Reliability of genetic networks is evolvable

Control of the living cell functions with remarkable reliability despite the stochastic nature of the underlying molecular networks -- a property presumably optimized by biological evolution. We here ask to what extent the property of a stochastic dynamical network to produce reliable dynamics is an evolvable trait. Using an evolutionary algorithm based on a deterministic selection criterion for the reliability of dynamical attractors, we evolve dynamical networks of noisy discrete threshold nodes. We find that, starting from any random network, reliability of the attractor landscape can often be achieved with only few small changes to the network structure. Further, the evolvability of networks towards reliable dynamics while retaining their function is investigated and a high success rate is found.Comment: 5 pages, 3 figure

A Mechanistic Explanation for Global Patterns of Liana Abundance and Distribution

One of the main goals in ecology is determining the mechanisms that control the abundance and distribution of organisms. Using data from 69 tropical forests worldwide, I demonstrate that liana (woody vine) abundance is correlated negatively with mean annual precipitation and positively with seasonality, a pattern precisely the opposite of most other plant types. I propose a general mechanistic hypothesis integrating both ecological and ecophysiological approaches to explain this pattern. Specifically, the deep root and efficient vascular systems of lianas enable them to suffer less water stress during seasonal droughts while many competitors are dormant, giving lianas a competitive advantage during the dry season. Testing this hypothesis in central Panama, I found that lianas grew approximately seven times more in height than did trees during the dry season but only twice as much during the wet season. Over time, this dry season advantage may allow lianas to increase in abundance in seasonal forests. In aseasonal wet forests, however, lianas gain no such advantage because competing plants are rarely limited by water. I extend this theory to account for the local, within‐forest increase in liana abundance in response to disturbance as well as the conspicuous decrease in liana abundance at high latitudes

Holographic thermalization in N=4 Super Yang-Mills theory at finite coupling

We investigate the behavior of energy momentum tensor correlators in holographic $\mathcal{N}=4$ super Yang-Mills plasma, taking finite coupling corrections into account. In the thermal limit we determine the flow of quasinormal modes as a function of the 't Hooft coupling. Then we use a specific model of holographic thermalization to study the deviation of the spectral densities from their thermal limit in an out-of-equilibrium situation. The main focus lies on the thermalization pattern with which the plasma constituents approach their thermal distribution as the coupling constant decreases from the infinite coupling limit. All obtained results point towards the weakening of the usual top-down thermalization pattern.Comment: 18 pages, 7 figures, v3: major revisio

Critical Entropy of Quantum Heisenberg Magnets on Simple-Cubic Lattices

We analyze the temperature dependence of the entropy of the spin-1/2 Heisenberg model on the three-dimensional simple-cubic lattice, for both the case of antiferromagnetic and ferromagnetic nearest neighbor exchange interactions. Using optimized extended ensemble quantum Monte Carlo simulations, we extract the entropy at the critical temperature for magnetic order from a finite-size scaling analysis. For the antiferromagnetic case, the critical entropy density equals 0.341(5)$k_B$, whereas for the ferromagnet, a larger value of 0.401(5) $k_B$ is obtained. We compare our simulation results to estimates put forward recently in studies assessing means of realizing the antiferromagnetic N\'eel state in ultra-cold fermion gases in optical lattices.Comment: 3 pages, 2 figures; published versio