Table of contents

This letter reports on a stochastic dynamical scenario whose associated stationary probability density function is exactly a generalised form, with a power law instead of exponencial decay, of the ubiquitous Gamma distribution. This generalisation, also known as F-distribution, was empirically proposed for the first time to adjust for high-frequency stock traded volume distributions in financial markets and verified in experiments with granular material. The dynamical assumption presented herein is based on local temporal fluctuations of the average value of the observable under study. This proposal is related to superstatistics and thus to the current nonextensive statistical mechanics framework. For the specific case of stock traded volume, we connect the local fluctuations in the mean stock traded volume with the typical herding behaviour presented by financial traders. Last of all, NASDAQ 1 and 2 minute stock traded volume sequences and probability density functions are numerically reproduced.

We show that if we consider the full statement of Faraday's law for a closed physical circuit, the standard Maxwell's equations in the presence of electric and magnetic charges have to include in their integral form a mixed term of the form ρ_mv_e^⊥, where ρ_m is the magnetic charge density and v_e^⊥ the perpendicular component of the velocity v_e of the electric charge.

A novel non-perturbative method of solving scattering problems for bound pairs on a lattice is developed. Two different break-ups of the Hamiltonian are employed to calculate the full Green operator and the wave function of the scattered pair. The calculation converges exponentially in the number of basis states used to represent the non-translation–invariant part of the Green operator. The method is general and applicable to a variety of scattering and tunneling problems. As the first application, the problem of pair tunneling through a weak link on a one-dimensional lattice is solved. It is found that at the momentum values close to ±π the pair tunnels much easier than one particle, with the transmission coefficient approaching unity. This anomalously high transmission is a consequence of the existence of a two-body resonant state localized at the weak link.

A well-known problem with the many-body approximations for interacting condensed bosons is the dichotomy between the "conserving" and "gapless" approximations, which either obey the conservations laws or satisfy the Hugenholtz-Pines condition for a gapless excitation spectrum, in the order. It is here shown that such a dichotomy does not exist for a system of composite bosons, which form as bound-fermion pairs in the strong-coupling limit of the fermionic attraction. By starting from the constituent fermions, for which conserving approximations can be constructed for any value of the mutual attraction according to the Baym-Kadanoff prescriptions, it is shown that these approximations also result into a gapless excitation spectrum for the boson-like propagators in the broken-symmetry phase.

We study time-delayed feedback control of noise-induced oscillations analytically and numerically for the paradigmatic model of the Van der Pol oscillator under the influence of white noise. We focus on the regime below the Hopf bifurcation where the deterministic system has a stable fixed point and does not exhibit oscillations. Analytical expressions for the power spectral density and the coherence properties of the stochastic delay differential equation in dependence upon noise intensity, delay time, and feedback strength are derived on the basis of a mean-field approximation, and are in good agreement with our numerical simulations of the full nonlinear model. Our analytical results elucidate how the correlation time of the controlled stochastic oscillations can be maximized as a function of delay time and feedback strength.

Multi-electron giant dipole resonances of atoms in crossed electric and magnetic fields are investigated. Stationary configurations corresponding to a highly symmetric arrangement of the electrons on a decentered circle are derived, and a normal-mode stability analysis is performed. A classification of the various modes, which are dominated either by the magnetic or Coulomb interactions, is provided. A six-dimensional wave-packet dynamical study, based on the MCTDH approach, is accomplished for the two-electron resonances, yielding in particular lifetimes of more than 0.1 μs for strong electric fields.

Electronic energy level patterns of small stable, pre-designed clusters composed of In, Ga and As atoms are calculated using a multi-configuration self-consistent field approximation. The structure and composition of the clusters are chosen to reflect their formation in confinement or on surfaces. Manipulations with these parameters permit to engineer computationally clusters with pre-designed electronic properties. Such virtually synthesized atomic clusters can serve as prototypes for experimental sub-nanoscale heterostructure (SNHS) units. Stability of such clusters was confirmed recently by experiment.

We propose a method to measure the entanglement of nearby spins by means of multiphoton correlation interference patterns generated by the scattering of two perpendicular pulsed laser beams with opposite circular polarization. As this method is based on optical read-out only, it provides the possibility to monitor with minimal intrusion the evolution and the decoherence of many-spin entanglement. This method is capable of retrieving all the amplitudes of a general many-spin state of arbitrary dimension. Explicit calculations are presented for a quantum dot spin system.

The 1.5 μm fluorescence shape and lifetime of Er^{3 +} -activated tellurite glasses have been investigated. The measures on bulk system have been compared with those obtained on powders, showing that the self-absorption effect broadens the emission spectrum and lengthens the lifetime. It has been demonstrated that the bandwidth and lifetime measurements depend on the absorption coefficient α(λ) and on the distance d between the focused exciting laser beam and the exit face of a bulk glass sample. The actual emission spectrum has been reconstructed from the α(λ)·d knowledge. Lifetime lengthening cannot be determined from α(λ)·d and, to obtain actual lifetime for highly Er^{3 +} -doped glasses, measurements on powders are required.

The impact of small drops on a water-covered sand bed provides a simple physical system to study erosion, sand entrainement and pattern formation. The patterns evidenced here start out nicely circular but this circular symmetry gets lost once the dropping frequency increases above threshold. Three-dimensional structures then form and grow logarithmically in time.

Breakdown and extinction curves have been measured for RF capacitive low-pressure discharges in nitrogen and hydrogen at a frequency of 13.56 MHz and discharge gaps between 6 and 25 mm. In particular, the low-pressure, high-voltage region of the extinction curves is reported for the first time. The shape of the extinction curves was found to be similar to that of the breakdown curves. At sufficiently large gaps (L > 10 mm) the RF extinction voltage was found to be multi-valued in the low-pressure region, as is observed for the breakdown voltage. In this region, extinction can occur when the voltage is increased because the width of the two sheaths occupies the whole discharge space.

The defect population is important for understanding the microstructure of δ-plutonium. Using spin-polarized density-functional theory, we calculate the formation energies of monovacancies as well as divacancies. We show that the unrelaxed values are quite independent of the magnetic configuration while atomic relaxations lead to smaller values, relaxation effects being larger for the disordered magnetic structure.

A rubber cylinder (R) is pressed against a glass plate (S) through a liquid drop (L). The liquid film, entrapped between R and S, dewets and a R/S dry contact, consisting in a band bordered by two straight contact lines, is formed. A row of equally spaced defects, graved on the glass plate, is used to pin and to deform periodically the R/L/S triple line. We observe the relaxation of this line by interference microscopy and we study the relaxation time vs. the period of the defects, the viscosity of the liquid, for hard and soft rubbers. A naive model, based on the balance between elastic and viscous forces, gives a plausible picture for these observations.

In frameworks of a nesting model for Q1D organic conductors at the antiferromagnetic (SDW) quantum critical point, the first-order transition separates the metallic state from the soliton phase having periodic domain structure. The low-temperature phase diagram also displays a 2nd-order transition line between the soliton and the uniformly gapped SDW phases. The results agree with the phase diagram of (TMTSF)₂PF₆ near critical pressure (Vuletic T. et al., Eur. Phys. J. B25 (2002) 319). The detection of the 2nd-order transition line is discussed. We comment on superconductivity at low temperature.

We explain why the so-called "trion line" in the absorption spectrum of doped wells, cannot be due to a set of 3-body trions but has to come from a singular many-body object, intrinsically wide in energy: the photocreated virtual exciton dressed by Coulomb and Pauli interactions with the well carriers. This understanding is experimentally supported by the highly asymmetrical shape of the circular dichroism spectra obtained with a spin-polarized Fermi sea: their sharp edge on the low-energy side and significant tail at high energy are well explained by this many-body object, while they completely rule out a set of trions, either free or bound.

We study the influence of structural lattice fluctuations on the elastic electron transport in single-wall carbon nanotubes within a density-functional-based scheme. In the linear-response regime, the linear conductance is calculated via configurational averages over the distorted lattice. Results obtained from a frozen-phonon approach as well as from molecular-dynamics simulations are compared. We further suggest that the effect of structural fluctuations can be qualitatively captured by the Anderson model with bond disorder. The influence of individual vibrational modes on the electronic transport is discussed as well as the role of zero-point fluctuations.

The melting transition of vortex lattice in type-II superconductors with magnetic field perpendicular to the anisotropy axis is studied in the framework of the elastic theory. It is found that the thermal fluctuations in the two directions transverse to the magnetic field are approximately proportional to each other with the constant, different from the anisotropy parameter, in a wide portion of phase diagram. One can introduce two Lindemann numbers with the ratio determined by the thermal fluctuations to draw a single melting line. The melting line thus obtained fits the experimental phase boundary quite well.

We study a generalization of the one-dimensional disordered Potts model, which exhibits glassy properties at low temperature. The real-space properties of inherent structures visited dynamically are analyzed through a decomposition into domains over which the energy is minimized. The size of these domains is distributed exponentially, defining a characteristic length scale which grows in equilibrium when lowering temperature, as well as in the aging regime at a given temperature. In the low-temperature limit, this length can be interpreted as the distance between "excited" domains within the inherent structures.

We investigate excitonic polaron states comprising a local exciton and phonons in the longitudinal optical (LO) mode by solving the Schrödinger equation. We derive an exact expression for the ground state (GS), which includes multi-phonon components with coefficients satisfying the Huang-Rhys factors. The recombination of GS and excited polaron states gives one set of sidebands in photoluminescence (PL): the multi-phonon components in the GS produce the Stokes lines and the zero-phonon components in the excited states produce the anti-Stokes lines. By introducing the mixing of the LO mode and environal phonon modes, the exciton will also couple with the latter, and the resultant polaron states result in another set of phonon sidebands. This set has a zero-phonon line higher and wider than that of the first set due to the tremendous number of the environal modes. The energy spacing between the zero-phonon lines of the first and second sets is proved to be the binding energy of the GS state. The common exciton origin of these two sets can be further verified by a characteristic Fano lineshape induced by the coherence in the mixing of the LO and the environal modes.

We present a new method to detect phase as well as generalized synchronization in a wide class of complex systems. It is based on the recurrences of the system's trajectory to the neighborhood of a former state in phase space. We illustrate the applicability of the algorithm for the paradigmatic chaotic Rössler system in the funnel regime and for noisy data, where other methods to detect phase synchronization fail. Furthermore, we demonstrate for electrochemical experiments that the method can easily detect phase and generalized synchronization in non-phase-coherent and even non-stationary time series.

The lattice Boltzmann algorithm efficiently simulates the Navier-Stokes equation of isothermal fluid flow, but ignores thermal fluctuations of the fluid, important in mesoscopic flows. We show how to adapt the algorithm to include noise, satisfying a fluctuation-dissipation theorem (FDT) directly at lattice level: this gives correct fluctuations for mass and momentum densities, and for stresses, at all wave vectors k. Unlike previous work, which recovers FDT only as k → 0, our algorithm offers full statistical mechanical consistency in mesoscale simulations of, e.g., fluctuating colloidal hydrodynamics.

We theoretically study sedimentation-diffusion equilibrium of dilute binary, ternary, and polydisperse mixtures of colloidal particles with different buoyant masses and/or charges. We focus on the low-salt regime, where the entropy of the screening ions drives spontaneous charge separation and the formation of an inhomogeneous macroscopic electric field. The resulting electric force lifts the colloids against gravity, yielding highly nonbarometric and even nonmonotonic colloidal density profiles. The most profound effect is the phenomenon of segregation into layers of colloids with equal mass-per-charge, including the possibility that heavy colloidal species float onto lighter ones.

We explore the limits of digital video microscopy which is established as a standard method in physics, chemistry and biology. At particle distances close to contact we observe small but systematic deviations between the optically measured and the real particle distances. This difference is caused by the overlap of the optical images between neighboring particles. Exemplarily we discuss the consequences of this effect on pair potential measurements of charge stabilized colloids in confined geometries.

We study a shape change of spherical microemulsion droplets when water-soluble polymers are confined inside of them. Upon confinement, spherical droplets deform to prolate ellipsoid droplets while keeping the total surface area and the total enclosed volume of all the droplets constant. We found that an increase of the degree of polymer confinement causes an increase in the uniaxial anisotropy of the prolate droplet, which leads to an isotropic-nematic transition in the concentrated droplet region. As a possible origin of this structural transition, we consider a loss of the conformational entropy of polymer chains due to the confinement.

A dynamic model for failures in biological organisms is proposed and studied both analytically and numerically. Each cell in the organism becomes dead under sufficiently strong stress, and is then allowed to be healed with some probability. It is found that unlike the case of no healing, the organism in general does not completely break down even in the presence of noise. Revealed is the characteristic time evolution that the system tends to resist the stress longer than the system without healing, followed by sudden breakdown with some fraction of cells surviving. When the noise is weak, the critical stress beyond which the system breaks down increases rapidly as the healing parameter is raised from zero, indicative of the importance of healing in biological systems.

We present a simple model of two-component fluid membranes undergoing simultaneously a phase separation and permanent exchange of lipids with the surrounding medium. The balance of these two effects leads to the formation of stable domains of particular lipid composition. The characteristic size of the domains is controlled by the exchange rates of the lipids. This provides a simple mechanism for raft formation in out-of-equilibrium binary fluid membrane.

Erratum of Europhys. Lett.63 p 139.