Table of contents

Effective long-range interactions in confined curved dimensions Observation of metastable hcp solid helium Interference-induced energy transport for biomolecular networks Stable p-type conductivity in ZnO -- A step towards oxide-based optoelectronics

We outline unimodular conformal and projective relativity (UCPR), an extension of unimodular relativity in which the conformal and projective structures play central roles. Under symmetry group, the pseudo-Riemannian metric naturally decomposes into a four-volume element and a conformal metric; and the affine connection decomposes into a one-form and a trace-free projective connection. In UCPR, these four space-time structures are treated as independent fields that have clear physical interpretations. A Palatini-type variational principle for the usual general relativity Lagrangian leads to a breakup of the Einstein field equations and the compatibility conditions between the metric and connection. We indicate how new gravitational theories may be generated by modifications of this Lagrangian and discuss two such cases. Finally, we discuss possible physical consequences of our results for quantum gravity.

Non-Markovian processes have recently become a central topic in the study of open quantum systems. We realize experimentally non-Markovian decoherence processes of single photons by combining time delay and evolution in a polarization-maintaining optical fiber. The experiment allows the identification of the process with strongest memory effects as well as the determination of a recently proposed measure for the degree of quantum non-Markovianity based on the exchange of information between the open system and its environment. Our results show that an experimental quantification of memory in quantum processes is indeed feasible which could be useful in the development of quantum memory and communication devices.

We report the experimental observation of the non-local geometric phase in Hanbury Brown-Twiss polarized intensity interferometry. The experiment involves two independent, polarized, incoherent sources, illuminating two polarized detectors. Varying the relative polarization angle between the detectors introduces a geometric phase equal to half the solid angle on the Poincaré sphere traced out by a pair of single photons. Local measurements at either detector do not reveal the effect of the geometric phase, which appears only in the coincidence counts between the two detectors, showing a genuinely non-local effect. We show experimentally that coincidence rates of photon arrival times at separated detectors can be controlled by the two-photon geometric phase. This effect can be used for manipulating and controlling photonic entanglement.

We propose the minimally nonlinear irreversible heat engine as a new general theoretical model to study the efficiency at the maximum power η^* of heat engines operating between the hot heat reservoir at the temperature T_h and the cold one at T_c (T_c⩽T_h). Our model is based on the extended Onsager relations with a new nonlinear term meaning the power dissipation. In this model, we show that η^* is bounded from the upper side by a function of the Carnot efficiency η_C≡1−T_c/T_h as η^*⩽η_C/(2−η_C). We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory.

In an integrable generalization of the nonlinear Schrödinger equation for nonlinear pulse propagation in monomode optical fibers, certain higher-order nonlinear effects are taken into account. Hereby for such a model, our investigation focuses on the following aspects: a) modulation instability analysis of solutions in the presence of a small perturbation; b) derivation of the infinite conservation laws based on the Lax pair; c) soliton solutions obtained in virtue of the bilinear method with symbolic computation; d) asymptotic analysis and graphical illustration of the solitons. With different choices of the wave numbers in the two-soliton solutions, solitonic characteristics has been discussed. Finally a new type of soliton, namely the "earthwormon", has been proposed in that the moving two-soliton structure looks like an earthworm in slice graphics.

Nonlinear wave patterns generated by the flow of polariton condensate past an obstacle are studied for quasi–one-dimensional microcavity geometry. It is shown that pumping and nonlinear damping play a crucial role in this process leading to sharp differences in subsonic and supersonic regimes. Subsonic flows result in a smooth disturbance of the equilibrium condensate around the obstacle whereas supersonic flow generates a dispersive shock wave in the flow upstream the obstacle and a long smooth downstream tail. Main characteristics of the wave pattern are calculated analytically and analytical results are in excellent agreement with the results of numerical simulations. The conditions for existence of stationary wave patterns are determined numerically.

The two-dimensional problem of the evanescent wave scattering by dielectric or metallic cylinders near the interface between two dielectric media is solved. A semianalytical method involving a special Green function and a numerical solution of the boundary integral equations is proposed. A configuration with a circular and a prolate elliptic cylinders is suggested to simulate the sample and the probe in near-field optical microscopy. The far-field energy flux through the probe is calculated as a function of its position. The oscillations of the signal are interpreted as a result of the interference between evanescent and cylindrical waves.

We present an experimental observation of Klein tunneling of light waves in lattices of evanescently coupled waveguides with a superimposed potential step. The incident wave packet "mass" which is a characteristic feature of Klein tunneling is generated by a minigap in the band structure of the lattice. We studied different masses and measured the tunneling rates across the potential step.

We investigate an array of identical phase oscillators non-locally coupled without time delay, and find that a chimera state with two coherent clusters exists which was only reported in delay-coupled systems previously. Moreover, we find that the chimera state is not stationary for any finite number of oscillators. The existence of the two-cluster chimera state and its time-dependent behaviors for finite number of oscillators are confirmed by the theoretical analysis based on the self-consistency treatment and the Ott-Antonsen ansatz.

In the two-quark model supposition for K₀^*(1430), the branching ratios and the direct CP-violating asymmetries for decays are studied by employing the perturbative QCD factorization approach. We find that although these two decays are both tree-dominated, the ratio of their penguin to tree contributions is very different: there is only a few percent for the decay , while about 37% in scenario I, even 51% in scenario II for the decay . It results that these two decays have very different values in the branching ratios and the direct CP asymmetries. The branching ratio of the decay is at the order of 10⁻⁵, and its direct CP asymmetry is about (20–30)%, whereas for the decay its direct CP-violating asymmetry is very large and about 90%, but difficult to measure because the branching ratio for this channel is small and only 10⁻⁷ order.

We discuss finite-size effects on the phase transition in the two-component, massive, three-dimensional Gross-Neveu model. From an analysis of four-point function and from the existence of a stable infrared fixed point of the beta-function, we get indications of the existence of a second-order phase transition. Using a generalized Matsubara prescription and zeta-function regularization techniques, we determine the dependence of the critical temperature on the size of the system.

We report the formation of nano-sized pits on poly(methyl methacrylate) after exposure to slow highly charged ion beams. The pits are formed on the polymer surface as a direct result of individual ion impacts. Intermittent contact mode atomic-force microscopy was employed to study the size evolution of the pits in dependence of potential and kinetic energies of the incident ions. A potential energy threshold value of approximately 7 keV was found for pit formation. Above this value an increase in potential energy results in an increasing pit volume, while the pit shape can be tuned by varying the kinetic energy.

To effectively alleviate the traffic congestion in urban areas, scientists and engineers have put forward intelligent traffic systems. The information feedback strategy, serving as the critical part of intelligent traffic systems, has been treated with growing emphasis. In this paper, we present two new strategies using the flux as feedback information. One is the time flux feedback strategy (TFFS), the other is the space flux feedback strategy (SFFS). We report the simulation results adopting these two feedback strategies together with the other previously reported ones in a two-route scenario with two exits. The result suggests that SFFS, which outperforms the other categories of feedback strategy, not only in terms of the value of vehicle number and average flux but also in terms of convenience of its application to real traffic conditions, is the best.

We show that the purely convective mapping matrix approach provides an extremely versatile tool to study advection-diffusion processes for extremely large Péclet values (∼10⁸ and higher). This is made possible due to the coarse-grained approximation that introduces numerical diffusion, the intensity of which depends in a simple way on grid resolution. This observation permits to address fundamental physical issues associated with chaotic mixing in the presence of diffusion. Specifically, we show that in partially chaotic flows, the dominant decay exponent of the advection diffusion propagator will eventually decay as Pe⁻¹ in the presence of quasiperiodic regions of finite measure, no matter how small they are. Examples of 2d and 3d partially chaotic flows are discussed.

Liquid marbles are liquid droplets covered with hydrophobic particles. This particular layer physically isolates them from the substrate on which they are deposited. In this study, we investigate the properties of such liquid marbles when impacting onto a solid substrate. The different behaviors during impact (non-bouncing, bouncing and rupture) are experimentally characterized and scenarios for understanding the transitions between the three regimes are proposed. Eventually, we highlight the importance of particle surface coverage by comparing the impact of a liquid marble on a smooth surface with the impact of a bare water drop on a rough superhydrophobic microtextured surface.

Despite the quantum nature of the process, collective scattering by dense cold samples of two-level atoms can be interpreted classically describing the sample as a macroscopic object with a complex refractive index. We demonstrate that resonances in Mie theory can be easily observable in the cooperative scattering by tuning the frequency of the incident laser field or the atomic number. The solution of the scattering problem is obtained for spherical atomic clouds who have the parabolic density characteristic of BECs, and the cooperative radiation pressure force calculated exhibits resonances in the cloud displacement for dense clouds. At odds with uniform clouds which show a complex structure including narrow peaks, these densities show resonances, yet only under the form of quite regular and contrasted oscillations.

How should a given amount of material be moulded into a cantilevered beam clamped at one end, so that it will have the furthest horizontal reach? Here, we formulate and solve this variational problem for the optimal variation of the cross-section area of a heavy cantilevered beam with a given volume V, Young's modulus E, and density ρ, subject to gravity g. We find that the cross-sectional area should vary according a universal profile that is independent of material parameters, with both the length and maximum reach-out distance of the branch that scale as (EV/ρg)^1/4, with a universal self-similar shape at the tip with the area of cross-section a∼s³, s being the distance from the tip, consistent with earlier observations of tree branches, but with a different local interpretation than given before. A simple experimental realization of our optimal beam shows that our result compares favorably with that of our observations. Our results for the optimal design of slender structures with the longest reach are valid for cross-sections of arbitrary shape that can be solid or hollow and thus relevant for a range of natural and engineered systems.

We present a new approach to the design of mixers. This approach relies on a sequence of tailored flows coupled with a new procedure to quantify the local degree of striation, called lamination. Lamination translates to the distance over which the molecular diffusion needs to act to finalise mixing. A novel in situ mixing is achieved by the tailored sequence of flows. This sequence is shown with the property that material lines and lamination grow exponentially, according to processes akin to the well-known baker's map. The degree of mixing (stirring coefficient) likewise shows exponential growth before the saturation of the stirring rate. Such saturation happens when the typical striations' thickness is smaller than the diffusion's length scale. Moreover, without molecular diffusion, the predicted striations' thickness would be smaller than the size of an atom of hydrogen within 40 flow turnover times. In fact, we conclude that about 3 minutes, i.e. 15 turnover times, are sufficient to mix species with very low diffusivities, e.g. suspensions of virus, bacteria, human cells, and DNA.

We study theoretically the capillary-gravity waves created at the water-air interface by a small two-dimensional perturbation in the frequently encountered case where a depth-dependent current is present in the fluid. Assuming linear wave theory, we derive a general expression of the wave resistance experienced by the perturbation as a function of the current profile in the case of an inviscid fluid. We then illustrate the use of this expression in the case of constant vorticity.

The formation of electrostatic shocks in a super-dense plasma composed of relativistically degenerate electrons and fully ionized ions is theoretically investigated. We find analytic solutions in the form of simple waves and derive expressions for shock speeds in limiting cases. The theory has applications to large-amplitude acoustic waves excited in white dwarf stars due to dramatic events such as collision with other astrophysical bodies or supernova explosions.

Homogeneous dielectric barrier discharge (DBD) in nitrogen at atmospheric pressure was produced and identified with a Townsend discharge. It was found that the manner of the discharge extinction is different from that in which most DBDs behave. DBD is normally extinguished with a rapidly reduced gas voltage as the dielectric charges up during the gas discharge. However, the dielectric barrier Townsend discharge in atmospheric nitrogen is extinguished while the gas voltage continues rising up or keeps constant. Based on the experimental results that there exist shallow traps (<1 eV) on the dielectric surface, the extraordinary extinction of the Townsend discharge was explained with the limited number of the shallowly trapped electrons on the dielectric surface that could not provide the Townsend discharge with sufficient secondary electrons.

Stable dusty structures —liquid and solid Coulomb crystals of SiO₂ aerosol— were found to form upon thermally initiated chain combustion of dichlorosilane, SiH₂Cl₂, in oxygen in rf plasma at reduced pressure. The addition of Cr(CO)₆ to combustible mixtures was found to improve the stability of dusty structures and uniformity of their size distribution.

The phenomenological conception of "dielectric catastrophe" applies to the explanation of dielectric-conductor transitions in metal hydrides, hydrogen, rare gases and alkali metals. This conception together with the simple cell model appears to be applicable for the hydrides, where it predicts the correct transition density. For the others substances it fails, but the cell models are still of use in the description of metallization.

The nonlinear dynamics of collisionless reconnecting modes is investigated, in the framework of a three-dimensional gyrofluid model. The collisionless regime is the relevant regime of high-temperature plasmas, where reconnection is made possible by electron inertia and has higher growth rates than resistive reconnection. The presence of a strong guide field is assumed, in a background slab model with Dirichlet boundary conditions in the direction of nonuniformity. Values of ion sound gyro-radius and electron collisionless skin depth much smaller than the current layer width are considered. Strong acceleration of growth is found at the onset to nonlinearity, while at all times the energy functional is well conserved. Nonlinear growth rates more than one order of magnitude higher than linear growth rates are observed when entering the small-Δ' regime.

We have studied silver ion dynamics in mixed network former molybdophosphate glasses by varying the glass network formers ratio. We have shown that the macroscopic ion transport is correlated to the characteristic microscopic length scale and the modification of the phosphate network structure due to the introduction of molybdate network former. The time-temperature superposition of the conductivity spectra onto a single master curve is independent of the mixing of the network formers.

Coaxial multi-layered structure is obtained when the Fe melt confined in the single-walled carbon nanotube (SWCNT) undergoes a rapid cooling. Owing to the inductive effect of the SWCNT, precursors of the long-range order (LRO) are generated in the confined Fe melt and finally been converted into local crystalline structures in the glassy Fe. A memory property has also been observed during the repeated phase transition process. Furthermore, the study of the size effect of tube diameter illustrates that the increasing diameter of the carbon tube is detrimental to the formation of local crystalline structures in nanoscale confinement.

The analytical expressions for the frequency and damping of the radial quadrupole and scissors modes, as obtained from the method of moments, are limited to the harmonic potential. In addition, the analytical results may not be sufficiently accurate as an average relaxation time is used and the high-order moments are ignored. Here, we numerically solve the Boltzmann model equation in the hydrodynamic, transition, and collisionless regimes to study mode frequency and damping. When the gas is trapped by the harmonic potential, we find that the analytical expressions underestimate the damping in the transition regime. Furthermore, we demonstrate that the numerical simulations are able to provide reasonable predictions for the collective oscillations in the Gaussian potentials. The present method can also be used to study many other problems, e.g. formation of quantum shockwave, expansion of atom cloud, and effective heat conductivity in very elongated traps.

We study a process termed agglomerative percolation (AP) in two dimensions. Instead of adding sites or bonds at random, in AP randomly chosen clusters are linked to all their neighbors. As a result the growth process involves a diverging length scale near a critical point. Picking target clusters with probability proportional to their mass leads to a runaway compact cluster. Choosing all clusters equally leads to a continuous transition in a new universality class for the square lattice, while the transition on the triangular lattice has the same critical exponents as ordinary percolation —violating blatantly the basic notion of universality.

We present comprehensive molecular dynamics results for the kinetics of surface-directed spinodal decomposition and surface enrichment in binary mixtures at wetting surfaces. We study the surface morphology and the growth dynamics of the wetting and enrichment layers. The growth law for the thickness of these layers shows a crossover from a diffusive regime to a hydrodynamic regime. We provide phenomenological arguments to understand this crossover.

We consider percolation on interdependent locally treelike networks, recently introduced by Buldyrev S. V. et al., Nature, 464 (2010) 1025, and demonstrate that the problem can be simplified conceptually by deleting all references to cascades of failures. Such cascades do exist, but their explicit treatment just complicates the theory —which is a straightforward extension of the usual epidemic spreading theory on a single network. Our method has the added benefits that it is directly formulated in terms of an order parameter and its modular structure can be easily extended to other problems, e.g. to any number of interdependent networks, or to networks with dependency links.

We consider the localisation properties of a lattice of coupled masses and springs with random mass and spring constant values. We establish the full phase diagrams of the system for pure mass and pure spring disorder. The phase diagrams exhibit regions of stable as well as unstable wave modes. The latter are of interest for the instantaneous-normal-mode spectra of liquids and the nascent field of acoustic metamaterials. We show the existence of delocalisation-localisation transitions throughout the phase diagram and establish, by high-precision numerical studies, that the universality of these transitions is of the Anderson type.

We investigate the evolution of the electronic structure of Ce₂Rh_{1- x}Co_xSi₃ as a function of x employing high resolution photoemission spectroscopy. Co substitution at the Rh sites in antiferromagnetic Ce₂RhSi₃ leads to a transition to a Kondo system, Ce₂CoSi₃ via the Quantum Critical Point (QCP) at x=0.6. High resolution photoemission spectra reveal distinct signature of the Kondo resonance feature (KRF) and its spin-orbit split component (SOC) in the whole composition range indicating finite Kondo temperature scale at QCP. The intensity ratio of KRF and SOC exhibits gradual increase with the decrease in temperature in the strong hybridization limit. The scenario is reversed if the Kondo temperature becomes lower than the Néel temperature. The dominant temperature dependence of the spin-orbit coupled feature in this regime suggests the importance of spin-orbit interactions in the realization of spin-density wave quantum criticality.

Room temperature ferromagnetism has been observed in nanoparticles of Y₂O₃ synthesized by a glycine-nitrate method. By analyzing different annealing conditions and pressing, it is found that the vacuum-heated sample shows the largest ferromagnetism and the annealed pellet sample also exhibits enhanced ferromagnetism. Furthermore, X-ray photoelectron spectroscopy results indicate that the observed ferromagnetism do not involve any impurities and the variation of the relative area of oxygen vacancies is in accord with the change of the saturation magnetization in the samples. Based on these experimental results, the correlation between the ferromagnetism and oxygen defects in Y₂O₃ nanoparticles is established.

We study mesoscopic fluctuations in a system in which there is a continuous connection between two distinct Fermi liquids, asking whether the mesoscopic variation in the two limits is correlated. The particular system studied is an Anderson impurity coupled to a finite mesoscopic reservoir described by the random matrix theory, a structure which can be realized using quantum dots. We use the slave boson mean-field approach to connect the levels of the uncoupled system to those of the strong-coupling Nozières' Fermi liquid. We find strong but not complete correlation between the mesoscopic properties in the two limits and several universal features.

We study the entanglement of two disjoint blocks in spin- chains obtained by merging solvable models, such as XX and quantum Ising models. We focus on the universal quantities that can be extracted from the Rényi entropies S_α. The most important information is encoded in some functions denoted by F_α. We compute F₂ and we show that F_α− 1 and F_v.N., corresponding to the von Neumann entropy, can be negative, in contrast to what observed in all models examined so far. An exact relation between the entanglement of disjoint subsystems in the XX model and that in a chain embodying two quantum Ising models is a by-product of our investigations.

Single crystals of SrFe_2−xRu_xAs₂ have been successfully synthesized using the FeAs self-flux method. The X-ray diffraction patterns indicate that the substitution of Fe by Ru leads to a decrease of the c parameter. Upon Ru substitution, the resistivity anomaly in the parent compound is progressively suppressed and superconductivity is stabilized at low temperatures for x⩾0.45. The superconducting region is dome-like, with an optimal T_c ∼15.5 K found around x=0.667. A phase diagram of temperature vs. doping, based on electrical transport, has been constructed. Results of upper and lower critical field are presented. Our results confirm that the substitution of Fe ions with isoelectronic Ru could suppress the magnetic/structural phase transition in the parent compound, and suggest that there is strong competition between magnetism, structure, and superconductivity in iron-based superconductors.

The manipulation of a ferromagnetic domain wall using a Spin-Polarized Scanning Tunneling Microscope (SP-STM) has been studied by means of a Landau-Lifshitz-Gilbert spin dynamics. We demonstrate that a ferromagnetic transverse domain wall can be shifted by the injection of a spin-polarized tunnel current. Depending on the tip polarization different scenarios occur where the domain wall will be pushed or pulled. Further, we show the possibility to reverse the magnetization inside the domain wall by using the current of the SP-STM tip and describe the predictions for the model system Fe/W(110).

The photoluminescence from individual quantum wells of artificially disordered weakly coupled multi-layers embedded in wide AlGaAs parabolic wells was investigated in a strong magnetic field. We show that the response of the individual wells is very different from the average response of the multi-layers studied by transport measurements and that photoluminescence represents a local probe of the quantum Hall state formed in three-dimensional electron system. The observed magnetic field induced variations of the in-layer electron density demonstrate the formation of a new phase in the quasi-three-dimensional electron system. The sudden change in the local electron density found at the Landau filling factor ν=1 by both the magneto-transport and the magneto-photoluminescence measurements was assigned to the quantum phase transition.

I consider a class of one-dimensional models where Majorana fermions interact with bosonic fields. Contrary to a more familiar situation where bosonic degrees of freedom are phonons and as such form a slow subsystem, I consider fast bosons. Such situation exists when the bosonic modes appear as collective excitations of interacting electrons as, for instance, in superconductors or carbon nanotubes. It is shown that an entire new class of excitations emerge, namely bound states of solitons and Majorana fermions. The latter bound states are not topological and their existence and number depend on the interactions and the soliton's velocity. Intriguingly the number of bound states increases with the soliton's velocity.

Building on the complete account of quantum contributions to conductivity, we demonstrate that the resistance of thin superconducting films exhibits a non-monotonic temperature behaviour due to the competition between weak localization, electron-electron interaction, and superconducting fluctuations. We show that superconducting fluctuations give rise to an appreciable decrease in the resistance even at temperatures well exceeding the superconducting transition temperature, T_c, with this decrease being dominated by the Maki-Thompson process. The transition to a global phase-coherent superconducting state occurs via the Berezinskii-Kosterlitz-Thouless (BKT) transition, which we observe both by power-law behaviour in current-voltage characteristics and by flux flow transport in the magnetic field. The ratio T_BKT/T_c follows the universal relation.

Superconductivity and structural properties of Ti_70−xZr₃₀Nb_x have been systematically investigated for x ranging from 0 to 60. Superconductivity is observed in the cubic β-phase with 10⩽x⩽ 60. Moreover, evident modifications in superconductivity and superstructure, being interpreted as Nb and Ti local orders, are discovered in samples with 25⩽x⩽ 50. This superstructure phase in general coexists with the cubic β-phase and yields two superconducting transitions in the superconducting materials. Electronic structure calculations reveal a relatively higher density of states for the superstructure phase at the Fermi level, therefore a strong electron-phonon coupling and higher superconducting T_c are expected in agreement with the experimental data.

Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

Disease awareness in infection dynamics can be modeled with adaptive contact networks whose rewiring rules reflect the attempt by susceptibles to avoid infectious contacts. Simulations of this type of models show an active phase with constant infected node density in which the interplay of disease dynamics and link rewiring prompts the convergence towards a well-defined degree distribution, irrespective of the initial network topology. We develop a method to study this dynamic equilibrium and give an analytic description of the structure of the characteristic degree distribution and other network measures. The method applies to a broad class of systems and can be used to determine the steady-state topology of many other adaptive networks.

We present the first systematic algorithm to estimate the maximum packing density of spheres when the grain sizes are drawn from an arbitrary size distribution. With an Apollonian filling rule, we implement our technique for disks in 2d and spheres in 3d. As expected, the densest packing is achieved with power-law size distributions. We also test the method on homogeneous and on empirical real distributions, and we propose a scheme to obtain experimentally accessible distributions of grain sizes with low porosity. Our method should be helpful in the development of ultra-strong ceramics and high-performance concrete.

Recommender systems are promising ways to filter the abundant information in modern society. Their algorithms help individuals to explore decent items, but it is unclear how they distribute popularity among items. In this paper, we simulate successive recommendations and measure their influence on the dispersion of item popularity by Gini coefficient. Our result indicates that local diffusion and collaborative filtering reinforce the popularity of hot items, widening the popularity dispersion. On the other hand, the heat conduction algorithm increases the popularity of the niche items and generates smaller dispersion of item popularity. Simulations are compared to mean-field predictions. Our results suggest that recommender systems have reinforcing influence on global diversification. Finally, the study of the hybrid method of mass diffusion and heat conduction reveals that the influence of recommender systems is actually controllable.

Temporal bursts are widely observed in many human-activated systems, which may result from both endogenous mechanisms like the highest-priority-first protocol and exogenous factors like the seasonality of activities. To distinguish the effects from different mechanisms is thus of theoretical significance. This letter reports a new timing method by using a relative clock, namely the time length between two consecutive events of an agent is counted as the number of other agents' events appeared during this interval. We propose a model, in which agents act either in a constant rate or with a power-law inter-event time distribution, and the global activity either keeps unchanged or varies periodically vs. time. Our analysis shows that the bursts caused by the heterogeneity of global activity can be eliminated by setting the relative clock, yet the bursts from real individual behaviors still exist. We perform extensive experiments on four large-scale systems, the search engine by AOL, a social bookmarking system —Delicious, a short-message communication network, and a microblogging system —Twitter. Seasonality of global activity is observed, yet the bursts cannot be eliminated by using the relative clock.

Network topology and its relationship to tie strengths may hinder or enhance the spreading of information in social networks. We study the correlations between tie strengths and topology in networks of scientific collaboration, and show that these are very different from ordinary social networks. For the latter, it has earlier been shown that strong ties are associated with dense network neighborhoods, while weaker ties act as bridges between these. Because of this, weak links act as bottlenecks for the diffusion of information. We show that on the contrary, in co-authorship networks dense local neighborhoods mainly consist of weak links, whereas strong links are more important for overall connectivity. The important role of strong links is further highlighted in simulations of information spreading, where their topological position is seen to speed up spreading dynamics. Thus, in contrast to ordinary social networks, weight-topology correlations enhance the flow of information across scientific collaboration networks.

In the present study, we analyze the radial-velocity distribution as a function of different stellar parameters such as stellar age, mass, rotational velocity and distance to the Sun for a sample of 6781 single low-mass field dwarf stars, located in the solar neighborhood. We show that the radial-velocity distributions are best fitted by q-Gaussians that arise within the Tsallis nonextensive statistics. The obtained distributions cannot be described by the standard Gaussian that emerges within Boltzmann-Gibbs (B-G) statistical mechanics. The results point to the existence of a hierarchical structure in phase space, in contrast to the uniformly occupied phase space of B-G statistical mechanics, driven by the q-Central Limit Theorem, consistent with nonextensive statistical mechanics.