Hyper-expanded interlayer separations in superconducting barium intercalates of FeSe.

Intercalation of Ba in ß-FeSe by ammonothermal synthesis results in the formation of different superconducting phases with interlayer distance ranging between 8.4 and 13.1 Å. The values of Tc are primarily dependent on Ba content, and are further modulated by the interlayer spacing through facile intercalation and deintercalation of ammonia.

Rationale for the crystallization of titania polymorphs in solution.

We use in situ X-ray absorption and diffraction studies to directly monitor the crystallization of different titania polymorphs in one and the same solution. We find that, despite the commonly accepted polymorphic-crossover from anatase to rutile triggered by the critical size of nanoparticles, in the solution their respective nucleation and growth are independent processes. Moreover, we find that 5.9 nm rutile nanoparticles are formed prior to the formation of 8.4 nm anatase nanoparticles. Our results suggest that the origins of this crystallization mechanism lie in the formation of an intermediate non-crystalline phase and in time-dependent changes in the chemical environment.

Metal-organic frameworks as hosts for photochromic guest molecules.

Several metal-organic framework compounds (MOF-5, MIL-68(Ga), MIL-68(In), MIL-53(Al)) were loaded with azobenzene (AZB), as confirmed by XRPD measurements and elemental analysis. By IR spectroscopy, it was shown that the light-induced trans/cis isomerization of AZB in these hybrid host-guest compounds is improved compared to that of solid AZB. A population of the excited cis state up to 30% has been obtained for AZB0.66@MIL-68(In). However, no light-induced trans/cis isomerization was observed for AZB0.5@MIL-53(Al). Structural models obtained from high-resolution synchrotron powder diffraction data show that AZB molecules are densely packed within the channels of MIL-53(Al) so that no trans/cis isomerization can occur. A different situation was observed for AZB in the larger channels of MIL-68(Ga). Thus, this investigation shows the influence of the host material on the switching behavior of the embedded AZB molecules.

Crystallization on heating and complex phase behavior of alpha-cyclodextrin solutions.

Solutions composed of alpha-cyclodextrin (alpha-CD), water, and various methylpyridines, in particular, 4-methylpyridine (4MP), undergo reversible liquid-solid transitions upon heating, the crystalline solid phases undergoing further phase transformations at higher temperatures. This unusual behavior has been characterized by an ensemble of measurements, including solubility, differential scanning calorimetry, quasielastic neutron scattering, as well as x-ray powder diffraction. For the alpha-CD/4MP system five crystalline phases have been identified. The unit cell parameters and corresponding changes with temperature indicate a scenario for the crystallization process. A simple model is proposed that mimics the observed disorder-order transition.

Comparación de dos técnicas quirúrgicas para abordaje de la región selar: transeptal transesfenoidal versus transnasal directa / Comparison between two surgicala techniques to approach the selar region: transeptal transesphenoidal versus direct transnasal

Se comparan los resultados operatorios entre las dos técnicas más usadas en lesiones aisladas de la región selar, respecto a exposición quirúrgica, morbilidad asociada y evolución postoperatoria. Se realiza un estudio descriptivo, retrospectivo, identificando aquellas lesiones neuroquirúrgicas de la silla turca diagnosticadas entre enero de 1995 y agosto de 2003, en el Hospital Clínico de la Universidad de Chile e intervenidas mediante técnica microendoscópica, con vías de abordaje transnasal directa o transeptal. Se analizaron ciento cincuenta y cuatro cirugías, 123 realizadas por vía transeptal y 31, por vía transnasal. No se observó diferencias significativas en la distribución de los grupos en cuanto a edad, sexo, motivo de consulta, evaluación otorrinolaringológica, imagenológica y éxito de abordaje. Hubo diferencias en el tiempo operatorio, siendo subjetivamente menor mediante la vía transnasal. La tasa de complicaciones intraoperatorias fue menor al 5 por ciento, sin diferencias significativas entre las dos técnicas analizadas, pero con mayor comodidad postoperatoria para aquellos pacientes intervenidos por vía transnasal. Se concluye que ambas técnicas son comparables en relación al éxito de abordaje y morbilidad asociada, observándose un menor tiempo operatorio mediante vía transnasal y con mayor comodidad para el paciente, con esta técnica, en el postoperatorio.