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81.
82.
本文用傅里叶及边缘泰勒展开的方法,导出了非圆截面托卡马克等离子体边缘磁面的解析解及其重构的方法。最后作为例子,给出了在TEXT-U装置中按实际参数重构的等离子体边缘磁面结构及重构的误差。 相似文献
83.
The nanometer sized particles of PbI2 were embedded in SiO2 films. X-ray diffraction and the TEM pictures showed the preservation of the bulk layered structure and symmetry. The PL spectrum of the nano-particles exhibited a pronounced blue shift of the exciton band due to quantum size effect. The Lead Iodide represents an exceptionally small exciton Bohr radius (aB = 19 Å) and a special case in which me mh. The prepared samples contained particles with mean radii, a, in the range aB < a < 3aB. Within this limit (with me mh), the experimental results suggest that the electron is localized nearly at the center of the particle, enabling the hole to move around it. Thus, the size confinement permits the creation of an acceptor-like exciton. The PL spectrum revealed additional states, associated with stoichiometric defects either at the interior or surface sites of the nano-particles. These defects act either as donor or acceptor states. The dynamics of the various recombination processes has been investigated by measuring the time resolved PL spectra. The results show a multiexponential behavior of the various recombination emission bands, indicating the occurrence of trapping and detrapping processes. Analysis of these results suggests that the existence of surface states give rise to these complex radiative decay processes. The correlation between donor-acceptor recombination emission bands in the aforementioned samples and lattice imperfections was examined, utilizing optically detected magnetic resonance (ODMR) spectroscopy. The results identified the following imperfection sites: an acceptor site associated with an isotropic Lead vacancy defect, [V−]pb2+ and a donor site, associated with an anisotropic Iodine vacancy, [V0]Iodine. 相似文献
84.
85.
First-principles plane-wave pseudopotential calculations of the adhesion, bonding and magnetism of the interface between the ferromagnetic bcc Fe and non-magnetic HfC are performed. The work of adhesion for C- and Hf-site Fe/HfC interfaces is calculated. High adhesion at C-site interface is found and Fe–C polar covalent bonds are formed across the interface. The magnetic moments of Fe atoms at interface are increased in both interfaces. The effect of the magnetism on the electronic structure of Fe/HfC interface is also investigated. It is shown that the change in band of majority-spin leads to enhance the magnetic moment of Fe. 相似文献
86.
We have studied the effect of the internal circumferential magnetic field HB created by the dc bias current IB on longitudinal and off-diagonal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that by changing the dc current IB it is possible to considerably change the MI dependencies. The bias current applied to such microwire transforms the symmetric and hysteretic MI curve to asymmetrical and anhysteretic. The minimum of longitudinal MI curve shifts from the zero-field point. Reversing the bias current causes reversal of the bias field direction and results in a mirroring of the MI curves. It is proposed to apply a cross-checking of two MI curves with IB of different polarity for magnetic field sensing. In particular, this method allows to overcome the drawbacks usually associated with longitudinal MI—namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. Moreover, the operating range of the longitudinal MI sensor, in contrast to the off-diagonal one, can be much extended as it exhibits a quite high sensitivity in the field range up to one order of magnitude higher than the anisotropy field. 相似文献
87.
Yuqing Li Ying Huang Shuhua QiLei Niu Yinling ZhangYanfei Wu 《Applied Surface Science》2012,258(8):3659-3666
Strontium ferrite particles were firstly prepared by sol-gel method and self-propagating synthesis, and then the polyaniline/strontium ferrite/multiwalled carbon nanotubes composites were synthesized through in situ polymerization approach. Structure, morphology and properties of the composite were characterized by various instruments. XRD analysis shows that the output of PANI increases with the increase of the content of MWCNTs, due to the large surface area of MWCNTs. Because of the coating of PANI, the outer diameter of MWCNTs increases from 10 nm to 20-40 nm. The electrical conductivity of the composites increases with the amount increase of MWCNTs and reaches 7.2196 S/cm in the presence of 2 g MWCNTs. The coercive force of the composites prepared with 2 g MWCNTs is 7457.17 Oe, which is much bigger than that of SrFe12O19 particles 6145.6 Oe, however, both the saturation magnetization and the remanent magnetization of the composite become much smaller than those of SrFe12O19 particles. The electromagnetic properties of the composite are excellent in the frequency range of 2-18 GHz, which mainly depend on the dielectric loss in the range of 2-9 GHz, and mainly on the magnetic loss in the range of 9-18 GHz. 相似文献
88.
L.Y. MaG. Chen J. LiJ. Zhu Z.Q. QiuY.Z. Wu 《Journal of magnetism and magnetic materials》2012,324(4):528-533
The in-plane magnetic anisotropy of Fe/NiO bilayers was studied quantitatively as a function of NiO thickness using the magneto-optical Kerr effect with a rotating field. For NiO thicker than the ordering transition thickness, the total in-plane fourfold anisotropy of the Fe layer decreases with NiO thickness in Fe/NiO/Au(001), but increases in Fe/NiO/MgO(001). Our result indicates that the exchange coupling in an Fe/NiO bilayer might induce an additional in-plane fourfold anisotropy, and the opposite thickness dependent behaviors may be attributed to the different Ni2+ antiferromagnetic spin orientations for NiO films grown on Au(001) and MgO(001) surfaces. 相似文献
89.
I.V. VasylenkoS.V. Kolotilov I.E. KotenkoK.S. Gavrilenko F. TunaG.A. Timсo R.E.P. WinpennyV.V. Pavlishchuk 《Journal of magnetism and magnetic materials》2012,324(4):595-601
Thermal decomposition of the trinuclear complex [Fe2CrO(CH3COO)6(H2O)3]NO3 at 300, 400 and 500 °C gave γ-Fe2O3 nanoparticles along with amorphous chromium oxide, while decomposition of the same starting compound at 600 and 700 °C led to the formation of α-(Fe2/3Cr1/3)2O3 nanoparticles. Size of γ-Fe2O3 nanoparticles, determined by X-ray diffraction, was in the range from 9 to 11 nm and increased with formation temperature growth. Average size of α-(Fe2/3Cr1/3)2O3 nanoparticles was about 40 nm and almost did not depend on the temperature of its formation. γ-Fe2O3 nanoparticles possessed superparamagnetic behavior with blocking temperature 180-250 K, saturation magnetization 29-35 emu/g at 5 K, 44-49 emu/g at 300 K and coercivity 400-600 Oe at 5 K. α-(Fe2/3Cr1/3)2O3 nanoparticles were characterized by low magnetization values (2.7 emu/g at 70 kOe). Such magnetic properties can be caused by non-compensated spins and defects present on the surface of these nanoparticles. The increase of α-(Fe2/3Cr1/3)2O3 formation temperature led to decrease of magnetization (being compared for the same fields), which may be caused by decrease of the quantity of defects or non-compensated spins (due to decrease of particles' surface). 相似文献
90.
Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at a depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nanoparticles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm3 volume optimal Halbach design yields a 5× greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (≤1 T), size (≤2000 cm3), and number of elements (≤36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ≤5°), thus yielding practical designs to improve magnetic drug targeting treatment depths. 相似文献