Multifilament niobium-tin conductors

A new Nb3Sn wire fabrication method has been developed, improving wire drawing workability and superconducting properties, such as stability and ac losses. A cross section of the single filament wire consists of a niobium tube with a copper sheathed tin rod inside and high conductivity copper tube outside. These constituents show scarcely any workhardening. Wires with 54 to 295 filaments were drawn down to 0.2 mm to 1.0 mm diameter. Heat-treatment conditions to obtain the highest critical current were clarified as a function of the tin content inside the niobium tube. The effect of bend strain in Nb3Sn on the critical current was also examined for samples with different wire diameters and Nb3Sn layer thickness. Losses were measured for twisted and non-twisted samples by means of magnetization experiments. Results were compared with calculated values. It was found that the effective resistivity between Nb3Sn filaments was one order of magnitude higher than that of pure copper. A coil was constructed using a 1 km long Nb3Sn composite having 258 filaments with 1 × 2 mm cross section. The maximum field obtained was 10.65T at 236A in the 6T backing field by NbTi solenoid.     

Heat transfer from plates to conductors: from toroidal field model coil tests analysis to ITER model

During a safety discharge of toroidal field type magnets, eddy currents and associated heat generation are induced in the plates. A model has been developed from the thermohydraulic code Gandalf with introduction of the equations of the heat diffusion from plates to conductors through the steel and insulation. The comparison of calculation and experimental results for the ITER toroidal field model coil is presented.Preliminary analysis for the ITER toroidal field coils is also presented, taking into account the conductor parameters, the magnetic field and the external hydraulic circuit. The possible quench of the magnetic system is discussed.     

Analysis of a fork-shaped rectangular coil facing moving sheet conductors

The electromagnetic induction method utilising eddy current plays an important role in a non-destructive material test. In testing slab-type material by electromotive force method, there is the fork-shaped coil method, which has two coils placed on both sides of the test piece. In most studies, circular coils have been analysed. However, it has been pointed out quantitatively that a rectangular coil is more useful than a circular coil for a non-destructive test. The authors derive a rigid theoretical formula with a test theory experiment.     

Image reconstruction of buried multiple conductors by genetic algorithms

This paper presents an inverse scattering problem for recovering the shapes of multiple conducting cylinders with the immersed targets in a half‐space by genetic algorithm. Two separate perfectly conducting cylinders of unknown shapes are buried in one half‐space and illuminated by transverse magnetic (TM) plane wave from the other half‐space. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations are derived, and the electromagnetic imaging problem is reformulated into an optimization problem. The improved steady state genetic algorithm is used to find out the global extreme solution. Numerical results are given to demonstrate the performance of the inverse algorithm. Good reconstruction can be obtained even when the initial guesses are far different from the exact shapes, and then the multiple scattered fields between two conductors are serious. In addition, the effect of Gaussian noise on the reconstruction is investigated. We can find that the effect of noise is negligible for the normalized standard deviations below 0.01. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 18, 276–281, 2008; Published online in Wiley InterScience (www.interscience.wiley.com).     

多跨覆冰导线脱冰振动模型风洞试验研究

覆冰导线脱冰可能造成金具、导线和杆塔等构件受力破坏,也可能会引起导线闪络、烧断等电力事故。设计了1∶50的三跨覆冰导线的缩尺模型,采用熔断集中荷载的方法模拟导线脱冰,共七种工况研究三跨导线中脱冰量、脱冰跨位置、覆冰厚度和风速等参数不同时,导线的冰跳高度、导线张力和绝缘子轴力变化规律。结果表明:边跨脱冰将引起比中间跨脱冰更大的竖向振动,跳跃高度增大了近7%,导线张力也有明显增大;在风荷载作用时,导线脱冰振动会受气动阻尼影响,跳跃高度和振动周期都有所减小,导线张力和悬垂绝缘子的轴力随着风荷载增大而增大。     

4分裂导线风洞试验中跨度折减法的适用性研究

跨度折减法通过系数γ缩小导线的跨度,在输电塔线系统风洞试验中应用广泛,但其对4分裂导线的适用性尚未澄清。基于4分裂导线气弹模型风洞试验,对比研究了不同跨度折减系数的两模型与正常缩尺模型的气动力和功率谱特性,并进一步探讨了湍流度和风向的影响。结果表明:导线风振响应中含有高阶振型,且气动力的平均值和脉动值随风速的增加均呈现非线性增大的趋势。湍流会增大导线气动力的平均值和脉动值,增大跨度折减模型与正常缩尺模型气动力均值间的差异。斜风会导致导线两端的气动力产生差异,且张力均值间的差异要显著高于阻力均值间的差异。对于γ为0.8的模型,除脉动量要略高于正常缩尺模型外,其他气动力特性均与正常缩尺模型保持了良好的一致性;但γ为0.5时的模型气动力特性均与正常缩尺模型存在较大差距。建议涉及4分裂导线的风洞试验,可采用γ为0.8左右的跨度折减,不建议采用较小的折减系数。     

High-throughput nuclear magnetic resonance analysis using a multiple coil flow probe

An automated method for high-throughput nuclear magnetic resonance (NMR) spectroscopy has been developed using a four-coil Multiplex NMR probe. The probe is constructed with solenoidal microcoils optimized for detection of small volume, mass-limited samples and a flow-through design. Four samples can be simultaneously injected into the Multiplex probe with a robotics liquid handler and then analyzed in rapid succession using a selective excitation experiment. Due to the simultaneous injection of four samples and the reduced analysis time with rapid selective excitation, the analysis rate achieved thus far is as low as 1 sample/34 s for 1D 1H NMR.     

Planning constant-stress accelerated life tests with multiple stresses based on D-optimal design

With the rapid technological advances, products are becoming more reliable. Then, multistress accelerated life testing (MALT) has been adopted in engineering to obtain failure information in a limited time. In order to make the testing procedure more efficient, it is necessary to better design the test plan. However, to date, relevant research on planning of MALT is limited. Multiple stresses will lead to plenty of stress-level combinations that require too much cost and time to implement. Besides, there may be interactions among multiple stresses, which need more experiments for parameter estimation. To solve these problems, we propose a novel planning method for constant-stress MALT under lognormal distribution using D-optimal design, which can reduce required test points efficiently and deal with second-order effects in models. In ALT, the log-linear model is often used to describe the life-stress relationship. Hence, D-optimal design is adopted in this paper to select test points from the whole test region. Then, optimal unit allocation plans are formulated under V/D-optimality criterion, respectively, where type I and type II censoring are both discussed. A real case of light-emitting device (LED) is presented to compare the proposed approach with other two existing methods. The results show that the proposed method performs better than other two existing methods both in prediction accuracy and estimation precision. Moreover, a sensitivity analysis reveals the robustness of the optimal plans determined by the proposed method.     

New fluorine ion conductors with tysonite-type structure

New fluorine fast ion conductors with tysonite-type structure have been obtained within the BiF₃1bBF₂ (B = Ba, Pb) systems: Bi_1?yBa_yF_3?y (0.05 ? y ? 0.17) and Bi_1?yPb_yF_3?y (0.075 ? y ? 0.175). The good electrical performances due to high polarizability cations set them among the best so far known fast anion conductors. Correlations between transport properties and structural data have been established.     

A new procedure of statistical approach characterization of ceramic filament fracture strength by bending tests

A procedure of ceramic filaments characterization has been proposed on the base of bending tests performed on continuous filaments. Using a specific bending device, fracture strength σ^R and Weibull modulus m related to commonly used tensile test procedure, can be derived from bending results thanks to a simple relation depending on the related Weibull’s modulus. The proposed new procedure is very rapid to perform and allows easy ceramic filaments acceptance testing in industrial contexts. The procedure has been validated by comparing fracture results obtained with the new procedure with those resulting from tensile tests.     

Mesoscopic transport of InAs-based conductors with superconducting electrodes

We summarize recent experimental results on transport of diffusive and ballistic InAs-based (2-dimensional electron gas) submicron sized conductors connected to superconducting niobium contacts. Both ensemble-averaged and sample-specific transport is shown to depend on the difference in the superconducting phases tuned by a magnetic field. The ballistic case can be understood using a simple model based on phase-conjugated trajectories. The results summarized here are based on research done with S.G. den Hartog, P.H.C. Magnée, A.F.Morpurgo, and B.J. van Wees. C.M.A.Kapteyn and S.Holl contributed as ERASMUS students. InAs heterostructures were provided by G.Borghs from IMEC, Leuven.     

Problems with conductors and dielectrics for cryogenic cables

The most important problems which need to be solved if superconducting power cables are to be used on a large scale are connected with the superconducting cable materials and the dielectrics used for insulation.Research work on superconducting materials for ac and dc cables is briefly reviewed together with stabilization problems for these materials. Three types of insulation are considered - vacuum, subcooled or supercritical helium, and foil wound insulation. The merits and problems encountered in each case are discussed.     

Silver nanowires with semiconducting ligands for low-temperature transparent conductors

Metal nanowire networks represent a promising candidate for the rapid fabrication of transparent electrodes with high transmission and low sheet-resistance values at very low deposition temperatures. A commonly encountered challenge in the formation of conductive nanowire electrodes is establishing high-quality electronic contact between nanowires to facilitate long-range current transport through the network. A new system involving nanowire ligand removal and replacement with a semiconducting sol-gel tin oxide matrix has enabled the fabrication of high-performance transparent electrodes at dramatically reduced temperatures with minimal need for post-deposition treatment.

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复合材料纤维张力缠绕预应力场动态特性

复合材料纤维张力缠绕技术通过提高纤维的张力水平可充分发挥纤维高强、高模优势,在成型过程中对结构进行预紧,成为解决高速转动部件径向变形大、界面强度低等问题新的有效途径。将每一层纤维的张力缠绕等效为一个含预应力复合材料薄环的叠加,基于正交各向异性复合材料缠绕层和各向同性金属芯模弹性变形理论,建立了纤维张力缠绕力学解析模型,得到芯模和缠绕层预应力场随缠绕层数及缠绕张力的变化规律,并通过复合材料纤维张力工艺试验验证了力学解析模型的正确性。研究发现了纤维张力缠绕中预应力“饱和”现象,并确定了影响张力缠绕预应力场的两个主要参数:缠绕层环径向刚度比E_θ/E_r和张力大小T（r）,为复合材料纤维张力缠绕成型工艺提供理论支撑。      

Conditional exact tests for Markovianity and reversibility in multiple categorical sequences

We propose conditional exact tests based on sufficient statistics to compare exchangeability, Markov exchangeability, and Markov exchangeability of the reversible type, when data consist of several sequences of categorical data. As particular cases, we can compare three classes of mixture models (mixtures of i.i.d. sequences, mixtures of Markov chains and of reversible Markov chains) and we can test Markovianity and reversibility of a single sequence.     

Small-Sized Hybrid Magnet with Pulsed Field Magnetization

Small-sized hybrid magnet (HM) operated in liquid nitrogen was constructed. It consists of two superconducting Y-Ba-Cu-O annuli, placed on soft magnetic cores made of permenduire. The magnetization of the superconducting annuli was realized by a pulsed method using two copper coils installed near the annuli. The trapped field value of 2.2 T with the radial (r ≈ 5 mm) homogeneity of 0.1 % can be achieved in the gap of 2 mm between magnetic cores. The magnetization procedure and time evolution of the trapped field are also discussed. The magnets of similar type are promising for application in compact electron spin resonance (ESR) spectrometers.     

The mechanical properties and microstructures of copper and brass joints soldered with eutectic tin-bismuth solder

The mechanical properties and microstructures ofcopper and brass soldered with eutectic tin-bismuth solder have been determined and the joints examined using metallographic techniques. Joints made with copper were stronger than those made with brass. At the copper/solder interface a uniform layer 2m thick of Cu_5.2Sn₅ was formed and at the brass/solder interface a uniform layer 2 m thick of (Cu, Zn)_2.9Sn and an irregular layer 2 to 5m thick of (Cu, Zn)_5.7Sn₅ were formed. Copper joints fractured etthocopper/solder interface and brass joints fractured in the internmetalic layer. Copper joints soldered with eutectic Sn-Bi were stronger than copper joints soldered with eutectic Sn-Pb and the reverse was true for brass joints. Results are also given for the effect of thermal shock on copper and brass joints soldered with Sn-Bi and Sn-Pb solders, and also for We fatigue and creep behaviour of joints soldered with eutectic Sn-Bi solder.