ALBERT

Description: Transportation and communication networks are ubiquitous in nature and society. Uncovering the underlying topology as well as link weights, is fundamental to understanding traffic dynamics and designing effective control strategies to facilitate transmission efficiency. We develop a general method for reconstructing transportation networks from detectable traffic flux data using the aid of a compressed sensing algorithm. Our approach enables full reconstruction of network topology and link weights for both directed and undirected networks from relatively small amounts of data compared to the network size. The limited data requirement and certain resistance to noise allows our method to achieve real-time network reconstruction. We substantiate the effectiveness of our method through systematic numerical tests with respect to several different network structures and transmission strategies. We expect our approach to be widely applicable in a variety of transportation and communication systems.

Description: The dynamic shot noise in a molecular quantum dot connected to two non-collinear ferromagnetic terminals under the perturbation of ac fields has been investigated by the nonequilibrium Green’s function approach. The formulas of current, current correlation, and shot noise have been presented in the weak electron-phonon (el-ph) interaction regime to address the cooperated behaviors generated by the photon and phonon perturbation. The photon and phonon perturbations induce quite different current correlations, and the noise suppression occurs unambiguously by increasing the phonon energy in the valley regime. The suppression of shot noise comes from drawing the unbalanced current correlation towards the balanced one, where coherent current correlation takes major role. The suppression of photon-assisted shot noise can be completed mainly by rotating polarization angle of the terminals, and increasing the phonon energy ħ ω 0 . The Fano factor is enhanced considerably by the el-ph interaction, and it is also enhanced by increasing the polarization angle from θ = 0 to θ = π .

Description: In this paper, we develop a new method for the multifractal characterization of two-dimensional nonstationary signal, which is based on the detrended fluctuation analysis (DFA). By applying to two artificially generated signals of two-component ARFIMA process and binomial multifractal model, we show that the new method can reliably determine the multifractal scaling behavior of two-dimensional signal. We also illustrate the applications of this method in finance and physiology. The analyzing results exhibit that the two-dimensional signals under investigation are power-law correlations, and the electricity market consists of electricity price and trading volume is multifractal, while the two-dimensional EEG signal in sleep recorded for a single patient is weak multifractal. The new method based on the detrended fluctuation analysis may add diagnostic power to existing statistical methods.

Description: We investigate the universality aspects of the four-dimensional random-field Ising model (RFIM) using numerical simulations at zero temperature. We consider two different, in terms of the field distribution, versions of the model, namely a Gaussian RFIM and an equal-weight trimodal RFIM. By implementing a computational approach that maps the ground-state of the system to the maximum-flow optimization problem of a network, we employ the most up-to-date version of the push-relabel algorithm and simulate large ensembles of disorder realizations of both models for a broad range of random-field values and system sizes. Using as finite-size measures the sample-to-sample fluctuations of the order parameter of the system, we propose, for both types of distributions, estimates of the critical field h c and the critical exponent ν of the correlation length, the latter suggesting that the two models in four dimensions share the same universality class.

Description: Some temporal networks, most notably citation networks, are naturally represented as directed acyclic graphs (DAGs). To detect communities in DAGs, we propose a modularity for DAGs by defining an appropriate null model (i.e., randomized network) respecting the order of nodes. We implement a spectral method to approximately maximize the proposed modularity measure and test the method on citation networks and other DAGs. We find that the attained values of the modularity for DAGs are similar for partitions that we obtain by maximizing the proposed modularity (designed for DAGs), the modularity for undirected networks and that for general directed networks. In other words, if we neglect the order imposed on nodes (and the direction of links) in a given DAG and maximize the conventional modularity measure, the obtained partition is close to the optimal one in the sense of the modularity for DAGs.

Description: Diffusion of information via networks has been extensively studied for decades. We study the general threshold model that embraces most of the existing models for information diffusion. In this paper, we first analyze diffusion processes under the linear threshold model, then generalize it into the general threshold model. We give a closed formula for estimating the final cascade size for those models and prove that the actual final cascade size is concentrated around the estimated value, for any network structure with node degrees ω (log  n ), where n is the number of nodes. Our analysis analytically explains the tipping point phenomenon that is commonly observed in information diffusion processes. Based on the formula, we devise an efficient algorithm for estimating the cascade size for general threshold models on any network with any given initial adopter set. Our algorithm can be employed as a subroutine for numerous algorithms for diffusion analysis such as influence maximization problem. Through experiments on real-world and synthetic networks, we confirm that the actual cascade size is very close to the value computed by our formula and by our algorithm, even when the degrees of the nodes are not so large.

Description: Building upon the findings of Muto et al. [Phys. Lett. A 136 , 33 (1989)] and Marchesoni and Lucheroni [Phys. Rev. E 44 , 5303 (1991)] about the growth of the number of (anharmonic) lattice solitons with increasing temperature and using a recent transport theory developed by the present authors [A.P. Chetverikov, W. Ebeling, G. Röpke, M.G. Velarde, Eur. Phys. J. B 87 , 153 (2014)] here we provide the fractional power law of the temperature dependence of resistivity in a rather general model for one-dimensional crystal lattices as, e.g., conducting polymers. We also show that the determining factor for the transport is the possibility of forming electron-soliton bound states (in short solectrons) with a most significant contribution arising from the (bosonic) bound state of two electrons to a soliton (in short bisolectrons).

Description: The electronic structure of isolated finite graphene nanoribbons is investigated by solving, at the Hartree-Fock (HF) level, the Pariser, Parr and Pople (PPP) many-body Hamiltonian. The study is mainly focused on 7-AGNR and 13-AGNR (Armchair Graphene Nano-Ribbons), whose electronic structures have been recently experimentally investigated. Only paramagnetic solutions are considered. The characteristics of the forbidden gap are studied as a function of the ribbon length. For a 7-AGNR, the gap monotonically decreases from a maximum value of ~6.5 eV for short nanoribbons to a very small value of ~0.12 eV for the longer calculated systems. Gap edges are defined by molecular orbitals that are spatially localized near the nanoribbon extremes, that is, near both zig-zag edges. On the other hand, two delocalized orbitals define a much larger gap of about 5 eV. Conductance measurements report a somewhat smaller gap of ~3 eV. The small real gap lies in the middle of the one given by extended states and has been observed by STM and reproduced by DFT calculations. On the other hand, the length dependence of the gap is not monotonous for a 13-AGNR. It decreases initially but sharply increases for lengths beyond 30 Å remaining almost constant thereafter at a value of ~2.1 eV. Two additional states localized at the nanoribbon extremes show up at energies 0.31 eV below the HOMO (Highest Occupied Molecular Orbital) and above the LUMO (Lowest Unoccupied Molecular Orbital). These numbers compare favorably with those recently obtained by means of STS for a 13-AGNR sustained by a gold surface, namely 1.4 eV for the energy gap and 0.4 eV for the position of localized band edges. We show that the important differences between 7- and 13-AGNR should be ascribed to the charge rearrangement near the zig-zag edges obtained in our calculations for ribbons longer than 30 Å, a feature that does not show up for a 7-AGNR no matter its length.

Description: We study the effect of interfacial phenomena in two-dimensional perfect and random (or disordered) q -state Potts models with continuous phase transitions, using, mainly, Monte Carlo techniques. In particular, for the total interfacial adsorption, the critical behavior, including corrections to scaling, are analyzed. The role of randomness is scrutinized. Results are discussed applying scaling arguments and invoking findings for bulk critical properties. In all studied cases, i.e., q = 3, 4, and q = 8, the spread of the interfacial adsorption profiles is observed to increase linearly with the lattice size at the bulk transition point.

Description: Inclusion of spin-dependent interactions in graphene in the vicinity of the Dirac points can be posed in terms of non-Abelian gauge potentials. Such gauge potentials being surrogates of physical electric fields and material parameters, only enjoy a limited gauge freedom. A general gauge transformation thus changes the physical model. We argue that this property can be useful in connecting reference physical situations, such as free particle or Rashba interactions to non-trivial physical Hamiltonians with a new set of spin-orbit interactions, albeit constrained to being isoenergetic. We analyse different combinations of spin-orbit interactions in the case of monolayer graphene and show how they are related by means of selected non-Abelian gauge transformations.

Description: The Hubbard model of bosons on two dimensional lattices with a lowest flat band is discussed. In these systems there is a critical density, where the ground state is known exactly and can be represented as a charge density wave. Above this critical filling, depending on the lattice structure and the interaction strength, the additional particles are either delocalised and condensate in the ground state, or they form pairs. Pairs occur at strong interactions, e.g., on the chequerboard lattice. The general mechanism behind this phenomenon is discussed.

Description: Investigations of the electronic properties and transport properties of Mg 2 Si under uniaxial [110] strain have been performed by using first-principle density-functional and Boltzmann’s transport theories. The effect of compressive and tensile uniaxial strains has been studied by changing the γ angle of the conventional cell from ± 1° to ± 4°. We show that, the Seebeck property of the constrained bulk lattice at high temperature, when plotted with respect to the charge carrier concentrations, is similar to that of the (110) thin film at low temperature. This behaviour is evidenced when superimposing the Seebeck coefficient curves of both materials by shifting down the S curve of the constrained structure by about 150 K with respect to the temperature.

Description: The probability density functions (PDFs) of earthquake energy fluctuations at different times have fat tails with a q -Gaussian form. We analyze the PDFs of energy fluctuations for different faulting styles and the relationship between the deviation from the Gaussian distribution and the faulting style. There are common features between the b -value and q -parameter dependence on the faulting styles. We suggest that the deviation from Gaussian distribution for the PDFs of earthquake energy fluctuation may be a useful indicator in earthquake-hazard research.

Description: This paper analyzes several interest rates time series from the United Kingdom during the period 1999 to 2014. The analysis is carried out using a pioneering statistical tool in the financial literature: the complexity-entropy causality plane. This representation is able to classify different stochastic and chaotic regimes in time series. We use sliding temporal windows to assess changes in the intrinsic stochastic dynamics of the time series. Anomalous behavior in the Libor is detected, especially around the time of the last financial crisis, that could be consistent with data manipulation.

Description: This paper demonstrates the effect of sintering parameters on the electrocaloric effect (ECE) in BaTiO 3 ferroelectric ceramics, especially the sintering temperature and atmosphere. The samples were prepared by solid-state reaction method. With the rise of sintering temperature from 1200 °C to 1350 °C, the grain size increases remarkably and the densification is improved. The 1350 °C sintered sample has better ferroelectricity and higher latent heat for ferroelectric-paraelectric phase transition than those of the 1200 °C sintered sample. Correspondingly, it exhibits much better ECE. If the sample is sintered in pure oxygen, instead of in air, all ferroelectricity, dielectric strength and ECE are further enhanced. The sample sintered at 1350 °C in oxygen exhibits an excellent ECE performance with ΔT max = 1.37 K and ΔS max = 1.75 J/kg K.

Description: The low energy continuum limit of graphene is effectively known to be modeled using the Dirac equation in (2 + 1) dimensions. We consider the possibility of using a modulated high frequency periodic driving of a two-dimensional system (optical lattice) to simulate properties of rippled graphene. We suggest that the Dirac Hamiltonian in a curved background space can also be effectively simulated by a suitable driving scheme in an optical lattice. The time dependent system yields, in the approximate limit of high frequency pulsing, an effective time independent Hamiltonian that governs the time evolution, except for an initial and a final kick. We use a specific form of 4-phase pulsed forcing with suitably tuned choice of modulating operators to mimic the effects of curvature. The extent of curvature is found to be directly related to ω −1 the time period of the driving field at the leading order. We apply the method to engineer the effects of curved background space. We find that the imprint of curvilinear geometry modifies the electronic properties, such as LDOS, significantly. We suggest that this method shall be useful in studying the response of various properties of such systems to non-trivial geometry without requiring any actual physical deformations.

Description: The structural, electronic, and optical properties of NpO 2 and PuO 2 have been investigated by means of the hybrid density functional theory (HDFT) using the full-potential linearized augmented plane (FP-LAPW) wave plus local orbitals (lo) method. The weight of exact Hartree-Fock (HF) exchange, α = 0.25, 0.35 and 0.40, are chosen for the hybrid density functional calculation. The obtained energy band gaps of NpO 2 and PuO 2 are 2.75 eV and 2.80 eV within α = 0.35 scheme, respectively, which are in excellent agreement with the recent experimental data. The calculated charge density and charge density differences in the (110) plane suggest the chemical bonds for the two actinide dioxides have main ionic character. Furthermore, the dielectric function and related optical parameters of the two compounds are firstly calculated using the HDFT method. In particular, the obtained refractive index n for PuO 2 is consistent well with the experimental value in the wavelength range of 400 to 900 nm. We also predicted the effective number of electrons ( n eff ) contributing in the inter-band transitions reach a saturation value above 32 eV per unit cell for NpO 2 and PuO 2 .

Description: We present a theory for Raman scattering on 2D quantum antiferromagnets. The microscopic Fleury-Loudon Hamiltonian is expressed in terms of an effective O (3)-model. Well within the Néel ordered phase, the Raman spectrum contains a two-magnon and a two-Higgs contribution, which are calculated diagramatically. The vertex functions for both the Higgs and magnon contributions are determined from a numerical solution of the corresponding Bethe-Salpeter equation. Due to the momentum dependence of the Raman vertex in the relevant B 1 g + E 2 g symmetry, the contribution from the Higgs mode is strongly suppressed. Except for intermediate values of the Higgs mass, it does not show up as separate peak in the spectrum but gives rise to a broad continuum above the dominant contribution from two-magnon excitations. The latter give rise to a broad, asymmetric peak at ω ≃ 2.44 J, which is a result of magnon-magnon interactions mediated by the Higgs mode. The full Raman spectrum is determined completely by the antiferromagnetic exchange coupling J and a dimensionless Higgs mass. Experimental Raman spectra of undoped cuprates turn out to be in very good agreement with the theory only with inclusion of the Higgs contribution. They thus provide a clear signature of the presence of a Higgs mode in spin one-half 2D quantum antiferromagnets.

Description: In the present work, the atomic and the electronic structures of Au 3 N, AuN and AuN 2 are investigated using first-principles density-functional theory (DFT). We studied cohesive energy vs. volume data for a wide range of possible structures of these nitrides. Obtained data were fitted to a Birch-Murnaghan third-order equation of state (EOS) so as to identify the most likely candidates for the true crystal structure in this subset of the infinite parameter space, and to determine their equilibrium structural parameters. The analysis of the electronic properties was achieved by the calculations of the band structure and the total and partial density of states (DOS). Some possible pressure-induced structural phase transitions have been pointed out. Further, we carried out GW 0 calculations within the random-phase approximation (RPA) to the dielectric tensor to investigate the optical spectra of the experimentally suggested modification: Au 3 N(D0 9 ). Obtained results are compared with experiment and with some available previous calculations.

Description: In this work, materials used in the field of accessories for electrical cables have been characterised from a thermomechanical and electrical point of view, so to offer a realistic picture of material behaviour under a service involving the combined application of electrical charges and thermo-mechanical stresses. In particular, both materials are based on ethylene-vinylacetate (EVA) blend with the introduction in one case of aluminium trihydrate, whereas in the other case, carbon black was added, the two materials being referred as insulating and semi-conductive, respectively. The two materials had different rheological and thermal characteristics, which had an effect on electrical behaviour: however, the application of levels of radiation up to 60 kGy did not prove to widely change the profile of either polymer blends.

Description: A formula to obtain the cyclotron transition line-widths for a system of electrons interacting with confined-acoustic phonons through the deformation potential in a quantum well is derived using the projection-reduction method. The result contains the distribution functions for the electrons and phonons properly. Therefore, the phonon absorption and emission processes can be explained in an organized manner and the result can be represented diagrammatically, through which insight into the quantum dynamics of electrons in a solid can be obtained. The formula is used to calculate the cyclotron transition line-widths in silicon. It is shown that the line-width increases with increasing temperature but the well width and magnetic field dependence of the line-width are complicated. It is also shown that only a few low-energy confined modes contribute significantly to the line-widths.

Description: This paper investigates multi-crossing dynamics of multi-particle Landau-Zener (LZ) systems applying Dynamic matrix approach (DMA) that is found to generalize probability amplitudes. It is also observed that for exceedingly low frequencies, the system exhibits one crossing while for high frequencies, the multi-crossing. It is shown that for particular phenomenological parameters of the system, there is total population transfer that achieves the values one or zero useful for implementing quantum logic gates.

Description: We study the thermodynamic properties of a single particle occupying one of three available energy levels in a non-equilibrium regime. The particle is thermally coupled to a classical Maxwell-Boltzmann thermal reservoir and can jump among the available levels by exchanging energy with the heat bath. The bottom and middle energy levels are simultaneously raised at a given rate regardless of particle occupation, but keeping the energy gaps among the three levels fixed. We explicitly calculate the work, heat and entropy production rates, and the classical efficiency. We also consider the case of a Bose-Einstein thermal reservoir and provide explicit expressions for the non-equilibrium, steady-state probabilities.

Description: We study the Shannon entropy of the cluster size distribution in classical as well as explosive percolation, in order to estimate the uncertainty in the sizes of randomly chosen clusters. At the critical point the cluster size distribution is a power-law, i.e. there are clusters of all sizes, so one expects the information entropy to attain a maximum. As expected, our results show that the entropy attains a maximum at this point for classical percolation. Surprisingly, for explosive percolation the maximum entropy does not match the critical point. Moreover, we show that it is possible to determine the critical point without using the conventional order parameter, just analysing the entropy’s derivatives.

Description: In this work we investigate time varying networks with complex dynamics at the nodes. We consider two scenarios of network change in an interval of time: first, we have the case where each link can change with probability p t , i.e. the network changes occur locally and independently at each node. Secondly we consider the case where the entire connectivity matrix changes with probability p t , i.e. the change is global. We show that network changes, occuring both locally and globally, yield an enhanced range of synchronization. When the connections are changed slowly (i.e. p t is low) the nodes display nearly synchronized intervals interrupted by intermittent unsynchronized chaotic bursts. However when the connections are switched quickly (i.e. p t is large), the intermittent behavior quickly settles down to a steady synchronized state. Furthermore we find that the mean time taken to reach synchronization from generic random initial states is significantly reduced when the underlying links change more rapidly. We also analyse the probabilistic dynamics of the system with changing connectivity and the stable synchronized range thus obtained is in broad agreement with those observed numerically.

Description: A procedure based on stochastic Langevin equations is presented and shows how a stochastic model of driver behavior can be estimated directly from given data. The Langevin analysis allows the separation of a given data-set into a stochastic diffusion- and a deterministic drift field. Form the drift field a potential can be derived. In particular the method is here applied on driving data from a simulator. We overcome typical problems like varying sampling rates, low noise levels, low data amounts, inefficient coordinate systems, and non-stationary situations. From the estimation of the drift- and diffusion vector-fields derived from the data, we show different ways how to set up Monte-Carlo simulations for the driver behavior.

Description: The evolution of cooperation is still an enigma. Resolution of cooperative dilemma is a hot topic as a perplexing interdisciplinary project, and has captured wide attention of researchers from many disciplines as a multidisciplinary field. Our main concern is the design of a networked evolutionary game model in which players show difference in memory capability. The idea of different memory capacities has its origin on the pervasive individual heterogeneity of real agents in nature. It is concluded that this proposed multiple memory capacity stimulates cooperation in lattice-structured populations. The networking effect is also investigated via a scale free network which is associated with the heterogeneous populations structure. Interestingly, results suggest that the effectiveness of a heterogeneous network at fostering cooperation is reduced in the presence of individual memory here. A thorough inquiry in the coevolutionary dynamics of individual memory and spatial structure in evolutionary games is planned for the immediate future.

Description: The quantum dynamics of a few bosons in a double well potential is studied using a Bose Hubbard model. We consider both signs for the on-site interparticle interaction and also investigated the situations where they are large and small. Interesting distinctive features are noted for the tunneling oscillations of these bosons corresponding to the above scenarios. Further, the sensitivity of the particle dynamics to the initial conditions has been studied. It is found that corresponding to an odd number of particles, such as three (or five), an initial condition of having unequal number of particles in the wells has interesting consequences, which is most discernible when the population difference between the wells is unity.

Description: We present a proposal for a single-parametric electron pump composed of a quantum dot between two unbiased leads with energy-gapped electron density of states (DOS). The model tight-binding Hamiltonian and the evolution operator technique are used in the calculations. The quantum dot is driven by the external harmonic field which leads to the pumping current flowing from the left or right electrode depending on the system parameters. We show that the net pumping current appears in the system if (i) there are at least two sideband states: one of them lying below and the second lying above the Fermi energy; (ii) the left and right lead DOS in the vicinity of these sideband states are different. Moreover, the energy-gapped structure of DOS is visible on the average quantum dot charge and the pumped current curves as well as on the transconductance characteristics. Thus mono-parametric pumping provides useful information about the system parameters, in particular about the lead DOS structure.

Description: We show that, contrary to previous belief, the transition to the antiferromagnetic state of Sr 2 IrO 4 in zero magnetic field does show up in the transverse resistivity. We attribute this to a change in transverse integrals associated to the magnetic ordering, which is evaluated considering hopping of the localized charge. The evolution of the resistivity anomaly associated to the magnetic transition under applied magnetic field is studied. It tracks the magnetic phase diagram, allowing to identify three different lines, notably the spin-flip line, associated with the reordering of the ferromagnetic component of the magnetization, and an intriguing line for field induced magnetism, also corroborated by magnetization measurements.

Description: The article deals with the mathematical model for media with hierarchical structure. Using the Hamiltonian formalism, the dynamical system describing the state of hierarchically connected structural elements was derived. According to the analysis of the Poincaré sections, we found the localized quasi-periodic and chaotic trajectories in the three-level hierarchical model. Moreover, studies of correlation functions showed that the power spectrum for three-level model possesses local maxima characterizing temporal scales with strong correlation. Using the Fourier analysis of the solution’s components, we have studied the distribution of energy injected in the system over hierarchical levels. Dynamical phenomena in the multi-level system were studied as well.

Description: Lottery is the most famous branch among all the games of chance. By analysing data from Mega-Sena, the major lottery in Brazil, we investigated the presence of persistent behaviour in the time series of the number of winners. We found that the demand for tickets grew collectively as an exponential driven by the size of the accumulated jackpot. Finally, we identified that a stochastic model grounded on the rolling-over feature of lotteries can generate correlations qualitatively similar to those observed empirically. The model is consistent with the idea that the growth in the number of bets, motivated by the size of the expected jackpot, is a mechanism generator of correlations in an apparently random scenario.

Description: We obtain a special Fano-like resonance in a semi-closed T-shaped waveguide with nanodisk resonator, in which only two bright plasmon modes work. It is found that the transmission spectrum occurs a red-shift by increasing either length of the nanoslot or radius of the nanodisk. Moreover, when the length of the nanoslot and radius of the nanodisk reach to some particular values at the same time, the transmission spectrum will show an inverse line shape or the Fano-like resonance will disappear. Meanwhile, the classical figure of merit obtained by calculation is as high as 199 with a sizable classical sensitivity value reaches to 1114 nm/RIU. The generalized figure of merit also comes to an impressive value of 7961 nm/RIU. Besides, it is worth noting that the maximums of these two kinds of FOM lie in the dips of different linewidth, which can be utilized in diverse types of sensors. Our studies further provide a guidance for fabricating planar devices in near-infrared region.

Description: We present a numerical study of ferromagnetic Josephson junctions with one intermediate layer and spin active interfaces in the ballistic regime, comparing the behaviour of one, two and three dimensional junctions. We find that in two and three dimensional junctions the geometries which lack spin flip scattering at one of the interfaces have a critical current that decays to zero, as we increase the magnetization of the intermediate layer towards the half metal limit. As known, magnetization direction inhomogeneity produces a long range supercurrent with width variation, even when spin flip scattering exists in one of the interfaces only, although of lower characteristic decay length, compared to junctions with spin flip scattering at both interfaces. In the case of a single spin-flip interface and large thickness of the junction, we find a dominant second harmonic in the current-phase relation, in agreement with earlier work. We apply a diagrammatic approach, which explains the strong second harmonic and the long range property of the supercurrent. We find that in the three dimensional junction case the main contribution to both the long range supercurrent and the second harmonic in thick Josephson junctions with one spin flip interface comes from diagrammatic terms that correspond to scattering loops inside the junction which are subject to anomalous Andreev reflections on the spin flip interface and normal Andreev reflections at the non spin flip interface, thus exhibiting the triplet nature of the phenomenon. We also find the emergence of the strong first harmonic for small variation of the magnetization geometry and comment on the effect of normal interface scattering and temperature on the second harmonic.

Description: We derive the distribution function of work performed by a harmonic force acting on a uniformly dragged Brownian particle subjected to a rotational torque. Following the Onsager and Machlup’s functional integral approach, we obtain the transition probability of finding the Brownian particle at a particular position at time t given that it started the journey from a specific location at an earlier time. The difference between the forward and the time-reversed form of the generalized Onsager-Machlup’s Lagrangian is identified as the rate of medium entropy production which further helps us develop the stochastic thermodynamics formalism for our model. The probability distribution for the work done by the harmonic trap is evaluated for an equilibrium initial condition. Although this distribution has a Gaussian form, it is found that the distribution does not satisfy the conventional work fluctuation theorem.

Description: We investigate, using Monte Carlo simulations, the phase diagram of a system of hard rectangles of size m × mk on a square lattice when the aspect ratio k is a non-integer. The existence of a disordered isotropic phase, a nematic with only orientational order, a columnar phase with orientational and partial translational order, and a high density phase with no orientational order is shown. The high density phase is a solid-like sublattice phase only if the length and width of the rectangles are not mutually prime, else, it is an isotropic phase. The minimum value of k beyond which the nematic and columnar phases exist are determined for m = 2 and 3. The nature of the transitions between different phases is determined, and the critical exponents are numerically obtained for the continuous transitions.

Description: We consider the quasi-static thermodynamic processes with constraints, but with additional uncertainty about the control parameters. Motivated by inductive reasoning, we assign prior distribution that provides a rational guess about likely values of the uncertain parameters. The priors are derived explicitly for both the entropy-conserving and the energy-conserving processes. The proposed form is useful when the constraint equation cannot be treated analytically. The inference is performed using spin-1/2 systems as models for heat reservoirs. Analytical results are derived in the high-temperatures limit. An agreement beyond linear response is found between the estimates of thermal quantities and their optimal values obtained from extremum principles. We also seek an intuitive interpretation for the prior and the estimated value of temperature obtained therefrom. We find that the prior over temperature becomes uniform over the quantity kept conserved in the process.

Description: An inertial Brownian motor under the influence of a biased biharmonic signal is investigated numerically. For a finite positive bias force, the maximized negative current occurs at a relatively large noise intensity ( D = 0.01), while the magnitude of the anomalous velocity is also very large (greater than 1.5). This result means one can observe remarkably abnormal transport behaviors at relatively high temperature by means of a biharmonic drive.

Description: The stability of supersolid (SS) state in lattice boson model is highly dependent on lattice topology and particle-particle interaction. We investigate hard-core bosons on dice lattice where the bosons interact via nearest-neighbor (NN) repulsion either on whole lattice or on sublattices, by using large-scale quantum Monte Carlo simulations which are based on a continuous-time worm algorithm. In the case with NN repulsion on the whole lattice, we confirm the particle density modulation which arises from the asymmetry between sublattices — honeycomb and triangular sublattices — of dice lattice. We then place emphasis on the case with NN repulsion on the sublattices, and demonstrate spontaneously broken translational symmetries on different sublattices which lead to various crystalline orders. By evaluating the coexistence of crystalline order and superfluidity, we identify a variety of SS phases and establish a rich phase diagram. The microscopic pictures of these SS phases are figured out. Further, we demonstrate paradigmatic examples of first-order solid-to-SS and SS-to-SS quantum phase transitions.

Description: Analytical techniques developed in the field of materials science are now widely applied to objects of art and archaeology to gain information about the material composition and structure and hence to understand the way of manufacturing artefacts. Reciprocally, ancient artefacts studies show potential important contribution in the materials science field. This topical review will cover all these input and output aspects between materials science and ancient artefacts through the study of the first ceramics made by men e.g. potteries. To study these heterogeneous and complex materials, an approach based on the decomposition into sub systems of materials and the applications of traditional and novel analytical methods to scan the different scales of the material is not only mandatory but also innovative.

Description: Magnetic domain walls are fundamental objects arising in ferromagnetic materials, largely investigated both through micromagnetic simulations and experiments. While current- and field-based techniques for inducing domain wall propagation have been widely studied for fundamental understanding and application-oriented purposes, the possibility to manipulate domain walls using mechanical stress in magnetoelastic materials has only recently drawn interest. Here, a complete analytical model describing stress-induced transverse domain wall movement in ferromagnetic nanostripe with variable cross-section is presented. This approach yields a nonlinear integro-differential equation describing the magnetization field. Its numerical implementation, based on the nonlinear relaxation method, demonstrates the possibility to precisely control the position of a domain wall through mechanical action.

Description: We investigate the escape rate of an overdamped, self-propelled spherical Brownian particle on a surface from a metastable potential well. Within a modeling in terms of a 1D constant speed of the particle’s active dynamics we consider the associated rate using both numerical and analytical approaches. Regarding the properties of the stationary state in the potential well, two major timescales exist, each governing the translational and the rotational dynamics of the particle, respectively. The particle radius is identified to present the essential quantity in charge of regulating the ratio between those timescales. For very small and very large particle radii, approximate analytic expressions for the particle’s escape rate can be derived, which, within their respective range of validity, compare favorably with the precise escape numerics of the underlying full two-dimensional Fokker-Planck description.

Description: A theoretical investigation of the effects of hill-like and cup-like parabolic confining electric potentials on photoionization cross section (PCS) in a spherical quantum dot is presented. The hill-like and the cup-like parabolic potentials are superimposed on an infinite spherical square well (ISSW) potential. As the cup-like parabolic potential intensifies, the peak of the PCS becomes redshifted for the s → p transition, and becomes blueshifted for the p → d , d → f (and so forth) transitions. The hill-like parabolic potential, on the contrary, blueshifts peaks of the PCS for s → p transitions, while it redshifts those of transitions between higher states as it intensifies. Consequently, the two potentials discriminate between transitions involving the ground state and those involving higher states.

Description: Recently it has been recognized that the electromotive force (emf) can be induced just by the spin precession where the generation of the electromotive force has been considered as a real-space topological pumping effect. It has been shown that the amount of the electromotive force is independent of the functionality of the localized moments. It was also demonstrated that the rigid domain wall (DW) motion cannot generate electromotive force in the system. Based on real-space topological pumping approach in the current study we show that the electromotive force can be induced by rigid motion of a deformed DW. We also demonstrate that the generated electromotive force strongly depends on the DW bulging. Meanwhile results show that the DW bulging leads to generation of the electromotive force both along the axis of the DW motion and normal to the direction of motion.

Description: We discuss the physics of the high temperature superconductivity in hole doped copper oxide ceramics in the pseudogap region. Starting from an effective reduced Hamiltonian relevant to the dynamics of holes injected into the copper oxide layers proposed in a previous paper, we determine the superconductive condensate wavefunction. We show that the low-lying elementary condensate excitations are analogous to the rotons in superfluid 4 He. We argue that the rotons-like excitations account for the specific heat anomaly at the critical temperature. We discuss and compare with experimental observations the London penetration length, the Abrikosov vortices, the upper and lower critical magnetic fields, and the critical current density. We give arguments to explain the origin of the Fermi arcs and Fermi pockets. We investigate the nodal gap in the cuprate superconductors and discuss both the doping and temperature dependence of the nodal gap. We suggest that the nodal gap is responsible for the doping dependence of the so-called nodal Fermi velocity detected in angle resolved photoemission spectroscopy studies. We discuss the thermodynamics of the nodal quasielectron liquid and their role in the low temperature specific heat. We propose that the ubiquitous presence of charge density wave in hole doped cuprate superconductors in the pseudogap region originates from instabilities of the nodal quasielectrons driven by the interaction with the planar CuO 2 lattice. We investigate the doping dependence of the charge density wave gap and the competition between charge order and superconductivity. We discuss the effects of external magnetic fields on the charge density wave gap and elucidate the interplay between charge density wave and Abrikosov vortices. Finally, we examine the physics underlying quantum oscillations in the pseudogap region.

Description: The time-dependent Mott transition in a periodic Anderson model with off-site, nearest-neighbor hybridization is studied within the framework of nonequilibrium self-energy functional theory. Using the two-site dynamical-impurity approximation, we compute the real-time dynamics of the optimal variational parameter and of different observables initiated by sudden quenches of the Hubbard- U and identify the critical interaction. The time-dependent transition is orbital selective, i.e., in the final state, reached in the long-time limit after the quench to the critical interaction, the Mott gap opens in the spectral function of the localized orbitals only. We discuss the dependence of the critical interaction and of the final-state effective temperature on the hybridization strength and point out the various similarities between the nonequilibrium and the equilibrium Mott transition. It is shown that these can also be smoothly connected to each other by increasing the duration of a U -ramp from a sudden quench to a quasi-static process. The physics found for the model with off-site hybridization is compared with the dynamical Mott transition in the single-orbital Hubbard model and with the dynamical crossover found for the real-time dynamics of the conventional Anderson lattice with on-site hybridization.

Description: The simplest model for itinerant ferromagnetism, the Stoner model, has so far eluded experimental observation in repulsive ultracold fermions due to rapid three-body recombination at large scattering lengths. Here we show that a ferromagnetic phase can be stabilised by imposing a moderate optical lattice. The reduced kinetic energy drop upon formation of a polarized phase in an optical lattice extends the ferromagnetic phase to smaller scattering lengths where three-body recombination is small enough to permit experimental detection of the phase. We also show, using time dependent density functional theory, that in such a setup ferromagnetic domains emerge rapidly from a paramagnetic initial state.

Description: One- and two-electron Green functions are simultaneously needed to determine the response functions of the electron gas in a random potential. Reliable approximations must retain consistency between the two types of Green functions expressed via Ward identities so that their output is compliant with macroscopic symmetries and conservation laws. Such a consistency is not directly guaranteed when summing nonlocal corrections to the local (dynamical) mean field. We analyze the reasons for this failure and show how the full Ward identity can generically be implemented in the diagrammatic approach to the vertex functions without breaking the analytic properties of the self-energy. We use the low-energy asymptotics of the conserving two-particle vertex determining the singular part of response and correlation functions to derive an exact representation of the diffusion constant in terms of Green functions of the perturbation theory. We then calculate explicitly the leading vertex corrections to the mean-field diffusion constant due to maximally-crossed diagrams.

Description: Uranium is an important radioactive material used in the field of nuclear energy and it is interesting from the scientific point of view because it possesses unique structure and properties. There exist several experimental reports on anomalies of physical properties of uranium that have not been yet explained. Manley et al. [Phys. Rev. Lett. 96 , 125501 (2006); Phys. Rev. B 77 , 214305 (2008)] speculate that the excitation of discrete breathers (DBs) could be the reason for anisotropy of thermal expansion and for the deviation of heat capacity from the theoretical prediction in the high temperature range. In the present work, with the use of molecular dynamics, the existence of DBs in α -uranium is demonstrated and their properties are studied. It is found that DB frequency lies above the phonon band and increases with DB amplitude. DB is localized on half a dozen of atoms belonging to a straight atomic chain. DB in uranium, unlike DBs in fcc, bcc and hcp metals, is almost immobile. Thus, the DB reported in this study cannot contribute to thermal conductivity and the search for other types of DBs in α -uranium should be continued. Our results demonstrate that even metals with low-symmetry crystal lattices such as the orthorhombic lattice of α -uranium can support DBs.

Description: A nonlinear Bazykin-Berezovskaya prey-predator model under the influence of parametric stochastic forcing is considered. Due to Allee effect, this conceptual population model even in the deterministic case demonstrates both local and global bifurcations with the change of predator mortality. It is shown that random noise can transform system dynamics from the regime of coexistence, in equilibrium or periodic modes, to the extinction of both species. Geometry of attractors and separatrices, dividing basins of attraction, plays an important role in understanding the probabilistic mechanisms of these stochastic phenomena. Parametric analysis of noise-induced extinction is carried out on the base of the direct numerical simulation and new analytical stochastic sensitivity functions technique taking into account the arrangement of attractors and separatrices.

Description: Zero-determinant strategies, which can unilaterally define a linear relationship between two individuals’ long-term payoff, have drawn much attention to comprehend the emergence of cooperation among individuals with repeated interactions. A subset of zero-determinant strategies, extortion strategy, can let an extortioner’s surplus exceed her opponent’s by a fixed percentage. On the other hand, the dual generosity strategy can ensure that a complier’s payoff is never larger than her opponent’s. In the framework of the prisoner’s dilemma game driven by payoff aspiration, we investigate in this paper the evolution of generosity strategy, in competition with extortion and unconditional defection strategies. We show that extortioners act as a catalyst to induce more defectors to change to compliers. Such influence will enhance when extortioners become more greedy. At a low aspiration level where individuals are easy to be satisfied with their current payoffs, different strategies can coexist. With the increase of aspiration level, unsatisfied individuals are likely to turn to compliers and build long-term reciprocity with their neighbors. However, at a high aspiration level, individuals are difficult to be satisfied with their payoffs and may randomly change their behaviors. Thus proper aspiration level promotes the emergence of generous behavior in the spatial prisoner’s dilemma game.

Description: We provide a compact expression of the ground-state energy of N -Cooper pairs valid from small to large sample volumes, as checked by numerically solving Richardson-Gaudin equations which give the exact eigenstates of BCS superconductors. This expression contains a contribution linear in the potential amplitude, dominant for small samples, and an exponential contribution dominant when the number of states available for pairing gets larger than a material-dependent threshold independent from sample size. These “available states” are the states feeling the BCS potential, reduced by the Pauli exclusion principle through a “ moth-eaten effect ” which comes from the composite boson nature of Cooper pairs. This work also presents an elegant derivation of the N -Cooper pair energy obtained recently, which makes use of the roots of the degree- N Hermite polynomial.

Description: How do local topological changes affect the global operation and stability of complex supply networks? Studying supply networks on various levels of abstraction, we demonstrate that and how adding new links may not only promote but also degrade stable operation of a network. Intriguingly, the resulting overloads may emerge remotely from where such a link is added, thus resulting in nonlocal failures. We link this counter-intuitive phenomenon to Braess’ paradox originally discovered in traffic networks. We use elementary network topologies to explain its underlying mechanism for different types of supply networks and find that it generically occurs across these systems. As an important consequence, upgrading supply networks such as communication networks, biological supply networks or power grids requires particular care because even adding only single connections may destabilize normal network operation and induce disturbances remotely from the location of structural change and even global cascades of failures.

Description: Structural and magnetic transitions of Ni 47.5- x Co x Mn 37.5 Sn 15 ( x  = 0, 1, 2 and 3.5) alloys were confirmed and studied by magnetic and resistivity measurements. Though a large magnetic entropy change ( Δ S M ) ~ 9.5 J/kg K was obtained for x  = 3.5 due to a change of only 1.5 T magnetic field, hysteresis losses limited its refrigerant capacity to a significant extent. A maximum –69% magnetoresistance was obtained due to a structural transition in the same sample in presence of 8 T field. It was found that the same material can be used for practical applications within a wide range of temperature as it shows large magnetoresistance at remote temperatures far below from its structural transition point.

Description: We investigate the dynamical interplay between magnetic and ferroelectric orders in a multiferroics with distorted spiral order. We find that the combing effect of the distortion of the spiral order and the effective spin anisotropy induced by the spin-lattice coupling results in the lifting of the degenerate gapped mode at the ordering wave vector, which is qualitatively in agreement with the experimental observations. In analogy to the perfect spiral spin structure, the electromagnon can be assigned to spin wave mode of the distorted helimagnet at the ordering wave vector. The electromagnon in the distorted helimagnets is also affected by the helix distortion which can be experimentally controlled.

Description: We report a study on thermodynamic properties of a two-dimensional electron gas confined in a sector of a circular cylinder immersed in a dc magnetic field perpendicular to its axis. This field configuration produces on the electrons in the curved surface, effects similar to a non-homogeneous magnetic field on a flat system. We study these effects by calculating the energy spectra for different curvature radius and symmetries of the magnetic field with respect to the surface. The analysis of the density of states, chemical potential and specific heat of these systems helps to understand the correlation between the externally controlled symmetry and their physical properties.

Description: During the past few years, users’ membership in the online system (i.e. the social groups that online users joined) were widely investigated. Most of these works focus on the detection, formulation and growth of online communities. In this paper, we study users’ membership in a coupled system which contains user-group and user-object bipartite networks. By linking users’ membership information and their object selection, we find that the users who have collected only a few objects are more likely to be “influenced” by the membership when choosing objects. Moreover, we observe that some users may join many online communities though they collected few objects. Based on these findings, we design a social diffusion recommendation algorithm which can effectively solve the user cold-start problem. Finally, we propose a personalized combination of our method and the hybrid method in [T. Zhou, Z. Kuscsik, J.G. Liu, M. Medo, J.R. Wakeling, Y.C. Zhang, Proc. Natl. Acad. Sci. 107 , 4511 (2010)], which leads to a further improvement in the overall recommendation performance.

Description: Realistic models of α -helix proteins are composed of three covalently-bonded strands, each of which is made of hydrogen-bonded peptide units. The modulational instability analysis of such complex molecular systems is carried out in this work. We show that the exciton-vibron coupling parameter contributes to the explosion and expansion of instability regions. The right choice of the modulational instability parameters leads to the formation of excitonic modulated pulse-like structures. It is argued that covalent bonds are compressed during the process of energy transport, while hydrogen bond oscillations display regular trains of breather-like objects. We also argue that the probable way of energy transport, from modulational instability, is through hydrogen bonds.

Description: A novel allotrope of carbon with P 2/ m symmetry was identified during an ab initio minima-hopping structural search which we call M 10-carbon. This structure is predicted to be more stable than graphite at pressures above 14.4 GPa and consists purely of s p 3 bonds. It has a high bulk modulus and is almost as hard as diamond. A comparison of the simulated X-ray diffraction pattern shows a good agreement with experimental results from cold compressed graphite.

Description: It is shown that the defect-deformational (DD) cooperative nucleation of ordered ensembles of nanoparticles on isotropic surfaces of solids with the participation of quasi-Rayleigh waves can be described by a closed two-dimensional nonlinear DD equation of the Kuramoto-Sivashinsry (KS) type. A solution to the linearized DDKS equation describes the threshold appearance of the periodic surface strain modulation accompanied by the simultaneous formation of adatom (surface defect) piles at extrema of the surface strain. Numerical solutions to the DDKS equation in linear and nonlinear regimes describe the formation of three types of surface structures of adatom piles (clusters): lamellar-like structures, cellular disordered and hexagonal ordered ones. In the well-developed nonlinear regime, generated ensembles of nanoparticles become trimodal regarding their size distribution due to the generation of the second harmonics, degenerate parametric decay and summation of wavevectors of DD gratings taking part in the DD selforganization. The selforganizing periodic cellular DD surface structure can serve as a selforganized template for the subsequent growth of nanoparticles in the processes of atoms deposition.

Description: Ab initio computational methods are used to study the relevance of van der Waals interactions in the case of a hydrogen molecule adsorption on the Ru(0001) surface. In addition to the clean surface, the effects of ruthenium adatom and vacancy on the process are studied. The adsorption characteristics are analyzed in terms of two dimensional cuts of the potential energy surface (PES). Based on the earlier studies for such systems, we mostly concentrate on the trajectories where the hydrogen molecule approaches the surface in parallel orientation. The results indicate that for a clean Ru(0001) the calculations applying the non-local van der Waals potentials yield higher barriers for the dissociation of the H 2 molecule. Of the high symmetry sites on Ru(0001), the top site is found to be the most reactive one. The vacancy and ruthenium adatom sites exhibit high dissociation barriers compared with the clean surface.

Description: In the present paper, the site-percolation problem corresponding to linear k -mers (containing k identical units, each one occupying a lattice site) on a simple cubic lattice has been studied. The k -mers were irreversibly and isotropically deposited into the lattice. Then, the percolation threshold and critical exponents were obtained by numerical simulations and finite-size scaling theory. The results, obtained for k ranging from 1 to 100, revealed that (i) the percolation threshold exhibits a decreasing function when it is plotted as a function of the k -mer size; and (ii) the phase transition occurring in the system belongs to the standard 3D percolation universality class regardless of the value of k considered.

Description: The nonlinear Landau-Zener tunneling of a Bose-Fermi mixture in a double-well potential is studied in the present paper. The effect of interaction parameters on bosonic and fermionic tunneling probability is studied for the mixture of 40 K- 87 Rb. The tunneling phenomena of the system can be controled by adjusting sweeping rate, intraspecies interaction, interspecies interaction and the numbers of bosons and fermions. It is noted that there are three different regions in phase diagram: self-trapping (ST), complete tunneling (CT) and incomplete tunneling (ICT).

Description: We present the exact solution, obtained by means of the Transfer Matrix (TM) method, of the 1D Hubbard model with nearest-neighbor (NN) and next-nearest-neighbor (NNN) Coulomb interactions in the atomic limit ( t  = 0). The competition among the interactions ( U , V 1 , and V 2 ) generates a plethora of T  = 0 phases in the whole range of fillings. U , V 1 , and V 2 are the intensities of the local, NN and NNN interactions, respectively. We report the T  = 0 phase diagram, in which the phases are classified according to the behavior of the principal correlation functions, and reconstruct a representative electronic configuration for each phase. In order to do that, we make an analytic limit T  → 0 in the transfer matrix, which allows us to obtain analytic expressions for the ground state energies even for extended transfer matrices. Such an extension of the standard TM technique can be easily applied to a wide class of 1D models with the interaction range beyond NN distance, allowing for a complete determination of the T  = 0 phase diagrams.

Description: The electronic structures of the Fe-doped perovskite ruthenates BaRu 1− x Fe x O 3 with x  = 0, 0.25, 0.5, 0.625, 0.75, and 1 are investigated through density-functional calculations. Large exchange splitting and small crystal field splitting are found in BaFeO 3 , and a contrary scenario can take place on BaRuO 3 as expected since the Ru atom has a highly extended 4 d orbital. The small exchange splitting and extended 4 d states are the reasons why the obtained spin magnetic moment (0.628 μ B ) is significantly lower than the spin only value (2 μ B ) for the t 2 g 3↑  t 2 g 1↓ electronic configuration for Ru 4+ ion. Further investigations suggest that Fe substitution at the Ru sites can suppress the bandwidths of Ru 4 d orbital, leading to the half-metallic behaviour in BaRu 1− x Fe x O 3 with x  = 0.625 and 0.75. The different orbital feature of the Ru 4+ ions in BaRu 0.375 Fe 0.625 O 3 is presented, which reflects the influence of Fe dopant on Ru 4 d orbitals.

Description: Current-driven domain wall dynamics is studied theoretically in the spin-valve nanostrips with parallel, perpendicular and tilted polarizers by Lagrangian formalism. In this description, the Slonczewski and field-like spin-transfer torques act as a Coulomb-type dissipation and an effective magnetic field, respectively. Considering a Walker profile, the wall behavior is governed by the dynamic equations about the center position, the out-of-plane angle, and the width of walls. It is found that the wall precesses after the steady motion breaks down for the parallel polarizer. The field-like spin-transfer torque favors a rapid increase of the steady velocity. The average velocity in the precession is nearly proportional to the current density. On the other hand, there is no precession for the perpendicular and tilted polarizers. Under the perpendicular polarizer, the wall stops when increasing current density. Moreover, there exist hysteresis and tri-stability for a large spin polarization. Under the tilted polarizer, it can be observed hysteretic, linear and nonlinear dependence of the wall velocity on the increasing current density. In the hysteresis, the wall experiences a switching of polarity or a reversal of motion.

Description: The effects of nonlinearities in the equations of motion of thermally fluctuating systems are investigated based on the Langevin equation. We identify the first terms in the expansions of equilibrium correlation functions and dynamic susceptibilities in powers of the thermal noise strength. The resulting expressions are explicitly evaluated for the case of overdamped diffusion in two monostable but anharmonic potentials, as well as in a double-well potential. The comparison to the results of numerical simulations allows to estimate the range of validity of our analytical results. Moreover, we provide a simple method to detect nonlinearities in the fluctuating time series data of a system in thermal equilibrium and discuss the resulting implications for the dynamics of composite systems. Finally, our findings shed light on the limitations of a recently introduced linear dynamic convolution theory, for which we derive a first-order correction term.

Description: We investigate the effect of a transverse field on a cylindrical core/shell spin-1 Ising nanowire, within the effective-field theory based on a probability distribution technique, in order to clarify how the relevant thermodynamic quantities such a magnetizations, hysteresis loops, compensation behaviors, are influenced by a transverse field. From these studies, following interesting phenomena are found. (i) Beside a singly hysteresis loop, double, triple or even quadruple hysteresis loops occurs in the system. (ii) The P and N types of compensation behavior are obtained in addition to the Q-, R- and S-types. We also compare our results with some experimental and theoretical results and find in a qualitatively good agreement.

Description: We introduce a new test for detection of power-law cross-correlations among a pair of time series – the rescaled covariance test. The test is based on a power-law divergence of the covariance of the partial sums of the long-range cross-correlated processes. Utilizing a heteroskedasticity and auto-correlation robust estimator of the long-term covariance, we develop a test with desirable statistical properties which is well able to distinguish between short- and long-range cross-correlations. Such test should be used as a starting point in the analysis of long-range cross-correlations prior to an estimation of bivariate long-term memory parameters. As an application, we show that the relationship between volatility and traded volume, and volatility and returns in the financial markets can be labeled as the power-law cross-correlated one.

Description: An analytical expression is derived for the electron thermionic current from heated metals by using a non equilibrium, modified Kappa energy distribution for electrons. This isotropic distribution characterizes the long high energy tails in the electron energy spectrum for low values of the index κ and also accounts for the Fermi energy for the metal electrons. The limit for large κ recovers the classical equilibrium Fermi-Dirac distribution. The predicted electron thermionic current for low κ increases between four and five orders of magnitude with respect to the predictions of the equilibrium Richardson-Dushmann current. The observed departures from this classical expression, also recovered for large κ , would correspond to moderate values of this index. The strong increments predicted by the thermionic emission currents suggest that, under appropriate conditions, materials with non equilibrium electron populations would become more efficient electron emitters at low temperatures.

Description: We describe linear and nonlinear transport across a strongly interacting single impurity Anderson model quantum dot with intermediate coupling to the leads, i.e. with tunnel coupling Γ of the order of the thermal energy k B T . The coupling is large enough that sequential tunneling processes (second order in the tunneling Hamiltonian) alone do not suffice to properly describe the transport characteristics. Upon applying a density matrix approach, the current is expressed in terms of rates obtained by considering a very small class of diagrams which dress the sequential tunneling processes by charge fluctuations. We call this the “dressed second order” (DSO) approximation. One advantage of the DSO is that, still in the Coulomb blockade regime, it can describe the crossover from thermally broadened to tunneling broadened conductance peaks. When the temperature is decreased even further ( k B T 〈 Γ ), the DSO captures Kondesque behaviours of the Anderson quantum dot qualitatively: we find a zero bias anomaly of the differential conductance versus applied bias, an enhancement of the conductance with decreasing temperature as well as universality of the shape of the conductance as function of the temperature. We can without complications address the case of a spin degenerate level split energetically by a magnetic field. In case spin dependent chemical potentials are assumed and only one of the four chemical potentials is varied, the DSO yields in principle only one resonance. This seems to be in agreement with experiments with pseudo spin [U. Wilhelm, J. Schmid, J. Weis, K.V. Klitzing, Physica E 14 , 385 (2002)]. Furthermore, we get qualitative agreement with experimental data showing a cross-over from the Kondo to the empty orbital regime.

Description: We use the Schwinger boson mean field theory to study the effect of frustration and dimerization in the quantum ferrimagnetic model in one and two-dimensions. We calculate the spin reduction, the gap of the antiferromagnetic branch, and the spin fluctuation at T  = 0 K. At finite temperature, the long-range order is destroyed because of the disappearance of the Bose condensation. The free energy, the magnetic susceptibility and the spin correlations at T  = 0 K, are calculated. The effects of frustration and dimerization are discussed.

Description: We considerer that a population of individuals governed by the Nagumo model is subjected to a crisis that stimulates a predisposition towards aggregation. We assume that this trend is based on the physical mechanisms of attraction between individuals. Then we describe the post-crisis dynamics and find possible states of survival (stationary solutions). We see a dynamic rich in options with several possible survival responses.

Description: We study a disordered 2D electron gas with a spectral node in a vicinity of the node. After identifying the fundamental dynamical symmetries of this system, the spontaneous breaking of the latter by a Grassmann field is studied within a nonlinear sigma model approach. This allows us to reduce the average two-particle Green’s function to a diffusion propagator with a random diffusion coefficient. The latter has non-degenerate saddle points and is treated by the conventional self-consistent Born approximation. This leads to a renormalized chemical potential and a renormalized diffusion coefficient, where the DC conductivity increases linearly with the density of quasiparticles. Applied to the special case of Dirac fermions, our approach provides a comprehensive description of the minimal conductivity at the Dirac node as well as for the V-shape conductivity inside the bands.

Description: In the present contribution we apply first principles calculations to investigate the electronic structures and stability of BN hydrogenated monolayers which include a substitutional carbon atom. For comparison, additional C hydrogenated structures are considered. The obtained results demonstrate that BN chair-like monolayers are more stable than boat-like configurations. It is found that the most stable structures present bond angles quite similar to the characteristic one observed for s p 3 hybridization. Moreover, a net magnetic moment arises from the introduction of a substitutional carbon impurity. In addition, the results indicate that carbon substitutionals can induce a remarkable reduction of the work function.

Description: Using a recently proposed algorithmic scheme for correlation dimension analysis of hyperchaotic attractors, we study two well-known hyperchaotic flows and two standard time delayed hyperchaotic systems in detail numerically. We show that at the transition to hyperchaos, the nature of the scaling region changes suddenly and the attractor displays two scaling regions for embedding dimension M  ≥ 4. We argue that it is an indication of a strong clustering tendency of the underlying attractor in the hyperchaotic phase. Because of this sudden qualitative change in the scaling region, the transition to hyperchaos can be easily identified using the discontinuous changes in the dimension ( D 2 ) at the transition point. We show this explicitely for the two time delayed systems. Further support for our results is provided by computing the spectrum of Lyapunov Exponents (LE) of the hyperchaotic attractor in all cases. Our numerical results imply that the structure of a hyperchaotic attractor is topologically different from that of a chaotic attractor with inherent dual scales, at least for the two general classes of hyperchaotic systems we have analysed here.

Description: We have investigated the realizability of the controlled-not (cnot) gate and characterized the gate operation by quantum process tomography for a chain of qubits, realized by electrons confined in self-assembled quantum dots embedded in the spin field-effect transistor. We have shown that the cnot gate operation and its process tomography are performable by using the spin exchange interaction and several local qubit rotations within the coherence time of qubits. Moreover we have taken into account the fluctuation of operation time and the imperfection of polarization of channel electrons as sources of decay of fidelity. The cnot process fidelity decreases only by at most 5% by the fluctuation of the operation time and its values as high as 0.49 and 0.72 are obtained for the channel spin polarizations of 0.6 and 0.8, respectively.

Description: The multivariable theory of nucleation in Langevin’s approach [N.V. Alekseechkin, J. Chem. Phys. 124 , 124512 (2006); N.V. Alekseechkin, J. Chem. Phys. 129 , 024512 (2008)] is applied to the problem of vapor bubbles formation in a liquid with arbitrary viscosity. The obtained expression for the nucleation rate of bubbles is valid for arbitrary relations between the kinetic parameters controlling the nucleation process: viscosity, inertia of a liquid, the rate of evaporation into a bubble and the rate of heat exchange between the bubble and ambient liquid. So, the presented theory yields a complete description of the vapor-bubbles nucleation kinetics in single-component liquids. Limiting cases with respect to the mentioned parameters are considered, in particular, the low-viscosity limit. It is shown that the low- and high-viscosity nucleation rates differ from each other qualitatively and quantitatively. The possibility of application of the theory to cavitation in superfluid helium-4 is discussed.

Description: The electronic and magnetic properties of 6H-SiC with Mn impurities have been calculated using GGA formalism. Various configurations of Mn sites were considered. It was found that 6H-SiC doped with Mn atoms possess a moment for both types of substitution. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The energy levels appearing in the band gap due to vacancies and due to Mn impurities are determined and the calculated densities of states (DOSs) are used to analyse the different value of the magnetic moments for different types of substitution. A model that explains the magnetic moment at Mn site is proposed.

Description: The Íslendinga sögur – or Sagas of Icelanders – constitute a collection of medieval literature set in Iceland around the late 9th to early 11th centuries, the so-called Saga Age . They purport to describe events during the period around the settlement of Iceland and the generations immediately following and constitute an important element of world literature thanks to their unique narrative style. Although their historicity is a matter of scholarly debate, the narratives contain interwoven and overlapping plots involving thousands of characters and interactions between them. Here we perform a network analysis of the Íslendinga sögur in an attempt to gather quantitative information on interrelationships between characters and to compare saga society to other social networks.

Description: We report the quasiparticle band structure and optical absorption spectrum of bulk LiBr calculated from first-principles approaches. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, the optical excitation is investigated by solving the Bethe-Salpeter equation for the electron-hole two-particle Green’s function. The obtained results for the band gap and optical absorption spectrum are in good agreement with experimental measurements.