Air sampler collects and protects minute particles

Air ejector impactor sampler collects and protects samples of particles greater than 0.1 micron in diameter. In operation, it causes impaction of particle-laden air onto several collection surfaces within a collection cylinder. When not operating, the collector cylinder is maintained in a retracted state within a protective envelope

Apparatus for sampling particulates in gases

A device for sampling particulates in gases is described. The device is used to obtain samples of the upper atmosphere. The equipment used a common source of gas pressure to provide the driving gas of an air ejector pump. The sample collection cylinder has many slit impactors running longitudinally on the outer surface of a cylinder and terminating just short of each end of the cylinder

Designing for tacit learning: an investigation of design strategies for multimedia supported learning in the crafts

There is an increasing interest and activity in the design of interactive multimedia to support learning in all fields of education and training. However, most of the theory to support such developments is concerned with learning explicit knowledge and there is little guidance available to designers of material for learning in areas with an element of tacit knowledge such as craft skills. This paper describes the foundation work for a long-term project concerned with learning in traditional rural crafts but with the intention to provide a methodological framework for the design of multimedia-based learning in all areas of craft knowledge. A review of established theory of learning and the use of multimedia for learning in areas of explicit knowledge indicates some important basic principles, for example the need to understand the interaction between the teacher and learner in the context of the subject being taught and the need for clear narrative structures to avoid students becoming "lost" in the multiple pathways of interactive media. Observational studies of learning using educational video in a craft context and a study of an experienced craftsman/teacher teaching a group of learners, complemented by study of learning in related contexts, have allowed problems and issues to be identified and design strategies to be developed. While these are provisional they provide an overview of the design problems and have been used to plan a programme of experimental design and evaluation to test and develop principles of effective multimedia design for craft learning. </p

Jacobi fields along harmonic 2-spheres in S3S^3 and S4S^4 are not all integrable

In a previous paper, we showed that any Jacobi field along a harmonic map from the 2-sphere to the complex projective plane is integrable (i.e., is tangent to a smooth variation through harmonic maps). In this paper, in contrast, we show that there are (non-full) harmonic maps from the 2-sphere to the 3-sphere and 4-sphere which have non-integrable Jacobi fields. This is particularly surprising in the case of the 3-sphere where the space of harmonic maps of any degree is a smooth manifold, each map having image in a totally geodesic 2-sphere.Comment: 43 pages. Some typos corrected; introduction expande

Thread cutting with 3-axis N/C milling machine

TAPDIE, a generalized macro written for the APT numerical control system, cuts threads in stock too big for conventional machines or for which conventional methods are unsuitable. TAPDIE computes the machine tool path necessary and the information is passed on to a post-processor which produces a control tape