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We consider the problem of failure detection in dynamic networks such as MANETs. Unreliable failure detectors are classical mechanisms which provide information about process failures. However, most of current implementations consider that the network is fully connected and that the initial number of nodes of the system is known. This assumption is not applicable to dynamic environments. Furthermore, such implementations are usually timer-based while in dynamic networks there is no upper bound for communication delays since nodes can move. This paper presents an asynchronous implementation of a failure detector for unknown and mobile networks. Our approach does not rely on timers and neither the composition nor the number of nodes in the system are known. We prove that our algorithm can implement failure detectors of class <>S when behavioral properties and connectivity conditions are satisfied by the underlying system.

During the aging of the red-blood cell, or under conditions of extreme echinocytosis, membrane is shed from the cell plasma membrane in the form of nano-vesicles. We propose that this process is the result of the self-adaptation of the membrane surface area to the elastic stress imposed by the spectrin cytoskeleton, via the local buckling of membrane under increasing cytoskeleton stiffness. This model introduces the concept of force balance as a regulatory process at the cell membrane, and quantitatively reproduces the rate of area loss in aging red-blood cells., Comment: 4 pages, 3 figures

Successful cell division requires a tight regulation of chromosome motion via the activity of molecular motors. Many of the key players at the origin of the forces generating the movement have been identified, but their spatial and temporal organization remains elusive. The protein complex Kinetochore on the chromosome associates with microtubules emanating from one of the spindle poles and drives the chromosome toward the pole. Chromokinesin motors on the chromosome arms also interact with microtubules, ejecting the chromosome away from the pole. In animal cells, a monooriented chromosome (associated to a single pole) periodically switches between phases of poleward and away from the pole movement[, a behavior tentatively explained so far by the existence of a complex switching mechanism within the kinetochore itself. Here we show that the interplay between the morphology of the mitotic spindle and the collective kinetics of chromokinesins can account for the highly non-linear periodic chromosome motion. Our analysis provides a natural explanation for the origin of chromosome directional instability and for the mechanism by which chromosomes feel their position in space., Comment: http://hogarth.pct.espci.fr/~pierre/

We propose a mechanism for mechanical regulation at the membrane of living cells, based on the exchange of membrane area between the cell membrane and a membrane reservoir. The reservoir is composed of invaginated membrane microdomains which are liable to flatten upon increase of membrane strain, effectively controlling membrane tension. We show that the domain shape transition is first order, allowing for coexistence between flat and invaginated domains. During coexistence, the membrane tension is controlled by the domains elasticity and by the kinetics of the shape transition. We show that the tension of the plasma membrane of living cells is inherently transient and dynamical, and that valuable insights into the organization of the cell membrane can be obtained by studying the variation of the cell membrane tension upon mechanical perturbation., Comment: http://hogarth.pct.espci.fr/~pierre/

We present a model for the kinetics of spontaneous membrane domain (raft) assembly that includes the effect of membrane recycling ubiquitous in living cells. We show that the domains have a broad power-law distribution with an average radius that scales with the 1/4 power of the domain lifetime when the line tension at the domain edges is large. For biologically reasonable recycling and diffusion rates the average domain radius is in the tens of nm range, consistent with observations. This represents one possible link between signaling (involving rafts) and traffic (recycling) in cells. Finally, we present evidence that suggests that the average raft size may be the same for all scale-free recycling schemes., Comment: 8 pages, 5 figures

We propose an alternative mechanism for the gating of biological membrane channels in response to membrane tension that involves a change in the slope of the membrane near the channel. Under biological membrane tensions we show that the energy difference between the closed (tilted) and open (untilted) states can far exceed kBT and is comparable to what is available under simple ilational gating. Recent experiments demonstrate that membrane leaflet asymmetries (spontaneous curvature) can strong effect the gating of some channels. Such a phenomenon would be more easy to explain under gating-by-tilt, given its novel intrinsic sensitivity to such asymmetry., Comment: 10 pages, 2 figures

The dynamical response of a lipid membrane to a local perturbation of its molecular symmetry is investigated theoretically. A density asymmetry between the two membrane leaflets is predominantly released by in-plane lipid diffusion or membrane curvature, depending upon the spatial extent of the perturbation. It may result in the formation of non-equilibrium structures (buds), for which a dynamical size selection is observed. A preferred size in the micrometer range is predicted, as a signature of the crossover between membrane and solvent dominated dynamical membrane response., Comment: 7 pages 3 figures

The influence of an electric field on a poorly conductive membrane such as a lipid bilayer is studied theoretically. The unbalanced electric stress created by an ionic current across a non-perfectly flat membrane gives rise to a destabilizing surface energy enhancing undulations. The deformation of a membrane attached to a frame and the subsequent force on the frame are derived and the electrohydrodynamic instability of a free floating membrane is also studied. We find a most unstable mode of undulation, of wavelength in the $\mu m$ range, connected to the crossover between membrane and solvent dominated dissipations., Comment: 8 pages, 2 figures

Motivated by numerous X-ray scattering studies of lamellar phases with membrane proteins, amphiphilic peptides, polymers, or other inclusions, we have determined the modifications of the classical Caille law for a smectic phase as a function of the nature and concentration of inclusions added to it. Besides a fundamental interest on the behavior of fluctuating systems with inclusions, a precise characterization of the action of a given protein on a lipid membrane (anchoring, swelling, stiffening ...) is of direct biological interest and could be probed by way of X-ray measurements. As a first step we consider three different couplings involving local pinching (or swelling), stiffening or tilt of the membrane. In the first two cases we predict that independent inclusions induce a simple renormalization of the bending and compression modulii of the smectic phase. The X-ray experiments may also be used to probe correlations between inclusions. Finally we show that asymmetric coupling (such as a local tilt of the membrane) results in a modification of the usual Caille law., Comment: 11 pages, 2 figures

The effective charge of a rigid polyelectrolyte (PE) approaching an oppositely charged surface is studied. The cases of a weak (annealed) and strongly charged PE with condensed counterions (such as DNA) are discussed. In the most interesting case of the adsorption onto a substrate of low dielectric constant (such as a lipid membrane or a mica sheet) the condensed counterions are not always released as the PE approaches the substrate, because of the major importance of the image charge effect. For the adsorption onto a surface with freely moving charges, the image charge effect becomes less important and full release is often expected., Comment: 8 pages, 1 figure

We investigate the equilibrium charge distribution along a single annealed polyelectrolyte chain under different conditions. The coupling between the conformation of the chain and the local charge distribution is described for various solvent qualities and salt concentration. In salt free solution, we find a slight charge depletion in the central part of the chain: the charges accumulate at the ends. The effect is less important if salt is added to the solution since the charge inhomogeneity is localized close to the chain ends over a distance of order of the Debye length. In the case of poor solvent conditions we find a different charging of beads and strings in the framework of the necklace model. This inhomogeneity leads to a charge instability and a first order transition between spherical globules and elongated chains., Comment: 20 pages, 4 figures