The ‘missing wedge’ is a long-standing problem in electron tomography, caused by the use of slab-like flat specimens, which increase in thickness when tilted to high angles. Attempts have been made to reduce the undesirable effects caused by the missing wedge, but the problem remains, particularly for the radiation-sensitive frozen-hydrated specimens used for high resolution imaging. Specimens with cylindrical symmetry offer a way to overcome this problem, since the thickness remains constant at all viewing angles. However, while this has been suggested before, it has never been demonstrated for frozen-hydrated specimens. In this work, I present a way to make cylindrical specimens for electron cryo-tomography, using thin-walled carbon tubes as specimen holders. The tubes are made in a multi-step process, involving carbon deposition on glass micropipette templates and subsequent removal of the glass. Tube diameters are typically a few hundred nanometres, with a wall thickness of 10–20 nm. To make frozen-hydrated specimens, the tubes are filled with an aqueous sample and then plunge-frozen in liquid ethane. Electron images acquired from the tubes have equal quality at all viewing angles, with a tilt range restricted only by the physical limits of the microscope. Tomograms from specimens such as gold particles and liposomes show that the effects of the missing wedge are substantially reduced, with much improved resolution along the electron beam axis. Structural features oriented in all directions are visible in the reconstructions, in marked contrast to tomograms acquired over a more restricted angular range. These results are promising, however some technical challenges remain before this method can be used routinely.

Historically, diagnosis has relied on clinical signs of disease, microscopy and serological testing. However, these approaches have a number of drawbacks for example, differential diagnosis, low sensitivity (microscopy) and the inability to differentiate past from current infections (serology). In the past decade the use of molecular techniques, such as the polymerase chain reactions (PCR) have gained favour. Many research groups have used these techniques to study the molecular epidemiology of diseases in sub-Saharan Africa. Such methodologies rely on the detection of genetic materials and as such are reliant on the specificity of their components and the quality of the starting materials. It is the aim of this thesis is to demonstrate improvements that can be made to sample collection that will help to enhance the reliability of these tests and highlight the importance of the diagnostic parameters. The model that I will use to demonstrate these improvements are African trypanosomes, these are the causative agents of sleeping sickness in humans and nagana in animals, and are wide spread across much of sub-Saharan Africa. My work will be presented as three main sections: Firstly, a comparison of the suitability of various different approaches to cattle blood sample collection – including the genetic materials prepared directly in the field and the use of Whatman FTA®cards – in terms of the provision of appropriate materials for molecular screening will be presented. It was found that uneven distribution of genetic materials occurs across the surface of the FTA®cards due to the matrix chemistry. Therefore suggestions for improvements for the preparation of materials to be stored on these cards and their downstream application are made. Secondly, a comparison between the specificity of the pan-Trypanosoma ITS-PCR reaction and the species-specific reactions is made. The ITS-PCR has gained favour in recent years as it is reported to be capable of identifying a wide range of trypanosomes, as this is a single nested PCR reaction the reduction in time and cost has been very appealing to researchers in this field. My work suggests that this test is not reliable in terms of the accurate detection of trypanosomes species, and in fact on a direct comparison of 969 samples, 37 parasitic events where identified by this approach compared to 197 when species-specific tests were applied. Thirdly, based on my findings from the previous two chapters I present two case studies, the first of which looks to evaluate the impact on the prevalence of trypanosome species in cattle after drug treatment during the Ugandan, Stamp Out Sleeping sickness (www.sleepingsickness.com) campaign. The results of this case study highlight the importance of understanding the relationship that occurs between trypanosome species in mixed infections, my second case study therefore looks to quantifying the infection load of Trypanosoma brucei and T. congolense within the midgut of their insect vector (Glossina morsitans morsitans) using qPCR.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This research study investigates the influence of specimen geometry and grading curve, on the performance of a typical South African unbound granular material. The experimental design incorporates three grading curves to evaluate the influence of grading. In addition, to evaluate the influence of specimen geometry, two specimen sizes were included into the experimental design. Laboratory testing consisted of monotonic tri-axial tests to evaluate the shear performance (Cohesion and Friction Angle) and more complex short duration dynamic tri-axial tests to evaluate the load spreading ability/stiffness (Resilient Modulus) of the selected materials. In order to achieve the objectives of this study, a large tri-axial apparatus was needed that could accommodate specimens as large as 300mm ϕ * 600mm high. This would allow a full grading of large aggregate (up to 50mm particle size) to be accurately evaluated. Further development and commissioning of such a large triaxial apparatus therefore formed part of this study. The representative parent material selected for testing consisted of a G2 graded crushed Hornfels stone. The material was dried and sieved into fractions where after it was carefully reconstituted to allow for accurate control of specimen grading during specimen preparation. The three grading curves consisted of two adjusted grading curves (referred to as S19 and G19C), adjusted from the full G2 grading, and the full G2 grading itself (referred to as the Full grading curve). Material property tests, Sieve Analysis, Bulk Relative Density (BRD) and Optimum Moisture Content (OMC) tests were performed to gain an understanding of the material characteristics. Moisture-Density relationship curves were developed to identify a common Moisture Content that, for all three grading curves, would yield a common Dry Density. A Moisture Content of 4.7% was identified that would yield a Dry Density of 2340 kg/m3 for all three grading curves. This density could be achieved for both sizes of specimen preparation apparatuses without damaging material particles. Specimens were compacted using the representative vibratory hammer compaction method, sealed and left for 24 hours to allow redistribution of moisture and initial development of Cohesion. The shear parameters (Cohesion and Friction Angle) were investigated through monotonic tri-axial testing. It was found that Cohesion and Friction Angle are influenced by both grading curve and specimen geometry. Cohesion was found to reduce as the coarseness of the material grading increased (i.e. finer S19 grading yielded higher Cohesion than its coarser G19C counterpart) and the Friction Angle was found to increase with increase coarseness (i.e. finer S19 grading yielded lower Friction Angles when compared to the G19C grading). The influence of specimen geometry was also investigated. It was observed than Cohesion decreased with an increase in specimen size. Friction Angle on the other hand was found to increase with increased specimen size. From dynamic tri-axial test results, it was observed that the Resilient Modulus is influenced by both specimen geometry and grading curve. The influence of specimen geometry however is complex and no constant trend throughout the grading curves tested could be identified. Grading curve however was found to increase the Resilient Modulus for coarser gradings (i.e. coarser G19C vs finer S19). Increased large particle-to-particle contact area yields higher friction within the material specimen, resulting in lower strains induced by higher stresses, i.e. higher Resilient Modulus. It was shown, for both monotonic and dynamic tri-axial tests, that the coarser G19C grading curve yields more representative results to that of the Full grading curve when compared to the finer S19 grading. This was observed for shear and resilient performance properties. Additionally, a simple design case study yields similar trends. In conclusion, material characterisation plays an important role in the design of unbound granular materials (UGM’s). Current laboratory characterisation techniques however used adjusted gradings to limit the effects stemming from the ratio between specimen diameter and maximum particle size. This research has shown that some of the current practices do not best represent the true in-situ grading. It has been shown that both grading curve and specimen geometry influence the performance of UGM’s which, in turn, influences the design of a pavement structure. Therefore, accurate modelling of the true in-situ grading, through testing apparatuses capable of accommodating in-situ gradings, is required. / AFRIKAANSE OPSOMMING: Hierdie navorsingsstudie evalueer die invloed van proefstukgeometrie en gradering, op die gedragseienskappe van ‘n tipiese Suid Afrikaanse ongebinde granulêre aggregaat. Om die invloed van gradering te evalueer, is ‘n eksperimentele ontwerp ontwikkel wat drie materiaal graderings insluit. Verder, om die invloed van proefstukgeometrie te evalueer, is twee proefstukgroottes toegevoeg tot die eksperimentele ontwerp. Monotoniese drie-assige toetse is uitgevoer om die skuifsterkte (Kohesie en Wrywingshoek) van die materiaal te ondersoek. Addisioneel is die styfheid (Veerkragmodulus) van die materiaal ondersoek deur dinamiese drieassige toetse. Om die doelwitte van hierdie studie te bereik was ‘n groot skaalse die-assige toets apparaat benodig wat groot, 300mm ϕ * 600mm hoogte, proefstukke kan akkommodeer. So ‘n apparaat laat toe dat die volle gradering van aggregaat (tot en met 50mm korrels) akkuraat geëvalueer kan word. Daarom vorm die ontwikkeling en opstelling van so ‘n apparaat deel van hierdie studie. Die tipiese Hornfels gebreekte klip, met ‘n G2 gradering, wat ondersoek is, was gedroog en in verskeie fraksies gesif om die akkuraatheid van proefstuk voorbereiding te beheer. Die drie graderings bestaan uit twee aangepaste graderings (S19 en G19C gradering skale), aangepas vanaf die volle G2 gradering, en die vol G2 gradering homself (verwys na as die “Full” gradering skaal). Materiaal gedragstoetse, Sif Analises, Nat Gekompakteerde Relatiewe Digtheid (BRD) en Optimum Vog Inhoud (OVI) toetse, was uitgevoer om die materiaal eienskappe te ondersoek. Om ‘n gemeenskaplike Vog Inhoud en Droë Digtheid, wat vir al drie graderings geld, te vind, is Vog-Digtheid verhoudingskurwes ontwikkel. Vanaf die kurwes is identifiseer dat ‘n Vog Inhoud van 4.7% ‘n Droë Digtheid van 2340 kg/m3 vir al drie graderings sal lewer. Vibrasie kompaksie is toegepas om albei skale van proefstukke te kompakteer waarna die proefstukke vir 24 uur geseel is om vogverspreiding en ontwikkeling van Kohesie toe te laat. Monotoniese drie-assige toetse is uitgevoer om die skuifsterkte parameters (Kohesie en Wrywingshoek) te ondersoek. Die resultate het gewys dat beide gradering en proefstukgeometrie die Kohesie en Wrywinshoek beinvloed. gradering lewer hoër Kohesie waardes i.v.m. die growwer G19C gradering). Die Wrywingshoek is gevind om te verhoog soos die grofheid van die gradering verhoog (m.a.w. die fyner S19 gradering het laer Wrywingshoeke gelewer i.v.m. die growwer G19C gradering). Resultate het verder gewys dat groter proefstukke laer Kohesie en hoër Wrywingshoeke lewer. Daar kan wel gedebateer word dat variasie in materiaal die verandering van die skuifsterkte parameters gee, maar die proefstukvariasie is beperk om sodoende die invloed daarvan onopmerkbaar te maak.. Verder is die verlaging in Kohesie en verhoging in Wrywingshoek, a.g.v. ‘n vergroting in proefstuk grootte, vir albei aangepaste graderings geobserveer. Dit is ‘n moontlike aanduiding dat die verandering nie materiaal afhanklik is nie maar eerder beinvloed word deur die grens toestande tydens kompaksie. Dinamiese drie-assige toets resultate het gewys dat die Veerkragmodulus beinvloed word deur beide proefstuk geometrie en gradering. Daar is gevind dat die invloed van proefstukgeometrie kompleks is, en geen konstante verhouding, wat vir alle toets graderings geld, kon identifiseer word nie. Vir die invloed van gradering is daar gewys dat die Veerkragmodulus hoër is vir die growwer gradering (m.a.w. G19C gradering lewer hoër styfheid as S19 gradering). ‘n Verhoging in korrel-tot-korrel kontak area lewer hoër interne wrywing in die proefstuk wat bydrae tot laer vervorming by hoër spannings, m.a.w. hoër Veerkragmodulus. Baie interessant, vir beide monotoniese en dinamiese drie-assige toetse is gevind dat die growwer G19C gradering, i.v.m. die fyner S19 gradering, die ware G2 (Full) gradering beter verteenwoordig. Hierdie observasie is geldig vir beide die skuifsterkte parameters en weerstands eienskappe. Aggregaat karakterisering is ‘n belangrike deel in die ontwerp van ‘n ongebinde granulêre materiaal laag. Huidige karakterisering metodes gebruik aangepaste graderings sodat resultate nie beinvloed word deur die verhouding tussen proefstuk diameter en maksimum klipgrootte nie. Hierdie ondersoek het gevind dat van die huidige aanpassings nie die ware gradering verteenwoordig nie. Die resultate wys dat beide gradering en proefstuk geometrie die gedrag van die ongebinde granulêre materiaal beinvloed, so ook die ontwerp van ‘n padstruktuur. Daar is dus ‘n behoefte om die ware gradering te ondersoek wat slegs moontlik is met groot skaalse toets apparaat, wat groot klip korrels kan toets. Verder, indien daar ‘n verstandhouding tussen huidige (klein skaalse) toets apparaat en groot skaalse apparaat ontwikkel kan word, kan resultate aangepas word, vanaf die klein skaalse resultate, om die ware materiaal gedrag meer te verteenwoordig.

The behaviour of spot welded joints is to be studied in shear mode by using the end notched flexure (ENF) specimen. The specimen counts on several spot welds spaced with the same gap along the entire length except for the notch. Different configurations of the test specimen spacing gap and spot diameter are to be preliminary designed in software PTC-CREO 2.0 in order to obtain accurate results. The results obtained from the software are to be compared with the experimental analysis performed by means of a servo-hydraulic testing machine. Both the virtual and the experimental results will be used to extract the stress-shear displacement relation around the first spot weld which is in contact with the notch, that is, the corresponding cohesive law. In addition, a comparison between adhesive and spot weld behaviours will be carried out by means of analytical equations in order to prove an existing equalisation between each other. Despite assuming several sources of error and after facing some problems related to the experimental work, accurate convergences between experimental and theoretical results were not accomplished in any of the three tests performed in lab. Due to the plastic deformation of the specimens in lab, the cohesive law was possible to be extracted only from the theoretical analysis, but not from the experimental one. In its place, the load-shear displacement was extracted. Some alternatives to solve this issue and to improve the performance of the tests are given at the end of this paper.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Les procédés de mise en forme des tôles minces sont largement utilisés dans l'industrie. L’utilisation optimale des alliages légers ou des aciers à haute résistance, propices à des économies d’énergie dans le domaine des transports, nécessite une connaissance approfondie de leurs limites de formabilité. Classiquement, la formabilité d’une tôle est caractérisée par l’apparition d’une striction localisée. Cependant, pour des chargements spécifiques (chemins de déformation complexes ...), la rupture caractérise la formabilité du matériau, la courbe limite de formage à rupture (CLFR) plutôt que celle à striction (CLFS) doit alors être considérée. Pour identifier la CLFS et la CLFR pour des chemins de déformation linéaires et non-linéaires, les méthodes conventionnelles requièrent différents dispositifs expérimentaux et différentes formes d'éprouvette pour atteindre une large gamme de chemins de déformation. L'essai de traction biaxiale, associé à une éprouvette cruciforme, est possible pour la réaliser. De plus, le changement de chemin est activé au cours de l’essai, sans déchargement. Le premier objectif de cette étude est de montrer que l'essai de traction biaxiale, associé à une forme unique d'éprouvette cruciforme, permet de tracer la CLFS et la CLFR pour plusieurs chemins de déformation, qu’ils soient linéaires ou non-linéaires. En premier lieu, des essais ont été réalisés sur des tôles d’alliage d’aluminium 5086 (épaisseur initiale de 4 mm) à partir d’une forme d’éprouvette déjà proposée au laboratoire. Une nouvelle forme d'éprouvette cruciforme a été proposée pour des tôles moins épaisses (2 mm), plus répandues. Cet éprouvette a été validée pour étudier la formabilité d’un acier dual phase DP600 pour plusieurs chemins de déformation. Le deuxième objectif est de discuter la validité de critères classiques de rupture ductile. Pour les deux matériaux, un critère a finalement été identifié pour prédire assez précisément les résultats expérimentaux. / Sheet metal forming is very common in industry for producing various components. The optimal use of light alloys or high strength steels in transportation for energy economy, requires in-depth analysis of their formability. Usually, the formability of sheet metal is controlled by the onset of localized necking. However, under specific loadings (complex strain paths...), fracture characterizes the formability and the forming limit curve at fracture (FLCF) instead of the forming limit curve at necking (FLCN) should be considered. For identifying FLCN and FLCF under linear and non-linear strain paths, conventional methods require different experimental devices and geometrical specifications of specimen to cover a wide range of strain paths. However, using the in-plane biaxial tensile test with just one shape of cruciform is sufficient for that, even changes of strain path without unloading can be made during the test. The first objective of this study is to show that the in-plane biaxial tensile test with a single type of cruciform specimen permits to investigate the FLCN and FLCF of sheet metals under different linear and non-linear strain paths. Firstly, the forming limit strains at fracture of AA5086 sheet (t=4 mm) under linear and non-linear strain paths have been characterized, by testing an existed dedicated cruciform specimen. Thinner sheet metals are often used in industry, so a new shape of cruciform specimen with an original thickness of 2 mm was proposed. This specimen is successfully used to investigate the formability of DP600 sheet under linear and two types of non-linear strain paths. The second objective is to discuss the validity of commonly used ductile fracture criteria to predict the onset of fracture. Some ductile fracture criteria were used to produce numerical FLCFs for AA5086 and DP600 sheet. Finally, for the two tested materials, it is possible to find a criterion to predict the experimental FLCFs for either linear or non-linear strain paths.

The master´s thesis deals with a process called cold kinetic deposition technology. Using this technology, a copper layer was formed on a sample with an aluminium base by high-pressure cold spraying at a pressure of 25 bar. In the experimental part, the influence of corrosion degradation in the salt chamber was assessed at the time cycles of 100 h, 200 h and 300h, where changes in internal and surface resistances before and after corrosion were measured. Subsequently, the analysis of corrosion products was performed, where the extent of corrosion attack was determined using an electron microscope. These methods led to a final evaluation of the boundary limits of the applied coating layer by cold kinetic deposition, after the effect of corrosion. Finally, a theoretical application of this technology was suggested. It was discovered that the sample placed and left in the corrosion chamber for the longest time was the most affected by corrosion. Finally, a theoretical application of cold kinetic deposition was proposed.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20428号 / 農博第2213号 / 新制||農||1048(附属図書館) / 学位論文||H29||N5049(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 井鷺 裕司, 教授 柴田 昌三, 教授 神﨑 護 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

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