267 research outputs found
A simulation of the IPS variations from a magnetohydrodynamical simulation
Calculations of the variations of interplanetary scintillation (IPS) from a disturbance simulated by a 3-D magnetohydrodynamical (MHD) model of the solar wind are presented. The simulated maps are compared with observations and it is found that the MHD model reproduces the qualitative features of observed disturbances. The disturbance produced by the MHD simulation is found to correspond in strength with the weakest disturbance which can be reliably detected by existing single station IPS observations
Observations of Detailed Structure in the Solar Wind at 1 AU with STEREO/HI-2
Heliospheric imagers offer the promise of remote sensing of large-scale
structures present in the solar wind. The STEREO/HI-2 imagers, in particular,
offer high resolution, very low noise observations of the inner heliosphere but
have not yet been exploited to their full potential. This is in part because
the signal of interest, Thomson scattered sunlight from free electrons, is
~1000 times fainter than the background visual field in the images, making
background subtraction challenging. We have developed a procedure for
separating the Thomson-scattered signal from the other background/foreground
sources in the HI-2 data. Using only the Level 1 data from STEREO/HI-2, we are
able to generate calibrated imaging data of the solar wind with sensitivity of
a few times 1e-17 Bsun, compared to the background signal of a few times 1e-13
Bsun. These images reveal detailed spatial structure in CMEs and the solar wind
at projected solar distances in excess of 1 AU, at the instrumental motion-blur
resolution limit of 1-3 degree. CME features visible in the newly reprocessed
data from December 2008 include leading-edge pileup, interior voids,
filamentary structure, and rear cusps. "Quiet" solar wind features include V
shaped structure centered on the heliospheric current sheet, plasmoids, and
"puffs" that correspond to the density fluctuations observed in-situ. We
compare many of these structures with in-situ features detected near 1 AU. The
reprocessed data demonstrate that it is possible to perform detailed structural
analyses of heliospheric features with visible light imagery, at distances from
the Sun of at least 1 AU.Comment: Accepted by Astrophysical Journa
The Thomson Surface. II. Polarization
The solar corona and heliosphere are visible via sunlight that is
Thomson-scattered off of free electrons, yielding a radiance against the
celestial sphere. In this second part of a three-article series, we discuss
linear polarization of this scattered light parallel and perpendicular to the
plane of scatter in the context of heliopheric imaging far from the Sun. The
difference between these two radiances, (pB), varies quite differently with
scattering angle, compared to the sum that would be detected in unpolarized
light (B). The difference between these two quantities has long been used in a
coronagraphic context for background subtraction and to extract some
three-dimensional information about the corona; we explore how these effects
differ in the wider-field heliospheric imaging case where small-angle
approximations do not apply. We develop an appropriately-simplified theory of
polarized Thomson scattering in the heliosphere, discuss signal-to-noise
considerations, invert the scattering equations analytically to solve the three
dimensional object location problem for small objects, discuss exploiting
polarization for background subtraction, and generate simple forward models of
several classes of heliospheric feature. We conclude that pB measurements of
heliospheric material are much more localized to the Thomson surface than are B
measurements, that the ratio pB/B can be used to track solar wind features in
three dimensions for scientific and space weather applications better in the
heliosphere than corona; and that, by providing an independent measurement of
background signal, pB measurements may be used to reduce the effect of
background radiances including the stably polarized zodiacal light.Comment: v2: text as accepted by APJ (before proofs); formatted with
emulateapj.cl
Pharmaceuticals in soils of lower income countries: Physico-chemical fate and risks from wastewater irrigation.
Population growth, increasing affluence, and greater access to medicines have led to an increase in active pharmaceutical ingredients (APIs) entering sewerage networks. In areas with high wastewater reuse, residual quantities of APIs may enter soils via irrigation with treated, partially treated, or untreated wastewater and sludge. Wastewater used for irrigation is currently not included in chemical environmental risk assessments and requires further consideration in areas with high water reuse. This study critically assesses the contemporary understanding of the occurrence and fate of APIs in soils of low and lower-middle income countries (LLMIC) in order to contribute to the development of risk assessments for APIs in LLMIC. The physico-chemical properties of APIs and soils vary greatly globally, impacting on API fate, bioaccumulation and toxicity. The impact of pH, clay and organic matter on the fate of organic ionisable compounds is discussed in detail. This study highlights the occurrence and the partitioning and degradation coefficients for APIs in soil:porewater systems, API usage data in LLMICS and removal rates (where used) within sewage treatment plants as key areas where data are required in order to inform robust environmental risk assessment methodologies
Major epidemiological changes in sudden infant death syndrome : a 20-year population-based study in the UK
Background
Results of case-control studies in the past 5 years suggest that the epidemiology of sudden infant death syndrome (SIDS) has changed since the 1991 UK Back to Sleep campaign. The campaign's advice that parents put babies on their back to sleep led to a fall in death rates. We used a longitudinal dataset to assess these potential changes.
Methods
Population-based data from home visits have been collected for 369 consecutive unexpected infant deaths (300 SIDS and 69 explained deaths) in Avon over 20 years (1984ā2003). Data obtained between 1993 and 1996 from 1300 controls with a chosen āreferenceā sleep before interview have been used for comparison.
Findings
Over the past 20 years, the proportion of children who died from SIDS while co-sleeping with their parents, has risen from 12% to 50% (p<0Ā·0001), but the actual number of SIDS deaths in the parental bed has halved (p=0Ā·01). The proportion seems to have increased partly because the Back to Sleep campaign led to fewer deaths in infants sleeping aloneārather than because of a rise in deaths of infants who bed-shared, and partly because of an increase in the number of deaths in infants sleeping with their parents on a sofa. The proportion of deaths in families from deprived socioeconomic backgrounds has risen from 47% to 74% (p=0Ā·003), the prevalence of maternal smoking during pregnancy from 57% to 86% (p=0Ā·0004), and the proportion of pre-term infants from 12% to 34% (p=0Ā·0001). Although many SIDS infants come from large families, first-born infants are now the largest group. The age of infants who bed-share is significantly smaller than that before the campaign, and fewer are breastfed.
Interpretation
Factors that contribute to SIDS have changed in their importance over the past 20 years. Although the reasons for the rise in deaths when a parent sleeps with their infant on a sofa are still unclear, we strongly recommend that parents avoid this sleeping environment. Most SIDS deaths now occur in deprived families. To better understand contributory factors and plan preventive measures we need control data from similarly deprived families, and particularly, infant sleep environments
Landslide tsunami case studies using a Boussinesq model and a fully nonlinear tsunami generation model
International audienceCase studies of landslide tsunamis require integration of marine geology data and interpretations into numerical simulations of tsunami attack. Many landslide tsunami generation and propagation models have been proposed in recent time, further motivated by the 1998 Papua New Guinea event. However, few of these models have proven capable of integrating the best available marine geology data and interpretations into successful case studies that reproduce all available tsunami observations and records. We show that nonlinear and dispersive tsunami propagation models may be necessary for many landslide tsunami case studies. GEOWAVE is a comprehensive tsunami simulation model formed in part by combining the Tsunami Open and Progressive Initial Conditions System (TOPICS) with the fully non-linear Boussinesq water wave model FUNWAVE. TOPICS uses curve fits of numerical results from a fully nonlinear potential flow model to provide approximate landslide tsunami sources for tsunami propagation models, based on marine geology data and interpretations. In this work, we validate GEOWAVE with successful case studies of the 1946 Unimak, Alaska, the 1994 Skagway, Alaska, and the 1998 Papua New Guinea events. GEOWAVE simulates accurate runup and inundation at the same time, with no additional user interference or effort, using a slot technique. Wave breaking, if it occurs during shoaling or runup, is also accounted for with a dissipative breaking model acting on the wave front. The success of our case studies depends on the combination of accurate tsunami sources and an advanced tsunami propagation and inundation model
On the autonomous detection of coronal mass ejections in heliospheric imager data
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95523/1/jgra21843.pd
Soil sterilisation methods for use in OECD 106: How effective are they?
publisher: Elsevier articletitle: Soil sterilisation methods for use in OECD 106: How effective are they? journaltitle: Chemosphere articlelink: https://doi.org/10.1016/j.chemosphere.2018.06.073 content_type: article copyright: Ā© 2018 Elsevier Ltd. All rights reserved
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