Curvature and torsion in growing actin networks

Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 seconds. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a 3D space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature rather than a fixed torque

On asymptotic Teichmüller space

In this article we prove that for any hyperbolic Riemann surface M of infinite analytic type, the little Bers space Q0(M) is isomorphic to c0. As a consequence of this result, if M is such a Riemann surface, then its asymptotic Teichm¨uller space AT(M) is bi-Lipschitz equivalent to a bounded open subset of the Banach space l∞/c0. Further, if M and N are two such Riemann surfaces, their asymptotic Teichm¨uller spaces, AT(M) and AT(N), are locally bi-Lipschitz equivalen

Changes in body composition and fatty acid profile during embryogenesis of quillback rockfish (Sebastes maliger)

We investigated developmental changes in the body compositions and fatty acid (FA) profiles of embryos and preparturition larvae of the quillback rockfish (Sebastes maliger). Comparisons of proximate composition data from early-stage embryos with data from hatched preparturition larvae taken from wild-caught gravid females indicated that embryos gain over one-third their weight in moisture while consuming 20% of their dry tissue mass for energy as they develop into larvae. Lipid contributed 60% of the energy consumed and was depleted more rapidly than protein, indicating a protein-sparing effect. Oil globule volume was strongly correlated with lipid levels, affirming its utility as an indicator of energetic status. FA profiles of early embryos differed significantly from those of hatched larvae. Differences in the relative abundances of FAs between early embryos and hatched larvae indicated different FA depletion rates during embryonic development. We conclude that some metabolically important FAs may prove useful in assessing the condition of embryos and preparturition larvae, particularly 20:4n-6, which cannot be synthesized by many marine fish and which is conserved during embryogenesis. Variability in body composition and energy use among rockfish species should be considered when interpreting any measures of condition

From search engine optimisation to search engine marketing management: development of a new area for information systems research

Search Engine Optimisation was a term used by web developers in the late 90s to highlight the importance of increasing a website’s position in search engines’ results. Further development of the Internet in terms of the diversity of its users and uses such as e-commerce, blogging and wikis have highlighted the need for technical staff to work more closely with marketing professionals resulting in a new area of work – Search Engine Marketing Management. The paper highlights the emerging role of Search Engine Marketing Management as a new and increasingly important area for future information systems researchers and research. Reaching beyond the 'simple' undifferentiated goal of increasing visitors to a website, a mature perspective of marketing is developing - that of realising strategic marketing objectives. The practical contribution of this paper is found in the development of awareness among management roles of the importance and nuances of search engines and the tactics required to harness the benefits of multiple online communication channels within organisational marketing strategy