No abstract

Twenty‐four strains of Emiliania huxleyi and two strains of Gephyrocapsa oceanica were grown at 15°C under identical culture conditions to assess genetic variability in key lipid biomarker profiles (C37‐C39 alkenones, C36 and C37 alkyl alkenoates, and C31‐C38 alkenes). Under our culture conditions, little divergence an biomarker composition was detected between E. huxleyi strains from different oceanic regions or between E. huxleyi and G. oceanica even though the strains originated from biogeographical regions as diverse as the subpolar North Atlantic and subtropical Western Pacific. The major differences observed were in tetraunsaturated alkenone abundance and alkene profiles, which tended to separate neritic from open ocean strains. Different strains from the same locality were as different as strains originating from widely separated ocean basins, indicating extreme genotypic diversity within a population. Replicate cultures of the same strain showed significant variability in their biomarker profiles even though the culture temperature varied by only ±0.3°C, indicating that their synthesis ratios are influenced by environmental and/or physiological variable(s), as yet unidentified, in addition to temperature. Strong covariance in C37 and C38 methyl alkenone unsaturation ratios (Uk37 and Uk38Mρ respectively) and, in coastal strains, C33, alkene and alkenone unsaturation ratios indicates that these compounds are biochemically linked.

No abstract

We solve the problem of a confined sheared active polar liquid crystal film with varying amounts of polarization, but a uniformly aligned director. Restricting our analysis to one-dimensional geometries, we demonstrate that with asymmetric boundary conditions, this system is characterized, macroscopically, by a linear shear stress vs. shear strain relationship that does not pass through the origin: at zero strain rate the fluid sustains a non-zero stress. Analytic solutions for the polarization, density and velocity fields are derived for asymptotically large or small systems, and are shown by comparison with precise numerical solutions to be good approximations for finite-size systems.

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