Theoretical study of the nitrogen reduction reaction catalyzed by a B-doped MoO2 six-membered ring.

In this study, two potential catalysts with double-B atom-doped atomic MoO2 (B2/MoO2) and single-B atom-doped atomic MoO2 (B/MoO2) were designed and constructed. The thermodynamics and selectivity of two catalysts in the nitrogen fixation reaction were analyzed by a DFT calculation method. The results show that B2/MoO2 shows better adsorption activation and reduction and can effectively activate nitrogen molecules by two adjacent boron atoms. It achieves an extremely low overpotential of -0.18 V and rapid NRR kinetics through an enzymatic mechanism. Therefore, B2/MoO2 is a very promising NRR candidate catalyst. This research shows that doping with diatomic B (as an active site) results in an excellent NRR catalytic activity, which provides a certain theoretical basis for the preparation of high-performance NRR catalysts.

Temporal effect of the spin-to-orbit conversion in tightly focused femtosecond optical fields.

Spin and orbital angular momenta are two of the most fundamental physical quantities that describe the complex dynamic behaviors of optical fields. A strong coupling between these two quantities leads to many intriguing spatial topological phenomena, where one remarkable example is the generation of a helicity-dependent optical vortex that converts spin to orbital degrees of freedom. The spin-to-orbit conversion occurs inherently in lots of optical processes and has attracted increasing attention due to its crucial applications in spin-orbit photonics. However, current researches in this area are mainly focused on the monochromatic optical fields whose temporal properties are naturally neglected. In this work, we demonstrate an intriguing temporal evolution of the spin-to-orbit conversion induced by tightly-focused femtosecond optical fields. The results indicate that the conversion in such a polychromatic focused field obviously depends on time. This temporal effect originates from the superposition of local fields at the focus with different frequencies and is sensitive to the settings of pulse width and central wavelength. This work can provide fundamental insights into the spin-orbit dynamics within ultrafast wave packets, and possesses the potential for applications in spin-controlled manipulations of light.

Time-varying orbital angular momentum in tight focusing of ultrafast pulses.

The orbital angular momentum (OAM) of light has important applications in a variety of fields, including optical communication, quantum information, super-resolution microscopic imaging, particle trapping, and others. However, the temporal properties of OAM in ultrafast pulses and in the evolution process of spin-orbit coupling has yet to be revealed. In this work, we theoretically studied the spatiotemporal property of time-varying OAM in the tightly focused field of ultrafast light pulses. The focusing of an incident light pulse composed of two time-delayed femtosecond sub-pulses with the same OAM but orthogonal spin states is investigated, and the ultrafast dynamicsa time delay of OAM variation during the focusing process driven by the spin-orbit coupling is visualized. Temporal properties of three typical examples, including formation, increase, and transformation of topological charge are investigated to reveal the non-uniform evolutions of phase singularities, local topological charges, self-torques, and time-varying OAM per photon. This work could deepen the understanding of spin-orbit coupling in time domain and promote many promising applications such as ultrafast OAM modulation, laser micromachining, high harmonic generation, and manipulation of molecules and nanostructures.

In situ nanopores enrichment of Mesh-like palladium nanoplates for bifunctional fuel cell reactions: A joint etching strategy.

Two-dimensional (2D) nanomaterials with nanopore display an enhancement effect on electrocatalysis behavior, whereas the nanopore engineering for 2D nanocatalysts remains an insurmountable challenge. We advance the synthesis of multilayer Pd nanoplates (Pd NPs) and two types of meshy nanoplates (Pd LMNPs/MNPs) with escalating nanopores from none and sparse to porous. Specially, an in situ nanopore enrichment on these Pd nanoplates hinges on a joint etching strategy with integrated manipulation of reaction kinetics. The optimized Pd MNPs exhibit exceptional oxygen reduction reaction performance, owing to the enhanced intermediates protonation on Pd site neighboring nanopore, which has been elucidated by density functional theory calculations. In addition, Pd MNPs also deliver excellent performances in fuel cell anodic reactions, including ethanol oxidation reaction and formic acid oxidation reaction. This study highlights a new strategy for in situ nanopores engineering, providing a prospect for designing superior nanocatalysts.

Few-layer metamaterials for spontaneous emission enhancement: publisher's note.

This publisher's note contains corrections to Opt. Lett.46, 190 (2021)OPLEDP0146-959210.1364/OL.413268.

Few-layer metamaterials for a spontaneous emission enhancement.

Multilayer hyperbolic metamaterials consisting of alternating metal and dielectric layers have important applications in spontaneous emission enhancement. In contrast to the conventional choice of at least dozens of layers in multilayer structures to achieve tunable Purcell effect on quantum emitters, our numerical calculations reveal that multilayers with fewer layers and thinner layers would outperform in the Purcell effect. These discoveries are attributed to the negative contributions by an increasing layer number to the imaginary part of the reflection coefficient and the stronger coupling between surface plasmon polariton modes on a thinner metal layer. This work could provide fundamental insights and a practical guide for optimizing the local density of optical states enhancement functionality of layered metamaterials.

Extraordinary spin-orbit interaction in the plasmonic lens with negative index material.

Spin-orbit interactions are inherent in many basic optical processes in anisotropic and inhomogeneous materials, under tight focusing or strong scattering, and have attracted enormous attention and research efforts. Since the spin-orbit interactions depend on the materials where they occur, the study of the effects of materials on the spin-orbit interactions could play an important role in understanding and utilizing many novel optical phenomena. Here, we investigate the effect of negative-index material on the spin-orbit interactions in a plasmonic lens structure in the form of a circular slot in silver film. Numerical simulations are employed to study the influence of the negative-index material on the plasmonic vortex formation and the plasmonic focusing in the structure under circularly polarized excitations bearing different orbital angular momentum. We reveal that the presence of negative-index material leaves the plasmonic vortex field distribution and the corresponding topological charge unaltered during the spin-to-orbital angular momentum conversion, whereas reverses the rotation direction of in-plane energy flux of the plasmonic vortex and shifts the surface plasmon polariton focus position to the opposite direction compared to the case without negative-index material. This work will help further the understanding of the regulation of optical spin-orbital interactions by material properties and design optical devices with novel functions.

[Endoscopic variceal ligation in prevention from esophageal variceal hemorrhage of advanced schistosomiasis patients].

OBJECTIVE: To evaluate the effect of the endoscopic esophageal variceal ligation on the prevention from recurrence of esophageal varices and variceal hemorrhage. METHODS: Forty-two advanced schistosomiasis patients with variceal hemorrhage in the treatment group received the endoscopic esophageal variceal ligation, and 30 patients in the control group did not, and all of them had oral propranolol, spironolactone and 5 single-isosorbide dinitrate etc. in hospital for the same period and had these drugs for 3-6 months after discharge. The re-examinations of endoscopy were performed once 3 to 6 months. RESULTS: The time of follow-up was from 2 to 3 years and the average was 29 months. In the treatment group, the rate of recurrence of esophageal varices was 19.0% (8/42) and the average time was 30 months; the incidence of esophageal variceal bleeding was 11.9% (5/42) and 2 patients died. In the control group, the rate of recurrence of esophageal varices was 43.3% (13/30) and the average time was 18 months; the incidence of esophageal variceal bleeding was 36.7% (11/30) and 7 patients died. The therapeutic efficacy of the treatment group was much superior to that of the control group. CONCLUSION: The endoscopic esophageal variceal ligation is effective and safe, and can become one of the preferred methods in the prevention from variceal hemorrhage.