A Study of the Crystallization and Amorphization Mechanisms of Metallic Glasses under Ion Bombardment

The recent development of metallic glasses has led to a growth in study and innovation of the unique material properties these systems have to offer. In general, metallic glasses offer high yield strength, great corrosion resistance and high elasticity. These properties, along with the ease of part creation through plastic forming, make it a desirable material for several different industry applications. For the nuclear industry in particular, metallic glasses are being researched as coatings for reactor vessels as well as coatings for fuel cladding for long term storage. However, metallic glasses do have drawbacks. Metallic glasses are defined by their amorphous structure, and as such have an undesirable brittle failure mode. The amorphous structure is also a meta-stable structure and under several stimuli including high heat, pressure shocks, irradiation and plastic deformation can cause crystallization within the metallic glass. This crystallization does allow for some improvement in ductility but reduces strength and corrosion resistance. The nuclear environment will subject metallic glass to all of the aforementioned stimuli. It is therefore important to know under what conditions crystallization will occur and the mechanism behind the phase change in order for this material to be effectively implemented. While crystallization under high heat and plastic deformation has been studied extensively, crystallization from irradiation is an understudied field. This behavior is difficult to describe and quantify due to its nuanced and unintuitive nature. This body of work is aimed at more completely understanding the crystallization and re-amorphization mechanisms in metallic glass due to ion bombardment. Thin film samples and bulk ribbon samples were both subjected to a variety of ion bombardment conditions. It was found that direct crystallization in thin film samples can be induced from irradiation induced excess free volume, while it can recover to an amorphous state from rapid damage cascade quenching. In bulk studies, it was found that the beam cannot induce direct crystallization, but can make a metallic glass amorphous after it has been crystallized. These findings will help determine the proper operation envelope for this material, so it can be used effectively in engineering applications

Congenital stenosis of the pylorus

The subject of Congenital Stenosis of the Pylorus presents interest alike for the Physician, the Pathologist and the Surgeon. The first recorded ob- servation was made in 1341 by Williamson of Leith. The symptoms described leave no doubt that the patient suffered from Congenital Stenosis of the Pylorus, whic proved fatal when the child was 5 weeks old. The Stomach and Pylorus were removed post mortem and were - exhibited at a meeting of the Edinburgh Anatomical Society, where the condition was considered to be Con - enital Scirrhus of the Pyloric extremity of the Stom- ach. In 1842 Dawoskk reported a case with similar !!symptoms, which proved fatal at the age of 10 weeks. At the post mortem examination a hard Pyloric tumour as found, the lumen of which would hardly admit a robe. Dawosky looked upon the condition as one of h ypertrophy with induration of the submucous tissue. Landerer, in 1879, and Maier, in 1335, again called attention to the subject of Congenital Pyloric Sten- osis by the publication of some observations they had ade, both clinical and anatomical. But their cases were all observed in adults, the two youngest patients being respectively 16 and 12 years of age, and they re now not generally regarded as true cases of Con - genital Stenosis of the Pylorus. In 1888 Hirschsprung recorded two cases of his. Both patients suffered from symptoms similar to those which will be described belo las typical of the condition and both died. From the post mortem examinations Hirschsprung was the first to ' recognise that the hypertrophy of the Pylorus was chie- ly of the muscular tissue. In 1889Peden showed a,spec - imen at a meeting of the Glasgow Pathological and Clines ical Society taken from the body of a child who had died from malnutrition, the result of Congenital Sten- osis of the Pylorus. At a meeting of the Pathological Society of London in 1891 Newton Pitt showed another specimen taken from an infant 7 weeks old at death, 1 and he drew attention to the hypertrophy of the musculi ar coat of the Stomach as well as the Pylorus. In 1891 Henschel published notes of four cases which poss4 iibly were cases of Congenital Stenosis of the Pylorus.; One of them recovered without operation and the others¡ died between the ages of 7 months and 2- years. At the post mortem examinations of the three fatal cases none of them revealed the marked muscular hypertrophy which is usually met with at the Pylorus. Thomson in 1896 published notes of two fatal cases (see below)¡ E nd of another the following year with full descrip- ions of the morbid anatomy. About the same time as homson published his first two cases, Gran recorded otes of three cases. Soon afterwards Finkelstein ublished.a paper on Congenital Stenosis of the Pylorue nd gave notes of a case of his own and three cases from Heubner's private practice. In 1896 De Bruyn op and Schwyzer each reported a case and the following ear Ashby published a paper on the subject with notes of two cases. In his book on "Disorders of Digestion in Infancy and Childhood" in 1897 W.S.Fenwick gave Totes of two cases of Congenital Stenosis of the Pylor- us, which he had treated. In 1898 cases were recorded Meltzer, by EAVElfEreN Batten and Rolleston, and in that year Stern had a case on which he operated. The following year, Still recorded three cases he had had under his charge, and Abel also operated on a case of Kehr's about the same time. Since then the literature on the subject of Congenital Stenosis of the Pylorus has been rapidly increasing, and a considerable number of cases have been recorded. The following have either written on the subject, or recorded cases - Blackadder Cantley and Dent, Dival, Fletcher, Greeff, Kehr, Lark- ins, Lobker, fonnier; Xicoll, Pritchard, Rolleston and Crofton- Atkins, Saunders, Schmidt, Simonson and South - worth. A complete bibliography will be found below.Owing to the kindness of Mr. H. J. Stiles and Dr. John Thomson I am enabled to give notes of their cases. The first three cases recorded have been published by Dr. Thomson and they are copied from the punished notes. Three of the cases were treated at the 'Min- burgh Children's Hospital by Dr. Thomson when I held the position of House Surgeon to the Hospital and I had ample opportunity of seeing the cases. Mr. Stiles operated upon two of these three cases and'i'assisted him at the operations

Temperature-Dependent Helium Ion-Beam Mixing in an Amorphous SiOC/Crystalline Fe Composite

Temperature dependent He-irradiation-induced ion-beam mixing between amorphous silicon oxycarbide (SiOC) and crystalline Fe was examined with a transmission electron microscope (TEM) and via Rutherford backscattering spectrometry (RBS). The Fe marker layer (7.2 ± 0.8 nm) was placed in between two amorphous SiOC layers (200 nm). The amount of ion-beam mixing after 298, 473, 673, 873, and 1073 K irradiation was investigated. Both TEM and RBS results showed no ion-beam mixing between Fe and SiOC after 473 and 673 K irradiation and a very trivial amount of ion-beam mixing (~2 nm) after 298 K irradiation. At irradiation temperatures higher than 873 K, the Fe marker layer broke down and RBS could no longer be used to quantitatively examine the amount of ion mixing. The results indicate that the Fe/SiOC nanocomposite is thermally stable and tends to demix in the temperature range from 473 to 673 K. For application of this composite structure at temperatures of 873 K or higher, layer stability is a key consideration

Imbalanced effector and regulatory cytokine responses may underlie mycobacterial immune restoration disease

Background: Immune restoration disease (IRD) is an adverse consequence of antiretroviral therapy, where the restored pathogen-specific response causes immunopathology. Mycobacteria are the pathogens that most frequently provoke IRD and mycobacterial IRD is a common cause of morbidity in HIV-infected patients co-infected with mycobacteria. We hypothesised that the excessive effector immune response in mycobacterial IRD reflects impaired regulation by IL-10. Results: We studied two patients who experienced mycobacterial IRD during ART. One patient developed a second episode of IRD with distinct clinical characteristics. Findings were compared with patients 'at risk' of developing IRD who had uneventful immune recovery. Peripheral blood mononuclear cells (PBMC) from all subjects were stimulated with mycobacterial antigens in the form of purified protein derivative (PPD). Supernatants were assayed for IFN? and IL-10. In response to PPD, PBMC from IRD patients generated IFN? during the first IRD episode, whilst cells from non-IRD controls produced more IL-10. Conclusion: We present preliminary data from two HIV-infected patients showing an imbalance between IFN? and IL-10 responses to mycobacterial antigens during mycobacterial IRD. Our findings suggest that imbalanced effector and regulatory cytokine responses should be investigated as a cause of IRD. © 2008 Lim et al; licensee BioMed Central Ltd

Dynamics of Genetic Circuits with Molecule Partitioning Errors in Cell Division and RNA-RNA Interactions

Many signaling and regulatory molecules within cells exist in very few copies per cell. Any process affecting even limited numbers of these molecules therefore has the potential to affect the dynamics of the biochemical networks of which they are a part. This sensitivity to small copy-number changes is what allows stochasticity in gene expression to introduce a degree of randomness in what cells do. While this randomness can be suppressed, it does not appear to be so in many biological systems, at least not to the maximum degree possible. This suggests that this randomness is not necessarily detrimental to cell populations, as it can produce qualitatively new behaviours in genetic networks which may be utilized by cells.In this thesis, two other mechanisms are investigated which, through their interaction with low copy-number molecules, are able to produce qualitatively different dynamics in genetic networks: the stochastic partitioning of molecules in cell division, and the direct interaction of two low copy-number molecules. For this, a novel simulator of chemical kinetics is first presented, designed to simulate the dynamics of genetic circuits inside growing populations of cells. It is then used to study a genetic switch where one repressive link is formed by direct interaction between RNA molecules. This arrangement was found to decouple the stability of the two noisy attractors of the network and the speeds of the state transitions. In other words, it allows the network to have two equally-stable noisy attractors, but differing state transition speeds.Next, the cell-to-cell diversity in RNA numbers (as quantified by the normalized variance) of a single gene over time in a growing model cell population was studied as a function of the division synchrony. In the model, synchronous cell divisions introduce transient increases in the cell-to-cell diversity in RNA numbers of the population, a prediction which was verified using single-molecule measurements of RNA numbers. Finally, the effects of the stochastic partitioning of regulatory molecules in cell division on the dynamics of two genetic circuits, a switch and a clock, were studied. Of these two circuits, the switch has the most dramatic changes in its dynamics, brought on by the inevitable negative correlation in molecule numbers that sister cells inherit. This negative correlation can allow a cell population to partition the phenotypes of the individual cells with less variance than a binomial distribution.These results advance our understanding of the different behaviours that can be produced in genetic circuits due to these two mechanisms. Since they produce unique behaviours, these mechanisms, and combinations thereof, are expected to be used for specialized purposes in natural genetic circuits. Further, since the downstream effects of these mechanisms may be more predictable than, e.g., modifying promoter sequences, they may also be useful in the design and implementation of future synthetic genetic circuits with specific behaviours.<br/

What makes good feedback good?

HE institutions persistently seek to increase student engagement and satisfaction with assessment feedback, but with limited success. This study identifies the attributes of good feedback from the perspective of recipients. In a distinctive participatory research design, student participants were invited to bring along actual examples of feedback that they perceived as either ‘good’ or ‘bad’ to 32 interviews with student researchers. Findings highlight the complex interdependency and contextual nature of key influences on students’ perspectives. The feedback artefact itself, its place in assessment and feedback design, relationships of the learner with peers and tutors, and students’ assessment literacy all affect students’ perspectives. We conclude that standardising the technical aspects of feedback, such as the feedback artefact or the timing or medium of its delivery is insufficient: a broader consideration of all key domains of influence is needed to genuinely increase student engagement and satisfaction with feedback

The detection of CMV in saliva can mark a systemic infection with CMV in renal transplant recipients

Human cytomegalovirus (CMV) is often transmitted through saliva. The salivary gland is a site of CMV replication and saliva can be used to diagnose congenital CMV infections. CMV replication is monitored in whole blood or plasma in renal transplant recipients (RTR) and associates with clinical disease. However, these assays may not detect replication in the salivary gland and there is little data linking detection in saliva with systemic infection and clinical sequelae. RTR (n = 82) were recruited \u3e 2 years after transplantation. An in-house quantitative PCR assay was used to detect CMV UL54 in saliva samples. CMV DNA was sought in plasma using a commercial assay. Vascular health was predicted using flow mediated dilatation (FMD) and plasma biomarkers. CMV-reactive antibodies were quantified by ELISA and circulating CMV-specific T-cells by an interferon-γ ELISpot assay. Vδ2− γδ T-cells were detected using multicolor flow cytometry reflecting population expansion after CMV infection. The presence of CMV DNA in saliva and plasma associated with plasma levels of antibodies reactive with CMV gB and with populations of circulating Vδ2− γδ T -cells (p \u3c 0.01). T-cells reactive to CMV immediate early (IE)-1 protein were generally lower in patients with CMV DNA in saliva or plasma, but the level of significance varied (p = 0.02–0.16). Additionally, CMV DNA in saliva or plasma associated weakly with impaired FMD (p = 0.06–0.09). The data suggest that CMV detected in saliva reflects systemic infections in adult RTR

Workers, mothers, pests: Co-evolutionary perspectives on domesticated cattle in early twentieth century North India

This thesis builds upon political, environmental and veterinary histories of domesticated cattle in South Asia, by offering the first study of animal husbandry in British Imperial and Hindu Nationalist discourses at the turn of the twentieth century. Drawing upon English and vernacular Hindi archives, comparative analysis demonstrates that the socio-cultural, material and environmental dynamics of animal domestication were influenced by perceptions of animal behaviour. It shows that in textbooks, reports and journals published by agriculturalists,cattle breeders and dairy farmers, four primary behaviours of cattle became the subject of competing ideas about the development and decline of cattle populations and agricultural society. These were the instincts to consume, rear, mate and live as a herd. North India offers a unique context in which to explore why colonial science and indigenous knowledge formed competing perspectives of how these behaviours contributed towards the coevolution of humans and cattle. Previous narratives shared the assumption that prior to the formalisation of animal husbandry in imperial institutions of the 1930s, human-cattle relations were unchanged from time immemorial. The purpose of this thesis is to challenge this assumption, to demonstrate that early twentieth century animal husbandry was shaped by a confluence of socio-cultural, environmental, and behavioural forces. Drawing on social, environmental, and animal histories, this thesis is able to demonstrate that changing norms of domestication were the product of compromise, interaction with and responses to, the physiology and behaviour of cattle

Stochastic sequence-level model of coupled transcription and translation in prokaryotes

<p>Abstract</p> <p>Background</p> <p>In prokaryotes, transcription and translation are dynamically coupled, as the latter starts before the former is complete. Also, from one transcript, several translation events occur in parallel. To study how events in transcription elongation affect translation elongation and fluctuations in protein levels, we propose a delayed stochastic model of prokaryotic transcription and translation at the nucleotide and codon level that includes the promoter open complex formation and alternative pathways to elongation, namely pausing, arrests, editing, pyrophosphorolysis, RNA polymerase traffic, and premature termination. Stepwise translation can start after the ribosome binding site is formed and accounts for variable codon translation rates, ribosome traffic, back-translocation, drop-off, and trans-translation.</p> <p>Results</p> <p>First, we show that the model accurately matches measurements of sequence-dependent translation elongation dynamics. Next, we characterize the degree of coupling between fluctuations in RNA and protein levels, and its dependence on the rates of transcription and translation initiation. Finally, modeling sequence-specific transcriptional pauses, we find that these affect protein noise levels.</p> <p>Conclusions</p> <p>For parameter values within realistic intervals, transcription and translation are found to be tightly coupled in <it>Escherichia coli</it>, as the noise in protein levels is mostly determined by the underlying noise in RNA levels. Sequence-dependent events in transcription elongation, e.g. pauses, are found to cause tangible effects in the degree of fluctuations in protein levels.</p