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991.
The effect of the grain boundary microstructure on the anisotropy and coercivity was investigated in an HDDR Nd-Fe-B permanent
magnetic alloy. Considering the special microstructure of its magnetic powder grain, an anisotropic theoretical model influenced
simultaneously by the structure defect at the grain boundary and the exchange coupling interaction was put forward. The variations
of the structure defect factors based on the nucleation and pinning mechanism with 2r
0/lex (where r
0 and lex are the defect thickness and the length of exchange coupling, respectively) were calculated. The results show that the coercivity
mechanism of an HDDR Nd-Fe-B permanent magnetic alloy is greatly related to its microstructure defect at the grain boundary.
For a fixed lex, when 2r
0/lex < 1.67, the coercivity is controlled by the pinning mechanism; when 2r
0/lex > 1.67, it is determined by the nucleation mechanism. The coercivity reaches the maximum when 2r
0/lex = 1.67. The calculation result is consistent well with the experimental result given by Morimoto et al.
Supported by the National Natural Science Foundation of China (Grant No. 50671055) 相似文献
992.
Geocenter motion (GCM) is one important topic for constructing and maintaining the terrestrial reference frame and its applications.
GCM is studied from CHAMP with the multi-step approach in this paper. Geometric orbits of CHAMP in 2001–2006 are precisely
determined with the kinematic method only from the satellite-borne GPS zero-difference data. Then a GCM time series is estimated
from the precise kinematic orbits based on the theory of satellite dynamics to fit the CHAMP’s real geometric orbits. We compare
the series with the geocenter series used in ITRF2005. Then the GCM series are analyzed with Fourier transform and wavelet
transformation. The mean motions within 6 years in TX, TY and TZ directions are respectively 0.8 mm, 2.2 mm, and 7.9 mm. The trends of GCM in the three directions are 0.495 mm/a, −0.004
mm/a, and 1.309 mm/a, respectively. The long-term movement (2001–2006) indicates that the crustal figure is changing. The
seasonal variations are the main component which may be excitated by the mass redistribution of Earth’s fluid layer, e.g.
ocean, atmosphere and continental water. The inter-annual variations are also found in the GCM series measured with CHAMP.
Supported by the International S&T Cooperation Program of China (Grant No. 2006DFA21980), the National Hi-tech R&D Program
of China (Grant No. 2006AA12z303), the National Natural Science Foundation of China (Grant No. 40774009), and the Natural
Science Foundation of Shandong Province, China (Grant No. Y2003E01) 相似文献
993.
S. H. Lee J. J. Choi W. K. Han S. W. Baek 《International Journal of Infrared and Millimeter Waves》1999,20(12):2011-2022
A design study of a double-anode magnetron-injection-gun is performed to incorporate the electron gun into a high power 28GHz gyroklystron amplifier operating at 70kV and 8.2A. The electron gun is designed to be used in a tapered magnetic field in the cathode region produced from an iron-free superconducting magnet. An electron trajectory code predicts a beam axial velocity spread of 5.9% at = 1.5, 70kV, 8.2A and 10.4kG, which is a high quality electron beam suitable for the high gain, high efficiency, five-cavity gyroklystron amplifier. The successful design of the high quality electron gun is attributed to a longer gap between the modulating anode and the grounded anode compared with the case of the first 28GHz electron gun built with an iron enclosed electromagnet. 相似文献
994.
Han D Kim YS Noz ME 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):1036-1041
Wigner rotations and Iwasawa decompositions are manifestations of the internal space-time symmetries of massive and massless particles, respectively. It is shown to be possible to produce combinations of optical filters which exhibit transformations corresponding to Wigner rotations and Iwasawa decompositions. This is possible because the combined effects of rotation, phase-shift, and attenuation filters lead to transformation matrices of the six-parameter Lorentz group applicable to Jones vectors and Stokes parameters for polarized light waves. The symmetry transformations in special relativity lead to a set of experiments which can be performed in optics laboratories. 相似文献
995.
Xufeng Wu Gaoquan Shi Feng'En Chen Shaohu Han Junbiao Peng 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):3049-3054
Poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV) with a molar mass of 26–47 × 104 g mol?1 and a polydispersity of 2.5–3.2 was synthesized by a liquid–solid two‐phase reaction. The liquid phase was tetrahydrofuran (THF) containing 1,4‐bis(chloromethyl)‐2‐methoxy‐5‐(2′‐ethylhexyloxy)benzene as the monomer and a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The solid phase consisted of potassium hydroxide particles with diameters smaller than 0.5 mm. The reaction was carried out at a low temperature of 0 °C and under nitrogen protection. No gelation was observed during the polymerization process, and the polymer was soluble in the usual organic solvents, such as chloroform, toluene, THF, and xylene. A polymer light‐emitting diode was fabricated with MEH‐PPV as an active luminescent layer. The device had an indium tin oxide/poly(3,4‐ethylenedioxylthiophene) (PEDOT)/MEH‐PPV/Ba/Al configuration. It showed a turn‐on voltage of 3.3 V, a luminescence intensity at 6.1 V of 550 cd/m2, a luminescence efficiency of 0.43 cd/A, and a quantum efficiency of 0.57%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3049–3054, 2004 相似文献
996.
We investigate neutron star properties by constructing a chiral SU(3) spontaneous breaking Lagrangian and using relativistic mean-field approximation. The results show that π- condensate appears at some baryon densities,and hyperons ∑- and A exist in neutron star matter at high density. In this model, neutron star's maximum mass is1.12Ms with corresponding radius about 8 km. 相似文献
997.
Tae Oan Ahn Jung Ho Kim Han Mo Jeong Sang Won Lee Lee Soon Park 《Journal of Polymer Science.Polymer Physics》1994,32(1):21-28
The compatibilizing effect of polyarylate-polystyrene (PAR-PS) block copolymer prepared from macroazo initiator was examined in polyarylate/polystyrene blends from the view-points of morphology, density, and thermal, mechanical, and rheological properties. PARPS block copolymer enhanced the mutual dissolution of the homopolymers. Reduced dispersed-domain size and increased density showed the efficiency of the block copolymer as a compatibilizing agent. Results from mechanical and rheological properties could also be explained by the compatibilizing effect of PAR-PS block copolymer in the blends. © 1994 John Wiley & Sons, Inc. 相似文献
998.
999.
1000.
Han Shifang 《ournal of non Newtonian Fluid Mechanics》1984,15(2):181-197
The theory of nearly-extensional flow is developed to study the stability of extensional flow. For such flows a simple constitutive equation is derived for slightly disturbed extensional flow when a ‘short memory’ assumption is admissible.Following Minoshima and White and utilizing the constitutive equation obtained, a stability analysis for non-Newtonian fluid sheets is presented. The theoretical analysis presented is specific for an integral consitutive equation. The influence of the fluid elasticity on the stability behaviour is investigated. It is shown that the fluid sheet stability depends upon λk, where λ is the relaxation time and K is the elongation rate. 相似文献