5,890 research outputs found
Vibrotactile Sensory Augmentation and Machine Learning Based Approaches for Balance Rehabilitation
Vestibular disorders and aging can negatively impact balance performance. Currently, the most effective approach for improving balance is exercise-based balance rehabilitation. Despite its effectiveness, balance rehabilitation does not always result in a full recovery of balance function. In this dissertation, vibrotactile sensory augmentation (SA) and machine learning (ML) were studied as approaches for further improving balance rehabilitation outcomes.
Vibrotactile SA provides a form of haptic cues to complement and/or replace sensory information from the somatosensory, visual and vestibular sensory systems. Previous studies have shown that people can reduce their body sway when vibrotactile SA is provided; however, limited controlled studies have investigated the retention of balance improvements after training with SA has ceased. The primary aim of this research was to examine the effects of supervised balance rehabilitation with vibrotactile SA. Two studies were conducted among people with unilateral vestibular disorders and healthy older adults to explore the use of vibrotactile SA for therapeutic and preventative purposes, respectively. The study among people with unilateral vestibular disorders provided six weeks of supervised in-clinic balance training. The findings indicated that training with vibrotactile SA led to additional body sway reduction for balance exercises with head movements, and the improvements were retained for up to six months. Training with vibrotactile SA did not lead to significant additional improvements in the majority of the clinical outcomes except for the Activities-specific Balance Confidence scale. The study among older adults provided semi-supervised in-home balance rehabilitation training using a novel smartphone balance trainer. After completing eight weeks of balance training, participants who trained with vibrotactile SA showed significantly greater improvements in standing-related clinical outcomes, but not in gait-related clinical outcomes, compared with those who trained without SA.
In addition to investigating the effects of long-term balance training with SA, we sought to study the effects of vibrotactile display design on people’s reaction times to vibrational cues. Among the various factors tested, the vibration frequency and tactor type had relatively small effects on reaction times, while stimulus location and secondary cognitive task had relatively large effects. Factors affected young and older adults’ reaction times in a similar manner, but with different magnitudes.
Lastly, we explored the potential for ML to inform balance exercise progression for future applications of unsupervised balance training. We mapped body motion data measured by wearable inertial measurement units to balance assessment ratings provided by physical therapists. By training a multi-class classifier using the leave-one-participant-out cross-validation method, we found approximately 82% agreement among trained classifier and physical therapist assessments.
The findings of this dissertation suggest that vibrotactile SA can be used as a rehabilitation tool to further improve a subset of clinical outcomes resulting from supervised balance rehabilitation training. Specifically, individuals who train with a SA device may have additional confidence in performing balance activities and greater postural stability, which could decrease their fear of falling and fall risk, and subsequently increase their quality of life. This research provides preliminary support for the hypothesized mechanism that SA promotes the central nervous system to reweight sensory inputs. The preliminary outcomes of this research also provide novel insights for unsupervised balance training that leverage wearable technology and ML techniques. By providing both SA and ML-based balance assessment ratings, the smart wearable device has the potential to improve individuals’ compliance and motivation for in-home balance training.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143901/1/baotian_1.pd
First-principles calculations of phase transition, elasticity, and thermodynamic properties for TiZr alloy
tructural transformation, pressure dependent elasticity behaviors, phonon,
and thermodynamic properties of the equiatomic TiZr alloy are investigated by
using first-principles density-functional theory. Our calculated lattice
parameters and equation of state for and phases as well as
the phase transition sequence of
are
consistent well with experiments. Elastic constants of and
phases indicate that they are mechanically stable. For cubic phase,
however, it is mechanically unstable at zero pressure and the critical pressure
for its mechanical stability is predicted to equal to 2.19 GPa. We find that
the moduli, elastic sound velocities, and Debye temperature all increase with
pressure for three phases of TiZr alloy. The relatively large values
illustrate that the TiZr alloy is rather ductile and its ductility is more
predominant than that of element Zr, especially in phase. Elastic wave
velocities and Debye temperature have abrupt increase behaviors upon the
transition at around 10 GPa and exhibit
abrupt decrease feature upon the
transition at higher pressure. Through Mulliken population analysis, we
illustrate that the increase of the \emph{d}-band occupancy will stabilize the
cubic phase. Phonon dispersions for three phases of TiZr alloy are
firstly presented and the phase phonons clearly indicate its
dynamically unstable nature under ambient condition. Thermodynamics of Gibbs
free energy, entropy, and heat capacity are obtained by quasiharmonic
approximation and Debye model.Comment: 9 pages, 10 figure
Electronic, mechanical, and thermodynamic properties of americium dioxide
By performing density functional theory (DFT) + calculations, we
systematically study the electronic, mechanical, tensile, and thermodynamic
properties of AmO. The experimentally observed antiferromagnetic
insulating feature [J. Chem. Phys. 63, 3174 (1975)] is successfully reproduced.
It is found that the chemical bonding character in AmO is similar to that
in PuO, with smaller charge transfer and stronger covalent interactions
between americium and oxygen atoms. The valence band maximum and conduction
band minimum are contributed by 2 hybridized and 5 electronic states
respectively. The elastic constants and various moduli are calculated, which
show that AmO is less stable against shear forces than PuO. The
stress-strain relationship of AmO is examined along the three low-index
directions by employing the first-principles computational tensile test method.
It is found that similar to PuO, the [100] and [111] directions are the
strongest and weakest tensile directions, respectively, but the theoretical
tensile strengths of AmO are smaller than those of PuO. The phonon
dispersion curves of AmO are calculated and the heat capacities as well
as lattice expansion curve are subsequently determined. The lattice thermal
conductance of AmO is further evaluated and compared with attainable
experiments. Our present work integrally reveals various physical properties of
AmO and can be referenced for technological applications of AmO
based materials.Comment: 23 pages, 8 figure
Hierarchical quantum master equation with semiclassical Drude dissipation
We propose a nonperturbative quantum dissipation theory, in term of
hierarchical quantum master equation. It may be used with a great degree of
confidence to various dynamics systems in condensed phases. The theoretical
development is rooted in an improved semiclassical treatment of Drude bath,
beyond the conventional high temperature approximations. It leads to the new
theory a simple modification but important improvement over the conventional
stochastic Liouville equation theory, without extra numerical cost. Its broad
range of validity and applicability is extensively demonstrated with two--level
electron transfer model systems, where the new theory can be considered as the
modified Zusman equation. We also present a criterion, which depends only on
the system--bath coupling strength, characteristic bath memory time, and
temperature, to estimate the performance of the hierarchical quantum master
equation.Comment: 10 pages, 8 figures, submitted to J. Chem. Phys. on 2009-08-0
Constraining the Skyrme effective interactions and the neutron skin thickness of nuclei using isospin diffusion data from heavy ion collisions
Recent analysis of the isospin diffusion data from heavy-ion collisions based
on an isospin- and momentum-dependent transport model with in-medium
nucleon-nucleon cross sections has led to the extraction of a value of MeV for the slope of the nuclear symmetry energy at saturation density.
This imposes stringent constraints on both the parameters in the Skyrme
effective interactions and the neutron skin thickness of heavy nuclei. Among
the 21 sets of Skyrme interactions commonly used in nuclear structure studies,
the 4 sets SIV, SV, G, and R are found to give values
that are consistent with the extracted one. Further study on the correlations
between the thickness of the neutron skin in finite nuclei and the nuclear
matter symmetry energy in the Skyrme Hartree-Fock approach leads to predicted
thickness of the neutron skin of fm for Pb, fm for Sn, and fm for Sn.Comment: 10 pages, 4 figures, 1 Table, Talk given at 1) International
Conference on Nuclear Structure Physics, Shanghai, 12-17 June, 2006; 2) 11th
China National Nuclear Structure Physics Conference, Changchun, Jilin, 13-18
July, 200
Ideal strengths and bonding properties of PuO2 under tension
We perform a first-principles computational tensile test on PuO based
on density-functional theory within local density approximation (LDA)+\emph{U}
formalism to investigate its structural, mechanical, magnetic, and intrinsic
bonding properties in the four representative directions: [001], [100], [110],
and [111]. The stress-strain relations show that the ideal tensile strengths in
the four directions are 81.2, 80.5, 28.3, and 16.8 GPa at strains of 0.36,
0.36, 0.22, and 0.18, respectively. The [001] and [100] directions are
prominently stronger than other two directions since that more PuO bonds
participate in the pulling process. Through charge and density of states
analysis along the [001] direction, we find that the strong mixed
ionic/covalent character of PuO bond is weakened by tensile strain and
PuO will exhibit an insulator-to-metal transition after tensile stress
exceeds about 79 GPa.Comment: 11 pages, 6 figure
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