In the last 30 days

• Open/close The game of go as a complex network

  B. Georgeot and O. Giraud 2012 EPL 97 68002 Tag this article

  Article References Full text PDF (841 KB) Enhanced article HTML

  We study the game of go from a complex network perspective. We construct a directed network using a suitable definition of tactical moves including local patterns, and study this network for different datasets of professional and amateur games. The move distribution follows Zipf's law and the network is scale free, with statistical peculiarities different from other real directed networks, such as, e.g., the World Wide Web. These specificities reflect in the outcome of ranking algorithms applied to it. The fine study of the eigenvalues and eigenvectors of matrices used by the ranking algorithms singles out certain strategic situations. Our results should pave the way to a better modelization of board games and other types of human strategic scheming.

• Open/close Self-assembled capillary arrows

  J. C. Loudet and B. Pouligny 2009 EPL 85 28003 Tag this article

  Article References Full text PDF (1.28 MB) View as HTML

  Anisotropic particles adsorbed at a water-air interface are known to aggregate due to capillary interactions. We show that the packing configuration of a pair of prolate ellipsoids critically depends on their relative size and/or aspect ratio mismatch. While identical particles simply pack side-by-side, particles of slightly different sizes are observed to systematically self-assemble into characteristic arrows, i.e. with a finite angle between their axes. The occurrence of such arrows cannot be explained within the far-field approximation of interacting polar quadrupoles. A numerical analysis is worked out which allows us to explore the near-field characteristics of the capillary interaction. Results clearly show the destabilization of the side-by-side configuration due to a size mismatch, in agreement with experimental observations.

• Open/close Community structure detection based on Potts model and network's spectral characterization

  Hui-Jia Li et al 2012 EPL 97 48005 Tag this article

  Article References Full text PDF (579 KB) Enhanced article HTML

  The Potts model was used to uncover community structure in complex networks. However, it could not reveal much important information such as the optimal number of communities and the overlapping nodes hidden in networks effectively. Differently from the previous studies, we established a new framework to study the dynamics of Potts model for community structure detection by using the Markov process, which has a clear mathematic explanation. Based on our framework, we showed that the local uniform behavior of spin values could naturally reveal the hierarchical community structure of a given network. Critical topological information regarding the optimal community structure could also be inferred from spectral signatures of the Markov process. A two-stage algorithm to detect community structure is developed. The effectiveness and efficiency of the algorithm has been theoretically analyzed as well as experimentally validated.

• Open/close On the nonlinear coupling between micro turbulence and mesoscale magnetic islands in a plasma

  W. A. Hornsby et al 2010 EPL 91 45001 Tag this article

  Article References Full text PDF (382 KB) View as HTML

  The interaction between small-scale turbulence (of the order of the ion Larmor radius) and mesoscale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long-wavelength modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Density and temperature gradients inside the island are below the threshold for turbulence generation, and the anomalous transport inside the island is determined by turbulence spreading. A finite radial temperature gradient inside the island is observed to persist despite the fast motion along the field, and is related to the trapped particles which do not move along the field around the island. Consequences for the stability of the neo-classical tearing mode are discussed.

• Open/close Lattice BGK Models for Navier-Stokes Equation

  Y. H. Qian et al 1992 Europhys. Lett. 17 479 Tag this article

  Article References Full text PDF (385 KB)

  We propose the lattice BGK models, as an alternative to lattice gases or the lattice Boltzmann equation, to obtain an efficient numerical scheme for the simulation of fluid dynamics. With a properly chosen equilibrium distribution, the Navier-Stokes equation is obtained from the kinetic BGK equation at the second-order of approximation. Compared to lattice gases, the present model is noise-free, has Galileian invariance and a velocity-independent pressure. It involves a relaxation parameter that influences the stability of the new scheme. Numerical simulations are shown to confirm the speed of sound and the shear viscosity.

• Open/close Observation of Riemannian geometric effects on electronic states

  Jun Onoe et al 2012 EPL 98 27001 Tag this article

  Article References Full text PDF (753 KB) Enhanced article HTML

  Einstein first applied Riemannian geometry to develop the general theory of relativity almost one hundred years ago and succeeded in understanding astronomical-scale phenomena such as the straining of time-space by a gravitational field. Whether or not Riemannian space affects the electronic properties of condensed matters on a much smaller scale is of great interest. Although Riemannian geometry has been applied to quantum mechanics since the 1950s, nobody has yet answered this question, because the electronic properties of materials with Riemannian geometry have not been examined experimentally. We report here the first observation of Riemannian geometrical effects on the electronic properties of materials such as Tomononaga-Luttinger liquids, which were previously theoretically predicted by our group. We present in situ high-resolution ultraviolet photoemission spectra of a one-dimensional metallic C ₆₀ polymer with an uneven periodic peanut-shaped structure.

• Open/close Evidence of deep-blue photon emission at high efficiency by common plastic OPEN ACCESS

  H. Nakamura et al 2011 EPL 95 22001 Tag this article

  Article References Full text PDF (235 KB) View as HTML

  Various scintillation devices are used in many countries and wide scientific fields. Key elements that determine the performance of a scintillation device are the number of photons emitted per incident radiation event and the emission of easy-to-measure blue photons. It is generally known that only materials with very complex compositions perform well as scintillators. However, we demonstrated that the scintillation performance of a newly developed plastic such as 100 percent pure polyethylene naphthalate exceeds that of conventional organic scintillators. By measuring the light output spectra and emission spectra of several samples, we revealed that the plastic emits a high number of photons per incident radiation event (~10500 photons/MeV), and, surprisingly, deep-blue photons (425 nm). Even though the plastic has a simple composition, it could replace the expensive organic scintillators that have been used in many applications.

• Open/close Thermodynamic and kinetic properties of the formation reactions of the donor-acceptor complexes HXPY (X=Al, B; Y=H, Cl, SH)

  Ping Yin et al 2006 Europhys. Lett. 75 254 Tag this article

  Article References Full text PDF (124 KB) View as HTML

  The optimized geometries, complexation energies, and transferred charges, etc. of the donor-acceptor complexes HXPY (X=Al, B; Y=H, Cl, SH) have been studied at the B3LYP/6-311+G (d, p), MP2/6-311+G (d, p) and/or CCSD(T)/6-311 +G (d, p) levels. The research results show that HBPY is more stable than the corresponding HAlPY (Y=H, Cl, SH), and Cl (or SH) substitution on phosphorus results in decreasing the stability of the complexes. The general statistical thermodynamics and Eyring transition state theory with Wigner correction were used to examine the thermodynamic and kinetic properties of these donor-acceptor complexes formation reactions. It is concluded that within the temperature range 200–800 K, the formation of HBPY is thermodynamically favored over that of the corresponding HAlPY especially at low temperature, and is kinetically favored over that of the relevant HAlPY (Y= H, Cl, SH) especially at high temperature.

• Open/close 2011— A vintage year for EPL

  Michael Schreiber Editor-in-Chief 2012 EPL 98 10000 Tag this article

  Article References Full text PDF (266 KB) Enhanced article HTML

• Open/close CPT symmetry and antimatter gravity in general relativity OPEN ACCESS

  M. Villata 2011 EPL 94 20001 Tag this article

  Article References Full text PDF (143 KB) View as HTML

  The gravitational behavior of antimatter is still unknown. While we may be confident that antimatter is self-attractive, the interaction between matter and antimatter might be either attractive or repulsive. We investigate this issue on theoretical grounds. Starting from the CPT invariance of physical laws, we transform matter into antimatter in the equations of both electrodynamics and gravitation. In the former case, the result is the well-known change of sign of the electric charge. In the latter, we find that the gravitational interaction between matter and antimatter is a mutual repulsion, i.e. antigravity appears as a prediction of general relativity when CPT is applied. This result supports cosmological models attempting to explain the Universe accelerated expansion in terms of a matter-antimatter repulsive interaction.