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Eshagh, Mehdi, ProfessorORCID iD iconorcid.org/0000-0003-0067-8631
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Publications (10 of 66) Show all publications
Eshagh, M., Johansson, F., Karlsson, L. & Horemuz, M. (2018). A case study on displacement analysis of Vasa warship. Journal of Geodetic Science, 8(1), 43-54
Open this publication in new window or tab >>A case study on displacement analysis of Vasa warship
2018 (English)In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 8, no 1, p. 43-54Article in journal (Refereed) Published
Abstract [en]

Monitoring deformation of man-made structures is very important to prevent them from a risk of collapse and save lives. Such a process is also used for monitoring change in historical objects, which are deforming continuously with time. An example of this is the Vasa warship, which was under water for about 300 years. The ship was raised from the bottom of the sea and is kept in the Vasa museum in Stockholm. A geodetic network with points on the museum building and the ship's body has been established and measured for 12 years for monitoring the ship's deformation. The coordinate time series of each point on the ship and their uncertainties have been estimated epoch-wisely. In this paper, our goal is to statistically analyse the ship's hull movements. By fitting a quadratic polynomial to the coordinate time series of each point of the hull, its acceleration and velocity are estimated. In addition, their significance is tested by comparing them with their respective estimated errors after the fitting. Our numerical investigations show that the backside of the ship, having highest elevation and slope, has moved vertically faster than the other places by a velocity and an acceleration of about 2 mm/year and 0.1 mm/year2, respectively and this part of the ship is the weakest with a higher risk of collapse. The central parts of the ship are more stable as the ship hull is almost vertical and closer to the floor. Generally, the hull is moving towards its port and downwards

Place, publisher, year, edition, pages
Versita, 2018
Keywords
error estimation; coordinate and displacement time series; significance test
National Category
Infrastructure Engineering
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12231 (URN)10.1515/jogs-2018-0006 (DOI)
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2018-10-22Bibliographically approved
Eshagh, M., Steinberger, B., Tenzer, R. & Tassara, A. (2018). Comparison of gravimetric and mantle flow solutions for sub-lithopsheric stress modeling and their combination. Geophysical Journal International, 213(2), 1013-1028
Open this publication in new window or tab >>Comparison of gravimetric and mantle flow solutions for sub-lithopsheric stress modeling and their combination
2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, no 2, p. 1013-1028Article in journal (Refereed) Published
Abstract [en]

Based on Hager and O’Connell’s solution to mantle flow equations, the stresses induced by mantle convection are determined using the density and viscosity structure in addition to topographic data and a plate velocity model. The solution to mantle flow equations requires the knowledge of mantle properties that are typically retrieved from seismic information. Large parts of the world are, however, not yet covered sufficiently by seismic surveys. An alternative method of modeling the stress field was introduced by Runcorn. He formulated a direct relation between the stress field and gravity data, while adopting several assumptions, particularly disregarding the toroidal mantle flow component and mantle viscosity variations. A possible way to overcome theoretical deficiencies of Runcorn’s theory as well as some practical limitations of applying Hager and O’Connell’s theory (in the absence of seismic data) is to combine these two methods. In this study, we apply a least-squares analysis to combine these two methods based on the gravity data inversion constraint on mantle flow equations. In particular, we use vertical gravity gradients from the Gravity field and steady state Ocean Circulation Explorer that are corrected for the gravitational contribution of crustal density heterogeneities prior to applying a localized gravity-gradient inversion. This gravitational contribution is estimated based on combining the Vening Meinesz-Moritz and flexural isostatic theories. Moreover, we treat the non-isostatic effect implicitly by applying a band-limited kernel of the integral equation during the inversion. In numerical studies of modeling, the stress field within the South American continental lithosphere we compare the results obtained after applying Runcorn and Hager and O’Connell’s methods as well as their combination. The results show that, according to Hager and O’Connell’s (mantle flow) solution, the maximum stress intensity is inferred under the northern Andes. Additional large stress anomalies are detected along the central and southern Andes, while stresses under most of old, stable cratonic formations aremuch less pronounced or absent. A prevailing stress-vector orientation realistically resembles a convergent mantle flow and downward currents under continental basins that separate Andean Orogeny from the Amazonian Shield and adjacent cratons. Runcorn’s (gravimetric) solution, on the other hand, reflects a tectonic response of the lithosphere to mantle flow, with the maximum stress intensity detected along the subduction zone between the Nazca and Altiplano plates and along the convergent tectonic margin between the Altiplano and South American plates. The results also reveal a very close agreement between the results obtained from the combined and Hager and O’Connell’s solutions. © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keywords
Gravitation; Integral equations; Least squares approximations; Lithology; Numerical methods; Plates (structural components); Seismology; Stresses; Structural geology; Viscosity, Continental basins; Continental lithosphere; Gravity anomalies and Earth structures; Gravity field and steady state ocean circulation explorers; Least squares analysis; Maximum stress intensity; Satellite gravity; Seismic information, Tectonics
National Category
Geophysics
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12246 (URN)10.1093/gji/ggy033 (DOI)000448720300021 ()2-s2.0-85044350246 (Scopus ID)
Available from: 2018-04-09 Created: 2018-04-09 Last updated: 2018-11-15Bibliographically approved
Eshagh, M., Steinberger, B., Tenzer, R. & Tassara, A. (2018). Comparison of gravimetric and mantle flow solutions for sub-lithospheric stress modeling and their combination. Geophysical Journal International, 213(2), 1013-1028
Open this publication in new window or tab >>Comparison of gravimetric and mantle flow solutions for sub-lithospheric stress modeling and their combination
2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, no 2, p. 1013-1028Article in journal (Refereed) Published
Abstract [en]

Based on Hager and O’Connell's solution to mantle flow equations, the stresses induced by mantle convection are determined using the density and viscosity structure in addition to topographic data and a plate velocity model. The solution to mantle flow equations requires the knowledge of mantle properties that are typically retrieved from seismic information. Large parts of the world are, however, not yet covered sufficiently by seismic surveys. An alternative method of modeling the stress field was introduced by Runcorn. He formulated a direct relation between the stress field and gravity data, while adopting several assumptions, particularly disregarding the toroidal mantle flow component and mantle viscosity variations. A possible way to overcome theoretical deficiencies of Runcorn's theory as well as some practical limitations of applying Hager and O’Connell's theory (in the absence of seismic data) is to combine these two methods. In this study, we apply a least-squares analysis to combine these two methods based on the gravity data inversion constraint on mantle flow equations. In particular, we use vertical gravity gradients from the Gravity field and steady state Ocean Circulation Explorer that are corrected for the gravitational contribution of crustal density heterogeneities prior to applying a localized gravity-gradient inversion. This gravitational contribution is estimated based on combining the Vening Meinesz-Moritz and flexural isostatic theories. Moreover, we treat the non-isostatic effect implicitly by applying a band-limited kernel of the integral equation during the inversion. In numerical studies of modeling, the stress field within the South American continental lithosphere we compare the results obtained after applying Runcorn and Hager and O’Connell's methods as well as their combination. The results show that, according to Hager and O’Connell's (mantle flow) solution, the maximum stress intensity is inferred under the northern Andes. Additional large stress anomalies are detected along the central and southern Andes, while stresses under most of old, stable cratonic formations are much less pronounced or absent. A prevailing stress-vector orientation realistically resembles a convergent mantle flow and downward currents under continental basins that separate Andean Orogeny from the Amazonian Shield and adjacent cratons. Runcorn's (gravimetric) solution, on the other hand, reflects a tectonic response of the lithosphere to mantle flow, with the maximum stress intensity detected along the subduction zone between the Nazca and Altiplano plates and along the convergent tectonic margin between the Altiplano and South American plates. The results also reveal a very close agreement between the results obtained from the combined and Hager and O’Connell's solutions.

Keywords
Gravity anomalies and Earth structure, Loading of the Earth, Satellite gravity
National Category
Geophysics
Identifiers
urn:nbn:se:hv:diva-12052 (URN)10.1093/gji/ggy033 (DOI)
Available from: 2018-02-01 Created: 2018-02-01 Last updated: 2018-11-06Bibliographically approved
Eshagh, M. (2018). Elastic thickness determination based on Vening Meinesz-Moritz and flexural theories of isostasy. Geophysical Journal International, 213(3), 1682-1692
Open this publication in new window or tab >>Elastic thickness determination based on Vening Meinesz-Moritz and flexural theories of isostasy
2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, no 3, p. 1682-1692Article in journal (Refereed) Published
Abstract [en]

Elastic thickness (Te) is one of mechanical properties of the Earth's lithosphere. The lithosphere is assumed to be a thin elastic shell, which is bended under the topographic, bathymetric and sediment loads on. The flexure of this elastic shell depends on its thickness or Te. Those shells having larger Te flex less. In this paper, a forward computational method is presented based on the Vening Meinesz–Moritz (VMM) and flexural theories of isostasy. Two Moho flexure models are determined using these theories, considering effects of surface and subsurface loads. Different values are selected for Te in the flexural method to see by which one, the closest Moho flexure to that of the VMM is achieved. The effects of topographic/bathymetric, sediments and crustal crystalline masses, and laterally variable upper mantle density, Young's modulus and Poisson's ratio are considered in whole computational process. Our mathematical derivations are based on spherical harmonics, which can be used to estimate Te at any single point, meaning that there is no edge effect in the method. However, the Te map needs to be filtered to remove noise at some points. A median filter with a window size of 5° × 5° and overlap of 4° works well for this purpose. The method is applied to estimate Te over South America using the data of CRUST1.0 and a global gravity model.

Keywords
GEODESY and GRAVITY, Gravity anomalies and Earth structure, Loading of the Earth
National Category
Geophysics
Identifiers
urn:nbn:se:hv:diva-12170 (URN)10.1093/gji/ggy075 (DOI)000434675800017 ()2-s2.0-85052655258 (Scopus ID)
Available from: 2018-02-26 Created: 2018-02-26 Last updated: 2018-09-27Bibliographically approved
Eshagh, M. & Pitoňák, M. (2018). Elastic Thickness Determination from on-orbit GOCE Data and CRUST1.0. Pure and Applied Geophysics
Open this publication in new window or tab >>Elastic Thickness Determination from on-orbit GOCE Data and CRUST1.0
2018 (English)In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136Article in journal (Refereed) Epub ahead of print
Abstract [en]

Elastic thickness (Te) is a parameter representing the lithospheric strength with respect to the loading. Those places, having large values of elastic thickness, flexes less. In this paper, the on-orbit measured gravitational gradients of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission are used for determining the elastic thickness over Africa. A forward computational method is developed based on the Vening Meinesz-Moritz (VMM) and flexural theories of isostasy to find a mathematical relation between the second-order derivative of the Earth’s gravity field measured by the GOCE satellite and mechanical properties of the lithosphere. The loading of topography and bathymetry, sediments and crystalline masses are computed from CRUST1.0, in addition to estimates of laterally-variable density of the upper mantle, Young’s modulus and Poisson’s ratio. The second-order radial derivatives of the gravitational potential are synthesised from the crustal model and different a priori values of elastic thickness to find which one matches the GOCE on-orbit gradient. This method is developed in terms of spherical harmonics and performed at any point along the GOCE orbit without using any planar approximation. Our map of Te over Africa shows that the intra-continental hotspots and volcanoes, such as Ahaggar, Tibesti, Darfur, Cameroon volcanic line and Libya are connected by corridors of low Te. The high values of Te are mainly associated with the cratonic areas of Congo, Chad and the Western African basin.

Place, publisher, year, edition, pages
Birkhäuser Verlag, 2018
Keywords
Elastic thickness, Forward modelling, GOCE gravitational gradients, Isostasy
National Category
Geophysics
Research subject
ENGINEERING, Geodesy
Identifiers
urn:nbn:se:hv:diva-13113 (URN)10.1007/s00024-018-2018-3 (DOI)
Note

First Online: 06 November 2018

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2018-11-14Bibliographically approved
Zampal, L., Tenzer, R., Eshagh, M. & Pitonak, M. (2018). Evidence of mantle upwelling/downwelling and localized subduction on Venus from the body-force vector analysis. Planetary and Space Science, 157, 48-62
Open this publication in new window or tab >>Evidence of mantle upwelling/downwelling and localized subduction on Venus from the body-force vector analysis
2018 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 157, p. 48-62Article in journal (Refereed) Published
Abstract [en]

Considering that Venus has a size very similar to Earth, thermal evolution of both planets should be comparable. Nonetheless, there is no clear evidence of plate tectonics or plate motions on Venus. Instead, various surface deformations attributed to volcanism, resurfacing, localized subduction and other geologic processes were recognized on the planet. In this study we attempt to classify the origin of lithospheric forces on Venus based on using topographic and gravity information. For this purpose, we also estimate the Venusian crustal thickness. In agreement with findings from previous studies, the signature of past or recent global tectonism in the body-force vector pattern on Venus is absent, while exhibiting only regional anomalies. The maximum intensity inferred in the Atla and Beta Regios is likely attributed to mantle upwelling. This is also confirmed by the gravity-topography spectral correlation and admittance analysis that shows the isostatic relaxation of these volcanic regions. The regional body-force pattern in the Bell Regio suggests that a much less pronounced force intensity there is possibly related to crustal load of lava flows. Elsewhere, the body-force intensity is relatively weak, with slightly more pronounced intensity around the Ishtar Terra and the Arthemis Chasmata. The body-force pattern in the Arthemis Chasmata supports the hypothesis that coronae structures are the result of mantle upwelling and the subsequent (localized) plume-induced subduction with only limited horizontal crustal motions. The prevailing divergent pattern of body-force vectors in the Ishtar Terra region suggests the presence of tensional forces due to the downwelling mantle flow that is responsible for a crustal thickening along the Freyja and Maxwell Montes. Except for the Atla and Beta Regios where the isostasy is relaxed by the (active) mantle plumes, the crustal thickness is spatially highly correlated with the topography, with a thin crust under the plains and a thick crust under the plateaus. The maximum Moho depth under the Maxwell Montes in the Ishtar Terra exceeds 90 km.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2018
Keywords
Crust, Gravity, Mantle, Moho, Body forces, Venus
National Category
Earth and Related Environmental Sciences
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12229 (URN)10.1016/j.pss.2018.03.013 (DOI)2-s2.0-85044384729 (Scopus ID)
Note

Available online 24 March 2018

Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2018-08-28Bibliographically approved
Alizadeh-Khameneh, M. A., Eshagh, M. & Jensen, A. O. (2018). Optimization of deformation monitoring networks using finite element strain analysis. Journal of Applied Geodesy, 2(2), 187-197
Open this publication in new window or tab >>Optimization of deformation monitoring networks using finite element strain analysis
2018 (English)In: Journal of Applied Geodesy, ISSN 1862-9016, E-ISSN 1862-9024, Vol. 2, no 2, p. 187-197Article in journal (Refereed) Published
Abstract [en]

An optimal design of a geodetic network can fulfill the requested precision and reliability of the network, and decrease the expenses of its execution by removing unnecessary observations. The role of an optimal design is highlighted in deformation monitoring network due to the repeatability of these networks. The core design problem is how to define precision and reliability criteria. This paper proposes a solution, where the precision criterion is defined based on the precision of deformation parameters, i. e. precision of strain and differential rotations. A strain analysis can be performed to obtain some information about the possible deformation of a deformable object. In this study, we split an area into a number of three-dimensional finite elements with the help of the Delaunay triangulation and performed the strain analysis on each element. According to the obtained precision of deformation parameters in each element, the precision criterion of displacement detection at each network point is then determined. The developed criterion is implemented to optimize the observations from the Global Positioning System (GPS) in Skåne monitoring network in Sweden. The network was established in 1989 and straddled the Tornquist zone, which is one of the most active faults in southern Sweden. The numerical results show that 17 out of all 21 possible GPS baseline observations are sufficient to detect minimum 3 mm displacement at each network point. © 2018 Walter de Gruyter GmbH, Berlin/Boston.

Keywords
Optimization; monitoring networks; GPS; deformation parameters; finite elements; strain analysis
National Category
Earth and Related Environmental Sciences
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12228 (URN)10.1515/jag-2017-0040 (DOI)2-s2.0-85045196739 (Scopus ID)
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2018-04-25Bibliographically approved
Seif, M. R., Sharifi, M. A. & Eshagh, M. (2018). Polynomial approximation for fast generation of associated Legendre functions. Acta Geodaetica et Geophysica, 53(2), 275-293
Open this publication in new window or tab >>Polynomial approximation for fast generation of associated Legendre functions
2018 (English)In: Acta Geodaetica et Geophysica, ISSN 2213-5812, Vol. 53, no 2, p. 275-293Article in journal (Refereed) Published
Abstract [en]

Today high-speed computers have simplified many computational problems, but fast techniques and algorithms are still relevant. In this study, the Hermitian polynomial approximation is used for fast evaluation of the associated Legendre functions (ALFs). It has lots of applications in geodesy and geophysics. This method approximates the ALFs instead of computing them by recursive formulae and generate them several times faster. The approximated ALFs by the Newtonian polynomials are compared with Hermitian ones and their differences are discussed. Here, this approach is applied for computing a global geoid model point-wise from EGM08 to degree and order 2160 and in propagating the orbit of a low Earth orbiting satellite. Our numerical results show that the CPU-time decreases at least two times for orbit propagation, and five times for geoid computation comparing to the case where recursive formulae for generation of ALFs are used. The approximation error in the orbit computation is at a sub-millimeter level over two weeks and that the computed geoid 0.01 mm, with a maximum of 1 mm

Place, publisher, year, edition, pages
Springer Netherlands, 2018
Keywords
Orbits, Approximation errors; Associated Legendre functions; Computational problem; Hermite polynomials; High speed computers; Low earth orbiting satellites; Newton polynomials; Orbit propagation, Polynomial approximation
National Category
Geophysics
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-12479 (URN)10.1007/s40328-018-0216-1 (DOI)000445505100007 ()2-s2.0-85047242977 (Scopus ID)
Note

First Online: 28 April 2018

Available from: 2018-06-15 Created: 2018-06-15 Last updated: 2018-10-25Bibliographically approved
Pitonak, M., Eshagh, M., Sprlak, M., Tenzer, R. & Novak, P. (2018). Spectral combination of spherical gravitational curvature boundary-value problems. Geophysical Journal International, 214(2), 773-791
Open this publication in new window or tab >>Spectral combination of spherical gravitational curvature boundary-value problems
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2018 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 214, no 2, p. 773-791Article in journal (Refereed) Published
Abstract [en]

Four solutions of the spherical gravitational curvature boundary-value problems can be exploited for the determination of the Earth’s gravitational potential. In this paper we discuss the combination of simulated satellite gravitational curvatures, that is, components of the third-order gravitational tensor, by merging these solutions using the spectral combination method. For this purpose, integral estimators of biased-and unbiased-types are derived. In numerical studies, we investigate the performance of the developed mathematical models for the gravitational field modelling in the area of Central Europe based on simulated satellite measurements. First, we verify the correctness of the integral estimators for the spectral downward continuation by a closed-loop test. Estimated errors of the combined solution are about eight orders smaller than those from the individual solutions. Second, we perform a numerical experiment by considering the Gaussian noise with the standard deviation of 6.5 x 10(-17) m(-1) s(-2) in the input data at the satellite altitude of 250 km above the mean Earth sphere. This value of standard deviation is equivalent to a signal-to-noise ratio of 10. Superior results with respect to the global geopotential model TIM-r5 (Brockmann et al. 2014) are obtained by the spectral downward continuation of the vertical-vertical-vertical component with the standard deviation of 2.104 m(2) s(-2), but the root mean square error is the largest and reaches 9.734 m(2) s(-2). Using the spectral combination of all gravitational curvatures the root mean square error is more than 400 times smaller but the standard deviation reaches 17.234 m(2) s(-2). The combination of more components decreases the root mean square error of the corresponding solutions while the standard deviations of the combined solutions do not improve as compared to the solution from the vertical-vertical-vertical component. The presented method represents a weight mean in the spectral domain that minimizes the root mean square error of the combined solutions and improves standard deviation of the solution based only on the least accurate components.

Place, publisher, year, edition, pages
Blackwell Publishing, 2018
Keywords
Geopotential theory; Inverse theory; Satellite geodesy
National Category
Geophysics
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-13107 (URN)10.1093/gji/ggy147 (DOI)000448238600002 ()
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-08Bibliographically approved
Eshagh, M., Ebadi, S. & Tenzer, R. (2017). Isostatic GOCE Moho model for Iran. Journal of Asian Earth Sciences, 138, 12-24
Open this publication in new window or tab >>Isostatic GOCE Moho model for Iran
2017 (English)In: Journal of Asian Earth Sciences, ISSN 1367-9120, E-ISSN 1878-5786, Vol. 138, p. 12-24Article in journal (Refereed) Published
Abstract [en]

One of the major issues associated with a regional Moho recovery from the gravity or gravity-gradient data is the optimal choice of the mean compensation depth (i.e., the mean Moho depth) for a certain area of study, typically for orogens characterised by large Moho depth variations. In case of selecting a small value of the mean compensation depth, the pattern of deep Moho structure might not be reproduced realistically. Moreover, the definition of the mean compensation depth in existing isostatic models affects only low-degrees of the Moho spectrum. To overcome this problem, in this study we reformulate the Sjöberg and Jeffrey’s methods of solving the Vening-Meinesz isostatic problem so that the mean compensation depth contributes to the whole Moho spectrum. Both solutions are then defined for the vertical gravity gradient, allowing estimating the Moho depth from the GOCE satellite gravity-gradiometry data. Moreover, gravimetric solutions provide realistic results only when a priori information on the crust and upper mantle structure is known (usually from seismic surveys) with a relatively good accuracy. To investigate this aspect, we formulate our gravimetric solutions for a variable Moho density contrast to account for variable density of the uppermost mantle below the Moho interface, while taking into consideration also density variations within the sediments and consolidated crust down to the Moho interface. The developed theoretical models are applied to estimate the Moho depth from GOCE data at the regional study area of the Iranian tectonic block, including also parts of surrounding tectonic features. Our results indicate that the regional Moho depth differences between Sjöberg and Jeffrey’s solutions, reaching up to about 3 km, are caused by a smoothing effect of Sjöberg’s method. The validation of our results further shows a relatively good agreement with regional seismic studies over most of the continental crust, but large discrepancies are detected under the Oman Sea and the Makran subduction zone. We explain these discrepancies by a low quality of seismic data offshore.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Crust; Integral inversion; Moho; Satellite gradiometry; Isostasy
National Category
Geophysics
Research subject
ENGINEERING
Identifiers
urn:nbn:se:hv:diva-10634 (URN)10.1016/j.jseaes.2017.01.033 (DOI)000401376300002 ()2-s2.0-85011982897 (Scopus ID)
Available from: 2017-01-27 Created: 2017-01-27 Last updated: 2017-12-18Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0067-8631

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