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The safety of converters is key to the stable operation of AC/DC hybrid power grids after AC faults. Thyristor valve current is a direct manifestation of the converter observability, but there are no measuring elements inside the converter, so the thyristor valve current can be reflected only indirectly through external electrical quantities. This paper proposes a virtual measurement scheme based on the temporal features of the converter terminal current. First, under the action of the trigger pulse, the polarity characteristics of the AC current and temporal features between the valves are utilized to predictively estimate the valve state. Then, when the bypass paths form, the conduction state of valve is constructed based on the relationship between AC and DC current. Last, when the valve is to be shut-off in the bypass path, the blocking state of the valve is corrected based on the unidirectional conductance characteristics of the valve. According to the above analysis, combined with the topological current equation of the converter, the valve current can be calculated in the whole process. Through the simulation of the different valve states and different bypass paths and analysis of the field record data, the validity of the scheme proposed is verified.

Two methods of TiO₂ addition were applied to prepare hydroxyapatite/TiO₂ (HA/TiO₂) composite, i.e., in-situ hydrolysis TiO₂ in HA powders (N-HA/TiO₂) and mixing commercial nano-sized HA and TiO₂ powder (C-HA/TiO₂). Effects of TiO₂ addition methods and sintering temperatures on phase, microstructure and microhardness were investigated for pressureless sintered HA/TiO₂ composites, and pure HA was investigated for comparison. Results show that TiO₂ from both in-situ hydrolysis and mixing commercial powder presented similar effects on phase structures and composition, and trended to chemically react with HA in the HA/TiO₂ composites at high sintering temperature. Weight loss for different composites was investigated by thermal analysis. Sintering behavior for two different composite was also discussed. The TiO₂ from in-situ hydrolysis can effectively enhance the TiO₂ distribution and densification for the N-HA/TiO₂ composites. Both two different composites showed typical grain growth and pore formation with the increase of sintering temperature. The N-HA/TiO₂ composite had a lower porosity, higher shrinkage and microhardness than that of C-HA/TiO₂ composite at sintering temperature from 700 °C to 1100 °C.

Many-objective optimization problems take challenges to multi-objective evolutionary algorithms. A number of nondominated solutions in population cause a difficult selection towards the Pareto front. To tackle this issue, a series of indicatorbased multi-objective evolutionary algorithms (MOEAs) have been proposed to guide the evolution progress and shown promising performance. This paper proposes an indicator-based manyobjective evolutionary algorithm called e-indicator-based shuffled frog leaping algorithm (e-MaOSFLA), which adopts the shuffled frog leaping algorithm as an evolutionary strategy and a simple and effective e-indicator as a fitness assignment scheme to press the population towards the Pareto front. Compared with four stateof-the-art MOEAs on several standard test problems with up to 50 objectives, the experimental results show that e-MaOSFLA outperforms the competitors.

The application of power electronics can introduce flexibility into power systems, but it can also cause harmonic problems. As a typical application of power electronics, high-voltage direct current (HVDC) transmission exhibits very prominent harmonic problems. In recent years, many HVDC protection maloperation events caused by harmonic problems have occurred in the field. The phenomena of harmonic transfer and amplification in HVDC transmission have an undeniable impact on the overall operation of a power system. Previous studies of these phenomena have relied mainly on detailed electromagnetic transient simulations. However, these simulations normally suffer from a large computational burden and low efficiency due to the complexity of the models and the small simulation time steps used. Therefore, an efficient analysis model of harmonics for various HVDC operating modes is presented in this paper. This model is based on port theory; every part of the HVDC transmission system is represented by an equivalent two-port component to construct a unified equivalent circuit. The proposed model is simple to calculate, and only the connections of the two-port components need to be changed to model different operation modes. The proposed two-port model is applied for the harmonic analysis of an HVDC transmission system, and the validity and accuracy of the model are confirmed by detailed electromagnetic simulations. Moreover, the model can be easily applied to HVDC systems for harmonic transfer and amplification, and the effects of the HVDC transmission power and smoothing reactor on harmonic transfer and amplification are analyzed.

Aimed at the security authentication problem between Near Field Communication (NFC) devices, this paper uses the technology of asymmetric encryption algorithm, symmetric encryption algorithm, hash function, timestamp and survival period to improve the confidentiality, performance and security of the protocol. The symmetric encryption algorithm encrypts the transmission content, while the asymmetric encryption algorithm encrypts the shared key. The whole authentication process is secure, and the key distribution is secure. The improved NFC device authentication protocol can effectively resist the brute force attack, man-in-the-middle attack and replay attack in the authentication process, it can reduce the number of message transmission in the authentication process, improve the transmission efficiency, enhance the confidentiality, integrity, non-repudiation and improve the security of NFC device authentication.

In order to eliminate the calculation error which is generated by the field point selection of finite-difference time-domain method on the interface of medium, this paper introduces a virtual field which is then unfolded by Taylor series, and gives the iterative formula of the nonstandard finite-difference time-domain method (NS-FDTD). The non-standard finite-difference time-domain method (NS-FDTD) is used to simulate plane wave irradiating vertically the novel sub-wavelength metal grating resonator, effects of the thickness of metal layer and the relative dielectric constant to extraordinary transmission characteristic are studied, and the extraordinary transmission mechanism is analyzed using the theory of Fabry-Perot cavity. A novel structure with extraordinary transmission characteristic is designed, and the extraordinary transmission characteristic in 450–900 THz band has also been studied using the method of NS-FDTD, the effect caused by some parameters such as thickness of metal layer, relative dielectric constant of dielectric layer has been given. The results show: as the thickness of the metal layer decreases, the factor of extraordinary transmission increases and moves towards high frequency, what’s more, the factor moves towards low frequency as the relative dielectric constant of dielectric layer increases. This study provides a theoretical basis for further research on metal film and its extraordinary transmission mechanism.

Two methods of TiO₂ addition were applied to prepare hydroxyapatite/TiO₂ (HA/TiO₂) composite, i.e.

This paper designs a broadband circularly polarized antenna covering the 25 GHz to 31 GHz band. The Vivaldi antenna is used as the basic structure to generate broadband electromagnetic waves; circular polarization is achieved by feeding through a circularly polarized bridge; a metal choke ring is used at the bottom to ensure the low side lobes of the antenna. The antenna consists of four basic Vivaldi antennas, a metal choke ring, a grounded substrate, and a feed network. The results show that the antenna covers the entire frequency band when the axial ratio is lower than 3 dB, and the impedance matching is better. The use of a choke ring structure ensures that the antenna electromagnetic waves are radiated upward, resulting in higher gain and lower side lobes. The highest gain in the included frequency band is 11.4 dB, and the simulation result is good. The antenna has high gain and low sidelobe characteristics.

Objective To discuss the association between single nucleotide polymorphism (SNP) of rs3811047 in IL-1 F7 gene and rheumatoid arthritis (RA) susceptibility among the Han population in central plains of China. Methods A total of 276 RA patients admitted to our hospital from December 2009 to December 2011 together with 276 healthy physical examinees in the same period were chosen as the subjects. The typing for rs3811047 SNP in IL-1 F7 gene was carried out by using ligase detection reaction and polymerase chain reaction technique. And the frequency of each allele and genotypes distribution was calculated so as to evaluate the association between genotype distribution and RA susceptibility. Results The frequency of A allele of rs3811047 in IL-1 F7 gene in RA group and control group was 16.27% and 17.68%, respectively, and that of G allele in two groups was 83.73% and 82.32%, respectively. The difference between two groups wasn't statistical significant ( P >0.05). The frequency of genotype AA, AG and GG in RA group was 2.19%, 27.84% and 69.97%, respectively, while that in control group was 2.94%, 29.78% and 67.28%, respectively. The difference of distribution of three genotypes was not statistically significant ( P >0.05). RA patients with A allele were better than those without A allele in joint swelling index, rest pain, HAQ scoring and blood sedimentation. There was significant difference between two groups in above indexes ( P P Conclusions No significant correlation between RA susceptibility among the Han population in central plains of China and rs3811047 SNP inIL-1 F7 gene is observed. However, A allele of rs3811047 has certain influence on the condition of RA patients.