Browsing by Author "Chen, J."

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    Evaluating Records of Environmental Change and Mass Extinctions during the Early Paleozoic
    McKenzie, N. R.; Gill, Benjamin C.; Wernette, S. J.; Chen, J.; Park, T. -Y.; Myrow, P. M.; Hughes, N. C. (2019-08-21)
    The interval between the Cambrian ‘explosion’ and the Great Ordovician Biodiversification Event (GOBE) is marred by biotic turmoil.Several mass extinction events have been recognized throughout the Cambrian,with multiple Furongian (late) Cambrian extinctions mostly seen within trilobite fauna of North America.These extinctions appear to correspond with episodic ocean anoxia and carbon cycle perturbations, all of which are set to the backdrop of an extensive greenhouse climate.Here we will present new chemostratigraphic and compiled biostratigraphic data from Cambrian successions of the NorthChina/Sino-Korean block(NCB). These data help identify newly recognized trilobite extinctions in upper Cambrian carbonate platform deposits of the NCB that may be correlative to North American events, demonstrating their global extent.These extinctions also correspond with marked G13Cexcursions. The cessation of these repeated extinctions coincides with global reductions in arc-volcanism and climatic cooling, implying a causal linkage between baseline climate conditions and this extensive interval of biospheric perturbations.Collectively, these data help further elucidate the harsh environmental conditions that hindered early animal evolution.
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    Generating Topological Chaos in Lid-Driven Cavity Flow
    Stremler, Mark A.; Chen, J. (AIP Publishing, 2007-10-01)
    Periodic motion of three stirrers in a two-dimensional flow can lead to chaotic transport of the surrounding fluid. For certain stirrer motions, the generation of chaos is guaranteed solely by the topology of that motion and continuity of the fluid. Work in this area has focused largely on using physical rods as stirrers, but the theory also applies when the "stirrers" are passive fluid particles. We demonstrate the occurrence of topological chaos for Stokes flow in a two-dimensional lid-driven cavity without internal rods. This approach to stirring can enhance mixing relative to a "standard" chaos-generating lid-driven cavity flow. (C) 2007 American Institute of Physics.
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    Topological Chaos And Mixing in a Three-Dimensional Channel Flow
    Chen, J.; Stremler, Mark A. (AIP Publishing, 2009-02-01)
    Passive mixing is investigated in a mathematical model of steady, three-dimensional, laminar flow through a rectangular channel. Efficient stirring is achieved by imposing spatially periodic transverse boundary velocities that generate asymmetric, counter-rotating rolls aligned with the channel axis. The flow is designed and analyzed using the concept of topological chaos, in which complexity is embedded in the flow through the motion of periodic orbits. A lid-driven flow producing topological chaos is found to stir better than a related flow with solid inserts considered previously [M. D. Finn, S. M. Cox, and H. M. Byrne, Phys. Fluids 15, L77 (2003)]. The results demonstrate that topological chaos and the Thurston-Nielsen classification theorem can provide insight into mixing enhancement in steady, three-dimensional flows.