The objective of the thesis is to understand the particle/substrate interaction of micron-sized High Purity (HP) aluminum (Al) powder particles with varying surface oxide/hydroxide layers, during single particle impact and determine the critical impact velocity (CIV). Advancements in analytical techniques enable in-situ supersonic impact of individual metallic micro-particles on substrates with micro-scale and nanosecond-level resolution. This novel capability allowed direct observation and measurement of a material-dependent threshold velocity, above which the particle underwent impact-induced material ejection and adhered to the substrate, (critical impact velocity). The data was then compared to empirical, as well as predicted values of the CIV from published data that were based upon theoretical iso-entropic fluid dynamics models. A major emphasis of this research was to perform, in-depth characterization of the Al powder in the as-received, gas atomized state and subsequent to controlled temperature and humidity exposure (designed to form a prescribed oxide and/or hydroxide surface layer) and finally after single particle impact. Analytical techniques including XPS, ICP, IGF, TEM and SEM were performed to determine the species of oxide and/or hydroxide, bulk chemical composition, oxygen content and thickness of the surface oxide/hydroxide layer. Finally, bulk samples of material were produced by the cold spray process, from powder representing select test groups and subsequently characterized to determine tensile and hardness properties, chemistry, microstructure and conductivity. A fundamental understanding of the role of surface oxidization in relationship to particle deformation during impact and the bonding mechanism will be applicable toward the development of optimized parameters for the cold spray (CS) process. Results from this study will aid in the development of industrial practices for producing, packaging and storing Al powders.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

“Children of a Former Future” argues that the political upheavals of the twentieth century have produced a body of German-language literature that approaches children and childhood differently from the ways these subjects are conventionally represented. Christa Wolf, Herta Müller, and Jenny Erpenbeck use the child as a device for narrating failed states; socialization into obedience; and the simultaneous violence and fragility of normative visions of the future. In their narratives of girlhood under authoritarian or repressive societies, these authors self-consciously decouple the child from the concept of futurity in order to avoid reproducing the same representational strategies as the twentieth-century authoritarian regimes that co-opted the child for political ends. Examining literature from the GDR, Communist Romania, and post-Reunification Germany, “Children of a Former Future” argues that these representations offer important insights into the fields of German literary studies, queer theory, and feminist scholarship. The dissertation contends that a historically-grounded reading of Cold War and post-Cold War German-language literature can meaningfully contribute to and complicate current feminist and queer scholarship on the child. This scholarship has focused primarily on historical, social, and cultural developments associated with Western democracies and capitalism. “Children of a Former Future” demonstrates how a consideration of literature from Socialist and post-Socialist context complicates these theorizations of the child. At the same time, the dissertation demonstrates how the analytical modes developed by queer and feminist scholarship can create new frameworks for the interpretation of German-language literature. “Children of a Former Future” examines authors who intentionally set out to complicate readers’ preconceptions about children in their writing, specifically the pervasive theme of childhood innocence. Written during the 1970s, Christa Wolf’s Kindheitsmuster (1976) examines the effects of authoritarianism on childhood development, as well as critiquing the German Democratic Republic’s founding historical myths. Herta Müller’s Niederungen (1982/4) and Herztier (1994) examine childhood in an ethnic German community in Communist Romania; Müller’s protagonists grapple with the legacies of their parents’ experiences with fascism and Soviet labor camps, as well as the experience of entering Romanian society as a cultural minority during the dictatorship of Nicolae Ceaușescu. Writing after the fall of the Berlin Wall, Jenny Erpenbeck’s Geschichte vom alten Kind (1999) and Wörterbuch (2005) critically examine the emotional impact of adult idealizations of childhood through the lens of post-authoritarian transition states. “Children of a Former Future” argues that these narratives use the child to reflect on socialization into obedience and conformity; kinship formations; social reproduction; trauma; and political life. Wolf, Müller, and Erpenbeck highlight the ramifications of the emotional burdens placed on children, particularly on girls. Their representations resist conventional idealizations of children and childhood. Intensely concerned with complicity, the authors scrutinize how children are taught to conform to and even revere repressive social systems. The authors posit that certain childrearing practices in fact enable the rise of authoritarianism, in that they condition children that love is contingent upon obedience. The dissertation argues that for these authors, examinations of childhood are at once opportunities to sift through the experiences that begin to constitute the individual self, and to analyze how these psychological dynamics contribute to, sustain, and reproduce larger social and political dynamics.

Este trabalho consiste basicamente em dois experimentos: Determinação da equação de estado de um gás frio aprisionado, e na comparação das temperaturas de uma amostra de átomos confinadas em dois tipos de armadilhas magneto-ópticas. No primeiro experimento utilizamos a generalização do conceito de pressão e volume que foram redefinidos de maneira apropriada para alcançamos uma equação de estado. Experimentalmente nossa amostra apresentou um desvio do esperado para um gás ideal, dessa forma utilizamos uma expansão virial com as novas definições de pressão e volume para investigar as interações entre os átomos. Já no segundo experimento utilizamos uma técnica que mede transiente temporal da absorção do feixe pelos átomos através de um fotodetector para a obtenção da temperatura. Neste experimento obtemos temperaturas equivalentes para as duas armadilhas. / This work consists of two experiments: Determination of the state equation a trapped cold gas, and the comparison of the temperatures of confined atoms in two types of magneto-optical traps. For the first experiment we generalized and defined a new pressure and volume concept and we reached a state equation. Experimentally our sample presented a deviation of the ideal gas, in that way we used a virial expansion with the new pressure and volume definitions to investigate the interactions among the atoms. In the second experiment we used a technique that measures temporal variation of the absorption of a probe beam that crosses the atoms by a photodetector, witch gives us the information about the temperature. We have found equivalent temperatures for the two traps.

A multi-disciplinary study of sediment core records from the Mingulay Reef Complex, a cold-water coral reefs system off western Scotland, highlights the potential of cold-water corals from which detailed centennial-scale palaeo-environmental reconstructions can be derived. This study provides a new insight on the mechanisms controlling Lophelia pertusa reef build-up, shifts in biodiversity, the physical/chemical/biological processes and the sedimentary regime. A detailed record of Mingulay Complex growth history shows unprecedented high average accumulation rates of 3 – 4 mm a-1. Marine radiocarbon reconstruction derived from paired 14C and U-series dated fossil corals revealed substantial abrupt oceanic shifts during the Holocene that have repetitively affected cold-water coral growth, eventually causing local disappearance. These periods of reduced accumulation rates are synchronous with other coral structures from the NE Atlantic illustrating basin wide events. Finally, trace/minor element ratios reproducibility within coral skeleton was investigated to test if palaeo-environmental reconstructions could be made from cold-water corals.

Salmonella enterica sv. typhimurium is a major food-borne pathogen, in part because of its ability to persist and multiply at low temperatures. Adaptation to refrigerated temperatures involves induction of a multigenic cold shock response (CSR); where gene expression is co-ordinately modified, to express cold shock proteins (CSPs). Characterisation of CspA, the major cold shock protein, instigated the identification of other CspA paralogues; which are highly conserved and widespread across species. Six CspA paralogues have previously been identified in S. typhimurium and a csp null strain, lacking all CspA paralogues made. This strain is unable to grow following cold shock, demonstrating that the CspA paralogues play an essential role during low temperature adaptation. The individual CspA paralogues exhibit distinct expression profiles; including expression of CspC and CspE at optimal temperature and CspA and CspB following cold shock. This work investigates the transcriptional changes of S. typhimurium during cold shock and the role of the CspA paralogues under both optimal and cold shock conditions. Using a bacteriophage Mu transposon library (Francis and Gallagher, 1993) this study identifies 7 novel cold induced targets and analyses their native expression levels in SL1344 and the csp null strain during cold shock. This revealed that the regulation of 5 discrete loci including tRNApro2, cpxP and 3 uncharacterised ORFS are mediated by CspA paralogues. In addition, the transcriptional profiles of a highly conserved and essential set of genes encoding known cold shock proteins, NusA, IF2, RbfA, PNPase and CsdA have been characterised. Comparative Northern analysis of SL1344 and the csp null strain has identified a role for CspA paralogues in mediating low temperature induction of three of these genes, through transcription anti-termination. Taken together these results demonstrate that during adaptation to low temperature CspA paralogues regulate expression of genes involved in the translational machinery and metabolic biosynthetic pathways: possibly through a number of transcriptional and post transcriptional processing events. Furthermore this study provides in vivo evidence of the RNA binding activity of the S. typhimurium CspA paralogues. Using fusion proteins, the RNA targets of CspE at 37°C and CspA at 10°C were isolated and analysed. This work identifies 17 direct binding targets for CspE and these indicate that CspE performs a role at optimal growth temperature in regulating components of metabolic (coaA and plsX), translational (EF-Tu, EF-G and IF3) and virulence associated (hha) pathways. Functional redundancy between CspE and CspA was suggested as both paralogues bound 16s rRNA. In light of these findings, the functions of CspA & CspE at optimal and low temperature are discussed. Overall this study has revealed novel information about low temperature adaptation of S. typhimurium, expanding our knowledge of the complexity and importance of the CSR in bacterial pathogens. In addition this work enhances our comprehension of the roles of the CspA paralogues at both optimal and low temperature.

In cold temperatures, the survival of Salmonella enterica serovar Typhimurium (S. Typhimurium) requires the action of cold shock protein A (CspA) paralogues. These are thought to melt misfolded ribonucleic acids, facilitating their translation at low temperatures. However, through phenotypic analysis of our SL1344 csp null mutant (lacking all CspA paralogues), it has been shown that CspA paralogues function during other environmental stresses, outwith temperature reduction, and play an essential role in colony formation of an SL1344 rpoS mutant at 37°C. The general stress σ subunit, RpoS, plays an important role in adapting cells to a number of stresses including oxidative stress, temperature changes, low pH and stationary phase. Under such conditions, RpoS acts as an ‘emergency co-ordinator’, subsequently inducing the transcription of necessary stress response genes. In Escherichia coli, RpoS is regulated posttranscriptionally by at least three small RNAs (sRNAs): OxyS, DsrA and RprA; that require interactions with the Sm-like RNA chaperone, Hfq. In S. Typhimurium, the stability of the RpoS protein itself is regulated by ClpXP, an ATP-dependent protease responsible for RpoS degradation, and a specific recognition factor that targets RpoS to this protease, MviA. The present study has shown that the CspA paralogues of S. Typhimurium are involved in the expression of RpoS and aims to elucidate the role of these proteins in RpoS production. Comparative phenotypic tests were carried out in strains carrying mutations in rpoS, hfq and the csp genes to gain insight into the interactions of Hfq and CspA paralogues, with respect to RpoS expression. Both significant phenotypic overlaps, such as peroxide sensitivity, and phenotypes unique to certain mutant strains, such as cold acclimation in the csp null strain, were observed. CspA paralogues and Hfq are functionally distinct, not only in their involvement in RpoS expression, but also in RpoS-independent processes, such as cold acclimation, motility and to some extent, growth at 37°C. The roles of Hfq and the CspA paralogues, in RpoS expression, were also assessed at the molecular level. A combination of qRT-PCR analysis, transcriptional fusions and immunoblotting (with anti-σ antibodies) has shown that DsrA and RprA are not essential for RpoS expression in S. Typhimurium, during stationary phase or exponential cold shock, and do not require Hfq under these conditions. Contrary to reports in E. coli, DsrA is not induced upon cold shock in SL1344. Northern blots have shown that neither Hfq nor the CspA paralogues are involved in regulating rpoS transcription during either stationary phase at 37°C or cold shock in exponential phase. Immunoblotting and translational fusions have identified different pathways for the regulation of RpoS during stationary phase at 37°C and cold shock in exponential phase. Hfq is involved during the former condition only, whilst CspA paralogues are involved in both. Protein stability experiments have shown that the CspA paralogues do not play a major role in stabilising RpoS protein against degradation. Together, these results have pointed to a role for both the CspA paralogues and Hfq in facilitating the efficient translation of rpoS mRNA. An SL1344 csp null rpoS mutant is unable to form colonies on LB agar at 37°C, a phenomenon found when introducing combinations of mutations to SL1344 for phenotypic assessment. A conditional rpoS mutant revealed that the SL1344 csp null rpoS strain is viable but non-culturable. From the csp gene family, only cspA and cspB were able to restore colony forming ability to the rpoS mutant. Further complementation experiments pointed to faulty cell division, due to abnormal RNase E activity, as the cause.

Major changes in expression occur in Arabidopsis in response to cold. It is now clear that genome-wide changes in alternative splicing (AS) also occur in Arabidopsis during the cold-response and many of the genes which undergo cold-induced AS have been linked to roles in either the regulation of the cold-response or regulation of AS. Mutations in splicing factors in Arabidopsis, such as STA1 and SRL1 have been shown to lead to both changes in AS and changes in cold-sensitivity/tolerance, suggesting an important the role for AS in regulating the cold-response. Less is known about the effect of cold on AS in barley or how AS impacts the barley cold-response. There are only a few studied examples of cold-induced AS changes in barley genes, although this is rapidly changing due to both the publication of the barley genome and next generation sequencing of the transcriptome. To investigate AS in the barley cold response, 11 barley genes with cold-induced AS changes were identified and the AS change was analyzed in detail. The barley genes FRY2 and SUA change AS after 30 minutes exposure to cold and are both genes have been linked to roles in regulating AS, indicating a complex role for AS in the earliest stages in the cold-response. The Serine Arginine (SR)-Rich protein genes have been shown to change AS and affect AS under stress conditions in Arabidopsis, rice and other plant species but little is known about the SR protein genes in barley or how the genes change splicing/expression in response to cold. The 16 members of the barley SR protein gene family were identified and analyzed for cold-induced expression changes using available microarray and RNA-Seq data. The HvRS41 gene showed a >2 fold increase in expression after 3h exposure to 6°C in a cold-based microarray experiment. A cold-based microarray experiment in Arabidopsis showed a similar cold-induced expression of the AtRS40 gene, a RS-type SR protein gene with high homology to HvRS41. The cold-induced expression of HvRS41 and AtRS40 indicate a role for the RS-type SR protein genes in the cold response. The RS-type SR proteins form a splicing complex with FRY2 which could potentially be regulated through both AS and expression change during the cold-response. The Barley SR Proteins were dived into six sub-groups previously established for plant SR protein genes. Five out of the six sub-groups of the barley SR protein genes contained AS which could be validated through RT-PCR based methods. The SR-type SR protein genes contained was shown to contain three genes (HvSR34, HvSR30a and HvSR34) within barley. All 3 barley SR-type protein genes showed AS change in response to low temperatures, indicating a role for the barley SR-type SR protein genes in regulating AS during the cold-response. The role for SR-type SR protein genes in regulating AS was tested through a creation of a barley transgenic line over-expressing gene the HvSR34. The HvSR34 overexpression lines are in the process of being tested for changes in AS and cold tolerance.

Tese de mestrado integrado. Engenharia Metalúrgica e de Materiais. Universidade do Porto. Faculdade de Engenharia. 2011

Producing fruits and vegetables in the Intermountain West can be challenging due a short growing season, extreme temperatures, and limited availability of irrigation water. This is particularly true of strawberries, where commercial production is limited due to late fall and early spring frosts that shorten the growing season. With the increasing demand for local produce as urban populations grow and as consumer buying habits change, growers are looking for ways to overcome these climatic challenges. High tunnels are one option growers can use. High tunnels are similar to greenhouses, but less expensive to construct and to maintain. Another way to protect crops against adverse climatic conditions is with low tunnels. As the name implies, they are a smaller version of a high tunnel, usually only tall enough to cover the canopy of the plant. Low tunnels can be used by themselves or in conjunction with (inside) a high tunnel. Adding heat is another option. However, heating can be expensive and may not be profitable. Targeting heat additions in the root zone may decrease cost of heat but still provide protection to the plant.These protection methods were evaluated in Cache Valley, Utah for effectiveness of increasing strawberry yield. High tunnels increased total yield, as did high tunnels used in conjunction with low tunnels. However, low tunnels by themselves were not able to increase yield in comparison to unprotected plants in the field. Targeted root zone heating was evaluated in both high and low tunnel with two target temperatures: 7 and 15 °C. There was no difference in total yield between the two temperatures, but both increased yield above the high tunnel alone and the 15 °C heating treatment moved the harvest season approximately 6.5 weeks earlier than unheated tunnels and approximately 12 weeks earlier than field production. The additional cost associated with using supplemental heat was offset by the increased yields and the higher value of early fruit.Separate experiments were carried out to determine susceptibility of strawberry leaves to damage from cold temperatures, which can then be used to provide guidelines for temperature management in high tunnels. Strawberry leaves were not significantly damaged when exposed to -3 °C, but significant damage occurred once leaves were exposed to -5 °C. To maximize the advantages of protected cultivation, growers should manage tunnels and heating to keep leaf temperatures above -3 °C. These results provide improved guidelines for growers interested in using protected cultivation strategies to provide fruit for local consumption in the Intermountain West.