1,522 research outputs found
Observation of Topologically Stable 2D Skyrmions in an Antiferromagnetic Spinor Bose-Einstein Condensate
We present the creation and time evolution of two-dimensional Skyrmion
excitations in an antiferromagnetic spinor Bose-Einstein condensate. Using a
spin rotation method, the Skyrmion spin textures were imprinted on a sodium
condensate in a polar phase, where the two-dimensional Skyrmion is
topologically protected. The Skyrmion was observed to be stable on a short time
scale of a few tens of ms but to have dynamical instability to deform its shape
and eventually decay to a uniform spin texture. The deformed spin textures
reveal that the decay dynamics involves breaking the polar phase inside the
condensate without having topological charge density flow through the boundary
of the finite-sized sample. We discuss the possible formation of half-quantum
vortices in the deformation process.Comment: 5 pages, 5 figure
Relaxation of superfluid turbulence in highly oblate Bose-Einstein condensates
We investigate thermal relaxation of superfluid turbulence in a highly oblate
Bose-Einstein condensate. We generate turbulent flow in the condensate by
sweeping the center region of the condensate with a repulsive optical
potential. The turbulent condensate shows a spatially disordered distribution
of quantized vortices and the vortex number of the condensate exhibits
nonexponential decay behavior which we attribute to the vortex pair
annihilation. The vortex-antivortex collisions in the condensate are identified
with crescent-shaped, coalesced vortex cores. We observe that the
nonexponential decay of the vortex number is quantitatively well described by a
rate equation consisting of one-body and two-body decay terms. In our
measurement, we find that the local two-body decay rate is closely proportional
to , where is the temperature and is the chemical potential.Comment: 7 pages, 9 figure
Observation of a Geometric Hall Effect in a Spinor Bose-Einstein Condensate with a Skyrmion Spin Texture
For a spin-carrying particle moving in a spatially varying magnetic field,
effective electromagnetic forces can arise due to the geometric phase
associated with adiabatic spin rotation of the particle. We report the
observation of a geometric Hall effect in a spinor Bose-Einstein condensate
with a skyrmion spin texture. Under translational oscillations of the spin
texture, the condensate resonantly develops a circular motion in a harmonic
trap, demonstrating the existence of an effective Lorentz force. When the
condensate circulates, quantized vortices are nucleated in the boundary region
of the condensate and the vortex number increases over 100 without significant
heating. We attribute the vortex nucleation to the shearing effect of the
effective Lorentz force from the inhomogeneous effective magnetic field.Comment: 9 pages, 11 figure
A real-time bilateral teleoperation control system over imperfect network
Functionality and performance of modern machines are directly affected by the implementation of real-time control systems. Especially in networked teleoperation applications, force feedback control and networked control are two of the most important factors and determine the performance of the whole system. In force feedback control, generally it is necessary but difficult and expensive to attach sensors (force/torque/pressure sensors) to detect the environment information in order to drive properly the feedback force. In networked control, there always exist inevitable random time-varying delays and packet losses, which may degrade the system performance and, even worse, cause the system instability. Therefore in this chapter, a study on a real-time bilateral teleoperation control system (BTCS) over an imperfect network is discussed. First, current technologies for teleoperation as well as bilateral teleoperation control systems are briefly reviewed. Second, an advanced concept for designing a bilateral teleoperation networked control (BTNCS) system is proposed and the working principle is clearly explained. Third, an approach to develop a force-sensorless feedback control (FSFC) is proposed to simplify the sensor requirement in designing the BTNCS while the correct sense of interaction between the slave and environment can be ensured. Forth, a robust adaptive networked control (RANC) -based master controller is introduced to deal with control of the slave over the network containing both time delays and information loss. Case studies are carried out to evaluate the applicability of the suggested methodology
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