334 research outputs found
Upper body balance control strategy during continuous 3D postural perturbation in young adults
We explored how changes in vision and perturbation frequency impacted upright postural control in healthy adults exposed to continuous multiaxial support-surface perturbation. Ten subjects were asked to maintain equilibrium in standing stance with eyes open (EO) and eyes closed (EC) during sinusoidal 3D rotations at 0.25 (L) and 0.50 Hz (H). We measured upper-body kinematics – head, trunk, and pelvis – and analyzed differences in horizontal displacements and roll, pitch, and yaw sways. The presence of
vision significantly decreased upper-body displacements in the horizontal plane, especially at the head level, while in EC the head was the most unstable segment. H trials produced a greater segment stabilization compared to L ones in EO and EC. Analysis of sways showed that in EO participants stabilized their posture by reducing the variability of trunk angles; in H trials a sway decrease for the examined segments was observed in the yaw plane and, for the pelvis only, in the pitch plane. Our results
suggest that, during continuous multiaxial perturbations, visual information induced: (i) in L condition, a continuous reconfiguration of multi-body-segments orientation to follow the perturbation; (ii) in H condition, a compensation for the ongoing perturbation. These findings were not confirmed in EC where
the same strategy – that is, the use of the pelvis as a reference frame for the body balance was adopted both in L and H
Robotic and clinical evaluation of upper limb motor performance in patients with Friedreich's Ataxia: an observational study
Background: Friedreich’s ataxia (FRDA) is the most common hereditary autosomal recessive form of ataxia. In this disease there is early manifestation of gait ataxia, and dysmetria of the arms and legs which causes impairment in daily activities that require fine manual dexterity. To date there is no cure for this disease. Some novel therapeutic approaches are ongoing in different steps of clinical trial. Development of sensitive outcome measures is crucial to prove therapeutic effectiveness. The aim of the study was to assess the reliability and sensitivity of quantitative and objective assessment of upper limb performance computed by means of the robotic device and to evaluate the correlation with clinical and functional markers of the disease severity.
Methods: Here we assess upper limb performances by means of the InMotion Arm Robot, a robot designed for clinical neurological applications, in a cohort of 14 children and young adults affected by FRDA, matched for age
and gender with 18 healthy subjects. We focused on the analysis of kinematics, accuracy, smoothness, and submovements of the upper limb while reaching movements were performed. The robotic evaluation of upper
limb performance consisted of planar reaching movements performed with the robotic system. The motors of the robot were turned off, so that the device worked as a measurement tool. The status of the disease was scored
using the Scale for the Assessment and Rating of Ataxia (SARA). Relationships between robotic indices and a range of clinical and disease characteristics were examined.
Results: All our robotic indices were significantly different between the two cohorts except for two, and were highly and reliably discriminative between healthy and subjects with FRDA. In particular, subjects with FRDA
exhibited slower movements as well as loss of accuracy and smoothness, which are typical of the disease. Duration of Movement, Normalized Jerk, and Number of Submovements were the best discriminative indices, as they were directly and easily measurable and correlated with the status of the disease, as measured by SARA.
Conclusions: Our results suggest that outcome measures obtained by means of robotic devices can improve the sensitivity of clinical evaluations of patients’ dexterity and can accurately and efficiently quantify changes over time in clinical trials, particularly when functional scales appear to be no longer sensitive
A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
[Abridged] We present a large, new set of stellar evolution models and
isochrones for an alpha-enhanced metal distribution typical of Galactic halo
and bulge stars; it represents a homogeneous extension of our stellar model
library for a distribution already presented in Pietrinferni et al.(2004). The
effect of the alpha-element enhancement has been properly taken into account in
the nuclear network, opacity, equation of state and, for the first time, the
bolometric corrections, and color transformations. This allows us to avoid the
inconsistent use - common to all alpha-enhanced model libraries currently
available - of scaled-solar bolometric corrections and color transformations
for alpha-enhanced models and isochrones. We show how bolometric corrections to
magnitudes obtained for the U,B portion of stellar spectra for T_{eff}<=6500K,
are significantly affected by the metal mixture, especially at the higher
metallicities. We also provide complete sets of evolutionary models for
low-mass, He-burning stellar structures covering the whole metallicity range,
to enable synthetic horizontal branch simulations. We compare our database with
several widely used stellar model libraries from different authors, as well as
with various observed color magnitude and color-color diagrams (Johnson-Cousins
BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and
globular clusters. We also test our isochrones comparing integrated optical
colors and Surface Brightness Fluctuation magnitudes with selected globular
cluster data. We find a general satisfactory agreement with the empirical
constraints.Comment: 46 pages, 20 figures, ApJ in press, the whole database presented in
this paper can be foud at http://www.te.astro.it/BASTI/index.ph
The shape of the Red Giant Branch Bump as a diagnostic of partial mixing processes in low-mass stars
We suggest to use the shape of the Red Giant Branch (RGB) Bump in metal-rich
globular clusters as a diagnostic of partial mixing processes between the base
of the convective envelope and the H-burning shell. The Bump located along the
differential luminosity function of cluster RGB stars is a key observable to
constrain the H-profile inside these structures. In fact, standard evolutionary
models that account for complete mixing in the convective unstable layers and
radiative equilibrium in the innermost regions do predict that the first
dredge-up lefts over a very sharp H-discontinuity at the bottom of the
convective region. Interestingly enough we found that both atomic diffusion and
a moderate convective overshooting at the base of the convective region
marginally affects the shape of the RGB Bump in the differential Luminosity
Function (LF). As a consequence, we performed several numerical experiments to
estimate whether plausible assumptions concerning the smoothing of the
H-discontinuity, due to the possible occurrence of extra-mixing below the
convective boundary, affects the shape of the RGB Bump. We found that the
difference between the shape of RGB Bump predicted by standard and by smoothed
models can be detected if the H-discontinuity is smoothed over an envelope
region whose thickness is equal or larger than 0.5 pressure scale heights.
Finally, we briefly discuss the comparison between theoretical predictions and
empirical data in metal-rich, reddening free Galactic Globular Clusters (GGCs)
to constrain the sharpness of the H-profile inside RGB stars.Comment: 15 pages, 8 postscript figures, ApJ in pres
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