Relative performance of different exposure modeling approaches for sulfur dioxide concentrations in the air in rural western Canada

<p>Abstract</p> <p>Background</p> <p>The main objective of this paper is to compare different methods for predicting the levels of SO₂air pollution in oil and gas producing area of rural western Canada. Month-long average air quality measurements were collected over a two-year period (2001–2002) at multiple locations, with some side-by-side measurements, and repeated time-series at selected locations.</p> <p>Methods</p> <p>We explored how accurately location-specific mean concentrations of SO₂can be predicted for 2002 at 666 locations with multiple measurements. Means of repeated measurements on the 666 locations in 2002 were used as the alloyed gold standard (AGS). First, we considered two approaches: one that uses one measurement from each location of interest; and the other that uses context data on proximity of monitoring sites to putative sources of emission in 2002. Second, we imagined that all of the previous year's (2001's) data were also available to exposure assessors: 9,464 measurements and their context (month, proximity to sources). Exposure prediction approaches we explored with the 2001 data included regression modeling using either mixed or fixed effects models. Third, we used Bayesian methods to combine single measurements from locations in 2002 (not used to calculate AGS) with different <it>priors</it>.</p> <p>Results</p> <p>The regression method that included both fixed and random effects for prediction (Best Linear Unbiased Predictor) had the best agreement with the AGS (Pearson correlation 0.77) and the smallest mean squared error (MSE: 0.03). The second best method in terms of correlation with AGS (0.74) and MSE (0.09) was the Bayesian method that uses normal mixture <it>prior </it>derived from predictions of the 2001 mixed effects applied in the 2002 context.</p> <p>Conclusion</p> <p>It is likely that either collecting some measurements from the desired locations and time periods or predictions of a reasonable empirical mixed effects model perhaps is sufficient in most epidemiological applications. The method to be used in any specific investigation will depend on how much uncertainty can be tolerated in exposure assessment and how closely available data matches circumstances for which estimates/predictions are required.</p

Cherenkov luminescence measurements with digital silicon photomultipliers: a feasibility study.

BackgroundA feasibility study was done to assess the capability of digital silicon photomultipliers to measure the Cherenkov luminescence emitted by a β source. Cherenkov luminescence imaging (CLI) is possible with a charge coupled device (CCD) based technology, but a stand-alone technique for quantitative activity measurements based on Cherenkov luminescence has not yet been developed. Silicon photomultipliers (SiPMs) are photon counting devices with a fast impulse response and can potentially be used to quantify β-emitting radiotracer distributions by CLI.MethodsIn this study, a Philips digital photon counting (PDPC) silicon photomultiplier detector was evaluated for measuring Cherenkov luminescence. The PDPC detector is a matrix of avalanche photodiodes, which were read one at a time in a dark count map (DCM) measurement mode (much like a CCD). This reduces the device active area but allows the information from a single avalanche photodiode to be preserved, which is not possible with analog SiPMs. An algorithm to reject the noisiest photodiodes and to correct the measured count rate for the dark current was developed.ResultsThe results show that, in DCM mode and at (10-13) °C, the PDPC has a dynamic response to different levels of Cherenkov luminescence emitted by a β source and transmitted through an opaque medium. This suggests the potential for this approach to provide quantitative activity measurements. Interestingly, the potential use of the PDPC in DCM mode for direct imaging of Cherenkov luminescence, as a opposed to a scalar measurement device, was also apparent.ConclusionsWe showed that a PDPC tile in DCM mode is able to detect and image a β source through its Cherenkov radiation emission. The detector's dynamic response to different levels of radiation suggests its potential quantitative capabilities, and the DCM mode allows imaging with a better spatial resolution than the conventional event-triggered mode. Finally, the same acquisition procedure and data processing could be employed also for other low light levels applications, such as bioluminescence

Prevalence of Arsenic-related Skin Lesions in 53 Widely-scattered Villages of Bangladesh: An Ecological Survey

A survey was carried out to provide a representative assessment of prevalence and risk of arsenic-related skin lesions in relation to geographical distribution of arsenic in wells of rural Bangladesh as a necessary background for research into effects in pregnancy and cancer risks. A systematic random sample of 53 villages in four divisions of Bangladesh served by Gonoshasthaya Kendra was selected, and all women aged 18 years or more (n=16,740) were listed. Trained paramedics recorded the presence of skin thickening and nodules on the palms and soles, together with information on tubewell use. The prevalence was related to the mean concentration of arsenic for the district as indicated by data from the British Geological Survey and to the date the first well in the village was installed. Overall, the observed prevalence was 176 cases (1.3%) in 13,705 women examined, varying from 0% in 26 villages to 23% in one; lesions were observed more frequently on hands than on feet. The estimate doubled with concentrations of arsenic from 11 to 6450 \u3bcg/L and increased more than 20 times at &gt;50 \u3bcg/L. In the absence of further information, priority for control measures should be directed at areas where the average concentrations of arsenic are above 50 \u3bcg/L, especially in villages where skin lesions have been identified

Effects of trace levels of nitrous oxide on psychomotor performance.

Twenty-four male student volunteers were exposed to 50 ppm of nitrous oxide or air in an exposure chamber for 4 h in two experimental sessions. The subjects completed a battery of psychomotor tests during the final 40 min of the exposure sessions. Nitrous oxide, at this low concentration, did not produce any statistically significant changes in performance

Studying Kaon-pion S-wave scattering in K-matrix formalism

We generalize our previous work on \pi\pi scattering to K\pi scattering, and re-analyze the experiment data of K\pi scattering below 1.6 GeV. Without any free parameter, we explain K\pi I=3/2 S-wave phase shift very well by using t-channel rho and u-channel K^* meson exchange. With the t-channel and u-channel meson exchange fixed as the background term, we fit the K\pi I=1/2 S-wave data of the LASS experiment quite well by introducing one or two s-channel resonances. It is found that there is only one s-channel resonance between K\pi threshold and 1.6 GeV, i.e., K_0^*(1430) with a mass around 1438~1486 MeV and a width about 346 MeV, while the t-channel rho exchange gives a pole at (450-480i) MeV for the amplitude.Comment: REVTeX4 file, 11 pages and 3 figure

Prevalence, temporal course and risk factors for phantom eye symptoms in uveal melanoma

BACKGROUND: Phantom eye symptoms (PES), particularly phantom visual sensations (PVS) and phantom eye pain (PEP), are common in enucleated patients and can lead to psychological distress. Current cross-sectional studies cannot examine the temporal course of symptoms, nor can they identify dynamic risk factors or consequences of PES.METHODS: Cohort study of 105 enucleated uveal melanoma patients returning self-report questionnaires, within 4 weeks of diagnosis and 6-, 12- and 24-months post-treatment. Questionnaires measuring PVS and PEP symptoms in the week prior to completion, pain severity, Hospital Anxiety and Depression Scale scores and the Functional Assessment of Cancer Therapy scale (FACT-G) measuring quality of life.RESULTS: PVS and PEP emerged after 6 months, were relatively stable over the study and did not remit. PVS showed 6-, 12- and 24-month prevalence rates of 44.6%, 48.2% and 30.2%, and PEP 16.1%, 18.4% and 17.5% respectively. PVS were generally elementary, with only 10–15% of the total cohort experiencing complex sensations. PEP was generally neither prolonged nor intense, except in a small proportion. PVS and PEP were showed moderate associations but did not predict each other prospectively. Anxiety within 4 weeks of diagnosis was a risk factor for the initiation of PEP. Neither PVS nor PEP prospectively predicted anxiety, depression or quality of life.CONCLUSIONS: PES were prevalent and non-remitting, beginning within 6 months of enucleation. PVS and PEP may not represent symptoms of a coherent syndrome. We discuss fndings with reference to theories of phantom sensations, and directions for clinical practise and research

A new analysis of πK\pi K scattering from Roy and Steiner type equations

With the aim of generating new constraints on the OZI suppressed couplings of chiral perturbation theory a set of six equations of the Roy and Steiner type for the $S$- and $P$-waves of the $\pi K$ scattering amplitudes is derived. The range of validity and the multiplicity of the solutions are discussed. Precise numerical solutions are obtained in the range E\lapprox 1 GeV which make use as input, for the first time, of the most accurate experimental data available at $E > 1$ GeV for both $\pi K\to\pi K$ and $\pi\pi\to K\bar{K}$ amplitudes. Our main result is the determination of a narrow allowed region for the two S-wave scattering lengths. Present experimental data below 1 GeV are found to be in generally poor agreement with our results. A set of threshold expansion parameters, as well as sub-threshold parameters are computed. For the latter, matching with the SU(3) chiral expansion at NLO is performed.Comment: 45 pages, 17 figures. v2: New title, minor correction