Structural behavior of uranium dioxide under pressure by LSDA+U calculations

The structural behavior of UO2 under high pressure up to 300GPa has been studied by first-principles calculations with LSDA+U approximation. The results show that a pressure-induced structural transition to the cotunnite-type (orthorhombic Pnma) phase occurs at 38GPa. It agrees well with the experimentally observed ~42 GPa. An isostructural transition following that is also predicted to take place from 80 to 130GPa, which has not yet been observed in experiments. Further high compression beyond 226GPa will result in a metallic and paramagnetic transition. It corresponds to a volume of 90A^3 per cell, in good agreement with a previous theoretical analysis in the reduction of volume required to delocalize 5f states.Comment: 10 pages, 8 figure

Possibly New Charmed Baryon States from Bˉ0→ppˉD0\bar B^0\to p\bar p D^{0} Decay

We examine the invariant mass spectrum of $D^{0}p$ in $\bar B^0\to p\bar p D^{0}$ decay measured by BABAR and find that through the 2-step processes of $\bar B^0\to {\bf B_c^+}(\to D^{0} p)\bar p$, where ${\bf B_c}$ denotes a charmed baryon state, some of the peaks can be identified with the established $\Sigma_c(2800)^+$, $\Lambda_c(2880)^+$ and $\Lambda_c(2940)^+$. Moreover, in order to account for the measured spectrum, it is necessary to introduce a new charmed baryon resonance with $(m,\,\Gamma)=(3212\pm 20,\,167\pm 34)$ MeV.Comment: 8 pages, 1 figure, title changed and discussions updated, version accepted for publication in Phys. Rev.

Study of Radiative Leptonic D Meson Decays

We study the radiative leptonic $D$ meson decays of D^+_{(s)}\to \l^+\nu_{\l}\gamma (\l=e,\mu,\tau), $D^0\to \nu\bar{\nu}\gamma$ and D^0\to \l^+\l^-\gamma ($l=e,\mu$) within the light front quark model. In the standard model, we find that the decay branching ratios of $D^+_{(s)}\to e^+\nu_e\gamma$, $D^+_{(s)}\to\mu^+\nu_{\mu}\gamma$ and $D^+_{(s)}\to\tau^+\nu_{\tau}\gamma$ are $6.9\times 10^{-6}$ ($7.7\times 10^{-5}$), $2.5\times 10^{-5}$ ($2.6\times 10^{-4}$), and $6.0\times 10^{-6}$ ($3.2\times 10^{-4}$), and that of D^0\to\l^+\l^-\gamma (\l=e,\mu) and $D^0\to\nu\bar{\nu}\gamma$ are $6.3\times 10^{-11}$ and $2.7\times 10^{-16}$, respectively.Comment: 23 pages, 6 Figures, LaTex file, a reference added, to be published in Mod. Phys. Lett.

Simulation of double robot cooperative sheet metal bending production line

Aiming at the problem that large sheet metal bending parts cannot be processed by single robot, and the manual assisted bending method has high labor intensity and low work efficiency; double robots work together to complete the handling of the plate; Firstly, according to the actual production requirements of sheet metal bending, the process planning and three-dimensional modeling of the production line are completed. Secondly, the kinematics analysis and base coordinate system calibration of the dual robot are completed. Then, by establishing the mathematical model of each unit, the end pose matrix in the local coordinate system of the robot is finally obtained, and the joint angles of the robot machine are obtained by inverse kinematics. Finally, the production line simulation is completed by Rapid offline programming. The research results show that the kinematics model is correct, and the production line can complete the sheet metal bending work without collision, which can provide reference for the research of large sheet metal bending

Shock Induced Order-disorder Transformation in Ni3Al

The Hugoniot of Ni3Al with L12 structure is calculated with an equation of state (EOS) based on a cluster expansion and variation method from first principles. It is found that an order-disorder transition occurs at a shock pressure of 205GPa, corresponding to 3750K in temperature. On the other hand, an unexpected high melting temperature about 6955K is obtained at the same pressure, which is completely different from the case at ambient pressure where the melting point is slightly lower than the order-disorder transition temperature, implying the high pressure phase diagram has its own characteristics. The present work also demonstrates the configurational contribution is more important than electronic excitations in alloys and mineral crystals within a large range of temperature, and an EOS model based on CVM is necessary for high pressure metallurgy and theoretical Earth model.Comment: 14 pages, 5 figure