International Journal of Modern Physics C

Numerical simulations are performed to study the flow characteristic of laminar confined impinging streams using the lattice Boltzmann method (LBM). The velocity distributions for different flow conditions and geometric configurations are presented. By examination of the contours for the velocity magnitude, the size of the impingement zone is measured out for the first time. It is found that both the inlet jet Reynolds number and the geometry of the system have effects on the size of the impingement zone. Simulation results demonstrated that LBM is a potentially reliable computational tool for simulations of impinging streams.

In this paper a novel scheme of the lattice BGK (LBGK) model with a force term has been proposed. Unlike the existing models, an appropriate term was added in the evolutionary equation. Through the Chapman–Enskog (C–E) procedure the Navier–Stokes (N–S) equations with a force term can be recovered with the kinetic viscosity. Three discrete methods of the added term have been discussed in detail. It can be proved that some existing models are the special cases of the model in this paper. We have taken the numerical simulation of the generalized Poiseuille flow driven by a constant force in a channel filled with a porous medium of porosity flow in 2D with different values of the parameters and compared the three models of different discrete schemes in the aspect of the numerical accuracy and stability.

We present tight binding molecular dynamics simulations of the diffusion and bonding of hydrogen in bulk diamond. The motion of hydrogen atoms and the resultant structural and electronic energy level changes are investigated. The hydrogen atoms were found to have a tendency to migrate to the surface layer of diamond, resulting in a local deformation of the lattice, creating new energy states above and below the Fermi energy in the bandgap of the diamond density of states. In the diamond bulk, at high hydrogen concentrations, vacancies created by a hydrogen atom are quickly filled with other hydrogen atoms causing a deformation of the diamond lattice, inducing H₂ formation. This creates new energy states above the Fermi energy and reduces the secondary bandgap of the diamond density of states.

The structural and electronic properties of the DPPC molecule have been investigated theoretically by performing semi-empirical self-consistent-field molecular-orbital theory calculations at the PM3 level in its ground state.

In this paper, the reversibility problem for 150 Wolfram cellular automata is tackled for null boundary conditions. It is explicitly shown that the reversibility depends on the number of cells of the cellular automaton. The inverse cellular automaton for each case is also computed.

This paper proposes a universal constructor implemented on a self-timed cellular automaton, which is a particular type of asynchronous cellular automaton. Our construction utilizes the asynchronous nature of the underlying cellular automaton in a direct way, as a result of which it is simpler than the conventional construction based on the simulation of a synchronous cellular automaton by an asynchronous cellular automaton. Our model employs 39 rotation-invariant rules and the state of each cell is encoded by 8 bits.

We present a cellular-automaton model of a reaction-diffusion excitable system with concentration dependent inhibition of the activator, and study the dynamics of mobile localizations (gliders) and their generators. We analyze a three-state totalistic cellular automaton on a two-dimensional lattice with hexagonal tiling, where each cell connects with 6 others. We show that a set of specific rules support spiral glider-guns (rotating activator-inhibitor spirals emitting mobile localizations) and stationary localizations which destroy or modify gliders, along with a rich diversity of emergent structures with computational properties. We describe how structures are created and annihilated by glider collisions, and begin to explore the necessary processes that generate this kind of complex dynamics.

An approach for chaotifying a stable controllable linear system via single input state-feedback is presented. The feedback controller designed is a sawtooth function of the system states, which can make the fixed point of the closed-loop system to be a snap-back repeller, thereby yielding chaotic dynamics. Based on the Marotto theorem, it is proven theoretically that the closed-loop system is chaotic in the sense of Li and Yorke. Finally, the simulation results are used to illustrate the effectiveness of the proposed theory.

We discuss the results of a computer simulation of the biopolymer crystal growth and aggregation based on the 2D lattice Monte Carlo technique and the HP approximation of the biopolymers. As a modeled molecule (growth unit) we comparatively consider the previously studied non-mutant lysozyme protein, Protein Data Bank (PDB) ID: 193L, which forms, under a certain set of thermodynamic-kinetic conditions, the tetragonal crystals, and an amyloidogenic variant of the lysozyme, PDB ID: 1LYY, which is known as fibril-yielding and prone-to-aggregation agent. In our model, the site-dependent attachment, detachment and migration processes are involved. The probability of growth unit motion, attachment and detachment to/from the crystal surface are assumed to be proportional to the orientational factor representing the anisotropy of the molecule. Working within a two-dimensional representation of the truly three-dimensional process, we also argue that the crystal grows in a spiral way, whereby one or more screw dislocations on the crystal surface give rise to a terrace. We interpret the obtained results in terms of known models of crystal growth and aggregation such as B-C-F (Burton-Cabrera-Frank) dislocation driven growth and M-S (Mullins-Sekerka) instability concept, with stochastic aspects supplementing the latter. We discuss the conditions under which crystals vs non-crystalline protein aggregates appear, and how the process depends upon difference in chemical structure of the protein molecule seen as the main building block of the elementary crystal cell.

The investigation of community structures in complex networks is an important issue in many domains and disciplines. In this paper, we propose a novel method to address the problem based on evaluation of the community structure. By testing the proposed algorithm on artificial and real-world networks, experimental results demonstrate that our approach is both accurate and fast. Our algorithm may shed light on uncovering the universal principles of network architectures and topologies.

Research in network science has shown that many naturally occurring and technologically constructed networks are scale free, that means a power law degree distribution emerges from a growth model in which each new node attaches to the existing network with a probability proportional to its number of links (= degree). Little is known about whether the same principles of local attachment and global properties apply to societies as well. Empirical evidence from six ethnographic case studies shows that complex social networks have significantly lower scaling exponents γ ~ 1 than have been assumed in the past. Apparently humans do not only look for the most prominent players to play with. Moreover cooperation in humans is characterized through reciprocity, the tendency to give to those from whom one has received in the past. Both variables — reciprocity and the scaling exponent — are negatively correlated (r = -0.767, sig = 0.075). If we include this effect in simulations of growing networks, degree distributions emerge that are much closer to those empirically observed. While the proportion of nodes with small degrees decreases drastically as we introduce reciprocity, the scaling exponent is more robust and changes only when a relatively large proportion of attachment decisions follow this rule. If social networks are less scale free than previously assumed this has far reaching implications for policy makers, public health programs and marketing alike.

In Penna model, the genetic disease which influences the existence of individual has been described by bit-string. In fact, the individual will get extragenetic disease and die of that. In this paper we consider the extragenetic disease and discuss the influence of disease-resistant capability and cure on the existence of species.