La détermination des propriétés des matériaux soumis à des chocs est un enjeu essentiel dans de nombreux domaines industriels. L’objectif de cette thèse est de proposer une nouvelle méthode fondée sur l’interrogation en bande millimétrique d’un solide soumis à un choc. Deux paramètres doivent être mesurés simultanément, la vitesse du choc et la vitesse matérielle associée afin de pouvoir construire la polaire de choc du matériau d’étude. Dans un premier temps, un état de l’art des techniques de mesure existantes est réalisé pour cibler les performances et limites de l’existant. Dans un second temps, on s’intéresse à la modélisation de la propagation des ondes électromagnétiques dans des milieux à plusieurs interfaces en mouvement et avec un gradient d’indice pour représenter des cas de choc soutenu et non soutenu. Enfin, des campagnes expérimentales d’impact plan sont présentées sur différents matériaux, inertes et explosifs, pour confronter la théorie développée aux résultats de mesure. Pour le cas des chocs soutenus, les résultats sont en très bon accord et permettent de valider le modèle. Le cas des chocs non soutenus est plus complexe. Une approche par réseau de neurones est envisagée pour permettre de remonter aux vitesses et aux indices de réfraction. Enfin, des mesures de la permittivité complexe de nombreux explosifs sont présentées. / The mechanical properties of solids under shock wave loading are a key factor in many industrial applications. This work aims at defining a new approach for the simultaneous measurement of shock wave and particle velocity during a shock event, using millimeter wave interrogation. With the two determined parameters, the shock polar of any material can be derived. First, a review of the classical methods to determine these quantities is presented, to identify the advantages and limits of such techniques. A modelization work is then performed to understand the propagation of electromagnetic waves in a stratified mediumwith moving interfaces and different refractive index in each of the layers. Such a configuration can be used to describe both steady and unsteady shocks on solids. Last, experimental results of plane impact tests on both inert and reactive materials are presented and analyzed to comfort the modelization. For steady shocks, the results are in very good agreement and prove the developed model to be adequate. The case of unsteady shocks is more complex, and a neural network approach is described to solve the problem. Finally, new data on the permittivity of high explosives and a new setup are described.

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To study combustion chemistry at low temperatures in a shock tube, it is of great importance to increase experimental test times, and this can be done by tailoring the interface between the driver and driven gases. Using unconventional driver-gas tailoring with the assistance of tailoring curves, shock-tube test times were increased from 1 to 15 ms for reflected-shock temperatures below 1000 K. Provided in this thesis is the introduction of tailoring curves, produced from a 1-D perfect gas model for a wide range of driver gases and the production and demonstration of successful driver mixtures containing helium combined with either propane or carbon dioxide. The He/CO2 and He/C3H8 driver mixtures provide a unique way to produce a tailored interface and, hence, longer test times, when facility modification is not an option. The tailoring curves can be used to guide future applications of this technique to other configurations. Nonreacting validation experiments using driver mixtures identified from the tailoring curves were performed over a range of reflected-shock temperatures from approximately 800 to 1400 K, and some examples of ignition-time experiments that could not have otherwise been performed are presented.

A Study Of Shock Analysis Using The Finite Element Method Verified With Euler-Bernoulli Beam Theory; Mechanical Effects Due To Pulse Width Variation Of Shock Inputs; And Evaluation Of Shock Response Of A Mixed Flow Fan David Jonathan González Campos For many engineers that use finite element analysis or FEA, it is very important to know how to properly model and obtain accurate solutions for complicated loading conditions such as shock loading. Transient acceleration loads, such as shocks, are not as common as static loads. Analyzing these types of problems is less understood, which is the basis for this study. FEA solutions are verified using classical theory, as well as experimental results. The complex loading combination of shock and high speed rotation is also studied. Ansys and its graphic user interface, Workbench Version 14.5, are the programs used to solve these types of problems. Classical theory and Matlab codes, as well as experimental results, are used to verify finite element solutions for a simple structure, such as a cantilevered beam. The discrepancy of these FEA results is found to be 2.3%. The Full Method and the Mode Superposition Method in Ansys are found to be great solution tools for shock loading conditions, including complex acceleration and force conditions. The Full Method requires less pre-processing but solutions could take days, as opposed to hours, to complete in comparison with the Mode Superposition Method, depending on the 3D Model. The Mode Superposition Method requires more time and input by the user but solves relatively quickly. Furthermore, a new representation of critical pulse width of the shock inputs is presented. Experimental and finite element analyses of a complete mixed flow fan undergoing ballistic shock is also completed; deformation results due to shock loading, combined with rotation and aerodynamic loading, account for 32.3% of the total deformation seen from experimental testing. Solution methods incorporated in Ansys, and validation of FEA results using theory, have great potential implications as powerful tools for engineering students and practicing engineers.

Converging cylindrical shock waves have been studied experimentally. Numericalcalculations based on the Euler equations and analytical comparisons basedon the approximate theory of geometrical shock dynamics have been made tocomplement the study.Shock waves with circular or polygonal shock front shapes have been createdand focused in a shock tube. With initial Mach numbers ranging from 2 to4, the shock fronts accelerate as they converge. The shocked gas at the centreof convergence attains temperatures high enough to emit radiation which isvisible to the human eye. The strength and duration of the light pulse due toshock implosion depends on the medium. In this study, shock waves convergingin air and argon have been studied. In the latter case, the implosion lightpulse has a duration of roughly 10 μs. This enables non-intrusive spectrometricmeasurements on the gas conditions.Circular shock waves are very sensitive to disturbances which deform theshock front, decreasing repeatability. Shocks consisting of plane sides makingup a symmetrical polygon have a more stable behaviour during focusing,which provides less run-to-run variance in light strength. The radiation fromthe gas at the implosion centre has been studied photometrically and spectrometrically.Polygonal shocks were used to provide better repeatability. Thefull visible spectrum of the light pulse created by a shock wave in argon hasbeen recorded, showing the gas behaving as a blackbody radiator with apparenttemperatures up to 6000 K. This value is interpreted as a modest estimation ofthe temperatures actually achieved at the centre as the light has been collectedfrom an area larger than the bright gas core.As apparent from experimental data real gas effects must be taken intoconsideration for calculations at the implosion focal point. Ideal gas numericaland analytical solutions show temperatures and pressures approaching infinity,which is clearly not physical. Real gas effects due to ionisation of theargon atoms have been considered in the numerical work and its effect on thetemperature has been calculated.The propagation of circular and polygonal have also been experimentallystudied and compared to the self-similar theory and geometrical shock dynamics,showing good agreement. / QC 20110502

Chlamydomonas priscuii is a psychrophilic green alga found 17 m below the permanently ice-covered surface of the Antarctic Lake Bonney, where it experiences a myriad of extreme environmental conditions, including low temperature, low light, and high salinity. While this habitat is extreme, it is also very stable, and this alga rarely experiences changes in its environment. Heat shock proteins (HSPs) are a ubiquitous family of chaperone proteins that perform important housekeeping and stress-related roles. In most organisms, including the model green alga Chlamydomonas reinhardtii, HSP expression is induced during abiotic stress to regain protein homeostasis – a process regulated by heat shock transcription factors (HSFs). This work shows that C. priscuii constitutively accumulates high protein levels of HSPs in steady-state conditions but fails to induce additional HSP accumulation during heat and low temperature, high and low salt, high light, and with canavanine treatment. In this study, a single HSF was identified in the C. priscuii genome. Comparative sequence analysis revealed that most domains characteristic of a functional HSF are conserved, but the expression of a full length HSF1 transcript could not be detected in the cell. Furthermore, the promoters of many C. priscuii HSPs lack binding sites for HSF. This work has shown that C. priscuii has a diminished ability to regulate HSP expression under stressful conditions, which we hypothesize is a result of life in an extreme but very stable environment. This is the first demonstration of a loss of HSP accumulation in green algae, which carries implications on the ability of psychrophiles to survive in the face of climate change.

As opposed to culture shock, where one experience difficulties going to a new country andculture, reverse culture shock is the difficulties one experiences when returning home.Reverse culture shock describes the phenomenon of the disorientation and negative feelingsoften experienced when an individual becomes a returning sojourner. This thesis examinesreverse culture shock in the reentry process and its effect on the returning student sojournersat Malmö University. Researching reverse culture shock is important as it is an area that isoften neglected in the context of student mobility, even though the majority of returningstudent sojourners experience it. There is a gap in the research around reverse culture shockwhere phenomenological qualitative research has been deprioritized for a much more tangibleapproach of quantitative research. The returning student sojourner’s stories are important ifone seeks to gain a deeper understanding of reverse culture shock and the reentry process. Thepurpose of this research is to encourage a deeper discussion about reverse culture shock atMalmö University and its impact on student sojourners returning from studying abroad. Thisresearch seeks to answer the question: to what extent are returning student sojourners atMalmö University affected by reverse culture shock? And what can the university do to assistthe reentry process? By utilizing qualitative research methods, three themes were identifiedwhich highlight aspects of the returning student sojourners experiences as they came homefrom their student mobility programs: social difficulties, a dream, and what the university cando to assist the reentry process. In conclusion, the student sojourners returned with a feelingof loneliness and isolation, an experience that felt like a dream, and with a wish for moresupport from their home institution.

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A coupled fluid-structure interaction solver capability is developed and validated. A high fidelity fluids solver, Loci-Chem, is coupled with a finite-element structural dynamics toolkit, MAST. The coupled solver is validated for the prediction of several panel instability cases in uniform flows and in the presence of an impinging shock for a range of subsonic and supersonic Mach numbers, dynamic pressures, and pressure ratios. The panel deflections and limit-cycle oscillation amplitudes, frequencies, and bifurcation point predictions compare very well with benchmark results for 2D simulations. The same procedures outlined in the validation study have been applied to simulations of varying dynamic pressures at M = 2 for an impinging oblique shockwave. The influence of inviscid, laminar and turbulent boundary layer profiles on the development of flow field characteristics has been analyzed, and laminar predictions characterized by a large flow separation results in vastly different behavior than that of traditional flutter.

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