The Past Ubiquity and Environment of the Lost Earth Buildings of Scotland.

This paper investigates the once ubiquitous vernacular earth-built structures of Scotland and how perceptions of such buildings were shaped and developed through periods of intense cultural and environmental change. We focus upon the past exploitation of traditional resources to construct vernacular architectures and on changes in the perception of the resultant buildings. Historic earth-built structures are today deeply hidden within the landscapes of Scotland, although they were once a common feature of both urban and rural settlements. Whilst the eighteenth and nineteenth century period of Improvement - during which many of these structures were destroyed, repurposed, or left to decay - has received extensive attention by historians, there exists no previous serious study of the human and environmental dimensions. Through analysis of the material aspects of landscape resource use and analysis of the historical perceptions of such use, we emphasize the national significance of this undervalued aspect of Scotland's built and cultural heritage, increasingly at risk of being lost completely, highlighting the prior ubiquity of mudwall structures.

Highly birefringent vaterite microspheres: production, characterization and applications for optical micromanipulation.

This paper reports on a simple synthesis and characterization of highly birefringent vaterite microspheres, which are composed of 20-30 nm sized nanocrystalls. Scanning electron microscopy shows a quite disordered assembly of nanocrystals within the microspheres. However, using optical tweezers, the effective birefringence of the microspheres was measured to be Deltan = 0.06, which compares to Deltan = 0.1 of vaterite single crystals. This suggests a very high orientation of the nanocrystals within the microspheres. A hyperbolic model of the direction of the optical axis throughout the vaterite spherulite best fits the experimental data. Results from polarized light microscopy further confirm the hyperbolic model.

Synthesis and surface modification of birefringent vaterite microspheres.

This paper reports on the synthesis of birefringent vaterite microspheres with narrow size distribution using a seeded growth method. In a post-treatment the microspheres were stabilized and functionalized through coating with a combination of organosilica and silica. The coating vastly enhanced the stability of the vaterite microspheres in biological buffers and allowed the attachment of biomolecules such as DNA or proteins. As an example, streptavidin was attached to the surface of the functionalized microspheres. These results pave the way for the use of birefringent vaterite particles for the micromanipulation of single biological molecules such as DNA or specific proteins in an optical trap capable of exerting and measuring torques. The stabilized birefringent microspheres may also find use for biosensor and biological screening applications.

Constant power optical tweezers with controllable torque.

We describe a means for controlling the spin angular-momentum flux of a laser beam at constant power, without introducing any elliptical or linear polarization. This allows a controllable torque, acting to spin the particle uniformly, to be exerted on a birefringent particle in optical tweezers. The constant power means that transverse and axial trapping, and heating due to absorption, are unaffected by changing the torque. The torque can be computer controlled and rapidly changed. In addition, the lateral trapping is kept constant. Very low torques can be obtained such that rotational Brownian motion of birefringent particles can be observed. This has the potential to greatly extend the quantitative applications of the rotation of birefringent objects in optical tweezers.

Picoliter viscometry using optically rotated particles.

Important aspects in the field of microrheology are studies of the viscosity of fluids within structures with micrometer dimensions and fluid samples where only microliter volumes are available. We have quantitatively investigated the performance and accuracy of a microviscometer based on rotating optical tweezers, which requires as little as one microliter of sample. We have characterized our microviscometer, including effects due to heating, and demonstrated its ability to perform measurements over a large dynamic range of viscosities (at least two orders of magnitude). We have also inserted a probe particle through the membrane of a cell and measured the viscosity of the intramembranous contents. Viscosity measurements of tears have also been made with our microviscometer, which demonstrate its potential use to study unstimulated eye fluid.

Mechanics of cellular adhesion to artificial artery templates.

We are using polymer templates to grow artificial artery grafts in vivo for the replacement of diseased blood vessels. We have previously shown that adhesion of macrophages to the template starts the graft formation. We present a study of the mechanics of macrophage adhesion to these templates on a single cell and single bond level with optical tweezers. For whole cells, in vitro cell adhesion densities decreased significantly from polymer templates polyethylene to silicone to Tygon (167, 135, and 65 cells/mm(2)). These cell densities were correlated with the graft formation success rate (50%, 25%, and 0%). Single-bond rupture forces at a loading rate of 450 pN/s were quantified by adhesion of trapped 2-microm spheres to macrophages. Rupture force distributions were dominated by nonspecific adhesion (forces <40 pN). On polystyrene, preadsorption of fibronectin or presence of serum proteins in the cell medium significantly enhanced adhesion strength from a mean rupture force of 20 pN to 28 pN or 33 pN, respectively. The enhancement of adhesion by fibronectin and serum is additive (mean rupture force of 43 pN). The fraction of specific binding forces in the presence of serum was similar for polystyrene and polymethyl-methacrylate, but specific binding forces were not observed for silica. Again, we found correlation to in vivo experiments, where the density of adherent cells is higher on polystyrene than on silica templates, and can be further enhanced by fibronectin adsorption. These findings show that in vitro adhesion testing can be used for template optimization and to substitute for in-vivo experiments.