Green chemistry: deliverance or distraction?

As the green chemistry principles are increasingly used in teaching chemistry at all levels, this perspective provides a critique of their strengths and weaknesses. It asks whether or not the principles have sufficient scientific validity to aid the proper understanding of the subject (as opposed to highlighting concerns about its application). Furthermore, as the principles are increasingly cited in research papers, it also questions whether evidence exists that they have led to improvements in the sustainability and environmental impact of chemical technology that would not otherwise have arisen as a result of conventional economic, feedstock, competitive, market and regulatory pressures had they not been promulgated.     

The dynamic balance of import and export of zinc in Escherichia coli suggests a heterogeneous population response to stress

Zinc is essential for life, but toxic in excess. Thus all cells must control their internal zinc concentration. We used a systems approach, alternating rounds of experiments and models, to further elucidate the zinc control systems in Escherichia coli. We measured the response to zinc of the main specific zinc import and export systems in the wild-type, and a series of deletion mutant strains. We interpreted these data with a detailed mathematical model and Bayesian model fitting routines. There are three key findings: first, that alternate, non-inducible importers and exporters are important. Second, that an internal zinc reservoir is essential for maintaining the internal zinc concentration. Third, our data fitting led us to propose that the cells mount a heterogeneous response to zinc: some respond effectively, while others die or stop growing. In a further round of experiments, we demonstrated lower viable cell counts in the mutant strain tested exposed to excess zinc, consistent with this hypothesis. A stochastic model simulation demonstrated considerable fluctuations in the cellular levels of the ZntA exporter protein, reinforcing this proposal. We hypothesize that maintaining population heterogeneity could be a bet-hedging response allowing a population of cells to survive in varied and fluctuating environments.     

Within-host viral dynamics of dengue serotype 1 infection

Dengue, the most common mosquito-borne viral infection of humans, is endemic across much of the world, including much of tropical Asia and is increasing in its geographical range. Here, we present a mathematical model of dengue virus dynamics within infected individuals, detailing the interaction between virus and a simple immune response. We fit this model to measurements of plasma viral titre from cases of primary and secondary DENV 1 infection in Vietnam. We show that variation in model parameters governing the immune response is sufficient to create the observed variation in virus dynamics between individuals. Estimating model parameter values, we find parameter differences between primary and secondary cases consistent with the theory of antibody-dependent enhancement (namely enhanced rates of viral entry to target cells in secondary cases). Finally, we use our model to examine the potential impact of an antiviral drug on the within-host dynamics of dengue. We conclude that the impact of antiviral therapy on virus dynamics is likely to be limited if therapy is only started at the onset of symptoms, owing to the typically late stage of viral pathogenesis reached by the time symptoms are manifested and thus treatment is started.     

Facial expression recognition in dynamic sequences: An integrated approach

Automatic facial expression analysis aims to analyse human facial expressions and classify them into discrete categories. Methods based on existing work are reliant on extracting information from video sequences and employ either some form of subjective thresholding of dynamic information or attempt to identify the particular individual frames in which the expected behaviour occurs. These methods are inefficient as they require either additional subjective information, tedious manual work or fail to take advantage of the information contained in the dynamic signature from facial movements for the task of expression recognition.     

Can intrafirm IT skills benefit interfirm integration and performance?

This study develops a model to examine whether intrafirm, hard and soft IT skills have cross-boundary effects on interfirm collaboration and integration, thus leading to better supply-chain performance. A model with eight hypotheses was developed and tested using data collected from 250 Taiwanese manufacturing firms. Seven hypotheses find empirical support. The results show that intrafirm IT skills indeed can benefit interfirm collaboration and integration and thus, supply-chain performance. Our findings suggest that the value of skilled IT professionals for interfirm integration, supply-chain performance and collaborative relationships between firms is critical for realizing that value.     

Measurement and prediction of the strength of rubberized concrete

Illegally discarded piles of automobile tires are sources of potential hazards. Current disposal methods are wasteful and costly as they require either consumption of landfill space or continuous costly maintenance. A solution to the problem of scrap-tire disposal is the potential use of tire chips and crumb rubber as mineral aggregate substitutes in Portland cement concrete mixes. In this study, some of the engineering properties of rubberized concrete were examined and a neural network was developed to predict its compressive and tensile strengths. Rubberized concrete was found to possess good esthetics, acceptable workability, and a smaller unit weight than normal concrete. However, rubberized concrete did not perform as well as normal concrete under repeated freeze-thaw cycles. It exhibited lower compressive and tensile strength than that of normal concrete. Unlike normal concrete, rubberized concrete had the ability to absorb a large amount of plastic energy under compressive and tensile loads. It did not demonstrate the typical brittle failure, but rather a ductile, plastic failure mode. Test results were analyzed so that a model can be developed to predict the strength of rubberized concrete. Two neural network models were developed to predict the reduction in the compressive and tensile strength as a result of replacing mineral aggregate with rubber aggregate. A maximum difference of 9·2% between test results and model prediction was detected during the testing of the neural networks.     

The decomposition of high grade bleaching powder (calcium hypochlorite)

The decomposition of commercial calcium hypochlorite (termed here High Grade Bleaching Powder, HGBP) has been studied by X-ray diffraction, differential thermal analysis, thermogravimetry and isothermal calorimetry, after storage at various temperatures and humidities. It was found that Ca(OCl)₂ can decompose by at least three main routes. These include disproportionation to give Ca(ClO₃)₂ and CaCl₂, and with the evolution of Cl₂ or O₂ depending on the presence or absence of water. The heat output of HGBP between 15 and 70°C differed considerably between samples and was found to increase after exposure to water vapour; some metal oxides also had a positive effect on the heat output. At 65°C the heat output oscillated, showing that both exothermic and endothermic reactions were taking place. At room temperature and in the absence of water HGBP appears to be stable.