Analysis of fatigue samples sectioned from commercial 319 (Al-Si-Cu-Mg) alloy cylinder block castings showed that shrinkage pore networks and oxide films played an important role in fatigue failure. A reduced pressure technique was employed to study the relationship between porosity and oxide films. Links between oxide films and porosity were made and mechanisms for the inflation of films into porosity networks were established. Tensile tests performed on samples cast with and without filters showed that the ultimate tensile strengths of the filtered group had a Weibull modulus 2.4 times that of the unfiltered. Samples with abnormally low strengths were found to contain oxide film defects. These films had an approximately 5 times greater damaging effect on strength than that predicted by reduction in cross sectional area. The fracture strengths of these flawed samples were found to obey a linear elastic fracture mechanics model (LEFM). A LEFM crack growth model was particularly successful in predicting the life of fatigue samples that initiated at oxide films. Having crack-like geometry, and a minute crack tip radius, oxide films effectively acted as preformed cracks. Consequently there was an absence of crack nucleation time, explaining the correlation of predicted propagation life to fatigue life.

In the first of the metalforming operations considered, that of plane-strain side-pressing, the finite-element predicted deformation behaviour of 60-40 brass and 7075 aluminium alloy has been compared with experiment. Both visioplasticity and hardness studies have been performed. The macrohardness survey was found to be the most appropriate in validating the use of the finite-element technique. The numerical calculations of the local stress and strain distributions are then used with a number of previously published continuum fracture criteria to predict the fracture initiation sites. For certain of the successful criteria the level of deformation at fracture has also been predicted using critical values of fracture found experimentally from an axisymmetric tensile test. For the operation of plane-strain side-pressing, very good agreement with both the experimental fracture initiation site, and the level of deformation at fracture, is reported for the criterion of a critical value of generalised plastic strain at fracture, and the equivalent criterion of generalised plastic work. The second metalforming operation considered is simple upsetting. The fracture initiation behaviour of 60-40 brass has been examined for specimens of the four initial aspect ratios of 0.5, 1.0, 1.5 and 2.0. Again, the generalised plastic strain/work criterion has successfully predicted the experimental fracture initiation sites in all cases. However, satisfactory levels of deformation at fracture predictions have only been found for the two lower aspect ratio specimens. A small range of strip compression and tension operations on 60-40 brass compose the third type of metalforming operation considered in this thesis. Yet again the generalised plastic strain/work criterion has successfully predicted the fracture initiation site found experimentally but not the level of deformation at fracture. Finally, the axisymmetric extrusion of 60-40 brass and 7075 aluminium alloy is examined. For the brass using the generalised plastic strain/work criterion, good agreement with experiment has been found for both the fracture initiation site and level of deformation at fracture found experimentally. However, for the aluminium alloy only the correct fracture initiation site has been found. In summary, it appears that the fracture criterion of a critical value of generalised plastic strain/work has successfully predicted the fracture initiation site found experimentally in all the operations considered in this thesis but has been unable to consistently predict the correct level of deformation at fracture. These differences in the predicted and experimental level of deformation at fracture cannot be explained with reference to the finite-element calculated levels of hydrostatic stress. Further work is necessary to explain this difference.

Using supramolecular principles, we have been designing luminescent lanthanide complexes with a defined hairpin bis-interlacator in order to obtain luminescent probes able to recognise DNA. The complexes are comprised of Platinum(II) terpyridine, which acts as a DNA recognition site and is brought together with a "remote" luminescent lanthanide unit. All the synthetic approaches were based on the accessibility of the lanthanide-platinum complexes by the self-assembly of different components in a one pot reaction. Thus, we have been able to isolate a water soluble heterometallic complex based on thiophenal linkage named [LnPt\(_2\)]Cl\(_2\). The complex has a relatively weak lanthanide luminescence, which increases upon addition of DNA. Photophysical and DNA binding properties of the lanthanide-platinum complex were investigated by UV-vis absorption, luminescent studies and circular and linear dichroism. Oligonucleotides of twelve bases were also used to investigate the intercalation [LnPt\(_2\)]Cl\(_2\) and the mono-intercalator AATP used as control compound. Using bidimensional NMR techniques, we investigated the binding site for [LnPt\(_2\)]Cl\(_2\) and AATP upon interaction with Dickerson-Drew sequence. The sulphur lanthanide-platinum linkage in [LnPt\(_2\)]Cl\(_2\) was replaced with an acetylide one in order to introduce new photophysical features. Thus the self-assembly procedures based on DTPA-bis(amido-acetylide) and a platinum(II) terpyridine led us to isolate a new lanthanide-platinum complex named [LnC\(\equiv\)CPt\(_2\)] (CH\(_3\)SO\(_3\))\(_2\). The photophysical properties and the DNA binding properties toward interaction with CT-DNA were investigated. The complex named LnC\(\equiv\)CPt\(_2\)](CH\(_3\)S)\(_3\))\(_2\) exhibited a relatively strong lanthanide luminescence that increased upon addition of DNA. The bi-functional metal complex [EuLPt](PF\(_6\)) (where Pt=platinum-2,2':6'2"-terpyridine and L=assymmetric DTPA bisamide ligand with a thiopheno pendant arm and a quinoline moiety) was synthesised and the interaction of [EuLPt](PF\(_6\)) with CT-DNA was examined by luminescence spectroscopy, linear and circular dichroism studies and thermal denaturation studies. The [EuLPt](PF\(_6\)) retained the ability to increase its luminescence upon the addition of CT-DNA. The binding properties of the complexes were tested toward interaction with plasmid DNA by gel electrophoresis and properties such as the unwinding angle were measured. The bis-intercalators [LnPt\(_2\)]Cl\(_2\) and [LnC\(\equiv\)CPt\(_2\)](CH\(_3\)SO\(_3\))\(_2\) showed the ability to uncoil DNA almost as well as cisplatin and at low concentrations, while almost double the amount of mono-intercalators, such as [EuLPt](PF\(_6\)) is required to observe the same uncoiling effect.

Ti-5Al-5Mo-5V-3Cr (Ti-5553), a relatively new generation beta titanium alloy has the advantage of high strength. It is a current generation alloy used in landing gear. Currently, landing gear components are large scale and processed through forging, followed by complex heat treatments. HIPping (hot isostatic pressing) is an alternative way to process this alloy. In this project, work was carried out on investigating microstructures and mechanical properties of HIPped Ti-5553 alloy. During comparisons on fracture toughness of different types of specimens, specimens are first heat treated to a similar strength level. And fracture toughness values are calculated at the same strength level circumstance. Various microstructures are obtained through different heat treatments. Different microstructures can be achieved through specified treated temperature/ time and quenching methods. Results show that larger grain size and coarser intergranular lath-like grain boundary alpha can improve the fracture toughness. One shell-like microstructure is obtained through different heat treatment conditions. Mechanical test was carried out on this kind of microstructure and compared to normal beta annealed microstructures. To investigate the influence of microstructure on fracture toughness, techniques including optical microscope (OM), scanning electron microscope (SEM), and confocal laser scanning microscope have been used.

Entomopathogenic nematodes (EPNs) (genera Heterorhabditis and Steinernema) kill their invertebrate hosts with the aid of a mutualistic bacterium. The bacteria (Xenorhabdus spp. for steinernematids and Photorhabdus spp. for heterorhabditids) are primarily responsible for killing the host and providing the nematodes with nutrition and defense against secondary invaders. Photorhabdus is a Gram-negative bacterium in the Enterobacteriaceae family with high virulence towards their insect hosts. To achieve high mortality rates Photorhabdus produces a variety of virulence factors such as toxins, lipases, proteases, secretion systems, and fimbriae. EPNs are amenable to laboratory rearing and mass production for biocontrol applications against insects using in vivo or in vitro methods; however, in vitro liquid culture is considered to be the most efficient. In this method the symbiotic bacteria are cultured prior to the addition of their partner EPN. This can leave the bacteria susceptible to a number of problems such as genetic drift and inadvertent selection. Regardless of the culture method the symbiotic bacteria exhibit trait deterioration or changes due to laboratory rearing. This project had three primary aims: 1) investigate the role of nutrition in trait deterioration, 2) examine virulence evolution using a phylogenetic context, and 3) identify genes that are necessary for survival and virulence inside the insect host. Prior to studying these objectives we first determined the optimal conditions for growing and counting viable cells of Photorhabdus. We discovered that growth is enhanced by the addition of pyruvate to growth media. To determine the role of nutrition in trait deterioration we repeatedly sub-cultured Photorhabdus in three different media types. Throughout this study we found that, in contrast to previous studies, trait deterioration does not always happen and the environment influences trait deterioration. Furthermore, based on our phylogenetic studies we found that Photorhabdus spp. are evolving to an increase in insect virulence. Lastly, using Tn-seq we determined a list of 84 genes that are needed for efficient virulence inside the insect host and provide suggestions for ongoing research efforts.

The rhizobia-legume symbiosis is the most agriculturally significant source of naturally fixed nitrogen, accounting for almost 25% of all biologically available nitrogen. Rhizobia-legume compatibility restrictions impose limits on symbiotic nitrogen fixation. In many cases, the molecular basis for symbiotic compatibility is not fully understood. The signals required for establishing a symbiotic partnership between nitrogen-fixing bacteria (e.g. Sinorhizobium meliloti) and leguminous plants (e.g. Medicago truncatula) have been partially characterized at the molecular level. The first stage of successful root colonization is competitive occupation of the rhizosphere (which is poorly understood). Here, the bacteria introduce themselves as potential symbiotic partners through the secretion of glycolipid "Nod" factors. In response, the host facilitates a more exclusive mode of colonization by the formation of a root nodule – a new organ capable of hosting dense intracellular populations of symbiotic rhizobia for nitrogen fixation. This dissertation reports the exhaustive identification of S. meliloti genes that permit competitive colonization of the M. truncatula rhizosphere, and includes a mechanistic study of one particular bacterial signaling pathway that is crucial for both rhizosphere colonization and nodulation. I have made use of Tn-seq technology, which relies on deep sequencing of large transposon mutant libraries to monitor S. meliloti genotypes that increase or decrease in relative abundance after competition in the rhizosphere. This work included the collaborative development of a new computational pipeline for performing Tn-seq analysis. Our analysis implicates a large ensemble of bacterial genes and pathways promoting rhizosphere colonization, provides hints about how the host plant shapes this environment, and opens the door for mechanistic studies about how changes in the rhizosphere are sensed and interpreted by the microbial community. Notable among these sensory pathways is a three-protein signaling system, consisting of FeuQ, FeuP, and FeuN, which are important for both rhizosphere colonization and nodule invasion by S. meliloti. The membrane-bound sensor kinase FeuQ can either positively or negatively influence downstream transcription of target genes by modulating the phosphorylation state of the transcriptional activator FeuP. FeuN, a small periplasmic protein, inhibits the positive mode of FeuPQ signaling by its direct interaction with the extracellular region of FeuQ. FeuN is essential for S. meliloti viability, underscoring the vital importance of controlling the activity of downstream genes. In summary, I have employed several powerful genetic, genomic, computational, and biochemical approaches to uncover a network of genes and pathways that coordinate root colonization and nodulation functions.

No description available.

&Ccedil / EMTAS Steel Plant produces alloy steels used principally by the automotive industry. Demands of customers for cleaner steel with &ldquo / fewer, smaller and homogenously distributed inclusions&rdquo / are getting tighter with time. The tight demands of the customers are checked by ultrasonic testing and faulty regions are cut off and scrapped which results in production losses in steel plants. Decreasing production losses due to scrapping by producing cleaner steels is therefore a major concern. The objective of this study is to investigate factors affecting the cleanliness of the steels produced by &Ccedil / EMTAS. With this objective, the steelmaking practice used was thoroughly investigated and the possible origins of inclusions in the final product was tried to be found. Based on the findings, process parameters like temperature, time, quantities of additives to steel, intensity of stirring etc. were varied with the objective of determining the optimum production practice.

Extensive research in recent years has failed to develop any essentially new method of large scale tungsten production. A new tungsten powder production technique from calcium tungstate (CaWO4) has recently been reported. In this thesis, this technique was further explored from the aspects of electrochemical reduction mechanism and kinetics, applicability to scheelite concentrates and industrial production. Cyclic voltammetry, constant potential and constant current electrochemical reduction tests were performed to determine the reversible cell potential. Analyses of the experimental results revealed that at least 2.2 V was required to compensate the potentials for the accompanying cell reaction and the electrode polarizations. A cell reaction was proposed by associating the experimental results and the Gibbs Energy changes of the possible reactions. An experiment (mixture) design was created to optimize the process parameters of the electrochemical reduction of CaWO4 to W in molten CaCl2-NaCl eutectic mixture. Temperature, applied voltage and the length of Kanthal wire winding of the CaWO4 pellets were selected as the process parameters and allowed to vary between the predetermined minimum and maximum values. The rates of the electrochemical reductions were interpreted from the variations of current and total charge vs. time graphs under different conditions. The analysis pointed out 640oC and 2.81 V from the created mixture design for the fastest reduction and it was seen that the effect of Kanthal wire winding on the output current was less pronounced when compared to the other two parameters. Another set of experiments was performed by full factorial design to investigate the cleaning procedure needed to remove calcium containing byproducts after electrochemical reduction experiments. Three levels were determined prior to the experiments for the selected three parameters / temperature, acid concentration and exposure time. Main effect and interaction graphs for calcium percent as a function of process parameters were plotted. Calcium contents of the samples were determined by XRF measurements. A 300 g/day capacity tungsten production line was manufactured to take the process one step closer to industrialization. Problems at larger scale were addressed as incomplete reduction, oxidation of graphite and corrosion of cathode materials. After careful research, AISI 316 Ti steel was found to impart sufficient resistance to highly corrosive environment. Oxidation of graphite anode inside the cell was lowered to acceptable levels by continuous nitrogen flow. Metallic tungsten powder was obtained from rich and flotation concentrates of Uludag Etibank Volfram Plant (closed in 1989) together with mainly iron. It was seen that tungsten and iron do not make compounds at the temperatures used for reduction (600-750oC). A basic diffusion model in the electrolyte was developed to better understand the decrease in current values and incomplete reduction encountered during large scale production. The model was used to simulate the recorded current vs. time graphs of selected experiments.

Bird¡¦s nest is the saliva from the Colloclia that have a lot of mucin and sialic acid. However the sialic acid is an important intermediate of influenza virus infection. In 2006, Guo et al was confirmed the Inhibitory effect of bird¡¦s nest extract on influenza virus infection. But the anti-virus component has not been isolated and purified. First, the bird's nest used in this study was proved to be a pure bird¡¦s nest by SDS-PAGE, sialic acid content and protein content. Qualification analysis by SDS-PAGE showed sample possessed three bands at about 50 kDa, 100 kDa and 150 kDa, by Warren assay showed sample possessed a sialic acid content about 10% of dry weight, by Kjeldahl method showed sample possessed a protein content about 50% of dry weight, and by fluorescence analysis in 365 nm showed sample emitted a blue-white light. According to the criteria on previous studies, the sample was considered to be a real and pure bird¡¦s nest. Subsequently, the sample was applied to pronase digestion and then separated by Bio-gel P2 for size exclusion chromatography. All fractions were performed carbohydrate analysis including sialic acid. In lectin blotting, Maackia amurensis agglutinin (MAA) lectin can interact with the fraction that suggest the structure of sialic acid is sialic acid-2,3 galactose in bird¡¦s nest. And carbohydrate membrane array to demonstrate the influenza virus of H5N1 and H1N1 can bind the fractions that suggest the antivirus effect of bird¡¦s nest. These fractions will be further analyzed by neutralization assay to study their antivirus effects in vitro.