520 research outputs found
Transversal adaptive filtering
This paper presents a tutorial on the gradient (G) and recursive least squares (RLS) algorithme, both commonly used in adaptive
transversal filters for estimating a linear model . It is shown how the algorithms utilize recursivity ta realize at the saine time the
averaging involved in the optimisation criterion as well as the minimization. In steady state both algorithms can be viewed as
minimizing the saure mean square error criterion. Then they have equivalent performances : the saure residual fluctuations up to
an equivalence between the adaptation step-size t of (G) and the forgetting rate (1-w) of (RLS) . Due to the criterion itself
emphasizing adaptation speed, it is the transient period which exhibits the (RLS) superiority . This is essentially at the price of a
four times higher complexity and of difficulties with controling numerical effects, related (in part) to the presence of divisions
that are not in (G) . A general methodology for decoupling the transient effects and permanent fluctuations is given ; the latter
are due to the measurement noise disturbing the model . The more general problem of tracking the model variations is treated
with that methodology and we emphasize the différence between the problems of tracking and of squeezing the transient period
for a fixed model : the corresponding adaptation step-sizes differ significantly .Synthèse sur les algorithmes du gradient et des moindres carrés rapides. En régime permanent, ils ont des performances équivalentes. C'est en régime transitoire que les moindres carrés sont supérieurs; ceci au prix d'une complexité environ quatre fois supérieure et de difficultés de contrôle des variables numérique
Mean-Field Interacting Boson Random Point Fields in Weak Harmonic Traps
A model of the mean-field interacting boson gas trapped by a weak harmonic
potential is considered by the \textit{boson random point fields} methods. We
prove that in the Weak Harmonic Trap (WHT) limit there are two phases
distinguished by the boson condensation and by a different behaviour of the
local particle density. For chemical potentials less than a certain critical
value, the resulting Random Point Field (RPF) coincides with the usual boson
RPF, which corresponds to a non-interacting (ideal) boson gas. For the chemical
potentials greater than the critical value, the boson RPF describes a divergent
(local) density, which is due to \textit{localization} of the macroscopic
number of condensed particles. Notice that it is this kind of transition that
observed in experiments producing the Bose-Einstein Condensation in traps
Dynamics of charge-displacement channeling in intense laser-plasma interactions
The dynamics of transient electric fields generated by the interaction of
high intensity laser pulses with underdense plasmas has been studied
experimentally with the proton projection imaging technique. The formation of a
charged channel, the propagation of its front edge and the late electric field
evolution have been characterised with high temporal and spatial resolution.
Particle-in-cell simulations and an electrostatic, ponderomotive model
reproduce the experimental features and trace them back to the ponderomotive
expulsion of electrons and the subsequent ion acceleration.Comment: 5 figures, accepted for publication in New Journal of Physic
Eynard-Mehta theorem, Schur process, and their pfaffian analogs
We give simple linear algebraic proofs of Eynard-Mehta theorem,
Okounkov-Reshetikhin formula for the correlation kernel of the Schur process,
and Pfaffian analogs of these results. We also discuss certain general
properties of the spaces of all determinantal and Pfaffian processes on a given
finite set.Comment: AMSTeX, 21 pages, a new section adde
Evidence of resonant surface wave excitation in the relativistic regime through measurements of proton acceleration from grating targets
The interaction of laser pulses with thin grating targets, having a periodic
groove at the irradiated surface, has been experimentally investigated.
Ultrahigh contrast () pulses allowed to demonstrate an enhanced
laser-target coupling for the first time in the relativistic regime of
ultra-high intensity >10^{19} \mbox{W/cm}^{2}. A maximum increase by a factor
of 2.5 of the cut-off energy of protons produced by Target Normal Sheath
Acceleration has been observed with respect to plane targets, around the
incidence angle expected for resonant excitation of surface waves. A
significant enhancement is also observed for small angles of incidence, out of
resonance.Comment: 5 pages, 5 figures, 2nd version implements final correction
Adaptive filtering techniques for gravitational wave interferometric data: Removing long-term sinusoidal disturbances and oscillatory transients
It is known by the experience gained from the gravitational wave detector
proto-types that the interferometric output signal will be corrupted by a
significant amount of non-Gaussian noise, large part of it being essentially
composed of long-term sinusoids with slowly varying envelope (such as violin
resonances in the suspensions, or main power harmonics) and short-term ringdown
noise (which may emanate from servo control systems, electronics in a
non-linear state, etc.). Since non-Gaussian noise components make the detection
and estimation of the gravitational wave signature more difficult, a denoising
algorithm based on adaptive filtering techniques (LMS methods) is proposed to
separate and extract them from the stationary and Gaussian background noise.
The strength of the method is that it does not require any precise model on the
observed data: the signals are distinguished on the basis of their
autocorrelation time. We believe that the robustness and simplicity of this
method make it useful for data preparation and for the understanding of the
first interferometric data. We present the detailed structure of the algorithm
and its application to both simulated data and real data from the LIGO 40meter
proto-type.Comment: 16 pages, 9 figures, submitted to Phys. Rev.
Conditional Intensity and Gibbsianness of Determinantal Point Processes
The Papangelou intensities of determinantal (or fermion) point processes are
investigated. These exhibit a monotonicity property expressing the repulsive
nature of the interaction, and satisfy a bound implying stochastic domination
by a Poisson point process. We also show that determinantal point processes
satisfy the so-called condition which is a general form of
Gibbsianness. Under a continuity assumption, the Gibbsian conditional
probabilities can be identified explicitly.Comment: revised and extende
Consensus Statement on Animals’ Relationship with Pediatric Oncohematological Patients, on Behalf of Infectious Diseases and Nurse Working Groups of the Italian Association of Pediatric Hematology-Oncology
: Contact with animals in pediatric oncohematologic patients is associated with many benefits, but the risk of contracting zoonoses, even if low, must be considered by clinicians. In order to assess the awareness about this topic, we surveyed the Italian pediatric oncohematology centers, which resulted in heterogeneous responses. The Infectious Diseases Working Group and the Nurse Working Group of the Italian Association of Pediatric Hematology-Oncology, together with veterinarians from the National Federation of Italian Veterinarians, drew up a consensus document to unify the indications to be given to families with the aim of guaranteeing a safe interaction between patients and animals and improving the collaboration of clinicians with veterinarians and families
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