Table of contents

The use of relativistic frame invariants is very well established, especially when it comes to the energy-momentum. Most traditional treatments use this particular invariant in order to calculate the "equivalent mass" of a system or, the "mass added to a system". In the following paper we will take a significant departure by avoiding the notion of mass altogether and by using frame-variant quantities like total energy E and momentum p in order to characterize relativistic systems of particles. The systems under evaluations are a most general hybrid made up of both massive particles and photons. We will show the effects of adding photons to a system of massive particles. The new approach is extremely important in applications like particle accelerators where we can only work with directly measurable quantities, the energy E and the momentum p. In paragraph 4 we will demonstrate also how the new approach allows us to calculate the effect of injecting electromagnetic energy in the form of photons in a particle condensate, a very important application for plasma physics.

Aging transition (AT) is studied for a ring of locally coupled Suart-Landau oscillators such that a fraction of them chosen randomly is inactivated. An AT is a transition to a steady state observed when the ratio of inactive oscillators p exceeds a critical value p_c. It is numerically shown that such a transition disappears for N→∞ as 1-p_c∝N^{- γ}, where N is the system size and the exponent γ depends on parameters. Moreover, it is found that the phase coherence of the system can improve by aging-induced disorder.

In this letter we present an analytic evidence of the nonintegrability of the discrete nonlinear Schrödinger equation, a well-known discrete evolution equation which has been obtained in various contexts of physics and biology. We use a reductive perturbation technique to show an obstruction to its integrability.

We study an evolutionary algorithm that locally adapts thresholds and wiring in Random Threshold Networks, based on measurements of a dynamical order parameter. If a node is active, with probability p an existing link is deleted, with probability 1- p the node's threshold is increased, if it is frozen, with probability p it acquires a new link, with probability 1- p the node's threshold is decreased. For any p<1, we find spontaneous symmetry breaking into a new class of self-organized networks, characterized by a much higher average connectivity than networks without threshold adaptation (p=1). While and evolved out-degree distributions are independent from p for p< 1, in-degree distributions become broader when p→1, indicating crossover to a power law. In this limit, time scale separation between threshold adaptions and rewiring also leads to strong correlations between thresholds and in-degree. Finally, evidence is presented that networks converge to self-organized criticality for large N, and possible applications to problems in the context of the evolution of gene regulatory networks and development of neuronal networks are discussed.

Stochastic differential equations in Hilbert space as random nonlinear modified Schrödinger equations have achieved great attention in recent years; of particular interest is the long-time behavior of their solutions. In this note we discuss the long-time behavior of the solutions of the stochastic differential equation describing the time evolution of a free quantum particle subject to spontaneous collapses in space. We explain why the problem is subtle and report on a recent rigorous result, which asserts that any initial state converges almost surely to a Gaussian state having a fixed spread both in position and momentum.

We consider a scattering problem for a nonlinear disordered lattice layer governed by the discrete nonlinear Schrödinger equation. The linear state with exponentially small transparency, due to the Anderson localization, is followed for an increasing nonlinearity, until it is destroyed via a bifurcation. The critical nonlinearity is shown to decay with the lattice length as a power law. We demonstrate that in the chaotic regimes beyond the bifurcation the field is delocalized and this leads to a drastic increase of transparency.

Rotational states for trapped bosons in an optical lattice are studied in the framework of the Hubbard model. Critical frequencies are calculated and the main parameter regimes are identified. Transitions are observed from edge superfluids to vortex lattices with Mott insulating cores, and subsequently to lattices of interstitial vortices. The former transition coincides with the Mott transition. Changes in symmetry of the vortex lattices are observed as a function of lattice depth. Predictions for experimental signatures are presented.

We introduce and investigate billiard systems with an adjusted ray dynamics that accounts for modifications of the conventional reflection of rays due to universal wave effects. We show that even small modifications of the specular reflection law have dramatic consequences on the phase space of classical billiards. These include the creation of regions of non-Hamiltonian dynamics, the breakdown of symmetries, and changes in the stability and morphology of periodic orbits. Focusing on optical microcavities, we show that our adjusted dynamics provides the missing ray counterpart to previously observed wave phenomena and we describe how to observe its signatures in experiments. Our findings also apply to acoustic and ultrasound waves and are important in all situations where wavelengths are comparable to system sizes, an increasingly likely situation considering the systematic reduction of the size of electronic and photonic devices.

The estimation of the amount of genuine cross-correlation strength from multivariate data sets is a nontrivial task, especially when the power spectra of the signals vary dynamically. In this case, the amount of random correlations may vary drastically, even when the length T of the data window used for the construction of the zero-lag correlation matrix is kept constant. In the present letter we introduce correlation measures that allow to distinguish quantitatively genuine and random cross-correlations. The measures are carefully tested by employing model data and exemplarily we demonstrate their performance by their application to a clinical electroencephalogram (EEG) of an epilepsy patient.

One can describe all regular systems regardless of their size by a simple equation that relates the relative masses of their constituents with respect to the mass of the system, to their relative distances from the center with respect to a transition radius equally defined for all systems. Based on this equation one can estimate the value of the Hubble constant from the distribution of matter inside a large enough sample of atomic and/or gravitational systems.

We show that the classical Kolmogorov and Richardson scaling laws in fully developed turbulence are consistent with a random Gaussian force field. Numerical simulations of a shell model for turbulence suggest that the fluctuations in the force (acceleration) field are scale independent throughout the inertial regime. We find that Lagrangian statistics of the relative velocity in a turbulent flow is determined by the typical force field, whereas the multiscaling is associated to extreme events in the force field fluctuations.

We present a new formulation of dissipative particle dynamics (DPD) that leads to correct hydrodynamics in flows around bluff bodies represented by a single particle. In particular, we introduce a shear drag coefficient and a corresponding term in the dissipative force, which along with the angular momentum incorporate non-central shear forces between particles and preserve angular momentum. We consider several prototype flows to verify the performance of the proposed formulation with comparisons against theoretical and continuum-based simulation results. Our method is similar to the Fluid Particle Method (FPM) of Espanol (Phys. Rev. E, 57 (1998) 2930) and it has the computational and implementation simplicity of the standard DPD approach.

We propose a device based on a Q-switched self-sustained oscillator with two nonlinear delayed feedback loops. Due to the appropriate phase transformation of the signal that influences the generation of each successive pulse, the phase difference between the two neighboring pulses evolves according to the Bernoulli doubling map. It corresponds to a hyperbolic chaotic attractor yielding a robust, structurally stable chaos. We discuss possible experimental implementations of the scheme.

This paper presents a novel approach to the investigation of the efficiency of Brownian motors in the framework of nonequilibrium theory. We derive an explicit expression of the entropy production rate (EPR) for a chemically driven Brownian motor and use this to develop an expression for motor efficiency in terms of the EPR. Our result is consistent with earlier derivations but is more general and physically transparent and thus applicable to a wider range of biological motors.

We study the effects of unparticle physics in the pair productions of top quarks at the LHC and ILC. By considering vector, tensor and scalar unparticle operators, as appropriate, we compute the total cross-sections for pair production processes depending on the scale dimension . We find that the existence of unparticles would lead to measurable enhancements on the SM predictions at the LHC. In the case of ILC this may become two orders of magnitude larger than that of SM, for smaller values of , a very striking signal for unparticles.

We study the influence of the electromagnetic vacuum force on the behaviour of a model device based on materials, like germanium tellurides, that undergo fast and reversible metal-insulator transitions on passing from the crystalline to the amorphous phase. The calculations are performed at finite temperature and fully accounting for the behaviour of the material dielectric functions. The results show that the transition can be exploited to extend the distance and energy ranges under which the device can be operated without undergoing stiction phenomena. We discuss the approximation involved in adopting the Casimir expression in simulating nano- and micro- devices at finite temperature.

In this paper, the dynamical screening three-Coulomb-wave (DS3C) model is applied to study the single ionization of helium by 102 eV electron impact. Triply differential cross-sections (TDCS) are calculated at different scattering angle θ₁ (8^°, 10^°, 15^°, 20^°) for both coplanar and perpendicular plane asymmetric geometries. Comparisons are made with experimental data and those of a three-Coulomb wave function (3C) model and a convergent close-coupling (CCC) model. The angular distribution and relative heights of the present TDCS are found to be in very good agreement with the experimental data in the perpendicular plane geometry. It is shown that three-body coupling effects are important in this geometry. Three-body coupling is expected to be weak in the coplanar geometry, although the precise absolute value of the cross-section is still sensitive to the interaction details.

Results of an ab initio density functional theory study of atomic and electronic relaxation at electrically charged surfaces of Au suggest that the outward relaxation of the top layer at negative excess charge is driven by electrostatic forces on the surface atoms due to the incomplete screening of the external electric field. The relaxation amplitude agrees well with experiments on Au(111) in electrolyte. Electron redistribution between bonding and antibonding states in the plane containing the surface atoms may contribute to the charge response of the surface stress.

A solid slender beam of length L, made from a material of Young's modulus Y and subject to a gentle compressive force F, requires a volume of material proportional to L³f^1/2 (where f≡F/(YL²)≪1) in order to be stable against Euler buckling. By constructing a hierarchical space frame, we are able to systematically change the scaling of the required material with f so that it is proportional to L³f^(G+1)/(G+2), through changing the number of hierarchical levels G present in the structure. Based on simple choices for the geometry of the space frames, we provide expressions specifying in detail the optimal structures (in this class) for different values of the loading parameter f. These structures may then be used to create effective materials which are elastically isotropic and have the combination of low density and high crush strength. Such a material could be used to make light-weight components of arbitrary shape.

We introduce common eigenstates of many-particle compatible observables in n-mode Fock space. These states make a complete and orthogonal set and can be realized by the use of beam splitter devices. The entanglement properties of these states are exhibited, their applications in solving many-body problems and in quantum communication are shown.

Electroconvection in a thin, sheared fluid film displays a rich sequence of bifurcations between different flow states as the driving voltage is increased. We present a numerical study of an annular film in which a radial potential difference acts on induced surface charges to drive convection. The film is also sheared by independently rotating the inner edge of the annulus. This simulation models laboratory experiments on electroconvection in sheared smectic liquid crystal films. The applied shear competes with the electrical forces, resulting in oscillatory and strongly subcritical bifurcations between localized vortex states close to onset. At higher forcing, the flow becomes chaotic via a Ruelle-Takens-Newhouse scenario. The simulation allows flow visualization not available in the physical experiments, and sheds light on previously observed transitions in the current-voltage characteristics of electroconvecting smectic films.

The cyclic oscillation behavior (granular clock) of a vibrofluidized granular gas is experimentally investigated in two kinds of N-compartment systems (cyclic and non-cyclic). For a cyclic system, the gas clusters cyclically into one of the compartments in a random order and the interval of the clustering transition has a tendency to decrease with the evolution of time. But for a non-cyclic system, the order and interval of the clustering are invariable. Specially, in a certain transition range a remarkable intermittent clustering behavior is observed at first in our experiments —the granular gas undergoing a cyclic oscillation shows a sudden uniform state and keeps it for a long time until the new cyclic cluster state emerges.

Polarization of electric double layers of colloidal rods due to an external alternating electric field is found to give rise to several phase/state transitions. Various phases and states are observed depending on the frequency and amplitude of the external electric field: i) non-chiral nematic domains (N-domains) in coexistence with an isotropic phase, ii) a chiral-nematic phase in the presence of the N-domains, iii) a chiral nematic phase, where now the N-domains are smaller and disconnected, and iv) dynamic states where the chiral nematic is melted, in the presence of disappearing and forming N-domains. Beyond a critical frequency (in the kHz range) the only stable state is the isotropic state. The phase/state diagram in the field amplitude vs. frequency plane is determined by means of polarization microscopy. In selected parts of the phase diagram, dynamic light scattering, electric birefringence and chiral-pitch measurements are performed to elucidate the nature of transition lines.

In this paper, we use the model is recently presented by us to study the wave properties of the traffic flow on highway with ramps. The results show that the model can perfectly reproduce the effects that ramps have on the formation, the propagation and the evolution of the traffic waves on the main road. Finally, we study the propagating velocity of the first-order wave on the main road and we can further prove that ramps might destroy the stability of the main road traffic flow.

The use of hydrogen plasma (H-plasma) treatment to improve field emission (FE) characteristics of self-synthesized tungsten oxide nanowires (TONWs) is reported. With a H-plasma treatment under a working power of 200 W and a pressure of 500 mtorr for 20 s, improved FE characteristics with a turn-on field (4.7 V/μm at 10 μA/cm²) lower than those of the as-grown case by 23% and a reduction in the effective emission barrier of 0.72 eV were obtained, which is attributed to the reduction in oxygen adsorption, decrease in the wire length and density, and transition of TONWs surfaces from well crystalline into the amorphous phase.

We study the flow of a homogeneous nematic cell under the simultaneous action of an applied electric field and an applied shear flow. Using a hydrodynamic model that describes the response of a flow-aligning nematic liquid crystal (5CB) we obtain the director's configuration and the velocity profile at the steady states. From these results we construct a phase diagram in the electric field vs. shear flow space that displays regions for which the system may have different steady-state configurations of the director's field. The selection of a given steady-state configuration depends on the history of the sample. Due to the competition between shear flow and electric field, the system's viscosity shows a complex non-Newtonian response with regions of shear thickening and thinning. Interestingly, as a consequence of the hysteresis of the system, this response may be asymmetric with respect to the direction of the shear flow. The results also show a moderate electrorheological effect which is also dependent on the history of the sample.

We present evidence from computer simulations for glassy dynamics in suspensions of monodisperse hard ellipsoids. In equilibrium, almost spherical ellipsoids show a first-order transition from an isotropic phase to a rotator phase. When overcompressing the isotropic phase into the rotator regime, we observe super-Arrhenius slowing-down of diffusion and relaxation, accompanied by two-step relaxation in positional and orientational correlators. The effects are strong enough for asymptotic laws of mode-coupling theory to apply. Glassy dynamics are unusual in monodisperse systems. Typically, polydispersity in size, a mixture of particle species or network-forming covalent bonds are prerequisite to prevent crystallization. Here, we show that a slight particle anisometry acts as a sufficient source of disorder. This sheds new light on the question of which ingredients are required for glass formation.

We report the existence of zero-energy surface states localized at zigzag edges of N-layer graphene. Working within the tight-binding approximation, and using the simplest nearest-neighbor model, we derive the analytic solution for the wave functions of these peculiar surface states. It is shown that zero-energy edge states in multilayer graphene can be divided into three families: i) states living only on a single plane, equivalent to surface states in monolayer graphene; ii) states with finite amplitude over the two last, or the two first layers of the stack, equivalent to surface states in bilayer graphene; iii) states with finite amplitude over three consecutive layers. Multilayer graphene edge states are shown to be robust to the inclusion of the next-nearest-neighbor interlayer hopping. We generalize the edge state solution to the case of graphite steps with zigzag edges, and show that edge states measured through scanning tunneling microscopy and spectroscopy of graphite steps belong to family i) or ii) mentioned above, depending on the way the top layer is cut.

We have investigated the giant magnetoresistance (GMR) responses of the pseudo spin valve elliptical rings placed in close proximity with individual magnetic elements. Significant modifications to the GMR responses were observed due to the effects of magnetostatic coupling between the rings and the magnetic elements. We have shown that the stability of the vortex state in the rings can be systematically controlled by varying the orientation and position of the individual magnetic elements relative to the ring structure. Our experimental observations were verified by micromagnetic simulations.

We investigate the electronic properties of corrugated graphene and show how rippling-induced pseudo-magnetic fields alter graphene's low-energy electronic properties by combining first-principle calculations with an effective field theory. The formation of flat bands near the Fermi level corresponding to pseudo-Landau levels is studied as a function of the rippling parameters. Quenched and relaxed ripples turn out to be fundamentally different is this respect: it is demonstrated, both numerically and analytically, that annealing of quenched ripples can destroy the flat bands.

In this paper we study the quantum phase transition between a quantum state with topological order and that without topological order (TQPT) in the transverse Wen-plaquette model. By mapping the transverse Wen-plaquette model onto the d=1 Ising model in a transverse field, some exact results of the TQPT are obtained. The transverse Wen-plaquette model undergoes a continuous TQPT which is characterized in terms of the expectation values of string operators. In particular, the duality relationship between open-string and closed-string is explored —the expectation value of closed-string operator and that of open-string operator play the role of "order parameter" and "disorder order parameter" of the topological order, respectively. At the critical point the "condensation" of both Z₂ vortex and Z₂ charge indicates that the TQPT is a new type of phase transition beyond the Landau-Ginzburg-Wilson paradigm.

The effect of next-nearest-neighbor (nnn) hopping on the spin and charge structures around vortices in underdoped high-temperature superconductors is studied at finite temperature by numerically solving the Bogoliubov-de Gennes equations based on a model Hamiltonian with competing antiferromagnetic spin density wave (SDW) and d-wave superconductivity orders. We show that one-dimensional (1D) y- or x-axis–oriented stripes for the SDW and the associated charge density wave (CDW) exist for small nnn hopping strengths. A coexistence of both y- and x-axis–oriented stripes may occur for a relatively large nnn hopping strength. The two-dimensional (2D) spatial modulations with fourfold symmetry can be obtained with further enlarging nnn hopping strength, implying the possible existence of 2D checkerboard-like SDW and CDW orders. In addition, a transition of "1D stripe to 2D checkerboard-like pattern" can take place with increasing temperature.

Surface plasmon polaritons (SPPs) have recently been recognized as an important future technique for microelectronics. Such SPPs have been studied using classical theory. However, current state-of-the-art experiments are rapidly approaching nanoscales, and quantum effects can then become important. Here we study the properties of quantum SPPs at the interface between an electron quantum plasma and a dielectric material. It is shown that the effect of quantum broadening of the transition layer is most important. In particular, the damping of SPPs does not vanish even in the absence of collisional dissipation, thus posing a fundamental size limit for plasmonic devices. Consequences and applications of our results are pointed out.

An exact solvable model of the coupled supersymmetric t-J chains interacting via the spin exchange interaction is proposed and solved by the means of the nested Bethe ansatz. It is shown, that in addition to the direct spin-exchange interaction an effective interaction between fermions of different chains called as "an effective attractive hard-core interaction" is realized in the model. The critical exponents describing asymptotic behavior of the correlation functions are calculated using the Bethe ansatz equations and the finite-state scaling analysis in conformal field theory. It is shown that the two-component Tomonaga-Luttinger liquid with the dominating correlations of fermion pairs is realized in the low-density region. This non-traditional behavior of the correlation functions is realized due to the effective attractive hard-core interaction between particles.

The problem of detecting a binding site —a substring of DNA where transcription factors attach— on a long DNA sequence requires the recognition of a small pattern in a large background. For short binding sites, the matching probability can display large fluctuations from one putative binding site to another. Here we use a self-consistent statistical procedure that accounts correctly for the large deviations of the matching probability to predict the location of short binding sites. We apply it in two distinct situations: a) the detection of the binding sites for three specific transcription factors on a set of 134 estrogen-regulated genes; b) the identification, in a set of 138 possible transcription factors, of the ones binding a specific set of nine genes. In both instances, experimental findings are reproduced (when available) and the number of false positives is significantly reduced with respect to the other methods commonly employed.

We investigate the dynamics of continuous attractor neural networks (CANNs). Due to the translational invariance of their neuronal interactions, CANNs can hold a continuous family of stationary states. We systematically explore how their neutral stability facilitates the tracking performance of a CANN, which is believed to have wide applications in brain functions. We develop a perturbative approach that utilizes the dominant movement of the network stationary states in the state space. We quantify the distortions of the bump shape during tracking, and study their effects on the tracking performance. Results are obtained on the maximum speed for a moving stimulus to be trackable, and the reaction time to catch up an abrupt change in stimulus.

Motivated by recent experiments showing the compressive buckling of microtubules in cells, we study theoretically the mechanical response of and force propagation along elastic filaments embedded in a non-linear elastic medium. We find that embedded microtubules buckle when their compressive load exceeds a critical value f_c, and that the resulting deformation is restricted to a penetration depth that depends on both the non-linear material properties of the surrounding cytoskeleton, as well as the direct coupling of the microtubule to the cytoskeleton. The deformation amplitude depends on the applied load f>f_c as (f-f_c)^1/2. This work shows how the range of compressive force transmission by microtubules can be tens of microns and is governed by the mechanical coupling to the surrounding cytoskeleton.

Membrane nanotubes or tethers extruded from cells exhibit dynamic features that are believed to exhibit viscoelastic rheological properties. We have performed typical microrheology experiments on tethers pulled from red blood cells by measuring the force response to small oscillatory extensions or compressions. Our data, supported by a simple theoretical model, show that the force response does not reflect any intrinsic viscoelastic properties of the tethers themselves, but instead is dominated by the drainage of the internal cellular fluid into and out of the oscillating nanoconduit over a frequency-dependent penetration depth. The simplicity of tether rheology suggests its usage as a probe for measuring the local viscosity of the cytosol near the plasma membrane.

The polarization of superluminal radiation is studied, based on the tachyonic Maxwell equations for Proca fields with negative mass-square. The cross-sections for the scattering of transversal and longitudinal tachyons by electrons are derived. The polarized superluminal flux vectors of dipole currents are calculated, and the power transversally and longitudinally radiated is obtained. Specifically, the polarization of the γ-ray spectrum of quasar 3C 279 is studied. Two flare spectra of this blazar at redshift 0.538 are fitted with tachyonic cascades generated by the thermal electron plasma in the active galactic nucleus. The transversal and longitudinal radiation components and the thermodynamic parameters of the ultra-relativistic plasma are extracted from the spectral map. An extended spectral plateau typical for tachyonic γ-ray spectra emerges in the MeV and low GeV range. The curvature of the adjacent GeV spectral slope is shown to be intrinsic, caused by the Boltzmann factor of the electron plasma rather than by intergalactic absorption.