Democracia y dise??os institucionales participativos en las pol??ticas urbanas: estudio de la experiencia brasilera contempor??nea

El art??culo analiza las instituciones participativas creadas en Brasil a nivel local a lo largo de las ??ltimas d??cadas, espec??ficamente en el ??mbito de las pol??ticas urbanas. Al inicio, evocamos los fundamentos normativos asociados a la democracia y a las instituciones participativas y abordamos el papel de los dise??os institucionales, sus variaciones y potenciales de radicalizaci??n democr??tica. En un segundo momento, contextualizamos las pol??ticas urbanas, se??alando las nuevas referencias legales que requieren la participaci??n y que encuadran el enfoque y el dise??o de las instituciones. Finalmente, analizamos elementos clave de los dise??os participativos, comparando consejos, conferencias, presupuestos participativos y participaci??n en los planes maestros, problematizando sus alcances y potenciales democratizadores

Role of tilt order in the asymmetric ripple phase of phospholipid bilayers

We present the electron density map of the asymmetric ripple phase of dilauroylphosphatidylcholine. We find that the primary feature characterizing the “asymmetry” of the rippled bilayers is the difference in the bilayer thickness in the two arms, and not the asymmetry of the bilayer height profile as is generally assumed. This difference in the bilayer thickness can be attributed to a mean tilt of the hydrocarbon chains of the lipid molecules along the direction of the ripple wave vector. We propose a Landau theory for this phase which takes into account the anisotropic elastic properties of a bilayer with tilt order

Elasticity of smectic liquid crystals with in-plane orientational order and dispiration asymmetry

The Nelson-Peliti formulation of the elasticity theory of isolated fluid membranes with orientational order emphasizes the interplay between geometry, topology, and thermal fluctuations. Fluid layers of lamellar liquid crystals such as smectic-C, hexatic smectics, and smectic-C∗ are endowed with in-plane orientational order. We extend the Nelson-Peliti formulation so as to bring these smectics within its ambit. Using the elasticity theory of smectics-C∗, we show that positive and negative dispirations (topological defects in Smectic-C∗ liquid crystals) with strengths of equal magnitude have disparate energies—a result that is amenable to experimental tests

Chiral symmetry breaking in three-dimensional smectic-C liquid-crystal domains

We report an observation of a unique type of spontaneous chiral symmetry breaking in three-dimensional domains of a smectic-C material consisting of achiral molecules. The observed helical structure clearly demonstrates the effect of an elastic coupling between the bend and the twist distortions in the c field. The sign and the magnitude of the coupling coefficient are determined experimentally. We also demonstrate that an external chiral bias field favors domains of one handedness

A novel modulated phase of liquid crystals: Covariant elasticity in the context of soft, achiral smectic-C materials

Ginzburg-Landau-de Gennes -type covariant theories are extensively used in connection with twist grain boundary (TGB) phases of chiral smectogens. We analyze the stability conditions for the linear, covariant elasticity theory of smectic-C liquid crystals in the context of achiral materials, and predict an equilibrium modulated structure with an oblique wavevector. We suggest that a previous experimental observation of stripes in smectic-C is consistent with the predicted structure.Comment: 4 pages, 3 figure

Small-angle grain boundaries in quasicrystals

The Read-Shockley treatment of small-angle grain boundaries in crystals is generalized to the case of quasicrystals. The dependence of the grain-boundary energy on the angle of mismatch between abutting quasicrystalline grains is calculated. It is found that, even for a symmetric tilt boundary in a quasicrystal, dislocations with at least two types of Burgers vectors are required; these dislocations have to be arranged quasiperiodically along the boundary. The possible clumping of these dislocations to form composites is discussed. Explicit calculations are presented for a pentagonal quasicrystal

Escape configuration lattice near the nematic-isotropic transition: Tilt analogue of blue phases

We predict the possible existence of a new phase of liquid crystals near the nematic-isotropic ($NI$) transition. This phase is an achiral, tilt-analogue of the blue phase and is composed of a lattice of {\em double-tilt}, escape-configuration cylinders. We discuss the structure and the stability of this phase and provide an estimate of the lattice parameter.Comment: 5 pages, 6 figures (major revision, typos corrected, references added

Laser induced rotation of trapped chiral and achiral nematic droplets

We study the response of optically trapped achiral and chiralised nematic liquid crystal droplets to linear as well as circular polarised light. We find that there is internal dissipation in rotating achiral nematic droplets trapped in glycerine. We also demonstrate that some chiralised droplets rotate under linearly polarised light. The best fit to our data on chiralised droplets indicates that rotational frequency of these droplets with radius R is approximately proportional to1/R^2, rather than to 1/R^3.Comment: 15 pages, 6 figure