Cu chemistry of YBa2Cu3O6+x investigated by nuclear quadrupole resonance

The nuclear quadrupole resonance (NQR) technique has been utilized to characterize the local oxygen coordination of inequivalent Cu sites in YBa₂Cu₃O_6+x(0 ≤ x ≤ 0.91). Essentially, four distinct NQR lines which correspond to 2, 3,4 oxygen coordinated Cu sites in the Cu-O chains and 5 oxygen coordinated Cu sites in the Cu-O planes have been observed. The zero-field NQR frequencies of these are centered at about 30.1, 24.0, 22.0 and 31.5 MHz for ⁶³Cu, respectively. For the antiferromagnetic ordered state (x ≤ 0.3), antiferromagnetic nuclear resonance (AFNR) has been observed at 90 MHz with quadrupole splittings associated with the moment-bearing Cu sites in the Cu-O planes. The relative intensities of these resonance lines depend on the oxygen content, and this gives us a microscopic understanding of the Cu chemistry of this system.     

Diffuse scattering of modulated structures and quasicrystals

The method of Fourier transforms is applied to the calculation of sharp (coherent) and diffuse (incoherent) scattering of modulated structures and quasicrystals. It is shown that the fundamental difference between both may best be described by introducing different distribution functions of atoms, before applying modulations of the structure.     

A new experimental technique for measuring the local birefringence and molecular orientation in liquid crystals

A new experimental technique is described for the measurement of local birefringence and molecular orientation in liquid crystals. This technique consists in analyzing the local channeled spectra obtained by optical polarising microscopy.     

Development of superconducting power devices in Europe

Europe celebrated last year (2008) the 100-year anniversary of the first liquefaction of helium by H. Kammerling Onnes in Leiden. It led to the discovery of superconductivity in 1911. Europe is still active in the development of superconducting (SC) devices. The discovery of high critical temperature materials in 1986, again in Europe, has opened a lot of opportunities for SC devices by broking the 4 K cryogenic bottleneck.     

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利用毕奥萨伐尔定律,通过对EAST内部等离子体电流的运动状态的研究,建立了EAST内部的磁场数学模型,并利用Matlab对实验数据的拟合分析,对模型进行了分析验证.通过误差分析,进而改进模型,研究表明改进后的模型与实验数据能较好吻合,误差较小.相关研究和结论对托卡马克真空室内磁场测量具有一定的指导意义,为进一步研究基于MEMS技术的超导托卡马克装置电磁测量诊断系统的微纳磁敏传感器奠定理论基础.     

使用改进的形状优化方法设计高均匀度的超导MRI磁体

针对设计带铁磁的超导磁共振成像磁体,提出了一种确定类的优化算法来优化极靴的形状以达到匀场的目的。这种方法集合了灵敏度分析、形状优化的理论和有限元方法计算非线性铁磁材料极靴的配置,来改善两个极靴之间大体积成像区的磁场均匀度。需要指出的是,本优化方法不受极靴初始形状的限制,均可以快速收敛。我们通过一个紧凑型的1.2T双平面磁共振磁体,展示了这种方法。     

电力安全与超导磁储能系统

随着我国大规模电力系统的逐步形成，电网的安全稳定问题日渐突出，保证电力系统的安全稳定运行已经成为电网发展和运行的重要任务．超导磁储能系统以其对系统功率需求的快速响应特性可以为提高电力系统的稳定性提供新的技术途径，同时对改善电能质量、提高可靠性也有很好的技术优势．本文在简要论证电力安全的重要性的基础上，对SMES提高系统的安全稳定性的优越性进行了分析，并介绍了国家863计划项目“高温超导磁储能系统”的工作进展．     

MO analysis of macroscopic supercurrent flow in MgB 2

We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB₂. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis. A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration, at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a network of strongly coupled Josephson junctions. Received 31 May 2001 and Received in final form 5 December 2001     

超导电流密度研究

由 GL超导波函数及 GL第二方程导出了零场下超导电流密度矢量的数学表达式 ,讨论了相关物理意义 ;并由 London第二方程验证了其正确性。     

Multi-qubit controlled-NOT gates and Greenberger–Horne–Zeilinger state generation using one qubit simultaneously controlling n qubits

Based on superconducting flux qubits coupled to a superconducting resonator. We propose a scheme for implementing multi-qubit controlled-NOT (C-NOT) gates and Greenberger–Horne–Zeilinger (GHZ) state with one flux qubit simultaneously controlling on n qubits. It is shown that the resonator mode is initially in the vacuum state, a high fidelity for operation procedure can be obtained. In addition, the gate operation time is independent of the number of the qubits, and can be controlled by adjusting detuning and coupling strengths. We also analyze the experimental feasibility that the conditions of the large detuning can be achieved by adjusting frequencies of the resonator and pulses.