Detection of Sulfite via the Trapping and Subsequent Electrochemical Detection of Hydrogen Sulfide

 The electrochemical oxidation of N,N-diethylphenylene-1,4-diamine (DEPD) and its subsequent reaction with sulfide has been exploited as a means of quantifying the latter. Re-oxidation of the resulting adduct was found to lead to an increase in the oxidative current which scaled linearly with sulfide concentration over the range 30 μM to 516 μM, although it was found that the upper limit could be extended through simply increasing the concentration of the DEPD indicator. As such the detection range is within an analytically relevant region with the detection limit of 4 μM comparing favourably with other electrochemical techniques. The approach has been extended to the detection of sulfite; this has been shown to be a facile yet robust process with complete recovery observed in the reductive conversion of sulfite to sulfide. Received December 12, 2000. Revision April 3, 2001.     

A dual‐time central difference finite volume scheme for interface capturing on unstructured meshes

This paper describes a central difference scheme for the prediction of flows with an interface. The interface is captured rather than tracked and the key to the current approach is a correction to the hydrostatic pressure. The correction enables the scheme to evaluate pressures at cell faces in a consistent manner so that the source term in the equations is correctly balanced at the interface and on non‐equispaced meshes. This prevents the development of large errors in the solution, which can lead to the divergence of the numerical scheme. The current approach allows interface flows to be calculated by a simple modification of existing central difference codes. Results for a number of test cases are presented, with comparisons made with both experimental data and other numerical solutions. Copyright © 2008 John Wiley & Sons, Ltd.     

Detecting macroeconomic phases in the Dow Jones Industrial Average time series

In this paper, we perform statistical segmentation and clustering analysis of the Dow Jones Industrial Average (DJI) time series between January 1997 and August 2008. Modeling the index movements and log-index movements as stationary Gaussian processes, we find a total of 116 and 119 statistically stationary segments respectively. These can then be grouped into between five and seven clusters, each representing a different macroeconomic phase. The macroeconomic phases are distinguished primarily by their volatilities. We find that the US economy, as measured by the DJI, spends most of its time in a low-volatility phase and a high-volatility phase. The former can be roughly associated with economic expansion, while the latter contains the economic contraction phase in the standard economic cycle. Both phases are interrupted by a moderate-volatility market correction phase, but extremely-high-volatility market crashes are found mostly within the high-volatility phase. From the temporal distribution of various phases, we see a high-volatility phase from mid-1998 to mid-2003, and another starting mid-2007 (the current global financial crisis). Transitions from the low-volatility phase to the high-volatility phase are preceded by a series of precursor shocks, whereas the transition from the high-volatility phase to the low-volatility phase is preceded by a series of inverted shocks. The time scale for both types of transitions is about a year. We also identify the July 1997 Asian Financial Crisis to be the trigger for the mid-1998 transition, and an unnamed May 2006 market event related to corrections in the Chinese markets to be the trigger for the mid-2007 transition.     

Build‐up of carboxylic acids in polyethylene and their relation to off‐flavor and carbonyl index

Oxidation of polyethylene (PE) gives a mixture of degradation products. Carboxylic acids are among the major ones. They are believed to cause off‐flavor in food and beverage packaging. Our previous research has shown that identification and use of indicator products gives earlier detection of oxidation in plastic materials. In the present study, the relation between off‐flavor in water extracts of PE and each of the carboxylic acids in the homologous series from propanoic to nonanoic acid were investigated. Also, a comparison between carbonyl index in solid PE and each of the carboxylic acids in the homologous series from propanoic to decanoic acid were examined. The amount of the carboxylic acids was assessed by head‐space solid‐phase microextraction (HS‐SPME) and gas chromatography–mass spectroscopy (GC‐MS). It was found that the amount of butanoic and hexanoic acid correlated well with the rated off‐flavor intensities in the water extracts. This confirmed earlier results on a linkage between these two carboxylic acids and highly rated off‐flavor intensities. Moreover, a relation between the build‐up of propanoic acid in the solid PE and carbonyl index was found. Hence, propanoic acid could be used as an indicator product for earlier oxidation detection in these PE materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1848–1859, 2007     

Structural and free‐volume analysis for alkyl‐substituted palladium‐catalyzed poly(norbornene): A combined experimental and Monte Carlo investigation

Increasing the length of an alkyl side chain on a rigid polynorbornene (PNB) backbone is shown to decrease the glass‐transition temperature of the resultant polymer, decrease the density of the bulk polymer, decrease the number and average free‐volume element size present, and decrease the permeability of gases through the polymer. Methyl‐, butyl‐, and hexyl‐substituted PNBs were investigated. Experimental results were compared with predictions based on molecular modeling. By using models that provided good agreement between the experimental and simulated wide‐angle diffraction patterns, the distributions of free‐volume elements were predicted. These predictions clearly indicate that the number of large free‐volume elements decreases as the length of the side chain increases, suggesting that the flexible aliphatic side chains can be largely accommodated within the free volume between the rigid PNB backbones. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 215–233, 2006     

Synthesis,stereochemistry, and opioid receptor binding activity of heterocyclic analogues of BW373U86

The synthesis of a series of heterocyclic analogues of (±)-4-((αR*)-α-((2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazmyl)-3-hydroxybenzyl)-N,N-diethylbenzarrude (BW373U86) for screening against opioid receptors is described. The intermediate α-heterocyclic benzyl alcohols 24 were synthesized either by low temperature reaction of lithioheterocycles with 3-((tert-butyldimethylsilyl)oxy)benzaldehyde ( 10 ) or by reaction of 3-((tert-butyldimethylsilyl)oxy)phenylmagnesium bromide ( 19 ) with heterocyclic carbaldehydes. The α-heterocyclic benzyl alcohols 24 were converted to chloromethines ( 25 ) with thionyl chloride and used to alkylate with trans-1-allyl-2,5-dimethylpiperazine ( 5 ) to give diastereomeric pairs of the target compounds. The bromoheterocycles were then derivatized to produce amides. Compounds that are potent and selective for the 5 or μ opioid receptors and some mixed δ/μ analogues are reported.     

Effective search space control for large and/or complex driver scheduling problems

For real life bus and train driver scheduling instances, the number of columns in terms of the set covering/partitioning ILP model could run into billions making the problem very difficult. Column generation approaches have the drawback that the sub-problems for generating the columns would be computationally expensive in such situations. This paper proposes a hybrid solution method, called PowerSolver, of using an iterative heuristic to derive a series of small refined sub-problem instances fed into an existing efficient set covering ILP based solver. In each iteration, the minimum set of relief opportunities that guarantees a solution no worse than the current best is retained. Controlled by a user-defined strategy, a small number of the banned relief opportunities would be reactivated and some soft constraints may be relaxed before the new sub-problem instance is solved. PowerSolver is proving successful by many transport operators who are now routinely using it. Test results from some large scale real-life exercises will be reported.     

Perceptions of Mathematics and Gender

This study examined students’ perceptions about gender and the subject of mathematics, as well as gender and mathematics learning. Secondary school students and pre‐service elementary teachers were surveyed using the Mathematics as a Gendered Domain and Who and Mathematics instruments developed by Leder and Forgasz ( Leder, 2001 ). The data indicate that, similar to findings from the 1970s, students believe that mathematics is gender neutral, although females hold this belief more strongly than males. Female secondary school students hold beliefs in gender neutrality more strongly than female pre‐service teachers. Data for secondary school students indicate that both males and females see differences in the way boys and girls act and are treated in mathematics classes (e.g., boys cause more distractions while girls care more about doing well). The data also show that secondary school males who believe they are good mathematics students tend to have more gender‐neutral perceptions than those who believe they are average or below average. No such pattern appears for secondary school females.