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Signal Processing Algorithms for Smartphone-Based Hearing Aid Platform; Applications and Clinical Testing
No full textDigital signal processing algorithms are widely utilized in hearing aid applications to im-
prove the quality of speech. The signal processing pipeline for speech involves several crucial
components that enhance hearing-impaired people’s listening. This thesis covers the devel-
opment of novel methods that can be used in the speech processing pipeline and clinical
testing. Each chapter of the dissertation focuses on the components of the speech process-
ing pipeline for smartphone-based hearing aid setup. The first algorithm, speech source
localization (SSL), which identifies the direction of the talker of interest using multiple mi-
crophones, is discussed. A speaker identification method is proposed as an assistive system
to the pipeline, and it can be used to boost the overall system’s performance. A clinical
testing system is developed to evaluate the new signal processing algorithms. An approach
is developed to use multiple microphones of iPhone simultaneously for real-time low-latency
audio applications. Real-time integration of several signal processing modules that appear in
digital hearing aids is developed as smartphone apps. Subjective evaluations are conducted
for the proposed methods to show noticeable improvements and compared with state of the
art methods. Additionally, the implementation of the proposed methods is explained on
smartphones and computers
Multiscale Methods for Fatigue and Dynamic Fracture Failure and High-performance Computing Implementation
No full textThis dissertation presents several multiscale methods for material failure and implementations on high-performance computing (HPC) platforms. The work is motivated by the
challenges in fully capturing the mechanics of failure using a single scale method. As such,
multiscale approaches that incorporate multiple temporal and spatial scales have been established. To address the high computational costs, efficient algorithms and their implementations on the HPC platform featuring many-core architectures have been developed.
Based on the topics being addressed, the dissertation is divided into two parts. First, a multiscale computational framework for high cycle fatigue (HCF) life prediction is established
by integrating the Extended Space-Time Finite Element Method (XTFEM) with multiscale
fatigue damage models. XTFEM is derived based on the time-discontinuous Galerkin approach, which is shown to be A-stable and high-order accurate. While the robustness of
XTFEM has been extensively demonstrated, the associated high computational cost remains a critical barrier for its practical applications. A novel hybrid iterative/direct solver
is proposed with a unique preconditioner based on Kronecker product decomposition of the
space-time stiffness matrix. XTFEM is further accelerated by utilizing HPC platforms featuring a hierarchy of distributed- and shared-memory parallelisms. A two-scale damage
model is coupled with XTFEM to capture nonlinear material behaviors under HCF loading
and accelerated by parallel computing using both CPUs and GPUs. Furthermore, an efficient
data-driven microstructure-based multiscale fatigue damage model is established by employing the Self-consistent Clustering Analysis, which is a reduced-order method derived from
Machine Learning. Robustness and efficiency of the framework are demonstrated through
benchmark problems. HCF simulations are conducted to quantify key effects due to mean
stress, multiaxial load conditions, and material microstructures.
In the second part, a concurrent multiscale method to dynamic fracture is established by
coupling Peridynamics (PD) with the classical Continuum Mechanics (CCM). PD is a novel
nonlocal generalization of CCM. It is governed by an integro-differential equation of motion,
which is free of spatial derivatives. This salient feature makes it attractive for problems
with spatial discontinuities such as cracks. However, it generally leads to a much higher
computational cost due to its nonlocality. There is a continuing interest to couple PD
with CCM to improve efficiency while preserving accuracy in critical regions. In this work,
Finite Element (FE) simulation is performed over the entire domain and coexists with a
local PD region where crack pre-exists or is expected to initiate. The coupling scheme
is accomplished by a bridging-scale projection between the two scales and a class of twoway nonlocal matching boundary conditions that eliminates spurious wave reflections at the
numerical interface and transmits waves from the FE domain to the PD region. An adaptive
scheme is established so that the PD region is dynamically relocated to track propagating
crack. Accuracy and efficiency of the proposed method are illustrated by wave propagation
examples. Its effectiveness and robustness in material failure simulation are demonstrated
by benchmark problems featuring brittle fracture.
Finally, conclusions are drawn from the research work presented and prospective future
developments of the established multiscale methods are provided
Bi-tensor Free Water Model With Positive Definite Diffusion Tensor and Fast Optimization
No full textDiffusion tensor imaging is a widely used imaging methodology to infer the microstructure of
brain tissues. When an image voxel contains partial volume of brain tissue with free water,
the traditional one tensor model is not appropriate. A bi-tensor free water elimination model
has been proposed to correct for the mixing effects. Moreover, recent studies have shown
that the free water volume derived from this model could be a biomarker for brain aging and
numerous brain disorders such as Parkinson’s and Alzheimer’s disease. However, the problem
of fitting this model is ill-posed without additional assumptions. Models by adding spatial
constraints or using data from multi-shell acquisition are proposed to stabilize the fitting,
but none of them restricts the diffusion tensor D to be positive definite, which is a necessary
condition. In this work, we formulate the bi-tensor model fitting as an optimization problem
over the space of symmetric positive definite matrices and show that the objective function
is a ratio of two geodesically convex functions. We also demonstrate by simulation that the
estimation may be highly biased with single-shell data in the presence of noise, so multi-shell
data are needed for the fitting of the bi-tensor free water elimination model. Inspired by the
Cholesky decomposition, we treat the diffusion tensor D as the product LLT where L is a
lower triangular matrix. The optimization is performed on L which guarantees the positive
definiteness of D. Our model are evaluated with both simulations and real human brain
data. Simulation results show that the model is computationally efficient and the two-shell
acquisition gives the best estimation
Essays in Revenue Management
No full textThis dissertation consists of three main chapters that develop new techniques for revenue
management and also demonstrate novel practical applications. These chapters focus on
developing pricing policies when prices of products are restricted to finite price points, analyzing the performance of state-independent policies in network revenue management, and
optimizing pricing and capacity decisions in railways.
In Chapter 2, we consider a stochastic multiproduct dynamic pricing problem in which the
prices of the products are restricted to discrete and finite sets. The focus of this work is to
analyze the deterministic variant of this problem (wherein customer-arrival rates are deterministic), which is a key subproblem whose solution can be used to build attractive policies
for the stochastic variant. We obtain efficient and effective solutions to the deterministic
problem, and prove worst-case optimality gaps for our solutions.
Chapter 3 studies the canonical network revenue management problems introduced in (Gallego and Van Ryzin, 1997) and (Liu and Van Ryzin, 2008). For all the state-independent
policies developed in the literature for these problems, we show that the optimality gaps
scale proportionally to ?k, where k is the scale of demand and supply.
In Chapter 4, we study revenue management in railways which distinguishes itself from
that in traditional sectors such as airline, hotel, and fashion retail. In railways, capacity is
substantially more flexible leading to a genuine necessity for the joint optimization of prices
and capacity. Discreteness in capacity and passengers traveling by standing in unreserved
coaches are other features unique to railways. Motivated by our work with a major railway
company in Japan, we analyze the problem of jointly optimizing pricing and capacity, and
develop four asymptotically optimal policies. We demonstrate the attractive performance
of our policies on test-suites of instances based on real-world operations of the high-speed
“Shinkansen” trains in Japan, and also develop rich insights based on our numerical results
Determining How FGF-10 Signaling and Mechanical Forces Are Integrated to Regulate Airway Branching Morphogenesis
No full textUnderstanding how the development of the lung airway occurs is a fundamental question that
can help improve understanding and treatment of congenital lung malformations, guide tissue
engineering strategies for building branched epithelial networks, and give insight into potentially
conserved mechanisms of development in other branched organs. In the mammalian lung, the
embryonic airway epithelium starts out as a simple, wishbone-shaped tube, which undergoes
multiple rounds of branching to form the bronchial tree in a process collectively known as
branching morphogenesis. This branched network is built by distinct branching modes: lateral
branching and bifurcations. New daughter branches form via lateral branching by emerging
along the length of the parent bronchi, and bifurcations cause the tip of a branch to split.
Throughout lung development, there is a complex network of signaling pathways present, but
fibroblast growth factor-10 (FGF-10) is thought to serve as the master regulator of airway
branching. FGF-10 is hypothesized to be expressed in a focal pattern within the pulmonary
mesenchyme, the tissue surrounding the epithelial airway, and provide a biochemical template
where a single source of growth factor stimulates the formation of an individual branch, possibly
through localized proliferation and chemotaxis. However, several recent studies have also
indicated mechanical forces can sculpt the branching of the lung airway. Here, we are interested
in studying the interplay between FGF-10 signaling and mechanical cues, including fluid
pressure and tissue stiffness, that initiate new epithelial branches. Taken together, these data will
help elucidate how biochemical and mechanical cues work in concert to give rise to the
macroscopic changes in tissue form that build branched epithelial networks
The Effect of Dual Task on Muscle Activity During Steady State and Gait Initiation
No full textBackground: Gait is considered a single task when done alone. Once an additional task as talking
is involved, it is referred to as dual task. This presents a cognitive load to the central nervous
system (CNS) affecting our motor control. This disturbance causes a reduction in our state of
balance, creating a higher opportunity for falls in aging adults. There are limited studies about
gait and dual task typically investigate the lower extremity muscle activation in gait initiation
(GI) or steady state (SS) gait with balance. Here, we are examining gait initiation and steady
state gait muscle activation patterns during dual task and single task gait. Purpose: To explore the
effects of dual task on healthy young adults on muscle activation in the biceps femoris (BF),
vastus lateralis (VL), tibialis anterior (TA), and gastrocnemius (GL). Method: 21 healthy young
adults performed single task walking and dual task walking on a 10-meter walkway. 10 VICON
motion capture cameras were used for collecting walking trial data to find steady state (foot
strikes and toe-offs). Force plates were used to find the deviation in the overground reaction to
identify gait initiation phases. Electromyography was used to collect muscle activity data.
Results: GI phases, mean muscle activation was reduced, not in Swing VL. Meanwhile, there
was only a difference between swing and stance for the offset phase. GI weight transition, mean
coactivation decreased. Although, there is a significant difference within Stance limb muscles.
SS stance phase, mean muscle activation decreased for BF, VL, and TA in dual task compared to
single task. In addition, BF, VL, TA, and GL showed significant differences. Conclusion: Under
the dual task condition GI Weight Transition, TA and BF (calves and hamstring muscles) can be
early predictors of poor balance relating back to older adults beginning their gait. In SS stance
phase, the VL and BF (quad and hamstring muscles) are more affected by dual task while
performing cyclic gait, which impedes on their stable balance control
Comparing Practical Approaches for Regression Models With Censored Covariates
No full textThe accelerated failure time (AFT) model is a useful linear model to estimate the effect of
some covariates on the failure time. Estimating the AFT model coefficients is challenging
when there are missing values in the covariate due to the limit of detection (LOD) or when
there are randomly censored covariates. Removing the subjects with the missing observations
in the complete-case (CC) analysis is the usual approach due to the simplicity and consistency
of the estimator. In small sample studies with a high missing proportion in more than one
covariate, dropping observations in the CC analysis may result in a non-convergence issue.
When the covariates are subject to the LOD, the missingness in the data is due to the
inability to measure the values beyond the LODs. The missing indicator (MDI) approach
could be a good alternative to the CC analysis. For small samples, the MDI is justified
in simulation studies for the AFT model with covariates subject to the lower, upper, and
interval LOD. In the linear and Cox models, the MDI outperforms other approaches too.
When the covariates are randomly censored, imputing the censored values could be useful in
parametric and semi-parametric AFT models. For the parametric AFT model, we proposed
a parametric imputation approach that takes advantage of the available information in the
censored covariate. The parametric imputation approach outperforms the CC analysis under
the correct parametric assumptions. In the absence of a correct parametric assumption and
under the semi-parametric AFT model, the MDI approach could be a good alternative to the
CC analysis that preserves the sample size. In application to the NCCTG lung cancer data,
the bias of the MDI estimator is less than that of the CC estimator when some covariates
are subject to artificial LOD
Beyond Nitrogen Limitation – Novel Mechanisms Regulating Glutamine Synthetase Expression in Escherichia coli and a Possible Alternative Pathway of Glutamine Synthesis
No full textThe expression of glnA (ammonia-assimilating glutamine synthetase) is high for
uropathogenic E. coli grown in urine. Because glnA is part of an operon that codes for
regulators of the nitrogen-regulated (Ntr) response, high glnA expression has been
interpreted to suggest nitrogen limitation, which is unexpected because of the high urinary
ammonia concentration which should suppress glnA expression. We present evidence
that glnA expression does not result from nitrogen limitation. First, in the presence of
ammonia, urea induced expression of glnA from the cAMP receptor protein (Crp)-
dependent glnAp1 promoter, which circumvents control from the nitrogen-regulated
glnAp2 promoter. This urea effect on glnA expression has not been previously described.
Second, the most abundant amino acids in urine inhibited GS activity, based on reversal
of the inhibition by glutamate and glutamine, and increased glnA expression. The
relevance of these inhibitory amino acids in natural environments has not been previously
demonstrated. Third, urea and the inhibitory amino acids did not induce other Ntr genes,
i.e., high glnA expression can be independent of other Ntr genes. Finally, the urea-
dependent induction did not result in GlnA synthesis because of a previously undescribed
translational control. We conclude that glnA expression in urea-containing environments
does not imply growth rate-limiting nitrogen restriction and is consistent with rapid growth
of uropathogenic E. coli.
ΔglnA mutants are glutamine auxotrophs, however, UTI89ΔglnA mutants, were
unexpectedly able to grow in a synthetic urine medium. This phenotype was conditional
and required the presence of both glutamate and ammonia, the substrates for glutamine
synthetase. Additionally, overexpression of proA, which is part of the proline biosynthesis
pathway, whose product catalyzes the formation of glutamate-5-semialdehyde, improved
growth. In contrast, an increase in proC expression, which directs pyrroline-5-carboxylate,
the cyclized form of glutamate-5-semialdehyde to proline, impaired growth. We describe
a possible alternate route of glutamine production in these mutants involving the enzymes
of proline synthesis and the substrates, glutamate and ammonia, via the intermediate
glutamate-5-semialdehyde. The pathway may be facilitated by a putative secondary
activity of the ProA enzyme – the reduction of a proposed imine intermediate to ultimately
form glutamine.
Members of the B2 clade of E. coli exhibit high glnA transcript levels in nitrogen-rich
glucose-tryptone medium. This increased expression did not translate to increased
protein production and enzyme activity as evidenced by low translation levels and
glutamine synthetase activity in these strains. Transcriptomic analysis revealed an
inverse correlation between phoB, a phosphate-dependent transcriptional regulator, and
glnA expression. Consistent with this, overexpression of phoB, reduced glnA transcription
levels. The effect was not a complete repression of glnA transcription. Additionally,
translational expression appeared to be stabilized upon phoB overexpression. Our
findings suggest a novel mechanism of glnA regulation at both the transcriptional and
translational levels that involves PhoB operating either directly or indirectly, and possibly
in combination with other unidentified factors
The Queer Future: Re-imagining Community in Queer Asian North American Literature, 1994–present
No full textMy dissertation examines how queer Asian diasporic authors reconstruct ideas about race, gender,
and sexuality in their literature and its film adaptations. Directly speaking to harassment that Asian
men and women have faced since the Coronavirus pandemic, my research has significant relevance
in the contemporary world. I argue that queer Asian writers transform various types of oppression
into storytelling to survive, and their philosophy of forming communities in literature – the key to
establishing a queer future – guides and is guided by their queer activism in the real world. My
analysis dialogues with the theories on queer futurity proposed by Lee Edelman and José Esteban
Muñoz and claims for a new definition of queer future. Whereas Edelman argues that queer folks
find no place in a reproductive future as a continuance of the present that is phobic to queer people,
Muñoz asserts that queer individuals should imagine a queer utopia where no one is discriminated
against. To join their conversation, I claim that the queer Asian diaspora empowers themselves by
telling the stories of those who suffer and reimagining a queer future advocating community
building, especially between queer Asians and Asian women. My project, by investigating the
transnational and postcolonial experience of queer Asian people, contributes to the research using
queer postcolonial critique.
I analyze the novels, memoirs, films, and LGBTQA+ activism of Shyam Selvadurai, Meredith
Talusan, Ocean Vuong, and Alexander Chee. Their artistic works all investigate how Asian bodies
are racialized and sexualized by multiple Western and Japanese colonial and imperial powers.
While reinterpreting the oppressive past, the queer Asian literature pictures a future that affirms
the value of the lives of people of color and queer folks. In each chapter of literary analysis,
therefore, I concentrate on how the queer Asian narrator revisits the family’s history,
reappropriates dominant Western and Eastern narratives to invent new storytelling, and envisions
a future depending on the collaboration of people of all races
Circularization of Tidal Disruption Streams for Schwarzschild Black Holes and Distribution of Orbital Inclinations of Tidally Disrupted Stars for Kerr Black Holes
No full textTidal Disruption Events (TDEs) occur when a star approaches sufficiently close to a supermassive black hole (SMBH) such that the tidal gravitational field of the SMBH overcomes the
self-gravity of the star, causing the star to rip apart. A stream of debris is formed from the
star’s remnants, which proceeds to orbit about the black hole. Relativistic apsidal precession
causes leading elements of the stream to collide with trailing elements, dissipating energy
on the way to circularization. We explore this circularization process for Schwarzschild, or
spherically symmetric, SMBHs, finding that the process is likely to take longer than was
first expected, and uncovering two distinct regimes of circularization. We then show work
on how TDE rates depend on orbital inclination for Kerr, or axisymmetric SMBHs