Educational Forum with Clinical Studies Current Science and Research

September 29, 2010

Effects of microcurrents in the boundary layer on the attachment of benthic heterotrophic nanoflagellates. Xanya Sofra Weiss Xanya Sofra Weiss

Filed under: Xanya Sofra Weiss — Tags: — Dr. Xanya @ 7:37 am

Marlene Willkomm, Annette Schlussel, Ellen Reiz, Hartmut Arndt; 2007

Surfaces in runningwater are covered by a boundary layer. Virtually nothing is known
about the importance of water currents in the microenvironment of nanofauna. Many questions have
been partially answered concerning the effect of surface topography on the hydrodynamics in the
vicinity of macrofauna; however, investigations of the 2 to 5 μm water layer where nanoprotists live
have been neglected. In the present study, we show that the flow velocity at a distance of a few
micrometres from the substrate is high enough to be very effective regarding the detachment of
nanoprotists. We analysed the impact of flow velocity (detachment from substrate) on 8 nano-
flagellate taxa (Entosiphon, Cercomonas, Codonosiga, Anthophysa, Bodo, Neobodo, Apusomonas,
Spumella) with different abilities to crawl and attach to the surface. A Plexiglas disc was used to gen-
erate a defined flow velocity on the surface of a Petri dish microcosm. Laminar flow in the boundary
layer was found between 0 and 700 μm above the substratum. The effect of 4 different flow velocities
on heterotrophic flagellates was investigated (0.3, 0.6, 0.9 and 1.2 m s–1at 5 mm above the substra-
tum, corresponding to flow velocities of 0.001 to 0.004 m s–1 at 10 μm above the substratum). The
colourless, gliding euglenid Entosiphon sulcatumshowed the highest resistance towards high flow
velocities. Another species, the crawling cercomonad Cercomonas crassicauda, had the weakest
attachment. Small changes in the micro-topography of the substrate (e.g. Ancylusshells) may signif-
icantly influence spatial distribution of nanoflagellates.

Xanya Sofra Weiss

Xanya Sofra Weiss

September 9, 2010

Macroscopic surface tension in a lattice Bhatnagar-Gross-Krook model of two immiscible fluids. Xanya Sofra Weiss Xanya Sofra Weiss

Filed under: Xanya Sofra Weiss — Tags: — Dr. Xanya @ 3:32 am

I. Ha;;iday, S.P Thompson, and C.M Care; 1998

We present a method by which an interface generating algorithm, similar to that of earlier lattice Boltzmann models of immiscible fluids, may be extended to a two component, two-speed two-dimensional (D2), nine-link (Q9) lattice Bhatnagar-Gross-Krook fluid. For two-dimensional, microcurrent-free planar interfaces between the two immiscible fluids we derive expressions for static interfacial tensions and interfacial distributions of the two fluids. Extending our analysis to curved interfaces, we propose a scheme for incorporating the influence of interfacial microcurrents that is based upon general symmetry arguments and is correct to second order in lattice velocity. The analysis demonstrates that the interfacial microcurrents have only second-order influence upon the macroscopic behavior of the model. We find good agreement between our calculations and simulation results based on the microcurrent stream function and surface tension results from the pressure tensor or Laplace law.

Xanya Sofra Weiss

Xanya Sofra Weiss

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