The transition form factors for semi-leptonic weak decays of J/ψ in QCD sum rules

Within the standard model, we investigate the semi-leptonic weak decays of J/ψ. The various form factors of J/ψ making the transition to a single charmed meson (D^(*) _(d,s)) are studied in the framework of QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of J/ψ and provide valuable information on non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode J/ψ→D^(*)- _s+e⁺+ν_e is at the order of 10^-10. PACS 13.20.Gd; 13.25.Gv; 11.55.Hx     

<Emphasis Type="Italic">In situ</Emphasis> X-ray diffraction study of structural evaluation in Fe<Subscript>73</Subscript>Cu<Subscript>1.5</Subscript>Nd<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> amorphous alloy at high temperature

The thermodynamics structural relaxation of Fe₇₃Cu_1.5Nd₃Si_13.5B₉ amorphous alloy from room temperature to 400°C has been investigated by measuring the structure factor with in situ X-ray diffraction. The structural information of the atomic configuration such as radial distribution function (RDF) and neighbor atomic distance was gained by Fourier transformation. The research result shows that the amorphous structure remains stable in the temperature range of 30 to 400°C but exhibits distinct changes in local atomic configuration with the increase of temperature. The quantitative determination of the neighbor atomic distance suggests that the degree of short-range order changes by the temperature altering the second nearest neighbor local atomic configuration of the amorphous when structural relaxation occurs. Supported by the Natural Science Foundation of Hebei Province of China (Grant No. A2007000296), the National Natural Science Foundation of China (Grant No. 50731005), SKPBRC (Grant Nos. 2007CB616915 and 2006CB605201), and PCSIRT (Grant No. IRT0650)     

Optical testing of star sensor (II): Alignment of star sensor from off-line pictures taken in orbital test

Alignment error of an image sensor relative to the optical axis of a star sensor head and alignment errors between four heads were calculated from pictures taken in an orbital experiment. When comparing the image sensor alignment parameters in the orbital test and a ground test, both values matched well. By determining the relative relationship of the four heads using four pictures taken at the same moment in orbit and uploading the parameters to the star sensor system in orbit, the estimated attitude error was improved from 0.29 to 0.17°, though the accuracy was limited by the ±0.2° determination accuracy of the satellite itself. We estimated the attitude determination accuracy from separation angles between boresights of the four heads, calculated from pattern matching between downloaded pictures and a star catalogue. The estimated accuracy, in terms of potential optical performance, was 0.60 arcmin at 3σ, which is sufficient to satisfy the specification of 1 arcmin.     

Dielectric relaxation and ac conductivity of sodium tungsten phosphate glasses

Studies of dielectric relaxation and ac conductivity have been made on three samples of sodium tungsten phosphate glasses over a temperature range of 77–420 K. Complex relative permitivity data have been analyzed using dielectric modulus approach. Conductivity relaxation frequency increases with the increase of temperature. Activation energy for conductivity relaxation has also been evaluated. Measured ac conductivity (σ_m(ω)) has been found to be higher than σ_dc at low temperatures whereas at high temperature σ_m(ω) becomes equal to σ_dc at all frequencies. The ac conductivity obeys the relation σ_ac(ω)=Aω ^S over a considerable range of low temperatures. Values of exponent S are nearly equal to unity at about 78 K and the values decrease non-linearly with the increase of temperature. Values of the number density of states at Fermi level (N(E _F)) have been evaluated at 80 K assuming values of electron wave function decay constant α to be 0.5 (Å)^?1. Values of N(E _F) have the order 10²⁰ which are well within the range suggested for localized states. Present values of N(E _F) are smaller than those for tungsten phosphate glasses.     

Nonequilibrium fluctuations from a nematic under a thermal gradient and a gravity field*

We use a fluctuating hydrodynamics (FH) approach to study the fluctuations of the hydrodynamic variables of a thermotropic nematic liquid crystal (NLC)in a nonequilibrium steady state (NESS). This NESS is produced by an externally imposed temperature gradient and a uniform gravity field. We calculate analytically the equilibrium and nonequilibrium seven modes of the NLC in this NESS. These modes consist of a pair of sound modes, one orientation mode of the director and two visco-heat modes formed by the coupling of the shear and thermal modes. We find that the nonequilibrium effects produced by the external gradients only affect the longitudinal modes. The analytic expressions for the visco-heat modes show explicitly how the heat and shear modes of the NLC are coupled. We show that they may become propagative, a feature that also occurs in the simple fluid and suggests the realization of new experiments. We show that in equilibrium and in the isotropic limit of the NLC, our modes reduce to well-known results in the literature. For the NESS considered we point out the differences between our our modes and those reported by other authors. We close the paper by proposing the calculation of other physical quantities that lend themselves to a more direct comparison with possible experiments for this system.     

Localization of weakly disordered flat band states

Certain tight binding lattices host macroscopically degenerate flat spectral bands. Their origin is rooted in local symmetries of the lattice, with destructive interference leading to the existence of compact localized eigenstates. We study the robustness of this localization to disorder in different classes of flat band lattices in one and two dimensions. Depending on the flat band class, the flat band states can either be robust, preserving their strong localization for weak disorder W, or they are destroyed and acquire large localization lengths ξ that diverge with a variety of unconventional exponents ν, ξ ~ 1 /W ^ν .     

General pairing mechanisms in the BCS-theory of superconductivity

Starting from the linearized BdG-equation we make the simple observation that pairing can occur between particles with total momenta different from zero, e.g., with equal momentum and opposite spin, in cases of an effective interaction acting in the center-of-mass coordinates.     

Fractality and degree correlations in scale-free networks

Fractal scale-free networks are empirically known to exhibit disassortative degree mixing. It is, however, not obvious whether a negative degree correlation between nearest neighbor nodes makes a scale-free network fractal. Here we examine the possibility that disassortativity in complex networks is the origin of fractality. To this end, maximally disassortative (MD) networks are prepared by rewiring edges while keeping the degree sequence of an initial uncorrelated scale-free network. We show that there are many MD networks with different topologies if the degree sequence is the same with that of the (u,v)-flower but most of them are not fractal. These results demonstrate that disassortativity does not cause the fractal property of networks. In addition, we suggest that fractality of scale-free networks requires a long-range repulsive correlation, in the sense of the shortest path distance, in similar degrees.