共查询到20条相似文献,搜索用时 187 毫秒
1.
用铁磁畴壁模型研究了非补偿界面铁磁/反铁磁双层膜中冷却场(包括大小及其方向)对交换偏置场hE的影响.结果表明:当冷却场的方向与反铁磁层磁易轴一致时,hE大小与冷却场大小无关.当冷却场的方向偏离磁易轴时,hE的大小随偏离角度的增大有缓慢的改变,但当冷却场的方向偏离到临界角度γc处,hE的大小发生突变,其γc的大小随冷却场的增大而增大.特别是当冷却场的偏离角度大于γc后,hE出现由负转正的现象,其转变点还与冷却场的大小有关.另外,hE与铁磁层原子层数NF的关系会发生由hE∝N-1F向hE∝N-λF的转变,其中λ>1.其发生转变的条件与NF、冷却场大小和方向密切相关.
关键词:
铁磁/反铁磁双层膜
交换偏置
冷却场 相似文献
2.
采用改进排列通道量子力学(Modified Arrangement Channel Quantum Mechanics,简称MACQM)方法和变分法,计算了H3体系正三角形和H4体系的正四面体结构的能量曲线.当H3体系原子核的间距R=1.74a0,波函数变分参数α=1.03时,体系能量有最低值-1.58161 a.u.;当H4体系原子核的间距R=1.60a0,波函数变分参数α=1.07时,体系能量有最低值-2.28097 a.u.,这表明H3体系的正三角形构型和H4的正四面体结构是可以稳定存在的. 相似文献
3.
本文对具有特定横向弛豫时间(T2)的硫酸铜溶液进行了多回波间隔(TE)的核磁共振(NMR)实验,并利用数值模拟对32组具有不同弛豫分量的模型进行了变TE模拟实验,定量研究了TE对致密油气、页岩气等低孔低渗储层NMR孔隙度的影响规律.实验结果表明,随着TE的增大,各T2弛豫组分NMR孔隙度先维持在100%左右,然后迅速衰减,当TE增加到一定数值时,趋近于0;不同T2弛豫组分NMR孔隙度开始迅速衰减及最后变为0的TE值存在显著差异.根据不同T2弛豫组分NMR孔隙度与TE的关系,将整个NMR测量分为无损测量区、快速衰减区、无效参数区和仪器盲区4个区域.对特定弛豫组分而言,在快速衰减区弛豫组分损失量与TE呈对数关系,本文还给出了该区域NMR孔隙度的校正公式及方法. 相似文献
4.
采用反冲离子飞行时间-散射离子位置灵敏符合测量技术,测量了能量范围在0.7v0—4.4v0(v0为玻尔速度)的碳离子Cq+(q=1—4)与He原子碰撞过程不同出射道靶原子的双电离与单电离截面比R,包括入射离子不损失电子(直接电离)的出射道(Rq,q),入射离子俘获一个电子的出射道(Rq,q-1)和入射离子损失一个电子的出射道(Rq,q+1),并研究了R随入射C离子的能量及电荷态的变化关系.实验表明,对给定电荷态的入射离子,靶原子的双电离与单电离截面比R与出射道有很强的依赖关系,即Rq,q<Rq,q+1<Rq,q-1.直接电离出射道截面比Rq,q与入射离子电荷态几乎无关,而入射离子俘获一个电子的出射道和损失一个电子的出射道靶原子双电离与单电离截面比Rq,q-1和Rq,q+1却与入射离子电荷态有很强的关系.采用原子极化理论和电子屏蔽与反屏蔽作用对实验结果进行了解释.
关键词:
离子-原子碰撞
电离
截面比 相似文献
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针对玉米生产中叶片氮素快速、无损检测的实际需求,使用叶级高光谱数据(400~2 500 nm),依据等效水厚度梯度划分叶片样本,建立了梯度连续的叶片氮素反演模型,初步探索了含水量因素对叶片反射率特性及反演模型精度的影响。首先获取叶级高光谱数据,再根据等效水厚度数值大小对样本进行排序及滑动划分,建立了子集集合。父集除原光谱数据之外还采用了三大类:(1)基线矫正类、(2)散射校正类和(3)平滑处理类光谱变换方法,而子集未使用任何光谱变换方法。建立全波段的PLSR反演模型,对比模型精度,初步定量评价了等效水厚度因素对建模精度的影响。研究结果表明:(1)四组数据中有三组父集反演精度低于最优子集的反演精度,另外一组持平(2018大田低氮:(父)R2CV=0.48<(子)R2CV=0.57, (父)RPDCV=1.38<(子)RPDCV=1.52;2018大田高氮:(父)R2CV=0.48<(子)R2CV=0.7, (父)RPDCV=1.39<(子)RPDCV=1.8;2019大田高氮:(父)R2CV=0.59<(子)R2CV=0.68, (父)RPDCV=1.57<(子)RPDCV=1.77);(2)四组数据的最优子集反演精度都达到甚至超过了定性模型水平,而父集只有两组;(3)制作反演数据集时在样本筛选问题上需要考虑等效水厚度因素,以避免过于宽泛的样本选择而导致整体反演精度的损失。综上,等效水厚度因素对玉米叶片氮素建模精度存在显著影响,不可忽视。在考虑该因素后,使用叶级高光谱数据对玉米叶片氮素进行快速无损检测的技术方法会更加可信、可行。 相似文献
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利用嵌入反应合成了有机-无机嵌入化合物Fe0.95PS3(MV)0.1 1(MV为1,1′- 二甲基-4,4′-联吡啶阳离子),对其结构和磁性进行了研究.x射线衍射数据表明,此嵌入化 合物的晶体结构仍为单斜晶系,空间群为C2/m,晶胞参数a=0.879 nm, b=0.944 nm, c=1.07 0 nm, β=114.76°.相对于纯FePS3, 层间距离增大0.33 nm.磁化率研究表明, 从室温降 到4.2 K
关键词:
嵌入化合物
Mssbauer谱
磁相互作用
分子磁体 相似文献
11.
The existence of force-free magnetic fields in the exterior domain of some compact simply connected surface S is proved via an iteration scheme. The iteration starts with an arbitrary exterior vacuum field, which contains flux tubes
originating and ending on S. At one cross-section of such a flux tube with S an arbitrary function α is prescribed. For small values of α (in the H?lder-norm 1, λ; 0 < λ < 1) the iteration is shown
to converge to a force-free field with the prescribed values of α in a flux tube which is close to the vacuum flux tube and
α≡ 0 outside. The force-free field is close (in the H?lder- norm 1,λ) to the starting vacuum field, in particular, it has
the same field line topology, the same boundary values on S and satisfies the same decay conditions in spatial infinity. It is in general three-dimensional and requires no continuous
symmetries.
Received: 20 June 1999 / Accepted: 25 October 1999 相似文献
12.
By comparing the contributions of pinning and viscous forces to the restoring force on flux ines in type II and highT
c superconductors, it is shown that the flux flow in highT
c superconducto rs should play an important role in determining the magnetic flux distribution and hence the hyste resis losses in a.c. fields. Both quantities are calculated in the extreme case of very large viscous forces with respect to the pinning force. The magnetic field and frequency dependence of the losses are changed with respect to the results obtained from the critical state model. The theoretical results are qualitatively confirmed by a.c. susceptibility measurements at different magnetic field amplitudes and frequencies. The quantitative differences indicate that the flux flow effects in highT
c superconductors are by far not so strong as expected and supposed by some theories. The reasons for these discrepancies are discussed. 相似文献
13.
ZHANG LingQian LIU ZhenXing MA ZhiWei SHEN Chao ZHOU XuZhi ZHANG XianGuo 《中国科学G辑(英文版)》2007,50(5):673-680
A 3-dimensional resistive MHD simulation was carried out to study the effect of the upward ions on the field-aligned currents
(FACs) in the near-earth magnetotail. The simulation results show that the up-flow ions originating from the nightside auroral
oval would drift into the center plasma sheet along the magnetic field lines in the plasma sheet boundary, and have an important
effect on the field-aligned currents. The main conclusions include that: 1) the upward-ions mainly affect the field-aligned
currents in the near-earth magnetotail (inside 15 Re); 2) the generated FACs in the near-earth region have two types, i.e.,
Region 1 FAC in the high-latitude and Region 2 FAC in the low-latitude; 3) FACs increase with the enhancement of the upward
ion flux; 4) with the same flux of the upward ions, FACs enhance with the increase of the velocity of the up-flow ions; 5)
the intensification of FACs is also closely related with the latitude of the upward ions, and the ions from the closed field
line region generate larger FACs; 6) the generation of FACs is closely related with B
y created by the upward ions.
Supported by the National Natural Science Foundation of China (Grant Nos. CNSF-40474058 and CNSF-40536030) 相似文献
14.
The minimization of residual stresses in magnetic systems with quasi-force-free current distribution
The feasibility of a magnet experiencing very low mechanical stresses is studied. Megagauss fields can be generated without failure of the solenoid winding and excessively increasing the winding dimensions if the current distribution is force-free in its inner part and the axial current closes in its outer part. The approximation of the quasi-force-free current distribution by discrete conductive layers is considered. Analysis and computations are performed for two force-free winding approximations. In the former case, the conductors are divided into N paired balanced layers where the azimuth and poloidal currents, respectively, pass. The equal and oppositely directed forces arising in the layers of a pair are transferred to insulating spacers between the layers. Stresses in the spacers can be reduced down to values N times as low as the magnetic field pressure B 0 2 /(2μ0) at the solenoid axis. If the current direction in each of the layers meets the balance condition, the residual stresses can be N 2 times lower than B 0 2 /(2μ0), because the tensile and compressive forces in the layers partially cancel. 相似文献
15.
N. A. Red’ko V. D. Kagan M. P. Volkov 《Journal of Experimental and Theoretical Physics》2010,111(2):241-245
The galvanomagnetic properties of single-crystal samples of the Bi0.93Sb0.07 semiconductor alloy with the electron density n = 1.6 × 1017 cm−3 in magnetic fields up to 14 T at T = 1.6 K have been investigated. The resistivity ρ and Hall coefficient R have been measured as functions of the magnetic field directed along the binary axis of a crystal for a current flowing through
a sample along the bisector axis; i.e., the components ρ22 and R
32, 1 have been measured. The strong anisotropy of the electron spectrum of the samples makes it possible to separately observe
quantum oscillations of the magnetoresistance ρ22(H) for H ‖ C
2 in low magnetic fields for two equivalent ellipsoids with small extremal cross sections (secondary ellipsoids) and in high
magnetic fields for electrons of the ellipsoid with a large extremal cross section (main ellipsoid). An increase in the energy
of the electrons of secondary ellipsoids in the quantum limit magnetic fields is accompanied by the flow of electrons to the
main ellipsoid; i.e., an electronic topological transition occurs from the three-valley electron spectrum to the single-valley
one. After the flow stops, the Fermi energy E
F increases from 18 meV to 27.8 meV. With an increase in the quantizing magnetic field, the Fermi energy of the electrons decreases
both in the region of quantum oscillations of the resistance that are attributed to the electrons of the secondary ellipsoids
and in the region of oscillations associated with the electrons of the main ellipsoid. The Hall coefficient R
32, 1 decreases in high magnetic fields; this behavior indicates the absence of the electron magnetic freezing effect. 相似文献
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17.
D.H. Kim T.J. Hwang Y.J. Cha W.K. Seong W.N. Kang 《Physica C: Superconductivity and its Applications》2009,469(15-20):1059-1062
We studied the flux pinning properties by grain boundaries in MgB2 films prepared by using a hybrid physical chemical vapor deposition method on the c-axis oriented sapphire substrates. All the films we report here had the columnar grains with the growth direction perpendicular to the substrates and the grain sizes in the range of a few hundred nanometers. At very low magnetic fields, no discernable grain-boundary (GB) pinning effect was observed in all measuring temperatures, but above those fields, the effect of GB flux pinning was observed as enhanced critical current densities (Jcs) and reduced resistances when an external magnetic field (B) was aligned parallel to the c-axis. We interpret the B dependence of Jc in the terms of flux line lattice shear inside the columnar grains activated by dislocations of Frank–Read source while the flux lines pinned by GB act as anchors for dislocations. Magnetic field dependence of flux pinning force density for B parallel to the c-axis was reasonably explained by the above model. 相似文献
18.
G. Zimbardo 《Il Nuovo Cimento C》1992,15(5):645-655
Summary Recently it has been shown that an X-type magnetic neutral line may form in Jupiter's nightside magnetosphere as the result
of the current flowing in the plasma disc. Still, a collisionless reconnection mechanism is required to tear up the magnetic
field. Recently, Büchner and Zelenyi showed that the chaotization of the electron motion can lead to fast collisionless reconnection
in the Earth's magnetotail. In their theory, enhanced pitch angle diffusion is obtained when the curvature parameter κe decreases to κe ≃ 1.6. We apply Büchner and Zelenyi's theory to Jupiter's magnetosphere. The curvature parameter is obtained from the measured
plasma parameters and from a self-consistent equilibrium model of the magnetic field, and the results for κe show that the larger the assumed plasma disc, the larger is the range where κe is less than or equal to the stochasticity threshold 1.6. This indicates that chaotic magnetic-field line reconnection may
occur in Jupiter's nightside magnetosphere around 60R
J from the planet, and is consistent with thein situ magnetic-field observations, that show the signature of magnetic islands and of tearing-mode instability in the relevant
region. We speculate that these processes, differently from the Earth's case, occur in a semi-steady way.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献
19.
Khotyaintsev YV Vaivads A André M Fujimoto M Retinò A Owen CJ 《Physical review letters》2010,105(16):165002
We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process. 相似文献
20.
建立了梯度磁场下金属熔体中晶粒迁移的一般动力学模型,导出了磁场对导电熔体黏度的影响规律,得到了迁移速度的解析解和迁移距离的分析解.导电熔体的有效黏度随磁场强度的平方成线性递增关系.迁移速度达到终极速度的时间为10-3s数量级.终极速度随着磁场强度的增加而迅速减小,表明强磁场对晶粒迁移有抑制作用.迁移距离和迁移率与磁场分布密切相关.为观察初晶硅的迁移状况,将Al-18wt%Si合金在650℃保温60min后,施加强梯度磁场(Bz=5 T,BzdBz/dz=-224T2·m-1)对熔体作用不同时间并淬火,结果表明,晶粒半径大于等于40μm的初晶硅在120s内大部分完成迁移,与理论计算符合.
关键词:
强梯度磁场
析出相
迁移
刚体动力学 相似文献