ALBERT

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.

Description: The aim of this article is to present an overview about the preparation method and physical properties of a new hybrid system consisting of single-walled carbon nanotubes (SWNTs) wrapped by conjugated polymers. The technique firstly demonstrated in 2007 has attracted great interest because of the high purity of the resulting semiconducting SWNTs and the possibility of applying them in electronic devices. Here, we will review recent progresses regarding the preparation of these nano-hybrids, their photophysical properties and application in field-effect transistors and photovoltaic devices.

Description: In this paper, we propose a family of weighted extended Koch networks based on a class of extended Koch networks. They originate from a r -complete graph, and each node in each r -complete graph of current generation produces mr -complete graphs whose weighted edges are scaled by factor  h in subsequent evolutionary step. We study the structural properties of these networks and random walks on them. In more detail, we calculate exactly the average weighted shortest path length (AWSP), average receiving time (ART) and average sending time (AST). Besides, the technique of resistor network is employed to uncover the relationship between ART and AST on networks with unit weight. In the infinite network order limit, the average weighted shortest path lengths stay bounded with growing network order (0 〈  h  〈 1). The closed form expression of ART shows that it exhibits a sub-linear dependence (0 〈  h  〈 1) or linear dependence ( h  = 1) on network order. On the contrary, the AST behaves super-linearly with the network order. Collectively, all the obtained results show that the efficiency of message transportation on weighted extended Koch networks has close relation to the network parameters  h , m  and  r . All these findings could shed light on the structure and random walks of general weighted networks.

Description: Specific heat and magnetization measurements demonstrate that the antiferromagnetic (AFM) phase transition at T N  = 5.7 K of EuTiO 3 is rapidly suppressed with Sr doping in Eu x Sr 1− x TiO 3 . Close to x  = 0.25, T N  = 0 K and AFM order vanishes. Above this critical concentration a finite transition temperature to an AFM phase is observed. The exchange couplings are derived as a function of x and the corresponding low temperature phase diagram is presented.

Description: Going beyond the limitations of our earlier works [X. Zheng, F. Wang, C.Y. Yam, Y. Mo, G.H. Chen, Phys. Rev. B  75 , 195127 (2007); X. Zheng, G.H. Chen, Y. Mo, S.K. Koo, H. Tian, C.Y. Yam, Y.J. Yan, J. Chem. Phys. 133 , 114101 (2010)], we propose, in this manuscript, a new alternative approach to simulate time-dependent quantum transport phenomenon from first-principles. This new practical approach, still retaining the formal exactness of HEOM framework, does not rely on any intractable parametrization scheme and the pole structure of Fermi distribution function, thus, can seamlessly incorporated into first-principles simulation and treat transient response of an open electronic systems to an external bias voltage at both zero and finite temperatures on the equal footing. The salient feature of this approach is surveyed, and its time complexity is analysed. As a proof-of-principle of this approach, simulation of the transient current of one dimensional tight-binding chain, driven by some direct external voltages, is demonstrated.

Description: The dynamics of α -helical proteins with interspine coupling by taking into account long-range dipole-dipole interactions and some additional higher order molecular excitations is studied. The model Hamiltonian is transformed into a set of three classical lattice equations, which are further reduced in the multiple scales analysis to a set of three coupled nonlinear Schrödinger (3-CNLS) equations. The linear stability analysis of continuous wave solutions of these 3-CNLS equations is performed and it reveals that the modulational instability (MI) gain is deeply influenced by the long-range interactions (LRI) parameter. Some classes of exact traveling wave solutions are constructed via the solutions of a φ 4 model through the F-expansion method and representative wave structures are graphically displayed including localized and periodic solutions. In order to confirm the analytical approach, the numerical experiments show that the solitons are stable at 70 ps. These solitons, exhibited in the model, are a possible carrier of bio-energy transport in the protein molecules.

Description: It is well-known that cooperative properties such as magnetic ordering can depend on the samples’ dimensions ( D s) in a qualitative way. However, there have been no samples with well-defined non-integer D s. The dimension of a given sample has been always discussed on the anisotropy of the electronic/crystal/magnetic structures, which has no definition suitable for quantitative discussion on dimensions vs. properties. On the other hand a particular type of porous samples, i.e. fractal bodies, can have well-defined non-integer D s dependent exclusively on the geometrical feature of structures, and physical properties of such materials remains unexplored. This paper reports on magnetic ordering in samples covering 2.5 ≤  D  ≤ 3, in addition to a way of precise control of the fractal dimensions of given samples simply by wax (alkylketene dimer). The results show that the magnetic ordering temperatures, i.e. Néel temperatures ( T N s), of CoO depend on D , and rapidly enhance immediately below D  = 3. This means that one can control or enhance the critical temperature simply by tuning D with keeping the remaining magnetic properties unchanged.

Description: We report low-temperature susceptibility and magnetisation data for the cubic pyrochlore Er 2 Ti 2 O 7 . By performing the measurements on single crystals we are able to establish the degree of magnetic anisotropy present in this compound and to determine the critical values for magnetic field induced transitions below the magnetic ordering temperature of 1.2 K. We also present a magnetic H - T phase diagram of this quantum XY antiferromagnet for different directions of an applied field.

Description: We simulate the three-dimensional quantum Heisenberg model with a spatially anisotropic ladder pattern using the first principles Monte Carlo method. Our motivation is to investigate quantitatively the newly established universal relation T N /√ c 3 ∝ ℳ s near the quantum critical point (QCP) associated with dimerization. Here T N , c , and ℳ s are the Néel temperature, the spinwave velocity, and the staggered magnetization density, respectively. For all the physical quantities considered here, such as T N and ℳ s , our Monte Carlo results agree nicely with the corresponding results determined by the series expansion method. In addition, we find it is likely that the effect of a logarithmic correction, which should be present in (3 + 1)-dimensions, to the relation T N /√ c 3 ∝ ℳ s near the investigated QCP only sets in significantly in the region with strong spatial anisotropy.

Description: Non-adiabatic effects in quantum escapes of a particle via a time-dependent potential barrier in a semi-infinite one-dimensional space are discussed. We describe the time-evolution of escape states in terms of scattering states of the open system with a time-periodic potential by Floquet’s theorem and the Lippmann-Schwinger equation, and calculate concretely the probability P ( t ) for a particle to remain in the initially confined region at time t in the case of a delta-function potential with a time-oscillating magnitude. The probability P ( t ) decays exponentially in time at early times, then decays as a power later, along with a time-oscillation in itself. We show that a larger time-oscillation amplitude of the potential leads to a faster exponential decay of P ( t ), while it can rather enhance the probability P ( t ) decaying as a power. An explanation based on an average of adiabatic decays of P ( t ) is given to describe qualitatively these contrastive properties of P ( t ) in different types of decay. By investigating quantitative differences between the survival probability given from a direct solution of the Schrödinger equation with the time-oscillating potential and that obtained by an average of adiabatic decays, we clarify non-adiabatic effects in the decay time and the power decay magnitude of P ( t ).

Description: We report on the magnetic properties of four isomorphous compounds of a family of quinternary oxalates down to 60 mK. In all these materials, the magnetic Fe II ions with a strong magneto-crystalline anisotropy form a distorted kagome lattice, topologically equivalent to a perfect kagome one if nearest-neighbor interactions only are considered. All the compounds order at low temperature in an antiferromagnetic arrangement with magnetic moments at 120°. A remarkable magnetic behavior emerges below the Néel temperature in three compounds (with inter-kagome-layer Zr, Sn, Fe but not with Al): the spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce an unfamiliar slow spin dynamics in the ordered phase observed by AC susceptibility, evolving from exchange-released spin-flips towards a cooperative behavior on decreasing the temperature.

Description: We extend our previous approach [J. Kurzyk, W. Wójcik, J. Spalek, Eur. Phys. J. B 66 , 385 (2008); J. Spałek, J. Kurzyk, R. Podsiadły, W. Wójcik, Eur. Phys. J. B 74 , 63 (2010)] to modeling correlated electronic states and the metal-insulator transition by applying the so-called statistically consistent Gutzwiller approximation (SGA) to carry out self-consistent calculations of the renormalized single-particle Wannier functions in the correlated state. The transition to the Mott-Hubbard insulating state at temperature T  = 0 is of weak first order even if antiferromagnetism is disregarded. The magnitude of the introduced self-consistent magnetic correlation field is calculated and shown to lead to a small magnetic moment in the magnetically uniform state. Realistic value of the applied magnetic field has a minor influence on the metallic-state characteristics near the Mott-Hubbard localization threshold. The whole analysis has been carried out for an extended Hubbard model on a simple cubic (SC) lattice and the evolution of physical properties is analyzed as a function of the lattice parameter for the renormalized 1 s -type Wannier functions. Quantum critical scaling of the selected physical properties is analyzed as a function of the lattice constant R  →  R c  = 4.1 a 0 , where R c is the critical value for metal-insulator transition and a 0  = 0.53 Å is the Bohr radius. A critical pressure for metallization of solid atomic hydrogen is estimated and is ~10 2 GPa.

Description: Magnetic particles are largely utilized in several applications ranging from magnetorheological fluids to bioscience and from nanothechnology to memories or logic devices. The behavior of each single particle at finite temperature (under thermal stochastic fluctuations) plays a central role in determining the response of the whole physical system taken into consideration. Here, the magnetization evolution is studied through the Landau-Lifshitz-Gilbert formalism and the non-equilibrium statistical mechanics is introduced with the Langevin and Fokker-Planck methodologies. As result of the combination of such techniques we analyse the stochastic magnetization dynamics and we numerically determine the convergence time, measuring the velocity of attainment of thermodynamic equilibrium, as function of the system temperature.

Description: We propose a lattice Monte Carlo model of two populations, predators and prey. We divide predators into cooperative predators and defective predators. Cooperative predators participate in hunting. On the other hand, defective predators only participate to dominate, i.e. take possession of, the food when a kill has already been made by a cooperative predator. Numerous factors have been taken into account in our research, such as individual mobility, predation and hunger time. The model we have constructed displays the features of the population that evolve through time and the spatial distribution of the population. We focus on the emergence of defective predators and how the parameters affect the system. The results indicate that prey can profit from the appearance of these defective predators in some specific situations. It has even been shown that the emergence of defective predators can sometimes save endangered systems.

Description: The remanent magnetization M r on easy-axis antiferromagnetic single crystal K 2 FeCl 5 ·H 2 O is investigated. The sign of the remanent magnetization depends on the direction of the applied magnetic field  H ; if it is perpendicular to the easy axis of antiferromagnet then the sign of the remanent magnetization is positive, i.e. it coincides with the sign of the magnetic field in which the sample was cooled down below  T N . Instead, if the magnetic field is directed along the easy axis then the sign of the remanent magnetization is negative and its absolute value is three orders of magnitude larger than usual magnetization M ( T N , H ).

Description: In this work, calculations and preliminary experimental data for determining the optimal condition for the selective bio-functionalization of magnetic tunneling junction (MTJ)-based biosensors are presented. Results on the detection of biomolecular recognition events employing MTJ-based sensor and magnetic beads are presented and interpreted through calculations, taking into account the dependence of the signal on the distribution of the beads with respect to the sensor. Furthermore, it is demonstrated by calculations that a significant increase in the sensor sensitivity and quantification capability can be achieved by selectively bio-functionalizing an area which corresponds to the sensor active area.

Description: In this work, by using the discrete dipole approximation (DDA), we have proposed a model for the growth of chiral nano-flower shaped sculptured nanoparticle in different sizes and different symmetries (e.g., 3-, 4- and 5-fold symmetries) and calculated the extinction spectra for these nanostructures identifying their plasmon peaks. Our results show that the extinction spectrum obtained experimentally for a chiral nano-flower sculptured thin film can be the result of the overlap of extinction spectra from an assembly of chiral nanoflowers forming the deposited thin film. Furthermore, we have investigated carefully the distribution of electric nearfields and have deduced the physical nature and direction of oscillations related to different plasmon peaks in the extinction spectra. Results show the existence of dipolar and quadrupolar oscillations in all structures while for the 4-fold symmetry chiral nano-flower, we have also observed octopolar oscillations. The calculated results are compared with the experimental results reported by us in [H. Savaloni, F. Haydari-Nasab, M. Malmir, Appl. Surf. Sci. 257 , 9044 (2011)]. In addition, using the homogenization theory we have shown that the optical response of metallic structures is affected by a limited thickness of thin film and further increase of the film thickness has no effect on the optical spectra.

Description: We investigate the properties of a recently introduced asymmetric association measure, called inner composition alignment (IOTA), aimed at inferring regulatory links (couplings). We show that the measure can be used to determine the direction of coupling, detect superfluous links, and to account for autoregulation. In addition, the measure can be extended to infer the type of regulation (positive or negative). The capabilities of IOTA to correctly infer couplings together with their directionality are compared against Kendall’s rank correlation for time series of different lengths, particularly focussing on biological examples. We demonstrate that an extended version of the measure, bidirectional inner composition alignment (biIOTA), increases the accuracy of the network reconstruction for short time series. Finally, we discuss the applicability of the measure to infer couplings in chaotic systems.

Description: We consider a simple mesoscopic model of an excitable thermochemical system for which the system temperature as a function of time has a form of irregular spikes. The interspike intervals are mapped onto elements of a formal alphabet. The time evolution of system temperature is represented by a string over this alphabet. We demonstrate that the entropy of such string reaches a minimum for the values of model parameters where the coherence resonance of interspike intervals is observed.

Description: We consider the influence of internal fluctuations on the behavior of a bistable thermochemical system with a low temperature stable focus surrounded by a stable limit cycle arising from the subcritical Hopf bifurcation. We use a master equation approach to study the transitions between basins of these attractors. Distribution functions of first passage times from the limit cycle to the focus are obtained for systems with various numbers of molecules and reaction heats. We consider in detail the specific, multi-peak form of the distributions caused by eccentric location of the limit cycles with respect to the focus.

Description: Magnetic nanoparticles were produced in ZnO single crystals using ion implantation of Ni along the [0001] channelling direction of ZnO. The particles were identified by X-ray diffraction and magnetization measurements as a distribution of superparamagnetic nickel nanoparticles having diameters in the range 2 − 3 nm. The depth distribution and size of the particles were determined using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The obtained results agree with magnetization and X-ray diffraction (XRD) data. From the determined depth distribution, the density change of implanted region of the material modified by the implantation procedure was estimated.

Description: Magnetic properties of Ising nanoparticles with spin-1/2 core and spin-3/2 shell structure are systematically studied by the use of the effective-field theory with correlations. Particular emphasis is given to the effects of the crystal-field, core and shell interactions and interface coupling on magnetizations, compensations points, magnetic susceptibilities and hysteresis behaviors. In order to confirm the stability of the solutions we also investigate the free energy of the system. According to values of Hamiltonian parameters, the system only undergoes a second-order phase transition. A number of characteristic behaviors are found, such as the existence of triple hysteresis loops for appropriate values of the system parameters affected by the crystal field, temperature, and interface coupling. Moreover, Q-, R-, N-, M-, P- and S-types of compensation behaviors in the Néel classification nomenclature exist in the system that are also strongly dependent on interaction parameters; hence, one or two compensation points have been found. The results are compared with those of recently published works and a qualitatively good agreement is found.

Description: Monte Carlo simulations of heterogeneous systems of copper at liquid-vapor equilibrium have been performed at several temperatures from 1400 to 2000 K, using the EAM potential of Zhou et al. [Phys. Rev. B 69 , 144113 (2004)]. Surface tension of the corresponding planar interfaces has been evaluated using thermodynamic and mechanical approaches. We have investigated the impact of the potential and the temperature on the surface tension of liquid copper. For the first time, calculation results are in very good agreement with experiments with a maximum deviation of 2% from experiments. Additionally, the Monte Carlo simulations provide a temperature coefficient (the derivative of surface tension in regard with temperature) in excellent agreement with the experimental coefficient. This was one of the main challenges of the present simulations.

Description: The classical preferential attachment model is sensitive to the choice of the initial configuration of the network. As the number of initial nodes and their degree grow, so does the time needed for an equilibrium degree distribution to be established. We study this phenomenon, provide estimates of the equilibration time, and characterize the degree distribution cutoff observed at finite times. When the initial network is dense and exceeds a certain small size, there is no equilibration and a suitable statistical test can always discern the produced degree distribution from the equilibrium one. As a by-product, the weighted Kolmogorov-Smirnov statistic is demonstrated to be more suitable for statistical analysis of power-law distributions with cutoff when the data is ample.

Description: Based on a two-dimensional atomistic model, we study the bifurcation associated with crack propagation and kinking. In the study, the varying parameter is the tensile and shear strain applied at the boundary. Both mode-I and mixed mode-I/II loading are considered.

Description: Firm growth process in the developing economies is known to produce divergence in their growth path giving rise to bimodality in the size distribution. Similar bimodality has been observed in wealth distribution as well. Here, we introduce a modified kinetic exchange model which can reproduce such features. In particular, we will show numerically that a nonlinear retention rate (or savings propensity) causes this bimodality. This model can accommodate binary trading as well as the whole system-side trading thus making it more suitable to explain the non-standard features of wealth distribution as well as firm size distribution.

Description: The browsing behavior of massive web users forms a flow network transporting user’ collective attention between websites. By analyzing the circulation of the collective attention we discover the scaling relationship between the impact of sites and their traffic. We construct three clickstreams networks, whose nodes were websites and edges were formed by the users’ switching between sites. The impact of site i , C i , is measured by the clickstreams controlled by this site in the circulation of clickstreams. We find that C i scales sublinearly with A i , the traffic of site i . Specifically, there existed a relationship C i  ~  A i γ ( γ  〈 1), which implies the decentralized structure of the clickstream circulation.

Description: We investigate the critical behavior of the three-dimensional random-field Ising model (RFIM) with a Gaussian field distribution at zero temperature. By implementing a computational approach that maps the ground-state of the RFIM to the maximum-flow optimization problem of a network, we simulate large ensembles of disorder realizations of the model for a broad range of values of the disorder strength  h and system sizes

Description: Within the composite operator method (COM), we report the solution of the Emery model (also known as p - d or three band model), which is relevant for the cuprate high- T c superconductors. We also discuss the relevance of the often-neglected direct oxygen-oxygen hopping for a more accurate, sometimes unique, description of this class of materials. The benchmark of the solution is performed by comparing our results with the available quantum Monte Carlo ones. Both single-particle and thermodynamic properties of the model are studied in detail. Our solution features a metal-insulator transition at half filling. The resulting metal-insulator phase diagram agrees qualitatively very well with the one obtained within dynamical mean-field theory. We discuss the type of transition (Mott-Hubbard (MH) or charge-transfer (CT)) for the microscopic (ab initio) parameter range relevant for cuprates getting, as expected a CT type. The emerging single-particle scenario clearly suggests a very close relation between the relevant sub-bands of the three- (Emery) and the single-band (Hubbard) models, thus providing an independent and non-perturbative proof of the validity of the mapping between the two models for the model parameters optimal to describe cuprates. Such a result confirms the emergence of the Zhang-Rice scenario, which has been recently questioned. We also report the behavior of the specific heat and of the entropy as functions of the temperature on varying the model parameters as these quantities, more than any other, depend on and, consequently, reveal the most relevant energy scales of the system.

Description: We perform a thorough study of the strainology of the Raman response in graphene, for different external perturbations, within the framework of a long-wavelength, effective field theory for the vibrational spectrum. We calculate the evolution of the G-peak for the cases of compressive and stretching strains, and we discuss our results in connection to the physics of the G-peak redshift due to bending/uniaxial strain and the G-peak blueshift due to a substrate. Furthermore, we calculate the Raman response for the cases of periodic buckling of nanoribbons and within a toy model for ripples, and in both cases we are able to obtain a rather broad, D-like-peak in the Raman spectrum, even for the case of defect free graphene. We discuss all our theoretical results in connection to recent Raman spectroscopy experiments.

Description: Spontaneous synchronization of an ensemble of metronomes placed on a freely rotating platform is studied experimentally and by computer simulations. A striking in-phase synchronization is observed when the metronomes’ beat frequencies are fixed above a critical limit. Increasing the number of metronomes placed on the disk leads to an observable decrease in the level of the emerging synchronization. A realistic model with experimentally determined parameters is considered in order to understand the observed results. The conditions favoring the emergence of synchronization are investigated. It is shown that the experimentally observed trends can be reproduced by assuming a finite spread in the metronomes’ natural frequencies. In the limit of large numbers of metronomes, we show that synchronization emerges only above a critical beat frequency value.

Description: We explore an unconventional route in the search for multiferroicity investigating the magnetic doping of La 2 Ti 2 O 7 (LTO), a ferroelectric layered perovskite, by density functional calculations. We find that substitution of Ti (in the 3 d 0 configuration) by V (3 d 1 ) produces: (i) robust ferromagnetic (FM) order, achieving multiferroicity; (ii) structural and magnetic anisotropy, as the dopants cluster in magnetic chains. Moreover, the FM V-chains possess antiferro orbital ordering. We show that the origin of the strong FM coupling lies in the fruitful host-dopant combination: the layered structure of the host prewires the orbitals  t 2 g with d xy and d xz lower in energy, the V dopants provide the full occupancy of the bonding levels. We further address the stability of chains vs. temperature and the role of oxygen vacancies in undoped as well as Sc-doped and V-doped LTO.

Description: We introduce a new migration rule, the directional migration, into evolutionary prisoner’s dilemma games defined in a square domain with periodic boundary conditions. We find that cooperation can be enhanced to a much higher level than the case in the absence of migration. Additionally, the presence of the directional migration has profound impact on the population structure: the directional migration drives individuals to form a number of dense clusters which resembles social cohesion. The evolutionary game theory incorporating the directional migration can reproduce some real characteristics of populations in human society and may shed light on the problem of social cohesion.

Description: In this paper, we investigate vibrational resonance in feedforward neuronal network coupled in an all-to-all fashion. In contrast to earlier most work, where only reliable synaptic connections are considered, we mainly examine the effects of unreliable synapses on signal propagation in this work. It is shown that the neurotransmitter release probability and excitatory synaptic strength largely influence the signal propagation, and better tuning of these synaptic parameters makes the feedforward neuronal network support stable signal propagation. Furthermore, it is found that high-frequency driving plays important roles in causing the response of the feedforward neuronal network to subthreshold low-frequency signal and strengthening the ability of the signal propagation between layers. In particular, the optimal amplitude of high-frequency driving is largely influenced by the stochastic effect of neurotransmitter release and the coupling strength. Finally, we compare our results with those obtained in corresponding feedforward neuronal networks connected with reliable synapses but in a random coupling fashion. It is demonstrated that unreliable synaptic coupling is more efficient than the random coupling for the transmission of local input signal. Considering that unreliable synapses are inevitable in neuronal communication, the presented results could have important implications for the weak signal detection and information propagation in neural systems.

Description: Many natural and social systems are characterized by bursty dynamics, for which past events trigger future activity. These systems can be modelled by so-called self-excited Hawkes conditional Poisson processes. It is generally assumed that all events have similar triggering abilities. However, some systems exhibit heterogeneity and clusters with possibly different intra- and inter-triggering, which can be accounted for by generalization into the “multivariate” self-excited Hawkes conditional Poisson processes. We develop the general formalism of the multivariate moment generating function for the cumulative number of first-generation and of all generation events triggered by a given mother event (the “shock”) as a function of the current time t . This corresponds to studying the response function of the process. A variety of different systems have been analyzed. In particular, for systems in which triggering between events of different types proceeds through a one-dimension directed or symmetric chain of influence in type space, we report a novel hierarchy of intermediate asymptotic power law decays ∼ 1/ t 1−( m +1) θ of the rate of triggered events as a function of the distance m of the events to the initial shock in the type space, where 0 〈 θ 〈 1 for the relevant long-memory processes characterizing many natural and social systems. The richness of the generated time dynamics comes from the cascades of intermediate events of possibly different kinds, unfolding via random changes of types genealogy.

Description: The integer quantum Hall effect (IQHE) on star lattice is studied through edge states in the context of spin liquid. We apply the bulk-edge correspondence to the star lattice and analyze the edge states and their topological orders for different spin liquid phases. The band structures and Chern number depend on the local spontaneous magnetic flux and hopping parameters due to the breaking of the time reversal and space inversion symmetries. We give the characteristics of bulk and edge energy structures and their corresponding Chern numbers in the uniform, nematic and chiral spin liquids. In particular, we obtain analytically the phase diagram of the topological orders for the chiral spin liquid states SL [ φ,φ, −2 φ ], where φ is the magnetic flux in two triangles and a dodecagon in one unit cell. Moreover, because of the direct connection between Chern number and the conductance of IQHE, we can further distinguish the different spin liquid phases through a Hall measurement.

Description: We present a novel and comprehensive model of 1/ f noise in nanoscale graphene devices that accounts for the unusual and so far unexplained experimental characteristics. We find that the noise power spectral density versus carrier concentration of single-layer sheet devices has a behavior characterized by a shape going from the M to the Λ type as the material inhomogeneity increases, whereas the shape becomes of V type in bilayer sheet devices for any inhomogeneity, or of M type at high carrier concentration. In single-layer nanoribbons, instead, the ratio of noise to resistance versus the latter quantity is approximately constant, whereas in the bilayer case it exhibits a linear decrease on a logarithmic scale as resistance increases and its limit for zero resistance equals the single-layer value. Noise at the Dirac point is much greater in single-layer than in bilayer devices and it increases with temperature. The origin of 1/ f noise is attributed to the traps in the device and to their relaxation time dispersion. The coupling of trap charge fluctuations with the electrode current is computed according to the electrokinematics theorem, by taking into account their opposite effects on electrons and holes, as well as the device inhomogeneities. The results agree well with experiments.

Description: The effects of multi-impurity quantum interference on triangular lattice f -wave superconductors are studied by self-consistently solving Bogoliubov-de Gennes equations within the t − t ′− J − V model. An overall phase diagram is presented, which shows that f -wave superconductivity dominates near 0.3 doping. Rich phenomena are induced by quantum interference effects, such as periodic modulations in charge orders, pyramid frustum structures, and a magnetic moment reverse transition, which are qualitatively different from the single-impurity case. We also examine the local density of states to show how localized quasiparticle states are created at or near the impurity sites, which can be directly measured by scanning tunneling microscopy experiments.

Description: Agglomerative clustering is a well established strategy for identifying communities in networks. Communities are successively merged into larger communities, coarsening a network of actors into a more manageable network of communities. The order in which merges should occur is not in general clear, necessitating heuristics for selecting pairs of communities to merge. We describe a hierarchical clustering algorithm based on a local optimality property. For each edge in the network, we associate the modularity change for merging the communities it links. For each community vertex, we call the preferred edge that edge for which the modularity change is maximal. When an edge is preferred by both vertices that it links, it appears to be the optimal choice from the local viewpoint. We use the locally optimal edges to define the algorithm: simultaneously merge all pairs of communities that are connected by locally optimal edges that would increase the modularity, redetermining the locally optimal edges after each step and continuing so long as the modularity can be further increased. We apply the algorithm to model and empirical networks, demonstrating that it can efficiently produce high-quality community solutions. We relate the performance and implementation details to the structure of the resulting community hierarchies. We additionally consider a complementary local clustering algorithm, describing how to identify overlapping communities based on the local optimality condition.

Description: A discretized version of the Burridge-Knopoff train model with (non-linear friction force replaced by) random pinning is studied in one and two dimensions. A scale free distribution of avalanches and the Omori law type behaviour for after-shocks are obtained. The avalanche dynamics of this model becomes precisely similar (identical exponent values) to the Edwards-Wilkinson (EW) model of interface propagation. It also allows the complimentary observation of depinning velocity growth (with exponent value identical with that for EW model) in this train model and Omori law behaviour of after-shock (depinning) avalanches in the EW model.

Description: We have investigated the photoluminescence (PL) dynamics of ZnO thin films under intense excitation conditions using an optical-Kerr-gating method. The PL bands originating from exciton-exciton scattering (P emission) and biexciton (M emission) have been observed at 10 K. The ultrashort gating time of 0.6 ps has enabled us to obtain precise information of the temporal profiles of the peak energies and the intensities of the P- and M-PL bands. We have found that the decay time of the P emission becomes longer with increasing film thickness, while that of the M emission is independent of the film thickness. Although the decay time of the P emission is an increasing function of the film thickness, the relation is not in proportion, which is contrary to the predicted proportionality based on a simple model of photon-like polariton propagation.

Description: We report dielectric function related optical properties namely dielectric constant, static dielectric constant, and absorption coefficients of C-substituted hexagonal boron nanotubes. The optical properties were computed for parallel and perpendicular polarized light in the framework of density functional theory. In this regard, three models of BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) have been undertaken for probing the effect of carbon impurity. Our calculations show high dielectric constant of armchair and chiral BNTs for parallel polarized light and magnitude becomes smaller for higher impurity concentration, while zigzag BNT exhibits reverse trend for high impurity concentration. For perpendicular polarized light, the magnitude of dielectric constant ε 1 ( ω ) is decreased and shifts at higher frequencies. The absorption is revealed highest for armchair followed by zigzag and chiral BNTs independent of impurity concentration. The intensity of absorption gets weaken for higher concentration. The chiral BNTs show smaller but uniform absorption in smaller frequency range results in uniform field emission. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.

Description: We present a detailed analysis of a laterally one-dimensional continuum model for target particle redeposition during ion-beam erosion under normal incidence. We show that the redeposition mechanism can be approximated by a Taylor expansion around the mean surface height and clarify the impact of redeposition on nano-scale patterning. Most importantly, we show that stable well-ordered periodic patterns can result in a common Kuramoto-Sivashinsky-like continuum model for ion-beam erosion in cooperation with the model for particle redeposition and identify parameter ranges where they appear.

Description: The stability of the mesoscopic multilayer structure resulting from the Casimir effect is investigated. For the multilayer structure composed of periodic metal and metamaterial layers, we focus on the formation of the restoring Casimir forces that simultaneously stably equilibrate each layer of the structure with the suitably chosen frequency-dependent electromagnetic properties of the materials. The stable equilibrium distances for the layers are discussed, and the influences of the metamaterial characteristic frequencies and of the layer thickness are shown. Since the system stability is induced only by the Casimir forces, this mesoscopic multilayer can be considered as a stable non-touching “Casimir solid”.

Description: The formation of embedded Co nanostructures is investigated on the atomic scale by performing self-learning kinetic Monte Carlo simulations. The atomic processes responsible for the formation of small nanostructures are identified. We demonstrate the specific role of the diffusion of dimers at 400 K. The diffusion of dimers leads to the acceleration of the time evolution and the decrease of the chain domination stage.

Description: The first-principle theoretical studies about the effects of the electric field and oxygen vacancies on the structural relaxation of rutile titanium dioxide and the impacts of the relaxed structures on the capacitor-voltage curves are reported. The results show that oxygen vacancies in the same side bring more unstable bonds between oxygen atoms and titanium atoms than they do in the two sides. Titanium atoms dominate the interactions with oxygen vacancies on the unstable bonds. The unstable bonds of Ti-O would be broken at an electric field of 2.6 MV/cm. The broken bonds caused by the electric field and oxygen vacancies can form the conduction path in rutile titanium dioxide. The static dielectric constants are dependent on the dispersion of oxygen vacancies. It is concluded that the capacitor-voltage curves of Metal/TiO 2 /P-Si structure are dependent on the oxygen vacancies. It can help us to clarify the atom-level mechanism of the conduction path in resistive switching in resistance random-access memory.

Description: The way in which information about behavior is represented at different levels of the motor pathway, remains among the fundamental unresolved problems of motor coding and sensorimotor integration. Insight into this matter is essential for understanding complex learned behaviors such as speech or birdsong. A major challenge in motor coding has been to identify an appropriate framework for characterizing behavior. In this work we discuss a novel approach linking biomechanics and neurophysiology to explore motor control of songbirds. We present a model of song production based on gestures that can be related to physiological parameters that the birds can control. This physical model for the vocal structures allows a reduction in the dimensionality of the behavior, being a powerful approach for studying sensorimotor integration. Our results also show how dynamical systems models can provide insight into neurophysiological analysis of vocal motor control. In particular, our work challenges the actual understanding of how the motor pathway of the songbird systems works and proposes a novel perspective to study neural coding for song production.

Description: With the recent advances of experimental techniques, the nonlinear ultrafast optical response of metal nano-objects can now be investigated both on ensembles and on single nanoparticles. Its connection with the metal electronic and lattice kinetics is studied on the basis of a model describing the wavelength and time-dependent modifications of the object material dielectric function. Its application is illustrated in the case of single silver nanospheres and gold nanorods, as well as on ensembles of noble metal nanoparticles and metal-semiconductor nano-hybrids. This quantitative analysis also permits to elucidate the physical mechanisms at the origin of ultrafast nonlinearities in confined metals at different timescales.

Description: The yearly aggregated tax income data of all, more than 8000, Italian municipalities are analyzed for a period of five years, from 2007 to 2011, to search for conformity or not with Benford’s law, a counter-intuitive phenomenon observed in large tabulated data where the occurrence of numbers having smaller initial digits is more favored than those with larger digits. This is done in anticipation that large deviations from Benford’s law will be found in view of tax evasion supposedly being widespread across Italy. Contrary to expectations, we show that the overall tax income data for all these years is in excellent agreement with Benford’s law. Furthermore, we also analyze the data of Calabria, Campania and Sicily, the three Italian regions known for strong presence of mafia, to see if there are any marked deviations from Benford’s law. Again, we find that all yearly data sets for Calabria and Sicily agree with Benford’s law whereas only the 2007 and 2008 yearly data show departures from the law for Campania. These results are again surprising in view of underground and illegal nature of economic activities of mafia which significantly contribute to tax evasion. Some hypothesis for the found conformity is presented.

Description: Core-level photoemission spectra of the Fabre salts with X = SbF 6 and PF 6 were taken using hard X-rays from PETRA III, Hamburg. In these salts TMTTF layers show a significant stack dimerization with a charge transfer of 1 e per dimer to the anion SbF 6 or PF 6 . At room temperature and slightly below the core-level spectra exhibit single lines, characteristic for a well-screened metallic state. At reduced temperatures progressive charge localization sets in, followed by a 2nd order phase transition into a charge-ordered ground state. In both salts groups of new core-level signals occur, shifted towards lower kinetic energies. This is indicative of a reduced transverse-conductivity across the anion layers, visible as layer-dependent charge depletion for both samples. The surface potential was traced via shifts of core-level signals of an adsorbate. A well-defined potential could be established by a conducting cap layer of 5 nm aluminum which appears “transparent” due to the large probing depth of HAXPES (8–10 nm). At the transition into the charge-ordered phase the fluorine 1 s line of (TMTTF) 2 SbF 6 shifts by 2.8 eV to higher binding energy. This is a spectroscopic fingerprint of the loss of inversion symmetry accompanied by a cooperative shift of the SbF 6 anions towards the more positively charged TMTTF donors. This shift does not occur for the X = PF 6 compound, most likely due to smaller charge disproportion or due to the presence of charge disorder.

Description: We studied the structural and dynamical properties of amorphous germanium dioxide (GeO 2 ) from low to high pressure by means of the classical molecular dynamics technique. The simulations were done in the micro-canonical ensemble, with systems at densities ranged from 3.16 to 6.79 g/cm 3 , using a pairwise potential. The network topology of the systems is analyzed at atomic level through partial pair correlations, coordination number and angular distributions. The dynamic properties were characterized by means of the vibrational density of states. According the density increases, a structural transformation from a short-range order, defined by a building block composed by a basic (GeO 4 ) tetrahedron, to a basic (GeO 6 ) octahedron is observed. The vibrational density of states also presents important changes when the density increases, with a low frequency band lessened, and a high density band wider and flatter.

Description: We apply the renormalized perturbation theory (RPT) to the symmetric Anderson impurity model. Within the RPT framework exact results for physical observables such as the spin and charge susceptibility can be obtained in terms of the renormalized values \(\tilde \mu = (\tilde \Delta ,\tilde U)\) of the hybridization Δ and Coulomb interaction U of the model. The main difficulty in the RPT approach usually lies in the calculation of the renormalized values themselves. In the present work we show how this can be accomplished by deriving differential flow equations describing the evolution of \(\tilde \mu = (\tilde \Delta )\) with Δ . By exploiting the fact that \(\tilde \mu = (\tilde \Delta )\) can be determined analytically in the limit Δ → ∞ we solve the flow equations numerically to obtain estimates for the renormalized parameters in the range 0 〈 U / πΔ 〈 3.5.

Description: A simple method has been introduced to render the equilibrium solution of the Wigner equation for all orders of the quantum correction. This process generates a recursion relation involving the coefficients of the different powers of the momentum. The technique relies on an appropriate guess for the trial solution and differs from the Wigner’s original work. The solution is yielded in a compact exponential form with a polynomial of momentum in the argument and regains Wigner’s form when expansion of the exponential factor is carried out. The study is also important in the investigation of various closed as well as open quantum mechanical systems. In addition, this solution may be employed to obtain the nonequilibrium one particle Wigner distribution in the relaxation-time approximation and under near-equilibrium condition.

Description: We study charge transport in a graphene zigzag nanoribbon driven by an external time-periodic kicking potential. Using the exact solution of the time-dependent Dirac equation with a delta-kick potential acting in each period, we study the time evolution of the population transfer probability and the time-dependent optical conductivity. By variation of the kicking parameters, the conductivity becomes widely tunable.

Description:    We show that Frenkel excitons can constitute a q -deformed boson gas in the high-density limit. Within the framework of the theory of q -deformed bosons, we further investigate the thermostatistical properties of such an exciton gas, which includes the mean occupation number, heat capacity, the phenomenon of Bose-Einstein condensation and so on. It can be found that these properties are slightly different from those of a standard boson gas. Moreover, we numerically calculate some of these properties under appropriate conditions. We consider that this work may provide insight into the theory of q bosons and may also be useful for further research on Frenkel excitons existing inside a nanomaterial. Content Type Journal Article Pages 1-7 DOI 10.1140/epjb/e2011-20004-7 Authors Q. J. Zeng, Department of Physics, Huazhong University of Science and Technology, Wuhan, 430074 P.R. China Z. Cheng, Department of Physics, Huazhong University of Science and Technology, Wuhan, 430074 P.R. China J.-H. Yuan, Department of Physics, Huazhong University of Science and Technology, Wuhan, 430074 P.R. China Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    We study the Langevin dynamics of a ferromagnetic Ginzburg-Landau Hamiltonian with a competing long-range repulsive term in the presence of an external magnetic field. The model is analytically solved within the self consistent Hartree approximation for two different initial conditions: disordered or zero field cooled (ZFC), and fully magnetized or field cooled (FC). To test the predictions of the approximation we develop a suitable numerical scheme to ensure the isotropic nature of the interactions. Both the analytical approach and the numerical simulations of two-dimensional finite systems confirm a simple aging scenario at zero temperature and zero field. At zero temperature a critical field h c is found below which the initial conditions are relevant for the long time dynamics of the system. For h 〈 h c a logarithmic growth of modulated domains is found in the numerical simulations but this behavior is not captured by the analytical approach which predicts a t 1/2 growth law at T = 0. Content Type Journal Article Pages 1-11 DOI 10.1140/epjb/e2011-20185-y Authors R. Díaz-Méndez, Nanophysics Group, Department of Physics, Electric Engineering Faculty, CUJAE, Ave 114 final, La Habana, Cuba A. Mendoza-Coto, Department of Theoretical Physics, Physics Faculty, University of Havana, La Habana, CP 10400 Cuba R. Mulet, Department of Theoretical Physics, Physics Faculty, University of Havana, La Habana, CP 10400 Cuba L. Nicolao, Dipartimento di Fisica, Università di Roma “La Sapienza”, P.le Aldo Moro 2, 00185 Roma, Italy D. A. Stariolo, Departamento de Física, Universidade Federal do Rio Grande do Sul and National Institute of Science and Technology for Complex Systems, CP 15051 91501-970, Porto Alegre, Brasil Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    First-principles calculations based on the density functional theory are performed to study the structural properties, spin-polarized electronic band structures, density of states and magnetic properties of the zinc blende In 1− x Mn x Sb ( x = 0.125, 0.25, 0.50, 0.75, 1.0). The calculated lattice constants of In 1− x Mn x Sb obey the Vegard’s law with a marginal upward bowing. With the increase of Mn concentration in In 1− x Mn x Sb, a transition from the semi-metallic to the half-metallic behavior happens such that the majority-spin valence states crosses the Fermi level and the minority-spin states have a gap at the Fermi level. A large exchange splitting (∼4 eV) is observed between Mn 3 d states of the majority-spins and the minority-spins. The total magnetic moment of In 1− x Mn x Sb half-metallic ferromagnets per Mn atom basis is 4 μ B . The total magnetic moment per Mn atom indicate that Mn atoms act as acceptors in InSb and contribute to holes in the lattice of InSb. Due to p-d hybridization, the free space charge of Mn reduces that results a loss in its magnetic moment. The loss in the magnetic moment of the Mn atoms is converted into a small local magnetic moments on the In and Sb sites. Content Type Journal Article Pages 1-6 DOI 10.1140/epjb/e2011-20047-8 Authors U. P. Verma, School of Studies in Physics, Jiwaji University, 474011, Gwalior, India N. Devi, School of Studies in Physics, Jiwaji University, 474011, Gwalior, India S. Sharma, School of Studies in Physics, Jiwaji University, 474011, Gwalior, India P. Jensen, FB C — Physical and Theoretical Chemistry, Bergische Universität, 42097 Wuppertal, Germany Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description: .   We investigate the scanning tunneling spectroscopy (STS) of a two-orbital Anderson impurity adsorbed on a metallic surface by using the numerical renormalization group (NRG) method. The density of state of magnetic impurity and the local conduction electron are calculated. We obtain the Fano resonance line shape in the STM conductance at zero temperature. For the impurity atom with antiferromagnetic inter-orbital exchange interaction and a spin singlet ground state, we show that a dip in the STM spectra around zero bias voltage regime and side peaks of spin excitation can be observed. The spin excitation energy is proportional to the exchange interaction strength. As the exchange interaction is ferromagnetic, the underscreened Kondo effect dominates the low energy properties of this system, and it gives rise to drastically different STM spectra as compared with the spin singlet case. Content Type Journal Article Pages 1-7 DOI 10.1140/epjb/e2011-20155-5 Authors G.-H. Ding, Department of Physics, Shanghai Jiao Tong University, Shanghai, 200240 P.R. China F. Ye, College of Material Science and Optoelectronics Technology, Graduated University of Chinese Academy of Science, Beijing, 100049 P.R. China B. Dong, Department of Physics, Shanghai Jiao Tong University, Shanghai, 200240 P.R. China Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    The distributions of edge currents in semi-infinite graphene under a uniform perpendicular magnetic field are investigated. We show unambiguously that the edge current is finite at the armchair edge but vanishes at the zigzag edge. It is shown that the current density oscillates with the distance away from the boundary and tends to zero deep inside the graphene. The study shows that the total current is independent of edge configurations. The interplay of the bulk and edge contributions to the total current is presented. The quantized plateaus of Hall conductivity at (4 e 2 / h )( n +1/2) provide a direct evidence of the connection between the edge states and topological properties of relativistic fermions in a magnetic field. Content Type Journal Article Pages 1-9 DOI 10.1140/epjb/e2011-20242-7 Authors W. Wang, School of Physics, Peking University, Beijing, 100871 P.R. China Z. S. Ma, School of Physics, Peking University, Beijing, 100871 P.R. China Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    In this study, the significant effect of the nonuniform composition in alloy quantum dots (QDs) on electronic structure is analyzed in depth. The equilibrium composition profiles in experimentally observed dome and barn shaped GeSi/Si QDs are determined by combining the finite element method and the method of moving asymptotes. Due to the composition variation, the total band edge of heavy hole is dominated by the band offset and spin-orbit coupling rather than the strain effect. The numerical results reveal that the wave function of heavy hole trends to be localized in the Ge-rich region at the top of the large QD. Moreover, the size effect gradually compensates the composition effect as the size of QD decreases. Content Type Journal Article Pages 1-6 DOI 10.1140/epjb/e2011-20153-7 Authors H. Ye, Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing, 100876 P.R. China P. Lu, Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing, 100876 P.R. China Z. Yu, Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing, 100876 P.R. China D. Wang, Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing, 100876 P.R. China Y. Liu, Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing, 100876 P.R. China Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    We explore the interplay between the elastic scattering of photoelectrons and the surface core level shifts with regard to the determination of core level binding energies in Au(111) and Cu 3 Au(100). We find that an artificial shift is created in the binding energies of the Au 4 f core levels, that exhibits a dependence on the emission angle, as well as on the spectral intensity of the core level emission itself. Using a simple model, we are able to reproduce the angular dependence of the shift and relate it to the anisotropy in the electron emission from the bulk layers. Our results demonstrate that interpretation of variation of the binding energy of core-levels should be conducted with great care and must take into account the possible influence of artificial shifts induced by elastic scattering. Content Type Journal Article Pages 1-5 DOI 10.1140/epjb/e2011-20057-6 Authors E. F. Schwier, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland C. Monney, Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland N. Mariotti, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland Z. Vydrovà, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland M. García-Fernández, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland C. Didiot, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland M. G. Garnier, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland P. Aebi, Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, 1700 Fribourg, Switzerland Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    The influence of noise on the generalized synchronization regime in the chaotic systems with dissipative coupling is considered. If attractors of the drive and response systems have an infinitely large basin of attraction, generalized synchronization is shown to possess a great stability with respect to noise. The reasons of the revealed particularity are explained by means of the modified system approach [A.E. Hramov, A.A. Koronovskii, Phys. Rev. E 71 , 067201 (2005)] and confirmed by the results of numerical calculations and experimental studies. The main results are illustrated using the examples of unidirectionally coupled chaotic oscillators and discrete maps as well as spatially extended dynamical systems. Different types of the model noise are analyzed. Possible applications of the revealed particularity are briefly discussed. Content Type Journal Article Pages 1-14 DOI 10.1140/epjb/e2011-11019-1 Authors O. I. Moskalenko, Faculty of Nonlinear Processes, Saratov State University, Astrakhanskaya, 83, 410012 Saratov, Russia A. E. Hramov, Faculty of Nonlinear Processes, Saratov State University, Astrakhanskaya, 83, 410012 Saratov, Russia A. A. Koronovskii, Faculty of Nonlinear Processes, Saratov State University, Astrakhanskaya, 83, 410012 Saratov, Russia A. A. Ovchinnikov, Faculty of Nonlinear Processes, Saratov State University, Astrakhanskaya, 83, 410012 Saratov, Russia Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    We discuss the effects of a novel ’intrinsic’ disorder in hole-doped rare-earth manganites. Using effective field theory as well as direct numerical simulations, we show that this disorder can have dramatic effects in terms of the transition from ferromagnetic insulator to ferromagnetic metal upon hole-doping, including an Anderson localized regime where variable range hopping may be observed. Content Type Journal Article Pages 1-6 DOI 10.1140/epjb/e2011-20189-7 Authors P. Sanyal, School of Physics, Hyderabad Central University, 500046 Hyderabad, India V. B. Shenoy, Centre for Condensed Matter Theory (CCMT), Department of Physics, Indian Institute of Science, 560012 Bangalore, India H. R. Krishnamurthy, Centre for Condensed Matter Theory (CCMT), Department of Physics, Indian Institute of Science, 560012 Bangalore, India T. V. Ramakrishnan, Centre for Condensed Matter Theory (CCMT), Department of Physics, Indian Institute of Science, 560012 Bangalore, India Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028

Description:    We provide a quantitative theoretical model study of the dynamical magnetic properties of optimally annealed Ga 1- x Mn x As. This model has already been shown to reproduce accurately the Curie temperatures for Ga 1- x Mn x As. Here we show that the calculated spin stiffness are in excellent agreement with those which were obtained from ab-initio based studies. In addition, an overall good agreement is also found with available experimental data. We have also evaluated the magnon density of states and the typical density of states from which the “mobility edge”, separating the extended from localized magnon states, was determined. The power of the model lies in its ability to be generalized for a broad class of diluted magnetic semiconductor materials, thus it bridges the gap between first principle calculations and model based studies. Content Type Journal Article Pages 1-5 DOI 10.1140/epjb/e2011-20320-x Authors A. Chakraborty, Département MCBT, Institut Néel, CNRS, 25 avenue des Martyrs, B.P. 166, 38042 Grenoble Cedex 09, France R. Bouzerar, Département MCBT, Institut Néel, CNRS, 25 avenue des Martyrs, B.P. 166, 38042 Grenoble Cedex 09, France G. Bouzerar, Département MCBT, Institut Néel, CNRS, 25 avenue des Martyrs, B.P. 166, 38042 Grenoble Cedex 09, France Journal The European Physical Journal B - Condensed Matter and Complex Systems Online ISSN 1434-6036 Print ISSN 1434-6028