Acoustic lattice Boltzmann model for immiscible binary fluids with a species-dependent impedance.

A lattice Boltzmann model is considered for immiscible binary fluids with species-dependent acoustic impedance. Acoustic waves and pulses are simulated within the model, and the reflection and transmission components at the fluid interface are found to compare well with theory. The model is then applied to simulate the acoustic field due to plane-wave propagation through a bubble.

Application of the lattice Boltzmann model to simulated stenosis growth in a two-dimensional carotid artery.

The lattice Boltzmann model is used to observe changes in the velocity flow and shear stress in a carotid artery model during a simulated stenosis growth. Near wall shear stress in the unstenosed artery is found to agree with literature values. The model also shows regions of low velocity, rotational flow and low near wall shear stress along parts of the walls of the carotid artery that have been identified as being prone to atherosclerosis. These regions persist during the simulated stenosis growth, suggesting that atherosclerotic plaque build-up creates regions of flow with properties that favour atherosclerotic progression.

Numerical simulation of particle motion in an ultrasound field using the lattice Boltzmann model.

In this paper we investigate the motion of small particles suspended in a fluid through which an ultrasound field is propagating. The application of the lattice Boltzmann model to this problem is considered using a two dimensional model. Particles in an ultrasound field are observed to move with a mean particle motion. Further, the time-averaged force on a fixed cylinder is computed and found to be in good agreement with a theoretical expression for the radiation force. Simulations are performed with a single particle, although the approach can equally be applied for a larger number of particles.

Application of the lattice Boltzmann method to arterial flow simulation: investigation of boundary conditions for complex arterial geometries.

The application of the lattice Boltzmann method (LBM) to carotid artery blood flow is investigated, in particular, the importance of the boundary conditions is considered. Simulations are presented using two different boundary conditions: the traditional half-way bounce-back and an extrapolation scheme. The two methods are described and compared with respect to arterial flow simulation. The results indicate that the extrapolation scheme is preferable in narrow arteries, or when a stenosis is present in a larger artery.

Evolution of turbulence in an oscillatory flow in a smooth-walled channel: a viscous secondary instability mechanism.

In this paper, a comparison is made of the evolution of turbulence in oscillatory channel flows with a zero-mean velocity in two and three dimensions, using the numerical technique of the lattice Boltzmann method. The results confirm a primary two-dimensional instability. Evidence is shown of a secondary, viscous three-dimensional instability mechanism acting in the oscillatory boundary layer, which is consistent with experimental observations.

PIV applied to eckart streaming produced by a medical ultrasound transducer.

Particle image velocimetry (PIV) is applied for the first time to study Eckart streaming induced by a medical ultrasonic transducer operating at a frequency of 3.3 MHz and effective acoustic intensities of 0.25 and 3 Wcm(-2). A temporal series of velocities in a two-dimensional plane were recorded resulting in an experimental set comprising over half a million velocity data points. These enabled average and fluctuating properties to be determined and clearly indicated the quasi-steady nature of the flow. The average large scale velocity fluctuations along the axis caused by this quasi-steady property were calculated to be 2 and 20 m ms(-1) at effective intensities of 0.25 and 3 Wcm(-2) respectively corresponding to approximately 25% of the peak flow velocity in both cases. Furthermore averaged shear rates were calculated with peak values of 1 and 8 s(-1) for the low and high intensities respectively. The present investigation indicates the usefulness of PIV for such studies and serves as a prelude to investigations of streaming in biological type fluids.

Atrial natriuretic peptide: a new cardiac hormone.

For centuries the heart's mechanical function has been described, and its role defined, as that of a pump to maintain blood pressure for tissue perfusion. In the past decade the heart has also been identified as an endocrine organ in that it secretes a hormone variously referred to as atrial polypeptide, atriopeptin, auriculin, cardionatrin, or atrial natriuretic peptide. This hormone interacts with other organ systems in multiple and complex ways. Studies are in progress to elucidate further its physiologic importance, mechanism of action, and pathophysiologic significance in the development of certain cardiovascular and renal diseases, as well as other conditions with sodium and water imbalance. Also of great importance is its potential pharmacologic application in the treatment of these same diseases.