In this study, new Tsai-type 1/1 quasicrystal approximants (ACs) in the RE-Au-SM systems (RE = Gd, Tb, Ho, Yb; SM = Si, Ge) were synthesized using high temperature synthesis techniques such as self-flux, arc-melting-annealing and novel arc-melting-self-flux methods. The syntheses not only provided appropriate samples for the intended structural and physical property measurements but could also be adapted to other systems, especially where crystal growth is a challenge. The newly developed arc-melting-self-flux method uses a temperature program that oscillates near the nucleation and melting points of the intended phase in order to obtain large single crystals. Self-flux methods employed to synthesize Ho-Au-Si and Tb-Au-Si ACs using a precursor alloy ≈Au79Si21 resulted in 100 mm3 and 8 mm3 single crystals, respectively. The crystal structures of the compounds are determined by either one or combinations of the following diffraction techniques; single crystal x-ray, powder x-ray, powder neutron and single crystal neutron diffraction methods.  The crystal structure refinements indicated that the compounds are essentially iso-structural with the prototype Tsai-type 1/1 approximant crystal, YbCd6. In the present compounds there are some structural variations at the cluster center and in the so-called cubic interstices located at (¼, ¼, ¼). For the current ACs; either thermoelectric, magnetic or both properties were investigated. The measured properties were understood further by correlating the properties with the atomic structures of the ACs. Significant differences are observed in the thermoelectric properties, particularly on the lattice thermal conductivities (Kphonon) of Gd-Au-Si, Gd-Au-Ge and Yb-Au-Ge ACs. The difference is attributed to the presence of chemical and positional disorder. Magnetic susceptibility and specific heat measurements revealed ferromagnetic transitions at low temperatures, Tc ≈ 22.5 K for Gd-Au-Si and Tc ≈ 13.1 K for Gd-Au-Ge. For a Tb-Au-Si AC with 14 % central-Tb occupancy, a ferrimagnetic-like transition was observed at Tc ≈ 9 K. Later, it was noted that the Tc and other magnetic properties depend on the occupancy of the central-RE site. Consistent decrease of Tc with increasing central-Tb occupancy is observed. The dependency of magnetic behavior with central-RE occupancy was clarified by solving the magnetic structure of the Tb-Au-Si AC.

To create functional surfaces for soft materials, such as polyurethanes, our approach is to use a semifluorinated surface modifier as minor component to the matrix material. The surface modifier, driving by reduction in surface energy, surface-concentrates to form a functionalized surface layer at the air-polymer interface. In our previous studies, linear PTMO-based polyurethanes were used as the matrix material. These systems undergo slow surface phase separation at room temperature due to the thermodynamically immiscibility of the soft blocks. In this study, chemically crosslinked matrix was developed to provides a steric hindrance to constrain the mobility of surface modifier and to form a kinetically stable surface. The physical property and morphology of base crosslinked matrix has been characterized using DSC, UTT, DMA and AFM. The surface morphology of surface modified crosslinked matrix has been characterized using AFM, DCA and XPS.

AbstractTHE PLACEMENT OF MINERAL TRIOXIDE AGGREGATE USING TWO DIFFERENT TECHNIQUESBy Anita Aminoshariae, D.D.S.A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth UniversityVirginia Commonwealth University, 2003Major Director: Gary R. Hartwell, D.D.S., M.S.Chairman and Professor, Department of EndodonticsThe purpose of this study was to determine if the adaptation of Mineral Trioxide Aggregate (MTA) to the walls of the samples would differ when placed into simulated root canals of varying length using two different placement and condensation methods. Hand condensation was compared to ultrasonic condensation. Eighty polyethylene tubes were divided into four groups of twenty tubes each. The tubes in the four groups were prepared to receive 3, 5, 7 and 10-mm lengths of MTA respectively. Each group of twenty tubes was then subdivided so that ten samples of each length would have MTA placed and condensed by the hand method and the other ten by the ultrasonic method. After condensation the samples were evaluated with a light microscope and radiographs for the degree of adaptation of the MTA to the tube walls and for the presence of voids within the MTA material itself. The results demonstrated an 80% agreement for findings between the light microscopy and radiographic evaluation. Hand condensation resulted in better adaptation to the tube walls and less voids than the ultrasonic method. There was no significant difference in the results for any of the four lengths of MTA placed by the hand method (p> 0.9). At this time hand condensation should be considered the preferred method for placement of MTA.

Photopolymerization, which uses light rather than heat to initiate polymerization, is a facile technique used to fabricate adhesives, protective coatings, thin films, photo-resists, dental restoratives, and other materials. Epoxide monomers, which are polymerized via cationic photoinitiation, have received less attention in fundamental research in comparison to free radical polymerized acrylate monomers. The characterization of propagation mechanisms, network structures, and physical properties is yet lacking. This project focused on the reactivity and physical properties of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (EEC), and the kinetic and physical effects of chain transfer agents (CTAs) in EEC based formulations were characterized. This characterization was carried out using real-time Raman spectroscopy, real-time infrared spectroscopy, dynamic mechanical analysis, simple gel fraction measurements, and atomic force microscopy. The effects of water, organic alcohols, processing conditions (e.g., UV light intensity, humidity, post-illumination curing temperature), and photoinitiation systems were investigated. In general, increasing the concentration of CTAs in a crosslinking epoxide resin increases the rate of polymerization and the overall epoxide conversion level. High CTA levels also correspond to lower glass transition temperatures (Tg) and lower crosslink densities. A post-illumination annealing was critical in obtaining stable physical properties for high Tg epoxide materials. In addition, humidity (water being the most universal contaminant type of CTA) was found to impact the surface properties of an epoxide polymer negatively by reducing the surface hardness. Hybrid acrylate-epoxide systems are much more complex and unpredictable in curing behavior. The use of hydroxy acrylates in hybrid systems allows for grafting between the epoxide and the acrylate domains, via the AM mechanism. Another intricacy of hybrid systems is the initiation system. In order to maximize the conversion of both the epoxide and the acrylate moieties, the free-radical photoinitiator must not hinder the polymerization of the epoxide monomer. Some very efficient free-radical photoinitiators limit the epoxide polymerization by absorbing the majority of the deep-UV incident photons. Finally, a renewable acrylate oligomer was synthesized to provide a green alternative to petroleum-based oligomers currently used. The oligomer was freely miscible and readily photopolymerized with a wide range of commercial monomers. The Tg relationship between the commercial monomers and the parent resin followed the Fox equation. The results of this research provide strategies for controlling epoxide kinetics and physical properties in neat and hybrid systems. This information is useful for tailoring resin formulations to specific end-use applications, especially in films, coatings, and adhesives. Hybrid epoxide-acrylate photopolymerization affords the unique opportunity to structure polymer networks in time and to engineer advanced material properties. These hybrid systems are based on formulations that contain both an epoxide moiety, which undergoes cationic ring-opening photopolymerization, and an acrylate moiety, which undergoes free-radical photopolymerization. Through the combination of these two independent reactive systems, hybrid polymers exhibit lower sensitivity to oxygen and moisture and offer advantages such as increased cure speed and improved film-forming properties. The ability to design the polymer network architecture and to tune mechanical properties can be realized through control of the cationic active center propagation reaction relative to the cationic chain transfer reaction. Specifically, grafted polymer networks can be developed through the covalent bonding of the epoxide chains to the acrylate chains via hydroxyl substituents. This work demonstrates the formation of these grafted polymer networks and overviews the physical properties obtained through control of hydroxyl content and hybrid formulation composition.

The objective of this study was to determine how Al2O3 nanoparticle concentration affected the specific heat, heat of fusion, melting point, thermal diffusivity and thermal conductivity of Alumina-Nitrate nanofluids. Al2O3 nanoparticles were dispersed in a eutectic of sodium nitrate and potassium nitrate (60:40 for mole fraction) to create nanofluids using a hot plate evaporation method and an air dryer method. The nominal Al2O3 (alumina) mass fraction was between 0 and 2%, and was determined as the ratio of the mass of Al2O3 nanoparticles to the total mass of the nanofluid. After the preparation of the nanofluids, Neutron Activation Analysis (NAA) was used to measure the actual Al2O3 mass fraction in the nanofluids. The specific heat, heat of fusion, and melting point were measured with a Modulated Differential Scanning Calorimeter (MDSC). The thermal diffusivity and thermal conductivity were measured with Laser Flash Analysis (LFA). The MDSC results showed that the addition of Al2O3 nanoparticles enhanced the specific heat of the nanofluids synthesize from both methods. There was a parabolic relation between the specific heat and the Al2O3 mass fraction for the nanofluids synthesized from the hot plate evaporation method, with a maximum 31% enhancement at 0.78% Al2O3 mass fraction. The nanofluids synthesized from the air dryer method also resulted in enhanced specific heats which were higher at the same Al2O3 mass fraction than those of the nanofluids synthesized from the hot plate evaporation method. It was not determined why this enhancement occurred. The results also showed that the introduction of Al2O3 nanoparticles had no significant effect on the heat of fusion and melting point of the nanofluids synthesized from either method. The LFA results showed that adding Al2O3 nanoparticles decreased the thermal diffusivity and the thermal conductivity of the nitrate eutectic.

Comprendre et connaitre les propriétés physiques et le comportement mécanique de l'andésite est important pour des applications industrielles comme la géothermie ou le stockage de CO2 mais aussi pour comprendre différents processus naturels. Tout d'abord, les effets de la fissuration thermique sur les propriétés physiques et les processus de rupture de l'andésite ont été étudiés via des expériences triaxiales à taux de déformation constant et à température ambiante. Deuxièmement, nous avons effectué des recherches sur les effets de l'altération sur le comportement physique et la minéralogie. Enfin, une série d'expériences a été réalisée afin d'étudier l'effet de la variation de la pression du fluide i) sur le comportement mécanique des échantillons d'andésite et ii) sur les activités d'émissions acoustiques. / The physical properties and mechanical behavior of andesite are of interest in the context of geothermal reservoir, CO2 sequestration and for several natural processes. The effects of thermal crack damage on the physical properties and rupture processes of andesite were investigated under triaxial deformation at room temperature. Secondly we did research on the effect of alteration on physical behavior and mineralogy. At last a series of experiments were performed in order to investigate the effect of fluid pressure variation i) on the mechanical behavior of andesite samples and ii) on acoustic emissions activities

Nos últimos anos, novas estratégias têm sido desenvolvidas na obtenção de incrementos da produtividade agrícola associados à manutenção da qualidade do solo. No entanto, as terras agrícolas vêm perdendo a sua qualidade física decorrente dos processos de compactação a que estão sendo expostas. A compactação do solo, destaca-se a nível mundial como um dos principais responsáveis pela redução da produtividade das culturas. Pesquisas têm descrito o processo de compressão de solos formados sob a influência de clima temperado, bem como modelos que relacionam esse processo com os atributos intrínsecos dos solos. A informação disponível também demonstra que o processo de compactação depende do sistema de manejo de solo adotado. Entretanto, existe a necessidade de desenvolver estudos que permitam uma melhor compreensão do processo de compactação de solos desenvolvidos sob clima tropical. Nesse sentido, este trabalho testou a hipótese de que o processo de compactação e os indicadores derivados da curva de compressão de solos tropicais são influenciados diferenciadamente pelo sistema de manejo aplicado, devido às alterações que o mesmo induz nas propriedades físicas do solo. O objetivo geral deste estudo foi avaliar quantitativamente o processo de compactação e os indicadores “índice de compressão” e “pressão de preconsolidação” de solos submetidos a diferentes intensidades de tráfego em um pomar de laranja e diferentes intensidades de pisoteio animal em uma pastagem irrigada e obter, se possível, relações que permitam estimar esses indicadores a partir de propriedades do solo facilmente mensuráveis. Os objetivos específicos foram: i) determinar a influência de diferentes intensidades de tráfego no processo de compactação e nos parâmetros índice de compressão e pressão de preconsolidação de um Latossolo Vermelho Amarelo sob pomar de laranja e, a partir desses indicadores, avaliar a heterogeneidade da compactação; ii) avaliar a influência do pisoteio animal na compressibilidade de um Argissolo Vermelho submetido aos sistemas de pastejo rotacionado intensivo: irrigado e não irrigado; e iii) obter funções que permitam estimar a capacidade de suporte de carga do solo a partir de uma propriedade facilmente mensurável e de extrema importância para o crescimento de plantas: a resistência do solo à penetração. Os resultados referentes ao primeiro objetivo indicaram que o processo de compactação foi influenciado pela intensidade de tráfego, visto que os valores de pressão de preconsolidação diferiram nas posições de amostragem entre rodado, rodado e projeção da copa em relação à linha de cultivo. A pressão de preconsolidação resultou ser um indicador mais sensível que o índice de compressão na avaliação da heterogeneidade da compactação em áreas citrícolas. Os resultados obtidos no segundo objetivo revelaram diferenças na compressibilidade do solo, refletindo-se nas curvas de compressão uniaxial dos sistemas de pastejo rotacionado intensivo irrigado e não irrigado. Os sucessivos ciclos de pastejo induziram aumento da pressão de preconsolidação do solo nos dois sistemas de pastejo, sendo significativamente superior no sistema de pastejo rotacionado intensivo irrigado. No que se refere ao terceiro objetivo, foi determinada uma relação significativa, positiva e linear entre a pressão de preconsolidação e a resistência do solo à penetração medida no laboratório e no campo. Estes resultados possibilitam afirmar que a capacidade de suporte de carga do solo pode ser estimada a partir de uma propriedade física facilmente mensurável como a resistência do solo à penetração avaliada no campo. / In the last years new strategies have been developed to obtain increment of the agricultural productivity maintaining the soil quality. However, the agricultural lands quality is decreasing as a consequence of the soil compaction process. Soil compaction is considered as one of the main factors responsible for the reduction of the cultures productivity. Researches related to soils formed under the influence of temperate climate have described the process of soil compression, and developed models that relate this process with the soil intrinsic attributes. Studies have also shown that the soil compression process depends on the soil management practices. However, it is still necessary to develop studies that allow a better understanding the compaction process of soils developed under tropical climate. In this context, this research tested the hypothesis that the soil compaction process is influenced differently by the management practices, due to the alterations that induce on the soil physical properties. The general objective of this study was to evaluate quantitatively the compaction process, and the indicators “compression index” and “preconsolidation pressure” of soils submitted to different traffic intensities in an orchard, and different animal trampling intensities in an irrigated short duration grazing system, and to obtain relationships that allow to estimate these indicators using easily measurable soil attributes. The specific objectives were: i) to determinate the influence of different traffic intensities in the soil compaction process, and in the compression index and preconsolidation pressure of an Haplustox under an orange orchard, and to use these indicators to evaluate the soil compaction heterogeneity; ii) to evaluate the influence of the animal trampling on the soil compressibility of an Hapludalf submitted to two rotation short-duration grazing systems: not irrigated and irrigated; and iii) to obtain functions that allow to estimate the load support capacity using an easily measurable and very important soil property for plant growth; i.e. the soil resistance to penetration. The results related to the first objective indicated that the compaction process was influenced by the traffic intensity, since that the preconsolidation pressure values were different between the sampling positions; i.e., between wheel track, wheel track, canopy projection, and row. The preconsolidation pressure demonstrated to be a more sensitive indicator than the compression index in the evaluation of the soil compaction heterogeneity in an orange orchards. The results related to the second objective have indicated differences in the soil compressibility, which in turn were expressed in the soil compression curves of the irrigated and not irrigated rotation short-duration grazing systems. The successive grazing cycles have induced increases of the soil preconsolidation pressure values of the two grazing systems, being significantly greater in the irrigated rotation short-duration grazing system. The results related to the third objective have demonstrated the existence of a significant, positive and linear relationship between the preconsolidation pressure values and the soil mechanical resistance that were measured in the laboratory and in the field. These results make possible to state that the soil load support capacity can be estimated using an easily measurable soil property; i.e. the soil resistance to penetration.

Nos últimos anos, novas estratégias têm sido desenvolvidas na obtenção de incrementos da produtividade agrícola associados à manutenção da qualidade do solo. No entanto, as terras agrícolas vêm perdendo a sua qualidade física decorrente dos processos de compactação a que estão sendo expostas. A compactação do solo, destaca-se a nível mundial como um dos principais responsáveis pela redução da produtividade das culturas. Pesquisas têm descrito o processo de compressão de solos formados sob a influência de clima temperado, bem como modelos que relacionam esse processo com os atributos intrínsecos dos solos. A informação disponível também demonstra que o processo de compactação depende do sistema de manejo de solo adotado. Entretanto, existe a necessidade de desenvolver estudos que permitam uma melhor compreensão do processo de compactação de solos desenvolvidos sob clima tropical. Nesse sentido, este trabalho testou a hipótese de que o processo de compactação e os indicadores derivados da curva de compressão de solos tropicais são influenciados diferenciadamente pelo sistema de manejo aplicado, devido às alterações que o mesmo induz nas propriedades físicas do solo. O objetivo geral deste estudo foi avaliar quantitativamente o processo de compactação e os indicadores "índice de compressão" e "pressão de preconsolidação" de solos submetidos a diferentes intensidades de tráfego em um pomar de laranja e diferentes intensidades de pisoteio animal em uma pastagem irrigada e obter, se possível, relações que permitam estimar esses indicadores a partir de propriedades do solo facilmente mensuráveis. Os objetivos específicos foram: i) determinar a influência de diferentes intensidades de tráfego no processo de compactação e nos parâmetros índice de compressão e pressão de preconsolidação de um Latossolo Vermelho Amarelo sob pomar de laranja e, a partir desses indicadores, avaliar a heterogeneidade da compactação; ii) avaliar a influência do pisoteio animal na compressibilidade de um Argissolo Vermelho submetido aos sistemas de pastejo rotacionado intensivo: irrigado e não irrigado; e iii) obter funções que permitam estimar a capacidade de suporte de carga do solo a partir de uma propriedade facilmente mensurável e de extrema importância para o crescimento de plantas: a resistência do solo à penetração. Os resultados referentes ao primeiro objetivo indicaram que o processo de compactação foi influenciado pela intensidade de tráfego, visto que os valores de pressão de preconsolidação diferiram nas posições de amostragem entre rodado, rodado e projeção da copa em relação à linha de cultivo. A pressão de preconsolidação resultou ser um indicador mais sensível que o índice de compressão na avaliação da heterogeneidade da compactação em áreas citrícolas. Os resultados obtidos no segundo objetivo revelaram diferenças na compressibilidade do solo, refletindo-se nas curvas de compressão uniaxial dos sistemas de pastejo rotacionado intensivo irrigado e não irrigado. Os sucessivos ciclos de pastejo induziram aumento da pressão de preconsolidação do solo nos dois sistemas de pastejo, sendo significativamente superior no sistema de pastejo rotacionado intensivo irrigado. No que se refere ao terceiro objetivo, foi determinada uma relação significativa, positiva e linear entre a pressão de preconsolidação e a resistência do solo à penetração medida no laboratório e no campo. Estes resultados possibilitam afirmar que a capacidade de suporte de carga do solo pode ser estimada a partir de uma propriedade física facilmente mensurável como a resistência do solo à penetração avaliada no campo. / In the last years new strategies have been developed to obtain increment of the agricultural productivity maintaining the soil quality. However, the agricultural lands quality is decreasing as a consequence of the soil compaction process. Soil compaction is considered as one of the main factors responsible for the reduction of the cultures productivity. Researches related to soils formed under the influence of temperate climate have described the process of soil compression, and developed models that relate this process with the soil intrinsic attributes. Studies have also shown that the soil compression process depends on the soil management practices. However, it is still necessary to develop studies that allow a better understanding the compaction process of soils developed under tropical climate. In this context, this research tested the hypothesis that the soil compaction process is influenced differently by the management practices, due to the alterations that induce on the soil physical properties. The general objective of this study was to evaluate quantitatively the compaction process, and the indicators "compression index" and "preconsolidation pressure" of soils submitted to different traffic intensities in an orchard, and different animal trampling intensities in an irrigated short duration grazing system, and to obtain relationships that allow to estimate these indicators using easily measurable soil attributes. The specific objectives were: i) to determinate the influence of different traffic intensities in the soil compaction process, and in the compression index and preconsolidation pressure of an Haplustox under an orange orchard, and to use these indicators to evaluate the soil compaction heterogeneity; ii) to evaluate the influence of the animal trampling on the soil compressibility of an Hapludalf submitted to two rotation short-duration grazing systems: not irrigated and irrigated; and iii) to obtain functions that allow to estimate the load support capacity using an easily measurable and very important soil property for plant growth; i.e. the soil resistance to penetration. The results related to the first objective indicated that the compaction process was influenced by the traffic intensity, since that the preconsolidation pressure values were different between the sampling positions; i.e., between wheel track, wheel track, canopy projection, and row. The preconsolidation pressure demonstrated to be a more sensitive indicator than the compression index in the evaluation of the soil compaction heterogeneity in an orange orchards. The results related to the second objective have indicated differences in the soil compressibility, which in turn were expressed in the soil compression curves of the irrigated and not irrigated rotation short-duration grazing systems. The successive grazing cycles have induced increases of the soil preconsolidation pressure values of the two grazing systems, being significantly greater in the irrigated rotation short-duration grazing system. The results related to the third objective have demonstrated the existence of a significant, positive and linear relationship between the preconsolidation pressure values and the soil mechanical resistance that were measured in the laboratory and in the field. These results make possible to state that the soil load support capacity can be estimated using an easily measurable soil property; i.e. the soil resistance to penetration.

To evaluate the strip tillage in organic bell pepper (Capsicum annuum L.) production as an integrated system for sustainable vegetable cropping two-years of field trials were conducted in 2011 and 2012. The field trials were conducted to determine the viability of strip tillage in conventional and organic bell pepper production systems by comparing plant growth, water status, and fruit yield to plastic mulch grown plants application under different irrigation regimes. The two-year field data demonstrated that organic pepper with strip tillage application was a viable combination that produced comparable yield to conventional plastic mulch system and utilized water more economically. In 2011 and 2013, strip-tilled rows and plastic mulched rows were used to evaluate the impact of tillage on soil hydraulic conductivity and water internal drainage characteristics. Results indicated that strip-tilled plots had significantly higher in-row penetration resistance compared to the plastic mulch system at depths up to 20 cm, but no differences between the systems were found for layers below 25 cm. In addition, there were no differences in hydraulic conductivity between strip tillage and plastic mulch in both study years over a 30-day period. Also, significant main effects were found for soil layer and time scale on hydraulic conductivity in the first 24 hour of the study in 2013. During field trials in 2011 and 2012, plant tissues were sampled for endophytic bacteria isolation and identification. Differences in endophytic bacteria were obtained among different production combinations. In 2013, endophytic bacteria isolates from 2011 and 2012 trials were re-inoculated to bell pepper grown in greenhouse to assess plant growth. Two Pseudomonas sp. and one Bacillus thioparans strain were screened to evaluate their affects on plant growth under both drought and non-drought conditions. After growth comparisons, the three endophytic strains were used to subsequently study the impacts of endophyte inoculation on regulating plant drought-linked gene expressions in 2014 by conducting real-time PCR. Results demonstrated that plant drought-linked genes, which especially involved plant ethylene biosynthesis, were significantly down-regulated after inoculating the endophytic bacterial strains.

No description available.