HTS双饼线圈的加工工艺及实验研究

详细介绍了高温超导双饼线圈的加工工艺和流程,针对绕制时带材弯曲形变使临界电流退化的技术难点,重点阐述了其解决方法。在液氮温度、自场环境下对采用该加工工艺制作的YBCO双饼线圈及Bi2223/Ag双饼线圈进行低温实验,测试其V-I特性曲线。实验结果表明:该工艺制作的双饼线圈性能良好,工艺安全可靠,是合适的。同时,实验测量数据也为线圈在磁体中的进一步应用提供了可靠依据。     

Effect of emitter layer doping concentration on the performance of silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15 nm)/a-Si:H(10 nm)/ epitaxial c-Si(47 μm)/epitaxial c-Si(3 μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot-wire chemical vapour deposition. The effect of the doping concentration of emitter layer S_d (S_d=PH₃/(PH₃+SiH₄+H₂)) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S_d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S_d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm², a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

Laser ranging based on electro-optic switch

Based on electro-optic switch effect in crystal, a novel laser ranging method is proposed. CW-laser emitted by laser transmitter propagates forward to the measured target, after being reflected by the target, and then goes back to the transmitter. Close to the transmitter, a special mono-block LiNbO₃ crystal is added into the round-trip light beams. High-voltage pulses with the sharp enough changes in rising edges are loaded on the crystal. Based on electro-optic effect, double refraction and internal double reflection effect in crystal, the crystal cuts off the round-trip light beams, and reflects a light pulse cut out by the crystal to a detector aside from the original beam path. The pulse width T is the period that laser propagates forward and back between the crystal and the target. The feasibility of the new idea is proved by our experiments and a brand-new way for the laser ranging is provided.     

Low temperature electronic transports in the presence of a density gradient

In this paper, we review low temperature electronic transport results in high quality two-dimensional electron systems. We discuss the quantization of the diagonal resistance, R_xx, at the edges of several quantum Hall states. Each quantized R_xx value turns out to be close to the difference between the two adjacent Hall plateaus in the off-diagonal resistance, R_xy. Moreover, peaks in R_xx occur at different positions in positive and negative magnetic fields. All three R_xx features can be explained quantitatively by a ∼1% cm electron density gradient. Furthermore, based on this observation, the well known but still enigmatic resistivity rule, relating R_xx to , finds a simple interpretation in terms of this gradient. In another sample, at 1.2 K, R_xx we observe a strongly linear magnetic field dependence. Surprisingly, this linear magnetoresistance also originates from the density gradient. Our findings throw an unexpected light on the relationship between the experimentally measured R_xx and the diagonal resistivity ρ_xx.     

Ar-buffer-assisted deposition of Cu13 on Cu(1 1 1) surfaces

In this paper, the deposition of Cu₁₃ onto Cu(1 1 1) surface through argon buffer layers was investigated by molecular dynamics (MD) simulations. The interactions between Cu-Cu, Cu-Ar, and Ar-Ar were described by Finnis-Sinclair (FS) tight-binding potential and L-J potential, respectively. The impact energy was chosen to be 2-6 eV/atom in order to compare with experimental results. It was observed that with Ar-buffer layers, the Cu cluster deposited on the surface may retain its free cluster symmetry (I_h). Whereas, on originally bare Cu surface, the deposited Cu cluster lost its original symmetry completely and was recrystalized to have the same fcc structure as the substrate. The Ar-buffer dissipates most of the translational energy of the incident cluster. Therefore, it prevents the cluster from being overheated upon impinging. Furthermore, the interaction between Ar and Cu benefits the confinement of the cluster structure. Our study shows that with Ar-buffer layers, the lateral spread of deposited clusters is 20% smaller than that on the bare Cu surface. This is consistent with the experimental findings.     

Structural characterization and ferromagnetic behavior of Fe-doped TiO2 powder by high-energy ball milling

Fe-doped TiO₂ powder was prepared by high-energy ball milling, using TiO₂ Degussa P-25 and α-Fe powders as the starting materials. The structure and magnetic properties of the Fe-doped TiO₂ powder were studied by X-ray diffraction, ⁵⁷Fe Mossbauer spectroscopy and vibrating sample magnetometer. The Reitveld refinement of XRD revealed that ball milling not only triggered incorporation of Fe in TiO₂ lattice but also induced the phase transformation from anatase to rutile in TiO₂ and consequently the milled Fe-doped TiO₂ powder contained only rutile.⁵⁷Fe Mössbauer effect measure showed that Fe atoms existed in Fe²⁺ and Fe³⁺ state, which were assigned to the solid solution Fe_xTi_1−xO₂. The magnetization measurements indicated that the milled Fe-doped TiO₂ powder was ferromagnetic above room temperature. The ferromagnetism in our milled Fe-doped TiO₂ powder seemingly does not come from Fe and iron oxides particles/clusters but from the Fe-doped TiO₂ powder matrices.     

消息重复型ARINC429总线事件消息包机载实时处理技术研究

ARINC429总线广泛应用于民用飞机中,在飞行试验中,消息重复型ARINC429事件信息的实时监控占用很大的遥测带宽资源;采用机载嵌入式数据处理模块,通过将其嵌入到机载测试系统中,通过采集器底板总线获取ARINC429采集模块采集到的数据,对飞机事件信息进行解析处理,并将处理结果通过遥测系统遥测下传至地面监控中心,大大降低了遥测带宽需求,对于飞行试验实时安全监控有重要意义。     

基于磁偶极子构造法几何建模的铁管磁异常正演

地下铁磁性金属管线受地球原磁场磁化产生磁场会改变原地磁场分布,而形成地磁异常;通过管道几何建模和磁偶极子构造法对管道磁异常进行正演分析;首先利用近似的立方体单元对管道进行几何建模并输出相应的立方体单元体积和中心坐标;然后将立方体单元近似为磁偶极子,使用磁偶极子构造法进行管道磁异常正演;最后研究了距径比,磁倾角,磁偏角,地球场强,管道材料磁化率对管道磁异常正演的影响;研究结果表明:在6倍距径比外,同一球面上测点磁异常值接近一致, 且管道磁异常正演结果不受磁倾角,磁偏角和材料磁化率的影响;随着地磁场强度增大,管道磁异常呈线性增大;研究成果将为自主研发高精度磁异常地下管线探测设备奠定理论基础。     

The Design of Single Mode Large Cross-section Glass-based Waveguides for Photonic Integrated Circuits

This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices.     

Microwave synthesis of magnetic Fe3O4 nanoparticles used as a precursor of nanocomposites and ferrofluids

Methods to synthesize magnetic Fe₃O₄ nanoparticles and to modify the surface of particles are presented in the present investigation. Fe₃O₄ magnetic nanoparticles were prepared by the co-precipitation of Fe³⁺ and Fe²⁺, NH₃·H₂O was used as the precipitating agent to adjust the pH value, and the aging of Fe₃O₄ magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe₃O₄ magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe₃O₄ crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe₃O₄ magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe₃O₄ nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe₃O₄ nanoparticles. The dispersion of Fe₃O₄ in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe₃O₄/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe₃O₄ magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe₃O₄ nanoparticles. The Fe₃O₄ magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10⁻⁸ and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe₃O₄ nanoparticles in the fluid was 36.19 nm.