213 research outputs found
BCS-BEC Crossover in Mix-dimensional Fermi Gases
We investigate a mix-dimensional Fermi-Fermi mixture in which one species is
confined in two-dimensional(2D) space while the other is free in
three-dimensional space(3D). We determine the superfluid transition temperature
for the entire BCS-BEC crossover including the important effects of
noncondensed pairs. We find that the transition temperature reduces while the
imbalance of mass is increased or lattice constant () is reduced. In
population imbalance case, the stability of superfluid is sharply destroyed by
increasing the polarization.Comment: 7 pages, 5 figure
Magnetic Impurities in Two-Dimensional Superfluid Fermi Gas with Spin-Orbit Coupling
We consider magnetic impurities in a two dimensional superfluid Fermi gas in
the presence of spin-orbit coupling. By using the methods of t-matrix and
Green's function, we find spin-orbit coupling has some dramatic impacts on the
effects of magnetic impurities. For the single impurity problem, the number of
bound states localized around the magnetic impurity is doubled. For the finite
concentration of impurities, the energy gap is reduced and the density of
states in the gapless region is greatly modified.Comment: 6 pages, 6 figure
RBF-based supervisor path following control for ASV with time-varying ocean disturbance
1028-1036A robust model-free path following controller is developed for autonomous surface vehicle (ASV) with time-varying ocean disturbance. First, the geometrical relationship between ASV and virtual tracking point on the reference path is investigated. The differentiations of tracking errors are described with the relative motion method, which greatly simplified the direct differential of tracking errors. Furthermore, the control law for the desired angular velocity of the vehicle and virtual tracking point are built based on the Lyapunov theory. Second, the traditional proportional-integral-derivative (PID) controller is developed based on the desired velocities and state feedback. The radial basic function (RBF) neural network taking as inputs the desired surge velocity and yaw angular velocity is developed as the supervisor to PID controller. Besides, RBF controller tunes weights according to the output errors between the PID controller and supervisor controller, based on the gradient descent method. Hence, PID controller and RBF supervisor controller act as feedback and feed forward control of the system, respectively. Finally, comparative path following simulation for straight path and sine path illustrate the performance of the proposed supervisor control system. The PID controller term reports loss of control even in the unknown disturbance
Topological Phase Separation In Trapped Ultracold Fermionic Gases
We investigate the harmonically trapped 2D fermionic systems with a effective
spin-orbit coupling and intrinsic s-wave superfluidity under the local density
approximation, and find that there is a critical value for Zeeman field. When
the Zeeman field larger than the critical value, the topological superfluid
phases emerge and coexist with the normal superfluid phase, topological phase
separation, in the trapped region. Otherwise, the superfluid phase is
topologically trivial.Comment: 6 pages, 3 figure
- …