27,835 research outputs found

    Exact O(g^2 alpha_s) top decay width from general massive two-loop integrals

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    We calculate the b-dependent self-energy of the top quark at O(g^2 \alpha_s) by using a general massive two-loop algorithm proposed in a previous article. From this we derive by unitarity the O(\alpha_s) radiative corrections to the decay width of the top quark, where all effects associated with the bb quark mass are included without resorting to a mass expansion. Our results agree with the analytical results available for the O(\alpha_s) correction to the top quark width

    Analysis on the hull girder ultimate strength of a bulk carrier using simplified method based on an incremental-iterative approach

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    The hull girder ultimate strength of a typical bulk carrier is analyzed using a simplified method based on an incremental-iterative approach. First, vertical bending moment is examined by seven different methods. The moment versus curvature curves and the values of the ultimate longitudinal moments at collapse states are determined for both hogging and sagging cases. Second, the ultimate strength under coupled vertical and horizontal bending moment is accounted. An interaction curve is obtained, which corresponds to the results of series of calculation for the ship hull subject to bending conditions with different angles of curvature. It is found that the interaction curve is asymmetrical because the hull cross section is not symmetrical with respect to the horizontal axis and the structural response of the elements under compression is different from that under tension due to nonlinearity caused by buckling. The angles of the resultant bending moment vector and that of the curvature vector are different in investigated cases. The interaction design equations proposed by other researches are also addressed to discuss the results presented by this study

    Chaos, Determinacy and Fractals in Active-Sterile Neutrino Oscillations in the Early Universe

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    The possibility of light sterile neutrinos allows for the resonant production of lepton number in the early universe through matter-affected neutrino mixing. For a given a mixing of the active and sterile neutrino states it has been found that the lepton number generation process is chaotic and strongly oscillatory. We undertake a new study of this process' sensitivity to initial conditions through the quantum rate equations. We confirm the chaoticity of the process in this solution, and moreover find that the resultant lepton number and the sign of the asymmetry produces a fractal in the parameter space of mass, mixing angle and initial baryon number. This has implications for future searches for sterile neutrinos, where arbitrary high sensitivity could not be determinate in forecasting the lepton number of the universe.Comment: 6 pages, 3 figure

    In-plane thermal conductivity of large single crystals of Sm-substituted (Y1−x_{1-x}Smx_{x})Ba2_{2}Cu3_{3}O7−δ_{7-\delta}

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    We have investigated the in-plane thermal conductivity κab(T,H)\kappa_{ab}(T,H) of large single crystals of optimally oxygen-doped (Y1−x_{1-x},Smx_{x})Ba2_{2}Cu3_{3}O7−δ_{7-\delta} (xx=0, 0.1, 0.2 and 1.0) and YBa2_{2}(Cu1−y_{1-y}Zny_{y})3_{3}O7−δ_{7-\delta}(yy=0.0071) as functions of temperature and magnetic field (along the c axis). For comparison, the temperature dependence of κab\kappa_{ab} for as-grown crystals with the corresponding compositions are presented. The nonlinear field dependence of κab\kappa_{ab} for all crystals was observed at relatively low fields near a half of TcT_{c}. We make fits of the κ(H)\kappa(H) data to an electron contribution model, providing both the mean free path of quasiparticles ℓ0\ell_{0} and the electronic thermal conductivity κe\kappa_{e}, in the absence of field. The local lattice distortion due to the Sm substitution for Y suppresses both the phonon and electron contributions. On the other hand, the light Zn doping into the CuO 2_{2} planes affects solely the electron component below TcT_{c}, resulting in a substantial decrease in ℓ0\ell_{0} .Comment: 7 pages,4 figures,1 tabl

    Spanning Properties of Theta-Theta Graphs

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    We study the spanning properties of Theta-Theta graphs. Similar in spirit with the Yao-Yao graphs, Theta-Theta graphs partition the space around each vertex into a set of k cones, for some fixed integer k > 1, and select at most one edge per cone. The difference is in the way edges are selected. Yao-Yao graphs select an edge of minimum length, whereas Theta-Theta graphs select an edge of minimum orthogonal projection onto the cone bisector. It has been established that the Yao-Yao graphs with parameter k = 6k' have spanning ratio 11.67, for k' >= 6. In this paper we establish a first spanning ratio of 7.827.82 for Theta-Theta graphs, for the same values of kk. We also extend the class of Theta-Theta spanners with parameter 6k', and establish a spanning ratio of 16.7616.76 for k' >= 5. We surmise that these stronger results are mainly due to a tighter analysis in this paper, rather than Theta-Theta being superior to Yao-Yao as a spanner. We also show that the spanning ratio of Theta-Theta graphs decreases to 4.64 as k' increases to 8. These are the first results on the spanning properties of Theta-Theta graphs.Comment: 20 pages, 6 figures, 3 table
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