28,533 research outputs found
Porous dust grains in debris disks
When modeling the density and grain size distribution in debris disks, the
minimum particle size is often significantly larger than the corresponding
blowout size. While the dust particles are usually modeled as compact,
homogenous spheres, we instead investigate the impact of porosity. The optical
properties of porous particles are determined, and the influences of porosity
on the blowout size and dust temperatures investigated. Using the method of
discrete dipole approximation, we calculate the scattering and absorption cross
sections of porous particles and derive the blowout size and the behavior of
the dust temperature. We investigate the influence on the beta-ratio. Blowout
sizes are calculated for various stellar luminosities and porosities, and an
approximation equation is derived to estimate the blowout size as a function of
these parameters. Furthermore, we investigate the influence of the porosity on
the dust equilibrium temperature. The blowout size increases with the particle
porosity and stellar luminosity. The dust temperature of porous particles is
lower than the one of the compact spheres, in particular the temperature of
blowout grains decreases for porous particles.Comment: 10 pages, 18 figure
A new small satellite sunspot triggering recurrent standard- and blowout-coronal jets
In this paper,we report a detailed analysis of recurrent jets originated from
a location with emerging, canceling and converging negative magnetic field at
the east edge of NOAA active region AR11166 from 2011 March 09 to 10. The event
presented several interesting features. First, a satellite sunspot appeared and
collided with a pre-existing opposite polarity magnetic field and caused a
recurrent solar jet event. Second, the evolution of the jets showed
blowout-like nature and standard characteristics. Third, the satellite sunspot
exhibited a motion toward southeast of AR11166 and merged with the emerging
flux near the opposite polarity sunspot penumbra, which afterward, due to flux
convergence and cancellation episodes, caused recurrent jets. Fourth, three of
the blowout jets associated with coronal mass ejections (CMEs), were observed
from field of view of the Solar Terrestrial Relations Observatory. Fifth,
almost all the blowout jet eruptions were accompanied with flares or with more
intense brightening in the jet base region, while almost standard jets did not
manifest such obvious feature during eruptions. The most important, the blowout
jets were inclined to faster and larger scale than the standard jets. The
standard jets instead were inclined to relative longer-lasting. The obvious
shearing and twisting motions of the magnetic field may be interpreted as due
to the shearing and twisting motions for a blowout jet eruption. From the
statistical results, about 30% blowout jets directly developed into CMEs. It
suggests that the blowout jets and CMEs should have a tight relationship.Comment: ApJ 18 pages, 7 figure
A blowout jet associated with one obvious extreme-ultraviolet wave and one complicated coronal mass ejection event
In this paper, we present a detailed analysis of a coronal blowout jet
eruption which was associated with an obvious extreme-ultraviolet (EUV) wave
and one complicated coronal mass ejection (CME) event based on the
multi-wavelength and multi-view-angle observations from {\sl Solar Dynamics
Observatory} and {\sl Solar Terrestrial Relations Observatory}. It is found
that the triggering of the blowout jet was due to the emergence and
cancellation of magnetic fluxes on the photosphere. During the rising stage of
the jet, the EUV wave appeared just ahead of the jet top, lasting about 4
minutes and at a speed of 458 - \speed{762}. In addition, obvious dark material
is observed along the EUV jet body, which confirms the observation of a
mini-filament eruption at the jet base in the chromosphere. Interestingly, two
distinct but overlapped CME structures can be observed in corona together with
the eruption of the blowout jet. One is in narrow jet-shape, while the other
one is in bubble-shape. The jet-shaped component was unambiguously related with
the outwardly running jet itself, while the bubble-like one might either be
produced due to the reconstruction of the high coronal fields or by the
internal reconnection during the mini-filament ejection according to the
double-CME blowout jet model firstly proposed by Shen et al. (2012b),
suggesting more observational evidence should be supplied to clear the current
ambiguity based on large samples of blowout jets in future studies.Comment: APJ, Accepted October 19, 201
Non-normal parameter blowout bifurcation: an example in a truncated mean field dynamo model
We examine global dynamics and bifurcations occurring in a truncated model of
a stellar mean field dynamo. This model has symmetry-forced invariant subspaces
for the dynamics and we find examples of transient type I intermittency and
blowout bifurcations to transient on-off intermittency, involving laminar
phases in the invariant submanifold. In particular, our model provides examples
of blowout bifurcations that occur on varying a non-normal parameter; that is,
the parameter varies the dynamics within the invariant subspace at the same
time as the dynamics normal to it. As a consequence of this we find that the
Lyapunov exponents do not vary smoothly and the blowout bifurcation occurs over
a range of parameter values rather than a point in the parameter space.Comment: Full paper with figures, also available on the web page
http://www.maths.qmw.ac.uk/~eoc. Physical Review E, accepte
Impending carotid blowout stabilization using an LT-D tube
Adequate stabilization of a patient presenting with a carotid blowout is one of the most challenging issues an on-call ENT surgeon can be confronted with. Reducing the bleeding and securing the airway are essential before more definitive management. We present the case of a 72-year-old patient with head and neck cancer who arrived at the emergency room with a carotid blowout and who was successfully stabilized using a King LT-D ventilation tube
The influence of dust grain porosity on the analysis of debris disc observations
Debris discs are often modelled assuming compact dust grains, but more and
more evidence for the presence of porous grains is found. We aim at quantifying
the systematic errors introduced when modelling debris discs composed of porous
dust with a disc model assuming spherical, compact grains. We calculate the
optical dust properties derived via the fast, but simple effective medium
theory. The theoretical lower boundary of the size distribution -- the
so-called 'blowout size' -- is compared in the cases of compact and porous
grains. Finally, we simulate observations of hypothetical debris discs with
different porosities and feed them into a fitting procedure using only compact
grains. The deviations of the results for compact grains from the original
model based on porous grains are analysed. We find that the blowout size
increases with increasing grain porosity up to a factor of two. An analytical
approximation function for the blowout size as a function of porosity and
stellar luminosity is derived. The analysis of the geometrical disc set-up,
when constrained by radial profiles, are barely affected by the porosity.
However, the determined minimum grain size and the slope of the grain size
distribution derived using compact grains are significantly overestimated.
Thus, the unexpectedly high ratio of minimum grain size to blowout size found
by previous studies using compact grains can be partially described by dust
grain porosity, although the effect is not strong enough to completely explain
the trend.Comment: accepted by MNRA
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