The authors demonstrate the feasibility of accurately modeling x-ray detector DQE(f) with completion times on the order of several minutes using a single CPU. Convenience of simulation can be achieved using GEANT4 which offers both gamma and optical photon transport capabilities.

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primarily DDT. Our data for the Bermuda petrel are entirely consistent with this pattern.Observations of aggressive behavior, increased nervousness, chipped eggshells, increased egg-breakage, and eggeating by parent birds of several of the above species (3, 6, 13) suggest symptoms of a hormonal disturbance or a calcium deficiency, or both. Moreover, DDT has been shown to delay ovulation and inhibit gonadal development in birds, probably by means of a hormonal mechanism, and low dosages of DDT or dieldrin in the diet of pigeons increased metabolism of steroid sex hormones by hepatic enzymes (16). A direct relation between DDT and calcium function has also been demonstrated, and these endocrine and calcium mechanisms could well be interrelated; DDT interferes with normal calcification of the arthropod nerve axon, causing hyperactivity of the nerve and producing symptoms similar to those resulting from calcium deficiency (17). Dogs treated with calcium gluconate are very resistant to DDT poisoning (18); female birds are more resistant than males (19), perhaps because of the calcium-mobilizing action of estrogenic hormones.Of major importance, then, was the discovery that a significant (P<.001) and widespread decrease in calcium content of eggshells occurred between 1946 and 1950 in the peregrine falcon, golden eagle, and sparrowhawk, Accipiter nisus (20). This decrease correlates with the widespread introduction of DDT into the environment during those years, and further correlates with the onset of reduced reproduction and of the described symptoms of calcium deficiency. These multiple correlations indicate a high probability that the decline in reproduction of most or all of these birds, including P. cahow, is causally related to their contamination by DDT residues.Other potential causes of the observed decline for the Bermuda petrel appear unlikely. The bird has been strictly protected and isolated since 1957, and it seems that human disturbance can be discounted. In such a small population, inbreeding could become important, but hatching failure is now consistent in pairs having earlier records of successful breeding, -and deformed chicks are never observed. Furthermore, the effects of inbreeding would not be expected to increase at a time when the total population, and probably the gene pool, is still increasing. The population 1 MARCH 1968 increase results from artificial protection since 1957 from other limiting factors, especially competition for nest sites with tropic birds (21).It is very unlikely that the observed DDT residues in P. cahow were accumulated from Bermuda: the breeding grounds are confined to a few tiny, isolated, and uninhabited islets never treated with DDT, and the bird's feeding habits are wholly pelagic. Thus the presence of DDT residues in all samples can lead only to the conclusion that this oceanic food chain, presumably including the plankton, is contaminated. This conclusion is supported by reported analyses showing residues inrelatedseabirds including two species of shearwaters ...

For the elucidation of structural features of unknown steroids available in minute quantities only, infrared spectrometry has been developed into a most powerful tool. It is possible by its use to determine the types of functional grouping and the number of carbonyls present in the molecule (cf. 1, 2). However, their exact localization is as yet feasible only in a limited number of specific cases. Ultraviolet absorption (cf. 3) and optical rotation measurements (cf. 4) have proved of help in deciding between alternative structural possibilities. The determination of mobilities in paper-chromatographic systems (inter al. 5 ) can render valuable clues toward the establishment of a more accurate structure and, in combination with the concept of conformational analysis (6)) the configuration of certain substituents may be deduced. In addition, oxidative degradations (cf. 7, 8, 9) followed by estimation of the liberated formaldehyde (inter al. 10) and acetaldehyde (11) as well as the Zimmermann chromogen (inter al. 12, 13) can be employed with advantage for the elucidation of side chain structure. The position of a ketone group may be more accurately defined by the ultraviolet spectrum of a derivative such as a phenylhydrazone (inter al. 3, 14, 15). The action of perchloric acid on certain substituted 2 , 4-dinitrophenylhydrazones should produce a bathochromic shift by extension of the conjugated system (cf. 16). The color formed after reaction of steroids with diphenylamine in acidic medium appears to depend on certain structural arrangements (17). A method has been recently devised for the recognition and estimation of A4-3-ketosteroids by measuring the formation of intensely fluorescent substances resulting from alkaline treatment (18,19). On the other hand, absorption spectra in concentrated sulfuric acid (cf. 20, 21)) valuable as they are for the characterization of individual compounds, do not lend themselves for extensive interpretation of structural elements (cf. 22, 23).In the papers presented in this series, an attempt is made to implement the methods enumerated, prompted by the specific need to determine structures of unknown A4-3-ketosteroids isolated in milligram quantities from biological material. In this communication it is desired to report on the changes encountered in the intense absorption of a number of A4-3-ketosteroids upon exposure to alkaline ethanol a t 23 and 60". Of particular interest were A4-3-ketosteroids containing hydroxyl substituents a t various positions and related substances with carbonyl functions. Alteration in spectral absorption of the color products has allowed correlation of certain structural features of these compounds. Some applications have been reported previously (24-27).* Paper I1 of this series pre-* Incidentally, by this method the presence of a certain impurity was easily detected in a sample, although i t had not been recognized in two paper-chromatographic systems. 1240

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