6,317 research outputs found
Helioseismology: a fantastic tool to probe the interior of the Sun
Helioseismology, the study of global solar oscillations, has proved to be an
extremely powerful tool for the investigation of the internal structure and
dynamics of the Sun. Studies of time changes in frequency observations of solar
oscillations from helioseismology experiments on Earth and in space have shown,
for example, that the Sun's shape varies over solar cycle timescales. In
particular, far-reaching inferences about the Sun have been obtained by
applying inversion techniques to observations of frequencies of oscillations.
The results, so far, have shown that the solar structure is remarkably close to
the predictions of the standard solar model and, recently, that the
near-surface region can be probed with sufficiently high spatial resolution as
to allow investigations of the equation of state and of the solar envelope
helium abundance. The same helioseismic inversion methods can be applied to the
rotational frequency splittings to deduce with high accuracy the internal
rotation velocity of the Sun, as function of radius and latitude. This also
allows us to study some global astrophysical properties of the Sun, such as the
angular momentum, the grativational quadrupole moment and the effect of
distortion induced on the surface (oblateness). The helioseismic approach and
what we have learnt from it during the last decades about the interior of the
Sun are reviewed here.Comment: 36 page
Helioseismology
International audienceHelioseismology, the study of solar oscillations, has proved to be an extremely powerful tool for the investigation of the internal structure and dynamics of the Sun. Here I will review the present status of helioseismic studies and comment on recent results and on prospects for future investigations to solve the most discussed open questions associated with solar structure modelling
The rotational shear layer inside the early red-giant star KIC 4448777
We present the asteroseismic study of the early red-giant star KIC 4448777,
complementing and integrating a previous work (Di Mauro et al. 2016), aimed at
characterizing the dynamics of its interior by analyzing the overall set of
data collected by the {\it Kepler} satellite during the four years of its first
nominal mission. We adopted the Bayesian inference code DIAMOND (Corsaro \& De
Ridder 2014) for the peak bagging analysis and asteroseismic splitting
inversion methods to derive the internal rotational profile of the star. The
detection of new splittings of mixed modes, more concentrated in the very inner
part of the helium core, allowed us to reconstruct the angular velocity profile
deeper into the interior of the star and to disentangle the details better than
in Paper I: the helium core rotates almost rigidly about 6 times faster than
the convective envelope, while part of the hydrogen shell seems to rotate at a
constant velocity about 1.15 times lower than the He core. In particular, we
studied the internal shear layer between the fast-rotating radiative interior
and the slow convective zone and we found that it lies partially inside the
hydrogen shell above and extends across the core-envelope
boundary. Finally, we theoretically explored the possibility for the future to
sound the convective envelope in the red-giant stars and we concluded that the
inversion of a set of splittings with only low-harmonic degree , even
supposing a very large number of modes, will not allow to resolve the
rotational profile of this region in detail.Comment: accepted for publication on Ap
Nonlinear control of leader-follower formation flying
This paper considers the problem of relative motion control involved in a leader-follower formation keeping mission. More specifically, center of mass dynamics of two Earth orbiting satellite is modeled, including the nonlinearity due to Earth oblateness. Next, the differential algebra is exploited to compute an high order Taylor expansion of the State-Dependent Riccati Equation (SDRE) solution. This new approach reduces the computational cost of the online Algebraic Riccati Equation solution required by SDRE algorithm; in fact, the differential algebraic formulation gives a polynomial representation which can be directly evaluated for SDRE solutions or exploited to define an initial first guess for iterative SDRE algorithms
Surgical management of rhinosinusitis in onco-hematological patients
ObjectivesIn onco-hematological diseases, the incidence of paranasal sinuses infection dramatically increase and requires a combination of medical and surgical therapy. Balloon dilatation surgery (DS) is a minimally invasive, tissue preserving procedure. The study evaluates the results of DS for rhinosinusitis in immunocompromised patients.MethodsA retrospective chart review was conducted in 110 hematologic patients with rhinosinusitis. Twenty-five patients were treated with DS technique and 85 patients with endoscopic sinus surgery (ESS). We considered the type of anesthesia and the extent of intra- and postoperative bleeding. Patients underwent Sino-Nasal Outcome Test (SNOT-20) to evaluate changes in subjective symptoms and global patient assessment (GPA) questionnaire to value patient satisfaction.ResultsLocal anesthesia was employed in 8 cases of DS and in 15 of ESS. In 50 ESS patients, an anterior nasal packing was placed and in 12 cases a repacking was necessary. In the DS group, nasal packing was required in 8 cases and in 2 cases a repacking was placed (P=0.019 and P=0.422, respectively). The SNOT-20 change score showed significant improvement of health status in both groups. However the DS group showed a major improvement in 3 voices: need to blow nose, runny nose, and facial pain/pressure. The 3-month follow-up GPA questionnaire showed an higher satisfaction of DS group.ConclusionBalloon DS represents a potentially low aggressive treatment and appears to be relatively safe and effective in onco-hematologic patients. All these remarks may lead the surgeon to consider a larger number of candidates for surgical procedure
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