Particle size correlations and the effects of limited mixing on agglomerating particulate systems
Abstract Population balance equations for particulate systems are derived based on two basic but tacit assumptions. The first is that a local volume of thorough particle mixing exists over which a more detailed balance equation may be averaged to obtain the population balance equation. The second is that there is a large enough population in the mixing volume that particle correlation effects do not become important. Both the foregoing assumptions are investigated for Brownian agglomeration. The volume of mixing is estimated by scaling arguments. Monte Carlo simulation techniques have been used to show that particle populations in the local mixing volume may be sufficiently small to cause correlation effects implying that the population balance predictions can be in error.
The Effects of Fluctuations in Liquid Water Content on the Evolution of Large Drops by Coalescence
Abstract Because of the nonlinearity of the coagulation equation the evolution of large drops by coalescence is likely to be very sensitive to liquid water content. This implies that a cloud containing pockets of high liquid water content can produce rain much more quickly than an identical cloud in which the liquid water content is uniform.
Communicative Competence: Theory and Classroom Practice
ABSTRACT Within the framework of viewing communicative competence as a prerequisite to linguistic competence, rather than vice versa, this paper considers the following: (1) the nature of communicative competence; (2) the implications of communicative competence for second language teaching; and (3) ways in which the teacher can begin to make a foreign language program more meaningful. Communicative competeuce is defined as what native speakers know which enables them to interact effectively with each other. Implications for the language teacher include: (T) the need for tests which measure the ability to use language; (2) the irrelevancy of sequencing surface features; (3) the need for emphasis on non-lizguistic aspects of communication; and (4) the need to re-examiLe attitudes toward students and language teaching. Practical suggestins for implementing communicative competence in the classroom include the use of spontaneous role-playing, discussions, games, radio, and the telephone. (AM)