Gauged Lifshitz scalar field theories in two dimensions

We present two-dimensional gauged Lifshitz scalar field theories by considering the duality relation between the source current and the Noether current. Requiring the duality partially, we obtain a gauged model which recovers the bosonized Schwinger model for the IR limit. For the exact duality, however, the source current is not conserved, which means that the resulting theory is anomalous, so that the number of degrees of freedom is increased. The second model is consistently formulated by adding the Wess–Zumino type action to maintain the gauge invariance.     

Communication: Propagator for diffusive dynamics of an interacting molecular pair

We introduce a new method of solution for the Fredholm integral equations of the second kind. The method would be useful when the direct iterative approach leads to a divergent perturbation series solution. By using the method, we obtain an accurate expression of the propagator for diffusive dynamics of a pair of particles interacting via an arbitrary central potential and hydrodynamic interaction. We test the accuracy of the propagator expression by calculating the diffusion-controlled geminate and bimolecular reaction rates. It is shown that our propagator expression provides very accurate results for the whole time region.     

The synthesis and spectral properties of a stimuli-responsive D–π–A charge transfer dye based on indole donor and 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptor moieties

A particular chromogenic and fluorophoric dye chemosensor was designed and synthesized, which was based on the stimuli-responsive D–π–A charge transfer system. Indole moiety as a donor unit and furan moiety as an acceptor unit were used. This prepared dye sensor showed the selective fluoride ion sensing effects in UV–vis absorption and fluorescence emission properties. Clear absorption changes and highly selective fluorescence quenching effects with fluoride ion were determined. Experimental data and images were collected and supported to provide a better understanding of this particular dye sensor.     

Theoretical study of formamide decomposition pathways

The chemical transformations of formamide (NH(2)CHO), a molecule of prebiotic interest as a precursor for biomolecules, are investigated using methods of electronic structure computations and Rice-Rampserger-Kassel-Marcus (RRKM) theory. Specifically, quantum chemical calculations applying the coupled-cluster theory CCSD(T), whose energies are extrapolated to the complete basis set limit (CBS), are carried out to construct the [CH(3)NO] potential energy surface. RRKM theory is then used to systematically examine decomposition channels leading to the formation of small molecules including CO, NH(3), H(2)O, HCN, HNC, H(2), HNCO, and HOCN. The energy barriers for the decarboxylation, dehydrogenation, and dehydration processes are found to be in the range of 73-78 kcal/mol. H(2) loss is predicted to be a one-step process although a two-step process is competitive. CO elimination is found to prefer a two-step pathway involving the carbene isomer NH(2)CHO (aminohydroxymethylene) as an intermediate. This CO-elimination channel is also favored over the one-step H(2) loss, in agreement with experiment. The H(2)O loss is a multistep process passing through a formimic acid conformer, which subsequently undergoes a rate-limiting dehydration. The dehydration appears to be particularly favored in the low-temperature regime. The new feature identifies aminohydroxymethylene as a transient but crucial intermediate in the decarboxylation of formamide.     

High-mobility graphene nanoribbons prepared using polystyrene dip-pen nanolithography

Graphene nanoribbons (GNRs) are fabricated by dip-pen nanolithography and polystyrene etching techniques on a SrTiO(3)/Nb-doped SrTiO(3) substrate. A GNR field-effect transistor (FET) shows bipolar FET behavior with a high mobility and low operation voltage at room temperature because of the atomically flat surface and the large dielectric constant of the insulating SrTiO(3) layer, respectively.     

Flavusides A and B, antibacterial cerebrosides from the marine-derived fungus Aspergillus flavus

Flavusides A (1) and B (2), two new antibacterial cerebroside derivatives, and the previously described phomaligol A (3), kojic acid (4), methyl kojic acid (5), and dimethyl kojic acid (6) have been isolated from the extract of a marine isolate of the fungus Aspergillus flavus. The structure and absolute stereochemistry of two cerebrosides were assigned on the basis of NMR and Tandem FAB-MS/MS experiments. Compounds 1, 2, and 3 exhibited a mild antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus. The minimum inhibitory concentration (MIC) values for each strain are as follows: compounds 1 and 2 showed 15.6 μg/ml for S. aureus and 31.2 μg/ml for methicillin-resistant S. aureus and multidrug-resistant S. aureus, and compound 3 exhibited 31.2 μg/ml for S. aureus and methicillin-resistant S. aureus and 62.5 μg/ml for multidrug-resistant S. aureus.     

Size tuned electrophoretic pyrazoline nanoparticles prepared through dispersion-polymerization

Highly monodispersed electrophoretic particles of size ranging from 550 to 160 nm could be prepared through dispersion-polymerization of methyl methacrylate and ethylene glycol dimethacrylate in presence of pyrazoline nanoparticles in a methanol-water mixture. The size of the fabricated electrophoretic particles could be controlled by adjusting the concentration of surfactant. Stearic acid, used as surfactant during the polymerization process also acts as charge controlling additive to control the electrophoric mobility of the particles. Maximum electrophoric mobility (-7.513×10(-5) cm(2)/Vs) was obtained for the 400 nm electrophoretic particles prepared with 1.5 wt.% of stearic acid surfactant. The electrophoric display cells prepared with our electrophoretic particles reveal good current voltage characteristics and color change under applied bias voltage.     

Comparative study of codon substitution patterns in foot-and-mouth disease virus (serotype O)

We compared genetic variations in the VP1 gene of foot-and-mouth disease viruses (FMDVs) isolated since 2000 from various region of the world. We analyzed relative synonymous codon usage (RSCU) and phylogenetic relationship between geographical regions, and calculated the genetic substitution patterns between Korean isolate and those from other countries. We calculated the ratios of synonymously substituted codons (SSC) to all observed substitutions and developed a new analytical parameter, EMC (the ratio of exact matching codons within each synonymous substitution group) to investigate more detailed substitution patterns within each synonymous codon group. We observed that FMDVs showed distinct RSCU patterns according to phylogenetic relationships in the same serotype (serotype O). Moreover, while the SSC and EMC values of FMDVs decreased according to phylogenetic distance, G + C composition at the third codon position was strictly conserved. Although there was little variation among the SSC values of 18 amino acids, more dynamic differences were observed in EMC values. The EMC values of 4- and 6-fold degenerate amino acids showed significantly lower values while most 2-fold degenerate amino acids showed no significant difference. Our findings suggest that different EMC patterns among the 18 amino acids might be an important factor in determining the direction of evolution in FMDV.     

X‐ray tomography of morphological changes after freeze/thaw in gas diffusion layers

Liquid water produced in a polymer electrolyte membrane fuel cell experiences a freeze/thaw cycle when the cell is switched off and on while operating at ambient temperatures below freezing. This freeze/thaw cycle permanently deforms the polymer electrolyte membrane fuel cell capillary structures and reduces both the cell life and its ability to generate electric power. The X‐ray tomography facility at the Pohang Accelerator Laboratory was used to observe the freeze/thaw effects on the gas diffusion layer (GDL), which is the thickest capillary layer in the cell. Morphological changes in the GDL under a water freeze/thaw cycle were observed. A scenario in which freeze/thaw cycles affect fuel cell performance is suggested based on images from X‐ray tomography.     

Statistical description of glass-forming alloys with chemical interaction: Application to Al-R systems

The statistical model for describing network-forming systems, developed in our previous works, is applied to study of metallic alloys with chemical bonding. The model is based on the representation of the sum of statistical weights over all possible configurations for a thermoreversible network in the form of a functional integral over a scalar field. The mean-field solution of the model is derived, and for particular case of a binary alloy having single element of chemical short-range order A₂B-type, thermodynamic and structural properties have been analyzed. This analysis allows to plot the temperature-concentration phase diagram of the model representing two immiscibility gap meeting in the distectic point. It is shown that at some temperatures and concentrations, geometry percolation of the network of chemical bonds and thus a sol-gel transition may take place. The critical percolation line was plotted in common with phase diagram. Then, the structural transitions, glass-forming ability and magnetic properties of Al-R alloys are discussed in the frames of this conception. It is proposed that the range of easy glass formation is confined on the left by the minimal concentration for the sol-gel transition and on the right by the concentration corresponding to the fractal-to-Euclidian crossover in the structure of percolation cluster. Finally, the abnormal growth of Al-REM magnetic susceptibility occurring above melting point of Al₂R compound is also explained.