| 1. |
- Li, W., et al.
(författare)
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On improvement of a conditional mornitoring technique for condition-based maintenance
- 2019
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Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : ASME Press. - 9784888982566
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Konferensbidrag (refereegranskat)abstract
- The condition-based maintenance (CMB) is a hot research topic to overcome the drawbacks belonging to the periodic maintenance used in nuclear power plants nowadays. Auto-Associative Kernel Regression (AAKR) is a widely applied condition monitoring technique which is the basis of a CBM. In this paper, the traditional AAKR is improved by using the ensemble learning technique. The modified AAKR is tested by steady-state operational data of a Tennessee-Eastman chemical process and the results show that it can significantly improve the auto- and cross-sensitivity without reducing the accuracy. This indicates a significant improvement in performance of this condition monitoring technique.
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| 2. |
- Qi, Z., et al.
(författare)
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Application of nonlinear principal component analysis technique to nuclear power plants
- 2019
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Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : ASME Press. - 9784888982566
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Konferensbidrag (refereegranskat)abstract
- Traditionally, manual calibration of sensors is required and performed during each refueling outage. If the traditional time-directed calibration is replaced by an online monitoring technique, the maintenance cost will be significantly reduced since only the abnormal sensors identified in on-line monitoring need to be re-calibrated or replaced off-line. The Nonlinear Principal Component Analysis (NLPCA), such as Auto-Associative Neural Network (AANN) and Auto-Associative Kernel Principal Component Analysis (AAKPCA), can describe the nonlinear correlation between sensors such as power, temperature, pressure and flowrate. In this paper, AANN and AAKPCA model are tested by simulated redundant data and Tennessee-Eastman process data. The results show that both of them have a high ability of prediction and a low sensitivity. Therefore, they are can be used in on-line monitoring.
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| 3. |
- Qi, Z., et al.
(författare)
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Sensor fault detection in nuclear power plant using auto-associative neural network
- 2019
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Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : American Society of Mechanical Engineers (ASME). - 9784888983051
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Konferensbidrag (refereegranskat)abstract
- Fault diagnosis system usually includes a prediction module and a diagnosis module. The prediction module is supposed to predict sensor values based on sensor observations, and the diagnosis module is used to determine whether a sensor has degradation or failure by comparing the difference between sensor observations and predictions. Auto-Associative Neural Network (AANN) is a widely applied data-driven prediction method consisting of input layer, mapping layer, bottleneck layer, de-mapping layer and output layer. AANN compresses the information contained in the input data (i.e. sensor observations) into bottleneck layer through mapping layer, and then reconstructs the sensor values at output layer based on the extracted nonlinear features stored in bottleneck layer through de-mapping layer. This paper focuses on the feasibility study of AANN model in fault diagnosis for nuclear power plants. The performance of AANN model was studied by using simulation data, and the AANN model was optimized by combining prejudgment and secondary prediction. The results show that the optimized AANN model can improve the performance comparing to original AANN model, and can be applied to the fault diagnosis for nuclear power plant sensors.
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| 4. |
- Zhang, Y., et al.
(författare)
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A feasibility study on application of redundancy sensors estimation technique to nuclear power plants
- 2019
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Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : ASME Press. - 9784888983051
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Konferensbidrag (refereegranskat)abstract
- Traditional periodic maintenance techniques being employed in nuclear power plants usually fail to detect the potential degradation in performance of a sensor timely, and may increase workload and radiation exposure of the maintenance staff. The Redundancy Sensors Estimation Technique (RSET) to be presented in this paper is a noninvasive and in-situ monitoring technique based on measurement theory. The technique allows staff to monitor redundant sensors on-line and to assess their performance instantly. If such a REST can be applied to a nuclear power plant, it is expected that it will improve the safety of the plant and reduce the costs of operation and maintenance. This paper is concerned with a feasibility study on the REST's application to a nuclear power plant. The results show that the RSET, featuring a strong generalization ability, can offer state estimation and fault diagnosis to signals from redundant sensors accurately. By adding drift data to the test dataset, the RSET can determine the signal drift accurately. The core algorithm of RSET can be explained by mathematical formulas and has high prediction accuracy. In conclusion, RSET can detect the performance degradation of redundant sensors in advance during the operation of plant.
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| 5. |
- Dobrovolsky, Alexander, et al.
(författare)
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Fabry-Perot Microcavity Modes in Single GaP/GaNP Core/Shell Nanowires
- 2015
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Ingår i: Small. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 11:47, s. 6331-6337
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires (NWs) are attracting increasing interest as nanobuilding blocks for optoelectronics and photonics. A novel material system that is highly suitable for these applications are GaNP NWs. In this article, we show that individual GaP/GaNP core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates can act as Fabry-Perot (FP) microcavities. This conclusion is based on results of microphotoluminescence (μ-PL) measurements performed on individual NWs, which reveal periodic undulations of the PL intensity that follow an expected pattern of FP cavity modes. The cavity is concluded to be formed along the NW axis with the end facets acting as reflecting mirrors. The formation of the FP modes is shown to be facilitated by an increasing index contrast with the surrounding media. Spectral dependence of the group refractive index is also determined for the studied NWs. The observation of the FP microcavity modes in the GaP/GaNP core/shell NWs can be considered as a first step toward achieving lasing in this quasidirect bandgap semiconductor in the NW geometry.
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| 6. |
- Gong, S., et al.
(författare)
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An investigation on dynamic thickness of a boiling liquid film
- 2015
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 90, s. 636-644
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by understanding the micro-hydrodynamics of boiling heat transfer and the mechanism of critical heat flux (CHF) occurrence, the present study is to investigate the boiling phenomenon in a liquid film whose dynamic thickness is recorded by a confocal optical sensor with the measurement accuracy of micrometres, while the bubble dynamics of the boiling in the film is visualized by a high-speed photography. This paper is focused on a statistical analysis of the measured thickness signals for the boiling condition ranging from low heat flux to high heat flux (near or at CHF). The dynamic thickness of liquid film appears oscillating with peak values, resulting from the liquid film movements due to nucleation of bubble(s) and its growth and rupture. The statistical analysis in a certain period indicates there emerge three distinct liquid film thickness ranges: 0-50 μm, 50-500 μm and 500-2500 μm, seemingly corresponding to the microlayer, macrolayer and bulk layer. With increasing heat flux to a specific extent, the bulk layer disappears, and then the macrolayer gradually decreases to ∼105 μm, beyond which the liquid film may lose its integrity and CHF occurs at 1.563 MW/m2.
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| 7. |
- Gu, H., et al.
(författare)
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Investigation on contact angle measurement methods and wettability transition of porous surfaces
- 2016
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 292, s. 72-77
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Tidskriftsartikel (refereegranskat)abstract
- Various solid surfaces (e.g., smooth titanium surface, smooth aluminum surface, polished copper surfaces, polished silver surfaces and porous copper surfaces) were prepared to quantify the reliability of half-angle algorithm and axisymmetric drop shape analysis (ADSA) algorithm for calculating contact angles. Besides, the effects of surface conditions on contact angle values were also investigated. The experimental results of 10 repeated tests for each surface show that both algorithms have good accuracy for an acute contact angle, while the ADSA algorithm is better than the half-angle algorithm for an obtuse contact angle. Furthermore, with the decrease of surface roughness, the contact angle increases but the standard deviation of contact angles by 10 repeated tests decreases. In addition, the porous layer on copper surface by electrochemical deposition shows a super hydrophilic property, but it could change to be super hydrophobic after exposed in ambient air for 24 h. Interestingly, the surface wettability reverses to be super hydrophilic again after it is immersed in water, and the inorganic contamination is the reason of formal change from the super hydrophilic status to the super hydrophobic status.
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| 8. |
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| 9. |
- Huang, Yuqing, et al.
(författare)
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Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 8, s. Article Number: 15401-
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional (3D) topological insulator (TI) is a unique quantum phase of matter with exotic physical properties and promising spintronic applications. However, surface spin current in a common 3D TI remains difficult to control and the out-of-plane spin texture is largely unexplored. Here, by means of surface spin photocurrent in Bi2Te3 TI devices driven by circular polarized light, we identify the subtle effect of the spin texture of the topological surface state including the hexagonal warping term on the surface current. By exploring the out-of-plane spin texture, we demonstrate spin injection from GaAs to TI and its significant contribution to the surface current, which can be manipulated by an external magnetic field. These discoveries pave the way to not only intriguing new physics but also enriched spin functionalities by integrating TI with conventional semiconductors, such that spin-enabled optoelectronic devices may be fabricated in such hybrid structures.
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| 10. |
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