Showing papers by "Makerere University published in 1983"

Hydrogen chemical potentials and diffusion coefficients in hydrogen diffusion membranes

Abstract: Palladium and palladium alloys are quite widely used as membranes for hydrogen permeation, because of their resistance to embrittlement and to irreversible deformations during cycles of absorption and desorption of hydrogen1–3. The isothermal relationships between hydrogen diffusion coefficient, DH, and hydrogen content, n (ratio of hydrogen/metal atoms) has both technological and academic interest. The most detailed form of relationships2,3 between DH and n have been those reported for deuterium in Pd75Ag25 by Hickman4 within the temperature range 300–500°C, and for protium in Pd7Ag23 within the range 30–75°C by Kussner5. For increasing values of n up to n ∼ 0.2, Kussner5 reported significant corresponding decreases of DH (by a factor of ∼ 8 from n=0 up to n ∼ 0.16 at 30°C). This is the reverse of trends in the values of DH with increasing n suggested by measurements of anelastic effects3,6,7 and also by the permeation rate measurements of Hickman4 at 300 and 400°C. Here we report measurements of diffusion through Pd81Pt19 alloy, the results of which are consistent with Gorskii's hypothesis relating long-range anelastic diffusion of lattice interstitials to elastic strain gradients.

Factors affecting insect pest occurrence in various cropping systems

Abstract: This paper discusses the effects of some controllable aspects of annual cropping systems on several components of insect pest occurrence. The components of cropping systems include spatial and temporal diversity at the farm level. Some effects of these factors on pest colonisation, numerical increase, emigration, damage, and carryover to future crops are illustrated and discussed. Examples of how cropping systems affect specialist and generalist insect pests are also given. Finally, the effectiveness and practicality of controlling insect pests by manipulating cropping systems is considered. Intercropping appears most likely to reduce insect pest occurrence under general conditions, however the need to manage several different crops simultaneously can present some constraints.