Table of contents

Bioconvection patterns are usually observed in the laboratory in shallow suspensions of randomly, but on average upwardly, swimming micro-organisms which are a little denser than water, but have also been found in situ in micropatches of zooplankton [Kils (1993), 1993. Bull. Mar. Sci. 53, 160–169]. The mechanism of upswimming differs between bottom-heavy algae and oxytactic bacteria. Rational continuum models have been formulated and analysed in each of these cases for low cell volume fraction. These will be described, as will new theoretical and experimental developments, including nonlinear analysis of the patterns, dispersion in shear flows, measurements of algal cell swimming behaviour, and new attempts to set up a model for more concentrated suspensions. The paper will review all work in this area since 1992, the year of the publication of the article "Hydrodynamic phenomena in suspensions of swimming micro-organisms" by Pedley and Kessler [1992b. Annu. Rev. Fluid Mech. 24, 313–358].

Recently, much progress has been made in revealing aerodynamic force mechanisms and predicting power requirements in insect flight. In this article, we review the research works in the past 10 years. We first summarize the kinematics of the flapping wing. Next we explore the unsteady high-lift mechanisms. Then we discuss the power requirements of hovering and forward flight in some insects. Finally, we mention recent studies on dragonfly flight.

Vascular endothelial cells are an interface between blood vessel walls and blood flow, and play important roles in physiological functions. Since endothelial cell responses to fluid shear stress have been implicated in the localization of atherosclerosis, the effect of shear stress on endothelial cell morphology and functions has been exclusively studied. After applying fluid shear stress, cultured endothelial cells show marked elongation and orientation in the flow direction. In addition, thick stress fibers of actin filaments appear and align along the cell long axis. Thus, the endothelial cell morphology is closely related to the cytoskeletal structure. The purpose of this review is to summarize endothelial cell responses to fluid flow which have been studied, focusing on the changes in cell shape and cytoskeletal structure. Numerical studies to simulate local flow field at the cellular level and the resulting intracellular stresses are also reviewed.

The heart is unique among other organs in that coronary arterial flow is exclusively diastolic and venous outflow is systolic. That is, arterial blood flows into intramyocardial coronary vessels during diastole and the stored blood is squeezed out mostly to epicardial veins and partly to the proximal arteries during the subsequent systole. Furthermore, coronary vessels function as highly organized flow regulators to match local blood flows with myocardial energy demands to support the viability of the heart. In this review, we first summarize the intramyocardial microvascular dynamics along with the description of a hierarchical system of coronary microvessels. Then, the spatial heterogeneity of blood supply to myocardium is demonstrated.

The mechanics of blood flow in microvessels and microvessel permeability are reviewed. In the first part, characteristics of blood flow in vivo and in vitro are described from a fluid-mechanical point of view, and mathematical models for blood flow in microvessels are presented. Possible causes of the increased flow resistance obtained in vivo compared to in vitro are examined, including the effects of irregularities of vessel lumen, the presence of endothelial surface glycocalyx and white blood cells. In the second part, the ultrastructural pathways and mechanisms whereby endothelial cells and the clefts between the cells modulate microvessel permeability to water and solutes are introduced. Previous and current models for microvessel permeability to water and solutes are reviewed. These models examine the role of structural components of interendothelial cleft, such as junction strands and surface glycocalyx, in the determination of water and solute transport across the microvessel walls. Transport models in the tissue space surrounding the microvessel are also described.