甲烷氧化偶联Mn_2O_3-Na_2WO_4/SiO_2催化剂——Ⅲ.高温(700—800℃)XRD和XPS研究

在本工作的研究报导Ⅰ和Ⅱ(见本期477页和481页)中,已对Mn_2O_3-Na_2WO_4/SiO_2催化剂活性相的表面分散状态、表面氧种和表面结构进行了详细表征。但甲烷氧化偶联反应在高温(700—800℃)下进行。本文进一步对该催化剂在此反应高温下的XRD和XPS研究表明,其表面状态较室温下有显著变化,结合前文的室温下表征结果,使我们对高温反应条件下该催化剂组分间协同作用、表面活性氧种和活性位结构性质有了进一步的理解,并有可能对其甲烷催化活化机理进行较为深入的探讨。     

Magnetic solid-phase extraction of triclosan using core-shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@MIL-100 magnetic nanoparticles,and its determination by HPLC with UV detection

The article describes the synthesis of core-shell magnetic nanoparticles (MNPs) of the type Fe₃O₄@MIL-100 (MIL standing for Material Institut Lavoisier), and their application as sorbent for magnetic solid-phase extraction (MSPE) of triclosan. The MNPs were prepared via circular self-assembly of ferric chloride and benzenetricarboxylic acid. The functionalized MNPs were characterized by transmission electron microscopy, FTIR and thermogravimetry. Following extraction, triclosan was eluted with ammoniacal methanol and then submitted to HPLC with UV detection. The amount of magnetic microspheres, sample pH and ionic strength, adsorption time, desorption time, desorption solvent and the volume of the eluent were optimized. Under optimum conditions, the method showed good linearity in the 0.1 to 50 mg·kg^?1 triclosan concentration range in toothpaste samples. Other features include (a) intra-day and inter-day relative standard deviations (RSD, for n = 4) of <5.5 %, (b) a 30 μg·kg^?1 limit of detection, and (c) extraction recoveries between 90.86 % and 101.1 %. The method was successfully applied to the determination of triclosan in children’s toothpaste.

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Graphical abstract The article describes the synthesis of core-shell magnetic nanoparticles (MNPs) of the type Fe₃O₄@MIL-100, and their application as sorbent for magnetic solid-phase extraction (MSPE) of triclosan.

     

Upper escape rate of Markov chains on weighted graphs

We obtain an upper escape rate function for a continuous time minimal symmetric Markov chain defined on a locally finite weighted graph. This upper rate function, which has the same form as the manifold setting, is given in terms of the volume growth with respect to an adapted path metric. Our approach also gives a weak form of Folz’s theorem on the conservativeness as a consequence.     

Optimal Properties of Orthogonal Arrays Based on ANOVA High-Dimensional Model Representation

Global sensitivity indices play important roles in global sensitivity analysis based on ANOVA high-dimensional representation, Wang et al. (2012) showed that orthogonal arrays are A-optimality designs for the estimation of parameter , the definition of which can be seen in Section 2. This paper presented several other optimal properties of orthogonal arrays under ANOVA high-dimensional representation, including E-optimality for the estimation of  and universal optimality for the estimation of , where  is the independent parameters of . Simulation study showed that randomized orthogonal arrays have less biased and more precise in estimating the confidence intervals comparing with other methods.     

Free electron laser induced two-photon photoconductivity in Hg1-xCdxTe

The Beijing free electron laser ( BFEL) has been employed for the first time to study the nonlinear photoconductivity characteristics of the typical infrared photoelectronic material Hg_1-xCd_xTe Taking advantage of the high photon flux density of BFEL, we have investigated the photoconductivity characteristics in Hg^1-xCd_x Te induced by two-photon absorption by means of the photoconductivity technique, observed the photoconductivity signals saturation, and studied the two-photon photoconductivity characteristics on different bias voltages across the sample.     

Periodic solution of a neutral delay model of single-species population growth on time scales

By using a fixed point theorem of strict-set-contraction, we present some sufficient conditions for the existence of at least one positive ω-periodic solution to a neutral delay model of single-species population growth on time scales. The significance of the present paper is that we address an open problem introduced by Kuang [Kuang Y. Delay differential equations with applications in population dynamics. New York: Academic Press; 1993] on time scales.     

Periodic solutions to a <Emphasis Type="Italic">p</Emphasis>-Laplacian neutral Rayleigh equation with deviating argument

By using the coincidence degree theory, we study a type of p-Laplacian neutral Rayleigh functional differential equation with deviating argument to establish new results on the existence of T-periodic solutions.     

A Note on the Volume Growth Criterion for Stochastic Completeness of Weighted Graphs

This paper gives complementary results of Folz (Trans Am Math Soc, 2013). We first generalize the weak Omori–Yau maximum principle to the setting of strongly local Dirichlet forms. As an application, we obtain an analytic approach to compare the stochastic completeness of a weighted graph with that of an associated metric graph. This comparison result played an essential role in the volume growth criterion of Folz (Trans Am Math Soc, 2013), who first proved it via a probabilistic approach. We also give an alternative analytic proof based on a criterion in Fukushima et al. (1994).     

Solvent effect in the chromatographic enantioseparation of 1,1′-bi-2-naphthol on a polysaccharide-based chiral stationary phase

Enantioseparation of 1,1′-bi-2-naphthol (BINOL) was performed on a polysaccharide-based chiral stationary phase, Chiralcel OD-H, under normal-phase mode. The effects of polar modifier in the mobile phase on the retention, enantioseparation and elution order were investigated in detail. Solvent-induced reversal of elution order for BINOL was observed. When linear alcohols were adopted, R-BINOL was always eluted first. S-BINOL was eluted first when 2-propanol was used as a polar modifier. Enantioseparation could not be obtained when sec-butyl alcohol or tert-butyl alcohol was used as a polar modifier. When isoamyl alcohol or cyclohexanol was used as a polar modifier, favorable enantioseparation was obtained as with 1-pentanol or 1-hexanol; also, R-BINOL was the first-eluted enantiomer. It is worth emphasizing that significantly better enantioseparation was obtained when higher alcohols were used as polar modifier of the mobile phase. A nonlinear characteristic for the ln α against 1/T plots was universally observed in this study though the ln k against 1/T plots exhibited a linear feature. Associated with the obtained thermodynamic parameters, some interesting inferences about chiral recognition mechanism were proposed.     

A Sensitive Electrochemical Immunosensor for α‐Fetoprotein Detection with Colloidal Gold‐Based Dentritical Enzyme Complex Amplification

A sensitive and specific electrochemical immunosensor was developed with α‐fetoprotein (AFP) as the model analyte by using gold nanoparticle label for enzymatic catalytic amplification. A self‐assembled monolayer membrane of mercaptopropionic acid (MPA) was firstly formed on the electrode surface through gold‐sulfur interaction. Monoclonal mouse anti‐human AFP was covalently immobilized to serve as the capture antibody. In the presence of the target human AFP, gold nanoparticles coated with polyclonal rabbit anti‐human AFP were bound to the electrode via the formation of a sandwiched complex. With the introduction of goat anti‐rabbit IgG conjugated with alkaline phosphatase, the dentritical enzyme complex was formed through selective interaction of the secondary antibodies with the colloidal gold‐based primary antibody at the electrode, thus affording the possibility of signal amplification for AFP detection. Current response arising from the oxidation of enzymatic product was significantly amplified by the dentritical enzyme complex. The current signal was proportional to the concentration of AFP from 1.0 ng mL^?1 to 500 ng mL^?1 with a detection limit of 0.8 ng mL^?1. This system could be extended to detect other target molecules with the corresponding antibody pairs.