arXiv subjects

Per Lyngs Hansen

Publications and source records attributed to Per Lyngs Hansen.

7 recordsLinked to original sources

arXiv2022

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

Optimization and expansion are two modes of staged evolution of complex systems where macroscopic observables change at a decreasing, respectively increasing, rate. A prime example of evolutionary expansion, Gross Domestic Product (GDP) time series gauge economic activities in changing societal structures,} and the accelerating trend of their growth probably reflects a manyfold increase of the human interactions that drive change. We show how optimization and expansion can coexist by replacing `wall clock time' $t$ as independent variable with a measure of human interactions intensity $τ$. Our analysis of eight centuries of yearly GDP data from three regions of Western Europe is carried out in two steps. First, a Monte Carlo algorithm is used to fit the GDP data to a piecewise continuous function comprising a sequence of exponentials with different exponents. In a second step, GDP data are plotted vs. $τ$ and shown to display two logarithmic regimes, both decelerating, that are joined by a power-law cross-over period. We connect the end of the first regime and the beginning of the second with the dawn of the Industrial Revolution and the societal impact of new transport, communication and production technologies that became widely available after World War I. We conclude that wealth evolution in terms of $τ$ is a decelerating process with the hallmarks of record dynamics optimization.

physics.soc-ph↗

arXiv2015

Non-Equilibrium Thermodynamics of Self-Replicating Protocells

We provide a non-equilibrium thermodynamic description of the life-cycle of a droplet based, chemically feasible, system of protocells. By coupling the protocells metabolic kinetics with its thermodynamics, we demonstrate how the system can be driven out of equilibrium to ensure protocell growth and replication. This coupling allows us to derive the equations of evolution and to rigorously demonstrate how growth and replication life-cycle can be understood as a non-equilibrium thermodynamic cycle. The process does not appeal to genetic information or inheritance, and is based only on non-equilibrium physics considerations. Our non-equilibrium thermodynamic description of simple, yet realistic, processes of protocell growth and replication, represents an advance in our physical understanding of a central biological phenomenon both in connection to the origin of life and for modern biology.

cond-mat.soft↗

arXiv2007

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.

cond-mat.soft↗

arXiv2002

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.

cond-mat.soft↗

arXiv2000

Osmotic Properties of Charged Cylinders: Critical Evaluation of Counterion Condensation Theory

The osmotic coefficient of B-DNA in water may, in moderately dilute solutions, deviate as much as 100 % from predictions based on a simple 'counterion condensation' theory. We determine the results for osmotic properties via a cell model description of the ionic atmosphere near a cylindrical polyelectrolyte. The cell model predictions for the osmotic properties disagree with predictions based on simple condensation theory, but are in surprisingly good harmony with experimental findings. We argue that the neglect of finite-radius effects makes simple condensation theory inapplicable at all but impractically low polyelectrolyte concentrations and, unable to reproduce osmotic properties of polyelectrolytes such as DNA.

cond-mat.soft↗

arXiv2000

Elastic moduli renormalization in self interacting stretchable polyelectrolytes

We study the effect of intersegment interactions on the effective bending and stretching moduli of a semiflexible polymer chain with a finite stretching modulus. For an interaction potential of a screened Debye-H\" uckel type renormalization of the stretching modulus is derived on the same level of approximation as the celebrated Odijk-Skolnick-Fixman result for the bending modulus. The presence of mesoscopic intersegment interaction potentials couples the bending and stretching moduli in a manner different from that predicted by the macroscopic elasticity theory. We advocate a fundamental change in the perspective regarding the dependence of elastic moduli of a flexible polyelectrolyte on the ionic conditions: stretchability. Not only are the persistence length as well as the stretching modulus dependent on the salt conditions in the solution, they are fundamentally coupled via the mesoscopic intersegment interaction potential. The theory presented here compares favorably with recent experiments on DNA bending and stretching.

cond-mat.soft↗

arXiv1999

Buckling, Fluctuations and Collapse in Semiflexible Polyelectrolytes

We present a systematic statistical mechanical analysis of the conformational properties of a stiff polyelectrolyte chain with intrachain attractions that are due to counterion correlations. We show that the mean-field solution corresponds to an Euler-like buckling instability. The effect of the conformational fluctuations on the buckling instability is investigated, first, qualitatively, within the harmonic (``semiclassical'') theory, then, systematically, within a 1/d-expansion, where d denotes the dimension of embedding space. Within the ``semiclassical'' approximation, we predict that the effect of fluctuations is to renormalize the effective persistence length to smaller values, but not to change the nature of the mean-field (i.e., buckling) behavior. Based on the 1/d-expansion we are, however, led to conclude that thermal fluctuations are responsible for a change of the buckling behavior which is turned into a polymer collapse. A phase diagram is constructed in which a sequence of collapse transitions terminates at a buckling instability that occurs at a place that varies with the magnitude of the bare persistence length of the polymer chain, as well as with the strength and range of the attractive potential.

cond-mat.soft↗