Nonseparating Independent Sets and Maximum Genus of Graphs

Acta Mathematicae Applicatae Sinica, English Series - A subset I of vertices of an undirected connected graph G is a nonseparating independent set (NSIS) if no two vertices of I are adjacent and G...     

The comparable structural,elastic anisotropic and thermophysical properties of advanced U–Si fuel to baseline UO2: a DTF method

The European Physical Journal B - Molecular dynamics and Monte Carlo methods are common measurements to study the diffusion coefficients of the fluid particles under restricted conditions. Here,...     

非富勒烯受体DA'D型稠环单元的结构修饰及电池性能研究

近年来,设计和合成高性能非富勒烯受体(NFAs)材料已经成为太阳能电池研究领域的前沿课题。基于DA'D型稠环结构的NFAs由于具有吸光系数高、能级和带隙可调、结构易于修饰、分子可高效合成、光电学性能优异等优点而受到了越来越广泛的关注。在短短7年的时间里,能量转换效率(PCE)从3%~4%提高到18%。2019年初邹应萍等报道了一个优秀的受体分子Y6,与PM6共混制备单结电池,获得了15.7%的能量转换效率。Y6类受体材料的中心给电子单元为DA'D型稠环结构,缺电子单元(A')通过氮原子与两个给电子单元(D)并联形成稠环结构,这有助于降低前线分子轨道能级并增强吸收,同时与氮相连的两个烷基链和位于噻吩并噻吩β位的两个侧链则有助于提高溶解度及调节结晶性。自Y6问世以来,人们对分子的结构剪裁进行了深入的研究,并报道了数十种新的结构。在这些新的受体中,DA'D部分的结构裁剪对提高器件效率和太阳能电池的性能起着至关重要的作用。本文对A'、D单元和侧链结构修饰的研究进展进行了综述。通过选择几组受体,对最近报道的分子进行分类,并将它们的光学、电化学、电学和光电性质与精确的结构修饰相关联,从而对结构-性能关系进行全面概述。     

Freeze–Thaw-Promoted Fabrication of Clean and Hierarchically Structured Noble-Metal Aerogels for Electrocatalysis and Photoelectrocatalysis

Noble-metal aerogels (NMAs) have drawn increasing attention because of their self-supported conductive networks, high surface areas, and numerous optically/catalytically active sites, enabling their impressive performance in diverse fields. However, the fabrication methods suffer from tedious procedures, long preparation times, unavoidable impurities, and uncontrolled multiscale structures, discouraging their developments. By utilizing the self-healing properties of noble-metal aggregates, the freezing-promoted salting-out behavior, and the ice-templating effect, a freeze–thaw method is crafted that is capable of preparing various hierarchically structured noble-metal gels within one day without extra additives. In light of their cleanliness, the multi-scale structures, and combined catalytic/optical properties, the electrocatalytic and photoelectrocatalytic performance of NMAs are demonstrated, which surpasses that of commercial noble-metal catalysts.     

On stochastic calculus with respect to q-Brownian motion

Following the approach and the terminology introduced in Deya and Schott (2013) [6], we construct a product Lévy area above the q-Brownian motion (for $q\in [0,1)$) and use this object to study differential equations driven by the process.We also provide a detailed comparison between the resulting “rough” integral and the stochastic “Itô” integral exhibited by Donati-Martin (2003) [7].     

Nickel (II) tetrapyridyl complexes as electrocatalysts and precatalysts for water oxidation

Two nickel complexes, [Ni(tpen)](ClO₄)₂.0.5CH₃COCH₃ ( 1 ) and [Ni(tpbn)](ClO₄)₂ ( 2 ), of tetrapyridyl ligands N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,2-ethanediamine (tpen) and N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiO_x composite (nickel oxide with general formula Ni_xO_yH_z) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiO_x composite active for WOR. The NiO_x composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2 . This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center.     

聚变堆相关的液态金属膜流初步实验研究

在磁约束核聚变堆的面对等离子部件设计中,液态金属锂膜流因具有带走杂质、保护面对等离子固壁等优点而被认为是优选方案之一. 然而,如何克服聚变堆中强磁场环境下产生的磁流体力学效应并形成大面积均匀铺展锂膜流动是目前亟需解决的问题.本文通过搭建室温液 态镓铟锡回路和高温液态锂回路,开展了两种不同特性的液态金属膜流实验, 并采用传统可视化方法获得了展向磁场存在时镓铟锡和锂在导电底板形成的液膜流动表面特征.实验结果 表明: 无磁场时,两种液态金属膜流流动表面波动特性与常规流体膜流均一致, 即随着流动雷诺数的增加表面波动变得更为混乱; 而展向磁场存在时,镓铟锡膜流表面波动变得更为规则, 且沿着磁场方向平行排列,表现为拟二维波动的特征; 而锂膜流却产生了明显的磁流体 力学阻力效应,表现为在流动方向局部产生锂滞留现象, 且滞留点随雷诺数增大向下游移动. 最后通过膜流受力分析,进一步阐述了锂膜流受到比镓铟锡膜流更为严重磁流体力学效应影响的原因.      

Cures for expansion shock and shock instability of Roe scheme based on momentum interpolation mechanism

The common defects of the Roe scheme are the non-physical expansion shock and shock instability. By removing the momentum interpolation mechanism (MIM), an improved method with several advantages has been presented to suppress the shock instability. However, it cannot prevent the expansion shock and is incompatible with the traditional curing method for expansion shock. To solve the problem, the traditional curing mechanism is analyzed. Effectiveness of the traditional curing method is discussed, and several defects are identified, one of which leads to incompatibility between curing shock instability and expansion shock. Consequently, an improved Roe scheme is proposed, which is with low computational costs, concise, easy to implement, and robust. More importantly, the proposed scheme can simultaneously solve the problem of shock instability and expansion shock without additional costs.     

Systemic Risk and Stochastic Games with Delay

We propose a model of inter-bank lending and borrowing which takes into account clearing debt obligations. The evolution of log-monetary reserves of banks is described by coupled diffusions driven by controls with delay in their drifts. Banks are minimizing their finite-horizon objective functions which take into account a quadratic cost for lending or borrowing and a linear incentive to borrow if the reserve is low or lend if the reserve is high relative to the average capitalization of the system. As such, our problem is a finite-player linear–quadratic stochastic differential game with delay. An open-loop Nash equilibrium is obtained using a system of fully coupled forward and advanced-backward stochastic differential equations. We then describe how the delay affects liquidity and systemic risk characterized by a large number of defaults. We also derive a closed-loop Nash equilibrium using a Hamilton–Jacobi–Bellman partial differential equation approach.