Crystalline Diradical Dianions of Pyrene-Fused Azaacenes

Although diradicals and azaacenes have been greatly attractive in fundamental chemistry and functional materials, the isolable diradical dianions of azaacenes are still unknown. Herein, we describe the first isolation of pyrene-fused azaacene diradical dianion salts [(18-c-6)K(THF)₂]⁺[(18-c-6)K]⁺⋅ 1 ^2−.. and [(18-c-6)K(THF)]²⁺⋅ 2 ^2−.. by reduction of the neutral pyrene-fused azaacene derivatives 1 and 2 with excess potassium graphite in THF in the presence of 18-crown-6. Their electronic structures were investigated by various experiments, in conjunction with theoretical calculations. It was found that both dianions are open-shell singlets in the ground state and their triplet states are thermally readily accessible owing to the small singlet–triplet energy gap. This work provides the first examples of crystalline diradical dianions of azaacenes with considerable diradical character.     

Preparation of two 99mTc(CO)3 labelled complexes with a 4-nitroimidazole isocyanide at different temperatures for molecular imaging of tumor hypoxia

Journal of Radioanalytical and Nuclear Chemistry - A 4-nitroimidazole isocyanide derivative (6) was synthesized and radiolabelled with 99mTc(CO)3 core in high yield. It was interesting to note that...     

对“Co2+鉴定”实验的再认识——批判性思维教育的最好案例之一

Taking the experiment of the "identification of Co²⁺" as an example, this article elaborates the flexible application of "flipped classroom" model in the chemical laboratory teaching. Specifically, students do the experiment first and have questions during the experimental process, then the teacher discusses and demonstrates with students base on their questions, leading students to reunderstand the classic experiment of the "identification of Co²⁺". Thus this article reveals about how to educate students to think and criticize in the teaching process.     

Age-Structured Population Dynamics with Nonlocal Diffusion

Random diffusive age-structured population models have been studied by many researchers. Though nonlocal diffusion processes are more applicable to many biological and physical problems compared with random diffusion processes, there are very few theoretical results on age-structured population models with nonlocal diffusion. In this paper our objective is to develop basic theory for age-structured population dynamics with nonlocal diffusion. In particular, we study the semigroup of linear operators associated to an age-structured model with nonlocal diffusion and use the spectral properties of its infinitesimal generator to determine the stability of the zero steady state. It is shown that (i) the structure of the semigroup for the age-structured model with nonlocal diffusion is essentially determined by that of the semigroups for the age-structured model without diffusion and the nonlocal operator when both birth and death rates are independent of spatial variables; (ii) the asymptotic behavior can be determined by the sign of spectral bound of the infinitesimal generator when both birth and death rates are dependent on spatial variables; (iii) the weak solution and comparison principle can be established when both birth and death rates are dependent on spatial variables and time; and (iv) the above results can be generalized to an age-size structured model. In addition, we compare our results with the age-structured model with Laplacian diffusion in the first two cases (i) and (ii).

     

Improvement of creep resistance of polytetrafluoroethylene films by nano-inclusions

To improve creep resistance of directional polytetrafluoroethylene (PTFE) films, epoxy grafted nano-SiO₂ is mixed with PTFE powder before sintering and calender rolling. The aligned macromolecular chains (especially those in amorphous region) of the composite films can be bundled up by the nanoparticles to share the applied stress together. In addition, incorporation of silica nanoparticles increases crystallinity of PTFE and favors microfibrillation of PTFE in the course of large deformation. As result, PTFE films exhibit lower creep strain and creep rate, and higher tensile strength and hardness. The work is believed to open an avenue for manufacturing high performance fluoropolymers by nano-inclusions.     

Interfacial Tension of Aqueous Three‐Phase Systems Formed by Triton X‐100/PEG/Dextran

A novel aqueous three‐phase system was formed spontaneously when a nonionic surfactant (Triton X‐100) and two polymers (PEG and dextran) were mixed. The interfacial tension between the phases was measured by the spinning drop method. It was shown that the values of interfacial tension were extremely small. The interfacial tensions of the top/middle phases were much lower than those of the middle/bottom phases. The interfacial tension was affected by component concentrations, temperature, added salts, and the density difference between two phases. Temperature exhibited a special effect on interfacial tension: with the increase of temperature, interfacial tension increases significantly.     

SYNCHRONIZATION STABILITY OF COMPLEX CONNECTED NETWORKS WITH DELAYS

Recently, much work has been devoted to the study of a large-scale complex system described by a network or a graph with complex topology, whose nodes are the elements of the system and whose edges represent the interactions among them. On the other hand, realistic modelling of many large networks with nonlocal interaction inevitably requires connection delays to be taken into account, since they naturally arise as a consequence of finite information transmission and processing speeds among the units. This paper gives the sufficient conditions guaranteeing the local and global synchronization stability of the complex connected networks by using Lyapunov functional.     

聚苯胺在电化学电容器中的应用

采用化学氧化聚和法制备了聚苯胺电极材料,所制备的聚苯胺具有高于420F/g的法拉第赝电容和良好的电化学特性.分别采用聚苯胺作为正极材料,高比容量活性碳作为负极,38%硫酸作为电解液制备了复合型电化学电容器.复合型电容器工作电压达到1.4V,最大电容器比容量达到57F/g,最大比能量达到15.5Wh/kg.电容器200mA/cm2放电条件下真实功率达到2.8W/g,峰值比功率达到20.4W/g.循环工作寿命超过1000次.     

Existence and stability of traveling wave fronts in reaction advection diffusion equations with nonlocal delay

This paper is concerned with the existence, uniqueness and globally asymptotic stability of traveling wave fronts in the quasi-monotone reaction advection diffusion equations with nonlocal delay. Under bistable assumption, we construct various pairs of super- and subsolutions and employ the comparison principle and the squeezing technique to prove that the equation has a unique nondecreasing traveling wave front (up to translation), which is monotonically increasing and globally asymptotically stable with phase shift. The influence of advection on the propagation speed is also considered. Comparing with the previous results, our results recovers and/or improves a number of existing ones. In particular, these results can be applied to a reaction advection diffusion equation with nonlocal delayed effect and a diffusion population model with distributed maturation delay, some new results are obtained.     

Probabilistic analysis of the frequencies of amino acid pairs within characterized protein sequences

Here, we describe a unique probabilistic evaluation of the 20, naturally occurring, amino acids and their distributions within the Swiss-Prot and Complete Human Genebank databases. We have developed a computational technique that imparts both directionality and length constraints into searches for unique combinations of amino acids within protein sequences. Using statistical approaches, we have carried out searches of all possible two- and three-residue motifs contained within these databases. This technique is based on the unusually high occurrence of a small number of these motifs when compared to the expected probability of finding a specific residue grouping within a given database. Subsequent filtering of this search to identify such unique combinations has provided several examples that can be used as markers to identify particular proteins within or across databases. We focus on three of these motifs, which were found to be of greatest interest to us. The CC, CM and a combination of the two, CCM motifs all occur either more or less frequently than would be predicted based on standard amino acid distributions within the entire human proteome.