Smectic layer instabilities in liquid crystals

Scientists aspire to understand the underlying physics behind the formation of instabilities in soft matter and how to manipulate them for diverse investigations, while engineers aim to design materials that inhibit or impede the nucleation and growth of these instabilities in critical applications. The present paper reviews the field-induced rotational instabilities which may occur in chiral smectic liquid-crystalline layers when subjected to an asymmetric electric field. Such instabilities destroy the so-named bookshelf geometry (in which the smectic layers are normal to the cell surfaces) and have a detrimental effect on all applications of ferroelectric liquid crystals as optical materials. The transformation of the bookshelf geometry into horizontal chevron structures (in which each layer is in a V-shaped structure), and the reorientation dynamics of these chevrons, are discussed in details with respect to the electric field conditions, the material properties and the boundary conditions. Particular attention is given to the polymer-stabilisation of smectic phases as a way to forbid the occurrence of instabilities and the decline of related electro-optical performances. It is also shown which benefit may be gained from layer instabilities to enhance the alignment of the liquid-crystalline geometry in practical devices, such as optical recording by ferroelectric liquid crystals. Finally, the theoretical background of layer instabilities is given and discussed in relation to the experimental data

Equity in informal science learning: a practice-research brief

This briefi ng paper reports fi ndings from the Youth Access & Equity in Informal Science Learning (ISL) project, a UK-US researcher-practitioner partnership funded by the Science Learning+ scheme. Our project focuses on young people aged 11-14 primarily from under-served and non-dominant communities and includes researchers and practitioners from a range of ISL settings: designed spaces (eg museums, zoos), community-based (eg after school clubs) and everyday science spaces (eg science media)

Youth equity pathways in informal science learning

This infographic reports findings from the Youth Access & Equity in Informal Science Learning (ISL) project, a UK-US researcher-practitioner partnership funded by the Science Learning+ Phase 1 scheme. Our project focuses on young people aged 11-14 primarily from under-served and non-dominant communities and includes researchers and practitioners from a range of ISL settings: designed spaces (eg museums, zoos), community-based (eg afterschool clubs) and everyday science spaces (eg science media)

Pathways in informal science learning: a practice-research brief

This briefing paper reports findings from the Youth Access & Equity in Informal Science Learning (ISL) project, a UK-US researcher-practitioner partnership funded by the Science Learning+ Phase 1 scheme. Our project focuses on young people aged 11-14 primarily from under-served and non-dominant communities and includes researchers and practitioners from a range of ISL settings, including designed spaces (eg museums, zoos), community based (eg afterschool clubs) and everyday science spaces (eg science media)

Elevated size and body condition and altered feeding ecology of the grouper Cephalopholis argus in non-native habitats

In 1956, the shallow-water grouper Cephalopholis argus was introduced from Moorea (French Polynesia), where grouper diversity (14 species) is high, to the Main Hawaiian Islands (MHI), where only 2 rare native deep-water groupers occur. In this non-native environment, the species has flourished and has become the dominant apex predator on many reefs. In the present study, a comparison of non-native populations of C. argus in the MHI with native populations in Moorea showed that mean total length (32.0 vs. 26.9 cm), mass (722 vs. 326 g), growth, and body condition were each significantly elevated in the MHI. In addition, while an ontogenetic shift towards larger prey occurred in both locations, it was faster and more consistent in Moorea than in the MHI. As a result, while small C. argus of comparable size in the 2 locations consumed similar-sized prey, large C. argus in Moorea consumed significantly longer and deeper-bodied prey than their counterparts in the MHI. This pattern was unrelated to the size distributions of available prey and may thus reflect stronger intra- and interspecific competition for small prey in Moorea. Although ecological release in a broader sense (i.e. a combination of predator release, parasite release, and competitive release) may play a role, the most direct explanation for the observed differences between C. argus in native habitats in Moorea (with many competing grouper species) and non-native habitats in the MHI (few competitors) would be competitive release (here used in the sense of benefits resulting from the reduction of interspecific competition)

Science Learning+ Youth Equity Pathways in Informal Science Learning: Survey findings

This document presents an overview of the quantitative survey data findings from the SL+ Equity Pathways in Informal Science Learning project. Further qualitative analysis on some of the open response data is yet to be completed. Findings are grouped into four areas: about the individuals taking part in the survey; their definitions and understanding of equity and related terms; their current equity practice; and their practices around equity work including reading, talking with colleagues and evaluation

Oxygen depletion in coastal seas and the effective spawning stock biomass of an exploited fish species

Environmental conditions may have previously underappreciated effects on the reproductive processes of commercially exploited fish populations, for example eastern Baltic cod, that are living at the physiological limits of their distribution. In the Baltic Sea, salinity affects neutral egg buoyancy, which is positively correlated with egg survival, as only water layers away from the oxygen consumption-dominated sea bottom contain sufficient oxygen. Egg buoyancy is positively correlated to female spawner age/size. From observations in the Baltic Sea, a field-based relationship between egg diameter and buoyancy (floating depth) could be established. Hence, based on the age structure of the spawning stock, we quantify the number of effective spawners, which are able to reproduce under ambient hydrographic conditions. For the time period 1993–2010, our results revealed large variations in the horizontal extent of spawning habitat (1000–20 000 km2) and oxygen-dependent egg survival (10–80%). The novel concept of an effective spawning stock biomass takes into account offspring that survive depending on the spawning stock age/size structure, if reproductive success is related to egg buoyancy and the extent of hypoxic areas. Effective spawning stock biomass reflected the role of environmental conditions for Baltic cod recruitment better than the spawning stock biomass alone, highlighting the importance of including environmental information in ecosystem-based management approaches

Structural properties of crumpled cream layers

The cream layer is a complex heterogeneous material of biological origin which forms spontaneously at the air-milk interface. Here, it is studied the crumpling of a single cream layer packing under its own weight at room temperature in three-dimensional space. The structure obtained in these circumstances has low volume fraction and anomalous fractal dimensions. Direct means and noninvasive NMR imaging technique are used to investigate the internal and external structure of these systems.Comment: 9 pages, 4 figures, accepted in J. Phys. D: Appl. Phy

Ordering of ferromagnetic nanoparticles in nematic liquid crystals

Dispersions of magnetic nanoparticles in a nematic liquid crystal were investigated as magnetic fields were applied in three different boundary condition geometries: (i) planar substrates and B ⊥ n, (ii) planar substrates and B / n, and (iii) homeotropic substrates and B ⊥ n. Particle chaining is observed when a magnetic field is applied, with a periodicity perpendicular to the chains. Furthermore, linear chains are observed for the magnetic field applied perpendicular to the director, while zigzag chains are formed when the magnetic field direction is parallel to the director field. This is attributed to a change from a dipolar defect configuration around dispersed nanoparticles, to a quadrupolar one, i.e. the change from satellite to Saturn-ring defects. This effect is largely independent of the sample thickness. The dynamic development of the chain length, as well as their two-dimensional order parameter was studied in all cases. Chain lengths increased rapidly until saturation at approximately l = 30 μm after a time of about t = 10 s. Similarly, the chain order parameters increased until saturation between S = 0.8-0.9, independent of sample geometry