70,451 research outputs found

    Superconductivity in ternary molybdenum sulfides

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    Three research papers are presented: (1) Superconductivity in Th-Zr Alloys; (2) Superconductivity in Pd-Si-H(D) alloys; and (3) Low Temperature Specific Heat of Amorphous Pd-Si Alloys

    Critical Relaxation and Critical Exponents

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    Dynamic relaxation of the XY model and fully frustrated XY model quenched from an initial ordered state to the critical temperature or below is investigated with Monte Carlo methods. Universal power law scaling behaviour is observed. The dynamic critical exponent zz and the static exponent η\eta are extracted from the time-dependent Binder cumulant and magnetization. The results are competitive to those measured with traditional methods

    Superfluid response in electron-doped cuprate superconductors

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    We propose a weakly coupled two-band model with dx2y2d_{x^2-y^2} pairing symmetry to account for the anomalous temperature dependence of superfluid density ρs\rho_s in electron-doped cuprate superconductors. This model gives a unified explanation to the presence of a upward curvature in ρs\rho_s near TcT_c and a weak temperature dependence of ρs\rho_s in low temperatures. Our work resolves a discrepancy in the interpretation of different experimental measurements and suggests that the pairing in electron-doped cuprates has predominately dx2y2d_{x^2-y^2} symmetry in the whole doping range.Comment: 4 pages, 3 figures, title changed and references adde

    Consistent forcing scheme in the cascaded lattice Boltzmann method

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    In this paper, we give a more pellucid derivation for the cascaded lattice Boltzmann method (CLBM) based on a general multiple-relaxation-time (MRT) frame through defining a shift matrix. When the shift matrix is a unit matrix, the CLBM degrades into an MRT LBM. Based on this, a consistent forcing scheme is developed for the CLBM. The applicability of the non-slip rule, the second-order convergence rate in space and the property of isotropy for the consistent forcing scheme is demonstrated through the simulation of several canonical problems. Several other existing force schemes previously used in the CLBM are also examined. The study clarifies the relation between MRT LBM and CLBM under a general framework

    A minimal approach to the scattering of physical massless bosons

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    Tree and loop level scattering amplitudes which involve physical massless bosons are derived directly from physical constraints such as locality, symmetry and unitarity, bypassing path integral constructions. Amplitudes can be projected onto a minimal basis of kinematic factors through linear algebra, by employing four dimensional spinor helicity methods or at its most general using projection techniques. The linear algebra analysis is closely related to amplitude relations, especially the Bern-Carrasco-Johansson relations for gluon amplitudes and the Kawai-Lewellen-Tye relations between gluons and graviton amplitudes. Projection techniques are known to reduce the computation of loop amplitudes with spinning particles to scalar integrals. Unitarity, locality and integration-by-parts identities can then be used to fix complete tree and loop amplitudes efficiently. The loop amplitudes follow algorithmically from the trees. A range of proof-of-concept examples is presented. These include the planar four point two-loop amplitude in pure Yang-Mills theory as well as a range of one loop amplitudes with internal and external scalars, gluons and gravitons. Several interesting features of the results are highlighted, such as the vanishing of certain basis coefficients for gluon and graviton amplitudes. Effective field theories are naturally and efficiently included into the framework. The presented methods appear most powerful in non-supersymmetric theories in cases with relatively few legs, but with potentially many loops. For instance, iterated unitarity cuts of four point amplitudes for non-supersymmetric gauge and gravity theories can be computed by matrix multiplication, generalising the so-called rung-rule of maximally supersymmetric theories. The philosophy of the approach to kinematics also leads to a technique to control color quantum numbers of scattering amplitudes with matter.Comment: 65 pages, exposition improved, typos correcte

    Bound States and Critical Behavior of the Yukawa Potential

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    We investigate the bound states of the Yukawa potential V(r)=λexp(αr)/rV(r)=-\lambda \exp(-\alpha r)/ r, using different algorithms: solving the Schr\"odinger equation numerically and our Monte Carlo Hamiltonian approach. There is a critical α=αC\alpha=\alpha_C, above which no bound state exists. We study the relation between αC\alpha_C and λ\lambda for various angular momentum quantum number ll, and find in atomic units, αC(l)=λ[A1exp(l/B1)+A2exp(l/B2)]\alpha_{C}(l)= \lambda [A_{1} \exp(-l/ B_{1})+ A_{2} \exp(-l/ B_{2})], with A1=1.020(18)A_1=1.020(18), B1=0.443(14)B_1=0.443(14), A2=0.170(17)A_2=0.170(17), and B2=2.490(180)B_2=2.490(180).Comment: 15 pages, 12 figures, 5 tables. Version to appear in Sciences in China

    Why Use a Hamilton Approach in QCD?

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    We discuss QCDQCD in the Hamiltonian frame work. We treat finite density QCDQCD in the strong coupling regime. We present a parton-model inspired regularisation scheme to treat the spectrum (θ\theta-angles) and distribution functions in QED1+1QED_{1+1}. We suggest a Monte Carlo method to construct low-dimensionasl effective Hamiltonians. Finally, we discuss improvement in Hamiltonian QCDQCD.Comment: Proceedings of Hadrons and Strings, invited talk given by H. Kr\"{o}ger; Text (LaTeX file), 3 Figures (ps file