Controlled assembly of mesoscale structures using DNA as molecular bridges

Mesoscale polyhedral structures from binary mixtures of microspheres of specific size ratios were prepared by using DNA as a molecular bridge. Carboxy-modified polystyrene beads were decorated with fluorescently labeled single-stranded DNA via carboxydiimide chemistry. Fluorescent resonance electron transfer in a confocal microscopy setting was utilized to corroborate DNA hybridization. Tetrahedrons were made by combining DNA-containing 0.818 and 0.211 mum beads, while octahedrons were obtained by bridging 0.818 and 0.364 mum beads. Confocal data in the reflection mode and SEM provide evidence for the formation of mesoscale building blocks.     

Electrochemical and surface analytical study of the formation of oxide films on monel-400 and copper in alkaline media

The nature of the oxide films formed on monel-400 and copper in presence of NaOH and N-methylpyrrolidine (a volatile amine) at pH 9.5 and in 0.1 M KNO₃ medium were investigated. The oxide films were grown by applying an anodic potential of +0.4 V (vs saturated calomel electrode) for 30 min. The compositions of the surface oxide films were analysed by X-ray photoelectron spectroscopy. In the case of copper in NaOH medium, Cu(0) and a very small amount of copper hydroxide were observed. However, in amine medium, Cu(0) and Cu-amine complex were found. For monel in NaOH, the anodic film was found to contain hydroxides of both copper and nickel. After sputtering, this film showed a small amount of metal oxide below the hydroxide layer as confirmed by the oxygen peak. In amine medium the anodic film was found to contain only nickel hydroxide and metallic copper. The depth profile analysis of films showed that the film developed was very thin and the nickel hydroxide was sputtered very easily from the film. Received: 27 May 1997 / Accepted: 8 September 1997     

On the resolution of certain discrete univariate max–min problems

Graph coloring is a classical NP-hard combinatorial optimization problem with many practical applications. A broad range of heuristic methods exist for tackling the graph coloring problem: from fast greedy algorithms to more time-consuming metaheuristics. Although the latter produce better results in terms of minimizing the number of colors, the former are widely employed due to their simplicity. These heuristic methods are centralized since they operate by using complete knowledge of the graph. However, in real-world environmets where each component only interacts with a limited number of other components, the only option is to apply decentralized methods. This paper explores a novel and simple algorithm for decentralized graph coloring that uses a fixed number of colors and iteratively reduces the edge conflicts in the graph. We experimentally demonstrate that, for most of the tested instances, the new algorithm outperforms a recent and very competitive algorithm for decentralized graph coloring in terms of coloring quality. In our experiments, the fixed number of colors used by the new algorithm is controlled in a centralized manner.     

Role of water contamination within the GC column of a GasBench II peripheral on the reproducibility of 18O/16O ratios in water samples

The GasBench II peripheral along with MAT 253 combination provides a more sensitive platform for the determination of water isotope ratios. Here, we examined the role of adsorbed moisture within the gas chromatography (GC) column of the GasBench II on measurement uncertainties. The uncertainty in ¹⁸O/¹⁶O ratio measurements is determined by several factors, including the presence of water in the GC. The contamination of GC with water originating from samples as water vapour over a longer timeframe is a critical factor in determining the reproducibility of ¹⁸O/¹⁶O ratios in water samples. The shift in isotope ratios observed in the experiment under dry and wet conditions correlates strongly with the retention time of analyte CO₂, indicating the effect of accumulated moisture. Two possible methods to circumvent or minimise the effect of adsorbed water on isotope ratios are presented here. The proposed methodology includes either the regular baking of the GC column at a higher temperature (120 °C) after analysis of a batch of 32 sample entries or conducting the experiment at a low GC column temperature (22.5 °C). The effects of water contamination on long-term reproducibility of reference water, with and without baking protocol, have been described.     

A polarographic study of methionine complexes of nickel and cobalt

A polarographic study of nickel and cobalt complexes of methionine has been carried out. In sodium perchlorate and tetramethyl-ammonium bromide (TMAB) media, catalytic hydrogen waves were observed owing to the lowering of hydrogen overvoltage on mercury by the adsorption of these complexes on the dropping electrode. The presence of tetrabutylammonium ion inhibits the catalytic activity.     

The multi-cavity free-electron laser

Analysis is made of a free-electron laser with many optical cavities where the cavities communicate with each other, not optically, but through the electron beam. Analytic analysis is made in a one-dimensional, linear approximation. A general expression is given for the growth rate in the exponential (high current) regime. In the regime where lethargy is important expressions are given in the two opposite limits of small and large numbers of cavities and bunches. Numerical simulation results, still in the one-dimensional approximation, but including nonlinearities, are presented. Three examples of the multi-cavity free-electron laser (MC/FEL) are presented.     

A polarographic study of methionine complexes of cadmium in mixed solvents

Methionine complexes of cadmium in 25 and 50 per cent aqueous mixtures of ethyl and methyl alcohol and dioxan have been studied. The half-wave potentials measured in both the alcohols were the same and the reduction was reversible. Three complex species withβ ₁=1·0×10⁴,β ₂=1·1×10⁷ andβ ₃=1·2×10⁹ were found in 25 per cent alcohol while four complexes withβ ₁=3·0×10⁴,β ₂=4·3×10⁷,β ₃=4·0×10⁹ andβ ₄=1·6×10¹¹ were observed in 50 per cent solutions. In the case of dioxan, the reduction was quasi-reversible (k _s=1·0×10^?3 cm sec^?1) in 25 per cent and irreversible (k _s=2·0×10^?4 cm sec^?1) in 50 per cent solutions. The stability constants, evaluated using the formal potentials, wereβ ₁=7·0×10³,β ₂-3·9×10⁵;β ₂=3·9×10⁸ andβ ₄=3·4×10¹⁰ in 25 per cent dioxan andβ ₁=1·5×10⁴,β ₂=3·4×10⁷.β ₃=7·5×10⁹ andβ ₄=9·0×10¹¹ in 50 per cent solutions.