Péter Szabó

In silico simulations reveal that replicators with limited dispersal evolve towards higher efficiency and fidelity

The emergence of functional replicases, acting quickly and with high accuracy, was crucial to the origin of life. Although where the first RNA molecules came from is still unknown, it is nevertheless assumed that catalytic RNA enzymes (ribozymes) with replicase function emerged at some early stage of evolution. The fidelity of copying is especially important because the mutation load limits the length of replicating templates that can be maintained by natural selection. An increase in template length is disadvantageous for a fixed digit copying fidelity, however, longer molecules are expected to be better replicases. An iteration for longer molecules with better replicase function has been suggested and analysed mathematically. Here we show that more efficient replicases can spread, provided they are adsorbed to a prebiotic mineral surface. A cellular automaton simulation reveals that copying fidelity, replicase speed and template efficiency all increase with evolution, despite the presence of molecular parasites, essentially because of reciprocal atruism (‘within-species mutualism’) on the surface, thus making a gradual improvement of replicase function more plausible.

Spatial Ecological Hierarchies: Coexistence on Heterogeneous Landscapes via Scale Niche Diversification

Spatially heterogeneous environments are generally characterized by nested landscape patterns with resource aggregations on several scales. Empirical studies indicate that such nested landscape patterns impose selection constraints on the perceptive scales of animals, but the underlying selection mechanisms are unclear. We investigated the selection dynamics of perceptive scale within a spatial resource utilization model, where the environment is characterized by its resource distribution and species differ in their perceptive scales and resource preemption capabilities. Using three model landscapes with various resource distributions, we found that the optimal perceptive scale is determined by scale-specific attributes of the landscape pattern and that the number of coexisting species increases with the number of characteristic scales. Based on the results of this model, we argue that resource aggregations on different scales act as distinct resources and that animal species of particular perceptive scales are superior in utilizing resource aggregations of comparable spatial extent. Due to the allometric relationship between body size and perceptive scale, such fitness difference might result in discontinuous body mass distributions.

Criticality of relaxation in dislocation systems.

Relaxation processes of dislocation systems are studied by two-dimensional dynamical simulations. In order to capture generic features, three physically different scenarios were studied and power-law decays found for various physical quantities. Our main finding is that all these are the consequence of the underlying scaling property of the dislocation velocity distribution. Scaling is found to break down at some cutoff time increasing with system size. The absence of intrinsic relaxation time indicates that criticality is ubiquitous in all states studied. These features are reminiscent of glassy systems and can be attributed to the inherent quenched disorder in the position of the slip planes.

Turning with the Others: Novel Transitions in an SPP Model with Coupling of Accelerations

Collective motion of living beings (e.g. fish schools, bird flocks, bacterial colonies) exhibits a large variety of emergent phenomena. We consider a self-propelled particle (SPP) model of collective motion in three dimensions, which is a generalized version of the original SPP model. By extending the factors influencing the ordering, the model assumes that the movement of particles depends on both the velocity and acceleration of neighboring particles.

A comparison of the observed trends and simulated changes in extreme climate indices in the Carpathian Basin by the end of this century

Global warming results in shifts of mean temperature and precipitation, and also, in frequency and intensity changes of climate extremes. In this paper, temperature and precipitation extreme indices are analysed and compared for the Carpathian Basin (located in Central/Eastern Europe). For past trends, daily meteorological observations from the 20th century are used. In the case of future changes (2071-2100 relative to 1961-1990, A2 and B2 scenarios), the simulated daily outputs are obtained from regional climate model experiments. The results suggest that the regional climate of the Carpathian Basin got warmer during the second half of the 20th century, especially in the last quarter. Regional warming is expected to continue in the 21st century, cold temperature extremes are projected to decrease in frequency, while warm extremes will tend to increase significantly. Regarding precipitation, the regional intensity and frequency of extreme precipitation have increased in the past decades, while the total precipitation decreased in the region and the mean climate became drier. The projected changes in different seasons are opposite to each other; the extreme precipitation events are expected to become more intense and frequent in winter, while a general decrease of the extreme precipitation indices is expected in summer.

The role of weakest links and system size scaling in multiscale modeling of stochastic plasticity

Plastic deformation of crystalline and amorphous matter often involves intermittent local strain burst events. To understand the physical background of the phenomenon a minimal stochastic mesoscopic model was introduced, where microstructural details are represented by a fluctuating local yielding threshold. In the present paper, we propose a method for determining this yield stress distribution by lower scale discrete dislocation dynamics simulations and using a weakest link argument. The success of scale-linking is demonstrated on the stress-strain curves obtained by the resulting mesoscopic and the discrete dislocation models. As shown by various scaling relations they are statistically equivalent and behave identically in the thermodynamic limit. The proposed technique is expected to be applicable for different microstructures and amorphous materials, too.

[Carbon/carbon implants in oral and maxillofacial surgery--Part 2].

In their previous report, the authors presented observations regarding the long-term application of carbon/carbon implants. After evaluating the good functional and aesthetic results, the effect of the human body on the structure and morphology of the implants was investigated with state of the art methods. An implant retrieved from the body after eight years was compared to implants which were sterilized but not implanted (reference). Carbon and oxygen were the main components of both implants, however, as a result of the interaction with the human body the amount of oxygen increased 3-4 times and phosphorus, sulphur, calcium and iron were detectable as trace elements on the surface. The width of the carbon fibres (5-7 µm) building up the implants was not changed during the interaction with the human body. The surface of the implant retrieved from the human body was covered with a 15-17 µm thick layer, not present on the reference implant, having a similar composition to that of the carbon fibres (high amount of calcium that is typical to bone tissue was not detected). According to these results, the structure and the morphology of the implants were not altered notably by the human body.

Plastic strain is a mixture of avalanches and quasireversible deformations: Study of various sizes

Size-dependence of plastic flow is studied by discrete dislocation dynamical simulation of systems with various numbers of interacting linear edge dislocations while the stress is slowly increased. Regions between avalanches in the individual stress curves as functions of the plastic strain were found nearly linear and reversible, where the plastic deformation obeys an effective equation of motion with a nearly linear force. For small plastic deformation, the means of the stress-strain curves are power law over two decades. Here and for somewhat larger plastic deformations, the mean stress-strain curves converge for larger sizes, while their variances shrink, both indicating the existence of a thermodynamical limit. The converging averages decrease with increasing size, in accordance with size-effects from experiments. For large plastic deformations, where steady flow sets in, thermodynamical limit was not realized in this model system.