33 research outputs found
Sensitivity of the g-mode frequencies to pulsation codes and their parameters
From the recent work of the Evolution and Seismic Tools Activity (ESTA,
Lebreton et al. 2006; Monteiro et al. 2008), whose Task 2 is devoted to compare
pulsational frequencies computed using most of the pulsational codes available
in the asteroseismic community, the dependence of the theoretical frequencies
with non-physical choices is now quite well fixed. To ensure that the accuracy
of the computed frequencies is of the same order of magnitude or better than
the observational errors, some requirements in the equilibrium models and the
numerical resolutions of the pulsational equations must be followed. In
particular, we have verified the numerical accuracy obtained with the Saclay
seismic model, which is used to study the solar g-mode region (60 to
140Hz). We have compared the results coming from the Aarhus adiabatic
pulsation code (ADIPLS), with the frequencies computed with the Granada Code
(GraCo) taking into account several possible choices. We have concluded that
the present equilibrium models and the use of the Richardson extrapolation
ensure an accuracy of the order of in the determination of the
frequencies, which is quite enough for our purposes.Comment: 10 pages, 5 figures, accepted in Solar Physic
Influence of Low-Degree High-Order p-Mode Splittings on the Solar Rotation Profile
The solar rotation profile is well constrained down to about 0.25 R thanks to
the study of acoustic modes. Since the radius of the inner turning point of a
resonant acoustic mode is inversely proportional to the ratio of its frequency
to its degree, only the low-degree p modes reach the core. The higher the order
of these modes, the deeper they penetrate into the Sun and thus they carry more
diagnostic information on the inner regions. Unfortunately, the estimates of
frequency splittings at high frequency from Sun-as-a-star measurements have
higher observational errors due to mode blending, resulting in weaker
constraints on the rotation profile in the inner core. Therefore inversions for
the solar internal rotation use only modes below 2.4 mHz for l < 4. In the work
presented here, we used an 11.5 year-long time series to compute the rotational
frequency splittings for modes l < 4 using velocities measured with the GOLF
instrument. We carried out a theoretical study of the influence of the
low-degree modes in the region 2 to 3.5 mHz on the inferred rotation profile as
a function of their error bars.Comment: Accepted for publication in Solar Physics. 17 Pages, 9 figure
Perspectives in Global Helioseismology, and the Road Ahead
We review the impact of global helioseismology on key questions concerning
the internal structure and dynamics of the Sun, and consider the exciting
challenges the field faces as it enters a fourth decade of science
exploitation. We do so with an eye on the past, looking at the perspectives
global helioseismology offered in its earlier phases, in particular the
mid-to-late 1970s and the 1980s. We look at how modern, higher-quality, longer
datasets coupled with new developments in analysis, have altered, refined, and
changed some of those perspectives, and opened others that were not previously
available for study. We finish by discussing outstanding challenges and
questions for the field.Comment: Invited review; to appear in Solar Physics (24 pages, 6 figures
Targeted isometric force impulses in patients with traumatic brain injury reveal delayed motor programming and change of strategy
The capability of quickly (as soon as possible) producing fast uncorrected and accurate isometric force impulses was
examined to assess the motor efficiency of patients with moderate to severe traumatic brain injury (TBI) and good motor
recovery at a clinical evaluation. Twenty male right-handed patients with moderate to severe TBI and 24 age-matched
healthy male right-handed controls participated in the study. The experimental task required subjects to aim brief and
uncorrected isometric force impulses to targets visually presented along with subjects’ force displays. Both TBI patients
and controls were able to produce force impulses whose mean peak amplitudes varied proportionally to the target load
with no detectable group difference. Patients with TBI, however, were slower than controls in initiating their responses
(reaction times [RTs] were longer by 125 msec) and were also slower during the execution of their motor responses,
reaching the peak forces requested 23 msec later than controls (time to peak force: 35% delay). Further, their mean dF/dt
(35 kg/sec) was slower than that of controls (53 kg/sec), again indicating a 34% impairment with respect to controls.
Overall, patients with TBI showed accurate but delayed and slower isometric force impulses. Thus, an evaluation taking
into account also response time features is more effective in picking up motor impairments than the standard clinical
scales focusing on accuracy of movement only