Sverre Holm

Most cited papers

• J.-F. Synnevåg, A. Austeng, and S. Holm, "Adaptive beamforming applied to medical ultrasound imaging," IEEE Trans. Ultrason., Ferroelect., Freq. Contr. (Special issue on high resolution ultrasonic imaging), vol. 54(8), Aug. 2007, pp. 1606-1613.
• W. Chen and S. Holm, "Fractional Laplacian time-space models for linear and nonlinear lossy media exhibiting arbitrary frequency dependency," J. Acoust. Soc. Amer., pp. 1424-1430, Apr. 2004.
• J.-F. Synnevåg, A. Austeng, and S. Holm, ”Benefits of Minimum-Variance Beamforming in Medical Ultrasound Imaging”, IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Sept. 2009.
• A. Austeng and S. Holm, "Sparse 2D Arrays for 3D Phased Array Imaging - Design Methods," IEEE Trans. Ultrasonics, Ferroelectrics and Frequency Control, Aug. 2002, pp. 1073-1086.
• W. Chen and S. Holm, "Modified Szabo’s wave equation models for lossy media obeying frequency power law," J. Acoust. Soc. Amer., pp. 2570-2574, Nov. 2003.

• Holm, Sverre (2026). Learning from C.S. Lewis’s view on evolution. Theofilos. ISSN 1893-7969. 15(1), p. 40–54. doi: https:/theofilos.no/wp-content/uploads/2026/05/Theofilos-vol-15-nr-1-2026-academia-3-260512-final.pdf. Full text in Research Archive Show summary

  “In the science, Evolution is a theory about changes; in the Myth, it is a fact about improvements” is what Lewis wrote in The Funeral of a Great Myth in the 1940’s, demonstrating both an acceptance of, and a scepticism towards the explanatory power of biological evolution. There seems to be an ambiguity in reading Lewis, as Peterson in 2010 called him a theistic evolutionist, or an evolutionary theist, while West in 2012 said that Lewis does not fit in with mainstream theistic evolution. This ambiguity more than anything else demonstrates the lack of precision in the label ‘theistic evolution’ as Lewis cannot possibly both be supportive of it and against it at the same time. This label covers such a wide range of views as to border on the meaningless. Also, one cannot understand Lewis’ scepticism towards explanations for improvements in evolution without considering his reading of Haldane, one of the founders of Neo-Darwinism, and an atheist. Nearly a century later, biologists still state that why the major evolutionary transitions happened defy explanation (Szathmáry, Smith, Nature 1995). These transitions are different from the term macroevolution, as they occur at an even higher level, e.g., from primates to human societies with natural language. Biologists seem to deal with this lack of explanation by either 1) accepting it, 2) by a more or less justified trust in a future resolution, or 3) by denying that there is progress at all, often leading to a low view of humans. I argue here that Lewis’s view can still guide us today in expressing awe and wonder over the process of evolution as well as scepticism to the claims of evolutionism that everything has been explained, what Lewis liked to call the Myth.

• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Austeng, Andreas; Holm, Sverre & Näsholm, Sven Peter (2026). Proof of concept for full-waveform inversion in ultrasound time-harmonic shear-wave elastography. Physics in Medicine and Biology. ISSN 0031-9155. 71(10), p. 1–22. doi: 10.1088/1361-6560/ae6af4. Full text in Research Archive Show summary

  Objective. In ultrasound time-harmonic elastography, tissue elasticity is estimated from the ultrasound-measured shear-wave displacement fields, generated by an external vibrator. Commonly used techniques to map from the ultrasound pulse-echo data to tissue elasticity maps, such as the phase-gradient and local-frequency estimation methods, base their estimates on a set of displacement field data and do not involve direct numerical modeling of the underlying shear-wave propagation. In the current proof-of-concept study, the objective is to develop a Full-Waveform Inversion (FWI) approach to ultrasound-based time-harmonic elastography, providing a physics-driven framework for improved tissue elasticity estimation. Approach. FWI is a methodology commonly applied in geophysics. It relies on simulating the wave propagation and scattering in heterogeneous media to model the intricate relationship between the observed wavefield and the propagation medium properties. Our FWI-based tissue-harmonic elastography approach is based on minimizing a cross-correlation based objective function that quantifies phase mismatches between measured and simulated shear waves. Results. Experiments on synthetic phantom data obtained from the fractional Kelvin-Voigt wave model demonstrate that our approach accurately reconstructs the shear wave speed of the medium, even in the presence of significant noise, and without relying on pre-filtering steps such as directional filtering, which selects waves based on their propagation direction. An improvement of approximately 0.4 m.s -1 within the inclusion region, compared to an established method, is observed for a noisy wavefield with decreasing signal-to-noise ratio, ranging from 20 to -10 dB from top to bottom of the ultrasound image. In addition, the reconstructed shear-wave speed map achieved a 50% reduction in standard deviation. Significance. This work demonstrates the potential for enhanced elasticity mapping using FWI-based reconstruction in time-harmonic elastography with prospective impacts for future clinical applications.

• Holm, Sverre & Bergli, Joakim (2025). Energy landscape interpretation of universal linearly increasing absorption with frequency. Journal of the Acoustical Society of America. ISSN 0001-4966. 157(2), p. 824–832. doi: 10.1121/10.0035647. Full text in Research Archive Show summary

  Absorption of elastic waves in complex media is commonly found to increase linearly with frequency, for both longitudinal and shear waves. This ubiquitous property is observed in media such as rocks, unconsolidated sediments, and human tissue. Absorption is due to relaxation processes at the level of atomic scales and up to the sub-micron scale of biological materials. The effect of these processes is usually expressed as an integral over relaxation frequencies or relaxation times. Here, this paper argues that these processes are thermally activated. Unusually for ultrasonics and seismics, the expression for absorption from the frequency or time domains can therefore be transformed to an integral over an activation energy landscape weighted by an energy distribution. The universal power-law property surprisingly corresponds to a flat activation energy landscape. This is the solution that maximizes entropy or randomness. Therefore, the linearly increasing absorption corresponds to the energy landscape with the fewest possible constraints.

• Simionato, Riccardo; Fasciani, Stefano & Holm, Sverre (2024). Physics-informed differentiable method for piano modeling. Frontiers in Signal Processing. 3. doi: 10.3389/frsip.2023.1276748. Full text in Research Archive Show summary

  Numerical emulations of the piano have been a subject of study since the early days of sound synthesis. High-accuracy sound synthesis of acoustic instruments employs physical modeling techniques which aim to describe the system’s internal mechanism using mathematical formulations. Such physical approaches are system-specific and present significant challenges for tuning the system’s parameters. In addition, acoustic instruments such as the piano present nonlinear mechanisms that present significant computational challenges for solving associated partial differential equations required to generate synthetic sound. In a nonlinear context, the stability and efficiency of the numerical schemes when performing numerical simulations are not trivial, and models generally adopt simplifying assumptions and linearizations. Artificial neural networks can learn a complex system’s behaviors from data, and their application can be beneficial for modeling acoustic instruments. Artificial neural networks typically offer less flexibility regarding the variation of internal parameters for interactive applications, such as real-time sound synthesis. However, their integration with traditional signal processing frameworks can overcome this limitation. This article presents a method for piano sound synthesis informed by the physics of the instrument, combining deep learning with traditional digital signal processing techniques. The proposed model learns to synthesize the quasi-harmonic content of individual piano notes using physics-based formulas whose parameters are automatically estimated from real audio recordings. The model thus emulates the inharmonicity of the piano and the amplitude envelopes of the partials. It is capable of generalizing with good accuracy across different keys and velocities. Challenges persist in the high-frequency part of the spectrum, where the generation of partials is less accurate, especially at high-velocity values. The architecture of the proposed model permits low-latency implementation and has low computational complexity, paving the way for a novel approach to sound synthesis in interactive digital pianos that emulates specific acoustic instruments.

• Chotiros, Nicholas P. & Holm, Sverre (2024). Modeling and simulation of underwater acoustic propagation through a random distribution of ice blocks. JASA Express Letters. 4(3). doi: 10.1121/10.0025395. Full text in Research Archive Show summary

  Acoustic propagation through a random distribution of 1 m ice cubes, from 100 to 1000 Hz, was simulated in a 3D finite element model. The effective sound speed and attenuation as functions of frequency were calculated from the simulated signals. Attempts were made to fit a number of models to the wave speed and attenuation, including single scattering, lossy water, and Biot approximations. An extended Biot model, developed for acoustic propagation in granular seabed sediments, was able to fit the simulation up to 300 Hz. Beyond this frequency, the simulation shows that multiple scattering dominates.

• Finden, Erlend; Skartlien, Roar; Holm, Sverre & Hamran, Svein-Erik (2024). Induced polarization in the transient electromagnetic method for detection of subsurface ice on Earth, Mars, and the Moon. Planetary and Space Science. ISSN 0032-0633. 254. doi: 10.1016/j.pss.2024.106007. Full text in Research Archive Show summary

  The transient electromagnetic method (TEM) can capture an induced polarization (IP) signature of subsurface ice. Using numerical modeling of a horizontally layered earth, we investigate how IP in TEM can be exploited for subsurface ice detection on Earth, Mars, and the Moon. In the model we implement electrical parameters from laboratory measurements of ice, planetary regolith simulants, and terrestrial soil from the literature. In contrast to currently applied forward models, we include two Cole–Cole relaxation terms to model the dielectric relaxation of adsorbed water or salt hydrate in addition to the relaxation of ice. On Earth, IP signals of shallow layers of silt mixed with 44–100 vol% ice embedded in resistive host layers of 3 km can be detected. Both at mid (45 N) and lower (35 N) latitudes on Mars, meter thick layers of massive ice can be detected at 10 m depth if the ice contains salts. Corresponding layers of 60 vol% ice mixed with Martian regolith simulant show similar detectability. For IP signals of lunar ice to be detected in ice volume fractions of 7.4%–46%, a development in TEM technology is required, including mitigation of early time interference, or enhancing the signal to noise level.

• Giannio, Giacomo; Holm, Sverre; Mangin, Gabrielle; Penney, Jake; Bacquët, Raphael & Mustapha, Rami [Show all 14 contributors for this article] (2024). Making sense of scattering: Seeing microstructure through shear waves. Science Advances. 10(31). doi: 10.1126/sciadv.adp3363. Full text in Research Archive Show summary

  The physics of shear waves traveling through matter carries fundamental insights into its structure, for instance, quantifying stiffness for disease characterization. However, the origin of shear wave attenuation in tissue is currently not properly understood. Attenuation is caused by two phenomena: absorption due to energy dissipation and scattering on structures such as vessels fundamentally tied to the material’s microstructure. Here, we present a scattering theory in conjunction with magnetic resonance imaging, which enables the unraveling of a material’s innate constitutive and scattering characteristics. By overcoming a three-order-of-magnitude scale difference between wavelength and average intervessel distance, we provide noninvasively a macroscopic measure of vascular architecture. The validity of the theory is demonstrated through simulations, phantoms, in vivo mice, and human experiments and compared against histology as gold standard. Our approach expands the field of imaging by using the dispersion properties of shear waves as macroscopic observable proxies for deciphering the underlying ultrastructures.

• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). Application of Spatial Autocorrelation in Experimental Time-Harmonic Elastography. IEEE International Symposium on Applications of Ferroelectrics (ISAF). ISSN 2375-0448. doi: 10.1109/UFFC-JS60046.2024.10793924. Full text in Research Archive
• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). An Autocorrelation-Based Approach for Estimating Shear Wave Speed using 2D Velocity Vector. IEEE International Symposium on Applications of Ferroelectrics (ISAF). ISSN 2375-0448. doi: 10.1109/UFFC-JS60046.2024.10794020. Full text in Research Archive
• Marthinsen, Eirik Brenner & Holm, Sverre (2023). Difference between Charge–Voltage Relations of Ordinary and Fractional Capacitors. Fractal and Fractional. 7(11). doi: 10.3390/fractalfract7110781. Full text in Research Archive Show summary

  In an ordinary time-varying capacitor, there is debate on whether a time-domain multiplication or a time-domain convolution of capacitance and voltage determines charge. The objective of this work is to resolve this question by experiments on a time-varying capacitor in parallel with a resistor. It was implemented by a motor-driven potentiometer and op-amps. The response matched a power-law function over about two decades of time, and not an exponential, for several sets of parameters. This confirms the time-domain multiplication model. This result is the opposite of that obtained for a constant phase element (CPE) in its common time- and frequency-varying capacitor interpretation. This demonstrates that a CPE is fundamentally different from an ordinary time- and frequency-varying capacitor.

• Chandrasekaran, Sri Nivas; Holm, Sverre & Näsholm, Sven Peter (2023). Wave equations of the two common sediment acoustic theories. Proceedings of Meetings on Acoustics (POMA). 51. doi: 10.1121/2.0001795. Full text in Research Archive Show summary

  Two popular theories for wave propagation in sediments, the Biot poroelastic theory and the Viscous Grain Shearing (VGS) theory, have been formulated in terms of dispersion relations. The lack of explicit wave equations for these models could be considered to be a weakness. Hence, providing wave equations that are fully consistent with these theories might confirm that they have a physical basis. In the Biot theory, it is the frequency-dependent viscodynamic operator that poses the problem as there is no equivalent time-domain operator. Previous work has shown that this factor can be approximated well with a simplified square root operator. Drawing on the parallel to the Cole-Davidson dielectric theory for complex media where the same factor appears, and using the equivalent time-domain operator, which is a fractional pseudo-differential operator, enables the formulation of wave equations for all three wave modes of the Biot theory. The same operator turns out to be central for transforming the dispersion relations of the VGS theory to time-space wave equations. In this case, the relation between the dispersion equations and the wave equations is exact. The wave equations of these two theories will enable a closer study of the properties of the medium models.

• Svensson, Siri Fløgstad; Halldórsso, Skarphéðinn; Latysheva, Anna; Garcia, Elies Fuster i; Hjornevik, Trine & Fraser-Green, Jorunn [Show all 12 contributors for this article] (2023). MR elastography identifies regions of extracellular matrix reorganization associated with shorter survival in glioblastoma patients. Neuro-Oncology Advances (NOA). 5(1). doi: 10.1093/noajnl/vdad021. Full text in Research Archive Show summary

  Background Biomechanical tissue properties of glioblastoma tumors are heterogeneous, but the molecular mechanisms involved and the biological implications are poorly understood. Here, we combine magnetic resonance elastography (MRE) measurement of tissue stiffness with RNA sequencing of tissue biopsies to explore the molecular characteristics of the stiffness signal. Methods MRE was performed preoperatively in 13 patients with glioblastoma. Navigated biopsies were harvested during surgery and classified as “stiff” or “soft” according to MRE stiffness measurements (|G*|norm). Twenty-two biopsies from eight patients were analyzed by RNA sequencing. Results The mean whole-tumor stiffness was lower than normal-appearing white matter. The surgeon’s stiffness evaluation did not correlate with the MRE measurements, which suggests that these measures assess different physiological properties. Pathway analysis of the differentially expressed genes between “stiff” and “soft” biopsies showed that genes involved in extracellular matrix reorganization and cellular adhesion were overexpressed in “stiff” biopsies. Supervised dimensionality reduction identified a gene expression signal separating “stiff” and “soft” biopsies. Using the NIH Genomic Data Portal, 265 glioblastoma patients were divided into those with (n = 63) and without (n = 202) this gene expression signal. The median survival time of patients with tumors expressing the gene signal associated with “stiff” biopsies was 100 days shorter than that of patients not expressing it (360 versus 460 days, hazard ratio: 1.45, P < .05). Conclusion MRE imaging of glioblastoma can provide noninvasive information on intratumoral heterogeneity. Regions of increased stiffness were associated with extracellular matrix reorganization. An expression signal associated with “stiff” biopsies correlated with shorter survival of glioblastoma patients.

• Frissell, Nathaniel A.; Ackerman, John R.; Alexander, Jesse N.; Benedict, Robert L.; Jr., William C. Blackwell & Boedicker, Rachel K. [Show all 64 contributors for this article] (2023). Heliophysics and amateur radio: citizen science collaborations for atmospheric, ionospheric, and space physics research and operations. Frontiers in Astronomy and Space Sciences. 10. doi: 10.3389/fspas.2023.1184171. Full text in Research Archive Show summary

  The amateur radio community is a global, highly engaged, and technical community with an intense interest in space weather, its underlying physics, and how it impacts radio communications. The large-scale observational capabilities of distributed instrumentation fielded by amateur radio operators and radio science enthusiasts offers a tremendous opportunity to advance the fields of heliophysics, radio science, and space weather. Well-established amateur radio networks like the RBN, WSPRNet, and PSKReporter already provide rich, ever-growing, long-term data of bottomside ionospheric observations. Up-and-coming purpose-built citizen science networks, and their associated novel instruments, offer opportunities for citizen scientists, professional researchers, and industry to field networks for specific science questions and operational needs. Here, we discuss the scientific and technical capabilities of the global amateur radio community, review methods of collaboration between the amateur radio and professional scientific community, and review recent peerreviewed studies that have made use of amateur radio data and methds. Finally, we present recommendations submitted to the U.S. National Academy of Science Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033 for using amateur radio to further advance heliophysics and for fostering deeper collaborations between the professional science and amateur radio communities. Technical recommendations include increasing support for distributed instrumentation fielded by amateur radio operators and citizen scientists, developing novel transmissions of RF signals that can be used in citizen science experiments, developing new amateur radio modes that simultaneously allow for communications and ionospheric sounding, and formally incorporating the amateur radio community and its observational assets into the Space Weather R2O2R framework. Collaborative recommendations include allocating resources for amateur radio citizen science research projects and activities, developing amateur radio research and educational activities in collaboration with leading organizations within the amateur radio community, facilitating communication and collegiality between professional researchers and amateurs, ensuring that proposed projects are of a mutual benefit to both the professional research and amateur radio communities, and working towards diverse, equitable, and inclusive communities.

• Holm, Sverre; Chandrasekaran, Sri Nivas & Näsholm, Sven Peter (2023). Adding a low frequency limit to fractional wave propagation models. Frontiers in Physics. 11, p. 1–8. doi: 10.3389/fphy.2023.1250742. Full text in Research Archive Show summary

  Power-law attenuation in elastic wave propagation of both compressional and shear waves can be described with multiple relaxation processes. It may be less physical to describe it with fractional calculus medium models, but this approach is useful for simulation and for parameterization where the underlying relaxation structure is very complex. It is easy to enforce a low-frequency limit on a relaxation distribution and this gives frequency squared characteristics for low frequencies which seems to fit some media in practice. Here the goal is to change the low-frequency behavior of fractional models also. This is done by tempering the relaxation moduli of the fractional Kelvin-Voigt and diffusion models with an exponential function and the effect is that the low-frequency attenuation will increase with frequency squared and the square root of frequency respectively. The time-space wave equations for the tempered models have also been found, and for this purpose the concept of the fractional pseudo-differential operator borrowed from the field of Cole-Davidson dielectrics is useful. The tempering does not remove the singularity in the relaxation moduli of the models, but this has only a minor effect on the solutions.

• Nyhoff, Børre; Aarskog, Alv I. & Holm, Sverre (2023). Geometric Construction of Pythagorean and Just Musical Scales and Commas. The Mathematical intelligencer. ISSN 0343-6993. doi: 10.1007/s00283-022-10260-4. Full text in Research Archive
• Sosa, Joaquin Aparicio; Alvarez, Fernando J.; Hernandez, Alvaro & Holm, Sverre (2022). A Survey on Acoustic Positioning Systems for Location-Based Services. IEEE Transactions on Instrumentation and Measurement. ISSN 0018-9456. doi: 10.1109/TIM.2022.3210943. Full text in Research Archive Show summary

  Positioning systems have become increasingly popular in the last decade for location-based services, such as navigation, and asset tracking and management. As opposed to outdoor positioning, where the global navigation satellite system became the standard technology, there is no consensus yet for indoor environments despite the availability of different technologies, such as radio frequency, magnetic field, visual light communications, or acoustics. Within these options, acoustics emerged as a promising alternative to obtain high-accuracy low-cost systems. Nevertheless, acoustic signals have to face very demanding propagation conditions, particularly in terms of multipath and Doppler effect. Therefore, even if many acoustic positioning systems have been proposed in the last decades, it remains an active and challenging topic. This article surveys the developed prototypes and commercial systems that have been presented since they first appeared around the 1980s to 2022. We classify these systems into different groups depending on the observable that they use to calculate the user position, such as the time-of-flight, the received signal strength, or the acoustic spectrum. Furthermore, we summarize the main properties of these systems in terms of accuracy, coverage area, and update rate, among others. Finally, we evaluate the limitations of these groups based on the link budget approach, which gives an overview of the system’s coverage from parameters such as source and noise level, detection threshold, attenuation, and processing gain.

• Chandrasekaran, Sri Nivas; Näsholm, Sven Peter & Holm, Sverre (2022). Wave equations for porous media described by the Biot model. Journal of the Acoustical Society of America. ISSN 0001-4966. 151(4), p. 2576–2586. doi: 10.1121/10.0010164. Full text in Research Archive Show summary

  Single-mode equivalent space-time representations of the acoustic wave propagating in a Biot poroelastic medium have previously been found only for asymptotic cases: In the low frequency regime, where the viscous skin depth is greater than the characteristic pore size, the time domain equivalent is represented with integer order temporal and spatial loss terms, whereas in the high frequency regime, it is represented with fractional order temporal and spatial loss terms. In the current work, a time domain representation in terms of a partial differential equation is proposed for all three wave solutions of the Biot model across all frequencies, and it is derived from the material response function of the Biot poroelastic medium with suitable approximations for the compressional modes and the dynamic permeability. The dynamic permeability in the time domain is represented by a fractional pseudo-differential operator. Optimal correction factors are introduced into the wave equation to compensate for the discrepancies in the compressional wave dispersion and attenuation. Additionally, the method for incorporating the squirt flow mechanism into the wave equation via the Extended Biot poroviscoelastic model is described. The proposed wave equation has a physical basis and satisfies the passivity criterion.

• Svensson, Siri Fløgstad; Arcos, José De; Darwish, Omar Isam; Fraser-Green, Jorunn; Storås, Tryggve & Holm, Sverre [Show all 9 contributors for this article] (2021). Robustness of MR Elastography in the Healthy Brain: Repeatability, Reliability, and Effect of Different Reconstruction Methods. Journal of Magnetic Resonance Imaging. ISSN 1053-1807. 53(5), p. 1510–1521. doi: 10.1002/jmri.27475. Full text in Research Archive Show summary

  Background Changes in brain stiffness can be an important biomarker for neurological disease. Magnetic resonance elastography (MRE) quantifies tissue stiffness, but the results vary between acquisition and reconstruction methods. Purpose To measure MRE repeatability and estimate the effect of different reconstruction methods and varying data quality on estimated brain stiffness. Study Type Prospective. Subjects Fifteen healthy subjects. Field Strength/Sequence 3T MRI, gradient-echo elastography sequence with a 50 Hz vibration frequency. Assessment Imaging was performed twice in each subject. Images were reconstructed using a curl-based and a finite-element-model (FEM)-based method. Stiffness was measured in the whole brain, in white matter, and in four cortical and four deep gray matter regions. Repeatability coefficients (RC), intraclass correlation coefficients (ICC), and coefficients of variation (CV) were calculated. MRE data quality was quantified by the ratio between shear waves and compressional waves. Statistical Tests Median values with range are presented. Reconstruction methods were compared using paired Wilcoxon signed-rank tests, and Spearman's rank correlation was calculated between MRE data quality and stiffness. Holm–Bonferroni corrections were employed to adjust for multiple comparisons. Results In the whole brain, CV was 4.3% and 3.8% for the curl and the FEM reconstruction, respectively, with 4.0–12.8% for subregions. Whole-brain ICC was 0.60–0.74, ranging from 0.20 to 0.89 in different regions. RC for the whole brain was 0.14 kPa and 0.17 kPa for the curl and FEM methods, respectively. FEM reconstruction resulted in 39% higher stiffness than the curl reconstruction (P < 0.05). MRE data quality, defined as shear-compression wave ratio, was higher in peripheral regions than in central regions of the brain (P < 0.05). No significant correlations were observed between MRE data quality and stiffness estimates. Data Conclusion MRE of the human brain is a robust technique in terms of repeatability. Caution is warranted when comparing stiffness values obtained with different techniques.

• Svensson, Siri Fløgstad; Garcia, Elies Fuster i; Latysheva, Anna; Fraser-Green, Jorunn; Nordhøy, Wibeke & Darwish, Omar Isam [Show all 11 contributors for this article] (2021). Decreased tissue stiffness in glioblastoma by MR elastography is associated with increased cerebral blood flow. European Journal of Radiology. ISSN 0720-048X. 147. doi: 10.1016/j.ejrad.2021.110136. Full text in Research Archive Show summary

  Purpose Understanding how mechanical properties relate to functional changes in glioblastomas may help explain different treatment response between patients. The aim of this study was to map differences in biomechanical and functional properties between tumor and healthy tissue, to assess any relationship between them and to study their spatial distribution. Methods Ten patients with glioblastoma and 17 healthy subjects were scanned using MR Elastography, perfusion and diffusion MRI. Stiffness and viscosity measurements G′ and G′′, cerebral blood flow (CBF), apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were measured in patients’ contrast-enhancing tumor, necrosis, edema, and gray and white matter, and in gray and white matter for healthy subjects. A regression analysis was used to predict CBF as a function of ADC, FA, G′ and G′′. Results Median G′ and G′′ in contrast-enhancing tumor were 13% and 37% lower than in normal-appearing white matter (P < 0.01), and 8% and 6% lower in necrosis than in contrast-enhancing tumor, respectively (P < 0.05). Tumors showed both inter-patient and intra-patient heterogeneity. Measurements approached values in normal-appearing tissue when moving outward from the tumor core, but abnormal tissue properties were still present in regions of normal-appearing tissue. Using both a linear and a random-forest model, prediction of CBF was improved by adding MRE measurements to the model (P < 0.01). Conclusions The inclusion of MRE measurements in statistical models helped predict perfusion, with stiffer tissue associated with lower perfusion values.

• Lino, Paolo; Maione, Guido; Garrappa, Roberto & Holm, Sverre (2021). An approach to optimal integer and fractional-order modeling of electro-injectors in compression-ignition engines. Control Engineering Practice. ISSN 0967-0661. 115(104890). doi: 10.1016/j.conengprac.2021.104890. Full text in Research Archive

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• Holm, Sverre (2025). The Imagined Conflict: On Science and God. Wipf and Stock Publishers. ISBN 9798385257638. 300 p. doi: https:/wipfandstock.com/9798385257638/the-imagined-conflict/. Full text in Research Archive Show summary

  Of course, there is a conflict between science and God, many say, and they do not even bother to ask for justification. This myth-based view is dominant in our culture. Sverre Holm regularly encounters attitudes that reflect such a perception, which is based more on opinion than on fact. This has inspired him to embark on the exciting task of elucidating how classical Christian faith, with a little effort, can go together with science. The result is an educational and engaging book for anyone interested in science, its history and philosophy. "Science is strangely vague when faced with the question of human consciousness and calls the origin of its most prominent characteristic, the ability to speak, a mystery. Nevertheless, there is no lack of certainty about how evolution can explain everything about human nature. Are we approaching the limits of what science can explain here?"

• Holm, Sverre & Aasmundtveit, Sven (2025). Vitenskap med overtoner. 21 naturforskere og deres gudstro. Lunde forlag (Veritas). ISBN 9788283850574. 248 p. doi: https:/www.forlagshusetlunde.no/vitenskap-med-overtoner. Full text in Research Archive Show summary

  Naturforskere med en gudstro har spilt en sentral rolle i vitenskapens utvikling gjennom mer enn fire hundre år. Noen tenker kanskje at troen på Gud som skaper og naturvitenskap må ha vært konfliktfylt, men naturforskernes historier sier noe helt annet. De hadde et guddommelig perspektiv på vitenskapen, og det gjorde arbeidet deres bedre, ikke dårligere. La deg inspirere av 21 av verdens viktigste naturforskere, blant annet: * Mary Anning, sin tids dyktigste fossiljeger * Nicolaus Steno, det ukjente universalgeniet * George Lemaître, den første som tenkte på Big Bang * George Cantor og hans hotell med uendelig mange rom Boken har to forfattere. Først presenterer professor Sverre Holm naturforskerens livsverk og tro, deretter reflekterer Sven Aasmundtveit over hva dette kan bety for oss i dag. Sammen gir de to stemmene oss Vitenskap med overtoner.

• Holm, Sverre (2021). Den innbilte konflikten. Om naturvitenskap og Gud. Veritas forlag. ISBN 9788283850369. 359 p. doi: https:/www.forlagshusetlunde.no/den-innbilte-konflikten. Full text in Research Archive Show summary

  Selvfølgelig er det konflikt mellom naturvitenskap og Gud, sier mange, og spør ikke om begrunnelse. Vår kultur har dannet seg en oppkonstruert konflikt mellom vitenskap og Gud. Professor Sverre Holm (Universitetet i Oslo) møter jevnlig holdninger som reflekterer en slik oppfatning. Dette har inspirert ham til å gi seg i kast med den spennende oppgaven å belyse hvordan klassisk kristen tro, med litt innsats, kan gå sammen med naturvitenskap. Resultatet er en lærerik og engasjerende bok for alle som er interessert i vitenskap, dens historie og filosofi. «Vitenskapen er underlig vag på hva bevissthet er, og kaller opphavet til dens fremste kjennetegn, språkevnen, et mysterium. Likevel mangler det ikke på skråsikkerhet om hvordan evolusjonen forklarer alt ved menneskets natur. Nærmer vi oss her grensen for hva naturvitenskap kan forklare?»

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• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Austeng, Andreas; Holm, Sverre & Näsholm, Sven Peter (2026). Improved Full-Waveform Inversion in Time-Harmonic Elastography. Full text in Research Archive
• Han, Chaoran; Ziksari, Mahsa Sotoodeh; Näsholm, Sven Peter; Austeng, Andreas; Cecconello, Elsa & Boukraa, Mohamed Aziz [Show all 8 contributors for this article] (2025). Shear-wave speed estimation in time harmonic elastography. Full text in Research Archive
• Holm, Sverre (2024). Forstår at kristne studenter er redde for å støte: – Tendensen har vært der lenge. [Journal]. Dagen. Full text in Research Archive
• Holm, Sverre (2024). Den innbilte konflikten. [Internet]. TVL. Full text in Research Archive Show summary

  34:48 - En klok mann har sagt at når du tar en slurk av vitenskapens glass så blir du ateist. Men nederst i glasset så venter Gud på deg. Vår neste gjest er godt bevandret i natur-vitenskapelige kretser. Du har kanskje hørt stemmen hans tidligere. Han har nemlig vært jevnlig ekspert i radioprogrammet Abels Tårn og er fysiker ved Universitetet i Oslo. Fysikkprofessor Sverre Holm, hjertelig velkommen hit!

• Holm, Sverre (2024). Som student ga en professor John Lennox et valg: Gud eller karriere? [Journal]. Dagen. Full text in Research Archive
• Holm, Sverre (2024). 10 kristne naturforskere du tenker på hver dag. Full text in Research Archive Show summary

  Ampère, Volta, Kelvin, Lemaître, Anning, Faraday, Marconi, Newton, Townes, Steno

• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). Application of Spatial Autocorrelation in Experimental Time-Harmonic Elastography. Full text in Research Archive
• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). An Autocorrelation-Based Approach for Estimating Shear Wave Speed Using 2D Velocity Vector. Full text in Research Archive
• Holm, Sverre (2024). Når Tone åpner kjøleskapet, skjer dette. [TV]. TV2. Full text in Research Archive Show summary

  DAB-radio blir taus når kjøleskapsdøren åpnes

• Holm, Sverre (2024). John Lennox: The quest for artificial general intelligence and the limits of science. [Internet]. YouTube. Full text in Research Archive Show summary

  We humans are insatiably curious, and have always been asking questions, such as the hard questions about origin and destiny. With the rise of artificial intelligence, these questions have become even more daunting. On the one hand, we live in a time of rapid scientific progress that holds enormous promise for many of the problems we face as humankind. So much so, in fact, that many see no need or use for other ways of solving the mysteries of our universe. They assume that science can explain everything. On the other hand, popular answers to questions about artificial general intelligence differ wildly: from utopian vistas of superhumans working alongside superintelligent Al to Orwellian outcomes where humans are controlled or outcompeted by superintelligent machines or superior versions of themselves. Lennox argues that the ethical considerations that we bring to bear on these questions is worldview dependent and has serious implications for our thinking about the future of humanity.

• Holm, Sverre (2023). Flukten fra lydene. [Journal]. Aftenposten Innsikt. Full text in Research Archive Show summary

  Du tror det er stille, men det er det egentlig aldri. Hva er lyd, og kan vi unnslippe den? Skrevet av Anlov Peter Mathisen

• Holm, Sverre (2023). Bilnøkkeltriks: – Det funket! [TV]. VGTV. Full text in Research Archive Show summary

  Med dette smarte trikse kan du åpne bilen din på flere meters avstand.

• Holm, Sverre; Chandrasekaran, Sri Nivas & Näsholm, Sven Peter (2023). Finding wave equations for sediment acoustics theories. Full text in Research Archive Show summary

  The two main theories for wave propagation in sediments, the Extended Biot theory and the Viscous Grain Shearing (VGS) theory, have been formulated in terms of dispersion equations only. Some have considered the lack of a wave equation to be a weakness that may indicate lack of a physical basis for these theories. In the Biot theory, it is the frequency-dependent viscodynamic operator which models viscous boundary effects in pores that poses the problem. It can be formulated as a ratio of Bessel functions for circular pores and as a ratio of tanh-functions for a 2D parallel plane duct. There is no simple equivalent time domain operator for use in the wave equation. In both geometries, the factor may, however, be approximated well with (1 + icω)1/2, where c is a constant. This factor also appears in the Cole-Davidson dielectric theory for complex media. The equivalent time domain operator, the fractional pseudo-differential operator, enables the formulation of wave equations for all three wave modes. The same operator turns out to be central for transforming the dispersion relations of the VGS theory to time-space wave equations. These wave equations enable a closer study of properties of the medium models than that obtained from dispersion relations alone.

• Holm, Sverre (2023). Fractional derivatives appear wherever there are power laws in physics. Full text in Research Archive
• Holm, Sverre (2023). The cautious acceptance of biological evolution by C S Lewis. Full text in Research Archive Show summary

  “In the science, Evolution is a theory about changes: in the Myth, it is a fact about improvements” is what Lewis wrote in the Funeral of a Great Myth in the 1940’s, demonstrating both an acceptance of and a skepticism to the explanatory power of biological evolution. There seems to be an ambiguity in reading Lewis, as Peterson in 2010 called him a theistic evolutionist, or an evolutionary theist, while West in 2012 said that Lewis does not fit in with mainstream theistic evolution. First, this interest in Lewis’ views more than half a century after his death is remarkable. Second, the ambiguity more than anything else demonstrates the lack of precision in the label “theistic evolution” as Lewis cannot possibly both be supportive of it and against it at the same time. Third, one cannot understand Lewis’ skepticism to explanations for improvements in evolution without considering his reading of Haldane, one of the founders of Neo-Darwinism. Nearly a century later, biologists still state that why the major evolutionary transitions happened defy explanation (Szathmáry, Smith, Nature 1995; Desmond, Biology & Philosophy, 2021). These transitions are different from the imprecise term macroevolution (up to the Phylum level), as they occur at an even higher level, e.g., from primates to human societies with natural language. Biologists seem to deal with this lack of explanation by either 1) accepting it, 2) by a more or less justified trust in a future resolution, or 3) by denying that there is progress at all, often leading to a low view of humans. I argue here that Lewis’ views can still guide us today in expressing awe and wonder over the process of evolution as well as skepticism to the claims of evolutionism or the Myth, as Lewis liked to call it, that everything is explained.

• Holm, Sverre (2023). Natural Occurrence of Fractional Derivatives in Physics. Full text in Research Archive
• Holm, Sverre & Grøn, Øyvind (2022). Bokkronikk: Innføring i fysikk, Renstrøm og Renstrøm 2020. Fra Fysikkens Verden. ISSN 0015-9247. 84(3), p. 60–63. Full text in Research Archive Show summary

  Dette er en fysikkbok som ikke bare gjentar historiske myter, men går til orginalkildene for å gjengi historikken på en mest mulig korrekt måte. Anmelderne er meget positive til boken og håper at den vil bli brukt til å erstatte de ofte mytebefengte fremstillingene i enkelte andre norske lærebøker. Teksten er hele veien krydret med gode eksempler som er regnet gjennom på en passe detaljert måte slik at den uerfarne leser kan følge med hele veien. Boken er skrevet i et prima språk med god logikk i setningene.

• Davidsen, Bjørn Are & Holm, Sverre (2022). Når skal skolen avsløre myter i læremidler? Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116. Full text in Research Archive Show summary

  I 2020 trakk Gyldendal første utgave av «Falske Fakta» fra markedet. Grunnen var enkel: En bok om falske fakta presenterte selv falske fakta. Man fikk ikke straff i middelalderen «hvis man sa at Jorden var rund». Kirken mente ikke «det var imot Bibelen» å mene dette. Mytene finnes også i læremidler. En årsak kan være lærerutdanningen. Selv Svein Sjøbergs «Naturfag som allmenndannelse - en kritisk fagdidaktikk» lener seg mot myten om en lang konflikt mellom tro og vitenskap. Likevel er nok populærvitenskap viktigere. En så respektert formidler som Eirik Newth hevder i «Jakten på sannheten» at i middelalderen begynte mange kristne «å tro at Jorden var flat». I stedet for å bli trukket fra markedet, er boken oversatt til 22 språk og fikk Brageprisen og Kulturdepartementets pris. Slik fagsjekk.no viser, sprer Newth myte etter myte. Teologer lurte ikke på om kvinner hadde sjel. Sykehusene ble ikke stengt »fordi prestene fortalte at folk bare kunne bli friske ved å be til gud». Kirken forbød ikke disseksjoner. Copernicus ventet ikke med å gi ut sin bok i frykt for kirkens reaksjoner. For bare å nevne noen. Newth hevder at gudstro hemmer forskning, men nevner ikke at de fleste oppdagerne i boken har en gudstro. Ja, en tro på mange guder styrker nok ikke jakten på lover i naturen, men tanken om Gud som lovgiver bak naturen kan ha bidratt avgjørende. Uansett nedtones oppdagernes tro. Selv en så engasjert kristen som Blaise Pascal blir den franske filosofen. Kardinal Nikolaus av Cusa som mente at verdensrommet er uendelig, kalles akademikeren. Biskop Steno som argumenterte for at fossiler er forsteinede dyr og planter, er dansken. Skal skolen leve opp til fagfornyelsen, bør mytene løftes frem som eksempler på hvor vanskelig kritisk tenkning er.

• Aparicio, Joaquin; Thio, Vincent Martello Kwie Hoe & Holm, Sverre (2022). Range evaluation between indoor microphones obtained from acoustic ambient noise cross-correlations. Full text in Research Archive
• Holm, Sverre (2022). Gud og vitenskap – Kan jeg tro på begge deler? Full text in Research Archive
• Holm, Sverre (2022). En innbilt konflikt mellom naturvitenskap og gudstro? Full text in Research Archive
• Holm, Sverre (2022). Gode grunner til at konflikten mellom vitenskap og Gud er innbilt. Full text in Research Archive
• Holm, Sverre (2021). Naturvitenskap og Gud er ikke konkurrenter. Dagen : kristelig dagblad. ISSN 0805-4738. Full text in Research Archive
• Holm, Sverre (2021). Ber kirken ta oppgjør med kirkehets i skolen. [Journal]. Dagen. Full text in Research Archive
• Holm, Sverre (2021). Long delayed radio echoes – the illusive secret of the ionosphere. Full text in Research Archive Show summary

  The first radio echoes with long delays were reported in 1927 by Jørgen Hals in Oslo, Norway on 9.54 MHz signals from the Netherlands. His first report exists at the National Library in Oslo and was later reported in Nature [Størmer, 1928]. Controlled experiments where delays ranged from 3 to 30 seconds confirmed the phenomenon and convinced most skeptics that the phenomenon was real [van der Pol, 1928]. About 15 different hypotheses have been presented over time for their cause [Shlionskiy 1985]. The five most likely ones will be presented here. They involve phenomena with long-distance travel such as around the world many times or reflection from plasma clouds. Another scenario is where the speed of propagation is substantially slower than normal as if there is mode conversion to mechanical waves in the ionosphere with or without nonlinearity [Vidmar, Crawford 1985]. The only one of the five which is understood well is when a signal is ducted in the magnetosphere and reflected from the opposite hemisphere. It may occur for frequencies up to 4 MHz and will give delays of up to 0.5 seconds. The further north, the longer the delay. Therefore, such medium delay echoes may sometimes be confused with round-the-world echoes of 138 ms, which however seldom occur at such low frequencies. There are examples of such echoes from Tasmania and St. Petersburg in the scientific literature. Amateur operator reports from New York, Georgia, California, Newfoundland, Denmark, and the UK [Martinez, 2007] from the last decades will be presented and analyzed and audio from some of them will be demonstrated. The delay is predictable from geomagnetic latitude using a simplified dipole model for the geomagnetic field line [Holm 2009]. The effect occurs during the dark hours and is most likely during winter months of years of low solar activity. A good report of such a phenomenon should involve a digital recording of audio using CW and not SSB signals. Delay measurement with amateur radio equipment is a challenge and needs to compensate for the usual delay between the onsets of the transmitter and sidetone signals.

• Holm, Sverre (2021). Lysloven på Kanariøyene. Full text in Research Archive
• Simionato, Riccardo; Fasciani, Stefano & Holm, Sverre (2024). Neural Modeling of Musical Devices. Universitetet i Oslo. Full text in Research Archive Show summary

  Modeling musical devices, whether instruments or effects, acoustic or electronic, is a dynamic area of research and development characterized by significant scientific relevance, a rich history, and far-reaching artistic implications. This multidisciplinary field encompasses a diverse range of perspectives, from musical acoustics to digital signal processing. Musical devices present nonlinear and time-variant characteristics that provide unique soundings and behaviors that are challenging to replicate in digital emulation. Thanks to the increasing computational power of general-purpose computers, deep learning has emerged as an approach for modeling musical devices, particularly analog audio effects. In this thesis a step forward in this direction is taken, broadening the understanding of the use of neural networks to model musical devices that process or generate sounds, with a focus on complex devices that pose challenges for current neural modeling methods. In this research, novel neural architectures are investigated, placing great emphasis on essential aspects of modeling networks such as low latency, computational efficiency, and interactivity, all of which are crucial to achieving ’playable’ emulations. Furthermore, the thesis develops architectures, subcomponents, and methods designed for wide applicability across different musical device categories with minimal need for customization. The primary focus lies on two case studies involving nonlinear, time-variant musical devices representative of the acoustic and analog realms: the compressor, as a processor, and the acoustic piano, as a generator. Besides proposing novel neural architecture for modeling musical devices, in this thesis, the understanding of learning strategies in neural models is advanced, and the application of neural techniques for parameter-sensitive musical behavior is refined. Additionally, it compiles a variety of datasets of the musical devices being studied.

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