VictorJuiz/thesis huggingface dataset:
A Smart Gate Driver IC for Enhancement Mode GaN Power Transistor with Dead-time Correction
Keywords: Dead-time control
Device Modeling
GaN HEMT
Gate driver IC
Segmented drivers
SenseFET Clamping

Researchers in power electronics have been optimizing silicon devices with novel structures and gate drivers to keep up with the growing demands for power management. However, the improvement has slowed down as silicon power devices approach their theoretical limits. The emergence of GaN power devices provides an avenue to meet the continuing demands for performance improvement. GaN demonstrates material properties such as wider bandgap, higher electron mobility, and higher critical electrical field when compared to silicon. In particular, the AlGaN/GaN HEMTs exhibit great potential of lower on-resistance and smaller gate capacitance, leading to reduced conduction and switching losses. Their fast switching frequency (>10’s MHz) can further help to reduce the size of the passive components. Driving enhancement mode (E-mode) GaN HEMT is similar to driving silicon power MOSFETs but with additional challenges. The optimum gate driving voltage for most E-mode HEMTs is 6 V but the maximum allowed gate voltage is 7 V, leaving a narrow driving window. This restricts the maximum dν/dt and di/dt as little gate ringing can be tolerated. Consequentially, the active driving technique is often employed to suppress the gate ringing while maintaining the fast turn-on and turn-off transitions. Moreover, the fast switching requires precise dead-time control to avoid shoot-through current between the supply voltage and ground. However, excessively long dead-times lead to unwanted reverse conduction and additional power loss. Therefore, high precision detection circuits are important for dead-time correction as the load current changes. In this thesis, a reverse conduction sensing circuit that can accommodate the large voltage swings at the switching node is designed to track the presence of reverse conduction. The proposed segmented gate driver IC for E-mode GaN power output stages, fabricated using TSMC’s 0.18 µm Gen-2 process, is equipped with dead-time correction for improving system efficiency and highly configurable gate drivers for ringing suppression. The one-step correction mode can optimize the dead-times for both the turn-on and turn-off edges within one switching cycle for switching frequencies of up to 10 MHz with 0.32 ns precision. This allows the power converters to maintain optimal conversion efficiency over a wide output current range.
Mitigating the Impact of Chemical Transport Model Biases on Top-down CO and NOx Emission Estimates using Multi-species Chemical Data Assimilation
Keywords: 4D-Var
atmospheric OH
chemical transport model
CO and NOx emissions
data assimilation

Chemical transport models such as GEOS-Chem simulate tropospheric CO-HOx-NOx-O3 chemistry, which determines the oxidizing power of the atmosphere as well as the abundance of tropospheric CO, NO2, and O3. Inverse modelling analyses to estimate CO and NOx emissions traditionally rely only on observations of the species of interest, neglecting chemical biases in the models employed in the analyses. However, top-down estimates of CO and NOx emissions are sensitive to tropospheric OH and O3, respectively. In this thesis, two approaches were used to mitigate the model biases to estimate CO and NOx emission. First, we developed a multi-species data assimilation framework using the GEOS-Chem 4D-Var data assimilation system. Satellite observations of CO, NO2, O3, HCHO, and HNO3 were assimilated to optimize CO and NOx emissions, as well as O3, HCHO and HNO3 initial conditions. After the assimilation, improved chemical states were produced with CO, NO2, and O3 fields that were in closer agreement with independent observations. The multi-species DA also provided a means of indirectly constraining the tropospheric OH. The resulting global mean tropospheric OH was more consistent with independent empirically derived OH estimates. We also examined the a posteriori CO and NOx emissions. During the study period, my thesis showed the a priori CO emissions were underestimated and the a priori NOx emissions were overestimated in the northern extratropics. The emission estimates in Europe, the Amazon, and equatorial Africa were most sensitive to the multi-species information assimilated into GEOS-Chem. Second, we assessed the utility of a new OMI-minus-OSIRIS (OmO) NO2 retrieval product for improving North American NOx emission estimates. We assimilated the OmO data using the nested version of GEOS-Chem with assimilated O3 boundary conditions. The results suggested that both the anthropogenic and biomass burning sources were significantly overestimated in the a priori. The changes in the a posteriori NOx emissions inferred from the OmO data between 2008 and 2011 were found to be in better agreement with the changes in independent NO2 observations than those estimated from OMI data.
Preparation of Cylindrical Polyferrocenylsilane Block Copolymer Micelles as Nanocarriers for Cancer Drug Delivery
Keywords: drug delivery
micelle
polyferrocenylsilane
polymer
self-assembly

Polyferrocenylsilane (PFS)-containing diblock copolymers (BCP) undergo crystallization-driven self-assembly in selective solvents to form cylindrical micelles. Owing to the crystalline core-forming PFS block, micelle length can be extended by seeded growth in a controlled manner. Advances in the preparation of rod-like PFS BCP micelles have offered a novel platform of using elongated nanoparticles (NPs) as drug delivery vehicles in cancer research. Studies have shown that the physicochemical properties of the nanocarriers, including size, shape and surface chemistry play a key role in influencing their transport in biological systems. Recent results suggest that elongated NPs may exhibit advantageous properties compared to the spherical NPs. As such, investigating the effects of nanoparticle shape and size on cellular uptake and tumor penetration ability is critical to the development of optimized delivery vehicles. To meet the main objectives of this thesis, a PFS BCP with a corona block consisting of statistical polymer of oligo(ethyleneglycol methacrylate) and aminopropylmethacylamide (PFS27-b-PAPMA3-stat-POEGMA48) was synthesized. The BCP formed long cylindrical micelles of uniform width in ethanol. A series of rod-like micelles with lengths ranging from 80 to 2000 nm and narrow length distributions were generated by seeded growth. These micelles demonstrated the ability to carry various pendant groups and were stable in aqueous media up to 3 months. Studies in two human breast cancer cell lines showed the micelles have no potential toxicity. Both the shape and size were found to influence the micelle cellular uptake and penetration into multicellular tumor spheroids (MCTSs). Micelles with an elongated shape and short length demonstrated the highest uptake by cells and deepest penetration in MCTS. Other objectives of this thesis include the synthesis of a series of PFS BCPs and homopolymers with an alkyne end group, and the investigation of micelle dissolution under self-seeding conditions using high temperature 1H and DOSY NMR.
Towards Development of a Robust Asynchronous EEG-BCI using Error-related Potentials
Keywords: Asynchronous BCI
Brain-computer interfaces
Classification
Cognitive mental tasks
Error-related potentials
Linear discriminant analysis

The primary goal of brain-computer interface (BCI) research is to provide a means of communication for individuals with severe motor impairments. For BCIs to be widely adopted by patients, they need to have a reliable accuracy. One method to achieve this goal is to automatically correct erroneous classifications by exploiting error-related potentials (ErrPs). The first objective of this research is to explore how does the introduction of error-based autocorrection impact the accuracy of a multi-class active BCI based on non-motor imagery (MI) cognitive tasks. Another unavoidable step toward making BCIs clinically viable is to develop self-paced BCIs that users can control whenever they intend to. The second objective of this research is to investigate the impact of ErrP-based autocorrection on the accuracy of self-paced BCIs based on non-MI cognitive tasks. The first two studies were designed to answer the first research question. In the first study, participants performed multiple iterations of five different cognitive tasks. To simulate errors, a random subset of 20% of the trials were followed by incorrect feedback. An average area-under-the-curve of 0.83 was reached for the detection of ErrPs which confirmed the presence of ErrPs in such BCIs. The second study explored the effect of ErrP-guided error correction in an online three-class active BCI (idle state and two personally selected cognitive tasks). ErrP-based error correction modestly but significantly improved the average online task classification accuracy (+7%) and the information transfer rate (+0.9 bits/min) of the BCI across participants. The third study was designed to answer the second research question. Using a self-paced EEG-BCI based on cognitive tasks, the possibility of improving the BCI performance using ErrPs was investigated. The BCI continuously analyzed the EEG data and displayed real-time feedback as soon as it detected a cognitive task. Then, the BCI analyzed the EEG data after the feedback onset to detect ErrPs. The average of post-error correction success rate across participants improved significantly compared to the pre-error correction value (+7%). The findings of these studies support the addition of ErrP-informed correction to maximize the accuracy of cue-based and self-paced BCIs based on non-MI cognitive tasks.
Geometric Inequalities on Riemannian Manifolds
Keywords: geodesic
homological filling function
minimal surface
quantitative geometry
Ricci curvature
Riemannian geometry

In this thesis, we will show three results which partially answer several questions in the field of quantitative geometry. We first show that there exists Riemannian metric on a 3-disk so that the diameter, volume and surface area of the boundary is bounded, but during any contraction of the boundary of the disk, there exists a surface with arbitrarily large surface area. This result answers a question of P. Papasoglu. The second result we will prove is that on any closed 4-dimensional simply-connected Riemannian manifolds with diameter ≤ D, volume > v > 0 and Ricci curvature |Ric|
Examining the Effectiveness of Lesson Study on Teachers’ Practice in Mathematics within a Secondary School Environment
Keywords: Calculus
Education
Lesson Study
Mathematics
Professional Development
Secondary School

Professional development is an important tool for enhancing teachers’ practices, content and pedagogical knowledge, which, in turn, helps to improve student achievement. This study examined the effectiveness of lesson study as a form of professional development for teaching Calculus at the secondary school level. The study employs a case study model of a team of teachers including one Grade 12 teacher, a Head of Mathematics Department in a private school, and the researcher. The research utilizes Murata’s (2010) lesson study cycle to plan, observe, and reflect on a specific research lesson and consider goal setting. Qualitative data was collected in the form of teacher interviews, classroom observations, and documentary analyses. Throughout the three-and-a-half-month study, participants completed six cycles of lesson study. This investigation found that lesson study shows promise as an effective form of professional development for teachers. The findings suggested that lesson study acted as a reflection for the teacher to examine his practice and student learning thus identifying the things that went well and overcoming the challenges within the classroom. It assisted in unraveling students’ thinking processes through the introduction of different teaching approaches leading to enhanced student learning and increased their engagement. The Lesson Study activities empowered students to become more engaged in the class and shifted the teacher’s attitude from a traditional orientation into a more student-centered classroom. The teacher was involved in the decision making thus improving his metacognition and empowering him to try new ideas.
Cellular Mechanisms of Embryonic Tissue Organization
Keywords: boundary compartment
cell intercalation
image analysis
junctional remodelling
laser ablation
quantitative morphogenesis

During early embryonic development, cell and tissue movements must be carefully orchestrated to prevent developmental anomalies. Here, I characterize cellular dynamics during axis elongation, a conserved developmental process in which the head-to-tail (anterior-posterior) axis of an animal extends. In Drosophila, early stages of axis elongation are driven by cell intercalation in the ectoderm, in which cells exchange neighbours through the formation of transient multicellular vertices. Vertices are resolved by the systematic assembly of new cell interfaces parallel to the head-to-tail axis of the embryo. I show that new junctions elongate in pulses anti-correlated with the periodic contractions of the cells anterior and posterior to the new contact. Inhibiting actomyosin contractility disrupts both the rate and directionality of new junction assembly. Disrupting contractility in the cells anterior and posterior to the new edge disrupts vertex resolution and slows down new edge elongation, while preventing contraction of the dorsal and ventral cells mainly affects the maintenance and lengthening of the new cell interface. Hypercontraction of the cells anterior and posterior to the new edge accelerates the rate of new edge assembly. Finally, applying ectopic tension orthogonal to the characteristic orientation of vertex resolution is sufficient to alter the direction of new edge formation, suggesting that local mechanical forces associated with actomyosin contractility direct the assembly of new cell contacts during multicellular vertex resolution during ectoderm extension. During later stages of axis elongation, a cell population on the underside of the embryo, the mesectoderm, undergoes oriented cell divisions to relieve strain generated from intercalating cells. Following mitoses, cell polarity is reversed in mesectoderm cells, resulting in the formation of supracellular myosin cables that segregate the mesectoderm from the ectoderm. Increased tension at the boundary prevents cell mixing and contributes to maintenance by stabilizing myosin. Mechanical and pharmacological cable disruption results in the premature internalization of the mesectoderm. Thus, our findings demonstrate that myosin cables can maintain tissue position while acting as boundaries that prevent cell mixing. Together, my work identifies two distinct mechanisms by which subcellular dynamics can translate into tissue-level organization during embryonic development.
The Person Case Constraint: Unconditional Interfaces and Faultless Derivations
Keywords: features
Merge
Morphosyntax
PCC
Syntax
valuation

This thesis advances a theoretical move toward a grammatical model devoid of interface conditions by proposing a novel feature-based structure-building mechanism. In the standardly assumed architecture of grammar, ungrammaticality is often explained in terms of a violation of some condition on an output of the syntactic module. However, some recent research in linguistics has attempted to move away from such an approach to ungrammaticality and proposed to reinterpret ungrammaticality as non-generability. In this approach, ill-formed structures are construed not as defective but as impossible to generate with the available syntactic operations. In order to advocate for the latter approach to ungrammaticality, this thesis examines an interface condition called the Person Licensing Condition (PLC), which was proposed to account for a linguistic phenomenon known as the Person Case Constraint (PCC). It is shown in the thesis that the PLC fails to capture cross-linguistic variation in the PCC patterns and in the way illicit structures are remedied. It is further argued that previous, Agree-based accounts of the PCC variation, also reliant on an interface condition, cannot fully explain all the patterns and that they obscure the source of the variation. This thesis proposes an alternative account of the PCC, which involves a version of Merge that is constrained by feature valuation, and what is known as articulated person features. The proposed syntactic system allows arguments to engage with each other by valuing the same unvalued feature, and this explains person restriction effects seen in the PCC patterns. Illicit argument combinations are underivable in the system, and an interface condition is not needed to account for ungrammaticality induced by the PCC. This novel account of the PCC also captures the variation fairly well, and because the variation is attributed to different ways syntactic elements are featurally specified in different languages, the reason why we obtain such variation is clear. In defending the person features used in the proposed syntactic mechanism, this thesis also speaks to the typology of grammatical persons and shows that the same features explain not only syntactic restrictions like the PCC but also a variety of morphological neutralization phenomena.
Sequence-function Relationships in Intrinsically Disordered Regions through the Lens of Evolution
Keywords: disordered
evolution
protein
signalling
yeast

Intrinsically disordered regions (IDRs) are regions of proteins that do not autonomously fold into stable secondary or tertiary structures. Though they defy the classical view of proteins as rigidly structured macromolecules, IDRs are widespread in living organisms, and are involved in a diverse array of functions. The majority of IDRs appear to be rapidly evolving at the level of the primary amino acid sequence, which makes it difficult to quantify evolutionary conservation and associate these regions with biological function using standard sequence analysis. The aim of my thesis research has thus been to understand evolutionary constraint and sequence-function relationships in IDRs. Using a functionally characterized IDR in the yeast protein Ste50, I first found that highly diverged amino acid sequences can encode conserved phenotypes in IDRs, showing that sequence divergence does not necessarily imply functional divergence in these regions. Using a phylogenetic comparative framework, I found that the net charge of the Ste50 IDR, rather than the precise amino acids, is a functional molecular feature that is preserved over evolution. I next expanded my evolutionary analysis of IDRs to the yeast proteome, and found that most highly diverged IDRs contain many molecular features that are preserved over evolution. I summarized the evolution of these molecular features with an "evolutionary signature" for each IDR, and found that groups of IDRs with similar evolutionary signatures are enriched for specific biological functions. I also found that IDRs with similar evolutionary signatures can rescue function in vivo despite negligible sequence similarity. Finally, I used these evolutionary signatures to train a statistical model, and found that they can be used to classify IDRs for a diverse set of biological functions. I identified the molecular features contributing to these functional predictions, and attributed distinct functions to specific IDRs in proteins with multiple IDRs. Overall, this work shows that there is rich functional information in IDR sequences, and that this information can be revealed through evolutionary analysis.
On the Space Complexity of Colourless Tasks
Keywords: colourless tasks
consensus
distributed computing
set agreement
space complexity

In this thesis, we prove lower bounds on the number of registers needed to solve colourless tasks in asynchronous shared memory systems. Many fundamental synchronization tasks, such as consensus, k-set agreement, and epsilon-approximate agreement, are colourless. We show that it is possible to transform any nondeterministic solo-terminating algorithm (including any randomized wait-free algorithm) into an obstruction-free algorithm that uses the same number of registers. This result extends to algorithms using any finite number of deterministic objects that support read operations. Hence, we can focus on proving lower bounds for obstruction-free algorithms. We prove a tight lower bound on the number of registers needed to solve obstruction-free consensus. We also prove the first non-constant lower bounds on the number of registers needed to solve obstruction-free k-set agreement and obstruction-free epsilon-approximate agreement. The bound for k-set agreement is asymptotically tight when k is a constant and the bound for epsilon-approximate agreement is asymptotically tight when epsilon is sufficiently small. To prove these bounds, we introduce a new technique, revisionist simulations. This technique allows us to prove a general theorem that yields lower bounds on the number of registers needed to solve any colourless task in an obstruction-free manner. Finally, we define the class of extension-based proofs and show that no extension-based proof can establish the impossibility of deterministically solving k-set agreement among n > k > 1 processes in a wait-free manner using registers.
Mechanisms of Post-transcriptional Control in Mammalian Neural Stem Cells
Keywords: cell fate specification
immunohistochemistry
neocortex
neural stem cells
post-transcriptional control
single-cell RNA sequencing

The diverse types of neurons that populate the mammalian forebrain are the fundamental requirement for the assembly of complex circuitry. However, the mechanisms regulating the genesis of these distinct neuronal populations from neural precursor cells (NPCs) are still not well understood. In this thesis, I address the question of whether post-transcriptional mechanisms regulate neuronal differentiation and fate specification within the developing forebrain. First, I show that embryonic NPCs are transcriptionally primed to make diverse neuronal subtypes, and that a Pum2-4E-T complex represses the translation of neuronal specifier mRNAs to ensure the appropriate temporal specification of daughter neurons. Second, I show that 4E-T mediated translational repression continues to act as a critical regulator of NPC maintenance and differentiation at postnatal stages. Based on the work presented in this thesis, I propose that translational repression mechanisms act to ensure the appropriate differentiation of transcriptionally primed NPCs in response to rapidly changing environmental cues.