Positional, Reorientational and Bond Orientational Order in DNA Mesophases

We investigate the orientational order of transverse polarization vectors of long, stiff polymer molecules and their coupling to bond orientational and positional order in high density mesophases. Homogeneous ordering of transverse polarization vector promotes distortions in the hexatic phase, whereas inhomogeneous ordering precipitates crystalization of the 2D sections with different orientations of the transverse polarization vector on each molecule in the unit cell. We propose possible scenarios for going from the hexatic phase, through the distorted hexatic phase to the crystalline phase with an orthorhombic unit cell observed experimentally for the case of DNA.Comment: 4 pages, 2 figure

Modulated Crystalline-B Phases in Liquid Crystals

Detailed x-ray scattering studies of the modulated phases of 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) are reported. In addition to the previously identified one-dimensional modulation that appears at the transition from the crystalline-B (CrB) phase with AB AB stacking to the CrB phase with orthorhombic stacking, there are two other modulation structures each of which contains two noncolinear modulations. The modulations are explained in terms of a phenomenological model in which domains are separated by walls for which the intralayer packing is identical to the lower-temperature crystalline-G phase. This model yields the measured values for both the modulation wave vector and the lattice distortion.Engineering and Applied Science

X-Ray and Optical Studies of the Thickness Dependence of the Phase Diagram of Liquid-Crystal Films

A comprehensive study of the thickness dependence of the phase diagram of freely suspended films of the liquid crystal 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) between $50 and 69^{\circ}C$ is reported. In thick films (thicker than about 300 layers and characteristic of bulk samples) there is a low-temperature crystalline-G phase followed by five crystalline-B phases with different stacking arrangements at higher temperatures. In thinner films there are two additional crystalline-B phases and two tilted hexatic phases, smectic-F and smectic-I, which do not appear in bulk samples. The in-plane and interlayer correlations in the tilted hexatic phases are anisotropic with a clear dependence on the molecular tilt direction; the in-plane correlations are more developed (longer range) perpendicular to the molecular tilt direction and the interlayer correlations are more developed parallel to the tilt direction.Engineering and Applied Science

X-Ray Studies of Tilted Hexatic Phases in Thin Liquid-Crystal Films

X-ray-diffraction studies of the structures and phase transitions of the tilted hexatic phases (smectic F and smectic I) in thin liquid-crystal films of 4-n-heptyloxybenzylidene-4-n-heptylaniline (70.7) are reported. The measured correlation lengths were strongly anisotropic in both phases. The smectic-I to smectic-F transition is first order as expected from the symmetry change. The smectic-F to smectic-G transition is first order with strong pretransition effects and becomes nearly second order as the film thickness is decreased.Engineering and Applied Science

Synchrotron X-Ray Observation of Surface Smectic-I Hexatic Layers on Smectic-C Liquid-Crystal Films

Synchrotron x-ray diffraction methods employing a position-sensitive detector were used to study smectic-C (SmC) and smectic-I (SmI) phases in thin (2–6 molecular layers) liquid-crystal films of 4-(n-heptyloxy)benzylidene-4-(n-heptyl)aniline (7O.7). Above $\sim 78^{\circ}C$, the entire film is SmC and below $\sim 69^{\circ}C$, the entire film is SmI, a stacked tilted hexatic. Between $69^{\circ}C and 78^{\circ}C$, the surface layers of the films are hexatic SmI and the interior layers are SmC. There is a pretransitional broadening of the surface hexatic peaks as the surface layers melt into the SmC phase.Engineering and Applied Science

Dislocation Model for Restacking Phase Transitions in Crystalline-B Liquid Crystals

A dislocation-mediated model is presented for restacking phase transitions that have been observed in a variety of lamellar (liquid crystalline) systems. The model explains the existence of nonhexagonal crystalline (smectic)-B phases in terms of dislocation-induced tilting of hexagonally packed layers. Ordered dislocation arrays explain both the symmetry and the amplitude of observed modulations. It is likely that the model will also be applicable to modulated lipid-water phases.Engineering and Applied Science

Synchrotron Studies of the First-Order Melting Transitions of Hexatic Monolayers and Multilayers in Freely Suspended Liquid-Crystal Films

Synchrotron x-ray diffraction has been used to study the surface and the interior hexatic-to-liquid (smectic-I to smectic-C) melting transitions of freely suspended liquid-crystal films of N-[4'-(n-heptyl)benzylidene]-4-(n-heptyl)aniline (7O.7) five molecular layers thick. Both the surface hexatic monolayers and the interior hexatic layers melt via hysteretic first-order transitions. After the two surface layers undergo a first-order transition to the smectic-I phase, the surface hexatic correlation length $\xi$ evolves smoothly from $\sim 100 to \sim 300 \mathring{A}$ with a roughly square-root form, $\xi \sim \mid T-T_c \mid ^{1/2}$.Engineering and Applied Science

Generation of small-scale structures in the developed turbulence

The Navier-Stokes equation for incompressible liquid is considered in the limit of infinitely large Reynolds number. It is assumed that the flow instability leads to generation of steady-state large-scale pulsations. The excitation and evolution of the small-scale turbulence is investigated. It is shown that the developed small-scale pulsations are intermittent. The maximal amplitude of the vorticity fluctuations is reached along the vortex filaments. Basing on the obtained solution, the pair correlation function in the limit $r\to 0$ is calculated. It is shown that the function obeys the Kolmogorov law $r^{2/3}$.Comment: 18 page

Chiral and herringbone symmetry breaking in water-surface monolayers

We report the observation from monolayers of eicosanoic acid in the L′2 phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of their nearest neighbors. In this region we find a structural transition, which we tentatively identify as the rotator-herringbone transition L2d−L2h

Near-infrared imaging of FSC 10214+4724 with the W. M. Keck Telescope

Near-infrared observations of the z = 2.286 IRAS source FSC 10214+4724, made with the near-infrared camera on the W. M. Keck Telescope, are reported. Deep broad-band images at 2.15 and 1.27 micrometers, and narrow-band images at 2.165 and 2.125 µm with 0.”6 to 0.”9 seeing show that FSC 10214+4724 consists of at least three distinct components in a compact group of galaxies. The source of the infrared luminosity appears to be in a strongly interacting galaxy that has a luminosity of ~100 times that of a present-day L* galaxy. The interaction suggests and 'age' of this galaxy of ≃ 10^9 yr. The Hα emission is resolved as a source of diameter ≃ 5 kpc, suggesting that a starburst contributes to the observed Hα emission. There is an excess of objects in the FSC 10214+4724 field that could represent galaxies in an associated cluster