Synergistic effects induced by oxy-fluorination of carbon preforms to improve the mechanical and thermal properties of carbon-carbon composites

Oxy-fluorination of carbon preforms with various F₂:O₂ gas mixtures were examined to improve the mechanical and thermal properties of carbon fiber-reinforced carbon composites (C/C composites). The oxy-fluorination of the preforms introduced functional groups onto the preform surface, which improved their thermal properties. Oxy-fluorination also improved the interfacial adhesion of the C/C composites, resulting in increased flexural strength and anti-oxidation. Two synergistic effects of oxy-fluorination on the carbon preform are suggested. One optimizes interfacial adhesion by forming hard chemical bonds and soft electrophilic bonds between the surface functional groups of the oxy-fluorinated carbon preforms and the functional groups of the carbon precursors. The other improves anti-oxidation of the C/C composites by improving the thermal properties of the carbon preform itself and interfacial adhesion which resulted in reducing pores, voids, and interfacial cracks.     

Multi-residue analysis of drugs of abuse in wastewater and surface water by solid-phase extraction and liquid chromatography-positive electrospray ionisation tandem mass spectrometry

A new-multi residue method was developed for the environmental monitoring of 65 stimulants, opiod and morphine derivatives, benzodiazepines, antidepressants, dissociative anaesthetics, drug precursors, human urine indicators and their metabolites in wastewater and surface water. The proposed analytical methodology offers rapid analysis for a large number of compounds, with low limits of quantification and utilises only one solid-phase extraction-ultra performance liquid chromatography-positive electrospray ionisation tandem mass spectrometry (SPE-LC-MS/MS) method, thus overcoming the drawbacks of previously published procedures. The method employed solid phase extraction with the usage of Oasis MCX sorbent and subsequent ultra performance liquid chromatography-positive electrospray ionisation tandem mass spectrometry. The usage of a 1.7 μm particle size column (1 mm×150 mm) resulted in very low flow rates (0.04 mLmin(-1)), and as a consequence gave good sensitivity, low mobile phase consumption and short retention times for all compounds (from 2.9 to 23.1 min). High SPE recoveries (>60%) were obtained for the majority of compounds. The mean correlation coefficients of the calibration curves were typically higher than 0.997 and showed good linearity in the range 0-1000 μgL(-1). The method limits of detection ranged from 0.1 ngL(-1) for compounds including cocaine, benzoylecgonine, norbenzoylecgonine and 2-oxo-3-hydroxy-LSD to 100 ngL(-1) for caffeine. Method quantification limits ranged from 0.5 to 154.2 ngL(-1). Intra- and inter-day repeatabilities were on average less than 10%. The method accuracy range was within -33.1 to 30.1%. The new multi-residue method was used to analyse drugs of abuse in wastewater and river water in the UK environment. Of the targeted 65 compounds, 46 analytes were detected at levels above the method quantification limit (MQL) in wastewater treatment plant (WWTP) influent, 43 in WWTP effluent and 36 compounds in river water.     

Novel molecularly imprinted microsphere using a single chiral monomer and chirality-matching (S)-ketoprofen template

We designed and synthesized a cinchonine derivative to be used as a novel chiral monomer. It was employed in a dual role of functional monomer and cross-linking monomer, displaying multi-binding sites for the template (S)-ketoprofen. Monodisperse molecularly imprinted core-shell microspheres were prepared using surface imprinting method on silica gel. The results show a substantial synergistic effect in the enantioselective recognition, confirming our initial hypothesis. Computational simulation of the monomer and template pre-arrangement strongly supports our proposed chiral recognition mechanism for the imprinted microspheres.     

Interactions of single-stranded DNA on microcantilevers

The microcantilever approach has attracted considerable attention in recent years as a means of label-free detection of a variety of biomolecular and chemical reactions. The underlying physics of the intermolecular interactions that result in mechanical motions is yet to be fully explored, but it seems both rich in science and of technological importance. This paper presents an overview of experiments and theories related to interactions of single-stranded DNA immobilized on microcantilevers. Experiments and theories show that, at high grafting density, hydration forces are the dominant factor determining cantilever deflections, not electrostatics or conformational entropy.     

Surface-segregated, high-voltage spinel LiMn1.5Ni0.42Ga0.08O4 cathodes with superior high-temperature cyclability for lithium-ion batteries

The substitution of a small amount of Ga in the high-voltage spinel cathode LiMn_1.5Ni_0.42Ga_0.08O₄ leads to superior cyclability at room temperature and 55 °C along with higher rate capability with conventional electrolytes compared to that found with the LiMn_1.5Ni_0.5O₄ cathode. The superior performance is attributed to the segregation of the inert Ga³⁺ ions to the surface during the synthesis process, providing a robust, more stable interface with the electrolyte at the high operating voltage (~ 4.7 V), along with the stabilization of the spinel structure with a disordering of the cations in the octahedral sites.     

An intermediate wavelength, weakly nonlinear theory for the evolution of capillary gravity waves

A new nonlinear evolution equation is derived for surface solitary waves propagating on a liquid-air interface where the wave motion is induced by a harmonic forcing. Instead of the traditional approach involving a base state of the long wave limit, a base state of harmonic waves is assumed for the perturbation analysis. This approach is considered to be more appropriate for channels of length just a few multiples of the depth. The dispersion relation found approaches the classical long wave limit. The weakly nonlinear dispersive waves satisfy a KdV-like nonlinear evolution equation with steeper nonlinearity.     

Numerical study on magneto-convection of cold water in an open cavity with variable fluid properties

The aim of the present study is to understand the problem of buoyancy and thermocapillary induced convection of cold water near its density maximum in an open cavity with temperature dependent properties in the presence of uniform external magnetic field. The governing equations are solved by the finite volume method. The results are discussed for various values of reference temperature parameter, density inversion parameter, Rayleigh, Hartmann and Marangoni numbers. It is observed that the temperature of maximum density leaves strong effects on fluid flow and heat transfer due to the formation of bi-cellular structure. Convection heat transfer is enhanced by thermocapillary force when buoyancy force is weakened.     

Robust airfoil optimization based on improved particle swarm optimization method

A robust airfoil optimization platform is constructed based on the modified particle swarm optimization method (i.e., the second-order oscillating particle swarm method), which consists of an efficient optimization algorithm, a precise aerodynamic analysis program, a high accuracy surrogate model, and a classical airfoil parametric method. There are two improvements for the modified particle swarm method compared with the standard particle swarm method. First, the particle velocity is represented by the combination of the particle position and the variation of position, which makes the particle swarm algorithm a second-order precision method with respect to the particle position. Second, for the sake of adding diversity to the swarm and enlarging the parameter searching domain to improve the global convergence performance of the algorithm, an oscillating term is introduced to the update formula of the particle velocity. At last, taking two airfoils as examples, the aerodynamic shapes are optimized on this optimization platform. It is shown from the optimization results that the aerodynamic characteristic of the airfoils is greatly improved in a broad design range.