The rate matching effect: A hidden property of aperiodic stochastic resonance

We study a system S generating Poisson events, and a corresponding dichotomous signal as well, perturbed by a system P, also generating Poisson events and a corresponding dichotomous signal. The rates of events productions for system and perturbation are gS and gP, respectively. We call S events the events produced by the system S and P events those produced by the perturbation P. We show that this simple model reproduces the essence of recent experimental and theoretical results on aperiodic stochastic resonance. More remarkably, this simplified version of aperiodic stochastic resonance allows us to discover a property that has been overlooked by the earlier research work. The rate matching condition gS=gP is the border between two distinctly different conditions: For gS<gP, the P events are attractors of the S events and for gS>gP they become repellers of the S events. The transition from the former to the latter condition is very marked and takes place in a short region of either gS or gP, depending on which is the parameter changed, thereby resulting in a discontinuous transition.     

Generic two-phase coexistence, relaxation kinetics, and interface propagation in the quadratic contact process: Analytic studies

The quadratic contact process is implemented as an adsorption-desorption model on a two-dimensional square lattice. The model involves random adsorption at empty sites, and correlated desorption requiring diagonal pairs of empty neighbors. A simulation study of this model [D.-J. Liu, X. Guo, J.W. Evans, Phys. Rev. Lett. 98 (2007) 050601] revealed the existence of generic two-phase coexistence between a low-coverage active steady-state and a completely covered absorbing state. Here, an analytic treatment of model behavior is developed based on truncation approximations to the exact master equations. Applying this approach for spatially homogeneous states, we characterize steady-state behavior as well as the kinetics of relaxation to the steady-states. Extending consideration to spatially inhomogeneous states, we obtain discrete reaction-diffusion type equations characterizing evolution. These are employed to analyze an orientation-dependence of the propagation of planar interfaces between active and absorbing states which underlies the generic two-phase coexistence. We also describe the dynamics and critical forms of planar perturbations of the active state and of droplets of one phase embedded in the other.     

Resonant phenomena in extended chaotic systems subject to external noise: The Lorenz’96 model case

We have investigated the effects of noise on an extended chaotic system. The chosen model is the Lorenz’96, a type of “toy” model used for climate studies. Through the analysis of the system’s time evolution and its time and space correlations, we have obtained numerical evidence for two distinct stochastic resonance-like behaviors. Such behaviors are seen when both the usual and a generalized signal-to-noise ratio functions are depicted as a function of the external noise intensity, or of the system size. The underlying mechanisms seem to be associated with a noise-induced chaos reduction. The possible relevance of these and other findings for an optimal climate prediction are discussed.     

Application of spectral methods for high-frequency financial data to quantifying states of market participants

Empirical analysis of the foreign exchange market is conducted based on methods to quantify similarities among multi-dimensional time series with spectral distances introduced in [A.-H. Sato, Physica A 382 (2007) 258-270]. As a result it is found that the similarities among currency pairs fluctuate with the rotation of the earth, and that the similarities among best quotation rates are associated with those among quotation frequencies. Furthermore, it is shown that the Jensen-Shannon spectral divergence is proportional to a mean of the Kullback-Leibler spectral distance both empirically and numerically. It is confirmed that these spectral distances are connected with distributions for behavioural parameters of the market participants from numerical simulation. This concludes that spectral distances of representative quantities of financial markets are related into diversification of behavioural parameters of the market participants.     

Evolution of growth and enhancement in power factor of InSb bulk crystal

Indium antimonide crystals were synthesized from the respective component elements using the vertical Bridgman technique. The grown crystals were characterized by using X-ray analysis, EDX, electrical conductivity and thermoelectric power measurements. The calculated structural parameters for the prepared crystal have a good agreement with the standard values. Crystallite size (D) of the obtained InSb crystals was calculated to be 62.4 nm. The measurements reveal higher values for Seebeck coefficient, electrical conductivity and power factor than the published results for the same compound.     

Coupling of electron spin with its rotation in semiconductors

The interplay between spin-orbit interaction in semiconductor valence bands and an adiabatic rotational distortion of the wave function of a charge carrier leads to the scalar spin-orbit-rotation term in the effective-mass Hamiltonian of the conduction-band electron. The physical origin of this result lies in the fact that, similarly to magnetic field effects, the motion of a particle and the phase of its wave function may be affected by the vector potential of the inertial Coriolis field. Here we present a straightforward derivation of this interaction within the multiband envelope function approximation.     

Optical properties and origin of infrared light scattering centers in undoped semi-insulating GaAs crystals

The wavelength dependence and polarization characteristics of the infrared light scattered from an undoped GaAs crystal were investigated in the 90° angle infrared light scattering configuration. The scattering is Rayleigh scattering from scatterers which are always associated with the dislocations, and they are classified into three types,S, L _A , andL _G scatterers, according to their polarization characteristics. TheS, L _A , andL _G -scatterers are thought to be small As clusters, large As precipitates and large Ga precipitates, respectively.     

Temperature dependence of persistent photo-conductivity due to DX centers in AlxGa1−xAs:Si

Conductivity and Hall effect measurements were performed on molecular beam epitaxy grown Al_xGa_1–xAs:Si samples, which show a large persistent photoconductivity effect. We observe one, two, and three minima in the temperature-dependent carrier concentration during the heating process after having first illuminated the samples (x=0.25, 0.30, and 0.37, respectively) at low temperature. We interpret this structure in terms of the existence of different types of large lattice relaxation DX centers.     

On the geometrical representation of the Jacobian in the path integral reduction problem

By using the formula for the scalar curvature of the manifold with the Kaluza-Klein metric we obtain the geometrical representation of the Jacobian resulted from the path integral reduction problem in Wiener path integrals for a scalar particle on a smooth compact Riemannian manifold with the given free isometric action of the compact semisimple Lie group.     

Fibril stability in solutions of twisted -sheet peptides: a new kind of micellization in chiral systems

The problem of fibril (fibre) formation in chiral systems is explored theoretically being supported by experiments on synthetic de novo 11-mer peptide forming self-assembled -sheet tapes. Experimental data unambiguously indicate that the tapes form fibrils of nearly monodisperse thickness ca . 8-10 nm. Fibril formation and stabilisation are attributed to inter-tape face-to-face attraction and their intrinsic twist, correspondingly. The proposed theory is capable of predicting the fibril aggregation number and its equilibrium twist in terms of molecular parameters of the primary tapes. The suggested novel mechanism of twist stabilisation of finite aggregates (fibrils) is different to the well-known stabilisation of micelles in amphiphilic systems, and it is likely to explain the formation and stability of fibrils in a wide variety of systems including proteinaceous amyloid fibres, sickle-cell hemoglobin fibres responsible for HbS anemia, corkscrew threads found in chromonics in the presence of chiral additives and native cellulose microfibrillar crystallites. The theory also makes it possible to extract the basic molecular parameters of primary tapes (inter-tape attraction energy, helical twist step, elastic moduli) from the experimental data. Received 7 May 1999 and Received in final form 15 February 2000