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Wyświetlanie 1-10 z 17
Tytuł:
Transient stability analysis and control of power systems with considering flux decay by energy function approach
Autorzy:
Lu, D.
Zhang, X.
Powiązania:
https://bibliotekanauki.pl/articles/201016.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
transient stability
dynamic performance
flux decay
structure preserving models
energy function
Opis:
In this paper, transient stability of power systems with structure preserving models is considered. A Hamiltonian function which can be regarded as a Lyapunov function for the system is proposed. Based on this, the influence of flux decay dynamics, especially during a fault, on transient stability is analyzed. With the increase of load power, the variation of stability boundary in the rotor angle/Eq plane is shown. The Energy-based excitation control, aiming at injecting additional damping into the post-fault system may reduce the critical clearing time (CCT). This can be demonstrated by the comparison of different flux decay dynamics in the fault-on condition, and the reason is illustrated by the relationship between rotor angle/Eq and the stability boundary. An improved control strategy is proposed and applied to increase the CCT. Simulation results verify that improvement is obtained both in transient stability and dynamic performance.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2012, 60, 1; 3-8
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Study on buildup of fine weakly magnetic minerals on matrices in high gradient magnetic separation
Autorzy:
Zheng, X.
Wang, Y.
Lu, D.
Powiązania:
https://bibliotekanauki.pl/articles/109662.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
particle buildup
force equilibrium
magnetic matrices
magnetic separation
Opis:
Buildup of magnetic mineral particles on matrices determines the saturated deposit volume of minerals, which is of great importance in the high gradient magnetic separation (HGMS) systems. In this paper buildup of fine weakly magnetic minerals on the matrix is studied with a force equilibrium model. Elaborate rules of particle buildup on the matrix are presented. An imaginary sector ring is used to approximately quantify the volume of saturated particle buildup. The influence of the particle size, magnetic induction, fluid viscosity and velocity as well as matrix size on saturated particle buildup is investigated and discussed. With the same matrix size, the saturated buildup volume decreases with the decrease of the particle size, applied magnetic induction and increase of the fluid viscosity and velocity. The saturated buildup volume normalized by the matrix volume, and the ratio of particle deposit volume to the matrix volume (Vd/Vm) decreases with the increase of the matrix size. Under the same matrices packing fraction, the total mineral deposit volume, when adopting small size matrices, is larger than that when adopting large size matrices. Only small size matrices can be used for recovery of minerals in size of several micrometers. Based on performed analyses, the ore feeding time in a cycle for a cyclic HGMS system and the rotation speed of the swivel for a continuous HGMS system under different circumstances are also discussed.
Źródło:
Physicochemical Problems of Mineral Processing; 2017, 53, 1; 94-109
1643-1049
2084-4735
Pojawia się w:
Physicochemical Problems of Mineral Processing
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Study on pre-concentration efficiency of wolframite from tungsten ore using gravity and magnetic separations
Autorzy:
Lu, D.
Wang, Y.
Jiang, T.
Sun, W.
Hu, Y.
Powiązania:
https://bibliotekanauki.pl/articles/109597.pdf
Data publikacji:
2016
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
tungsten ore
pre-concentration
separation efficiency
gravity separation
magnetic separation
Opis:
Pre-concentration is effectively applied in recovering wolframite from tungsten ore, due to its benefits of further upgrading tungsten ore and improving separation efficiency. The most important pre-concentration techniques for tungsten ore include gravity separation and magnetic separation, based on the fact that there are appreciable differences, between the desired wolframite and the gangue minerals, in density and magnetic susceptibility. This study investigated the separation efficiency of gravity pre-concentration (Falcon Concentrator) and high-gradient magnetic pre-concentration (SLon VPHGMS) for the beneficiation of a Canada tungsten ore. It is a low-grade type of ore with high silica and arsenic content, and an average content of WO3 is about 0.45%. The optimum conditions for different operational parameters of two pre-concentration separators were studied on this low-grade material. The results presented in this paper suggested that although both pre-concentration techniques were effective for producing pre-concentrates containing high WO3, magnetic pre-concentration showed significantly better separation efficiency. Over 90% of the feed was rejected as the final tailings, meanwhile, over 85% of arsenic minerals were removed with tailings, while the WO3 loss was less than 15%.
Źródło:
Physicochemical Problems of Mineral Processing; 2016, 52, 2; 718-728
1643-1049
2084-4735
Pojawia się w:
Physicochemical Problems of Mineral Processing
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Three-dimensional biomechanical modeling and simulation of trephine cutting cornea for keratoplasty
Autorzy:
Su, P.
Lu, D.
Deng, S.
Zhang, L.
Hao, Y.
Yang, Y.
Powiązania:
https://bibliotekanauki.pl/articles/307486.pdf
Data publikacji:
2018
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
rogówka
biomechanika
kryterium wytężeniowe
FEM
cornea
biomechanics
failure criterion
finite element simulation
Opis:
Trephination is one of the basic operations of keratoplasty, and the biomechanical mechanism of the operation can be revealed based on three-dimensional modeling and simulation of trephine cutting cornea. Methods: Based on the analysis of the physical and biomechanical characteristics of corneal trephination, a three-dimensional numerical model of corneal trephination is built, where the cornea can be simplified to two layers structure including stroma and epithelium, and the trephine cuts the cornea under the vertical motion load and the rotational motion load. A three-dimensional failure criterion of corneal material is proposed based on the yield strength theory. On this basis, trephination simulation is carried out, and the units of corneal material are removed from the model when they meet the defined failure criterion. Results: Under the given parameters including the velocity, the angle and the angular velocity, the trephine force curves, include the linear cutting force and the rotary cutting force are obtained, and show the change of the forces with displacement during the process of trephination simulation. The maps of the equivalent stress show the destruction and deformation of the cornea. Then, the experiment of robotic trephination is carried out under the same parameters and the effectiveness of the simulation is evaluated. Conclusions: Based on mechanics theory and finite element method, the process of trephine cutting cornea has been reproduced, and the interaction mechanism is revealed, which lays the foundation for the development of real-time simulation and virtual system of the corneal surgery.
Źródło:
Acta of Bioengineering and Biomechanics; 2018, 20, 2; 23-33
1509-409X
2450-6303
Pojawia się w:
Acta of Bioengineering and Biomechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Reverse flotation of ultrafine magnetic concentrate by using mixed anionic/cationic collectors
Autorzy:
Lu, D.
Hu, Y.
Li, Y.
Jiang, T.
Sun, W.
Wang, Y.
Powiązania:
https://bibliotekanauki.pl/articles/110550.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
ultrafine magnetite
collector mixture
reverse flotation
closed flotation
Opis:
Compared to reverse cationic flotation, the advantages of reverse anionic flotation include relatively lower sensitivity to slimes and lower reagent cost. Besides, anionic collectors were found to have excellent capability of selectively separating an ultrafine magnetite ore. Addition of a small amount of cationic collector into the anionic collector as the collector mixture can improve the metallurgical results of removing silicates in reverse flotation. In this paper, NaOL and DDA were used for reverse flotation of the ultrafine magnetic concentrate. The separation performance of the collector mixture was investigated at different ratios of NaOL and DDA. The results showed that a better separation performance was obtained for the collector mixture than for NaOL alone. There was an optimal molar ratio between NaOL and DDA equal to 10:1. In the flotation system with the presence of the collector mixture, the good selectivity was found when starch was used as a depressor for magnetite and CaO was used as an activator for quartz. The influences of starch and CaO dosages on the separation performance of magnetite, quartz and chlorite had been investigated through micro-flotation tests. The infrared spectral analysis showed stretching vibration peaks of chemical adsorption of the collector mixture on the magnetite surface. The peaks were not present when starch was used as the depressor for magnetite. The closed flotation tests on the magnetic concentrate with the particle size of -25 μm were performed in the laboratory. The Fe concentrate assaying 64.52 % was obtained with Fe recovery of 80.66%, for the Fe content of feed equal to 52.98%.
Źródło:
Physicochemical Problems of Mineral Processing; 2017, 53, 2; 724-736
1643-1049
2084-4735
Pojawia się w:
Physicochemical Problems of Mineral Processing
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A novel method for 3D measurement of RFID multi-tag network using a machine vision system
Autorzy:
Zhuang, X.
Yu, X.
Zhao, Z.
Zhang, W.
Liu, Z.
Lu, D.
Dong, D.
Powiązania:
https://bibliotekanauki.pl/articles/221058.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
3D measurement
RFID multi-tag network
dual-CCD system
neural network
machine vision
Opis:
The three-dimensional (3D) coordinate measurement of radio frequency identification (RFID) multi-tag networks is one of the important issues in the field of RFID, which affects the reading performance of RFID multi-tag networks. In this paper, a novel method for 3D coordinate measurement of RFID multi-tag networks is proposed. A dual-CCD system (vertical and horizontal cameras) is used to obtain images of RFID multi-tag networks from different angles. The iterative threshold segmentation and the morphological filtering method are used to process the images. The template matching method is respectively used to determine the two-dimensional (2D) coordinate and the vertical coordinate of each tag. After that, the 3D coordinate of each tag is obtained. Finally, a back-propagation (BP) neural network is used to model the nonlinear relationship between the RFID multi-tag network and the corresponding reading distance. The BP neural network can predict the reading distances of unknown tag groups and find out the optimal distribution structure of the tag groups corresponding to the maximum reading distance. In the future work, the corresponding in-depth research on the neural network to adjust the distribution of tags will be done.
Źródło:
Metrology and Measurement Systems; 2018, 25, 3; 475-486
0860-8229
Pojawia się w:
Metrology and Measurement Systems
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Improving spodumene flotation using a mixed cationic and anionic collector
Autorzy:
Wang, Y.
Zhu, G.
Yu, F.
Lu, D.
Wang, L.
Zhao, Y.
Zheng, H.
Powiązania:
https://bibliotekanauki.pl/articles/109883.pdf
Data publikacji:
2018
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
spodumene
lithium
silicates
flotation
anionic surfactant
cationic surfactant
Opis:
Lithium, a rare-earth element, has been in increasing demand. Spodumene flotation is an important and challenging step for lithium extraction and production from lithium ore. In the present work, flotation tests for three pure minerals (i.e., spodumene, quartz and feldspar) and a real spodumene ore were carried out at laboratory scale. The results showed that YOA, a mixture of oleic acid and dodecylamine with the molar ration of 10:1, could be used as collector to produce a spodumene concentrate with grade of 5.59% Li2O from the feed ore with grade of 1.48% Li2O where 85.24% of Li2O was recovered to the concentrate. The measured zeta potential, contact angle and adsorption capacity indicated that YOA was preferentially adsorbed on spodumene instead of on quartz or feldspar, with the spodumene surface being more hydrophobic than that of feldspar or quartz. The adsorption energies of YOA on spodumene were calculated and the results provided insights into the superior flotation performance obtained in the present work.
Źródło:
Physicochemical Problems of Mineral Processing; 2018, 54, 2; 567-577
1643-1049
2084-4735
Pojawia się w:
Physicochemical Problems of Mineral Processing
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Occupational Safety of Farmers in the Vegetable Industry
Autorzy:
Lu, J. L. D. P.
Powiązania:
https://bibliotekanauki.pl/articles/89820.pdf
Data publikacji:
2011
Wydawca:
Centralny Instytut Ochrony Pracy
Tematy:
farmers
pesticide exposure
pesticide-related problems
geographic information system (GIS)
pesticide residue
Opis:
This study aimed to determine unsafe farming practices, nonergonomically designed equipment, and possible adverse health effects of pesticide exposure. Data were gathered with a structured survey, physical examination and blood extraction. Environmental monitoring was done for vegetables to determine multipesticide residue. Forty-eight percent of respondents reported feeling sick because of work. Vegetable residue was found in 16.67% of the samples. Vegetable profenofos of ~1 mg exceeded the necessary average daily intake of a maximum of 0.006 mg. Data also showed nonergonomically designed tools and unsafe work practices that increased pesticide exposure such as re-entering recently sprayed areas, a damaged backpack sprayer, spills during spraying, and no ventilation in greenhouses.
Źródło:
International Journal of Occupational Safety and Ergonomics; 2011, 17, 4; 445-453
1080-3548
Pojawia się w:
International Journal of Occupational Safety and Ergonomics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Cryptosystems using subgroup distortion
Autorzy:
Chatterji, I.
Kahrobaei, D.
Lu, N. Y.
Powiązania:
https://bibliotekanauki.pl/articles/375856.pdf
Data publikacji:
2017
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
hyberbolic groups
symmetric key
distortion
grupy hiperboliczne
klucz symetryczny
zniekształcenie
Opis:
In this paper we propose cryptosystems based on subgroup distortion in hyperbolic groups. We also include concrete examples of hyperbolic groups as possible platforms.
Źródło:
Theoretical and Applied Informatics; 2017, 29, 1-2; 14-24
1896-5334
Pojawia się w:
Theoretical and Applied Informatics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dynamic dependencies and return connectedness among stock, gold and Bitcoin markets: Evidence from South Asia and China
Autorzy:
Zeng, Hongjun
Lu, Ran
Ahmed, Abdullahi D.
Powiązania:
https://bibliotekanauki.pl/articles/22443106.pdf
Data publikacji:
2023
Wydawca:
Instytut Badań Gospodarczych
Tematy:
South Asia and China
gold
Bitcoin
dependency and connectedness
COVID-19
Opis:
Research background: In order to examine market uncertainty, the paper depicts broad patterns of risk and systematic exposure to global equity market shocks for the major South Asian and Chinese equity markets, as well as for specific assets (gold and Bitcoin). Purpose of the article: The purpose of this paper is to investigate the dynamic correlation among the major South Asian equity markets (India and Pakistan), the Chinese equity markets, the MSCI developed markets, Bitcoin, and gold markets. Methods: While applying the GARCH-Vine-Copula model and the TVP-VAR Connectedness approach, major patterns of dependency and interconnectedness between these markets are investigated. Findings & value added: We find that risk shocks from developed equity markets are critical in these dynamic links. A net return spillover from Bitcoin to the Chinese and Pakistani stock markets throughout the sample period is reported. Interestingly, gold can be applied to hedge and diversify positions in China and major South Asian markets, particularly following the COVID-19 outbreak. Our paper presents three main original add valued: (1) This paper adds global factors to the targeted study of risk transmission among South Asian and Chinese stock markets for the first time. (2)The assets of Bitcoin and gold were added to the study of risk transmission among South Asian and Chinese stock markets for the first time, enabling the research in this paper to observe the non-linear link among the South Asian and Chinese stock markets with them. (3) Our research adds to these lines of inquiry by giving empirical evidence on how COVID-19 altered the dependent structure and return spillover dynamics of Bitcoin, gold and South Asian and Chinese stock markets for the first time. Our results have critical implications for investors and policymakers to effectively understand the nature of market forces and develop risk-averse strategies.
Źródło:
Equilibrium. Quarterly Journal of Economics and Economic Policy; 2023, 18, 1; 49-87
1689-765X
2353-3293
Pojawia się w:
Equilibrium. Quarterly Journal of Economics and Economic Policy
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-10 z 17

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