Alkaline oxygen evolution: exploring synergy between fcc and hcp cobalt nanoparticles entrapped in N-doped graphene

Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm^–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H⁺ ion transport.     

Optimal design of gears contact interface modification for an objective as minimum impact resistance of initial meshing-in time domain

Meccanica - In gear pair actual alternating meshing process, the comprehensive errors of the transmission system and the thermal elastic deformation of the teeth body cause the gears in the meshing...     

Interactions of the vector breathers for the coupled Hirota system with $$4\times 4$$ 4 × 4 Lax pair

Nonlinear Dynamics - In this paper, we investigate the interactions of the vector breathers for the coupled Hirota system with $$4\times 4$$ Lax pair. Firstly, we give the first-order breather...     

疏水缔合悬浮稳定剂的合成及其对固井水泥浆稠度和悬浮稳定性的影响

针对大温差条件下固井水泥浆在固井过程中可能存在的悬浮失稳问题，本研究采用水溶液自由基聚合法来合成具有疏水缔合结构的聚合物作为悬浮稳定剂(PAAN)。通过红外光谱仪、凝胶渗透色谱仪、热重分析仪、高温流变仪、SEM、紫外分光光度计等表征PAAN的结构，发现PAAN随温度升高，形成分子间疏水缔合网状结构，保证了体系的粘度，从而起到有效的悬浮稳定作用。研究发现在40~110 ℃下，0.6%加量的PAAN可以保证固化后的水泥石柱顶部和底部密度差<0.01 g/cm³，且水泥浆稠化时间基本不变，表明PAAN可以保证水泥浆体系具有良好的悬浮稳定效果，且对水泥浆的其他性能无不良影响。     

Subdominant H60 antigen-specific CD8 T-cell response precedes dominant H4 antigen-specific response during the initial phase of allogenic skin graft rejection

In allogeneic transplantation, including the B6 anti-BALB.B settings, H60 and H4 are two representative dominant minor histocompatibility antigens that induce strong CD8 T-cell responses. With different distribution patterns, H60 expression is restricted to hematopoietic cells, whereas H4 is ubiquitously expressed. H60-specific CD8 T-cell response has been known to be dominant in most cases of B6 anti-BALB.B allo-responses, except in the case of skin transplantation. To understand the mechanism underlying the subdominance of H60 during allogeneic skin transplantation, we investigated the dynamics of the H60-specific CD8 T cells in B6 mice transplanted with allogeneic BALB.B tail skin. Unexpectedly, longitudinal bioluminescence imaging and flow cytometric analyses revealed that H60-specific CD8 T cells were not always subdominant to H4-specific cells but instead showed a brief dominance before the H4 response became predominant. H60-specific CD8 T cells could expand in the draining lymph node and migrate to the BALB.B allografts, indicating their active participation in the anti-BALB.B allo-response. Enhancing the frequencies of H60-reactive CD8 T cells prior to skin transplantation reversed the immune hierarchy between H60 and H4. Additionally, H60 became predominant when antigen presentation was limited to the direct pathway. However, when antigen presentation was restricted to the indirect pathway, the expansion of H60-specific CD8 T cells was limited, whereas H4-specific CD8 T cells expanded significantly, suggesting that the temporary immunodominance and eventual subdominance of H60 could be due to their reliance on the direct antigen presentation pathway. These results enhance our understanding of the immunodominance phenomenon following allogeneic tissue transplantation.     

Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes

The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g^?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g^?1 for the CNOs/Ppy bilayer (electrochemical deposition).     

Vinylic MIDA Boronates: New Building Blocks for the Synthesis of Aza‐Heterocycles

A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif.