| 1. |
- Kemna, Andreas, et al.
(författare)
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An overview of the spectral induced polarization method for near-surface applications
- 2012
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Ingår i: Near Surface Geophysics. - : Wiley. - 1873-0604 .- 1569-4445. ; 10:6, s. 453-468
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Tidskriftsartikel (refereegranskat)abstract
- Over the last 15 years significant advancements in induced polarization (IP) research have taken place, particularly with respect to spectral IP (SIP), concerning the understanding of the mechanisms of the IP phenomenon, the conduction of accurate and broadband laboratory measurements, the modelling and inversion of IF data for imaging purposes and the increasing application of the method in near-surface investigations. We summarize here the current state of the science of the SIP method for near-surface applications and describe which aspects still represent open issues and should be the focus of future research efforts. Significant progress has been made over the last decade in the understanding of the microscopic mechanisms of IP; however, integrated mechanistic models involving different possible polarization processes at the grain/pore scale are still lacking. A prerequisite for the advances in the mechanistic understanding of IP was the development of improved laboratory instrumentation, which has led to a continuously growing data base of SIP measurements on various soil and rock samples. We summarize the experience of numerous experimental studies by formulating key recommendations for reliable SIP laboratory measurements. To make use of the established theoretical and empirical relationships between SIP characteristics and target petrophysical properties at the field scale, sophisticated forward modelling and inversion algorithms are needed. Considerable progress has also been made in this field, in particular with the development of complex resistivity algorithms allowing the modelling and inversion of IF data in the frequency domain. The ultimate goal for the future are algorithms and codes for the integral inversion of 3D, time-lapse and multi-frequency IF data, which defines a 5D inversion problem involving the dimensions space (for imaging), time (for monitoring) and frequency (for spectroscopy). We also offer guidelines for reliable and accurate measurements of IP spectra, which are essential for improved understanding of IP mechanisms and their links to physical, chemical and biological properties of interest. We believe that the SIP method offers potential for subsurface structure and process characterization, in particular in hydrogeophysical and biogeophysical studies.
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| 2. |
- Dehnert, Andreas, et al.
(författare)
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Cosmogenic isotope burial dating of fluvial sediments from the Lower Rhine Embayment, Germany
- 2011
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Ingår i: Quaternary Geochronology. - 1871-1014 .- 1878-0350.
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Tidskriftsartikel (refereegranskat)abstract
- Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to PlioePleistocene fluvial successionsfrom the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1)measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrationsbased on a first-order conceptualisation of the geological context and the principal succession ofdepositions and subsequent erosional and burial phases, and (3) using parameter estimation to identifyvalues for the a priori unknown model parameters (burial age, initial nuclide concentrations, terraceerosion rates) that result in minimal disagreement between hypothetical and measured nuclideconcentrations.
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| 3. |
- Kessouri, Pauline, et al.
(författare)
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Induced polarization applied to biogeophysics: recent advances and future prospects
- 2019
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Ingår i: Near Surface Geophysics. - : Wiley. - 1873-0604 .- 1569-4445. ; 17:6, s. 595-621
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides an update on the fast-evolving topic of the induced polarization (IP) method applied to biogeophysics. It emphasizes new understandings of the IP phenomena associated with biological activity, pointing out new developments and applications, and identifying existing knowledge gaps. The focus is on the use of IP as related to living organisms, including micro-organisms and plants (both roots and stems). We first discuss observed links between the IP signal and microbial cell structure, activity and biofilm formation. We provide an up-to-date conceptual model of the electrical behavior of the microbial cell and biofilm and examine the role of extracellular electron transfer mechanisms on the functionality and development of biofilms. We review the latest biogeophysical studies, including work on hydrocarbon biodegradation, contaminant sequestration, soil strengthening and peatland characterization. We then elaborate on the IP signature of the plant root zone, relying on a state-of-the-art conceptual model of the biogeophysical mechanisms of a plant root cell. The first laboratory surveys show that single roots and root system are highly polarizable. They also present encouraging results for imaging the root system embeded in a medium and gaining information on the mass density, the structure or the physiological characteristics of the root system. IP is also used to characterize wood and tree structures in the lab but also at the field scale, through tomography of the stem. Finally, we discuss up- and down-scaling between lab and field studies as well as joint interpretation. We emphasize the need for intermediate scale studies and the benefits of using IP as a time-lapse monitoring method. We conclude with the promising integration of IP in global mechanistic models to better understand and quantify subsurface biogeochemical processes.
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| 4. |
- Leroy, Philippe, et al.
(författare)
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Spectral induced polarization of Na-montmorillonite dispersions
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 505, s. 1093-1110
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Tidskriftsartikel (refereegranskat)abstract
- Montmorillonite (Mt) clays have a high specific surface area and surface charge, which confer them remarkable adsorption properties. Nevertheless, their electrochemical and aggregation behavior are not completely elucidated because of the complexity of their microstructural and interfacial properties. In this work, the conductive and dispersive properties of Na-Mt suspensions of weight fractions 0.5-5.2% were investigated for the first time using the spectral induced polarization method. A four-electrode system was used to reduce errors introduced by electrode polarization and contact resistances. Complex conductivity spectra in the low-frequency range of 0.1 Hz to 45 kHz were successfully described using a triple layer model of the basal surface of Mt and a complex conductivity model that considers conduction of the diffuse layer and polarization of the Stern layer. Aggregate size distributions were inferred from inverted relaxation time distributions. We found that the negative and permanent surface charge of the basal plane of Na-Mt controls its quadrature (imaginary) conductivity, which is not very sensitive to pH and salinity (NaCI) in the 100 Hz to 45 kHz frequency range. For lower frequencies, the sudden increase of the quadrature conductivity at the highest salinities was explained by considering coagulation of Na-Mt particles.
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