Modelling spatial oscillations in soil borehole bacteria.

Spatial oscillations in groundwater contaminant concentrations can be successfully explained by consideration of a competitive microbial community in conditions of poor nutrient supply, in which the effects of spatial diffusion of the nutrient sources are included. In previous work we showed that the microbial competition itself allowed oscillations to occur, and, in common with other reaction-diffusion systems, the addition of spatial diffusion transforms these temporal oscillations into travelling waves, sometimes chaotic. We therefore suggest that irregular chemical profiles sometimes found in contaminant plume borehole profiles may be a consequence of this competition.

Oscillations in soil bacterial redox reactions.

Spatial oscillations in soil contaminant concentration profiles are sometimes observed, but rarely commented on, or are attributed to noisy data. In this paper we consider a possible mechanism for the occurrence of oscillatory reactant profiles within contaminant plumes. The bioremediative reactions which occur are effected by bacteria, whose rôle is normally conceived of as being passive. Here we argue that competition, for example between heterotrophic and fermentative bacteria, can occur in the form of an activator-inhibitor system, thus promoting oscillations. We describe a simple model for the competition between two such microbial populations, and we show that in normal oligotrophic groundwater conditions, oscillatory behaviour is easily obtained. When such competition occurs in a dispersive porous medium, travelling waves can be generated, which provide a possible explanation for the observed soil column oscillations.

A delay recruitment model of the cardiovascular control system.

We develop a nonlinear delay-differential equation for the human cardiovascular control system, and use it to explore blood pressure and heart rate variability under short-term baroreflex control. The model incorporates an intrinsically stable heart rate in the absence of nervous control, and allows us to compare the baroreflex influence on heart rate and peripheral resistance. Analytical simplifications of the model allow a general investigation of the rôles played by gain and delay, and the effects of ageing.

The New World order and international health.

PIP: New global and national health challenges require a new response. National health situations are increasingly influenced by the international transfer of health risks posed by environmental threats, overuse of resources, international migration, trade in harmful legal products (tobacco), traffic of illicit drugs, and diffusion of potentially inappropriate and costly medical technologies and treatment policies. This situation calls for reform of national health systems, and a natural extension of such reform is reform of the world health system. The first step toward this goal should be to achieve consensus about the essential core functions of international health organizations their division of labor. Currently international health agencies have overlapping mandates and duplicate efforts, and they have neglected the following essential functions: monitoring emerging diseases, setting consumer health standards, providing international coordination to control the transfer of health risks, coordinating research efforts and technological development, designing information systems to facilitate development of national and global health policies, accumulating knowledge about cost-effectiveness of medical technologies and interventions, and creating a process for sharing information about national health system reform. Reform "essentialists" identify the following core functions for international health organizations: surveillance and control of globally-threatening diseases, promotion of research and technological development, development of standards and norms for international certification, protection of international refugees, and assisting vulnerable populations. Others give international health organizations a more expansive role including redistributing resources from rich to poor countries, political advocacy, direct regulation of transnational corporations, and intervention in national health projects. Consensus must be reached to effect reform.^ieng

Free trade and occupational health policy: an argument for health and safety across the North American workplace.

This article considers the argument that the North American Free Trade Agreement (NAFTA) would encourage US and Canadian industry to relocate their hazardous manufacturing operations to Mexico. Proponents of this view believe that this industrial flight south would worsen working conditions in Mexico as well as lower occupational health and safety standards in the US and Canada. In evaluating this argument, the article examines working conditions in US-owned factories in the Mexican maquiladora zone, reviews the current occupational health and safety regulatory structure in Mexico, and considers those institutions established by the European Community to protect workers against the flight of hazardous industries. The article concludes that the harmonization of labor norms throughout North American and the establishment of a functional North American regulatory structure following the precedents set by the European Community are necessary steps to ensure that NAFTA does not produce the feared flight of hazardous industries to Mexico nor degrade the health of workers in Mexico, Canada, or the US.