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Publications (10 of 18) Show all publications
Li, B., Mo, Y., Zou, L., Liu, R. & Cvetkovic, V. (2020). Influence of surface roughness on fluid flow and solute transport through 3D crossed rock fractures. Journal of Hydrology, 582, Article ID 124284.
Open this publication in new window or tab >>Influence of surface roughness on fluid flow and solute transport through 3D crossed rock fractures
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2020 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 582, article id 124284Article in journal (Refereed) Published
Abstract [en]

The influence of surface roughness on fluid flow and solute transport through three-dimensional (3D) crossed rock fractures are investigated by numerical simulations. Three crossed fracture models with different degrees of surface roughness are established by two intersecting rough-walled fractures with four branches. The fracture surface morphological data are measured from three natural fractures in sandstone and granite rock samples. The fluid flow is simulated by solving the Navier-Stokes equations and solute transport is simulated by solving the advective-diffusion equation. By rotating one fracture plane while fixing the other, series of intersection models with different angles between the two crossed fractures are established to investigate the influence of the intersecting angle. Simulation results of the rough-walled fractures are compared with the smooth parallel-plate model, showing that the surface roughness significantly enhances channeling and mixing for fluid flow and solute transport at fracture intersections. The mechanism is that the complex geometry of the intersection for rough-walled models results in reallocation of fluid pathways at the intersection, which consequently affect the mixing behavior depending on the Peclet number. The intersecting angle affects the channeling and mixing behavior because it influences the geometrical structure of the fracture intersection. The correlation between the mixing ratio and the geometrical characteristics of intersections is quantified by a relative roughness parameter. The results reveal that the widely adopted smooth parallel-plate model may lead to significant uncertainty in predicting the solute transport in crossed fractures, especially at intersections with unmated fracture surfaces. The correlation between the mixing ratio and the roughness parameter developed in this study can be incorporated into discrete fracture network models to improve their performance in estimating solute transport in fractured rocks.

Place, publisher, year, edition, pages
Elsevier B.V., 2020
Keywords
Channeling flow, Crossed rock fracture, Mixing ratio, Peclet number, Surface roughness, Diffusion in liquids, Flow of fluids, Fracture, Geometry, Mixing, Navier Stokes equations, Plates (structural components), Rocks, Solute transport, Advective-diffusion equation, Discrete fracture network models, Fracture intersections, Geometrical characteristics, Mixing ratios, Rock fractures, Rough-walled fractures
National Category
Geophysical Engineering
Identifiers
urn:nbn:se:kth:diva-272262 (URN)10.1016/j.jhydrol.2019.124284 (DOI)000517663700091 ()2-s2.0-85075447095 (Scopus ID)
Note

QC 20200420

Available from: 2020-04-20 Created: 2020-04-20 Last updated: 2020-04-20Bibliographically approved
Shamu, J., Zou, L., Kotzé, R., Wiklund, J. & Håkansson, U. (2020). Radial Flow Velocity Profiles of a Yield Stress Fluid between Smooth Parallel Disks. Rheologica Acta
Open this publication in new window or tab >>Radial Flow Velocity Profiles of a Yield Stress Fluid between Smooth Parallel Disks
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2020 (English)In: Rheologica Acta, ISSN 0035-4511, E-ISSN 1435-1528Article in journal (Refereed) Published
Keywords
2D-radial flow, plug-flow region, velocity profile, ultrasound velocimetry, slip, yield stress fluid (YSF), cement-based grouts
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering; Materials Science and Engineering; Civil and Architectural Engineering, Soil and Rock Mechanics
Identifiers
urn:nbn:se:kth:diva-251625 (URN)10.1007/s00397-020-01203-x (DOI)000521961000004 ()2-s2.0-85081572143 (Scopus ID)
Funder
Svenska Byggbranschens Utvecklingsfond (SBUF), 13470Rock Engineering Research Foundation (BeFo), 399
Note

QC 20190521

Available from: 2019-05-16 Created: 2019-05-16 Last updated: 2020-05-11Bibliographically approved
Zou, L., Håkansson, U. & Cvetkovic, V. (2020). Yield-power-law fluid propagation in water-saturated fracture networks with application to rock grouting. Tunnelling and Underground Space Technology, 95, Article ID 103170.
Open this publication in new window or tab >>Yield-power-law fluid propagation in water-saturated fracture networks with application to rock grouting
2020 (English)In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 95, article id 103170Article in journal (Refereed) Published
Abstract [en]

Cement grouting is widely applied in rock tunneling and underground construction to reduce groundwater inflow and increase the tightness of rock masses. The rock grouting process involves complex non-Newtonian grouts propagation in fracture networks. In this study, a two-phase flow model extended for yield-power-law fluid (e.g., cement grout) propagation in water-saturated fracture networks is presented. The effective transmissivity is scaled from analytical solutions for single-phase yield-power-law fluids flow between a pair of smooth parallel plates. This extended two-phase flow model for fracture networks is verified based on a unique set of experimental data. The full experiment dataset is presented in this work for the first time. Impacts of rheological parameters and time-dependent rheological properties of injected yield-power-law fluids on propagation processes are investigated through numerical simulations. A measure referred to as the propagation volume fraction is defined as an indicator of the propagation process. The results generally show that the rheological properties significantly affect the evolution of the propagation volume fraction. The propagation rate reduces with increased yield stress, consistency index and flow index. The two-phase flow of yield-power-law fluid propagation in a heterogeneous fracture network is also simulated, showing that the heterogeneity of fracture apertures may significantly affect the propagation process. For the heterogeneous case, with two-point distribution of apertures, the propagation volume fraction can be represented by using the harmonic mean aperture. Since the yield-power-law constitutive model covers a wide range of non-Newtonian fluids, the results presented in this work can be used for studying non-Newtonian fluid propagation in a variety of homogeneous or heterogeneous fracture networks, which can be used for rock grouting design.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Rock grouting, Two-phase flow, Yield-power-law fluids, Propagation volume fraction, Fracture networks
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-266172 (URN)10.1016/j.tust.2019.103170 (DOI)000501654300025 ()2-s2.0-85074254010 (Scopus ID)
Note

QC 20200113

Available from: 2020-01-13 Created: 2020-01-13 Last updated: 2020-01-13Bibliographically approved
Zou, L., Li, B., Mo, Y. & Cvetkovic, V. (2019). A High-Resolution Contact Analysis of Rough-Walled Crystalline Rock Fractures Subject to Normal Stress. Rock Mechanics and Rock Engineering
Open this publication in new window or tab >>A High-Resolution Contact Analysis of Rough-Walled Crystalline Rock Fractures Subject to Normal Stress
2019 (English)In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453XArticle in journal (Refereed) Published
Abstract [en]

Analysis of rock fracture deformation by normal stress is important for quantifying hydromechanical properties of fractured rocks that are related to a large number of geophysical problems and geoengineering applications. Experimental and numerical results for the closure of crystalline rock fractures subject to normal stress are presented in this study. An efficient high-resolution, half-space elastic–plastic contact model for analyzing the closure of crystalline rock fractures based on the Boussinesq’s solution is validated by high-precision and high-resolution experimental data. Using the validated elastic–plastic model, we investigate the correlation between fracture-specific stiffness and multi-scale surface roughness. The wavelet analysis method and the extended averaged slope magnitude for asperity heights (referred to as Z23D) are introduced to characterize the multi-scale surface roughness. The results show that the elastic–plastic contact model is effective and precise in modeling the closure of crystalline rock fractures, which matches better with the test results than the elastic model. The multi-scale features of surface roughness can be well characterized by the wavelet analysis and the extended roughness parameter Z23D. The specific stiffness is nonlinearly correlated with the multi-scale surface roughness that possibly follows a power law. The validated elastic–plastic contact model and the multi-scale surface roughness characterization methods, as well as the nonlinear correlation between the specific stiffness and the multi-scale surface roughness presented in this study, are helpful for evaluating the dependence of mechanical behaviors of rock fractures on its multi-scale surface roughness.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Elastic–plastic contact, Fracture closure, Fracture-specific stiffness, Normal stress, Surface roughness, Wavelet analysis, End effectors, Fracture, Geometry, Rocks, Stiffness, Multi-scale features, Non-linear correlations, Plastic contact, Roughness parameters, Specific stiffness, Wavelet analysis method
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-268579 (URN)10.1007/s00603-019-02034-w (DOI)2-s2.0-85077044773 (Scopus ID)
Note

QC 20200506

Available from: 2020-05-06 Created: 2020-05-06 Last updated: 2020-05-06Bibliographically approved
Frampton, A., Hyman, J. D. & Zou, L. (2019). Advective Transport in Discrete Fracture Networks With Connected and Disconnected Textures Representing Internal Aperture Variability. Water resources research, 55(7), 5487-5501
Open this publication in new window or tab >>Advective Transport in Discrete Fracture Networks With Connected and Disconnected Textures Representing Internal Aperture Variability
2019 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 55, no 7, p. 5487-5501Article in journal (Refereed) Published
Abstract [en]

Flow and transport in three-dimensional discrete fracture networks with internal variability in aperture and permeability are investigated using a numerical model. The analysis is conducted for three different texture types representing internal variability considering various correlation lengths and for an increase in domain size corresponding to an increase in network complexity. Internal variability in discrete fracture networks generally increases median travel times and delays arrival of bulk mass transport when compared against reference cases without texture, corresponding to smooth fractures. In particular, internal variability textures with weak connectivity increase travel times nonlinearly with domain size increase, further delaying bulk mass arrival. Textures with strong connectivity can however decrease median travel times, accelerating bulk mass arrival, but only for limited ranges of correlation length and domain size. As domain size increases, travel times of textures with strong connectivity converge toward travel times obtained for classical multivariant Gaussian textures. Thus, accounting for internal fracture variability is potentially significant for improving conservative estimates of bulk mass arrival, flow channeling, and advective and reactive transport in large-scale discrete fracture networks. Further, early mass arrival can arrive significantly earlier for textures with strong connectivity and classical Gaussian textures corresponding to intermediate connectivity but are only slightly affected by textures with weak connectivity. Thus, accounting for internal variability in fractures is also important for accurate estimates of early solute mass arrival. The overall impact on predictive transport modeling will depend on the extent of, or lack of, internal fracture connectivity structure in real-world fractured rocks. Plain Language Summary This study investigates transport of waterborne substances in subsurface fractured bedrock, a topic which is of relevance to applications such as subsurface disposal of spent nuclear fuel, storage of carbon dioxide, and disposal of other hazardous material. A physically based numerical model for simulating water flow in the fractured bedrock system is used. Many model-based studies assume fractures to be smooth planes, which are an acknowledged simplification; however, real-world fractures are known to have rough surface asperities. In our study, we account for fracture roughness by assuming textures with different connectivity structure and investigate how this impacts waterborne transport in bedrock. We demonstrate that this type of fracture roughness can control important features of flow and waterborne mass transport. Specifically, most of the mass will generally arrive later than expected when compared to a smooth fracture plane assumption. However, we also observe that a small percentage of mass can, under certain circumstances, arrive earlier than what would be expected if smooth fracture planes are assumed. This means that the assumption of smooth fracture planes should generally be considered a conservative simplifying assumption in the context of subsurface storage, but it is less likely to be accurate when considering early mass arrival.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-257826 (URN)10.1029/2018WR024322 (DOI)000481444700018 ()2-s2.0-85068535484 (Scopus ID)
Note

QC 20190906

Available from: 2019-09-06 Created: 2019-09-06 Last updated: 2019-09-06Bibliographically approved
Zou, L., Håkansson, U. & Cvetkovic, V. (2019). Cement grout propagation in 2D fracture networks: impact of rheology. In: Sergio A.B. da Fontoura, Ricardo Jose Rocca, José Pavón Mendoza (Ed.), Proceedings in Earth and Geosciences: Rock Mechanics for Natural Resources and Infrastructure Development. Paper presented at The 14th ISRM congress, September 13 to 18, 2019 Brazil (pp. 2486-2493). CRC Press, 6
Open this publication in new window or tab >>Cement grout propagation in 2D fracture networks: impact of rheology
2019 (English)In: Proceedings in Earth and Geosciences: Rock Mechanics for Natural Resources and Infrastructure Development / [ed] Sergio A.B. da Fontoura, Ricardo Jose Rocca, José Pavón Mendoza, CRC Press, 2019, Vol. 6, p. 2486-2493Conference paper, Published paper (Refereed)
Abstract [en]

Cement grouts propagation into a two-dimensional water-saturated fracture networks with different values of rheological properties are simulated by using an extended two-phase flow model. The cement grouts are typical non-Newtonian fluids that contain yield stress, which are often assumed as Bingham fluids. The aim of this study is to investigate the impact of Bingham rheological properties, i.e. yield stress and plastic viscosity, on cement gouts propagation in two-dimensional fracture networks. The results generally show that the rheological properties of cement grouts, i.e. yield stress and plastic viscosity, significantly affect cement grouts propagation in the fracture network. The propagation rate in the fracture networks reduces with the increase of the yield stress and the plastic viscosity of the cement grouts.

Place, publisher, year, edition, pages
CRC Press, 2019
Keywords
rock grouting; cement grout; fracture networks; rheology
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering, Soil and Rock Mechanics
Identifiers
urn:nbn:se:kth:diva-260046 (URN)
Conference
The 14th ISRM congress, September 13 to 18, 2019 Brazil
Funder
Rock Engineering Research Foundation (BeFo)
Note

QC 20190930

Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-30Bibliographically approved
Zou, L., Håkansson, U. & Cvetkovic, V. (2019). Cement grout propagation in two-dimensional fracture networks: Impact of structure and hydraulic variability. International Journal of Rock Mechanics And Mining Sciences, 115, 1-10
Open this publication in new window or tab >>Cement grout propagation in two-dimensional fracture networks: Impact of structure and hydraulic variability
2019 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 115, p. 1-10Article in journal (Refereed) Published
Abstract [en]

Analysis of cement grout propagation in water-saturated two-dimensional discrete fracture networks is presented in this study. A two-phase flow model for Bingham fluids flow in a single saturated fracture is extended to simulate cement grouts propagation in saturated networks. Using this extended model, the impacts of network structure and hydraulic variability, i.e., network geometry and aperture distribution, on the propagation process are investigated through numerical simulations. Cement grout propagation in 50 realizations of a two-dimensional discrete fracture network (2D DFN) are simulated with different cases of aperture variability, i.e. constant aperture, uncorrelated and length-correlated heterogeneous apertures following a truncated lognormal distribution. The results indicate that network structure and hydraulic variability significantly affect the grout propagation in 2D DFN systems. The randomized network structure and uncorrelated heterogeneous apertures significantly delay the propagation rate and largely increase the variability range of the propagation volume fraction. In contrast, in the case with length-correlated heterogeneous apertures, the propagation rate increases, while the variability range and rate of change of the propagation volume fraction decreases. The extended two-phase flow model for fracture networks and the simulation results presented in this work are useful for basic understanding of the processes relevant for design, monitoring and execution of rock grouting.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Rock grouting, Bingham fluids, Two-phase flow, Discrete fracture networks, Propagation volume fraction, Uncertainty quantification
National Category
Geophysical Engineering
Identifiers
urn:nbn:se:kth:diva-245902 (URN)10.1016/j.ijrmms.2019.01.004 (DOI)000459008800001 ()2-s2.0-85060117035 (Scopus ID)
Note

QC 20190311

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Zou, L., Håkansson, U. & Cvetkovic, V. (2019). Characterization of effective transmissivity for cement grout flow in rock fractures. In: Proceedings of Nordic Grouting Symposium 2019: . Paper presented at Nordic Grouting Symposium 2019, 02-03 Sep 2019, Hilton Helsinki Airport, Vantaa, Finland.
Open this publication in new window or tab >>Characterization of effective transmissivity for cement grout flow in rock fractures
2019 (English)In: Proceedings of Nordic Grouting Symposium 2019, 2019Conference paper, Published paper (Refereed)
Abstract [en]

Cement grouting has been widely used in rock engineering. Proper characterization of the effective transmissivity for cement grout flow in rock fractures is primarily important for the design of rock grouting. In practice, the hydraulic transmissivity of groundwater flow in rock fractures characterized by hydraulic tests, i.e., pumping or slug test, is often used for the design of rock grouting. However, cement grouts used in rock grouting practice are typical non-Newtonian fluids contain yield stress, which has different effective transmissivity from the Newtonian groundwater. Therefore, using the groundwater transmissivity characterized by hydraulic tests may cause significant uncertainty in modeling and design of cement rock grouting. In this study, we focus on the effective transmissivity of non-Newtonian cement grout flow in a single fracture, aiming to illustrate the difference between the effective transmissivity of non-Newtonian cement grouts and the hydraulic transmissivity of the Newtonian groundwater. The cement grout is assumed as a Bingham fluid. The theoretical solution for the effective transmissivity of Bingham grout for homogeneous fractures is presented. This solution is compared with the theoretical hydraulic transmissivity, i.e., the cubic law. The results generally illustrate the significant differences between the effective transmissivity of non-Newtonian cement grouts and the hydraulic transmissivity of groundwater. The effective transmissivity of non-Newtonian cement grout is nonlinear which a function of injection pressure. Using the hydraulic transmissivity for rock grouting may underestimate the propagation length of the cement grout in rock fractures. The obtained result is helpful for rock grouting design in practice to reduce the potential uncertainties caused by using the hydraulic transmissivity.

Keywords
Cement grouting; Effective transmissivity: Hydraulic aperture: Propagation length
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-257893 (URN)
Conference
Nordic Grouting Symposium 2019, 02-03 Sep 2019, Hilton Helsinki Airport, Vantaa, Finland
Funder
Rock Engineering Research Foundation (BeFo)
Note

QC 20190917

Available from: 2019-09-08 Created: 2019-09-08 Last updated: 2019-09-17Bibliographically approved
Zou, L., Håkansson, U. & Cvetkovic, V. (2019). Non-Newtonian grout flow in single rough-walled rock fractures. In: : . Paper presented at Münchenbryggeriet i Stockholm 19-20 mars 2019.
Open this publication in new window or tab >>Non-Newtonian grout flow in single rough-walled rock fractures
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Modeling of cement grout flow in rock fractures plays an important role in the design of rock grouting. Cement grouts used in rock grouting practice are typical non-Newtonian fluids containing yield stress, and are often assumed as Bingham fluids. Natural rock fractures typically consist of rough surfaces. Therefore, in reality, rock grouting process actually involves non-Newtonian fluid flow in rough-walled fractures, which is rarely studied in the literature. In this work, we focus on the impact of surface roughness and present direct numerical simulations of non-Newtonian grouts flow in single rough-walled fractures, using a regularized method to approximate the yield-stress. The rough-walled rock fracture models are created from a laser-scanned surface of a granite rock sample, to represent realistic features of natural rock fractures. The numerical results generally show nonlinear behaviors of non-Newtonian fluid flow in rough-walled fractures. The surface roughness significantly reduces the effective transmissivity when Reynolds number is relatively large. The obtained result can be used for upscaling analysis in practice, in order to reduce the potential uncertainties caused by the surface roughness of the rock fractures.

Abstract [sv]

Modellering av cement-baserade injekteringsmedels strömning i bergsprickor spelar en viktig roll för prediktion och design. De medel som används vid injektering är typiskt icke- Newtonska, med en flytgräns, och antas därför vara av Bingham typ. Naturliga bergsprickor har vanligtvis en rå och ojämn yta. Analyser av injekteringsförlopp borde därför innehålla både icke-Newtonska vätskor och råhet hos sprickorna, vilket oftast inte är fallet i den litteratur som finns tillgänglig idag. I föreliggande arbete fokuseras på inverkan av bergsprickors råhet och numeriska beräkningar redovisas för icke-Newtonska injekteringsmedels strömning i enskilda sprickor, med hjälp av en regulariserad metod för hantering av brukets flytgräns. Sprickytornas råhet modelleras från laser-scannade ytor av granitprover för att erhålla så realistiska förhållanden som möjligt. Resultaten visar på icke-linjära effekter och att de råa sprickytorna har en avgörande inverkan på spricktransmissiviteten och att resultaten kan användas för att minska osäkerheten vid praktisk tillämpning.

Keywords
Rock grouting; cement grout; rough-walled rock fracture; Effective transmissivity
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering; Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-248043 (URN)
Conference
Münchenbryggeriet i Stockholm 19-20 mars 2019
Funder
Rock Engineering Research Foundation (BeFo)
Note

QC 20190412

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-06-11Bibliographically approved
Zou, L., Cvetkovic, V., Jing, L. & Ivars, D. M. (2018). Impact of Normal Stress Caused Closure on Fluid Flow and Solute Retention in Rock Fractures. In: : . Paper presented at The International Conference on Coupled Processes in Fractured Geological Media: Observation, Modeling, and Application (CouFrac).CouFrac – November 12-14, 2018, Wuhan, China..
Open this publication in new window or tab >>Impact of Normal Stress Caused Closure on Fluid Flow and Solute Retention in Rock Fractures
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Modeling of coupled hydro-mechanical and chemical (HMC) processes in fractured rocks is an important topic for many geoengineering projects.  Over the past decades, many efforts have been devoted to study the flow and transport in single fractures with consideration of mechanical effects. It is generally known that the mechanical effects, i.e. normal and shear deformation, significantly affect fluid flow and solute transport processes in rough-walled rock fractures since the deformation may largely alter the structure of fracture apertures that directly controls transmissivity. Due to complicated physical processes combined with complexity of geometry structures, many issues remain open questions, such as fracture surface roughness characterization, deformation dependence of transmissivity and advective transport in natural rock fractures. In this work, we attempt to investigate the impact of stress caused closure on fluid flow and solute advective transport in a rough-walled fracture through numerical modeling.  A rough-walled fracture model is created based on a laser-scanned rock surface. The Bandis’s model is used to describe the fracture closure subject to normal stress. The flow is modeled by solving Reynolds equation and the advective transport is simulated through Lagrangian particle tracking. The results show that the normal stress caused fracture closure creates asperity contacts and reduces the mean aperture, which significantly reduces transmissivity, and affects the travel time and transport resistance. With increases of normal stress, the specific surface area reduces nonlinearly due to the nonlinear closure. In practice, especially for important hydrogeological projects, e.g. nuclear waste disposal, it is important to consider the coupled HMC processes in design and risk assessment.

Keywords
normal stress; rock fracture; fluid flow; solute transport
National Category
Infrastructure Engineering Water Engineering Geophysical Engineering
Research subject
Civil and Architectural Engineering, Soil and Rock Mechanics; Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-260378 (URN)
Conference
The International Conference on Coupled Processes in Fractured Geological Media: Observation, Modeling, and Application (CouFrac).CouFrac – November 12-14, 2018, Wuhan, China.
Note

QC 20190930

Available from: 2019-09-28 Created: 2019-09-28 Last updated: 2019-09-30Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0958-7181

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