Cycling performance and efficiency of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

As an alternative to Nafion® ion exchange membrane, an inexpensive commercially-available Radel® polymer was sulfonated, fabricated into a thin membrane, and evaluated for its performance in a vanadium redox flow battery (VRFB). The sulfonated Radel (S-Radel) membrane showed almost an order of magnitude lower permeability of VO²⁺ ions (2.07 × 10^?7 cm²/min), compared to Nafion 117 (1.29 × 10^?6 cm²/min), resulting in better coulombic efficiency (~ 98% vs. 95% at 50 mA/cm²) and lower capacity loss per cycle. Even though the S-Radel membrane had a slightly higher membrane resistance, the energy efficiency of the VRFB with the S-Radel membrane was comparable to that of Nafion because of its better coulombic efficiency resulting from the lower vanadium ion crossover. The S-Radel membrane exhibited good performance up to 40 cycles, but a decline in performance at later cycles was observed, likely as a result of membrane degradation.     

OH-radical induced degradation of hydroxybenzoic- and hydroxycinnamic acids and formation of aromatic products—A gamma radiolysis study

The OH-radical induced degradation of hydroxybenzoic acids (HBA), hydroxycinnamic acids (HCiA) and methoxylated derivatives, as well as of chlorogenic acid and rosmarinic acid was studied by gamma radiolysis in aerated aqueous solutions. Primary aromatic products resulting from an OH-radical attachment to the ring (hydroxylation), to the position occupied by the methoxyl group (replacement –OCH₃ by ?OH) as well as to the propenoic acid side chain of the cinnamic acids (benzaldehyde formations) were analysed by HPLC–UV and LC–ESI–MS. A comparison of the extent of these processes is given for 3,4-dihydroxybenzoic acid, vanillic acid, isovanillic acid, syringic acid, cinnamic acid, 4-hydroxycinnamic acid, caffeic acid, ferulic acid, isoferulic acid, chlorogenic acid, and rosmarinic acid. For all cinnamic acids and derivatives benzaldehydes were significant oxidation products. With the release of caffeic acid from chlorogenic acid the cleavage of a phenolic glycoside could be demonstrated. Reaction mechanisms are discussed.     

Degradation kinetics of telithromycin determined by HPLC method

The degradation kinetics of the antibiotic telithromycin using a stability-indicating high-performance liquid chromatography (HPLC) method is demonstrated. The photodegradation is performed by UVC lamp-254 nm (15W), installed in a chamber internally coated with mirrors, where telithromycin solutions prepared from coated tablets are placed in quartz cells. To promote oxidation, the reaction between the telithromycin solution and 3% hydrogen peroxide solution is carried out. The kinetics parameters of order of reaction and the rate constants of the degradation are determined for both conditions. The degradation process of telithromycin can be described by first-order kinetics under both experimental conditions used in this study. The results reveal the photo and oxidation lability of the drug and confirm the reliability of HPLC method for telithromycin in the presence of its degradation products.     

Pupils’ attitudes towards mathematics: a comparative study of Norwegian and English secondary students

Comparing English and Norwegian pupils’ attitude towards mathematics, in this article I develop a deeper understanding of the factors that may shape and influence ‘pupil attitude towards mathematics’, and argue for it as a socio-cultural construct embedded in and shaped by students’ environment and context in which they learn mathematics. The theoretical framework leans on work by Zan and Di Martino (The Montana Mathematics Enthusiast, Monograph 3, pp. 157–168, 2007) to elicit Norwegian and English pupils’ attitude of mathematics as they experience it in their respective environments. Whilst there were differences which could be seen to be accounted for by differently ‘figured’ environments, there are also many similarities. It was interesting to see that, albeit based on a small statistical sample, in both countries students had a positive attitude towards mathematics in year 7/8, which dropped in year 9, and increased again in years 10/11. This result could be explained and compared with other larger scale studies (e.g. Hodgen et al. in Proceedings of the British Society for Research into Learning Mathematics. 29(3), 2009). The analysis of pupils’ qualitative comments (and classroom observations) suggested seven factors that appeared to influence pupil attitude most, and these had ‘superficial’ commonalities, but the perceptions that appeared to underpin these mentions were different, and could be linked to the environments of learning mathematics in their respective classrooms. In summary, it is claimed that it is not enough to identify the factors that may shape and influence pupil attitude, but more importantly, to study how these are ‘lived’ by pupils, what meanings are made in classrooms and in different contexts, and how the factors interrelate and can be understood.     

Observation of transverse polarization asymmetries of charged pion pairs in e+e- annihilation near √s = 10.58 GeV

The interference fragmentation function translates the fragmentation of a quark with a transverse projection of the spin into an azimuthal asymmetry of two final-state hadrons. In e(+)e(-) annihilation the product of two interference fragmentation functions is measured. We report nonzero asymmetries for pairs of charge-ordered π(+)π(-) pairs, which indicate a significant interference fragmentation function in this channel. The results are obtained from a 672 fb(-1) data sample that contains 711 × 10(6) π(+)π(-) pairs and was collected at and near the Υ(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider.     

Intertwining operators and the restriction of representations of rank-one orthogonal groups

We give a complete classification of intertwining operators (breaking symmetry operators  ) between spherical principal series representations of O(n+1,1)$O(n+1,1)$ and O(n,1)$O(n,1)$ together with explicit formulae of the distribution kernels. Further we use this to determine the breaking symmetry operators between their irreducible composition factors.     

Formation of unexpected ions from a first‐generation polyamidoamine dendrimer by use of methanol: an artefact due to electrospray emitter corrosion?

We report the formation of unexpected ions during the analyses of a first‐generation polyamidoamine dendrimer in negative ion mode using an ion trap equipped with an electrospray ionisation source. These surprising ions corresponded to an increase of 12 m/z units over those expected. The formation of the unexpected ions was dependent on the tuning of the solution flow rate and the capillary high voltage. In addition, measurements of unusual value of the current suggested that a reaction was occurring in the corona plasma. The influence of methanol in this phenomenon was demonstrated by using CD₃OH in the sample preparation. We propose two structures to explain the observed adduct based on the results of MS² experiments and by referring to previous work dealing with 12 m/z units addition. We showed that a corona discharge caused by alterations taking place to the electrospray capillary emitter was the origin of these unexpected ions. Finally, we discuss the mechanism involved in the formation of the ions and we propose means to control such artefacts. Copyright © 2010 John Wiley & Sons, Ltd.     

Desorption kinetics of model polar stratospheric cloud films measured using Fourier Transform Infrared Spectroscopy and Temperature‐Programmed Desorption

This study combines Fourier transform infrared (FTIR) spectroscopy and temperature‐programmed desorption to examine the evaporation kinetics of thin films of crystalline nitric acid hydrates, solid amorphous H₂O/HNO₃ mixtures, H₂O–ice, ice coated with HCl, and solid HNO₃. IR spectroscopy measured the thickness of each film as it evaporated, either at constant temperature or during a linear temperature ramp (temperature‐programmed infrared, TPIR). Simultaneously, a mass spectrometer measured the rate of evaporation directly by monitoring the evolution of the molecules into the gas phase (temperature‐programmed desorption, TPD). Both TPIR and TPD data provide a measurement of the desorption rate and yield the activation energy and preexponential factor for desorption. TPD measurements have the advantage of producing many data points but are subject to interference from experimental difficulties such as uneven heating from the edge of a sample and sample‐support as well as pumping‐speed limitations. TPIR experiments give clean but fewer data points. Evaporation occurred between 170 and 215 K for the various films. Ice evaporates with an activation energy of 12.9 ± 1 kcal/mol and a preexponential factor of 1 × 10^32±1.5 molec/cm² s, in good agreement with the literature. The beta form of nitric acid trihydrate, β–NAT, has an E_des of 15.6 ± 2 kcal/mol with log A = 34.3 ± 2.3; the alpha form of nitric acid trihydrate, α–NAT, is around 17.7 ± 3 kcal/mol with log A = 37.2 ± 4. For nitric acid dihydrate, NAD, E_des is 17.3 ± 2 kcal/mol with log A = 35.9 ± 2.6; for nitric acid monohydrate, NAM, E_des is 13 ± 3 kcal/mol with log A = 31.4 ± 3. The α–NAT converts to β–NAT during evaporation, and the amorphous solid H₂O/HNO₃ mixtures crystallize during evaporation. The barrier to evaporation for pure nitric acid is 14.6 ± 3 kcal/mol with log A = 34.4 ± 3. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 295–309, 2001     

A straightforward method for analysing the grain-size distribution in tungsten carbide - cobalt hardmetals

Measurement of the grain-size distribution of sintered hardmetals is indispensable in research and production. In this study we present a method consisting of etching hardmetals in order to remove the cobalt binder and to analyse the remaining tungsten-cobalt (WC) crystallites on the basis of scanning electron microscopy images subjected to a PC-based image analysis by use of MATLAB®. Sample preparation is easy and quick to perform, i.e. it does not require metallographic polishing. It consists of either deep etching of the cobalt binder of cut and optionally hand-ground surfaces or etching of fracture surfaces. Two different computational routines and one combination thereof are described. Two hardmetal grades with average WC grain sizes slightly larger as well as smaller than 200 nm were investigated. The results of the computer algorithms are compared to data obtained by manual linear intercept analysis. The analysis has good potential to avoid time-consuming metallographic preparation and pre-treatment for grain-size analysis, which is especially true for hardmetals with extremely fine grain size.