Table of contents

We study the dynamics of a deterministic walk confined in a narrow two-dimensional space randomly filled with point-like targets. At each step, the walker visits the nearest target not previously visited. Complex dynamics is observed at some intermediate values of the domain width, when, while drifting, the walk performs long intermittent backward excursions. As the width is increased, evidence of a transition from ballistic motion to a weakly non-ergodic regime is shown, characterized by sudden inversions of the drift velocity with a probability slowly decaying with time, as 1/t at leading order. Excursion durations, first-passage times and the dynamics of unvisited targets follow power law distributions. For parameter values below this scaling regime, precursory patterns in the form of "wild" outliers are observed, in close relation with the presence of log-oscillations in the probability distributions. We discuss the connections between this model and several evolving biological systems.

A new adaptive coupling scheme is introduced into chaotic phase synchronization in complex networks. The coupling could adjust adaptively according to the energy difference between two chaotic oscillators. Thus it needs less total and net energy to compensate the energy exchange of chaotic systems with its environment in synchronization. In complex networks, the adaptive coupling could suppress the negative influence of the heterogeneities in parameter and degree distributions. We investigate the scheme in three kinds of network topologies, i.e. coupled two oscillators, global coupled lattice, and scale-free complex network. The adaptive coupling scheme has better performance in synchronization ability compared with four other schemes.

To reveal the dynamic mechanism underlying Parkinsonian resting tremor, we applied a phase dynamics modelling technique to local field potentials and accelerometer signals recorded in three Parkinsonian patients with implanted depth electrodes. We detect a bidirectional coupling between the subcortical oscillation and the tremor. The tremor → brain driving is a linear effect with a small delay corresponding to the neural transmission time. In contrast, the brain → tremor driving is a nonlinear effect with a long delay in the order of 1–2 mean tremor periods. Our results are well reproduced for an ensemble of 41 tremor epochs in three Parkinsonian patients and confirmed by surrogate data tests and model simulations. The uncovered mechanism of tremor generation suggests to specifically counteract tremor by desynchronizing the subcortical oscillatory neural activity.

The diffusion process of N hard rods in a 1D interval of length is studied using scaling arguments and an asymptotic analysis of the exact N-particle probability density function (PDF). In the class of such systems, the universal scaling law of the tagged particle's mean absolute displacement reads, ⟨|r|⟩∼⟨|r|⟩_free/n^μ, where ⟨|r|⟩_free is the result for a free particle in the studied system and n is the number of particles in the covered length. The exponent μ is given by, μ=1/(1+a), where a is associated with the particles' density law of the system, ρ∼ρ₀L^-a, 0⩽a⩽1. The scaling law for ⟨|r|⟩ leads to, ⟨|r|⟩∼ρ₀^(a−1)/2(⟨|r|⟩_free)^(1+a)/2, an equation that predicts a smooth interpolation between single-file diffusion and free-particle diffusion depending on the particles' density law, and holds for any underlying dynamics. In particular, for normal diffusion, with a Gaussian PDF in space for any value of a (deduced by a complementary analysis), and, , for anomalous diffusion in which the system's particles all have the same power-law waiting time PDF for individual events, ψ∼t^-1-β, 0<β<1. Our analysis shows that the scaling ⟨r²⟩∼t^1/2 in a "standard" single file is a direct result of the fixed particles' density condition imposed on the system, a=0.

We study the single production of top quarks in e⁺e⁻, ep and pp collisions in the context of unparticle physics through the Flavor Violating (FV) unparticle vertices and compute the total cross-sections for single top production as functions of scale dimension . We find that among all, LHC is the most promising facility to probe the unparticle physics via single top quark production processes.

Following our earlier work (J. Phys. A, 38 (2005) 957; J. Math. Phys., 48 (2007) 052302), we derive noncommuting phase-space structures which are combinations of both the κ-Minkowski and the Snyder algebra by exploiting the reparametrisation symmetry of the recently proposed Lagrangian for a point particle (Ghosh S., Phys. Rev. D, 74 (2006) 084019) satisfying the exact Doubly Special Relativity dispersion relation in the Magueijo-Smolin framework.

We show that electrically and magnetically frustrated Josephson junction arrays (JJAs) realize topological order with a non-trivial ground-state degeneracy on manifolds with non-trivial topology. The low-energy theory has the same gauge dynamics of the unfrustrated JJAs but for different, "fractional" degrees of freedom, a principle reminescent of Jain's composite electrons in the fractional quantum Hall effect.

We report a new method to detect photoassociation (PA) resonance signals through the collective dipole oscillations produced by a momentum transfer from the PA excitation lasers to an ultracold atomic cloud confined by a magnetic trap. Using the amplitudes of these oscillations for several molecular excited states, we derive a precise value for the s-wave scattering length between the ultracold atoms. This new and simple method provides results in excellent agreement with previous spectroscopic PA measurements based on atom losses or temperature rise. We present a simple model interpreting the momentum and energy transferred from the PA process to trap confined ultracold atoms.

The canonical laboratory set-up to study two-dimensional turbulence is the electromagnetically driven shallow one- or two-layer fluid. Stereo-Particle-Image-Velocimetry measurements in such driven shallow flows revealed strong deviations from quasi–two-dimensionality, which are attributed to the inhomogeneity of the magnetic field and, in contrast to what has been believed so far, the impermeability condition at the bottom and top boundaries. These conjectures have been confirmed by numerical simulations of shallow flows without surface deformation, both in one- and two-layer fluids. The flow simulations reveal that the observed three-dimensional structures are in fact intrinsic to flows in shallow fluids because they do not result primarily from shear at a no-slip boundary: they are a direct consequence of the vertical confinement of the flow.

The dynamics of a vesicle suspension in a shear flow between parallel plates has been investigated under microgravity conditions, where vesicles are only submitted to hydrodynamic effects such as lift forces due to the presence of walls and drag forces. The temporal evolution of the spatial distribution of the vesicles has been recorded thanks to digital holographic microscopy, during parabolic flights and under normal gravity conditions. The collected data demonstrates that vesicles are pushed away from the walls with a lift velocity proportional to , where is the shear rate, R the vesicle radius and z its distance from the wall. This scaling as well as the dependence of the lift velocity upon the vesicle aspect ratio are consistent with the theoretical predictions by Olla (J. Phys. II7 (1997) 1533).

Hamiltonian monodromy —a topological property of the bundle of regular tori of a static Hamiltonian system which obstructs the existence of global action-angle variables— occurs in a number of integrable dynamical systems. Using as an example a simple integrable system of a particle in a circular box with quadratic potential barrier, we describe a time-dependent process which shows that monodromy in the static system leads to interesting dynamical effects.

We investigate the spontaneous triboelectrification of similar materials. This effect, first reported in 1927, has been little studied but is easily reproduced. We find in two separate experimental systems, where materials are prepared in the same way and rubbed symmetrically, that symmetry breaking occurs so that one material becomes positive and the other negative. Curiously, the distribution of charges on the materials appears to be self-similar, with different charge patterns on the positive and the negative surface. We propose a mechanism in which an initial localized charge may spawn the production of smaller localized charges of the same polarity.

In 1997, a Rayleigh-Bénard experiment evidenced a significant increase of the heat transport efficiency for Rayleigh numbers larger than Ra∼10¹² and interpreted this observation as the signature of Kraichnan's "Ultimate Regime" of convection. According to Kraichnan's 1962 prediction, the flow boundary layers above the cold and hot plates —in which most of the fluid temperature drop is localized— become unstable for large enough Ra and this instability boosts the heat transport compared to the other turbulent regimes. Using the same convection cell as in the 1997 experiment, we show that the reported heat transport increase is accompanied with enhanced and increasingly skewed temperature fluctuations of the bottom plate, which was heated at constant power levels. Thus, for Ra<10¹², the bottom plate fluctuations can simply be accounted from those in the bulk of the flow. In particular, they share the same spectral density at low frequencies, as if the bottom plate was following the slow temperature fluctuations of the bulk, modulo a constant temperature drop across the bottom boundary layer. Conversely, to account for the plate's temperature fluctuations at higher Ra, we no-longer can ignore the fluctuations of the temperature drop across the boundary layer. These observations, consistent with a boundary layer instability, provide new evidence that the transition reported in 1997 corresponds to the triggering of the Ultimate Regime of convection.

The field-emission–related effects play a significant role in the deviation of the breakdown voltage from that predicted by Paschen's law in the range of micrometer gaps. Beginning from a certain gap spacing, breakdown voltage diverges from the climbing curve seen in the left half of the Paschen curve. In this paper, the equation governing the DC breakdown in microgaps has been solved analytically. The derived analytical relation indicates that the DC breakdown voltage in microgaps depends on the gap size d and the pressure p, particularly, rather than on the product pd. The new theoretical expression allows key features to be identified suggesting that the inclusion of the field emission at micron and submicron gaps is necessary to describe properly the experimental data. The expression presented here can receive a wider interest due to its applicability to the breakdown voltage for a series of gases, gaps and pressures and can serve as ready-to-use guidelines for system engineers and designers.

The X-ray emission from an X-pinch was measured with diamond photoconducting detectors and a pinhole camera, and the results show that the X-ray source of the X-pinch is extremely small in size and high in brightness. As such, the X-pinch could be considered as an X-ray point source having a high spatial coherence that is required by a simplified scheme of X-ray phase-contrast imaging. The X-pinch was used as X-ray source for the phase-contrast imaging of a weakly X-ray–absorbing mosquito and an image with high contrast was obtained.

The energy confinement time in controlled-fusion devices is governed by the turbulent evolution of low-frequency electromagnetic fluctuations of nonuniform magnetized plasmas. The necessary kinetic calculation of turbulent transport consumes much more computer resources than fluid simulations. An alternative approach is based on water-bag–like weak solution of collisionless kinetic equations, allowing to reduce the Vlasov equation into a set of hyrodynamic equations while keeping its kinetic behaviour. In this paper we apply this concept to gyrokinetic modeling, and focus on the weak turbulence theory of the gyro-water-bag model. As a result we obtain a set of nonlinear diffusion equations where the source terms are the divergence of the parallel fluctuating Reynolds stress of each bag. These source terms describe the process of correlated radial scattering and parallel acceleration which is required to generate a sheared parallel flow and may have important consequences for the theory of both intrinsic rotation and momentum transport bifurcations which are closely related to confinement improvements and internal transport barrier dynamics in tokamaks. Using the kinetic resonance condition our quasilinear equations can be recast in a model whose the mathematical structure is the same as the famous Keller-Segel model, widely used in chemotaxis to describe the collective transport (diffusion and aggregation) of cells attracted by a self-emitted chemical substance. Therefore the second result of the paper is the derivation of a set of reaction-diffusion equations which describes the interplay between the turbulence process in the radial direction and the back reaction of the zonal flow in the poloidal direction.

The morphological, crystallographical and electronic structure of a well-ordered pseudomorphic sulphur monolayer (S ML) bonded at the (001) surface of a niobium substrate was investigated experimentally and theoretically. The system exhibits strong sulphur-niobium bonds with fourfold symmetry which do not exist in bulk niobium chalcogenides. These bonds enhance the localization of occupied bands near the Fermi energy in two Nb MLs under the S ML and, due to changed symmetry and stoichiometry, push the p-states of the S ML to deeper binding energies as compared to Nb chalcogenides. The S ML shows strong iono-covalent bonding to Nb(001) with bonding states mainly due to S-3p and antibonding states due to Nb-4d orbitals.

Analcime under pressure undergoes a phase transition at ∼1.0 GPa from a cubic () form to a low-symmetry triclinic () form. We use geometric simulation to relate the pressure behavior of analcime to a recently discovered property of zeolite frameworks, the "flexibility window", defined as the range of densities over which the tetrahedral units in the framework can in principle be made geometrically ideal. Our results show that the range of stability of the cubic phase in analcime is defined by the flexibility window of the cubic framework. Analcime at low density can undergo tetragonal distortion while remaining within the flexibility window, consistent with experimental reports of non-cubic symmetries. On compression to higher densities, the capacity for tetragonal distortion is greatly reduced, accounting for the dramatic reduction in symmetry at the pressure-induced phase transition.

The ac electrical conductivity of magnetoelectric K₃Fe₅F₁₅ was investigated as a function of frequency and temperature. While at higher temperatures charge transport is governed by a thermally activated process, at lower temperatures the real part of the complex ac electric conductivity was found to follow the universal dielectric response σ'∝ν^s, being typical for hopping or tunnelling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunnelling of small polarons revealed that, below 80 K, this mechanism governs the charge transport in the K₃Fe₅F₁₅ magnetoelectric fluoride system.

We study the extra term of particle current in a 2D k-cubic Rashba spin-orbit coupling system and the integer quantization of the Hall conductance in this system. We provide a correct formula of charge current in this system and the careful consideration of extra currents provides a stronger theoretical basis for the theory of the quantum Hall effect which has not been considered before. The non-trivial extra contribution to the particle current density and local conductivity, which originates from the cubic dependence on the momentum operator in the Hamiltonian, will have no effect on the integer quantization of the Hall conductance. The extension of Noether's theorem for the 2D k-cubic Rashba system is also addressed. The two methods reach to exactly the same results.

Colossal enhancement of magnetoresistance has been achieved over a broad temperature range which extends up to the room temperature, in ferromagnetic metal-charge–ordered insulator manganite multilayers. The artificially created phase coexistence in the multlayers reproduces the characteristic signatures of metastability in the magnetotransport properties commonly observed in electronically phase-separated manganites.

Green's matrix method as well as the newly defined resonance capacity of surface plasmon are presented and applied to select the strong resonances for arbitrary shaped subwavelength metallic structures. The resonance capacity distributions for a certain structure type make it possible to tailor the metallic resonant properties in the selected wavelength. Moreover, the resonance capacity is found to be almost immune to the incident wavelength for a definite structure zoomed in or out in the subwavelength scale . Our numerical calculations are also in agreement with the previous experimental results on nanoantennas.

According to a long-standing conjecture of Berry and Tabor, the distribution of the spacings between consecutive levels of a "generic" integrable model should follow Poisson's law. In contrast, the spacings distribution of chaotic systems typically follows Wigner's law. An important exception to the Berry-Tabor conjecture is the integrable spin chain with long-range interactions introduced by Haldane and Shastry in 1988, whose spacings distribution is neither Poissonian nor of Wigner's type. In this letter we argue that the cumulative spacings distribution of this chain should follow the "square root of a logarithm" law recently proposed by us as a characteristic feature of all spin chains of Haldane-Shastry type. We also show in detail that the latter law is valid for the rational counterpart of the Haldane-Shastry chain introduced by Polychronakos.

The interplay between different ordered phases, such as superconducting, charge or spin ordered phases, is of central interest in condensed-matter physics. The very recent discovery of superconductivity with a remarkable T_c=26 K in Fe-based oxypnictide La(O_1−xF_x)FeAs (see Kamihara Y. et al., J. Am. Chem. Soc., 130 (2008) 3296) is a surprise to the scientific community and has generated tremendous interest. The pure LaOFeAs itself is not superconducting but shows an anomaly near 150 K in both resistivity and dc magnetic susceptibility. Here we provide combined experimental and theoretical evidences showing that a spin-density-wave (SDW) state develops at low temperature, in association with electron Nematic order. The electron-doping by F suppresses the SDW instability and induces the superconductivity. Therefore, the La(O_1−xF_x)FeAs offers an exciting new system showing competing orders in layered compounds.

Superconducting behavior has been observed in the Sr₂RuO₄-Sr₃Ru₂O₇ eutectic system as grown by the flux-feeding floating-zone technique. A supercurrent flows across a single interface between Sr₂RuO₄ and Sr₃Ru₂O₇ areas at distances that are far beyond those expected in a conventional proximity effect. The current-voltage characteristics within the Sr₃Ru₂O₇ macrodomain, as extracted from the eutectic, exhibit signatures of superconductivity in the bilayered Sr₃Ru₂O₇ region. Detailed microstructural, morphological and compositional analyses address issues on the concentration and the size of Sr₂RuO₄ inclusions within the Sr₃Ru₂O₇ matrix. We speculate on the possibility of inhomogeneous superconductivity in the eutectic Sr₃Ru₂O₇ and exotic pairing induced by the Sr₂RuO₄ inclusions.

We have investigated the temperature dependence of the Hall coefficient and the resistivity of an organic Mott insulator, β'-(BEDT-TTF)₂ICl₂ under ambient and hydrostatic pressures up to 2 GPa. The charge gap, Δ, the effective mass, m^*, and the scattering lifetime of carriers on Mott Hubbard bands were evaluated by analyzing these transport properties. We found that m^* and Δ are written approximately as 1/m^*∝(1-Δ/U_eff) in the low-pressure region and obtained the value of the effective on-site Coulomb energy, U_eff, of ∼445 meV. Moreover, we reveal that the effective scattering lifetime is proportional to the average distance between carriers in the two-dimensional plane, which suggests the existence of a scattering process attributable to carrier-carrier umklapp scattering in the Mott insulating state.

The problem of efficient transport on a complex network is studied in this paper. We find that there exists an optimal way to allocate resources for information processing on each node to achieve the best transport capacity of the network, or the largest input information rate which does not cause jamming in network traffic, provided that the network structure and routing strategy are given. More interestingly, this achievable network capacity limit is closely related to the topological structure of the network, and is actually inversely proportional to the average distance of the network, measured according to the same routing rule.

Interfaces in two-dimensional systems exhibit unexpected complex dynamical behaviors, the dynamics of a border connecting a stripe pattern and a uniform state is studied. Numerical simulations of a prototype isotropic model, the subcritical Swift-Hohenberg equation, show that this interface has transversal spatial periodic structures, zigzag dynamics and complex coarsening process. Close to a spatial bifurcation, an amended amplitude equation and a one-dimensional interface model allow us to characterize the dynamics exhibited by this interface.

The tuning process of a large apparatus of many components could be represented and quantified by constructing parameter-tuning networks. The experimental tuning of the ion source of the neutral beam injector of the HT-7 Tokamak is presented as an example. Stretched-exponential cumulative degree distributions are found in the parameter-tuning networks. An active-walk model with eight walkers is constructed. Each active walker is a particle moving with friction in an energy landscape; the landscape is modified by the collective action of all the walkers. Numerical simulations show that the parameter-tuning networks generated by the model also give stretched exponential functions, in good agreement with experiments. Our methods provide a new insight to understand the action of humans in the parameter-tuning of experimental processes, and our model could be helpful for the experimental research and other optimization problems.

Large strain-amplitude oscillatory shear flows can cause significant structural changes in concentrated suspensions of deformable colloidal spheres that have volume fractions exceeding the quiescent jamming limit of hard solid spheres. In contrast to hard spheres, which can jam, lock-up, and even break fixed-gap shearing devices, droplets can readily deform and remain lubricated. By introducing shear oscillation light scattering, we explore how shear-induced droplet deformation facilitates un-jamming, ordering, disordering, and re-jamming of uniform concentrated droplets as a function of the amplitude, frequency, and phase of an applied oscillatory shear.

Using measurements of atmospheric temperatures, we create a weighted network in different regions on the globe. The weight of each link is composed of two numbers —the correlations strength between the two places and the time delay between them. A characterization of the different typical links that exist is presented. A surprising outcome of the analysis is a new dynamical quantity of link blinking that seems to be sensitive especially to El Niño even in geographical regimes outside the Pacific Ocean.

In this paper we investigate the jamming degree in weighted scale-free gradient networks, where the gradient flow is described as the edge weight w_ij=(k_i*k_j)^α, which is related with the end-point degrees of a link, and α can be adjusted to be α>0 or α<0. With the new definition of the jamming coefficient, we numerically calculate the jamming coefficient as a function of α, the connectivity ⟨k⟩, and the degree exponent γ. The results indicate that for each γ, there exists an optimal value of α^*, at which the jamming coefficient is minimized. The value of α^* depends on the connectivity ⟨k⟩. With the increase of ⟨k⟩, α^* shifts from zero to the minimum value we examined. Furthermore, there exists a critical value of α_c, which is numerically estimated to be about 0.5. Namely, when α<α_c, a homogeneous network will get a higher level of congestion, otherwise, the opposite will happen.

For a cell moving in hydrodynamic flow above a wall, translational and rotational degrees of freedom are coupled by the Stokes equation. In addition, there is a close coupling of convection and diffusion due to the position-dependent mobility. These couplings render calculation of the mean encounter time between cell surface receptors and ligands on the substrate very difficult. Here we show for a two-dimensional model system how analytical progress can be achieved by treating motion in the vertical direction by an effective reaction term in the mean first passage time equation for the rotational degree of freedom. The strength of this reaction term can either be estimated from equilibrium considerations or used as a fit parameter. Our analytical results are confirmed by computer simulations and allow to assess the relative roles of convection and diffusion for different scaling regimes of interest.

A new inflationary scenario whose exponential potential V(Φ) has a quadratic dependence on the field Φ in addition to the standard linear term is confronted with the five-year observations of the Wilkinson-Microwave Anisotropy Probe and the Sloan Digital Sky Survey data. The number of e-folds (N), the ratio of tensor-to-scalar perturbations (r), the spectral scalar index of the primordial power spectrum (n_s) and its running (dn_s/d ln k) depend on the dimensionless parameter α multiplying the quadratic term in the potential. In the limit α→0 all the results of the exponential potential are fully recovered. For values of α≠0, we find that the model predictions are in good agreement with the current observations of the Cosmic Microwave Background (CMB) anisotropies and Large-Scale Structure (LSS) in the Universe.