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  • 1
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    Study on the Subsynchronous Resonance Control Method Based on the DFIG Grid-Side Converter (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-11-06
    Description: DFIG-based series-compensated can increase the capacity of wind power transmission, but it can also cause the sub-synchronous resonance (SSR) problem. Based on the mechanism of subsynchronous resonance in DFIG, the electromagnetic torque variation under the variation of rotor speed can be divided into two parts, i.e. rotor torque variation and stator torque variation. Supplementary controller is added to the stator side converter, which is generated to provide positive damping. MATLAB simulation is carried out to compare the result of supplementary damping. Results show that supplementary damping controller makes DFIG keep stable under various rotor speeds and RSC inner-loop gain.
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 2
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    Research Progresses and Suggestions of Manufacturing Technologies of Engine Bearing Bushes (2017)
    Institute of Physics (IOP)
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    Publication Date: 2017-12-22
    Description: Bearing bush is a key part of diesel engine, and its performance directly influences the life of whole machine. Several manufacturing technologies of bearing bush such as centrifugal casting, sintering, electroplating and magnetron sputtering have been overviewed. Their bond strength, porosity, production efficient, layer thickness, frictional coefficient and corresponding materials analyzed and compared. Results show that the porosity and oxidation of sintering and centrifugal casting are higher than that of other two methods. However, the production efficiency and coating thickness are better than that of electroplating and magnetron sputtering. Based on above comparisons and discussions, the improvements of all manufacturing technologies are suggested and supersonic cold spraying is suggested. It is proved that cold spraying technology is the best choice in the future with the developing of low frictional materials.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 3
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    What Signatures Dominantly Associate with Gene Age? (2016)
    Oxford University Press
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    Publication Date: 2016-10-15
    Description: As genes originate at different evolutionary times, they harbor distinctive genomic signatures of evolutionary ages. Although previous studies have investigated different gene age-related signatures, what signatures dominantly associate with gene age remains unresolved. Here we address this question via a combined approach of comprehensive assignment of gene ages, gene family identification, and multivariate analyses. We first provide a comprehensive and improved gene age assignment by combining homolog clustering with phylogeny inference and categorize human genes into 26 age classes spanning the whole tree of life. We then explore the dominant age-related signatures based on a collection of 10 potential signatures (including gene composition, gene length, selection pressure, expression level, connectivity in protein–protein interaction network and DNA methylation). Our results show that GC content and connectivity in protein–protein interaction network (PPIN) associate dominantly with gene age. Furthermore, we investigate the heterogeneity of dominant signatures in duplicates and singletons. We find that GC content is a consistent primary factor of gene age in duplicates and singletons, whereas PPIN is more strongly associated with gene age in singletons than in duplicates. Taken together, GC content and PPIN are two dominant signatures in close association with gene age, exhibiting heterogeneity in duplicates and singletons and presumably reflecting complex differential interplays between natural selection and mutation.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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  • 4
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    Green synthesis of silver nanoparticles using wolfberry fruits extract and their photocatalytic performance (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-02-03
    Description: Spherical Ag nanoparticles (NPs) was synthesized using the Chinese wolfberry fruits extract (WFE) as surfactant and reductant. The hydrolysis time and the reaction time were systematically investigated. The whole synthesis process must be kept boiling in order to enhance the reducing ability of WFE and decrease the reaction time. Under the optimized hydrolysis time of 10 min, the reaction time just need 5 min. Ag NPs were characterized by means of UV-vis, EDX, TEM, HR-TEM, and SAED. It was found that Ag NPs exhibited the surface plasmon resonance wavelength of 408 nm, a small average size of 12.1 nm, and the face-centered cubic structure. Obtained Ag NPs were used as photocatalyst for the reduction of 4-nitrophenol and revealed a high photocatalytic activity and stability. The rate constant was 0.043 min -1 , which suggested the reduction of 4-nitrophenol was fast. Clearly, Ag NPs synthesized in the totally green method have a potential application in the field of the w...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 5
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    Differential acoustic resonance spectroscopy: improved theory and application in the low frequency range (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-26
    Description: Differential acoustic resonance spectroscopy (DARS) was developed to examine changes in the resonant frequencies of a cavity perturbed by the introduction of a centimetre-sized sample. Resonant frequency shifts, measured at different resonance modes and between empty and sample-loaded cavities, were used to infer the acoustic properties of the loaded samples in the low frequency range (0.5–2 kHz). To some extent, this laboratory-based measurement technique fills an experimental gap between the low-frequency stress–strain method (quasi-static to several kHz) and the ultrasonic transmission technique (hundreds of kHz to MHz). By means of an effective perturbation model against the DARS system, this study presents a Green's function-based theoretical derivation of an amended DARS perturbation formula under a general impedance boundary condition. Numerical and experimental results show that the amended DARS perturbation is able to reflect the DARS operation mechanism more accurately and more precisely than past efforts. In addition, inversion was performed by fitting the resonance frequencies, measured at various locations inside the DARS resonance cavity, in a least-square sense to estimate the acoustic properties of a test sample. Inversion implementation at different resonance modes makes it possible to perform direct dispersion analysis on reservoir rocks at different low-frequency bands. The results of this study show that the DARS laboratory device, in conjunction with the amended perturbation formula and the proposed inversion strategy, are useful tools for estimating the acoustic properties of centimetre-sized rock samples in the low frequency range.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Submicron patterning of DNA oligonucleotides on silicon (2004)
    Oxford University Press
    Details
    Publication Date: 2004-08-03
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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