Research on the Design of Operating Condition of Multi-Resistance Superconducting DC Current Limiter

[Introduction] The working principle of the resistive superconducting current limiter is based on the zero resistance effect of the superconductor, which is connected in series in the line and basically has no resistance during normal operation. When the circuit is short-circuited and the current exceeds the critical current, the superconductor loses excess and the resistance value increases rapidly, which plays a role in limiting the short-circuit current. So the superconducting DC (Direct Current) current limiter has little effect on the power grid when it is in normal operation. When the system short-circuit current exceeds the critical current, it will quickly limit the current value, effectively reducing the requirements for DC equipment. Based on Nan'ao ±160 kV multi-terminal VSC-HVDC (Voltage Source Converter Based High Voltage Direct Current) system, the possible operating conditions of superconducting DC current limiter are discussed, and how to realize the possible operating conditions is analyzed. [Method] For the five possible operating conditions, it was recommended to set disconnector to achieve automatic switching of operating conditions. [Result] The proposed scheme of electrical connection and compact layout is given based on the configuration of the equipment. And according to different operating conditions, the corresponding current path diagram is given. [Conclusion] The possible working conditions of superconducting DC current limiter and the automatic switching electrical connection and compact layout can be obtained by similar analysis for other flexible DC transmission systems

Research on Flexible Interconnection of Urban Power Grid

[Introduction] Due to its flexibility and rapid control ability, voltage source converter based high voltage direct current (VSC-HVDC) technology can be used in asynchronous grid interconnection, renewable energy grid-connection, and urban grid power supply. In this paper, the flexible and compact interconnection scheme of urban power grid is proposed to realize the interconnection and improve safety and stability of the urban power grid. [Method] According to the current situation of the power grid, and considering the difficulty of implementing new transmission lines in urban areas and the difficulty of controlling the construction period, the site selection and interconnection scheme were carried out from the perspective of exploiting potential of existing substations and transmission lines. The interconnection scale was determined comprehensively by combining the system requirements, the transmission capacity of the original lines, and the feasibility of capacity increase transformation. Due to the shortage of urban land, compact equipment and indoor compact layout was recommended. [Result] The flexible and compact back-to-back converter station is adopted to realize the interconnection, significantly reduce the short-circuit current level of the system and improve the security and stability of the urban power grid. The compact design which can save about 40% of the space is adopted to meet the need to alleviate the scarcity of urban land resources. [Conclusion] The compact and flexible interconnection proposed plays a good role in guiding the application of VSC-HVDC technology in urban power grid interconnection and has high reference value

Super resolution dual-layer CBCT imaging with model-guided deep learning

Objective: This study aims at investigating a novel super resolution CBCT imaging technique with the dual-layer flat panel detector (DL-FPD). Approach: In DL-FPD based CBCT imaging, the low-energy and high-energy projections acquired from the top and bottom detector layers contain intrinsically mismatched spatial information, from which super resolution CBCT images can be generated. To explain, a simple mathematical model is established according to the signal formation procedure in DL-FPD. Next, a dedicated recurrent neural network (RNN), named as suRi-Net, is designed by referring to the above imaging model to retrieve the high resolution dual-energy information. Different phantom experiments are conducted to validate the performance of this newly developed super resolution CBCT imaging method. Main Results: Results show that the proposed suRi-Net can retrieve high spatial resolution information accurately from the low-energy and high-energy projections having lower spatial resolution. Quantitatively, the spatial resolution of the reconstructed CBCT images of the top and bottom detector layers is increased by about 45% and 54%, respectively. Significance: In future, suRi-Net provides a new approach to achieve high spatial resolution dual-energy imaging in DL-FPD based CBCT systems

Entanglement detection beyond the CCNR criterion for infinite-dimensions

In this paper, in terms of the relation between the state and the reduced states of it, we obtain two inequalities which are valid for all separable states in infinite-dimensional bipartite quantum systems. One of them provides an entanglement criterion which is strictly stronger than the computable cross-norm or realignment (CCNR) criterion.Comment: 11 page

Necessary and sufficient conditions for local creation of quantum discord

We show that a local channel cannot create quantum discord (QD) for zero QD states of size $d\geq3$ if and only if either it is a completely decohering channel or it is a nontrivial isotropic channel. For the qubit case this propertiy is additionally characteristic to the completely decohering channel or the commutativity-preserving unital channel. In particular, the exact forms of the completely decohering channel and the commutativity-preserving unital qubit channel are proposed. Consequently, our results confirm and improve the conjecture proposed by X. Hu et al. for the case of $d\geq3$ and improve the result proposed by A. Streltsov et al. for the qubit case. Furthermore, it is shown that a local channel nullifies QD in any state if and only if it is a completely decohering channel. Based on our results, some protocols of quantum information processing issues associated with QD, especially for the qubit case, would be experimentally accessible.Comment: 8 page

Understanding the multi-scale structure and digestibility of different waxy maize starches

This work concerns different cultivars of waxy maize starch (WMS), from which a significant correlation between the multi-scale structure and the digestibility has been identified. WMSs show a typical A-type crystalline polymorph. The surface porosity of WMS granules facilitates their digestibility. In contrast, the in vitro digestion results indicate that the resistant starch (RS) content increased with higher contents of amylose, single helices, and surface short-range ordered structures. Resistant starch (RS) was found to be made up of single helices and perfect crystallites formed by the fraction of chains with a degree of polymerization (DP) between 13 and 24. Slowly digestible starch (SDS) consists of single helices. Rapidly digestible starch (RDS) is mainly composed of disordered molecular chains in the amorphous regions of starch. This work reveals the relationship between the multiscale structure and digestibility of different WMSs and can provide guidance for the application of WMSs in food or non-food fields