Two-state model for the SmAP_{R} phase with randomized layer polarization exhibited by some compounds with bent-core molecules.

One of the unusual liquid crystalline phases exhibited by some compounds with bent-core (BC) molecules is designated as SmAP_{R}, in which transverse polarization (P) of smectic layers with upright molecules has a random orientational distribution. Most of such compounds undergo a transition to the SmAP_{A} phase with antiferroelectric order of adjacent layers as the temperature is lowered. Second harmonic studies have shown that the medium consists of polarized domains with only a few hundred molecules, the number increasing at lower temperatures.

Simple molecular model for ferroelectric nematic liquid crystals exhibited by small rodlike mesogens.

Nematic liquid crystals (NLCs) are the prime example of a liquid medium with an apolar orientational order. In the past couple of years, the ferroelectric nematic (FN) phase has been discovered in some compounds with small rodlike molecules with large longitudinal dipole moments and very restricted chemical structures, as the temperature is lowered from the NLC. We propose a simple model in which the molecules are idealized as cylindrical rods with longitudinal surface charge density waves.

Challenges, experiences, and postoperative outcomes in setting up first successful lung transplant unit in India.

Background: Lung transplantation (LT) has emerged as a definitive cure for a plethora of end-stage lung diseases (ESLDs). With improvements in immune-suppression protocols, the posttransplantation survival rates have gone up.

Aim: The study reported the initial experience of the India's single largest lung transplant program on clinicopathological profile, procedures, challenges encountered, and outcomes.

Some geometrical aspects of packing of bent-core molecules in the triclinic smectic-C_{g} liquid crystals and simple models of the modulated SmC_{gmod} phase.

Organic compounds with bent-core (BC) molecules usually form the layered smectic liquid crystals with tilted molecules and polarization (P) which lies in the plane of the layer. A few such compounds have been found in which P itself tilts out of the plane of the layer, and the medium with general tilt (SmC_{g}) of the molecules has the low chiral triclinic symmetry. We discuss the geometric constraints of molecular packing in this structure to show that projecting groups attached to one of the arms of the BC molecules favors the formation of the SmC_{g} phase.

Curvature elasticity of smectic-C liquid crystals and formation of stripe domains along thickness gradients in menisci of free-standing films.

Smectic liquid crystals with a layering order of rodlike molecules can be drawn in the form of free standing films across holes. Extensive experimental studies have shown that smectic-C (SmC) liquid crystals (LCs) with tilted molecules form periodic stripes in the thinner parts of the meniscus, which persist over a range of temperatures above the transition of the bulk medium to the SmA phase in which the tilt angle is zero. The prevailing theoretical models cannot account for all the experimental observations.

Saddle-splay-induced periodic edge undulations in smectic-A disks immersed in a nematic medium.

We report experimental studies on the phase behavior of binary mixtures of 1″,7″-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) and 4,4-diheptyloxyazoxybenzene, which exhibit, apart from the nematic (N) and twist-bend nematic (N_{TB}) phases, the induced smectic-A (Sm-A) phase for weight fraction of CB7CB between 0.05 and 0.70.

A two-state model for the modulated B liquid crystalline phase exhibited by bent-core molecules.

Liquid crystals (LC) made of bent-core (BC) organic molecules have been intensively studied over the past two decades. The B LC consists of smectic layers in which tilted molecules have an in-plane polar packing, the polarization vector ( P ) having a splay distortion forming stripes of tens of nanometers in width, and undulated layers giving rise to 2D rectangular or oblique lattices. The prevailing phenomenological theory attributes this structure to a strong coupling between molecular tilt in the layers and div P .

Simple model for the stripe phase in compounds with bent-core molecules which exhibit a lower-temperature ferroelectric smectic-A phase.

Bent-core (BC) molecules usually exhibit polar packing in smectic layers in which the long or bow axes tilt with respect to the layer normal. In many compounds, the tilt angle goes to zero, and typically the polarization (P) of neighboring layers has an antiferroelectric order (SmAP_{AF}). A careful molecular engineering has led to the discovery of the ferroelectric SmAP_{F} phase in a few BC compounds.

Microscale Structures Arising from Nanoscale Inhomogeneities in Nematics Made of Bent-Shaped Molecules.

Nanoscale structures in fluid media normally require techniques such as freeze fracture electron microscopy and atomic force microscopy for their visualization. As demonstrated in the present study, the surface modification due to nanoscale clusters occurring intrinsically in nematics made of bent-shaped molecules with either rigid or flexible cores leads to microscale structures, which are visible in an optical microscope. The underlying physical mechanism proposed here involves a quasiperiodic change in anchoring conditions on untreated glass plates for the medium made of islands of clusters surrounded by unclustered molecules.

Two-state model for nematic liquid crystals made of bent-core molecules.

Nematic (N) liquid crystals made of bent-core molecules exhibit unusual physical properties such as an intermediate phase between the N and isotropic (I) phases, a very weak NI transition as inferred from magnetic birefringence measurements in a low field, which is apparently incompatible with a large shift in the NI transition temperature (T_{ni}) measured under a high field. Using our conformational studies on the aromatic cores, we propose that only conformers which are more straightened than those in the ground state (GS) form clusters with a few layers, which persist even in the isotropic phase, as inferred from x-ray and rheological experiments. We present a Landau-de Gennes theory of the medium, including an orientational coupling between the clusters and the GS molecules, which accounts for all the unusual properties.

Tubular growth and bead formation in the lyotropic lamellar phase of a lipid.

We use fluorescence confocal polarised microscopy (FCPM) to study tubular growth upon hydration of dry DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) in water and water-glycerol mixtures. We have developed a model to relate the FCPM intensity profiles to the multilamellar structures of the tubules. Insertion of an additional patch inside a tubule produces a beaded structure, while a straight configuration is retained if the growth is on the outside.

Comment on "Origin of tilted-phase generation in systems of ellipsoidal molecules with dipolar interactions''.

In this Comment, I point out that the physical origin of molecular tilt in the smectic phase, found in the Monte Carlo simulations of systems of rodlike molecules with two terminal antiparallel transverse dipole moments by Bose and Saha [Phys. Rev. E 86, 050701(R) (2012)], is similar to the one proposed by McMillan.

A simple model for the rotation of a trapped chiral nematic droplet under the action of a linearly polarized laser beam.

There have been recent reports of continuous rotation of chiral nematic droplets in restricted ranges of diameter/pitch (d /p) values, trapped by a linearly polarized laser beam. We have developed a simple model to calculate the distortion in the helical structure of a set of flat layers, caused by the action of the strong electric field of the propagating laser beam on the dielectric anisotropy of the medium. The resulting change in the polarization state of the beam passing through the sample is then used to calculate the torque on the sample as a function of the azimuthal angle of the first layer.

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 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 wave vector. We suggest that a previous experimental observation of stripes in smectic-C is consistent with the predicted structure.

A rare disappearing right atrial mass.

Cardiac tuberculosis is rare and usually involves the pericardium. Myocardial tuberculoma is a very rare occurrence and only a few cases have been reported. We describe a rare case of cardiac tuberculoma involving the whole of the lateral right atrial wall, extending from the superior vena cava/right atrial junction up to a tricuspid valve.

Splay and bend elastic constants in the nematic phase of some disulfide bridged dimeric compounds.

We report measurements of the temperature dependences of the splay (K11) and bend (K33) elastic constants of several homologues and a binary mixture of disulfide bridged symmetric dimers made of alkoxy cyanobiphenyl monomeric units. All of them have an even number m of carbon and sulfur atoms in the linking chain and expected to have linear conformations. Both K(11) and K(33) alternate depending on the parity of x which is the number of carbon atoms in the alkyl chain of a monomer.

Temperature- and electric-field-induced inverse Freedericksz transition in a nematogen with weak surface anchoring.

We report electric field dependence of the anchoring transition in a mesogen on cooling in a cell with perfluoropolymer treated surfaces. Below a crossover voltage V(co) the transition is discontinuous between planar and homeotropic alignments, and as the temperature is lowered, the transition temperature decreases quadratically with the field. Above V(co) the transition is continuous between planar and tilted alignments, the transition temperature decreasing essentially linearly with the rms field.

Orientational order in liquid crystals exhibited by some binary mixtures of rod-like and bent-core molecules.

We report measurements of the temperature variations of the optical birefringence in the nematic (N) and partial bilayer SmA (SmA(d)) phases in 4-n-octyloxy 4(')-cyanobiphenyl made of rod-like (R) molecules and five mixtures of this compound with 1,3-phenylene bis[4-(3-methylbenzoyloxy)] 4(')-n-dodecylbiphenyl 4(')-carboxylate, made of bent-core (BC) molecules. The birefringence decreases with the concentration x of the BC molecules but the macroscopic order parameter initially decreases upto 11 mol% of BC molecules and subsequently increases with x. This is attributed to the possible formation of polar clusters of BC molecules.

Anomalous temperature dependence of elastic constants in the nematic phase of binary mixtures made of rodlike and bent-core molecules.

We report on two anomalous trends in the temperature dependences of the splay (K11) and bend (K33) elastic constants in the nematic (N) phase of mixtures of compounds with rodlike (R) and bent-core (BC) molecules: As the sample is cooled from the isotropic to N transition point, (i) K33 increases, attains a maximum value and then decreases, and (ii) close to the N to smectic A (SmA) transition point, K11 decreases sharply. At higher temperatures the bow axes of BC molecules are aligned along the director n, strongly favoring a bend distortion of n as the orientational order parameter is increased. Close to the N-SmA transition point the smecticlike short-range order builds up, and the arrow axes of BC molecules are aligned along n, facilitating a splay distortion of n.

Effect of high electric fields on the nematic to isotropic transition in a material exhibiting large negative dielectric anisotropy.

We report the experimental high electric field phase diagram of a nematic liquid crystal which exhibits a large negative dielectric anisotropy. We measure simultaneously the birefringence (Deltan) and the dielectric constant (epsilon( perpendicular)) at various applied fields as functions of the local temperature of an aligned sample. We also measure the higher harmonics of the electrical response of the medium.

Self-propulsion of nematic drops: novel phase separation dynamics in impurity-doped nematogens.

We report a novel phase separation dynamics, mediated by self-propelled motion of the nucleated drops, in a mixture of a nematogen and an isotropic dopant. We show that surface flow, induced by the gradient in the concentration of the dopant expelled by the growing drops, provides the driving force for the propulsion of nematic droplets. While the liquid crystal-isotropic transition is used here to demonstrate the phenomenon, self-propulsion should be observable in many other systems in which the dynamics of a conserved order parameter is coupled to a nonconserved order parameter.

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 transition. This phase is an achiral, tilt analogue of the blue phase and is composed of a lattice of double-tilt, escape-configuration cylinders. We discuss the structure and the stability of this phase and provide an estimate of the lattice parameter.

A frustrated packing model for the B6-B1-SmAPA sequence of phases in banana shaped molecules.

A vast majority of compounds with bent core or banana shaped molecules exhibit the phase sequence B6-B1-B2 as the chain length is increased in a homologous series. The B6 phase has an intercalated fluid lamellar structure with a layer spacing of half the molecular length. The B1 phase has a two dimensionally periodic rectangular columnar structure.

Giant-block twist grain boundary smectic phases.

Study of a diverse set of chiral smectic materials, each of which has twist grain boundary (TGB) phases over a broad temperature range and exhibits grid patterns in the Grandjean textures of the TGB helix, shows that these features arise from a common structure: "giant" smectic blocks of planar layers of thickness l(b) > 200 nm terminated by GBs that are sharp, mediating large angular jumps in layer orientation between blocks (60 degrees < Delta < 90 degrees ), and lubricating the thermal contraction of the smectic layers within the blocks. This phenomenology is well described by basic theoretical models applicable in the limit that the ratio of molecular tilt penetration length-to-layer coherence length is large, and featuring GBs in which smectic ordering is weak, approaching thin, melted (nematic-like) walls. In this limit the energy cost of change of the block size is small, leading to a wide variation of block dimension, depending on preparation conditions.

Selective imaging of 3D director fields and study of defects in biaxial smectic A liquid crystals.

We report on the selective imaging of different director fields in a biaxial smectic A (SmAb) liquid crystal using Fluorescence Confocal Polarizing Microscopy (FCPM) and Polarizing Microscopy (PM). The patterns of two directors, namely the director n(a) perpendicular to the lamellae and the director n(b) in their planes are visualized by doping the liquid crystal with two fluorescent dyes with different orientation of the transition dipoles with respect to the lamellar matrix. The properties of defects such as disclinations and focal conic domains (FCDs) are consistent with the non-polar D2h-symmetry of the SmA(b) mesophase in the studied mixture of bent-core and rod-like molecules: (1) majority of defects in the director n(b) are half-integer "+/-1/2" disclinations; (2) the integer-strength "+/-1" defects tend to split into the "+/-1/2" disclinations.