribution of an anthropogenic effect on climate   总被引：1，自引：0，他引：1  

Benjamin D. Santer  Karl E. Taylor  Tom M. L. Wigley  Joyce E. Penner  Philip D. Jones  Ulrich Cubasch 《Climate Dynamics》1995,12(2):77-100

It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered [R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO₂ forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined sulfate aerosol/CO₂ experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of control run used to estimate natural variability noise properties. The R (t) trends for the CO₂-only signal are not significant in any season. C (t) trends for signals from both the CO₂-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here. The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless, we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global mean) components of a combined CO₂/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the detailed spatial signature in response to combined CO₂ and sulfate aerosol forcing, but not in response to CO₂ forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO₂-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change. Received: 10 November 1994 / Accepted: 19 July 1995  相似文献   

Estimating australian forest fire danger under conditions of doubled carbon dioxide concentrations     

Tom Beer  Allyson Williams 《Climatic change》1995,29(2):169-188

The most appropriate indices with which to quantify Australian bushfire danger are the McArthur fire danger meters. These meters use meteorological information to produce a fire danger index that is directly related to the chance of a fire starting - and to the severity of a fire once it has started. The Mark 5 forest-fire danger meter uses air temperature, relative humidity and wind speed, plus a drought factor that is calculated using daily rainfall and temperature information.Three years of daily data generated from the CSIRO four-level general circulation model, and thirty years of daily data generated from the CSIRO nine-level model were used to estimate the daily McArthur forest fire danger index for simulations corresponding to present conditions, and to those corresponding to doubled atmospheric CO₂. The performance of these models with respect to fire danger was tested by comparing the fire danger index for Sale (in the Eastern part of Victoria, South-eastern Australia) calculated from analysis of daily climatological data with the modelled annual cumulative forest fire danger index for the grid point that was representative of Sale. Data from both models for all Australian grid points were also examined. Both models predict an increase in fire danger over much of Australia for their doubled CO₂ scenarios.The results from the models confirm that annually averaged daily relative humidity is the single most important variable in the estimation of forest fire danger on an annual basis, yet the models tend to produce relative humidities that are slightly too low so that the fire danger is overestimated. A simple one-box model of evaporation indicates that the value of relative humidity to be expected under an altered climatic regime depends on the modelled relation between actual and potential evaporation, the present values of relative humidity and evaporation rate, as well as on the expected changes in wind speed.  相似文献   

The Application of Petroleum Hydrocarbon Fingerprint Characterization in Site Investigation and Remediation     

Dawn A. Zemo  James E. Bruya  Tom E. Graf 《Ground Water Monitoring & Remediation》1995,15(2):147-156

Tremendous resources have been and continue to be spent investigating and remediating petroleum hydrocarbon compounds (PHCs) in soil and ground water. Investigating and planning a remedial strategy for sites affected by PHCs is often a challenging task because of the complex chemical nature of the PHCs. the complex regulatory environment related to PHC cleanup, and the use of analytical methods that provide quantitation but not identification of PHCs. From a technical standpoint, the PHC impacting soil and/or ground water is frequently inadequately characterised, both in identification as well as in is general properties (solubility, toxicity). From a regulatory standpoint, promulgated or recommended total petroleum hydrocarbon (TPH) cleanup levels generally relate to assumed properties of specific unweathered products and are inconsistent among different agencies and regions. This produces a prime situation for unwillingly spending more resources on investigation or remediation than may be necessary, especially when the PHC in the subsurface has different properties from unweathered products such as gasoline or diesel.
Accurately identifying the PHC and its nature, a process known as fingerprint characterization, is critical to the determination of appropriate regulatory goals and design of cost-effective remedial approaches. This paper presents several case studies in which fingerprint characterization made a significant difference in the project outcome. In each instance the nature of the organic material was better understood, the regulatory cleanup levels were negotiated based on the nature of the material, and a remedial approach was implemented that differed significantly from and was generally less costly than what would have been required without fingerprint characterization data.  相似文献   

Dissolution of secondary copper sulphides using complex-forming agents (EDTA,EDA). Part I: Covellite dissolution in EDTA and EDA     

J. Tomásek  L. Neumann 《International Journal of Mineral Processing》1982,9(1):23-40

Problems of dissolution of the so-called secondary copper sulphides are very important for dynamic as well as percolation leaching of ores. This paper deals with dissolution kinetics of sulphides in an alkaline medium, using complex-forming agents in connection with possibility to leach basic, partially oxidized ores. Natural minerals and their polydispersions were investigated and the so-called geometrical model was used for evaluation. Basic dependences of the dissolution rate on the reagent concentration and pH value of the leaching solution were found and an attempt at their mathematical expression and physical interpretation was made. The first part of this work refers to the systems of covellite-ethylene diamine tetra-acetic acid (EDTA) and covellite-ethylene diamine (EDA). The established dependences are not only of theoretical but also of practical importance.  相似文献   

Dissolution of secondary copper sulphides using complex-forming agents (EDTA,EDA). Part II: Chalcocite dissolution in EDTA and EDA     

J. Tomášek  L. Neumann 《International Journal of Mineral Processing》1982,9(1):41-57

This work is immediate continuation of Part I, using an identical method and evaluation for kinetic studies. The systems chalcocite-ethylene diamine tetra-acetic acid and chalcocite-ethylene diamine were studied. It was necessary to refine the geometrical model method for chalcocite in order to establish dissolution kinetics of polydispersions. This work confirms that chalcocite leaching proceeds through covellite even in the medium of complex-forming agents and kinetic equations for both leaching stages were evaluated with an attempt at physical interpretation.  相似文献