[en] Aligned YBa₂Cu₃O_7-δ ceramics have been obtained using a field of 1 T without being embedded in epoxy. Thermopower, XRD, and SEM are used to characterize the aligned ceramics. For the sample with δ=0.05, the thermopower exhibits a strong anisotropy. The ab-plane thermopower behaves distinctly from that along the c-axis. The ab-plane thermopower shows remarkable similarities to that along the b-axis in an untwinned single crystal. The magnitude and temperature dependence of the c-axis thermopower are almost identical to those of a twinned single crystal. For samples with larger oxygen deficiency, the anisotropy remains. These measurements indicate that these ceramics are well aligned along their crystallographic directions. This also makes available the anisotropic thermopower measurements of ceramic samples by aligning polycrystallites using magnetic forces

[en] We report measurements of resistance and thermopower of RE_1.2Sr_1.8Mn₂O_7+δ (RE=Nd, Pr) ceramics up to a magnetic field of 5 T. Nitrogen annealing has dramatic effects on the transport in reducing the resistivity, shifting peak resistivity to a higher temperature, and shifting thermopower to more negative values. The value of Δ_JT increases as a result of nitrogen annealing, indicating an enhanced Jahn-Teller distortion due to the increased Mn³⁺ concentration. These results are consistent with the effects of nitrogen annealing on the transport of RE=La

[en] By law of conservation of parity we show that Dirac equation in an electromagnetic field can be split up into two uncoupled two-component equations. As a result, we shall find twice as many as the conventional solutions. For free particles four linearly independent plane wave solutions which hold for E > 0 and also for E < 0 can be established. In a Coulomb field we shall easily find the stationary solutions.

[en] Inequivalent invariance constraints upon solutions for Dirac spin-(1/2) particles under conservation of space inversion, time reversal, and charge conjugation have been established, respectively, from standard representation. For space inversion we explicitly show that the wave functions for zero mass neutrinos satisfy only one constraint. For free particles we show that the conventional plane wave solutions as well as Foldy-Wouthuysen representation conditionally comply with the inversion constraints. As a result, only two positive energy solutions and two negative energy solutions can be established. Instead, by law of conservation of parity one shall obtain four linearly independent plane wave solutions which hold not only for positive energies but also for negative energies. We explicitly point out why conventional approach fails to obtain such result. In contrast with free particles one expects intuitively that in a Coulomb field, one can establish twice as many as conventional solutions. Indeed, one shall find easily from inversion constraints that additional linearly independent degenerate bound states have to be established. We present the explicit result.

[en] In order to meet the need of development of integrative flexible joint, this paper presents a higher precision measuring system for angular stiffness test of integrative flexible joint. The main parts of the system include PC, precision motorized goniometric stage, precision motorized rotary stage and high accuracy torque sensor. The measuring and control program is developed on the platform of LabVIEW. The measuring system developed has angular resolution at 0.00032 deg. (about 1'') theoretically in determining the angular displacement of the joint round its equatorial axis and torque accuracy at 0.005 mN · m. The developed program, which presents a friendly GUI, can implement the data acquisition and processing, measuring procedure automatically. In comparison with other measuring devices with similar purposes, the measuring device can improve the measuring efficiency and accuracy distinctly while has advantages of simple configuration, low cost and high stability

[en] Based on visual measurement techniques, the real-time robotic welding tracking system achieves real-time adjustment for robotic welding according to the position and shape changes of a workpiece. In system design, the sensor design technique is so important that its performance directly affects the precision and stability of the tracking system. Through initiative visual measurement technology, a camera unit for real-time sampling is built with multiple-strip structured light and a high-performance CMOS image sensor including 1.3 million pixels; to realize real-time data process and transmission, an image process unit is built with FPGA and DSP. Experiments show that the precision of this sensor reaches 0.3mm, and band rate comes up to 10Mbps, which effectively improves robot welding quality.With the development of advanced manufacturing technology, it becomes an inexorable trend to realize the automatic, flexible and intelligent welding product manufacture. With the advantage of interchangeability and reliability, robotic welding can boost productivity, improve work condition, stabilize and guarantee weld quality, and realize welding automation of the short run products [1]. At present, robotic welding has already become the application trend of automatic welding technology. Traditional welding robots are play-back ones, which cannot adapt environment and weld distortion. Especially in the more and more extensive arc-welding course, the deficiency and limitation of play-back welding technology becomes more prominent because of changeable welding condition. It becomes one of the key technology influencing the development of modern robotic welding technology to eliminate or decrease uncertain influence on quality of welding such as changing welding condition etc [2]. Based on visual measuring principle, this text adopts active visual measuring technology, cooperated with high-speed image process and transmission technology to structure a tracking sensor, to realize real-time measurement of the space location and posture information of the work piece and reliable and accurate tracking of the welding seam

[en] Epoxy resin is often used as raw material of anticorrosion, but in the curing process of resin, a large number of micropores are prepared in the solvent evaporation method, which reduces the performance of anticorrosion. In order to reduce internal defects and improve corrosion resistance, GO was compounded with SiO₂ modified by KH550 to prepare for GO-SiO₂. By means of mechanical stirring and ultrasonic dispersion, GO-SiO₂ was added to epoxy resin to prepare for the anticorrosive coating. SEM was used to observe the coating morphology, and the physical and electrochemical properties of the coatings with different mass fractions of GO-SiO₂ are tested for corrosion resistance. The results show that 3 wt% GO-SiO₂ coating shows the best performance, the coating hardness reaches H, the adhesion grade is II. (paper)

[en] We report fabrication of the c-axis oriented Ca₃Co_3.95Fe_0.05O_9+δ films by a simple sol-gel spin coating method. The films prepared in the temperature range of 650-700 deg. C show nonmetallic temperature dependence of resistivity in the whole investigated temperature range, whereas the films prepared in the temperature range of 750-775 deg. C show metallic temperature dependence in the high temperature regime. Sintering the films at higher temperature leads to larger grains, lower resistivity and smaller thermoelectric power. This can be explained in the framework of the barrier theory and confirmed by the higher hole carrier concentration from the Hall measurements according to Seto's derivation between the carrier concentration and the barrier height. The temperature dependence of resistivity resembles that of the in-plane single crystal of Ca₃Co₄O_9+δ in terms of the Fermi-liquid behavior. The effects of lower sintering temperature on the transport coefficient A and Fermi-liquid scale T* of Fe-substituted cobaltite films seems to be similar to applying hydrostatic pressure on a single crystal of Ca₃Co₄O_9+δ. The temperature dependence of resistivity in the nonmetallic region follows the variable-range hopping conduction in the form of T^-1/3, due to the 2-dimensional character of the films

[en] In the study, ZrO_x films were deposited on substrates by the sol-gel technique. X-ray photoelectron spectroscopy, x-ray diffraction, photoluminescence and conductivity measurements were used to characterize the films. The authors found that the displacement current of oxygen-rich ZrO_x films was smaller than that of oxygen-deficient ZrO_x films. According to the experimental results, the authors suggested that donor-like oxygen-vacancy related and crystallographic defects within the ZrO_x film controlled carrier flow and resulted in hysteresis-type current-voltage characteristics of indium tin oxide/ZrO_x/Au devices.

[en] By deintercalation of Na⁺ followed by inserting bilayers of water molecules into the host lattice, the layered cobalt oxide of γ-Na_0.7CoO₂ undergoes a topotactic transformation to a layered cobalt oxyhydrate of Na_0.35(H₂O)_1.3CoO_2-δ with the c-axis expanded from c ∼ 10.9 A to c ∼ 19.6 A. In this paper, we demonstrate that the superconducting phase of c ∼ 19.6 A can be directly obtained by simply immersing γ-Na_0.7CoO₂ powders in electrolyzed/oxidized (EO) water, which is readily available from a commercial electrolyzed water generator. We found that high oxidation-reduction potential of EO water drives the oxidation of the cobalt ions accompanying by the formation of the superconductive c ∼ 19.6 A phase. Our results demonstrate how EO water can be used to oxidize the cobalt ions and hence form superconducting cobalt oxyhydrates in a clean and simple way and may provide an economic and environment-friendly route to oxidize the transition metal of complex metal oxides