Suchergebnisse

This paper presents an attempt to find an optimal procedure for determining the height parameters of fracture surfaces. This is a useful task that may significantly increase the reliability of topographic analyses of solids. The paper focuses on seeking an optimum number of measuring sites to ensure sufficient reliability of the resulting height parameters determined by the confocal technique. The statistical tests show that the number may be close to 25 measuring sites.

This paper presents a study of the surface height irregularities of cement pastes subjected to fast dynamic fractures. The height irregularities are quantified by the values of the three-dimensional profile parameters. The studied dynamical irregularities show a similar analytical behavior to those obtained by static fractures.

A three-dimensional absolute profile parameter was used to characterize the height irregularities of the fracture surfaces of cement pastes. The dependence of these irregularities on porosity was studied and its non-linear character was proved. An analytical form for the detected non-linearity was suggested and then experimentally tested. The surface irregularities manifest scale-invariance properties.

A recently published fractal model of the fracture surfaces of porous materials is discussed, and a series of explanatory remarks are added. The model has revealed a functional dependence of the compressive strength of porous materials on the fractal dimension of fracture surfaces. This dependence has also been confirmed experimentally. The explanatory remarks provide a basis for better establishing the model.

Ultraviolet tests focused on population statistics of electron avalanches were not included in our earlier work [1], [2]. Now they have been performed, and it is shown that a recently derived statistical pattern fits all the measured data very well.

A new theoretical concept of fractal multiplication of electron avalanches has resulted in forming a generalized distribution function whose multiparameter character has been subjected to detailed discussion.

We have studied the severe systematic deviations of populations of electron avalanches from the Furry distribution, which has been held to be the statistical law corresponding to them, and a possible explanation has been sought. A new theoretical concept based on fractal avalanche multiplication has been proposed and is shown to be a convenient candidate for explaining these deviations from Furry statistics.

The question of the universality of a dimension of fracture surfaces is discussed, and it is shown that such a general parameter may exist at least for a particular class of materials.

Time series of pulsating microdischarges were analysed. The results showed that deterministic chaos is present in these series. The estimated values of the correlation coefficients indicated a strong chaotic discharge behaviour.

The multifractal image analysis of Lichtenberg figures has confirrmed a self- similar arrangement of surface streamers belonging to the special case of electrostatic separation discharges propagating along a surface of polymeric dielectrics.

Asymptotic behaviour of the DIAL and DRAL non-isothermal models, derived previously for the diffusion of water vapour through a porous building structure, is studied under the assumption that the initially non-isothermal structure becomes purely isothermal.

Statistical distributions (exponential and Pareto) of DC partial microdischarges running within sandwich electrode systems are discussed from the viewpoint of a normalisation procedure which may influence some features of the final distribution.

Two models for non-isothermal diffusion of water vapour in building materials have been developed and their numerical outputs compared with a standard isothermal approximation.

Glaser's condensation scheme with incorporated non-isothermal diffusion is presented and its consequences are studied. Keywords: non-isothermal diffusion, partial pressure profile, condensation in building structures, Glaser's condensation scheme.

Non-isothermal diffusion is analysed using Fick's laws. The exact relations for non-isothermal diffusion flux and partial pressure profiles in porous building materials are derived and discussed.