Yb3+:KY(WO4)2晶体生长与光谱性能

采用泡生法生长YbKYW晶体, 通过XRD分析确认所生长的晶体为β-YbKYW. TG-DTA测量结果表明, 晶体的熔点为1045 ℃, 相变温度为1010 ℃. 测得晶体红外光谱和拉曼光谱, 对其峰值所属振动的归属进行了指认, 并测量了晶体的吸收光谱和荧光光谱. 结果表明, YbKYW晶体在940, 980 nm附近有很强的吸收峰, 主峰980 nm处的吸收截面积为1.34×10-19 cm2;该晶体在990, 1010, 1030 nm附近都有较强的荧光发射峰, 其中最强发射峰1030 nm的发射线宽高达16 nm, 有望作为可调谐激光器的增益介质. 计算得其1030 nm受激发射截面积为3.1×10-20 cm2.     

Growth and annealing of zinc-blende CdSe thin films on GaAs (0 0 1) by molecular beam epitaxy

CdSe thin films have been grown on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). The effects of substrate temperature and annealing treatment on the structural properties of CdSe layers were investigated. The growth rate slightly decreases due to the accelerated desorption of Cd from CdSe surface with an increase in the temperature. The sample grown at 260 °C shows a polycrystalline structure with rough surface. As the temperature increases over 300 °C, crystalline CdSe (0 0 1) epilayers with zinc-blende structure are achieved and the structural quality is improved remarkably. The epilayer grown at 340 °C displays the narrowest full-width at half-maximum (FWHM) from (0 0 4) reflection in double-crystal X-ray rocking curve (DCXRC) and the smallest root-mean-square (RMS) roughness of 0.816 nm. Additionally, samples fabricated at 320 °C were annealed in air for 30 min to study the films’ thermal stability. X-ray diffraction (XRD) results indicate that the zinc-blende structure remains unchanged when the annealing temperature is elevated to 460 °C, meaning a good thermal stability of the cubic CdSe epilayers.     

Evaluation of in vitro antioxidant activities of soyasaponins from soy hypocotyls in human HepG2 cell line

Soyasaponins were shown to have a wide range of biological activities in previous studies; however, the activities of their monomeric compounds are unclear. The aim of this study was to evaluate the in vitro antioxidant activities of soyasaponins in HepG2 cells. Four soyasaponins were isolated from soy hypocotyls and identified as soyasaponin Aa, Ab, Ba, and Bb. The protective effects of these soyasaponins against production of hydrogen peroxide-induced reactive oxygen species in cells were investigated. The cellular antioxidant activity of soyasaponins was found to be in a dose-dependent manner at concentrations ranging between 25 and 400 μg/mL in 24 h. Finally, based on cell morphology observations, group A soyasaponins showed better cellular antioxidant activity and anti-oxidative enzyme activity than group B ones, with an optimal concentration of 100 μg/mL.     

Modeling,nonlinear dynamic analysis and control of fractional PMSG of wind turbine

This study aims to reveal the laws of the relationship between fractional-order system and integer-order system. Meanwhile, delayed feedback control is introduced to control the fractional-order PMSG (permanent magnet synchronous generator) model of a wind turbine. First, the fractional-order mathematical model of PMSG is established. Next, numerical simulations under different system orders are given and the system dynamic behaviors are analyzed in detail. Then, the delayed feedback control method is introduced to control the fractional-order PMSG and the control results when different parameters vary are analyzed. Complex dynamics are presented and some interesting phenomena are discovered. It is found that the system order influences the dynamics of the system in many aspects such as chaos pattern, bifurcation behavior, period window, shape and size of strange attractor. The delayed time, feedback gain, feedback limitation, system order can obviously influence the control result except the initial state of the system. Moreover, the feedback limitation has a minimum to successfully control the system to stable states and the system order also has a maximum to do so.     

Au-impregnated polyacrylonitrile (PAN)/polythiophene (PTH) core-shell nanofibers with high-performance semiconducting properties

FETs based on Au-impregnated polyacrylonitrile (PAN)/polythiophene (PTH) core-shell nanofibers have been fabricated and exhibit high mobility (～2.0 cm(2) V(-1) s(-1)).     

Which mechanism operates in the electron-transfer process at liquid/liquid interfaces?

We present a more general expression for the relationship of potential dependence, which implies that a change in the interfacial drop across the interface has little effect on the free energy of the reaction, but mainly affects the surface concentration of reactant in each phase. Abundant experimental results from several well-known groups are analyzed in great detail to confirm our conclusion. At the same time, we define a new parameter named Frumkin correction factor to describe this relationship of potential dependence, which expresses the thermodynamic effect of double diffuse layers within both phases in contrast with the so often suggested kinetic electron-transfer (ET) coefficient; we also find that it depends on two intimately related aspects: the charges of reactive species and the ratio of the diffuse layer potential to the total potential within each phase, so it is quite arbitrary to ignore the diffuse layer effect in the aqueous phase just because of its relatively small values. In addition, a fascinating question on the inverted region at liquid/liquid interfaces has been successfully interpreted by an opposite surface concentration effect, which was often considered as a kinetic Marcus inverse by most groups.     

Skeletal remodeling of chalcone-based pyridinium salts to access isoindoline polycycles and their bridged derivatives

Simultaneous deconstructive ring-opening and skeletal reconstruction of an inert, aromatic pyridinium ring is of great importance in synthetic communities. However, research in this area is still in its infancy. Here, a skeletal re-modeling strategy was developed to transform chalcone-based pyridinium salts into structurally intriguing polycyclic isoindolines through a dearomative ring-opening/ring-closing sequence. Two distinct driving forces for the deconstruction of the pyridinium core were involved in these transformations. One was the unprecedented harnessing of the instability of in situ generated cyclic β-aminoketones, and the other was the instability of the resultant N,N-ketals. The desired isoindoline polycycles could undergo the Wittig reaction with various phosphorus ylides to achieve structural diversity and complexity. Notably, by tuning the Wittig conditions by addition of one equivalent of base, an additional bridged ring was introduced. A plausible mechanism was proposed on the basis of control experiments and theoretical calculations.

A novel skeletal remodeling strategy to transform chalcone-based pyridinium salts into structurally intriguing polycyclic isoindolines was achieved through a dearomative ring-opening/ring-closing sequence.     

Hydrothermal syntheses, structures, and magnetic properties of (NH4)2NaVF6 and Na3VF6

The single crystals of perovskite fluorides (NH₄)₂NaVF₆ and Na₃VF₆ were synthesized under mild hydrothermal conditions. The structures of the compounds were determined by means of single-crystal and powder X-ray diffraction analyses, respectively. (NH₄)₂NaVF₆ has a cubic elpasolite-type structure and crystallizes in the space group with lattice constant a=8.495(0) Å. Rietveld refinement indicates that Na₃VF₆ has a monoclinic structure and is in space group P2₁/n. The compounds were characterized by scanning electron microscopy, thermogravimetric and differential thermal analysis, and variable temperature magnetic susceptibility. With the temperature decreasing, the magnetic studies of the compounds showed the magnetic ordering was related to the crystallographic features and isolated magnetic units.     

??????????????????????

通过对拉压杆概念的回顾以及出现在教科书中几个实例的分析,一方面说明规范化载荷平衡分析的必要性,另一方面展示杆件分析类型的标准与意义.     

Semi-Synthesis of Harringtonolide Derivatives and Their Antiproliferative Activity

Harringtonolide (HO), a natural product isolated from Cephalotaxus harringtonia, exhibits potent antiproliferative activity. However, little information has been reported on the systematic structure−activity relationship (SAR) of HO derivatives. Modifications on tropone, lactone, and allyl positions of HO (1) were carried out to provide 17 derivatives (2–13, 11a–11f). The in vitro antiproliferative activity against four cancer cell lines (HCT-116, A375, A549, and Huh-7) and one normal cell line (L-02) was tested. Amongst these novel derivatives, compound 6 exhibited comparable cell growth inhibitory activity to HO and displayed better selectivity index (SI = 56.5) between Huh-7 and L-02 cells. The SAR results revealed that the tropone and lactone moieties are essential for the cytotoxic activities, which provided useful suggestions for further structural optimization of HO.