Electrochemical investigation on MEH-PPV/C60 nanocomposite Langmuir–Schaefer films

Ultrathin films of MEH-PPV/C₆₀ nanocomposite with various C₆₀ content were fabricated onto ITO-coated glasses by means of Langmuir–Schaefer method. The cyclic voltammetric investigation on these ultrathin films suggested that these nanocomposites show distinct electrochemical behaviors at various composition ratios.     

Stepwise conformational transition of crystalline disodium adenosine 5′-triphosphate with relative humidity as studied by high resolution solid state 13C and 31P NMR

Stepwise conformational transition of disodium adenosine 5′-triphosphate (Na₂ATP) crystals as a function of relative humidity (RH), was examined by means of high resolution solid state NMR spectroscopy. The presence of two types of molecules, A and B, with altered conformations in an asymmetric unit, is evident from both ³¹P and ¹³C NMR spectra, irrespective of the three different crystalline forms, mono-, di- and trihydrates, in which, cell parameters changed linearly with RH. Hydration-dependent conformational transition from the monohydrate (RH 0–10%) through dihydrate (20–40%) to trihydrate (60–90%), was well monitored by stepwise upfield displacements of the C1′ ¹³C signals of ribose moiety (molecule B), although, the corresponding peak for the molecule A, is almost unchanged. This means that, adaptation of stepwise structural transitions to the linear expansion of cell parameters is almost entirely ascribed to the conformational readjustment of the molecule B, together with varying proportion of two types of hydrate forms, at the RH range of 20–40%. We consider that, small clusters or thin layers are formed in the beginning of the transition and subsequently, the number of them, rather than the size or thickness increases, because the phosphorous spin–lattice relaxation times, T₁^P, for the three phosphorous nuclei, including those of mixed state, of the two hydrate forms, turned out to be similar due to sufficient fast spin diffusion rates among them. Since only one direction of the cell parameters is changed, as determined by the previous X-ray diffraction study, we conclude that thin layer type micro crystals might be produced during the stepwise transition. Further, it was found that, these molecules acquired motional flexibility mainly at the bound water molecules, together with increased relative humidity, as determined by a variety of relaxation parameters.     

Direct numerical simulation of the turbulent flow in a pipe with annular cross section

The turbulent flow in a pipe of annular cross section is studied for the first time through a direct numerical simulation (DNS) using the Navier–Stokes equations written in cylindrical coordinates. To this aim a novel numerical method is developed, which extends to the cylindrical coordinate system an existing, efficient method designed for cartesian coordinates, and allows us to eliminate the pressure and formulate the problem in two scalar unknowns. The unnecessary increase of resolution at smaller radius typically brought about by polar coordinates, with its consequent stability limitations, is avoided by changing the number of azimuthal Fourier modes with the radial coordinate itself. In addition, the azimuthal extension of the computational domain is reduced, for the cases with lowest curvature, by considering only a part of the annulus, without loss of physical significance of the results. A computer code based on this method is run on a desktop PC for the simulation (with up to 16 million degrees of freedom) of the turbulent flow in a pipe with annular cross section, in a range of relatively low curvatures. This investigation highlights that curvature effects are already evident, even on first order turbulence statistics like the mean axial velocity distribution, in a low-curvature range where it is commonly believed that the flow should be hardly distinguishable from the flow over a plane surface.     

SiCN thin film prepared at room temperature by r.f. reactive sputtering

Silicon–carbon nitride (SiCN) thin films were deposited on Si substrate at room temperature by r.f. reactive sputtering. Fourier transform infrared spectroscopy (FTIR), optical absorption spectra (α(λ)) and electrical conductivity (σ) were studied for the thin films. The effect of the annealing on IR and σ was investigated at different temperatures. IR analysis indicates that Si–H, C–N, Si–C, Si–N, C–N and CN bonds are present in a-SiCN:H films. A shift of the stretching mode for Si–H bond to the high-wavenumber side is observed with increasing the nitrogen flow ratio γ_N2(=N₂/(Ar+H₂+N₂+CH₄)). The shift is from 2000 to 2190 cm⁻¹ when γ_N2=13.7%. The study shows that the film structure and optical and electrical properties are obviously modified readily by controlling the process parameters of deposition. The improvement in the film properties, e.g., good thermal stability, is explained mainly in terms of the cross-linked structure between the Si, C and N atoms.     

Study of the spin reorientation phenomenon in Nd2(Fe, Si)14BHy

We have studied the influence of the Si for Fe substitution and of the H insertion on the spin reorientation phenomenon in the Nd₂Fe₁₄B phases. To determine the temperature of spin reorientation and the tilt angle between the c-axis and the easy magnetisation direction, we have measured the angular dependence of the components of the magnetisation vector. Our measurements are based on powder samples that have been previously aligned under an external magnetic field. The Si for Fe substitution induces a decrease of the spin reorientation temperature and of the tilt angle. Meanwhile, we have found that the tilt angles are almost the same for Nd₂Fe₁₃SiB and Nd₂Fe₁₂Si₂B. These features are analysed in terms of changes in the crystal electric field and the unit cell volume induced by the Si for Fe substitution. The insertion of hydrogen in the Si-containing samples leads to an additive decrease of the spin reorientation temperature. This decrease is not linked to a change in the tilt angle at 4 K but to a different thermal behaviour in the H-containing samples. The magnitude of the effects of H insertion on the crystal electric field in comparison with the Si for Fe substitution is discussed together with the role of the lattice expansion.     

Theoretical studies on the reactions OH + CH3COCCl2 X (X = F, Cl, Br)

Theoretical investigations are carried out on the title reactions by means of the direct dynamics method. The optimized geometries, frequencies and minimum energy path are obtained at the MP2/6-31 + G(d,p) level, and energetic information is further refined at the MC-QCISD (single-point) level. The rate constants for both reactions are calculated by the improved canonical variational transition state theory with the small-curvature tunneling correction in a wide temperature range 200–3,000 K. The theoretical rate constant is in good agreement with the available experimental data. Furthermore, the effects of different halogen substitution on the rate constants are also discussed.     

The Decomposition and uniqueness of n-Lie Superalgebras

In this paper, the definitions and some properties of n-Lie superalgebras are presented. Our main aim is to study the decomposition and uniqueness of finite dimensional n-Lie superalgebras with trivial center. Aecoding to the decomposition of n-Lie superalgebras, we obtain the decomposition of inner derivation superalgebras and derivation superalgebras respectively. Furthermore, we discuss some properties about the centroid of n-Lie superalgebras, so we can see its application in the decomposition of n-Lie superalgebras.     

电喷雾萃取电离质谱快速测定牙膏胶体中的二甘醇

将自行研制的电喷雾萃取电离源(EESI)和LTQ XL质谱仪耦合, 建立了选择性离子化快速测定牙膏胶状纳米级复杂基质样品中微量二甘醇的EESI-MS方法. 实验结果表明, 二甘醇与NH4+, Na+和K+离子在一级质谱中形成特征非共价配合物, 其它大量组分如纳米粒子及胶质等对测定无干扰. 该方法的样品消耗量约0.1 g, 灵敏度高, 单个样品的分析时间不到2 min, 可用于牙膏胶体中低含量二甘醇的选择性快速测定.     

鸡蛋中三聚氰胺的表面解吸常压化学电离串联质谱法成像

以表面解吸常压化学电离(SDAPCI)串联质谱中获得的三聚氰胺特征碎片离子(m/z 85)为探针,对熟鸡蛋切面进行二维质谱扫描,用不同颜色表示三聚氰胺信号强度的高低,获得了熟鸡蛋切面中三聚氰胺的质谱影像.三聚氰胺的空间分辨率达0.06 mm2,最小采样面积占成像面积的十万分之五.图像表明,绝大部分三聚氰胺(＞99.8%),分布在蛋清中,但分布不均匀;而蛋黄中基本不含三聚氰胺.     

Preparation and properties of UV irradiation-induced crosslinked sulfonated poly(ether ether ketone) proton exchange membranes

The crosslinkable sulfonated poly(ether ether ketone)s (SPEEKs) were synthesized by nucleophilic substitution reaction of diallyl bisphenol A, tert-butylhydroquinone, 4,4′-difluorobenzophenone and sodium 5,5′-carbonylbis(2-fluorobenzene-sulfonate). The SPEEKs with high intrinsic viscosity showed good solubility and could be cast into flexible and transparent membranes. The SPEEK membranes containing benzophenone (BP) and triethylamine (TEA) photo-initiator system were treated by UV light to promote crosslinking. The experimental results revealed that the crosslinked membrane with 10 min irradiation time showed the most potential as proton exchange membrane for direct methanol fuel cell applications. When the irradiation time increased from 0 to 10 min, the water uptake decreased from 29.1 to 26.1%, and the tensile modulus and the tensile strength enhanced sharply from 0.80 to 1.44 GPa and from 40.3 to 63.4 MPa, respectively. In addition, the methanol diffusion coefficient reduced sharply from 1.70 × 10⁻⁶ to 7.42 × 10⁻⁷ cm²/s with only slight sacrifice in the proton conductivity, which made the crosslinked membrane with 10 min irradiation time possess the highest selectivity.