11,938 research outputs found
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
XMM-Newton Detection of Hot Gas in the Eskimo Nebula: Shocked Stellar Wind or Collimated Outflows?
The Eskimo Nebula (NGC 2392) is a double-shell planetary nebula (PN) known
for the exceptionally large expansion velocity of its inner shell, ~90 km/s,
and the existence of a fast bipolar outflow with a line-of-sight expansion
velocity approaching 200 km/s. We have obtained XMM-Newton observations of the
Eskimo and detected diffuse X-ray emission within its inner shell. The X-ray
spectra suggest thin plasma emission with a temperature of ~2x10^6 K and an
X-ray luminosity of L_X = (2.6+/-1.0)x10^31 (d/1150 pc)^2 ergs/s, where d is
the distance in parsecs. The diffuse X-ray emission shows noticeably different
spatial distributions between the 0.2-0.65 keV and 0.65-2.0 keV bands.
High-resolution X-ray images of the Eskimo are needed to determine whether its
diffuse X-ray emission originates from shocked fast wind or bipolar outflows.Comment: 4 pages, 2 figures, accepted in Astronomy and Astrophysics Letter
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
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