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Biomedical subjects

S Richardson

Publications and source records attributed to S Richardson.

At least 181 records · Page 10Linked to original sources
PubMed1970

Characterization of Labeled Residues from 5-Diazouracil-2-C Incorporated into Ribonucleic Acids of Filamentous Escherichia coli.

E. coli B, filamented with 5-diazouracil (DZU)-2-(14)C, yielded ribonucleic acid (RNA)-(DZU-2-(14)C) which was converted by pancreatic ribonuclease to (14)C-mono-and oligo-nucleotides. The mixed (14)C-mononucleotides isolated by diethylaminoethyl-cellulose fractionation were identified as cytidylic, uridylic, and hydroxyuridylic acids, by using a combination of paper chromatography and treatment with alkaline phosphatase and cytidine deaminase. Rifampin blocked incorporation of DZU-2-(14)C under conditions which inhibit RNA synthesis. Division inhibition by DZU-2-(14)C and the incorporation into Escherichia coli B were retarded by uracil but not by other RNA bases. In a pyrimidine-requiring E. coli, DZU substituted for uracil or cytosine to an extent limited by toxic effects. Cytosine and uracil retarded these effects and retarded the incorporation of DZU-2-(14)C into the pyrimidineless strain. A small proportion of DZU-2-(14)C was converted by the latter strain into hydroxyuridylic acid, but the bulk of the incorporated label was in cytidylic and uridylic acid, as in the wild strain.

Journal Article↗
PubMed1969

Growth-physiological changes in Escherichia coli and other bacteria during division inhibition by 5-diazouracil.

Diazouracil (DZU) was shown to increase the mean cell volume of several bacterial species. The filaments which it induced with Escherichia coli B and Lactobacillus casei were examined in section by electron microscopy. In addition to the inhibition of division of E. coli by DZU, its effects were studied on mass increase, viability, and deoxyribonucleic acid, ribonucleic acid, and protein synthesis. The dependence of cell age on the division-inhibitory effect of DZU was examined in synchronous cultures. The division-inhibitory effect was not reversed by pantoyllactone, an antagonist of ultraviolet filamentation, or by l-tyrosine, which had been reported to antagonize DZU activity.

Azo Compounds↗
PubMedDate not supplied

Some comments on misspecification of priors in Bayesian modelling of measurement error problems.

In this paper we discuss some aspects of misspecification of prior distributions in the context of Bayesian modelling of measurement error problems. A Bayesian approach to the treatment of common measurement error situations encountered in epidemiology has been recently proposed. Its implementation involves, first, the structural specification, through conditional independence relationships, of three submodels-a measurement model, an exposure model and a disease model- and secondly, the choice of functional forms for the distributions involved in the submodels. We present some results indicating how the estimation of the regression parameters of interest, which is carried out using Gibbs sampling, can be influenced by a misspecification of the parametric shape of the prior distribution of exposure.

Algorithms↗
PubMedDate not supplied

Statistical issues in the analysis of disease mapping data.

In this paper we discuss a number of issues that are pertinent to the analysis of disease mapping data. As an illustrative example we consider the mapping of larynx cancer across electoral wards in the North West Thames region of the U.K. Bayesian hierarchical models are now frequently employed to carry out such mapping. In a typical situation, a three-stage hierarchical model is specified in which the data are modelled as a function of area-specific relative risks at stage one; the collection of relative risks across the study region are modelled at stage two; and at stage three prior distributions are assigned to parameters of the stage two distribution. Such models allow area-specific disease relative risks to be 'smoothed' towards global and/or local mean levels across the study region. However, these models contain many structural and functional assumptions at different levels of the hierarchy; we aim to discuss some of these assumptions and illustrate their sensitivity. When relative risks are the endpoint of interest, it is common practice to assume that, for each of the age-sex strata of a particular area, there is a common multiplier (the relative risk) acting upon each of the stratum-specific risks in that area; we will examine this proportionality assumption. We also consider the choices of models and priors at stages two and three of the hierarchy, the effect of outlying areas, and an assessment of the level of smoothing that is being carried out. For inference, we concentrate on the description of the spatial variability in relative risks and on the association between the relative risks of larynx cancer and an area-level measure of socio-economic status.

Age Factors↗
PubMedDate not supplied

Spatial variation of natural radiation and childhood leukaemia incidence in Great Britain.

This paper describes an analysis of the geographical variation of childhood leukaemia incidence in Great Britain over a 15 year period in relation to natural radiation (gamma and radon). Data at the level of the 459 district level local authorities in England, Wales and regional districts in Scotland are analysed in two complementary ways: first, by Poisson regressions with the inclusion of environmental covariates and a smooth spatial structure; secondly, by a hierarchical Bayesian model in which extra-Poisson variability is modelled explicitly in terms of spatial and non-spatial components. From this analysis, we deduce a strong indication that a main part of the variability is accounted for by a local neighbourhood 'clustering' structure. This structure is furthermore relatively stable over the 15 year period for the lymphocytic leukaemias which make up the majority of observed cases. We found no evidence of a positive association of childhood leukaemia incidence with outdoor or indoor gamma radiation levels. There is no consistent evidence of any association with radon levels. Indeed, in the Poisson regressions, a significant positive association was only observed for one 5-year period, a result which is not compatible with a stable environmental effect. Moreover, this positive association became clearly non-significant when over-dispersion relative to the Poisson distribution was taken into account.

Air Pollution, Indoor↗
PubMedDate not supplied

A three-state Markov model of Plasmodium falciparum parasitemia.

A three-state Markov model taking into account clinical signs of malaria infections by P. falciparum is described. The three states considered are the noninfected (state 0), the infected exhibiting no clinical signs (state 1), and the infected with clinical signs (state 2). Methods for estimating the transition rates from longitudinal data are indicated. This model was used to assess the effect on children of an intervention trial on the use of mosquito nets impregnated with insecticide. The trial was conducted in West Africa (Burkina Faso) between 1985 and 1987. The analysis showed that the intervention was most effective on transition rates between state 1 and state 2.

Burkina Faso↗
PubMedDate not supplied

ACE: a peer education and counseling program meets the needs of incarcerated women with HIV/AIDS issues.

In this article, female prisoners who are peer educators and counselors in an HIV/AIDS program at Bedford Hills Correctional Facility, New York State's only maximum security prison for women, describe the positive role of a peer support program. Using examples from their own experiences, the women discuss the strengths of the AIDS Counseling and Education Program (ACE) in meeting the medical and psychosocial needs of the prison population concerning HIV/AIDS. The role of nurses in a correctional setting is discussed throughout the article and a final section discusses how nurses working together with peer health workers can create an effective team to meet the challenges of the AIDS epidemic within a correctional setting.

Acquired Immunodeficiency Syndrome↗