1,620 research outputs found
MIMO nonlinear PID predictive controller
A class of nonlinear generalised predictive controllers (NGPC) is derived for multi-input multi-output (MIMO) nonlinear systems with offset or steady-state response error. The MIMO composite controller consists of an optimal NGPC and a nonlinear disturbance observer. The design of the nonlinear disturbance observer to estimate the offset is particularly simple, as is the associated proof of overall nonlinear closed-loop system stability. Moreover, the transient error response of the disturbance observer can be arbitrarily specified by simple design parameters. Very satisfactory performance of the proposed MIMO nonlinear predictive controller is demonstrated for a three-link nonlinear robotic manipulator example
Magnetoresistance of Three-Constituent Composites: Percolation Near a Critical Line
Scaling theory, duality symmetry, and numerical simulations of a random
network model are used to study the magnetoresistance of a
metal/insulator/perfect conductor composite with a disordered columnar
microstructure. The phase diagram is found to have a critical line which
separates regions of saturating and non-saturating magnetoresistance. The
percolation problem which describes this line is a generalization of
anisotropic percolation. We locate the percolation threshold and determine the
t = s = 1.30 +- 0.02, nu = 4/3 +- 0.02, which are the same as in
two-constituent 2D isotropic percolation. We also determine the exponents which
characterize the critical dependence on magnetic field, and confirm numerically
that nu is independent of anisotropy. We propose and test a complete scaling
description of the magnetoresistance in the vicinity of the critical line.Comment: Substantially revised version; description of behavior in finite
magnetic fields added. 7 pages, 7 figures, submitted to PR
The Spectrum of the Neumann Matrix with Zero Modes
We calculate the spectrum of the matrix M' of Neumann coefficients of the
Witten vertex, expressed in the oscillator basis including the zero-mode a_0.
We find that in addition to the known continuous spectrum inside [-1/3,0) of
the matrix M without the zero-modes, there is also an additional eigenvalue
inside (0,1). For every eigenvalue, there is a pair of eigenvectors, a
twist-even and a twist-odd. We give analytically these eigenvectors as well as
the generating function for their components. Also, we have found an
interesting critical parameter b_0 = 8 ln 2 on which the forms of the
eigenvectors depend.Comment: 25+1 pages, 3 Figures; typos corrected and some comments adde
Multichannel wavelength conversion of 40 Gbit/s NRZ DPSK signals in a highly nonlinear dispersion flattened lead silicate fibre
We experimentally demonstrate the wavelength conversion of three wavelength multiplexed 40 Gbit/s Differential Phase Shift Keyed (DPSK) signals in a 2.2m length of highly nonlinear, dispersion tailored W-type lead-silicate optical fibre
Lyapunov spectrum of asymptotically sub-additive potentials
For general asymptotically sub-additive potentials (resp. asymptotically
additive potentials) on general topological dynamical systems, we establish
some variational relations between the topological entropy of the level sets of
Lyapunov exponents, measure-theoretic entropies and topological pressures in
this general situation. Most of our results are obtained without the assumption
of the existence of unique equilibrium measures or the differentiability of
pressure functions. Some examples are constructed to illustrate the
irregularity and the complexity of multifractal behaviors in the sub-additive
case and in the case that the entropy map that is not upper-semi continuous.Comment: 44 page
Ratio of Tensions from Vacuum String Field Theory
We show analytically that the ratio of the norm of sliver states agrees with
the ratio of D-brane tensions. We find that the correct ratio appears as a
twist anomaly.Comment: 13 pages, lanlmac; version to appear in JHE
A single-mode, high index-contrast, lead silicate glass fibre with high nonlinearity, broadband near-zero dispersion at telecommunication wavelengths
We report on the design, fabrication and characterization of a single-mode W-type lead silicate glass fibre with flattened and near-zero dispersion profile at telecom wavelengths and high nonlinearity of 820 W-1km-1 at 1.55 ”m
Kinetic energy driven superconductivity in doped cuprates
Within the t-J model, the mechanism of superconductivity in doped cuprates is
studied based on the partial charge-spin separation fermion-spin theory. It is
shown that dressed holons interact occurring directly through the kinetic
energy by exchanging dressed spinon excitations, leading to a net attractive
force between dressed holons, then the electron Cooper pairs originating from
the dressed holon pairing state are due to the charge-spin recombination, and
their condensation reveals the superconducting ground-state. The electron
superconducting transition temperature is determined by the dressed holon pair
transition temperature, and is proportional to the concentration of doped holes
in the underdoped regime. With the common form of the electron Cooper pair, we
also show that there is a coexistence of the electron Cooper pair and
antiferromagnetic short-range correlation, and hence the antiferromagnetic
short-range fluctuation can persist into the superconducting state. Our results
are qualitatively consistent with experiments.Comment: 6 pages, Revtex, two figures are included, corrected typo
Non-universality of elastic exponents in random bond-bending networks
We numerically investigate the rigidity percolation transition in
two-dimensional flexible, random rod networks with freely rotating cross-links.
Near the transition, networks are dominated by bending modes and the elastic
modulii vanish with an exponent f=3.0\pm0.2, in contrast with central force
percolation which shares the same geometric exponents. This indicates that
universality for geometric quantities does not imply universality for elastic
ones. The implications of this result for actin-fiber networks is discussed.Comment: 4 pages, 3 figures, minor clarifications and amendments. To appear in
PRE Rap. Com
Vacuum String Field Theory ancestors of the GMS solitons
We define a sequence of VSFT D-branes whose low energy limit leads exactly to
a corresponding sequence of GMS solitons. The D-branes are defined by acting on
a fixed VSFT lump with operators defined by means of Laguerre polynomials whose
argument is quadratic in the string creation operators. The states obtained in
this way form an algebra under the SFT star product, which is isomorphic to a
corresponding algebra of GMS solitons under the Moyal product. In order to
obtain a regularized field theory limit we embed the theory in a constant
background B field.Comment: 1+16 pages; v2: typos corrected; v3: two appendices added, final
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