Determination and risk assessment of by-products resulting from photocatalytic oxidation of toluene

The generation of harmful by-products during photocatalytic oxidation (PCO) of volatile organic compounds (VOCs) is a bottleneck problem for the application of PCO technology in indoor environment. Toluene is a typical VOC found in indoor air. In this work, the by-products at ppb level were studied during PCO decomposition of toluene in a plate-type reactor and identified using PTR-MS (proton transfer reaction-mass spectrometry) and GC–MS (gas chromatography–mass spectroscopy). The results indicated that benzaldehyde, methanol, acetaldehyde, acetone/propionaldehyde, formic acid/ethanol and acetic acid were the main by-products in the gas phase. By adjusting the concentration of water vapor, some compounds adsorbed on the TiO₂ surface were ascertained, which resulted in the deactivation of TiO₂. They were benzoic acid, benzene, acrylaldehyde, butyraldehyde and pentanal. Some of these by-products have not been reported in the literature. Possible photocatalytic oxidation pathways of toluene were proposed. A health-related index (HRI) was introduced to assess the risk level to human health of these ppb-level by-products. It concludes that although some undesired by-products (even carcinogenic) are generated during PCO decomposition of toluene, it seems that these by-products do not have negative effects to human health because of their low concentrations.     

Case Study: Impact of Reservoir Stratification on Interflow Travel Time

A case study is presented on the relation between interflow travel time and reservoir stratification. A simulation model is calibrated and validated for the Wachusett Reservoir in Massachusetts. The Reservoir has a major controlled inflow which traverses the reservoir as an interflow. The model is used with a range of alternate inflow schedules and the resulting travel time of the interflow is examined. The inflow density is within the range of densities found in the reservoir thermocline and the inflow rate is sufficient to maintain a continuous interflow. Under these conditions it is found that a linear relation exists between the average interflow travel time, as measured by the arrival of a specified fraction of interflow water at the outlet, and the degree of stratification, as measured by the maximum difference in reservoir thermocline temperature, at the initiation of the inflow. The results may be useful for operation of the reservoir under study subject to continued validation of the simulation model used.     

Finite element Euler computations in three dimensions

An explicit finite element solution procedure for the three dimensional Euler equations is presented. The solution domain is automatically meshed using a tetrahedral mesh generator which is an extension of our previous two dimensional work. Several examples are included to illustrate the performance of the generator and solver. An adaptive mesh regeneration procedure is used for the first time in three dimensions.     

Size exclusion chromatographic approach for the evaluation of processes for upgrading heavy petroleum

A new application of size exclusion chromatography for the evaluation of processes for upgrading heavy crudes is described. The comparison of the elution curves of a feedstock of heavy crude, selected for an upgrading process, is made with the resulting products of the process. A quantitative assessment of the extent of the improvement as a result of the hydrogenation in the crude is presented by defining an algorithm which measures the conversion of material up to 550 °C. The defined conversion is correlated with conventional crude properties and there is a linear relation between the conversion obtained by s.e.c. and certain selected properties. The results for a number of products are included and the relation between conversion and process conditions is discussed.     

Application of 13C nmr spectroscopy to the elucidation of the electrochemical oxidation mechanism of the l-ascorbic and d-araboascorbic acids

The previously proposed electrochemical oxidation mechanism of the l-ascorbic and d-araboascorbic acids in basic medium must be rejected because of the variation in the carbon chemical shifts and coupling constants with the pH, which shows that the supposed rupture of the furanose rings at pH ～ 9 does not occur. Electrolysis in basic medium yields the same products as those obtained when the pH of the products of the electrolysis in acid medium are raised to pH ～ 11. This suggests that the oxidation mechanisms in acid and basic media are similar. The assigned carbon chemical shifts of the oxidation products in acid medium $\text{3}$ (or $\text{4}$) and in basic medium $\text{5}$ (or $\text{6}$) and $\text{7}$ (or $\text{8}$) are reported.     

Image quality and position variability assessment in minutiae-based fingerprint verification

The assessment of a complete minutiae-based fingerprint automatic verification system, when degrading variability factors are included, is presented. A new large public fingerprint database, the so-called MCYT Fingerprint Database, is used to evaluate the performance of the system in verification tasks. The design of this database, in terms of controlled variability in fingerprint positioning, has made it possible to determine the system performance when the test or the stored images are subject to changes in fingerprint core placing. Some procedures are proposed to cope with this problem, including a multiple-reference strategy. Human supervision and labelling of the image quality of the acquired fingerprint images has also been accomplished, permitting a precise assessment of the proposed minutiae extraction and pattern matching processes. Results, including enhanced procedures for both position variability control and image quality consideration, are presented in terms of DET plots, leading to highly competitive verification scores in terms of EER (equal error rate).     

Etude du diagramme de phases et cristallogenese des phosphovanadates de plomb

The phase diagram of lead phosphovanadate Pb₃(P_xV_1?xO₄)₂ for 0.5 ≤ x ≤ 1 has been investigated. Liquidus and solidus have been determined by means of differential thermal analysis and X-ray techniques. These results are confirmed through a molecular absorption spectrophotometry analysis of phosphor and vanadium, by comparing the compositions of lead phosphovanadate single crystals, grown by Czochralski pulling, with that of the starting melts. Good optical and crystallographic quality crystals of large size are obtained for x = 0 and x = 0.5, while for other compositions, they are still suitable for physical measurements. A definite, congruently melting compound with trigonal symmetry at room temperature is found for x = 0.5.     

The role of nickel in hydrodesulphurisation catalysts

The acidity and activity of promoted (with NiO) and unpromoted MoO₃/A1₂O3 catalysts were studied by ammonia adsorption, titration using acid/base colour indicators, and thiophene hydrodesulphurisation. The incorporation of nickel into supported MoO₃ produced significant changes in activity, which was attributed to changes in the number and strength of the acid sites. Specifically, the nickel decreased the concentration of highly acid sites and increased the number of sites with intermediate acidity in the oxide catalyst. At the same time, the nickel markedly increased the steady state catalytic activity but decreased the initial activity. Carbon and sulphur analyses, as well as acid site concentration of used catalysts, suggest that this behaviour may be associated with modifications brought about by nickel on MoS₂ crystallite growth and on deactivation by carbon deposition. These suggestions are found to be consistent with other effects attributed to the promoter, such as hydrogen spill-over and p-semiconductivity.     

Selective insulation with poly(tetrafluoroethylene) of substrate electrodes for electrochemical background reduction in scanning electrochemical microscopy

We describe a wet process for the fabrication of poly(tetrafluoroethylene) (PTFE)-covered electrodes in which arrays of holes ( approximately 200 microm) are formed. The PTFE coating provides electrical insulation of most of the electrode surface with selected regions exposed for electrochemical experiments. The arrays of microholes can be controllably patterned and filled with precursor solutions using a piezoelectric dispenser. A micrometer spot of electrocatalyst is produced after reduction of the precursor. The application is tested for scanning electrochemical microscopy (SECM) in the tip generation-substrate collection (TG-SC) studies of electrocatalysts. The method is shown to reduce the substrate background currents that are included in the electrochemical signal read from the local perturbation induced with the SECM tip to the substrate in the TG-SC mode of SECM. This background current reduction is consistent with the decrease in the exposed area of the electrode. The general methodology for the fabrication of the substrate electrodes and two proof-of-concept applications in the TG-SC SECM modality are described.     

Constructing and analyzing the fitness landscape of an experimental evolutionary process

Iterative saturation mutagenesis (ISM) is a promising approach to more efficient directed evolution, especially for enhancing the enantioselectivity and/or thermostability of enzymes. This was demonstrated previously for an epoxide hydrolase (EH), after five sets of mutations led to a stepwise increase in enantioselectivity. This study utilizes these results to illuminate the nature of ISM, and identify the reasons for its operational efficacy. By applying a deconvolution strategy to the five sets of mutations and measuring the enantioselectivity factors (E) of the EH variants, DeltaDeltaG( not equal) values become accessible. With these values, the construction of the complete fitness-pathway landscape is possible. The free energy profiles of the 5!=120 evolutionary pathways leading from the wild-type to the best mutant show that 55 trajectories are energetically favored, one of which is the originally observed route. This particular pathway was analyzed in terms of epistatic effects operating between the sets of mutations at all evolutionary stages. The degree of synergism increases as the stepwise evolutionary process proceeds. When encountering a local minimum in a disfavored pathway, that is, in the case of a dead end, choosing another set of mutations at a previous stage puts the evolutionary process back on an energetically favored trajectory. The type of analysis presented here might be useful when evaluating other mutagenesis methods and strategies in directed evolution.