| 1. |
- Glasbey, JC, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
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| 3. |
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| 4. |
- Cossarizza, A., et al.
(författare)
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Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)
- 2019
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Ingår i: European Journal of Immunology. - : Wiley. - 0014-2980 .- 1521-4141. ; 49:10, s. 1457-1973
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Tidskriftsartikel (refereegranskat)abstract
- These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.
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| 5. |
- Kuschmierz, Paul, et al.
(författare)
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European first-year university students accept evolution but lack substantial knowledge about it : A standardized European cross-country assessment
- 2021
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Ingår i: Evolution. - : BioMed Central (BMC). - 1936-6426 .- 1936-6434. ; 14:1, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- Background: Investigations of evolution knowledge and acceptance and their relation are central to evolution education research. Ambiguous results in this field of study demonstrate a variety of measuring issues, for instance differently theorized constructs, or a lack of standardized methods, especially for cross-country comparisons. In particular, meaningful comparisons across European countries, with their varying cultural backgrounds and education systems, are rare, often include only few countries, and lack standardization. To address these deficits, we conducted a standardized European survey, on 9200 first-year university students in 26 European countries utilizing a validated, comprehensive questionnaire, the “Evolution Education Questionnaire”, to assess evolution acceptance and knowledge, as well as influencing factors on evolution acceptance. Results: We found that, despite European countries’ different cultural backgrounds and education systems, European first-year university students generally accept evolution. At the same time, they lack substantial knowledge about it, even if they are enrolled in a biology-related study program. Additionally, we developed a multilevel-model that determines religious faith as the main influencing factor in accepting evolution. According to our model, knowledge about evolution and interest in biological topics also increase acceptance of evolution, but to a much lesser extent than religious faith. The effect of age and sex, as well as the country’s affiliation, students’ denomination, and whether or not a student is enrolled in a biology-related university program, is negligible. Conclusions: Our findings indicate that, despite all their differences, most of the European education systems for upper secondary education lead to acceptance of evolution at least in university students. It appears that, at least in this sample, the differences in knowledge between countries reflect neither the extent to which school curricula cover evolutionary biology nor the percentage of biology-related students in the country samples. Future studies should investigate the role of different European school curricula, identify particularly problematic or underrepresented evolutionary concepts in biology education, and analyze the role of religious faith when teaching evolution.
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| 6. |
- Fiori, A., et al.
(författare)
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Debates—Stochastic subsurface hydrology from theory to practice : The relevance of stochastic subsurface hydrology to practical problems of contaminant transport and remediation. What is characterization and stochastic theory good for?
- 2016
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Ingår i: Water resources research. - : Blackwell Publishing. - 0043-1397 .- 1944-7973. ; 52:12, s. 9228-9234
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of stochastic subsurface hydrology stemmed from the realization that the random spatial variability of aquifer properties has a profound impact on solute transport. The last four decades witnessed a tremendous expansion of the discipline, many fundamental processes and principal mechanisms being identified. However, the research findings have not impacted significantly the application in practice, for several reasons which are discussed. The paper discusses the current status of stochastic subsurface hydrology, the relevance of the scientific results for applications and it also provides a perspective to a few possible future directions. In particular, we discuss how the transfer of knowledge can be facilitated by identifying clear goals for characterization and modeling application, relying on recent recent advances in research in these areas.
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| 7. |
- Zech, A., et al.
(författare)
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Evidence Based Estimation of Macrodispersivity for Groundwater Transport Applications
- 2023
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Ingår i: Ground Water. - : Wiley. - 0017-467X .- 1745-6584. ; 61:3, s. 346-362
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Tidskriftsartikel (refereegranskat)abstract
- The scope of this work is to discuss the proper choice of macrodispersion coefficients in modeling contaminant transport through the advection dispersion equation (ADE). It is common to model solute concentrations in transport by groundwater with the aid of the ADE. Spreading is quantified by macrodispersivity coefficients, which are much larger than the laboratory observed pore-scale dispersivities. In the frame of stochastic theory, longitudinal macrodispersivity is related to the hydraulic conductivity spatial variability via its statistical moments (mean, variance, integral scales), which are generally determined by geostatistical analysis of field measurements. In many cases, especially for preliminary assessment of contaminant spreading, these data are not available and ad hoc values are adopted by practitioners. The present study aims at recommending dispersivity values based on a thorough analysis of tens of field experiments. Aquifers are classified as of weak, medium, and high heterogeneity and for each class a range of macrodispersivity values is recommended. Much less data are available for the transverse macrodispersivities, which are significantly smaller than the longitudinal one. Nevertheless, a few realistic values based on field data, are recommended for applications. Transport models using macrodispersivities can predict mean concentrations, different from the local ones. They can be used for estimation of robust measures, like plumes spatial moments, longitudinal mass distribution and breakthrough curves at control planes.
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| 8. |
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| 9. |
- de Barros, F. P. J., et al.
(författare)
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Aquifer heterogeneity controls on adverse human health effects and the concept of the hazard attenuation factor
- 2016
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Ingår i: Water resources research. - : Blackwell Publishing. - 0043-1397 .- 1944-7973. ; 52:8, s. 5911-5922
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the probability distribution of the hazard attenuation factor for a noncarcinogenic reactive compound captured by a well in heterogeneous porous formations. The hazard attenuation factor is defined as the ratio between the hazard index HI at a detection well and at the source. Heterogeneity of the aquifer is represented through the multi-indicator model (a collection of blocks of independent permeability) while flow and transport are solved by the means of the self-consistent approach that is able to deal with any degree of heterogeneity. Due to formation heterogeneity, HI is a random variable and similar for hazard attenuation index. The latter can be fully characterized by its cumulative distribution function (CDF), which in turn can be related to the statistics of the travel time of solute particles, from the source to the detection well. The approach is applied to the case of a solute which undergoes decay and a well with a screen much smaller than the correlation scale of hydraulic conductivity. The results show that the probability of exceeding a given acceptable threshold of the hazard index is significantly affected by the level of heterogeneity comparable to the one observed for the MADE site, and the distance between the source and the well.
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| 10. |
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| 11. |
- Fiori, A., et al.
(författare)
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Advective transport in heterogeneous aquifers : Are proxy models predictive?
- 2015
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 51:12, s. 9577-9594
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Tidskriftsartikel (refereegranskat)abstract
- We examine the prediction capability of two approximate models (Multi-Rate Mass Transfer (MRMT) and Continuous Time Random Walk (CTRW)) of non-Fickian transport, by comparison with accurate 2-D and 3-D numerical simulations. Both nonlocal in time approaches circumvent the need to solve the flow and transport equations by using proxy models to advection, providing the breakthrough curves (BTC) at control planes at any x, depending on a vector of five unknown parameters. Although underlain by different mechanisms, the two models have an identical structure in the Laplace Transform domain and have the Markovian property of independent transitions. We show that also the numerical BTCs enjoy the Markovian property. Following the procedure recommended in the literature, along a practitioner perspective, we first calibrate the parameters values by a best fit with the numerical BTC at a control plane at x(1), close to the injection plane, and subsequently use it for prediction at further control planes for a few values of sigma(2)(gamma) <= 8. Due to a similar structure and Markovian property, the two methods perform equally well in matching the numerical BTC. The identified parameters are generally not unique, making their identification somewhat arbitrary. The inverse Gaussian model and the recently developed Multi-Indicator Model (MIM), which does not require any fitting as it relates the BTC to the permeability structure, are also discussed. The application of the proxy models for prediction requires carrying out transport field tests of large plumes for a long duration.
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| 12. |
- Fiori, A., et al.
(författare)
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Stochastic modeling of solute transport in aquifers : From heterogeneity characterization to risk analysis
- 2015
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 51:8, s. 6622-6648
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Tidskriftsartikel (refereegranskat)abstract
- The article presents a few recent developments advanced by the authors in a few key areas of stochastic modeling of solute transport in heterogeneous aquifers. First, a brief review of the Lagrangian approach to modeling plumes longitudinal mass distribution and temporal (the breakthrough curve) mass arrival, is presented. Subsequently, transport in highly heterogeneous aquifers is analyzed by using a recently developed predictive model. It relates the non-Gaussian BTC to the permeability univariate pdf and integral scale, with application to the MADE field observations. Next, the approach is extended to transport of reactive solute, combinnig the effects of the random velocity field and multirate mass transfer on the BTC, with application to mass attenuation. The following topic is modeling of the local concentration field as affected by mixing and dilution due to pore scale dispersion. The results are applied to the analysis of concentration measurements at the Cape Cod field experiment. The last section incorporates the results of the preceding ones in health risk assessment by analyzing the impact of concentration prediction on risk uncertainty. It is illustrated by assessing the effect of identification of macrodispersivity from field characterization and transport modeling, upon the probability of health risk.
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| 13. |
- Stevanovic, D., et al.
(författare)
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ESSENCE-Q: Slavic language versions for developmental screening in young children
- 2018
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Ingår i: Neuropsychiatric Disease and Treatment. - : Informa UK Limited. - 1178-2021. ; 14, s. 2141-2148
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The Early Symptomatic Syndromes Eliciting Neurodevelopmental Clinical Examinations- Questionnaire (ESSENCE-Q) was developed as a brief screener to identify children with developmental concerns who might have neurodevelopmental disorders (NDDs). This study aimed to translate the ESSENCE -Q into south Slavic languages, namely, Bosnian, Bulgarian, Croatian, Macedonian, Montenegrin, Serbian, and Slovenian, and to evaluate its psychometric properties for screening purposes in clinical settings. Patients and methods: In the study, the ESSENCE-Q was completed for 251 "typically developing" children and 200 children with 1 or more diagnosed NDDs, all aged 1-6 years. Internal consistency and construct validity were tested first, followed by generating receiver operating characteristic curves and the area under the curve. Optimal cutoff values were then explored. Results: The Cronbach's alpha coefficients were 0.91, 0.88, and 0.86 for ESSENCE-Q parent-completed form, and the telephone and direct interview forms administered by trained nurse or specialist, respectively. The 3 versions produced area under the curve values (95% confidence interval): 0.96 (0.93-0.99), 0.91 (0.86-0.95), and 0.91 (0.86.-0.97), respectively. An optimal cutoff for ESSENCE-Q parent-completed form was found to be >= 3 points, while for the telephone and direct interviews, it was >= 5 points. Conclusion: We found adequate measurement properties of the south Slavic languages versions of the ESSENCE-Q as a screener for NDDs in clinical settings. This study provided additional data supporting sound psychometric properties of the ESSENCE-Q.
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| 14. |
- Zech, A., et al.
(författare)
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Is unique scaling of aquifer macrodispersivity supported by field data?
- 2015
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 51:9, s. 7662-7679
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Tidskriftsartikel (refereegranskat)abstract
- Spreading of conservative solutes in groundwater due to aquifer heterogeneity is quantified by the macrodispersivity, which was found to be scale dependent. It increases with travel distance, stabilizing eventually at a constant value. However, the question of its asymptotic behavior at very large scale is still a matter of debate. It was surmised in the literature that macrodispersivity scales up following a unique scaling law. Attempts to define such a law were made by fitting a regression line in the log-log representation of an ensemble of macrodispersivities from multiple experiments. The functional relationships differ among the authors, based on the choice of data. Our study revisits the data basis, used for inferring unique scaling, through a detailed analysis of literature marcodispersivities. In addition, values were collected from the most recent tracer tests reported in the literature. We specified a system of criteria for reliability and reevaluated the reliability of the reported values. The final collection of reliable estimates of macrodispersivity does not support a unique scaling law relationship. On the contrary, our results indicate, that the field data can be explained as a collection of macrodispersivities of aquifers with varying degree of heterogeneity where each exhibits its own constant asymptotic value. Our investigation concludes that transport, and particularly the macrodispersivity, is formation-specific, and that modeling of transport cannot be relegated to a unique scaling law. Instead, transport requires characterization of aquifer properties, e.g., spatial distribution of hydraulic conductivity, and the use of adequate models.
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| 15. |
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| 16. |
- Carruba, V., et al.
(författare)
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On the identification of the first two young asteroid families in g-type non-linear secular resonances
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 528:1, s. 796-814
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Tidskriftsartikel (refereegranskat)abstract
- Linear secular resonances happen when there is a commensurability between the precession frequency of the pericenter, g, or longitude of the node, s, of an asteroid and a planet. Non-linear resonances are higher order combinations of these frequencies. Here, we studied the three most diffusive g-type non-linear secular resonances using Artificial Neural Networks. We identified a population of more than 2100 resonant objects in the g − 2g6 + g5 and g − 3g6 + 2g5 resonances. This allows the creation of a Convolutional Neural Network model for the g − 2g6 + g5 resonance, able to predict the status of several thousands of asteroids in seconds. We identified 12 new possible dynamical groups among the resonant population, including the 5507 and 170776 families, which have both estimated ages of less than 7 Myr. These are the two first-ever identified young families in resonant configurations of the investigated resonances, which allows for setting limits on their original ejection velocity field.
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| 17. |
- Cvetkovic, J T, et al.
(författare)
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Increased levels of autoantibodies against copper-oxidized low density lipoprotein, malondialdehyde-modified low density lipoprotein and cardiolipin in patients with rheumatoid arthritis
- 2002
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Ingår i: Rheumatology. - 1462-0324 .- 1462-0332. ; 41, s. 988-995
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Tidskriftsartikel (refereegranskat)abstract
- Objectives. To analyse the association of autoantibodies against cardiolipin (CL) and oxidized low density lipoproteins [copper-oxidized low density lipoprotein (oxLDL), malondialdehyde-modified LDL (MDA-LDL)] with rheumatoid arthritis (RA) and cardiovascular complications. Methods. One hundred and twenty-one patients with RA were consecutively included. Autoantibodies were determined by ELISA. Healthy individuals from the same region were used as controls. Results. Levels of IgG, IgM and IgA antibodies against MDA-LDL and CL, as well as IgG and IgA antibodies against oxLDL were increased in the patients (P<0.01). The prevalence of IgG, IgM and IgA antibodies against CL was higher than in the normal population (74, 82 and 14%, respectively). The prevalence of IgG and IgA antibodies against oxLDL was also significantly increased (35 and 25%, respectively) and so was the prevalence of IgG and IgM antibodies against MDA-LDL (17 and 26%, respectively) compared with controls. The levels of IgM and IgA antibodies against aCL and IgM against MDA-LDL were increased in patients with extra-articular manifestations. Patients who developed myocardial infarction had a higher prevalence of IgG antibodies against MDA-LDL (P=0.04). There were substantial correlations between the levels of antibodies against oxLDL, MDA-LDL and CL. Conclusions. RA patients had increased levels and prevalence of autoantibodies against CL, oxLDL and MDA-LDL, with associations to severity of disease and cardiovascular complications.
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| 18. |
- Cvetkovic, M, et al.
(författare)
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International survey of neuromonitoring and neurodevelopmental outcome in children and adults supported on extracorporeal membrane oxygenation in Europe
- 2023
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Ingår i: Perfusion. - : SAGE Publications. - 1477-111X .- 0267-6591. ; 38:2, s. 245-260
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Tidskriftsartikel (refereegranskat)abstract
- Adverse neurological events during extracorporeal membrane oxygenation (ECMO) are common and may be associated with devastating consequences. Close monitoring, early identification and prompt intervention can mitigate early and late neurological morbidity. Neuromonitoring and neurocognitive/neurodevelopmental follow-up are critically important to optimize outcomes in both adults and children. Objective: To assess current practice of neuromonitoring during ECMO and neurocognitive/neurodevelopmental follow-up after ECMO across Europe and to inform the development of neuromonitoring and follow-up guidelines. Methods: The EuroELSO Neurological Monitoring and Outcome Working Group conducted an electronic, web-based, multi-institutional, multinational survey in Europe. Results: Of the 211 European ECMO centres (including non-ELSO centres) identified and approached in 23 countries, 133 (63%) responded. Of these, 43% reported routine neuromonitoring during ECMO for all patients, 35% indicated selective use, and 22% practiced bedside clinical examination alone. The reported neuromonitoring modalities were NIRS ( n = 88, 66.2%), electroencephalography ( n = 52, 39.1%), transcranial Doppler ( n = 38, 28.5%) and brain injury biomarkers ( n = 33, 24.8%). Paediatric centres (67%) reported using cranial ultrasound, though the frequency of monitoring varied widely. Before hospital discharge following ECMO, 50 (37.6%) reported routine neurological assessment and 22 (16.5%) routinely performed neuroimaging with more paediatric centres offering neurological assessment (65%) as compared to adult centres (20%). Only 15 (11.2%) had a structured longitudinal follow-up pathway (defined followup at regular intervals), while 99 (74.4%) had no follow-up programme. The majority ( n = 96, 72.2%) agreed that there should be a longitudinal structured follow-up for ECMO survivors. Conclusions: This survey demonstrated significant variability in the use of different neuromonitoring modalities during and after ECMO. The perceived importance of neuromonitoring and follow-up was noted to be very high with agreement for a longitudinal structured follow-up programme, particularly in paediatric patients. Scientific society endorsed guidelines and minimum standards should be developed to inform local protocols.
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| 19. |
- Cvetkovic, Vladimir, et al.
(författare)
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Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden) : 2. Transport model and effective parameter estimation
- 2007
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 43:11
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Tidskriftsartikel (refereegranskat)abstract
- [1] Transport and retention of sorbing tracers in a single, altered crystalline rock fracture on a 5 m scale is investigated. We evaluate the results of a comprehensive field study ( referred to as Tracer Retention Understanding Experiments, first phase ( TRUE- 1)), at a 400 m depth of the Aspo Hard Rock Laboratory ( Sweden). A total of 16 breakthrough curves are analyzed, from three test configurations using six radioactive tracers with a broad range of sorption properties. A transport- retention model is proposed, and its applicability is assessed based on available data. We find that the conventional model with an asymptotic power law slope of - 3/ 2 ( one- dimensional diffusion into an unlimited rock matrix) is a reasonable approximation for the conditions of the TRUE- 1 tests. Retention in the altered rock of the rim zone appears to be significantly stronger than implied by retention properties inferred from generic ( unaltered) rock samples. The effective physical parameters which control retention ( matrix porosity and retention aperture) are comparable for all three test configurations. The most plausible in situ ( rim zone) porosity is in the range 1% - 2%, which constrains the effective retention aperture to the range 0.2 - 0.7 mm. For all sorbing tracers the estimated in situ sorption coefficient appears to be larger by at least a factor of 10, compared to the value inferred from through- diffusion tests using unaltered rock samples.
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| 20. |
- Cvetkovic, Vladimir, et al.
(författare)
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Tracer travel and residence time distributions in highly heterogeneous aquifers : Coupled effect of flow variability and mass transfer
- 2016
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Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707.
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Tidskriftsartikel (refereegranskat)abstract
- The driving mechanism of tracer transport in aquifers is groundwater flow which is controlled by the heterogeneity of hydraulic properties. We show how hydrodynamics and mass transfer are coupled in a general analytical manner to derive a physically-based (or process-based) residence time distribution for a given integral scale of the hydraulic conductivity; the result can be applied for a broad class of linear mass transfer processes. The derived tracer residence time distribution is a transfer function with parameters to be inferred from combined field and laboratory measurements. It is scalable relative to the correlation length and applicable for an arbitrary statistical distribution of the hydraulic conductivity. Based on the derived residence time distribution, the coefficient of variation and skewness of residence time are illustrated assuming a log-normal hydraulic conductivity field and first-order mass transfer. We show that for a low Damkohler number the coefficient of variation is more strongly influenced by mass transfer than by heterogeneity, whereas skewness is more strongly influenced by heterogeneity.
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| 21. |
- Cvetkovic, Vladimir, et al.
(författare)
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Transport and retention from single to multiple fractures in crystalline rock at Aspo (Sweden) : 1. Evaluation of tracer test results and sensitivity analysis
- 2010
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 46, s. W05505-
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the breakthrough curves obtained within a comprehensive experimental program for investigating the retention properties of crystalline rock, referred to as Tracer Retention Understanding Experiments (TRUE). The tracer tests were conducted at the Aspo Hard Rock Laboratory (Sweden) in two phases jointly referred to as TRUE Block Scale (TBS); the TBS tests comprise a total of 17 breakthrough curves with nonsorbing and a range of sorbing tracers. The Euclidian length scales are between 10 and 30 m, compared to 5 m for the earlier tests TRUE-1. The unlimited diffusion model is consistent with measured breakthrough curves and is adopted here for evaluation. The model has four independent parameters, two of which are related to advection and dispersion, one which is related to diffusion-sorption, and one which is related to surface sorption; the individual retention parameters or properties cannot be inferred from breakthrough curves alone and require additional constraints. The mean water residence times for the TBS tests are in the range 15-250 h, whereas the coefficient of variation of the water residence times is in the range 0.4-0.6. A consistent trend is found in the calibrated retention parameters with the sorption affinities of the tracers involved. Using Bode sensitivity functions, it is shown that sensitivity increases for the retention parameter with increasing sorption affinity; for nonsorbing tracers, diffusion and hydrodynamic dispersion are shown to "compete," exhibiting similar effects; hence, their estimates are uncertain. The analysis presented here exposes a few fundamental limitations and sensitivities when evaluating diffusion-controlled retention in the subsurface; it is general and applicable to any site with comparable tracer test data. In part 2, it will be shown how discrete fracture network simulations based on the hydrostructural information available can be used for further constraining individual retention parameters, in particular, the active specific surface area (s(f)) and the rock matrix porosity (theta).
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| 22. |
- Cvetkovic, Vladimir, et al.
(författare)
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Transport and retention from single to multiple fractures in crystalline rock at Aspo (Sweden) : 2. Fracture network simulations and generic retention model
- 2010
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Ingår i: Water resources research. - : American Geophysical Union. - 0043-1397 .- 1944-7973. ; 46, s. W05506-
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges. In this work we use comprehensive hydrostructural information and present a detailed simulation study of flow and advective transport in a discrete fracture network (DFN) that replicates the Tracer Retention Understanding Experiments (TRUE) Block Scale rock volume at the Aspo Hard Rock Laboratory (Sweden). Simulated water residence time tau and hydrodynamic retention parameter beta are used as independent constraints for estimating material retention properties as presented in paper 1 of this series, whereas simulated mean water residence times are compared with observed values. We find that the DFN simulations reproduce water residence times reasonably well, indicating that the characterization data are sufficient and that the DFN model does capture dominant features of the flow paths analyzed. The empirical quadratic law that relates aperture and transmissivity seems to better reproduce calibrated mean water residence times than the theoretical cubic law for the five flow paths. The active specific surface area (beta/tau) [1/L] as inferred from simulations is used for defining a generic retention model for the dominant rock type (Aspo diorite) that matches fairly well the entire range of calibrated retention parameters of the TRUE tests. The combination of paper 1 and this work provides a general, comprehensive methodology for evaluating tracer test results in crystalline rock where a comparable amount of information is available; critical to this methodology is that tracer tests are carried out using tracers with sufficiently different sorption affinities (of factor 10-100).
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| 23. |
- Dagan, G., et al.
(författare)
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Tailing of the breakthrough curve in aquifer contaminant transport : The impact of permeability spatial variability
- 2008
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Konferensbidrag (refereegranskat)abstract
- A contaminant plume of mass Mo is inserted at time t = 0 at an injection plane at × = 0 in an aquifer of spatially variable conductivity K. The log-conductivity Y = InK is modelled as stationary and isotropic, of univariate distribution f(Y), and of finite integral scale I. The flow of water is uniform in the mean (natural gradient) and the plume is of large transverse extent relative to the integral scale. Advective transport and longitudinal spread are quantified by the solute mass arrival ("breakthrough curve", BTC) M(t,x) at a control plane at × > I. For a large plume (ergodic conditions) the relative mass flux μ(t,x) = (l/Mo)M/t is approximately equal to the probability density function of travel times of solute particles f(τx) and the latter is used to analyse transport. f(τx) is derived by adopting a structural model of the aquifer that contains spherical or cubic inclusions of uniform size and of independent Y that fill the space. Such a structure can represent any formation of given f(Y) and I. The flow and transport solutions are obtained by a simple semianalytical model and by accurate numerical simulations. The travel time distribution at few control planes is determined for a log-normal f(K) first. Under the assumption of weak heterogeneity, i.e. for small variance σy 2 and for x»I, the travel time distribution is symmetrical and Gaussian. Subsequently, by using the semi-analytical model and numerical simulations we derive f(τx) for a highly heterogeneous formation of σ y 2 = 2. The main finding is f(τx) is highly skewed due to the presence of a thin, but long tail, for large travel times. The tail is of significance to applications that deal with aquifer pollution and remediation. The tail is related to the large residence time of solute particles in blocks of low conductivity. A simple relationship is established between the tail of f(Y) for low K and that f(τx) for large τ. To further examine the impact of the log-conductivity distribution on BTC tailing, a non-Gaussian model, the subordinate model, is adopted for f(Y). This distribution depends on an additional parameter Is; travel time distribution tends to normal for Is→0, whereas the tails of the two distributions are different for Is > 0. This choice reflects the difficulty of identification of the tail of f(Y) based on field data. The relevance of results to applications is examined in terms of impact of conductivity spatial distribution, as well as influence of plume size (non-ergodic behaviour) and diffusion.
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| 24. |
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| 25. |
- Fiori, A., et al.
(författare)
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A first-order analysis of solute flux statistics in aquifers : The combined effect of pore-scale dispersion, sampling, and linear sorption kinetics
- 2002
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 38:8
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Tidskriftsartikel (refereegranskat)abstract
- [1] We consider steady groundwater flow of uniform mean in aquifers of random, spatially variable, hydraulic conductivity. Analytical expressions for the statistical moments of mass fluxes of sorbing solutes in presence of pore-scale dispersion are derived, where the reactive solutes undergo first-order sorption kinetics. The developments which lead to the analytical formulation of the solute flux are rigorous in the first-order analysis framework, and results obtained are valid for weakly heterogeneous formations. The methodology is exemplified for a two-dimensional aquifer, assuming that the source is of small transverse extent compared to the heterogeneity length scales. The examples show that pore-scale dispersion has a relatively small effect on the mean point flux, whereas the point flux variance shows much larger sensitivity to pore-scale dispersion. The variance first decreases as the reaction rate departs from the nonreactive limit, but for equilibrium reactions it is of the same order as for nonreactive solutes. The effect of averaging the solute flux over a finite sampling area is also investigated. It is found that for the expected area-averaged flux the mixing effect induced by sampling tends to supersede that caused by pore-scale dispersion. On the contrary, pore-scale dispersion may have a strong effect on the flux variance also when sampling effects are taken into account.
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| 26. |
- Fiori, A., et al.
(författare)
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Tailing of the breakthrough curve in aquifer contaminant transport : Equivalent longitudinal macrodispersivity and occurrence of anomalous transport
- 2008
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Konferensbidrag (refereegranskat)abstract
- We analyse the mass arrival (breakthrough curve) at control planes at × of a plume of conservative solute injected at time t = 0 in the plane × = 0. The formation is of random three-dimensional stationary and isotropic conductivity K, characterized by the univariate normal distribution f(Y), Y = lnK, and the integral scale I. The flow is uniform in the mean, of velocity U, and longitudinal transport is quantified by f(z,x), the probability density function (pdf) of travel time r at x. We characterize transport by an equivalent longitudinal macrodispersivity αL(x), which is proportional to the variance of the travel time. If αL is constant, transport is coined as Fickian, while it is anomalous if αL increases indefinitely with x. If f(z,x) is normal (for × I), transport is coined as Gaussian and the mean concentration satisfies an ADE with constant coefficients. For the subordinate structural model transport is anomalous, in spite of the closeness of the conductivity distribution to the lognormal one. To further analyse anomalous behaviour, a relationship is established between the shape of f(K) for K→0 and the behaviour of αL, arriving at criteria for normal or anomalous transport. The model is used in order to compare results with the recent ones presented in the literature, which are based on the Continuous Time Random Walk (CTRW) approach. It is found that a class of anomalous transport cases proposed by CTRW methodology cannot be supported by a conductivity structure of finite integral scale.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Gupta, A., et al.
(författare)
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Material transport from different sources in a network of streams through a catchment
- 2002
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 38:7
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Tidskriftsartikel (refereegranskat)abstract
- [1] A probabilistic model for material transport in a stream network is developed based on geomorphology of the subcatchment and water transit time distribution. A tracer may be a point source or a source distributed over the entire catchment. The tracer particles are transported by advection through streams of different order and also diffuse and react chemically with the sediments lying at the bottom of the streams. Stochastic analysis of travel time is complicated by microscopic exchange processes, which act to retain the tracer in the surrounding medium. These include kinetically controlled exchange with the storage zones, diffusion into the bed sediment, and linear equilibrium sorption. In addition, degradation delays the downstream tracer movement. The sensitivity analysis indicates that for 50% mass arrival the mean arrival time is increased by 3 times for a change in mass transfer parameter, chi*, by 10 times. This increase is further pronounced for higher mass arrivals and higher chi*. The results on a specific application example show that a mere doubling of the uncertain value of diffusive mass transfer rate in the bed sediment reduces the probability that 25% of solute mass arrives at the outlet by approximate to90%. The high sensitivity of the probability of the solute mass arrival at the outlet to the uncertain diffusive mass transfer rate implies uncertainty also in predictions of the solute transport process. Thus it can be concluded that the correct estimation of mass transfer rate in the bed sediments within a catchment plays an important role in field-scale estimation of transport parameters.
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| 31. |
- Gupta, A., et al.
(författare)
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Temporal moment analysis of tracer discharge in streams : Combined effect of physicochemical mass transfer and morphology
- 2000
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 36:10, s. 2985-2997
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Tidskriftsartikel (refereegranskat)abstract
- In environmental applications it is often of interest to predict the rates at which contaminant mass is discharged at a given cross section of streams and rivers. We present a Lagrangian methodology for evaluating tracer discharge (mass per unit time) at specified control cross sections (CCS) of streams. The key transport processes included in the analysis are advection, degradation/decay, and kinetically controlled mass transfer in storage zones and in bed sediment. The transport in the bed sediment is described as a diffusion process, where the tracer may sorb onto the sediment. We have derived a general solution for tracer discharge in the Laplace domain wherefrom temporal moments are computed. The derived solutions may account for deterministic changes in morphological characteristics along stretches of streams. The results are illustrated for zeroth and first two moments where we show the combined effect of advection, degradation, physicochemical mass transfer, and morphology. For illustrative purposes, we assume morphology to change downstream following power laws suggested by Langbein [1947] and Leopold and Maddock [1953]. The moments depend nonlinearly on the downstream distance, following power laws that reflect the power laws for the hydraulic geometry. We define two main dimensionless parameters, namely, kinetic storage parameter alpha* and bed parameter M, that control the amount of tracer mass eventually discharged at any given CCS. For M approximate to greater than or equal to 0.3 the most dominant mechanism that controls the amount of ultimately discharged tracer mass is the exchange with the bed sediment. Once estimated from field data for stretches of specified streams, the dimensionless parameters can be used in the derived expressions for predictive purposes.
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| 32. |
- Hassan, A. E., et al.
(författare)
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Computational issues in the determination of solute discharge moments and implications for comparison to analytical solutions
- 2001
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Ingår i: Advances in Water Resources. - 0309-1708 .- 1872-9657. ; 24:6, s. 607-619
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Tidskriftsartikel (refereegranskat)abstract
- Solute discharge moments (mean and variance) are computed using numerical modeling of flow and advective transport in two-dimensional heterogeneous aquifers and are compared to theoretical results, The solute discharge quantifies the temporal evolution of the total contaminant mass crossing a certain compliance boundary. In addition to analyzing the solute discharge moments within a classical absolute dispersion framework, we also analyze relative dispersion formulation, whereby plume meandering (deviation from mean flow path caused by velocity variations at scales larger than plume size) is removed. This study addresses some important issues related to the computation of solute discharge moments from random walk particle tracking experiments, and highlights some of the important differences between absolute and relative dispersion frameworks. Relative dispersion formulation produces maximum uncertainty that coincides with the peak mean discharge. Absolute dispersion, however, results in earlier arrival of the uncertainty peak as compared to the first moment peak. Simulations show that the standard deviation of solute discharge in a relative dispersion framework requires increasingly large temporal sampling windows to smooth out some of the large fluctuations in breakthrough curves associated with advective transport. Using smoothing techniques in particle tracking to distribute the particle mass over a volume rather than at a point significantly reduces the noise in the numerical simulations and removes the need to use large temporal windows. Same effect can be obtained by adding a local dispersion process to the particle tracking experiments used to model advective transport. The effect of the temporal sampling window bears some relevance and important consequences for evaluating risk-related parameters. The expected value of peak solute discharge and its standard deviation are very sensitive to this sampling window and so will be the risk distribution relying on such numerical models.
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| 33. |
- Hassan, A. E., et al.
(författare)
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Evaluation of analytical solute discharge moments using numerical modeling in absolute and relative dispersion frameworks
- 2002
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 38:2
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional numerical simulations are used to validate the analytical solutions for the solute discharge moments. In addition to the analysis of classical absolute dispersion we also consider relative dispersion whereby plume meandering (deviation from mean flow path caused by velocity variations at scales larger than plume size) is removed. The numerical simulations are used within a Monte Carlo framework to assess the accuracy and robustness of the analytical predictions of the solute discharge moments (mean and variance). Results show that the analytical predictions deviate from the numerical simulations as the log conductivity variance increases. Deviation occurs for the mean as well as the variance of the solute discharge. The absolute dispersion formulation, however, shows better agreement with the numerical simulations than does the relative dispersion for strong heterogeneity and vice versa for small variability. The relative dispersion results, however, depend on the prediction of the ensemble mean of the plume arrival time, which differs between simulations and analytical solution. Using the first-order analytical estimate for this parameter leads to a much better agreement between the numerical and the analytical results for solute discharge moments in the relative dispersion case.
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| 34. |
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| 35. |
- Molin, Staffan, et al.
(författare)
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Microbial risk assessment in heterogeneous aquifers : 2. Infection risk sensitivity
- 2010
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 46, s. W05519-
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Tidskriftsartikel (refereegranskat)abstract
- The entire chain of events of human disease transmitted through contaminated water, from pathogen introduction into the source (E. coli, rotavirus, and Hepatitis A), pathogen migration through the aquifer pathway, to ingestion via a supply well, and finally, the potential infection in the human host, is investigated. The health risk calculations are based on a relevant hazardous event with safe setback distances estimated by considering the infection risk from peak exposure in compliance with an acceptable level defined by a regulatory agency. A site-specific hypothetical scenario is illustrated for an aquifer with similar characteristics as the Cape Cod site, Massachusetts (United States). Relatively large variation of safe distances for the three index pathogens is found; individually, none of the index pathogens could predict the safe distance under the wide range of conditions investigated. It is shown that colloid filtration theory (CFT) with spatially variable attachment-detachment rates yields significantly different results from the effective CFT model (i.e., assuming spatially constant parameters).
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| 36. |
- Severino, G., et al.
(författare)
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On the velocity covariance for steady flows in heterogeneous porous formations and its application to contaminants transport
- 2005
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Ingår i: Computational Geosciences. - : Springer Science and Business Media LLC. - 1420-0597 .- 1573-1499. ; 9:4, s. 155-177
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Tidskriftsartikel (refereegranskat)abstract
- We consider groundwater steady flow in a heterogeneous porous formation of random and stationary log-conductivity Y = ln K, characterized by the mean < Y >, and the two point correlation function C (Y) which in turn has finite, and different horizontal and vertical integral scales I and I (v) , respectively. The fluid velocity V, driven by a given head drop applied at the boundary, has constant mean value U equivalent to (U, 0, 0). Approximate explicit analytical expressions for transverse velocity covariances are derived. The adopted methodology follows the approach developed by Dagan and Cvetkovic (Spatial moments of kinetically sorbing plume in a heterogeneous aquifers, Water Resour. Res. 29 (1993) 4053) to obtain a similar result for the longitudinal velocity covariance. Indeed, the approximate covariances of transverse velocities are determined by requiring that they have the exact first order variances as well as zero integral scale (G. Dagan, Flow and Transport in Porous Formations (Springer, 1989)) , and provide the exact asymptotic limits of the displacement covariance of the fluid particles obtained by Russo (On the velocity covariance and transport modeling in heterogeneous anisotropic porous formations 1. Saturated flow, Water Resour. Res., 31 (1995) 129). Comparisons with numerical results show that the proposed expressions compare quite well in the early time regime, and for Ut/I > 100. Since most of the applications, like assessing the effective mobility of contaminants or quantifying the potential hazards of nuclear repositories, require predictions over higher times the proposed approximate expressions provide acceptable results. The main advantage related to such expressions is that they allow obtaining closed analytical forms of spatial moments pertaining to kinetically sorbing contaminant plumes avoiding the very heavy computational effort which is generally demanded. For illustration purposes, we consider the movement of one contaminant species, and show how our approximate spatial moments compare with the numerical simulations.
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| 37. |
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| 38. |
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| 39. |
- Srzic, Veljko
(författare)
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Significance of transport dynamics on concentration statistics and expected mass fraction based risk assessment in the subsurface
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis relies on a Langrangian framework used for conservative tracer transport simulations through 2-D heterogeneous porous media. Conducted numerical simulations enable large sets of concentration values in both spatial and temporal domains. In addition to the advection, which acts on all scales, an additional mechanism considered is local scale dispersion (LSD), accounting for both mechanical dispersion and molecular diffusion. The ratio between these two mechanisms is quantified by the Peclet (Pe) number. In its base, the thesis gives answers to contaminant concentration features when influenced by: i) different log-conductivity variance; ii) log-conductivity structures defined by the same global variogram but with different log conductivity patterns cor-related; and iii) for a wide range of Peclet values. Results conducted by Monte Carlo (MC) analysis show a complex interplay between the aforementioned pa-rameters, indicating the influence of aquifer properties to temporal LSD evolu-tion. A stochastic characterization of the concentration scalar is done through moment analysis: mean, coefficient of variation (CVC), skewness and kurtosis as well as through the concentration probability density function (PDF). A re-markable collapse of higher order to second-order concentration moments leads to the conclusion that only two concentration moments are required for an accurate description of concentration fluctuations. This explicitly holds for the pure advection case, while in the case of LSD presence the Moment Deriv-ing Function (MDF) is involved to ensure the moment collapse validity. Fur-thermore, the expected mass fraction (EMF) concept is applied in groundwater transport. In its origin, EMF is function of the concentration but with lower number of realizations needed for its determination, compared to the one point PDF. From practical point of view, EMF excludes meandering effect and incorporates information about exposure time for each non-zero concentration value present. Also, it is shown that EMF is able to clearly reflect the effects of aquifer heterogeneity and structure as well as the Pe value. To demonstrate the uniqueness of the moment collapse feature and ability of the Beta distribution to account for the concentration frequencies even in real cases, Macrodisper-sion Experiment (MADE1) data sets are used.
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| 40. |
- Trinchero, P., et al.
(författare)
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A Particle-Based Conditional Sampling Scheme for the Simulation of Transport in Fractured Rock With Diffusion Into Stagnant Water and Rock Matrix
- 2020
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 56:4
-
Tidskriftsartikel (refereegranskat)abstract
- In situ experiments and field-scale characterization studies have pointed out that, in fractured crystalline media, groundwater flow is highly channelized. This implies that, at the scale of a single fracture, only part of the fracture surface area is in contact with flowing water, while the rest of in-plane water is essentially stagnant and can be accessed by solutes via molecular diffusion. Despite their importance for contaminant retention, to date, there are no numerical or analytical approaches that could be used to assess the implication of stagnant water zones on solute transport in realistic large-scale Discrete Fracture Network-based models. Here, we present an efficient and flexible algorithm for the simulation of transport in fractured rock with diffusion into stagnant water and rock matrix. The algorithm is a generalization of a previously developed numerical framework for time domain particle tracking in sparsely fractured rock. The key of the generalization is that total time in fracture (τf) is first evaluated using a Monte Carlo sampling and then a second sampling is performed conditioned on τf. The algorithm has been successfully validated against existing independent solutions and the implication of diffusion into stagnant water and secondary diffusion into the matrix has been assessed for a realistic modeling scenario. The results show that, due to diffusion into stagnant water, contaminants are more strongly retarded. This increased retention is more significant for sorbing species, as a larger number of sorption sites is accessible. A high sensitivity to the flowing channel/stagnant water zone geometry has also been observed.
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| 41. |
- Vigouroux, Guillaume, et al.
(författare)
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A scalable dynamic characterisation approach for water quality management in semi-enclosed seas and archipelagos
- 2019
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Ingår i: Marine Pollution Bulletin. - : Elsevier BV. - 0025-326X .- 1879-3363. ; 139, s. 311-327
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Tidskriftsartikel (refereegranskat)abstract
- In semi-enclosed seas, eutrophication may affect both the coastal waters and the whole sea. We develop and test a modelling approach that can account for nutrient loads from land as well as for influences and feedbacks on water quality across the scales of a whole semi-enclosed sea and its coastal zones. We test its applicability in the example cases of the Baltic Sea and one of its local archipelagos, the Archipelago Sea. For the Baltic Sea scale, model validation shows good representation of surface water quality dynamics and a generally moderate model performance for deeper waters. For the Archipelago Sea, management scenario simulations show that successful sea measures may have the most important effects on coastal water quality. This highlights the need to consistently account for whole-sea water-quality dynamics and management effects, in addition to effects of land drivers, in modelling for characterisation and management of local water quality.
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| 42. |
- Widestrand, H., et al.
(författare)
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Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden) : 1. Experimental setup and microscale characterization of retention properties
- 2007
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 43:10
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Tidskriftsartikel (refereegranskat)abstract
- [ 1] Mineralogical and retardation properties of rock materials responsible for water-rock interaction in in situ migration experiments with sorbing radioactive tracers were studied in laboratory experiments. The porosity was studied by water saturation measurements and the PMMA method was used for detailed porosity characterization of heterogeneity distributions and porosity profiles toward the fracture surface. Mylonite and altered diorite sampled in the rim zone of the fracture and representative bulk rock types were investigated by batch sorption measurements with crushed materials and through-diffusion and in-diffusion experiments in intact rock pieces. Autoradiography was used for visualization of in-diffusion profiles of sorbing tracers. The use of detailed porosity information and quantitative data on heterogeneity in porosity is shown to significantly improve the interpretation and evaluation of laboratory-scale diffusion experiments. We show through the combined approach of detailed porosity characterization and laboratory sorption and diffusion investigations that we can distinguish retention properties of bulk rock and altered rock and provide qualitative and quantitative data of heterogeneous rock properties that expand the possibility for including relevant processes in the interpretation of the results of in situ tracer tests.
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| 43. |
- WORMAN, A, et al.
(författare)
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SYSTEM HETEROGENEITY AS VARIABLE FOR SOLUTE TRANSPORT IN STREAMS
- 1995
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Ingår i: JOURNAL OF HYDRAULIC ENGINEERING-ASCE. - : ASCE-AMER SOC CIVIL ENG. - 0733-9429. ; 121:11, s. 782-791
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Contaminant migration in streaming waters is characterized by a large number of physical and biochemical transfer mechanisms that often exhibit marked spatial and temporal variabilities. To quantify the mass transport and particularly the mass retention i
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| 44. |
- Zou, L., et al.
(författare)
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Impacts of dead-ends on flow and transport in fractured rocks
- 2018
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Ingår i: 2nd International Discrete Fracture Network Engineering Conference, DFNE 2018. - : American Rock Mechanics Association (ARMA).
-
Konferensbidrag (refereegranskat)abstract
- Detailed simulation of flow and transport through a rough-walled fracture-matrix system with fracture dead-ends is performed. The analysis demonstrates a significant impact of fracture dead-ends on fluid flow and solute transport processes in the modelled system. Two 2D representative rock fracture-matrix models with and without fracture dead-ends are constructed based on high-resolution laser-scanned measurements of a granite rock fracture surface. Simulations of flow and transport with three Péclet numbers (Pe) ranging from 0.1 to 10 are conducted using a code implementing the finite volume method (FVM) to solve the Navier-Stokes equations (NSE) for water flow in the fracture, and the advection-diffusion equation (ADE) is adopted to solve for transport in the whole fracture-matrix system, also accounting for matrix diffusion. The features of the velocity fields and evolution of concentration distributions as well as breakthrough curves of the two modelled cases are presented and analyzed, with results showing that fracture dead-ends significantly affect solute transport processes and cause important retardation of transport in the fracture. This indicates that overly conservative assessments of solute mass arrivals may be made when fracture dead-ends are ignored in discrete fracture network modelling.
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