Simulations of extensional flow in microrheometric devices

We present a detailed numerical study of the flow of a Newtonian fluid through microrheometric devices featuring a sudden contraction–expansion. This flow configuration is typically used to generate extensional deformations and high strain rates. The excess pressure drop resulting from the converging and diverging flow is an important dynamic measure to quantify if the device is intended to be used as a microfluidic extensional rheometer. To explore this idea, we examine the effect of the contraction length, aspect ratio and Reynolds number on the flow kinematics and resulting pressure field. Analysis of the computed velocity and pressure fields show that, for typical experimental conditions used in microfluidic devices, the steady flow is highly three-dimensional with open spiraling vortical structures in the stagnant corner regions. The numerical simulations of the local kinematics and global pressure drop are in good agreement with experimental results. The device aspect ratio is shown to have a strong impact on the flow and consequently on the excess pressure drop, which is quantified in terms of the dimensionless Couette and Bagley correction factors. We suggest an approach for calculating the Bagley correction which may be especially appropriate for planar microchannels

Shortness at birth is associated with insulin resistance in pre-pubertal Jamaican children

Aim: To investigate the relationship between anthropometry at birth and glucose/insulin metabolism in childhood using the response to an oral glucose challenge.Method: Four hundred mother/child pairs on whom gestational and birth data were available were studied. After an overnight fast, anthropometric measurements were made on the children and an oral glucose tolerance test performed. The plasma concentrations of insulin, pro-insulin and 32-33 split pro-insulin were also measured. Skinfold thicknesses were used to calculate percentage body fat and fat mass was derived from the percentage fat and absolute weight.Results: The mean age of the children was 8 y (range 7.5-10.5), and six exhibited impaired glucose tolerance based on WHO criteria. Insulin concentration 120 min after the oral glucose load (a measure of insulin resistance) was inversely related to length at birth (P&lt;0.005). The children who were in the shortest quartile at birth and were heaviest at 8 y old had the highest insulin concentration.Conclusion: Shortness at birth is related to insulin resistance. Such insensitivity to the action of insulin is greater in heavier children.<br/

Hemodynamics: An Introduction

International audienceThe cardiovascular transport circuit is involved in both mass and heat transfer. It carries blood cells as well as oxygen and nutrients to cells of the body’s organs through the perfusing systemic arterial bed and wastes produced by working cells to their final destinations through draining veins. Blood flows throughout the body in the vasculature due to a pressure difference between the ventricular outlet and atrial inlet. Blood is propelled in the systemic and pulmonary circulation by the synchronized action of the left and right apposed cardiac pumps, respectively. Hemodynamics is related to the flow features in the heart and blood vessels, in normal and pathological conditions, in particular the pressure–flow relations and transport of substances by blood to given target organs. It can be required in therapy planning and optimization