Determination of the Liquid Water Diffusivity from Transient Moisture Transfer Experiments

The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at a lower moisture content bound.

To describe the moisture diffusivity including liquid water and water vapour transports, a new parametric description of the moisture diffusivity is presented, which shows sufficient flexibility both in the hygroscopic and overhygroscopic ranges. When permeability is calculated from diffusivity, the permeability should monotonically increase with decreasing capillary pressure. In the hygroscopic region it should coincide with the measured water vapour permeabilities.

[Reproductive behavior after the demographic transition]

"The article analyses [Bulgaria's] demographic revolution as a relatively independent process, yet at the same time as part and parcel of the global revolution.... The author considers the conditions influencing [reproductive] behaviour prior to the demographic revolution..., pointing out...the importance of social factors.... It is emphasised that the completion of the demographic revolution in the demographically advanced countries practically solves the problem of the population's size and growth...and paves the road for [improvements in health, education, qualifications, and cultural and living standards]." (SUMMARY IN ENG)