16,576 research outputs found
Zero-mode contribution to the light-front Hamiltonian of Yukawa type models
Light-front Hamiltonian for Yukawa type models is determined without the
framework of canonical light-front formalism. Special attention is given to the
contribution of zero modes.Comment: 14 pages, Latex, revised version with minor changes, Submitted to
J.Phys.
Fuzzy logic control of telerobot manipulators
Telerobot systems for advanced applications will require manipulators with redundant 'degrees of freedom' (DOF) that are capable of adapting manipulator configurations to avoid obstacles while achieving the user specified goal. Conventional methods for control of manipulators (based on solution of the inverse kinematics) cannot be easily extended to these situations. Fuzzy logic control offers a possible solution to these needs. A current research program at SRI developed a fuzzy logic controller for a redundant, 4 DOF, planar manipulator. The manipulator end point trajectory can be specified by either a computer program (robot mode) or by manual input (teleoperator). The approach used expresses end-point error and the location of manipulator joints as fuzzy variables. Joint motions are determined by a fuzzy rule set without requiring solution of the inverse kinematics. Additional rules for sensor data, obstacle avoidance and preferred manipulator configuration, e.g., 'righty' or 'lefty', are easily accommodated. The procedure used to generate the fuzzy rules can be extended to higher DOF systems
Gauge Invariant Regularization of Quantum Field Theory on the Light-Front
Gauge invariant regularization of quantum field theory in the framework of
Light-Front (LF) Hamiltonian formalism via introducing a lattice in transverse
coordinates and imposing boundary conditions in LF coordinate for gauge
fields on the interval is considered. The remaining ultraviolet
divergences in the longitudinal momentum are removed by gauge invariant
finite mode regularization. We find that LF canonical formalism for the
introduced regularization does not contain usual most complicated second class
constraints connecting zero and nonzero modes of gauge fields. The described
scheme can be used either for the regularization of conventional gauge theory
or for gauge invariant formulation of effective low-energy models on the LF.
The lack of explicit Lorentz invariance in our approach leads to difficulty
with defining the vacuum state. We discuss this difficulty, particulary, in the
connection with the problem of taking the limit of continuous space.Comment: LaTeX 2.09, 15 pages, Proceedings of "12th V.Fock School of Physics",
St-Petersburg 200
Trans-spectral orbital angular momentum transfer via four-wave mixing in Rb vapor
We report the transfer of phase structure and, in particular, of orbital angular momentum from near-infrared pump light to blue light generated in a four-wave-mixing process in Rb-85 vapor. The intensity and phase profile of the two pump lasers at 780 and 776 nm, shaped by a spatial light modulator, influences the phase and intensity profile of light at 420 nm, which is generated in a subsequent coherent cascade. In particular, we observe that the phase profile associated with orbital angular momentum is transferred entirely from the pump light to the blue. Pumping with more complicated light profiles results in the excitation of spatial modes in the blue that depend strongly on phase matching, thus demonstrating the parametric nature of the mode transfer. These results have implications on the inscription and storage of phase information in atomic gases
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