CIVINS / The recent trend of using fine water mist systems to replace the legacy HALON-1301 fire suppression systems warrants further study into other applications of the water mist systems. Preliminary research and investigation indicates that fine mists (20-25 micro droplet size) may reduce peak overpressures of a shock wave traveling through a space. Such pressure reductions could be used to mitigate the destructive effects of a shock wave (initiated by an explosive device) traveling through a structure. Currently these blast mitigation effects have only been demonstrated in small-scale shock tube tests and computer simulations. Uncertainty exists as to the scalability of such a system. The intention of this research is to investigate the applicability of such a blast mitigation system for shipboard use. Study into the degree of mitigation necessary to make a system practical for shipboard installation was conducted. In addition, a theoretical study of the mechanisms of blast mitigation using water mists was completed. / CIVINS

One of the major challenges facing clinicians is how to effectively manage excessive host immune response to pathogenic insults resulting in sepsis. This is demonstrated by the fact that despite over half-century research efforts, sepsis and its spectrum of diseases (severe sepsis and septic shock) are still associated with poor clinical outcome. Currently, sepsis is a leading cause of death in intensive care units. The immune system protects the host against pathogens and is therefore armed with an arsenal of deadly ammunitions (including chemicals, cells and proteins) necessary for the elimination of microbes. It is therefore paramount that the immune system must develop mechanisms necessary to prevent destruction of the host it is designed to protect. A good example of such a mechanism is found in the subset of lymphocytes known as regulatory T cells (Tregs). There is unequivocal experimental evidence of the role of Tregs in the maintenance of immune homeostasis and self tolerance and aberrant Treg function has been linked with several inflammatory diseases. Since sepsis is a disease marked by a hyper-inflammatory state, I investigated the possible role of Tregs in dampening sepsis-induced excessive inflammation. Using a murine model of lipopolysaccharide (LPS) infusion and bacterial infection, I show that Tregs are essential for survival during sepsis because their depletion leads to acute death to an otherwise non-lethal dose of LPS. This enhanced susceptibility to LPS following Treg depletion was also observed using live E. coli infection. Next, I probed the mechanism by which Tregs protect against LPS challenge. I found that defective Treg function leads to exaggerated activity of two immune cells – CD4+ effector T cells and neutrophils in response to LPS, leading to severe inflammatory response. Hence, this work successfully illustrates the critical role of Tregs in regulating other immune cells and the catastrophic consequences of defective Treg function during an immune response. Overall, this work highlights the significant role of Tregs in the regulation of bacteria associated inflammatory processes. The findings hold implications for the successful management of sepsis and have potential for use in development of adequate therapeutic intervention for sepsis. / October 2016

Under shock compression it is believed that crystalline materials undergo complex, rapid, micro-structural changes to relieve the large applied shear stresses. The mechanisms involved, such as dislocation flow and deformation twinning, under the generated high strain rates are not fully understood and in situ measurements of defects have proven elusive. This work presents the development of a nanosecond x-ray diffraction technique based on the white-light Laue method, and its first use in studying shock compressed copper. Observations of diffuse scattering are interpreted as stress-dependent lattice rotations due to dislocation glide. The results are compared with MD simulations of shocks in copper which are shown not to agree. Simulations of tantalum, shocked along the [001] axis, are demonstrated to undergo deformation twinning. A novel order parameter for identifying twin variants is developed and the deformation twinning mechanism under shock compression is identified.

Une coagulopathie aigüe traumatique est constatée chez environ un tiers des patients traumatisés sévères. Ce trouble précoce, endogène et spécifique nécessite l’association d’importantes lésions tissulaires et d’une hémorragie. La phase initiale est caractérisée par l’expression d’un phénotype hémorragique responsable d’une mortalité précoce, la phase tardive par l’expression d’un profil pro-thrombotique responsable d’une mortalité retardée. La physiopathologie de ce phénomène est encore mal comprise. Celle-ci pourrait impliquer une dysrégulation de la voie de la protéine C, une CIVD fibrinolytique, une diminution des stocks en fibrinogène, une altération de la fonction plaquettaire et une agression endothéliale. Plusieurs auteurs ont relevé l’absence de modèle animal pertinent pour vérifier ces hypothèses. Les objectifs de ce travail de thèse ont été la mise au point d’un modèle animal de coagulopathie aigüe traumatique et l’étude de sa physiopathologie. Une première étude a été réalisée, permettant la mise au point d’un modèle murin de coagulopathie traumatique. Celle-ci a mis en évidence un trouble de la coagulation précoce, endogène et spécifique associé à l’expression d’un phénotype hémorragique et répondant à tous les critères clinico-biologiques d’une coagulopathie aigue traumatique. Une deuxième étude basée sur ce modèle a été réalisée afin de mettre en évidence les mécanismes généraux intervenant dans la physiopathologie de la coagulopathie aigüe traumatique. Le rôle protecteur du fibrinogène a été confirmé dans cette étude. Le profil clinicobiologique observé associait une génération de thrombine normale, une discrète thrombopénie et un phénotype hémorragique. Celui-ci infirmait l’hypothèse d’une CIVD mais était compatible avec celle d’une fibrinolyse médiée par une production accrue de protéine C activée. / An acute traumatic coagulopathy is observed in about one-third of severely traumatized patients. This early, endogenous and specific disorder occurs when tissue damages are combined with hemorrhage. The early phase of this condition is characterized by the expression of a bleeding phenotype and a lengthening in prothrombin time.The late phase is characterized by a pro-thrombotic profile leading to multiple organ failure. The physiopathology of this phenomenon is still poorly understood. This could involve a dysregulation of the protein C pathway, fibrinolytic DIC, a decrease in fibrinogen, impairment in platelet function and endothelial damages. Various authors have emphasized the lack of relevant animal model to study this phenomenon.The objective of this work was to develop an animal model of acute traumatic coagulopathy to study its pathophysiology. A first study was performed and led to the development of a murine model of traumatic coagulopathy. This study revealed a hemostasis disorder that meets all the criteria of acute traumatic coagulopathy. Then, a second study based on this model was performed to observe general hemostasis disorders occurring in the context of traumaassociated hemorrhage. This study confirmed the protective role of fibrinogen against ATC. The clinicalbiological profile observed in the case of ATC combining normal thrombin generation, subtle thrombocytopenia and hemorrhagic phenotype observed in the case of ATC invalidated the hypothesis of DIC but was compatible with fibrinolysis mediated by an increase in activated protein C.

This work is a preliminary attempt to study the effect between thermal shock and abrasive wear in WC-Co alloys. This was done by evaluating the thermal shock resistance of a WC-12wt%Co mining grade as a function of temperature, number of thermal shock cycles and making comparisons between the abrasive wear responses of samples subjected to thermal shock and samples not subjected to thermal shock. A furnace was designed for the thermal shock treatments. Abrasive wear tests were performed on a 2-body sliding wear apparatus using 80-grit SiC abrasive paper as a counter-face. Stereo and electron microscopy as well as microprobe techniques were used to analyse the effects of thermal shock. It is confirmed that thermal shock has a negative effect on the wear rate of WC-12wt%Co. The results showed an initial high mass loss rate during abrasive wear testing, which increased with increasing temperature and a decrease in wear rate with time until the wear rates converged for all samples. The surface analysis after thermal shock indicated voids on and below the surface, stained surfaces, a thin oxide layer and the possibility of WC decarburization which accelerated the wear response.

Student Number : 9910049F - MSc (Eng) dissertation - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built Environment / Cavitation was generated in tap water samples by the transmission of tension waves into the liquid, using a hydrodynamic shock tube. The liquid cavitated at absolute negative pressures of about -1 bar. Simulations of bubble responses showed qualitative agreement with experimental observations of oscillatory growth and collapse cycles. Pressure records showed secondary pressure pulsations, confirming the oscillatory nature of the collapse at each rise in pressure. More quantitative comparison of theory and photographic records would require a camera with a higher capture rate. Experiments using another experimental facility involved liquid compression waves with peak static pressures of up to about 1 MPa, which were transmitted from a conventional gas shock tube into a liquid section and were intended to be reflected at the free surface as expansion waves. These experiments were unsuccessful in producing absolute negative pressures or cavitation that was visible through an optical observation section. This was attributed to transition layer effects and pulse attenuation, which contributed to lowering of the peak negative pressure behind the expansion wave, as well as the depth of the transducer and observation section below the free surface, which may have been too low for the peak tension to be superimposed on the lower pressure behind the incident compression wave. Pressure records suggested that, for lower driver pressures, cavitation occurred below the observation section, although this could not be verified optically.

Student Number : 9900131F - MSc (Eng) dissertation - School of Mechanical Engineering - Faculty of Engineering / Recent high-resolution numerical studies of weak shock reflections have shown that a complex flow structure exists behind the triple point which consists of multiple shocks, expansion fans and triple points. This region had not been detected earlier in experimental observations or numerical studies of weak shock reflections due to the small size of this region. New components were designed and built to modify an existing large-scale shock tube in order to obtain experimental observations to validate the numerical results. The shock tube produced a large, expanding cylindrical incident wave which was reflected off a 15° corner on the roof of the section to produce a weak shock Mach reflection with a large Mach stem in the test section. The shock tube was equipped with PCB high-speed pressure transducers and digital scope for data acquisition, and a schlieren optical system to visualise the region behind the triple point. The tests were conducted over a range of incident wave Mach numbers (M12 = 1.060-1.094) and produced Mach stems of between 694 mm and 850 mm in length. The schlieren photographs clearly show an expansion fan centered on the triple point in all the successful tests conducted. In some of the more resolved images, a shocklet can be seen terminating the expansion fan, and in others a second expansion fan and/or shocklet can be seen. A ‘von Neumann reflection’ was not visualised experimentally, and hence it has been proposed that the four-wave reflection found in these tests be named a ‘Guderley reflection’. The experimental validation of Hunter & Tesdall’s (2002) work resolves the ‘von Neumann Paradox’.

<p>This study is concerned with investigating the effects of warm laser shock peening (wLSP) on the enhancement of mechanical performance of laser welded joints. A 3-D finite element model is presented which predicts the surface indentation geometry and in-depth compressive residual stresses generated by wLSP. To define the LSP pressure on the surface of the material, a 1-D confined plasma model is implemented to predict plasma pressure generated by laser-coating interaction in an oil confinement regime. Residual stresses predicted by the finite element model for wLSP reveal higher magnitude and depth of compressive residual stresses than room temperature laser shock peening. A novel dual laser wLSP experimental setup is developed for simultaneous heating of the sample, to a prescribed temperature, and to perform wLSP. The heating laser power is tuned to achieve a predefined temperature in the material through predictive analysis with a 3-D transient laser heating model.</p><p>Laser welded joints of AA6061-T6 and TZM alloy in bead-on-plate (BOP) and overlap configurations, created by laser welding with a high power fiber laser, were post processed with wLSP. To evaluate the strength of the welded joints pre- and post-processing, tensile testing and tensile-shear testing were carried out. To understand the failure modes in tensile-shear testing of the samples, a 3-D finite element model of the welded joint was developed with weld regions’ material strength properties defined through microhardness testing. The stress concentration regions predicted by the finite element model clearly explain the failure regions in the experimental tensile testing analysis. The tensile tests and tensile-shear tests carried out on wLSP processed AA6061-T6 samples demonstrate an enhancement in the joint strength by about 20% and ductility improvement of about 33% over as-welded samples. The BOP welds of TZM alloy processed with wLSP demonstrated an enhancement in strength by about 30% and lap welds demonstrated an increase in joint strength by 22%.<br></p><p></p>

RNA-dependent control of gene expression is crucial for bacterial adaptation to environmental stresses, such as fluctuations in ambient temperature. In the enteric pathogen Salmonella Typhimurium, a drastic downshift in temperature immediately triggers the “cold shock response” in which selective expression of cold shock proteins (CSPs) aids acclimatisation. The major cold shock protein, CspA, and some of its homologues function as RNA chaperones and play critical roles in destabilising aberrant RNA secondary structures that form at reduced temperatures. However, the precise roles and targets of this protein family remain unclear. With the aim of generating a genome-wide map of protein-RNA interactions, in vivo UV cross-linking and analysis of cDNA (CRAC) was performed. This novel, high-throughput technique allows identification of all RNA targets for a particular protein, which in this case was the cold-induced protein CspA, and constitutively expressed CspE. CRAC results reveal a remarkable number and diversity in the RNA targets of these CSPs. For example, CspA targets approximately 25% of the RNA encoded by the Salmonella genome. CspA and CspE were shown to target mRNAs encoding proteins involved in metabolism, stress, cell division and RNA turnover, as well as a number of mRNAs that are cold shock-inducible. Bioinformatic analyses have shown that mainly protein coding regions are targeted and, interestingly, 5’ untranslated regions (UTR) and small RNAs, which often play roles as regulators of translational control. There also appears to be a reproducible pattern of repeated binding along mRNA transcripts, suggesting a role for these Csps in maintaining mRNAs in a linear conformation, which is required for efficient translation. To validate targets, phenotypic analyses were performed, including growth studies during amino acid starvation, and the response to heat shock and UV DNA damage. These experiments confirmed involvement of the paralogues, and further bioinformatic analysis revealed that these proteins were targeting key regulatory regions on some specific targets. A more in-depth analysis was carried out on one target – the general stress response sigma factor RpoS (σS) and a model of CspA paralogue involvement in regulating the mRNA of this target is presented. Overall, the in vivo data from this study suggests that these cold shock proteins are crucial for modulating key cellular processes beyond that which their name implies.

During take-off, the aerodynamic performance of a transonic engine intake is dominated by the flow-field over the nacelle lower lip, around which the flow might accelerate to supersonic speeds. A shock wave might appear and impinge on the incoming boundary layer. Flow separation may result from this interaction, leading to severe flow distortion. In order to maximise fuel efficiency by reducing aerodynamic drag, slimmer nacelle designs are currently being pursued by manufacturers. Understanding the impact of design choices on the development of shock-wave boundary layer interactions (SBLI) is crucial, as these phenomena have a severe effect on the stability of the flow inside the nacelle. The available literature is rather scarce and unable to assess the nature and severity of SBLIs, which remain to be addressed in the context of nacelles at incidence. To address this shortcoming, a novel experimental rig has been designed exclusively to assess the detrimental effects resulting from shock-induced separation for a number of intake lip shapes and inflow conditions. For the reference intake shape, the flow field around the lower lip during on-design take-off conditions was found to be relatively benign, with minimal shock-induced separation. As incidence is increased by 2◦, from the reference incidence of 23◦, this separation gets noticeably larger and unsteadiness develops. The downstream boundary layer is more distorted and reflects the losses across the interaction. This is exacerbated at even higher incidence. Increasing the mass flow rate over the lip up to 15% of the initial value had only minor effects on performance. The parametric investigation revealed a significant effect of lip shape on the position and severity of the SBLI. In particular, a slimmer nacelle performed poorly, favouring shock development very close to the lip nose and promoting large scale separation as the incidence increases. From correlation studies based on the parametric investigation, it appears that the extent of shock-induced separation is the main factor affecting the aerodynamic performance. Somewhat surprisingly, this was found to be independent of shock strength but potentially related to the severity of the diffusion downstream of the shock. Alongside delaying flow reattachment, this diffusion is also likely to have a direct detrimental effect on the boundary layer development close to the engine fan.