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Publications (10 of 103) Show all publications
Lin, D., Hägg, L., Wadbro, E., Berggren, M. & Löfstedt, T. (2025). Structured regularization using approximate morphology for Alzheimer's disease classification. In: 2025 IEEE 22nd International Symposium on Biomedical Imaging (ISBI): . Paper presented at 2025 IEEE 22nd International Symposium on Biomedical Imaging (ISBI), Houston, TX, USA, April 11-17, 2025 (pp. 1-4).
Open this publication in new window or tab >>Structured regularization using approximate morphology for Alzheimer's disease classification
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2025 (English)In: 2025 IEEE 22nd International Symposium on Biomedical Imaging (ISBI), 2025, p. 1-4Conference paper, Published paper (Refereed)
Abstract [en]

Structured regularization allows machine learning models to consider spatial relationships among parameters, leading to results that generalize better and are more interpretable compared to norm penalties. In this study, we evaluated a novel structured regularization method that incorporates approximate morphology operators defined using harmonic mean-based fW-filters. We extended this method to multiclass classification and conducted experiments aimed at classifying magnetic resonance images (MRI) of subjects into four stages of Alzheimer's disease progression. The experimental results demonstrate that the novel structured regularization method not only performs better than standard sparse and structured regularization methods in terms of prediction accuracy (ACC), F1 scores, and the area under the receiver operating characteristic curve (AUC), but also produces interpretable coefficient maps.

Series
Proceedings (International Symposium on Biomedical Imaging), ISSN 1945-7928, E-ISSN 1945-8452
Keywords
Structured regularization, MRI, Alzheimer’s disease, Classification, Interpretation
National Category
Computer graphics and computer vision Neurosciences Artificial Intelligence
Identifiers
urn:nbn:se:umu:diva-239040 (URN)10.1109/ISBI60581.2025.10981098 (DOI)2-s2.0-105005824554 (Scopus ID)979-8-3315-2052-6 (ISBN)979-8-3315-2053-3 (ISBN)
Conference
2025 IEEE 22nd International Symposium on Biomedical Imaging (ISBI), Houston, TX, USA, April 11-17, 2025
Funder
Swedish Research Council, 2021-04810Lions Cancerforskningsfond i Norr, LP 24-2367
Available from: 2025-05-21 Created: 2025-05-21 Last updated: 2025-06-02Bibliographically approved
Lin, D., Hägg, L., Wadbro, E., Berggren, M. & Löfstedt, T. (2025). Structured regularization with object size selection using mathematical morphology. Pattern Analysis and Applications, 28, Article ID 70.
Open this publication in new window or tab >>Structured regularization with object size selection using mathematical morphology
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2025 (English)In: Pattern Analysis and Applications, ISSN 1433-7541, E-ISSN 1433-755X, Vol. 28, article id 70Article in journal (Refereed) Published
Abstract [en]

We propose a novel way to incorporate morphology operators through structured regularization of machine learning models. Specifically, we introduce a feature map in the models that performs structured variable selection. The feature map is automatically processed by approximate morphology operators and is learned together with the model coefficients. Experiments were conducted with linear regression on both synthetic data, demonstrating that the proposed methods are effective in selecting groups of parameters with much less noise than baseline models, and on three-dimensional T1-weighted brain magnetic resonance images (MRI) for age prediction, demonstrating that the proposed methods enforce sparsity and select homogeneous regions of non-zero and relevant regression coefficients. The proposed methods improve interpretability in pattern analysis. The minimum size of features in the structured variable selection can be controlled by adjusting the structuring element in the approximate morphology operator, tailored to the specific study of interest. With these added benefits, the proposed methods still perform on par with commonly used variable selection and structured variable selection methods in terms of the coefficient of determination and the Pearson correlation coefficient.

Place, publisher, year, edition, pages
Springer Nature, 2025
Keywords
Structured regularization, Approximate morphology operators, Feature selection, fW-mean filters
National Category
Artificial Intelligence Computer graphics and computer vision
Identifiers
urn:nbn:se:umu:diva-236995 (URN)10.1007/s10044-025-01444-7 (DOI)001455367400002 ()2-s2.0-105001489397 (Scopus ID)
Funder
Swedish Research Council, 2021-04810Lions Cancerforskningsfond i Norr, LP 24-2367
Available from: 2025-03-27 Created: 2025-03-27 Last updated: 2025-04-29Bibliographically approved
Lu, P., Wadbro, E., Berggren, M. & Hassan, E. (2025). Topology optimization of dualband metallic antennas with minimum-size control. In: 2025 19th European Conference on Antennas and Propagation (EuCAP): . Paper presented at 2025 19th European Conference on Antennas and Propagation (EuCAP), Stockholm, Sweden, April 4, 2025 (pp. 1-4). IEEE
Open this publication in new window or tab >>Topology optimization of dualband metallic antennas with minimum-size control
2025 (English)In: 2025 19th European Conference on Antennas and Propagation (EuCAP), IEEE, 2025, p. 1-4Conference paper, Published paper (Refereed)
Abstract [en]

We use a density-based topology optimization approach to design dualband planar metallic antennas. The design problem is formulated based on the time-domain Maxwell's equations, solved using the finite-difference timedomain (FDTD) method. The antenna design is formulated as an optimization problem where the received and reflected energy by the antenna in two frequency bands, centered around 2.5 GHz and 5.5 GHz, are optimized. Two design examples that exhibit outstanding performance are presented. In one design case, we employ a nonlinear filtering scheme to impose size control on the optimized design and ensure manufacturability.

Place, publisher, year, edition, pages
IEEE, 2025
Keywords
Uncertainty, Dual band, Receiving antennas, Nonlinear filters, Reflector antennas, Topology, Size control, Time-domain analysis, Optimization, Finite difference methods, antennas, electromagnetics, Maxwell’s equations, topology optimization, nonlinear filter
National Category
Communication Systems
Identifiers
urn:nbn:se:umu:diva-239304 (URN)10.23919/EuCAP63536.2025.10999941 (DOI)978-88-31299-10-7 (ISBN)979-8-3503-6632-7 (ISBN)
Conference
2025 19th European Conference on Antennas and Propagation (EuCAP), Stockholm, Sweden, April 4, 2025
Funder
eSSENCE - An eScience CollaborationSwedish Research Council, 2018-03546
Available from: 2025-05-27 Created: 2025-05-27 Last updated: 2025-05-28Bibliographically approved
Setta, M., Hägg, L. & Wadbro, E. (2024). A boundary strip indicator for material distribution-based topology optimization. Structural and multidisciplinary optimization (Print), 67(8), Article ID 149.
Open this publication in new window or tab >>A boundary strip indicator for material distribution-based topology optimization
2024 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 67, no 8, article id 149Article in journal (Refereed) Published
Abstract [en]

This article proposes a boundary strip indicator for density-based topology optimization that can be used to estimate the design’s surface area (perimeter in 2D) or identify a coating layer. We investigate the theoretical properties of the proposed boundary strip indicator and propose a differentiable approximation that preserves key properties, such as non-negativity. Finally, we use the boundary strip indicator in a heat conduction design optimization problem for a coated structure. The resulting designs show a strong dependence on the properties of the coating.

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
Boundary strip, Morphological operators, Non-linear filters, Perimeter, Topology optimization
National Category
Computer Sciences Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-228895 (URN)10.1007/s00158-024-03872-1 (DOI)001295914600001 ()2-s2.0-85201683441 (Scopus ID)
Funder
eSSENCE - An eScience CollaborationSwedish Research Council, 2022-03783
Available from: 2024-09-10 Created: 2024-09-10 Last updated: 2024-09-10Bibliographically approved
Wiberg, V., Wallin, E., Fälldin, A., Semberg, T., Rossander, M., Wadbro, E. & Servin, M. (2024). Sim-to-real transfer of active suspension control using deep reinforcement learning. Robotics and Autonomous Systems, 179, Article ID 104731.
Open this publication in new window or tab >>Sim-to-real transfer of active suspension control using deep reinforcement learning
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2024 (English)In: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 179, article id 104731Article in journal (Refereed) Published
Abstract [en]

We explore sim-to-real transfer of deep reinforcement learning controllers for a heavy vehicle with active suspensions designed for traversing rough terrain. While related research primarily focuses on lightweight robots with electric motors and fast actuation, this study uses a forestry vehicle with a complex hydraulic driveline and slow actuation. We simulate the vehicle using multibody dynamics and apply system identification to find an appropriate set of simulation parameters. We then train policies in simulation using various techniques to mitigate the sim-to-real gap, including domain randomization, action delays, and a reward penalty to encourage smooth control. In reality, the policies trained with action delays and a penalty for erratic actions perform nearly at the same level as in simulation. In experiments on level ground, the motion trajectories closely overlap when turning to either side, as well as in a route tracking scenario. When faced with a ramp that requires active use of the suspensions, the simulated and real motions are in close alignment. This shows that the actuator model together with system identification yields a sufficiently accurate model of the actuators. We observe that policies trained without the additional action penalty exhibit fast switching or bang–bang control. These present smooth motions and high performance in simulation but transfer poorly to reality. We find that policies make marginal use of the local height map for perception, showing no indications of predictive planning. However, the strong transfer capabilities entail that further development concerning perception and performance can be largely confined to simulation.

Place, publisher, year, edition, pages
Elsevier, 2024
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Physics Topics
Research subject
Physics; computer and systems sciences
Identifiers
urn:nbn:se:umu:diva-226893 (URN)10.1016/j.robot.2024.104731 (DOI)001260733600001 ()2-s2.0-85196769514 (Scopus ID)
Projects
Mistra Digital Forest
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, Grant DIA 2017/14 #6Wallenberg AI, Autonomous Systems and Software Program (WASP)
Available from: 2024-06-23 Created: 2024-06-23 Last updated: 2025-04-24Bibliographically approved
Mousavi, A., Berggren, M., Hägg, L. & Wadbro, E. (2024). Topology optimization of a waveguide acoustic black hole for enhanced wave focusing. Journal of the Acoustical Society of America, 155(1), 742-756
Open this publication in new window or tab >>Topology optimization of a waveguide acoustic black hole for enhanced wave focusing
2024 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 155, no 1, p. 742-756Article in journal (Refereed) Published
Abstract [en]

The waveguide acoustic black hole (WAB) effect is a promising approach for controlling wave propagation in various applications, especially for attenuating sound waves. While the wave-focusing effect of structural acoustic black holes has found widespread applications, the classical ribbed design of waveguide acoustic black holes (WABs) acts more as a resonance absorber than a true wave-focusing device. In this study, we employ a computational design optimization approach to achieve a conceptual design of a WAB with enhanced wave-focusing properties. We investigate the influence of viscothermal boundary losses on the optimization process by formulating two distinct cases: one neglecting viscothermal losses and the other incorporating these losses using a recently developed material distribution topology optimization technique. We compare the performance of optimized designs in these two cases with that of the classical ribbed design. Simulations using linearized compressible Navier–Stokes equations are conducted to evaluate the wave-focusing performance of these different designs. The results reveal that considering viscothermal losses in the design optimization process leads to superior wave-focusing capabilities, highlighting the significance of incorporating these losses in the design approach. This study contributes to the advancement of WAB design and opens up new possibilities for its applications in various fields.

Place, publisher, year, edition, pages
Acoustical Society of America, 2024
Keywords
Acoustical properties, Acoustic phenomena, Acoustic waves, Black holes, Finite-element analysis, Mathematical optimization, Boundary integral methods, Optimization problems, Liquid solid interfaces, Navier Stokes equations
National Category
Computer Sciences
Identifiers
urn:nbn:se:umu:diva-214110 (URN)10.1121/10.0024470 (DOI)001153140300001 ()38284824 (PubMedID)2-s2.0-85183806282 (Scopus ID)
Funder
eSSENCE - An eScience CollaborationSwedish Research Council, 2018-03546Swedish Research Council, 2022-03783
Note

Originally included in thesis in manuscript form. 

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2024-02-14Bibliographically approved
Mousavi, A., Uihlein, A., Pflug, L. & Wadbro, E. (2024). Topology optimization of broadband acoustic transition section: a comparison between deterministic and stochastic approaches. Structural and multidisciplinary optimization (Print), 67(5), Article ID 67.
Open this publication in new window or tab >>Topology optimization of broadband acoustic transition section: a comparison between deterministic and stochastic approaches
2024 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 67, no 5, article id 67Article in journal (Refereed) Published
Abstract [en]

This paper focuses on the topology optimization of a broadband acoustic transition section that connects two cylindricalwaveguides with different radii. The primary objective is to design a transition section that maximizes the transmission of aplanar acoustic wave while ensuring that the transmitted wave exhibits a planar shape. Helmholtz equation is used to modellinear wave propagation in the device. We utilize the finite element method to solve the state equation on a structured meshof square elements. Subsequently, a material distribution topology optimization problem is formulated to optimize the dis-tribution of sound-hard material in the transition section. We employ two different gradient-based approaches to solve theoptimization problem: namely, a deterministic approach using the method of moving asymptotes (MMA), and a stochasticapproach utilizing both stochastic gradient (SG) and continuous stochastic gradient (CSG) methods. A comparative analysisis provided among these methodologies concerning the design feasibility and the transmission performance of the optimizeddesigns, and the computational efficiency. The outcomes highlight the effectiveness of stochastic techniques in achievingenhanced broadband acoustic performance with reduced computational demands and improved design practicality. Theinsights from this investigation demonstrate the potential of stochastic approaches in acoustic applications, especially whenbroadband acoustic performance is desired.

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
Topology optimization, Stochastic methods, Acoustic transition section, Material distribution approach
National Category
Fluid Mechanics
Identifiers
urn:nbn:se:umu:diva-224228 (URN)10.1007/s00158-024-03784-0 (DOI)001219759200019 ()2-s2.0-85193022139 (Scopus ID)
Funder
German Research Foundation (DFG), 416229255 - SFB 1411Swedish Research Council, 2022-03783eSSENCE - An eScience Collaboration
Available from: 2024-05-13 Created: 2024-05-13 Last updated: 2025-02-09Bibliographically approved
Aoshima, K., Fälldin, A., Wadbro, E. & Servin, M. (2024). World modeling for autonomous wheel loaders. Automation, 5(3), 259-281
Open this publication in new window or tab >>World modeling for autonomous wheel loaders
2024 (English)In: Automation, ISSN 2673-4052, Vol. 5, no 3, p. 259-281Article in journal (Refereed) Published
Abstract [en]

This paper presents a method for learning world models for wheel loaders performing automatic loading actions on a pile of soil. Data-driven models were learned to output the resulting pile state, loaded mass, time, and work for a single loading cycle given inputs that include a heightmap of the initial pile shape and action parameters for an automatic bucket-filling controller. Long-horizon planning of sequential loading in a dynamically changing environment is thus enabled as repeated model inference. The models, consisting of deep neural networks, were trained on data from a 3D multibody dynamics simulation of over 10,000 random loading actions in gravel piles of different shapes. The accuracy and inference time for predicting the loading performance and the resulting pile state were, on average, 95% in 1.21.2 ms and 97% in 4.54.5 ms, respectively. Long-horizon predictions were found feasible over 40 sequential loading actions.

Place, publisher, year, edition, pages
MDPI, 2024
Keywords
wheel loader, earthmoving, automation, bucket-filling, world modeling, deep learning, multibody simulation
National Category
Robotics and automation Computer graphics and computer vision Other Physics Topics
Research subject
Physics; Automatic Control
Identifiers
urn:nbn:se:umu:diva-227746 (URN)10.3390/automation5030016 (DOI)001323274900001 ()2-s2.0-85205125062 (Scopus ID)
Funder
Wallenberg AI, Autonomous Systems and Software Program (WASP)
Available from: 2024-07-07 Created: 2024-07-07 Last updated: 2025-02-05Bibliographically approved
Hosseini, S. A., Wadbro, E., Ngoc Do, D. & Lindroos, O. (2023). A scenario-based metaheuristic and optimization framework for cost-effective machine-trail network design in forestry. Computers and Electronics in Agriculture, 212, Article ID 108059.
Open this publication in new window or tab >>A scenario-based metaheuristic and optimization framework for cost-effective machine-trail network design in forestry
2023 (English)In: Computers and Electronics in Agriculture, ISSN 0168-1699, E-ISSN 1872-7107, Vol. 212, article id 108059Article in journal (Refereed) Published
Abstract [en]

Designing an optimal machine trail network is a complex locational problem that requires an understanding of different machines’ operations and terrain features as well as the trade-offs between various objectives. With the overall goal to minimize the operational costs of the logging operation, this paper proposes a mathematical optimization model for the trail network design problem and a greedy heuristic method based on different randomized search scenarios aiming to find the optimal location of machine trails —with potential to reduce negative environmental impact. The network is designed so that all trees can be reached and adapted to how the machines can maneuver while considering the terrain elevation's influence. To examine the effectiveness and practical performance of the heuristic and the optimization model, it was applied in a case study on four harvest units with different topologies and shapes. The computational experiments show that the heuristic can generate solutions that outperform the solutions corresponding to conventional, manual designs within practical time limits for operational planning. Moreover, to highlight certain features of the heuristic and the parameter settings’ effect on its performance, we present an extensive computational sensitivity analysis.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Algorithm design, Forest machine-trail optimization, Heuristic, GRASP, Transportation
National Category
Computer Sciences
Identifiers
urn:nbn:se:umu:diva-212483 (URN)10.1016/j.compag.2023.108059 (DOI)001054785000001 ()2-s2.0-85165537328 (Scopus ID)
Funder
Vinnova, 2018-03344Swedish Research Council Formas, 942-2015-62
Available from: 2023-08-03 Created: 2023-08-03 Last updated: 2025-04-24Bibliographically approved
Mousavi, A., Berggren, M. & Wadbro, E. (2023). Extending material distribution topology optimization to boundary-effect-dominated problems with applications in viscothermal acoustics. Materials & design, 234, Article ID 112302.
Open this publication in new window or tab >>Extending material distribution topology optimization to boundary-effect-dominated problems with applications in viscothermal acoustics
2023 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 234, article id 112302Article in journal (Other academic) Published
Abstract [en]

A new formulation is presented that extends the material distribution topology optimization method to address boundary-effect-dominated problems, where specific boundary conditions need to be imposed at solid–fluid interfaces. As an example of such a problem, we focus on the design of acoustic structures with significant viscous and thermal boundary losses. In various acoustic applications, especially for acoustically small devices, the main portion of viscothermal dissipation occurs in the so-called acoustic boundary layer. One way of accounting for these losses is through a generalized acoustic impedance boundary condition. This boundary condition has previously been proven to provide accurate results with significantly less computational effort compared to Navier–Stokes simulations. To incorporate this boundary condition into the optimization process at the solid–fluid interface, we introduce a mapping of jumps in densities between neighboring elements to an edge-based boundary indicator function. Two axisymmetric case studies demonstrate the effectiveness of the proposed design optimization method. In the first case, we enhance the absorption performance of a Helmholtz resonator in a narrow range of frequencies. In the second case, we consider an acoustically larger problem and achieve an almost-perfect broadband absorption. Our findings underscore the potential of our approach for the design optimization of boundary-effect-dominated problems.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Design optimization, Topology optimization, Helmholtz equation, Acoustic boundary layer, Absorption coefficient, Broadband absorption
National Category
Computer Sciences
Identifiers
urn:nbn:se:umu:diva-214109 (URN)10.1016/j.matdes.2023.112302 (DOI)001123495100001 ()2-s2.0-85171333478 (Scopus ID)
Funder
eSSENCE - An eScience CollaborationSwedish Research Council, 2018-03546Swedish Research Council, 2022-03783
Note

Originally included in thesis in manuscript form. 

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2025-04-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-8704-9584

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