Haematite natural crystals: non-linear initial susceptibility at low temperature

Several works have reported that haematite has non-linear initial susceptibility at room temperature, like pyrrhotite or titanomagnetite, but there is no explanation for the observed behaviours yet. This study sets out to determine which physical property (grain size, foreign cations content and domain walls displacements) controls the initial susceptibility. The performed measurements include microprobe analysis to determine magnetic phases different to haematite; initial susceptibility (300 K); hysteresis loops, SIRM and backfield curves at 77 and 300 K to calculate magnetic parameters and minor loops at 77 K, to analyse initial susceptibility and magnetization behaviours below Morin transition. The magnetic moment study at low temperature is completed with measurements of zero field cooled-field cooled and AC susceptibility in a range from 5 to 300 K. The minor loops show that the non-linearity of initial susceptibility is closely related to Barkhausen jumps. Because of initial magnetic susceptibility is controlled by domain structure it is difficult to establish a mathematical model to separate magnetic subfabrics in haematite-bearing rocks.

Arte y filosofía:Correlaciones entre el pensamiento estético de Jacques Rancière y Alain Badiou y el arte político de los colectivos artísticos Claire Fontaine, Raqs Media Collective y Estrella del Oriente

La presente tesis titulada Arte y Filosofía: Correlaciones entre el pensamiento estético de Jacques Rancière y Alain Badiou y el arte político de los colectivos artísticos Claire Fontaine, Raqs Media Collective y Estrella del Oriente, tiene como objetivo evidenciar y sostener, en la actualidad, un vínculo entre el arte y la filosofía, no mirando al arte como objeto de la filosofía, sino analizando las similitudes que se establecen cuando, tanto el arte como la filosofía, persiguen las mismas cosas. Para propiciar dicho vínculo nos amparamos en el pensamiento filosófico de Jacques Rancière y Alain Badiou, y en la práctica artística contemporánea de los siguientes colectivos: Claire Fontaine, Raqs Media Collective y Estrella del Oriente. En primer lugar hemos analizado y relacionado el pensamiento estético de ambos filósofos, indagando en lo han dicho sobre el arte y analizando también los conceptos claves y los cruces posibles entre sus teorías estéticas. Y en segundo lugar hemos pensado las prácticas del arte contemporáneo desde las ideas y ciertas categorías filosóficas presentes en ambos autores, sumando también las propias ideas que se desligan del pensamiento de los artistas y del análisis de sus obras. Consideramos que de esta forma hacemos un recorrido teórico en relación a lo que dicen los filósofos sobre el arte, lo que dicen los artistas sobre sus obras y lo que dicen las obras sobre el orden de las cosas...

Diketonylpyridinium cations as a support of new ionic liquid crystals and ion-conductive materials: analysis of counter-ion effects

Ionic liquid crystals (ILCs) allow the combination of the high ionic conductivity of ionic liquids (ILs) with the supramolecular organization of liquid crystals (LCs). ILCs salts were obtained by the assembly of long-chained diketonylpyridinium cations of the type [HOO^(R(n)pyH)] + and BF_(4)^(-) , ReO_(4)^(-), NO_(3)^(-), CF_(3)SO_(3)^(-), CuCl_(4)^(2-) counter-ions. We have studied the thermal behavior of five series of compounds by differential scanning calorimetry (DSC) and hot stage polarized light optical microscopy (POM). All materials show thermotropic mesomorphism as well as crystalline polymorphism. X-ray diffraction of the [HOO^(R(12)pyH)][ReO_(4)] crystal reveals a layered structure with alternating polar and apolar sublayers. The mesophases also exhibit a lamellar arrangement detected by variable temperature powder X-ray diffraction. The CuCl_(4)^(2-) salts exhibit the best LC properties followed by the ReO_(4)^(-) ones due to low melting temperature and wide range of existence. The conductivity was probed for the mesophases in one species each from the ReO_(4)^(-) , and CuCl_(4)^(2-) families, and for the solid phase in one of the non-mesomorphic Cl^(-) salts. The highest ionic conductivity was found for the smectic mesophase of the ReO_(4)^(-) containing salt, whereas the solid phases of all salts were dominated by electronic contributions. The ionic conductivity may be favored by the mesophase lamellar structure.