57,592 research outputs found
Neural self-tuning adaptive control of non-minimum phase system
The motivation of this research came about when a neural network direct adaptive control scheme was applied to control the tip position of a flexible robotic arm. Satisfactory control performance was not attainable due to the inherent non-minimum phase characteristics of the flexible robotic arm tip. Most of the existing neural network control algorithms are based on the direct method and exhibit very high sensitivity, if not unstable, closed-loop behavior. Therefore, a neural self-tuning control (NSTC) algorithm is developed and applied to this problem and showed promising results. Simulation results of the NSTC scheme and the conventional self-tuning (STR) control scheme are used to examine performance factors such as control tracking mean square error, estimation mean square error, transient response, and steady state response
Spinor Bose Condensates in Optical Traps
In an optical trap, the ground state of spin-1 Bosons such as Na,
K, and Rb can be either a ferromagnetic or a "polar" state,
depending on the scattering lengths in different angular momentum channel. The
collective modes of these states have very different spin character and spatial
distributions. While ordinary vortices are stable in the polar state, only
those with unit circulation are stable in the ferromagnetic state. The
ferromagnetic state also has coreless (or Skyrmion) vortices like those of
superfluid He-A. Current estimates of scattering lengths suggest that the
ground states of Na and Rb condensate are a polar state and a
ferromagnetic state respectively.Comment: 11 pages, no figures. email : [email protected]
Geometry of Deformed Boson Algebras
Phase-space realisations of an infinite parameter family of quantum
deformations of the boson algebra in which the -- and the --deformed
algebras arise as special cases are studied. Quantum and classical models for
the corresponding deformed oscillators are provided. The deformation parameters
are identified with coefficients of non-linear terms in the normal forms
expansion of a family of classical Hamiltonian systems. These quantum
deformations are trivial in the sense that they correspond to non-unitary
transformations of the Weyl algebra. They are non-trivial in the sense that the
deformed commutators consistently quantise a class of non-canonical classical
Poisson structures.Comment: 20 pages, late
Boson Mott insulators at finite temperatures
We discuss the finite temperature properties of ultracold bosons in optical
lattices in the presence of an additional, smoothly varying potential, as in
current experiments. Three regimes emerge in the phase diagram: a
low-temperature Mott regime similar to the zero-temperature quantum phase, an
intermediate regime where MI features persist, but where superfluidity is
absent, and a thermal regime where features of the Mott insulator state have
disappeared. We obtain the thermodynamic functions of the Mott phase in the
latter cases. The results are used to estimate the temperatures achieved by
adiabatic loading in current experiments. We point out the crucial role of the
trapping potential in determining the final temperature, and suggest a scheme
for further cooling by adiabatic decompression
Models for the integer quantum Hall effect: the network model, the Dirac equation, and a tight-binding Hamiltonian
We consider models for the plateau transition in the integer quantum Hall
effect. Starting from the network model, we construct a mapping to the Dirac
Hamiltonian in two dimensions. In the general case, the Dirac Hamiltonian has
randomness in the mass, the scalar potential, and the vector potential.
Separately, we show that the network model can also be associated with a
nearest neighbour, tight-binding Hamiltonian.Comment: Revtex, 15 pages, 7 figures; submitted to Phys. Rev.
Network Coding Over SATCOM: Lessons Learned
Satellite networks provide unique challenges that can restrict users' quality
of service. For example, high packet erasure rates and large latencies can
cause significant disruptions to applications such as video streaming or
voice-over-IP. Network coding is one promising technique that has been shown to
help improve performance, especially in these environments. However,
implementing any form of network code can be challenging. This paper will use
an example of a generation-based network code and a sliding-window network code
to help highlight the benefits and drawbacks of using one over the other.
In-order packet delivery delay, as well as network efficiency, will be used as
metrics to help differentiate between the two approaches. Furthermore, lessoned
learned during the course of our research will be provided in an attempt to
help the reader understand when and where network coding provides its benefits.Comment: Accepted to WiSATS 201
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