Reactive uptake coefficients for heterogeneous reaction of N2O5 with submicron aerosols of NaCl and natural sea salt

The kinetics of uptake of gaseous N2O5 on submicron aerosols containing NaCl and natural sea salt have been investigated in a flow reactor as a function of relative humidity (RH) in the range 30-80% at 295±2K and a total pressure of 1bar. The measured uptake coefficients, γ, were larger on the aerosols containing sea salt compared to those of pure NaCl, and in both cases increased with increasing RH. These observations are explained in terms of the variation in the size of the salt droplets, which leads to a limitation in the uptake rate into small particles. After correction for this effect the uptake coefficients are independent of relative humidity, and agree with those measured previously on larger droplets. A value of γ=0.025 is recommended for the reactive uptake coefficient for N2O5 on deliquesced sea salt droplets at 298K and RH>40%.

Methodological rigour in assessing participatory development

There have been few rigorous assessments of the effectiveness of participatory processes for natural resource management. In Bangladesh an approach known as Participatory Action Plan Development (PAPD) has been developed and applied. By combining problem identification and solution analysis by separate stakeholder groups with plenary sessions it is claimed to result in consensus and more effective community based management. Methodological issues in assessing the effectiveness of such development are discussed and good practice illustrated. Under the same project there were sites where PAPD had been used and others without its use so a comparative assessment could be made. However, for an appropriate assessment it is important to identify clear testable hypotheses regarding the expected benefits, appropriate measures, and other factors which may affect or confound the outcome. The paper illustrates how participatory assessment involving both individual opinions and focus groups can be systematically recorded, quantified and used with other data in statistical analysis. By using statistical modelling methods at an appropriate level of aggregation and controlling for other factors, benefits from PAPD were found to be significant. The systematic approaches and practices recommended from this example can be applied in similar situations to test the effectiveness of participatory processes using participatory assessments.

Dilettantes, discipline and discourse: requirements management for construction

Requirements management (RM), as practised in the aerospace and defence sectors, attracts interest from construction researchers in response to longstanding problems of project definition. Doubts are expressed whether RM offers a new discipline for construction practitioners or whether it repeats previous exhortations to adopt a more disciplined way of working. Whilst systems engineering has an established track record of addressing complex technical problems, its extension to socially complex problems has been challenged. The dominant storyline of RM is one of procedural rationality and RM is commonly presented as a means of controlling dilettante behaviour. Interviews with RM practitioners suggest a considerable gulf between the dominant storyline in the literature and how practitioners operate in practice. The paper challenges construction researchers interested in RM to reflect more upon the theoretical debates that underpin current equivalent practices in construction and the disparity between espoused and enacted practice.

Growth inhibition of mammalian cells by synthetic and natural photosensitising agents

A mammalian cell line, J774, was susceptible to both synthetic and natural photosensitising agents after irradiation with long-wave ultraviolet light. Both UV-A light and psoralen did not affect cell growth individually; a reduction in visual confluency was achieved only when psoralen and UV-A light were used in combination. The maximum visual confluency decreased by 55% when 50 ppm psoralen was added to a growing culture and irradiated with UV light for 3 min. Decreasing the UV-A exposure times from 3 min to 3 s did not greatly affect the maximum total visual confluence reached using different synthetic psoralen concentrations, but did affect the rate at which cell death occurred. The 3 min exposure time resulted in a rapid decrease in cell numbers in comparison to 3 s exposure time. Synthetic psoralen was found to have an increasing photosensitising activity with increasing concentration using a logarithmic shift between 0.5 ppm and 50 ppm. A visual confluency of 45% was achieved using concentrations of 50 ppm psoralen, and 70% visual confluency using 0.5 ppm. Natural mixtures of furanocoumarins containing psoralens, obtained from two separate parsley sources, were found to have greater efficacy at inhibiting the growth cycle of the cells when compared to the synthetic psoralen.