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Understanding Proximal Multi-joint Coordination in Response to Transfemoral Amputation and Generalized End-limb Loading Using Neuromusculoskeletal Modeling
No full textLimb amputation and its adverse effects continue to pose significant public health problems in
the United States and abroad. In the US, there are approximately 500 amputations performed
every day. While this patient population continues to grow, currently-available prosthetic
technologies and clinical care do not consistently return patients to the quality of life these
individuals had pre-amputation. While many prior studies have focused on how the use of lower-
limb prostheses affect coordination of their ipsilateral and contralateral legs during gait, few seek
to quantify the upstream effects at joints that are proximal to the amputation and do so in a
systematic way that considers generalized (i.e., not task specific) end-limb loading. To better
understand the challenges faced by individuals with transfemoral amputation, we designed a
series of in silico studies to first apply forces at the distal end of the residual limb of varying
magnitude and direction to compare how muscles that span the ipsilateral hip joint are recruited
to stabilize the limb. In this Aim and those that follow, neuromusculoskeletal simulations were
performed using two different models of limb amputation surgery (myodesis and myoplasty). In
the second Aim, we identified how transfemoral amputation and generalized end-limb loading
alter the joint reaction forces and moments of the lumbopelvic joint by simulating varying levels
of residual femur abduction and end-limb force. In the final Aim of this research, we quantify
how transfemoral amputation alters residual limb stability under varying end-limb forces.
Collectively, we show that how amputated muscles within the residual limb are surgically
reconstructed and recruited differs from those of intact unaltered musculature and able-bodied
individuals. Our models suggest these muscles are less sensitive to end-limb force direction and
that significant co-contraction of agonist and antagonistic muscle groups is required to stabilize
the residual limb. We also suggest that myodesis amputation surgery can enhance the force
production of amputated muscle groups, relative to myoplasty surgery. However, negative
tradeoffs associated with frontal-plane limb stability and an overall profile of limb stability that
is asymmetric arise with such musculotendon tension-preserving procedures. Regarding
mechanical loading of the lower back, this work highlights how posterior and medially-directed
end-limb forces, similar to those that would occur during the loading response phase of gait,
causes lumbopelvic joint reaction forces to increase in an abnormal manner for individuals with
transfemoral amputation, and that poor muscle anchoring (as studied by increasing residual
femur abduction) exacerbate these issues. By using computerized neuromusculoskeletal models
and dynamic simulations to systematically and thoroughly explore the internal biomechanical
mechanisms at work in individuals with transfemoral amputation, these studies offer an avenue
to inform surgical planning, prosthetic intervention and rehabilitation strategies for this patient
population
An Internet of Things Platform for Improved Water Management Using Underground Soil Moisture Sensing
No full textEfficient use of water resources is becoming of paramount importance in agriculture due to
their scarcity and less predictable availability impacted by climate change. Profitability of
traditional farming methods to meet the increasing population demand for food production
has been negatively affected, thus requiring efficient irrigation systems and water management practices through technology. In this thesis, a cost-effective Internet of Things - IoT
platform that incorporates underground soil moisture sensing is presented with the aim of
increasing the penetration of applied technologies in the farming market. The platform features a Sub-1 GHz IEEE802.15.4g-based wireless sensor network concentrator (WSNC) with
LTE backhaul which provides Internet connectivity in rural areas towards a cloud server.
The WSNC connects sensor nodes to the collector node over a wireless link following a star
topology network. The sensor node is enhanced with a helical antenna designed specifically
for underground operation along with a power amplifier to compensate signal attenuation in
the soil-air path to the WSNC. Based on the number of collectors and physical layers that
are supported, the implemented WSNC offers three configurations: Single Collector (SC),
Multi Collector (MC) and MC - Multi Rate (MR).
The SC-WSNC supports a total of 50 sensor nodes whereas the MC-WSNC can support up
to 200 devices by hosting several independent Wireless Sensor Networks (WSNs) operating
on a unique frequency channel. To improve the system performance, a load balancing algorithm and a sensor handover mechanism are developed for the MC-WSNC to uniformly
distribute the number of aggregated sensor nodes across the available collectors. The MR
capability added to the MC-WSNC and the sensor nodes dynamically optimizes the energy
consumption and radio link margin of the sensor nodes for improved battery lifetime and
connection reliability.
The SC-WSNC has been experimentally evaluated in terms of coverage range in aboveground and underground scenarios with a detailed end-to-end delay characterization using
state-of-art tools in every network segment. The results reveal the limitations of the system
in covering large farming areas due to both the high attenuation in the combined physical
media and the limited number of sensor nodes that can be attached to one collector. In
contrast, the MC-WSNC is evaluated using a test-bed consisting of up to four co-located
collectors and fifty sensor nodes. The performance evaluation is carried out under race conditions in the WSNs to emulate high dense networks with different network sizes and channel
gaps. The experimental results show that the MC-WSNC proportionally scales up the capacity of the network and reduces both the energy consumption and the packet error rate
of the sensor nodes. The MR feature - implemented as a physical layer switch at the sensor
nodes - further reduces the overall network power consumption and increases the network
throughput while at the same time accounts for varying radio link conditions
Fishing Line Based Twisted and Coiled Polymer (TCP) Muscles and Thermoelectric Coolers for Improved Frequency of Actuation
No full textThe combination of muscles, bones, cartilage, and ligaments that are essential for mobility can
result in different configurations of a musculoskeletal system design. The most used actuators for
robotic movement are tendon driven systems using DC-motor-based. Besides DC motors,
pneumatic artificial muscles are of interest for biologically inspired musculoskeletal systems due
to pneumatic muscles’ similarity to natural muscles in terms of length-load curves, their
compliance, rapid contraction, and the high power/weight ratio. Actuators such as the electric
motors and pneumatic artificial muscles used in robotics have their own drawbacks. Although
electric motors are energy efficient actuators, they require complex transmission systems, resulting
in limitations in terms of size and space. Above all, electric motors do not fit in the bio-inspired
design approach. On the other hand, pneumatic artificial muscles require a compressor to force a
gas into the actuators to create a pressure difference between the inside and the ambient
environment for actuation. This makes pneumatic artificial muscles bulky in an overall system.
We investigate twisted and coiled polymer (TCP) artificial muscles for actuation of limb
movements using fishing line and a resistive heater nichrome (TCPFL
NR). The actuation by these
muscles is due to their contraction and expansion while exposed to different temperatures. TCP
muscles have been deeply researched in the University of Texas at Dallas and have been
implemented on multiple robotic arms. One of the major drawbacks observed after using these
muscles is the time it takes to move back to its initial length after actuation. Hence a method of
cooling is required to increase the rate of cooling such that the muscles take shorter time to get
back to their initial length. This thesis proposes the use of Peltier cooling mechanism that should
be employed during the contraction and extension of TCP muscles. The addition of a Peltier
module decreases the time it takes for the muscle to expand back to its original length. Currently,
for a typical TCP muscle of diameter 3 mm, the muscles are only subjected to natural convection
for cooling and takes about 40 seconds to cool down for 10 seconds actuation stimuli. Due to this,
the robotic fingers, attached to the TCP muscles, also take 40 seconds to retract back to their initial
length. Current research focuses on the improvement of TCP muscles as actuators for use in robots.
The primary area of improvement would be the actuation frequency of the artificial muscles to
ensure realistic applications of TCPFL
Toward Accurate Timing Analysis of Transistor-level Programmable Fabric
No full textEver since the transistor was invented in 1947, state-of-art semiconductors are powering up
modern life. They’re the backbone of smartphones, PCs, and many other devices. In addition to those traditional applications, recent technology innovations, including the artificial-
intelligence (AI) applications, Internet of Things, blockchain technology and automotive
driving, have rendered the unshakable importance of the state-of-art semiconductor. According to a report from Mckinsey on Semiconductors, in 2017 alone [1], the semiconductor
industry generated $97 billion in economic profit. The semiconductor industry has also
evolved over the past few decades to produce chips in increasingly advanced technologies.
The chip design methodology has also advanced along with the continued scaling of the
submicron Very Large Scale Integrated Circuits (VLSI). The sophisticated VLSI design flow
includes many precise steps. Those steps are system specification, architectural design,
functional design, logic design, circuit design, physical design, fabrication, packaging, and
testing. Among the numerous steps, timing analysis plays an eminent role in verifying the
timing perspective of the designed digital circuits. Timing analysis is used to verify whether
a digital circuit can operate at a certain speed. Nowadays, Static Timing Analysis (STA) is
the most widely used technique as it is efficient and provides a complete verification of all
timing paths.
Transistor-level programmable fabrics have received interest recently as more compact embedded field-programmable gate arrays (eFPGAs) for hardware obfuscation, in which a crucial part of the design is implemented in the eFPGA and the rest of the design is implemented
as an ASIC. However, state-of-the-art static timing analysis (STA) tools are developed either
for ASICs or LUT based FPGAs and do not support the new architecture. In this work,
we propose an instance-based characterization solution which enables the use of electronic
design automation (EDA) tools such as PrimeTime from Synopsys for static timing analysis
for transistor-level programmable fabrics. Such fabrics have one or more pass transistors in
the interconnect for each net. Pass transistors cannot be handled accurately enough in the
SPEF (Standard Parasitic Exchange Format) for a cell instance. Furthermore, logic gates
(or cells) for such fabrics often have a separate input to the pMOS pull-up network and the
nMOS pull-down network. Dual inputs in this manner cannot be handled accurately enough
since conventional methods have to take the longest delay among the inputs, which often
overestimates the downstream delay.
To address these limitations, we individually characterize each cell instance in a transistor-
level programmable fabric, from predecessor cell instance output to characterized cell instance output, including all parasitics, thereby circumventing the need to handle parasitics
during STA. Experimental results corroborate that the proposed instance-based characterization is very accurate
Symmetries of Einstein’s Equations in Vacuum and Their Geodesics
No full textThis thesis explores symmetries of vacuum Einstein equations that are static and at least
axially symmetric, i.e., Ricci-flat Lorentzian geometries that admit a timelike Killing vector
field and a closed spacelike Killing vector field among their isometries. We study symmetries of the geodesics in these spacetimes as well as symmetries of the system of Einstein
equations describing such spacetimes. Geodesics in three dimensions have symmetries and
associated conserved quantities absent in four and higher dimensions. We employ the socalled direct method for computing the conserved quantities. For the static axisymmetric
system in vacuum, we found all symmetries of the system which enabled us to explain why
one cannot obtain algebraic prescriptions for generating new solutions from old ones beyond
those already known. Symmetries of the geodesics in spherical symmetry show that there
is no general connection between cosmological constant and projective equivalence and that
one can find an appropriate coordinate system where the effect of cosmological constant
disappears from the bending angle, unlike in the static coordinates
Leveling Up: Measuring the Effects of Election Laws and Institutions on Voter Participation
No full textWhat effect do election laws and administration have on voter turnout? How do we measure
voter turnout? This dissertation attempts to answer these questions by measuring the effect of
various election laws and policies on voter turnout at three distinct levels of measurement. In
Chapter 2, an original measure which captures the effects of state election laws is developed and
its effect on turnout is tested at statewide level. In Chapter 3, a novel dataset of substate level
turnout is developed at the county level. The resulting dataset is tested to see if the effects of
election laws on turnout are consistent at both the statewide and county levels. In Chapter 4,
using voter registration records from Texas, the effects of convenience voting measures, such as
drive-through voting and 24-hour voting locations, are examined to see if their use increases the
likelihood of an individual voting. The results show that Harris County’s efforts to making
voting easier and safter increased turnout, especially among young voters
Bayesian Statistical Methods for Urinary Microbiome Data Analysis
No full textMicrobiome data is generated by high-throughput next-generation sequencing technology.
These data are typically characterized by zero inflation, overdispersion, high dimensionality,
sample heterogeneity, non-linearity, and compositionality. Three popular areas of interest
in microbiome research requiring statistical methods that can account for the characterizations of microbiome data include detecting differentially abundant taxa across phenotype
groups, identifying associations between the microbiome and covariates, and constructing
microbiome networks to characterize ecological associations of microbes. These three areas
are referred to as differential abundance analysis, integrative analysis, and network analysis,
respectively. Bayesian statistical methods can account for the uncertainty in model param-
eter estimation, provides posterior summaries that are easy to interpret, and can handle
small sample sizes unlike frequentist parametric statistical methods. Here, we present three
Bayesian statistical methods applied to urinary microbiome data of recurrent urinary tract
infections in postmenopausal women from a collaborative study between The University of
Texas at Dallas and The University of Texas Southwestern Medical Center. First, we present
our Bayesian Proportion Test to perform differential abundance analysis to determine if taxonomic functional data are significantly different between experimental groups. Second, we
present our Bayesian Correlation Test to conduct exploratory integrative analysis of associations between microbiome and clinical data. Last, we present our Bayesian stochastic block
model with a Markov random field prior that performs community detection using information from both the adjacency matrix and the taxonomic tree hierarchy. To the best of our
knowledge, current stochastic block models only incorporate the network information given
by the adjacency matrix and none of them incorporate information from the taxonomic tree
hierarchy. Thus, the inclusion of the taxonomic tree information is the novelty of our model
and we demonstrate its superior performance to other commonly used methods. We also
show that the inclusion of the taxonomic tree information does not affect model performance
even in the case when this information is not relevant for performing community detection
Liminal Bodies: the Grand Narratives of Myth, Magic, Religion, and Science in the Evolution of Speculative Literature
No full textWhich hybrid forms have historically divided societies and why is this stratification dangerous?
What defines which liminal bodies are met with hostility and social rejection and which are met
with adulation and reverence? How can the defamiliarization present in the liminal forms
integral to the thematic functioning of science fiction and fantasy texts be used as a vehicle for
literalizing the expression of these social problems? Reconciling the false binaries of
religion/science, magic/religion, and hybrid/purebred exposes the artificiality of hierarchical
categorizations involving dominant and supplementary terms in sociopolitical consciousness. By
analyzing the operation of liminal bodies at the individual and social levels in works of
speculative fiction, the interconnections between myth, magic, religion, and science can be
examined without attaching a temporal precedent that legitimizes the institution of contemporary
science over magic for the fact that it is contingent upon objective, external methods of
validation. Science fiction explores the concepts of myth, magic, religion, and science in tandem
through its multifaceted rendition of how hybrid bodies are simultaneously loathed as "Other"
and revered as liminal in a way that makes them both dangerous but necessary for individual and
social evolution. By dissecting the destructive and generative powers of liminality, science
fiction literature reveals that the desire to use magic and/or science to establish order and contain
bodies that exist in more than one literal or figurative categorical designation inevitably leads to
chaos
A First Principles Approach to Closing the “10-100 eV GAP” for Electron Thermalization in Wurtzite GaN
No full textSince the 1960s, when radiation-induced disruption of electronic devices in space was first
observed, the study of the effects of ionizing radiation on electronics has grown into an extensive
field of its own. The present work is concerned with accurately modelling the energy-loss
processes that control the thermalization of hot carriers (electrons and/or electron-hole pairs) that
are generated by high-energy radiation in wurtzite GaN, using an ab initio approach. Current
physical models of the nuclear/particle physics community cover the high-energy range (kinetic
energies exceeding ~100 eV), and the electronic-device community has done extensive work in
the lower-energy range (below ~10 eV). However, the processes that control the energy losses and
thermalization of electrons and holes in the intermediate energy range of about 10-100 eV are
poorly known (the “10-100 eV gap”). The aim of this research is to close this gap. To this end,
Density Functional Theory (DFT) is utilized to obtain the band structure of GaN for bands reaching
energies above 100 eV. Furthermore, charge-carrier scattering rates for the major charge-carrier
interactions (phonon scattering, impact ionization, and plasmon emission) are calculated, using the
DFT results and first-order perturbation theory (Fermi’s Golden Rule). With this information, the
thermalization of electrons starting at 100 eV is simulated in a Monte Carlo code, allowing the
electrons to interact stochastically according to the calculated interaction rates and generate
electron-hole pairs as they go, which are also tracked in the simulation. Full thermalization of
electrons is complete within 1 ps, and that of holes is complete in approximately half the time.
Electrons lose 90% of their energy (90 eV) during the first few ~0.1 fs, due to rapid plasmon
emission and impact ionization at high energies. The remainder is lost more slowly as phonon
emission dominates at lower energies (below ~10 eV). During the thermalization, hot electrons
generate electron-hole pairs with an average energy of ~8.9 eV/pair (11-12 pairs per hot electron).
Additionally, upon full thermalization, the average electron displacement from its original position
is found to be on the order of 100 nm
What Lab Test Should I Perform Next for This Patient? Feature Acquisition of Subsets at Test-time With Tractable Models
No full textWe address a problem setting where given a history of examples with all features, the goal
is to predict the best subset of features to acquire for a new example that only has baseline
features. This problem is inspired by clinical settings, where some features such as demo-
graphics are cheaply and easily obtained, while others such as blood tests and MRIs may
be more costly, time-consuming, or invasive. We propose the Feature Acquisition of Subsets
at Test-time (FAST) algorithm, which uses a tractable probabilistic model during training
to efficiently compute the best subsets of past examples with all features (such as rigorously
tested patients from a clinical study), so it can learn to use only baseline features to predict
the single best subset of features to acquire for a new example during testing (such as using
demographics to predict the best lab test for a new patient entering a clinic). Motivated by
medical settings, we present the effectiveness of FAST on four real medical data sets