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Kabanshi, A., Andersson, H., Sundberg, M., Senkic, D. & Sandberg, M. (2024). Assessing airborne infection risk through a model of airflow evacuation and recirculation dynamics.. In: : . Paper presented at RoomVent Conference, April 22-25, Stockholm, Sweden.
Open this publication in new window or tab >>Assessing airborne infection risk through a model of airflow evacuation and recirculation dynamics.
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2024 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In a ventilated room, the indoor airflows are complicated but can generally be defined by an internal recirculating airflow generated by flooding of ventilation air. This concept categorizes the internal room flow (air and contaminants) as consist of two populations: One leaving the room and the other recirculating. The one recirculating is spreading the contaminants while the one leaving is evacuating the contaminants, which are quantified by the transfer probability between the source and other locations in the room and by purging flow rate, respectively. This concept accounts for spatial and temporal aspects in risk of airborne infection transmission. The current paper proposes and discusses a revised risk infection model based on this concept and has demonstrated applicability of the model with a test measurement setup with both mixing and displacement ventilation systems. The results emphasize the importance of considering both spatial and temporal factors in assessing airborne infection risks. It underscores the need for dynamic models like the proposed revised Wells-Riley model to provide a more accurate representation of infection risks in various indoor environments. Additionally, it discusses the necessity for longer measurement periods to fully understand the evolving nature of these risks. 

Keywords
Infectious respiratory disease, Airborne infection risk, Air recirculation, purging flowrate, Contaminant flooding
National Category
Building Technologies Mechanical Engineering
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-44122 (URN)
Conference
RoomVent Conference, April 22-25, Stockholm, Sweden
Available from: 2024-04-26 Created: 2024-04-26 Last updated: 2024-04-29Bibliographically approved
Lin, Y., Sandberg, M., Cehlin, M., Claesson, L. & Wigö, H. (2024). Experimental studies of single-sided ventilation for semi-enclosed models with horizontal opening. In: Proceedings of the 17th ROOMVENT Conference: . Paper presented at The 17th ROOMVENT Conference, Stockholm, Sweden, April 22 - 25, 2024.
Open this publication in new window or tab >>Experimental studies of single-sided ventilation for semi-enclosed models with horizontal opening
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2024 (English)In: Proceedings of the 17th ROOMVENT Conference, 2024Conference paper, Published paper (Refereed)
Abstract [en]

As a preliminary investigation of the wind-driven purging process for densely built environments through the canopy layer, the ventilation efficiency of standalone semi-enclosed models incorporating a horizontal opening in the roof façade was investigated in the wind tunnel. For comparison, two models with different geometries were constructed, and each model was tested individually. Both models were equipped with replaceable roof covers, enabling the adjustment to the opening size. The ventilation efficiency was evaluated by continuous releasing and sampling of the tracer gas, from which the normalized purging velocity (PFVn) was derived. Additionally, the flow condition over the opening was monitored using the Laser Doppler Anemometer. It was found that separation flows from the frontal edge(s) of the model could introduce secondary circulations across large openings, resulting in dramatic increases in PFVn. Both the rectangular prism model and cylinder model possessed higher PFVn compared to prior studies on single-sided ventilation, while close values were observed with cylinder model mounted under the wind tunnel floor. Besides, the vertical distribution of integral length scales of streamwise velocity indicated the stratification feature of separation flows under low-turbulent incoming flow conditions. Measurement results provide validation data for further simulation studies including more detailed structures.

Keywords
Urban ventilation, purging velocity, wind tunnel, tracer gas, single-sided ventilation, semi-enclosed model
National Category
Fluid Mechanics Energy Engineering
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-44569 (URN)
Conference
The 17th ROOMVENT Conference, Stockholm, Sweden, April 22 - 25, 2024
Funder
Swedish Research Council Formas, 2018–00238
Available from: 2024-06-12 Created: 2024-06-12 Last updated: 2025-02-05Bibliographically approved
Andersson, H., Sundberg, M., Senkic, D., Sandberg, M. & Kabanshi, A. (2024). FAST-AIR: Fast analytic systems for tracer-gas assessment in indoor research: Development and testing of CO2 tracer-gas system.. In: : . Paper presented at RoomVent Conference, 22nd - 25th April, Stockholm Sweden.
Open this publication in new window or tab >>FAST-AIR: Fast analytic systems for tracer-gas assessment in indoor research: Development and testing of CO2 tracer-gas system.
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2024 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The time constant of ventilation of rooms in buildings is between 15 minutes (in office spaces) to 2 hours (in residential buildings). Currently, most of the tracer gas system analyzers on the market have a minute-based time constant and depending on the channels a cycle of sampling and analysis may take up to 6 minutes, E.g., 6 channel system. Essentially, only mean values are recorded with most present tracer gas analyzers. This is a hindrance for detailed temporal analysis of conditions in the room and consequently is does not capture the resolution of the influence of the internal flow on air and contaminant distribution. The current paper presents work on the development and testing of a fast response CO2 tracer-gas system with a time constant of 1 second. In contrast to the present analyzers, not only the mean values but also the whole statistical distribution of variables can be recorded, and pulse responses can be analyzed. This makes the system viable for measurement and analysis of not only spatial but also temporal distribution of contaminants. For example, recirculating airflow in the room generated by flooding of ventilation air is possible to be measured and thus making it easy to extend the analyses of the process of ventilation far beyond the possibilities with current systems.

Keywords
Tracer-gas Analyzer, fast response, temporal distribution, contaminant transport, indoor measurements
National Category
Mechanical Engineering Building Technologies
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-44121 (URN)
Conference
RoomVent Conference, 22nd - 25th April, Stockholm Sweden
Funder
Swedish Research Council Formas, Dnr: 2021-01606
Available from: 2024-04-26 Created: 2024-04-26 Last updated: 2024-05-02Bibliographically approved
Lin, Y., Cehlin, M., Ameen, A., Sandberg, M. & Wallhagen, M. (2024). Influence of Urban Morphologies on the Effective Mean Age of Air at Pedestrian Level and Mass Transport Within Urban Canopy Layer. Buildings, 14, Article ID 3591.
Open this publication in new window or tab >>Influence of Urban Morphologies on the Effective Mean Age of Air at Pedestrian Level and Mass Transport Within Urban Canopy Layer
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2024 (English)In: Buildings, E-ISSN 2075-5309, Vol. 14, article id 3591Article in journal (Refereed) Published
Abstract [en]

This study adapted the mean age of air, a time scale widely utilized in evaluating indoor ventilation, to assess the impact of building layouts on urban ventilation capacity. To distinguish it from its applications in enclosed indoor environments, the adapted index was termed the effective mean age of air (TE). Based on an experimentally validated method, computational fluid dynamic (CFD) simulations were performed for parametric studies on four generic parameters that describe urban morphologies, including building height, building density, and variations in the heights or frontal areas of adjacent buildings. At the breathing level (z = 1.7 m), the results indicated three distinct distribution patterns of insufficiently ventilated areas: within recirculation zones behind buildings, in the downstream sections of the main road, or within recirculation zones near lateral facades. The spatial heterogeneity of ventilation capacity was emphasized through the statistical distributions of TE. In most cases, convective transport dominates the purging process for the whole canopy zone, while turbulent transport prevails for the pedestrian zone. Additionally, comparisons with a reference case simulating an open area highlighted the dual effects of buildings on urban ventilation, notably through the enhanced dilution promoted by the helical flows between buildings. This study also serves as a preliminary CFD practice utilizing TE with the homogenous emission method, and demonstrates its capability for assessing urban ventilation potential in urban planning.

Place, publisher, year, edition, pages
MDPI, 2024
Keywords
urban ventilation; effective mean age of air; pollutant transport; computational fluid dynamics; building layout
National Category
Fluid Mechanics
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-45997 (URN)10.3390/buildings14113591 (DOI)001366684600001 ()2-s2.0-85210230933 (Scopus ID)
Funder
Swedish Research Council Formas, 2018-00238
Available from: 2024-11-12 Created: 2024-11-12 Last updated: 2025-02-09Bibliographically approved
Jiang, Z., Kobayashi, T., Yamanaka, T., Sandberg, M., Yamasawa, H. & Shohei, M. (2024). The similitude of indoor airflow in natural ventilation for a reduced-scale model: Investigation of nonisothermal flow fields by RANS simulation. Building and Environment, 262, Article ID 111842.
Open this publication in new window or tab >>The similitude of indoor airflow in natural ventilation for a reduced-scale model: Investigation of nonisothermal flow fields by RANS simulation
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2024 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 262, article id 111842Article in journal (Refereed) Published
Abstract [en]

Reduced-scale experiments and simulations are important approaches in natural ventilation research, and the similarity requirement is fundamental for generalising the flow characteristics obtained from reduced-to full-scale conditions. However, the similarity requirement of a nonisothermal natural ventilation flow in a reduced-scale model poses additional challenges because of the reduced approaching flow, which can potentially result in Reynolds dependence issues. This study investigated the Reynolds number (Re) independence of indoor airflow in natural ventilation under isothermal and nonisothermal conditions using computational fluid dynamics (CFD) with Reynolds-averaged Navier–Stokes. A wind tunnel experiment was first conducted to validate the accuracy of the CFD using a reduced-scale model. Indoor airflow fields characterised by the same Archimedes number (Ar) but with varying approaching wind velocities and temperatures were compared between the full-scale and 1/10 reduced-scale simulations. The dimensionless ventilation rate showed the least dependence on the Re number, while the temperature field was very sensitive to the Re number, especially in the near-wall region. However, the temperature field on the ventilation pathway is much less dependent on the Re number, the deviation of which is less than 10 % compared to the full-scale simulation. The temperature distribution in the reduced-scale simulation exhibits a thermal stratification pattern similar to that in the full-scale simulation.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Similarity, Natural ventilation, Buoyant flow, Reynolds number independence, Computational fluid dynamics (CFD)
National Category
Civil Engineering
Identifiers
urn:nbn:se:hig:diva-45270 (URN)10.1016/j.buildenv.2024.111842 (DOI)001273680400001 ()2-s2.0-85198594911 (Scopus ID)
Available from: 2024-07-24 Created: 2024-07-24 Last updated: 2024-12-16Bibliographically approved
Jiang, Z., Kobayashi, T., Yamanaka, T., Sandberg, M., Yamasawa, H., Miyazawa, S. & Miura, R. (2024). Wind tunnel experiment of ventilation rate and airflow characteristics in natural ventilation induced by wind and buoyancy effects. The International Journal of Ventilation
Open this publication in new window or tab >>Wind tunnel experiment of ventilation rate and airflow characteristics in natural ventilation induced by wind and buoyancy effects
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2024 (English)In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044Article in journal (Refereed) Epub ahead of print
Abstract [en]

In this paper, the investigation focused on natural ventilation induced by wind and buoyancy effects through a wind tunnel experiment. A scaled-down model of a single-zone building featuring two opposing openings at varying heights was subjected to uniform heating from a source on the interior floor. Wind pressure coefficient differences were measured in a sealed model to assess the wind’s driving force. Indoor and outdoor temperatures were recorded to ascertain the buoyancy-driven driving force. The ventilation rate was assessed using the tracer gas constant emission method, while airflow characteristics were quantified through particle image velocimetry (PIV). The comparison between predicted and measured ventilation rates revealed generally good accuracy in cases where wind assists buoyancy. However, errors were evident in cases of opposing wind and buoyancy due to neglecting the effect of wind turbulence. The airflow in cases of opposing wind and buoyancy effects demonstrates the most dynamic changes, as illustrated through flow visualizations and transient temperature fluctuations at the openings.

Place, publisher, year, edition, pages
Taylor & Francis, 2024
Keywords
buoyancy-driven ventilation; Natural ventilation; ventilation rate; wind tunnel experiment; wind-driven ventilation
National Category
Civil Engineering
Identifiers
urn:nbn:se:hig:diva-45906 (URN)10.1080/14733315.2024.2419284 (DOI)001340776600001 ()2-s2.0-85207490848 (Scopus ID)
Available from: 2024-11-04 Created: 2024-11-04 Last updated: 2024-11-08Bibliographically approved
Jiang, Z., Kobayashi, T., Yamanaka, T., Sandberg, M., Choi, N., Kobayashi, N., . . . Toyosawa, K. (2024). Wind-induced ventilation rate of single-sided ventilation in a building with internal partition. The International Journal of Ventilation, 23(3), 237-258
Open this publication in new window or tab >>Wind-induced ventilation rate of single-sided ventilation in a building with internal partition
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2024 (English)In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 23, no 3, p. 237-258Article in journal (Refereed) Published
Abstract [en]

Wind-induced single-sided ventilation is a prevalent form of natural ventilation extensively used in buildings. Nevertheless, prior experimental investigations predominantly focused on single-zone buildings, neglecting the multizone buildings with internal partitions which is representative of more common scenarios. This study addresses this gap by investigating the impact of internal partitions on single-sided ventilation, employing a combination of wind tunnel experiment and numerical analysis. Airflow rate (AFR) was measured with a split-fibre probe and purging flow rate (PFR) was assessed by the tracer gas methodology. The PFR exhibits greater sensitivity to internal partitions in unidirectional airflow compared to bidirectional flow. Large Eddy Simulation (LES) was conducted to elucidate the intricate airflow characteristics in single-sided ventilation. The ventilation efficiency (ratio of PFR and AFR) derived from LES ranges between 0.74 and 0.79, which means that <80% of the AFR actively contributes to the removal of contaminants. Notably, the investigation discerned that the AFR of a single room approximates that of the entire room, whereas the PFR of a single room is smaller than that of the whole room. The disparities in AFR and PFR were caused by the recirculating flow, which was elaborated by the theoretical analysis.

Place, publisher, year, edition, pages
Taylor & Francis, 2024
Keywords
Natural ventilation, wind tunnel experiment, Large Eddy Simulation, single-sided ventilation, ventilation rate
National Category
Civil Engineering
Identifiers
urn:nbn:se:hig:diva-43910 (URN)10.1080/14733315.2024.2319475 (DOI)001174527800001 ()2-s2.0-85186417795 (Scopus ID)
Available from: 2024-03-15 Created: 2024-03-15 Last updated: 2024-12-17Bibliographically approved
Jiang, Z., Kobayashi, T., Yamanaka, T. & Sandberg, M. (2023). A literature review of cross ventilation in buildings. Energy and Buildings, 291, Article ID 113143.
Open this publication in new window or tab >>A literature review of cross ventilation in buildings
2023 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 291, article id 113143Article in journal (Refereed) Published
Abstract [en]

There is a growing body of literature that recognizes that natural ventilation plays avital role in indoor air quality, thermal comfort and building energy consumption. This papersystematically reviews the previously published research of the most efficient and typical naturalventilation type - cross ventilation, aiming to present the main research topics in contemporaryresearch and provide an agenda for future studies. The methodologies, airflow pattern, ventilationmodels and influencing parameters of cross ventilation were comprehensively summarized anddiscussed. The chained analysis and data-driven methods are the potential approaches to study crossventilation more efficiently. The comparisons of different ventilation models of cross ventilationhelp to better understand the basic mechanisms that drive the cross ventilation airflow.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Cross ventilation, Natural ventilation, Power balance model, Local dynamic similarity, Discharge coefficient
National Category
Energy Engineering
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-41743 (URN)10.1016/j.enbuild.2023.113143 (DOI)001009105400001 ()2-s2.0-85159367213 (Scopus ID)
Available from: 2023-05-09 Created: 2023-05-09 Last updated: 2023-07-20Bibliographically approved
Jiang, Z., Kobayashi, T., Sandberg, M., Yamanaka, T., Kobayashi, N., Choi, N., . . . Toyosawa, K. (2023). Analysis of single-sided ventilation flows of a generic isolated building using particle tracking method in LES simulation. Building and Environment, 235, Article ID 110230.
Open this publication in new window or tab >>Analysis of single-sided ventilation flows of a generic isolated building using particle tracking method in LES simulation
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2023 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 235, article id 110230Article in journal (Refereed) Published
Abstract [en]

The main objective of this study is to investigate the airflow patterns in single-sided ventilation of isolated buildings in which the ventilation rate can not be easily predicted by the conventional Orifice equation. The research focuses on buildings with two openings located either at the front or back external wall, with building aspect ratios of 1:1 and 1:2.The study utilizes Large Eddy Simulation (LES) with the particle tracking technique validated by velocity data obtained from a wind tunnel experiment. Ventilation performance is evaluated by Airflow Rate (AFR) and Purging Flow Rate (PFR). AFR was obtained based on the instantaneous velocity over the openings, and PFR was determined by the tracer gas method. The results show that the influence of pulsation flow and eddy penetration both exist in single-sided ventilation. The comparison of AFR and PFR indicates part of the airflow through the opening does not contribute to effectively removing the indoor contaminants, which is quantitively evaluated by ventilation efficiency (ev) defined as the ratio of PFR and AFR. In order to explicitly observe and depict the airflow, the massless particles were emitted at the opening, and the trajectories were analysed. The Probability Density Function (PDF) of indoor residence and indoor travel distance was calculated. The high probability of short indoor travel distance and the residence time, which is mainly caused by the eddy at the openings and time-variant pulsation flow, can explain the difference between AFR and PFR.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Natural ventilation; Single-sided ventilation; CFD; LES; Ventilation efficiency; Particle tracking
National Category
Energy Engineering
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-41242 (URN)10.1016/j.buildenv.2023.110230 (DOI)2-s2.0-85151061834 (Scopus ID)
Available from: 2023-03-28 Created: 2023-03-28 Last updated: 2023-04-13Bibliographically approved
Kabanshi, A., Chocarro de Erauso, B. & Sandberg, M. (2023). Experimental study on augmentation of mixing within a stratified indoor environment by erosion of density interface. In: E3S Web of Conferences: . Paper presented at IAQVEC 2023. 11th International Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings, Tokyo, 20-23 May 2023. , 396, Article ID 02037.
Open this publication in new window or tab >>Experimental study on augmentation of mixing within a stratified indoor environment by erosion of density interface
2023 (English)In: E3S Web of Conferences, 2023, Vol. 396, article id 02037Conference paper, Published paper (Refereed)
Abstract [en]

The current study aims to address the problem associated with warm air heating in passive houses. Warm air eating is cheaper and easy to operate in passive houses, however, this creates problems of shortcut ventilation and thermal discomfort due to stratification as warm air is confined to the ceiling. In the current study, we explore a new method of creating resonance between stratification frequency and the periodic variation of the ventilation supply frequency to increase mixing of the supplied warm air and the room air consequently destratifying the room conditions. A basic water model study is used to understand the interaction between the frequency variations and the resulting standing waves with stratification characteristics in a room. Measurements at three different input frequencies and at three input paddle locations have been performed, gathering vertical temperature gradients and visualization data from them. The results show the shift in the inversion point because of an increase augmentation across the inversion between the fluids with different densities close to resonance. There is also a dependency on paddle location showing that the type of ventilation system will have different mixing rates due to different fluid energetic behaviours.  

Series
E3S Web of Conferences, ISSN 2555-0403
Keywords
Stratification, Mixing, Density interface, Water model, Pasive houses
National Category
Fluid Mechanics
Research subject
Sustainable Urban Development
Identifiers
urn:nbn:se:hig:diva-41918 (URN)10.1051/e3sconf/202339602037 (DOI)2-s2.0-85164475352 (Scopus ID)
Conference
IAQVEC 2023. 11th International Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings, Tokyo, 20-23 May 2023
Available from: 2023-05-31 Created: 2023-05-31 Last updated: 2025-02-09Bibliographically approved
Projects
A new ventilation technique based on velocity variation as a method to improve thermal comfort and ventilation efficiency [2008-64_Formas]; University of GävleTowards an optimisation of urban-planning and architectural parameters for energy use minimisation in miditerranean cities (Urban Net) [2008-327_Formas]; University of Gävle; Publications
Sandberg, M., Neophytou, M., Fokaides, P., Panagiotou, I., Ioannou, I., Petrou, M., . . . Ivanov, A. (2011). Towards optimization of urban planning and architectural parameters for energy use minimization in Mediterranean cities. In: WREC 2011: . Paper presented at The Word Renewable Energy Congress 2011, Linköping 8-13 May 2011.
Energy saving in churches: Measuring air leakage, soiling and micro climate [P34964-1_Energi]; University of GävleStadsventilation [2018-00238_Formas]; University of Gävle; Publications
Lin, Y., Sandberg, M., Cehlin, M., Claesson, L. & Wigö, H. (2024). Experimental studies of single-sided ventilation for semi-enclosed models with horizontal opening. In: Proceedings of the 17th ROOMVENT Conference: . Paper presented at The 17th ROOMVENT Conference, Stockholm, Sweden, April 22 - 25, 2024. Lin, Y., Cehlin, M., Ameen, A., Sandberg, M. & Wallhagen, M. (2024). Influence of Urban Morphologies on the Effective Mean Age of Air at Pedestrian Level and Mass Transport Within Urban Canopy Layer. Buildings, 14, Article ID 3591. Cehlin, M., Lin, Y., Sandberg, M., Claesson, L. & Wallhagen, M. (2023). Towards benchmarking of urban air quality based on homogenous surface emission. Results in Engineering (RINENG), 20, Article ID 101617. Lin, Y., Sandberg, M., Cehlin, M., Claesson, L. & Wigö, H. (2022). Evaluation of the Equivalent Purging Flow Rate for Single-side Ventilated Model with Tracer Gas Measurements. In: 5th International Conference on Building Energy and Environment (COBEE 2022): . Paper presented at COBEE 2022, Concordia University, Montreal, Canada, 25-29 July 2022. Springer, Article ID 1419. Buccolieri, R., Lin, Y., Wigö, H. & Sandberg, M. (2021). Drag force rose representing the interaction between urban geometries and wind. In: 15th ROOMVENT (Roomvent 2020) virtual conference: Energy efficient ventilation for healthy future buildings. Paper presented at 15th Roomvent virtual conference, 15-17 February 2021, Turin, Italy (pp. 85-88). Cehlin, M., Ameen, A., Sandberg, M., Claesson, L., Wigö, H. & Lin, Y. (2020). Urban Morphology and City Ventilation. In: : . Paper presented at 10th International Conference on Future Environment and Energy (ICFEE 2020).
Ventilation as a strategy to reduce indoor transmission of airborne diseases: development of new strategies and a risk assessment model [2021-01606_Formas]; University of Gävle; Publications
Kabanshi, A., Andersson, H., Sundberg, M., Senkic, D. & Sandberg, M. (2024). Assessing airborne infection risk through a model of airflow evacuation and recirculation dynamics.. In: : . Paper presented at RoomVent Conference, April 22-25, Stockholm, Sweden.
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1121-2394

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