817 research outputs found

    Cross-spectral purity of the Stokes parameters in random nonstationary electromagnetic beams

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    We consider cross-spectral purity in random nonstationary electromagnetic beams in terms of the Stokes parameters representing the spectral density and the spectral polarization state. We show that a Stokes parameter being cross-spectrally pure is consistent with the property that the corresponding normalized time-integrated coherence (two-point) Stokes parameter satisfies a certain reduction formula. The current analysis differs from the previous works on cross-spectral purity of nonstationary light beams such that the purity condition is in line with Mandel's original definition. In addition, in contrast to earlier works concerning the cross-spectral purity of the polarization-state Stokes parameters, intensity-normalized coherence Stokes parameters are applied. It is consequently found that in addition to separate spatial and temporal coherence factors the reduction formula contains a third factor that depends exclusively on the polarization properties. We further show that cross-spectral purity implies a specific structure for the electromagnetic spectral spatial correlations. The results of this work constitute foundational advances in the interference of random nonstationary vectorial light.Comment: 5 pages, 1 figur

    Weight transitions and psychosocial factors : A longitudinal cohort study of Finnish primary school children with overweight

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    For targeted prevention and treatment of childhood obesity, primary health care needs methods to identify children potentially developing obesity. The objectives of this study were to examine transitions across weight categories and their association with psychosocial family- and school-related factors, data on which were retrieved from health records. This longitudinal cohort study comprised 507 Finnish children with overweight, identified from a random sample of 2000 sixth graders in Helsinki in 2013. We applied Markov multistate models to analyze the transition rates over six primary school years between BMI SDS categories of normal weight, overweight and obesity, as assessed by Finnish BMI-for-age reference, and to examine relations between transition rates and family- and school-related factors. Among 3116 pairs of consecutive growth measurements from 225 girls and 282 boys aged 6–14, 719 transitions from weight category to another occurred. The highest 1-year probabilities were 0.76 for girls to stay in overweight and 0.80 for boys to stay in obesity. Transitions from normal weight to overweight and from obesity to overweight were more probable than vice versa. Transitions from overweight into obesity were among girls associated with older age (HR 2.63) and divorced or single parents (HR 2.29), as well as among boys with experiences of crises (HR 2.40) and being bullied (HR 1.66). Factors identifiable in school health care and associated with the probability of transition towards obesity should be considered when planning individual support and intervention programs. © 2020 The AuthorsPeer reviewe

    Socioeconomic deprivation, urban-rural location and alcohol-related mortality in England and Wales

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    Background: Many causes of death are directly attributable to the toxic effects of alcohol and deaths from these causes are increasing in the United Kingdom. The aim of this study was to investigate variation in alcohol-related mortality in relation to socioeconomic deprivation, urban-rural location and age within a national context. Methods: An ecological study design was used with data from 8797 standard table wards in England and Wales. The methodology included using the Carstairs Index as a measure of socioeconomic deprivation at the small-area level and the national harmonised classification system for urban and rural areas in England and Wales. Alcohol-related mortality was defined using the National Statistics definition, devised for tracking national trends in alcohol-related deaths. Deaths from liver cirrhosis accounted for 85% of all deaths included in this definition. Deaths from 1999-2003 were examined and 2001 census ward population estimates were used as the denominators. Results: The analysis was based on 28,839 deaths. Alcohol-related mortality rates were higher in men and increased with increasing age, generally reaching peak levels in middle-aged adults. The 45-64 year age group contained a quarter of the total population but accounted for half of all alcohol-related deaths. There was a clear association between alcohol-related mortality and socioeconomic deprivation, with progressively higher rates in more deprived areas. The strength of the association varied with age. Greatest relative inequalities were seen amongst people aged 25-44 years, with relative risks of 4.73 (95% CI 4.00 to 5.59) and 4.24 (95% CI 3.50 to 5.13) for men and women respectively in the most relative to the least deprived quintiles. People living in urban areas experienced higher alcohol-related mortality relative to those living in rural areas, with differences remaining after adjustment for socioeconomic deprivation. Adjusted relative risks for urban relative to rural areas were 1.35 (95% CI 1.20 to 1.52) and 1.13 (95% CI 1.01 to 1.25) for men and women respectively. Conclusions: Large inequalities in alcohol-related mortality exist between sub-groups of the population in England and Wales. These should be considered when designing public health policies to reduce alcohol-related harm

    Exploring potential mortality reductions in 9 European countries by improving diet and lifestyle: A modelling approach.

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    BACKGROUND: Coronary heart disease (CHD) death rates have fallen across most of Europe in recent decades. However, substantial risk factor reductions have not been achieved across all Europe. Our aim was to quantify the potential impact of future policy scenarios on diet and lifestyle on CHD mortality in 9 European countries. METHODS: We updated the previously validated IMPACT CHD models in 9 European countries and extended them to 2010-11 (the baseline year) to predict reductions in CHD mortality to 2020(ages 25-74years). We compared three scenarios: conservative, intermediate and optimistic on smoking prevalence (absolute decreases of 5%, 10% and 15%); saturated fat intake (1%, 2% and 3% absolute decreases in % energy intake, replaced by unsaturated fats); salt (relative decreases of 10%, 20% and 30%), and physical inactivity (absolute decreases of 5%, 10% and 15%). Probabilistic sensitivity analyses were conducted. RESULTS: Under the conservative, intermediate and optimistic scenarios, we estimated 10.8% (95% CI: 7.3-14.0), 20.7% (95% CI: 15.6-25.2) and 29.1% (95% CI: 22.6-35.0) fewer CHD deaths in 2020. For the optimistic scenario, 15% absolute reductions in smoking could decrease CHD deaths by 8.9%-11.6%, Salt intake relative reductions of 30% by approximately 5.9-8.9%; 3% reductions in saturated fat intake by 6.3-7.5%, and 15% absolute increases in physical activity by 3.7-5.3%. CONCLUSIONS: Modest and feasible policy-based reductions in cardiovascular risk factors (already been achieved in some other countries) could translate into substantial reductions in future CHD deaths across Europe. However, this would require the European Union to more effectively implement powerful evidence-based prevention policies

    Population assessment of future trajectories in coronary heart disease mortality.

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    Background: Coronary heart disease (CHD) mortality rates have been decreasing in Iceland since the 1980s, largely reflecting improvements in cardiovascular risk factors. The purpose of this study was to predict future CHD mortality in Iceland based on potential risk factor trends. Methods and findings: The previously validated IMPACT model was used to predict changes in CHD mortality between 2010 and 2040 among the projected population of Iceland aged 25–74. Calculations were based on combining: i) data on population numbers and projections (Statistics Iceland), ii) population risk factor levels and projections (Refine Reykjavik study), and iii) effectiveness of specific risk factor reductions (published meta-analyses). Projections for three contrasting scenarios were compared: 1) If the historical risk factor trends of past 30 years were to continue, the declining death rates of past decades would level off, reflecting population ageing. 2) If recent trends in risk factors (past 5 years) continue, this would result in a death rate increasing from 49 to 70 per 100,000. This would reflect a recent plateau in previously falling cholesterol levels and recent rapid increases in obesity and diabetes prevalence. 3) Assuming that in 2040 the entire population enjoys optimal risk factor levels observed in low risk cohorts, this would prevent almost all premature CHD deaths before 2040. Conclusions: The potential increase in CHD deaths with recent trends in risk factor levels is alarming both for Iceland and probably for comparable Western populations. However, our results show considerable room for reducing CHD mortality. Achieving the best case scenario could eradicate premature CHD deaths by 2040. Public health policy interventions based on these predictions may provide a cost effective means of reducing CHD mortality in the future

    Spectral scale transformations of nonstationary optical fields

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    The notions of cross-spectral purity and spectral invariance of light impose specific structures for the field coherence. Such concepts were originally introduced for stationary light and recently extended to nonstationary fields. In this work, we establish general conditions for transforming scalar, pulsed, isodiffracting light beams produced, for instance, in usual spherical-mirror laser resonators, to nonstationary secondary sources that exhibit cross-spectral purity or spectral invariance. Further, we introduce hybrid refractive-diffractive imaging systems which perform the desired transformation accurately over a wide spectral range irrespective of the spatial coherence of the incident isodiffracting beam.publishedVersionPeer reviewe