## M atb

where M = cumulative mass of the material passed at sieving time t (grams), t = sieving time (seconds), b = a constant nearly equal to 1 and a = sieving rate constant, with units of gs~1b. This model has had some practical utility but its validity in describing data, even for short times, is questionable and depends on how the data are truncated.

One mechanistic model starts by assuming that the probability of particle passage at time t is directly proportional to the mass of material on the sieve. Thus, the mass of material remaining (Mt) at sieving time t is described in differential form by:

dMt ~dT

where A is a constant depending on the sieve and sieving conditions, R is a radius of the particle, D is the sieve opening and fs is a grouping of factors that describe particle shape. Tests of this model have not been extensive. It should work best for longer times.

An alternative or modified proportional model has been used with some success over a wide range of sieving times. This model starts by assuming that the constant k in the differential equation above is a function of time, k = k*/tm. Then the differential equation can be written as:

## Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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