Continuous SiCN Fibers with Interfacial SiC_<i>x</i>N_<i>y</i> Phase as Structural Materials for Electromagnetic Absorbing Applications

SiCN ceramics are one of the most important electromagnetic wave (EMW) absorbing materials for application in harsh environments, but research studies on optimizing phase distribution in SiCN ceramics for excellent EMW absorbing properties are still lacking. Herein, continuous SiCN fibers with an interfacial SiCxNy phase were prepared through nanochannel diffusion-controlled nitridation of polycarbosilane fibers with an NH3 gas flow. The existence of the interfacial SiCxNy phase distributed between the carbon-rich SiC phase and Si3N4 phase can improve the impedance matching and efficiently promote the production of macroscopic dipole moments in the heterointerfaces of SiCxNy–SiC and SiCxNy–Si3N4 for an enhanced multifarious polarization relaxation loss. The EMW absorption properties can be further improved by optimizing the microstructure with a continuous carbon-rich SiC phase for possessing an excellent conductive loss by converting the EMW energy into current flow. Finally, under the synergy of the interfacial SiCxNy phase and the continuous carbon-rich SiC phase, SiCN fibers can present excellent EMW absorption properties with extremely strong absorption ability (reflection loss of −63.7 dB), ultrathin thickness (1.78 mm), and wide effective absorption bandwidth (4.20 GHz). These obtained SiCN fibers also possess excellent mechanical properties with the tensile strength higher than 2.0 GPa and excellent high-temperature stability up to 1500 °C. This work provides a strategic method for optimizing the microstructure of SiCN ceramics for admirable EMW absorption properties, and the obtained SiCN fibers can be used as reinforcements of ceramic matrix composites for stealth applications under harsh environments

Identification potential inhibitors against the <i>Streptococcus</i> quorum-sensing signal pathway

Streptococcal infections are common in human and antibiotics are frequently prescribed in clinical practice. However, infections caused by drug-resistant strains are particularly difficult to treat using common antibiotics. Hence, there is an urgent need for new antibiotics. Quorum sensing is a regulatory mechanism involving cell communication that is thought to play an important role in various bacterial infections, including those caused by Streptococcus. The ATP-binding cassette transporter ComA of Streptococcus is essential for quorum-sensing signal production. The inhibition of the ComA peptidase domain (ComA PEP) suppresses the quorum-sensing pathway and resulting changes in phenotype and/or behavior. Using virtual screening and molecular dynamics simulations, two promising candidate compounds, ZINC32918029 and ZINC6751571, were found. These compounds had similar binding modes and interactions to the experimentally determined reference inhibitor 6CH. However, a significantly stronger negative binding energy was achieved (−113.501 ± 15.312 KJ/mol and −103.153 ± 11.912 KJ/mol for ZINC32918029 and ZINC6751571, respectively). Molecular dynamics simulations also revealed that ZINC32918029 and ZINC6751571 had a strong affinity for ComA PEP. These results indicate that ZINC32918029 and ZINC6751571 are promising candidate inhibitors of the Streptococcus quorum-sensing pathway. Communicated by Ramaswamy H. Sarma</p

The simulated and observed meteorological parameters in the YRD region.

The simulated and observed meteorological parameters in the YRD region.</p

The simulated and observed PM_2.5 concentrations in the YRD region.

The simulated and observed PM2.5 concentrations in the YRD region.</p

Seasonal variations of the simulated PM_2.5 components in the YRD region.

Seasonal variations of the simulated PM2.5 components in the YRD region.</p

The simulated (red) and observed (black) PM_2.5 concentrations (μg m^-3) in 26 cities over the YRD region.

The simulated (red) and observed (black) PM2.5 concentrations (μg m-3) in 26 cities over the YRD region.</p

Seasonal variations of the simulated PM_2.5 concentrations in the YRD region.

Seasonal variations of the simulated PM2.5 concentrations in the YRD region.</p

The simulated PM_2.5 in the YRD region under different emission control scenarios.

The simulated PM2.5 in the YRD region under different emission control scenarios.</p

Scatter plots of simulated versus observed hourly PM_2.5 concentrations at the 26 cities in the YRD region.

Also shown are the reduced-major axis regression lines (solid lines), the regression slopes (s) and correlation coefficients (r). Grey dashed lines indicate the 1:1 ratio.</p