International Journal of Modern Physics C

We present the main results of our microcanonical simulation of the Wess–Zumino–Witten action functional. This action, being highly nontrivial and capable of exhibiting many different phase transitions, is chosen to be representative of general complex actions. We verify the applicability of microcanonical simulation by successfully obtaining two of the many critical points of the Wess–Zumino–Witten (WZW) action. The microcanonical algorithm has the additional advantage of exhibiting critical behavior for a small 8 × 8 lattice. We also briefly discuss the subtleties that, in general, arise in simulating a complex action. Our algorithm for complex actions can be extended to the study of D-branes in the WZW action.

In this work we study the distribution of time intervals between avalanches in a rice pile model. This model has shown that the crossover from power law to stretched exponential behaviors observed experimentally in the granular dynamics of rice piles can be well described as a long-range effect resulting from a change in the transport properties of individual grains. In this work we show that the change in the transport properties is also reflected in the behavior of the distribution of time intervals between avalanches.

Surface growth in random media is usually governed by both the surface tension and the random local forces. Simulations on lattices mimic the former by imposing a maximum gradient m on the surface heights, and the latter by site-dependent random growth probabilities. Here we consider the limit m → ∞, where the surface grows at the site with minimal random number, independent of its neighbors. The resulting height distribution obeys a simple scaling law, which is destroyed when local surface tension is included. Our model is equivalent to Yee's simplification of the Bak–Sneppen model for the extinction of biological species, where the height represents the number of times a biological species is exchanged.

Infrared absorption on GaAs doped with the isotopes of silicon under hydrogen or deuterium plasma treatment has shown the presence of two new localized modes, all in the range of 625–1725 cm^-1. We present a simple nine-atom molecular model to compute these defect modes by assuming the hydrogen or deuterium to be bound in the antibonding position of the substituted Si atom, resulting in a defect complex of C_3V symmetry. The two new vibrational modes of the paired Si are found with a small isotope shift, when H is replaced by D. Group theoretical methods are employed for the precise identification of the localized modes.

Using a hybrid simulation method, structural and dynamic response properties of chain macromolecules are studied in a heterogeneous gel matrix in presence of an electrophoretic field E(t) = E_b + E_ssin(2π ft), where E_b is the static field and E_s is the amplitude of sinusoidal field of frequency f. We find that the oscillating field enhances the macromolecular mobility at E_s > E_b while it becomes ineffective at E_s < E_b, consistent with the experimental work of Masubuchi et al. Enhanced segmental and global movement of molecules at E_s > E_b leads to interesting effects such as (i) a significant decrease in molecular clustering, (ii) reduced radius of gyration, and (iii) its linear response to E_b. Power law behavior of molecular motion, i.e., the variation rms displacement (R) with the time steps (t), R ∝ t^ν, is sensitive to temperature, molecular weight, and field.

A new model for stock markets using integer values for each stock price is presented. In contrast with previously reported models, the variables used in the model are not of binary type, but of more general integer type. It is shown how the behavior of the noise and fundamentalists traders can be taken into account simultaneously in the time evolution of each stock price. The simulated time series generated by the model is analyzed in different ways order to compare parameters with those of real markets.

We consider a variant of the so-called Bornholdt spin model of a market dynamics, in which the random couplings with neighbors are incorporated. We observe that the occurrence of high returns decreases with a power law as the number of market participants becomes large up to three dimension.

In this paper, numerical results on two-dimensional vapor–liquid equilibrium calculated by lattice Boltzmann method have been presented. Artefacts resulted by the finite lattice-size have been reviewed. A set of criteria for minimal lattice-size to avoid lattice artefacts is given.

Fuzzy logic represents an extension of classical logic, giving modes of approximate reasoning in an environment of uncertainty and imprecision. Fuzzy inference systems incorporates human knowledge into their knowledge base on the conclusions of the fuzzy rules, which are affected by subjective decisions. In this paper we show how the reinforcement learning technique can be used to tune the conclusion part of a fuzzy inference system. The fuzzy reinforcement learning technique is illustrated using two examples: the cart centering problem and the autonomous navigation problem.

An accelerated version of the lattice Boltzmann equation aimed at fast attainment of steady-state flow conditions is presented. Significant computational savings as compared to the standard explicit LBE scheme are obtained for cavity flows in two dimensions.

Muon reactivation coefficient are determined for muonic He for up to six (n = 1, 2, 3, …, 6) states of formation and at temperature T_p = 100 eV and for various relative ion densities. In the next decade it may be possible to explore new conditions for further energy gain in muon catalyzed fusion system, μCF, using nonuniform (temperature and density) plasma states. Here, we have considered a model for inhomogeneous μCF for mixtures of D/T and H/D/T. Using coupled dynamical equations it is shown that the neutrons yield per muon injection, Y_n (neutrons/muon), in the dt branch of an inhomogeneous H/D/T mixture is at least 2.24 times higher than similar homogeneous systems and this rate for a D/T mixture is 1.92. Also, we have compared the neutron yield in the dt branch of homogeneous D/T and H/D/T mixtures (temperature range T = 300–800 K, and density ϕ = 1 LHD). It is shown that Y_n(D/T)/Y_n(H/D/T) = 1.32, which is in good agreement with recently measured experimental values. In other words our calculations show that the addition of protonium to a D/T mixture leads to a significant decrease in the cycling rate for the physical conditions described herein.

Monte Carlo simulation (MCS) on the thermal properties in Gd–Mg alloy becomes essential as there are only limited experiments available. A realistic Johnson potential is used to workout the specific heats for various temperatures and hence the Debye temperature. The results from the present simulation technique are very well compared with our shell model calculation. The need of better X-ray measurements for Debye–Waller factor and Debye temperature other than the measurements of Subadhra and Sirdeshmukh, is discussed in detail.