939 research outputs found
Improving Torque Analysis and Design Using the Air-Gap Field Modulation Principle for Permanent-Magnet Hub Machines
No full textThe Double Permanent Magnet Vernier (DPMV) machine is well known for its high torque density and magnet utilization ratio. This paper aims to investigate the torque generation mechanism and its improved design in DPMV machines for hub propulsion based on the field modulation principle. Firstly, the topology of the proposed DPMV machine is introduced, and a commercial PM machine is used as a benchmark. Secondly, the rotor PM, stator PM, and armature magnetic fields are derived and analyzed considering the modulation effect, respectively. Meanwhile, the contribution of each harmonic to average torque is pointed out. It can be concluded that the 7th-, 12th-, 19th- and 24th-order flux density harmonics are the main source of average torque. Thanks to the multi-working harmonic characteristics, the average torque of DPMV machines has significantly increased by 31.8% compared to the counterpart commercial PM machine, while also reducing the PM weight by 75%. Thirdly, the auxiliary barrier structure and dual three-phase winding configuration are proposed from the perspective of optimizing the phase and amplitude of working harmonics, respectively. The improvements in average torque are 9.9% and 5.4%, correspondingly
Short-Circuit Current Reduction in Dual Three-Phase Permanent-Magnet Machine by Asymmetric Pitch for High-Reliability Applications
No full textThis paper proposes a short-circuit current (SCC) reduction method for dual three-phase (DTP) permanent-magnet machines by asymmetric pitch technique. The conventional DTP winding configuration with symmetric pitch is used as a benchmark. The above two windings are named as asymmetric and symmetric configurations, respectively. Firstly, the asymmetric configuration with physical isolation is introduced and distinguished based on the spatial distribution. Secondly, the stator magnetomotive forces generated by different configurations are analyzed, and the effects of asymmetric configuration on harmonic order and content are studied with emphasis. Afterwards, the SCC and braking torque of different configurations are analyzed and compared under fault condition. The asymmetric configuration has great significance to reduce the SCC and braking torque. Moreover, it exhibits comparable torque ripple compared to the symmetric counterpart, although with a reduction slightly in average torque. Finally, the 48-slot/8-pole DTP permanent-magnet machines with different configurations are manufactured. The experiments are conducted and compared to validate theoretical analysis and reliability improvement design
Effects of Soil Physical and Chemical Properties on the Quality of Nanjing ‘Yuhua’ Tea, a Type of Famous Green Tea
No full textTea has become one of the most popular drinks worldwide because of its special taste and health benefits. ‘Yuhua’ tea is a famous specialty of Nanjing, China, a green tea produced from Camelia sinensis. It belongs to the green tea category and is one of the top ten most famous teas in China. The physical and chemical properties of soil are very important to the quality of tea. However, at present, there are few instances of research on the soil of the ‘Yuhua’ tea cultivation area. To provide the theoretical basis for improving the final quality of ‘Yuhua’ tea by soil management measures, the effects of the soil’s physical and chemical properties on the contents of important chemical components (free amino acids, tea polyphenols, and caffeine) of ‘Yuhua’ tea in three different cultivation areas in Nanjing were studied. The quality of ‘Yuhua’ tea is greatly influenced by the physical and chemical properties of the soil in which the tea plant grows. The free amino acid content and tea polyphenol content of tea leaves were significantly and negatively correlated with soil bulk density, pH, and water-soluble calcium content, while a significantly positive correlation was noticed between the two criteria and soil effective nitrogen, phosphorus, and potassium content. Additionally, the growth of the tea tree will be hampered and perhaps stressed if the soil’s helpful mineral concentration is too low. The tea tree may produce more caffeine as a result, which could lower the quality of the tea leaves. Therefore, implementing targeted soil management techniques is the key to promoting tea tree growth and improving tea quality. This study laid the foundation for the adoption of corresponding soil management measures to improve the quality of ‘Yuhua’ tea
The Rate That the Earth Is Getting Further Away From the Sun
No full textAbstract: The mass of the Sun is reduced due to the radiation of the Sun, which causes that the planets are getting further away from the Sun. According to theoretical derivation, the rate that the planet is getting further away from the Sun equals the rate of solar mass reduction. Currently the rate that the Earth is getting further away from the Sun equals 1.02m per century, for Mercury it equals to 0.40m per century, and for Pluto it equals 40.32m per century
Iridium-catalyzed asymmetric hydrogenation for synthesis of chiral cyclic amines
No full textChiral cyclic amines play extremely important roles in pharmaceutical and agrochemical industries. The asymmetric reduction of pyridine compounds remains a long-standing challenge.With the addition of an easy-removal protecting group, benzyl, on the nitrogen, the pyridine ring was dearomatized. This strategy proved to help achieve direct reduction on pyridines under mild conditions to access cyclic peperidines. A neutral iridium MP2-SegPhos catalytic system was developed to hydrogenate various N-benzyl-2-arylpyridines with high enantioselectivities.Reduction of di-substituted pyridines and isoquinoline substrates were also fulfilled with good to excellent enantioselectivity. Mechanism studies have remained unclear despite the significant progress made in the reduction methodologies. The three double bonds (both C=C and C=N bonds) present in the pyridine ring adds additional complexities. Based on the NMR studies and isotopic experimental evidences an outer-sphere mechanism was proposed involving two tautormerizations and proton-hydride delivery. Crucial tetrahydropyridine complex and other key intermediates were identified and characterized.Ph.D.Includes bibliographical referencesby Yuhua Huan
The Hydraulic Calculation and Reformation Application of Yuhua Heating Network in Shijiazhuang Based on Graph Theory
No full textIn heat source ability sufficient situation, Yuhua network in Shijiazhuang had some phenomenon, such as uneven heating, serious disorders, the far-end heating reliability was insufficient. Based on the basic principle of Graph theory, this article carried on the detailed hydraulic calculation to the annular pipe network, determined and implemented the reasonable transformation program, finally carried on the investigation and study test to the actual operation network after reformation. The results show that after reformation, the actual heating network runs well, improves the heating security and reliability, so the hydraulic calculation method based on Graph theory is accurate, and has certain guiding sense to other pipe networks' energy conservation reformation.</jats:p
Volume growth and uniqueness of nonnegative solutions of differential inequalities on manifolds
No full textSun Y. Volume growth and uniqueness of nonnegative solutions of differential inequalities on manifolds. Bielefeld University: Bielefeld University; 2014
On positive solutions of semi-linear elliptic inequalities on Riemannian manifolds
No full textGrigoryan A, Sun Y. On positive solutions of semi-linear elliptic inequalities on Riemannian manifolds. CALCULUS OF VARIATIONS AND PARTIAL DIFFERENTIAL EQUATIONS. 2019;58(6): 207.We determine the critical exponent for certain semi-linear elliptic problem on a Riemannian manifold assuming the volume regularity and Green function estimates
Photoelectron Holographic Study for Atomic Site Occupancy for Si Dopants in Si-Doped κ-Ga2O3(001)
No full textLow-threshold and high efficiency lasing upon band-edge excitation in a cholesteric liquid crystal
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Yuko Matsuhisa, Yuhua Huang, Ying Zhou, and Shin-Tson Wu, Ryotaro Ozaki, Yuuki Takao, Akihiko Fujii, and Masanori Ozaki, Appl. Phys. Lett. 90, 091114 (2007) and may be found at https://doi.org/10.1063/1.2710777.A low threshold and high efficiency laser based on dye-doped cholesteric liquid crystals (CLCs) is demonstrated using an input excitation with the same handedness of circular polarization as the helical structure of the sample at the shorter wavelength band edge of the reflection band. The responsible mechanism originates from the dramatic increase of the optical density of state (DOS) at the band edges. The calculated DOS of the CLC system confirms the authors’ experimental results
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