Mean Action Time Research Articles

Modelling the wetting and cooking of a single cereal grain

Three models are presented for the wetting of whole grains of cereal. Two are for temperatures below gelatinization temperatures, one of which incorporates the effects of swelling of the grain. A third model is presented for wetting of a grain at temperatures above gelatinization, and hence cooking the grain. The models are developed as partial differential equations, and solved in a variety of ways. A model that ignores swelling at temperatures below gelatinization is solved for wetting times by using the concept of mean action time, which reduces the problem to an exactly solvable linear Poisson equation. The other two models, which include swelling and cooking respectively, are solved approximately, taking advantage of the steep nonlinear diffusion fronts that develop. The aim of the modelling is to improve understanding of the cooking of whole-grain cereals prior to processing into breakfast cereals. Moisture penetration curves are obtained and compared. Regions where the penetration rate is approximately linear are noted, suggesting that nonlinear diffusion equations are a promising way to model grain wetting and cooking.

Block-size determination in fractured porous media

A flow-reversal method involving the injection and retrieval of fluid from a fractured, porous medium at a different temperature to that of the system in its undisturbed state is described and assessed as a potential technique for measuring the thermal transients of blocks of fractured porous media. Formulae are obtained for the zeroth- and first-order time moments of the thermal history of the fluid when it is well mixed in the injection-retrieval hole, injected at a temperature T 1 (different to the uniform temperature T 0 the undisturbed system) at a fixed rate Q, for a time t 1 , and then withdrawn through the same drill hole at the same fixed rate Q. These formulae have a potential for determining some geometric parameters of the block structure, including the block surface-to-volume ratio and the mean action time for conductive heating.

Outputs and time lags for linear bioreactors

Linear systems of convection reaction-diffusion equations for bioreactors are shown to have a structure which allows a geometric factorization of steady state problems giving a significant reduction in their dimensionality. Moreover, convection dominated linear systems with quasisymmetric reaction terms may be further simplified by matrix transformations, which uncouple the differential equations. The boundary conditions are also uncoupled when the diagonal diffusivity matrix D governing diffusion in the bioparticle is a scalar multiple of the corresponding matrix H describing the diffusivity characteristic of the fluid boundary layers around the bioparticles. The dominant transient behaviour of the systems may be handled by establishing an analogous system of time independent equations for mean action time variables and higher moments. These equations have the same amenable structure. Outputs, time lags and various mean residence and first passage times, associated with establishing steady outputs from a concentration free initial state, can be expressed in terms of the steady state solutions and mean action time variables.

Physiological reactions of man to acceleration of maximal duration and intensity in the spine-chest axis

The maximum tolerance to accelerations acting in the back-chest direction at an angle of 65° to the longitudinal axis of the human body was determined on a large-radius centrifuge. The following were studied: cardiovascular system, external respiration system, movement coordination, bioelectrical activity of the brain and of various groups of skeletal muscles, and subjective sensations. Definite stages were revealed in the body responses, which were most pronounced during the action of the average acceleration values (6–10 g). For 6 g the mean action time was 653 seconds, for 8 g-186.4 seconds, for 10 g-57.6 seconds, for 12 g-27.6 seconds, for 14 g-17.7 seconds and for 15 g-10.4 seconds.