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

Human wealth evolution is an accelerating expansion underpinned by a decelerating optimization process

Eight centuries of yearly GDP data from three regions of Western Europe, corresponding to present days UK, France and Sweden, gauge economic interactions that reflect the societal structures in which they unfold. In short, they provide an insight on human wealth evolution. Our data analysis is carried out in two steps. First, a Monte Carlo algorithm is used to fit the GDP time series to a piecewise continuous function comprising a sequence of exponentials with different exponents. These arguably correspond to different social and technological stages of societal organization. As a function of time, human wealth evolution features an accelerating trend and is thus an evolutionary expansion process. The intensity of human interactions driving the evolutionary process has increased manyfold over the centuries. This motivates our second analysis, where `wall clock time' as independent variable is replaced with a measure of human interactions intensity $\tau$. In terms of this interaction variable $\tau$, human wealth evolution displays two different logarithmic regimes, both decelerating, and connected by a rapid cross-over. The latter occurs around the outbreak of World War I and coincides with the transition in Western Europe from a mainly agricultural to a mainly industrial and urbanized society. Finally, wealth evolution in terms of $\tau$ shows the hallmarks of record dynamics optimization

Tight Coupling of Metabolic Oscillations and Intracellular Water Dynamics in <i>Saccharomyces cerevisiae</i>

We detected very strong coupling between the oscillating concentration of ATP and the dynamics of intracellular water during glycolysis in Saccharomyces cerevisiae. Our results indicate that: i) dipolar relaxation of intracellular water is heterogeneous within the cell and different from dilute conditions, ii) water dipolar relaxation oscillates with glycolysis and in phase with ATP concentration, iii) this phenomenon is scale-invariant from the subcellular to the ensemble of synchronized cells and, iv) the periodicity of both glycolytic oscillations and dipolar relaxation are equally affected by D2O in a dose-dependent manner. These results offer a new insight into the coupling of an emergent intensive physicochemical property of the cell, i.e. cell-wide water dipolar relaxation, and a central metabolite (ATP) produced by a robustly oscillating metabolic process