Properties and migration

Some physical properties of He are listed in Table lO-I. For exploration, diffusivity in sample media (air, water, soil, rock) and materials that could be used as sample containers, both of which are largely functions of the small atomic radius, are of prime importance, along with solubility in water. 

Water in equilibrium with the atmosphere at STP contains 0.044 pL He/L H2O (Weiss, 1971). The solubility of He in water decreases with rising temperature thus, over the temperature range 0-40 C, it declines from 0.049 to 0.042 pL He/L H2O. Solubility is also depressed by salinity (Smith and Keimedy, 1982) for example, at 25°C the solubility decreases from 0.044 to 0.037 pL He/L H2O as salinity increases from 0 to 3.5% (seawater). 

Experimental determination of He diffusion was attempted by Duddridge et al. (1991), who injected He-rich gas at a depth of 35 m into permeable limestones cut by a fault. They recorded a pulse of He in shallow soil gas 5-20 hours later within 10 m of the fault suboutcrop and up to 53 hours later 20 m from the fault suboutcrop. However, the concentration increase recorded (0.032 ppm) is well within the error of the analytical system (mass spectrometer with constant pressure inlet, as discussed below, and analytical sensitivity of 0.030 ppm), the data are patchy with many samples showing no pulse, and there is no estimate of background variation or the effect of changing environmental conditions. Conclusions about diffusion rates based on these data may not be reliable. 

Diffusion is not the only mechanism by which He (or indeed any gas) migrates. The evaluation by Newton and Round (1961) suggested that, as a significant proportion of He in sedimentary rocks is dissolved in water, the migration of He is dominated by flow, even if the flow rate is estimated at only 30 cm per annum. Therefore, once He enters an aquifer, it is transported rapidly and essentially unidirectionally by flow, compared to the random 

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Lightfastness in rubber, which meets almost all requirements, is accompanied by good curing properties and migration resistance. The resulting pigmented articles are very resistant to water and detergent solutions. 

Tuning of Blend Properties and Migration Resistance Through the Architecture of Plasticizer... 

Fig. 10 Loading scatter plot including mechanical and material properties and migration behavior of PVC/PBA films containing 40wt% of linear PBA or branched TMP-based plasticizers. Dotted ellipse properties that are positively correlated to observations TMP8, IMP 10, DOP, and DEHP (also marked by a dotted ellipse) in Fig. 10. Properties placed in the opposite quadrant of the plot are negatively correlated to the variables inside the dotted ellipse. Reprinted from [41] Wiley-VCH Verlag GmbH Co. Wiley-VCH Verlag GmbH Co. (2006)...

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

The insoluble, hydrophobic disperse dyes readily dye nylon, and because their mode of attraction is completely nonionic they are completely insensitive to chemical variations and pH. Small molecular-sized disperse dyes (ca mol wt 400) show very high rates of diffusion and excellent migration properties and they are insensitive to physical variations in the nylon. As the molecular size of disperse dyes increases they show increasing sensitivity to physical variation. 

Finally, inadequate hole cleaning results in an overloading of the annulus with cuttings, especially in very high penetration rate, poor mud properties, and insufficient annular velocity or circulation time. Inadequate hole cleaning can also be experienced in deviated wells with the formation of cutting beds on the low side migrating in a sand dune fashion. 

The effectiveness of an internal antistatic agent incorporated in the melt depends primarily on its molecular structure. This determines properties vital to the antistatic effect such as polarity and migration. The aliphatic C)4-C,7 chain in the alkanesulfonates imparts the required migration property to polar plastics, whereas the polar group is responsible for their hygroscopic behav-... 

The mobility of a species ut is a parameter connecting diffusion and migration processes. This section will be concerned primarily with the qualitative theory of mobility, which has characteristic properties for... 

Tissues consist of smaller repeating units on the scale of hundreds of micrometers in vivo. The 3D architecture of these repeating tissue units underlies the coordination of multicellular processes, emergent mechanical properties, and integration with other organ systems via the microcirculation [11], Furthermore, the local cellular environment presents biochemical, cellular, and physical stimuli that orchestrate cellular fate processes such as proliferation, differentiation, migration, and apoptosis. Thus, successful fabrication of a fully functional tissue must include both an appropriate environment for cell viability and function at the microscale... 

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