Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 1977 / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Chemistry

The growing number of candidates for allied health programs and the continued quest for identification of ideal candidates increases the pressure for allied health programs to continually improve their selection process. Despite past and recent research and the significant amount of literature on admission criteria for selective allied health programs, there is limited research on faculty perceptions of the interview as part of the admission criteria. For this study, interviews were conducted with fifteen allied health faculty members who teach in a program with selective admissions. The interviews consisted of seven open-ended questions and were audio-recorded, then transcribed through Temi.com. The transcriptions were analyzed for common themes. The participants agreed that an interview is an important component of the selective admissions criteria particularly for assessing the candidate’s ability to communicate and interact with others.

This study examined the changes that occur in spontaneous speech when speakers are distracted by background audio. Forty young adults answered open ended questions under five audio conditions (pink noise, movie dialogue, heated debate, classical music, and contemporary music) and a silent condition. Acoustic parameters assessed during the sessions included mean and variability of the fundamental frequency (F0), mean and variability of intensity, speaking time ratio, and disfluency ratio. It was hypothesized that there would be significant increases in the mean and variability of F0 as well as the mean and variability of intensity. There were statistically significant increases in mean and variability of intensity and mean F0 across most audio conditions. There were no significant changes in variability of intensity in the pink noise condition and no significant changes in variability of F0 in any audio condition. We hypothesized that the speaking time ratio would decrease in the presence of background audio compared to the silent baseline. Results demonstrate significant increases in speaking time ratio except for the classical music condition. It was expected that the disfluency ratio of speech production for each participant would increase in the presence of background audio, with informational masking demonstrating the most increase. Results revealed a significant increase in disfluency ratios across background audio conditions except for the pink noise and classical music conditions. Participants reported the heated debate and contemporary music to be the most distracting. These results have potential clinical implications regarding the type of environment where therapy is given, and what type of everyday situations might cause the most difficulties with fluency as well as the processing and production of speech.

The composites industry can be positively influenced by composite materials that are processed faster, are lighter in weight, are higher in stiffness and strength, and that are more recyclable. There has been considerable interest in the use of thermotropic liquid crystalline polymers (TLCPs) to reinforce thermoplastic materials. In a novel process developed by Baird and coworkers, wholly thermoplastic composites are produced via a patented, dual extrusion process. This unique process yields a fiber which consists of numerous continuous fibrils of the liquid crystalline polymer encased in a thermoplastic matrix. These fibers have been used to form random mats and woven pre-forms, which have then been compression molded to form composite parts. Because of the high cost associated with these thermotropic liquid crystalline polymers and the desire to generate recyclable composites, a process was developed in this research to separate the liquid crystalline component from polypropylene (PP) composites. The overall objectives of this work were to develop a process to reclaim the liquid crystalline component of these thermoplastic composites, to determine the effect the process had on the properties of the reclaimed liquid crystalline polymer, and finally to determine whether or not the reclaimed liquid crystalline polymer could be used again to generate a reinforcing component. An ancillary objective was to see if the polypropylene could also be reclaimed, and if it had further use as a polymeric resin. In the present work, a novel process was developed that allows the liquid crystalline component to be reclaimed for further use in the composite material or in other applications that require thermotropic liquid crystalline polymers. The polypropylene component, which has undergone molecular weight reduction, can also be reclaimed by this process. This process consisted of using an organic peroxide and reactive extrusion to selectively degrade only the polypropylene, and not the thermotropic liquid crystalline polymer. The degraded polypropylene was selectively dissolved away from the liquid crystalline polymer by stirring the extruded melt in boiling mineral oil. The remaining solids, of thermotropic liquid crystalline polymer, were collected via centrifugation, cleaned of the mineral oil by boiling in kerosene, and then dried in a convection oven. The purity of the reclaimed thermotropic liquid crystalline polymer was determined by density measurements, while the physical properties of the reclaimed material were determined by rheological tests. The mechanical properties were determined via Instron testing of injection molded plaques made from mixtures of reclaimed material and pure thermotropic liquid crystalline polymer. From this work, it was found that over 70 wt% of the thermotropic liquid crystalline polymer, DuPont HX8000, could be successfully separated from the polypropylene to a degree of 96.0%. From Instron testing, it was found that up to 40 wt% of the reclaimed HX8000 could be blended with the pure HX8000, with no loss in mechanical properties. Furthermore, it was seen that up to 83 % of the HX8000 component (40 wt%) of PP 6523 (60 wt%) composites could be replaced with reclaimed HX8000 without seeing any losses in mechanical properties. It was also found that the degraded polypropylene could be successfully separated, via centrifugation at a temperature of 253 K, and could be potentially used as resin for non-wovens. The projected material cost of the reclaimed HX8000, based on the ability to purchase and to process in bulk, was determined to be 90 % less than the virgin HX8000. / Master of Science

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A new processing technique, known as hydrophobic displacement, was explored as a means of simultaneously removing both mineral matter and surface moisture from coal in a single process. Previous thermodynamic analysis suggests that coal moisture will be spontaneously displaced by any oil with a contact angle greater than ninety degrees in water. Based on these results, six methods of hydrophobic displacement were evaluated: hand shaking, screening, air classification, centrifugation, filtration, and displacement. In the first five methods hydrophobic displacement took place during the cleaning stage. A recyclable non-polar liquid (i.e. pentane) was used to agglomerate coal fines followed by a physical separation step to remove the coal agglomerates from the mineral-laden slurry. Bench-scale tests were performed to identify the conditions required to create stable agglomerates. Only the last method, displacement, did not utilized agglomeration and performed hydrophobic displacement during dewatering, not cleaning. A procedure was also developed for determining moisture content from evaporation curves so that the contents of water and pentane remaining in a sample could be accurately distinguished. Two primary coal samples were evaluated in the test program, i.e., dry pulverized 80 mesh x 0 clean coal and 100 mesh x 0 flotation feed. These samples were further screened or aged (oxidized) to provide additional test samples. The lowest moisture, 7.5%, was achieved with centrifugation of the pulverized 80 mesh x 0 clean coal sample. Centrifugation provided the most reliable separation method since it consistently produced low moisture, high combustible recoveries, and high ash rejections. Hand shaking produced the next lowest moisture at 16.2%; however, the low moistures were associated with a drop in combustible recovery. There was also a great deal of error in this process due to its arbitrary nature. Factors such as oxidation, size distribution, and contact angle hysteresis influenced the concentrate moistures, regardless of the method utilized. / Master of Science

This study examined the changes that occur in spontaneous speech when speakers are distracted by background audio. Forty young adults answered open ended questions under five audio conditions (pink noise, movie dialogue, heated debate, classical music, and contemporary music) and a silent condition. Acoustic parameters assessed during the sessions included mean and variability of the fundamental frequency (F0), mean and variability of intensity, speaking time ratio, and disfluency ratio. It was hypothesized that there would be significant increases in the mean and variability of F0 as well as the mean and variability of intensity. There were statistically significant increases in mean and variability of intensity and mean F0 across most audio conditions. There were no significant changes in variability of intensity in the pink noise condition and no significant changes in variability of F0 in any audio condition. We hypothesized that the speaking time ratio would decrease in the presence of background audio compared to the silent baseline. Results demonstrate significant increases in speaking time ratio except for the classical music condition. It was expected that the disfluency ratio of speech production for each participant would increase in the presence of background audio, with informational masking demonstrating the most increase. Results revealed a significant increase in disfluency ratios across background audio conditions except for the pink noise and classical music conditions. Participants reported the heated debate and contemporary music to be the most distracting. These results have potential clinical implications regarding the type of environment where therapy is given, and what type of everyday situations might cause the most difficulties with fluency as well as the processing and production of speech.

<p> The single selective inversion recovery experiment, developed by Bain and Cramer, has been used with great success in elucidating the molecular dynamics of three systems.</p> <p> The isomerization of d,l bis(1-indenyl)dimethylsilane to its meso isomer proceeds through sequential [1,5]-suprafacial shifts; ΔH+ for the process was evaluated as 21.9 ± 0.5 kcal/mol. There is only one mechanism operating at a detectable rate below about 150°C. Below 100°C this process is too slow to be detected by DNMR, but it is readily followed by classical kinetics methods. Above 100°C, the isomerization may be followed by 1D selective inversion experiments. The isoindene intermediate is conveniently trapped as its double Diels-Alder adduct showing that the rearrangement occurs relatively rapidly on the chemical time-scale.</p> <p> The barrier to hindered rotation about the Mn - C(4) sigma bond in (n^1 -Cpp)Mn(CO)3(PEt3)2 was measured. The observed value of ΔH+ was 13.1 ± 0.2 kcal/mol. ΔS+ was determined to be -11.2 ± 0.7 eu. As the compound is thermally sensitive, it would have been impossible to use lineshape analysis to determine the barrier. 1D selective inversion recovery experiments were used.</p> <p> A combination of 13C NOESY, 13C single selective inversion, and 13C lineshape analysis experiments identified the exchange pathways and determined temperature-dependent rate constants for the N,N'-[dimethyl-(2,2'dithiobisacetyl)]ethylenediamine (DADS) system. DADS exists as five exchanging rotamers in solution. Two of the conformers are symmetric, with C2 symmetry (ZZ1 and ZZ2). The other three conformers are asymmetric, with one amide group cis and the other trans (ZE1, ZE2, ZE3).</p> <p> The NOESY experiments gave a site-to-site map of the exchange processes at several temperatures. At room temperature, ZE1 is exchanging with both ZE2 and ZE3, but there appears to be no exchange between ZE2 and ZE3. This process seems to occur via hindered rotation about the disulfide bond, with ΔH+ = 15.3 ± 0.4 kcal/mol, and ΔS+ = -6.3 ± 1.1 eu.</p> <p> At higher temperatures, ZZ1 and ZZ2 start to exchange with ZE1 via hindered rotation about the amide bonds. ΔH+ for the process was determined to be 19.8 ± 0.4 kcal/mol, and ΔS+ was found to be 0.7 ± 1.2 eu. The barrier agrees quite well with that measured for the uncyclized precursor to DADS. ΔH+ was found to be 19.3 ± 0.7 kcal/mol, while ΔS+ was determined to be 2.5 ± 2.1 eu.</p> / Thesis / Master of Science (MSc)

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