Sensitive electrochemical sensor of tryptophan based on Ag@C core–shell nanocomposite modified glassy carbon electrode

We here reported a simple electrochemical method for the detection of tryptophan (Trp) based on the Ag@C modified glassy carbon (Ag@C/GC) electrode. The Ag@C core–shell structured nanoparticles were synthesized using one-pot hydrothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier transform-infrared spectroscopy (FTIR). The electrochemical behaviors of Trp on Ag@C/GC electrode were investigated and exhibited a direct electrochemical process. The favorable electrochemical properties of Ag@C/GC electrode were attributed to the synergistic effect of the Ag core and carbon shell. The carbon shell cannot only protect Ag core but also contribute to the enhanced substrate accessibility and Trp-substrate interactions, while nano-Ag core can display good electrocatalytic activity to Trp at the same time. Under the optimum experimental conditions the oxidation peak current was linearly dependent on the Trp concentration in the range of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with a detection limit of 4.0 × 10⁻⁸ M (S/N = 3). In addition, the proposed electrode was applied for the determination of Trp concentration in real samples and satisfactory results were obtained. The technique offers enhanced sensitivity and may trigger the possibilities of the Ag@C nanocomposite towards diverse applications in biosensor and electroanalysis.     

锂离子电池硼酸盐电极材料的研究进展

硼酸盐作为新一代锂离子电池电极材料,其具有摩尔质量小、资源丰富、环境友好和理论比容量高等优点.本文对LiFeBO3、LiMnBO3和LiCoBO3等硼酸盐正极材料以及Fe3BO6、FeBO3、Cr3BO6、Co2B2O5、Cu3B2O6和VBO3等硼酸盐负极材料的结构、制备方法、电化学性能的研究现状进行了综述,并对存在的主要问题提出了改进方法.     

Oscillation criteria of neutral type impulsive hyperbolic equations

In this paper, oscillatory properties of all solutions for neutral type impulsive hyperbolic equations with several delays under the Robin boundary condition are investigated and several new sufficient conditions for oscillation are presented.     

Enantiomeric separations of chiral polychlorinated biphenyls on three polysaccharide-type chiral stationary phases by supercritical fluid chromatography

Enantiomeric separations of 18 chiral polychlorinated biphenyls (PCBs) were investigated on three polysaccharide-type chiral stationary phases (CSPs; Sino-Chiral OJ, Chiralpak IB, and Chiralcel OD) by supercritical fluid chromatography (SFC). With these commonly used polysaccharide CSPs, 17 PCBs except PCB 135 (R(S) = 0.81) were well resolved (R(S) > 1.5) under appropriate mobile phases and temperatures. Using Sino-Chiral OJ, 14 PCBs could be baseline-separated, while only one and nine PCBs could be completely separated using Chiralpak IB and Chiralcel OD, respectively. The influence of column temperature was studied for the optimization of resolution, as well as for the type and percentage of organic modifier in the mobile phase. The resolution decreased as the temperature increased in the range of 26-40 °C in which the enantiomeric separations were an enthalpy-driven process. The addition of modifiers in the mobile phase decreased the resolution of the PCB enantiomers, but it clearly shortened their retention time. These separation results indicate that SFC is a promising chromatographic technique for chiral separation and enantiopure standard preparation.     

Spreading of partially coherent polychromatic Hermite-Gaussian beams propagating through non-Kolmogorov turbulence

The spreading of partially coherent polychromatic Hermite-Gaussian (PCPHG) beams propagating through non-Kolmogorov turbulence is studied, where the effect of non-Kolmogorov turbulence and beam bandwidth on the beam width spreading and angular spread is stressed. It is shown that the variation of the relative beam width of PCPHG beams with the generalized exponent parameter of non-Kolmogorov turbulence is non-monotonic. The larger bandwidth of PCPHG beams is, the smaller the relative beam width and the smaller the relative angular spread. Therefore, PCPHG beams with larger bandwidth are less affected by non-Kolmogorov turbulence than those with smaller bandwidth. PCPHG beams are less sensitive to the effect of non-Kolmogorov turbulence than fully coherent polychromatic Hermite-Gaussian (FCPHG) beams and polychromatic Gaussian Schell-model (PGSM) beams. The results are illustrated by numerical examples and interpreted.     

The influence on intrinsic light emission of calcium tungstate and molybdate powders by multivalence Pr codoping

For trivalent praseodymium (Pr³⁺) and quadrivalent praseodymium (Pr⁴⁺) codoped CaMO₄ (M = W, Mo) powders, the luminescence propriety of matrix is obviously influenced by carrier concentration. The light emission intensity of CaWO₄ matrix decreases exponentially with increasing of Pr concentration because oxygen-deficient (WO₃·V_O^··\mathrm{WO}_{3}\cdot V_{\mathrm{O}}^{\bullet \bullet}) obtains an electron supplied by Pr³⁺ (5d). However, the light emission intensity of CaMoO₄ is enhanced by Pr codoping because the quasi-free electrons increase the probability of radiative combination. The difference of photoluminescence properties in the two materials are attributed to the bonding character of M and O in the CaMO₄ structure.     

InGaAs/GaAs应变量子阱结构在1054nm激光器中的应用

采用金属有机物化学气相淀积(MOCVD)方法生长了InGaAs/GaAs应变量子阱,通过优化生长条件和采用应变缓冲层结构获得量子阱,将该量子阱结构应用于1 054 nm激光器的制备。经测试该器件具有9 mA低阈值电流和0.4 W/A较高的单面斜率效率,在驱动电流为50 mA时测得该应变量子阱光谱半宽为1.6nm,发射波长为1 054 nm。实验表明:通过优化工艺条件和采用应变缓冲层等手段,改善了应变量子阱质量,该结果应用于1 054 nm激光器的制备,取得了较好的结果。     

Effects of group-velocity mismatch and cubicquintic nonlinearity on cross-phase modulation instability in optical fibers

The synthetic effects of group-velocity mismatch and cubic-quintic nonlinearity on cross-phase modulation induced modulation instability in loss single-mode optical fibers have been numerically investigated. The results show that the quintic nonlinearity plays a role similar to the case of neglecting the group-velocity mismatch in modifying the modulation instability, namely, the positive and negative quintic nonlinearities can still enhance and weaken the modulation instability, respectively. The group-velocity mismatch can considerably change the gain spectrum of modulation instability in terms of its shape, peak value, and position. In the normal dispersion regime, with the increase of the group-velocity mismatch parameter,the gain spectrum widens and then narrows, shifts to higher frequencies, and the peak value gets higher before approaching a saturable value. In the abnormal dispersion regime, two separated spectra may occur when the group-velocity mismatch is taken into account. With the increase of the group-velocity mismatch parameter, the peak value of the gain spectrum gets higher and shorter before tending to a saturable value for the first and second spectral regimes, respectively.     

LEAST—SQUARES SOLUTION OF AXB=D OVER SYMMETRIC POSITIVE SEMIDEFINITE MATRICES X

Least-squares solution of AXB=D with respect to symmetric positive semidefinite matrix X is considered.By making use of the generalized singular value ecomposition,we derive general analytic formulas,and present necessary and sufficient conditions for guaranteeing the existence of the solution.By applying MATLAB 5.2，we give some numerical examples to show the feasibility and accuracy of this construciton technique in the finite precision arithmetic.     

THE EXISTENCE OF POSITIVE PERIODIC SOLUTIONS IN A LOGISTIC DIFFERENCE MODEL WITH A FEEDBACK CONTROL

Consider the following nonautonomous delayed periodic logistic difference model with feedback control termwhich describes the evolution of a single species. The existence of a positive periodic solution is established by using the method of Mawhin's coincidence degree. This work has important significance in both theory and applications.