Interaction induced mergence of Dirac points in Non-Abelian optical lattices

We study the properties of an ultracold Fermi gas loaded in a square optical lattice and subjected to an external and classical non-Abelian gauge field. We calculate the energy spectrum of the system and show that the Dirac points in the energy spectrum will remain quite stable under onsite interaction of certain strength. Once the on-site interaction grows stronger than a critical value, the Dirac points will no longer be stable and merge into a single hybrid point. This mergence implies a quantum phase transition from a semimetallic phase to a band insulator. The on-site interaction between ultracold fermions could be conveniently controlled by Feshbach resonances in current experiments. We proposed that this remarkable interaction induced mergence of Dirac points may be observed in the ultracold fermi gas experiments

Quantum resonance and anti-resonance for a periodically kicked Bose-Einstein Condensate in a one dimensional Box

We investigate the quantum dynamics of a periodically kicked Bose-Einstein Condensate confined in a one dimensional (1D) Box both numerically and theoretically, emphasizing on the phenomena of quantum resonance and anti-resonance. The quantum resonant behavior of BEC is different from the single particle case but the anti-resonance condition ($T = 2\pi$ and $\alpha = 0$) is not affected by the atomic interaction. For the anti-resonance case, the nonlinearity (atom interaction) causes the transition between oscillation and quantum beating. For the quantum resonance case, because of the coherence of BEC, the energy increase is oscillating and the rate is dramatically affected by the many-body interaction. We also discuss the relation between the quantum resonant behavior and the KAM or non-KAM property of the corresponding classical system.Comment: 7 pages, 7 figure

Parametric Study on Self-centering Precast Concrete Frames with Hysteretic Dampers

The self-centering precast concrete frame structure combines the advantages of industrialization and low earthquake damage, and its energy dissipation capacity and seismic performance have always been the focus of research. This paper proposed a kind of self-centering precast concrete frame with hysteretic dampers (SCPCHD). Its modular design makes the energy dissipation device and components easy to repair and replace. In order to obtain the optimal design, the finite element models of SCPCHD frames with different layout types of post-tensioned (PT) tendons and different shapes of hysteretic dampers are established, and the elastoplastic dynamic time-history analyses are carried out. The results show that the layout types and vertical margin of PT tendons have little effect on the displacement response of the frame structure. Compared to linear PT tendons, polygonal PT tendons can better bear the bending moment of the beam and reduce the stress of longitudinal reinforcements in the beam. The reduce effect of shortening the vertical margin on the tensile damage of beam concrete is obvious in the frame with polygonal PT tendons, but not obvious in the frame with linear PT tendons. Rational design of the prestressing force also plays a crucial role in the energy dissipation capacity of SCPCHD frames