Enhanced robustness of zero-line modes in graphene via magnetic field

We systematically studied the influence of magnetic field on zero-line modes (ZLMs) in graphene and demonstrated the physical origin of their enhanced robustness by employing nonequilibrium Green’s functions and the Landauer–Büttiker formula. We found that a perpendicular magnetic field can separate the wavefunctions of the counter-propagating kink states into opposite directions. Specifically, the separation vanishes at the charge neutrality point and increases as the Fermi level deviates from the charge neutrality point and can reach a magnitude comparable to the wavefunction spread at a moderate field strength. Such spatial separation of oppositely propagating ZLMs effectively suppresses backscattering and is more significant under zigzag boundary condition than under armchair boundary condition. Moreover, the presence of magnetic field enlarges the bulk gap and suppresses the bound states, thereby further reducing the scattering. These mechanisms effectively increase the mean free paths of the ZLMs to approximately 1 μm in the presence of a disorder.     

Number of irreducible polynomials and pairs of relatively prime polynomials in several variables over finite fields

We discuss several enumerative results for irreducible polynomials of a given degree and pairs of relatively prime polynomials of given degrees in several variables over finite fields. Two notions of degree, the total degree and the vector degree, are considered. We show that the number of irreducibles can be computed recursively by degree and that the number of relatively prime pairs can be expressed in terms of the number of irreducibles. We also obtain asymptotic formulas for the number of irreducibles and the number of relatively prime pairs. The asymptotic formulas for the number of irreducibles generalize and improve several previous results by Carlitz, Cohen and Bodin.     

One-step synthesis of magnetic composite UiO-66/Fe3O4/GO for the removal of radioactive cesium ions

Journal of Radioanalytical and Nuclear Chemistry - In this study, the UiO-66/Fe3O4/GO composite was prepared by one step method for removal of cesium ions (Cs+) in water and exhibited excellent...     

Radioanalysis of ultra-low level radionuclides for environmental tracer studies and decommissioning of nuclear facilities

Journal of Radioanalytical and Nuclear Chemistry - Determination of long-lived radionuclides is critical for environmental radioactivity investigation, environmental processes studies and...     

连续函数与p幂可和函数的Jackson算子逼近

对f∈X是(X是G2x或D2x.1≤p< ∞)以及Jackson算子证明了如下不等式‖J.（f）-f‖x≤1+2π/3-3/（4π）+89π/24（2n2+1）ω（f·1/n）x,从而改进和推广了文献[1]的工作。     

Synthesis, characterization, and photovoltaic properties of a low band gap polymer based on silole-containing polythiophenes and 2,1,3-benzothiadiazole

A new low band gap silole-containing conjugated polymer, PSBTBT, was designed and synthesized. Photovoltaic properties of PSBTBT were initially investigated, and an average power conversion efficiency (PCE) of 4.7% with a best PCE of 5.1% was recorded under illumination (AM 1.5G, 100 mW/cm(2)). The response range of the device covers the whole visible range from 380 to 800 nm. These results indicate that PSBTBT is a promising polymer material for applications in polymer solar cells.     

Two-dimensional β-ketoenamine linked azo covalent organic frameworks as heterogeneous catalysts for photo-induced RCMP

Photo-induced reversible complexation-mediated polymerization (RCMP) is a green and economical method to prepare polymers with precise molecular weights, narrow molecular weight distributions and functionally active chain ends. Covalent organic frameworks (COFs) are a promising heterogeneous photocatalyst for mediating RCMP due to their adjustable structure, band gap, and porosity. In this work, 1,3,5-triformylphloroglucinol (Tp) and p-azoaniline (Azo) were selected to construct 2D β-ketoenamine linked Tp-Azo-COF as a heterogeneous photocatalyst to trigger RCMP under white light irradiation. A series of polymers with controllable molecular weight and narrow molecular weight distribution were successfully prepared by using Tp-Azo-COF as photocatalysis. On/off light experiments confirmed the good spatiotemporal control feature, and chain expansion experiments demonstrated the high “activity” of polymer chain ends. Furthermore, the mechanistic research elucidated that electron transfer between Tp-Azo-COF and initiator occurred, allowing the formation of reactive radicals to mediate RCMP. Density functional theory calculations revealed that the coordination of iodine on the initiator to catalyst obviously reduced the bond dissociation energy, leading to enhance in the polymerization rate. This work provides a platform for constructing heterogeneous photocatalysts with more efficient and stable to mediate RCMP.     

Elution–extrusion counter-current chromatographic separation and theoretical mechanism of antioxidant from Robinia pseudoacacia flower

Robinia pseudoacacia flowers have attracted much attention because of numerous bioactivities. In this study, its extract showed the potential scavenging ability for 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) and 1,1-diphenyl-2-picrylhydrazyl free radicals. Under the guidance of antioxidant activity, the antioxidant extract was enriched by liquid-liquid extraction. The partition coefficients of the two main components in antioxidant extracts differed greatly, so in this study, elution-extrusion counter-current chromatography with the solvent system of n-hexane-ethyl acetate-methanol-water (2.5:5:2.5:5, v/v) was used to enhance the separation efficiency, and the two main components were successfully obtained. Among them, kaempferol showed strong antioxidant activity, which can be responsible for the activity of the extract. In order to deeply understand the antioxidant mechanism of kaempferol, the thermodynamics, frontier molecular orbital, and kinetics of scavenging free radicals were investigated by density functional theory. The results showed that 4′-OH in kaempferol was the most active group, which can scavenge free radicals by hydrogen atom transfer in non-polar solvents and activate 3-OH to generate double hydrogen atom transfer in the gas phase. But in polar solvents, it was more inclined to clear radicals through single electron transfer and proton transfer. The kinetic result showed that kaempferol needed 9.17 kcal/mol of activation energy to scavenge free radicals.     

Plasma Copolymerization of Pyrrole with Si-Compounds

The plasma copolymerization of pyrrole with hexamethyldisiloxane, hexamethyldisilane and hexamethyldisilazane was investigated with regard to the polymer deposition characteristics and the properties of the product films. Deposition rates were evaluated by monitoring the weight increase of the deposits over time, and the effect of varying the experimental set up parameters was determined. The results of deposition rates and quantitative IR analysis suggested that the increasing amounts of Si-components were incorporated into the polymer matrix as the supply ratio of the Si-monomer was increased. The Si-component in the copolymer brought some dramatic effects on the physical properties of the films and changed the hydrophobicity of the surfaces, as reflected in the advancing and receding contact angle measurements. The experimental results obtained are discussed in terms of the contribution of the polar and dispersion components of surface energy.     

Synthesis and structure of upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns and change of cavity in response to fluoride anion

The upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns were constructed effectively by macrocyclic condensation reaction of diamines with dichlorinated tetraoxacalix[2]arene[2]triazine intermediates that were synthesized from the stepwise fragment coupling reactions of 3,5-dihydroxybenzoic acid esters with cyanuric chlorides. Because of the formation of conjugation of amino groups with triazine rings, tetraoxacalix[2]arene[2]triazine azacrowns existed in a mixture of syn- and anti-isomeric forms. Both fluorescence titration and 1H NMR spectroscopic study showed that tetraoxacalix[2]arene[2]triazine azacrowns interacted with fluoride anion, leading to cavity changes of the host molecules.