3 research outputs found
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 Co<sub>9</sub>S<sub>8</sub>‑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