| 1. |
- Kristan, Matej, et al.
(författare)
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The first visual object tracking segmentation VOTS2023 challenge results
- 2023
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Ingår i: 2023 IEEE/CVF International conference on computer vision workshops (ICCVW). - : Institute of Electrical and Electronics Engineers Inc.. - 9798350307443 - 9798350307450 ; , s. 1788-1810
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking Segmentation VOTS2023 challenge is the eleventh annual tracker benchmarking activity of the VOT initiative. This challenge is the first to merge short-term and long-term as well as single-target and multiple-target tracking with segmentation masks as the only target location specification. A new dataset was created; the ground truth has been withheld to prevent overfitting. New performance measures and evaluation protocols have been created along with a new toolkit and an evaluation server. Results of the presented 47 trackers indicate that modern tracking frameworks are well-suited to deal with convergence of short-term and long-term tracking and that multiple and single target tracking can be considered a single problem. A leaderboard, with participating trackers details, the source code, the datasets, and the evaluation kit are publicly available at the challenge website1
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| 2. |
- Lai, Hui-Wen, et al.
(författare)
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Precipitation variability related to atmospheric circulation patterns over the Tibetan Plateau
- 2024
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Ingår i: International Journal of Climatology. - 0899-8418 .- 1097-0088. ; 44:1, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation is affected by intricate atmospheric dynamic and thermodynamic processes. Horizontal winds are frequently used to represent the dynamic component as winds play a critical role in transporting moisture. Previous studies on precipitation over the Tibetan Plateau (TP) focused on the influence of summer monsoons and westerlies in isolation. However, the collective seasonal dynamics and their combined effects on the precipitation distribution remain less explored. This study aims to determine the seasonal evolutions of the wind patterns and the associated regional precipitation patterns over the TP using a neural network approach and focuses on their interannual variability and long-term trends. A self-organizing map (SOM) was used to classify the wind patterns based on 500 hPa winds and related precipitation from the ERA5 reanalysis. The classified wind patterns show seasonal shifts between the Asian summer monsoon circulations and the westerlies along with the westerly jets migrating between the north and south of the TP from summer to winter. The locations of abundant precipitation during the winter and transition seasons are mainly associated with variations in the intensity and locations of the strong westerlies. There is a significant positive trend in the occurrences of the summer-type wind pattern, which has likely led to a wetter TP, and an earlier-ended winter and advanced spring wind patterns. The interannual variability of westerlies is highly related to the variability of precipitation in the western TP during its wet season (January–April). In the eastern TP, the interannual variability of the precipitation is linked to the wind patterns associated with the westerly jets to the south of the TP, while precipitation variability in the central TP is controlled by thermodynamic components. This study reveals the spatial precipitation distributions according to the different wind patterns and identifies the contributions from atmospheric components to the regional precipitation over the TP.
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| 3. |
- Paraschos, Georgios Filippos, et al.
(författare)
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Ordered magnetic fields around the 3C 84 central black hole
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Context . 3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz. Aims. Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84. Methods . We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited (u, v)-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. Results . We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of νm = (113 ± 4) GHz, a corresponding synchrotron self-absorbed magnetic field of BSSA = (2.9 ± 1.6) G, and an equipartition magnetic field of Beq = (5.2 ± 0.6) G. Three components are resolved with the highest fractional polarisation detected for this object (mnet = (17.0 ± 3.9)%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84. Conclusions . The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited (u, v)-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84.
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| 4. |
- Yang, Jun, 1979, et al.
(författare)
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Intermediate-mass black holes: finding of episodic, large-scale, and powerful jet activity in a dwarf galaxy
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 520:4, s. 5964-5973
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Tidskriftsartikel (refereegranskat)abstract
- Dwarf galaxies are characterized by a very low luminosity and low mass. Because of significant accretion and ejection activity of massive black holes, some dwarf galaxies also host lo w-luminosity acti ve galactic nuclei (AGNs). In a few dwarf AGNs, very long baseline interferometry (VLBI) observations have found faint non-thermal radio emission. SDSS J090613.77 + 561015.2 is a dwarf AGN owning an intermediate-mass black hole (IMBH) with a mass of M-BH = 3 . 6 (+5.9) (-2.3 )x 10 (5) M(? )and showing a rarely seen two-component radio structure in its radio nucleus. To further probe their nature, i.e. the IMBH jet activity, we performed additional deep observations with the European VLBI Network (EVN) at 1.66 and 4.99 GHz. We find the more diffuse emission regions and structure details. These new EVN imaging results allow us to reveal a two-sided jet morphology with a size up to about 150 mas (projected length similar to 140 pc) and a radio luminosity of about 3 x 10( 38) erg s( -1). The peak feature has an optically thin radio spectrum and thus more likely represents a relatively young ejecta instead of a jet base. The EVN study on SDSS J090613.77 + 561015.2 demonstrates the existence of episodic, relatively large-scale, and powerful IMBH jet activity in dwarf AGNs. Moreo v er, we collected a small sample of VLBI-detected dwarf AGNs and investigated their connections with normal AGNs. We notice that these radio sources in the dwarf AGNs tend to have steep spectra and small linear sizes, and possibly represent ejecta from scaled-down episodic jet activity.
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| 5. |
- Chen, Wen, 1988, et al.
(författare)
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VLBI Astrometry of radio stars to link radio and optical celestial reference frames. I. HD 199178 & AR Lacertae
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 524:4, s. 5357-5367
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Tidskriftsartikel (refereegranskat)abstract
- To accurately link the radio and optical Celestial Reference Frames (CRFs) at optical bright end, i.e. with GaiaG-band magnitude ≾13, increasing number and improving sky distribution of radio stars with accurate astrometric parameters from both Very Long Baseline Interferometry (VLBI) and Gaia measurements are mandatory. We selected two radio stars HD 199178 and AR Lacertae as the target for a pilot program for the frame link, using the Very Long Baseline Array at 15 GHz at six epochs spanning about 1 yr, to measure their astrometric parameters. The measured parallax of HD 199178 is 8.949 ± 0.059 mas and the proper motion is μαcos δ = 26.393 ± 0.093 and μδ = −0.950 ± 0.083 mas yr−1, while the parallax of AR Lac is 23.459 ± 0.094 mas and the proper motion is μαcos δ = −51.906 ± 0.138 and μδ = 46.732 ± 0.131 mas yr−1. Our VLBI measured astrometric parameters have accuracies about 4–5 times better than the corresponding historic VLBI measurements and comparable accuracies with those from Gaia, validating the feasibility of frame link using radio stars. With the updated astrometric parameters for these two stars, there is a ∼25 per cent reduction of the uncertainties on the Y-axis for both orientation and spin parameters.
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| 6. |
- Eme, Laura, et al.
(författare)
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Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes
- 2023
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 618:7967, s. 992-
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Tidskriftsartikel (refereegranskat)abstract
- In the ongoing debates about eukaryogenesis-the series of evolutionary events leading to the emergence of the eukaryotic cell from prokaryotic ancestors-members of the Asgard archaea play a key part as the closest archaeal relatives of eukaryotes(1). However, the nature and phylogenetic identity of the last common ancestor of Asgard archaea and eukaryotes remain unresolved(2-4). Here we analyse distinct phylogenetic marker datasets of an expanded genomic sampling of Asgard archaea and evaluate competing evolutionary scenarios using state-of-the-art phylogenomic approaches. We find that eukaryotes are placed, with high confidence, as a well-nested clade within Asgard archaea and as a sister lineage to Hodarchaeales, a newly proposed order within Heimdallarchaeia. Using sophisticated gene tree and species tree reconciliation approaches, we show that analogous to the evolution of eukaryotic genomes, genome evolution in Asgard archaea involved significantly more gene duplication and fewer gene loss events compared with other archaea. Finally, we infer that the last common ancestor of Asgard archaea was probably a thermophilic chemolithotroph and that the lineage from which eukaryotes evolved adapted to mesophilic conditions and acquired the genetic potential to support a heterotrophic lifestyle. Our work provides key insights into the prokaryote-to-eukaryote transition and a platform for better understanding the emergence of cellular complexity in eukaryotic cells.
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| 7. |
- Fan, Lulu, et al.
(författare)
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The Hyperluminous, Dust-obscured Quasar W2246-0526 at z=4.6: Detection of Parsec-scale Radio Activity
- 2020
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 905:2
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Tidskriftsartikel (refereegranskat)abstract
- WISE J224607.56-052634.9 (W2246-0526) is a hyperluminous (L-bol 1.7 x 10(14) L), dust-obscured, and radio-quiet quasar at redshift z = 4.6. It plays a key role in probing the transition stage between dusty starbursts and unobscured quasars in the coevolution of galaxies and supermassive black holes (SMBHs). To search for the evidence of the jet activity launched by the SMBH in W2246-0526, we performed very long baseline interferometry observations of its radio counterpart with the European VLBI Network (EVN) plus the enhanced Multi Element Remotely Linked Interferometer Network (e-MERLIN) at 1.66 GHz and the Very Long Baseline Array (VLBA) at 1.44 and 1.66 GHz. The deep EVN plus e-MERLIN observations detect a compact (size <= 32 pc) sub-mJy component contributing about 10% of its total flux density, which spatially coincides with the peak of dust continuum and [C II] emissions. Together with its relatively high brightness temperature ( >= 8 x 10(6) K), we interpret the component as a consequence of nonthermal radio activity powered by the central SMBH, which likely originates from a stationary jet base. The resolved-out radio emission possibly come from a diffuse jet, quasar-driven winds, or both, while the contribution by star formation activity is negligible. Moreover, we propose an updated geometry structure of its multiwavelength active nucleus and shed light on the radio quasar selection bias toward the blazars at z > 4.
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| 8. |
- Felsberg, Michael, et al.
(författare)
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The Thermal Infrared Visual Object Tracking VOT-TIR2015 Challenge Results
- 2015
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Ingår i: Proceedings of the IEEE International Conference on Computer Vision. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467383905 ; , s. 639-651
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Konferensbidrag (refereegranskat)abstract
- The Thermal Infrared Visual Object Tracking challenge 2015, VOTTIR2015, aims at comparing short-term single-object visual trackers that work on thermal infrared (TIR) sequences and do not apply prelearned models of object appearance. VOT-TIR2015 is the first benchmark on short-term tracking in TIR sequences. Results of 24 trackers are presented. For each participating tracker, a short description is provided in the appendix. The VOT-TIR2015 challenge is based on the VOT2013 challenge, but introduces the following novelties: (i) the newly collected LTIR (Linköping TIR) dataset is used, (ii) the VOT2013 attributes are adapted to TIR data, (iii) the evaluation is performed using insights gained during VOT2013 and VOT2014 and is similar to VOT2015.
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| 9. |
- Jiang, Pengfei, et al.
(författare)
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VLBI astrometry on the white dwarf pulsar AR Scorpii
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 520:2, s. 2942-2951
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Tidskriftsartikel (refereegranskat)abstract
- AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical, and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network at 5 GHz and the Chinese VLBI Network plus the Warkworth 30-m telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax (pi = 8.52(-0.07)(+0.04) mas) and proper motion (mu(alpha) = 9.48(-0.07)(+0.04) mas yr(-1), mu(delta) = -51.32(-0.38)(+0.22) mas yr (-1)). The new VLBI results agree with the optical Gaia astrometry. Our kinematic analysis reveals that the Galactic space velocities of AR Sco are quite consistent with that of both intermediate polars and polars. Combined with the previous tightest VLBI constraint on the size, our parallax distance suggests that the radio emission of AR Sco should be located within the light cylinder of its white dwarf.
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| 10. |
- Yang, Jun, 1979, et al.
(författare)
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A compact core-jet structure in the changing-look Seyfert NGC 2617
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 503:3, s. 3886-3895
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Tidskriftsartikel (refereegranskat)abstract
- The nearby face-on spiral galaxy NGC 2617 underwent an unambiguous 'inside-out' multiwavelength outburst in Spring 2013, and a dramatic Seyfert-type change probably between 2010 and 2012, with the emergence of broad optical emission lines. To search for the jet activity associated with this variable accretion activity, we carried out multiresolution and multiwavelength radio observations. Using the very long baseline interferometric (VLBI) observations with the European VLBI Network at 1.7 and 5.0 GHz, we find that NGC 2617 shows a partially synchrotron self-absorbed compact radio core with a significant core shift, and an optically thin steep-spectrum jet extending towards the north up to about 2 pc in projection. We also observed NGC 2617 with the electronic Multi-Element Remotely Linked Interferometer Network at 1.5 and 5.5 GHz, and revisited the archival data of the Very Large Array (VLA) and the Very Long Baseline Array (VLBA). The radio core had a stable flux density of similar to 1.4 mJy at 5.0 GHz between 2013 June and 2014 January, in agreement with the expectation of a supermassive black hole in the low accretion rate state. The northern jet component is unlikely to be associated with the 'inside-out' outburst of 2013. Moreover, we report that most optically selected changing-look active galactic nuclei (AGN) at z < 0.83 are sub-mJy radio sources in the existing VLA surveys at 1.4 GHz, and it is unlikely that they are more active than normal AGN at radio frequencies.
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