The Intervertebral disc (IVD), comprised of two distinct regions, namely the fibrous annulus fibrosus (AF) and the gelatinous nucleus pulposus (NP), is a fibrocartilage pad located between adjoining vertebrae of the spine. The function of the IVD is to provide stability to the spine, while maintaining movement. IVD degeneration, also known as degenerative disc disease (DDD), is the process whereby the IVD tissue degrades, resulting in loss of function to the disc. Low back pain (LBP) is associated with the degeneration of the IVD, making it important to investigate the pathogenesis of DDD, as this could lead to novel therapies for the prevention and/or treatment of LBP. Mechanical stimuli (MS) are known to be important for IVD cell matrix homeostasis, with cells of the AF and NP responding to physiological forces with a trend towards increased matrix anabolism, while non-physiological forces lead to matrix catabolism. Furthermore, recent evidence suggests that IVD cells derived from degenerate tissue may have lost their ability to respond to physiological MS in the 'normal' anabolic manner, potentially leading to the progression of DDD. It is therefore important to investigate the response of IVD cells derived from both non-degenerate and degenerate tissue to MS, to ascertain whether there is a difference with degeneration. If the response is found to be altered with degeneration, then elucidation of the potentially altered mechanotransduction pathway utilised by degenerate cells could lead to the discovery of novel therapeutic targets for the treatment of DDD. To date, the majority of IVD MS studies have concentrated on the response of NP cells to hydrostatic pressure, with only a limited number of AF studies available. Thus, the first aim of this PhD was to investigate the response of human AF cells derived from non-degenerate and degenerate IVDs to the physiologically relevant mechanical stimulus of cyclic tensile strain (CTS), to ascertain whether the response (regulation of matrix protein and matrix degrading enzyme gene expression) was frequency-dependent or altered with IVD degeneration. Using an in vitro mechanical loading system (Flexcell® Tension Plus™ system, Flexcell International) capable of delivering a CTS of 10% strain, 0.33Hz or 1.0Hz for 20 minutes, the response of AF cells derived from non-degenerate IVDs was found to be frequency-dependent (reduced catabolism at 1.0Hz, with decreased MMP -3 and ADAM-TS -4 gene expression; and catabolic at 0.33Hz, with decreased types I and II collagen and increased MMP -9 gene expression). Furthermore, the response of AF cells to 1.0Hz CTS was shown to be altered with IVD degeneration, depicted by a switch from reduced catabolism (decreased MMP -3 and ADAM-TS -4) in non-degenerate AF cells, to reduced anabolism (decreased aggrecan and type I collagen gene expression) in degenerate AF cells. Subsequently, the second aim of the PhD was to attempt to elucidate the mechanotransduction pathways operating in human AF cells derived from non-degenerate and degenerate IVDs, to ascertain whether the mechanotransduction pathway was altered with IVD degeneration. An identical mechanical stimulation regime was used (1.0Hz CTS) in parallel with functional inhibitors against the cytokines interleukin (IL) -1 and -4, and the cell surface receptors, RGD-recognising integrins. Additionally, the involvement of the cytokine associated transcription factors, nuclear factor kappa beta (NFκB) and signal transducer and activator of transcription (STAT) -6, as well as the integrin-associated kinase, focal adhesion kinase (FAK) was investigated in 1.0Hz CTS-treated non-degenerate AF cells. The response to 1.0Hz CTS (reduced catabolism) of AF cells derived from non-degenerate IVDs occurred in an IL -1, IL -4 and RGD-recognising integrin-dependent manner, with FAK being phosphorylated. Of significant interest, the altered response of AF cells derived from degenerate IVDs to 1.0Hz CTS (reduced anabolism) occurred independently of either cytokine and independently of RGD-recognising integrins, suggesting an altered mechanotransduction pathway in operation and warranting further investigation.

Dans ce travail de thèse, nous avons étudié différentes approches qui devraient permettre d’obtenir l’effet laser dans le germanium. Nous avons pu montrer expérimentalement l’influence du dopage et de la déformation sur la structure de bande du germanium, et l’adéquation avec les modèles concluants à l’existence de gain. Nous avons exploré les possibilités offertes par l’hétéro-épitaxie sur III-V pour obtenir une déformation en tension du germanium. Nous avons évalué la déformation résultante par des mesures croisées de rayons X, de diffusion Raman et de photoluminescence, et étudié l’évolution de la qualité des couches épitaxiées en fonction de la déformation et de l’épaisseur. Une nouvelle méthode de déformation du germanium, s’appuyant sur le dépôt par plasma de couches contraintes de nitrure, a été introduite et étudiée. L’effet laser a été recherché par la conception de guides ridges et microdisques déformés par ces dépôts. Plusieurs voies d’application de la déformation dans ces cavités ont été explorées à travers des simulations par éléments finis et la conception de structures de test. Cette optimisation préalable nous a permis d’observer sur les microdisques une déformation biaxiale de 1.11%. En uniaxial, nous avons pu appliquer au germanium une déformation de 1.07% et montrer expérimentalement l’importance de la direction de la déformation dans l’augmentation de la luminescence. Nous avons pu observer et mesurer un gain optique net de 80 cm⁻¹ dans des structures déformées uniaxialement à 0.8%. / In this PhD work, we studied different approaches that should lead to a germanium laser. We have experimentally shown the influence of strain and doping on the germanium band structure, and the adequacy of the existing models. We explored the possibilities offered by heteroepitaxy on III-V compounds to apply stress. We investigated the resulting strain by cross-checking X-rays, Raman spectroscopy and photoluminescence measurements, and analysed the quality of the grown layers depending on strain and thickness. A new method to apply strain to the germanium, by means of plasma deposited stressed nitride layers, was introduced and studied. Lasing has been pursued by conceiving ridges and microdisks strained by this method. An optimization of the geometry was performed through finite element modeling and the production of test structures. This optimization allowed to achieve a maximum biaxial strain of 1.1%. For uniaxial strains, we observed a maximum of 1.07% and showed experimentally the importance of the crystalline orientation in the enhancement of the emission. We demonstrated a modal gain value of 80 cm⁻¹ in ridges uniaxially strained at 0.8%.

Two experimental projects involving perovskite manganese oxide compounds are presented. The first involved dielectric and transport studies of the insulator-metal transition as a function of charge-carrier doping in La1-xCaxMnO3 (0 < x < 0.15) bulk samples. The results provide new insight into the role of competing magnetic, lattice and Coulomb energies in determining the insulator-metal transition near x=0.22. The second project involved the growth, structural characterization, and resistive anisotropy of a-axis oriented Nd0.2Sr0.8MnO3 thin films with thicknesses t in the range 10 nm< t < 150 nm. Thicker films develop regular crack arrays which are the origin of a highly anisotropic in-plane electrical resistance. These cracks form parallel to the crystallographic c-axis on films with tensile strain deposited on NdGaO3 (100) and La0.3Sr0.7Al0.65Ta0.35O3 (110) substrates. Films grown under compressive strain on LaAlO3 (110) substrates have no cracks.

As traffic loads increase and bridges age the need for structural health monitoring is growing. With the digitalization of our society, new non-contact full-field measurement techniques have been developed. These techniques have the potential to be used in monitoring of existing bridges. Today visual inspections are carried out every sixth year. These only give a rough estimate of the structure's health and only provide information about the surface of the structure. In addition to these inspections, traditional sensors like linear variable differential transformers and strain gauges are used to measure parameters such as displacement and strain. For existing bridges in reinforced concrete it is especially important to monitor reinforcement strains, as high strains could be indicative of overloading of the structure or even that a failure is about to occur. The methods available to measure reinforcement strain in existing bridges today are not very effective and have some limitations. The aim of this thesis is thus to evaluate the possibility to predict reinforcement strain based on surface strain measurements obtained by a non-contact full-field optical measurement system. In this study the software ARAMIS was used to measure surface strains, and traditional strain gauges were used to measure reinforcement strain. Strain distribution were evaluated at the initiation of cracks, during sections of cyclic loading and at a load close to the yielding point of the reinforcement. A correlation factor between the strain registered in the software and the strain obtained from the strain gauges was introduced. Based on the results in this study it is not possible to predict exact reinforcement strain based on surface measurements. Digital image correlation does however show potential to be used as a non-contact full-field measurement technique for in-situ measurements. Before this is reality there is still a need for further research in this area.

The continued scaling of feature size in silicon (Si)-based complimentary metal-oxide-semiconductor (CMOS) technology has led to a rapid increase in compute power. Resulting from increases in device densities and advances in materials and transistor design, integrated circuit (IC) performance has continued to improve while operational power (VDD) has been substantially reduced. However, as feature sizes approach the atomic length scale, fundamental limitations in switching characteristics (such as subthreshold slope, SS, and OFF-state power dissipation) pose key technical challenges moving forward. Novel material innovations and device architectures, such as group IV and III-V materials and tunnel field-effect transistors (TFETs), have been proposed as solutions for the beyond Si era. TFETs benefit from steep switching characteristics due to the band-to-band tunneling injection of carriers from source to channel. Moreover, the narrow bandgaps of III-V and germanium (Ge) make them attractive material choices for TFETs in order to improve ON-state current and reduce SS. Further, Ge grown on InₓGa₁₋ₓAs experiences epitaxy-induced strain (ε), further reducing the Ge bandgap and improving carrier mobility. Due to these reasons, the ε-Ge/InₓGa₁₋ₓAs system is a promising candidate for future TFET architectures. In addition, the ability to tune the bandgap of Ge via strain engineering makes ε-Ge/InₓGa₁₋ₓAs heterostructures attractive for nanoscale group IV-based photonics, thereby benefitting the monolithic integration of electronics and photonics on Si. This research systematically investigates the material, optical, and heterointerface properties of ε-Ge/InₓGa₁₋ₓAs heterostructures on GaAs and Si substrates. The effect of strain on the heterointerface band alignment is comprehensively studied, demonstrating the ability to modulate the effective tunneling barrier height (Ebeff) and thus the threshold voltage (VT), ON-state current, and SS in future ε-Ge/InₓGa₁₋ₓAs TFETs. Further, band structure engineering via strain modulation is shown to be an effective technique for tuning the emission properties of Ge. Moreover, the ability to heterogeneously integrate these structures on Si is demonstrated for the first time, indicating their viability for the development of next-generation high performance, low-power logic and photonic integrated circuits on Si. / Master of Science

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Le silicium (Si) et le germanium (Ge) sont les matériaux de base utilisés dans les circuits intégrés. Cependant, à cause de leur gap indirect, ces matériaux ne sont pas adaptés à la fabrication de dispositifs d'émission de lumière, comme les lasers ou diodes électroluminescentes. Comparé au Si, le Ge pur possède des propriétés optiques uniques, à température ambiante son gap direct est de seulement 140 meV au-delà du gap indirect tandis qu'il est supérieur à 2 eV dans le cas du Si. Compte tenu du coefficient de dilatation thermique du Ge, deux fois plus grand que celui du Si, une croissance de Ge sur Si à hautes températures suivie d'un refroidissement à température ambiante permet de générer une contrainte en tension dans le Ge. Cependant, l'existence d'un désaccord de maille de 4,2% entre deux matériaux conduit à une croissance Stranski-Krastanov avec la formation des films rugueux et contenant de forte densité des dislocations. Nous avons mis en évidence l'existence d'une fenêtre de température de croissance, permettant de supprimer la croissance tridimensionnelle de Ge/Si. En combinant la croissance à haute température à des recuits thermiques par cycles, une contrainte de 0,30% a pu être obtenue. Le dopage de type n a été effectué en utilisant la décomposition de GaP, ce qui produit des molécules P2 ayant un coefficient de collage plus grand par rapport à celui des molécules P4. En particulier, en mettant en oeuvre la technique du co-dopage en utilisant le phosphore et l'antimoine, nous avons mis en évidence une augmentation de l'émission du gap direct du Ge à environ 150 fois, ce qui constitue l'un des meilleurs résultats obtenus jusqu'à présent. / Silicon (Si) and germanium (Ge) are the main materials used as active layers in microelectronic devices. However, due to their indirect band gap, they are not suitable for the fabrication of light emitting devices, such as lasers or electroluminescent diodes. Compared to Si, pure Ge displays unique optical properties, its direct bandgap is only 140 meV above the indirect one. As Ge has a thermal expansion coefficient twice larger than that of Si, tensile strain can be induced in the Ge layers when growing Ge on Si at high temperatures and subsequent cooling down to room temperature. However, due to the existence of a misfit as high as 4.2 % between two materials, the Ge growth on Si proceeds via the Stranski-Krastanov mode and the epitaxial Ge films exhibits a rough surface and a high density of dislocations. We have evidenced the existence of a narrow substrate temperature window, allowing suppressing the three-dimensional growth of Ge on Si. By combining high-temperature growth with cyclic annealing, we obtained a tensile strain up to 0.30 %. The n-doping in Ge was carried out using the decomposition of GaP to produce the P2 molecules, which have a higher sticking coefficient than the P4 molecules. In particular, by implementing a co-doping technique using phosphorus and antimony, we have evidenced an intensity enhancement of about 150 times of the Ge direct band gap emission. This result represents as one of the best results obtained up to now.

The development of composite materials by combining two or more constituents with improved mechanical properties, when compared to either of the constituents alone, has existed since biblical times when straw or horse hair was mixed with clay or mud to produce bricks. During the second half of the twentieth century, modern composites known as fiber reinforced polymers (FRP) - consisting of a reinforcing phase (fibers) embedded into a matrix (polymeric resin or binder) - were developed to meet the performance challenges of space exploration and air travel. With time, externally-bonded FRP applications for strengthening of reinforced concrete (RC) structures gained popularity within the construction industry. To date, the confinement of RC columns using FRP systems is a convenient and well established solution to strengthen, repair and retrofit structural concrete members. This technology has become mainstream due to its cost effectiveness, and relative ease and speed of application with respect to alternative rehabilitation techniques such as steel or concrete jackets. However, significant margins exist to advance externally-bonded composite rehabilitation technologies by addressing economic, technological, and environmental issues posed by the use of organic polymer matrices, some of which are addressed in this dissertation. Articulated in three studies, the dissertation investigates the development of a sustainable, reversible, and compatible fiber reinforced cement-based matrix (FRC) composite system for concrete confinement applications in combination with a novel test method aimed at characterizing composites under hydrostatic pressure. Study 1 develops and characterizes a FRC system from different fiber and inorganic matrix combinations, while evaluating the confinement effectiveness in comparison to a conventional FRP system. The feasibility of making the application reversible was investigated by introducing a bond breaker between the concrete substrate and the composite jacket in a series of confined cylinders. The prototype FRC system produced a substantial increase in strength and deformability with respect to unconfined cylinders. A superior deformability was attained without the use of a bond breaker. The predominant failure mode was loss of compatibility due to fiber-matrix separation, which points to the need of improving fiber impregnation to enable a more efficient use of the constituent materials. Additionally semi-empirical linear and nonlinear models for ultimate compressive strength and deformation in FRC-confined concrete are also investigated. Study 2 compares through a life cycle assessment (LCA) method two retrofitting strategies: a conventional organic-based, with the developed inorganic-based composite system presented in Study 1, applied to concrete cylinders by analyzing three life cycle impact indicators: i) Volatile Organic Compound (VOC) emissions, ii) embodied energy, and, iii) carbon foot print. Overall the cement-based composite provides an environmentally-benign alternative over polymer-based composite strengthening system. Results also provide quantitative information regarding the environmental and health impacts to aid with the decision-making process of design when selecting composite strengthening systems. Study 3 is divided into two parts, Part A presents the development of a novel "Investigation of Circumferential-strain Experimental" (ICE) methodology for characterization of circumferential (hoop) strain of composite laminates, while Part B uses the experimental data reported in Part A to explicitly evaluate the effect of FRP jacket curvature and laminate thickness on strain efficiency. Results showed that the proposed ICE methodology is simple, effective and reliable. Additionally, the ultimate circumferential strain values increased with increasing cylinder diameter, while being consistently lower when compared to similar flat coupon specimens under the same conditions. The ultimate FRP tensile strain was found to be a function of the radius of curvature and laminate thickness, for a given fiber ply density and number. The effect of these findings over current design guidelines for FRP confined concrete was also discussed.

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