Search

A new refiner containing (Ti + V)B2phase was prepared in this study. It consists of a special VB2–TiB2core–shell structure, and the size of most (Ti + V)B2granular phase is between 100 and 500 nm. Considering Al–7Si alloy as the research object, the refining ability of Al–Ti–B, Al–V–B, and Al–(Ti + V)–B was compared under the condition of same content of added B. The grain refiner containing (Ti + V)B2can significantly reduce the grain size of Al–7Si. Al–(Ti + V)–B refines the as-cast grain size from 854.6 ± 28 to 136.93 ± 2.45 μm, which is better than the results obtained for Al–Ti–B- and Al–V–B-based refiners.

The quantum spin Hall effect protected by C_6 symmetry [realized in the domain wall (DW) formed by a trivial-photonic crystal (TPC) and a nontrivial-PC (NPC)] and the quantum valley Hall effect protected by C_3 symmetry [realized in the DW formed by two valley PCs (VPCs)] have been widely researched due to their excellent topological properties. The topological edge states (TESs) and topological corner states (TCSs) at DWs between different symmetric structures remain to be explored, which is essential for connecting waveguides with different symmetries to construct optical communication devices. In this Letter, there is (are) one TES (two TESs) for the DW1 and DW3 (DW2 and DW4) between the TPC (NPC) and two VPCs. Through simulation calculations of the Wilson-loop of the TPC and NPC and the Berry curvature distribution of VPCs, the corresponding relationship between the topological invariant and the number of TESs is obtained. Based on the TPC, NPC, and two VPCs, the waveguides are constructed to verify the realization of TESs. The parity of the gapped TESs is analyzed, and its relationship with the TCSs is obtained. Moreover, box-shaped structures are constructed to verify the appearance of TCSs. These results have a guiding significance for the research of the interaction between topological states protected by different symmetries.

Novel phenomena found in non-Hermitian systems and robust edge states have attracted much attention. When non-Hermitian parameters (gain and loss) are above a critical value, the non-Hermitian photonic crystal (PC) bandgaps close, leading to a mixture of the topological edge state (TES) and topological corner state (TCS) with the bulk state. Meanwhile, new bandgaps also open, in which new TES and TCS can appear. Thus, with appropriate non-Hermitian parameters, TES can emerge in both the original bandgaps and the newly opened bandgaps. The results described here will further enrich understanding of the topological properties of non-Hermitian systems.

Fragile topology (FT) opens a new direction in topological photonics, but a new type of photonic crystal (PC) with FT remains to be proposed. In this Letter, the double-site honeycomb lattice (DSHL) PC is proposed by rotating the double dielectric rods (DDR) six times, forming unit cell, and then arraying the unit cells in a triangular lattice. Quantum spin Hall effect occurs by manipulating the DDR in the tangential and radial directions of the unit cell. First, the band structures of DSHL PCs with different structural parameters are calculated, and the laws of topological phase transition are analyzed statistically. Then, to prove the FT properties of two groups of topological nontrivial DSHL PCs, the Wannier-center positions of the bulk bands are calculated by the Wilson–Loop method. Finally, the topological edge states and two groups of topological corner states, which are in the same bulk-state bandgap, are realized successfully. The DSHL PC provides good platforms for both the research of topological photonics and the device design and application, which has a broad prospect.

The topological corner state (TCS) and topological edge state (TES) have created new approaches to manipulate the propagation of light. The construction of a topological coupled cavity-waveguide (TCCW) based on the TCS and TES is worth looking forward to, due to its research prospects in realizing high-performance micro-nano integrated photonic devices. In this Letter, the TCCW is proposed in two-dimensional (2D) photonic crystal (PC), which possesses strong optical localization, high quality factor, and excellent robustness compared with the conventional coupled cavity-waveguide (CCCW). This work will pave the way toward designing high-performance logic gates, lasers, filters, and other micro-nano integrated photonics devices and expanding their applications.

The pantograph catenary system is an important part of the traction power supply system. In order to monitor the dynamic parameters of the rigid catenary accurately in real-time, we propose a new coarse-to-fine approach to locate and detect the pantograph-catenary contact points using DCNNs. For the contact area, which is relatively small enough for the target region, we refer to a real-time object detection method with both speed and accuracy advantages, YOLOv3. And then based on the geometric relationship between the pantograph and the catenary, we use Hoff line detection to achieve accurate detection of contact points. Our method consists of two stages. We first train Yolov3 to detect the local region of the contact points accurately by using the pantograph-catenary datasets. Obtained images of the coarse region detection, we then choose the canny edge detection and Hough transformation to detection the pantograph-catenary contact points. The experiment results from two video datasets show that our proposed method can accurately track the pantograph-catenary contact points by the continuous detection, which could provide research refers to the real-time automatic monitoring of the pantograph-catenary system.

Topological photonics have led to robust optical behavior of optical devices, which has alleviated the influence of manufacturing defects and perturbations on the device performance. Meanwhile, temporal coupled-mode theory (t-CMT) has been developed and applied widely. However, the t-CMT of cascaded coupled cavities (CCC) system and its corresponding high-order filter has yet to be established. Here, the t-CMT of CCC system is established based on the existing t-CMT. By combining the CCC with topological waveguides, a versatile design scheme of high-order nonreciprocal add-drop filter (HONAF) is proposed. The relationship between the coupling effect of cavities and transmission and the filtering performance of HONAF is analyzed quantitatively. Then, a method to improve the transmission efficiency and quality factor of the filter is given. The proposed HONAF is based on the combination of gyromagnetic photonic crystals and decagonal Penrose-type photonic quasicrystals. The transmission and filtering performance of the HONAF are numerically analyzed, which verifies the consistency between theoretical prediction and numerical simulation. The established t-CMT of CCC system can be widely used in coupled resonator optical waveguides and their related systems. The proposed HONAF with excellent performance can also be applied to wavelength division multiplexing/demultiplexing systems.