32,108 research outputs found
Biomechanical mechanisms underlying exosuit-induced improvements in walking economy after stroke
Stroke-induced hemiparetic gait is characteristically asymmetric and metabolically expensive. Weakness and impaired control of the paretic ankle contribute to reduced forward propulsion and ground clearanceâwalking subtasks critical for safe and efficient locomotion. Targeted gait interventions that improve paretic ankle function after stroke are therefore warranted. We have developed textile-based, soft wearable robots that transmit mechanical power generated by off-board or body-worn actuators to the paretic ankle using Bowden cables (soft exosuits) and have demonstrated the exosuits can overcome deficits in paretic limb forward propulsion and ground clearance, ultimately reducing the metabolic cost of hemiparetic walking. This study elucidates the biomechanical mechanisms underlying exosuit-induced reductions in metabolic power. We evaluated the relationships between exosuit-induced changes in the body center of mass (COM) power generated by each limb, individual joint powers, and metabolic power. Compared to walking with an exosuit unpowered, exosuit assistance produced more symmetrical COM power generation during the critical period of the step-to-step transition (22.4±6.4% more symmetric). Changes in individual limb COM power were related to changes in paretic (R2= 0.83, P= 0.004) and nonparetic (R2= 0.73, P= 0.014) ankle power. Interestingly, despite the exosuit providing direct assistance to only the paretic limb, changes in metabolic power were related to changes in nonparetic limb COM power (R2= 0.80, P= 0.007), not paretic limb COM power (P> 0.05). These findings provide a fundamental understanding of how individuals poststroke interact with an exosuit to reduce the metabolic cost of hemiparetic walking.Accepted manuscript2019-03-0
Projectile-shape dependence of impact craters in loose granular media
We report on the penetration of cylindrical projectiles dropped from rest
into a dry, noncohesive granular medium. The cylinder length, diameter,
density, and tip shape are all explicitly varied. For deep penetrations, as
compared to the cylinder diameter, the data collapse onto a single scaling law
that varies as the 1/3 power of the total drop distance, the 1/2 power of
cylinder length, and the 1/6 power of cylinder diameter. For shallow
penetrations, the projectile shape plays a crucial role with sharper objects
penetrating deeper.Comment: 3 pages, 3 figures; experimen
Evaluation of automated decisionmaking methodologies and development of an integrated robotic system simulation. Volume 2, Part 2: Appendixes B, C, D and E
The derivation of the equations is presented, the rate control algorithm described, and simulation methodologies summarized. A set of dynamics equations that can be used recursively to calculate forces and torques acting at the joints of an n link manipulator given the manipulator joint rates are derived. The equations are valid for any n link manipulator system with any kind of joints connected in any sequence. The equations of motion for the class of manipulators consisting of n rigid links interconnected by rotary joints are derived. A technique is outlined for reducing the system of equations to eliminate contraint torques. The linearized dynamics equations for an n link manipulator system are derived. The general n link linearized equations are then applied to a two link configuration. The coordinated rate control algorithm used to compute individual joint rates when given end effector rates is described. A short discussion of simulation methodologies is presented
Evaluation of automated decisionmaking methodologies and development of an integrated robotic system simulation, volume 2, part 1. Appendix A: Software documentation
Documentation of the preliminary software developed as a framework for a generalized integrated robotic system simulation is presented. The program structure is composed of three major functions controlled by a program executive. The three major functions are: system definition, analysis tools, and post processing. The system definition function handles user input of system parameters and definition of the manipulator configuration. The analysis tools function handles the computational requirements of the program. The post processing function allows for more detailed study of the results of analysis tool function executions. Also documented is the manipulator joint model software to be used as the basis of the manipulator simulation which will be part of the analysis tools capability
GP experience and understandings of providing followâup care in prostate cancer survivors in England
Survival times for prostate cancer have increased substantially, meaning more survivors will be discharged to General Practitioners' (GP) services. The detection of recurrence and monitoring of symptoms and longâterm sideâeffects in prostate cancer survivors requires the active involvement of GPs in their followâup care. In order to address this, the transition and discharge from hospital to primary care must be managed effectively. The objective of this study was to examine the preparedness, concerns and experiences of GPs in relation to their role in providing followâup care to prostate cancer survivors. Purposive sampling was used to recruit GPs with experience in providing care to prostate cancer survivors. Twenty semiâstructured telephone interviews were conducted with GPs across England. The interviews were audioârecorded, transcribed verbatim and analysed using thematic analysis. Participants described their current role in the followâup pathway, a number of challenges and barriers in assuming this role, and potential ways to resolve these and improve their involvement. They expressed a range of views about their preparedness and willingness to take over followâup care after discharge for this group of patients. GPs had reservations about workload, lack of resources, expertise and deficiencies in communication with hospitals. Findings from this study suggest that GPs will be ready to take over the followâup care of prostate cancer survivors if better information, additional training and adequate resources are provided and communication lines with hospital specialists are clear. Understanding the issues faced by GPs and overcoming identified barriers to providing followâup care to prostate cancer survivors will provide the insight necessary to make the process of transferring care from secondary to primary teams a more straightforward task for all stakeholders
Elemental Abundances of Nearby Galaxies through High Signal-to-Noise XMM-Newton Observations of ULXs
(abridged) In this paper, we examined XMM Newton EPIC spectra of 14
ultra-luminous X-ray sources (ULXs)in addition to the XMM RGS spectra of two
sources (Holmberg II X-1 and Holmberg IX X-1). We determined oxygen and iron
abundances of the host galaxy's interstellar medium (ISM) using K-shell (O) and
L-shell (Fe) X-ray photo-ionization edges towards these ULXs. We found that the
oxygen abundances closely matched recent solar abundances for all of our
sources, implying that ULXs live in similar local environments despite the wide
range of galaxy host properties. Also, we compare the X-ray hydrogen column
densities (n_H) for 8 ULX sources with column densities obtained from radio H I
observations. The X-ray model n_H values are in good agreement with the H I n_H
values, implying that the hydrogen absorption towards the ULXs is not local to
the source (with the exception of the source M81 XMM1). In order to obtain the
column density and abundance values, we fit the X-ray spectra of the ULXs with
a combined power law and one of several accretion disk models. We tested the
abundances obtained from the XSPEC models bbody, diskbb, grad, and diskpn along
with a power law, finding that the abundances were independent of the thermal
model used. We comment on the physical implications of these different model
fits. We also note that very deep observations allow a breaking of the
degeneracy noted by Stobbart et al. (2006) favoring a high mass solution for
the absorbed grad + power law model.Comment: 18 pages, accepted to Ap
Inverse-kinematics one-neutron pickup with fast rare-isotope beams
New measurements and reaction model calculations are reported for single
neutron pickup reactions onto a fast \nuc{22}{Mg} secondary beam at 84 MeV per
nucleon. Measurements were made on both carbon and beryllium targets, having
very different structures, allowing a first investigation of the likely nature
of the pickup reaction mechanism. The measurements involve thick reaction
targets and -ray spectroscopy of the projectile-like reaction residue
for final-state resolution, that permit experiments with low incident beam
rates compared to traditional low-energy transfer reactions. From measured
longitudinal momentum distributions we show that the \nuc{12}{C}
(\nuc{22}{Mg},\nuc{23}{Mg}+\gamma)X reaction largely proceeds as a direct
two-body reaction, the neutron transfer producing bound \nuc{11}{C} target
residues. The corresponding reaction on the \nuc{9}{Be} target seems to largely
leave the \nuc{8}{Be} residual nucleus unbound at excitation energies high in
the continuum. We discuss the possible use of such fast-beam one-neutron pickup
reactions to track single-particle strength in exotic nuclei, and also their
expected sensitivity to neutron high- (intruder) states which are often
direct indicators of shell evolution and the disappearance of magic numbers in
the exotic regime.Comment: 8 pages, 5 figure
Halcyornis toliapicus (aves: Lower Eocene, England) indicates advanced neuromorphology in Mesozoic Neornithes
Our recent X-ray micro computer-tomographic (ÎŒCT) investigations of Prophaethon shrubsolei and Odontopteryx toliapica from the Lower Eocene London Clay Formation of England revealed the avian brain to have been essentially modern in form by 55 Ma, but that an important vision-related synapomorphy of living birds, the eminentia sagittalis of the telencephalon, was poorly developed. This evidence suggested that the feature probably appeared close to the end of the Mesozoic. Here we use ÎŒCT analysis to describe the endocranium of Halcyornis toliapicus, also from the London Clay Formation. The affinities of Halcyornis have been hotly debated, with the taxon referred to the Charadriiformes (Laridae), Coraciiformes (Alcedinidae, and its own family Halcyornithidae) and most recently that Halcyornithidae may be a possible senior synonym of Pseudasturidae (Pan-Psittaciformes). Unlike Prophaethon and Odontopteryx, the eminentia sagittalis of Halcyornis is strongly developed and comparable to that of living species. Like those London Clay taxa, the eminentia sagittalis occupies a rostral position on the telencephalon. The senses of Halcyornis appear to have been well developed. The length of the cochlear duct of the inner ear indicates a hearing sensitivity within the upper range of living species, and enlarged olfactory lobes suggest a reasonable reliance on sense of smell. The optic nerves were especially well developed which, together with the strong development of the eminentia sagittalis, indicates a high degree of visual specialization in Halcyornis. The advanced development of the eminentia sagittalis further supports a Mesozoic age for the appearance of this structure and associated neural architectural complexity found in extant Aves. The eminentia sagittalis of living Psittaciformes is situated caudally on the telencephalon, making a Pan-Psittaciformes relationship unlikely for Halcyorni
Stars in the Hubble Ultra Deep Field
We identified 46 unresolved source candidates in the Hubble Ultra Deep Field,
down to i775 = 29.5. Unresolved objects were identified using a parameter S,
which measures the deviation from the curve-of-growth of a point source.
Extensive testing of this parameter was carried out, including the effects of
decreasing signal-to-noise and of the apparent motions of stars, which
demonstrated that stars brighter than i775 = 27.0 could be robustly identified.
Low resolution grism spectra of the 28 objects brighter than i775 = 27.0
identify 18 M and later stellar type dwarfs, 2 candidate L-dwarfs, 2 QSOs, and
4 white dwarfs. Using the observed population of dwarfs with spectral type M4
or later, we derive a Galactic disk scale height of 400 \pm 100 pc for M and L
stars. The local white dwarf density is computed to be as high as (1.1 \pm 0.3)
x10^(-2) stars/pc^3. Based on observations taken 73 days apart, we determined
that no object in the field has a proper motion larger than 0.027"/year (3
sigma detection limit). No high velocity white dwarfs were identified in the
HUDF, and all four candidates appear more likely to be part of the Galactic
thick disk. The lack of detected halo white dwarfs implies that, if the dark
matter halo is 12 Gyr old, white dwarfs account for less than 10% of the dark
matter halo mass.Comment: 35 pages, 11 figures, accepted by Ap
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