Extreme Huygens' metasurfaces based on quasi-bound states in the continuum

We introduce the concept and a generic approach to realize Extreme Huygens' Metasurfaces by bridging the concepts of Huygens' conditions and optical bound states in the continuum. This novel paradigm allows creating Huygens' metasurfaces whose quality factors can be tuned over orders of magnitudes, generating extremely dispersive phase modulation. We validate this concept with a proof-of-concept experiment at the near-infrared wavelengths, demonstrating all-dielectric Huygens' metasurfaces with different quality factors. Our study points out a practical route for controlling the radiative decay rate while maintaining the Huygens' condition, complementing existing Huygens' metasurfaces whose bandwidths are relatively broad and complicated to tune. This novel feature can provide new insight for various applications, including optical sensing, dispersion engineering and pulse-shaping, tunable metasurfaces, metadevices with high spectral selectivity, and nonlinear meta-optics

The advantage ratio of mineral resources reserves in various cities of Guangxi.

The advantage ratio of mineral resources reserves in various cities of Guangxi.</p

The relationship between energy & electricity consumption, GDP.

The relationship between energy & electricity consumption, GDP.</p

Assessment of mining economy, social governance and environmental conservation.

Assessment of mining economy, social governance and environmental conservation.</p

The advantage ratio of resource industry sectors in various cities of Guangxi.

The advantage ratio of resource industry sectors in various cities of Guangxi.</p

Time-varying Huygens' meta-devices for parametric waves

Huygens' metasurfaces have demonstrated almost arbitrary control over the shape of a scattered beam, however, its spatial profile is typically fixed at fabrication time. Dynamic reconfiguration of this beam profile with tunable elements remains challenging, due to the need to maintain the Huygens' condition across the tuning range. In this work, we experimentally demonstrate that a time-varying metadevice which performs frequency conversion can steer transmitted or reflected beams in an almost arbitrary manner, with fully dynamic control. Our time-varying Huygens' metadevice is made of both electric and magnetic meta-atoms with independently controlled modulation, and the phase of this modulation is imprinted on the scattered parametric waves, controlling their shapes and directions. We develop a theory which shows how the scattering directionality, phase and conversion efficiency of sidebands can be manipulated almost arbitrarily. We demonstrate novel effects including all-angle beam steering and frequency-multiplexed functionalities at microwave frequencies around 4 GHz, using varactor diodes as tunable elements. We believe that the concept can be extended to other frequency bands, enabling metasurfaces with arbitrary phase pattern that can be dynamically tuned over the complete 2\pi range

Spatio-temporal heterogeneity of the coupling effect among mining economy, social governance and environmental conservation.

Spatio-temporal heterogeneity of the coupling effect among mining economy, social governance and environmental conservation.</p

Regional advantage classification criteria.

In order to solve the problem of coordinated development among mining economy, social governance and environmental conservation in global resource-based cities, we choose Guangxi Zhuang Autonomous Region as the research area. The advantage of resource endowment and resource industry was measured by location quotient and input-output method. The panel data related to mining governance from 2010 to 2021 were selected to build the evaluation and coupling analysis model between mining economic, social governance and environmental conservation, and the spatial-temporal heterogeneity and coupling effect of them were analyzed by comprehensive empowerment evaluation, spatial autocorrelation analysis and barrier degree methods. The results show that: (1) Except for the overall upward trend of social governance, the development level of mining economy and environmental conservation are basically stable; (2) The resource-rich areas have obvious mining economic advantages, and the central cities have good social governance capabilities, and the environmental conservation effectiveness is uncertain; (3) The coupling effect between mining economy and social governance is stronger than that between mining economy and environment conservation, and the synergistic coupling effect of the three is relatively random. Finally, we put forward some policy response strategies to Guangxi, and theoretical and practical reference would be provided for resource-based cities around the world.</div

Spatial distribution characteristics of mining economy, social governance and environmental conservation.

Spatial distribution characteristics of mining economy, social governance and environmental conservation.</p

Investment intensity of R&D personnel and funds in resource industry sectors of Guangxi from 2010 to 2021 (Ten thousand yuan).

Investment intensity of R&D personnel and funds in resource industry sectors of Guangxi from 2010 to 2021 (Ten thousand yuan).</p