Polyaniline nanotubes: conditions of formation

The courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm^?1, depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter‐ions only. The PANI morphology is thus not controlled by the nature of counter‐ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH‐dependent self‐assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry     

BTEX degradation in a cold-climate wetland system.

A pilot-scale subsurface vertical-flow wetland system was constructed at the former BP Refinery in Casper, Wyoming in order to determine benzene, toluene, ethylbenzene and xylene (BTEX) degradation rates in a cold-climate application. The pilot system, consisting of 4 cells, each dosed at a nominal flow rate of 5.4 cubic metres per day, was operated between August and December 2002. The pilot tested the effects of wetland mulch and aeration on system performance. Areal rate constants (kA values) were calculated based on an assumed three tanks in series (3TIS). The presence of wetland sod and aeration both improved treatment performance. Mean kA values were 244 m/yr for cells without sod or aeration, and improved to 356 m/yr for cells with sod and aeration. Based on the results of the pilot system, a full-scale wetland system (capable of operating at 6,000 m3/day) was started up in May 2003. The full-scale system achieved permit compliance within one week of startup, but is currently being loaded at only 45% of the design hydraulic load, and 15% of the design BTEX mass load, resulting in a mean kA value of approximately 350 m/yr.     

An interconnected 2D-TM EBG structure for millimeter and submillimeter waves

Due to their unique properties, electromagnetic bandgap (EBG) materials are of high interest for applications in communication technology for many frequency bands from microwave up to optical frequencies. We have investigated in both simulation and experiment a two dimensionally periodic EBG structure made by reactive ion etching of silicon with a bandgap for transverse magnetic waves in the millimeter wave range around 100 GHz. The structure comprises both a large bandgap and a high mechanical stability due to interconnecting dielectric bridges.     

Transport of L-leucine in the fission yeast Schizosaccharomyces pombe

Transport of L -leucine into Schizosaccharomyces pombe cells from the stationary phase of growth (after preincubation for 60 min with 1% glucose) proceeds uphill, practically unidirectionally, and is mediated by at least two systems: a high-affinity system with a K_T of 0·045 mmol 1^?1 and J_max of 3·3 nmol min^?1 (mg dry weight)^?1 and a low-affinity system with a K_T of 1·25 mmol 1^?1 and J_max of 16·0 nmol min^?1 (mg dry weight)^?1. The high-affinity system has a pH optimum at 3.2, the accumulation ratio is highest at a cell density of 2–4 mg dry weight per ml and decreases with increasing leucine concentration. Transport of leucine by the high-affinity system is strongly inhibited by proton conductors, ammonium ions and by most amino acids, but only L -phenylalanine, L -isoleucine, L -valine and L -cysteine behave as fully competitive inhibitors. Systems of L -leucine transport in S. pombe are not constitutive. Transport activity appears only after preincubation of cells with a suitable source of energy. If cycloheximide is added during preincubation with glucose, no transport systems for leucine are synthesized. After removal of glucose, the activity of transport systems decays with a half-time of about 20 min. The presence of cyclic AMP increases the initial rate of leucine uptake only in cells preincubated with glucose and in the absence of cycloheximide.     

Testing of gas and liquid fuel burners for power and process industries

The object of the present paper is a review of issues related to the testing of gas and liquid fuel burners which are amongst the most important items of equipment in materials processing and energy producing industries. The text gives basic information about fuels, types of burners and their testing and also about modelling of combustion and formation of pollutants, mainly nitrogen oxides. The first two sections of the text provide an overview of fuels and burner types. The most part of the paper deals with an assessment of conditions and equipment required for testing of gas and liquid fuel burners. Conditions that must be satisfied in burner tests in order to preserve comparable operating conditions as in the real application are stressed. Last part provides an outline of the utilisation of statistical analysis methods and modelling by computational fluid dynamics (CFDs) including the formation of pollutants.     

The Chemistry and Biology of 6‐Hydroxyceramide,the Youngest Member of the Human Sphingolipid Family

Sphingolipids are crucial for the life of the cell. In land‐dwelling mammals, they are equally important outside the cell—in the extracellular space of the skin barrier—because they prevent loss of water. Although a large body of research has elucidated many of the functions of sphingolipids, their extensive structural diversity remains intriguing. A new class of sphingolipids based on 6‐hydroxylated sphingosine has recently been identified in human skin. Abnormal levels of these 6‐hydroxylated ceramides have repeatedly been observed in atopic dermatitis; however, neither the biosynthesis nor the roles of these unique ceramide subclasses have been established in the human body. In this Minireview, we summarize the current knowledge of 6‐hydroxyceramides, including their discovery, structure, stereochemistry, occurrence in healthy and diseased human epidermis, and synthetic approaches to 6‐hydroxysphingosine and related ceramides.     

Voltage-mode multifunction filter with mutually independent Q and \omega _0 control feature using VDDDAs

The paper focuses on the application possibilities of the newly presented voltage differencing active building block called voltage differencing differential difference amplifier. Using this active element, a multifunction frequency filter is designed featuring the possibility of mutually independent control of quality factor Q and characteristic frequency \(\omega _0\) by means of active elements. The structure of the filter is based on the idea of the Akerberg-Mossberg (AM) filter, i.e. the integrators in the structure are always realized only by two active elements. This fact results in better phase compensation for the filter. Compared to the AM opamp based filter, the newly proposed structure features high-impedance inputs, low-impedance output, and all basic frequency responses. The performance of the proposed structure has been verified by SPICE simulations using the TSMC \(0.18\,\upmu \hbox {m}\) level-7 SCN018 CMOS process parameters with \(\pm 0.9\,\hbox {V}\) supply voltage.     

Measurement and analysis of dynamic and acoustic parameters of rail fastening

A new method using time and frequency related transformations has been developed for the evaluation of response signals obtained by rail fastening analysis. In the paper the laboratory measurements and dynamic and acoustic parameter analyses of flexible fastening of Vossloh SKL14 type have been described. The method can also be used for designing new rail fastening systems and their parts.     

Characterization of yttria-stabilized zirconia thin films deposited by electron beam evaporation on silicon substrates

Structure, phase composition and electrical conductivity of thin yttria-stabilized zirconia (YSZ) films deposited by electron beam evaporation on a silicon (1 0 0) substrate at different temperatures i.e. room temperature (r.t.), 700 and 830°C, as well as the quality of the YSZ–Si interface have been investigated. The phase composition was verified by Raman spectroscopy and by infrared (i.r.) transmission measurements. The structure of films changed in agreement with their electrical conductivity depending on the deposition temperature. Both structure and thereby electrical conductivity were influenced by the high concentration of Y2O3 stabilizer used and by the post-deposition thermal treatment of films. The deposition temperature was also important in determining the quality of the YSZ–Si interface and hence the accessible sweep of the surface potential. The capacitance–voltage characteristics of the metal–insulator–semiconductor (MIS) structures incorporating YSZ films measured at r.t. showed hysteresis and positive shifts of the flat-band voltages. © 1998 Chapman & Hall