Philosophiae Doctor - PhD / The combination of ion track technology and chemical etching as a tool to enhance polymer gas properties such as permeability and selectivity is regarded as an avenue to establish technology commercialization and enhance applicability. Traditionally, permeability and selectivity of polymers have been major challenges especially for gas applications. However, it is important to understand the intrinsic polymer properties in order to be able to predict or identify their possible ion-polymer interactions thus facilitate the reorientation of existing polymer structural configurations. This in turn can enhance the gas permeability and selectivity properties of the polymers. Therefore, the choice of polymer is an important prerequisite. Polyethylene terephthalate (PET) belongs to the polyester group of polymers and has been extensively studied within the context of post-synthesis modification techniques using swift heavy ion irradiation and chemical treatment which is generally referred to as ‘track-etching’. The use of track-etched polymers in the form of symmetrical membranes structures to investigate gas permeability and selectivity properties has proved successful. However, the previous studies on track-etched polymers films have been mainly focused on the preparation of symmetrical membrane structure, especially in the case of polyesters such as PET polymer films. Also, polyolefins such as polymethyl pentene (PMP) have not been investigated using swift heavy ions and chemical etching procedures. In addition, the use of ‘shielded’ material on PET and PMP polymer films prior to swift heavy ion irradiation and chemical etching to prepare asymmetrical membrane structure have not been investigated. The gas permeability and selectivity of the asymmetrical membrane prepared from swift heavy ion irradiated etched 'shielded' PET and PMP polymer films have not been determined. These highlighted limitations will be addressed in this study. The overall objective of this study was to prepare asymmetric polymeric membranes with porous surface on dense layer from two classes of polymers; (PET and PMP) in order to improve their gas permeability and selectivity properties. The research approach in this study was to use a simple and novel method to prepare an asymmetric PET and PMP polymer membrane with porous surface and dense layer by mechanical attachment of ‘shielded’ material on the polymer film before swift heavy ion irradiation. This irradiation approach allowed for the control of swift heavy ion penetration depth into the PET and PMP polymer film during irradiation. The procedure used in this study is briefly described. Commercial PET and PMP polymer films were mechanically ‘shielded’ with aluminium and PET foils respectively. The ‘shielded’ PET polymer films were then irradiated with swift heavy ions of Xe source while ‘shielded’ PMP polymer films were irradiated with swift heavy ions Kr. The ion energy and fluence of Xe ions was 1.3 MeV and 106 respectively while the Kr ion energy was 3.57 MeV and ion fluence of 109. After swift heavy ion irradiation of ‘shielded’ PET and PMP polymer films, the attached ‘shielded’ materials were removed from PET and PMP polymer film and the irradiated PET and PMP polymer films were chemically etched in sodium hydroxide (NaOH) and acidified chromium trioxide (H2SO4 + CrO3) respectively. The chemical etching conditions of swift heavy ion irradiated ‘shielded’ PET was performed with 1 M NaOH at 80 ˚C under various etching times of 3, 6, 9 and 12 minutes. As for the swift heavy ion irradiated ‘shielded’ PMP polymer film, the chemical etching was performed with 7 M H2SO4 + 3 M CrO3 solution, etching temperature was varied between 40 ˚C and 80 ˚C while the etching time was between 40 minutes to 150 minutes. The SEM (surface and cross-section micrograph) morphology results of the swift heavy ion irradiated ‘shielded’ etched PET and PMP films showed that asymmetric membranes with a single-sided porous surface and dense layer was prepared and remained unchanged even after 12 minutes of etching with 1 M NaOH solution as in the case of PET and 2 hours 30 minutes of etching with 7 M H2SO4 + 3 M CrO3 as observed for PMP polymer film. Also, the swift heavy ion irradiated ‘shielded’ etched PET polymer film showed the presence of pores on the polymer film surface within 3 minutes of etching. After 12 minutes chemical etching with 1 M NaOH solution, the dense layer of swift heavy ion irradiated ‘shielded’ etched PET polymer film experienced significant reduction in thickness of about 40 % of the original thickness of as-received PET polymer film. The surface morphology of swift heavy ion irradiated ‘shielded’ etched PET polymer film by SEM analysis revealed finely distributed pores with spherical shapes for the swift heavy ion irradiated ‘shielded’ etched PET polymer film within 6 minutes of etching with 1 M NaOH solution. Also, after 9 minutes and 12 minutes of etching with 1 M NaOH solution of the swift heavy ion irradiated ‘shielded’ etched PET polymer film, the pore walls experienced complete collapse with intense surface roughness. Interestingly, the 12 minutes etched swift heavy ion ‘shielded’ irradiated PET did not lose its asymmetrical membrane structure despite the collapse of the pore walls. In the case of swift heavy ion irradiated ‘shielded’ etched PMP polymer film, SEM morphology analysis showed that the pores retained their shape with the presence of defined pores without intense surface roughness even after extended etching with 7 M H2SO4 + 3 M CrO3 for 2 hours 30 minutes. Also, the pores of swift heavy ion irradiated ‘shielded’ etched PMP polymer films were observed to be mono dispersed and not agglomerated or overlapped. The SEM cross-section morphology of the swift heavy ion irradiated ‘shielded’ etched PMP polymer film showed radially oriented pores with increased pore diameters in the PMP polymer film which indicated that etching was radial instead of lateral, and no through pores were observed showing that the dense asymmetrical structure was retained. The SEM results revealed that the pore morphology i.e. size and shape could be accurately controlled during chemical etching of swift heavy ion ‘shielded’ irradiated PET and PMP polymer films. The XRD results of swift heavy ion irradiated ‘shielded’ etched PET revealed a single diffraction peak for various times of chemical etching in 1 M NaOH solution at 3, 6, 9 and 12 minutes. The diffraction peak of swift heavy ion irradiated ‘shielded’ etched PET was observed to reduce in intensity and marginally shifted to lower angles from 25.95˚ 2 theta to 25.89˚ 2 theta and also became broad in shape. It was considered that the continuous broadening of diffraction peaks due to an increase in etching times could be attributed to disorderliness of the ordered region within the polymer matrix and thus decreases in crystallinity of the swift heavy ion irradiated ‘shielded’ etched PET polymer film. The XRD analysis of swift heavy ion irradiated ‘shielded’ etched PMP polymer films indicated the presence of the diffraction peak at 9.75˚ 2 theta with decrease in intensity while the diffraction peaks located at 13.34˚, 16.42˚, 18.54˚ and 21.46˚ 2 theta disappeared after chemical etching in acidified chromium trioxide (H2SO4 + CrO3) after 2 hours 30 minutes. The TGA thermal profile analysis of swift heavy ion irradiated ‘shielded’ etched PET did not show the evolution of volatile species or moisture at lower temperatures even after 12 minutes of etching in 1 M NaOH solution in comparison with commercial PET polymer film. Also, it was observed that the swift heavy ion irradiated layered’ etched PET polymer film started to undergo degradation at a higher temperature than untreated PET which resulted in an approximate increase of 50 ˚C in comparison with the commercial PET polymer film. The TGA results of swift heavy ion irradiated ‘shielded’ etched PMP polymer film revealed an improvement of about 50 ˚C in thermal stability before thermal degradation even after etching in acidified chromium trioxide for 2 hours 30 minutes at 80 ˚C. Spectroscopy (IR) analysis of the swift heavy ion irradiated ‘shielded’ etched PET and PMP polymer films showed the presence of characteristic functional groups associated with either PET or PMP structures. The variations of irradiation and chemical etching conditions revealed that the swift heavy ion ‘shielded’ irradiated etched PET polymer film experienced continuous degradation of available functional groups as a function of etching time and also with complete disappearance of some functional groups such as 1105 cm-1 and 1129 cm-1 compared with the as-received PET polymer film which are both associated with the para-substituted position of benzene rings. In the case of swift heavy ion irradiated ‘shielded’ etched PMP polymer film, spectroscopic (IR) analysis showed significant variations in the susceptibility of associated functional groups within the PMP polymer film with selective attack and emergence of some specific functional groups such as at 1478 cm-1, 1810 cm-1 and 2115 cm-1 which were assigned to methylene, CH3 (asymmetry deformation), CH3 and CH2 respectively Also, the IR results for swift heavy ion irradiated ‘shielded’ etched PMP polymer showed that unsaturated olefinic groups were the dominant functional groups that were being attacked by during etching with acidified chromium trioxide (H2SO4+CrO3) which is an aggressive chemical etchant. The gas permeability analysis of swift heavy ion irradiated ‘shielded’ etched PET and PMP polymer films showed that the gas permeability was improved in comparison with the as-received PET and as-received PMP polymer films. The gas permeability of swift heavy ion irradiated ‘shielded’ etched PET increased as a function of etching time and was found to be highest after 12 minutes of chemical etching in 1 M NaOH at 80 ˚C. In the case of swift heavy ion irradiated ‘shielded’ etched PMP, the gas permeability was observed to show the highest gas permeability after 2 hours 30 minutes of etching in H2SO4 + CrO3 solution. The gas permeability analysis for swift heavy ion irradiated ‘shielded’ PET and PMP polymer films was tested for He, CO2 and CH4 and the permeability results showed that helium was most permeable compared with CO2 and CH4 gases. In comparison, the selectivity analysis was performed for He/CO2 and CH4/He and the results showed that the selectivity decreased with increasing in etching time as expected. This study identified some important findings. Firstly, it was observed that the use of ‘shielded’ material on PET and PMP polymer films prior to swift heavy ion irradiation proved successful in the creation of asymmetrical polymer membrane structure. Also, it was also observed that the chemical etching of the ‘shielded’ swift heavy ion irradiated PET and PMP polymer films resulted in the presence of pores on the swift heavy ion irradiated side while the unirradiated sides of the PET and PMP polymer films were unaffected during chemical etching hence the pore depth could be controlled. In addition, the etching experiment showed that the pores geometry can be controlled as well as the gas permeability and selectivity properties of swift heavy ion ‘shielded’ irradiated etched PET and PMP polymer films. The process of polymer bulk and surface properties modification using ion-track technology i.e. swift heavy ion irradiation and subsequent chemical treatment of the irradiated polymer serves to reveal characteristic pore profiles unique to the prevailing ion-polymer interaction and ultimately results in alteration of the polymer characteristics.

[EN] Plant viruses are obligate intracellular parasites which were used to develop recombinant plant virus vectors to express heterologous proteins and to modify endogenous metabolic pathways of natural products in plants. The main limitation of many plant virus-based systems is the difficulty to co-express various heterologous proteins in the same cell with proper subcellular localization, which is a crucial question in metabolic engineering. This work provides a solution to overcome this problem by using a potyvirus-based vector system. Potyviruses (genus Potyvirus, family Potyviridae) are plus-strand single-stranded RNA viruses, which have a genome expression strategy that allows the equimolar production of most viral proteins. On the basis of an infectious clone of Tobacco etch virus (TEV), Bedoya et al. (2010) developed an expression system in which the RNA-dependent RNA polymerase (NIb) gene was replaced by an expression cassette, harboring several heterologous proteins. This viral vector was able to express three fluorescent proteins with nucleocytoplasmic localization in equimolar amounts in transgenic tobacco plants in which NIb was supplemented in trans. Despite of the apparent simplicity of potyvirus genome expression strategy, foreign cDNA insertion is a complicated task. Thus, our first goal was to analyze the effect of gene insertion on TEV genome stability. As a result of this work, a novel insertion position was discovered at the amino-terminal end of the potyvirus polyprotein, which opened the possibility to explore new questions of recombinant protein expression. Since metabolic pathways are highly compartmentalized, proper subcellular targeting of enzymes is an essential task. Thus, our second objective centralized on the subcellular targeting of expressed proteins from the TEV-based viral vector. cDNAs coding for the green fluorescent protein (GFP) fused to chloroplast, nucleus and mitochondria targeting signal sequences were inserted into the newly described amino-terminal insertion position or into an internal site, replacing the NIb cistron. Our results showed that for protein delivery to chloroplasts and mitochondria, foreign genes have to be inserted at the amino-terminal site of the viral vector, but for nuclear delivery, both insertion positions are suitable. The last objective of this work was to investigate whether the potyvirus-based vector was able to express an entire heterologous multistep biosynthetic pathway in plant cells. For this aim we purposed to produce lycopene, a plant pigment with health promoting properties. To do so, we inserted cDNAs coding for the enzymes of a three-step metabolic pathway of bacterial origin into the potyvirus-based vector. Infected tobacco plants developed orange symptoms indicating lycopene accumulation, which was confirmed by high-performance liquid chromatography analysis and microscopy observations. Our results also illustrated that the sole expression of Pantoea ananatis phytoene synthase, crtB, is enough to induce carotenoid accumulation, conferring yellow coloration to the infected tissue and serves as reporter system to visually track viral infection in several plant species. / [ES] Los virus de plantas son parásitos intracelulares obligados que han sido utilizados para desarrollar vectores virales y expresar proteínas heterólogas y modificar rutas metabólicas endógenas de productos naturales. La principal limitación de muchos sistemas basados en virus de plantas es la dificultad de coexpresar diversas proteínas heterólogas en la misma célula con la localización subcelular apropiada, lo cual es una cuestión crucial en ingeniería metabólica. Este trabajo presenta una solución para superar este problema mediante el uso de un vector viral basado en un potyvirus. Los potyvirus (género Potyvirus, familia Potyviridae) son virus de RNA de cadena positiva simple que tienen una estrategia de expresión génica que permite la producción de la mayoría de las proteínas virales en cantidades equimolares. Basado en un clon infeccioso del virus del grabado del tabaco (Tobacco etch virus, TEV) Bedoya et al. (2010) desarrollaron un sistema de expresión en el que el gen de la RNA polimerasa dependiente de RNA (NIb) fue sustituido por un casete de expresión, que albergaba varias proteínas heterólogas. Este vector viral fue capaz de expresar tres proteínas fluorescentes con localización nucleocitoplásmica en cantidades equimolares en plantas de tabaco transgénicas que complementaban el cistron NIb en trans. A pesar de la aparente simplicidad de la estrategia de expresión génica de los potyvirus, la inserción de un cDNA foráneo es una tarea complicada. Por lo tanto, nuestro primer objetivo fue analizar el efecto de la inserción en la estabilidad del genoma de TEV. Como resultado de este trabajo, descubrimos una nueva posición de inserción en el extremo amino-terminal de la poliproteína viral que nos permitió explorar otras cuestiones sobre la expresión de proteínas recombinantes. Dado que las vías metabólicas son muy compartimentalizadas, la adecuada localización subcelular de enzimas es una tarea esencial en ingeniería metabólica. Por eso, nuestro segundo objetivo se centró en la distribución de las proteínas heterológas expresadas con el vector viral a diferentes orgánulos subcelulares. cDNAs que codificaban la proteína fluorescente verde (green fluorescent protein, GFP) fusionada a péptidos señal se insertaron en la nueva posición amino-terminal y en un sitio interno, sustituyendo el cistrón NIb, para enviarla al cloroplasto, núcleo y a la mitocondria. Nuestros resultados mostraron que para la distribución de proteínas al cloroplasto y mitocondria, los genes foráneos deben ser insertados en el sitio amino-terminal del vector viral, pero para la distribución nuclear, ambas posiciones son adecuadas. El último objetivo de este trabajo fue estudiar si el vector viral basado en potyvirus es capaz de expresar una ruta biosíntética de múltiples pasos en células vegetales. Para ello nos propusimos producir licopeno, un pigmento vegetal con propiedades beneficiosas para la salud humana. Para ello, insertamos un cDNA que codificaba las enzimas de una ruta metabólica de tres pasos de origen bacteriano en el vector viral. Las plantas de tabaco infectadas con el vector viral desarrollaron síntomas de color naranja indicando la acumulación de licopeno, que fue confirmado por análisis de cromatografía líquida de alta eficacia y observaciones de microscopía. Nuestros resultados también ilustraron que la sola expresión de la fitoeno sintasa de Pantonea ananatis, crtB, es suficiente para inducir la acumulación de carotenoides que confieren una coloración amarilla al tejido infectado y sirve como sistema reportero visual en varias especies de plantas. / [CAT] Els virus de plantes són paràsits intracel·lulars obligats que han estat utilitzats per a desenvolupar vectors virals i expressar proteïnes heteròlogues y modificar rutes metabòliques endògenes de productes naturals silenciant certs gens o expressant factors de transcripció i enzims metabòlics. La principal limitació de molts sistemes basats en virus de plantes és la dificultat de coexpressar diverses proteïnes heteròlogues en la mateixa cèl·lula amb la localització subcel·lular apropiada, cosa que és una qüestió crucial en enginyeria metabòlica. Aquest treball presenta una solució per a superar aquest problema mitjançant l'ús d'un vector viral basat en un potyvirus. Els potyvirus (gènere Potyvirus, família Potyviridae) són virus d'RNA de cadena positiva simple que tenen una estratègia d'expressió gènica que permet la producció de la majoria de les proteïnes virals en quantitats equimolars. Basat en un clon infecciós del virus del gravat del tabac (Tobacco etch virus, TEV) Bedoya et al. (2010) van desenvolupar un sistema d'expressió en el qual el gen de l'RNA polimerasa depenent d'RNA (NIb) va ser substituït per un casset d'expressió, que albergava diverses proteïnes heteròlogues. Aquest vector viral va ser capaç d'expressar tres proteïnes fluorescents amb localització nucleocitoplàsmica en quantitats equimolars en plantes de tabac transgèniques que complementaven el cistró NIb en trans. Malgrat l'aparent simplicitat de l'estratègia d'expressió gènica dels potyvirus, la inserció d'un cDNA forà és una tasca complicada. Per tant, el nostre primer objectiu va ser analitzar l'efecte de la inserció en l'estabilitat del genoma de TEV. Com a resultat d'aquest treball, hem descobert una nova posició d'inserció en l'extrem amino terminal de la poliproteïna viral que ens va permetre explorar altres qüestions sobre l'expressió de proteïnes recombinants. Atès que les vies metabòliques són molt compartimentalitzades, l'adequada localització subcel·lular d'enzims és una tasca essencial en enginyeria metabòlica. Per açò, el nostre segon objectiu es va centrar en la distribució de les proteïnes heteròlogues expressades amb el vector viral a diferents orgànuls subcelul·lars. cDNAs que codificaven la proteïna fluorescent verda (green fluorescent protein, GFP) fusionada a pèptids senyal es van inserir en la nova posició amino terminal i en un lloc intern, substituint el cistró NIb, per a enviar-la al cloroplast, nucli i al mitocondri. Els nostres resultats van mostrar que per a la distribució de proteïnes al cloroplast i mitocondri, els gens forans han de ser inserits en el lloc amino terminal del vector viral, però per a la distribució nuclear, ambdues posicions són adequades. El lloc amino terminal va resultar ser més adequat per a produir quantitats més grans de proteïnes recombinants, però el lloc d'inserció intern va demostrar ser més estable. Sobre la base d'aquests resultats, hem sigut capaços de distribuir dues proteïnes fluorescents diferents als cloroplasts i nuclis des d'un únic vector viral. L'últim objectiu d'aquest treball va ser estudiar si el vector viral basat en potyvirus és capaç d'expressar una ruta biosintètica de múltiples passos en cèl·lules vegetals. Per açò ens vam proposar produir licopè, un pigment vegetal amb propietats beneficioses per a la salut humana. Per això inserírem un cDNA que codificaba els tres enzims de una ruta metabòlica de tres passos d'origen bacterià en el vector viral. Les plantes de tabac infectades amb el vector viral van desenvolupar símptomes de color taronja indicant l'acumulació de licopè, que va ser confirmat per anàlisi de cromatografia líquida d'alta eficàcia i observacions de microscòpia. Els nostres resultats també van il·lustrar que la sola expressió de fitoè sintasa de Pantonea ananatis, crtB, és suficient per a induir l'acumulació de carotenoides que confereixen una colora / Majer, E. (2016). Metabolic engineering of plants using a disarmed potyvirus vector [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68477 / TESIS

Magister Chirurgiae Dentium (MChD) / A total of 25 third molar teeth (erupted [9], as well as unerupted [16]), from subjects who had lived continuously since birth in an area where the water fluoride concentration was more than 1,8 ppm, were studied. (The range was 1,8 ppm - 2,64 ppm of F-). The subjects had no systemic fluoride supplementation. Tooth brushing with a fluoride containing dentifrice and, perhaps, occasional fluoride mouth rinsing was the only additional exposure to fluoride. The acid-etch biopsy technique was used to determine the fluoride and calcium concentrations at various depths on the enamel surface. The fluoride concentration of the buffered etch solution was determined with an adapted fluoride ion-selective electrode technique, and the amount of calcium by flame atomic absorption spectrophotometry. Six consecutive etchings were done on the mesio-buccal and mesio-lingual cusps of each tooth; the teeth were then washed in an alkali and the same procedure repeated on the disto-buccal and disto-lingual cusps. The depth of etch of each biopsy was calculated assuming that human enamel contains 37% Ca and has a density of 2,95g/ml. It was previously reported, (Grobler & Joubert, 1988), that the enamel fluoride levels of the mesio-buccal and mesio-Iingual sides did not differ from that of the disto-buccal and disto-Iingual sides. The average etch depth and fluoride concentration value as calculated from the values for the two cusps per tooth were used for statistical analysis. The mean etch depths (pm) and mean enamel fluoride concentrations of alkali-washed and unwashed enamel of both erupted and unerupted teeth were tabled, together with the standard deviations and range for each etch. Contrary to the results obtained from a low F- area, no significant difference (p>O.05) could be found in the etch depth between erupted and unerupted enamel in this study. Graphs were plotted by a line fitted to the mean enamel fluoride concentration and mean etch depths values of unwashed erupted, unwashed unerupted, alkali-washed erupted and alkali-washed unerupted third molar teeth. These graphs were compared to the graphs obtained in a comparable study done by Grobler and Kotze (1990), on erupted and unerupted third molar teeth from a low fluoride area (F- < 0,10 ppm). Results indicate that the enamel fluoride concentration in the bulk of the enamel of teeth from a high fluoride area (> 1,8 ppm), is higher than that of teeth from a low fluoride area « 0,10 ppm ). In contrast to the teeth from a low fluoride area, where there was a significant increase (p<0.05) in the fluoride concentration of the outer layer (± 4 J,lm) of erupted enamel when compared to that of the unerupted enamel, no notable increase in the F- content of the enamel was observed in the present study of teeth from a high fluoride area (p>0,05). There was, in addition, no significant (p>0.05) difference between the enamel fluoride content of alkali-washed and unwashed, erupted and unerupted teeth, which showed that very little CaF 2-like material was gained by the enamel after eruption. In both studies the subjects had brushed with a fluoride dentifrice for a period of 1 - 16 years. It was expected that this topical exposure would increase the surface enamel concentration in the high fluoride area similar to the increase found in the low fluoride area. However, this was not the case, and as all the teeth from the high fluoride area exhibited some degree of fluorosis, it was concluded that posteruptive fluoride uptake by fluorotic human enamel without severe enamel loss is limited. This is in agreement with work done by Richards, Fejerskov, Baelum and Likimani (1989).

December 2011. A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. Introduction: The purpose of this study is to compare the shear bond strengths (SBSs) of two new commercial adhesive systems to a conventional multistep bonding system incorporating a 35% phosphoric acid gel. In addition, the amount of adhesive remaining on each tooth following debonding will be analyzed and compared using the adhesive remnant index (ARI). Methods: 88 human premolar teeth chosen from the Nova Southeastern tooth databank were randomly divided into four groups. Group I (control group): Transbond XT primer and adhesive (35% phosphoric acid), Group II: iBond Total Etch system with iBond 35 gel (35% phosphoric acid), Group III: iBond Total Etch system with iBond 20 gel (20% phosphoric acid). Group IV: iBond Self Etch. A scanning electron microscope (SEM) was utilized to qualitatively examine the enamel surface of one randomly selected tooth per group immediately after etching, leaving 21 teeth per group available for the debonding procedure (n=21). Following bonding of the stainless steel brackets (3M Unitek, Monrovia, CA), the teeth were stored in water at 37°C ± 2°C for forty-eight hours. A universal testing machine (Instron, Canton, MA) was then used to determine the shear bond strength of each bracket. Additionally, the amount of adhesive remaining on each tooth following debonding was recorded using 10x light microscopy. Results: A 1-way ANOVA revealed that no statistical differences in bond strength were found between the four groups. SBS values of groups I (11.7 ± 3.9), II (11.6 ± 4.6), III (10.3 ± 4.1), and IV (10.8 ± 3.9) demonstrated mean SBSs considered adequate. The iBond Total Etch (20%) and iBond Total Etch (35%) groups were more likely to have an ARI score of 2-3 than the control group (Transbond XT). No significant differences were found between iBond Self Etch and the control group. Conclusion: The SBS's of all three groups, as compared to the control group, were adequate. The iBond Total Etch system, whether used with iBond 20 gel or iBond 35 gel, had more adhesive remaining on the tooth surface after debonding. Standardization amongst shear bond strength studies is significantly needed in the near future in order to accurately compare findings.

<blockquote><div><div>Methods and techniques for tailoring the surface morphology of metallic surfaces are determined in part by the complex behavior of elemental interactions in conjunction with electrochemical reactions. In this work, we show how the surface morphology can be predicted based on experimental data resulting from polarization curves and compositional differences of Fe- and Ni-based superalloys. Electrochemical treatments utilizing NaCl as the electrolyte were adapted using parameters such as the pitting resistance equivalent (PRE) number and polarization curves to obtain both rough and smooth surfaces. Utilizing these metrics, we electrochemically etched Inconel 600, SS304, Inconel 718 and Inconel 625 obtaining average surface roughness values that ranged from 0.05 to 57.4 μm indicating the success of tailoring the technique to obtaining rough and smooth surfaces. The effect of current density, current pulsing, and temperature were varied to elucidate roughness and pitting behavior, and strong correlations to the PRE number and polarization curve properties of the alloy were observed. Heat treatments and subsequent evolution to the microstructure in the form of grain growth and precipitation altered the etching behavior. These techniques can be used in preventing corrosion failure and enhancing electrochemical machining</div></div></blockquote>

It is challenging to achieve low-resistive ohmic contacts to III-nitride semiconductors due to their wide bandgap. A common way to reduce the contact resistance is to recess the ohmic area prior to metallization. In the minimization of the contact resistance, parameters like the recess depth, anneal temperature and design of the metal stack are commonly optimized. In this work, three other approaches have been evaluated. All experiments were performed on AlGaN/GaN heterostructures. The fabricated ohmic contacts were recess etched, metallized with a Ta/Al/Ta stack, and annealed at 550-575◦C.Firstly, it is shown that the laser writer intensity, transmittance and focus offset during optical lithography affect the contact resistance. The reason is believed to be the variation in the resist profile, which has an impact on the metal coverage. At the optimum intensity/transmittance/focus condition, which generates a relatively medium undercut, a contact resistance of 0.23 Ωmm was obtained.In the second approach, the metal layer of annealed contacts was removed by wet etching, followed by the re-deposition of a metal stack and annealing. The purpose was to increase the amount of N vacancies in the AlGaN, which are responsible for the contact formation. A minimum contact resistance of 0.41 Ωmm was achieved with this method, compared to 0.28 Ωmm with the regular method (without remetallization).In the last approach, the bottom Ta layer was sputtered, whereas evaporation was used in all other cases. The minimum contact resistance was found to be 0.6 Ωmm, which was higher than for the evaporated contacts. The reason was assumed that the thickness of sputtered Ta should be thinner than the evaporated Ta due to its higher density. Moreover, the obtained lower sheet resistance is assumed to caused by the atomic scale damage due to the high energy ions during sputtering. / En utmaning med III-nitrid-halvledare är att uppnå låg-resistivitetskontakter, på grund av deras breda bandgap. Ett konventionellt tillvägagångsätt för att reducera kontaktresistansen är att fördjupa ohmska ytan före metallisering. I strävandet av att minska den ohmska resistansen sker vanligtvis en optimering av följande parametrar, recessddjup, anlöpningstemperatur och metallagersdesign. I detta arbete så har samtliga tre parametrar evaluerats. Alla experiment utfördes på AlGaN/GaNheterostrukturer. De tillverkade ohmska kontakterna var recesssetsade, metalliserade med ett Ta/Al/Ta lager och anlöpt vid 550-575◦C.Den primära undersökningen, visar att laserritar-intensitet, -transmission och fokusförskjutning under optisk litografi inverkar på kontaktresistansen. Anledningen antas vara variation i resistprofilen, vilket påverkar metallbeläggningen. Vid optimal intensitet/transmission/fokus-förhållanden, (som genererar en underskärning), blev den resulterande kontaktresistansen 0.23 Ωmm uppmätt.I en sekundär undersökning, avlägsnas ohmska kontaktens metallager genom våtetsning, följt av en återdeponering av ett nytt metallager, samt anlöpning. Syftet var att öka mängden N-vakanser i AlGaN-lagret, som formar ohmska kontakten. Minsta kontaktresistansen uppmätt var 0.41Wmm, att jämföras med 0.28 Ωmm, som uppnåddes genom den konventionella metoden (utan återmetallisering).Den sista undersökningen jämförde sputtrade med evaporerade bottenlager av Ta, (evaporation användes som standardmetod i de tidigare undersökningarna). Med sputtrning blev den minsta kontakresistansen 0.6 Ωmm, (högre än de evaporerade kontakterna). En hypotetisk förklarning kan vara att det sputtrade Ta-lagret är tunnare än det evaporerade Ta-lagret, på grund av en dess högre densitet. Därutöver, den uppmätta lägre skiktresistansen antas bero på den skada i atomskala som sker vid de höga energi-kollisioner som joner skapar vid sputtrning.

Diagnostics is important in the development and implementation of pest management strategies. The virus diagnostic capabilities of several plant pathology collaborators within the Integrated Pest Management Collaborative Research Support Program (IPM CRSP) host countries were evaluated with the aid of a survey. Very few plant disease diagnostic clinics had funds to cover daily operations despite over half of the responding clinics receiving an operational budget. Academically and government affiliated clinics within the developing host countries had little access to molecular tools and equipment, relying mostly on biological and serological methods. Clinics affiliated with private companies and within the USA relied more upon molecular assays. Ten CMV isolates identified by tissue blot immunoassay (TBIA) were collected from a garden at the Historic Smithfield Plantation on the Virginia Tech campus, and from Painter, Virginia on the Eastern Shore. Three CMV isolates from Smithfield were biologically compared to six early CMV isolates stored since the 1970s, while all isolates were compared serologically and molecularly. Sequences obtained after reverse transcription-polymerase chain reaction (RT-PCR) assigned the CMV isolates into subgroups, with eleven to subgroup 1A and three to subgroup 2. The subgroup assignments were confirmed by TBIA using CMV subgroup-specific monoclonal antibodies (Agdia Inc). At Smithfield Plantation, another virus, Turnip mosaic virus (TuMV) was identified from Dame's Rocket (Hesperis matronalis L.). This is the first report of TuMV in Virginia.  In TBIA virus-infected plant samples are blotted onto nitrocellulose membranes, dried, and processed. Membranes can be stored for long periods of time and transported safely across borders without risk of introducing viruses into new environments, but virus remains immunologically active for several months. Methods were developed with CMV and three potyviruses, using the same membranes, for detecting viral RNA by RT-PCR and direct sequencing of PCR products.. Amplification by RT-PCR  was possible after membrane storage for up to 15 months. The membranes also performed well with samples sent from IPM CRSP host countries and within the USA. This method should improve molecular diagnostic capabilities in developing countries, as samples can be blotted to membranes and sent to a centralized molecular laboratory for analysis. / Ph. D.

No description available.

A technology for fabricating fiber optic pressure sensors is described. This technology is based on intermediate-layer bonding of a fused silica ferrule to a patterned, micro-machined fused silica diaphragm, providing low temperature fabrication of optical pressure sensor heads that can operate at high temperature. Fused silica ferrules and fused silica diaphragms are chosen to reduce the temperature dependence. The fused silica diaphragms have been micro-machined using wet chemical etching in order to form extrinsic Fabry-Perot (FP) interferometric cavities. Sol-gel is used as an intermediate-layer for both fiber-ferrule bonding and ferrule-diaphragm bonding at relatively low temperature (250 °C). The pressure sensors fabricated in the manner can operate at temperatures as high as 600 °C. The self-calibrated interferometric-intensity-based (SCIIB) technology, which combines fiber interferometry and intensity-based sensing method into a single sensor system, is used to test and monitor the pressure sensor signal. The light returned from the FP cavity is split into two channels. One channel with longer coherence length can test the effective interference generated by the FP cavity, while the other channel with shorter coherence length can get signal proportional only to the source power, fiber attenuation, and other optical losses. The ratio of the signals from the two channels can compensate for all unwanted factors, including source power variations and fiber bending losses. [11] / Master of Science

In the past few years, the demands for high speed semiconductor integrated circuits have warranted new techniques in their fabrication process which will meet the ever-shrinking dimensions. The gaseous plasma assisted etching is one of these revolutionary processes. However, the plasma and the etch process are very complex in nature. It has been very difficult to understand various species present in the plasma and their role in the etch reaction. In addition, the submicron geometries also require interconnect materials which will satisfy the necessary properties such as thermal stability and low electrical resistance. Titanium (Ti) and titanium nitride (TiN) are widely used as barriers between aluminum (Al) and silicon (Si) to prevent the destructive intermixing of these two materials. The process of patterning of the interconnect containing Ti and TiN along with Al has been a challenge to the semiconductor process engineers. Therefore, complete characterization of the plasma etch process of Ti and TiN films and development of mathematical models to represent the responses such as the etch rate and uniformity is necessary for a good understanding of the etching process. A robust and well controlled metal etch process usually results in good die yield per wafer and hence can translate into higher profits for the semiconductor manufacturer. The objective of this dissertation is to characterize the plasma etch processes of Ti and TiN films in chlorine containing plasmas such as BCl₃ and Cl₂/N₂ and to develop mathematical models for the etch processes using statistical experimental design and analysis technique known as Response Surface Methodology (RSM). In this work, classical experiments are conducted on the plasma etch process of Ti and TiN films by varying the process parameters, such as gas flow, radio frequency (RF) power, reaction pressure, and temperature, one parameter at a time, while maintaining the other parameters constant. The variation in the etch rate with the change in the process parameter of the film is studied and the results were explained in terms of the concepts of plasma. These experiments, while providing very good understanding of the main effects of the parameters, yield little or no information on the higher order effects or interaction between the process parameters. Therefore, modern experimental design and analysis techniques using computerized statistical methods need to be employed for developing mathematical models for these complex plasma etch processes. The second part of this dissertation concentrates on the Design and Analysis of Experiments using Response Surface Methodology (RSM) and development of models for the etch rate and the etch uniformity of the Ti and TiN films in chlorine-containing plasmas such as Cl₂/N₂ and Cl₂/N₂/BCl₃. A complete characterization of the plasma etch process of Ti and TiN films is achieved with the RSM technique and a well fitting and statistically significant models have been developed for the process responses, such as the etch rate and the etch uniformity. These models also provide a means for quantitative comparison of main effects, which are also known as first order effects, second order effects and two factor interactions. The models, thus developed, can be effectively used for an etch process optimization, prediction of the responses without actually conducting the experiments, and the determination of process window. This dissertation work has achieved a finite study of the plasma etch process of Ti and TiN films. There is tremendous potential and scope for further research in this area, limited only by the available resources for wafer processing. A few of the possibilities for further research is discussed in the next few sentences. The optimized process derived from the RSM technique needs to be implemented in the actual production process of the semiconductor ICs and its effects on the wafer topography, etch residue and the resulting die yield have to be studied. More research studies are needed to examine the effect of process parameters such as temperature, the size and shape of the etch chamber, the quality of the film being etched, among other parameters. It is worth emphasizing in this respect that this dissertation marks beginning of research work into the ever-increasing complexities of gas plasma. / Ph. D.