The relative probabilities for alternate processes initiated by a nucleon-nucleon collision depend on the dynamics involved and on the volume in phase space accessible to each final state. According to Fermi this last aspect alone may be of decisive importance. Such an assignment would follow were an approximate statistical equilibrium reached. The volume occupied by the incident nucleons and the associated pion clouds will have very large energy density at the instant of collision. Knowing that the interactions of the pion fields are strong, Fermi assumes that this energy is suddenly distributed among the various degrees of freedom present in the interaction volume in accord with statistical laws. He then computes the statistical probability that a certain number of pions will be created with a given energy distribution. It is then assumed that the energy will rapidly dissolve and that the particles into which the energy has been converted will fly out in all directions. Fermi argues that this approach may give a fairly good approximation to the actual case; since the number of possible states of the given energy is large and the probability of establishing a state to its average statistical weight will be increased by the number …

Report presenting an experimental investigation to determine the porosity characteristics of perforated materials for normal and parallel flow. The results indicated that the porosity of the material is primarily governed by its open ratio, but that density has a slight effect. When the material was tested under parallel-flow conditions, the effective porosity dropped markedly as the stream velocity increased.