142,839 research outputs found

    Disassortativity of random critical branching trees

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    Random critical branching trees (CBTs) are generated by the multiplicative branching process, where the branching number is determined stochastically, independent of the degree of their ancestor. Here we show analytically that despite this stochastic independence, there exists the degree-degree correlation (DDC) in the CBT and it is disassortative. Moreover, the skeletons of fractal networks, the maximum spanning trees formed by the edge betweenness centrality, behave similarly to the CBT in the DDC. This analytic solution and observation support the argument that the fractal scaling in complex networks originates from the disassortativity in the DDC.Comment: 3 pages, 2 figure

    The q-component static model : modeling social networks

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    We generalize the static model by assigning a q-component weight on each vertex. We first choose a component (μ)(\mu) among the q components at random and a pair of vertices is linked with a color μ\mu according to their weights of the component (μ)(\mu) as in the static model. A (1-f) fraction of the entire edges is connected following this way. The remaining fraction f is added with (q+1)-th color as in the static model but using the maximum weights among the q components each individual has. This model is motivated by social networks. It exhibits similar topological features to real social networks in that: (i) the degree distribution has a highly skewed form, (ii) the diameter is as small as and (iii) the assortativity coefficient r is as positive and large as those in real social networks with r reaching a maximum around f0.2f \approx 0.2.Comment: 5 pages, 6 figure

    Substrate-tuning of correlated spin-orbit oxides

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    We have systematically investigated substrate-strain effects on the electronic structures of two representative Sr-iridates, a correlated-insulator Sr2_2IrO4_4 and a metal SrIrO3_3. Optical conductivities obtained by the \emph{ab initio} electronic structure calculations reveal that the tensile strain shifts the optical peak positions to higher energy side with altered intensities, suggesting the enhancement of the electronic correlation and spin-orbit coupling (SOC) strength in Sr-iridates. The response of the electronic structure upon tensile strain is found to be highly correlated with the direction of magnetic moment, the octahedral connectivity, and the SOC strength, which cooperatively determine the robustness of JeffJ_{eff}=1/2 ground states. Optical responses are analyzed also with microscopic model calculation and compared with corresponding experiments. In the case of SrIrO3_3, the evolution of the electronic structure near the Fermi level shows high tunability of hole bands, as suggested by previous experiments

    The Commercial Stainless Steel Tube Enveloping Technique for MgB2

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    A commercial stainless steel tube was employed to synthesize MgB2. The specimen was prepared by a stoichiometric mixture of Mg and B. The specimen that had been enveloped in the commercial stainless steel tube was synthesized for 2 hours at 1193 K. X-ray spectra showed there were no second phases like MgO. The transition temperature of the specimen was 37.5 K with a sharp transition width within 1K. The specimen showed a good connection between grains and critical current density as calculated with the Bean model is more than 100,000 A/cm2 at 20 K and in zero field.Comment: 6 pages, 5 figure

    Structural instability and the Mott-Peierls transition in a half-metallic hollandite : K2_{2}Cr8_{8}O16_{16}

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    In order to explore the driving mechanism of the concomitant metal-insulator and structural transitions in quasi-one-dimensional hollandite K2_{2}Cr8_{8}O16_{16}, electronic structures and phonon properties are investigated by employing the {\it ab initio} density functional theory (DFT) calculations. We have found that the imaginary phonon frequency reflecting the structural instability appears only in the DFT+UU (UU: Coulomb correlation) calculation, which indicates that the Coulomb correlation plays an essential role in the structural transition. The lattice displacements of the softened phonon at X explain the observed lattice distortions in K2_{2}Cr8_{8}O16_{16} perfectly well, suggesting the Peierls distortion vector {\bf Q} of X (0, 0, 1/2). The combined study of electronic and phonon properties reveals that half-metallic K2_{2}Cr8_{8}O16_{16}, upon cooling, undergoes the correlation-assisted Peierls transition to become a Mott-Peierls ferromagnetic insulator at low temperature

    Reality conditions for (2+1)-dimensional gravity coupled with the Dirac field

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    The canonical formalism of three dimensional gravity coupled with the Dirac field is considered. We introduce complex variables to simplify the Dirac brackets of canonical variables and examine the canonical structure of the theory. We discuss the reality conditions which guarantee the equivalence between the complex and real theory.Comment: 13 pages, late

    A central limit theorem for descents and major indices in fixed conjugacy classes of SnS_n

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    The distribution of descents in fixed conjugacy classes of SnS_n has been studied, and it is shown that its moments have interesting properties. Kim and Lee showed, by using Curtiss' theorem and moment generating functions, how to prove a central limit theorem for descents in arbitrary conjugacy classes of SnS_n. In this paper, we prove a modified version of Curtiss' theorem to shift the interval of convergence in a more convenient fashion and use this to show that the joint distribution of descents and major indices is asymptotically bivariate normal.Comment: 18 page

    Opulent Operetta and Marvelous Musicals

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    Program listing performers and works performe

    The nature of Itinerant Ferromagnetism of SrRuO3 : A DFT+DMFT Study

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    We have investigated the temperature (T)-dependent evolution of electronic structures and magnetic properties of an itinerant ferromagnet SrRuO3, employing the combined scheme of the density functional theory and the dynamical mean-field theory (DFT+DMFT). The inclusion of finite dynamical correlation effects beyond the DFT well describes not only the incoherent hump structure observed in the photoemission experiment but also the T-dependent magnetic properties in accordance with experiments. We have shown that the magnetization of SrRuO3 evolves with the Stoner behavior below the Curie temperature (Tc), reflecting the weak itinerant ferromagnetic behavior, but the local residual magnetic moment persists even above Tc, indicating the local magnetic moment behavior. We suggest that the ferromagnetism of SrRuO3 has dual nature of both weak and local moment limits, even though the magnetism of SrRuO3 is more itinerant than that of Fe.Comment: 5 pages, 4 figure