3,219 research outputs found
Optimal molecular alignment and orientation through rotational ladder climbing
We study the control by electromagnetic fields of molecular alignment and
orientation, in a linear, rigid rotor model. With the help of a monotonically
convergent algorithm, we find that the optimal field is in the microwave part
of the spectrum and acts by resonantly exciting the rotation of the molecule
progressively from the ground state, i.e., by rotational ladder climbing. This
mechanism is present not only when maximizing orientation or alignment, but
also when using prescribed target states that simultaneously optimize the
efficiency of orientation/alignment and its duration. The extension of the
optimization method to consider a finite rotational temperature is also
presented.Comment: 14 pages, 12 figure
A nonadiabatic semi-classical method for dynamics of atoms in optical lattices
We develop a semi-classical method to simulate the motion of atoms in a
dissipative optical lattice. Our method treats the internal states of the atom
quantum mechanically, including all nonadiabatic couplings, while position and
momentum are treated as classical variables. We test our method in the
one-dimensional case. Excellent agreement with fully quantum mechanical
simulations is found. Our results are much more accurate than those of earlier
semi-classical methods based on the adiabatic approximation.Comment: 7 pages, 5 figures, submitted to European Physical Journal
Influence of the lattice topography on a three-dimensional, controllable Brownian motor
We study the influence of the lattice topography and the coupling between
motion in different directions, for a three-dimensional Brownian motor based on
cold atoms in a double optical lattice. Due to controllable relative spatial
phases between the lattices, our Brownian motor can induce drifts in arbitrary
directions. Since the lattices couple the different directions, the relation
between the phase shifts and the directionality of the induced drift is non
trivial. Here is therefore this relation investigated experimentally by
systematically varying the relative spatial phase in two dimensions, while
monitoring the vertically induced drift and the temperature. A relative spatial
phase range of 2pi x 2pi is covered. We show that a drift, controllable both in
speed and direction, can be achieved, by varying the phase both parallel and
perpendicular to the direction of the measured induced drift. The experimental
results are qualitatively reproduced by numerical simulations of a simplified,
classical model of the system
Laser control for the optimal evolution of pure quantum states
Starting from an initial pure quantum state, we present a strategy for
reaching a target state corresponding to the extremum (maximum or minimum) of a
given observable. We show that a sequence of pulses of moderate intensity,
applied at times when the average of the observable reaches its local or global
extremum, constitutes a strategy transferable to different control issues.
Among them, post-pulse molecular alignment and orientation are presented as
examples. The robustness of such strategies with respect to experimentally
relevant parameters is also examined.Comment: 16 pages, 9 figure
ROBOTS CONTROL BY ADAPTIVE GAIN SMOOTH SLIDING OBSERVER-CONTROLLER AND PARAMETER IDENTIFICATION
An adaptive gain, smooth sliding observer-controller are developed to control uncertain parameters, -degree of freedom rigid robotic manipulators. Furthermore, an on-line, closed loop identification scheme, for time-varying parameters is proposed in order to obtain useful information despite loads, external disturbances and faults detection. In order to reduce the chattering, a smooth switching function (parameterised tangent hyperbolic function) is used instead of pure relay one, into the observer and the controller. The gains of the switching functions are adaptively updated, depending on the estimation error and tracking error, respectively. By using adaptive gains, the transient and tracking responses are improved. Simulation results with a two degree of freedom (DOF) robot manipulator are presented to show the interest of the approach
Flexible Joints Robotic Manipulator Control By Adaptive Gain Smooth Sliding Observer-Controller
An adaptive gain sliding observer for uncertain parameter nonlinear systems together with an adaptive gain sliding controller is proposed in this paper. It considered nonlinear, SISO affine systems, with uncertainties in steady-state functions and parameters. A further parameter term, adaptively updated, has been introduced in steady state space model of the controlled system, in order to obtain useful information despite fault detection and isolation. By using of the sliding observer with adaptive gain, the robustness to uncertainties is increased and the parameters adaptively updated can provide useful information in fault detection. Also, the state estimation error is bounded accordingly with bound limits of the uncertainties. The both of them, the sliding adaptive observer and sliding controller are designed to fulfill the attractiveness condition of its corresponding switching surface. An application to a single arm with flexible joint robot is presented. In order to alleviate chattering, a parameterized tangent hyperbolic has been used as switching function, instead of pure relay one, to the observer and the controller. Also, the gains of the switching functions, to the sliding observer and sliding controller are adaptively updated depending of estimation error and tracking error, respectively. By the using adaptive gains, the transient and tracking response can be improved
Sign- vs. goal-tracking in a feature positive discrimination task with nicotine: Importance of spatial location of the conditional stimulus
We assessed whether sign-tracking developed along with goal-tracking in a Pavlovian drug discrimination task. Rats had nicotine sessions intermixed with saline sessions. For nicotine sessions, 15-sec illumination of a light near (Experiment 1) or far (Experiment 2) from the dipper receptacle was followed by sucrose. Saline sessions were similar except sucrose was withheld. Regardless of location, the light evoked goal-tracking only on nicotine sessions. Only rats with the light near the dipper developed sign-tracking
Sign- vs. goal-tracking in a feature positive discrimination task with nicotine: Importance of spatial location of the conditional stimulus
We assessed whether sign-tracking developed along with goal-tracking in a Pavlovian drug discrimination task. Rats had nicotine sessions intermixed with saline sessions. For nicotine sessions, 15-sec illumination of a light near (Experiment 1) or far (Experiment 2) from the dipper receptacle was followed by sucrose. Saline sessions were similar except sucrose was withheld. Regardless of location, the light evoked goal-tracking only on nicotine sessions. Only rats with the light near the dipper developed sign-tracking
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