9,248 research outputs found
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 Decay
We examine the invariant mass spectrum of in decay measured by BABAR and find that through the 2-step processes of
, where denotes a
charmed baryon state, some of the peaks can be identified with the established
, and . Moreover, in
order to account for the measured spectrum, it is necessary to introduce a new
charmed baryon resonance with 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 meson decays of D^+_{(s)}\to
\l^+\nu_{\l}\gamma (\l=e,\mu,\tau), and D^0\to
\l^+\l^-\gamma () within the light front quark model. In the standard
model, we find that the decay branching ratios of , and
are (), (), and
(), and that of D^0\to\l^+\l^-\gamma (\l=e,\mu) and
are and ,
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
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