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Theoretical physicists working at a blackboard collaboration pod in the Beecroft building.
Credit: Jack Hobhouse

Amin Doostmohammadi

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  • Rudolf Peierls Centre for Theoretical Physics
a.dstmhmdi@gmail.com
Telephone: 01865 (2)73334
Rudolf Peierls Centre for Theoretical Physics
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  • Publications

Low-Reynolds-number swimming at pycnoclines.

Proceedings of the National Academy of Sciences of the United States of America 109:10 (2012) 3856-3861

Authors:

Amin Doostmohammadi, Roman Stocker, Arezoo M Ardekani

Abstract:

Microorganisms play pivotal functions in the trophic dynamics and biogeochemistry of aquatic ecosystems. Their concentrations and activities often peak at localized hotspots, an important example of which are pycnoclines, where water density increases sharply with depth due to gradients in temperature or salinity. At pycnoclines organisms are exposed to different environmental conditions compared to the bulk water column, including reduced turbulence, slow mass transfer, and high particle and predator concentrations. Here we show that, at an even more fundamental level, the density stratification itself can affect microbial ecology at pycnoclines, by quenching the flow signature, increasing the energetic expenditure, and stifling the nutrient uptake of motile organisms. We demonstrate this through numerical simulations of an archetypal low-Reynolds-number swimmer, the "squirmer." We identify the Richardson number--the ratio of buoyancy forces to viscous forces--as the fundamental parameter that quantifies the effects of stratification. These results demonstrate an unexpected effect of buoyancy on low-Reynolds-number swimming, potentially affecting a broad range of abundant organisms living at pycnoclines in oceans and lakes.
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Airfoil Flow Separation and Stall Prediction Using a Neural-Network Approach

ASME International (2010) 37-43

Authors:

Amir Nejat, Saeed Alem Varzaneh Esfehani, Amin Doostmohammadi
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Instability of Viscoelastic Fluids in Blasius Flow

ASME International (2010) 385-393

Authors:

Amin Doostmohammadi, Seyyedeh Negin Mortazavi
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