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Atmospheric transmittance models for absorbing gases with constant mixing ratios were described in the two preceding papers of this series. In this paper a method for calculating atmospheric transmittances for absorbing gases with variable mixing ratios is described. Because the model uses only arithmetic operations, it is computationally fast as well as accurate. Details of the computational algorithm are given, including the calculation of the expansion coefficients. In a test of eleven independent profiles, the resulting transmittances agreed with line-by-line calculations in an rms sense to within 0.0090 in the worst case and to within 0.0018 in all other cases. This paper also includes a discussion for computing transmittances when several gases absorb in the same spectral interval. These three papers provide a complete treatment for modeling transmittances in inhomogeneous atmospheres.

Herpes simplex virus mutants PAAr5, AraAr6, AraAr7, AraAr9, and AraAr13, which previously had been shown to be resistant to arabinosyladenine (araA) alone, were found to be resistant to araA in the presence of high concentrations of the adenosine deaminase inhibitor, deoxycoformycin. The marker conferring resistance to araA and deoxycoformycin in mutant PAAr5 was mapped finely to an 0.8-kilobase-pair region in the herpes simplex virus DNA polymerase locus. These results indicate that the mutants are resistant to araA itself rather than to its deamination product and confirm the importance of the viral polymerase in the antiviral action of araA.

Seven herpes simplex virus mutants which have been previously shown to be resistant to arabinosyladenine were examined for their sensitivities to four types of antiviral drugs. These drugs were a pyrophosphate analog, four nucleoside analogs altered in their sugar moieties, two nucleoside analogs altered in their base moieties, and one altered in both. The seven mutants exhibited five distinct phenotypes based on their sensitivities to the drugs relative to wild-type strain KOS. All mutants exhibited resistance to acyclovir and arabinosylthymine, as well as marginal resistance to iododeoxyuridine, whereas all but one exhibited resistance to phosphonoformic acid. The mutants exhibited either sensitivity or hypersensitivity to other drugs tested--2'-nor-deoxyguanosine, 5-methyl-2'-fluoroarauracil, 5-iodo-2'-fluoroarauracil, and bromovinyldeoxyuridine--some of which differed only slightly from drugs to which the mutants were resistant. These results suggest ways to detect and treat arabinosyladenine-resistant isolates in the clinic. Antiviral hypersensitivity was a common phenotype. Mutations conferring hypersensitivity to 2'-nor-deoxyguanosine in mutant PAAr5 and to bromovinyldeoxyridine in mutant tsD9 were mapped to nonoverlapping regions of 1.1 and 0.8 kilobase pairs, respectively, within the herpes simplex virus DNA polymerase locus. Thus, viral DNA polymerase mediates sensitivity to these two drugs. However, we could not confirm reports of mutations in the DNA polymerase locus conferring resistance to these two drugs. All of the mutants exhibited altered sensitivity to two or more types of drugs, suggesting that single mutations affect recognition of the base, sugar, and triphosphate moieties of nucleoside triphosphates by viral polymerase.

Models exist which allow the calculation of atmospheric transmittance at a given zenith angle for an absorbing gas with a constant mixing ratio. However, many applications require transmittances at several zenith angles. A simple, fast, and accurate model for calculating the angular dependence is given. This model is computationally fast because only the four arithmetic operations are used. Details for calculating the expansion coefficients are provided. When this technique is combined with a procedure for calculating transmittances at a fixed angle, it is possible to calculate transmittances for slant paths at arbitrary zenith angles and temperature profiles, provided the mixing ratio is constant. This technique was evaluated with a method capable of calculating transmittances at zero zenith angle with an accuracy of 0.0031. For zenith angles ranging from 0 degrees to 40 degrees , transmittances agree with line-by-line calculations to within 0.0038.