Origin of dc and ac electric transport phenomena in carbon/manganese oxide nanocomposite

Hybrid organic/inorganic nanocomposites based on manganese oxide nanoparticles enriched pyrogallol-formaldehyde matrix (PF/MnO) were synthesized by sol-gel technique. After a drying step, the samples were heated during 2 h at different pyrolysis temperatures between 600 and 1000 °C in tubular furnace under open nitrogen atmosphere. The obtained nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrical technics in the measurement temperature range between 80 and 300 K. The XRD spectra show that PF/MnO nanocomposites are crystallized with the appearance of different phases: the graphite (C), the manganese oxide (MnO), the metallic manganese (Mn) and the manganese dioxide (MnO₂) with proportions depending on pyrolysis temperature. The measurement temperature dependence conductivity can be explained by Godet-Variable Range Hopping (3D-GVRH) conduction model in all samples with the presence of an exponential distribution of localized states. The voltage-current V(I) characteristics show the presence of negative differential resistance (NDR) in some samples. The ac conductance exhibits the dominance of hopping conduction mechanism and the Small Polaron Hopping (SPH) model. The Nyquist plots for the PF/MnO-650 °C nanocomposite obey at Cole-Cole model. The impedance spectra were fitted by an equivalent circuit involving two contributions attributed to grains and grain boundaries.     

Shadow-casted ultrathin surface coatings of titanium and titanium/silicon oxide sol particles via ultrasound-assisted deposition

Ultrasound-assisted deposition (USAD) of sol nanoparticles enables the formation of uniform and inherently stable thin films. However, the technique still suffers in coating hard substrates and the use of fast-reacting sol–gel precursors still remains challenging. Here, we report on the deposition of ultrathin titanium and titanium/silicon hybrid oxide coatings using hydroxylated silicon wafers as a model hard substrate. We use acetic acid as the catalyst which also suppresses the reactivity of titanium tetraisopropoxide while increasing the reactivity of tetraethyl orthosilicate through chemical modifications. Taking the advantage of this peculiar behavior, we successfully prepared titanium and titanium/silicon hybrid oxide coatings by USAD. Varying the amount of acetic acid in the reaction media, we managed to modulate thickness and surface roughness of the coatings in nanoscale. Field-emission scanning electron microscopy and atomic force microscopy studies showed the formation of conformal coatings having nanoroughness. Quantitative chemical state maps obtained by x-ray photoelectron spectroscopy (XPS) suggested the formation of ultrathin (<10 nm) coatings and thickness measurements by rotating analyzer ellipsometry supported this observation. For the first time, XPS chemical maps revealed the transport effect of ultrasonic waves since coatings were directly cast on rectangular substrates as circular shadows of the horn with clear thickness gradient from the center to the edges. In addition to the progress made in coating hard substrates, employing fast-reacting precursors and achieving hybrid coatings; this report provides the first visual evidence on previously suggested “acceleration and smashing” mechanism as the main driving force of USAD.     

Hydroxyl Radical Generation and DNA Nuclease Activity: A Mechanistic Study Based on a Surface‐Immobilized Copper Thioether Clip‐Phen Derivative

Coordination compounds of copper have been invoked as major actors in processes involving the reduction of molecular oxygen, mostly with the generation of radical species the assignment for which has, so far, not been fully addressed. In the present work, we have carried out studies in solution and on surfaces to gain insights into the nature of the radical oxygen species (ROS) generated by a copper(II) coordination compound containing a thioether clip‐phen derivative, 1,3‐bis(1,10‐phenanthrolin‐2‐yloxy)‐N‐(4‐(methylthio)benzylidene)propan‐2‐amine (2CP‐Bz‐SMe), enabling its adsorption/immobilization to gold surfaces. Whereas surface plasmon resonance (SPR) and electrochemistry of the adsorbed complex indicated the formation of a dimeric Cu^I intermediate containing molecular oxygen as a bridging ligand, scanning electrochemical microscopy (SECM) and nuclease assays pointed to the generation of a ROS species. Electron paramagnetic resonance (EPR) data reinforced such conclusions, indicating that radical production was dependent on the amount of oxygen and H₂O₂, thus pointing to a mechanism involving a Fenton‐like reaction that results in the production of OH^..     

Exactly solvable chain of interacting electrons with correlated hopping and pairing

A generalization of the Mattis-Nam model Mattis and Nam (1972) [7], which takes into account a correlated hopping and pairing of electrons, is proposed, its exact solution is obtained. In the framework of the model the stability of the zero energy Majorana fermions localized at the boundaries is studied in the chain in which electrons interact through both the on-site Hubbard interaction and the correlated hopping and pairing. The ground-state phase diagram of the model is calculated, the region of existence of topological states is determined. It is shown that low-energy excitations destroy bonds between electrons in the chain, leading to an insulator state.     

二维胶体玻璃中玻色峰与结构无序度的关联

本文从实验上研究了胶体玻璃在相同面密度下随着体系结构无序程度的增加, 振动态密度和玻色峰的变化规律. 通过调制两种不同粒径的温敏性水凝胶的数量比来改变体系的无序程度. 通过分析无序体系的声子模式得到体系的振动特性. 研究发现, 随着无序度的增加, 态密度在低频区域增强、玻色峰增高、玻色峰的峰值向低频区域移动. 不同无序程度的样品引起玻色峰的低频声子模式都表现出准局域的特点, 且低频准局域声子模式与样品中无序结构存在关联.     

政府奖励对报废汽车回收模式选择的作用机制研究——基于企业社会责任视角

随着我国报废汽车数量的增多,由其造成的交通隐患、环境污染和资源浪费已成为重要社会问题,而如何设计合理可行的回收模式成为解决问题的关键。以制造商主导为前提,提出了基于企业社会责任的报废汽车回收模型,构建了制造商回收、销售商回收和第三方回收模式下的回收流程和数学模型,通过实例对考虑和不考虑企业社会责任两种情况下的回收模型进行了分析,探讨了不同政府奖励下报废汽车回收模式的策略选择。通过研究发现:(1)不论是否考虑企业社会责任,随着政府奖励的增加,制造商最终都会选择由自己进行回收;(2)当考虑企业社会责任时,政府奖励和决策者经济责任偏好都会导致决策的改变,随着政府奖励和赋予经济责任权重的同步增加,制造商的决策由第三方企业回收模式或销售商回收模式变成了制造商回收模式,表明政府奖励和企业社会责任对报废汽车回收模式选择具有显著影响。     

Ligand Taxonomy for Bioinorganic Modeling of Dioxygen-Activating Non-Heme Iron Enzymes

Novel functions emerge from novel structures. To develop efficient catalytic systems for challenging chemical transformations, chemists often seek inspirations from enzymatic catalysis. A large number of iron complexes supported by nitrogen-rich multidentate ligands have thus been developed to mimic oxo-transfer reactivity of dioxygen-activating metalloenzymes. Such efforts have significantly advanced our understanding of the reaction mechanisms by trapping key intermediates and elucidating their geometric and electronic properties. Critical to the success of this biomimetic approach is the design and synthesis of elaborate ligand systems to balance the thermodynamic stability, structural adaptability, and chemical reactivity. In this Concept article, representative design strategies for biomimetic atom-transfer chemistry are discussed from the perspectives of “ligand builders”. Emphasis is placed on how the primary coordination sphere is constructed, and how it can be elaborated further by rational design for desired functions.     

Reversible Activation of Water by an Air- and Moisture-Stable Frustrated Rhodium Nitrogen Lewis Pair

[Cp*Rh(κ³N,N′,P- L )][SbF₆] (Cp*=C₅Me₅), bearing a guanidine-derived phosphano ligand L , behaves as a “dormant” frustrated Lewis pair and activates H₂ and H₂O in a reversible manner. When D₂O is employed, a facile H/D exchange at the Cp* ring takes place through sequential C(sp³)−H bond activation.     

基于实际路网情境的配送车辆调度优化

在实际路网情境下结合车道数、车道宽度、路口信号灯设置等路网物理特性,构建了考虑综合交通阻抗的多车型车辆调度模型,提出了两阶段求解策略:第1阶段设计了改进A-star精确解算法用于计算客户时间距离矩阵;第2阶段针对实际路网的特征设计了混合模拟退火算法求解调度方案。以大连市某配送中心运营实例进行路网情境仿真试验,结果表明:改进A-star算法较改进Dijkstra算法具有更短的路径搜索时间;混合模拟退火算法求解结果较实际调度方案优化了13.1% 的综合成本;路网增流、区域拥堵和路段禁行三类路网情境均能对配送方案的车辆配置、路径选择、客户服务次序、作业时间和违约费用等5方面内容产生干扰,调度计划的制定需要详细考虑这些因素的变化。