Structure and magnetic properties of Ni0.11ZnxCo0.03Fe2.86-xO4 ferrite films deposited on Ag-coated glass substrates by wet chemical method

Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ spinel ferrite films with x = 0.00, 0.23, 0.34, 0.43 and 0.51 were prepared on Ag-coated glass substrates from nitrate and dimethylamine borane solution at 80 °C. The Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ ferrite films are singe-phased spinel ferrite. With the Zn content x increasing from 0 to 0.51, the lattice constant of the ferrite films increases from 0.8383 to 0.8425 nm. The Ni_0.11Zn_0.51Co_0.03Fe_2.35O₄ film is about 500 nm thick and composed of uniform equiaxed granules of about 40–50 nm. The Raman spectrum analysis indicates that the Zn²⁺ ions occupy the A sites. Saturation magnetization increases with x increasing from 0 to 0.35, reaches a maximum value of 460 kA/m at x = 0.35, and then decreases with further increase of x. Coercivity decreases monotonically from 12.3 to 1.7 kA/m with x increasing from 0 to 0.51. The change in magnetic properties may be explained by the decrease of A–B interactions and the anisotropy constant due to the incorporation of non-magnetic Zn²⁺ ions.     

智能型毫瓦级超声功率计的设计

智能型毫瓦级超声功率计主要用于医用超声源的测量,是采用磁电式力平衡机构抵偿超声辐射压力的方法测量超声功率,其特点是充分利用单片微机控制测量机构,实现自动平衡、自动测量、自动保护,使这种测量方法真正实用化。     

Magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism in FeCoNiZMn_x(Z=Si,Al,Sn,Ge)high entropy alloys

We design high entropy alloys(HEAs) with different induction elements(Si/Al/Sn).In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization(Ms)is caused only by the change of electron spin state,each set of HEAs contains a different amount of Mn.Synergistic effects among induction elements that induce the magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism are found.Ms of added Mn reduces when a particular induction element(Si_0.4/Al_0.4/Sn_0.4) exists,while a larger increment of Ms appears when two induction elements coexist,Si_0.4Al_0.4(25.79 emu/g) and Sn_0.4Al_0.4(15.43 emu/g).This is reflected in the microcosmic magnetic structure for the emergence of closed domains due to large demagnetization energy,which is confirmed by the Lorentz transmission electron microscope(LTEM) data.The calculated magnetic moments and the exchange integral constants from density functional theory based on the Exact Muffin-Tin Orbits fo rmalism reveal that the magnetic state and the strength of fe rromagnetic and anti-ferromagnetic coupling determine the variation of Ms in different chemical environments.The difference in energy levels of coexisting multiple induction elements also leads to a larger increment of Ms,Si_0.4Al_0.4Sn_0.4(29.78 emu/g),and Si_0.4Al_0.4Ge_0.4Sn_0.4(31.00 emu/g).     

多模态网络融合在轻度认知障碍分类中的应用

针对早期轻度认知障碍（MCI）根据医学诊断认知量表评估极有可能无法判断的问题,提出了一种多模态网络融合的MCI辅助诊断分类方法。基于图论的复杂网络分析方法在神经影像领域的应用已得到广泛认可,但采用不同模态的成像技术研究脑部疾病对大脑网络拓扑结构属性的影响会产生不同结果。首先,使用弥散张量成像（DTI）与静息态功能磁共振成像（rs-fMRI）数据构建大脑结构和功能连接的融合网络。然后,融合网络的拓扑属性被施以单因素方差分析（ANOVA）,选择具有显著差异的属性作为分类特征。最后,利用支持向量机（SVM）留一法交叉验证对健康组和MCI组分类,估算准确率。实验结果表明,所提方法的分类结果准确率达到94.44%,相较单一模态数据法的分类结果有明显提高。所提方法诊断出的MCI患者在扣带回、颞上回以及额叶和顶叶部分区域等许多脑区表现出显著异常,与已有研究结果基本一致。     

密闭机柜磁场屏蔽效能研究

本文介绍机柜的电磁屏蔽原理和影响屏蔽效能的因素,对某舰载密闭铸铝机柜的低频磁场屏蔽效能进行了测试,得出具有工程实用价值的数据,对同类机箱机柜的屏蔽效能有参考评估作用,并针对本机柜门、结构和材料对屏蔽效能的影响给出了详细分析。     

基于形态学重建滤波的脑部磁共振图像分割

在阐述形态学基本原理、形态学重建滤波原理和方法的基础上,提出了形态学交变序列重建滤波,并应用于脑部磁共振图像分割。试验结果表明,该方法能有效地滤除无用的信息而保留图像原始形状不变。再应用形态学梯度运算、测地距离和流域变换方法就能准确地分割出脑部磁共振图像的头盖骨和脑膜。     

多功能8字线圈的优化设计与实验

为了改善线圈磁聚焦性能,扩大线圈功能应用,改进8字线圈,通过混合优化算法优化线圈主要可变参数,得出不同尺寸的8字线圈。建立线圈仿真模型,优化仿真分析8字线圈的聚焦性与功能效果。制作与仿真模型一致的实验模型,使用长为1 m、宽为1 m、厚度为5 mm的均匀钢板与一根实心导管来测试验证仿真结果。通过对比函数证明了理论仿真的有效性。改进后不同尺寸的8字形线圈模型可以实现多功能运用,在一定的聚焦性下,该线圈可以灵活运用到亥姆赫兹线圈、经颅磁刺激线圈阵列的模型以及功能磁刺激线圈阵列中。     

超导核磁共振成像主磁体无源数值匀场技术的研究

本文提出了超导核磁共振成像主磁体无源数值匀场的概念,发展了一种优化无源数值匀场方法。将优化无源数值匀场方法应用于中国科健有限公司研制的国产第一台超导核磁共振成像主磁体,其结果令人满意。     

高性能力矩器的设计

力矩器是力平衡加速度表的关键组件。在力矩器的设计中,采用了新的永磁、软磁材料,优化了力矩设计,计算了磁路工作磁场强度。给出了反馈力矩系数,分析了力矩系数对提高加速度表量程和保证精度的作用。     

Magnetic anisotropy in (Ga,Mn)As on GaAs(1 1 3)As studied by magnetotransport and ferromagnetic resonance

The magnetic anisotropy of a 40-nm-thick (Ga,Mn)As film with 5% Mn grown on GaAs(1 1 3)A is studied by means of magnetotransport and ferromagnetic resonance (FMR) spectroscopy. In addition to the cubic and a weak uniaxial in-plane anisotropy, two uniaxial out-of-plane contributions along [1 1 3] and [0 0 1] are found. Using the anisotropy parameters determined from FMR, the longitudinal and transverse resistivities measured as a function of magnetic field orientation and strength are well modelled within the framework of a single ferromagnetic domain. In particular, the low-field data which are strongly affected by sudden jumps of the magnetization are well reproduced.