Synthesis of Amphiphilic ABCBA-Type Pentablock Copolymer from Consecutive ATRPs and Self-Assembly in Aqueous Solution

Summary: A novel amphiphilic ABCBA-type pentablock copolymer with properties that are sensitive to temperature and pH, poly(2-dimethylaminoethyl methacrylate)-block-poly(2,2,2-trifluoroethyl methacrylate)-block-poly(ε-caprolactone)-block-poly(2,2,2- trifluoroethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PDMAEMA- b-PTFEMA-b-PCL-b-PTFEMA-b-PDMAEMA), was synthesized via consecutive atom transfer radical polymerizations (ATRPs). The copolymers obtained were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (NMR) spectroscopy, respectively. The aggregation behaviors of the pentablock copolymers in aqueous solution with different pH (pH = 4.0, 7.0 and 8.5) were studied. Transmission electron microscopic images revealed that spherical micelles from self-assembly of the pentablock copolymer were prevalent in all cases. The mean diameters of these micelles increased from 34, 46, to 119 nm when the pH of the aqueous solution decreased from 8.5, 7.0, to 4.0, respectively.     

Effect of tubular chiralities of single-walled ZnO nanotubes on electronic transport

The electronic transport properties of single-walled ZnO nanotubes with different chiralities are investigated by nonequilibrium Green's function combined with density functional theory. In this paper we consider three representative ZnO nanotubes, namely (3, 3) armchair, (5, 0) zigzag, and (4, 2) chiral, with a similar diameter of about 5.4 Å. Short nanotubes exhibit good conductance behavior. As the tube length increases, the conductance decreases at low bias and the nanotubes indicate semiconducting behavior. The current-voltage characteristics of the nanotubes longer than 3 nm depend weakly on the length of the tubes. The armchair and chiral ZnO nanotubes with the same length and diameter have almost overlapped current-voltage curves. The electron transport behaviors are analyzed in terms of the transmission spectra, density of states and charge population of these nanotubes. The results indicate that the resonant peaks above the Fermi level are responsible for electric currents. However, the zigzag ZnO nanotubes exhibit asymmetric current-voltage curves attributed to the built-in polarization field and give larger current than the armchair and chiral nanotubes at the same bias. The features explored here strongly suggest that the ZnO nanotubes are stable, flexible structures, which are valuable in Nano-Electromechanical System.     

Initial growth and microstructure feature of Ag films prepared by very-high-frequency magnetron sputtering

The initial growth and microstructure feature of Ag films formation were investigated, which were prepared by using the very-high-frequency(VHF)(60 MHz) magnetron sputtering. Because of the moderate energy and very low flux density of ions impinging on the substrate, the evolutions of initial growth for Ag films formation were well controlled by varying the sputtering power. It was found that the initial growth of Ag films followed the island(Volmer—Weber, VW) growth mode, but before the island nucleation, the adsorption of Ag nanoparticles and the formation of Ag clusters dominated the growth. Therefore, the whole initial stages of Ag films formation included the adsorption of nanoparticles, the formation of clusters, the nucleation by the nanoparticles and clusters simultaneously, the islands formation, and the coalescence of islands.     

Effect of driving frequency on the structure of silicon grown on Ag(111) films by very-high-frequency magnetron sputtering

The effect of driving frequency on the structure of silicon grown on Ag(111) film is investigated, which was prepared by using the very-high-frequency(VHF)(40.68 MHz and 60 MHz) magnetron sputtering. The energy and flux density of the ions impinging on the substrate are also analyzed. It is found that for the 60-MHz VHF magnetron sputtering, the surface of silicon on Ag(111) film exhibits a small cone structure, similar to that of Ag(111) film substrate, indicating a better microstructure continuity. However, for the 40.68-MHz VHF magnetron sputtering, the surface of silicon on Ag(111) film shows a hybrid structure of hollowed-cones and hollowed-particles, which is completely different from that of Ag(111)film. The change of silicon structure is closely related to the differences in the ion energy and flux density controlled by the driving frequency of sputtering.     

xLi[Li1/3Mn2/3]O2-(1-x)LiNi5/12Mn5/12Co2/12O2(0≤x≤0.8)的结构与电化学性能

采用喷雾干燥法制备了xLi[Li_1/3Mn_2/3]O₂-(1-x)LiNi_5/12Mn_5/12Co_2/12O₂(0≤x≤0.8)系列富锂层状固溶体正极材料, 并通过X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、X射线光电子能谱(XPS)、电化学阻抗测试(EIS)以及充放电测试等多种手段研究了样品组分中Li₂MnO₃ 含量变化对材料结构及电化学性能的影响.研究发现, 材料的微观结构随着Li₂MnO₃含量的增加而逐渐发生转变.当x≤0.2时, 样品的微观结构与其母体材料LiNi_5/12Mn_5/12Co_2/12O₂相似; 而当x≥0.4时, 样品的微观结构与Li₂MnO₃有很高的相似性.当x=0.3时, 材料表现出两相共存的特征.HRTEM结果显示, 随着Li₂MnO₃含量的增加, 样品中过渡金属原子的排列逐渐由长程有序转变为长程无序而短程有序, 并且在高Li₂MnO₃含量的样品中观察到了金属阳离子混排的现象.充放电测试结果表明, 当x≤0.6时, 材料的放电比容量随着x的增加而增加; 当x>0.6时, 其放电比容量则随着x的增加而下降; 当x=0.6时, 放电比容量最高, 室温及高温(50℃)下分别为260 和304 mA·h/g.EIS研究结果表明, 这种微观结构上由有序向无序的转变会导致材料电荷转移阻抗的增加, 进而影响材料的电化学性能.     

Entanglement Resonance of End Spins in Different Spin Chains

The entanglement resonance in anisotropic spin-1/2 Heisenberg chains of different couplings is investigated when the nearest neighbor coupling is periodically modulated with external magnetic field. When the modulation frequency equals twice of the magnetic field, the entanglement resonance is larger than that at other modulation frequencies and decreases as the number of spins in the chain increases. When the modulation frequency equals the
magnetic field, the entanglement resonance can be reduced to a quite low value by varying the coupling along z axis.     

依赖机器的两台机自由作业排序问题

文章研究加工时间仅依赖于机器的两台机自由作业排序问题 O2 | pij = pi, p2 < p1 < 2p2, Non-Idle | ΣCj。项思明和唐国春(1998)证明了可将该问题转化成指派问题。俞文ci 和应刚(1998)给出了这一问题的显式解,并用较长的篇幅证明其显式解的正确性;他们还举例说明所给出的显式最优排序并不排除其他形式的最优解的存在;但他们未说明所给出的显式解何时才是唯一最优解。本文将给出问题 O2 | pij = pi, p2 < p1 < 2p2, Non-Idle | ΣCj的显式解的直观的最优性证明,并讨论问题显式解何时是唯一的最优解。     

Staggered Quadrupolar Phase and Bicritical Point of Spin-1 Bond and Anisotropy Dilution Blume-Emery-Griffiths Model

Within the effective field theory (EFT), staggered quadrupolar phase and bicritical point of spin-1 bond and anisotropy dilution Blume-Emery-Griffiths model is studied on simple cubic lattice in the restricted range of biquadratic interaction and bilinear interaction ratio α≤-1. The phase diagrams present a line of staggered quadrupolar-paramagnetic (SQ-P) phase and a line of ferromagnetic-paramagnetic (F-P) phase, separated by a bicritical point (BCP). A large negative ratio and two different dilution factors magnify the range of the SQ phase and reduce range of ferromagnetic phase in T-α or T-D plane. These parameters can assist the reentrant behavior of the SQ-P line and suppress that of the F-P line. The influence of bond dilution on the BCP is dissimilar to that of anisotropy dilution. There is a degenerate pattern at ground state in T-D plane. Some results obtained by the pure BEG model is in qualitative agreement with the results of Monte Carlo simulations.     

Ferromagnetic Properties of Bond-Dilution and Random Positive or Negative Uniaxial Anisotropy Blume-Capel Model

We study the ferromagnetic properties of spin-1 system, which is considered in the frame of the bonddilution and random positive or negative anisotropy Blume-Capel model in the effective field theory and a cutting approximation. The investigation of phase diagrams displays some rich properties of the trajectory of tricritical point,reentrant phenomena at low temperatures. Under certain both bond concentrations and random negative anisotropy,there are new transition lines of double tricritical points. So special emphasis is placed on the influence of the bond dilution and random anisotropy on phase diagrams. The magnetizations of the system are also discussed. Some results have not been revealed in previous reports.     

窄域上2D弱阻尼KdV方程的局部吸引子

得到了窄域上2D的非自共轭且非扇形的弱阻尼KdV方程的局部吸引子的存在性.