Measurement of mixing processes with combined digital particle image velocimetry and planar laser induced fluorescence

A combined digital particle image velocimetry (DPIV) and planar laser induced fluorescence (PLIF) approach was developed to measure both the time mean and turbulent mass transport in mixing processes. The system couples the two well-known techniques to enable synchronized planar measurements of flow velocities and concentrations in a study area. The potential interference effect between the seeding particles for DPIV and the fluorescent dye excitation for PLIF was carefully investigated. The performance of the system was verified with the experimental results of a turbulent round jet discharging into a stagnant environment. Comparison between the measurements obtained in the present study with the large body of existing information on pure jets is satisfactory. The key advantage of the shorter duration required with this approach compared to point-based techniques is highlighted.     

Solution-grown zinc oxide nanowires

We review two strategies for growing ZnO nanowires from zinc salts in aqueous and organic solvents. Wire arrays with diameters in the nanoscale regime can be grown in an aqueous solution of zinc nitrate and hexamethylenetetramine. With the addition of poly(ethylenimine), the lengths of the wires have been increased to 25 mum with aspect ratios over 125. Additionally, these arrays were made vertical by nucleating the wires from oriented ZnO nanocrystals. ZnO nanowire bundles have been produced by decomposing zinc acetate in trioctylamine. By the addition of a metal salt to the solution, the ZnO wires can be doped with a range of transition metals. Specifically, ZnO nanowires were homogeneously doped with cobalt and showed a marked deviation from paramagnetic behavior. We conclude by highlighting the use of these solution-grown nanowire arrays in dye-sensitized solar cells. The nanowire cells showed an improvement in the charge collection efficiency over traditional nanoparticle cells.     

High-pressure laminar flame speeds and kinetic modeling of carbon monoxide/hydrogen combustion

Laminar flame speeds were accurately measured for CO/H₂/air and CO/H₂/O₂/helium mixtures at different equivalence ratios and mixing ratios by the constant-pressure spherical flame technique for pressures up to 40 atmospheres. A kinetic mechanism based on recently published reaction rate constants is presented to model these measured laminar flame speeds as well as a limited set of other experimental data. The reaction rate constant of CO + HO₂ → CO₂ + OH was determined to be k = 1.15 × 10⁵T^2.278 exp(−17.55 kcal/RT) cm³ mol⁻¹ s⁻¹ at 300-2500 K by ab initio calculations. The kinetic model accurately predicts our measured flame speeds and the non-premixed counterflow ignition temperatures determined in our previous study, as well as homogeneous system data from literature, such as concentration profiles from flow reactor and ignition delay time from shock tube experiments.     

Stable vortex-bright-soliton structures in two-component Bose-Einstein condensates

We report the numerical realization of robust two-component structures in 2D and 3D Bose-Einstein condensates with nontrivial topological charge in one component. We identify a stable symbiotic state in which a higher-dimensional bright soliton exists even in a homogeneous setting with defocusing interactions, due to the effective potential created by a stable vortex in the other component. The resulting vortex-bright-solitons, generalizations of the recently experimentally observed dark-bright solitons, are found to be very robust both in the homogeneous medium and in the presence of external confinement.     

Measurement of gut microbial metabolites in cardiometabolic health and translational research

The human gut microbiota is a functioning endocrine organ and stands at the intersection between dietary components and health or disease. There are very many microbial metabolites with numerous structures and functions arising from the gut microbial fermentation of foods and become signals for biological communication in the human body. These small molecules can be absorbed and delivered to distant organs through the circulatory system to build the gut–systemic axis. The gut microbial metabolomes are thus believed to play important roles in regulating cardiometabolic health and provide opportunities in mechanistic research and new drug discovery. Measurement of these novel microbial metabolites in clinical samples may serve as a tool for investigating disease biomarkers. In the past decade, the development of untargeted and targeted metabolomics approaches using NMR, LC/MS, and GC/MS has contributed to the exploration of gut microbial metabolomes in cardiometabolic health and disease. Some important targets are currently being translated into clinical applications. In this review article, we introduce an oral carnitine challenge test developed as an example to demonstrate the potential applications in personalized nutrition based on the function of gut microbiota. It is a method taking the gut microbiota as a bioreactor and provides fermentable materials as inputs and measures the outputs of targeted microbial byproducts in the blood or urine. This challenge test may be extended to measure metabolites from microbial fermentation related to other endocrinological or inflammatory diseases. We review current gut metabolome research approaches and propose a gut microbial functional measurement using a challenge test. We suggest that the maturation in measuring gut microbial metabolites may provide an important piece to complete the puzzle of precision medicine.     

Cleaving of microstructured polymer optical fibres

The issue of how best to cleave PMMA microstructured polymer optical fibres (mPOF) is addressed. The impact of the following parameters on the cleaving process is considered: (i) temperature of the cutting blade, (ii) temperature of the platen holding the fibre, (iii) time allowed for thermal equilibration between fibre and platen, (iv) blade speed, and (v) blade condition. The strong influence of a temperature-dependent phase transition in the polymer on the cleaving process is established. Optically acceptable mPOF end-faces can be achieved but only over a limited range of cleavage conditions.     

Determination of chlorpheniramine maleate in tablets by second-derivative absorption spectrophotometry

A rapid method for the determination of chlorpheniramine maleate in tablets using second-derivative absorption spectrophotometry is described. The method has the advantage of requiring simple sample preparation and having accuracy comparable to the official acid-alkaline solvent extraction procedure. Results of recovery tests were close to 100%.     

Fluctuations in fluids out of thermal equilibrium

After a brief review of dynamic correlations in equilibrium fluids, we consider the long-range correlations between the fluctuations in a fluid subjected to a large stationary temperature gradient. These long-range correlations enhance and modify the Rayleigh spectrum of the fluid. We elucidate that the modifications of the Rayleigh line are determined by the coupling of the entropy fluctuations to the transverse velocity fluctuations. Recent attempts to test the theoretical predictions with the aid of light-scattering experiments are discussed.