The mechanism of the oxidative polymerization of aniline and the formation of supramolecular polyaniline structures

Polyaniline is one of the most important conducting and responsive polymers. A molecular mechanism for the oxidation of aniline is proposed. This mechanism explains the specific features of aniline oligomerization and polymerization in various acidity ranges. The formation of polyaniline precipitates, colloids and thin films is reviewed and discussed on the basis of the chemistry of aniline oxidation. The generation of nanostructures, i.e. granules, nanotubes, nanowires and microspheres, is also considered. Oligomers containing phenazine constitutional units play an important role in self‐assembly to form templates. Polyaniline chains then grow from these templates and produce the various individual morphologies. Copyright © 2008 Society of Chemical Industry     

Exhaust hood for steam turbines-single-flow arrangement

In the past, increased attention was given to the development of an optimal shape for the inlet part of LP turbine casings in SKODA POWER. A double-flow design is typically used for high power output turbines. An optimized shape for the internal diffuser has been found, which transforms the kinetic energy of steam into increased pressure, thus effectively increasing the thermodynamic efficiency of the stage. Some conclusions have been drawn from laboratory experiments, others derived directly from on-site measurements at power plants. The conclusions from the development of double-flow turbines form the basis for the design of the single-flow turbine arrangement. Single-flow design is typically used for lower output turbines. There are still some limitations in applying this arrangement. The designer needs to resolve the bearing position and how to ensure access to them. Reinforcing the ribs and supports are used, therefore, to ensure the rigidity of the entire casing. The optimization of the single-flow diffuser shape is therefore the subject of the study presented below.     

Interaction of vitamins E and K: effect of high dietary vitamin E on phylloquinone activity in chicks

Age-standardised mortality rates are often used in epidemiologic studies to describe the dimension of social inequalities in mortality. This, however, conceals any age-dependence of social inequality. In an ecologic study, all causes and cause-specific mortality of all citizens of Bochum, FRG, who died 1988-1990, were evaluated using 13.171 death certificates. Data was aggregated on census tract level. The social status of a census tract was determined using 6 variables from the census 1987 describing the socio-economic situation in each census tract. Census tracts were grouped into quintiles according to their social status. Age and sex-specific mortality rates as well as rate ratios, using the quintile with the highest social status as reference, were calculated. Results for men (n = 6.288) indicate that social inequality is age-dependent for total mortality. Social differentials are especially marked for the age groups 35-64 years. For age group < 35 years and > 84 years no social differentiation in mortality is visible. Similar patterns are found with mortality from cardiovascular diseases (ICD-9: 390-459) and cancer (ICD-9: 140-208). Mortality from diseases related to health behaviour such as lung cancer or diseases associated with high alcohol intake are characterised by social inequalities above average in the middle age groups. For total mortality in women (n = 6.883) large social differentials are found for age groups 25-34 years and 45-54 years. Efforts to reduce social inequality on community level should especially be aimed at adolescents and young adults living in underprivileged areas.     

Control of polyaniline conductivity and contact angles by partial protonation

Many studies require a specific value of conductivity when investigating conducting polymers. The conductivity of polyaniline can efficiently be controlled by partial protonation of the polyaniline base. Although this is a simple task in principle, practical guidelines are missing. In the present study, the changes in the conductivity of polyaniline base after immersion in aqueous solutions of various acids are reported. Polyaniline base has been reprotonated in aqueous solutions of picric, camphorsulfonic and phosphoric acids. The conductivity of partially reprotonated polyaniline varied between 10⁻⁹ and 10⁰ S cm⁻¹. The relation between the pH of a phosphoric acid solution, which was in equilibrium with polyaniline, and the conductivity σ is pH = 0.77 − 0.64 log(σ [S cm⁻¹]). The wettability, i.e. water contact angles, can similarly be set by partial protonation to between 78° for polyaniline base and 44° for polyaniline reprotonated in 1 mol L⁻¹ phosphoric acid. In solutions of picric acid, the transition from the non‐conducting to the conducting state occurs over a narrow range of acid concentrations, and the tuning of conductivity is consequently difficult. Phosphoric acid is well suited for the control of conductivity of polyaniline because of the moderate dependence of the conductivity on the acid concentration or pH. Copyright © 2007 Society of Chemical Industry     

Trace metals in Phragmites australis and Phalaris arundinacea growing in constructed and natural wetlands

Constructed wetlands with horizontal subsurface flow (HF CWs) designed for treatment of municipal sewage have been monitored extensively with respect to removal of organics, suspended solids, nitrogen, phosphorus and bacteria. However, the information on the removal of various metals and metalloids in these systems is very limited. During the period 2002-2004 aboveground and belowground biomass of Phragmites australis (common reed) and Phalaris arundinacea (reed canarygrass) were sampled in three HF CWs in the Czech Republic. Concentrations of monitored elements in both aboveground and belowground plant tissues were similar to those found in plants growing in natural stands. The concentrations were much lower as compared to those found in plants growing in wetlands receiving acid mine drainage waters, waters from smelters or highway runoff. Concentrations decrease in the order of roots>rhizomes>leaves>stems. The leaf:stem concentration ratios were quite similar for all monitored elements ranging between 1.0 and 1.9. The root:leaf concentration ratio varied widely between 1.5 (Cu) and 54 (Cr) with a mean value of 20.0. Belowground/aboveground plant tissue concentration ratios varied from 2.2 (Cu) to 32 (Cr) with the average value of 9.9.     

Laminated alumina/zirconia ceramic composites prepared by electrophoretic deposition

The electrophoretic deposition of alumina and zirconia powders from isopropanolic suspension in the presence of monochloroacetic acid was studied in the constant-current regime. The different levels of electric current during deposition from 250 μA to 48 mA were used. The green density of the deposit depends on the current density and then on the particle velocity during deposition, reaching values from 58% to 61% according to the electric current used. It was found that the lower the green density of the green deposit, the larger the pores. The low green density led to low final fired density and subsequently to the low Vickers hardness HV5 ranging from 2000 to 1650 depending on electric current used. Based on these findings microlaminates having various thickness ratios to achieve different residual stress levels were prepared consisting of alternating layers of alumina and zirconia.     

Influence of the substrate temperature and annealing on the 1.54-µm erbium photoluminescence of a-Si:H films obtained using a glow discharge

Effective Er photoluminescence is observed at room temperature in a-Si:H films doped with Er atoms through a gas phase using powdered Er(TMND)₃ as a source of Er ions. It is shown that the conditions for deposition of the films and their subsequent annealing influence the photoluminescence intensity and its temperature dependence. The observed behavior is attributed to restructuring of the amorphous silicon matrix within an Auger excitation mechanism involving defects. Fiz. Tekh. Poluprovodn. 33, 208–210 (February 1999)     

Assessment of photovoltaic potential in urban areas using open-source solar radiation tools

This study presents a methodology for the assessment of photovoltaic potential in urban areas using open-source solar radiation tools and a 3-D city model implemented in a geographic information system (GIS). The solar radiation tools are represented by the r.sun solar radiation model and PVGIS estimation utility. The applicability of the methodology has been demonstrated on a selected urban area of a small city in eastern Slovakia. The relevant attributes of buildings have been mapped and implemented in a GIS database. The selected urban area consists of various urban zones characterized by different morphology and functionality. The photovoltaic potential of buildings has been assessed using the PVGIS estimation utility. The analysis has shown a high photovoltaic potential that could cover about 2/3 of current electricity consumption in the city. However, this potential exhibits large spatial and temporal variations caused by global and local factors. This study has also shown that national assessments of photovoltaic potential can be improved by extrapolation of local assessments using spatial databases of urban areas.