Direct numerical simulation of low Reynolds number flows in an open‐channel with sidewalls

A direct numerical simulation of low Reynolds number turbulent flows in an open‐channel with sidewalls is presented. Mean flow and turbulence structures are described and compared with both simulated and measured data available from the literature. The simulation results show that secondary flows are generated near the walls and free surface. In particular, at the upper corner of the channel, a small vortex called inner secondary flows is simulated. The results show that the inner secondary flows, counter‐rotating to outer secondary flows away from the sidewall, increase the shear velocity near the free surface. The secondary flows observed in turbulent open‐channel flows are related to the production of Reynolds shear stress. A quadrant analysis shows that sweeps and ejections are dominant in the regions where secondary flows rush in toward the wall and eject from the wall, respectively. A conditional quadrant analysis also reveals that the production of Reynolds shear stress and the secondary flow patterns are determined by the directional tendency of the dominant coherent structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Fluorescent coumarinyldithiane as a selective chemodosimeter for mercury(II) ion in aqueous solution

A coumarin-based dithiane (1) was synthesized for the selective detection of Hg²⁺ with respect to dual chromo- and fluorogenic changing events in an aqueous solution by the mercury-promoted transformation of a dithiane group into an aldehyde functional unit. The Hg²⁺-selective response of the chemodosimeter was clearly observed in aqueous buffer as well as in human blood plasma medium.     

ICT-based Cu(II)-sensing 9,10-anthraquinonecalix[4]crown

A series of calix[4]arene-based chromogenic sensors bearing the 9,10-anthraquinone moiety have been synthesized and examined for their abilities to recognize various cations such as Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Cd²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Co²⁺, and Cu²⁺ by UV-vis spectroscopy. In acetonitrile, the presence of Cu²⁺ induces the formation of the 1:1 ligand/metal complex, which exhibits a new absorption band centered at 450 nm, and leads to an obvious color change from yellow to red.     

Shape-Controlled Nanocrystals for Catalytic Applications

The activity, selectivity, and long-term stability of catalyst nanoparticles can be enhanced by shape modulation. Such shaped catalytic nanocrystals have well-defined surface crystalline structures on which the cleavage and recombination of chemical bonds can be rationally controlled. Metal and metal oxide nanocrystals have been synthesized in various shapes using wet chemistry techniques such as reducing metal precursors in the presence of the surface-capping agents. The surface-capping agents should be removed prior to the catalytic chemical reaction, which necessitates clean catalytically active surface. The removal process should be performed very carefully because this removal often causes shape deformation. A few examples in which the surface-capping agents contribute positively to the chemical reactions have been reported. The examples described in this review include shaped metal, metal composite, and metal oxide nanocrystals that show enhanced catalytic activity, selectivity, and long-term stability for various gas-phase, liquid-phase, or electrocatalytic reactions. Although most of the studies using these shaped nanocrystals for catalytic applications have focused on low-index surfaces, nanocrystals with high-index facets and their catalytic applications have recently been reported. By bridging surface studies with nanoparticle catalysts using shape modulation, catalysts with improved properties can be rationally designed.     

Comparison of four scattering mechanisms in cyclotron resonance in InSb

Summary  Four scattering mechanisms are compared in the quantum limit cyclotron resonance inn-InSb on the basis of a many body theory introduced recently. In the quite low temperature region (T<70 K ) for the wavelength of the electromagnetic wave of 84 μ m, the electrons are scattered mostly by the ionized impurities, although the deformation potential phonon and the piezoelectric scattering are non-negligible. In the high temperature region (T>70 K ) the polar optical phonon scattering is found to be most dominant. It is also shown that the impurities give place to the phonons for the scattering mechanism above 70 K. On the other hand, at 20 K the ionized impurity scattering is dominant in the magnetic field region 0.2 T<B<2 T. This work has been supported by the Basis Science Research Institute Program, Korea Ministry of Education (Project No. BSRI-96-2405).     

Candidate gene polymorphisms for diabetes mellitus, cardiovascular disease and cancer are associated with longevity in Koreans

Long-lived people may have a unique genetic makeup that makes them more resistant than the general population to prevalent age-related diseases; however, not much is known about genes involved in the longevity. To identify susceptibility variants controlling longevity, we performed a high-throughput candidate gene study using 137 Koreans over 90 yr old and 213 young healthy Koreans. We evaluated 463 informative markers located in 176 candidate genes mostly for diabetes mellitus, cardiovascular disease and cancer under five genetic models. We estimated the odds ratios for each allele, genotype, haplotype, and gene-gene interaction using logistic regression analysis. Associations between 13 genes and longevity were detected at a P-value less than 0.01. Particularly, the rs671 (A) allele of the aldehyde dehydrogenase 2 family (mitochondrial) (ALDH2) gene was associated with longevity only in men (OR 2.11, P = 0.008). Four genes, proprotein convertase subtilisin/kexin type 1 (PCSK1, P = 0.008), epidermal growth factor receptor (EGFR, P = 0.003), paired box 4 (PAX4, P = 0.008), and V-yes-1 Yamaguchi sarcoma viral related oncogene homolog (LYN, P = 0.002) consistently yielded statistical evidence for association with longevity. The findings of the current study may provide a starting point for future studies to unravel genetic factors controlling longevity in Koreans.     

Design of new HDPE/silica nanocomposite and its enhanced melt strength

Linear polymers are restricted to use in processes that involve severe extensional deformation, such as fiber spinning, film blowing, and thermoforming. To extend their applicability, the extensional properties of polymer melts should be enhanced such that strain hardening, which is defined as an increase in extensional viscosity under a large strain that deviates from the linear viscoelastic curve, is pronounced. In this study, a novel preparation method of linear polymer/inorganic nanocomposites was proposed with a main focus on enhanced melt strength. The design of molecular structure consists of three components—linear polymer, compatibilizer, and surface-modified particles. High-density polyethylene was used as a linear polymer while polyethylene grafted with maleic anhydride was used as a compatibilizer. Silica particles were synthesized and modified on their surfaces by 3-aminopropyltriethoxysilane. The strain hardening behavior of the surface-modified silica composites was pronounced. However, such a result was not observed for the composites of the same composition with pure-silica. In addition, the dispersion of the modified silica was much better than that of pure-silica.     

Interfacial localization of nanoclay particles in oil-in-water emulsions and its reflection in interfacial moduli

The localization of nanoclay particles dispersed in the oil phase of a model oil-in-water emulsion depends on the wetting property of layered nanoparticles. Investigation at a single droplet interface shows that nanoclay is located at different interfacial regions depending on the hydrophilic property of the nanoclay surface. Hydrophobic nanoclays do not present Pickering phenomena at the interface and hardly form an interfacial layer. Hydrophilic nanoclay particles quickly move to the interface and form a Pickering interface with a high interfacial shear modulus. With surfactant, poor hydrophilic nanoclays can be located at the interface due to improvement of the wetting behavior caused by the surfactants dissolved in the aqueous continuous phase. With ionic molecules changing the wetting behavior of particles, the interfacial localization of nanoclays can be controlled and improve the mechanical property of emulsion.     

UV band Splitting of chromogenic azo-coupled calix[4]crown upon cation complexation

Calixcrown-6 compounds carrying a pair of phenylazo moieties on the upper rim and two OH groups, one OH group, and two OR groups on the lower rim have been prepared in both the cone and partial cone conformations. UV/vis spectral measurements showed a red shift upon the addition of Ca2+ to the calixcrown carrying two OH groups and a blue shift for the calixcrown carrying two OR groups. For the compounds with two OR groups on the lower rim and a fixed partial cone conformation, a blue shift caused by electrostatic interaction between the oxygen atoms of OR and the metal ion as well as a red shift caused by the pi-metal complexation between the rotated calix benzene and the metal ion were observed.