44 research outputs found
Influence of the flexoelectricity on the stable configuration of a nematic layer with opposite boundary conditions
No full textWe discuss the influence of flexoelectricity on the critical thickness of a hybrid aligned nematic liquid crystal cell. We show that the critical thickness is independent of the flexoelectrical properties of the nematic only under the hypothesis that the distorted-undistorted transition is of second order. Afterall, the only effect of flexoelectricity is to introduce a very large elastic anisotropy. On the other hand, if first order transitions are considered, the flexoelectricity may play an important role. We also consider the surface polarization which can be different from zero for symmetry considerations. The analysis shows that its influence on the critical thickness or on the order of the transitions is negligible when there is no applied electric field. Some considerations on the terms connected with the surface polarization are also reported. The analysis is performed by supposing the nematic material a perfect insulator.Nous discutons l'influence de la flexoélectricité sur l'épaisseur critique d'une cellule hybride nématique. Nous montrons que cette épaisseur critique est indépendante des propriétés flexoélectriques du nématique dans un cas seulement : celui où la transition distordu/non distordu est du 2e ordre. Dans ce cas, la flexoélectricité ne fait qu'introduire une très grande anisotropie élastique. Par contre, si on considère le cas de transitions du 1er ordre, la flexoélectricité peut jouer un rôle important. Nous considérons aussi la polarisation de surface, qui peut être non nulle à cause de la symétrie du système. L'analyse montre que son influence sur l'épaisseur critique ou sur l'ordre des transitions est négligeable quand il n'y a pas de champ électrique appliqué; les termes qui sont reliés à la polarisation de surface sont également discutés. L'analyse est faite en supposant que le matériau nématique est un isolant parfait
A conjecture on the Mada theory for nematic liquid crystal-surface interaction
No full textWe discuss a recent theory proposed by Mada about the nematic liquid crystal-surface interaction. We point out certain anomalies in his calculation and we present the correct boundary conditions for his model. Furthermore we analyse the Freedericksz threshold vs. sample thickness and the pretilt angle vs. temperature with the revised theory.Nous discutons une nouvelle théorie proposée par Mada sur l'interaction surface-cristal liquide nématique. Nous soulignons certaines anomalies dans son calcul, et présentons les conditions aux limites correctes pour son modèle. En outre nous analysons le seuil de la transition de Freedericksz en fonction de l'épaisseur de l'échantillon et la dépendance en température de l'angle d'inclinaison à la paroi
The 2008–2010 subsidence of dallol volcano on the spreading erta ale ridge: Insar observations and source models
No full textIn this work, we study the subsidence of Dallol, an explosive crater and hydrothermal area along the spreading Erta Ale ridge of Afar (Ethiopia). No volcanic products exist at the surface. However, a diking episode in 2004, accompanied by dike-induced faulting, indicates that Dallol is an active volcanic area. The 2004 diking episode was followed by quiescence until subsidence started in 2008. We use InSAR to measure the deformation, and inverse, thermoelastic and poroe-lastic modelling to understand the possible causes of the subsidence. Analysis of InSAR data from 2004–2010 shows that subsidence, centered at Dallol, initiated in October 2008, and continued at least until February 2010 at an approximately regular rate of up to 10 cm/year. The inversion of InSAR average velocities finds that the source causing the subsidence is shallow (depth between 0.5 and 1.5 km), located under Dallol and with a volume decrease between −0.63 and −0.26 × 106 km3/year. The most likely explanation for the subsidence of Dallol volcano is a combination of out-gassing (depressurization), cooling and contraction of the roof of a shallow crustal magma chamber or of the hydrothermal system
Maternal attachment style, personality structure and post-partum depressive symptoms: a pilot study.
No full text
I disturbi di personalità in Compendio di psichiatria e salute mentale
No full textIl capitolo si propone di definire cosa sono i disturbi di personalità e come possono essere classificati in un'ottica categoriale e dimensionalwe. Vengono descritte inoltre le varie tipologie di personalità e il loro trattamento
