Studies on the use of cholesteric liquid crystals (CLCs) as sensing phase for detection of organic vapours in air are described. Stock solutions of 1.0% (w/v) cholesteryl nonanoate (CN) and ...cholesteryl chloride (CC) were prepared in tetrahydrofuran. Binary mixtures, with compositions ranging from 0.18 to 0.25% of CC and 0.82–0.75% of CN, respectively, were prepared by appropriate mixing of the stock solutions. Films were cast by pipetting three 10
μl aliquots of the CLC solution mixture onto a glass disk, whose reverse side was made black to absorb unscattered light. The glass disk was adapted to the common end of a bifurcated optical fibre bundle and placed in a glass vial, which provided a headspace of organic vapours. Measurements were carried out at 27±1
°C, a temperature in which the CLC mixtures maintain their liquid crystalline properties. The responses of the CLC mixtures to vapours of ethanol, acetone, benzene, pyridine and hexane were investigated. The colour of the sensing phases depended on their compositions and exposure to organic vapours gives rise to a change in the optical characteristics of liquid crystals. It was found that the CLC layers containing 0.23–0.25% of CC had no significant change in optical properties when exposed to organic vapours and that ethanol did not cause any optical changes in the liquid crystal layers. Benzene as well as hexane always turned all the coloured liquid crystalline layers to colourless. The CLC layers exhibited different behaviours to vapours of acetone and pyridine. For example, the wavelengths of maximum scattering for the 0.19% CC layer were 530
nm in air, 545
nm in pyridine and 580
nm in acetone. The CLC layers showed reversibility. The lifetimes of these layers (interval of time in which the liquid crystalline phase exists, before crystallisation) were investigated by employing acetone and
n-hexane vapours. Average lifetimes of 14–15
min were found for films in contact with these vapours, while a lifetime of 205
min was possible when the CLC film was exposed to air.
The benefits and constraints of the design/build learning model as developed for landscape architecture curriculum at the University of Washington are described. Design/build projects integrate ...design, construction and professional practice and address concerns of landscape educators and professionals for preparing students for practice. Projects have focused on ecological, social and health issues in under-served communities. Students are immersed in the community design process and challenged to work as a team, to plan and communicate design responsively. Design and construction are synthesized in the principle that a linking of thinking and making is fundamental to good design. Students are encouraged to test and explore traditional and non-traditional materials and construction processes. Constraints include a condensed schedule for completing projects. As a service learning model, the University sees beneficial community relations. Examples include a public wash facility using harvested rainwater, a garden for children infected with AIDS, a healing garden for a cancer support facility and an adopt-a-park for an inner city community in Seattle, Washington. An outline of the process, a typical schedule, results of a student survey and funding sources are given.
Tests on vented and non-vented urinary drainage bags were carried out to establish if differences existed in the flow of fluid into them and whether air bubbles and air trapping were affected by ...venting. At flow rates of 3-12 ml sec-1 there was consistent flow into the vented bag until it was full. There was no air trapping in the bag, and no retrograde flow of air bubbles or fluid up the tube. Flow rates into non-vented bags were strongly affected by air in the drainage tube but, if this cleared, the flow rate was high until the bags were nearly full, at which time air was pushed into the tube. If air remained in the tube the flow rate was reduced. The non-vented bags required a higher pressure in the drainage tube to fill them than the vented bags, and allowed air bubbles to ascend from the bag up the drainage tube.
