Setting up virgin stress conditions in discrete element models.

In the present work, a methodology for setting up virgin stress conditions in discrete element models is proposed. The developed algorithm is applicable to discrete or coupled discrete/continuum modeling of underground excavation employing the discrete element method (DEM). Since the DEM works with contact forces rather than stresses there is a need for the conversion of pre-excavation stresses to contact forces for the DEM model. Different possibilities of setting up virgin stress conditions in the DEM model are reviewed and critically assessed. Finally, a new method to obtain a discrete element model with contact forces equivalent to given macroscopic virgin stresses is proposed. The test examples presented show that good results may be obtained regardless of the shape of the DEM domain.

[Evolution of radiologic changes in lungs of workers occupationally exposed to asbestos dust]. / Ewolucja zmian radiologicznych pluc u pracowników zawodowo narazonych na pyl azbestu.

The dynamic of radiological changes in lungs of 458 workers exposed to chrysotile asbestos dust and in 65 retired workers previously exposed to the same dust was assessed. There was a 5-year interval between initial and control examinations in the group of acting workers and an 8-year interval in the group of retired workers. The control examination of workers with employment below 10 years did not reveal radiological changes which could indicate asbestosis. In the group of 400 workers with employment over 10 years new cases of asbestosis were diagnosed in 34 persons (8.5%) during the control examination. During the control examination progress of pleural changes was observed in 4% of males and 3.8% of females. As the period of exposure to asbestos had expanded the occurrence of small, irregular shadows, especially in persons working longer than 15 years, was more often noticed. The aforesaid aberrations have progressed in 11.7% of males and 9.5% of females when compared with the results of the initial examination. In the group of retired workers 15 (23.1%) new cases of asbestosis were detected 8 years after the termination of occupational exposure. Small, irregular shadows, limited in number as well as pleural changes have progressed in approximately 22% of retired males and females.