International Journal of Modern Physics C

We show that the dramatic dependence of pressure on the parameters of the inter-molecular potential can be exploited to tune them to their best values. We support the viability of this strategy by a careful study of a fully diffusive Lennard–Jones fluid, showing that Lennard–Jones parameters can be easily optimized to better than a 1% accuracy.

The three-dimensional structures of the heptapeptide deltorphin (H-Tyr¹-D-Met²-Phe³-His⁴-Leu⁵-Met⁶-Asp⁷-NH₂) are studied in aqueous solution using Energy Landscape Paving (ELP) method. The effect of a solvation energy term on the conformations are determined by analyzing Ramachandran plots. The structures are compared with experimental NMR data. By minimizing the energy structures, the low-energy microstates of the molecule in aqueous solution are determined.

In this work, we extend the recursive search method to locate the critical point and to obtain the relevant critical exponents of a nonequilibrium phase transition. In particular, the method is applied to the contact process which presents a nonequilibrium phase transition between a steady active to a single inactive absorbing state belonging to the directed percolation universality class. We present the appropriate scaling analysis which allows for precise estimates of the critical parameters with a relatively small computational effort. The proposed scheme can be directly applied to general model systems presenting nonequilibrium transitions into absorbing states including reaction–diffusion and pair contact processes.

In the consensus model with bounded confidence, studied by Deffuant et al. (2000), two randomly selected people who differ not too much in their opinion both shift their opinions towards each other. Now we restrict this exchange of information to people connected by a scale-free network. As a result, the number of different final opinions (when no complete consensus is formed) is proportional to the number of people.

Permutation group approach to the one-dimensional XXX Heisenberg open spin-1/2 chain with nearest neighbor interaction is proposed, which is formulated not only for half-filling excitations, but also for general case. Regularity of energy matrices and the corresponding wavefunctions are made up by using an induction method, which makes it possible to study the eigenvalue problem systematically. A Mathematica package for generating the energy matrices is implemented according to this procedure.

An algorithm to generate toroidal or helical cage structures has been developed. Any toroidal or helical structure can be generated following four stages. In the first stage a Fonseca type unit cell and its symmetrical counterpart is formed which represents one-fifth of a toroid. In the second stage one-fifth fragment of the torus is fully obtained by applying geometry optimization to the structure obtained in the first stage. In the third stage the torus fragment obtained in the second stage is reproduced five times and connected to each other to generate either toroidal or helical structure. In the last stage a final optimization process is reapplied to get the complete structure desired.

Here is a sand-pile introduced by Bak et al. The system accumulates particles one by one. From time to time it topples. Every toppling initiates an event. The distribution of the events' size follows a power law for all the events except the strongest ones. The fraction of the strongest events does not depend on the system length. The number of particles and their clustering increase before the strongest events.

Using a lattice model based on Monte Carlo simulations, we study the role of the reproduction pattern on the fate of an evolving population. Each individual is under the selection pressure from the environment and random mutations. The habitat ("climate") is changing periodically. Evolutions of populations following two reproduction patterns are compared, asexual and sexual. We show, via Monte Carlo simulations, that sexual reproduction by keeping more diversified populations gives them better chances to adapt themselves to the changing environment. However, in order to obtain a greater chance to mate, the birth rate should be high. In the case of low birth rate and high mutation probability there is a preference for the asexual reproduction.

We removed from the Penna model for biological aging any random killing Verhulst factor. Deaths are due only to genetic diseases and the population size is fixed, instead of fluctuating around some constant value. We show that these modifications give qualitatively the same results obtained in an earlier paper, where the random killings (used to avoid an exponential increase of the population) were applied only to newborns.

In the present paper, a comparative study of numerical solutions for steady flows with heat transfer based on the finite volume method (FVM) and the relatively new lattice Boltzmann method (LBM) is presented. In the last years, the LB methods have challenged the classical FV methods to solve the Navier–Stokes equations and have proven to be superior in accuracy and efficiency for certain applications. Most of these studies were related to the transport of mass and momentum. In the meantime, significant effort has been invested in the application of the LBM to simulate flows including heat transfer. The studies in the present paper are the analysis of performance and accuracy aspects of LBM applied to the prediction of these flows. For a fully developed laminar flow between parallel plates, analytical solutions for the heat transfer in fully developed thermal boundary layers are available and may be compared with the respective numerical results. Finally, a hybrid approach is proposed to circumvent numerical problems of the thermal LB methods.

In high-T_c superconductors dopant atoms supply holes or excess electrons, and electric conduction is established in the neighborhood of the dopant. We propose that percolation of these conducting areas leads to global electric conduction. To investigate these processes numerical procedures to simulate continuum percolation are developed. The relation between the concentration of connecting discs and the fraction of the area of the plane covered by all discs is computed in the whole range between next nearest neighbor site percolation and continuum percolation. This method is applied to investigate underdoped copper oxides where small hole or excess electron concentrations are insufficient to establish electric conduction. The results of this study are applied to the model of mobile charge carriers which consist of or are accompanied by diffusing d-electrons. Our investigations show that with increasing doping the Neel temperature of the antiferromagnetism vanishes and spin glass states appear in accordance with experiments. Furthermore, the peaks in the specific heat become very broad. This broadening due to randomness and loss of translation invariance has been observed in nuclear magnetic resonance peaks of doped superconducting cuprates.

Isothermal gas flows in microchannels is studied using the lattice Boltzmann method. A novel equation relating Knudsen number with relaxation time is derived. The slip-velocity on the solid boundaries is reasonably realized by combining the bounce-back reflection with specular reflection in a certain proportion. Predicted characteristics in a two-dimensional microchannel flow, including slip-velocity, nonlinear pressure drop, friction factors, velocity distribution along the streamwise direction and mass flow rate, are compared with available analytical and experimental results and good agreement is achieved.