Depinning of semiflexible polymers in (1+1) dimensions

We present a theoretical analysis of a simple model of the depinning of an anchored semiflexible polymer from a fixed planar substrate in (1+1) dimensions. We consider a polymer with a discrete sequence of pinning sites along its contour. Using the scaling properties of the conformational distribution function in the stiff limit and applying the necklace model of phase transitions in quasi-one-dimensional systems, we obtain a melting criterion in terms of the persistence length, the spacing between pinning sites, a microscopic effective length which characterizes a bond, and the bond energy. The limitations of this and other similar approaches are also discussed. In the case of force-induced unbinding, it is shown that the bending rigidity favors the unbinding through a ``lever-arm effect''

Dogs, disease, and wildlife

No abstract available

Dogs, disease, and wildlife

No abstract available

Fluctuating Interfaces in Microemulsion and Sponge Phases

A simple Ginzburg-Landau theory with a single, scalar order parameter is used to study the microscopic structure of microemulsions and sponge phases. The scattering intensity in both film and bulk contrast, as well as averages of the internal area $S$, the Euler characteristic $\chi_E$, and the mean curvature squared $$, are calculated by Monte Carlo methods. The results are compared with results obtained from a variational approach in combination with the theory of Gaussian random fields and level surfaces. The results for the location of the transition from the microemulsion to oil/water coexistence, for the scattering intensity in bulk contrast, and for the dimensionless ratio $\chi_E V^2/S^3$ (where $V$ is the volume) are found to be in good quantitative agreement. However, the variational approach fails to give a peak in the scattering intensity in film contrast at finite wavevector, a peak which is observed both in the Monte Carlo simulations and in experiment. Also, the variational approach fails to produce a transition from the microemulsion to the lamellar phase.Comment: 23 pages (LaTeX) + 15 figures appended, figures 10-13 upon request, LMU-WAG-94053

Fisheries conservation and management: finding consensus in the midst of competing paradigms

[Extract] The state of the world's fisheries has been a prominent and controversial scientific and social issue over the past 20 years (Banobi, Branch & Hilborn, 2011). Influential research has suggested that we have preferentially 'fished down' top ocean predators before targeting their prey (Pauly et al., 1998) and that, as a consequence, these marine predators have declined by 90% (Myers & Worm, 2003). Even worse, it has been argued that current trends will lead to the global collapse of all fisheries by 2048 (Worm et al., 2006). These paradigms have been challenged by recent findings. The original basis for fishing down marine food webs (Pauly et al., 1998) was based on trophic levels – the average position within food webs, where microscopic algae are at trophic level one, herbivores at trophic level two and predators at trophic level three or higher. Pauly et al. (1998) found a precipitous decline in the average trophic level of commercial catches. However, recent analyses of catches and unbiased data from scientific surveys and stock assessments show that mean trophic levels are increasing rather than decreasing, and that this indicator does not reliably track changes in marine ecosystem health (Branch et al., 2010). In any case, in most ecosystems where average trophic level has declined, such trends are due not to waning top-predator catches ('fishing down'), but to increasing catches of low-trophic-level species, or 'fishing through' (Essington, Beaudreau & Wiedenmann, 2006). Where collapses have occurred, they are up to twice as frequent in small, short-lived species low on the food web than in long-lived predators (Pinsky et al., 2011)