arXiv subjects

K. Malarz

Publications and source records attributed to K. Malarz.

47 records · Page 3Linked to original sources

arXiv2003

Average distance in growing trees

Two kinds of evolving trees are considered here: the exponential trees, where subsequent nodes are linked to old nodes without any preference, and the Barabási--Albert scale-free networks, where the probability of linking to a node is proportional to the number of its pre-existing links. In both cases, new nodes are linked to $m=1$ nodes. Average node-node distance $d$ is calculated numerically in evolving trees as dependent on the number of nodes $N$. The results for $N$ not less than a thousand are averaged over a thousand of growing trees. The results on the mean node-node distance $d$ for large $N$ can be approximated by $d=2\ln(N)+c_1$ for the exponential trees, and $d=\ln(N)+c_2$ for the scale-free trees, where the $c_i$ are constant. We derive also iterative equations for $d$ and its dispersion for the exponential trees. The simulation and the analytical approach give the same results.

cond-mat.stat-mech↗

arXiv2003

New algorithm for the computation of the partition function for the Ising model on a square lattice

A new and efficient algorithm is presented for the calculation of the partition function in the $S=\pm 1$ Ising model. As an example, we use the algorithm to obtain the thermal dependence of the magnetic spin susceptibility of an Ising antiferromagnet for a $8\times 8$ square lattice with open boundary conditions. The results agree qualitatively with the prediction of the Monte Carlo simulations and with experimental data and they are better than the mean field approach results. For the $8\times 8$ lattice, the algorithm reduces the computation time by nine orders of magnitude.

cond-mat↗

arXiv2002

Social phase transition in Solomon network

In this paper the Solomon network is simulated by means of 1D and 2D Ising model with additional -- not only geometrical -- neighbors. A "social phase transition" at a non-zero Curie-like temperature is observed, also in one dimension. The critical exponent describing the behavior of the magnetization in the vicinity of the transition is also evaluated.

cond-mat↗

arXiv2002

Chaotic Dynamics of Forest Fires

In the thermodynamic limit, a probabilistic cellular automaton can be approximated by a deterministic nonlinear map. Here we construct such a map for the forest fire problem. The construction is based on the results of the Monte Carlo simulation, performed on a square lattice of million cells. The results of the calculation are analyzed by means of the Hoshen--Kopelman algorithm (HKA). The only parameter of the map describes the probability that a tree appears at an empty cell during one time step. The obtained map seems to be non-differentiable at the percolation threshold. The Lyapunov exponent for the map is positive. Also, we found the cycle of length three by means of the method of symbolic dynamics. The results are illustrated by the experimental data on the forest fires in Canada in years 1970--2000. Although these data are fortunately far from thermodynamic limit, their qualitative character is reproduced for smaller lattices.

cond-mat↗

arXiv2002

Are Forest Fires Predictable?

Dynamic mean field theory is applied to the problem of forest fires. The starting point is the Monte Carlo simulation in a lattice of million cells. The statistics of the clusters is obtained by means of the Hoshen--Kopelman algorithm. We get the map $p_n\to p_{n+1}$, where $p_n$ is the probability of finding a tree in a cell, and $n$ is the discrete time. We demonstrate that the time evolution of $p$ is chaotic. The arguments are provided by the calculation of the bifurcation diagram and the Lyapunov exponent. The bifurcation diagram reveals several windows of stability, including periodic orbits of length three, five and seven. For smaller lattices, the results of the iteration are in qualitative agreement with the statistics of the forest fires in Canada in years 1970--2000.

cond-mat↗

arXiv2001

Cooperation and Surviving with Limited Resources

A network of agents cooperate on a given area. Time evolution of their power is described within a set of nonlinear equations. The limitation of resources is introduced via the Verhulst term, equivalent to a global coupling. Each agent is fed by some other agents from his neighborhood. Two subsequent stages of the time evolution can be observed. Initially, the richness of everybody increases distinctly, but its distribution becomes wide. After some transient time, however, resources are exhausted. Richness of some agents falls to zero and they are eliminated. Cooperation becomes less effective, what leads to subsequent falls. Finally, small percent of agents survive in a steady state. We investigate, how the cooperation influences the rate of surviving.

cond-mat↗

arXiv2001

A simple solid-on-solid model of epitaxial film growth: submonolayer substrate coverage

In this work we investigate influence of substrate temperature on the surface morphology for substrate coverage below one monolayer. The model of film growth is based on random deposition enriched by limited surface diffusion. Also anisotropy in the growth is involved. We found from computer simulations for simple cubic lattice and solid-on-solid model, that the surface morphology changes with increasing temperature from isotropically distributed isolated small islands, through anisotropic 1-D stripes to larger 2-D anisotropic islands and again randomly distributed single atoms. The transition is also marked in height-height correlation function dependence on temperature, as directly seen by snapshots from simulations. The results are in good qualitative agreement with already published results of kinetic Monte Carlo simulations, as well as with some experimental data.

cond-mat↗

arXiv2000

Advantages and Disadvantages of Layer Growth Model in Which Particles Maximize Number of Lateral Bonds

In this paper we would like give a short review of our recent works and current investigation in modeling of solid film surfaces growth based on computer Monte Carlo simulations. We also discuss effect of some simplification in growth rules on speed-up of computations, and the time evolution of surface morphology (for example its roughness or anisotropy). We obtained qualitative agreement of computer simulation with experimental results for homoepitaxially grown simple metal films.

cond-mat↗

arXiv1999

A simple solid-on-solid model of epitaxial thin films growth: inhomogeneous multilayered sandwiches

In this work a simple solid-on-solid (SOS) model of inhomogeneous films epitaxial growth is presented. The results of the computer simulations based on the random deposition (RD) enriched by a local relaxation which tends to maximize the number of a particle-particle lateral bonds (PPLB) against barriers blocking diffusion are presented. The influence of strength of the atoms interactions and barriers for diffusion on film roughness and possible bridges between the layers in tri-layered sandwich system are considered. For magnetic layers with a nonmagnetic spacer the bridging is responsible for direct magnetic coupling between layers. Also variations of the spacer thickness, when scanning the film surface, is essential for uniformity of the magnetic coupling between the layers. Number of bridges for very thin spacer, and variation of the spacer thickness are discussed in this work.

cond-mat↗

arXiv1999

A simple solid-on-solid model of epitaxial thin films growth: surface roughness and dynamics

The random deposition model must be enriched to reflect the variety of surface roughness due to some material characteristics of the film growing by vacuum deposition or sputtering. The essence of the computer simulation in this case is to account for possible surface migration of atoms just after the deposition, in connection with binding energy between atoms (as the mechanism provoking the diffusion) and/or diffusion energy barrier. The interplay of these two factors leads to different morphologies of the growing surfaces from flat and smooth ones, to rough and spiky ones. In this paper we extended our earlier calculation by applying some extra diffusion barrier at the edges of terrace-like structures, known as Ehrlich-Schwoebel barrier. It is experimentally observed that atoms avoid descending when the terrace edge is approach and these barriers mimic this tendency. Results of our Monte Carlo computer simulations are discussed in terms of surface roughness, and compared with other model calculations and some experiments from literature. The power law of the surface roughness $σ$ against film thickness $t$ was confirmed. The nonzero minimum value of the growth exponent $β$ near 0.2 was obtained which is due to the limited range of the surface diffusion and the Ehrlich-Schwoebel barrier. Observations for different diffusion range are also discussed. The results are also confronted with some deterministic growth models.

cond-mat↗

arXiv1999

A simple solid-on-solid model of epitaxial thin films growth: surface morphology anisotropy

In this paper we present a generalization of a simple solid-on-solid epitaxial model of thin films growth, when surface morphology anisotropy is provoked by anisotropy in model control parameters: binding energy and/or diffusion barrier. The anisotropy is discussed in terms of the height-height correlation function. It was experimentally confirmed that the difference in diffusion barriers yields anisotropy in morphology of the surface. We got antisymmetric correlations in the two in-plane directions for antisymmetric binding.

cond-mat↗