112 research outputs found

    The generation of tsunamis

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    Tsunamis are gravity-driven water waves. Most are generated by vertical displacement of the seabed that propagates through the water column to the sea surface. The resulting elevated surface wave collapses through gravity and then propagates outward from the source. Dispersion of the initial wave generates a multiple wave train. Tsunamis are mainly (∼80%) generated by earthquakes, but other mechanisms include subaerial and submarine landslides and volcanic collapse and eruption. Other, less frequent, tsunami mechanisms include bolide (asteroid) impact and weather events (meteotsunamis), but these are generated at the water surface, respectively, from external impact and from wind friction. The magnitude of a tsunamigenic earthquake has the main control on the tsunami, although “tsunami” earthquakes generate tsunamis much larger than expected from their earthquake source magnitude. Tsunamigenic earthquake mechanisms include interplate boundary rupture, splay faulting, and intraplate rupture. Landslide tsunami mechanisms include slumps and translational failures that may be initiated from either the bottom or the top. Landslide volume, water depth, and initial acceleration are the main controls on tsunami magnitude, although other factors such as the failure mechanism and the location of initiation are influential. There are three main aspects of a tsunami; (i) initial wave generation, (ii) propagation, and (iii) onland run-up. Initial wave generation from earthquakes is mainly from seabed vertical displacement, and a rule of thumb suggests that in most instances the maximum initial wave elevation is up to twice this. The maximum initial wave elevation from a landslide tsunami is theoretically determined by the ocean depth and thus could be thousands of meters. Local tsunami run-up elevations vary with source mechanism and vary considerably. Although dependent on local bathymetry and topography, these are likely to be more elevated and focused from submarine landslides than from earthquakes. The different mechanisms generate different tsunami wave frequencies; these determine travel distances, with the low frequency tsunamis from earthquakes traveling much farther than tsunamis from landslides, which are much higher frequency. Final onland run-up is mainly dependent on source mechanism as well as local offshore bathymetry and coastal topography

    Challenging the view that lack of fibre causes childhood constipation

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    Objectives: To assess evidence supporting the view that ‘low fibre causes childhood constipation’. Design: Triangulation integrated three approaches: a systematic review NICE guideline CG99 examining effectiveness of increasing fibre; a cohort study, Avon Longitudinal Study of Parents and Children (ALSPAC), to assess if constipation (or hard stools) can precede fibre intake at weaning; and a literature search for twin studies to calculate heredity. Setting: CG99 examined the literature regarding the effectiveness of increasing fibre. ALSPAC asked parents about: hard stools at 4 weeks, 6 months and 2.5 years and constipation at age 4–10 years, as well as fibre intake at 2 years. Twin studies and data from ALSPAC were pooled to calculate concordance of constipation comparing monozygotic and dizygous twin pairs. Participants: CG99 reported six randomised controlled trials (RCTs). ALSPAC hard stool data from 6796 children at 4 weeks, 9828 at 6 months and 9452 at 2.5 years plus constipation data on 8401 at 4–10 years were compared with fibre intake at 2 years. Twin studies had 338 and 93 twin pairs and ALSPAC added a further 45. Results: Increasing fibre did not effectively treat constipation. Hard stools at 4 weeks predated fibre and at 6 months predicted lower fibre intake at 2 years (p=0.003). Heredity explained 59% of constipation. Conclusions: RCTs indicate that increasing fibre is not an effective treatment for constipation in children. Hard stools can precede and predict later fibre intake. Genetic inheritance explains most childhood constipation. Extended treatment with stool softeners may improve fibre intake and limit long-term damaging sequelae of constipation

    Are financial incentives cost-effective to support smoking cessation during pregnancy?

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    Aims  To investigate the cost-effectiveness of up to £400 worth of financial incentives for smoking cessation in pregnancy as an adjunct to routine health care.  Design  Cost-effectiveness analysis based on a Phase II randomized controlled trial (RCT) and a cost–utility analysis using a life-time Markov model.  Setting  The RCT was undertaken in Glasgow, Scotland. The economic analysis was undertaken from the UK National Health Service (NHS) perspective.  Participants  A total of 612 pregnant women randomized to receive usual cessation support plus or minus financial incentives of up to £400 vouchers (US 609), contingent upon smoking cessation.  Measurements  Comparison of usual support and incentive interventions in terms of cotinine-validated quitters, quality-adjusted life years (QALYs) and direct costs to the NHS.  Findings  The incremental cost per quitter at 34–38 weeks pregnant was £1127 (1716).This is similar to the standard look-up value derived from Stapleton & West's published ICER tables, £1390 per quitter, by looking up the Cessation in Pregnancy Incentives Trial (CIPT) incremental cost (£157) and incremental 6-month quit outcome (0.14). The life-time model resulted in an incremental cost of £17 [95% confidence interval (CI) = –£93, £107] and a gain of 0.04 QALYs (95% CI = –0.058, 0.145), giving an ICER of £482/QALY ($734/QALY). Probabilistic sensitivity analysis indicates uncertainty in these results, particularly regarding relapse after birth. The expected value of perfect information was £30 million (at a willingness to pay of £30 000/QALY), so given current uncertainty, additional research is potentially worthwhile.  Conclusion  Financial incentives for smoking cessation in pregnancy are highly cost-effective, with an incremental cost per quality-adjusted life years of £482, which is well below recommended decision thresholds

    Reliability of self reported smoking status by pregnant women for estimating smoking prevalence: a retrospective, cross sectional study

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    Objective To determine what impact reliance on self reported smoking status during pregnancy has on both the accuracy of smoking prevalence figures and access to smoking cessation services for pregnant women in Scotland

    Minimizing sample bias due to stigmatized behaviours: the representativeness of participants in a cohort study of alcohol in pregnancy

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    Background Stigmatized behaviours are often underreported, especially in pregnancy, making them challenging to address. The Alcohol and Child Development Study (ACDS) seeks to inform prevention of foetal alcohol harm, linking self-report as well as a maternal blood alcohol biomarker with child developmental outcomes. Samples were requested using passive, generic consent. The success of this approach at minimizing bias is presented comparing characteristics of women who provided samples to those who did not. Methods All pregnant women in the study city were sent a Patient Information Sheet (PIS) with their first NHS obstetric appointment letter. The PIS informed them that the NHS would like to take an extra blood sample for research purposes, unless they opted out. Neither the women nor the midwives were informed that the samples might be tested for an alcohol biomarker. This paper examines the extent to which women who provided the extra sample were representative of women where no sample was provided, in terms of routinely collected information: age; body mass index; area-based deprivation; previous pregnancies, abortions and caesarians; smoking status and carbon monoxide level; self-reported alcohol use, gestation and birth weight of their baby. Chi-square and Mann-Whitney U tests were used to compare groups. Results 3436 (85%) of the 4049 pregnant women who attended their appointment provided the extra sample. Women who did not were significantly younger (p

    New High-Resolution Modeling of the 2018 Palu Tsunami, Based on Supershear Earthquake Mechanisms and Mapped Coastal Landslides, Supports a Dual Source

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    The Mw 7.5 earthquake that struck Central Sulawesi, Indonesia, on September 28, 2018, was rapidly followed by coastal landslides and destructive tsunami waves within Palu Bay. Here, we present new tsunami modeling that supports a dual source mechanism from the supershear strike-slip earthquake and coastal landslides. Up until now the tsunami mechanism: earthquake, coastal landslides, or a combination of both, has remained controversial, because published research has been inconclusive; with some studies explaining most observations from the earthquake and others the landslides. Major challenges are the numerous different earthquake source models used in tsunami modeling, and that landslide mechanisms have been hypothetical. Here, we simulate tsunami generation using three published earthquake models, alone and in combination with seven coastal landslides identified in earlier work and confirmed by field and bathymetric evidence which, from video evidence, produced significant waves. To generate and propagate the tsunamis, we use a combination of two wave models, the 3D non-hydrostatic model NHWAVE and the 2D Boussinesq model FUNWAVE-TVD. Both models are nonlinear and address the physics of wave frequency dispersion critical in modeling tsunamis from landslides, which here, in NHWAVE are modeled as granular material. Our combined, earthquake and coastal landslide, simulations recreate all observed tsunami runups, except those in the southeast of Palu Bay where they were most elevated (10.5 m), as well as observations made in video recordings and at the Pantoloan Port tide gauge located within Palu Bay. With regard to the timing of tsunami impact on the coast, results from the dual landslide/earthquake sources, particularly those using the supershear earthquake models are in good agreement with reconstructed time series at most locations. Our new work shows that an additional tsunami mechanism is also necessary to explain the elevated tsunami observations in the southeast of Palu Bay. Using partial information from bathymetric surveys in this area we show that an additional, submarine landslide here, when simulated with the other coastal slides, and the supershear earthquake mechanism better explains the observations. This supports the need for future marine geology work in this area

    Assessing maternal alcohol consumption in pregnancy : comparison of confidential postnatal maternal interview and measurement of alcohol biomarkers in meconium

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    Knowledge of alcohol consumption in pregnancy is important for early identification of children with fetal alcohol spectrum disorder. We investigated whether alcohol biomarkers fatty acid ethyl esters (FAEEs) and ethyl glucuronide (EtG) in meconium are predicted by maternal or newborn demographics and/or correlate with confidential early postnatal self-report of alcohol consumption in pregnancy. Anonymised, observational population-based study. Inner-city maternity unit, Glasgow, UK. Singleton mother/infant dyads delivering every fourth day. Mother: confidential postnatal interview. Baby: meconium sample for FAEEs and EtG. 840/908 mothers consented. 370 (46.4%) reported alcohol consumption in pregnancy, generally of modest amount; for 114 (13.6%) this was after 20 weeks' gestation. Alcohol consumption in later pregnancy was more commonly reported by older (31.3 vs 29.5 years) women of white British ethnicity (
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