Deck the Walls with Anisotropic Colloids in Nematic Liquid Crystals.

Nematic liquid crystals (NLCs) offer remarkable opportunities to direct colloids to form complex structures. The elastic energy field that dictates colloid interactions is determined by the NLC director field, which is sensitive to and can be controlled by boundaries including vessel walls and colloid surfaces. By molding the director field via liquid-crystal alignment on these surfaces, elastic energy landscapes can be defined to drive structure formation. We focus on colloids in otherwise defect-free director fields formed near undulating walls. Colloids can be driven along prescribed paths and directed to well-defined docking sites on such wavy boundaries. Colloids that impose strong alignment generate topologically required companion defects. Configurations for homeotropic colloids include a dipolar structure formed by the colloid and its companion hedgehog defect or a quadrupolar structure formed by the colloid and its companion Saturn ring. Adjacent to wavy walls with wavelengths larger than the colloid diameter, spherical particles are attracted to locations along the wall with distortions in the nematic director field that complement those from the colloid. This is the basis of lock-and-key interactions. Here, we study ellipsoidal colloids with homeotropic anchoring near complex undulating walls. The walls impose distortions that decay with distance from the wall to a uniform director in the far field. Ellipsoids form dipolar defect configurations with the colloid's major axis aligned with the far field director. Two distinct quadrupolar defect structures also form, stabilized by confinement; these include the Saturn I configuration with the ellipsoid's major axis aligned with the far field director and the Saturn II configuration with the major axis perpendicular to the far field director. The ellipsoid orientation varies only weakly in bulk and near undulating walls. All configurations are attracted to walls with long, shallow waves. However, for walls with wavelengths that are small compared to the colloid length, Saturn II is repelled, allowing selective docking of aligned objects. Deep, narrow wells prompt the insertion of a vertical ellipsoid. By introducing an opening at the bottom of such a deep well, we study colloids within pores that connect two domains. Ellipsoids with different aspect ratios find different equilibrium positions. An ellipsoid of the right dimension and aspect ratio can plug the pore, creating a class of 2D selective membranes

From isovists to visibility graphs: a methodology for the analysis of architectural space

An isovist, or viewshed, is the area in a spatial environment directly visible from a location within the space. Here we show how a set of isovists can be used to generate a graph of mutual visibility between locations. We demonstrate that this graph can also be constructed without reference to isovists and that we are in fact invoking the more general concept of a visibility graph. Using the visibility graph, we can extend both isovist and current graph-based analyses of architectural space to form a new methodology for the investigation of configurational relationships. The measurement of local and global characteristics of the graph, for each vertex or for the system as a whole, is of interest from an architectural perspective, allowing us to describe a configuration with reference to accessibility and visibility, to compare from location to location within a system, and to compare systems with different geometries. Finally we show that visibility graph properties may be closely related to manifestations of spatial perception, such as way-finding, movement, and space use

Urban dynamics in the Flemish countryside: a comparative study on morphological patterns and local economy dynamics

The article examines two aspects of urbanisation in the rural areas of Flanders, the northern part of Belgium. On the one hand, the evolution of the built environment is studied in terms of built-up density and the corresponding morphological sprawl pattern, from the beginning of the 19th century up until now. On the other hand, the economy dynamics in the rural areas are investigated. This shift in economic activities can be seen as part of a broader urbanisation process, with aspects such as tertiarisation and broadening of agriculture. The main driving factors behind these transformations are discussed based on literature study. It becomes clear that urbanisation of the countryside is the combined result of economic, physical, cultural and political evolutions. The comparative study in eight case municipalities with different spatial characteristics maps the evolution of the built environment and continuity of the economic activities. Temporal and regional differences are analysed and related to more location-specific driving factors. The sprawl pattern seems to have a historical ground, whereas the difference in density is related to the evolution path. Regarding the local economy dynamics, no clear regional differences can be found. The professions and other business services category has the highest density. The amount of tertiary activities proves the importance of tertiarisation on the countryside. Both studied evolutions tend to change the open space profoundly. Therefore, insights are crucial in order to develop location specific policies

Laser Space Communications Study /LACE/ FINAL Summary Report

Program planning to determine atmospheric effects on laser space-ground cummunication syste