4,297 research outputs found
Bayesian Coronal Seismology
In contrast to the situation in a laboratory, the study of the solar
atmosphere has to be pursued without direct access to the physical conditions
of interest. Information is therefore incomplete and uncertain and inference
methods need to be employed to diagnose the physical conditions and processes.
One of such methods, solar atmospheric seismology, makes use of observed and
theoretically predicted properties of waves to infer plasma and magnetic field
properties. A recent development in solar atmospheric seismology consists in
the use of inversion and model comparison methods based on Bayesian analysis.
In this paper, the philosophy and methodology of Bayesian analysis are first
explained. Then, we provide an account of what has been achieved so far from
the application of these techniques to solar atmospheric seismology and a
prospect of possible future extensions.Comment: 19 pages, accepted in Advances in Space Researc
Wave Heating of the Solar Atmosphere
Magnetic waves are a relevant component in the dynamics of the solar
atmosphere. Their significance has increased because of their potential as a
remote diagnostic tool and their presumed contribution to plasma heating
processes. We discuss our current understanding on coronal heating by magnetic
waves, based on recent observational evidence and theoretical advances. The
discussion starts with a selection of observational discoveries that have
brought magnetic waves to the forefront of the coronal heating discussion.
Then, our theoretical understanding on the nature and properties of the
observed waves and the physical processes that have been proposed to explain
observations are described. Particular attention is given to the sequence of
processes that link observed wave characteristics with concealed energy
transport, dissipation, and heat conversion. We conclude with a commentary on
how the combination of theory and observations should help us understanding and
quantifying magnetic wave heating of the solar atmosphere.Comment: Accepted for publication in Royal Society of London Philosophical
Transactions Series
Model comparison for the density structure along solar prominence threads
Quiescent solar prominence fine structures are typically modelled as density
enhancements, called threads, which occupy a fraction of a longer magnetic flux
tube. The profile of the mass density along the magnetic field is however
unknown and several arbitrary alternatives are employed in prominence wave
studies. We present a comparison of theoretical models for the field-aligned
density along prominence fine structures. We consider Lorentzian, Gaussian, and
parabolic profiles. We compare their theoretical predictions for the period
ratio between the fundamental transverse kink mode and the first overtone to
obtain estimates for the ratio of densities between the central part of the
tube and its foot-points and to assess which one would better explain observed
period ratio data. Bayesian parameter inference and model comparison techniques
are developed and applied. Parameter inference requires the computation of the
posterior distribution for the density gradient parameter conditional on the
observable period ratio. Model comparison involves the computation of the
marginal likelihood as a function of the period ratio to obtain the
plausibility of each density model and the computation of Bayes Factors to
quantify the relative evidence for each model, given a period ratio
observation. A Lorentzian density profile, with plasma density concentrated
around the centre of the tube seems to offer the most plausible inversion
result. A Gaussian profile would require unrealistically large values of the
density gradient parameter and a parabolic density distribution does not enable
us to obtain well constrained posterior probability distributions. However, our
model comparison results indicate that the evidence points to the Gaussian and
parabolic profiles for period ratios in between 2 and 3, while the Lorentzian
profile is preferred for larger period ratio values.Comment: 9 pages, 5 figures, accepted in A&
No unique solution to the seismological problem of standing kink MHD waves
The aim of this paper is to point out that the classic seismological problem
using observations and theoretical expressions for the periods and damping
times of transverse standing magnetohydrodynamic (MHD) waves in coronal loops
is better referred to as a reduced seismological problem. Reduced emphasises
the fact that only a small number of characteristic quantities of the
equilibrium profiles can be determined. Reduced also implies that there is no
unique solution to the full seismological problem. Even the reduced
seismological problem does not allow a unique solution. Bayesian inference
results support our mathematical arguments and offer insight into the
relationship between the algebraic and the probabilistic inversions.Comment: 10 pages, accepted in A&
Determination of the cross-field density structuring in coronal waveguides using the damping of transverse waves
Time and spatial damping of transverse magnetohydrodynamic (MHD) kink
oscillations is a source of information on the cross-field variation of the
plasma density in coronal waveguides. We show that a probabilistic approach to
the problem of determining the density structuring from the observed damping of
transverse oscillations enables us to obtain information on the two parameters
that characterise the cross-field density profile. The inference is performed
by computing the marginal posterior distributions for density contrast and
transverse inhomo- geneity length-scale using Bayesian analysis and damping
ratios for transverse oscillations under the assumption that damping is
produced by resonant absorption. The obtained distributions show that, for
damping times of a few oscillatory periods, low density contrasts and short
inho- mogeneity length scales are more plausible in explaining observations.
This means that valuable information on the cross-field density profile can be
obtained even if the inversion problem, with two unknowns and one observable,
is a mathematically ill-posed problem.Comment: 5 pages, 3 figures, accepte
Conference Report The 16th Asia Europe Economic Forum. EU-Asia trade and investment connectivity
Global economic trends over the last decades have steadily increased the links between Asia and Europe. For both regions, a growing economic interdependency represents an opportunity to build strong, fair and sustainable relations. Nonetheless, constant global economic disruptions, political uncertainty and a rapid change in economic dynamics make cooperation no easy task for policy makers.
With strong recognition of this challenge, the Asia Europe Economic Forum (AEEF) contributes to interregional cooperation with the diversification and consolidation of the links between Asia and Europe. The AEEF was established in 2006 by Jean Pisani-Ferry, the then-director of the Brussels-based think tank Bruegel, as a high-level forum to bring together Asian and European senior policy makers and experts. As such, the Forum is a platform for research-based exchange and discussion on global issues and mutual interests. It is here where Asian and European policy experts can learn from each other, thereby gaining a deeper understanding of the economic and political ties between Asia and Europe. The AEEF is all about bringing countries together and building partnerships with regard to shared interests—the AEEF is all about connectivity (see Box 1).
Determination of Transverse Density Structuring from Propagating MHD Waves in the Solar Atmosphere
We present a Bayesian seismology inversion technique for propagating
magnetohydrodynamic (MHD) transverse waves observed in coronal waveguides. The
technique uses theoretical predictions for the spatial damping of propagating
kink waves in transversely inhomogeneous coronal waveguides. It combines wave
amplitude damping length scales along the waveguide with theoretical results
for resonantly damped propagating kink waves to infer the plasma density
variation across the oscillating structures. Provided the spatial dependence of
the velocity amplitude along the propagation direction is measured and the
existence of two different damping regimes is identified, the technique would
enable us to fully constrain the transverse density structuring, providing
estimates for the density contrast and its transverse inhomogeneity length
scale
PTP1B promotes focal complex maturation, lamellar persistence and directional migration
Previous findings established that ER-bound PTP1B targets peripheral cell-matrix adhesions and positively regulates cell adhesion to fibronectin. Here we show that PTP1B enhances focal complex lifetime at the lamellipodium base, delaying their turnover and facilitating α-actinin incorporation. We demonstrate the presence of catalytic PTP1BD181A-α-actinin complexes at focal complexes. Kymograph analysis revealed that PTP1B contributes to lamellar protrusion persistence and directional cell migration. Pull-down and FRET analysis also showed that PTP1B is required for efficient integrin-dependent downregulation of RhoA and upregulation of Rac1 during spreading. A substrate trap strategy revealed that FAK/Src recruitment and Src activity are essential for the generation of PTP1B substrates in adhesions. PTP1B targets the negative regulatory site of Src (phosphotyrosine 529), paxillin and p130Cas at peripheral cell-matrix adhesions. We postulate that PTP1B modulates more than one pathway required for focal complex maturation and membrane protrusion, including α-actinin-mediated cytoskeletal anchorage, integrin-dependent activation of the FAK/Src signaling pathway, and RhoA and Rac1 GTPase activity. By doing so, PTP1B contributes to coordinated adhesion turnover, lamellar stability and directional cell migration.Fil: Burdisso, Juan Eduardo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; ArgentinaFil: González, Angela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; ArgentinaFil: Arregui, Carlos Oscar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; Argentin
Seismology of Standing Kink Oscillations of Solar Prominence Fine Structures
We investigate standing kink magnetohydrodynamic (MHD) oscillations in a
prominence fine structure modeled as a straight and cylindrical magnetic tube
only partially filled with the prominence material, and with its ends fixed at
two rigid walls representing the solar photosphere. The prominence plasma is
partially ionized and a transverse inhomogeneous transitional layer is included
between the prominence thread and the coronal medium. Thus, ion-neutral
collisions and resonant absorption are the considered damping mechanisms.
Approximate analytical expressions of the period, the damping time, and their
ratio are derived for the fundamental mode in the thin tube and thin boundary
approximations. We find that the dominant damping mechanism is resonant
absorption, which provides damping ratios in agreement with the observations,
whereas ion-neutral collisions are irrelevant for the damping. The values of
the damping ratio are independent of both the prominence thread length and its
position within the magnetic tube, and coincide with the values for a tube
fully filled with the prominence plasma. The implications of our results in the
context of the MHD seismology technique are discussed, pointing out that the
reported short-period (2 - 10 min) and short-wavelength (700 - 8,000 km) thread
oscillations may not be consistent with a standing mode interpretation and
could be related to propagating waves. Finally, we show that the inversion of
some prominence physical parameters, e.g., Alfv\'en speed, magnetic field
strength, transverse inhomogeneity length-scale, etc., is possible using
observationally determined values of the period and damping time of the
oscillations along with the analytical approximations of these quantities.Comment: Accepted for publication in Ap
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