Metamaterials are artificial structures that are usually described by effective medium parameters on the macroscopic scale, and these metamaterials are referred to as 'analog metamaterials'. Here, we propose 'digital metamaterials' through two steps. First, we present 'coding metamaterials' that are composed of only two types of unit cells, with 0 and π phase responses, which we name '0' and '1' elements, respectively. By coding '0' and '1' elements with controlled sequences (i.e., 1-bit coding), we can manipulate electromagnetic (EM) waves and realize different functionalities. The concept of coding metamaterials can be extended from 1-bit coding to 2-bit coding or higher. In 2-bit coding, four types of unit cells, with phase responses of 0, π/2, π, and 3π/2, are required to mimic the '00', '01', '10' and '11' elements, respectively. The 2-bit coding has greater freedom than 1-bit coding for controlling EM waves. Second, we propose a unique metamaterial particle that has either a '0' or '1' response controlled by a biased diode. Based on this particle, we present 'digital metamaterials' with unit cells that possess either a '0' or '1' state. Using a field-programmable gate array, we realize digital control over the digital metamaterial. By programming different coding sequences, a single digital metamaterial has the ability to manipulate EM waves in different manners, thereby realizing 'programmable metamaterials'. The above concepts and physical phenomena are confirmed through numerical simulations and experiments using metasurfaces. Smart materials offering great freedom in manipulating electromagnetic radiation have been developed. This exciting new concept was realized by Tie Jun Cui and co-workers at the Southeast University, China, who developed digital metamaterials consisting of two kinds of unit cells whose different phase responses allow them to act as '0' and '1' bits. These cells can be judiciously arranged in sequences to enable controlled manipulation of electromagnetic waves. This is one-bit coding; higher-bit coding is possible by employing more kinds of unit cells. The researchers developed a metamaterial cell whose binary response can be controlled by a biased diode. By using a field-programmable gate array, they demonstrated that this digital metamaterial can be programmed. Such metamaterials are attractive for controlling radiation beams in antennas and for realizing other 'smart' metamaterials.
A rapid multi-residue method based on the Quick Easy Cheap Effective Rugged and Safe (QuEChERS) sample preparation method and gas chromatography triple quadrupole tandem mass spectrometry (GC/MS/MS) for the analysis of 78 pesticide residues in cranberry extract has been developed. The method involved extraction with acetone (containing 1 % acetic acid): n-hexane (1∶1, V/V), followed by primary secondary amine (PSA) and graphitized carbon black (GCB) clean up. The analyses were carried out with GC/MS/MS. The method was validated using cranberry extract spiked at 0.01 mg·kg −1 , 0.05 mg·kg −1 and 0.1 mg·kg −1 and the average recovery by the method varied from 69.5% to 115.8% with RSDs < 16.6%. The method showed good linearity and the LOQs for the pesticides studied were lower than 31.5 µg·kg −1 . This method was successfully applied to analysis cranberry extract samples.
The application of layered double hydroxides (LDHs) in supercapacitors is encouraged by their high capacitances but still limited by deficient cycling stability. The remarkable capacitance decay of LDHs during cycling mainly results from the narrowing of the interlayer distance due to the interlayer anion replacement. A polymer encapsulation strategy is developed to improve the cycling stability of LDHs by inhibiting the anion exchange, opening a new avenue to develop stable LDH-based supercapacitor materials.
Abstract Carbon-supported platinum and ruthenium nanoparticles were synthesized by a microwave-assisted polyol heating process. TEM observations showed that the Pt and Ru particles prepared as such have uniform shapes and sizes, and well dispersed on the carbon surface. The average particle size was 3.1 nm for Pt and 2.9 nm for Ru.
Abstract Layered oxides are widely used as the electrode materials for metal ion batteries. However, for large radius size ions, such as Zn 2+ and Al 3+ , the tightly stacked layers and poor electrical conductivity of layered oxides result in restricted number of active sites and sluggish reaction kinetics. In this work, a facile in‐situ construction strategy is provided to synthesize layered oxide nanosheets/nitrogen‐doped carbon nanosheet (NC) heterostructure, which shows larger interlayer spacing and better electrical conductivity than the layered oxides. As a result, the Zn 2+ ion diffusion inside the interlayer gallery is greatly enhanced and the storage sites inside the gallery can be better used. Meanwhile, the NC layers and oxide nanosheets are bridged by the C─O bonds to form a stable structure, which contributes to a better cycling stability than the pure layered oxides. The optimal V 2 O 5 @NC‐400 cathode shows a capacity of 467 mA h g −1 at 0.1 A g −1 for 300 cycles, and long‐term cyclic stability of 4000 cycles at 5 A g −1 with a capacity retention of 92%. All these performance parameters are among the best for vanadium oxide‐based cathode materials.
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