| 1. |
- Muhammad, Zahir, et al.
(författare)
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Anisotropic phonon and magnon vibration and gate-tunable optoelectronic properties of nickel thiophosphite
- 2023
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal phosphorus trichalcogenides retain spin-charge coupling and lattice vibrations in different layers, which are useful for spintronic and optoelectronic devices. The phonon, magnons and excitonic properties of two-dimensional ternary nickel-phosphorus trisulfides (NiPS3) are investigated using Raman spectroscopy and photoluminescence (PL) study. With magnetic exchange interaction, an exotic phonon scattering degenerates the optical phonons into in-plane Ag and Bg modes. We have observed eight Raman modes with two acoustic anisotropic magnon modes (M1, M2) below the critical temperature for co-(XX), while only M1 at cross (XY) polarizations. The M1 mode is coupled with the phonon Bg mode that can survive after transition temperature. The phonon and magnon modes soften with variations in temperature, which is attributed to anharmonic phonon–phonon coupling and interlayer forces. The polarized Raman shows the two-fold and four-fold symmetry orientations of the phonon and magnon modes, respectively, which exhibit strong in-plane anisotropic phonon/magnon. The PL spectra revealed the existence of bound excitonic features and ensemble emitters in NiPS3. The robust interlayer excitation and structural stability further revealed the optothermal properties. Moreover, the fabricated field-effect transistor on NiPS3 reveals p-type semiconducting nature with an ON/OFF ratio of 5 × 106 and mobility of ∼16.34 cm2 V−1 s−1. In contrast, the rectification ratio indicates their diode characteristics. Similarly, the photocurrent is enhanced by changing the wavelength of light, which shows the potential for optoelectronics. The strong spin-charge interaction provides new insights into these materials’ magneto-optical and thermal properties for memory devices.
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| 2. |
- Zhang, L., et al.
(författare)
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A nearly end-to-end deep learning approach to fault diagnosis of wind turbine gearboxes under nonstationary conditions
- 2023
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Ingår i: Engineering applications of artificial intelligence. - : Elsevier Ltd. - 0952-1976 .- 1873-6769. ; 119
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Tidskriftsartikel (refereegranskat)abstract
- Fault diagnosis of wind turbine gearboxes is crucial in ensuring wind farms’ reliability and safety. However, nonstationary working conditions, such as load change or speed regulation, may result in an accuracy deterioration of many existing fault diagnosis approaches. To overcome the issue, this research proposes a nearly end-to-end deep learning approach to fault diagnosis of wind turbine gearboxes using vibration signals. Concretely, we adopt Empirical Mode Decomposition (EMD) to decompose vibration signals into a series of Intrinsic Mode Functions (IMFs). Then, the multi-channel IMFs are fed into a 1D Convolutional Neural Network (CNN) for automatic feature learning and fault classification. Since EMD is a signal processing technique requiring no prior knowledge, the model architecture can be viewed as nearly end-to-end. The proposed approach was validated in a real-world dataset; it proved deep learning models have an overwhelming advantage in representation capacity over traditional shallow models. It also demonstrated that the introduction of EMD as a preprocessing step improves both the training efficiency and the generalization ability of a deep model, thus leading to a better fault diagnosis efficacy under variable working conditions.
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| 3. |
- Zhang, Liangwei, et al.
(författare)
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A Review on Deep Learning Applications in Prognostics and Health Management
- 2019
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Ingår i: IEEE Access. - : IEEE. - 2169-3536. ; 7, s. 162415-162438
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Forskningsöversikt (refereegranskat)abstract
- Deep learning has attracted intense interest in Prognostics and Health Management (PHM), because of its enormous representing power, automated feature learning capability and best-in-class performance in solving complex problems. This paper surveys recent advancements in PHM methodologies using deep learning with the aim of identifying research gaps and suggesting further improvements. After a brief introduction to several deep learning models, we review and analyze applications of fault detection, diagnosis and prognosis using deep learning. The survey validates the universal applicability of deep learning to various types of input in PHM, including vibration, imagery, time-series and structured data. It also reveals that deep learning provides a one-fits-all framework for the primary PHM subfields: fault detection uses either reconstruction error or stacks a binary classifier on top of the network to detect anomalies; fault diagnosis typically adds a soft-max layer to perform multi-class classification; prognosis adds a continuous regression layer to predict remaining useful life. The general framework suggests the possibility of transfer learning across PHM applications. The survey reveals some common properties and identifies the research gaps in each PHM subfield. It concludes by summarizing some major challenges and potential opportunities in the domain.
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| 4. |
- Zhang, Liangwei, et al.
(författare)
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End-To-End Unsupervised Fault Detection Using A Flow-Based Model
- 2021
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Ingår i: Reliability Engineering & System Safety. - : Elsevier. - 0951-8320 .- 1879-0836. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- Fault detection has been extensively studied in both academia and industry. The rareness of faulty samples in the real world restricts the use of many supervised models, and the reliance on domain expertise for feature engineering raises Other barriers. For this reason, this paper proposes an unsupervised, end-to-end approach to fault detection based on a flow-based model, the Nonlinear Independent Components Estimation (NICE) model. A NICE model models a target distribution via a sequence of invertible transformations to a prior distribution in the latent space. We prove that, under certain conditions, the L2-norm of normal samples’ latent codes in a trained NICE model is Chi-distributed. This facilitates the use of hypothesis testing for fault detection purpose. Concretely, we first apply Zero-phase Component Analysis to decorrelate the data of normal states. The whitened data are fed to a NICE model for training, in a maximum likelihood sense. At the testing stage, samples whose L2-norm of latent codes fail in the hypothesis testing are suspected of being generated by different mechanisms and hence regarded as potential faults. The proposed approach was validated on two datasets of vibration signals; it proved superior to several alternatives. We also show the use of NICE, a type of generative model, can produce real-like vibration signals because of the model's bijective nature.
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| 5. |
- Liu, Lang, et al.
(författare)
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Effect of the Cement–Tailing Ratio on the Hydration Products and Microstructure Characteristics of Cemented Paste Backfill
- 2019
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Ingår i: Arabian Journal for Science and Engineering. - : Springer. - 2193-567X .- 2191-4281. ; 44:7, s. 6547-6556
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Tidskriftsartikel (refereegranskat)abstract
- Cemented paste backfill (CPB) has been widely incorporated into mining practice as an ideal way to protect the environment and eliminate hidden dangers in mines. In this study, the feasibility of CPB was validated using full tailings from the Xianglushan Tungsten Mine. Through a microexperiment of CPB with different C/Ts, digital images of pores were obtained, and the hydration products were identified for processing with the particle and pore identification and analysis system. The evolution of hydrated products under different cement–tailing ratios (C/Ts) was analyzed. Then, microquantitative indices, such as the porosity and fractal dimensions, were used to analyze the evolution of the pore structures under different C/Ts. The results showed that CPB slump of different proportions ranged between 196 and 232 mm, and its flowability met the basic principle of pumping. When the C/T of the CPB mixture was increased from 1:12 to 1:4, the backfill changed from a nonuniform structure with sparse pores to a dense network structure with a few holes and pores. The C/T had a significant effect on the quantitative characteristics. With an increased C/T, the porosity and average pore area generally decreased, resulting in a decrease in the porosity and enhanced mechanical characteristics. The C/T of the CPB also influenced the fractal dimension and roundness. When the C/T increased from 1:12 to 1:4, there was a decreasing trend in the fractal dimension and roundness. Additionally, the size difference between the pores decreased, and the pores were round, resulting in increased uniaxial compressive strength of the CPB. The probability entropy values of the backfill with different C/Ts were all greater than 0.93, and the pore distribution had no obvious orientation.
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| 6. |
- Liu, Lang, et al.
(författare)
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Quantitative investigation on micro-parameters of cemented paste backfill and its sensitivity analysis
- 2020
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Ingår i: Journal of Central South University. - : Springer. - 2095-2899 .- 2227-5223. ; 27:1, s. 267-276
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of cemented paste backfill (CPB) depend heavily on its pore structural characteristics and micro-structural changes. In order to explore the variation mechanisms of macro-mechanical characteristics and micro-structure of CPB. CPB specimens with different mass concentrations prepared from the full tailings of Xianglushan Tungsten Ore were micro-tests. Moreover, acquired pore digital images were processed by using the pores (particles) and cracks analysis system (PCAS), and a sensitivity analysis was performed. The results show that as the mass concentration of CPB increases from 70% to 78%, the porosity, the average pore area and the number of pores drop overall, leading to a decline in the pores opening degree and enhancing the mechanical characteristics. As the mass concentration of CPB increases, the trend of fractal dimension, probability entropy and roundness is reduced, constant and increased, which can result in an enhancement of the uniformity, an unchanged directionality and more round pores. According to the definition of sensitivity, the sensitivities of various micro-parameters were calculated and can be ranked as porosity > average pore area > number of pores > roundness > fractal dimension > probability entropy.
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| 7. |
- Muhammad, Zahir, et al.
(författare)
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Temperature Modulating Fermi Level Pinning in 2D GeSe for High‐Performance Transistor
- 2022
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Ingår i: Advanced Electronic Materials. - : John Wiley & Sons. - 2199-160X. ; 8:7
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Tidskriftsartikel (refereegranskat)abstract
- 2D layered germanium selenide (GeSe) material possesses in-plane anisotropy because of low-symmetry crystal structure with a new degree of freedom for enhanced optical and electronic properties. However, their systematic vibrational and electronics properties are still under the scope to study. Herein, the vibrational properties of GeSe sheets are studied by Raman spectroscopy. Whereas, the temperature-dependent electronic band structure is studied using angle-resolved photoemission spectroscopy (ARPES) combined with density functional theory calculations. Moreover, the field-effect transistor (FET) is fabricated on a few-layer GeSe with high performance. The vibrational modes (Formula presented.) and (Formula presented.) demonstrates linear softening as the temperature increases, with temperature coefficient value associated by anharmonic phonon–phonon/electron coupling. Besides, the enhanced dielectric screening effect of long-range Coulomb and interlayer interaction is observed from bulk to monolayer. Similarly, ARPES results further show Fermi level movement toward the valance band as increased temperature represents hole doping to pining the Fermi level, which indicates superior carrier concentration for electronic properties. The fabricated FET device on six layers GeSe exhibits high carrier mobility of 52.89 cm2 V−1 s−1 with an on/off ratio above 4 × 105 at room temperature, while it decreased below the room temperature. Our results provide the important figure of merit for GeSe-based novel nanoelectronic and thermoelectric devices.
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| 8. |
- Wang, Haibin, et al.
(författare)
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Strain in Copper/Ceria Heterostructure Promotes Electrosynthesis of Multicarbon Products
- 2023
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 17:1, s. 346-354
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Tidskriftsartikel (refereegranskat)abstract
- Elastic strains in metallic catalysts induce enhanced selectivity for carbon dioxide reduction (CO2R) toward valuable multicarbon (C2+) products. However, under working conditions, the structure of catalysts inevitably undergoes reconstruction, hardly retaining the initial strain. Herein, we present a metal/metal oxide synthetic strategy to introduce and maintain the tensile strain in a copper/ceria heterostructure, enabled by the presence of a thin interface layer of Cu2O/CeO2. The tensile strain in the copper domain and deficient electron environment around interfacial Cu sites resulted in strengthened adsorption of carbonaceous intermediates and promoted*CO dimerization. The strain effect in the copper/ceria heterostructure leads to an improved C2+ selectivity with a maximum Faradaic efficiency of 76.4% and a half-cell power conversion efficiency of 49.1%. The fundamental insights gained from this system can facilitate the rational design of heterostructure catalysts for CO2R.
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| 9. |
- Yan, Baili, et al.
(författare)
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Binderless zeolite NaX microspheres with enhanced CO2 adsorption selectivity
- 2019
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 278, s. 267-274
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Tidskriftsartikel (refereegranskat)abstract
- Zeolite NaX@NaA core-shell microspheres were prepared via a post-treatment secondary growth of zeolite NaA films on outer surface of binderless zeolite NaX microspheres. The obtained core-shell microspheres were composed of intergrown octahedral NaX particles inside, with particles size of ca. 500–750 nm, and continuous zeolite NaA films on the outer surface with the thickness of about 2 μm. Higher CO2 separation performance was observed for the core-shell microspheres comparing to the parental binderless zeolite NaX microspheres. The ideal separation factors of zeolite NaX@NaA core-shell microspheres for CO2/CH4 and CO2/N2 were 13 and 47, and the adsorption selectivities for the corresponding binary mixtures were 308 and 923, significantly higher than the binderless zeolite NaX microspheres of 9 and 19 as well as 264 and 735, respectively. After K+ ion exchanging, the core-shell zeolite microspheres have even higher adsorption selectivities of 326 and 1109 for CO2/CH4 and CO2/N2 binary mixtures. The crushing strength of the binderless zeolite NaX microspheres was increased from 0.46 MPa to 3.42 MPa after the secondary growth. In addition, the growth of zeolite A film was resultant from interzeolite conversion and the interzeolite conversion was investigated by the conversion of zeolite NaX to NaA crystals in NaA membrane synthesis gel.
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| 10. |
- Yan, Baili, et al.
(författare)
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Preparation of hollow zeolite NaA/chitosan composite microspheres via in situ hydrolysis-gelation-hydrothermal synthesis of TEOS
- 2018
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 257, s. 262-271
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Tidskriftsartikel (refereegranskat)abstract
- In situ hydrolysis-gelation-hydrothermal (HGH) synthesis of tetraethylorthosilicate (TEOS) technique was developed to prepare hollow zeolite NaA/chitosan composite microspheres. The chitosan solution coated calcium alginate microspheres served as template to generate hollow structure, which were pre-modified by oleic acid and coated by TEOS. Furthermore, the calcium alginate microspheres were prepared by a simple homemade double T-junction mixer. During the hydrothermal process, the TEOS hydrolyzed and provided silica source for the zeolite NaA shell, meanwhile the inner calcium alginate microsphere core dissolved by the alkaline synthesis mixture and left the hollow structure. The obtained products were characterized by XRD, FT-IR, SEM, TG et al. techniques. The preparation method for calcium alginate microspheres template was simple and the preparation process had no NaA crystal seeds been involved. The hollow size could be adjusted by controlling the synthesis parameters of calcium alginate/chitosan microspheres. In addition, the functional magnetic γ-Fe2O3 nanoparticles could be introduced into the cavity during synthesis of calcium alginate/chitosan microspheres and guest magnetic γ-Fe2O3 nanoparticles had no effect on the properties of host zeolite NaA. The obtained functional magnetic hollow NaA/chitosan microspheres had decent adsorption performance for Cu2+ ions and were easy to recycle.
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