E. Stahl – författare

Once the basic idea of hypertext had spread rapidly throughout the world via the Internet, the reception of hypertexts soon became subject of empirical research among psychologists, cognitive scientists, and educational researchers. As easy to use software for the writing of hypertexts (HTML editors) is now broadly available, there are no longer any technical obstacles for the use of hypertext production in teaching and learning. This book presents and analyses the learning effects that can be anticipated from the production of hypertexts. It includes laboratory experiments, studies on the production of hypertexts in the context of educational institutions, and reports on software environments designed for the production of hypertext. It includes theoretical, empirically and developmentally oriented contributions. The first three chapters link up directly with research on traditional writing while addressing aspects of the interaction between content and rhetoric during hypertext writing. The next three chapters focus on cooperative learning of students in and through the production of hypertexts. The following two chapters look at new technological possibilities, namely, a software environment for transforming textbooks into personalized hypertexts and the design of hypervideos. The final chapter discusses potential methods for further research.

123 phase and hence have no direct bearing on the retention time of solutes. However in gas-solid chromatography, a considerable quantity of the mobile phase may be adsorbed on the surface of the stationary adsorbent which diminishes the column''s effective length and ability to retain solutes. In this respect helium has been found to be preferable to most other gases (GREENE and Roy, 1957) because it is adsorbed to the least extent. 3. Packed columns offer a considerable resistance to flow, which may create a pressure differential between inlet and outlet of sufficient magnitude to cause an unfavorable flow rate through a significant length of the column. A reduced inlet/outlet pressure ratio can be obtained by using light molecular weight gases toward which the column packing shows the greatest permeability. The flow rate of the mobile phase is normally adjusted by altering the column inlet pressure, for which purpose commercial pressure regulators of sufficient accuracy are available. Quantitative measurements of the flow rate can be made by a number of methods, including rotameters, orifice meters, soapfilm flow meters and displacement of water. The former two methods are the most con­ venient but the least accurate; moreover they create a back pressure and are temperature dependent whereas although the moving soap bubble is cumbersome to employ and unusable for continuous readings, it is preferred when the highest accuracy is required.