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Metachrony is defined as coordinated asynchronous movement throughout multiple appendages, such as the cilia of cells and swimmerets of crustaceans. Used by species of crustaceans and microscopic cells to move through fluid, the process of metachronal propulsion was investigated. A rigid crustacean model with paddles moving in symmetric strokes was created to simulate metachronal movement. Coupled with the surrounding fluid domain, the immersed boundary method was employed to analyze the fluid–structure interactions. To explore the effect of a nonlinear morphology on the efficiency of metachronal propulsion, a range of crustacean body shapes was generated and simulated, from upward curves to downward curves. The highest propulsion velocity was found to be achieved when the crustacean model morphology was a downward curve, specifically a parabola of leading coefficient k = −0.4. This curved morphology resulted in a 4.5% higher velocity when compared to the linear model. As k deviated from −0.4, the propulsion velocity decreased with increasing magnitude, forming a concave downward trend. The impact of body shape on propulsion velocity is shown by how the optimal velocity with k = −0.4 is 71.5% larger than the velocity at k = 1. Overall, this study suggests that morphology has a significant impact on metachronal propulsion. [ABSTRACT FROM AUTHOR]

In this work, we build upon our previous finding that hydrodynamic porosity, θmobile, is an exponential function of pore-scale flow velocity (or interstitial Reynolds number). We previously discovered this relationship for media with a square cavity geometry – a highly idealized case of the dead-ended pore spaces in a porous medium. Thus, we demonstrate the applicability of this relationship to media with other cavity geometries. We do so by applying our previous analysis to rectangular and non-rectangular cavity geometries (i.e., circular, and triangular). We also study periodic flow geometries to determine the effect of upstream cavities on those downstream. We show that not only does our exponential relationship hold for media with a variety of cavity geometries, but it does so almost perfectly with a coefficient of determination (R²) of approximately 1 for each new set of simulation data. Given this high fit quality, it is evident that the exponential relationship we previously discovered is applicable to most, if not all, unwashed media. [ABSTRACT FROM AUTHOR]

Earth's climate has undergone significant fluctuations in the geologic past. We focus on the glacial episodes that followed the major waves of invasion of land plants. Twice in Earth's history the impacts of land plant innovations on the atmosphere through increased CO2 drawdown have precipitated sufficient cooling to produce ice ages. Each time, however, adaptation of soil ecosystems eventually helped re-establish apparent steady-state conditions, i.e., new equilibrium temperature and atmospheric CO2 content, ending each of the glacial episodes. In each case, the time interval between the initial innovation and the emergence from the glacial episode was approximately 60 Myr. The consistency of the time scale of the response invites an explanation in terms of a universal rate of dispersal of genetic information that encapsulates the biogeochemical cycle of cellulose production and decay. In this paper, we postulate that the long time for adaptation is a consequence of the time required for the spread of an entire clade though the soil to continental scale. Although 60 Myr appears to be a long time, it is very short compared to the time required for diffusion to transport even molecules like HCO3- or sugar through the soil over a continental distance of 5,000 km, which is between 1014 and 1016 years for solutes with such soil diffusion constants in the range 10-11 m²s-1. Horizontal solute transport through heterogeneous media by advection might be considered as a dispersal mechanism, but is also known to require enormous time scales (ca. 150 Myr for 500 m). We also seek a relevant mechanism in the known scaling of plant and fungal growth rates as a function of time, which can facilitate as well the movement of bacteria, and predicted these rates theoretically on the basis of the universal optimal 2D paths tortuosity from percolation. Comparison with actual data pairs (7,000) for plant and fungal growth rates were used to verify these predictions over 13 orders of magnitude of time, from about one minute to 100 kyr; extrapolation over less than three additional orders of time yields a continental-scale transport time of 80 Myr. We now interpret this prediction in terms of Margulis' understanding of emergent behavior of coupled (soil and plant) ecosystems responding to climate shocks induced by plant innovations. [ABSTRACT FROM AUTHOR]

One factor that slows groundwater remediation is the sequestration of contaminant in dead-end pores, that is, pores that are not flushed through by flow through the aquifer. Furthermore, rebound of apparently remediated aquifers can occur as a result of the eventual release of the contaminant trapped in these dead-end pores. Since the operational costs generally outweigh the capital costs of a remediation project, reduction of the duration of treatment should reduce the overall cost of the average remediation. It has been shown that a rapidly pulsed flow can increase the mixing between dead-end and well-connected pores through computational fluid dynamics models with idealized pore geometry and column tests. A rapidly pulsed flow induces a deep sweep upon a sudden increase in velocity and a vortex ejection upon a sudden decrease in velocity that substantially accelerates the remediation of contaminant from these dead-end pores. To examine rapidly pulsed pumping in a more realistic configuration, a model vertical circulation well was constructed. The porous medium was well-sorted crushed glass to minimize sorption. Removal of a fluorescent dye, which represents a dissolved contaminant, under a rapidly pulsed flow was compared to a steady flow. The modeled well revealed accelerated removal of dissolved contaminants under a rapidly pulsed flow. [ABSTRACT FROM AUTHOR]