Superalloys used in aeroengines are designed to offer superior strength at increasingly higher operating temperatures. In order to optimise the working efficiency and provide additional protection to the components such as turbine blades; a thermal barrier coating (TBC) system is applied. The TBC is a multilayer system consisting of mainly two layers i.e. bond coat (BC) and topcoat (TC). In addition, a third layer grows between the TC and BC during oxidation known as a reaction layer or thermally grown oxide (TGO). The function of the TC (usually, yttria stabilised zirconia (YSZ)) is to provide thermal insulation to aeroengine parts or reduce their surface temperatures; whereas, the BC provides binding between the TC and the substrate, and oxidation resistance to the underlying alloy by forming an adherent and continuous oxide i.e. α-Al2O3. During service, in the absence of mechanical damage to the TBC, most failures are attributed to the BC performance. The most frequently adopted BCs are; β-(Pt, Ni)Al, Pt-γ-Ni/γ’-Ni3Al and MCrAlY. In addition, reactive elements (REs) are incorporated in the BCs due to their ability to enhance oxidation resistance significantly. In the present study βNiAl based coatings/BCs and alloys with and without REs (Zr and Hf) and Pt were prepared. For the coatings CMSX-4 single crystal superalloy was used as a substrate material and pack aluminising/cementation or in-situ chemical vapour deposition (CVD) as a coating process. The isothermal oxidation testing was carried out at 1150oC for 50 and 100 hours in air. The preparation and oxidation performance of a δNi2Al3 coating was carried out, as, this is a starting material for βNiAl matrix based coatings/or BCs. The oxidation of δNi2Al3 coating showed large volumetric changes (thickness variations), multiphase TGO, TGO/coating interface melting and spallation during oxidation. In contrast, the ‘simple βNiAl’ coating (or βNiAl matrix) was found to exhibit comparably enhanced thermal stability than that of the δNi2Al3 coating. Moreover, a detailed study of the simple βNiAl coating was also carried out in order to understand the oxidation performance. The coating before oxidation in the as-deposited condition was found to contain residual compressive stresses of 140 – 200 MPa. In contrast, after oxidation analysis exhibited substantial interdiffusion between the coating and the substrate resulting in a large reduction of the Al content and influx of substrate elements into the coating. This in turn caused coating transformation from βNiAl to the γ’-Ni3Al phase and formation of a multiphase TGO (TiO2, NiAl2O4, and ϴ-Al2O3 intrusion in α-Al2O3). Moreover, the degree of the TGO spallation and residual stresses increased with the oxidation time. In order to enhance the oxidation performance of the βNiAl coatings, the substrate pre-treatment was carried out i.e. CMSX-4 superalloy was electrolytically etched to remove the γ-Ni phase and fabricate βNiAl coatings on the remaining γ’-Ni3Al. This coating is termed as E-βNiAl. In comparison to simple βNiAl, the E-βNiAl coating showed improved spallation resistance. However, E-βNiAl revealed increased surface area due to etching of the substrate and triggered fast TGO growth rates when tested in an un-polished condition. Furthermore, simple βNiAl coatings were doped with Zr and Hf separately using a two-step aluminising method. The appropriate addition of either Zr or Hf was found to reduce the substrate elements (W, Ta, Cr and Ti etc.) in the coating before and after oxidation. After oxidation, examination of the presence of Zr or Hf in the coating was found to confirm the commonly reported beneficial effects. The TGOs grown on these coatings were almost pure α-Al2O3 which subsequently reduced growth and stresses. In addition to Zr/& Hf doped coatings, a study on Hf and Zr doped βNiAl bulk alloys was also carried out in order to understand the dopant effects on the oxidation resistance of βNiAl alloys in the absence of interdiffusion (as in case of coatings). In general, the commonly reported oxidation benefits were confirmed by the addition of these elements such as reduced TGO growth, oxide pegging, a columnar morphology of the TGO and segregation of REs at alumina grain boundaries etc. In addition, two more beneficial effects are suggested to be the ‘TGO crack filling up (or crack-healing)’ and formation of the ‘dense-TGO’. Within this study, the investigation of commercially available Pt-βNiAl BC was also carried out in air and vacuum atmospheres. The results demonstrated that the initial chemistry and elemental distribution (particularly Al/& Pt) was found to affect the TGO growth and phases significantly. In addition to its well established beneficial effects, the main effect of a Pt addition is suggested to be the stabilisation of the βNiAl structure even at a lower Al content.

The objective of this work is to advance the mechanistic understanding of cathodic electrocoating. These efforts are focused on the initial processes responsible for deposition, which are examined through direct experimentation and simulation. Electrocoating is a global industrial process providing a corrosive resistant base paint to automobile bodies. Presently, empirical models are used to model coating thickness; these models tend to overpredict deposition in occluded areas. Convection is implemented to study the behavior of adhered surface H2 bubbles on the substrate surfaces. The impact of surface H2 bubbles and early e-coat deposition on the local current density is studied using simulations. Results show an increased local current density around surface H2 bubbles and early e-coat deposition influences film growth. When surface H2 bubbles are displaced before sufficient e-coat is deposited the lack of increased local current density slows deposition. However, when sufficient e-coat is deposited and then surface H2 bubbles are displaced, the induction period is unaffected since the early deposition is sufficient to keep the local current density high enough to drive deposition. Solution factors are qualitatively studied using a diluted e-coat dispersion and a anionic exchange membrane cell. Experiments demonstrate a visual change in the solution near the cathode and indicates a coagulation of micelles in this region. Experiments also demonstrate a rise in pH is associated with the induction time, but is not necessary for e-coat deposition. Film resistance is used to understand film growth and film morphology during industrial electrocoating. Interruption experiments demonstrate H2 bubbles may influence film resistance. Film density and resistivity results cannot be completely explained with understood physics, underlining the importance of future resistance studies. These results provide an increased understanding of fundamental processes responsible for initial deposition, which is the foundation needed for advanced physics-based models of the electrocoating process.

Assembly of virus capsid protein (CP) into icosahedrally symmetric particles is an intriguing and elegant process. In most cases of virus assembly, a large number of identical protein subunits self-assemble to generate a shell that protects the viral genome. Studies on virus assembly have resulted in a new scientific technique that uses these proteinaceous shells as nano-particles for a variety of biological applications. The current thesis deals with understanding the factors that govern the assembly of the Sesbania mosaic virus (SeMV) and a pleomorphic virus, Tobacco streak virus (TSV). CP of SeMV, a T=3 plant virus, consists of a disordered N-terminal R-domain and an ordered S-domain. The importance of the R-domain in the assembly was probed by replacement with polypeptides such as the B-domain of Staphylococcus aureus protein A and polypeptides P10 and P8 of SeMV. These chimera assembled into T=3 or larger virus like particles (VLPs). Addition of divalent cations resulted in the formation of heterogeneous nucleoprotein complexes that disappeared upon treatment with EDTA/RNAse. One of the chimeras (N∆65-B) purified in a dimeric form by affinity chromatography assembled into T=1 VLPs during crystallization. The three dimensional structure of these VLPs showed that they were devoid of divalent ions and the B-domain was disordered. These studies demonstrate the importance of N-terminal residues, metal ions in virus assembly and robustness of the assembly process. Also, the B-domain was functional in N∆65-B VLPs, suggesting possible biotechnological applications. Tobacco streak virus (TSV) is a polymorphic virus and a major plant pathogen. TSV capsids encapsidate the tri-partite ss-RNA genome of the virus in three spheroidal particles of diameters 27, 30 and 33 nm, respectively. CPs of ilarviruses are also involved in genome activation. The labile nature of ilarviruses has posed difficulties in their structure determination. This thesis describes the first crystal structure of truncated TSV-CP. The core of TSV CP conforms to the canonical β-barrel jelly roll tertiary structure found in other viral coat proteins. Dimers of CP with swapped C-terminal arms (C-arm) were observed in the two crystal structures determined. The C-arm was found to be flexible and responsible for the polymorphic and pleomorphic nature of TSV capsids. Mutations in the hinge region of the C-arm that reduce the flexibility resulted in the formation of more uniform particles. TSV CP was also found to be structurally similar to that of Alfalfa mosaic virus (AMV) accounting for similar mechanism of genome activation in alfamo and ilar viruses.

No description available.

Doctor of Philosophy / Department of Civil Engineering / Mustaque A. Hossain / Tack coat is a thin layer of asphaltic material used to bind a newly-placed lift of hot-mix asphalt (HMA) pavement to a previously-placed lift or a new HMA overlay/inlay and existing pavement. The purpose of a tack coat is to ensure that a proper bond occurs so that traffic loads are carried by the entire HMA structure. Proper bonding exists when HMA layers act as a monolithic structure, transferring loads from one layer to the next. This depends on appropriate selection of tack coat material type and application rate, and is essential to prevent slippage failure and premature cracking in the wearing surface. This study focuses on development of a three-dimensional finite element (FE) model of HMA pavement structure in order to assess HMA interface bonding. The FE model was constructed using commercially available ABAQUS software to simulate an Accelerated Pavement Testing (APT) experiment conducted at the Civil Infrastructure Systems Laboratory (CISL) at Kansas State University. Mechanistic responses measured in the CISL experiment, such as localized longitudinal strain at the interface, were used to calibrate the FE model. Once calibrated, the model was used to predict mechanistic responses of the pavement structure by varying the tack coat property to reflect material characteristics of each application. The FE models successfully predicted longitudinal strains that corresponded to APT results.

Plant parasitic nematodes cause billons of dollars in annual crop losses. One of the most damaging is the root-knot nematode, Meloidogyne incognita, which is known to attack more than 3000 plants. This research will contribute to the understanding of host-plant resistance through characterization of the early infection processes of Meloidogyne incognita race 3 in susceptible (Lahontan) and resistant (Moapa) alfalfa cultivars by light microscopy and transmission electron microscopy. Neither differential penetration of M. incognita J2 into Lahontan, nor migration of J2 from Moapa, played a significant role in the resistance mechanism(s). Coiled nematodes in the cortex were observed in greater numbers in the Moapa 48 hours after inoculation. This position was interpreted as a sign of disorientation and starvation. By 96 hours after inoculation, no coiled nematodes were observed in Lahontan. In Moapa, resistance probably depends not only on the failure of the J2 to identify a suitable feeding site and initiate giant cells, but also on its inability to maintain the giant cells, once they are initiated. At the ultrastructural level, 48 hours after inoculation, the most evident change in both cultivars was the appearance of a uniform interstitial material (IM) between the nematode cuticle and the root cell wall. At 96 hours, IM in Moapa was completely agglutinated while in Lahontan it was still uniform or only slightly agglutinated. Due to these clear differences between both cultivars I propose that the IM plays a role in the resistance of Moapa to M. incognita. Immunolabeling techniques were employed to determine if the distribution of the nematode's surface coat, deposited in host tissues, differs in resistant and susceptible alfalfa cultivars. At 72 hours after inoculation, labeling of surface coat epitopes in Moapa was stronger than at 24 and 48 hours after inoculation. Labeling was observed on the nematode's cuticle, the plant cell wall, and the IM. In Lahontan, 72 and 96 hours after penetration, labeling of the surface coat epitopes was observed on the nematode's cuticle, the root cell walls, and the cell wall junctions of cells near the nematode, but not in direct contact with the cell.

West Nile virus (WNV) is a mosquito-borne virus that infects many bird species. Examination of American crows and house sparrows from the Winnipeg region confirmed that WNV levels were at least 1000 times higher in crows than sparrows. No species differences were observed in the level of transcripts encoding a putative WNV receptor, β3 integrin. Differences in mosquito vector competence can be due to differences in the ability of WNV to enter mosquito cells. Using RNAi techniques, the role of two clathrin coat adaptor proteins in facilitating WNV infections in mosquito cells was examined, and the findings suggest that these proteins may act as resistance factors in Aedes aegypti, and as susceptibility factors in Culex quinquefasciatus. These findings will contribute to our understanding of the molecular basis of vector competence in different mosquitoes, and may help us determine whether other species could serve as potential vectors of this health-threatening virus. / October 2015

Les cellules épidermiques des téguments des graines d’Arabidopsis thaliana, espèce myxospermique, libèrent un halo de mucilage polysaccharidique lors de leur imbibition. Les polysaccharides du mucilage sont produits et accumulés au cours du développement de la graine, selon un processus de différenciation déjà largement décrit (Western et al. 2006). Au laboratoire, une mutation naturelle a été mise en évidence chez l’accession Djarly, dont les graines ne libèrent pas de mucilage au cours de leur imbibition. Le clonage positionnel a démontré que le locus affecté chez Djarly code pour un inhibiteur de pectine méthylestérase (PMEI6). Les PMEIs exercent un contrôle négatif sur l’activité des pectines méthylestérases (PME), enzymes qui déméthylestérifient les homogalacturonanes, par la formation d’un complexe PME-PMEI (Di Matteo et al., 2005 ; Hothorn et al., 2004). Des études génétiques, cytologiques et biochimiques ont prouvé que PMEI6 régule la méthylestérification des homogalacturonanes du mucilage et des parois cellulaires distales des cellules épidermiques de la graine retardant la libération du mucilage séminal. L’expression de PMEI6 dépend des régulateurs de transcription GLABRA2 et MUM1. L’activité PME dans les cellules épidermiques des graines est aussi modulée par la subtilisine serine protéase AtSBT1.7, et le phénotype additif du mutant pmei6 atsbt1.7 indique que PMEI6 régule d’autres PMEs. Djarly fait partie d’un groupe de vingt accessions, dont les graines flottent à cause de modifications des propriétés du mucilage séminal. Ces accessions portent au moins dix mutations indépendantes, qui affectent au moins 4 locus différents. Cette étude nous a permis de proposer que la modification des propriétés du mucilage est impliquée dans l’adaptation à l’environnement local, permettant la dispersion à longue distance des graines par l’eau. / Upon imbibition, the myxospermous seeds of Arabidopsis thaliana, form a mucilage from hydrated polysaccharides released from the epidermal cells of the seed coat. These polysaccharides are produced and accumulated during seed development in a differentiation process that has been described in detail (Western et al. 2006). A screen of Arabidopsis accessions identified Djarly as a natural mucilage mutant affected in mucilage release on imbibition. The locus defective in Djarly was identified by map-based cloning as encoding a pectin methylesterase inhibitor (PMEI6). Theseproteinaceous inhibitors negatively control the activity of pectin methylesterases (PME), enzymes that demethylesterify HG, through the formation of a PME-PMEI complex (Di Matteo et al., 2005; Hothorn et al, 2004). Genetic, cytological and biochemical studies demonstrated that PMEI6 regulates methylesterification of homogalacturonans present in mucilage and the outer cell wall of seed coat epidermal cells. Delayed seed mucilage release in pmei6 mutants results, therefore, from the reduced level of homogalacturonan methylesterification. Expression of PMEI6 required the transcription regulators GLABRA2 and MUM1. PME activity in seed coat epidermal cells is also modulated by the subtilisin serine protease AtSBT1.7, and the additive phenotype of pmei6 atsbt1.7 mutants indicates that PMEI6 regulates different PMEs. Djarly is one of twenty accessions where seeds float due to modifications of mucilage properties. At least ten independent mutations are responsible for the mucilage modifications in these accessions, affecting at least 4 different loci. This study has led us to propose that these mucilage modifications are local adaptations that allow longdistance seed disperal on water.

The presented work investigates various theories about the significance of felid coat patterns. Most of the hypotheses are based on the theory of adaptive function of animal colouration. As regards felids, it is generally believed that the coat pattern has the function of aggressive resemblance. Early testimonies about cryptic properties of colouration of cats are summarized to provide the historical perspective of the problem. Other putative adaptive functions of patterns are investigated (intraspecific communication, thermoregulation) and close attention is paid to the option that the spotted coat of the leopard (Panthera pardus) serves as a cue for recognition from the perspective of prey. In the next stage, some of the hypotheses are tested by statistical means. The problem is simplified into search for association between a given category of a coat pattern (e.g. spots, stripes) and usual habitat of felid species (e.g. forest, grassland). Pagel's test for correlated changes is employed to account for phylogenetic relationships. In addition to broadly acknowledged hypotheses, the validity of proposition that juvenile coat patterns have the function of protective resemblance is tested. Finally, the problem of colouration of felids is linked to broader context of theoretical biology. Apart from prevailing...

Metais são largamente empregados em implantes (endopróteses), principalmente nos que tem finalidade ortopédica. O meio fisiológico representa um meio extremamente agressivo, provocando corrosão que pode resultar em sérios problemas aos pacientes que recebem os implantes. Passou-se a utilizar revestimentos sobre o metal-base de implantes para melhorar a sua resistência à corrosão. Mais recentemente, revestimentos porosos de cerâmica, que permitem ao tecido ósseo um crescimento por entre a porosidade, passaram a ser empregados, pois assim dispensam o uso de cimentos acrílicos na fixação da prótese ao osso. A hidroxiapatita (HA) é um dos revestimentos cerâmicos cuja aplicação comercial tem crescido bastante, principalmente em cirurgias de substituição total de quadril (total hip replacement). A corrosão eletroquímica em metais comumente empregados em endopróteses e que aceitam o revestimento de hidroxiapatita (aços inox F138 grau 2, 316L grau 1 e liga Co-Cr-Mo F75)foi estudada, de forma a determinar se este tipo de revestimento influi ou não na corrosão. Através de testes, e análises metalográficas e de microscopia eletrônica de varredura, foi analisada a corrosão destes materiais em dois meios fisiológicos (Soro Bovino e Soro Fisiológico), comparando-se os resultados obtidos com e sem revestimento de hidroxiapatita. / MetaIs are widely used in implants (endoprostheses), mainly in orthopedic ones. The physiologic solution is very aggressive, and promote the metal corrosion, that may drive the patient that receive the implant to serious complications. Coatings over the base metal are being applied to improve the corrosion resistance. Recently, ceramic porous-coating began to be used. This kind of coating allows the bone tissue to ingrowth into the pores of HA-coated, and so avoid the use of acrylic cements do bind the protesis to the bone. The hidroxiapatite (HA) is one of the ceramic coatings that the commercial use have been growing, mainly in total hip replacement surgeries. The Electro-Chemical corrosion in the most common metaIs used in endoprostheses, that accept the HA-coat was studied (stainless steels F138 grade 1 and 316L grade 2 and F75 Co-Cr-Mo alloy). By this way, this study aimed to tell if the HA-coat has any influence in the corrosion rate. Trough chemical-electro corrosion tests, and metallographies, and electronic microscopy, the corrosion of these metaIs was analyzed in two different physiologic solutions, confronting the results between HA-coated and non coated samples. Coated samples had, in both solutions, a lower corrosion rate. The bovine solution was more agressive between non coated samples. But fisiologic solution was more agressive with coated samples. Between coated samples, F75 alloy had the lower corrosion rate. But F138 stainless steel without coating was the less corroded.