For written discussion SYNOPSISAfter a brief review of previous work relating to regime channels the Paper describes experiments which demonstrated in each test the full range of crosssectional shapes taken up by a self-formed regime channel in non-cohesive material. In one run of the laboratory flume at a given discharge it was possible to produce at the upstream end a cross-section with zero bed-load and, at the downstream end, a wider cross-section through which the maximum bed-load for stability was passing.The dimensions and shapes of these two limiting sections are analysed theoretically, using the tractive force criterion as a basis. The analysis shows that the breadth, maximum depth, and cross-sectional area for a given discharge, are each determined by the slope and the characteristics of the sand.No solution is offered to the age-old problem of relating velocity or crosssectional area to the channel and sand characteristics by means of a theoretical analysis, but empirical formulae have been developed from the results of the experiments. Confirmation was obtained, remarkable in view of the small scale of the tests, of the well-known Lacey equation relating wetted perimeter and discharge. This and other empirical equations allow the dimensions of the limiting cross-sections to be determined from the discharge alone.Certain phenomena observed during the channel formation are described and also the onset of braiding-the formation of islands and splitting of the channel. The instability of a channel due to the accumulation of maximum bed-load is thought to result in braiding of the channel, followed, under certain conditions, by fully developed meanders. Reversal of the process due to cessation of bed-load was also demonstrated in certain prolonged tests.NOTATION AI = Area of cross-section of channel at zero bed-load section (Section 1). Aa = Total area of cross-section of channel at start of braiding (Section 2). A" = Part of Az vertically above the curved banks of section 2 (Pig. 11). a = Area of sand particle over which shear stress T acts. B1 = Water surface width at zero bed-load section (Section 1). Ba = Total surface width at start of braiding (Section 2). B" = Part of surface width covering the curved banks of Section 2 (Fig. 11). 485
The female radium dial workers have now experienced significant mortality from cancers other than the bone sarcomas and head carcinomas long known to be radium induced. The relationships of radium exposure to mortality from cancers of the stomach, pancreas, colon, rectum, liver, lung, breast, cervix, and corpus uteri, and from leukemia were studied in 1,285 pre-1930 dial workers. Mortality was compared with that expected from rates for US white females, with and without adjustment for local area mortality rates, and with mortality in dial workers exposed from 1930 to 1949. For the 693 cases whose body content of radium has been measured since 1955, dose-response relationships of cancer to systemic intake of radium and duration of employment were examined. Liver, pancreatic, cervical, and uterine cancers were clearly unrelated to radium exposure. Other cancers of the digestive tract appeared to be indirectly, if at all, associated with work in radium facilities. Lung cancer requires further investigation; inhalation exposures of the dial workers were reviewed. Analyses of the breast cancer data uncovered several observations inconsistent with the previously suggested causal association with radium exposure. Multiple myeloma was also reviewed. A threefold excess risk of death due to multiple myeloma has occurred, but is more closely correlated with duration of employment (a surrogate for external gamma radiation) than with radium intake.
Pulmonary function test results on 224 parochial schoolchildren collected during and after the Pittsburgh air pollution episode of November 1975 were reanalyzed to determine whether a small subgroup of susceptible children could be defined. Individual regressions of three-quarter second forced expiratory volumes (FEV.75) and forced vital capacities (FVC) on time over the six-day study period were calculated, and the distributions of individual slopes for the four exposed and two control schools were compared. Excesses of strong upward trends in the exposed areas would suggest effects of suspended particulate air pollution by indicating significant improvement following the episode. A highly statistically significant excess of strong upward trends in the FVC among exposed students was observed, and was consistent by sex and by school within sex. Approximately 10--15% of the students appear susceptible to an average impairment of about 20% of the FVC. The findings are limited by the small number of subjects with strong post-episode upward trends in the FVC, and by lack of validation by replication of the study design, but do suggest that episode levels of suspended particulates induce lung damage, and that this may occur only in a small susceptible subgroup. Children with low baseline pulmonary function values, histories of asthma, or with acute respiratory symptoms immediately following the episode were not found to be especially susceptible to these effects of suspended particulates.
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