New transgenic crops are currently being developed which will be tolerant to dicamba and 2,4-D herbicides. This technology could greatly benefit producers who are impacted by weed species that have developed resistance to other herbicides, like glyphosate-resistant Palmer Amaranth. Adoption of this new technology is likely to be rapid and widespread which will lead to an increase in the amount of dicamba and 2,4-D applied each season. It is well-documented that these herbicides are very injurious to soybeans, cotton, tomatoes, and most other broadleaf crops, and their increased use brings along increased chances of physical spray drift onto susceptible crops. Because of these risks, research is being conducted on new herbicide formulation/spray nozzle combinations to determine management options which may minimize physical spray drift.

Thesis advisor: Danielle Hedegard / There are an estimated 150,000 Brazilians currently in the state of Massachusetts living, working, and living as immigrants in the “nation of immigrants” (McDonnell and de Lourenco, 2009; p. 241). The population often goes unnoticed, lost among a sea of immigrants in the landscape of Massachusetts. Occupying sub jobs, these Brazilian immigrants very often lose their status, and voices in the process of immigration to the United States. Over time, many Brazilians are able to achieve economical and occupational success in Massachusetts and decide to make the United States their home. Guided by the research questions: “How do Brazilian immigrants’ perceptions of the American Dream change with respect to reality and their lived experiences?” and “What are the lived experience of Brazilian immigrants?” I intend to understand this transition from temporary immigrant to permanent resident, and how the American Dream plays into these shifting expectations. / Thesis (BA) — Boston College, 2012. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Sociology Honors Program. / Discipline: Sociology.

International schools and the concept of an international education are a relatively new phenomenon, but their growth is almost unparalleled by any other service industry. Anecdotal evidence suggests that the number of international schools has risen over the last forty years from less than one hundred to close to, if not exceeding, two thousand today. At the same time, organisations like the International Baccalaureate are seeing the curriculum programmes they offer, being taken up by national and international schools, as they seek to educate tomorrow’s citizens in the face of ever increasing globalization. However, the growth and increased accessibility of international schools has brought with it a more discerning customer. This study, with the use of segmentation theory, will show that international schools are fully aware of the ‘wants and needs’ of their ‘customers’ and deliberately recruit teachers who will satisfy certain predetermined criteria and, in doing so, ensure their own continued success. Using data drawn from a well established international schools’ recruitment agency and supplemented by information drawn directly from a number of international schools, this study will show that the majority of international schools, whenever possible and finances allowing, look to employ Western trained, English speaking teachers who preferably have previous experience of the curricular being offered.

Linear thermoplastic polyesters are commonly used in high volume applications such as food containers, films and textile fibers. The physical and mechanical properties of these materials are well documented and are a function of chemical structure and morphology (e.g. semi-crystalline, amorphous, etc.). Polyesters, as are many organic polymers, are quite flammable. Polydimethylsiloxane homopolymer exhibits low mechanical strength and, even at high molecular weight, exists as a viscous fluid rubbery gum due to its low glass transition temperature of approximately -123°C. However, one of the many attractive properties of this polymer is its relatively low flammability and if properly designed, organic "sand-like" silicates are produced in oxidizing atmospheres at elevated temperatures (e.g. 500-700°C). This thesis discusses the synthesis and characterization of novel, high molecular weight cycloaliphatic and aromatic polyester/ poly(dimethylsiloxane) segmented copolymers. The cycloaliphatic copolymers were synthesized via a melt process using a high trans content 1,4 dimethylcyclohexanedicarboxylate, and 1,4 butanediol or cyclohexanedimethanol, while the partially aromatic systems were synthesized using dimethyl terephthalate and butanediol. Primary and secondary aminopropyl terminated poly(dimethylsiloxane) oligomers of controlled molecular weight were endcapped with excess diester to form an amide linked diester terminated oligomer. The latter was then incorporated into the copolymer via melt transesterification to afford a multiphase segmented copolymer. Selected compositions showed enhanced ductility and hydrophobic surface modification. The polysiloxane segment was effeciently incorporated into the copolymers and was unaffected by the transesterification catalyst under typical reaction conditions. The homopolymers and copolymers were characterized by solution, thermal, and mechanical, and surface techniques. The segmented copolymers were demonstrated to be microphase separated as determined by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and transmission electron microscopy. The surface of the copolymers was enriched with the polysiloxane segment as evidenced by contact angle analysis. Thermal gravimetric analysis of the segmented copolymers containing identical amounts of PDMS, but varying in the primary or secondary nature of their amide linkages, exhibited quantitatively identical char yields and weight loss behavior. The segmented copolymers exhibited char yields in air superior to those of their respective homopolymers. Additionally, aromatic poly(tetramethyleneoxide) (PTMO) based polyether/polyester segmented copolymers were modified with poly(dimethylsiloxane). DMA revealed an apparent shift (higher Tg) of the PTMO segment reflecting an increase in phase mixing with the "hard" polyester segment, possibly induced by the hydrophobic PDMS phase. / Master of Science

This thesis addresses the systematic modification of poly(tetramethylene oxide) (PTMO), polyether based segmented thermoplastic polyurethane with a secondary aminoalkyl functional polydimethylsiloxane (PDMS), which was intended to improve the fire resistance of polyurethane systems. The PDMS oligomer was successfully incorporated into the polyurethane backbone via one step solution polymerization. The effect of PDMS content on thermal stability, morphology, surface composition, mechanical properties, and fire resistance of polyurethane was investigated. These polymers displayed a complex two phase morphology and composition-dependant mechanical properties. The PDMS segment microphase separated from other polyurethane segments and varying microphase separation morphologies were observed with differing PDMS content. Spherical dispersed complex phases and co-continuous phases occurred when the PDMS content was 15wt% and 55wt%, respectively. Similar thermal stability was observed for both the polyurethane control and the PDMS modified polyurethanes, but the later displayed increased char yield in air with increased PDMS concentration. Quantitative measurements of the fire resistance of the modified polyurethanes by cone calorimetry showed that the peak heat release rate of the 15wt% siloxane modified samples dropped 67wt%, compared with the polyurethane control. However, the peak heat release rate did not further change with increasing siloxane content. Excellent mechanical properties, in terms of tensile strength and elongation, were found for the modified polyurethane with 15wt% of PDMS. Higher PDMS levels did reduce tensile strength, probably because of the reduction in strain crystallizing PTMO content. The PDMS modification, which resulted in improved fire resistance and excellent mechanical properties, is attributed to the low surface energy of the PDMS segment that tended to migrate to the surface of the polymer. It could be oxidized into a partially silicate-like material upon heating in air. In addition, the syntheses of primary and secondary aminoalkyl functional PDMS based segmented polyureas are described herein. Two-phase morphology was observed for all the polyurea samples, even when the hard segment concentration was as low as 6wt%. All these polyureas formed clear transparent films that exhibited good mechanical properties even with very high PDMS content, up to 94wt%. They also demonstrated similar thermal stability, independent of the PDMS end group. However, the nature of the end group, i.e. primary or secondary aminoalkyl, had a dramatic effect on mechanical and morphological properties of these PDMS based polyureas, which was interpreted in terms of the level of hydrogen bonding. / Ph. D.

Ammonium ionenes are polycations that have quaternary nitrogens in their macromolecular backbone and are synthesized via step-growth polymerization technique. They offer interesting coulombic properties, and the synthetic design provides control over charge density. Non-covalent interactions including nucleobase hydrogen bonding and electrostatics were studied in ammonium ionenes. The non-covalent interactions are expected to increase the effective molecular weight of polymeric precursors and induce microphase separation due to intermolecular associations. The influence of non-covalent interactions on structure-property relationships of ammonium ionenes were studied regarding mechanical (tensile, DMA), thermal (DSC, TGA), and morphological (AFM, SAXS) properties. Hydrogen bonding interaction (10-40 kJ/mol) was introduced using DNA nucleobase pairs such as adenine and thymine. Novel adenine and thymine functionalized segmented and non-segmented ammonium ionenes were successfully synthesized using Michael addition chemistry. In non-segmented systems, we investigated the influence of spacer length on homoassociation and heteroassociation of complementary nucleobase-containing ionenes. Based on DSC analyses, complementary non-segmented ionenes made miscible blends. The Tgs of ionene blends with shorter spacer length (4 bonds between the nucleobase and secondary amine in the polymer backbone) followed the Fox equation, which indicated no intermolecular interactions. The longer alkyl spacer (9 bonds between nucleobase and secondary amine in the polymer backbone) provided efficient flexibility for the self-assembly process to occur. Thus, increasing the spacer length from 4-bonds to 9-bonds, the Tgs of the blends deviated from both Fox and Gordon-Taylor equations and demonstrated the presence of hydrogen bonding interactions. In segmented systems, we investigated the association between nucleobase-containing ionenes and their complementary guest molecules. Job's method revealed a 1:1 stoichiometry for the hydrogen-bonded complexes. These association constants for the 1:1 complexes, based on the Benesi-Hildebrand model were 94 and 130 M-1 respectively, which were in agreement with literature values for adenine and thymine nucleobase pairs (10-100 M-1). DSC thermograms confirmed no macrophase separation for 1:1 [ionene-A/T]:[guest molecule] complexes based on the disappearance of the melting peak of the guest molecule. Morphological studies including atomic force microscopy (AFM) demonstrated a reduced degree of microphase separation for the 1:1 complexes due to the disruption of adenine-adenine or thymine-thymine interactions. Poly(dimethyl siloxane)-based ammonium ionenes having various hard segment contents were synthesized. The charge density or hard segment content was tuned for appropriate application using low molecular weight monomer. The change in hard segment content had a profound effect on thermal, mechanical, rheological, and gas permeability. Microphase separation was confirmed using DSC and DMA in these systems. DMA showed that the rubbery plateau modulus extended to higher temperatures with increasing hard segment content. Tensile analysis demonstrated systematic increase in modulus of PDMS-ionenes with increasing hard segment content. Oxygen transmission rates decreased linearly as the wt% hard segment increased. / Ph. D.

This is a sandwich thesis / In an interrupted time series (ITS) design, data are collected at multiple time points before and after the implementation of an intervention or program to investigate the effect of the intervention on an outcome of interest. ITS design is often implemented in healthcare settings and is considered the strongest quasi-experimental design in terms of internal and external validity as well as its ability to establish causal relationships. There are several statistical methods that can be used to analyze data from ITS studies. Nevertheless, limitations exist in practical applications, where researchers inappropriately apply the methods, and frequently ignore the assumptions and factors that may influence the optimality of the statistical analysis. Moreover, there is little to no guidance available regarding the application of the various methods, and a standardized framework for analysis of ITS studies does not exist. As such, there is a need to identify and compare existing ITS methods in terms of their strengths and limitations. Their methodological challenges also need to be investigated to inform and direct future research. In light of this, this PhD thesis addresses two main objectives: 1) to conduct a scoping review of the methods that have been employed in the analysis of ITS studies, and 2) to develop improved methods that address a major limitation of the statistical methods frequently used in ITS data analysis. These objectives are addressed in three projects. For the first project, a scoping review of the methods that have been used in analyzing ITS data was conducted, with the focus on ITS applications in health research. The review was based on the Arksey and O’Malley framework and the Joanna Briggs Handbook for scoping reviews. A total of 1389 studies were included in our scoping review. The articles were grouped into methods papers and applications papers based on the focus of the article. For the methods papers, we narratively described the identified methods and discussed their strengths and limitations. The application papers were summarized using frequencies and percentages. We identified some limitations of current methods and provided some recommendations useful in health research. In the second project, we developed and presented an improved method for ITS analysis when the data at each time point are aggregated across several participants, which is the most common case in ITS studies in healthcare settings. We considered the segmented linear regression approach, which our scoping review identified as the most frequently used method in ITS studies. When data are aggregated, heterogeneity is introduced due to variability in the patient population within sites (e.g. healthcare facilities) and this is ignored in the segmented linear regression method. Moreover, statistical uncertainty (imprecision) is introduced in the data because of the sample size (number of participants from whom data are aggregated). Ignoring this variability and uncertainty will likely lead to invalid estimates and loss of statistical power, which in turn leads to erroneous conclusions. Our proposed method incorporates patient variability and sample size as weights in a weighted segmented regression model. We performed extensive simulations and assessed the performance of our method using established performance criteria, such as bias, mean squared error, level and statistical power. We also compared our method with the segmented linear regression approach. The results indicated that the weighted segmented regression was uniformly more precise, less biased and more powerful than the segmented linear regression method. In the third project, we extended the weighted method to multisite ITS studies, where data are aggregated at two levels: across several participants within sites as well as across multiple sites. The extended method incorporates the two levels of heterogeneity using weights, where the weights are defined using patient variability, sample size, number of sites as well as site-to-site variability. This extended weighted regression model, which follows the weighted least squares approach is employed to estimate parameters and perform significance testing. We conducted extensive empirical evaluations using various scenarios generated from a multi-site ITS study and compared the performance of our method with that of the segmented linear regression model as well as a pooled analysis method previously developed for multisite studies. We observed that for most scenarios considered, our method produced estimates with narrower 95% confidence intervals and smaller p-values, indicating that our method is more precise and is associated with more statistical power. In some scenarios, where we considered low levels of heterogeneity, our method and the previously proposed method showed comparable results. In conclusion, this PhD thesis facilitates future ITS research by laying the groundwork for developing standard guidelines for the design and analysis of ITS studies. The proposed improved method for ITS analysis, which is the weighted segmented regression, contributes to the advancement of ITS research and will enable researchers to optimize their analysis, leading to more precise and powerful results. / Thesis / Doctor of Philosophy (PhD)

Esta dissertação apresenta o desenvolvimento de um equipamento para a execução de estacas escavadas com injeção sob pressão, logo após a fase de escavação, de argamassa de cimento e areia. O processo utiliza segmentos de trados que são introduzidos no solo através da combinação de rotação e empuxo axial de compressão. A extração dá-se simultaneamente à injeção de argamassa, e o monitoramento das pressões de injeção é feito através de um manômetro, com o objetivo de garantir a integridade do fuste. Um motor a diesel fornece até 92 kW a 1800 rpm e é responsável pelo acionamento dos diversos conjuntos hidráulicos. O equipamento, montado numa plataforma sobre pneus, é autopropelido e autocarregável podendo ser transportado em caminhões comuns com dois eixos traseiros. Esse tipo de estaca, denominado estaca hélice segmentada, poderá representar uma alternativa interessante às estacas tradicionais, principalmente em locais onde as construções vizinhas possam sofrer danos devido à utilização de estacas de deslocamento ou onde os custos envolvidos na utilização de equipamento mais pesado e sofisticado possam inviabilizar a sua aplicação / This work presents the development of equipment for execution of segmented auger piles with injection of cement mortar under pressure, soon after the excavation phase. The process uses segmented augers that are installed in the ground through the rotation and pull-down combination. The extraction is made at the same time as the cement mortar injection and the injection pressures are monitored by a manometer, to assure the shaft integrity. A diesel motor offers up 92 kW at 1800 rpm and is responsible for the movement of several hydraulic units. The equipment mounted on a tire platform, is self-propelling and can raise itself to be loaded onto common trucks. This kind of pile, called segmented pile, will be an interesting alternative for the traditional piles, mainly at sites where the neighboring constructions will be damage by the utilization of the displacement pile, or where the costs involved in the utilization of heavier and sophisticated equipment can make its application unfeasible

Esta dissertação apresenta o desenvolvimento de um equipamento para a execução de estacas escavadas com injeção sob pressão, logo após a fase de escavação, de argamassa de cimento e areia. O processo utiliza segmentos de trados que são introduzidos no solo através da combinação de rotação e empuxo axial de compressão. A extração dá-se simultaneamente à injeção de argamassa, e o monitoramento das pressões de injeção é feito através de um manômetro, com o objetivo de garantir a integridade do fuste. Um motor a diesel fornece até 92 kW a 1800 rpm e é responsável pelo acionamento dos diversos conjuntos hidráulicos. O equipamento, montado numa plataforma sobre pneus, é autopropelido e autocarregável podendo ser transportado em caminhões comuns com dois eixos traseiros. Esse tipo de estaca, denominado estaca hélice segmentada, poderá representar uma alternativa interessante às estacas tradicionais, principalmente em locais onde as construções vizinhas possam sofrer danos devido à utilização de estacas de deslocamento ou onde os custos envolvidos na utilização de equipamento mais pesado e sofisticado possam inviabilizar a sua aplicação / This work presents the development of equipment for execution of segmented auger piles with injection of cement mortar under pressure, soon after the excavation phase. The process uses segmented augers that are installed in the ground through the rotation and pull-down combination. The extraction is made at the same time as the cement mortar injection and the injection pressures are monitored by a manometer, to assure the shaft integrity. A diesel motor offers up 92 kW at 1800 rpm and is responsible for the movement of several hydraulic units. The equipment mounted on a tire platform, is self-propelling and can raise itself to be loaded onto common trucks. This kind of pile, called segmented pile, will be an interesting alternative for the traditional piles, mainly at sites where the neighboring constructions will be damage by the utilization of the displacement pile, or where the costs involved in the utilization of heavier and sophisticated equipment can make its application unfeasible

A volume equation for predicting individual tree volume, and a taper function for describing a stem profile were developed for a little known species, Styrax tonkinensis (Siam benzoin) in northern Laos. The species has high potential commercial value and can make an important contribution to the local economy. It can provide two different types of products, a non-wood product (benzoin resin) and timber. In Laos, the most important product is currently resin, and the use of timber for commercial purposes is rare. One reason is that information about the timber is not available. In Vietnam, on the other hand, the species is an import pulpwood species. Data used in this study came from 73 trees. Trees were purposely selected to ensure coverage of a full range of tree sizes. Measurement was undertaken only on over-bark diameters due to some constraints, limitations and problems during the field data collection. However, due to the importance of under-bark volume for this species, a small available dataset was used to build a bark model as an interim guide to the errors associated with using over-bark models for estimating under-bark volumes. From this bark model, errors in estimating under-bark volumes of trees with diameters at breast height between 10cm and 17 cm were approximately 18%. Nineteen individual volume models, and 7 individual taper functions were compared for bias and precision. Collective names for the volume equations tested include single-entry, double-entry, logarithmic, combined variables. Most volume models had similar bias but a few were clearly biased. The models with similar bias were further evaluated by four common statistics including bias, standard error of estimates, standard deviation of residuals and mean absolute deviation. The results showed that a five parameter model was ranked first, and was the most precise model. However, the magnitudes of difference in prediction errors between this model and other models, particularly the three parameter model were not significant. For practical purposes, the simpler model was preferred. Seven taper functions tested here belong to three different groups including single taper equations, compatible taper equations and segmented taper equations. Evaluation of taper equations used the same residual analysis procedures and criteria as those applied with volume equations. Graphical residual analysis showed that most taper models had similar precision with their errors in diameter predictions being similar in range. However, some models showed obvious bias. The most highly ranked taper model was a compatible taper model of polynomial form. It was the least biased model. The second ranked model was a single, simple model. This latter model is relatively simple to apply, but it is not compatible with the volume model, yielding slightly different estimates of volume if it is integrated and rotated around the longitudinal axis of a tree. However, if the sole purpose is to describe tree taper, it is the best model to use.