Texte remanié de: Th. doct.--Sociol.--Paris 8, 1995. / Bibliogr. p. 267-271. Index.

No description available.

Las células de la cresta neural (CCN) conforman una población transitoria presente solo en etapas muy tempranas del desarrollo embrionario de vertebrados. Estas células se caracterizan por su multipotencia y capacidad migratoria, y es sabido que defectos en el proceso de migración lleva a severos trastornos congénitos conocidos como neurocristopatias. Las CCN, para adquirir sus propiedades migratorias, sufren un proceso de transición epiteliomesénquima (TEM), similar a lo que ocurre durante el inicio de la metástasis tumoral. Se ha determinado que los microARNs conforman un grupo de reguladores claves de la TEM tumoral. Considerando lo dicho, nos planteamos como objetivo determinar la existencia de una red regulatoria epigenéticamicroARN que desempeñe un papel importante en la migración de las CCN. Es así que, mediante análisis in silico, se encontró que los reguladores claves de la TEM en las CCN, tales como son los genes PHD12 y Snail2, son blancos tentativos del mismo miR-203. Al analizar la expresión de miR-203 mediante hibridación in situ y RT-qPCR se observó que se expresa fuertemente desde estadios muy tempranos en la placa neural y el tubo neural. Sin embargo, su expresión disminuye en el tubo neural dorsal coincidentemente con el inicio de la migración de las CCN. Por otra parte, se observó mediante secuenciación por bisulfito, que la región genómica de miR-203 se encuentra hipermetilada en las CCN pre-migratorias, a diferencia de la hipometilación encontrada en las células del tubo neural ventral y CCN migratorias. Finalmente, la pérdida de función de miR-203, utilizando un vector “esponja” de microARNs, lleva a una migración prematura de las CCN. Estos resultados en conjunto indican que la inhibición de la expresión de miR-203, mediante metilación del ADN, permite el aumento de la expresión de los genes PHD12 y Snail2 los cuales están directamente involucrados en la TEM de las CCN. Los resultados obtenidos en este proyecto pueden tener grandes implicancias que permitirán tener un mayor entendimiento sobre los errores que pueden conducir a un desarrollo anormal, así como también para comprender la metástasis tumoral.

Implication de SIP1 (Smad Interacting Protein 1) dans la transition épithélio-mésenchymateuse associée à la progression métastatique

The Lena West property near Lac des Bois, NT, held by Diamondex Resources Ltd., is an area of interest for exploration for kimberlitic features. In 2005, Frontier Geosciences Inc. was contracted to carry out seismic reflection and time-domain transient electromagnetic (TEM) surveys to investigate the possibility of kimberlite pipes being the cause of total magnetic intensity (TMI) anomalies previously identified on the property. One small part of the property, Area 1915, was surveyed with two perpendicular seismic reflection lines 1550 m and 1790 m long and three TEM lines consisting of six or seven individual soundings each with a 200 m transmitter loop. The results generated by Frontier Geosciences did not indicate any obvious vertical features that correlated with the TMI anomaly. The purpose of this study is to reprocess the seismic reflection data using different approaches than those of Frontier Geosciences and to invert the TEM data using a 1-D inversion code, EM1DTM recently developed by the UBC Geophysical Inversion Facility, to improve upon previous results and enhance the interpretation. A secondary objective is to test the robustness of EM1DTM when applied to observed TEM data, since prior to this study it had only been applied to synthetic data. Selective bandpass filtering, refraction and residual statics and f-x deconvolution procedures contributed to improved seismic images to the recorded two-way traveltime of 511.5 ms (approximately 1100 m depth). The TEM data were successfully inverted and converted to pseudo 2-D recovered resistivity sections that showed similar results to those from Frontier Geosciences. On the final seismic reflection sections, several strong reflectors are identified and the base of the overlying sedimentary layers is interpreted at a depth of ~600 m. The TEM results show consistent vertical structure with minimum horizontal variation across all lines to a valid depth of ~150 m. However, neither TEM nor seismic reflection results provide any information that correlates well with the observed TMI anomaly.

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Abstract SrTiO3 is cubic at room temperature, and retains cubic until the phase transition to tetragonal at 105K (-168oC). It is a wide-band-gap semiconductor having an energy gap Eg ≈ 3.0 eV, when its semiconductivity is greatly improved by doping with donor oxides, e.g.Nb2O5 or heat treatment in low oxygen partial pressures (Po2). Donor oxides in solid solution with SrTiO3 forming substitutional defects create electron or cation vacancies as the principal charge compensation defect. In-gap levels are also modified by the oxygen partial pressure (Po2) adopted in sintering, which generates oxygen vacancies in order to maintain the overall charge neutrality in the ceramic. In this research, donor-doping and Po2 used in sintering are investigated for the in-gap-level modification using the cathodoluminescence (CL) spectrometry equipped with a scanning electron microscope (SEM). Other analytical techniques, e.g. transmission electron microscopy (TEM) will be used for characterizing the defect structure. Preliminary results suggest that the in-gap levels are registered at 3.10 eV and 2.69 eV, representing the intrinsic Eg and a donor-level created by oxygen vacancies, respectively.

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Pressureless-sintering of non-stoichiometric barium titanate (BaTiO3) powder of TiO2-excess compositions has been investigated. Crystalline phases were analysed by X-ray diffractometry. Attention has been paid to the analysis of the corresponding sintered microstructure by adopting scanning and transmission electron microscopy. Large plate-like grains grown abnormally containing {111} double twin lamellae are commonly found in low-temperature (1332oC) sintered BaTiO3, by presence of a liquid phase, or by twinning, or as discussed in this experiments by partial dislocations. Samples were sintered in air at 1250oC for 1¡B4 and 50 h. In this respect, the emphasis is discussed about the role of the partial dislocations in the early stage of twin formation. Both analytic dislocations exist on the {111} double twin lamellae within abnormal grain and the interface between abnormal grain and normal grain. In the experimental process, dislocation type with the Burgers vector ‹110› and ‹112› has been found except for the ‹111›. For the Burgers vector ‹110› in the perovskite structure, it is possible to envisage that edge dislocations with [100] Burgers vector can be dissociated in their climb plane ([100] ¡÷ 1/2[101] + 1/2[10 ]). Moreover, the perovskite structure has been deformed form ‹110› dislocation (perfect dislocation). Oppositely, the [112] Burgers vector has been formed both partial dislocation type and perfect dislocation type. For sintering at 50 h, we can conjecture the grain growth mold by Shockley or Frank partial dislocation affect on the macroscopic step. Experimental results show that Shockley and Frank partial dislocations have not been found on the {111} double twin lamellae.

The microstructure of £b'-Cu6Sn5 during in the early stage of growth was studied. Sn was electroplated onto thin Cu foil at room temperature and the specimen was annealed at 150 ºC for 30 s. The Cu and Sn on the £b'-Cu6Sn5 surfaces were removed electrolytically and the specimens were analyzed with scanning and transmission electron microscopes. The £b'-Cu6Sn5 grains on the Cu side were as small as 5 nm but grew rapidly to 0.3 to 0.5 £gm on the Sn side. The orientation relationships between £b'-Cu6Sn5 and Cu were studied by a thin film technique. Cu was evaporated onto the NaCl (001) and (111) surfaces to form epitaxial Cu thin films and Sn was then evaporated onto the Cu films to form £b'-Cu6Sn5. Two types of orientation relationships were found, i.e., (1) [204]£b'//[001]Cu (zone axis), (40-2)£b'//(110)Cu, and (020)£b'//(1-10)Cu, and (2) [204]£b'//[111]Cu (zone axis), (40-2)£b'// Cu, and (020)£b'//(-1-12)Cu. The interfaces were analyzed. (Chapter 1) A very thin £b-Cu6Sn5 layer was formed by dipping thin Cu foil into molten Sn at 240 ºC for 1 second and quenching in ice water. The Sn and Cu on the £b-Cu6Sn5 surface were removed electrolytically to study the surface morphologies. The £b-Cu6Sn5 grains on the Sn side had a worm-type shape, about 0.3-0.5 £gm wide and up to 2 £gm long, but those on the Cu side were very small, about 5 nm in size. The nucleation and growth of the £b-Cu6Sn5 grains were discussed. The orientation relationships between £b-Cu6Sn5 and Cu were determined by transmission electron microscopy. The (11-20) plane of £b-Cu6Sn5 was found to be the interface with both the Cu (001) and (-111) surfaces, and a common orientation relationship of (0001)£b//(110)Cu was observed. The match of atoms between £b-Cu6Sn5 and Cu on the above interfaces were analyzed. (Chapter 2) A thin film technique was developed to study the orientation relationship and interface between £`-Cu3Sn and Cu by transmission electron microscopy. Epitaxial Cu thin films were grown on the NaCl (001) and (111) surfaces and Sn was evaporated to form £`-Cu3Sn directly without breaking the vacuum. The orientation relationship Z=[001]£`//[111]Cu, (100) £` //(-110)Cu, and (010)£` //(-1-12)Cu was found on the Cu (111) surface, but none on the Cu (001) surface. The interface was analyzed. (Chapter 3) The formation of the Fe-Al inhibition layer in hot-dip galvanizing is a confusing issue for a long time. This work presents a characterization result on the inhibition layer formed on a TiNb-stabilized interstitial-free steel after a short time galvanizing. The Fe-Al and steel interface was free from oxide, so that the Fe-Al intermetallic compound could directly nucleate on ferrite grains. TEM electron diffraction showed that only Fe2Al5 was formed and it had a well-defined orientation relationship of [110]FA// [111]Fe, (001)FA//(0-11)Fe and (1-10)FA//(2-1-1)Fe with Fe substrate where FA stands for Fe2Al5. The interfaces between Fe2Al5 and Fe are discussed. The Fe2Al5 grains nucleated epitaxially on Fe substrate had very small grain size, 20 nm or less, and several variants were intimately mixed. The grains grew rapidly to hundreds of nanometers toward the Zn side. (Chapter 4) The orientation relationships and interfaces of £_-AuSn with the Au (001), (110) and (111) surfaces were studied with transmission electron microscopy. Au was evaporated onto the NaCl (001), (011) and (111) surfaces to form epitaxial Au thin films and Sn was evaporated onto the Au film to form £_-AuSn. Two types of orientation relationships were found: (1) (11-20)£_//(001)Au, (0001)£_//(110)Au, and (1-100)£_//(-110)Au, which was found on the (11-20)£_/(001)Au and the(1-100)£_/(-110)Au interfaces; and (2) (11-20)£_//(-111)Au, (0001)£_//(110)Au, and (1-100)£_//(-11-2)Au, which was found on the (11-20)£_/(-111)Au interface. The interfaces were analyzed by the structures of the surfaces and the orientation relationships. The nucleation of £_-AuSn on these interfaces was also discussed. (Chapter 5)