Chaoran Han

• Han, Chaoran; John, Cater, & Oliver, Sinnen, (2025). An mTSP model for multiple telescope short-term scheduling | Experimental Astronomy. Experimental astronomy (Print). ISSN 0922-6435. 60. doi: 10.1007/s10686-025-10022-y. Full text in Research Archive Show summary

  Pulsar observation scheduling is a highly dynamic problem with uncertainty caused by scintillation and environmental interference. In the scheduling systems used by observatories today, this uncertainty is usually accounted for by using a short-term scheduling process. In order to observe as many pulsars as possible within a certain period of time, it becomes imperative for multiple telescopes or sub-arrays to observe multiple targets at the same time. However, there is little research on the speed improvement and cost-efficiency improvement of such “parallel" observation with multiple telescopes. In this work, we have designed a multiple telescope short-term scheduling simulation system, based on extending previously proposed scheduling heuristics using a single telescope pulsar scheduling simulator. Additionally, we propose a more complex multiple telescope short-term scheduling policy based on the multiple travelling salesperson problem (mTSP). Realistic datasets within the simulation environment are used to evaluate the proposed algorithms with multiple telescopes. The results show that multiple telescopes can significantly reduce the time to observe a set of pulsars. The previous single telescope heuristics adapt surprisingly well to the multiple telescope scenario and the novel mTSP policy is competitive, with potential for future improvements.

• Han, Chaoran; Näsholm, Sven Peter; Austeng, Andreas & Arnestad, Håvard (2025). Taylor-Series Based Derivation of the Resolution of Null Subtraction Imaging for a Uniform Linear Array. IEEE Open Journal of Ultrasonics, Ferroelectrics, and Frequency Control Society (OJUFFC). 5, p. 19–22. doi: 10.1109/OJUFFC.2025.3550096. Full text in Research Archive Show summary

  Null subtraction imaging (NSI) is a non-linear beamformer that aims to improve the spatial resolution of ultrasound images. NSI incoherently combines three delay-and-sum (DAS) outputs from the same RF data using three related apodizations on receive. NSI has been advocated to have many advantages in different domains such as B-mode imaging, plane wave imaging, power Doppler imaging, and for large-pitch arrays. However, despite its increasing popularity, an explicit relationship between NSI resolution (interpreted as the mainlobe width) and various parameters (such as the DC offset value c, array aperture, and wavelength) is not known, making system design and intuitive reasoning about the method difficult. Therefore, in the current work, we derive the theoretical NSI array pattern and give an approximate expression for the −6 dB mainlobe width. Our derivation is based on a Taylor series-expansion of the analytical NSI array pattern, which is valid over the mainlobe region for the range of c values typically seen in the literature. The results show that the NSI mainlobe width is proportional to cλ/D, which is the DC offset value multiplied by the wavelength and divided by the aperture size, and therefore has a similar wavelengh and aperture dependency as the classical DAS mainlobe. The work is validated numerically, also showing that the NSI mainlobe width approaches the DAS mainlobe width as c approaches infinity.

• Han, Chaoran; Arnestad, Håvard; Austeng, Andreas & Näsholm, Sven Peter (2024). Spectral Estimation Inspired by a Non-Linear Beamformer: Insights into Null-Subtraction Imaging. In Viggen, Erlend Magnus (Eds.), Proceedings of the 47th Scandinavian Symposium on Physical Acoustics. Norsk Fysisk Selskap. ISSN 9788281230248. p. 1–4. Full text in Research Archive Show summary

  Beamforming and spectral estimation are two highly related and, in many ways, analogous signal processing topics. Spectral estimation is typically associated with analysing the signal temporally, and is used to determine signal power distribution across different frequency components f . Correspondingly, beamforming is a spatial signal processing technique used to estimate the distribution of signal power with different wavenumbers k (interpretable as different directions under far-field and narrowband conditions). Spectral estimation methods often have a beamforming counterpart, as exemplified by Capon’s minimum variance beamformer [1] and the minimum variance spectral esti- mator [2]. New non-linear beamforming methods are actively researched and proposed for use in medical ultrasound. Unfortunately, the true capabilities of beamforming meth- ods can be difficult to evaluate from first principles when they are applied in an active, near-field, and broadband imaging setup. In the current work, we evaluate a recently pro- posed beamforming method through the analysis of its capabilities as a spectral estimator, thereby gaining new knowledge about the method’s capabilities. ... Continuation in the full extended abstract PDF publicly available here: https://www.researchgate.net/profile/Chaoran-Han-2/publication/379997487_Spectral_Estimation_Inspired_by_a_Non-Linear_Beamformer_Insights_into_Null-Subtraction_Imaging_Extended_abstract/links/6626875839e7641c0be0cea3/Spectral-Estimation-Inspired-by-a-Non-Linear-Beamformer-Insights-into-Null-Subtraction-Imaging-Extended-abstract.pdf?origin=publicationDetail&_sg%5B0%5D=P_FHkxDhVdwXcuUoUxVfT0g9KjTMsLjPTujIw9DWCwPSmTH4axLlPyDZ8WnS3Zp8I7n0Uh912A07oj-pJ6tJ8Q.ip_pJB4CBbvS1xuL01_dgetRbxpiwwXtAK8olGsK9x4uy1h6BLCTp9fi3KzlriwEZ5_C3Jww-NkZQl7gfmrONg&_sg%5B1%5D=SRH62o47Gu0k0pUDqBtdzE5InmIKFV65ujV4sU5PTZiEOGYJzGKcbuaavLsqWTfNuR1rUo40Nn08ywq1qOwY-xgFXgiqOakmcKU4GG9LREJC.ip_pJB4CBbvS1xuL01_dgetRbxpiwwXtAK8olGsK9x4uy1h6BLCTp9fi3KzlriwEZ5_C3Jww-NkZQl7gfmrONg&_iepl=&_rtd=eyJjb250ZW50SW50ZW50IjoibWFpbkl0ZW0ifQ%3D%3D&_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6ImhvbWUiLCJwYWdlIjoicHVibGljYXRpb24iLCJwcmV2aW91c1BhZ2UiOiJzZWFyY2giLCJwb3NpdGlvbiI6InBhZ2VIZWFkZXIifX0

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• Han, Chaoran; Alix, Corentin; Näsholm, Sven Peter; Austeng, Andreas; Salles, Sébastien & Karabiyik, Yücel (2026). Transverse Oscillation-Based Velocity Estimation in Ultrasound Time-Harmonic Elastography. Full text in Research Archive
• Han, Chaoran; Boukraa, Mohamed Aziz; Näsholm, Sven Peter; Austeng, Andreas; Ziksari, Mahsa Sotoodeh & Karabiyik, Yücel (2025). A Simulation Framework for Ultrasound Time Harmonic Elastography (THE). 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
• Han, Chaoran; Näsholm, Sven Peter; Austeng, Andreas & Arnestad, Håvard (2024). Taylor-Series Based Derivation of the Resolution of Null Subtraction Imaging for a Uniform Linear Array. Full text in Research Archive

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