Le collagène est un élément majeur de l'architecture des organes chez les mammifères. Cette protéine s'organise en structures tridimensionnelles (3D) spécifiques à chaque tissu et responsables de leurs propriétés biophysiques et biomécaniques. La microscopie multiphoton permet de visualiser le collagène fibrillaire dans les tissus biologiques, sans aucun marquage, grâce aux signaux de génération de second harmonique (SHG). Cette thèse présente des mesures SHG résolues en polarisation (P-SHG), dans le but de caractériser la structure 3D du collagène dans divers tissus, de l'échelle moléculaire à l'échelle macroscopique.Nous avons d'abord étudié la sensibilité et la fiabilité des mesures P-SHG, afin de valider cette technique comme un outil quantitatif d'observation de la structure 3D du collagène dans des tissus intacts.En collaboration avec le Laboratoire de Chimie de la Matière Condensée de Paris, cette technique a ensuite été appliquée à l'étude de systèmes modèles de collagène présentant une organisation de type cristal liquide, afin de caractériser les conditions physico-chimiques menant à des phases proches de celles observées à l’état stabilisé dans la cornée.Enfin, nous présentons une imagerie SHG en différence circulaire (CD-SHG), permettant de déterminer la polarité des fibrilles de collagène par rapport au plan de l'image. Ces mesures sont complémentaires de l'information obtenue en P-SHG. Une première mise en place expérimentale de cette technique est présentée dans des coupes histologiques de cornée humaine. Nous présentons de plus les résultats préliminaires d'une imagerie corrélative CD-SHG/I-SHG, en collaboration avec l'INRS, donnant une information complète sur la polarité des fibrilles de collagène. / Collagen is a key element of organs architecture in mammals. This protein is organized in tridimensional (3D) structures specific to each tissue and responsible for its biophysical and biomechanical properties. Multiphoton microscopy allows the visualization of unstained fibrillar collagens in biological tissues, by use of their endogenous second harmonic generation (SHG) signals. This work focuses on polarization-resolved SHG measurements (P-SHG), in order to characterize the collagen 3D structure in tissues, from the molecular scale to the macroscopic scale.We first studied the sensitivity and the reliability of those P-SHG measurements, and validated this technique as a quantitative tool to probe collagen structure in intact tissues.In collaboration with the Laboratoire de Chimie de la Matière Condensée de Paris, this technique was then applied to the study of collagen model systems with a liquid crystal like organization, in order to find the physico-chemical conditions leading to organizations close to the one observed in cornea.Finally, we introduced SHG circular difference measurements (CD-SHG). This technique allowed us to probe the polarity of collagen fibrils with respect to the image plane. Those measurements complement P-SHG measurements. An experimental implementation of this technique is introduced, as well as preliminary measurements in cornea. We present also preliminary results from CD-SHG/I-SHG correlative imaging, in collaboration with INRS, giving full information about collagen polarity.

No description available.

This thesis studies CP violation in the decay of the Ξ− hyperon, also known as the cascade baryon, which decays in the sequence Ξ− → Λπ− → pπ−π−. A difference between the angular distribution of this decay sequence and the angular distribution of the charge conjugate decay sequence ͞Ξ+ →͞Λπ+ → ͞pπ+π+, after taking into account the inversion of the momenta due to the parity operation, is indicative of CP violation. The decay sequence is described by three asymmetry parameters: αΞ, αΛ and φΞ, while the charge conjugate decay's sequence is described by: ͞αΞ, ͞αΛ and ͞φΞ. A measure of CP violation is given by the CP violating observables: AΞ, AΛ and ΦΞ. The aim of this thesis is to study how the normalised statistical uncertainties in the asymmetry parameters and in the CP violating observables depend on the magnitude of the polarisation vector (polarisation) of the cascade and the anticascade. This was done by simulating 1.0×107 Ξ− → Λπ− → pπ−π− and  ͞Ξ+ →͞Λπ+ → ͞pπ+π+ decays for different values of polarisation of the cascades using Monte Carlo, and then utilising maximum likelihood estimation and error propagation to estimate the uncertainties in the parameters and in the observables. It was shown using the methods of this thesis that the normalised statistical uncertainties in the asymmetry parameters and the CP violating observables decreased whenever the polarisation was increased, although with diminishing returns. In the region of 10% − 50% polarisation, the decrease in the uncertainties was substantial. An increase from 10% to 50% polarisation lowered all of the uncertainties by 76% − 80%. In the region of 50% − 100% polarisation, the decrease in the uncertainties was slightly less. An increase from 50% to 100% polarisation lowered the uncertainties in αΞ,  ͞αΞ and AΞ by roughly 33%, in αΛ,  ͞αΛ and AΛ by roughly 40%, and in φΞ,  ͞φΞ and ΦΞ it went down by 53%. It was also shown that, if one were to produce 60% polarised cascades and use the method of this thesis, it would require a sample of 1.1×1011 − 1.3×1011 Ξ− → Λπ− → pπ−π− and  ͞Ξ+ →͞Λπ+ → ͞pπ+π+ decays to reach the precision in the observables of the order given by the Standard Model. However, if one wished to match the uncertainty given by the most recent and best measurement of the observables, using 60% polarised cascades, one would only need a sample of 5.7×104 − 8.6×104 for each decay sequence.

There are 5 distinct aspects to this study. (i) Two histological stains for collagen were compared against each other for the first time, namely Herovici's technique and picrosirius-polarization. (ii) Skin samples from embalmed cadaveric tissue from human cadavers were compared against samples taken from surgical patients. (iii) Skin samples were studied from different regions of the body to assess if dermal structure correlates with scarring potential. (iv) Skin samples were sectioned in a plane parallel to the epidermis to gain further insight into dermal structure. (v) A novel basement membrane stain was produced. Type I and type III collagen are important structural constituents of dermis and play a crucial role in wound healing. Only two traditional histological methods are thought to differentiate between them, so avoiding the need for antibodies. These were compared against each other for the first time in order to establish differences in image quality and discrimination between Type I and type III collagen. Neither technique requires antibodies, however picrosirius requires polarisation microscopy. to result in a clearer, consistently reproducible collagen staining pattern than the picrosirius method and more importantly did not require elaborate apparatus to analyze. Additionally other cellular elements were visible. Skin samples for research are often obtained from surgical excision. This clearly limits which tissues are available for comparative study to those areas operated on. Studying samples from embalmed medical school cadavers has the great advantage of studying areas of the body not routinely available from common surgical procedures. It was therefore desirable to assess whether embalmed cadaveric tissues exhibited different properties by virtue of their age and the embalming process compared to fresh surgical specimens, in order to give confidence that studies utilising the former would be equally valid. To test this, 58 skin samples from embalmed medical school cadavers were compared to skin samples from 38 fresh operative specimens. The levels of tissue preservation and processing artefacts were similar in both groups. Embalmed medical school cadavers clearly offer an opportunity to study tissue areas not routinely available during surgery. This is the first time such a comparison has been made. Many things will affect the final appearance of the scar, but the single most important determinant is the body region affected. The most common areas for unfavourable scarring, specifically keloid or hypertrophic scarring have been shown to be the ear, deltoid and sternal areas. To test the hypothesis that there is no difference in histological structure of skin that correlates to body region, comparative histology was undertaken exploring the regional variations of skin characteristics in 58 cadaveric samples. Closely comparable samples were taken from the deltoid (9), abdomen (13), sternum (10), post-auricular (5), earlobe (12) and eyelid (9). Epidermal thickness, epidermal appendage density and collagen fibre orientation were examined and qualitative structural differences were assessed for each region Skin samples were then grouped by both topographical location of the body and scarring potential. Skin samples exhibited qualitative and quantifiable regional variations in the characteristics studied. Epidermal thickness and appendage counts did not correlate with scarring potential. Both however were statistically significantly higher in skin sampled from the head compared to the trunk. Bundles of collagen fibres in the reticular dermis were grouped according to their orientation in relation to the coronal plane; either parallel, oblique or perpendicular. The ratio of oblique to parallel fibres was statistically significantly higher in body areas with poorer scarring prognosis. This corresponds to a more disorganised arrangement of collagen fibres in these areas. Further qualitative understanding of dermal collagen fibres came from perpendicular to conventional histological samples. This new method stained basement membranes purple, cytoplasm was stained greenish-brown and nuclei dark brown. Collagen fibres were either thin and blue or thick and green. This method was compared to PAS staining and although required more preparative steps allows greater identification of other cellular structures.

<p> Although the electronic pairing hypothesis of Bardeen, Cooper and Schrieffer is verified by experiment, the lattice polarisation mechanism for over-screening the repulsion between mates in a pair need not be the sole mechanism. </p> <p> Alternatives to the lattice polarisation mechanism are discussed and a new approach to electronic polarisation is developed. Propagator formalism is reworked using a charge density propagator to avoid the Dyson equation for the screened potential. The fermi liquid approach to electrons in a metal is avoided, too, because it misses the correlations which give a solid its atomicity. An atomic picture is contrived instead and used to predict what observable features of a superconductor are influenced by atomic correlations. </p> / Thesis / Doctor of Philosophy (PhD)

Elektrokemisk korrosionsanalys av legeringar är en essentiell del av den större materialanalysen som måste utföras när en legerings lämplighet för en viss applikation evalueras. Nickelbaserade legeringar är kända för sin utmärkta korrosionsresistans, och de Ni-Cr-Mo-baserade legeringarna 59, 625, och 718 är också så kallade superlegeringar. Superlegeringar karaktäriseras med att legeringarna behåller sina mekaniska, termiska, och korrosion egenskaper även vid temperaturer nära smältpunkten. Den elektrokemiska korrosionsanalysen av legeringarna 59, 625, och 718 utfördes med OCP, cyklisk polarisation, samt EIS. Experimenten utfördes i en tre-elektrod elektrokemisk cell med en Ag/AgCl referenselektrod och en platina motelektrod, så väl som en Gamry Reference 600+ potentiostat. Detta arbete framhäver vikten att utföra cyklisk polarisation i korrosionsanalysen eftersom metod kan upptäcka viktiga skillnader mellan till synes liknande legeringar, vilket kunde ses vid jämförelsen av legering 718 med 625 och 59. EIS visas också vara en kraftfull analytisk verktyg genom sin förmåga att approximera verkliga elektrokemiska system genom att använda elektriska kretsar, så väl som EIS:s förmåga att användas som ett komplementärt analytiskt verktyg för att assistera i interpretationen av cyklisk polarisationsdata. / Electrochemical corrosion analysis of alloys forms an essential part of the larger material analysis procedure that needs to be performed when evaluating the feasibility of an alloy for a certain application. Nickel-based alloys are known for having excellent corrosion resistance, and the Ni-Cr-Mo-based alloys 59, 625, and 718 are also known as superalloys. Superalloys are characterized by the alloy maintaining its mechanical, thermal, and corrosion properties even at temperatures close to the melting point. The electrochemical corrosion analysis of alloys 59, 625, and 718 was performed with OCP, cyclic polarization, and EIS. The experiments made use of a three-electrode electrochemical cell with an Ag/AgCl reference electrode and a platinum counter electrode, as well as a Gamry Reference 600+ potentiostat. This work highlights the importance of performing cyclic polarization in the corrosion analysis since the method can reveal important differences in seemingly similar alloys, which was seen when comparing alloy 718 with 625 and 59. EIS is also shown to be a powerful analytical tool through the method's ability to approximate real electrochemical systems using electrical circuits, as well as the ability of EIS to be used as a complementary analytical tool to assist in interpreting cyclic polarization data.

No / The use of the hybrid method of moments/finite difference time domain technique can be effective for solution of electromagnetic problems which are intractable for a single numerical method. Using this method, a study of the effects of human proximity on the polarisation purity of different types of circularly-polarised handset antennas for personal satellite communications was undertaken. Associated with this, assessments of the specific absorption rate in the head were made. The method gave stable results, in accordance with physical expectations; good agreement with the pure method of moments was shown in simplified cases omitting the head

Titre de l'écran-titre (visionné le 28 mars 2023) / Par sa symétrie singulière, une impulsion laser de polarisation radiale de type TM$_{0,1}$ a la particularité de développer un important champ électrique longitudinal, soit une composante de champ oscillant dans la direction de l'axe optique, dans un contexte de forte focalisation. Cet attribut lui permet d'être particulièrement bien adaptée à l'accélération de particules chargées dans le vide. Un électron se trouvant sur le passage d'une impulsion TM$_{0,1}$ suffisamment puissante peut se synchroniser avec un demi-cycle optique du champ longitudinal et être entraîné avec ce dernier pour ainsi acquérir une énergie substantielle - ce mécanisme est généralement nommé accélération directe ou accélération sous-cycle. Ce schéma d'accélération est caractérisé par une complication inévitable ; tout faisceau laser, peu importe son état de polarisation, subit une déformation de la porteuse en traversant la région focale. Cette déformation, connue sous le nom de déphasage de Gouy, a pour effet de condamner les électrons à une désynchronisation hâtive avec l'impulsion laser, nuisant ainsi à un transfert optimal d'énergie. L'idée de base de ce projet de doctorat est donc la suivante : nous souhaitons diminuer la variation totale du déphasage de Gouy d'une impulsion de type TM$_{0,1}$ sur l'axe optique afin de faciliter l'accord de phase entre les électrons et le champ, et ainsi améliorer les performances énergétiques de l'accélération directe d'électrons. Toutefois, au moment d'entamer ce doctorat, la valeur du déphasage de Gouy total des différentes composantes vectorielles du faisceau TM$_{0,1}$ fortement focalisé est encore incomplètement établie. La première partie de ce projet est donc consacrée à la compréhension des résultats disparates présents dans la littérature à ce sujet. En proposant un formalisme unificateur, nous montrons que la valeur totale du déphasage de Gouy de la composante longitudinale est toujours de 2π sur l'axe optique. Considérant cette valeur a priori immuable, la seconde partie de ce projet consiste à trouver un moyen de la réduire. Cela est fait en développant une famille de solutions aux équations de Maxwell, à l'aide des intégrales de Richards et Wolf, ayant le profil d'intensité et l'état de polarisation d'un faisceau TM$_{0,1}$, mais ayant un déphasage de Gouy ajustable. En utilisant ce nouveau type d'impulsion dans des simulations numériques d'accélération d'électrons pour différentes valeurs de déphasage de Gouy total, nous montrons qu'il s'agit d'un paramètre décisif dans le processus d'accélération sous-cycle et que la diminution de cette valeur est toujours avantageuse du point de vue énergétique. / Due to its singular symmetry, a TM$_{0,1}$ radially polarized laser pulse has the particularity of developing a strong longitudinal electric field, i.e. a field component oscillating in the direction of the optical axis, in a context of strong focusing. This attribute makes it particularly well suited to accelerate charged particles in vacuum. An electron in the path of a sufficiently strong TM$_{0,1}$ pulse can be synchronized and trapped in a single half-cycle of the longitudinal field to acquire substantial energy - this mechanism is generally referred to as direct acceleration or sub-cycle acceleration. This acceleration scheme is characterized by an unavoidable complication; any laser beam, regardless of its polarization state, undergoes a deformation of the carrier as it passes through the focal region. This deformation, known as the Gouy phase shift, causes the electrons to get preemptively out of sync with the pulse, thus hindering optimal energy transfer. The idea behind this PhD project is the following; we want to decrease the total Gouy phase variation of a TM$_{0,1}$-like pulse on the optical axis in order to facilitate the phase matching between the electrons and the field, and thereby improve the energetic performances of direct electron acceleration. However, at the beginning of this project, the value of the total Gouy phase shift of the different vector components of the strongly focused TM$_{0,1}$ beam is still not fully established. The first part of this project is therefore devoted to understanding the disparate results in the literature on that matter. By proposing a unifying formalism, we show that the total value of the Gouy phase shift for the longitudinal component is always 2π on the optical axis. Considering this a priori unchangeable value, the second part of this project is to find a way to reduce it. This is done using Richards and Wolf integrals to develop a family of solutions to Maxwell's equations for a beam with the same intensity profile and polarization state as the TM$_{0,1}$ beam, but with a tunable Gouy phase. By using this new type of pulse in numerical simulations of electron acceleration for different values of total Gouy phase variation, we show that it is indeed a decisive parameter in the sub-cycle acceleration process and decreasing this value is always beneficial from an energy point of view.

Durch elektrochemische Impedanzspektroskopie während der anodischen Oxidation von Aluminium werden in der vorliegenden Arbeit die elektrochemischen Vorgänge während der Oxidbildung quantitativ und zeitabhängig untersucht. Es wird ein Modell vorgeschlagen und diskutiert, welches das Impedanzverhalten während der anodischen Oxidation in Schwefel-, Oxal- und Phosphorsäure über einen großen Bereich von Konzentrationen und Stromdichten abbilden kann. Aus den gewonnenen Ergebnissen werden die kapazitive Wirkung der Sperrschicht am Porengrund, der Eintritt von Ladungsträgern in die Sperrschicht, der Ionentransport durch die Sperrschicht sowie die Oxidbildungsreaktion selbst als wesentlich für das Impedanzverhalten identifiziert. Die ermittelten Zusammenhänge und Konstanten können als Grundlage für Modellvorstellungen dienen, welche das Verhalten elektrischer Prozessgrößen und die Ausbildung der charakteristischen Oxidstruktur bei der anodischen Oxidation von Aluminium verknüpfen. / In the present work, the electrochemical subprocesses of the oxide formation on aluminium by anodic oxidation are investigated using electrochemical impedance spectroscopy. The time dependence of the impedance behaviour and the quantitative relations between the process parameters and the impedance behaviour are considered. A model for the representation of the electrochemical behaviour during the anodic oxidation in sulphuric, oxalic and phosphoric acid is proposed and discussed for a wide range of anion concentrations and current densities. On the basis of the obtained results, the capacitive effect of the barrier layer, the charge transfer resistance of the barrier layer, the ion transport within the barrier layer and the oxide formation are identified as the dominating effects for the impedance behaviour. The established relations can serve as a basis for models, which interrelate both the electrochemical behaviour and the geometrical formation of the characteristic pore structure.

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