2,049 research outputs found
Envelope solitons induced by high-order effects of light-plasma interaction
The nonlinear coupling between the light beams and non-resonant ion density
perturbations in a plasma is considered, taking into account the relativistic
particle mass increase and the light beam ponderomotive force. A pair of
equations comprising a nonlinear Schrodinger equation for the light beams and a
driven (by the light beam pressure) ion-acoustic wave response is derived. It
is shown that the stationary solutions of the nonlinear equations can be
represented in the form of a bright and dark/gray soliton for one-dimensional
problem. We have also present a numerical analysis which shows that our bright
soliton solutions are stable exclusively for the values of the parameters
compatible with of our theory.Comment: 9 pages, 5 figure
Coherent States for Particle Beams in the Thermal Wave Model
In this paper, by using an analogy among {\it quantum mechanics}, {\it
electromagnetic beam optics in optical fibers}, and {\it charge particle beam
dynamics}, we introduce the concept of {\it coherent states} for charged
particle beams in the framework of the {\it Thermal Wave Model} (TWM). We give
a physical meaning of the Gaussian-like coherent structures of charged particle
distribution that are both naturally and artificially produced in an
accelerating machine in terms of the concept of coherent states widely used in
quantum mechanics and in quantum optics. According to TWM, this can be done by
using a Schr\"{o}dinger-like equation for a complex function, the so-called
{\it beam wave function} (BWF), whose squared modulus is proportional to the
transverse beam density profile, where Planck's constant and the time are
replaced by the transverse beam emittance and by the propagation coordinate,
respectively. The evolution of the particle beam, whose initial BWF is assumed
to be the simplest coherent state (ground-like state) associated with the beam,
in an infinite 1-D quadrupole-like device with small sextupole and octupole
aberrations, is analytically and numerically investigated.Comment: 21 pages, Late
Self consistent thermal wave model description of the transverse dynamics for relativistic charged particle beams in magnetoactive plasmas
Thermal Wave Model is used to study the strong self-consistent Plasma Wake
Field interaction (transverse effects) between a strongly magnetized plasma and
a relativistic electron/positron beam travelling along the external magnetic
field, in the long beam limit, in terms of a nonlocal NLS equation and the
virial equation. In the linear regime, vortices predicted in terms of
Laguerre-Gauss beams characterized by non-zero orbital angular momentum (vortex
charge). In the nonlinear regime, criteria for collapse and stable oscillations
is established and the thin plasma lens mechanism is investigated, for beam
size much greater than the plasma wavelength. The beam squeezing and the
self-pinching equilibrium is predicted, for beam size much smaller than the
plasma wavelength, taking the aberrationless solution of the nonlocal Nonlinear
Schroeding equation.Comment: Poster presentation P5.006 at the 38th EPS Conference on Plasma
Physics, Strasbourg, France, 26 June - 1 July, 201
Nonlocal effects in high energy charged particle beams
Within the framework of the thermal wave model, an investigation is made of
the longitudinal dynamics of high energy charged particle beams. The model
includes the self-consistent interaction between the beam and its surroundings
in terms of a nonlinear coupling impedance, and when resistive as well as
reactive parts are included, the evolution equation becomes a generalised
nonlinear Schroedinger equation including a nonlocal nonlinear term. The
consequences of the resistive part on the propagation of particle bunches are
examined using analytical as well as numerical methods.Comment: 6 pages, 6 figures, uses RevTeX
Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. II. Temporal evolution of the eruptive source
The occurrence of new FU Orionis-like objects is fundamental to understand
the outburst mechanism in young stars and their role in star formation and disk
evolution. Our work is aimed at investigating the properties of the recent
outburst of V1647 Ori. Using optical and mid infrared long slit spectroscopy we
monitored V1647 Ori in outburst between February 2004 and January 2006. The
optical spectrum is characterized by Halpha and Hbeta in P-Cygni profile and by
many weak FeI and FeII emission lines. Short timescale variability was measured
in the continuum and line emission. On January 2006 we detected for the first
time forbidden emission lines ([OI], [SII] and [FeII]). These lines are likely
produced by an Herbig-Haro object driven by V1647 Ori. The mid infrared the
spectrum of V1647 Ori is flat and featureless at all epochs. The SED changed
drastically: the source was much redder in the early outburst than in the final
phase. The magnitude rise and the SED of V1647 Ori resembles that of a FUor
while the duration and recurrence of the outburst resemble that of a EXor. The
optical spectrum is clearly distinct from either the absorption line spectrum
of a FUor or the T Tauri-like spectrum of an EXor. Our data are consistent with
a disk instability event which led to an increase of the mass accretion rate.
The data also suggest the presence of a circumstellar envelope around the
star+disk system. The peculiar N band spectrum might be explained by dust
sublimation in the outer layers of the disk. The presence of the envelope and
the outburst statistics suggest that these instability events occur only in a
specific stage of a Class I source (e.g. in the transition phase to an
optically visible star surrounded by a protoplanetary disk). We discuss the
outburst mechanisms in term of the thermal instability model.Comment: 12 pages, 7 figures, accepted for publication in A&
Water depletion in the disk atmosphere of Herbig AeBe stars
We present high resolution (R = 100,000) L-band spectroscopy of 11 Herbig
AeBe stars with circumstellar disks. The observations were obtained with the
VLT/CRIRES to detect hot water and hydroxyl radical emission lines previously
detected in disks around T Tauri stars. OH emission lines are detected towards
4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as the
velocity profile of each component of the doublet. Its characteristic
double-peak profile demonstrates that the gas is in Keplerian rotation and
points to an emitting region extending out to ~ 15-30 AU. The OH, emission
correlates with disk geometry as it is mostly detected towards flaring disks.
None of the Herbig stars analyzed here show evidence of hot water vapor at a
sensitivity similar to that of the OH lines. The non-detection of hot water
vapor emission indicates that the atmosphere of disks around Herbig AeBe stars
are depleted of water molecules. Assuming LTE and optically thin emission we
derive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast to
T Tauri disks for which the column density ratio is 0.3 -- 0.4.Comment: Accepted for publication in Ap
A Deadbeat Observer for Two and Three-dimensional LTI Systems by a Time/Output-Dependent State Mapping
The problem of deadbeat state reconstruction for non-autonomous linear systems
has been solved since several decades, but all the architectures formulated since now require
either high-gain output injection, which amplifies measurement noises (e.g., in the case of
sliding-mode observers), either state augmentation, which yields a non-minimal realization of
the deadbeat observer (e.g., in the case of integral methods and delay-based methods). In this
context, the present paper presents, for the first time, a finite-time observer for continuous-time
linear systems enjoying minimal linear-time-varying dynamics, that is, the observer has the same
order of the observed system. The key idea behind the proposed method is the introduction of
an almost-always invertible time/output-dependent state mapping which allows to recast the
dynamics of the system in a new observer canonical form whose initial conditions are known
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