La doped HoMn2O5 in studying the influence of the local structure distortion on the magnetic transition has been investigated systematically. It is found that by doping of La ions in a proper percentage, 0.1≤x≤0.2, the formation of the possible impurity RMnO3 (113) phase could be suppressed; single phases of LaxHo1-xMn2O5 (0.1≤x≤0.2) can be formed in one atmosphere of flowing oxygen. For x=0.2, an weak ferromagnetic transition on top of the paramagnetic background appears at 150K and saturated at 75K, which implies that the compound undergoes a ferromagnetic to antiferromagnetic transition. In addition, the lattice didn¡¦t appear a huge phase transition at low temperature, it¡¦s observed local distortion behavior within 100~150K, and back to normal structure as high temperature ones. It¡¦s convinced that will be associated with the magnetic properties, which need further examination and experiment.

Thèse de doctorat : Chimie et Electrochimie Analytiques : Nancy 1 : 2007. / Titre provenant de l'écran-titre. Bibliogr.

Reproduction de : Thèse de doctorat : Chimie, Chimie-physique : Metz : 2002. / Titre provenant de l'écran-titre. Notes bibliographiques.

Reproduction de : Thèse de doctorat : Physique. Optoélectronique : Lyon 1 : 2003. Reproduction de : Thèse de doctorat : Physique. Optoélectronique : Université de Tunis El-Manar : 2003. / Thèse soutenue en co-tutelle. Titre provenant de l'écran titre. 92 réf. bibliogr.

Healthy skin is a sign of positive self-worth, attractiveness and vitality. Compromises to this are frequently caused by extended periods of recreation in the sun and in turn exposure to the harmful effects of UV radiation. To maintain strength and integrity, protection of the skin is paramount. This can be achieved by implementing skin-care products which contain sunscreen active ingredients that provide UV protection. Unfortunately, photo-degradation, toxicity, and photo-allergies limit the effectiveness of present day sunscreen ingredients. Currently, this is moderated by physically embedding within inert silica particles, but leaching of the active ingredient can occur, thereby negating protective efforts. Alternatively, this research details the preparation and investigation of bridged silsesquioxane analogues of commercial ingredients which can be chemically grafted to the silica matrix. Studies with bridged salicylate particles detail facile preparation, minimized leaching, and enhanced UV stability over physically encapsulated and pendant salicylate counterparts. In terms of UVB protective ability, the highest maintenance of sun protection factor (SPF) after extended UV exposure was achieved with bridged incorporation, and has been attributed to corollary UV stability. Additionally, bridged salicylate particles can be classified as broad-spectrum, and rate from moderate to good in terms of UVA protective ability. Particles incorporated with a bridged curcuminoid silsesquioxane were also prepared and displayed comparable results. As such, an attractive method for sunscreen isolation and stabilization has been developed to eliminate the problems associated with current sunscreens, all while maintaining the established UV absorbance profiles of the parent compound. To appreciate the technology utilized in this research, a thorough understanding of sol-gel science as it pertains to hybrid organic/silica particles, including methods of organic fragment incorporation and insight on the effect of incorporation method on ingredient leaching and UV stability, is vital. This was afforded by analysis of hybrid fluorescent dansyl particles, prepared by both O/W microemulsion polymerization and a modified Stöber process, which detailed that covalent entrapment of bridged dansyl silsesquioxane is the incorporation method of choice to ensure minimized leaching and enhanced UV stability. As such, use of this method can provide exciting applications in fields where stability and retainment of the embedded ingredient is paramount for efficacy.

No description available.

No description available.

Th. univ.--Sci. pétrolières--Paris 6, 1994. / Diplôme délivré en association avec l'Ecole nationale supérieure du pétrole et des moteurs. 1995 d'après la déclaration de dépôt légal. Bibliogr. p. 202-208. Résumé en français et en anglais.

Tübingen, Univ., Diss., 2002.

Zugl.: Karlsruhe, Univ., Diss., 2009 / Hergestellt on demand. - Zusätzliches Online-Angebot unter http://uvka.ubka.uni-karlsruhe.de/shop/isbn/978-3-86644-414-0