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Biomedical subjects

J M Ottino

Publications and source records attributed to J M Ottino.

8 recordsLinked to original sources
PubMed2004

Dynamics of a drop at a fluid interface under shear.

We analyze the dynamics of a two-dimensional drop lying on a fluid interface, sometimes called a liquid lens, subjected to simple shear flow. The three fluids, the drop and the two external fluids, meet at a triple point (or a triple line in three dimensions). A requirement for steady drop shapes is that the triple points are stationary. This leads to a flow topology different than that of a freely suspended drop. Results are substantiated with numerical results using a level set method for interface evolution and treatment of triple points. Possible implications for new drop instabilities are also discussed.

Journal Article↗
PubMed2003

Competition between chaos and order: mixing and segregation in a spherical tumbler.

We investigate the competition between granular mixing and segregation in a sphere rotating and rocking on two orthogonal axes. Operation corresponds to the continuous-flow regime and the flow within the sphere is three-dimensional and time-periodic. Experimental results are organized in a frequency/amplitude phase diagram showing modes of segregation (band formation/no axial bands); segregated bands are remarkably robust and survive rocking amplitudes as large as 60 degrees over a wide range of frequencies. Details differ, but the phenomenon occurs under both dry and slurry conditions, that is, when all air is replaced by a liquid. Experimental space-time plots of the stationary segregated patterns agree well with Poincaré maps obtained using a continuum model of the flow, suggesting that the final segregation patterns are relatively independent of materials tumbled.

Journal Article↗
PubMed2003

Dynamics of axial segregation and coarsening of dry granular materials and slurries in circular and square tubes.

We study segregation and coarsening dynamics of dry granular materials and slurries in tubes with circular and square cross sections. Space-time plots show key differences between the four cases, including band splitting and wave formation, depending upon the rotational speed. However, the fraction of the surface occupied by bands of small-rich particles is nearly constant in all experiments, leading to quasi-1D behavior, and the rate of coarsening, when it occurs, is logarithmic in all cases. Coarsening rates are very similar except in the case with the longest development time.

Journal Article↗
PubMed2001

Modes of granular segregation in a noncircular rotating cylinder.

Axial segregation is a well-known example of segregation of granular materials. However, at present, there is no conclusive explanation as to why it occurs. Most studies of axial segregation to date are based on cylinders with circular cross sections, and models focus on the character of the surface flow without accounting explicitly for the influence of any subsurface detail. The present experiments demonstrate that the cross section of the mixer has a significant influence on axial segregation and that subsurface dynamics are, in fact, important. Unlike circular mixers, in square mixers the subsurface segregation patterns change with filling level, as does the time dependence of axial segregation. Furthermore, when radial segregation patterns in noncircular mixers most closely resemble that observed for circular cylinders, the time dependence for axial band formation deviates the most. These results challenge segregation theories of axial segregation that ignore subsurface effects.

Journal Article↗
PubMed2001

Self-organization in granular slurries.

We report the existence of self-organization in wet granular media or slurries, mixtures of particles of different sizes dispersed in a lower density liquid. As in the case of dry granular mixtures, axial banding (alternating bands rich in small and large particles in a long rotating cylinder) and radial segregation (in quasi-2D containers) are observed in slurries. However, when compared with the dry counterpart axial segregation is significantly faster and the spectrum of outcomes is richer. Moreover, experiments with suitable fluids reveal, for the first time, the internal structure of axially segregated systems, something that up to now has been accessible only via magnetic resonance imaging experimentation.

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PubMed1999

Segregation-driven organization in chaotic granular flows.

An important industrial problem that provides fascinating puzzles in pattern formation is the tendency for granular mixtures to de-mix or segregate. Small differences in either size or density lead to flow-induced segregation. Similar to fluids, noncohesive granular materials can display chaotic advection; when this happens chaos and segregation compete with each other, giving rise to a wealth of experimental outcomes. Segregated structures, obtained experimentally, display organization in the presence of disorder and are captured by a continuum flow model incorporating collisional diffusion and density-driven segregation. Under certain conditions, structures never settle into a steady shape. This may be the simplest experimental example of a system displaying competition between chaos and order.

Journal Article↗
PubMedDate not supplied

Transport in a grooved perfusion flat-bed bioreactor for cell therapy applications.

This study considers the transport of oxygen (a growth-associated solute) and lactate (a metabolic byproduct) in a flat-bed perfusion chamber modified to retain cells through the addition of grooves, perpendicular to the direction of flow, at the chamber bottom. The chamber has been successfully applied to hematopoietic cell culture and may be useful for other basic and applied biomedical applications. The objective of this study is to characterize the culture environment in terms of solute transport under various operational conditions. This will allow one to improve the design and operating strategy of the perfusion system for maximizing cell numbers. The system is numerically simulated using the finite element package FIDAP. The reaction kinetics describing oxygen uptake by cells are simplified to zero order to give an upper bound for the oxygen consumption. A flat-bed chamber without grooves is considered here as a benchmark. We show that the growth environment is not oxygen limited (local oxygen concentration above 10 microM) for a variety of flow rates and culture conditions (qO2 = 0.1 micromol/(10(6) cells h)). With a medium flow rate of 2.5 mL/min through the reactor, the model predicts that the 29-cm2 reactor can support at least 33.4 x 10(6) total cells when the inlet medium is in equilibrium with high (20%) oxygen concentration. The culture becomes oxygen limited however for the same flow rate for low (5%) oxygen concentration and can only support 7.2 x 10(6) total cells. Comparison of grooved vs nongrooved chambers reveals that the presence of grooves only affects solute transport on a local scale. This result is attributed to the small size (200 microgram) of the cavities relative to the chamber dimensions. The comparison also yields an empirical relation that allows for rapid estimation of oxygen and lactate concentrations in the grooves using only the numerical simulation of the simpler nongrooved chamber. Finally, our investigation shows that, while decreasing the spacing between cavities decreases the total number of cells the reactor can support, the efficiency of the reactor is increased by 25% (on an area basis) without growth restriction.

Bioreactors↗