The fluid motion produced by a periodic array of identical, axisymmetric, thincored vortex rings ... more The fluid motion produced by a periodic array of identical, axisymmetric, thincored vortex rings is investigated. It is well known that such an array moves uniformly without change of shape or form in the direction of the central axis of symmetry, and is therefore an equilibrium solution of Euler’s equations. In a frame of reference moving together with the system of vortex rings, the motion of passive fluid particles is investigated as a function of the two non-dimensional parameters that define this system: ε = a/R, the ratio of minor radius to major radius of the torus-shaped vortex rings, and λ = L/R, the separation of the vortex rings normalized by their radii. Two bifurcations in the streamline topology are found that depend significantly on ε and λ; these bifurcations delineate three distinct shapes of the ‘atmosphere’ of fluid particles that move together with the vortex ring for all time. Analogous to the case of an isolated vortex ring, the atmospheres can be ‘thin-bodied’...
Chaotic advection in pulsed sourcesink systems. [Physics of Fluids 31, 469 (1988)]. Scott W. Jon... more Chaotic advection in pulsed sourcesink systems. [Physics of Fluids 31, 469 (1988)]. Scott W. Jones, Hassan Aref. Abstract. The onset of chaos in passive advection of particles by flow caused by a pulsed sourcesink system is documented. ...
2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2012
In this study, we investigate the application of contactless dielectrophoresis (cDEP) for isolati... more In this study, we investigate the application of contactless dielectrophoresis (cDEP) for isolating cancer cells from blood cells. Devices with throughput of 0.2 mL/hr (equivalent to sorting 3×10(6) cells per minute) were used to trap breast cancer cells while allowing blood cells through. We have shown that this technique is able to isolate cancer cells in concentration as low as 1 cancer cell per 10(6) hematologic cells (equivalent to 1000 cancer cells in 1 mL of blood). We achieved 96% trapping of the cancer cells at 600 kHz and 300 V(RMS).
Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 2004
Chaotic advection can play an important role in efficient microfluidic mixers. We discuss a desig... more Chaotic advection can play an important role in efficient microfluidic mixers. We discuss a design paradigm that exploits chaotic advection and illustrate by two recent examples, namely enhancing gene expression profiling and constructing an in-line microfluidic mixing channel, how application of this paradigm has led to successful micromixers. We suggest that 'designing for chaos', that is, basing practical mixer design on chaotic advection analysis, is a promising approach to adopt in this developing field which otherwise has little to guide it and is constrained by issues of scale and manufacturability.
Abstract. A number of instability and bifurcation problems related to the dynamics of vortex wake... more Abstract. A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal-Reynolds number relation for vortex wakes, the bifurcation diagram for exotic wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the ...
A new approach to regular and chaotic fluid advection is presented that utilizes the Thurston–Nie... more A new approach to regular and chaotic fluid advection is presented that utilizes the Thurston–Nielsen classification theorem. The prototypical two-dimensional problem of stirring by a finite number of stirrers confined to a disk of fluid is considered. The theory shows that for particular ‘stirring protocols’ a significant increase in complexity of the stirred motion – known as topological chaos – occurs when three or more stirrers are present and are moved about in certain ways. In this sense prior studies of chaotic advection with at most two stirrers, that were, furthermore, usually fixed in place and simply rotated about their axes, have been ‘too simple’. We set out the basic theory without proofs and demonstrate the applicability of several topological concepts to fluid stirring. A key role is played by the representation of a given stirring protocol as a braid in a (2+1)-dimensional space–time made up of the flow plane and a time axis perpendicular to it. A simple experiment ...
The fluid motion produced by a periodic array of identical, axisymmetric, thincored vortex rings ... more The fluid motion produced by a periodic array of identical, axisymmetric, thincored vortex rings is investigated. It is well known that such an array moves uniformly without change of shape or form in the direction of the central axis of symmetry, and is therefore an equilibrium solution of Euler’s equations. In a frame of reference moving together with the system of vortex rings, the motion of passive fluid particles is investigated as a function of the two non-dimensional parameters that define this system: ε = a/R, the ratio of minor radius to major radius of the torus-shaped vortex rings, and λ = L/R, the separation of the vortex rings normalized by their radii. Two bifurcations in the streamline topology are found that depend significantly on ε and λ; these bifurcations delineate three distinct shapes of the ‘atmosphere’ of fluid particles that move together with the vortex ring for all time. Analogous to the case of an isolated vortex ring, the atmospheres can be ‘thin-bodied’...
Chaotic advection in pulsed sourcesink systems. [Physics of Fluids 31, 469 (1988)]. Scott W. Jon... more Chaotic advection in pulsed sourcesink systems. [Physics of Fluids 31, 469 (1988)]. Scott W. Jones, Hassan Aref. Abstract. The onset of chaos in passive advection of particles by flow caused by a pulsed sourcesink system is documented. ...
2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2012
In this study, we investigate the application of contactless dielectrophoresis (cDEP) for isolati... more In this study, we investigate the application of contactless dielectrophoresis (cDEP) for isolating cancer cells from blood cells. Devices with throughput of 0.2 mL/hr (equivalent to sorting 3×10(6) cells per minute) were used to trap breast cancer cells while allowing blood cells through. We have shown that this technique is able to isolate cancer cells in concentration as low as 1 cancer cell per 10(6) hematologic cells (equivalent to 1000 cancer cells in 1 mL of blood). We achieved 96% trapping of the cancer cells at 600 kHz and 300 V(RMS).
Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 2004
Chaotic advection can play an important role in efficient microfluidic mixers. We discuss a desig... more Chaotic advection can play an important role in efficient microfluidic mixers. We discuss a design paradigm that exploits chaotic advection and illustrate by two recent examples, namely enhancing gene expression profiling and constructing an in-line microfluidic mixing channel, how application of this paradigm has led to successful micromixers. We suggest that 'designing for chaos', that is, basing practical mixer design on chaotic advection analysis, is a promising approach to adopt in this developing field which otherwise has little to guide it and is constrained by issues of scale and manufacturability.
Abstract. A number of instability and bifurcation problems related to the dynamics of vortex wake... more Abstract. A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal-Reynolds number relation for vortex wakes, the bifurcation diagram for exotic wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the ...
A new approach to regular and chaotic fluid advection is presented that utilizes the Thurston–Nie... more A new approach to regular and chaotic fluid advection is presented that utilizes the Thurston–Nielsen classification theorem. The prototypical two-dimensional problem of stirring by a finite number of stirrers confined to a disk of fluid is considered. The theory shows that for particular ‘stirring protocols’ a significant increase in complexity of the stirred motion – known as topological chaos – occurs when three or more stirrers are present and are moved about in certain ways. In this sense prior studies of chaotic advection with at most two stirrers, that were, furthermore, usually fixed in place and simply rotated about their axes, have been ‘too simple’. We set out the basic theory without proofs and demonstrate the applicability of several topological concepts to fluid stirring. A key role is played by the representation of a given stirring protocol as a braid in a (2+1)-dimensional space–time made up of the flow plane and a time axis perpendicular to it. A simple experiment ...
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Papers by Mark Stremler