Formality of Sphere Bundles

We study the formality of orientable sphere bundles over connected compact manifolds. When the base manifold is formal, we prove that the formality of the bundle is equivalent to the vanishing of the Bianchi-Massey tensor introduced by Crowley-Nordstr\"{o}m. As an example, this implies that the unit tangent bundle over a formal manifold can only be formal when the base manifold has vanishing Euler characteristic or a rational cohomology ring generated by one element. When the base manifold is not formal, we give an obstruction for the formality of sphere bundles whose Euler class is reducible.Comment: 18 page

Adsorption of Calcium and Magnesium Ions and Thickening Effect

Waste water rich in high-concentration Ca2+、Mg2+ in a block of Daqing Oilfield,  the influence of Ca2+and Mg2+ on polymer solution viscosity is considered. To use of  sodium humate solution which compound by turf and NaOH complexed Ca2+ and Mg2+, reduced the impact of Ca2+ and Mg2+ on the polymer solution viscosity, so reached oilfield reinjection water viscosity standards. Research show that polymer solution viscosity lossed seriously when Ca2+ and Mg2+ content in 0 ~ 200mg / L, viscosity loss rate reached maximum 63.2% and 70.7%, respectively. The adsorption ratio of Ca2+ reached 77.50% when amount of sodium humate solution were 8mL. Similarly, the adsorption ratio of Mg2+ reached 83.60% when amount of sodium humate solution were 6mL. This indicated that sodium humate have great adsorption to Ca2+ and Mg2+. Indoor experimental results confirmed the feasibility of using sodium humate complexed Ca2+ and Mg2+ to prevent viscosity of polymer solution reduced, and provides a reference for the field test

Changing distribution of migrant population and influencing factors in urban China: economic transition, public policy, and amenities

Journal Articl

Ab initio study of electron-phonon interaction in phosphorene

The monolayer of black phosphorous, or phosphorene, has recently emerged as a new 2D semiconductor with intriguing highly anisotropic transport properties. Existing calculations of its intrinsic phonon-limited electronic transport properties so far rely on the deformation potential approximation, which is in general not directly applicable to anisotropic materials since the deformation along one specific direction can scatter electrons traveling in all directions. We perform a first-principles calculation of the electron-phonon interaction in phosphorene based on density functional perturbation theory and Wannier interpolation. Our calculation reveals that 1) the high anisotropy provides extra phase space for electron-phonon scattering, and 2) optical phonons have appreciable contributions. Both effects cannot be captured by the deformation potential calculations.Comment: 25 pages, 15 figure

Significant reduction of lattice thermal conductivity by electron-phonon interaction in silicon with high carrier concentrations: a first-principles study

Electron-phonon interaction has been well known to create major resistance to electron transport in metals and semiconductors, whereas less studies were directed to its effect on the phonon transport, especially in semiconductors. We calculate the phonon lifetimes due to scattering with electrons (or holes), combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon interaction, all from first-principles, and evaluate the effect of the electron-phonon interaction on the lattice thermal conductivity of silicon. Unexpectedly, we find a significant reduction of the lattice thermal conductivity at room temperature as the carrier concentration goes above 1e19 cm-3 (the reduction reaches up to 45% in p-type silicon at around 1e21 cm-3), a range of great technological relevance to thermoelectric materials.Comment: 19 pages, 5 figure