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Low voltage power electronics are made from dislocation free silicon heavily doped with arsenic or antimony to provide low electrical resistivity. Attempts to grow crystals with decreased resistivity have led to a higher probability of twinning during growth, so that the crystal no longer possesses the required crystallographic orientation for device fabrication. The source of the twins must be identified so that crystal growth process conditions can be designed to eliminate this defect mechanism, allowing lower resistivity crystals to be grown reliably. In lightly doped crystals, twinning was ascribed to presence of carbon impurity or a low probability atomic stacking accident, neither of which should be affected by increased concentration of arsenic or antimony. Crystals that twinned during growth were characterized by resistivity, Laue back-reflection x-ray diffraction, optical and scanning electron microscopy, energy dispersive x-ray spectroscopy, spreading resistance, x-ray computed tomography and electron backscatter diffraction. The twin nucleation site of silicon crystals that were grown heavily doped with arsenic or antimony were compared to lightly doped crystals which twinned, and crystals that exhibited other defects. The initial twinning in the <100> orientation heavily doped crystals occurred from small gas bubbles bursting at a {111} facet at the three phase boundary, and forming a twin orientation domain on that facet. The gas bubbles likely consist of argon, the process gas used during solidification to remove silicon monoxide gas from the growth system. The higher levels of arsenic or antimony dopant may have changed the silicon surface tension, or provided additional impurities into the liquid silicon. Either effect may have changed the number or size of argon bubbles in the liquid silicon, leading to a higher incidence of gas bubbles near the {111} facet during solidification. Similar but smaller crater features were observed on two lightly boron-doped silicon crystals that twinned. Two other lightly doped crystals formed twins from carbon inclusions, consistent with carbon as a cause. Some heavily-doped twinned samples also show high concentrations of metals at the twin nucleation site, which could affect surface energy. Measurement of the geometry of crystal surface-to-facet radius eliminated a recently-proposed twin nucleation theory from consideration. Constitutional supercooling was demonstrated to not be a major contributing factor to twin nucleation. It was shown that deliberately introducing additional arsenic dopant during solidification would nucleate twins, but twins did not occur if only elemental carbon was introduced.

Epigenetic studies hold the promise of addressing some of the fundamental questions of human biology including development, cell differentiation, and the aetiological mechanisms of complex disease. Over the last years, several new large scale high throughput technologies have been developed to allow genome wide profiling of epigenetic signals such as DNA methylation and histone modifications. Two of such technologies were developed in our laboratory enabling a genome wide microarray based profiling of DNA methylation signatures and a high throughput method for the site specific interrogation of the density of methylated cytosine. Using these techniques, we identified a DNA methylation difference in the 3’UTR of the DLX1 gene with potentially functional implications to discordance in risk taking behavior in a single pair of MZ twins. We modeled a power analysis on the effect size of the detected difference and determined that approximately 6~25 discordant twin pairs will be adequate to yield 80% power across the entire 12 K CpG island microarray platform using our epigenomic microarray profiling technique. We performed a DNA methylome analysis of MZ twins in white blood cells (WBC), buccal epithelial cells, and gut (rectum) biopsies (N=57 pairs in total) using 12K CpG island microarrays providing the basis for the first annotation of epigenetic metastability of ~6,000 unique genomic regions in MZ twins. We performed a classical twin study on DNA methylation differences in WBC and buccal epithelial cells from 39 pairs of MZ twins to 40 pairs of DZ twins. DZ co-twins exhibited significantly higher epigenetic difference compared to the MZ co-twins in buccal cells (p=1.2x10-294). While such higher epigenetic discordance in DZ twins can result from DNA sequence differences, our in silico SNP analyses and comparison of methylomes in inbred vs. outbred mice favour the hypothesis that this is due to epigenomic differences in the zygotes. This study suggests that molecular mechanisms of heritability may not be limited to DNA sequence differences.

Epigenetic studies hold the promise of addressing some of the fundamental questions of human biology including development, cell differentiation, and the aetiological mechanisms of complex disease. Over the last years, several new large scale high throughput technologies have been developed to allow genome wide profiling of epigenetic signals such as DNA methylation and histone modifications. Two of such technologies were developed in our laboratory enabling a genome wide microarray based profiling of DNA methylation signatures and a high throughput method for the site specific interrogation of the density of methylated cytosine. Using these techniques, we identified a DNA methylation difference in the 3’UTR of the DLX1 gene with potentially functional implications to discordance in risk taking behavior in a single pair of MZ twins. We modeled a power analysis on the effect size of the detected difference and determined that approximately 6~25 discordant twin pairs will be adequate to yield 80% power across the entire 12 K CpG island microarray platform using our epigenomic microarray profiling technique. We performed a DNA methylome analysis of MZ twins in white blood cells (WBC), buccal epithelial cells, and gut (rectum) biopsies (N=57 pairs in total) using 12K CpG island microarrays providing the basis for the first annotation of epigenetic metastability of ~6,000 unique genomic regions in MZ twins. We performed a classical twin study on DNA methylation differences in WBC and buccal epithelial cells from 39 pairs of MZ twins to 40 pairs of DZ twins. DZ co-twins exhibited significantly higher epigenetic difference compared to the MZ co-twins in buccal cells (p=1.2x10-294). While such higher epigenetic discordance in DZ twins can result from DNA sequence differences, our in silico SNP analyses and comparison of methylomes in inbred vs. outbred mice favour the hypothesis that this is due to epigenomic differences in the zygotes. This study suggests that molecular mechanisms of heritability may not be limited to DNA sequence differences.

Teacher absenteeism is a major concern in many school districts around the country. There have been numerous studies on the topic, but we as educators are still dealing with the problems of teacher absenteeism. To get a good understanding of teacher and administrator perceptions of this problem, a quantitative research approach was used. Quantitative data was gathered using a questionnaire with 28 Likert scale questions. One hundred teachers and three administrators participated in this part of the study. In addition, structured questions were used to interview three teachers and three administrators. Multiple regression analyses were conducted to determine which predictor variables presented in the demographic section of the questionnaire contributed to variation in the various dependent variables, e.g. attendance. All multiple regression analyses were performed at the .05 level of statistical significance. The t-test for attendance indicated that the predictor variable, age, was statistically significant and could be concluded that the older the teacher, the less absenteeism. The t-test for attendance indicated that the predictor variable, degree, was statistically significant and could be concluded that the higher the degree, the less absenteeism. The t-test for operating procedures indicated that the predictor variable, years of experience, was statistically significant and could be concluded that the more experience, the more familiar were teachers with the operating procedures of the school. The t-test for training indicated that the predictor variable, years experience, was statistically significant and could be concluded that the more experience, the more inclined regular teachers were for substitute teacher training. The survey responses revealed many similarities between the teachers and administrators. Teachers and administrators believe there is reduced student achievement taking place when there are substitute teachers in the classroom. Because of this, all teachers and administrators feel the need for extensive professional development for substitute teachers. Teachers and administrators agree that student attendance is affected by substitute teachers in the classrooms. From all points of view, it is strongly believed that operational procedures are greatly affected when several regular teachers are absent at the same time and substitutes are in their classrooms.

Solvent-free extrusion emulsification (SFEE) is new top-down technique specially suited to high viscosity polymers (100-1000 Pa.s) for producing sub-micron (100-500 nm) particles inside a twin screw extruder (TSE) without the use of hazardous solvents. SFEE has been difficult to implement in industry due to process sensitivities and a lack of mechanistic knowledge on how the polymer-water morphology must develop prior to inversion. To devise a mechanistic explanation of the critical stages of the process, an inline orifice-plate type viscometer was developed to monitor rheological changes previously witnessed in early batch studies. The general variables of study throughout the thesis included the manner by which sodium hydroxide (NaOH) can be added as well as the NaOH content necessary, resin-to-water (R/W) ratio, and surfactant content. The last study in the thesis explores the influence of matrix viscosity, which was accomplished by crosslinking the polyester. The striated lamellae morphology of the polyester-water system, critically controlling the final particle size, depended on two factors, specifically surface energy (determined by endgroup conversion and added surfactant) and matrix viscosity. Analysis of the rheological response indicated that a higher polar surface energy contribution had the greatest influence on the morphological state, demonstrating a steeper viscosity transition due to more favourable and more rapid incorporation of water within the polyester matrix. A strong correlation was repeatedly found between particle size and this viscosity transition, which has been related to the thickness of striated lamellae through a theory of lamellae coarsening (or thinning as is more relevant to the current process). The reported lamellae coarsening model in the literature, which shows the predominant effects of interfacial energy and viscosity on lamellae thickness in a mixed phase system showed excellent correspondence to the results in this thesis. Among the variables of study in this thesis, the dissolution of the sodium hydroxide species (when added as a solid particle) and the kinetics of end-groups conversion proved to be rate-limiting phenomena to generating thinner striated lamellae. The ionic strength of the system was notably important to the viscosity change occurring in the process as water was added for the first time and subsequently influenced the particle size produced, particularly when additional surfactant was not added and the system relied exclusively on the carboxylate endgroups present. Finally, with mounting evidence that SFEE showed significant sensitivity to the matrix viscosity, a final study examined the effectiveness of SFEE in the face of ever increasing viscous force by blending a crosslinked polyester into the neat resin at different weight fractions. With higher viscosity there was a corresponding decrease in interfacial area growth between the polyester and water, resulting in increased particle size but even with a viscosity near 800 Pa.s, far above a traditional oil-in-water system, it was still found possible in this study to create nano-sized particles by SFEE. / Thesis / Doctor of Philosophy (PhD)

This thesis covers a systematic examination of wet granulation in a twin screw extruder. Granulation of the excipient, (alpha)-lactose monohydrate, was done with the aid of PVP in an aqueous solution which acted as a binding agent. The influences on agglomeration by the following processing parameters were studied: screw elements design, screw rotational speed, binding solution concentration, and binder addition method. Qualitative efforts had also been made in modeling the process to gain valuable insight into how the elements affected agglomeration and granule rupture. A commercial software package PFC^2D, based on the Discrete Element Method (DEM), was used to simulate the dynamic behavior of the screw elements in the barrel. Within the optimal range of 7.5 -10wt% binder concentration, all the screw profiles were studied for their capacity to produce desirable granules suited to solid oral dosage form production. By increasing the rotational speed from 30 RPM to 80 RPM, the granules size of the conveying, discharging and chopping elements decreased whereas this operating parameter had little effect on granule size within kneading blocks. The nominal particle size produced by a screw element increased from 300(mu)m to 1mm when dispersive mixing was its dominant purpose (i.e. the kneading block), thereby meeting our criteria for a suitable granule in tab letting. Similar size development of the granules was not found with the other conveying or distributive mixing elements. In regards to particle shape, the kneading blocks produced elongated shape granules while other elements tested in this study produced smaller, more spherical agglomerates. Either shape was found effective in tabletting. Wet granulation was not feasible with more extreme concentrations of the aqueous binder (i.e. 5 wt% or 12 wt%) in this project, and the hand pre-blend method was the only approach found suitable for metering this additive into the system while maintaining steady feeding rates and output. / Thesis / Master of Applied Science (MASc)

Digital twins are virtual renditions of the actual world that include real-world assets, connections, activities, and processes. Recent developments in technologies play a key role in advancing the digital twin concept in urban planning, designing, and monitoring. Moreover, the latest developments in remote sensing technology have resulted in accurate city-scale light detection and ranging (LiDAR) data, which can be used to represent urban objects (buildings, vegetation, roads, and utilities), enabling the creation of digital twin of urban landscapes. This study aims to build a digital twin of the University of North Texas (UNT) using LiDAR and GIS data. In this research, LiDAR point clouds are used to create 3D building and vegetation modeling along with other GIS data (bicycle racks and parking areas) in creating a digital twin model. 3D Basemap solutions of ArcGIS Pro and ArcGIS Online Scene Viewer, respectively, are used to create an initial 3D urban model and build the ultimate digital twin of UNT. The emergency management floorplans of UNT buildings are incorporated into the digital twin to increase emergency management efficiency. Moreover, solar power potential for individual buildings at UNT has been estimated using the Digital Surface Model (DSM) and integrated into the digital twin model to identify the buildings with the highest solar energy capacity. This study indicates that implementing a digital twin in a university enhances campus efficiency, safety, and sustainability, serving as a central system for a smart campus and contributing to intelligent urban growth.

A three-dimensional flow field produced by supersonic twin-jet impingement is studied using a large eddy simulation (LES). The numerical model consists of two parallel axisymmetric jets of diameter 𝐷*, 3𝐷* apart, issuing from a plane which is at a distance H*=4𝐷* above the ground. The jet diameter 𝐷*, mean velocity 𝑊ₒ*, mean density 𝜌ₒ* and mean temperature 𝑇ₒ* at the jet center in the exit plane are used as reference values. The Mach number and Reynolds number of the jets are M=1.5 and Re=550,000, respectively. This model is closely related to the experimental setup of Elavarasan <i>et al.</i>(Elavarasan <i>et al.</i>, 2000). The three-dimensional time-dependent compressible Navier-Stokes equations are solved using the method of lines. The convective terms are discretized using a fifth-order WENO scheme, whereas the viscous terms are discretized using a fourth-order central-differencing scheme. A low-storage five-stage fourth-order Runge-Kutta scheme is used to advance the solution in time. Code verification is achieved by comparison with flat-plate boundary-layer linear stability analysis, and computational data by Bendiks <i>et al.</i> (Bendiks <i>et al.</i>, 1999). for a compressible turbulent round jet. Instantaneous flow, mean flow and Reynolds stresses for the twin-jet impingement are presented and discussed. The results reveal the existence of flapping behavior in the fountain. The flapping fountain is the vortical structure formed by the alternating merging of a primary vortex tube with a secondary vortex tube induced by the neighboring primary vortex tube. The nondimensional period of flapping is found to be 7𝐷*/𝑊ₒ*. High unsteadiness and strong interaction between the fountain and the jets are also observed. Due to the high diffusion and spreading rate of the fountain, the interaction between the fountain and the jets is only significant up to a height which is less than 3𝐷*. It is found that the mean peak velocity in the fountain is 0.40406 𝑊ₒ* and it occurs at 0.536607𝐷* from the ground. The suitability of the fifth-order WENO scheme to simulate turbulent flow field with embedded shocks is also demonstrated by its capability to capture unsteady shock waves in the impingement regions. / Ph. D.

Thesis advisor: June Horowitz / Parents who simultaneously grieve the loss of one twin and nurture the surviving twin experience a paradox of grief and joy. The acute grief of losing a twin coincides with a critical time in the development of the parental role and relationship with the surviving twin. Very few researchers have addressed the unique parenting situation in which one twin infant dies. The aim of this qualitative descriptive study was to describe the experience of parents who lose one twin in utero, at birth, or in the neonatal period. The study question was "What is the parenting experience of mothers and fathers who simultaneously face the grief of the loss of one twin while nurturing the surviving twin during infancy?" Nine parents, recruited via a support group, were interviewed. Systematic content analysis, emphasizing in-vivo coding (participant's own words), was conducted until data saturation was reached. A comprehensive description of the experience of raising a surviving twin was constructed. Four descriptive themes were identified: (1) Living with ambiguity: the irony of raising a lone twin, belonging and not belonging, and at least there is one; (2) Communicating the family journey: telling or not telling, deciding who needs to know, and how many children; (3) Parenting with wonder and worry: doubt and hyper-vigilance, unanswered questions, and the living twin as a unique person; and (4) Life is different now: loss of innocence, honoring both twins, making and keeping relationships, work-life challenges, and accepting that it doesn't go away. Issues raised by parents included the ambiguity and irony of losing one twin, no one understands, multiple losses, and living with this loss. The description of this experience gives insight to the dynamics and burden of this loss. Data from this study can inform pediatric nurses about the issues, concerns, and needs of parents who sustain this kind of loss. Therapeutic interventions based by the tenets of family-centered nursing care can be developed by understanding the long-term effects of grief on parenting. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Connell School of Nursing. / Discipline: Nursing.