journal of science education
Classroom
In this section of Resonance, we invite readers to pose questions likely
to be raised in a classroom situation. We may suggest strategies for dealing
with them, or invite responses, or both. “Classroom” is equally
a forum for raising broader issues and sharing personal experiences and
viewpoints on matters related to teaching and learning science.
An Appreciation of Free Radicals
2. Free Radical Reactions in Industry
The Initiation of the Polymer Industry
Until the early 1930’s, free radical chemistry was essentially confined to laboratory research. Its defining moment came when an accidental discovery was made at the Imperial Chemical Company in 1932. Ethylene was being subjected to high pressure (1400 atm) at about 170oC. Among fifty attempts, one experiment in which benzaldehyde was present gave a white waxy solid. A few months later, another accidental discovery was made. Ethylene in the reaction vessel had leaked out. To compensate the loss, an additional quantity of ethylene was pumped in. This time, polymer formed readily. The cause for this was found to be oxygen present in the right amount (~3-4%) as an impurity in ethylene. Several other such accidental discoveries were made, which helped in developing the polymer industry.
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Introduction
The January 2000 issue of this journal carried a nice article [1] on continued fractions by Shailesh Shirali. After discussing various continued fractions for numbers related to e, he left us with the intriguing question as to how one could possibly evaluate the continued fraction.
The question is interesting because this continued fraction is simpler-looking than the ones which were studied in that article. We answer this question here and show that the discussion naturally involves the Bessel functions, thus explaining the title. However, we shall begin with some details about continued fractions which complement his discussion. One place where continued fractions are known to appear naturally is in the study of the so-erroneously-called Pell's equation.
Starting from August 2004, Resonance is publishing in the Classroom section, a series of short articles, ‘Earthquake Tips’, related to earthquakes, their effects on civil structures, and design and construction of earthquake resistant buildings. The concepts are clearly explained with sketches and analogies. We hope the Resonance readers will benefit from this series of articles.
Earthquake Tips have been brought out by the Department of Civil Engineering, IIT Kanpur and sponsored by Building Materials and Technology Promotion Council, New Delhi, India. These articles are reproduced here with permission from IIT Kanpur and BMTPC, New Delhi.
Learning Earthquake Design and Construction
15. Why is Vertical Reinforcement Required in Masonry Buildings?
16. How to make Stone Masonry Buildings
Earthquake Resistant?
Response of Masonry Walls
Horizontal bands are provided in masonry buildings to improve their earthquake performance. These bands include plinth band, lintel band and roof band. Even if horizontal bands are provided, masonry buildings are weakened by the openings in their walls (Figure 1). During earthquake shaking, the masonry walls get grouped into three sub-units, namely spandrel masonry, wall pier masonry and sill masonry.Behaviour during Past India Earthquakes
Stone has been used in building construction in India since ancient times since it is durable and locally available. There are huge numbers of stone buildings in the country, ranging from rural houses to royal palaces and temples. In a typical rural stone house, there are thick stone masonry walls (thickness ranges from 600 to 1200 mm) built using rounded stones from riverbeds bound with mud mortar. These walls are constructed with stones placed in a random manner, and hence do not have the usual layers (or courses) seen in brick walls. These uncoursed walls have two exterior vertical layers (called wythes) of large stones, filled in between with loose stone rubble and mud mortar. A typical uncoursed random (UCR) stone masonry wall is illustrated in Figure 1. In many cases, these walls support heavy roofs (for example, timber roof with thick mud overlay).
.Suggestions/comments may be sent to: eqtips@iitk.ac.in
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