459 research outputs found
On the connection between different noise structures for LPV-SS models
Different representations to describe noise processes and finding connections
or equivalence between them have been part of active research for decades, in
particular for linear time-invariant case. In this paper the linear
parameter-varying (LPV) setting is addressed; starting with the connection
between an LPV state-space (SS) representation with a general noise structure
and the LPV-SS model in an innovation structure, i.e., the Kalman filter. More
specifically, the considered LPV-SS representation with general noise structure
has static, affine dependence on the scheduling signal; however, we show that
its companion innovation structure has a dynamic, rational dependency
structure. Following, we would like to highlight the consequences of
approximating this Kalman gain by a static, affine dependency structure. To
this end, firstly, we use the "fading memory" effect of the Kalman filter to
reason how the Kalman gain can be approximated to depend only on a partial
trajectory of the scheduling signal. This effect is shown by proving an
asymptotically decreasing error upper bound on the covariance matrix associated
to the innovation structure in case the covariance matrix is subjected to an
incorrect initialization or disturbance. Secondly, we show by an example that
an LPV-SS representation that has dynamical, rational dependency on the
scheduling signal can be transformed into static, affinely dependent
representation by introducing additional states. Therefore, an approximated
Kalman gain can, in some cases, be represented by a static, affine Kalman gain
at the cost of additional states.Comment: 6 page
Affine parameter-dependent Lyapunov functions for LPV systems with affine dependence
This paper deals with the certification problem for robust quadratic stability, robust state convergence, and robust quadratic performance of linear systems that exhibit bounded rates of variation in their parameters. We consider both continuous-time (CT) and discrete-time (DT) parameter-varying systems. In this paper, we provide a uniform method for this certification problem in both cases and we show that, contrary to what was claimed previously, the DT case requires a significantly different treatment compared to the existing CT results. In the established uniform approach, quadratic Lyapunov functions, which are affine in the parameter, are used to certify robust stability, robust convergence rates, and robust performance in terms of linear matrix inequality feasibility tests. To exemplify the procedure, we solve the certification problem for L2-gain performance both in the CT and the DT cases. A numerical example is given to show that the proposed approach is less conservative than a method with slack variables.</p
Bayesian identification of LPV-BJ models : a multidimensional kernel approach
poster, no abstract available
Anderson-Yuval approach to the multichannel Kondo problem
We analyze the structure of the perturbation expansion of the general
multichannel Kondo model with channel anisotropic exchange couplings and in the
presence of an external magnetic field, generalizing to this case the
Anderson-Yuval technique. For two channels, we are able to map the Kondo model
onto a generalized resonant level model. Limiting cases in which the equivalent
resonant level model is solvable are identified. The solution correctly
captures the properties of the two channel Kondo model, and also allows an
analytic description of the cross-over from the non Fermi liquid to the Fermi
liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques
Topological (Sliced) Doping of a 3D Peierls System: Predicted Structure of Doped BaBiO3
At hole concentrations below x=0.4, Ba_(1-x)K_xBiO_3 is non-metallic. At x=0,
pure BaBiO3 is a Peierls insulator. Very dilute holes create bipolaronic point
defects in the Peierls order parameter. Here we find that the Rice-Sneddon
version of Peierls theory predicts that more concentrated holes should form
stacking faults (two-dimensional topological defects, called slices) in the
Peierls order parameter. However, the long-range Coulomb interaction, left out
of the Rice-Sneddon model, destabilizes slices in favor of point bipolarons at
low concentrations, leaving a window near 30% doping where the sliced state is
marginally stable.Comment: 6 pages with 5 embedded postscript figure
A recent rebuilding of most spirals ?
Re-examination of the properties of distant galaxies leads to the evidence
that most present-day spirals have built up half of their stellar masses during
the last 8 Gyr, mostly during several intense phases of star formation during
which they took the appearance of luminous infrared galaxies (LIRGs). Distant
galaxy morphologies encompass all of the expected stages of galaxy merging,
central core formation and disk growth, while their cores are much bluer than
those of present-day bulges. We have tested a spiral rebuilding scenario, for
which 75+/-25% of spirals have experienced their last major merger event less
than 8 Gyr ago. It accounts for the simultaneous decreases, during that period,
of the cosmic star formation density, of the merger rate, of the number
densities of LIRGs and of compact galaxies, while the densities of ellipticals
and large spirals are essentially unaffected.Comment: (1) GEPI, Obs. Meudon, France ;(2)Max-Planck Institut fuer
Astronomie, Germany (3) National Astronomical Observatories, CAS, China. Five
pages, 1 figure. To be published in "Starbursts: From 30 Doradus to Lyman
Break Galaxies", held in Cambridge, ed. R. de Grijs & R. M. Gonzalez Delgado
(Dordrecht: Kluwer
Multi-Channel Kondo Necklace
A multi--channel generalization of Doniach's Kondo necklace model is
formulated, and its phase diagram studied in the mean--field approximation. Our
intention is to introduce the possible simplest model which displays some of
the features expected from the overscreened Kondo lattice. The conduction
electron channels are represented by sets of pseudospins \vt_{j}, , which are all antiferromagnetically coupled to a periodic array of
|\vs|=1/2 spins. Exploiting permutation symmetry in the channel index
allows us to write down the self--consistency equation for general . For
, we find that the critical temperature is rising with increasing Kondo
interaction; we interpret this effect by pointing out that the Kondo coupling
creates the composite pseudospin objects which undergo an ordering transition.
The relevance of our findings to the underlying fermionic multi--channel
problem is discussed.Comment: 29 pages (2 figures upon request from [email protected]), LATEX,
submitted for publicatio
Quantum phase transition in a two-channel-Kondo quantum dot device
We develop a theory of electron transport in a double quantum dot device
recently proposed for the observation of the two-channel Kondo effect. Our
theory provides a strategy for tuning the device to the non-Fermi-liquid fixed
point, which is a quantum critical point in the space of device parameters. We
explore the corresponding quantum phase transition, and make explicit
predictions for behavior of the differential conductance in the vicinity of the
quantum critical point
Charge-density wave formation in Sr_{14}Cu_{24}O_{41}
The electrodynamic response of the spin-ladder compound
SrCaCuO () has been studied from
radiofrequencies up to the infrared. At temperatures below 250 K a pronounced
absorption peak appears around 12 cm in SrCuO for
the radiation polarized along the chains/ladders ().
In addition a strongly temperature dependent dielectric relaxation is observed
in the kHz - MHz range. We explain this behavior by a charge density wave which
develops in the ladders sub-system and produces a mode pinned at 12 cm.
With increasing Ca doping the mode shifts up in frequency and eventually
disappears for because the dimensionality of the system crosses over from
one to two dimensions, giving way to the superconducting ground state under
pressure.Comment: One name added to author list 4 pages, 2 figures, email:
[email protected]
The Local Bubble and Interstellar Material Near the Sun
The properties of interstellar matter (ISM) at the Sun are regulated by our
location with respect to the Local Bubble (LB) void in the ISM. The LB is
bounded by associations of massive stars and fossil supernovae that have
disrupted natal ISM and driven intermediate velocity ISM into the LB interior
void. The Sun is located in such a driven ISM parcel. The Local Fluff has a
bulk velocity of 19 km/s in the LSR, and an upwind direction towards the center
of the gas and dust ring formed by the Loop I supernova remnant interaction
with the LB. When the ram pressure of the LIC is included in the total LIC
pressure, and if magnetic thermal and cosmic ray pressures are similar, the LIC
appears to be in pressure equilibrium with the local hot bubble plasma.Comment: Proceedings of Symposium on the Composition of Matter, honoring
Johannes Geiss on the occasion of his 80th birthday. Space Science Reviews
(in press
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