A Novel Mode-Division Multiplexer/Demultiplexer with Ultra-Large Bandwidth and Ultra-Low Insertion Loss Based on Five-Core Photonic Crystal Fiber

A novel mode-division multiplexer/demultiplexer (MUX/DMUX) based on a five-core photonic crystal fiber (PCF) is proposed in this study. The structural parameters of MUX/DMUX were optimized using finite-difference eigenmode (FDE) and eigenmode expansion methods. The numerical simulation results show that the device can simultaneously multiplex five modes of LP01, LP11, LP21, LP31, and LP12 in the main core with an ultra-low insertion loss. At 1.55 μm, the mode conversion efficiency and insertion loss of the five modes were greater than 93.5% and less than 0.29 dB, respectively. The proposed MUX/DMUX is compact, with a length of only 1.84 mm. In addition, the device can operate efficiently with crosstalk of less than -11.34 dB over an ultra-wide bandwidth of 620 nm (from 1.33–1.95 μm, covering E-, S-, C-, L-, U-bands), offering great potential in future mode-division multiplexing systems

Sulfur Vacancy-Rich Carbonaceous Co₉S₈‑ZnS Nanotubes for the Oxygen Evolution Reaction

Metal sulfide electrocatalysts with high activity toward the oxygen evolution reaction (OER) are crucial for renewable energy technologies. However, it remains challenging to rationally design and synthesize metal sulfides integrated with high conductivity and rich porosity to achieve a superior activity. Herein, we report a brand-new, carbonaceous Co9S8-ZnS nanotube (Co9S8-ZnS/NTC) electrocatalyst synthesized via a two-step procedure including zinc-trimesic acid (ZnBTC) fiber nanocrystallization and its assembling with ZIF-67 before solid-state transformation (including sulfuration, gas-phase ion exchange, and carbonization). It is found that rich sulfur vacancies (point defect) and a hollow cavity (3-dimensional defect) are integrated into the resulting carbonaceous Co9S8-ZnS nanotube, originated from the non-equilibrium interdiffusion, which could facilitate electron transfer and OH– transport during the oxygen evolution. As expected, the designed Co9S8-ZnS/NTC delivers a low overpotential of 290 mV, a Tafel slope of 69 mV–1, an electrical resistance of 44 Ω for OER at 10 mA cm–2 in alkaline media, and a high electrochemically active surface area and turnover frequency of 12.2 mF cm–2 and 0.70 O2 s–1, respectively, at 1.50 V, superior to single-component electrocatalysts of Co9S8 and ZnS anchored on N-doped carbon. Density functional theory calculation demonstrates that the sulfur vacancy in Co9S8-ZnS/NTC delivers the decreased theoretical overpotential (1.29 V) and the enhanced activity of its neighboring Co sites, which was also beneficial to OER kinetics. Sulfur vacancy reparation results in a much lower electrocatalytic activity (overpotential, 465 mV) for Co9S8-ZnS/NTC, indicative of its critical role in OER. The concept demonstrated in this study paves the avenue to design other high-performance non-noble electrocatalysts for OER

Structure-Based Design of Novel Chemical Modification of the 3′-Overhang for Optimization of Short Interfering RNA Performance

Short interfering RNAs (siRNAs) are broadly used to manipulate gene expression in mammalian cells. Although chemical modification is useful for increasing the potency of siRNAs <i>in vivo</i>, rational optimization of siRNA performance through chemical modification is still a challenge. In this work, we designed and synthesized a set of siRNAs containing modified two-nucleotide 3′-overhangs with the aim of strengthening the interaction between the 3′-end of the siRNA strand and the PAZ domain of Ago2. Their efficiency of binding to the PAZ domain was calculated using a computer modeling program, followed by measurement of RNA–Ago2 interaction in a surface plasmon resonance biochemical assay. The results suggest that increasing the level of binding of the 3′-end of the guiding strand with the PAZ domain, and/or reducing the level of binding of the sense strand through modifying the two-nucleotide 3′-overhangs, affects preferential strand selection and improves siRNA activity, while we cannot exclude the possibility that the modifications at the 3′-end of the sense strand may also affect the recognition of the 5′-end of the guiding strand by the MID domain. Taken together, our work presents a strategy for optimizing siRNA performance through asymmetric chemical modification of 3′-overhangs and also helps to develop the computer modeling method for rational siRNA design