Photonic Floquet Skin-Topological Effect.

Non-Hermitian skin effect and photonic topological edge states are of great interest in non-Hermitian physics and optics. However, the interplay between them is largely unexplored. Here, we propose and demonstrate experimentally the non-Hermitian skin effect constructed from the nonreciprocal flow of Floquet topological edge states, which can be dubbed "Floquet skin-topological effect." We first show the non-Hermitian skin effect can be induced by structured loss when the one-dimensional (1D) system is periodically driven. Next, based on a two-dimensional (2D) Floquet topological photonic lattice with structured loss, we investigate the interaction between the non-Hermiticity and the topological edge states. We observe that all the one-way edge states are imposed onto specific corners, featuring both the non-Hermitian skin effect and topological edge states. Furthermore, a topological switch for the skin-topological effect is presented by utilizing the phase-transition mechanism. Our experiment paves the way for realizing non-Hermitian topological effects in nonlinear and quantum regimes.

Topologically crafted spatiotemporal vortices in acoustics.

Vortices in fluids and gases have piqued the human interest for centuries. Development of classical-wave physics and quantum mechanics highlighted wave vortices characterized by phase singularities and topological charges. In particular, vortex beams have found numerous applications in modern optics and other areas. Recently, optical spatiotemporal vortex states exhibiting the phase singularity both in space and time have been described. Here, we report the topologically robust generation of acoustic spatiotemporal vortex pulses. We utilize an acoustic meta-grating with broken mirror symmetry which exhibits a topological phase transition with a pair of phase singularities with opposite topological charges emerging in the momentum-frequency domain. We show that these vortices are topologically robust against structural perturbations of the meta-grating and can be employed for the generation of spatiotemporal vortex pulses. Our work paves the way for studies and applications of spatiotemporal structured waves in acoustics and other wave systems.

[Fabrication of Supported Titanium Xerogel Adsorbent and Performance Evaluation for Arsenite Removal].

Although the adsorption capacity of titanium xerogel(TAX) for arsenite(As(Ⅲ)) is high(254 mg·g-1), the adsorption rate is slow. Therefore, TAX was loaded onto activated carbon, sponge, and resin to fabricate a supported adsorbent, and the arsenite removal performance was evaluated. Except sponge, activated carbon and resin could successfully load TAX. The results showed that resin and activated carbon loaded TAX improved the As(Ⅲ) removal performance, and more significantly by the resin-based materials. Through wet digestion and adsorption kinetics experiments, the amount of titanium loaded was approximately 1.4% and 5% in the activated carbon-based(TAX@AC) and resin-based(TAX@resin) materials, respectively. For the initial concentration of 1.0 mg·L-1 As(Ⅲ) solution, the adsorption rate constant of TAX@D201 was 0.85 mg·(g·min) -1, which was 21 times higher than that of unloaded TAX[0.04 mg·(g·min) -1]. Columns packed with TAX@resin could effectively lower arsenite concentration for up to 560 bed volumes, which is 2.8 times greater than that of the iron-based composites with the same metal mass. Therefore, loading TAX on macroporous resin is an effective strategy and provides an effective approach for the application of TAX in arsenite-containing groundwater.

Dual-Band Fano Resonance of Low-Frequency Sound Based on Artificial Mie Resonances.

It is reported both experimentally and numerically that dual-band acoustic Fano resonances (AFRs) of low-frequency sound are realized by a compound unit array composed of two types of multiple-cavity unit cells with different inner radii. Eigenmode analyses show that two types of monopolar Mie resonance (MMR) modes can be observed below 650 Hz, which arise from the coupling resonance of the overall structure and the Helmholtz resonance of each resonance cavity, respectively. Based on the MMRs with the out-of-phase characteristic induced by the mutual coupling of the two types of unit cells, the dual-band AFRs, in which the quality factor of the AFR II can exceed 600 when the ratio of the inner radii is closed to 1.0, can be observed. More interestingly, the application of the dual-band AFRs in sound encryption communication is further discussed. The proposed multiple-cavity unit cell and its associated dual-band AFRs provide diverse routes to design multiband sound devices with versatile applications, such as filtering, sensing, and communication.