Multiple Superconducting Gaps, Anisotropic Spin Fluctuations and Spin-Orbit Coupling in Iron-Pnictides

This article reviews the NMR and NQR studies on iron-based high-temperature superconductors by the IOP/Okayama group. It was found that the electron pairs in the superconducting state are in the spin-singlet state with multiple fully-opened energy gaps. The antiferromagnetic spin fluctuations in the normal state are found to be closely correlated with the superconductivity. Also the antiferromagnetic spin fluctuations are anisotropic in the spin space, which is different from the case in copper oxide superconductors. This anisotropy originates from the spin-orbit coupling and is an important reflection of the multiple-bands nature of this new class of superconductors.Comment: 20 pages, 16 figure

Photonic quasicrystal nanopatterned silicon thin film for photovoltaic applications

In this paper, the authors numerically studied the optical properties of a silicon photonic quasicrystal (PQC) nanohole array for photovoltaic applications. With the same active layer thickness, the ultimate efficiency of a solar cell integrated with an optimized PQC nanohole array can be enhanced by 9.01% and 1.40% compared to that with an ordered square lattice of a nanohole array and a random nanohole array, respectively. The absorptance enhancement is mainly due to the higher-order rotational symmetry in PQC structures, which leads to the presence of additional resonant modes, the broadening of existing modes and the reduction of surface reflectance. The angular response for both transverse-electric and transverse-magnetic modes are also analyzed in detail

Bounded Integral Control of Input-to-State Practically Stable Non-linear Systems to Guarantee Closed-loop Stability

A fundamental problem in control systems theory is that stability is not always guaranteed for a closed-loop system even if the plant is open-loop stable. With the only knowledge of the input-to-state (practical) stability (ISpS) of the plant, in this note, a bounded integral controller (BIC) is proposed which generates a bounded control output independently from the plant parameters and states and guarantees closed-loop system stability in the sense of boundedness. When a given bound is required for the control output, an analytic selection of the BIC parameters is proposed and its performance is investigated using Lyapunov methods, extending the result for locally ISpS plant systems. Additionally, it is shown that the BIC can replace the traditional integral controller (IC) and guarantee asymptotic stability of the desired equilibrium point under certain conditions, with a guaranteed bound for the solution of the closed-loop system. Simulation results of a dc/dc buck-boost power converter system are provided to compare the BIC with the IC operation

Improved Synchronverters with Bounded Frequency and Voltage for Smart Grid Integration

Synchronverters are grid-friendly inverters that mimic conventional synchronous generators and play an important role in integrating different types of renewable energy sources, electric vehicles, energy storage systems, etc., to the smart grid. In this paper, an improved synchronverter is proposed to make sure that its frequency and voltage always stay within given ranges, while maintaining the function of the original synchronverter. Furthermore, the stability region characterised by the system parameters is analytically obtained, which guarantees that the improved synchronverter is always stable and converges to a unique equilibrium as long as the power exchanged at the terminal is kept within this area. Extensive OPAL-RT real-time simulation results are presented for the improved and the original self-synchronised synchronverters connected to a stiff grid and for the case when two improved synchronverters are connected to the same bus with one operating as a weak grid, to verify the theoretical development

Novel drug carriers: From grafted polymers to cross-linked vesicles

A simple and straightforward method of self-assembling grafted copolymers was developed to fabricate cross-linked polymer vesicles, which could conjugate anticancer drug cis-platinum and possess the capability of a high drug loading content, and a steady release rate