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Foreign Aid: a Tool to Escape the Conflict Trap?
No full textIn developing countries of the Global South, civil conflicts pose a significant hindrance to the
process of development. The risk of a civil conflict recurring in these countries within ten years
after the end of a conflict is high, creating a conflict trap that perpetuates economic underdevel-
opment. This study investigates the relationship between the likelihood of a conflict recurrence
and the level of foreign aid. The findings suggest that higher levels of foreign aid after the end of
a conflict are positively associated with the likelihood of a conflict recurrence. However, higher
foreign aid in a given year is associated with a lower likelihood of a conflict recurrence in the
following year. The decomposition of foreign aid data by foreign aid donor shows that this rela-
tionship only applies to foreign aid from multilateral organizations such as the World Bank and
the IMF. While there are indications that a country’s level of democratization may influence the
relationship between foreign aid and conflict recurrence, there is no evidence to suggest that the
human rights situation has any influence on this relationship
An Efficient 3D Mathematical Model to Predict Structural Dynamics and Chatter in Cold Rolling Mills
No full textThe research described in this dissertation aims to provide a highly efficient predictive
computational tool to improve the dimensional quality of cold rolled metal strip, particularly for
high-value, thin specialty alloys. The corresponding objectives of this work are to (1) understand
the transfer of high-fidelity roll grinding errors that may generate complex geometric defects on
the strip, and to investigate a novel method for correction of such defects; and (2) develop a
highly efficient 3D dynamic predictive model for the time-history of mill and strip transient
behavior, including highly damaging chatter vibrations. First, a novel approach that can
potentially correct for high-fidelity geometric defects in cold rolled strip is proposed. High-
fidelity flatness defects in thin cold-rolled strip that arise from highly localized thickness strain
variations present an ongoing challenge to the metals industry. A primary cause of such defects,
based on rolling practice, but for which the effects have not been rigorously investigated, may be
the transfer of localized diameter deviations from the work rolls that arise from roll grinding
errors due to grinding performance inaccuracies. The proposed research addresses the effects of
high-fidelity roll diameter deviation transfer to the strip, as well as their correction. Parametric
case studies are first undertaken using a 4-high mill to investigate the influences that roll
diameter, strip reduction, strip width, and material strength have on the 3D transfer of high-
fidelity work roll diameter deviations to the rolled sheet. The studies are conducted with an
efficient 3D mathematical roll-stack model that predicts the associated high-fidelity strip
thickness profile deviations using the simplified-mixed finite element method (SM-FEM).
Reduction deviations, which strongly correlate to strip flatness/shape defects, are first quantified
and analyzed to understand the transfer characteristics of localized work-roll grinding deviations
relative to benchmarked perfectly smooth work rolls. Results of the study reveal that the high-
fidelity transfer depends not only on the specific roll grinding deviation amplitude and mill
loading, but also on the location of the roll diameter deviations along the roll face length due to
non-negligible 3D bulk roll-stack deformations, as well as the effective stiffness ratio between
the work roll and the strip. The inability of conventional flatness control devices to correct for
high-fidelity roll diameter deviations is also demonstrated. Based on this work, suggested is a
novel corrective approach to identify customized work roll grinding profiles that are tailored to
strip with specific pre-existing high-fidelity defect patterns generated in previous rolling passes.
Using the described SM-FEM modeling technique, high-fidelity “corrective” roll diameter
profiles could eventually be applied in-situ during rolling, whereby the profiles are “engineered”
to account for the predicted 3D mill deflections, contact force distributions, and coupled
micro/macro scale deformation mechanics. Following investigation of the SM-FEM formulation
to high-fidelity static problems involving the transfer of roll grinding error to the strip, the SM-
FEM method is adapted to create a general purpose 3D structural dynamics model capable of
predicting the transient behavior of the mill components and strip thickness profile geometry.
Over the last three decades, computational models have been developed and employed in effort
to understand dynamic disturbances in the rolling operation. Such disturbances can potentially
lead to self-excitation (chatter vibrations) and result in significant gauge variations in the exit
strip, as well as strip rupture and/or damage to the mill in extreme cases. Numerous challenges
exist, however, in adequately modeling the 3D dynamic behavior. For instance, highly coupled
relationships exist between several rolling process parameters, including the rolling force/torque,
strip entry/exit tensions, rolling speed, roll gap profile, friction, neutral point, etc. In addition,
both “hard” and “soft” nonlinearities are present, including continuous changes in the roll/strip
contact conditions, elastic-plastic deformation of the strip, and nonlinear elastic flattening the
rolls. These factors make it very difficult to effectively and efficiently model the rolling
operation even under a quasi-static (or steady-state) assumption. Moreover, the existing models
that account for structural dynamics of the rolling process exploit many simplifications, such as
modeling the mill structure as linear lumped parameter system, and symmetry in the motions of
rolls, among other assumptions. Even with these assumptions, the current state-of-the-art models
are generally not capable of accommodating conventional strip thickness profile/flatness control
mechanisms, such as roll bending, roll shifting, or non-uniform machined roll profiles, which
severely restricts the flexibility/applicability to accommodate complex mill structures. A 3D
general purpose dynamic model that can incorporate profile/flatness control mechanisms in
addition to complex mill configurations (like 12-high or 20-high cluster mills) can provide
significant new insights into rolling dynamics and chatter investigations. Accordingly, the
presented research combines the static SM-FEM mathematical formulation with a Newmark-
Beta time integration technique to develop a highly-efficient, stable, high-fidelity global-stiffness
based transient structural dynamics model. Case studies are carried out to demonstrate the
features and capabilities of the presented model in addressing the aforementioned research gaps
and challenges. Based on the results, the presented structural dynamics model is able to
efficiently capture time histories due to discrete disturbances on both vertical and cluster-type
mill configurations. For chatter investigation, however, an appropriate roll-bite model to capture
the relationships among the coupled rolling process parameters that influence the roll-bite
contact mechanics is required to be coupled to accommodate the real time interactions between
the structural dynamics and roll-bite mechanics. In addition to the aforementioned assumptions
and simplifications in mill structural dynamic modeling, presence of both hard, and soft non-
linearities as well as material non-linearities in the roll bite contact mechanics has led to
exclusive use of linearized relationship in the current state-of-the-art chatter models, while 3D
chatter models are non-existent in the literature. Accordingly, following the development of
general-purpose 3D dynamic model, the dynamic simplified mixed-finite element method (D-
SM-FEM) is coupled with a roll-bite process model. A critical part in replicating the dynamic
interaction between the rolling process and the mill structural dynamics in this work relates to
real-time variations in the “working point” or “operating point” relationship between specific
rolling force and the plastic strain of the rolled strip which changes according to perturbations in
the roll gap, position of entry/exit plane, entry/exit velocity, and tensions. These variations in the
working point are incorporated in the presented chatter model via the concept of a “dynamic strip
modulus” based on the secant (or tangent) relationship between the specific rolling force and
plastic strain at the working point, but where the strip modulus is updated at every time-step.
Case studies are presented using 4-high mill with aim to demonstrate the ability of the presented
3D chatter model to address the lack of available chatter models in literature employing 3D bulk
body deformation effects, and to address some of the limitations identified above. The
capabilities of the model to predict the stability, or dynamic instability is also illustrated with
accompanying 3D plots showing the true mode shapes. Case studies are also undertaken to
demonstrate the effect of asymmetric (with varying lower housing stiffness) mill stand
assumptions. The results reveal interesting phase relationships not elucidated in previous
research, as well as detailed effects from the 3D modeling on the strip profile and shape/flatness
The Cognitive, Neurophysiologic, and Connectivity Effects of Multiple Sclerosis on Information Processing Speed and Memory
No full textMultiple sclerosis (MS) is an autoimmune disease of the central nervous system that can negatively
impact both motor and cognitive ability. About 70% of MS patients experience cognitive
impairment with reduced information processing speed (IPS) and memory decrements as the most
prevalent. IPS, defined as the amount of time needed to process elementary cognitive operations,
might be especially critical for cognitive functions that require the coordination of widely
distributed brain regions. Current models of working memory posit that it is a widely distributed
system involving persistent neural activity in various brain regions during memory delays. In my
dissertation, I first hypothesize that reduced IPS in MS disrupts the timely coorination needed
between the brain regions associated with working memory function and that this reduced IPS
underlies memory declines in MS patients. Furthermore, MS-related neuroinflammation might
lead to a strain on oxygen resource availability that can cause neurologic and neurocognitive
deficits. Therefore, my second hypothesis is that MS-related metabolic resource constraints
impede the ability of neurons to fire persistently and are associated with MS-related reductions in
IPS performance. Additionally, timely coordination of interregional connectivity is critical for IPS
and memory function. Therefore, dysfunction to the persistent neural activity within a region could
affect interregional connectivity. Therefore, my third hypothesis is that, due to altered metabolic
resource availability, connectivity between brain regions involved in cognitive function is
adversely affected. To test these hypotheses, MS and healthy control (HC) participants underwent
extensive neuropsychological evaluation and then advanced dual-echo functional magnetic
resonance imaging (fMRI) to obtain measures of blood-oxygen-level-dependent (BOLD) signal,
cerebral blood flow, maximum blood-oxygen capacity (the factor M), and cerebral metabolic rate
of oxygen (CMRO2) while they performed an IPS task. Participants also underwent resting-state
fMRI and structural diffusion imaging to investigate functional and structural connectivity.
Neuropsychological evaluation results showed that MS-related variability in IPS explained
variability in verbal episodic and working memory ability in MS patients even after controlling for
motor, visual, disease and demographic variables, and after using a composite variable to attenuate
task-specific variability. Neurophysiologic results showed that levels of metabolism in the
dorsolateral prefrontal cortex (dlPFC), and area known to be associated with IPS, significantly
predicted IPS ability in MS patients. Connectivity analysis results showed that MS-related changes
in prefrontal metabolism that significantly explained IPS ability were explained by MS-related
changes in resting-state connectivity from the cerebellum. Furthermore, disrupted functional and
structural connectivity between the cerebellum and parahippocampal gyri was associated with
verbal learning and episodic memory impairment. These results suggest that MS-related metabolic
disruptions in an executive area, the dlPFC, are associated with reduced IPS and connectivity
changes in MS, and that this disruption has negative effects on episodic and working memory
Perovskite Nanophotonic Devices and Topological Photonic Devices
No full textSolution processed organic-inorganic lead halide perovskites have rapidly emerged as a promising
gain material for development of the next generation of nanophotonic device ranging from
nanolasers, nano LEDs, and solar cells. Here, continuous-wave operation of MAPbI3 perovskite
nanolaser is achieved at room temperature with ultralow threshold, which is enabled by thermal
nanoimprint lithography that directly patterns perovskite into laser cavities and improves
perovskite’s emission characteristics. In the meantime, hyperbolic metamaterials and metasurfaces
(HMMs), a special class of anisotropic media, has drawn tremendous research attention recently
owing to its remarkable ability to manipulate electromagnetic waves at the subwavelength scale.
However, the inevitable metal loss hinders the development of HMMs. Here, a luminescent
perovskite HMM operating at 760 nm is achieved using alternating layers of MAPbI3 perovskite
and Au, where the loss in Au is maximally compensated by MAPbI3. Simultaneously, topological
photonics is a rapidly emerging field, aiming to apply topological physics in photonic systems.
The topological protected photonic edge mode is immune to the system disorders and
imperfections. However, all photonic edge modes reported in the pioneering works are from lattice
systems. Here, a topological band theory is developed in continuous HMM through a nonHermitian Hamiltonian formulated Maxwell’s equations. Two types of edge mode can be induced
by including gyromagnetic and chiral effect in HMM and can be numerically observed. Finally, a
topological micro ring laser array that possesses edge mode lasing is designed and experimentally
achieved on the III-V semiconductor platform
Sustainability Centered Photoresin Design for 3D Printing Using Dynamic Covalent Chemistry
No full textContemporary society is and will be facing from now on, worrying environmental challenges that
reflect the actions from current and previous generations with a lesser sense of environmental
awareness. As science and technology advance, it is our responsibility to learn and do better to
ensure we stop and prevent future damage to the earth, carrying on sustainability principles into
every step we take forward. The design of new materials is especially important in today’s state of
the world because physical tangible materials like plastic, represent the most visibly detrimental
callings for action. Numerous sustainable alternatives from feedstocks to end-of-life management
have been explored over the last couple of decades, which have paved the way for more eco-
conscious design of plastics. Abiding by these sustainability centered strategies will avoid
worsening the already alarming plastic crisis and will be a great starting point for future
generations to move forward. As society develops and advances technologically, the design of new
polymeric materials requires the consideration for compatibility with the latest technological
developments, to make sure that these new materials could be candidates to replace existing non
sustainable ones. In plastic manufacturing, 3D printing technologies show great promise for
adoption as the default methods in the near future, based on their versatility, resolution, on demand
production and sustainability attributes. 3D printing allows rapid prototyping, creation of complex
parts, diverse applications, and democratization of manufacturing. In terms of sustainability, 3D-
printing’s on demand production capabilities, significantly reduce the need for transportation,
storage and waiting time, which overall reduces the carbon footprint of the final products. There
are some challenges for ensuring that the products from 3D printing technologies do not represent
a threat to the environment and these could be addressed through different actions in each step of
the process. Selection of renewable feedstocks obtained through sustainable processes is required
since the beginning design stages. Compatibility with the best resolution 3D printing technologies
like vat photopolymerization 3D printing, will ensure the products perform to expectations,
reducing the possibility of creating waste before their use. Vat photopolymerization 3D printing
like stereolithography (SLA) or digital light projection (DLP), mostly produce thermosetting
polymers which usually lack the ability to be recycled, and due to their thermal and chemical
resistance, they could represent a threat to the environment after their end-of-life if not correctly
disposed. To overcome this challenge, efforts to create vat photopolymerization printed
thermosets, are to be accompanied with a sustainable end-of-life disposal mechanism in mind.
Lately, disposal mechanisms like reprocessing, degrading and chemical recycling, have been made
possible through incorporating the use of dynamic covalent chemistry (DCC) in the synthetic
design. The research presented in this dissertation includes sustainability alternatives for every
step of the photo-resin design process, to create materials with low environmental impact,
compatible with DLP 3D printing.
Chapter 1 provides background information on the current environmental challenges associated
with plastics, as well as literature examples on how DCC has endowed 3D printed materials with
smart properties and mechanical performance that make them competitive, as well as disposal
possibilities to handle the materials at their end-of-life without representing a threat to the
environment.
Chapter 2 describes the design of five bio-based resins for DLP printing with self-healing
capabilities through the use of DCC. Transimination exchange reactions were chosen as the
dynamic reactions based on their excellent performance without requiring the addition of a
catalyst. These five resins possess bio-based content, are DLP printable, show varied mechanical
performances, have self-healing and reprocessability capabilities.
Chapter 3 describes the design of three completely bio-based photoresins using monomers derived
from lignin, and a crosslinker with beta-hydroxy moieties that allows transesterification reactions
to occur with assistance of a catalyst. Through dynamic transesterification reactions the resulting
DLP printed thermosets exhibit self-healing and one of the formulations can be readily reprocessed
with above 70% recovery of the mechanical performance. A post processing annealing step,
improves the mechanical strength of the materials, increasing the competitiveness of these bio-
based materials with conventional oil derived alternatives.
Chapter 4 describes the development of resins with 70 wt % bio-based content using lignin,
vanillin, and soybean oil. Methacrylated lignin has multiple hydroxy moieties that can be activated
with the use of a catalyst to perform transesterification exchanges. These dynamic behaviors
allowed the thermosets to self-heal and be reprocessed lowering their environmental impact.
Chapter 5 includes the design of two resin formulations polymerized through thiol-ene chemistry,
which enables degradation and chemical recyclability of the resulting thermosets.
These two thermosets were synthesized with bio-based feedstocks and posses imine moieties
capable of performing transamination reactions for self-healing behaviors.
This research aims to describe sustainable alternatives for every step of the process of designing
new polymeric materials, competitive through their smart properties, mechanical performance and
compatibility with DLP 3D printing
The Relationship Between Age, Cognitive Performance, and the Neural Correlates of Episodic Memory Encoding and Retrieval
No full textCognitive aging is associated with a disproportionate decline in episodic memory, the ability to
recollect contextual details of previously experienced events. Understanding the mechanisms
which underlie age-related episodic memory decline is a critical precursor to developing
interventions aimed at ameliorating memory deficits in healthy and pathological aging.
Considerable empirical evidence suggests that age-related episodic memory deficits arise from
numerous factors which differentially impact multiple neural processes and brain regions. The
present work focuses on examining some contributors which have been proposed under this
framework. Study 1 investigates age-related neural dedifferentiation, a phenomenon characterized
by age-related reductions in the neural selectivity of category-selective cortical regions. Our
analyses reveal robust age effects on neural differentiation for scene, but not for face stimuli,
adding to prior evidence indicating that age-related neural dedifferentiation is not a ubiquitous
phenomenon. Study 1 also reveals that the strength of neural differentiation during encoding is
predictive of subsequent memory performance independently of age. The work in Study 1 is
complemented by Study 4 in which neural dedifferentiation is operationalized at the level of
individual exemplars (as opposed to stimulus categories). To examine item-level neural
differentiation, we framed our analyses in terms of age differences in repetition suppression
effects, which revealed null effects of age. Collectively, Studies 1 and 4 highlighting the functional
significance of age-related neural dedifferentiation and emphasize the urgent need to advance our
understanding of the factors that lead to age differences in neural selectivity and specificity.
Moving on to Study 2, the work described therein examines age differences in retrieval gating, the
ability to regulate the retrieval of mnemonic information according to behavioral goals. Study 2
provides the first evidence that older adults do not engage in retrieval gating, indicating that
episodic memory decline may arise as consequence of a decline in the engagement of goal-
dependent retrieval strategies. Lastly, Study 3 reveals novel evidence for age differences in the
retrieval-related anterior shift, the phenomenon whereby the peak neural activity at retrieval occurs
in more anterior portions of single cortical regions relative to encoding. Our analyses show that
the shift is greater in older than younger adults, and that greater shift is associated with worse
memory performance independently of age. In line with prior empirical work proposing a posterior
(perceptual) to anterior (conceptual) gradient in the brain, these findings indicate that the age-
related increase in anterior shift may be reflective of an increased reliance on gist-based low-
fidelity retrieval in older age. Taken together, the studies comprising this dissertation enhance our
understanding of the behavioral and neural correlates of cognitive aging and advance the collective
knowledge in the field cognitive neuroscience of age-related episodic memory decline
Mild Methods for Alkyl Radical Generation and Their Translation to Radiochemistry for Molecular Imaging Probe Development
No full textThis thesis describes the development of mild methodologies toward alkyl radical formation and
their application to positron emission tomography (PET) imaging probe development. The first
transition metal- and light-free auxiliary enabled remote functionalization of unactivated aliphatic
alcohols was developed. This protocol enabled the selective activation of inert tertiary, secondary,
and even primary CH bonds of primary, secondary, and tertiary alcohols toward β-,
- and
-
diazenes. Subsequent hydrogenation afforded the corresponding aminoalcohols in good to
excellent yields. Aerobic oxidation of secondary diazenes yielded sterically bulky 1,3-
hydroxyketones in good yields. Next, the alkyl Heck-type reaction of activated and unactivated
tertiary alkyl halides was developed, building on previous work on the photoinduced palladium-
catalyzed exogenous photosensitizer- and oxidant-free alkyl Heck-type reaction of primary and
secondary alkyl halides with vinyl arenes and heteroarenes. The method featured a broad
functional group tolerance toward valuable synthons bearing quaternary centers at the allylic
position in good to excellent yields. When phenyl vinyl ether was used as a coupling partner, the
reaction proceeded by radical-polar crossover (RPC) pathway to afford double addition mixed
acetal products. This protocol was integrated with rapid, Markovnikov selective iodofluorination
of alkenes in the first one-pot formal alkenylfluorination of alkenes as a modular prosthetic group
(PG) toolkit for PET imaging probe development. A new class of aliphatic prosthetic groups was
synthesized en route to valuable organofluorine compounds. The methodology was translated to
radiochemistry in generally good radiochemical yields, and an automated protocol for PG-
synthesis was developed. The RPC mechanism was expanded to afford
-fluoroethers, in the first
photoinduced Pd(0/I/II)-catalyzed direct alkyl(radio)fluorination of electron rich alkenes
Strains, Psychological Strains, and Sexual Assault Perpetration: Investigating (Psychologically-informed) General Strain Theory
No full textAlthough backed up by a plethora of research evidencing its good predictive ability when it comes
to crime commission, General Strain Theory (GST) has never really been applied to sex crimes.
Although GST traditionally emphasizes ecological strains, previous research has evidenced the
saliency of various personality traits in sex offenders, including those related to sex offenders’
psyche and decision-making (e.g., Petruccelli et al., 2017). Furthermore, it has previously been
demonstrated that multidisciplinary theoretical integration, through the incorporation of
dispositional factors, can be beneficial to GST (Stogner, 2011, 2014). Using cross-sectional data
from the ACHA-NCHA for the Fall 2015 through 2018 academic semesters, this dissertation
investigates the adequacy of GST for the study of sexual crimes and compares its fitness to that of
a revised, psychologically-informed version of GST. Results from this research support GST and
echo previous literature in that several strains emerged significantly associated with the odds of
sexual assault commission and the latter associations were significantly mediated by anger.
Incorporating measures of “psychological strains” (promiscuity, irresponsibility, and sexual
sensation-seeking) drastically increased the fitness of the model for sexual assault perpetration,
and one strain (i.e., promiscuity) emerged as significantly related to increased odds of sexual
assault perpetration. Implications for future research are discussed
Distributed Design of Strong Structurally Controllable and Maximally Robust Networks
No full textThe design of multiagent networks with certain properties is in general a difficult problem.
From a network control perspective, controllability and robustness are two important but
opposing properties. In this dissertation, we address the problem of designing networks
that are both structurally controllable and maximally robust. To achieve this objective,
we propose several network constructions that are strong structurally controllable, for given
network parameters the number of nodes N , leaders NL, and diameter D. To measure
controllability, we employ the zero-forcing process, and subsequently, maximize the number
of edges in the networks. We also evaluate network robustness using Kirchhoff index. To
validate our approach, we compare our network constructions with optimal clique chains and
perform numerical evaluations.
Furthermore, we present a set of graph grammars that enable the distributed construction
of these networks. Our work not only exploits the trade-off between controllability and
robustness but also provides an optimal graph structure under specific conditions, and a
near-optimal one for most cases
UltraEdit: an in-situ Design Environment for Ultrasound Haptization
No full textThe ultrasound display is a promising technology that enables users to feel haptic feedback in
virtual environments without the need for wearable devices, which is an opportunity to fully
incorporate the sense of touch into a virtual reality setting and greatly improve immersion.
However, the technology suffers from a lack of support in enabling users to create personalized
haptic feedback for objects without a significant amount of time and technical knowledge.
This work presents UltraEdit, an in-situ design environment to directly edit ultrasound
haptic sensations in VR through barehand interactions. Users edit haptic sensations as
tangible objects called blobs using their fingers to adjust or add touch feedback to 3D objects.
Users can utilize a variety of one and two-handed gestures to create, edit, copy, and apply
blobs directly to 3D objects, enabling them to effectively utilize a workspace of multiple
haptic sensations and provide a single virtual object with many different sensations. This
design environment is evaluated by conducting an exploratory user study with a combination
of haptic designers, expert VR developers, and novice VR developers, where the usability,
efficacy, and learnability of UltraEdit is assessed. Participants find UltraEdit easy to learn
and remember, enjoyable to interact with, and effective in haptizing virtual objects