2,130 research outputs found
Forecast or Fall: Prediction's Importance to Postural Control
To interact successfully with an uncertain environment, organisms must be able to respond to both unanticipated and anticipated events. For unanticipated events, organisms have evolved stereotyped motor behaviors mapped to the statistical regularities of the environment, which can be trigged by specific sensory stimuli. These “reflexive” responses are more or less hardwired to prevent falls and represent, maybe, the best available solution to maintaining posture given limited available time and information. With the gift of foresight, however, motor behaviors can be tuned or prepared in advance, improving the ability of the organism to compensate for, and interact with, the changing environment. Indeed, foresight's improvement of our interactive capacity occurs through several means, such as better action selection, processing, and conduction delay compensation and by providing a prediction with which to compare our actual behaviors to, thereby facilitating error identification and learning. Here we review the various roles foresight (prediction) plays in maintaining our postural equilibrium. We start by describing some of the more recent findings related to the prediction of instability. Specifically, we cover recent advancements in the understanding of anticipatory postural behaviors that are used broadly to stabilize volitional movement and compensate for impending postural disturbances. We also describe anticipatory changes in the state, or set, of the nervous system that may facilitate anticipatory behaviors. From changes in central set, we briefly discuss prediction of postural instability online before moving into a discussion of how predictive mechanisms, such as internal models, permit us to tune, perhaps our highest level predictive behaviors, namely the priming associated with motor affordances. Lastly, we explore methods best suited to expose the contribution of prediction to postural equilibrium control across a variety of contexts
The SWELLS survey. IV. Precision measurements of the stellar and dark matter distributions in a spiral lens galaxy
We construct a fully self-consistent mass model for the lens galaxy J2141 at
z=0.14, and use it to improve on previous studies by modelling its
gravitational lensing effect, gas rotation curve and stellar kinematics
simultaneously. We adopt a very flexible axisymmetric mass model constituted by
a generalized NFW dark matter halo and a stellar mass distribution obtained by
deprojecting the MGE fit to the high-resolution K'-band LGSAO imaging data of
the galaxy, with the (spatially constant) M/L ratio as a free parameter. We
model the stellar kinematics by solving the anisotropic Jeans equations. We
find that the inner logarithmic slope of the dark halo is weakly constrained
(gamma = 0.82^{+0.65}_{-0.54}), and consistent with an unmodified NFW profile.
We infer the galaxy to have (i) a dark matter fraction within 2.2 disk radii of
0.28^{+0.15}_{-0.10}, independent of the galaxy stellar population, implying a
maximal disk for J2141; (ii) an apparently uncontracted dark matter halo, with
concentration c_{-2} = 7.7_{-2.5}^{+4.2} and virial velocity v_{vir} =
242_{-39}^{+44} km/s, consistent with LCDM predictions; (iii) a slightly oblate
halo (q_h = 0.75^{+0.27}_{-0.16}), consistent with predictions from
baryon-affected models. Comparing the stellar mass inferred from the combined
analysis (log_{10} Mstar/Msun = 11.12_{-0.09}^{+0.05}) with that inferred from
SPS modelling of the galaxies colours, and accounting for a cold gas fraction
of 20+/-10%, we determine a preference for a Chabrier IMF over Salpeter IMF by
a Bayes factor of 5.7 (substantial evidence). We infer a value beta_{z} = 1 -
sigma^2_{z}/sigma^2_{R} = 0.43_{-0.11}^{+0.08} for the orbital anisotropy
parameter in the meridional plane, in agreement with most studies of local disk
galaxies, and ruling out at 99% CL that the dynamics of this system can be
described by a two-integral distribution function. [Abridged]Comment: Accepted for publication in MNRAS. 17 pages, 9 figure
Suppressing a Blocked Balance Recovery Step: A Novel Method to Assess an Inhibitory Postural Response
Stepping to recover balance is an important way we avoid falling. However, when faced with obstacles in the step path, we must adapt such reactions. Physical obstructions are typically detected through vision, which then cues step modification. The present study describes a novel method to assess visually prompted step inhibition in a reactive balance context. In our task, participants recovered balance by quickly stepping after being released from a supported forward lean. On rare trials, however, an obstacle blocked the stepping path. The timing of vision relative to postural perturbation was controlled using occlusion goggles to regulate task difficulty. Furthermore, we explored step suppression in our balance task related to inhibitory capacity measured at the hand using a clinically feasible handheld device (ReacStick). Our results showed that ReacStick and step outcomes were significantly correlated in terms of successful inhibition (r = 0.57) and overall reaction accuracy (r = 0.76). This study presents a novel method for assessing rapid inhibition in a dynamic postural context, a capacity that appears to be a necessary prerequisite to a subsequent adaptive strategy. Moreover, this capacity is significantly related to ReacStick performance, suggesting a potential clinical translation
Which Exercise Interventions Can Most Effectively Improve Reactive Balance in Older Adults? A Systematic Review and Network Meta-Analysis
Background: Reactive balance is the last line of defense to prevent a fall when the body loses stability, and beneficial effects of various exercise-based interventions on reactive balance in older adults have been reported. However, their pooled evidence on the relative effects has yet to be described. Objective: To review and evaluate the comparative effectiveness of various exercise-based interventions on reactive balance in older adults. Methods: Nine electronic databases and reference lists were searched from inception to August 2021. Eligibility criteria according to PICOS criteria were as follows: (1) population: older adults with the mean age of 65 years or above; (2) intervention and comparison: at least two distinct exercise interventions or one exercise intervention with no-exercise controlled intervention (NE) compared in each trial; (3) outcome: at least one measure of reactive balance; (4) study: randomized controlled trial. The main network meta-analysis was performed on data from the entire older adult population, involving all clinical conditions as well as healthy older adults. Subgroup analyses stratified by characteristics of participants (healthy only) and reactive balance outcomes (simulated slip or trip while walking, simulated forward falls, being pushed or pulled, and moveable platform) were also conducted. Results: Thirty-nine RCTs (n = 1388) investigating 17 different types of exercise interventions were included in the network meta-analysis. Reactive balance training as a single intervention presented the highest probability (surface under the cumulative ranking (SUCRA) score) of being the best intervention for improving reactive balance and the greatest relative effects vs. NE in the entire sample involving all clinical conditions [SUCRA = 0.9; mean difference (95% Credible Interval): 2.7 (1.0 to 4.3)]. The results were not affected by characteristics of participants (i.e., healthy older adults only) or reactive balance outcomes. Summary/Conclusion: The findings from the NMA suggest that a task-specific reactive balance exercise could be the optimal intervention for improving reactive balance in older adults, and power training can be considered as a secondary training exercise
The SWELLS Survey. I. A large spectroscopically selected sample of edge-on late-type lens galaxies
The relative contribution of baryons and dark matter to the inner regions of
spiral galaxies provides critical clues to their formation and evolution, but
it is generally difficult to determine. For spiral galaxies that are strong
gravitational lenses, however, the combination of lensing and kinematic
observations can be used to break the disk-halo degeneracy. In turn, such data
constrain fundamental parameters such as i) the mass density profile slope and
axis ratio of the dark matter halo, and by comparison with dark matter-only
numerical simulations the modifications imposed by baryons; ii) the mass in
stars and therefore the overall star formation efficiency, and the amount of
feedback; iii) by comparison with stellar population synthesis models, the
normalization of the stellar initial mass function. In this first paper of a
series, we present a sample of 16 secure, 1 probable, and 6 possible strong
lensing spiral galaxies, for which multi-band high-resolution images and
rotation curves were obtained using the Hubble Space Telescope and Keck-II
Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The
sample includes 8 newly discovered secure systems. [abridged] We find that the
SWELLS sample of secure lenses spans a broad range of morphologies (from
lenticular to late-type spiral), spectral types (quantified by Halpha
emission), and bulge to total stellar mass ratio (0.22-0.85), while being
limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for
exploring the relationship between dark and luminous matter in a broad range of
galaxies. We find that the deflector galaxies obey the same size-mass relation
as that of a comparison sample of elongated non-lens galaxies selected from the
SDSS survey. We conclude that the SWELLS sample is consistent with being
representative of the overall population of high-mass high-inclination disky
galaxies.Comment: 21 pages, 6 figures, MNRAS, in pres
Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed
to locate quasars during the epoch of reionization. In this paper we present
the discovery of the first four CFHQS quasars at redshift greater than 6,
including the most distant known quasar, CFHQS J2329-0301 at z=6.43. We
describe the observational method used to identify the quasars and present
optical, infrared, and millimeter photometry and optical and near-infrared
spectroscopy. We investigate the dust properties of these quasars finding an
unusual dust extinction curve for one quasar and a high far-infrared luminosity
due to dust emission for another. The mean millimeter continuum flux for CFHQS
quasars is substantially lower than that for SDSS quasars at the same redshift,
likely due to a correlation with quasar UV luminosity. For two quasars with
sufficiently high signal-to-noise optical spectra, we use the spectra to
investigate the ionization state of hydrogen at z>5. For CFHQS J1509-1749 at
z=6.12, we find significant evolution (beyond a simple extrapolation of lower
redshift data) in the Gunn-Peterson optical depth at z>5.4. The line-of-sight
to this quasar has one of the highest known optical depths at z~5.8. An
analysis of the sizes of the highly-ionized near-zones in the spectra of two
quasars at z=6.12 and z=6.43 suggest the IGM surrounding these quasars was
substantially ionized before these quasars turned on. Together, these
observations point towards an extended reionization process, but we caution
that cosmic variance is still a major limitation in z>6 quasar observations.Comment: 15 pages, 9 figures, AJ, in press, minor changes to previous versio
Unveiling the Active Nucleus of Centaurus A
We report new HST WFPC2 and NICMOS observations of the center of the nearest
radio galaxy Centaurus A (NGC 5128) and discuss their implications for our
understanding of the active nucleus and jet. We detect the active nucleus in
the near-IR (K and H) and, for the first time, in the optical (I and V),
deriving the spectral energy distribution of the nucleus from the radio to
X-rays. The optical and part of the near-IR emission can be explained by the
extrapolation of the X-ray power law reddened by A_V~14mag, a value consistent
with other independent estimates.
The 20pc-scale nuclear disk discovered by Schreier et al. (1998) is detected
in the [FeII] 1.64mic line and presents a morphology similar to that observed
in Pa alpha with a [FeII]/Pa alpha ratio typical of low ionization Seyfert
galaxies and LINERs. NICMOS 3 Pa alpha observations in a 50"x50" circumnuclear
region suggest enhanced star formation (~0.3Msun/yr) at the edges of the
putative bar seen with ISO, perhaps due to shocks driven into the gas.
The light profile, reconstructed from V, H and K observations, shows that
Centaurus A has a core profile with a resolved break at ~4" and suggests a
black--hole mass of ~10^9 Msun. A linear blue structure aligned with the
radio/X-ray jet may indicate a channel of relatively low reddening in which
dust has been swept away by the jet.Comment: 19 pages, 13 figures, Astrophysical Journal, in press. High quality
figures available at http://www.arcetri.astro.it/~marconi/colpic.htm
The clustering of intermediate redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey
We measure the quasar two-point correlation function over the redshift range
2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a
homogeneous subset of the data consisting of 27,129 quasars with spectroscopic
redshifts---by far the largest such sample used for clustering measurements at
these redshifts to date. The sample covers 3,600 square degrees, corresponding
to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology,
and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After
accounting for redshift errors we find that the redshift space correlation
function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm
0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which
integrates out the effects of peculiar velocities and redshift errors, is fit
well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range
4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence
to the clustering amplitude, in part because of the limited dynamic range in
our sample. Our results are consistent with, but more precise than, previous
measurements at similar redshifts. Our measurement of the quasar clustering
amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the
data to models to constrain the manner in which quasars occupy dark matter
halos at z~2.4 and infer that such quasars inhabit halos with a characteristic
mass of ~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per
cent.Comment: 20 pages, 18 figures. Minor modifications to match version accepted
by journa
The SWELLS survey. III. Disfavouring "heavy" initial mass functions for spiral lens galaxies
We present gravitational lens models for 20 strong gravitational lens systems
observed as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS)
project. Fifteen of the lenses are taken from paper I while five are newly
discovered systems. The systems are galaxy-galaxy lenses where the foreground
deflector has an inclined disc, with a wide range of morphological types, from
late-type spiral to lenticular. For each system, we compare the total mass
inside the critical curve inferred from gravitational lens modelling to the
stellar mass inferred from stellar population synthesis (SPS) models, computing
the stellar mass fraction f* = M(SPS)/M(lens). We find that, for the lower mass
SWELLS systems, adoption of a Salpeter stellar initial mass function (IMF)
leads to estimates of f* that exceed 1. This is unphysical, and provides strong
evidence against the Salpeter IMF being valid for these systems. Taking the
lower mass end of the SWELLS sample sigma(SIE) < 230 km/s, we find that the IMF
is lighter (in terms of stellar mass-to-light ratio) than Salpeter with 98%
probability, and consistent with the Chabrier IMF and IMFs between the two.
This result is consistent with previous studies of spiral galaxies based on
independent techniques. In combination with recent studies of massive
early-type galaxies that have favoured a heavier Salpeter-like IMF, this result
strengthens the evidence against a universal stellar IMF.Comment: Accepted for publication in MNRAS. Some changes (none major) to
address the referee's comments. 18 pages, 8 figure
Pickleball for Inactive Mid-Life and Older Adults in Rural Utah: A Feasibility Study
Many diseases, disabilities, and mental health conditions associated with aging can be delayed or prevented through regular exercise. Several barriers to exercise, many of which are exacerbated in rural communities, prevent mid-life and older adults from accessing its benefits. However, recently, a racquet sport named pickleball has become popular among older adults, and it appears to overcome some of these barriers. We conducted a feasibility study to evaluate the impact of a six-week pickleball intervention on measures of muscle function, cognitive function, perceived pain, and cardio-metabolic risk, as well as several psychosocial factors contributing to adherence in sedentary rural participants. Participants improved their vertical jump, cognitive performance, and reported a decrease in self-reported pain, suggesting improved physical and cognitive health across the sample. Participants also reported high levels of satisfaction and demonstrated good adherence over the duration of the study. Perhaps of greatest value was the overwhelmingly positive response from participants to the intervention and follow-up interviews reporting a desire to continue pickleball play beyond the study period. Overall, pickleball appears to be a promising intervention to, (1) elicit functional- and cognitive-related improvements, and (2) motivate mid-life and older adults to adhere to exercise sufficiently long to benefit their health
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