One-pot synthesis of 5,6-disubstituted 3<Emphasis Type="Italic">H</Emphasis>-pyrrolizines organocatalyzed by piperidinium acetate

The organocatalyst, piperidinium acetate formed in situ, was utilized as an efficient catalyst for one-pot synthesis of 5,6-disubstituted 3H-pyrrolizines with halogen (Cl, Br), methoxy and ethyl ester groups. Absorption and emission spectra properties were also compared in dichloromethane, toluene, methanol, and DMSO. Electronic spectra were altered slightly by these substituents, which can be well explained by TD-DFT calculations. And the selected four orbital energies indicated that electrons transited smoothly from the pyrrolizine ring to the indole unit.     

A two-photon fluorescent probe with a large turn-on signal for imaging hydrogen sulfide in living tissues

A two-photon fluorescence turn-on H₂S probe GCTPOC–H₂S based on a two-photon platform with a large cross-section, GCTPOC, and a sensitive H₂S recognition site, dinitrophenyl ether was constructed. The probe GCTPOC–H₂S exhibits desirable properties such as high sensitivity, high selectivity, functioning well at physiological pH and low cytotoxicity. In particular, the probe shows a 120-fold enhancement in the presence of Na₂S (500 μM), which is larger than the reported two-photon fluorescent H₂S probes. The large fluorescence enhancement of the two-photon probe GCTPOC–H₂S renders it attractive for imaging H₂S in living tissues with deep tissue penetration. Significantly, we have demonstrated that the probe GCTPOC–H₂S is suitable for fluorescence imaging of H₂S in living tissues with deep penetration by using two-photon microscopy. The further application of the two-photon probe for the investigation of biological functions and pathological roles of H₂S in living systems is under progress.     

Synthesis and electrical properties of ZnO nanowires

Vertically aligned ZnO nanowires were synthesized on the p(+) silicon chip by modifying the CVD process with a vapor trapping design. Scanning electron microscopy was used to investigate the morphology of as-obtained nanowires. X-ray diffraction showed that the obtained nanowires were ZnO crystalline. The rectifying characteristics of the p-n heterojunction composed of ZnO nanowires and a p(+) silicon chip were observed. The positive turn-on voltage was 0.5V and the reverse saturation current was 0.01mA. These vertically aligned ZnO nanowires showed a low field emission threshold of 4V/microm at a current density of 0.1microA/cm(2). The dependence of emission current density on the electric field followed Fowler-Nordheim relationship.     

Antifungal activity of phenolic monoterpenes and structure-related compounds against plant pathogenic fungi

The aim of this work is to explore the possibility of using the phenolic monoterpenes (PMs) as leading compounds with antifungal activity against plant disease. The in vitro antifungal activities of carvacrol and thymol against seven kinds of plant pathogenic fungi were evaluated on mycelium growth rate method, and the results showed that carvacrol and thymol exhibited broad spectrum antifungal activity. Structure requirement for the antifungal activity of PMs was also investigated. The preliminary conclusion was that phenolic hydroxyl and monoterpene were basic structures for the antifungal activity of PMs, and the position of phenolic hydroxyl showed less effect. Ester derivatives of carvacrol and thymol were more effective than carvacrol and thymol against plant pathogenic fungi. We suggested that carvacrol, thymol and their ester derivatives could potentially be used as new fungicide leading compounds.     

Cluster synchronization of linearly coupled complex networks via linear and adaptive feedback pinning controls

Cluster synchronization is investigated for complex networks via linear and adaptive feedback control strategies. It is shown that two different controllers can be designed to achieve the cluster synchronization. Unlike most existing papers, we need not nondelayed and delayed coupling matrices to be symmetric or irreducible. Finally, two examples are given to illustrate the effectiveness of the proposed methods.     

JFNK方法在S N输运计算中的应用

JFNK(Jacobian-free Newton-Krylov)方法是一种求解非线性方程的高效迭代算法。传统输运计算中的负通量修正与k-特征值迭代使得原本线性的输运计算转变为非线性问题数值求解。为提高非线性输运问题的计算效率,将这两类非线性问题离散成残差形式的非线性方程组,并采用JFNK方法对其进行迭代求解。分析不同约束条件对JFNK方法性能的影响,并将其与NK(Newton-Krylov)方法进行对比。针对JFNK方法的内迭代过程,分析两类子空间方法(GMRES(m)与LGMRES)对整体计算效率的影响。数值结果表明：①相比于传统的幂迭代方法,JFNK方法具有更高的计算效率;②Jacobian矩阵向量积的差分近似对结果没有影响,且基于物理的约束条件比标准的数学约束更加高效;③LGMRES可以充分利用子空间的信息,从而使得JFNK方法整体表现更加高效。     

Adaptive fixed-time control for nonlinear systems against time-varying actuator faults

Nonlinear Dynamics - The adaptive fixed-time control problem for nonlinear systems with time-varying actuator faults is investigated in this paper. A novel adaptive fixed-time controller is...     

Electron transfer in quantum-dot-sensitized ZnO nanowires: ultrafast time-resolved absorption and terahertz study

Photoinduced electron injection dynamics from CdSe quantum dots to ZnO nanowires is studied by transient absorption and time-resolved terahertz spectroscopy measurements. Ultrafast electron transfer from the CdSe quantum dots to ZnO is proven to be efficient already on a picoseconds time scale (τ = 3-12 ps). The measured kinetics was found to have a two-component character, whose origin is discussed in detail. The obtained results suggest that electrons are injected into ZnO via an intermediate charge transfer state.     

Characteraction of Ag-doped ZnO thin film synthesized by sol–gel method and its using in thin film solar cells

Pure 2% and 4% Ag-doped ZnO thin films have been synthesized on glass substrates by sol–gel method. The structure, morphology and optical properties of the samples have been studied by X-ray diffractometer (XRD), scanning probe microscope, UV–vis spectrophotometer, respectively. The XRD result shows that the pure ZnO has a wurtzite hexagonal structure, no phase segregation is observed. The surface morphology of pure ZnO thin film shows that the grains are growing preferentially along the c-axis orientation perpendicular to the substrates. The transmittance spectra reveal that all samples have high transmittance above 90% in visible region. With Ag doping content increase, a red shift is observed. The performance of Ag-doped ZnO films using in thin film solar cells are simulated. The results show that 4% Ag-doped ZnO thin film can greatly improve the absorption of the cells. Compare to pure ZnO, solar cell's energy conversion efficiency improvement of 2.47% is obtained with 4% Ag doped ZnO thin film.