Design, construction and testing of the Communications Technology Satellite protection against spacecraft charging

Detailed discussions are presented of the measures taken on the Communications Technology Satellite (CTS or Hermes) which provide protection against the effects of spacecraft charging. These measures include: a comprehensive grounding philosophy and implementation; provision of command and data line transmitters and receivers for transient noise immunity; and a fairly restrictive EMI specification. Ground tests were made on materials and the impact of these tests on the CTS spacecraft is described. Hermes, launched on 17 January 1976 on a 2914 Delta vehicle, has successfully completed 10 months of operations. Anomalies observed are being assessed in relation to spacecraft charging, but no definite correlations have yet been established. A list of conclusions with regard to the CTS experience is given and recommendations for future spacecraft are also listed

Five or six step scenario for evolution?

The prediction that (due to the limited amount of hydrogen available as fuel in the Sun) the future duration of our favourable terrestrial environment will be short (compared with the present age of the Earth) has been interpreted as evidence for a hard step scenario. This means that some of the essential steps (such as the development of eukaryotes) in the evolution process leading to the ultimate emergence of intelligent life would have been hard, in the sense of being against the odds in the available time, so that they are unlikely to have been achieved in most of the earth-like planets that may one day be discovered in nearby extra-solar systems. It was originally estimated that only one or two of the essential evolutionary steps had to have been hard in this sense, but it has become apparent that this figure may need upward revision, because recent studies of climatic instability suggest that the possible future duration of our biologically favourable environment may be shorter than had been supposed, only about one Giga year rather than five. On the basis of the statistical requirement of roughly equal spacing between hard steps, it is argued that the best fit with the fossil record is now obtainable by postulating the number of hard steps to be five, if our evolution was exclusively terrestrial, or six if, as now seems very plausible, the first step occurred on Mars.Comment: 11 pages Late

The two-stage clonal expansion model in occupational cancer epidemiology: Results from three cohort studies

Copyright © 2010 by the BMJ Publishing Group Ltd. All rights reserved.Objectives: The objective of this work was to apply the two-stage clonal expansion model, with the intention to expand the literature on epidemiological applications of the model and demonstrate the feasibility of incorporating biologically based modelling methods into the widely used retrospective cohort study. Methods: The authors fitted the two-stage clonal expansion model model to three occupational cohort studies: (1) a cohort of textile workers exposed to asbestos and followed for lung cancer mortality; (2) a cohort of diatomaceous earth workers exposed to silica and also followed for lung cancer mortality; and (3) a cohort of automotive manufacturing workers exposed to straight metalworking fluid (MWF) and followed for larynx cancer incidence. The model allowed the authors to estimate exposure effects in three stages: cancer initiation (early effects), promotion or malignant transformation (late effects). Results: In the first cohort, the authors found strong evidence for an early effect of asbestos on lung cancer risk. Findings from analyses of the second cohort suggested early and less evidently late effects of silica on lung cancer risk. In the MWF (third) cohort, there was only weak evidence of straight MWF exposure effects on both early and late stages. The authors also observed a late birth cohort effect on larynx cancer risk. Conclusions: The findings for asbestos and silica were essentially confirmatory, supporting evidence for their early effects on lung cancer from a large body of literature. The effect of straight MWF on larynx cancer was less clear.This work was supported by a grant from the US National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention,R01-OH03575, and a grant from the Centers for Disease Control and Prevention/ Association of Teachers of Preventive Medicine number TS 0699