39,530 research outputs found
On theories of random variables
We study theories of spaces of random variables: first, we consider random
variables with values in the interval , then with values in an arbitrary
metric structure, generalising Keisler's randomisation of classical structures.
We prove preservation and non-preservation results for model theoretic
properties under this construction: i) The randomisation of a stable structure
is stable. ii) The randomisation of a simple unstable structure is not simple.
We also prove that in the randomised structure, every type is a Lascar type
On the spectrum of the transfer operators of a one-parameter family with intermittency transition
We study the transfer operators for a family depending
on the parameter , which interpolates between the tent map and the
Farey map. In particular, considering the action of the transfer operator on a
suitable Hilbert space, we can define a family of infinite matrices associated
to the operators and study their spectrum by numerical methods.Comment: 6 pages, 3 figure
Pancharatnam and Berry Phases in Three-Level Photonic Systems
A theoretical analysis of Pancharatnam and Berry phases is made for biphoton
three-level systems, which are produced via frequency degenerate co-linear
spontaneous parametric down conversion (SPDC). The general theory of
Pancharatnam phases is discussed with a special emphasis on geodesic 'curves'in
Hilbert space. Explicit expressions for Pancharatnam, dynamical and geometrical
phases are derived for the transformations produced by linear phase-converters.
The problem of gauge invariance is treated along all the article
Gravitational energy as dark energy: Concordance of cosmological tests
We provide preliminary quantitative evidence that a new solution to averaging
the observed inhomogeneous structure of matter in the universe [gr-qc/0702082,
arxiv:0709.0732], may lead to an observationally viable cosmology without
exotic dark energy. We find parameters which simultaneously satisfy three
independent tests: the match to the angular scale of the sound horizon detected
in the cosmic microwave background anisotropy spectrum; the effective comoving
baryon acoustic oscillation scale detected in galaxy clustering statistics; and
type Ia supernova luminosity distances. Independently of the supernova data,
concordance is obtained for a value of the Hubble constant which agrees with
the measurement of the Hubble Key team of Sandage et al [astro-ph/0603647].
Best-fit parameters include a global average Hubble constant H_0 = 61.7
(+1.2/-1.1) km/s/Mpc, a present epoch void volume fraction of f_{v0} = 0.76
(+0.12/-0.09), and an age of the universe of 14.7 (+0.7/-0.5) billion years as
measured by observers in galaxies. The mass ratio of non-baryonic dark matter
to baryonic matter is 3.1 (+2.5/-2.4), computed with a baryon-to-photon ratio
that concords with primordial lithium abundances.Comment: 4 pages, 2 figures; v2 improved statistics, references added, to
appear in ApJ Letter
A new approach for Guaranteed ellipsoidal state estimation
The 19th World Congress of the International Federation of Automatic Control 2014. Cape Town, SudáfricaThis paper proposes a new ellipsoid-based guaranteed state estimation approach for linear discrete-time systems with bounded perturbations and bounded measurement noise. This approach is based on the minimization of the radius of the ellipsoidal state estimation set. Firstly, the ellipsoidal state estimation is computed by off-line solving a Linear Matrix Inequality optimization problem. Secondly, a new online method is developed in order to improve the accuracy of the estimation but it leads to an increase of the online computation load. A new scaling technique is proposed to reduce the computation time, while keeping a good accuracy of the state estimation. An illustrative example is analyzed in order to show the advantages of the proposed approach
Comparison between two state estimation techniqueds for linear systems
20th World Congress of the International Federation of Automatic Control, Jul 2017, Toulouse, FranceThis paper presents a comparison in terms of accuracy and complexity between two
approaches used for state estimation of linear systems: a classic Kalman filter and a guaranteed
set-membership state estimation technique. The main goal of this paper is to analyze the
advantages of these techniques and to combine them in the future in a new accurate and simple
extension that handles system uncertainties and chance constraints. Two academic examples
illustrate the main differences between the compared techniques
Absence of kinetic effects in reaction-diffusion processes in scale-free networks
We show that the chemical reactions of the model systems of A+A->0 and A+B->0
when performed on scale-free networks exhibit drastically different behavior as
compared to the same reactions in normal spaces. The exponents characterizing
the density evolution as a function of time are considerably higher than 1,
implying that both reactions occur at a much faster rate. This is due to the
fact that the discerning effects of the generation of a depletion zone (A+A)
and the segregation of the reactants (A+B) do not occur at all as in normal
spaces. Instead we observe the formation of clusters of A (A+A reaction) and of
mixed A and B (A+B reaction) around the hubs of the network. Only at the limit
of very sparse networks is the usual behavior recovered.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Facilitated diffusion of proteins on chromatin
We present a theoretical model of facilitated diffusion of proteins in the
cell nucleus. This model, which takes into account the successive
binding/unbinding events of proteins to DNA, relies on a fractal description of
the chromatin which has been recently evidenced experimentally. Facilitated
diffusion is shown quantitatively to be favorable for a fast localization of a
target locus by a transcription factor, and even to enable the minimization of
the search time by tuning the affinity of the transcription factor with DNA.
This study shows the robustness of the facilitated diffusion mechanism, invoked
so far only for linear conformations of DNA.Comment: 4 pages, 4 figures, accepted versio
Universal statistical properties of poker tournaments
We present a simple model of Texas hold'em poker tournaments which retains
the two main aspects of the game: i. the minimal bet grows exponentially with
time; ii. players have a finite probability to bet all their money. The
distribution of the fortunes of players not yet eliminated is found to be
independent of time during most of the tournament, and reproduces accurately
data obtained from Internet tournaments and world championship events. This
model also makes the connection between poker and the persistence problem
widely studied in physics, as well as some recent physical models of biological
evolution, and extreme value statistics.Comment: Final longer version including data from Internet and WPT tournament
Dynamic Magneto-Conductance Fluctuations and Oscillations in Mesoscopic Wires and Rings
Using a finite-frequency recursive Green's function technique, we calculate
the dynamic magneto-conductance fluctuations and oscillations in disordered
mesoscopic normal metal systems, incorporating inter-particle Coulomb
interactions within a self-consistent potential method. In a disordered metal
wire, we observe ergodic behavior in the dynamic conductance fluctuations. At
low , the real part of the conductance fluctuations is essentially
given by the dc universal conductance fluctuations while the imaginary part
increases linearly from zero, but for greater than the Thouless energy
and temperature, the fluctuations decrease as . Similar
frequency-dependent behavior is found for the Aharonov-Bohm oscillations in a
metal ring. However, the Al'tshuler-Aronov-Spivak oscillations, which
predominate at high temperatures or in rings with many channels, are strongly
suppressed at high frequencies, leading to interesting crossover effects in the
-dependence of the magneto-conductance oscillations.Comment: 4 pages, REVTeX 3.0, 5 figures(ps file available upon request),
#phd0
- …