On a Powder Consolidation Problem
The problem of the consolidation of an aerated fine powder under gravity is considered. The industrial relevance of the problem is discussed and a mathematical model is introduced. The mathematical structure is that of a coupled system for three unknowns, pressure, stress, and height of the powder in the (axisymmetric) bunker containing it. The system itself consists of a parabolic PDE, an ODE, and an integral equation determining a free boundary corresponding to the height of the powder. Existence and uniqueness of a solution is established. A numerical method based on a formulation of the semidiscretized problem as an index 1 DAE is proposed and implemented. The feasibility of the approach is illustrated by computational results.
Deaeration of powders in hoppers
Abstract Air is entrained when fine powders are loaded from a height into a container. The air takes some time to dissipate, which gives rise to problems in bag filling, silo loading, charging of bulk tankers etc. An analysis of the percolation of air through a granular bed is presented, together with an analytical solution via consolidation theory. Although the solution is approximate, the mathematics is straightforward and highlights the effect of different boundary conditions on deaeration behaviour. The mathematics also enables the prediction of large-scale deaeration behaviour from bench-scale tests on a powder. Measurements of air pressures in the interstices of the powder (pore air pressures), and their variation with time, in a large-scale hopper are presented, and compared with predictions from the theory.
An automated retinal image quality grading algorithm
This paper introduces an algorithm for the automated assessment of retinal fundus image quality grade. Retinal image quality grading assesses whether the quality of the image is sufficient to allow diagnostic procedures to be applied. Automated quality analysis is an important preprocessing step in algorithmic diagnosis, as it is necessary to ensure that images are sufficiently clear to allow pathologies to be visible. The algorithm is based on standard recommendations for quality analysis by human screeners, examining the clarity of retinal vessels within the macula region. An evaluation against a reference standard data-set is given; it is shown that the algorithm's performance correlates closely with that of clinicians manually grading image quality.