Model of coexistence of annual plants in a heterogeneous habitat

We propose a computer simulation type model describing dynamics of a system of annual plants competing for just one resource and living in a heterogeneous habitat. Plants do interact via blocking a part of the resource in the nearest neighbourhood. Species differ in only one aspect – demand for the resource. Plant which has supply equal demand has the largest probability to survive, while any deviation diminishes it. Heterogeneity in space is introduced in two ways - by a gradient reducing supply along one axis and a system of patches, each having a different level of the resource. We show that without any trade-off mechanism, speciation or immigrants, coexistence of species is possible in a stationary state. We find out also that the two descriptions of the heterogeneity lead to nearly the same numbers of surviving species, although the spatial structures and order of abundance of the populations are different

The Effect of Solid Inhibitors on Hydrogen-air Combustion

The use of hydrogen as an energy carrier is a promising solution for enabling the transition towards increased use of renewable energy sources in the global energy mix. However, hydrogen-air mixtures are highly reactive, and conventional technologies for explosion protection have limited applicability for hydrogen systems. As such, it is not straightforward to achieve the same level of safety for hydrogen energy systems, compared to systems based on conventional hydrocarbon fuels. The last decades have seen the development of innovative solutions for chemical inhibition of vapour cloud explosions with solid inhibitors, such as sodium bicarbonate and potassium carbonate (Roosendans and Hoorelbeke, 2019). Both substances are non-toxic, non-flammable, lowcost and relatively harmless to the environment, compared to for example halons. Although solid suppressants can be highly effective for hydrocarbons (Babushok and Tsang, 2000), experiments indicate that the same compounds are not very effective for the inhibition of hydrogen-air mixtures. The absence of carbon implies that hydrogen combustion is inherently different from hydrocarbons, however, the combustion of hydrocarbons includes the elementary reactions involved in combustion of hydrogen-air mixtures. These elementary reactions change when exposed to solid inhibitors like sodium or potassium compounds (Roosendans, 2018). Simulations of chemical kinetics based on these elementary reactions show that potassium compounds should yield a significant reduction of flame velocity. The same simulations show a significantly higher generation of radicals for hydrogen combustion compared to hydrocarbon combustion. Thus, more inhibitor is needed for effective inhibition of premixed hydrogen-air flames. For a solid inhibitor to be effective, the compound must evaporate in the flame zone, and this process appears to be the main hurdle for effective inhibition of hydrogen explosions. This paper presents results from dedicated experiments and simulations with chemical kinetics software that elaborate on previous findings and improve the understanding of the underlying mechanics of solid inhibitors in hydrogen-air combustion.publishedVersio

Introducing Small-World Network Effect to Critical Dynamics

We analytically investigate the kinetic Gaussian model and the one-dimensional kinetic Ising model on two typical small-world networks (SWN), the adding-type and the rewiring-type. The general approaches and some basic equations are systematically formulated. The rigorous investigation of the Glauber-type kinetic Gaussian model shows the mean-field-like global influence on the dynamic evolution of the individual spins. Accordingly a simplified method is presented and tested, and believed to be a good choice for the mean-field transition widely (in fact, without exception so far) observed on SWN. It yields the evolving equation of the Kawasaki-type Gaussian model. In the one-dimensional Ising model, the p-dependence of the critical point is analytically obtained and the inexistence of such a threshold p_c, for a finite temperature transition, is confirmed. The static critical exponents, gamma and beta are in accordance with the results of the recent Monte Carlo simulations, and also with the mean-field critical behavior of the system. We also prove that the SWN effect does not change the dynamic critical exponent, z=2, for this model. The observed influence of the long-range randomness on the critical point indicates two obviously different hidden mechanisms.Comment: 30 pages, 1 ps figures, REVTEX, accepted for publication in Phys. Rev.