Arsenic detection by nanogold/conducting‐polymer‐modified glassy carbon electrodes

This article discusses the results for the development of a nanogold‐particle/polyaniline‐modified glassy carbon electrode for the detection of arsenic(III) in water. A thin polyaniline film was electropolymerized onto a glassy carbon electrode. The gold nanoparticle was then deposited onto the polyaniline‐coated glassy carbon electrode via potential step electrolysis from 1.1 to 0 V versus Ag/AgCl/NaCl (saturated) for 45 s from a 0.5M H₂SO₄ solution containing 0.1 mM NaAuCl₄ in the absence and presence of a 0.1 mM KI additive. The surface of the modified electrode was examined with scanning electron microscopy. Cyclic and anodic stripping voltammetry of arsenic(III) was performed on the modified electrode. The thus modified nanogold‐particle/polyaniline‐modified glassy carbon electrode prepared in the presence of the I^? (KI) additive showed a high sensitivity in detecting arsenic(III) in water, and with stripping voltammetry, a limit of detection of 0.4 ppb arsenic was obtained, which is much lower than the arsenic guideline limit of the World Health Organization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1306–1311, 2007     

Solid Solubility of GeO2 in SnO2

Subsolidus equilibrium relations were reexamined in the SnO₂-rich portion of the system GeO₂-SnO₂ (60 to 98 mol% SnO₂). A limited solid solution based on SnO₂ was confirmed; 4mol% GeO₂ dissolved in SnO₂ at 1250 C, and glass was formed on quenching over the compositional range above 4mol% GeO₂. Phase relutions in the system are discussed with reference to the polymorphism of GeO₂ and its glass-forming ability, and a possible phase diagram is given .     

Point mutation of alanine (31) to valine prohibits the folding of reduced lysozyme by sulfhydryl--disulfide interchange

In the preceding paper in this issue, we described the overproduction of one mutant chicken lysozyme in Escherichia coil.Since this lysozyme contained two amino acid substitutions (Ala³¹ValandAsn¹⁰⁶Ser)in addition to an extra methionine residue at theNH₂-terminus the substituted amino acid residues were convertedback to the original ones by means of oligonucleotide-directedsite-specific mutagenesis and in vitro recombination. Thus fourkinds of chicken lysozyme [Met^–1 Val³¹Ser¹⁰⁶-, Met^–1Ser¹⁰⁶-,Met^–1 Val³¹-and Met^–1 (wild type)] wereexpressed in E. coli. From the results of folding experimentsof the reduced lysozymes by sulfhydryl-disulfide interchangeat pH 8.0 and 38°C, follow ed by the specific activity measurementsof the folded en zymes, the following conclusions can be drawn:(i) an extra methionine residue at the NH₂-terminus reducesthe folding rate but does not affect the lysozyme activity ofthe folded enzyme; (ii) the substitution of Asn¹⁰⁶ by Ser decreasesthe activity to 58% of that of intact native lysozyme withoutchanging the folding rate; and (iii) the substitution of Ala³¹Val prohibits the correct folding of lysozyme. Since the wildtype enzyme (Met^–1-lysozyme) was activated in vitro withoutloss of specific activity, the systems described in this study(mutagenesis, overproduction, purification and folding of inactivemutant lysozymes) may be useful in the study of folding pathways,expression of biological activity and stability of lysozyme.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.     

Densely Aligned Multichannel Polymer Waveguide With Low Inter-Channel Crosstalk

We succeeded in fabricating an acrylate-polymer based four-channel parallel optical waveguide with densely aligned graded-index (GI) circular cores (58-mum pitch) by the preform method. Although inter-channel optical crosstalk is concerned in such highly integrated channels, we verify a strong confinement effect of electric field at the core center achieved by parabolic refractive index profile (GI). Low inter-channel crosstalk is demonstrated by the polymer waveguides with densely aligned GI cores.     

Usability of AMeDAS Sunshine Duration Data for Statistical Evaluation of Spatial Average Irradiance Fluctuation Characteristics

In order to mitigate the impacts of high‐penetration photovoltaic power generation systems (HP‐PVS) on the electric power system operation, the statistical evaluation of the aggregated power output fluctuation characteristics of HP‐PVS is important. By using the multipoint irradiance data observed for a year in the Chubu region of Japan, we have evaluated the fluctuation characteristics of spatial average irradiance. However, the study period is not enough for a statistical evaluation. Therefore, this study assessed the usability of the sunlight duration data of AMeDAS (Automated Meteorological Data Acquisition System) for the statistical evaluation of fluctuation characteristics in terms of the daily maximum fluctuation width in 120 min. The method of irradiance estimation from the sunlight duration data at single point proposed in the preceding study was modified to be suitable for the spatial average irradiance estimation by taking into account the smoothing effect of irradiance fluctuation among several points. The results suggest that the AMeDAS sunlight duration data would be useful for statistical evaluation of the fluctuation characteristics of the spatial average irradiance of an electric power system service area.     

Superconductivity in polycrystalline diamond thin films

Superconductivity was discovered in heavily boron-doped diamond thin films deposited by the microwave plasma assisted chemical vapor deposition (MPCVD) method. Advantages of the MPCVD deposited diamond are the controllability of boron concentration in a wide range, and a high boron concentration, especially in (111) oriented films, compared to that of the high-pressure high-temperature method. The superconducting transition temperatures are determined to be 8.7 K for T_c onset and 5.0 K for zero resistance by transport measurements. And the upper critical field is estimated to be around 7 T.     

Photonic encoder and decoder for optical code-division multiplexing with time-to-space converters and angle-multiplexed holograms

A photonic encoder-decoder pair for optical code-division multiplexing (OCDM) that uses time-to-space converters and angle-multiplexed holograms is proposed. The encoder converts the pulse from each input port into a specific code and multiplexes input signals into the output port. The hologram in the decoder generates a correlation waveform between the transmitted code and the recorded code. The performance of the OCDM system with the encoder-decoder pair is estimated. The maximum spectral efficiency for 8-bit length orthogonal codes in the worst case at a bit-error rate of 10(-9) is 0.17 (bits/s)/Hz when the number of channels is 8.     

A probabilistic modeling of MOSAIC learning

Humans can generate accurate and appropriate motor commands in various, and even uncertain, environments. MOSAIC (MOdular Selection And Identification for Control) was originally proposed to describe this human ability, but this model is hard to analyze mathematically because of its emphasis on biological plausibility. In this article, we present an alternative and probabilistic model of MOSAIC (p-MOSAIC) as a mixture of normal distributions and an online EM-based learning method for its predictors and controllers. A theoretical consideration shows that the learning rule of p-MOSAIC corresponds to that of MOSAIC except for some points which are mostly related to the learning of controllers. The results of experiments using synthetic datasets demonstrate some practical advantages of p-MOSAIC. One is that the learning rule of p-MOSAIC stabilizes the estimation of “responsibility.” Another is that p-MOSAIC realizes more accurate control and robust parameter learning in comparison to the original MOSAIC, especially in noisy environments, due to the direct incorporation of the noises into the model. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

Robust boosting algorithm against mislabeling in multiclass problems

We discuss robustness against mislabeling in multiclass labels for classification problems and propose two algorithms of boosting, the normalized Eta-Boost.M and Eta-Boost.M, based on the Eta-divergence. Those two boosting algorithms are closely related to models of mislabeling in which the label is erroneously exchanged for others. For the two boosting algorithms, theoretical aspects supporting the robustness for mislabeling are explored. We apply the proposed two boosting methods for synthetic and real data sets to investigate the performance of these methods, focusing on robustness, and confirm the validity of the proposed methods.