Biomedical subjects

Greg S Karczmar

Publications and source records attributed to Greg S Karczmar.

3 recordsLinked to original sources

PubMed2006

Three-dimensional shear in granular flow.

The evolution of granular shear flow is investigated as a function of height in a split-bottom Couette cell. Using particle tracking, magnetic-resonance imaging, and large-scale simulations, we find a transition in the nature of the shear as a characteristic height H* is exceeded. Below H* there is a central stationary core; above H* we observe the onset of additional axial shear associated with torsional failure. Radial and axial shear profiles are qualitatively different: the radial extent is wide and increases with height, while the axial width remains narrow and fixed.

Colloids↗

PubMed2005

Effect of air on granular size separation in a vibrated granular bed.

Using high-speed video and magnetic resonance imaging (MRI) we study the motion of a large sphere in a vertically vibrated bed of smaller grains. As previously reported we find a nonmonotonic density dependence of the rise and sink time of the large sphere. We show that air drag causes relative motion between the intruder and the bed during the shaking cycle and is ultimately responsible for the observed density dependence of the risetime. We investigate in detail how the motion of the intruder sphere is influenced by size of the background particles, initial vertical position in the bed, ambient pressure, and convection. We explain our results in the framework of a simple model and find quantitative agreement in key aspects with numerical simulations to the model equations.

Journal Article↗

PubMed2004

Intruders in the dust: air-driven granular size separation.

Using MRI and high-speed video we investigate the motion of a large intruder particle inside a vertically shaken bed of smaller particles. We find a pronounced, nonmonotonic density dependence, with both light and heavy intruders moving faster than those whose density is approximately that of the granular bed. For light intruders, we furthermore observe either rising or sinking behavior, depending on intruder starting height, boundary condition, and interstitial gas pressure. We map out the phase boundary delineating the rising and sinking regimes. A simple model can account for much of the observed behavior and shows how the two regimes are connected by considering pressure gradients across the granular bed during a shaking cycle.

Journal Article↗