Substance spreading

FIGURE 4.21 In diffusion, the molecules of one substance spread into the region occupied by molecules of another in a series of random steps, undergoing collisions as they move. 

High diffusibility Dissolved substances spread in a supercritical fluid at speeds between those of liquids and real gases. 

Drake once suggested that an advanced civilization could place a technetium cloud around its star. This radioactive metal is observed on Earth only when it is produced artificially, and only weakly on the Sun, because it is short-lived and rapidly decays away. Drake estimated that aliens could mark a star using only a few hundred tons of light-absorbing substance spread around the star. 

Since 1990 extended radioecological monitoring based on radiation mapping has been implemented into the radioecological survey practice [2]. Completeness of the environmental contamination information has been attained through generation of radiation field maps with simultaneous indication of source-term location areas, boundaries of radioactive substance spreading, identification of radiation-hazardous zones with indication of the most probable man-caused radionuclide transfer paths. 

With regard to the last factor, Leitner has specified that the values of the persistences given above refer to substances spread on " open flat land in dry weather. They may be doubled if the substance lies on broken ground and tripled if it is in wooded country. ... 

The actual picture of the substance spread (Fig. 6.9) differs from that presented in Fig. 6.8. 

Hazardous Ranking System (HRS) The principal screening tool used by EPA to evaluate risks to public health and environment associated with abandoned or uncontrolled hazardous waste sites. The HRS calculates a score based on the potential for hazardous substances spreading from the site through the air, surface water, or groundwater and on other factors such as nearby population. This score is the primary factor in deciding if the site should be on the National Priorities List and, if so, what ranking it should have there. 

Hernan Cortes was the first to bring cocoa and vanilla to Spain, and from there these aromatic substances spread right across Europe. 

Experience and accident statistics alike demonstrate that, apart from accidents within technical installations, losses affecting human beings and the environment may occur outside the technical installation itself. There may be interrelationships between accident and environmental strain, The effect of an accident in a technical installation becomes obvious the moment toxic or flammable substances spread in the air, the water, or on the ground, or whenever pressure waves propagate in the air or in the ground and lead to environmental damage. The causes, e,g., may be mechanical damage to machinery, explosions, or fires. The influence of environmental stress on the evolution of the accident, on the other hand, is... 

Coating (M.E., cote, n.). A layer of any substance spread over a surface modem synthesized materials, such as polyurethane resins, that replace older paint materials. 

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