Mg gas infiltration for the fabrication of MgB2 pellets using nanosized and microsized B powders

MgB₂ superconductor pellets were synthesized through Mg gas infiltration method using nanosized- and microsized B powders. There was a marked difference in the superconducting properties of the two samples, particularly in the pinning force and dominant pinning mechanism. The microstructures of the samples were observed using HR-TEM and STEM-HAADF, and the results showed that the primary reason for the difference in the superconducting properties is the distribution of the nanosized second-phase particle MgO. Additionally, a feasible reaction model for the Mg gas infiltration method was established. Compared to the Mg liquid infiltration method, the gas infiltration showed better penetrability ability with a small amount of residual Mg. This study presents a novel synthesis process to fabricate an MgB₂ pellet with superior density and superconducting properties. This method can be used in multiple applications such as superconducting bearings, compact superconductor magnets, and magnetic shielding.     

Adaptive robust control of fully-constrained cable driven parallel robots

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.     

Elemental substitution at Tl-site of TlSr2CaCu2O7 superconductor: A review

This review is on the effects of elemental substitutions at the Tl-site of TlSr₂CaCu₂O₇ (Tl-1212) superconductor. The objective of this paper was to determine the elements that enhance or suppress the superconducting transition temperature, T_c of (Tl_1-xM_x)Sr₂CaCu₂O₇ phase. The elements included in this review were M = Pb, Bi, Cr, V, Re, Zr, In, Er, Gd, Na, K, Rb and Se. The relations between transition temperature and the ionic radius, coordination number, valence state and optimization of the hole concentration of the selected elements were studied. The preparation methods, sintering temperature, Tl-1212 phase and structural stability were also discussed. All alkali metals (K, Na and Rb) suppressed the transition temperature of the Tl-1212 phase. The transition temperature generally decreased linearly with ionic radius except for Cr which showed the highest T_c although its ionic radius is smaller.     

A novel fault detection method for VSC-HVDC transmission system of offshore wind farm

VSC-HVDC transmission system is going to become the most economical way of power delivery for large and remote offshore wind farms. An accurate and fast fault detection method is necessary to protect sensitive devices of these systems and maintain uninterrupted power delivery. This paper investigates an innovative technique for recognizing DC zone faults including HVDC cable faults and unbalancing of DC capacitor bank. Sheath voltage is presented as a novel criterion for detecting abnormal situations in the system. Transient voltage of cable sheath and Wavelet transform are used to identify different types of DC faults. Extensive simulation examples are performed on EMTDC–PSCAD platform and post-processed using MATLAB. The results illustrate that the proposed technique gives a robust performance and can be applied to protection scheme of offshore wind farms.     

A novel quasi-oppositional harmony search algorithm and fuzzy logic controller for frequency stabilization of an isolated hybrid power system

The intermittent wind power in isolated hybrid distributed generation (IHDG) may cause serious problems associated with frequency (f) and power (P) fluctuation. Energy storage devices such as battery, super capacitor, and superconducting magnetic energy storage (SMES) may be used to reduce these fluctuations associated with f and P. This paper presents a study of IHDG power system for improving both f and P deviation profiles with the help of SMES. The studied IHDG power system is consisted of wind turbine generator and diesel engine generator. Both f and P control problems of the studied power system model are addressed in presence or absence of SMES. Fuzzy logic based proportional–integral–derivative (PID) controller with SMES is used for the purpose of minimization of f and P deviations. The different tunable parameters of the PID controller and those of the SMES are tuned by a novel quasi-oppositional harmony search algorithm. Performance study of the IHDG power system model is carried out under different perturbation conditions. The results demonstrate minimum f and P deviations may be achieved by using the proposed fuzzy logic based PID controller along with SMES.     

Aspects of parallel wire cable reliability

Recently developed models for the assessment of the strength and fatigue life of cables are presented and illustrated. The illustrations are based on experimental data and experience gained from the design and assessment of several major cable supported bridges. It is shown how inspection results may be used to update the reliability of cables. The procedure is illustrated using results of Ultra Sonic inspections. Finally, aspects of design and assessment of stay cables are considered. Special emphasis is given to the effect of design philosophy and corrosion protection on the resistance factors for the stay cable resistance.     

电缆实体火灾模拟实验与电缆的选用

介绍了电缆（支架明敷、支架穿管明敷、防火桥架内敷设、防火桥架内穿管敷设、穿管埋墙暗敷5种电缆敷设方式）实体火灾模拟实验的结果，分析了不同类型的电缆的选用。鉴于矿物绝缘电缆良好的耐火性能。推荐使用。     

浅谈高强钢绞线——聚合物砂浆加固技术

高强钢绞线-聚合物砂浆加固技术是由韩国开发的一种较新的加固技术,与传统的加固技术相比有其显著的优越性.     

考虑拉索拉力增量时多跨拉索的固有横振

往考虑由振动引起的拉索拉力增量基础上,把具有中间支承的多跨拉索转化为在多个集中荷载作用下单跨拉索的强迫振动,然后采用 Laplace 变换求得了多跨连续拉索固有振动的解析解,讨论分析了拉索拉力增量对多跨连续拉索固有振动频率的影响。     

南京火车站钢屋盖斜拉索张拉的优化和调整

南京火车站主站房预应力钢屋盖采用桅杆斜拉索悬挂钢结构型式。本文通过拉索张拉分析,掌握结构特点和拉索索力相互影响程度,优化张拉方案,简便施工,并根据工程实际需要,调整张拉方案。