298 research outputs found
Applying a potential across a biomembrane: electrostatic contribution to the bending rigidity and membrane instability
We investigate the effect on biomembrane mechanical properties due to the
presence an external potential for a non-conductive non-compressible membrane
surrounded by different electrolytes. By solving the Debye-Huckel and Laplace
equations for the electrostatic potential and using the relevant stress-tensor
we find: in (1.) the small screening length limit, where the Debye screening
length is smaller than the distance between the electrodes, the screening
certifies that all electrostatic interactions are short-range and the major
effect of the applied potential is to decrease the membrane tension and
increase the bending rigidity; explicit expressions for electrostatic
contribution to the tension and bending rigidity are derived as a function of
the applied potential, the Debye screening lengths and the dielectric constants
of the membrane and the solvents. For sufficiently large voltages the negative
contribution to the tension is expected to cause a membrane stretching
instability. For (2.) the dielectric limit, i.e. no salt (and small wavevectors
compared to the distance between the electrodes), when the dielectric constant
on the two sides are different the applied potential induces an effective
(unscreened) membrane charge density, whose long-range interaction is expected
to lead to a membrane undulation instability.Comment: 16 pages, 3 figures, some revisio
Prospecting for organic fungicides and resistance inducers to control scab (Venturia inaequalis) in organic apple production
As a part of the REPCO project we are prospecting for plant extracts and other materials to control apple scab in order to find substitutes for copper fungicides in organic apple production. Two routine screening systems are used to evaluate the potential of materials to control apple scab; one testing the effect of materials on conidium germination on glass slides, and one testing the effect of materials on scab development on apple seedlings grown in growth chambers. Several interesting materials have been identified and a number have been selected for testing in experimental organic apple orchards. Studies of the mode of action of promising materials including induced resistance are on-going and work on improvement of timing and formulation is initiated at KVL
Osmotic properties of polyethyleneglycols: quantitative features of brush and bulk scaling laws
From glycosylated cell surfaces to sterically stabilized liposomes, polymers
attached to membranes attract biological and therapeutic interest. Can the
scaling laws of polymer "brushes" describe the physical properties of these
coats? We delineate conditions where the Alexander - de Gennes theory of
polymer brushes successfully describes the intermembrane distance vs. applied
osmotic stress data of Kenworthy et al. for PEG-grafted multilamellar liposomes
[Biophys. J. (1995) 68:1921]. We establish that the polymer density and size in
the brush must be high enough that, in a bulk solution of equivalent density,
the polymer osmotic pressure is independent of polymer molecular weight (the
des Cloizeaux semi-dilute regime of bulk polymer solutions). The condition that
attached polymers behave as semi-dilute bulk solutions offers a rigorous
criterion for brush scaling-law behavior. There is a deep connection between
the behaviors of polymer solutions in bulk and polymers grafted to a surface at
a density such that neighbors pack to form a uniform brush. In this regime,
two-parameter unconstrained fits of the Alexander - de Gennes brush scaling
laws yield effective monomer lengths of 3.3 to 3.5 AA, which agree with
structural predictions. The fitted distances between grafting sites are larger
than expected from the nominal content of PEG-lipids; the chains apparently
saturate the surface. Osmotic stress measurements can be used to estimate the
actual densities of membrane-grafted polymers.Comment: 26 pages with figure
Third Party Tracking in the Mobile Ecosystem
Third party tracking allows companies to identify users and track their
behaviour across multiple digital services. This paper presents an empirical
study of the prevalence of third-party trackers on 959,000 apps from the US and
UK Google Play stores. We find that most apps contain third party tracking, and
the distribution of trackers is long-tailed with several highly dominant
trackers accounting for a large portion of the coverage. The extent of tracking
also differs between categories of apps; in particular, news apps and apps
targeted at children appear to be amongst the worst in terms of the number of
third party trackers associated with them. Third party tracking is also
revealed to be a highly trans-national phenomenon, with many trackers operating
in jurisdictions outside the EU. Based on these findings, we draw out some
significant legal compliance challenges facing the tracking industry.Comment: Corrected missing company info (Linkedin owned by Microsoft). Figures
for Microsoft and Linkedin re-calculated and added to Table
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