Phase transition and scaling in Kuramoto model with high-order coupling

Nonlinear Dynamics - The classical Kuramoto model serves as a useful tool for studying synchronization transitions in coupled oscillators that is limited to the sinusoidal and pairwise...     

The peridynamic differential operator for solving time-fractional partial differential equations

Nonlinear Dynamics - In this paper, the numerical solution of time-fractional convection diffusion equations (TF-CDEs) is considered as a generalization of classical ones, nonexponential relaxation...     

Collective sustained oscillations in excitable small-world networks: the moderate fundamental loop or the minimum Winfree loop?

Nonlinear Dynamics - The problem of self-sustained oscillations in excitable complex networks is the central issue under investigation, among which the exploration of the key factors in determining...     

Fabricating Dual-Atom Iron Catalysts for Efficient Oxygen Evolution Reaction: A Heteroatom Modulator Approach

Understanding the thermal aggregation behavior of metal atoms is important for the synthesis of supported metal clusters. Here, derived from a metal–organic framework encapsulating a trinuclear Fe^III₂Fe^II complex (denoted as Fe₃) within the channels, a well-defined nitrogen-doped carbon layer is fabricated as an ideal support for stabilizing the generated iron nanoclusters. Atomic replacement of Fe^II by other metal(II) ions (e.g., Zn^II/Co^II) via synthesizing isostructural trinuclear-complex precursors (Fe₂Zn/Fe₂Co), namely the “heteroatom modulator approach”, is inhibiting the aggregation of Fe atoms toward nanoclusters with formation of a stable iron dimer in an optimal metal–nitrogen moiety, clearly identified by direct transmission electron microscopy and X-ray absorption fine structure analysis. The supported iron dimer, serving as cooperative metal–metal site, acts as efficient oxygen evolution catalyst. Our findings offer an atomic insight to guide the future design of ultrasmall metal clusters bearing outstanding catalytic capabilities.     

Quantum Thermalization and Vanishing Thermal Entanglement in the Open Jaynes–Cummings Model

The quantum thermalization of the Jaynes–Cummings (JC) model in both equilibrium and non-equilibrium open-system cases is studied, in which the two subsystems, a two-level system and a single-mode bosonic field, are in contact with either two individual heat baths or a common heat bath. It is found that in the individual heat-bath case, the JC model can only be thermalized when either the two heat baths have the same temperature or the coupling of the JC system to one of the two baths is turned off. In the common heat-bath case, the JC system can be thermalized irrespective of the bath temperature and the system–bath coupling strengths. The thermal entanglement in this system is also studied. A counterintuitive phenomenon of vanishing thermal entanglement in the JC system is found and proved.     

Radial flow velocity profiles of a yield stress fluid between smooth parallel disks

In rock grouting, idealized 2D-radial laminar flow of yield stress fluids (YSF) is a fundamental flow configuration that is used for cement grout spread estimation. A limited amount of works have presented analytical and numerical solutions on the radial velocity profiles between parallel disks. However, to the best of our knowledge, there has been no experimental work that has presented measured velocity profiles for this geometry. In this paper, we present velocity profiles of Carbopol (a simple YSF), measured by pulsed ultrasound velocimetry within a radial flow model. We describe the design of the physical model and then present the measured velocity profiles while highlighting the plug-flow region and slip effects observed for three different apertures and volumetric flow rates. Although the measured velocity profiles exhibited wall slip, there was a reasonably good agreement with the analytical solution. We then discuss the major implications of our work on radial flow.

     

Computational Study on the Charge Transport and Optical Spectra of Anthracene Derivatives in Aggregates

A recent experiment [Angew. Chem. Int. Ed. 2017 , 56, 722–727] found that a (1 : 9) blend film of two anthracene derivatives, 2-fluorenyl-2-anthracene ( FlAnt ) and 2-anthryl-2-anthracence ( 2 A ), exhibit both efficient white light emission and high hole mobility, thus promising for organic light-emitting transistors (OLETs). Employing quantum chemistry at the polarizable continuum model (PCM) and the quantum mechanics/molecular mechanics (QM/MM) levels, we investigated the excited-state structures, optical spectra, band structure and the carrier mobility for FlAnt and 2 A from solution to aggregate phases. We suggest using the ratio of intermolecular excitonic coupling J and intramolecular excited state relaxation energy E to judge the bathochromic shift in optical emission in aggregates. For FlAnt , ρ=J/E is calculated to be less than 0.17, a critical value we identified earlier, and the spectra in solution and aggregate phases present quite similar features (blue emission). However, ρ is ∼0.5 for 2 A systems, and the calculated emission in the aggregate phase exhibits a remarkable bathochromic shift. In addition, the 0–0 emission is strongly suppressed in the herringbone stacking. These observations justify the experimental findings that (i) 2 A is blue emissive in solution but yellow-green in the aggregate phase, whereas FlAnt is always blue, and (ii) the blend of them show white emission. By using the “quantum nuclear tunneling” model we proposed earlier, we found the hole mobility for FlAnt and 2 A are 0.5 and 4.2 cm² V⁻¹ s⁻¹, respectively, indicating both are good hole transport materials.     

Coordinate Bond Breaking Induced by Collapse of Poly(\begin{document}$N$\end{document}-isopropyl acrylamide) as Ligands of a Rare Earth Complex

A novel water-soluble luminescent complex consisting of Eu(ally-dbm)\begin{document}$_3$\end{document}-2Tppo and poly(N-isopropyl acrylamide) (PNIPAM) is synthesized through a series of chemical reactions. The structure of the complex is characterized by TGA, GPC, HNMR, and the thermal-responsive fluorescence of the complex in aqueous solution is investigated. It is found that PNIPAM collapse above the lower critical solution temperature causes the coordination bond breaking, leading to weakening of the fluorescence from Eu\begin{document}$^{3+}$\end{document} and enhancing of the fluorescence from the ligands. When temperature decreases, the fluorescence from Eu\begin{document}$^{3+}$\end{document} is found to boost up and the fluorescence from ligands weakens accordingly. It is deduced from this phenomenon that the ligands re-coordinate with europium ions again along with the temperature decreasing, which is further confirmed by IR measurements. This thermal-responsive fluorescence is of reversibility, which can be used as molecular probes for biological imaging and collapse studying of PNIPAM.     

光学共振增强的表面铯激活银纳米结构光阴极

金属光阴极因其超短脉冲发射和运行寿命长的特性从而具有重要应用价值,但是较高的功函数和较强的电子散射使其需要采用高能量紫外光子激发且光电发射量子效率极低.本文利用Mie散射共振效应增强银纳米颗粒中的局域光学态密度,提升光吸收率和电子的输运效率,并利用激活层降低银的功函数,从而增强光阴极在可见光区的量子效率.采用时域有限差分方法分析银纳米球阵列的光学共振特性,采用磁控溅射和退火工艺在银/氧化锡铟复合衬底上制备银纳米球,紧接着在其表面沉积制备铯激活层,最后在高真空腔体中测试光电发射量子效率.实验结果表明平均粒径150 nm的银纳米球光阴极在425 nm波长的量子效率超过0.35%,为相同激活条件下银薄膜光阴极的12倍,峰值波长与理论计算的Mie共振波长相符合.