539,565 research outputs found
Relationship Between Static Mobility of the First Ray and First Ray, Midfoot, and Hindfoot Motion During Gait
The relationship between a static measure of dorsal first ray mobility and dynamic motion of the first ray, midfoot, and hindfoot during the stance phase of walking was investigated in healthy, asymptomatic subjects who represented the spectrum of static flexibility. Static first ray mobility of 15 subjects was measured by a load cell device and ranged from stiff (3.1 mm) to lax (8.0 mm). Using three-dimensional motion analysis, mean first ray dorsiflexion/eversion and mid-/hindfoot eversion peak motion, time-to-peak, and eversion excursion were evaluated. Subjects with greater static dorsal mobility of the first ray demonstrated significantly greater time-topeak hindfoot eversion and eversion excursion (p \u3c .01), and midfoot peak eversion and eversion excursion (p \u3c .01). No significant association was found between static first ray mobility and first ray motion during gait. This research provides evidence that the dynamic response of the foot may modulate the consequences of first ray mobility and that compensory strategies are most effective when static measures of dorsal mobility are most extreme
Motion sickness evaluation and comparison for a static driving simulator and a dynamic driving simulator
This paper deals with driving simulation and in particular with the important issue of motion sickness. The paper proposes a methodology to evaluate the objective illness rating metrics deduced from the motion sickness dose value and questionnaires for both a static simulator and a dynamic simulator. Accelerations of the vestibular cues (head movements) of the subjects were recorded with and without motion platform activation. In order to compare user experiences in both cases, the head-dynamics-related illness ratings were computed from the obtained accelerations and the motion sickness dose values. For the subjective analysis, the principal component analysis method was used to determine the conflict between the subjective assessment in the static condition and that in the dynamic condition. The principal component analysis method used for the subjective evaluation showed a consistent difference between the answers given in the sickness questionnaire for the static platform case from those for the dynamic platform case. The two-tailed Mann–Whitney U test shows the significance in the differences between the self-reports to the individual questions. According to the two-tailed Mann–Whitney U test, experiencing nausea (p = 0.019 < 0.05) and dizziness (p = 0.018 < 0.05) decreased significantly from the static case to the dynamic case. Also, eye strain (p = 0.047 < 0.05) and tiredness (p = 0.047 < 0.05) were reduced significantly from the static case to the dynamic case. For the perception fidelity analysis, the Pearson correlation with a confidence interval of 95% was used to study the correlations of each question with the x illness rating component IRx, the y illness rating component IRy, the z illness rating component IRz and the compound illness rating IRtot. The results showed that the longitudinal head dynamics were the main element that induced discomfort for the static platform, whereas vertical head movements were the main factor to provoke discomfort for the dynamic platform case. Also, for the dynamic platform, lateral vestibular-level dynamics were the major element which caused a feeling of fear
A Portable, Low-Cost Wheelchair Ergometer Design Based on a Mathematical Model of Pediatric Wheelchair Dynamics
Evaluation and training of wheelchair propulsion improves efficiency and prevents orthopaedic injury in pediatric manual wheelchair users. Ergometers allow static propulsion and emulate typical conditions. Currently available ergometers have deficiencies that limit their use in motion analysis. A new ergometer is developed and evaluated based on a model of wheelchair inertial dynamics that eliminates these deficiencies. This makes integrated motion analysis of wheelchair propulsion in current community, home, and international outreach efforts possible
Mapless Online Detection of Dynamic Objects in 3D Lidar
This paper presents a model-free, setting-independent method for online
detection of dynamic objects in 3D lidar data. We explicitly compensate for the
moving-while-scanning operation (motion distortion) of present-day 3D spinning
lidar sensors. Our detection method uses a motion-compensated freespace
querying algorithm and classifies between dynamic (currently moving) and static
(currently stationary) labels at the point level. For a quantitative analysis,
we establish a benchmark with motion-distorted lidar data using CARLA, an
open-source simulator for autonomous driving research. We also provide a
qualitative analysis with real data using a Velodyne HDL-64E in driving
scenarios. Compared to existing 3D lidar methods that are model-free, our
method is unique because of its setting independence and compensation for
pointcloud motion distortion.Comment: 7 pages, 8 figure
Bloch oscillations, Zener tunneling and Wannier-Stark ladders in the time-domain
We present a time-domain analysis of carrier dynamics in a semiconductor
superlattice with two minibands. Integration of the density-matrix equations of
motion reveals a number of new features: (i) for certain values of the applied
static electric field strong interband transitions occur; (ii) in static fields
the complex time-dependence of the density-matrix displays a sequence of stable
plateaus in the low field regime, and (iii) for applied fields with a periodic
time-dependence the dynamic response can be understood in terms of the
quasienergy spectra.Comment: 4 pages, 6 PostScript figures available from [email protected], REVTEX
3.
Motion of discrete interfaces in periodic media
We study the motion of discrete interfaces driven by ferromagnetic
interactions in a two-dimensional periodic environment by coupling the
minimizing movements approach by Almgren, Taylor and Wang and a
discrete-to-continuous analysis. The case of a homogeneous environment has been
recently treated by Braides, Gelli and Novaga, showing that the effective
continuous motion is a flat motion related to the crystalline perimeter
obtained by -convergence from the ferromagnetic energies, with an
additional discontinuous dependence on the curvature, giving in particular a
pinning threshold. In this paper we give an example showing that in general the
motion does not depend only on the -limit, but also on geometrical
features that are not detected in the static description. In particular we show
how the pinning threshold is influenced by the microstructure and that the
effective motion is described by a new homogenized velocity.Comment: arXiv admin note: substantial text overlap with arXiv:1407.694
A black hole instability in five dimensions?
We study the moduli-space scattering of a two-charge supertube in the
background of a rotating BPS D1-D5-P black hole in 4+1 dimensions, extending
the static analysis of Bena and Kraus (hep-th/0402144). While the magnetic
forces associated with this motion change the details considerably, the final
conclusion is similar to that of the static analysis: we find that one can
bring the supertube to the horizon, so that the BMPV black hole and the
supertube merge. However, our analysis shows that this can occur even at
significantly larger values of the angular momentum than was indicated by the
static analysis. For a range of parameters, conservation laws and the area
theorem forbid the result of the merger from being any single known object:
neither near-extremal black holes nor non-supersymmetric black rings are
allowed. Such results suggest that the merger triggers an instability of the
rotating D1-D5-P black hole, perhaps leading to bifurcation into a pair of
black objects.Comment: 25 pages, 4 figures; v2: references adde
Studies on the Seismic Design of Low-Rise Steel Buildings
The behavior of low-rise steel shear buildings, moment frame buildings,
and X-braced buildings, subjected to earthquake base motion, is studied using inelastic
time-history analysis. Two simpler methods of analysis, the modal method
and the quasi-static building code approach, are evaluated for practical use in
calculating. response quantities. The application of the results of these studies
to the practical design of buildings is discussed.National Science Foundation Grant No. AEN 75-0845
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