Parametric mode-mode coupling between drift waves in plasmas

Parametric mode-mode coupling between drift waves in plasma

Superconductivity in spinel oxide LiTi2O4 epitaxial thin films

LiTi2O4 is a unique material in that it is the only known oxide spinel superconductor. Although bulk studies have demonstrated that superconductivity can be generally described by the Bardeen-Cooper-Schreiffer theory, the microscopic mechanisms of superconductivity are not yet resolved fully. The sensitivity of the superconducting properties to various defects of the spinel crystal structure provides insight into such mechanisms. Epitaxial films of LiTi2O4 on single crystalline substrates of MgAl2O4, MgO, and SrTiO3 provide model systems to systematically explore the effects of lattice strain and microstructural disorder. Lattice strain that affects bandwidth gives rise to limited variations in the superconducting and normal state properties. Microstructural disorder such as antiphase boundaries that give rise to Ti network disorder can reduce the critical temperature, but Ti network disorder combined with Mg interdiffusion can affect the superconducting state much more dramatically. Thickness dependent transport studies indicate a superconductor-insulator transition as a function of film thickness regardless of lattice strain and microstructure. In addition, surface sensitive X-ray absorption spectroscopy has identified Ti to retain site symmetry and average valence of the bulk material regardless of film thickness.Comment: 25 pages, 7 figures, v2 - expanded Fig 1,2,7 with added discussion

Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies

Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss (HBT) interferometry signatures for the particle-emitting sources of pions and kaons produced in the heavy ion collisions at GSI-FAIR energies. The evolution of the sources is described by relativistic hydrodynamics with the system equation of state of the first-order phase transition from quark-gluon plasma (QGP) to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. We find that the HBT radii of kaons are smaller than those of pions for the same initial conditions. Both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources are sensitive to the initial energy density. They are significantly prolonged when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This prolongations of the HBT lifetimes of pions and kaons may likely be observed in the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure

Minimizing Unsatisfaction in Colourful Neighbourhoods

Colouring sparse graphs under various restrictions is a theoretical problem of significant practical relevance. Here we consider the problem of maximizing the number of different colours available at the nodes and their neighbourhoods, given a predetermined number of colours. In the analytical framework of a tree approximation, carried out at both zero and finite temperatures, solutions obtained by population dynamics give rise to estimates of the threshold connectivity for the incomplete to complete transition, which are consistent with those of existing algorithms. The nature of the transition as well as the validity of the tree approximation are investigated.Comment: 28 pages, 12 figures, substantially revised with additional explanatio

Heavy Quarkonia and Quark Drip Lines in Quark-Gluon Plasma

Using the potential model and thermodynamical quantities obtained in lattice gauge calculations, we determine the spontaneous dissociation temperatures of color-singlet quarkonia and the `quark drip lines' which separate the region of bound $Q\bar Q$ states from the unbound region. The dissociation temperatures of $J/\psi$ and $\chi_b$ in quenched QCD are found to be 1.62$T_c$ and $1.18T_c$ respectively, in good agreement with spectral function analyses. The dissociation temperature of $J/\psi$ in full QCD with 2 flavors is found to be 1.42$T_c$. For possible bound quarkonium states with light quarks, the characteristics of the quark drip lines severely limit the stable region close to the phase transition temperature. Bound color-singlet quarkonia with light quarks may exist very near the phase transition temperature if their effective quark mass is of the order of 300-400 MeV and higher.Comment: 8 pages, 2 figures, in LaTex, invited talk presented at the International Conference on Strangeness in Quark Matter, UCLA, March 26-31, 200

The Effect of Spectral Composition on the Photochemical Production of Hydrogen Peroxide in Lake Water

Hydrogen peroxide was produced when samples of lake water were exposed to direct or filtered sunlight in which UV or UV(B+C) light was selectively removed. In all cases, the concentration of hydrogen peroxide increased linearly with time-integrated irradiance. While both visible and UV light can induce the formation of hydrogen peroxide, the contribution from the latter was disproportionately large as it was responsible for about two-thirds of the formation of hydrogen peroxide. Among the UV lights, the contributions from UV-A and UV-(B+C) light were 70% and 30% respectively. The contribution from UV-A light was equivalent to about one half of the total production of hydrogen peroxide. Thus, relative to its contribution to the total irradiance in the solar spectrum, UV-A light is the most efficient type of light for the formation of hydrogen peroxide in lake waters

The role of magnetic anisotropy in spin filter junctions

We have fabricated oxide based spin filter junctions in which we demonstrate that magnetic anisotropy can be used to tune the transport behavior of spin filter junctions. Until recently, spin filters have been largely comprised of polycrystalline materials where the spin filter barrier layer and one of the electrodes are ferromagnetic. These spin filter junctions have relied on the weak magnetic coupling between one ferromagnetic electrode and a barrier layer or the insertion of a nonmagnetic insulating layer in between the spin filter barrier and electrode. We have demonstrated spin filtering behavior in La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where the interface anisotropy plays a significant role in determining transport behavior. Detailed studies of chemical and magnetic structure at the interfaces indicate that abrupt changes in magnetic anisotropy across the non-isostructural interface is the cause of the significant suppression of junction magnetoresistance in junctions with MnCr2O4 barrier layers.Comment: 7 pages, 7 figure