电场诱导氧化石墨烯的极化动力学特性研究

本文通过外加电场改变氧化石墨烯团簇分子的共振能量,利用激光激发氧化石墨烯产生的共振荧光特性测量氧化石墨烯在电场作用下的极化动力学特性. 发现存在外加电场使得荧光共振峰的半高全宽趋于饱和的时间特性,而不同的氧化石墨烯团簇分子的荧光共振峰的暂态特性同时反映了电场对氧化石墨烯产生定向极化和变形极化的动力学特性. 关键词： 氧化石墨烯 团簇分子 电场 极化动力学     

Quantum anomalous Hall effect and related topological electronic states

Over a long period of exploration, the successful observation of quantized version of anomalous Hall effect (AHE) in thin film of magnetically doped topological insulator (TI) completed a quantum Hall trio—quantum Hall effect (QHE), quantum spin Hall effect (QSHE), and quantum anomalous Hall effect (QAHE). On the theoretical front, it was understood that the intrinsic AHE is related to Berry curvature and U(1) gauge field in momentum space. This understanding established connection between the QAHE and the topological properties of electronic structures characterized by the Chern number. With the time-reversal symmetry (TRS) broken by magnetization, a QAHE system carries dissipationless charge current at edges, similar to the QHE where an external magnetic field is necessary. The QAHE and corresponding Chern insulators are also closely related to other topological electronic states, such as TIs and topological semimetals, which have been extensively studied recently and have been known to exist in various compounds. First-principles electronic structure calculations play important roles not only for the understanding of fundamental physics in this field, but also towards the prediction and realization of realistic compounds. In this article, a theoretical review on the Berry phase mechanism and related topological electronic states in terms of various topological invariants will be given with focus on the QAHE and Chern insulators. We will introduce the Wilson loop method and the band inversion mechanism for the selection and design of topological materials, and discuss the predictive power of first-principles calculations. Finally, remaining issues, challenges and possible applications for future investigations in the field will be addressed.     

Microstructure,Rheology, and Potential Oil Absorbency of Poly(Butyl Methacrylate) and Poly(Hydroxyethyl Methacrylate) Blends

To prepare oil-absorptive polymers with moderate cross-linking structure, poly(butyl methacrylate) (PBMA) was synthesized as a linear hydrophobic polymer by suspension polymerization. In addition, hydroxyethyl methacrylate (HEMA), as a monomer, which could construct a network structure among the macromolecules via hydrogen bond interactions, was solution polymerized in dimethylacetamide (DMAc) with PBMA, yielding a polymer blend of PBMA and PHEMA. The solution of the polymer blend was investigated by rotational viscometry and extended rheometry. The results showed that the viscosity varied greatly with the temperature and shear rate for three different compositions. Fourier transform infrared (FTIR) spectra indicated that an entanglement or interlocking cross-linking structure of molecular chains was constructed by hydrogen bonds. The results from nuclear magnetic resonance (NMR) spectra exhibited a downfield movement of the proton peak as influenced by end groups or hydroxyls in the polymer chains. The rheological measurements demonstrated that the cross-linking structure greatly affected the rheological behavior of the blend solution. In addition, the cross-linking structure was also evaluated by oil absorbency of films.     

Interaction between isoamyl adenine and rice cytokinin oxidase

Cytokinin (CTK) dehydrogenase is responsible for regulating the endogenous CTK content by oxidative removal of the side chain. Herein, we have applied fluorescence method to study the interaction between CTK dehydrogenase and CTK in vitro and obtain some parameters of their interaction. We found that addition of isopentenyl adenine can quench the fluorescence of CTK dehydrogenase, and the quenching mechanism was to be a static quenching procedure. We have measured the number of binding sites n and the apparent binding constant K and have calculated the thermodynamics parameter ΔH, ΔG, and ΔS by fluorescence quenching method. Based on thermodynamics parameter’s results, we concluded that their binding reaction was both entropy driven and the enthalpy driven, and the Van der Waals force and hydrogen bond force played a major role in the interaction. Based on the synchronous fluorescence spectrometry results, we demonstrated that the binding site between isopentenyl adenine and CTK dehydrogenase is in the microenvironment of both tryptophan and tyrosine. The fluorescence signal of coenzyme, flavin adenine dinucleotide, decreases gradually with the addition of isopentenyl adenine. And this method can be used for isopentenyl adenine routine assay. Under optimized experimental parameters, the linear segment increases from 0.6 µM to 100 µM with a regression equation of ΔF = 0.04 + 0.15c_ip (r = 0.999, c_ip in µM) with the detection limit of 0.15 µM iP.     

Effect of hydrogen introduced by channelling implantation on the microstructures in silicon wafers

High-resolution transmission electron microscopy has been employed to study the platelet defects before annealing and the extended defects generated by annealing in the channelling-implanted silicon wafers. It has been found that there apparently appear platelet defects of quite great size and spacing at the maximum projected range of ions (R _max). Additionally, the cracks induced by annealing at 550 °C are generated around R _max instead of the average projected range of ions (R _p) as it is in the non-channelling-implanted samples. Moreover, after annealing at 1000 °C, cracks without branches and cavities arranging in a single array, different from the forked cracks and cavities arranged in several arrays in the non-channelling-implanted samples, are observed in the channelling-implanted silicon wafers. It is suggested that those special microstructure characteristics are ascribed to the channelling effect of implanted hydrogen ions.     

A nonsmooth Newton method for variational inequalities,I: Theory

This paper presents a modified damped Newton algorithm for solving variational inequality problems based on formulating this problem as a system of equations using the Minty map. The proposed modified damped-Newton method insures convergence and locally quadratic convergence under the assumption of regularity. Under the assumption ofweak regularity and some mild conditions, the modified algorithm is shown to always create a descent direction and converge to the solution. Hence, this new algorithm is often suitable for many applications where regularity does not hold. Part II of this paper presents the results of extensive computational testing of this new method.Corresponding author.     

A NONMONOTONE TRUST REGION METHOD FOR NONLINEAR LEAST SQUARES PROBLEMS

In this paper we present a nonmonotone trust region method for nonlinear least squares problems with zero-residual and prove its convergence properties. The extensive numerical results are reported which show that the nonmonotone trust region method is generally superior to the usual trust region method.     

Bergman空间A~p（ψ）中函数之零点

设Ｄ是Ｃ中的单位圆盘及为［０，１）上的正规函数。对于０＜Ｐ＜∞，这样的函数用于定义一个带权为￣ｐ（｜ｚ｜）／（１－｜ｚ｜￣２）的Ｂｅｒｇｍａｎ空间Ａ￣ｐ．本文刻画了Ａ￣ｐ中函数之零点集的结构．作为应用，又给出了Ａ￣ｐ中函数序列插值的条件。     

An improved evaluation of the neutron background in the PandaX-Ⅱ experiment

In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively.