An analysis of the changes to the mechanical and acoustical properties of paper caused by the damage mechanisms present in the fibre structure

This paper will analyse two of the likely damage mechanisms present in a paper fibre matrix when placed under controlled stress conditions: fibre/fibre bond failure and fibre failure. The failure process associated with each damage mechanism will be presented in detail focusing on the change in mechanical and acoustic properties of the surrounding fibre structure before and after failure. To present this complex process mathematically, geometrically simple fibre arrangements will be chosen based on certain assumptions regarding the structure and strength of paper, to model the damage mechanisms. The fibre structures are then formulated in terms of a hybrid vibro-acoustic model based on a coupled mass/spring system and the pressure wave equation. The model will be presented in detail in the paper. The simulation of the simple fibre structures serves two purposes; it highlights the physical and acoustic differences of each damage mechanism before and after failure, and also shows the differences in the two damage mechanisms when compared with one another. The results of the simulations are given in the form of pressure wave contours, time-frequency graphs and the Continuous Wavelet Transform (CWT) diagrams. The analysis of the results leads to criteria by which the two damage mechanisms can be identified. Using these criteria it was possible to verify the results of the simulations against experimental acoustic data. The models developed in this study are of specific practical interest in the paper-making industry, where acoustic sensors may be used to monitor continuous paper production. The same techniques may be adopted more generally to correlate acoustic signals to damage mechanisms in other fibre-based structures.

Strategies for water pollution control in Dhaka, Bangladesh: an institutional and economic analysis

This paper presents primary data based on research carried out as part of a large World Bank project. Results from our survey show that water pollution in Dhaka watershed has reached alarming levels and is posing significant threats to health and economic activity, particularly among the poor and vulnerable. Rice productivity in the watershed area, for example, has declined by 40% in recent years and vegetable cultivation in the riverbeds has been severely damaged. We also found significant correlation between water pollution and diseases such as jaundice, diarrhoea and skin problems. It was reported that the cost of treatment of skin diseases for one episode could be as high as 29% of the weekly earnings of poor households. Given the magnitude of the contamination problem, a multi-agent stakeholder approach was necessary to analyse the institutional and economic constraints that would need to be addressed in order to improve environmental management. This approach, in turn, enabled core strategies to be developed. The strategies were better understood around three types of actors in industrial pollution, i.e. (1) principal actors, who contribute directly to industrial pollution; (2) stakeholders, who exacerbate the situation by inaction; and (3) the potential actors in mitigation of water contamination. Within a carrot-and-stick framework, nine strategies leading to the strengthening of environmental management were explored. They aim at improving governance and transparency within public agencies and private industry through the setting up of incentive structures to advance compliance and enforcement of environmental standards. Civil society and the population at large are, on the other hand, encouraged to contribute actively to the mitigation of water pollution by improving the management of environmental information and by raising public awareness.