A hybrid model of schistosomiasis with snail latency

A hybrid model (i.e., a model with both stochastic and deterministic ingredients) is established for the transmission of schistosomiasis in a community. The model allows for latency and differential mortality in the snail population. An important threshold behavior is predicted. It gives conditions under which the infection will be eradicated. The efficiencies of various methods of control or eradication are studied.     

A test and calibration process for microcalorimeters used a thermal power meters

A test and calibration process for microcalorimeters is described. The method has been developed with particular reference to instruments used for measurements of thermal power produced by suspensions of living cells. The process investigated is the hydrolysis of triacetin in imidazole/acetic acid buffer. The power levels are regulated by changing the buffer composition. The power will decrease slowly and very nearly linearly with time. Five test solutions, power levels 7–90 μW·ml^?1, have been characterized at 37°C and one of them at 25°C (13 μW·ml^?1). The power values for these reaction mixtures can be accurately calculated (±0.5%) as a function of time during extended reaction periods, about 20 h or more.     

Magnesium ions in catecholamine fluorescence histochemistry

Summary The effects of high concentrations of magnesium ions in the cryostat and Vibratome procedures for visualization of catecholamine fluorescence in the central nervous system have been investigated. In cryostat sections, obtained from specimens perfused with a formaldehyde and glyoxylic acid containing buffer, the addition of high concentrations of MgSO₄ to the perfusion solution enhances the fluorescence intensity and reduces the unspecific background fluorescence and the diffusion of the catecholamine fluorophore. This improves the visualization of all portions of the central catecholamine-containing neurons. Similar effects are obtained in the formaldehyde-Vibratome technique by the introduction of an immersion bath containing MgSO₄ after the sectioning procedure. The use of the magnesium perfusion or immersion steps furthermore increases the reproducibility of the Vibratome and cryostat techniques. The paper describes the improved Vibratome and cryostat techniques used in our laboratory.     

On transmission and control of schistosomiasis, with comments on Macdonald''s model

A hybrid model for the transmission of schistosomiasis with snail latency is established, based on hypotheses that are essentially identical to those used by Macdonald. Measures of the efficiencies of control of endemic schistosomiasis are introduced. Relations are derived between control efficiency ratios and epidemiological quantities. A measure of resilience of an endemic infection is introduced; it quantifies the minimum effort required for eradication. Studies are made of the control efficiency ratios and an eradication effort ratio as functions of the minimum eradication effort. The results are applied in an objective analysis of Macdonald's 1965 model of schistosomiasis. Some weaknesses in Macdonald's methodology are discovered, and we prove that Macdonald's conclusion of inefficiency of improved sanitation does not have general validity.     

Charge injection and charge storage in lipid multilayers

Charge injection and charge storage in lipid multilayers on top of semiconductors have been studied by measuring the small signal capacitance of the structure as a function of applied dc-voltage. It is shown that the injection of holes (and electrons) into the lipid is a thermally activated process, and that no marked difference exists in charge injection properties of simple fatty acids of different carbon chain lengths around room temperature. The charge injection and charge storage properties could be changed by modifications of the lipids. Incorporation of some unsaturated molecules increase the charge injection, and introduction of lipid soluble substances decreases the possibility to store charge etc. The results of some experiments on this line are reported.     

The Nature of Selection on Anhydrobiotic Capacityin Tardigrades

Tardigrades are well known for their capacity to enter an anhydrobiotic state, and remain ametabolic for several years. Yet the evolutionary background, and the forces of natural selection that act on anhydrobiotic capacity have remained unexplored. In this paper, I review the basic problem of anhydrobiosis and the phenotypic traits that may be the main targets of natural selection for improved anhydrobiotic capacity. I also make an attempt to put anhydrobiosis into a life history perspective, and discuss this life form in the perspective of energetic and genetic constraints.