Passive optical separation and enrichment of cells by size difference

A size-selective cell sorting microfluidic device that utilizes optical force is developed. The device consists of a three-dimensional polydimethylsiloxane microstructure comprised of two crossed microchannels in a three-dimensional configuration. A line shaped focused laser beam is used for automatic size-selective cell sorting in a continuous flow environment. As yeast cells in an aqueous medium are fed continuously into a lower channel, the line shaped focused laser beam is applied (perpendicular to the direction of flow) at the junction of the two crossed channels. The scattering force of the laser beam was employed to push cells matching specific criteria upward from one channel to another. The force depends on the size of the cells, the laser power, and the fluid flow speed. The variation in size of yeast cells causes them to follow different routes at the intersection. For flow speeds below 30 μm∕s, all yeast cells larger than 3 μm were removed from the main stream. As a result, a high purity sample of small cells can be collected at the outlet of bottom channel.     

Mapping Social Studies Teachers' Implementation Behaviour on an Innovation Configuration

Many large-scale studies (Berman and McLaughlin 1975; Emrick and Peterson, 1978) and reviews (Fullan and Pomfret, 1977) have indicated the need for curriculum developers to pay more attention to the process of implementing new curriculum materials. This study draws upon the tools of the Concerns-based Adoption Model developed by Hall and Loucks to gather information about teacher implementation behaviour in relation to the Curriculum Development Institute of Singapore (CDIS) Social Studies curriculum package. The Innovation Configurations checklist and an openended teacher-concerns questionnaire were administered to 725 teachers from 70 primary schools during two survey periods, March to May 1986 and July to September 1986. Analysis of the data provided understanding of teachers' actual use of the various components of the curriculum and their main concerns. Unacceptable and weak teacher practices were revealed in the field-trips, project work, testing and the teaching of concepts components of the curriculum package. In addition, teachers seemed more concerned about the content area of Social Studies rather than the skills which the curriculum package advocated. The data forms a basis for the development of more effective implementation-facilitating activities.