Isocratic liquid chromatographic determination of three paraben preservatives in hygiene wipes using a reversed phase core-shell narrow-bore column

The first HPLC method for the separation of three paraben preservatives (methyl-, ethyl- and propyl parabens) using a core-shell analytical column is reported in this study. The separation was completed in less than 8 min at a low flow rate of 0.4 mL min⁻¹ and an isocratic mobile phase containing 20% acetonitrile as organic modifier. The backpressure was < 200 bar in all cases, enabling the usage of conventional HPLC equipment. The proposed analytical procedure was validated for linearity (0.5–20 μg L⁻¹), limits of detection (15–43 μg L⁻¹) and quantification (50–142 μg L⁻¹), selectivity, within day (1.3–1.5%) and day-to-day (3.4–4.6%) precision and accuracy. The proposed method has been applied to the determination of the selected paraben preservatives in commercially available hygiene wipes. The mean percent recoveries were found to be in the range of 98.0–98.4%.      

Two New Recurrent Levels for <Emphasis Type="Italic">C</Emphasis><Superscript>0</Superscript>-Flows

The central problem in dynamical systems is the asymptotic behavior or topological structure of the orbits. Nevertheless only orbits of points with certain recurrence and form a set of full measure are truly of importance. Of course, such a set is desired to be as small (in the sense of set inclusion) as possible. In this paper we discuss such two sets: the set of weakly almost periodic points and the set of quasi-weakly almost periodic points. While the two sets are different from each other by definitions, we prove that their closures both coincide with the measure center (or the minimal center of attraction) of the dynamical systems. Generally, a point may have three levels of orbit-structure: the support of an invariant measure generated by the point, its minimal center of attraction and its ω-limit set. We study the three levels of orbit-structure for weakly almost periodic points and quasi-weakly almost periodic points. We prove that quasi-weakly almost periodic points possess especially rich topological orbit-structures. We also present a necessary and sufficient condition for a point to belong to its own minimal center of attraction.     

Exact solutions of （3＋1）-dimensional nonlinear incompressible non-hydrostatic Boussinesq equations

The symmetries and the exact solutions of the (3+1)-dimensional nonlinear incompressible non-hydrostatic Boussinesq (INHB) equations, which describe atmospheric gravity waves, are studied in this paper. The calculation on symmetry shows that the equations are invariant under the Galilean transformations, the scaling transformations, and the space-time translations. Three types of symmetry reduction equations and similar solutions for the (3+1)-dimensional INHB equations are proposed. Traveling and non-traveling wave solutions of the INHB equations are demonstrated. The evolutions of the wind velocities in latitudinal, longitudinal, and vertical directions with space-time are demonstrated. The periodicity and the atmosphere viscosity are displayed in the (3+1)-dimensional INHB system.     

Morphine-induced conditioned place preference in mice: Metabolomic profiling of brain tissue to find “molecular switch” of drug abuse by gas chromatography/mass spectrometry

Conditioned place preference (CPP) is a widely used model to explore the mechanism of context-dependent learning. In this work, we developed a GC–MS method to investigate the metabolites in mice brain which was used to study the mechanism of context-dependent learning associated with rewarding effect of morphine. Metabolites were extracted from brain tissues and derivatized followed by analysis by gas chromatography/mass spectrometry (GC–MS). In total, 69 peaks were identified as known compounds. By a Wilcoxon ran sum test with p value ≤0.05, 21 metabolites were selected and considered as the potential biomarkers of morphine in mice brain. Using principal component analysis (PCA) and receiver-operator characteristic (ROC) curves, a model was constructed with a combination of these 21 metabolic markers. Multivariate statistics of the model yielded separation between the two groups with an area under the curve value of 0.947. Some metabolites were further discussed in detail about their pathway. Results showed that our technique can be successfully applied to profile for biomarkers and in understanding molecular mechanisms of drug abuse.     

Active role of hydrogen bond and ambient water in Meyer–Schuster rearrangements in high‐temperature water

Meyer–Schuster rearrangements of 2‐phenyl‐3‐butyn‐2‐ol with H₃O⁺ and (H₂O)₆ model in high‐temperature water (HTW) have been investigated by the use of density functional theory calculations. In the substrate 2‐phenyl‐3‐butyn‐2‐ol catalyzed by H₃O⁺ and (H₂O)₆, the Meyer–Schuster rearrangements were predicted by the frontier molecular orbital theory. The results show that the rearrangement does not involve the carbonium ion intermediates, but the first transition state is carboniumion like. Dehydration and hydration may occur via the intermolecular proton relay along the hydrogen‐bond chains and the second step of reaction path is a total acid–base catalytic process. Based on the results, a model considered both HTW ambient and water molecules are proposed to represent mechanisms of other reactions in HTW. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

函数与其反函数图像交点的个数及位置

讨论了函数与其反函数图像交点的个数及位置.同时举例说明我们的结果是精确的.