International Journal of Modern Physics B

We introduce a helix-based complex, which we will call a multiply-twisted helix, in which a one-dimensional array of components, e.g. atoms or nanoclusters, is twisted, producing a helix, which if itself twisted, produces a doubly-twisted helix, which we can think of as the simplest multiply-twisted helix. In the hierarchy of helical structures, the mean number of nearest neighbors can be controlled by adjusting the number of components in a round of helices. The Hubbard model is used to analyze the Mott transition in a multiply-twisted helix, where electrons can move not only along a one-dimensional array but also between sub-rounds in adjacent larger rounds. The critical strength of electron–electron interaction in a Mott transition can also be controlled by adjusting the number of components in a round, as suggested by our mean-field analysis of half-filled electrons.

Low-temperature equilibrium dynamical behavior of the linear ac susceptibility in d-dimensional Ising spin glass with short-range interactions between spins in transverse field is investigated in terms of droplet model. The real part of linear ac susceptibility as functions of temperature T and frequency of external ac field ω is calculated. Frequency and temperature dependence of shows a glassy behavior. For instance, we find a broad maximum for which shifts towards higher temperatures with increasing frequency of ac-field. The temperature of maximum T_f(ω) depends on frequency and increases with frequency up to the magnitude where starts to decrease.

A qualitative agreement of our calculations with experimental data, for example, in quantum dipole magnet LiHo_xY_1-xF₄ and proton glasses, is found.

We investigate the Hubbard Hamiltonian's properties in the continuum limit by implementing the procedures of the Method of Coherent Structures (MCS). We obtain field equations of motion and analyse the phase dynamics of the resultant classical spin fields. We have performed analytical and numerical calculations to find appropriate physically acceptable solutions to the equations of motion in one-dimensional space. In two-dimensional space, among other types, we have found several different spin phases of vortex type, spiral patterns and parabolic spin arrangements. Our results are consistent with earlier Hartree–Fock finite-grid numerical simulations.

In a previous publication we derived a criterion for defining interatomic surfaces in condensed systems based on the zero flux surface (ZFS) of the electronic wavefunction's gradient which holds the condition of flux zero at every point. Here this criterion is examined and physical as well as mathematical properties are illustrated and discussed; in the light of this discussion we conclude that the definition illustrated in this work represents a natural extension of Bader's definition of atoms in molecules.

Linear theory for phonon scattering by discrete breathers in the discrete nonlinear Schrödinger equation using the transfer matrix approach is presented. Transmission and reflection coefficients are obtained as a function of the wave vector of the input phonon. The occurrence of a nonzero transmission, which in fact becomes perfect for a symmetric breather, is shown to be connected with localized eigenmodes thresholds. In the weak-coupling limit, the perfect reflection is shown to exist, which requires two scattering channels. A necessary condition for a system to have a perfect reflection is also considered in a general context.

This paper describes a new self-adapting control algorithm for reactive autonomous agents. The architecture of the autonomous agents integrates the reactive behavior with reinforcement learning. We show how these components perform on-line adaptation of the autonomous agents to various complex navigation situations by constructing an internal model of the environment. Also, a discussion on cooperation and coordination of teams of agents is presented.

Some homologues of alkyloxy cyanobipheny1 (6OCB, 8OCB, 9OCB, 10OCB) have been investigated by employing positron lifetime spectroscopy. In each of these compounds, temperature dependent positron lifetime measurements have been carried out, both in the heating as well as cooling cycles. Besides detecting many interesting features like solid-crystalline polymorphism, anti-parallel bimolecular association, formation of cybotactic groups in the nematic phase, positron annihilation parameters have been able to reveal anomalous structural changes taking place in these compounds.