| 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. |
- Huang, Jianqing, et al.
(författare)
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A detailed study on the micro-explosion of burning iron particles in hot oxidizing environments
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- As a promising carbon-free fuel, iron powder can directly combust with air and has great potential to provide clean and high-grad heat for various applications. The combustion characteristics of iron particles are of great significance for developing iron combustion model, designing efficient combustor, and optimizing combustion technologies. In this work, the micro-explosion behavior of burning iron particles was experimentally investigated based on optical diagnostics. With two high-speed cameras operating at 10,000 frames per second, the three-dimensional (3D) motion and mean surface temperature of burning iron particles during the micro-explosion process were measured using the stereo imaging technique and two-color pyrometry, respectively. The probability of micro-explosions in different oxidizing environments were statistically studied. Three distinct micro-explosion modes have been observed. The results showed that the micro-explosion of burning iron particles heavily depended on oxygen concentration. The micro-explosion would slightly reduce the particle surface temperature by 30–70 K within 0.5 ms, since a lot of smaller fragments were produced. In addition, the 3D velocity of most fragments would sharply increase to 2–6 times within 0.2 ms after the micro-explosion occurred. Regarding the mechanism of the micro-explosion, three types of potential gas sources inside the particle were discussed. The sharp gradients of gas temperature and oxygen concentration may facilitate the rapid increase of the internal pressure in the particle, which eventually causes the micro-explosion.
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| 3. |
- Watts, Anna L., et al.
(författare)
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Dense matter with eXTP
- 2019
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Ingår i: Science China Physics, Mechanics & Astronomy. - : Science Press. - 1674-7348 .- 1869-1927. ; 62:2
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Forskningsöversikt (refereegranskat)abstract
- In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.
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| 4. |
- Xu, Changdan, et al.
(författare)
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CTCs Detection and Whole-exome Sequencing Might Be Used to Differentiate Benign and Malignant Pulmonary Nodules
- 2023
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Ingår i: Chinese Journal of Lung Cancer. - 1009-3419. ; 26:6, s. 449-460
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Tidskriftsartikel (refereegranskat)abstract
- Background and objective Low-density computed tomography (LDCT) improved early lung cancer diagnosis but introduces an excess of false-positive pulmonary nodules data. Hence, accurate diagnosis of early-stage lung cancer remains challenging. The purpose of the study was to assess the feasibility of using circulating tumour cells (CTCs) to differentiate malignant from benign pulmonary nodules. Materials and methods 122 patients with suspected malignant pulmonary nodules detected on chest CT in preparation for surgery were prospectively recruited. Peripheral blood samples were collected before surgery, and CTCs were identified upon isolation by size of epithelial tumour cells and morphological analysis. Laser capture microdissection, MALBAC amplification, and whole-exome sequencing were performed on 8 samples. The diagnostic efficacy of CTCs counting, and the genomic variation profile of benign and malignant CTCs samples were analysed. Results Using 2.5 cells/5 mL as the cut-off value, the area under the receiver operating characteristic curve was of 0.651 (95% confidence interval: 0.538-0.764), with a sensitivity and specificity of 0.526 and 0.800, respectively, and positive and negative predictive values of 91.1% and 30.3%, respectively. Distinct sequence variations differences in DNA damage repair-related and driver genes were observed in benign and malignant samples. TP53 mutations were identified in CTCs of four malignant cases; in particular, g.7578115T>C, g.7578645C>T, and g.7579472G>C were exclusively detected in all four malignant samples. Conclusion CTCs play an ancillary role in the diagnosis of pulmonary nodules. TP53 mutations in CTCs might be used to identify benign and malignant pulmonary nodules.
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| 5. |
- Xu, Leilei, et al.
(författare)
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Large eddy simulation of spray and combustion characteristics of biodiesel and biodiesel/butanol blend fuels in internal combustion engines
- 2023
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Ingår i: Applications in Energy and Combustion Science. - 2666-352X. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Biofuel is a crucial renewable and environmentally friendly energy source for addressing greenhouse gas emissions and other energy-related issues. Biodiesel and butanol, among alternative biofuels, possess complementary physical and chemical properties, offering multiple possibilities for their use in existing internal combustion engines. However, biodiesel's distinctly different physical and combustion properties from conventional diesel fuels make its combustion process substantially different. The complex composition of biodiesel presents significant challenges in accurately simulating its spray combustion characteristics. This paper presents a systematic evaluation of six single-component surrogate fuel models and a five-component model for the prediction of biodiesel spray characteristics under various conditions using large-eddy simulation (LES). The results show that single-component surrogate fuel models can only predict the gaseous penetration of biodiesel but not the liquid-phase penetration. A five-component fatty acid methyl ester surrogate fuel model is proposed, demonstrating an accurate simulation of biodiesel spray evaporation characteristics under different conditions. Based on the five-component evaporation model, LES is utilized to examine three strategies of biodiesel/butanol-fueled internal combustion engines: direct injection of pure biodiesel in conventional diffusion-controlled combustion (CDC) engines, direct injection of biodiesel–butanol blend in CDC engines, and biodiesel/butanol reactivity-controlled compression ignition (RCCI) engines. The simulation results are validated against engine experiment results, showing that the five-component model can successfully predict spray and combustion characteristics in internal combustion engines. The RCCI concept can significantly reduce NOx emissions; however, CO and UHC emissions are higher than in the CDC engines due to incomplete combustion in the fuel-lean butanol/air mixture.
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| 6. |
- Xu, Leilei, et al.
(författare)
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Performance and emission characteristics of an ammonia/diesel dual-fuel marine engine
- 2023
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Ingår i: Renewable and Sustainable Energy Reviews. - 1364-0321. ; 185
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Tidskriftsartikel (refereegranskat)abstract
- This study explores the challenges and possibilities of using ammonia (NH3) as a carbon-free fuel for marine propulsion in a Wärtsilä ammonia/diesel dual-fuel engine using a reactivity-controlled compression ignition (RCCI) concept. The main issues in ammonia RCCI engines are high ammonia slip and high emissions of nitrogen oxides and nitrous oxide. A joint experimental and computational investigation was conducted to understand the combustion process, pollutant and greenhouse gas (GHG) formation mechanisms, and the effects of injector configuration and injection timing on engine performance. A comparative assessment between the ammonia/diesel RCCI engine and a baseline natural gas/diesel RCCI engine showed that, upon replacing premixed natural gas with ammonia and maintaining the same energy share of diesel (8.5% of the total energy from diesel), the engine yielded considerably poor combustion efficiency. Increasing diesel usage to 24% share of the total energy allowed a successful engine operation, cutting GHG by 70%. However, higher diesel usage increased CO and CO2 emissions. N2O emission was attributed to the slow premixed ammonia/air flame propagation and near-wall flame quenching. The primary sources of NO emissions in ammonia/diesel RCCI engines were identified as fuel-NOx from premixed ammonia oxidation and thermal NOx in the diesel flame region. A recommendation was put forth for enhancing the operating conditions and injection strategies of ammonia RCCI engines. The proposed operation and injection strategy results in a 45% reduction in CO emission, a 60% reduction in total GHG emissions, and, notably, an 89% decrease in CO2 emissions compared to the LNG/diesel engine.
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| 7. |
- Xu, Shijie, et al.
(författare)
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Phase change and combustion of iron particles in premixed CH4/O2/N2 flames
- 2024
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Ingår i: Combustion and Flame. - 0010-2180. ; 259
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Tidskriftsartikel (refereegranskat)abstract
- Metal powder is a promising carbon-free and recyclable energy carrier. Direct combustion of the micron-sized iron particles involves complex physical and chemical processes, such as heat transfer, surface reaction, and phase change. In this work, computational modelling of these processes is investigated and validated against experiments. A single iron particle combustion and phase change model is proposed in an Eulerian–Lagrangian framework. The new phenomenological model considers five stages, i.e., solid phase oxidation, melting of iron oxides and raw iron, liquid phase oxidation, cooling of liquid iron oxides, and solidification of super-cooled liquid iron oxides. The proposed model is first validated and then adopted in simulations of micron-sized iron particle combustion in premixed CH4/O2/N2 flames to study the effects of ambient temperature and oxygen concentration on single iron combustion. Results show that the new model is capable of replicating the melting, heterogeneous surface reaction, cooling, and solidification processes. Two-stage solidification is observed in experiments and modelled in simulations. This two-stage solidification includes a fast solidification with a significant temperature rise (∼150–200 K) and a thermal equilibrium solidification featuring a constant temperature and a slight particle radiant intensity decrease. In addition, a diffusion-controlled mechanism is identified during the melting process, in which the oxygen concentration dominates the melting time and the subsequent burning time. Furthermore, it is found that the reaction between iron and CH4/O2/N2 flame products, such as CO2 and H2O, plays a non-negligible role in the iron combustion process.
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| 8. |
- Yang, Miao, et al.
(författare)
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CFD Simulation of Biomass Combustion in an Industrial Circulating Fluidized Bed Furnace
- 2023
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Ingår i: Combustion Science and Technology. - 0010-2202. ; 195:14, s. 3310-3340
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a three-dimensional computational fluid dynamics (CFD) model is employed to investigate the hydrodynamic and combustion characteristics of biomass particles in an industrial-scale circulating fluidized bed (CFB) furnace. The CFD model considered here is based on the Eulerian-Lagrangian framework, the multi-phase particle-in-cell (MP-PIC) collision model, the coarse grain method (CGM), and a recently developed distribution kernel method (DKM). The challenge of simulating industrial-scale CFB furnaces using CFD lies in the large number of particles in the system. MP-PIC and CGM showed that local particle overloading could occur, causing the numerical simulation to diverge. The combination of MP-PIC with CGM and DKM was shown to overcome this problem. The CFD predictions werecompared with onsite temperature experiments in the furnace, and the predicted furnace temperature agreed fairly well with the measured data. Using the CFD results, the study analyzed the transient solids mixing and fluidization characteristics, as well as the thermochemical process in biomass combustion. The simulated individual particle provided insight into the physical and chemical processes of the granular flow in the dilute/dense regions of the CFB furnace. The simulated results revealed the CO and NOx emission processes in the furnace.
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| 9. |
- Zhang, Yanzhi, et al.
(författare)
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Numerical study on liquid ammonia direct injection spray characteristics under engine-relevant conditions
- 2023
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619. ; 334
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on CFD modeling of the fuel/air mixing characteristics of liquid ammonia under direct injection engine-relevant conditions. Several questions are addressed including, whether the widely used Lagrange particle tracking (LPT) spray models developed for traditional fossil fuels are suitable for ammonia spray, whether certain improvement of the current models should be introduced, and under what conditions the improvement of models needs to be considered. It is found that liquid ammonia spray characteristics can be well reproduced by the current Lagrange-based spray models under non-flash boiling conditions. However, there are obvious gaps between measurements and predictions under strong flash boiling conditions. A strong flash boiling region is found near the nozzle while its intensity decreases downstream due to the significant cooling effect of ammonia spray, and initial superheat degree defined as the ratio of ambient pressure to the saturation vapor pressure at initial fuel temperature, can be adopted to determine the boundary of flash boiling model that needs to be employed in the modeling of liquid ammonia spray. Spray included angle is a crucial parameter within the LPT simulation framework to reproduce the collapse effect for multi-plume sprays. The flash model considering only the evaporation promotion effect cannot replicate the ammonia spray characteristics and it does not result in obvious differences compared with the results from the normal evaporation model. Liquid ammonia is a thermal sensitive fuel and has a strong tendency of flash boiling, and a more accurate flash boiling model that considers the thermal breakup effect should be proposed to accurately predict ammonia fuel/air mixing characteristics under wide engine-relevant conditions.
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| 10. |
- Zhong, Shenghui, et al.
(författare)
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Assessment of grid/filter size dependence in large eddy simulation of high-pressure spray flames
- 2022
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 329
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Tidskriftsartikel (refereegranskat)abstract
- With the increase of computing power, large eddy simulation (LES) within the Lagrangian–Eulerian two-phase flow framework has evolved as an useful numerical tool to gain insights to the spray combustion processes in advanced internal combustion engines. However, the inherent effect of grid/filter size (G/FS) on the physics revealed by LES is not fully understood. In this paper, we present several new viewpoints on this by analyzing the results from a Lagrangian–Eulerian LES study of Engine Combustion Networks Spray A with a newly developed multi-region adaptive mesh refinement method in OpenFOAM. It is found that G/FS affects the predicted spray characteristics, the modes of spray combustion, the ignition delay time and the liftoff length in different ways. First, owing to the nature of Lagrangian particle-in-cell approach, the spray liquid penetration length converges as the G/FS approaches to the nozzle diameter. The convergence behavior is rather independent of the spray model parameters. Second, it is critical to have a well resolved spray liquid region; the main spray combustion characteristics, e.g., the mean pressure rise profile, the onsets of the cool flame and hot flame, and the main flame structure, are shown to be similar and independent of G/FS once the liquid region is properly resolved. However, the detailed flame structures at the liftoff position are sensitive to G/FS; the upstream auto-ignition events, the low temperature ignition assisted flame propagation and the hot flame propagation, are shown to partially rely on the adopted G/FS. Finally, it is found that a finer G/FS predicts a slower fuel/oxidizer mixing and a shorter flame liftoff length, yielding a higher soot mass.
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