Optically transparent graphene-based cognitive metasurface for adaptive frequency manipulation

Optically transparent microwave absorbing metasurfaces have shown great potential and are needed in multiple applications environments containing optical windows owing to their ability to reduce backscattering electromagnetic(EM)signals while keeping continuous optical observation.Meanwhile,they are also required to have adaptive EM manipulation capability to cope with complex and capricious EM environments.As a general approach,distributed circuit components,including positive-intrinsic-negative diodes and varactors and sensing components,are integrated with passive absorbing metasurfaces to realize adaptive control of microwave absorption.However,these circuit elements generally require bulky electrical wires and complex control circuits to regulate the operating state,resulting in the absorbing structures being optically opaque.Hence,it is a great challenge to realize self-operating absorbers while maintaining optical transparency.Here,we report an optically transparent cognitive metasurface made of patterned graphene sandwich structures and a radio frequency detector,which can achieve adaptive frequency manipulation to match incident EM waves.As a proof-of-principle application example,we realize a closed-loop automatic absorber system prototype of the proposed graphene metasurface with self-adaptive frequency variation,without any human intervention.The approach may facilitate other adaptive metadevices in microwave regime with high-level recognition and manipulation and,more generally,promote the development of intelligent stealth technologies.

VAT Neutrality and Corporate Cash Holdings—Based on the Research of Uncredited VAT Refund Policy

This paper regards the uncredited value-added tax(VAT)refund policy promulgated in 2018 as an exogenous shock to improve the neutrality for VAT.Based on the statistics of listed companies in the non-financial sectors from 2013 to 2020,this paper applies the difference-in-differences(DID)approach to study the impact of the uncredited VAT refund policy on corporate cash holdings.The study finds that the policy has eased the impact of non-tax-neutral impact of non-refundable tax credits and lowered the level of corporate cash holdings.Furthermore,the analysis of capital sources verified that the policy has optimized the corporate capital conditions.These findings have proved to be robust after a series of tests.At the level of cross-sectional differences,the uncredited VAT refund policy exerts both"resource effect"and"signal effect",enabling companies to reduce cash holdings in the dimensions of both tax endowment and market expectation.At the level of policy effects,the policy improved the corporate behavior of high cash holdings for the production and operation cycle,with more notable impact on enterprises with higher tax credit rating.At the level of economic consequences,the adjustment of corporate cash holdings induced by uncredited VAT refund policy has significantly improved operating performance and reduced performance volatility,with a greater impact on enterprises with high capital intensity.The research findings evaluate the uncredited VAT refund policy from the perspective of tax neutrality,laying a theoretical foundation for further optimizing the uncredited VAT refund policy and the modern fiscal,tax and financial systems.

Distribution characteristics and its controlling factor of lacustrine high-quality source rocks in the Bozhong sag,Bohai Bay Basin

Distribution of Paleogene lacustrine high-quality source rocks in the Bozhong sag in Bohai Bay Basin is analyzed through data of geochemistry,geology and well logging,and its differences under the control of climate and tectonics is also well discussed.Distribution characteristics of the high-quality source rocks developed in the saline environment controlled by the climate are quite different from that developed in the rapid subsidence environment controlled by tectonics.The high-quality source rocks in Member 1 of Shahejie Formation developed in the saline environment account for 81.9%of total subsag area,and are distributed widely and extensively.The high-quality source rocks in Member 3 of Shahejie Formation and Member 3 of Dongying Formation is developed in the tectonic subsidence environment,and horizontally,the subsag subsidence rates has a positive correlation with the area proportion of the high-quality source rocks in the sag;vertically,the reduction-oxidation interface of the lake controls the enrichment of highquality source rocks.Controlled by the saline environment and rapid subsidence environment,the highquality source rocks in the Bozhong sag and adjacent areas have three types of development condition:the saline water,the tectonic subsidence,and joint control of the saline water and the tectonic subsidence.The humid climate and low subsidence rate are not favorable for development of high-quality source rocks.