377 research outputs found
Effects of hypothalamic knife cuts and experience on maternal behavior in the rat
Recent investigations suggest that the disruption of placentophagia, pup-directed maternal behavior, and nestbuilding seen after lesions of the medial preoptic area (MPO) or the lateral hypothalamus may be due to the interruption at different points of a single longitudinal neural system mediating these behaviors. To test this, we compared the effects of knife cuts on the lateral border of the MPO, and of the posterior medial forebrain bundle (MFB), with asymmetrical cuts combining a unilateral MPO cut with a contralateral MFB cut. We observed placentophagia, nestbuilding, and pup-directed maternal behaviors at, and after, parturition in both primiparous and biparous rats. In primiparae, MPO cuts (a) disrupted placentophagia, (b) delayed the onset of crouching and pup-licking, and (c) eliminated retrieval and nestbuilding. Asymmetrical cuts (a) disrupted placentophagia, and (b) delayed the onset of maternal behavior. In biparous rats, MPO cuts eliminated nestbuilding and retrieval. MFB cuts (a) disrupted placentophagia, and (b) eliminated nestbuilding. Asymmetrical cuts (a) delayed nestbuilding. These results suggest the involvement of a longitudinal neural system in the production of immediate pup-directed maternal behavior, placentophagia, and nestbuilding in parturient primiparae, but which is not critical for the eventual display of maternal behavior and nestbuilding in maternally naive rats, nor for the immediate onset of placentophagia and maternal behavior in maternally experienced rats
Simulations suggest walking with reduced propulsive force would not mitigate the energetic consequences of lower tendon stiffness
Aging elicits numerous effects that impact both musculoskeletal structure and walking function. Tendon stiffness (kT) and push-off propulsive force (FP) both impact the metabolic cost of walking and are diminished by age, yet their interaction has not been studied. We combined experimental and computational approaches to investigate whether age-related changes in function (adopting smaller FP) may be adopted to mitigate the metabolic consequences arising from changes in structure (reduced kT). We recruited 12 young adults and asked them to walk on a force-sensing treadmill while prompting them to change FP (±20% & ±40% of typical) using targeted biofeedback. In models driven by experimental data from each of those conditions, we altered the kT of personalized musculoskeletal models across a physiological range (2–8% strain) and simulated individual-muscle metabolic costs for each kT and FP combination. We found that kT and FP independently affect walking metabolic cost, increasing with higher kT or as participants deviated from their typical FP. Our results show no evidence for an interaction between kT and FP in younger adults walking at fixed speeds. We also reveal complex individual muscle responses to the kT and FP landscape. For example, although total metabolic cost increased by 5% on average with combined reductions in kT and FP, the triceps surae muscles experienced a 7% local cost reduction on average. Our simulations suggest that reducing FP during walking would not mitigate the metabolic consequences of lower kT. Wearable devices and rehabilitative strategies can focus on either kT or FP to reduce age-related increases in walking metabolic cost
The effects of plantarflexor weakness and reduced tendon stiffness with aging on gait stability
Falls among older adults are a costly public health concern. Such falls can be precipitated by balance disturbances, after which a recovery strategy requiring rapid, high force outputs is necessary. Sarcopenia among older adults likely diminishes their ability to produce the forces necessary to arrest gait instability. Age-related changes to tendon stiffness may also delay muscle stretch and afferent feedback and decrease force transmission, worsening fall outcomes. However, the association between muscle strength, tendon stiffness, and gait instability is not well established. Given the ankle’s proximity to the onset of many walking balance disturbances, we examined the relation between both plantarflexor strength and Achilles tendon stiffness with walking-related instability during perturbed gait in older and younger adults–the latter quantified herein using margins of stability and whole-body angular momentum including the application of treadmill-induced slip perturbations. Older and younger adults did not differ in plantarflexor strength, but Achilles tendon stiffness was lower in older adults. Among older adults, plantarflexor weakness associated with greater whole-body angular momentum following treadmill-induced slip perturbations. Weaker older adults also appeared to walk and recover from treadmill-induced slip perturbations with more caution. This study highlights the role of plantarflexor strength and Achilles tendon stiffness in regulating lateral gait stability in older adults, which may be targets for training protocols seeking to minimize fall risk and injury severity
Angle-dependent normalization of neutron-proton differential cross sections
Systematic errors in the database of differential cross sections below
350 MeV are studied. By applying angle-dependent normalizations with the help
of the energy-dependent Nijmegen partial-wave analysis PWA93 the
-values of some seriously flawed data sets can be reduced significantly
at the expense of a few degrees of freedom. It turns out that in these special
cases the renormalized data sets can be made statistically acceptable such that
they do not have to be discarded any longer in partial-wave analyses of the
two-nucleon scattering data.Comment: 11 pages, 1 figure; expanded versio
Effective chiral lagrangian in the chiral limit from the instanton vacuum
We study the effective chiral Lagrangian in the chiral limit from the
instanton vacuum. Starting from the nonlocal effective chiral action, we derive
the effective chiral Lagrangian, using the derivative expansion to order
in the chiral limit. The low energy constants, , , and
are determined and compared with various models and the corresponding empirical
data. The results are in a good agreement with the data. We also discuss about
the upper limit of the sigma meson, based on the present results.Comment: 14 pages, 5 figures, submitted to Phys.Rev.
These legs were made for propulsion: advancing the diagnosis and treatment of post-stroke propulsion deficits
Advances in medical diagnosis and treatment have facilitated the emergence of precision medicine. In contrast, locomotor rehabilitation for individuals with acquired neuromotor injuries remains limited by the dearth of (i) diagnostic approaches that can identify the specific neuromuscular, biomechanical, and clinical deficits underlying impaired locomotion and (ii) evidence-based, targeted treatments. In particular, impaired propulsion by the paretic limb is a major contributor to walking-related disability after stroke; however, few interventions have been able to target deficits in propulsion effectively and in a manner that reduces walking disability. Indeed, the weakness and impaired control that is characteristic of post-stroke hemiparesis leads to heterogeneous deficits that impair paretic propulsion and contribute to a slow, metabolically-expensive, and unstable gait. Current rehabilitation paradigms emphasize the rapid attainment of walking independence, not the restoration of normal propulsion function. Although walking independence is an important goal for stroke survivors, independence achieved via compensatory strategies may prevent the recovery of propulsion needed for the fast, economical, and stable gait that is characteristic of healthy bipedal locomotion. We posit that post-stroke rehabilitation should aim to promote independent walking, in part, through the acquisition of enhanced propulsion. In this expert review, we present the biomechanical and functional consequences of post-stroke propulsion deficits, review advances in our understanding of the nature of post-stroke propulsion impairment, and discuss emerging diagnostic and treatment approaches that have the potential to facilitate new rehabilitation paradigms targeting propulsion restoration.R01 AG067394 - NIA NIH HHS; R01 HD095975 - NICHD NIH HHS; K01 HD079584 - NICHD NIH HHSPublished versio
Numerical Results for Ground States of Mean-Field Spin Glasses at low Connectivities
An extensive list of results for the ground state properties of spin glasses
on random graphs is presented. These results provide a timely benchmark for
currently developing theoretical techniques based on replica symmetry breaking
that are being tested on mean-field models at low connectivity. Comparison with
existing replica results for such models verifies the strength of those
techniques. Yet, we find that spin glasses on fixed-connectivity graphs (Bethe
lattices) exhibit a richer phenomenology than has been anticipated by theory.
Our data prove to be sufficiently accurate to speculate about some exact
results.Comment: 4 pages, RevTex4, 5 ps-figures included, related papers available at
http://www.physics.emory.edu/faculty/boettcher
Nonlinear ion-acoustic (IA) waves driven in a cylindrically symmetric flow
By employing a self-similar, two-fluid MHD model in a cylindrical geometry,
we study the features of nonlinear ion-acoustic (IA) waves which propagate in
the direction of external magnetic field lines in space plasmas. Numerical
calculations not only expose the well-known three shapes of nonlinear
structures (sinusoidal, sawtooth, and spiky or bipolar) which are observed by
numerous satellites and simulated by models in a Cartesian geometry, but also
illustrate new results, such as, two reversely propagating nonlinear waves,
density dips and humps, diverging and converging electric shocks, etc. A case
study on Cluster satellite data is also introduced.Comment: accepted by AS
Spectral Properties of Quasiparticle Excitations Induced by Magnetic Moments in Superconductors
The consequences of localized, classical magnetic moments in superconductors
are explored and their effect on the spectral properties of the intragap bound
states is studied. Above a critical moment, a localized quasiparticle
excitation in an s-wave superconductor is spontaneously created near a magnetic
impurity, inducing a zero-temperature quantum transition. In this transition,
the spin quantum number of the ground state changes from zero to 1/2, while the
total charge remains the same. In contrast, the spin-unpolarized ground state
of a d-wave superconductor is found to be stable for any value of the magnetic
moment when the normal-state energy spectrum possesses particle-hole symmetry.
The effect of impurity scattering on the quasiparticle states is interpreted in
the spirit of relevant symmetries of the clean superconductor. The results
obtained by the non-self-consistent (T matrix) and the self-consistent
mean-field approximations are compared and qualitative agreement between the
two schemes is found in the regime where the coherence length is longer than
the Fermi length.Comment: to appear in Phys. Rev. B55, May 1st (1997
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