A computer solution for the dynamic load, lubricant film thickness and surface temperatures in spiral bevel gears

A complete analysis of spiral bevel gear sets is presented. The gear profile is described by the movements of the cutting tools. The contact patterns of the rigid body gears are investigated. The tooth dynamic force is studied by combining the effects of variable teeth meshing stiffness, speed, damping, and bearing stiffness. The lubrication performance is also accomplished by including the effects of the lubricant viscosity, ambient temperature, and gear speed. A set of numerical results is also presented

Radiative Leptonic Decays of BcB_c Meson

To the leading order, the radiative leptonic decays $B_c \to \gamma \ell \bar \nu$ ($\ell=e, \mu$) are studied carefully. In the study, a non-relativistic constituent quark model and the effective Lagrangian for the heavy flavour decays are used. As a result, the branching ratios turn out to be of the orders of $10^{-5}$ for $B_c \to \gamma \mu \bar \nu$ or for $B_c \to \gamma e \bar \nu$. Based on this study, we point out the decays being accessible experimentally at the future LHC, and the possibility to determine the decay constant $f_{B_c}$ through the radiative decays.Comment: 9 pages Latex, including 2 figure

Half quantum spin Hall effect on the surface of weak topological insulators

We investigate interaction effects in three dimensional weak topological insulators (TI) with an even number of Dirac cones on the surface. We find that the surface states can be gapped by a surface charge density wave (CDW) order without breaking the time-reversal symmetry. In this sense, time reversal symmetry alone can not robustly protect the weak TI state in the presence of interactions. If the translational symmetry is additionally imposed in the bulk, a topologically non-trivial weak TI state can be obtained with helical edge states on the CDW domain walls. In other words, a CDW domain wall on the surface is topologically equivalent to the edge of a two-dimensional quantum spin Hall insulator. Therefore, the surface state of a weak topological insulator with translation symmetry breaking on the surface has a "half quantum spin Hall effect", in the same way that the surface state of a strong topological insulator with time-reversal symmetry breaking on the surface has a "half quantum Hall effect". The on-site and nearest neighbor interactions are investigated in the mean field level and the phase diagram for the surface states of weak topological insulators is obtained.Comment: 6 pages and 4 figure

"Economic Geography with Tariff Competition"

A simple two-country model of economic geography is constructed in order to examine the effect of tariff competition on the spatial distribution of manufacturing activities as well as on welfare. We show that when the transport cost is sufficiently small, tariff competition with firm migration leads to a core-periphery economy, where one of the two countries imposes no tariff in Nash equilibrium. We also show that when the transport cost is sufficiently large, tariff competition harms the welfare of the two countries, implying that each country is better off by mutually binding agreement of free trade.

Direct CP violation in τ±→K±ρ0(ω)ντ→K±π+π−ντ\tau^\pm\rightarrow K^\pm \rho^0 (\omega)\nu_\tau \rightarrow K^\pm \pi^+\pi^-\nu_\tau

We study the direct CP violation in the $\tau^\pm\rightarrow K^\pm \rho^0 (\omega)\nu_\tau \rightarrow K^\pm \pi^+\pi^-\nu_\tau$ decay process in the Standard Model. An interesting mechanism involving the charge symmetry violating mixing between $\rho^0$ and $\omega$ is applied to enlarge the CP asymmetry. With this mechanism, the maximum differential and localized integrated CP asymmetries can reach $-(5.6^{+2.9}_{-1.7})\times10^{-12}$ and $6.3^{+2.4}_{-3.3}\times 10^{-11}$, respectively, which still leave plenty room for CP-violating New Physics to be discovered through this process