Taylor dispersion of gyrotactic swimming micro-organisms in a linear flow

The theory of generalized Taylor dispersion for suspensions of Brownian particles is developed to study the dispersion of gyrotactic swimming micro-organisms in a linear shear flow. Such creatures are bottom-heavy and experience a gravitational torque which acts to right them when they are tipped away from the vertical. They also suffer a net viscous torque in the presence of a local vorticity field. The orientation of the cells is intrinsically random but the balance of the two torques results in a bias toward a preferred swimming direction. The micro-organisms are sufficiently large that Brownian motion is negligible but their random swimming across streamlines results in a mean velocity together with diffusion. As an example, we consider the case of vertical shear flow and calculate the diffusion coefficients for a suspension of the alga <i>Chlamydomonas nivalis</i>. This rational derivation is compared with earlier approximations for the diffusivity

Infrastructure Hydromentalities:Water Sharing, Water Control and Water (In)Security

The purpose of this book is to present an overview of the latest research, policy, practitioner, academic and international thinking on water security—an issue that, like water governance a few years ago, has developed much policy awareness and momentum with a wide range of stakeholders. As a concept it is open to multiple interpretations, and the authors here set out the various approaches to the topic from different perspectives. Key themes addressed include: Water security as a foreign policy issue The interconnected variables of water, food, and human security Dimensions other than military and international relations concerns around water security Water security theory and methods, tools and audits. The book is loosely based on a masters level degree plus a short professional course on water security both given at the University of East Anglia, delivered by international authorities on their subjects. It should serve as an introductory textbook as well as be of value to professionals, NGOs, and policy-makers