13,613 research outputs found
Absence of hot gas within the Wolft-Rayet Bubble around WR16
We present the analysis of XMM-Newton archival observations towards the
Wolf-Rayet (WR) bubble around WR16. Despite the closed bubble morphology of
this WR nebula, the XMM-Newton observations show no evidence of diffuse
emission in its interior as in the similar WR bubbles NGC6888 and S308. We use
the present observations to estimate a 3-\sigma upper limit to the X-ray
luminosity in the 0.3-1.5 keV energy band equal to 7.4x10^{32} erg s^{-1} for
the diffuse emission from the WR nebula, assuming a distance of 2.37 kpc. The
WR nebula around WR16 is the fourth observed by the current generation of X-ray
satellites and the second not detected. We also examine FUSE spectra to search
for nebular O VI absorption lines in the stellar continuum of WR16. The present
far-UV data and the lack of measurements of the dynamics of the optical WR
bubble do not allow us to confirm the existence of a conductive layer of gas at
T~3x10^5 K between the cold nebular gas and the hot gas in its interior. The
present observations result in an upper limit of n_e < 0.6 cm^-3 on the
electron density of the X-ray emitting material within the nebula.Comment: 6 pages, 3 figures, 1 table; To appear in Astronomy and Astrophysic
How to excite the internal modes of sine-Gordon solitons
We investigate the dynamics of the sine-Gordon solitons perturbed by
spatiotemporal external forces. We prove the existence of internal (shape)
modes of sine-Gordon solitons when they are in the presence of inhomogeneous
space-dependent external forces, provided some conditions (for these forces)
hold. Additional periodic time-dependent forces can sustain oscillations of the
soliton width. We show that, in some cases, the internal mode even can become
unstable, causing the soliton to decay in an antisoliton and two solitons. In
general, in the presence of spatiotemporal forces the soliton behaves as a
deformable (non-rigid) object. A soliton moving in an array of inhomogeneities
can also present sustained oscillations of its width. There are very important
phenomena (like the soliton-antisoliton collisions) where the existence of
internal modes plays a crucial role. We show that, under some conditions, the
dynamics of the soliton shape modes can be chaotic. A short report of some of
our results has been published in [J. A. Gonzalez et al., Phys. Rev. E, 65
(2002) 065601(R)].Comment: 14 .eps figures.To appear in Chaos, Solitons and Fractal
Spatiotemporal chaotic dynamics of solitons with internal structure in the presence of finite-width inhomogeneities
We present an analytical and numerical study of the Klein-Gordon kink-soliton
dynamics in inhomogeneous media. In particular, we study an external field that
is almost constant for the whole system but that changes its sign at the center
of coordinates and a localized impurity with finite-width. The soliton solution
of the Klein-Gordon-like equations is usually treated as a structureless
point-like particle. A richer dynamics is unveiled when the extended character
of the soliton is taken into account. We show that interesting spatiotemporal
phenomena appear when the structure of the soliton interacts with finite-width
inhomogeneities. We solve an inverse problem in order to have external
perturbations which are generic and topologically equivalent to well-known
bifurcation models and such that the stability problem can be solved exactly.
We also show the different quasiperiodic and chaotic motions the soliton
undergoes as a time-dependent force pumps energy into the traslational mode of
the kink and relate these dynamics with the excitation of the shape modes of
the soliton.Comment: 10 pages Revtex style article, 22 gziped postscript figures and 5 jpg
figure
Redefining the boundaries of interplanetary coronal mass ejections from observations at the ecliptic plane
On 2015 January 6-7, an interplanetary coronal mass ejection (ICME) was
observed at L1. This event, which can be associated with a weak and slow
coronal mass ejection, allows us to discuss on the differences between the
boundaries of the magnetic cloud and the compositional boundaries. A fast
stream from a solar coronal hole surrounding this ICME offers a unique
opportunity to check the boundaries' process definition and to explain
differences between them. Using Wind and ACE data, we perform a complementary
analysis involving compositional, magnetic, and kinematic observations
providing relevant information regarding the evolution of the ICME as
travelling away from the Sun. We propose erosion, at least at the front
boundary of the ICME, as the main reason for the difference between the
boundaries, and compositional signatures as the most precise diagnostic tool
for the boundaries of ICMEs.Comment: 9 pages and 7 figures in the original forma
Flapping states of an el astically anchored wing in a uniform flow
Linear stability analysis of an elastically anchored wing in a uniform flow
is investigated both analytically and numerically. The analytical formulation
explicitly takes into account the effect of the wake on the wing by means of
Theodorsen's theory. Three different parameters non-trivially rule the observed
dynamics: mass density ratio between wing and fluid, spring elastic constant
and distance between the wing center of mass and the spring anchor point on the
wing. We found relationships between these parameters which rule the transition
between stable equilibrium and fluttering. The shape of the resulting marginal
curve has been successfully verified by high Reynolds number direct numerical
simulations. Our findings are of interest in applications related to energy
harvesting by fluid-structure interaction, a problem which has recently
attracted a great deal of attention. The main aim in that context is to
identify the optimal physical/geometrical system configuration leading to large
sustained motion, which is the source of energy we aim to extract.Comment: 10 pages, 11 figures, submitted to J. Fluid. Mec
Numerical test of the Cardy-Jacobsen conjecture in the site-diluted Potts model in three dimensions
We present a microcanonical Monte Carlo simulation of the site-diluted Potts
model in three dimensions with eight internal states, partly carried out in the
citizen supercomputer Ibercivis. Upon dilution, the pure model's first-order
transition becomes of the second-order at a tricritical point. We compute
accurately the critical exponents at the tricritical point. As expected from
the Cardy-Jacobsen conjecture, they are compatible with their Random Field
Ising Model counterpart. The conclusion is further reinforced by comparison
with older data for the Potts model with four states.Comment: Final version. 9 pages, 9 figure
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