Finite-size effects on the Hamiltonian dynamics of the XY-model

The dynamical properties of the finite-size magnetization M in the critical region T<T_{KTB} of the planar rotor model on a L x L square lattice are analyzed by means of microcanonical simulations . The behavior of the q=0 structure factor at high frequencies is consistent with field-theoretical results, but new additional features occur at lower frequencies. The motion of M determines a region of spectral lines and the presence of a central peak, which we attribute to phase diffusion. Near T_{KTB} the diffusion constant scales with system size as D ~ L^{-1.6(3)}.Comment: To be published in Europhysics Letter

An Hour of Last Things: An Interview with George P. Elliott

In an interview with the editor, George P. Elliott discusses nihilism , science fiction, erotic language, the intricacies of human relationships, and his conservative liberalism\u27.\u2

Universal Fluctuations in Correlated Systems

The probability density function (PDF) of a global measure in a large class of highly correlated systems has been suggested to be of the same functional form. Here, we identify the analytical form of the PDF of one such measure, the order parameter in the low temperature phase of the 2D-XY model. We demonstrate that this function describes the fluctuations of global quantities in other correlated, equilibrium and non-equilibrium systems. These include a coupled rotor model, Ising and percolation models, models of forest fires, sand-piles, avalanches and granular media in a self organized critical state. We discuss the relationship with both Gaussian and extremal statistics.Comment: 4 pages, 2 figure

Electric Dipole Moments of Leptons in the Presence of Majorana Neutrinos

We calculate the two-loop diagrams that give a non-zero contribution to the electric dipole moment d_l of a charged lepton l due to possible Majorana masses of neutrinos. Using the example with one generation of the Standard Model leptons and two heavy right-handed neutrinos, we demonstrate that the non-vanishing result for d_l first appears in order O(m_l m_\nu^2 G_F^2), where m_\nu is the mass of the light neutrino and the see-saw type relation is imposed. This effect is beyond the reach of presently planned experiments.Comment: 13 page

Towards Scalable Visual Exploration of Very Large RDF Graphs

In this paper, we outline our work on developing a disk-based infrastructure for efficient visualization and graph exploration operations over very large graphs. The proposed platform, called graphVizdb, is based on a novel technique for indexing and storing the graph. Particularly, the graph layout is indexed with a spatial data structure, i.e., an R-tree, and stored in a database. In runtime, user operations are translated into efficient spatial operations (i.e., window queries) in the backend.Comment: 12th Extended Semantic Web Conference (ESWC 2015

Relevance of soft modes for order parameter fluctuations in the Two-Dimensional XY model

We analyse the spin wave approximation for the 2D-XY model, directly in reciprocal space. In this limit the model is diagonal and the normal modes are statistically independent. Despite this simplicity non-trivial critical properties are observed and exploited. We confirm that the observed asymmetry for the probability density function for order parameter fluctuations comes from the divergence of the mode amplitudes across the Brillouin zone. We show that the asymmetry is a many body effect despite the importance played by the zone centre. The precise form of the function is dependent on the details of the Gibbs measure, giving weight to the idea that an effective Gibbs measure should exist in non-equilibrium systems, if a similar distribution is observed.Comment: 12 pages, 9 figure

Formation and stability of icosahedral phase in Al65Ga5Pd17Mn13 alloy

In this work, we present the formation and characterization of a quaternary (pseudo ternary) icosahedral quasicrystal in Al65Ga5Pd17Mn13 alloy. The X ray diffraction and transmission electron microscopy confirmed the formation of icosahedral B2 type and O crystalline (orthorhombic structure) phases in as cast alloy. The icosahedral phase gets formed after annealing at 800 C for 60 hours. The formation of icosahedral phase in AlGaPdMn quaternary alloy by present technique has been studied for the first time. The Energy dispersive X-ray analysis investigations suggest the presence of Ga (5 at) in the alloy. It is interesting to note that pseudo twelve fold pattern in the as cast alloy has been observed. Icosahedral AlGaPdMn provides a new opportunity to investigate the various characteristics including surface characteristics. Attempts will be made to discuss the micromechanisms for the formation of quasicrystalline phase in Al-Ga-Pd-Mn alloys.Comment: 14 pages 5 figure