N.m.r. study of the ferroelectric phase transition in a 7030mol% copolymer of vinylidene fluoride (VF2) and trifluoroethylene (TrFE)

Nuclear magnetic resonance (n.m.r.) studies of ¹⁹F nuclei in a $\text{70}\text{30}\text{mol}\text{\%}$ random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T₂ components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T₁ appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T₁ were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals.     

应用10mm薄板铸锭制备的NdFeB烧结磁体

NdFeB薄板铸锭具有晶粒细，富钕相分布均匀及在稀土含量较低时可以防止α－Fe相出现的特点，是一种适合制备高性能烧磁体的合金铸锭，本文介绍了一种用10mm薄板铸锭和球磨制粉方法制备烧结磁体的工艺，在设备要求较低的情况下制备得到了Br=1.37T,(BH)max=320kJ/m^3(40MGOe)的烧结磁体，同时比较了使用常规铸锭和常规工艺的结果，强调了氢爆法在该工艺中的重要作用，最后对该工艺的改进方向和10mm铸锭的应用前景进行了阐述。     

二维加速度激光传感器的设计

以角锥棱镜作为惯性元件,利用光学干涉原理,可以实现对运动物体的二维加速度测量。本文给出了二维加速度激光传感器的设计理论和测量原理。     

Development of a Sensor Fusion Strategy for Robotic Application Based on Geometric Optimization

Fusion of multi-sensor information is an important technology, which is growing exponentially due to its tremendous application potential in many areas. Effective fusion of data from sensors is very critical in increasing an intelligent system's capability to accomplish complex tasks. Appropriate fusion technologies are needed to be developed specially when a system requires redundant sensors to be used. More the redundancy in sensors, more is the computational complexity for controlling the system and more is its intelligence level. This research presents a strategy developed for multiple sensor fusion, based on geometric optimization. Each sensor's uncertainty has been modeled using classical Lagrangian optimization techniques. However, the uniqueness and effectiveness of the present technique lies on the fact that starting from the optimized value as initial estimate the accuracy of the sensory information has further been improved up to any pre defined bounded range, by developing two architectures – FFA (fission–fusion architecture) and FDD (fusion in differential domain). Sufficient evidences and analyses have been provided in the paper to show its effectiveness in various applications.     

Magnetic separations in biotechnology—a review

Magnetic separation technology has a broad range of potential applications in both small and large scale biotechnology. This review considers a selection of magnetic techniques and their possible uses.     

非晶软磁合金的巨磁阻抗效应及应用

近来在ＦｅＣｏＳｉＢ等Ｃｏ基非晶体丝带中现了巨磁阻抗效应，由于在一小的直流纵向偏置场下该效应能使丝带两端的交流电压发生大而灵敏的变化，因而在磁记录头和传顺技术中具有巨大的应用科学潜能，受到各国学者的关注，本文简单介绍了巨磁阻抗效应的来源，并综述了近年来非晶体软磁合金材料的的巨磁阻抗效应及应用的研究进展，文章最后说明了尚待深入解决的问题。     

压阻式压力传感器及其应用电路设计

介绍了压阻式传感器的工作原理以及相关应用电路，并给出了一个应用示例加以说明。     

Magnetic field hysteresis of critical currents in Bi(2223)/Ag tapes and a way to overcome it

Experiments showing hysteresis of critical currents versus the external magnetic field I_c(B_e) were performed with two multifilamentary Bi(2223)/Ag tapes. The I_c(B_e) hysteresis is observable in the transversal as well as in the longitudinal orientation of the long axis of the tape with respect to the magnetic field. Based on the idea that the hysteresis is the effect of trapped flux in a network of well-connected current paths, a way to overcome this effect has been proposed and experimentally verified. The induced frozen-in screening currents are split into several parallel current patterns by cycling the external magnetic field around the adjusted value. Using the proposed method, the ‘neutral’ I_c(B_e) characteristics have been found. Approximate calculations of the penetration depth of the trapped flux show that the network of well-connected current paths could be formed by several disk-shaped grains (≈ Φ8 × 0.4 μ) stacked into more or less axially ordered (quasi cylindrical) colonies of average dimensions estimated to ≈ Φ8 × 4 μm.     

Recent developments of high-performance NEOMAX magnets

For further improvement in achieving extremely high magnetic properties of Nd- Fe- B sintered magnets, extensive investigation has been done to densify the magnet up to the theoretical value, to increase the volume fraction of the Nd ₂Fe₁₄B matrix phase, and to achieve a high degree of alignment. By controlling chemical composition and the amount of constituent phases,improving particle size distribution, and adopting the isostatic pressing method to get better alignment of fine particles, we have succeeded in obtaining a high-performance magnet having residual flux density (B_r) of 1.495 T (14.95 kG), maximum energy product [(BH)_max] of 431 kj/m³ (54.2 MGOe), and intrinsic coercivity (iH_c) of 845 kA/m (10.62 kOe).