Preparation and characterization of carbonyl iron/glass composite absorber as matched load for isolator

Composite absorbers made from 66 wt% carbonyl iron and 34 wt% low melting point glass powder were prepared by a pressureless sintering technique in a nitrogen atmosphere. Apparent porosity and bending strength of the as-prepared composites were investigated. The microstructure, heat resisting properties and electromagnetic properties were characterized by scanning electron microscopy, thermal gravimetric analysis–differential scanning calorimetry and vector network analyzer. The results show that the carbonyl iron/glass composite absorbers were difficult to densify. As the sintering temperature and soaking time increased, the apparent porosity first decreased and then increased, whereas the bending strength showed the opposite change. The composite absorber sintered at 520 °C for 40 min achieved the minimum apparent porosity of 13.08% and the highest bending strength of 52 MPa. Compared to the carbonyl iron/silicone rubber absorber, the carbonyl iron/glass composite absorber exhibited better heat resisting properties, and the initial oxidation temperature was increased about 200 °C. The composite absorber with a thickness of 1.25 mm showed a good microwave absorbing property in 8–12 GHz.     

Analysis of magnetic disaccommodation in La-Co-substituted strontium ferrites

M-type strontium ferrites substituted by La³⁺-Co²⁺(Sr_1−xLa_xFe_12−xCo_xO₁₉) were prepared by ceramic process. Effects of the substituted amount of La³⁺ and Co²⁺ on structure and magnetic properties of Sr_1−xLa_xFe_12−xCo_xO₁₉ compounds have systematically been investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and magnetic disaccommodation. In the measurement range from 80 to 500 K, the magnetic disaccommodation is represented by means of isochronal curves. It is well known that magnetic disaccommodation cannot be obviously found in the M-type of pure strontium ferrites. However, three peaks were observed in Sr_1−xLa_xFe_12−xCo_xO₁₉, and this behavior is explained in terms of the presence of Fe²⁺ cation and to the site occupation by the magnetic Co²⁺ ionic within the hexagonal structure.     

Infrared broadband emission of bismuth–thulium co-doped lanthanum–aluminum–silica glasses

The Bi–Tm co-doped SiO₂–Al₂O₃–La₂O₃ (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission was investigated by the optical absorption and photoluminescence spectra. The super broadband near-infrared emission from 1000 to 2100 nm, which covered the whole O, E, S, C and L bands, was observed in the Bi–Tm co-doped samples, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm^{3+ 3}H₄→³F₄ transition (1440 nm) as well as Tm^{3+ 3}F₄→³H₆ transition (1800 nm). Relative luminescence intensity at 1270, 1440 and 1800 nm wavelength varied depending on the mixing ratio of Bi and Tm and the full-width at half-maximum (FWHM) extending from 1000 to 1600 nm could be 400 nm. These results indicated that Bi–Tm co-doped SiO₂–Al₂O₃–La₂O₃ glasses could provide potential applications in tunable lasers as well as the broadband optical amplifiers in WDM system.     

Structural and physical properties of ZnO:Al films grown on glass by direct current magnetron sputtering with the oblique target

ZnO:Al films were deposited on glass substrates at 300 K and 673 K by direct current magnetron sputtering with the oblique target. The Ar pressure was adjusted to 0.4 Pa and 1.2 Pa, respectively. All the films have a wurtzite structure and grow with a c-axis orientation in the film growth direction. The films grow mainly with columnar grains perpendicular to the substrate and some granular grains also exist in the films. The film deposited at 673 K and 0.4 Pa has the largest grains whereas that prepared at 300 K and 0.4 Pa consists of the smallest grains and is porous. The films exhibit an n-type semiconducting behavior at room temperature. The ZnO:Al film deposited at 673 K and 0.4 Pa has the lowest resistivity (3.40 × 10⁻³ Ω cm), the highest free electron concentration (4.63 × 10²⁰ cm⁻³) and a moderate Hall mobility (4.0 cm² V⁻¹ s⁻¹). The film deposited at 300 K and 0.4 Pa has the highest resistivity and the lowest free electron concentration and Hall mobility. A temperature dependence of the resistivity reveals that the carrier transport mechanism is Mott’s variable range hopping in the temperature region below 100 K and thermally activated band conduction above 215 K. The activation energy for the film deposited at 300 K and 0.4 Pa is 41 meV and that for the other films is about 35 meV. All the films have an average optical transmittance of over 85% in the visible wavelength range. The absorption edge of the film deposited at 300 K and 0.4 Pa shifts to the longer wavelength (redshift) relative to the films prepared under the other conditions.     

氧等离子体处理对纳米二氧化硅溶胶涂覆高强、高模聚乙烯纤维拉伸性能的影响

基于艾琳方程,提出用于定量分析纤维表面和纳米涂覆层间的纳米界面结构的理论模型.实验结果表明,纤维高分子链段受力塑性变形时,纳米界面结构内纳米微粒阻碍其形貌变化产生热激活体积,该热激活体积是纳米界面结构性能的重要表征;氧等离子体处理对纳米二氧化硅溶胶涂覆高强、高模聚乙烯纤维有增韧作用.由不同处理样品的扫描电子显微镜图片和傅里叶变换红外光谱曲线对比分析可知,经氧等离子体处理纳米二氧化硅溶胶涂覆高强、高模聚乙烯纤维的纳米涂覆层纳米颗粒分布均匀,纳米颗粒还填补纤维表面微观缺陷,活性官能团被引入到纤维表面. 关键词： 激活体积 氧等离子体 高强、高模聚乙烯纤维 纳米界面结构     

镝掺杂锆钛酸铅镧透明陶瓷的结构和电光性能

针对锆钛酸铅镧(PLZT)电光陶瓷在光调制器应用中存在工作电压偏高、场致滞后明显等不足,以镧系镝(Dy)元素对锆钛酸铅镧(Pb0.88La0.12)(Zr0.4Ti0.6)0.96O3 [PLZT(12/40/60)]线性电光材料进行掺杂改性.采用热压技术研制镝掺杂锆钛酸铅镧[Pb0.88(La1-xDyx)0.12](Zr0.40Ti0.60)0.96O3](PLDZT)(x=0.1～0.5)透明电光陶瓷.系统考察了PLDZT透明陶瓷的光学性能和电光特性及其与材料结构的相关性.研究表明,Dy掺杂导致材料晶格畸变,微量Dy掺杂有效提高了 PLZT(12/40/60)透明陶瓷的光学透过率,并且使典型的线性电光材料呈现二次电光效应特征,二次电光系数R约为5.59×10-15m2/V2;同时掺杂改性的PLDZT(x=0.1)透明陶瓷的驱动电压较未改性PLZT材料明显降低.     

Correction of B0 susceptibility induced distortion in diffusion-weighted images using large-deformation diffeomorphic metric mapping

Geometric distortion caused by B0 inhomogeneity is one of the most important problems for diffusion-weighted images (DWI) using single-shot, echo planar imaging (SS-EPI). In this study, large-deformation, diffeomorphic metric mapping (LDDMM) algorithm has been tested for the correction of geometric distortion in diffusion tensor images (DTI). Based on data from nine normal subjects, the amount of distortion caused by B0 susceptibility in the 3-T magnet was characterized. The distortion quality was validated by manually placing landmarks in the target and DTI images before and after distortion correction. The distortion was found to be up to 15 mm in the population-averaged map and could be more than 20 mm in individual images. Both qualitative demonstration and quantitative statistical results suggest that the highly elastic geometric distortion caused by spatial inhomogeneity of the B0 field in DTI using SS-EPI can be effectively corrected by LDDMM. This postprocessing method is especially useful for correcting existent DTI data without phase maps.     

高温超导电缆直流测试电源平台的搭建

根据高温超导电缆测试用直流电源平台的要求,建立了硬件平台。该平台为模块化结构,具有输出精度高,便于扩展等特点;为方便操作,建立了基于LabVIEW的软件平台,对直流电源平台进行远程控制,并给出了远程控制的程序流程图,实现了电流的匀速上升和下降以及上升过程中的中断操作;利用该电源平台进行了超导电缆的临界电流测试实验,验证了直流电源平台符合高温超导电缆的测试要求。     

Difference-frequency ultrasound generation from microbubbles under dual-frequency excitation

The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.