fit in this cavity better than in other parts of the lipid bilayer. The proximity of 02 would then enhance the effect of paramagnetic relaxation on the fluorine atoms and raise qF. In the meantime, <7h of the aliphatic protons near the cavity would also increase.However, this would only contribute to a very small fraction of the weighted average of all protons. Thus, we observe qF > qH in the bilayers. Since the cavity may have a better chance to be located near the middle part of the PFD molecule (Figure 4B), the increase in qF of the la, le, and 2a fluorine atoms would be larger than that in qF of the 2e fluorine (Table I). This is in contrast to the situation in bulk PFD liquid, in which qF of the 2e fluorine (2.45 ± 0.05 s™1 atm™1 at 75.38 MHz) is slightly larger than qF of other fluorine atoms (2.17 ± 0.08 for la, 2.15 ± 0.04 for le, and 2.20 ± 0.03 for 2a, all in s™1 atm™1 at 75.38 MHz),10 because the small end of an ellipsoid is sterically more favorable for the approach of 02 in an isotropic liquid. The values of qF at 250 MHz (2.05-2.25 s™1 atm™1) are smaller, and the differences are also less. 19 The qF values of PFD droplets decrease further at 282.23 MHz (Table I). However, the differences in the qF values for the PFD droplets as well as the decane solution of PFD are too small to be significant, possibly due to the change in medium and larger experimental uncertainties. Since the corresponding F-19 signals of m-PFD are very broad and unresolved at 298 K,12,13 the interaction between lipid bilayers cannot be determined by NMR under these conditions. Because of the low solubility of PFD in the lipid bilayers,9 molecules of the two isomers are not likely to either interact or interfere with each other.PFTPA is a flexible molecule. Therefore, a schematic representation like Figure 4 may not be entirely adequate. However, the lipid bilayer would still experience a local perturbation by a dissolved PFTPA molecule. It is well-known that solutions of fluorocarbons in hydrocarbons exhibit nonideal behavior.24™27 The (24) Hildebrand,

This handbook has been prepared to facilitate the design of earthen covers to control radon emission from uranium mill tailings. Radon emissions from bare and covered uranium mill tailings can be estimated from equations based on diffusion theory. Basic equations are presented for calculating surface radon fluxes from covered tailings, or alternately, the cover thicknesses required to satisfy a given radon flux criterion. Also described is a computer code, RAECOM, for calculating cover thicknesses and surface fluxes. Methods are also described for measuring diffusion coefficients for radon, or for estimating them from empirical correlations. Since long-term soil moisture content is a critical parameter in determining the value of the diffusion coefficient, methods are given for estimating the long-term moisture contents of soils. The effects of cover defects or advection are also discussed and guidelines are given for determining if they are significant. For most practical cases, advection and cover defect effects on radon flux can be neglected. Several examples are given to demonstrate cover design calculations, and an extensive list of references is included.

The slight reverse curvature in the plot of logP versus 1/T (P, vapor pressure; T, absolute temperature) may be explained on the basis of the nonideal behavior of the vapor together with the change in heat of vaporization with temperature. If it is assumed that ΔH is linear with T and that the van der Waals a/V2 term is a first approximation to the deviation from the ideal, the following equation may be obtained by integration of the Clapeyron equation: logP=A+BT+C logT+DPT2.The last term is the nonideal gas correction with constant D=a/2.303R2. With constants A, B, and C determined empirically, the equation reproduces experimental vapor pressures from the triple point to the critical point with an average deviation of 0.3 percent.

Increased iron content of cells and tissue may increase the risk of cancer. In particular, high available iron status may increase the risk of a radiation-induced cancer. There are two possible mechanisms for this effect: iron can catalyze the production of oxygen radicals, and it may be a limiting nutrient to the growth and development of a transformed cell in vivo. Given the high available iron content of the western diet and the fact that the world is changing to the western model, it is important to determine if high iron increases the risk of cancer.

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