Composites prepared by penetrating poly(ethylene oxide) chains into mesoporous silica

Mesoporous silica was synthesized by hydrolysis of tetraethylorthosilicate (TEOS, formula Si(OCH₂CH₃)₄) at ambient temperature in a basic ethanol-water solution, with cetyltrimethyl ammonium bromide as a template. It had a surface area of approximately 1,400 m²/g, and an average pore diameter of approximately 40 Å. Portions were blended into three samples of poly(ethylene oxide) (PEO) of varying molecular weights, in the hope of making novel composites by penetrating some of the PEO chains into the silica channels. Differential Scanning Calorimetry (DSC) and X-ray diffraction (XRD) were used to characterize the structures of the PEO/mesoporous silica composites after they were held at 100 °C for up to 30 min. In both experiments, the melting temperature of the PEO decreased and ultimately disappeared. These results suggest that the PEO chains did penetrate into the silica pores, and since they were constrained in the pores, their crystallization was suppressed. This provides an interesting parallel to the disappearance of the glass transition temperatures of polymers constrained in the cavities of zeolites or in the galleries of intercalated clays.     

Electrogenerated Chemiluminescence Ethanol Biosensor Based on Carbon Nanotube‐Titania‐Nafion Composite Film

Mesoporous titania‐Nafion composite doped with carbon nanotube (CNT) has been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) and alcohol dehydrogenase on an electrode surface to yield a highly sensitive and stable electrogenerated chemiluminescence (ECL) ethanol biosensor. The presence of CNT in the composite film increases not only the sensitivity of the ECL biosensor but also the long‐term stability of the biosensor. The present biosensor responds linearly to ethanol in the wide concentration ranges from 1.0×10^?5 M to 1.0×10^?1 M with a detection limit of 5.0×10^?6 M (S/N=3). The present ECL ethanol biosensor exhibited higher ECL response compared to that obtained with the ECL biosensor based on the corresponding composite without CNT. The present CNT‐based ECL biosensor showed good long‐term stability with 75% of its initial activity retained after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

Synthesis and Crystal Structure of a Three-dimensional Cd(Ⅱ) Coordination Polymer [Cd(μ1,3-SCN)(μ3-pco)]n (pco = Pyrazine-2-carboxylate 4-oxide Anion)

The three-dimensional complex [Cd(μ1,3-SCN)(μ3-pco)]n has been synthesized with μ1,3-SCN- and pco as mixed bridged ligands. The crystal belongs to monoclinic, space group P21/n with a = 10.3777(16), b = 6.2592(9), c = 13.150(2) (A), β= 97.317(2)°, V=847.2(2) (A)3, Z= 4,C6H3CdN3O3S, Mr = 309.575, Dc = 2.427 g/cm3, F(000) = 592 and μ = 2.804 mm-1. The structure was refined to R = 0.0255 and wR = 0.0550 for 1712 observed reflections (I＞2σ(I)). In the crystal the Cd(Ⅱ) ions are coordinated by μ1,3-SCN- and μ3-pco bridge ligands to form a three-dimensional structure.     

Multi-Hop Question Generation Using Hierarchical Encoding-Decoding and Context Switch Mechanism

Neural auto-regressive sequence-to-sequence models have been dominant in text generation tasks, especially the question generation task. However, neural generation models suffer from the global and local semantic semantic drift problems. Hence, we propose the hierarchical encoding–decoding mechanism that aims at encoding rich structure information of the input passages and reducing the variance in the decoding phase. In the encoder, we hierarchically encode the input passages according to its structure at four granularity-levels: [word, chunk, sentence, document]-level. Second, we progressively select the context vector from the document-level representations to the word-level representations at each decoding time step. At each time-step in the decoding phase, we progressively select the context vector from the document-level representations to word-level. We also propose the context switch mechanism that enables the decoder to use the context vector from the last step when generating the current word at each time-step.It provides a means of improving the stability of the text generation process during the decoding phase when generating a set of consecutive words. Additionally, we inject syntactic parsing knowledge to enrich the word representations. Experimental results show that our proposed model substantially improves the performance and outperforms previous baselines according to both automatic and human evaluation. Besides, we implement a deep and comprehensive analysis of generated questions based on their types.     

Experimental study on oblique water entry of two tandem spheres with collision effect

Journal of Visualization - In this paper, the hydrodynamic characteristics associated with oblique water entry of two tandem spheres were experimentally investigated using high-speed photography....     

The viscosity approximation method for asymptotically nonexpansive mappings in Banach spaces

A recent trend in the iterative methods for constructing fixed points of nonlinear mappings is to use the viscosity approximation technique. The advantage of this technique is that one can find a particular solution to the associated problems, and in most cases this particular solution solves some variational inequality. In this paper, we try to extend this technique to find a particular common fixed point of a finite family of asymptotically nonexpansive mappings in a Banach space which is reflexive and has a weakly continuous duality map. Both implicit and explicit viscosity approximation schemes are proposed and their strong convergence to a solution to a variational inequality is proved.     

Analytical solutions to mathematical models of the surface and bulk erosion of solid polymers

The process by which polymeric materials hydrolyze and disappear into their environments is often called erosion. Two types of erosion have been defined according to how the hydrolysis takes place. If hydrolysis occurs throughout the entire specimen at the same time, it is called bulk erosion. If the hydrolysis is mainly confined to a region near the surface of the specimen and the surface continuously degrades by moving inward, it is termed surface erosion. In this article, a kinetic relationship for bulk erosion is developed. This relationship provides a method for estimating the hydrolysis kinetic constants for bulk‐eroding polymers. This same relationship is also applicable to surface erosion at a microscopic level. Through its combination with a diffusion–reaction equation and the provision of moving boundary conditions, an analytical solution to the steady‐state surface‐erosion problem is obtained. The erosion rate, erosion front width, and induction time can all be expressed as simple functions of the rate of polymer bond hydrolysis, water diffusivity, and solubility, plus other parameters that can be experimentally determined. The erosion front width is the product of the induction time and the erosion rate. The ratio of the erosion front width to the polymer specimen thickness is a parameter that determines whether the specimen undergoes surface or bulk erosion. Theoretical results are compared with experimental observations from the literature, and agreement is found. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 383–397, 2005     

Al-Doped Dumbbell-Like ZnO for Enhanced Ethanol Sensing Performance

Russian Journal of Applied Chemistry - A dumbbell-like Al doped ZnO(AZO) microstructure was successfully synthesized via a facile, controllable and one-pot hydrothermal method. The samples were...     

Simultaneous determination of VD2, VD3, 25(OH) D2, and 25(OH) D3 in human plasma using electrospray LC–MS/MS as well as its application to evaluate VD plasma levels in depressive,schizophrenic patients and healthy individuals

Vitamin D measurements in biological fluids by liquid chromatography–tandem mass spectrometry (LC–MS/MS) have been widely used but remain challenging at very low concentration levels. Rapid, high recovery, sensitive and reliable measurements of vitamin D, as well as its primary metabolites using LC–MS/MS are urgently needed for a routine clinical laboratory. Herein, we reported a novel electrospray LC–MS/MS method for determining vitamin D and its primary metabolites using the supported liquid extraction method to achieve higher recoveries, with optimized pH values to achieve optimal derivatization efficiency for higher sensitivity and selected chromatographic conditions to shorten the separation time. The method has been validated with respect to selectivity, recovery, matrix effects, accuracy and precision, stabilities, carryover and dilution effects. The method has been successfully applied to quantify the VD plasma concentrations of depressive, schizophrenic patients and healthy individuals. The result showed that there were significant differences in plasma VD levels between mental disorder patients with healthy individuals, and the total VD levels in mental disorder patients were much higher than healthy individuals, which might require larger clinical samples for validation.     

Advantage of Preserving Bi-orientation Structure of Isotactic Polypropylene through Die Drawing

The isotactic polypropylene(iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle(80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP.