Urokinase and the intestinal mucosa: evidence for a role in epithelial cell turnover

The enzyme nitric oxide synthase catalyzes the oxidation of the amino acid L-arginine to L-citrulline and nitric oxide in an NADPH-dependent reaction. Nitric oxide plays a critical role in signal transduction pathways in the cardiovascular and nervous systems and is a key component of the cytostatic/cytotoxic function of the immune system. Characterization of nitric oxide synthase substrates and cofactors has outlined the broad details of the overall reaction and suggested possibilities for chemical steps in the reaction; however, the molecular details of the reaction mechanism are still poorly understood. Recent evidence suggests a role for the reduced bound pterin in the first step of the reaction--the hydroxylation of L-arginine.     

Bishop, Eysenck, Block, and psychoticism.

J. Block (see record 1978-28560-001) questioned evidence for the validity of the Eysenck Psychoticism (P) scale based on the psychophysiological findings of G. S. Claridge and H. J. Chappa (see record 1974-02520-001) that Ss high in psychoticism showed an unusual and counterintuitive relationship between 2-flash threshold and skin conductance. The present authors argue that Block's criticism that the result may be ephemeral is incorrect for 3 reasons. First, the cut-off point used to define the low skin conductance range over which the relationship was most evident was not as arbitrary as Block suggests. Second, replication data demonstrated the same result. And third, the unusual psychophysiology found in high P Ss has also been observed in normal Ss under LSD-25 and in acute schizophrenics. However, the present authors also point out that all their work on psychoticism was based on an earlier version of the Eysenck Personality Inventory (the Psychoticism-Extraversion-Neuroticism Inventory), whose items may have more face validity than the published version. Finally, D. V. M. Bishop's (see record 1978-30744-001) interpretation of the present authors' dimensional concept of psychoticism is corrected. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A method for calculating Bayesian uncertainties on internal doses resulting from complex occupational exposures

Estimating uncertainties on doses from bioassay data is of interest in epidemiology studies that estimate cancer risk from occupational exposures to radionuclides. Bayesian methods provide a logical framework to calculate these uncertainties. However, occupational exposures often consist of many intakes, and this can make the Bayesian calculation computationally intractable. This paper describes a novel strategy for increasing the computational speed of the calculation by simplifying the intake pattern to a single composite intake, termed as complex intake regime (CIR). In order to assess whether this approximation is accurate and fast enough for practical purposes, the method is implemented by the Weighted Likelihood Monte Carlo Sampling (WeLMoS) method and evaluated by comparing its performance with a Markov Chain Monte Carlo (MCMC) method. The MCMC method gives the full solution (all intakes are independent), but is very computationally intensive to apply routinely. Posterior distributions of model parameter values, intakes and doses are calculated for a representative sample of plutonium workers from the United Kingdom Atomic Energy cohort using the WeLMoS method with the CIR and the MCMC method. The distributions are in good agreement: posterior means and Q(0.025) and Q(0.975) quantiles are typically within 20 %. Furthermore, the WeLMoS method using the CIR converges quickly: a typical case history takes around 10-20 min on a fast workstation, whereas the MCMC method took around 12-72 hr. The advantages and disadvantages of the method are discussed.     

The retarding action of sugars on cement hydration

Sugars retard the hydration of Portland cement. The effectiveness of different sugars is compared from studies of solution analysis, calorimetry, calcium binding ability and alkaline stability. The best retarders, sucrose and raffinose, have a remarkable ability to solubilize cement constituents and in particular give rise to dramatic increases in the amount of silica in solution. However, ¹³C and ²⁹Si N.M.R. do not reveal the existence of sucrose-silicate complexes. The retarding action of sugars is explained in terms of adsorption onto and poisoning of hydrate surfaces.     

Some general considerations of a membrane/osmosis model for portland cement hydration

The proposed analogy between the process of membrane formation and osmosis in “silicate gardens” and Portland cement hydration is discussed. The major similarity is considered to be the formation of solids at a fluid interface at which the local supersaturation is high so that colloidal solids having no long-range order are produced. A membrane/osmosis model is then applied in explanation of various features of cement hydration, including the dormant period, the action of gypsum and morphological features such as “Hadley grains”.     

Internal dose assessments: uncertainty studies and update of ideas guidelines and databases within CONRAD project

The work of Task Group 5.1 (uncertainty studies and revision of IDEAS guidelines) and Task Group 5.5 (update of IDEAS databases) of the CONRAD project is described. Scattering factor (SF) values (i.e. measurement uncertainties) have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Based upon this work and other published values, default SF values are suggested. Uncertainty studies have been carried out using both a Bayesian approach as well as a frequentist (classical) approach. The IDEAS guidelines have been revised in areas relating to the evaluation of an effective AMAD, guidance is given on evaluating wound cases with the NCRP wound model and suggestions made on the number and type of measurements required for dose assessment.     

Avoiding biased estimates of dose when nothing is known about the time of intake

A common problem in internal dosimetry occurs in routine monitoring, when it is required to estimate an intake from a measurement made at the end of a monitoring interval, and the time of intake is unknown. ICRP suggests that it should be assumed that the intake occurred in the middle of the monitoring period. However, it has been shown that this will, in the long-term, lead to biased estimates of a worker's intake and dose. In order to overcome this biasing, the United States Department of Energy (USDOE) recommends a different method based on calculating the intakes for all possible intake times in the interval and then taking an arithmetic average. In a recent paper, it has been shown that both the ICRP and USDOE methods were biased and that the only unbiased estimator of the true intake was obtained by assuming a constant chronic intake throughout the monitoring interval. In all of the analyses carried out to date on this 'Constant Chronic' method, it was assumed that the measurements were exact. In this paper, the effects of assuming either normally or log-normally distributed measurement errors are explored, and the effect on the bias of the intake estimate is investigated.