Phenolic compounds (PCs) could be applied to reduce reactive oxygen species (ROS) levels, and are used to prevent and treat diseases related to oxidative stress. QSAR study was applied to elucidate the relationship between the molecular descriptors and physicochemical properties of polyphenol analogues and their DPPH radical scavenging capability, to guide the design and discovery of highly-potent antioxidant substances more efficiently. PubMed database was used to collect 99 PCs with antioxidant activity, whereas, 105 negative PCs were found in ChEMBL database; their molecular descriptors were generated with Python's Rdkit package. While the molecular descriptors significantly related to the antioxidant activity of PCs were filtered by t-test. The prediction QSAR model was then established by discriminant analysis, and the obtained model was verified by the back-substitution and Leave-One-Out cross-validation methods along with heat map. It was revealed that the anti-DPPH radical activity of PCs was correlated with the drug-likeness and molecular fingerprints, physicochemical, topological, constitutional and electronic property. The established QSAR model could explicitly predict the antioxidant activity of polyphenols, thus were applicable to evaluate the potential of candidates as antioxidants.
A compact circularly polarized (CP) spiral antenna with enhanced impedance and 3-dB axial ratio (AR) bandwidths that is fed by a tapered coax balun is presented. The antenna is composed of a two-arm nonself-complementarity planar equiangular spiral, a z-directional helix, absorbing material with a stepped cylindrical honeycomb structure, and a ground plane. The z-directional helix is used to extend the current path and to improve the impedance matching and AR in the low-frequency band. The coupling between the nonself-complementarity planar spiral arms is increased, which improves the impedance matching in the low-frequency band and the AR at approximately 5.55 GHz. The stepped cylindrical absorbing material can reduce the reverse current and improve the AR in the high-frequency band. The measured results show that the impedance bandwidth and 3-dB AR bandwidths range from 0.5 to 6 GHz and from 0.5 to 5.8 GHz, respectively. The overall size of the proposed antenna is 0.189λ L × 0.065λ L (diameter × height, where λ L is the free-space wavelength at the starting frequency). INDEX TERMS Spiral antenna, absorbing material, ultrawideband, miniaturization.
A compact wideband four‐arm circularly polarized (CP) spiral antenna with both sum mode (1) and difference mode (2) is presented. The antenna is composed of a modified four‐arm equiangular spiral, a four‐arm z‐directional helix, a ring‐shaped absorber, and a ground plane. By using the modified equiangular spiral and the z‐directional helix, the impedance matching of mode 1 and mode 2 is improved, and the cross‐polarization discrimination of mode 2 is also improved in the low frequency band. The z‐directional helix is also applied to achieve a compact size of the antenna and an enhanced AR bandwidth of mode 2. A prototype of the four‐arm spiral antenna is fabricated and measured with a beamformer operating at 0.5 to 2 GHz. It is shown that both sum and difference radiation patterns are generated in the whole frequency band of 0.5 to 2 GHz. The overall size is 0.486λ0.5 GHz × 0.097λ0.5 GHz (diameter × height, λ0.5 GHz is the free‐space wavelength at 0.5 GHz).
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