No abstract

Using an effective Hamiltonian derived from the QCD multipole expansion, we calculate the cross sections of gluo-dissociation of heavy quarkonia in the quark-gluon plasma, by including both the chromo-electric dipole (E 1 ) as well as the chromo-magnetic dipole (M 1 ) transition mechanisms. While the former allows to reproduce the results from operator-product-expansion calculations in the Coulomb approximation, the latter as a novel contribution is shown to be significant at low energies close to the threshold. Using thus obtained cross sections, we further carry out a full calculation of the gluo-dissociation rates for various charmonia and bottomonia within a non-relativitic in-medium potential model. The M 1 contribution turns out to be most prominent for the J/ψ and accounts for ∼ 10% − 25% of the total (E1 + M 1) dissociation rate at temperatures close to the transition temperature.

We study heavy quarkonia in the frame of potential model in electromagnetic and rotational fields. The rotation itself cannot induce charmonium dissociation, but its coupling to the magnetic field can largely enhance or reduce the Lorentz potential and therefore affects the charmonium properties strongly. The charmonium wave function is significantly broadened in the direction of the Lorentz force, which leads to the charmonium transition from strongly interacting bound state to magnetic and rotational interaction controlled bound state. The condition for the transition seems possible to be realized in high energy nuclear collisions.

Porous silicon nitride ceramics have attracted a considerable attention due to their excellent overall performance, but poor porosity homogeneity and structural shrinkage induced by prolonged high temperature sintering limit its further application. Herein, as a three-in-one solution for the above issues, for the first time we develop a novel approach that integrates the merits of gelcasting-SHS (self-propagating high-temperature synthesis) to prepare porous Si3N4 ceramics to simultaneously achieve high porosity, high strength, high toughness, and low thermal conductivity across a wide temperature range. By regulating the solid content, porous Si3N4 ceramics with homogeneous pore structure are obtained, where the pore size falls inbetween 1.61 and 4.41 µm, and the elongated grains are interlaced and interlocked to form micron-sized coherent interconnected pores. At the same time, porous Si3N4 ceramics with porosity of 67.83% to 78.03% are obtained, where the compressive strength reaches 11.79 to 47.75 MPa and fracture toughness reaches 1.20 to 6.71 MPa·m1/2.

No abstract