8,691 research outputs found
The Coronal Analysis of SHocks and Waves (CASHeW) Framework
Coronal Bright Fronts (CBF) are large-scale wavelike disturbances in the
solar corona, related to solar eruptions. They are observed in extreme
ultraviolet (EUV) light as transient bright fronts of finite width, propagating
away from the eruption source. Recent studies of individual solar eruptive
events have used EUV observations of CBFs and metric radio type II burst
observations to show the intimate connection between low coronal waves and
coronal mass ejection (CME)-driven shocks. EUV imaging with the Atmospheric
Imaging Assembly(AIA) instrument on the Solar Dynamics Observatory (SDO) has
proven particularly useful for detecting CBFs, which, combined with radio and
in situ observations, holds great promise for early CME-driven shock
characterization capability. This characterization can further be automated,
and related to models of particle acceleration to produce estimates of particle
fluxes in the corona and in the near Earth environment early in events. We
present a framework for the Coronal Analysis of SHocks and Waves (CASHeW). It
combines analysis of NASA Heliophysics System Observatory data products and
relevant data-driven models, into an automated system for the characterization
of off-limb coronal waves and shocks and the evaluation of their capability to
accelerate solar energetic particles (SEPs). The system utilizes EUV
observations and models written in the Interactive Data Language (IDL). In
addition, it leverages analysis tools from the SolarSoft package of libraries,
as well as third party libraries. We have tested the CASHeW framework on a
representative list of coronal bright front events. Here we present its
features, as well as initial results. With this framework, we hope to
contribute to the overall understanding of coronal shock waves, their
importance for energetic particle acceleration, as well as to the better
ability to forecast SEP events fluxes.Comment: Accepted for publication in the Journal of Space Weather and Space
Climate (SWSC
Solar Coronal Structures and Stray Light in TRACE
Using the 2004 Venus transit of the Sun to constrain a semi-empirical
point-spread function for the TRACE EUV solar telescope, we have measured the
effect of stray light in that telescope. We find that 43% of 171A EUV light
that enters TRACE is scattered, either through diffraction off the entrance
filter grid or through other nonspecular effects. We carry this result forward,
via known-PSF deconvolution of TRACE images, to identify its effect on analysis
of TRACE data. Known-PSF deconvolution by this derived PSF greatly reduces the
effect of visible haze in the TRACE 171A images, enhances bright features, and
reveals that the smooth background component of the corona is considerably less
bright (and hence much more rarefied) than commonly supposed. Deconvolution
reveals that some prior conlclusions about the Sun appear to have been based on
stray light in the images. In particular, the diffuse background "quiet corona"
becomes consistent with hydrostatic support of the coronal plasma; feature
contrast is greatly increased, possibly affecting derived parameters such as
the form of the coronal heating function; and essentially all existing
differential emission measure studies of small features appear to be affected
by contamination from nearby features. We speculate on further implications of
stray light for interpretation of EUV images from TRACE and similar
instruments, and advocate deconvolution as a standard tool for image analysis
with future instruments such as SDO/AIA.Comment: Accepted by APJ; v2 reformatted to single-column format for online
readabilit
Bioaccumulation surveillance in Milford Haven Waterway
Biomonitoring of contaminants (metals, organotins, PAHs, PCBs) was
carried out along the Milford Haven Waterway (MHW) and at a reference site in the
Tywi Estuary during 2007-2008. The species used as bioindicators encompass a
variety of uptake routes - Fucus vesiculosus (dissolved contaminants); Littorina
littorea (grazer); Mytilus edulis and Cerastoderma edule (suspension feeders); and
Nereis diversicolor (omnivore which often reflects contaminants in sediment).
Differences in feeding strategy and habitat preference have subtle implications for
bioaccumulation trends though, with few exceptions, contaminant body burdens in
Milford Haven (MH) were higher than those at the Tywi reference site, reflecting
inputs.
Elevated concentrations of metals were occasionally observed at individual MH sites,
whilst As and Se (molluscs and seaweed) were, for much of MHW, consistently at the
higher end of the UK range. However, for the majority of metals, distributions in MH
biota were not exceptional by UK standards. Several metal-species combinations
indicated increases in bioavailability at upstream sites, which may reflect the
influence of geogenic or other land-based sources – perhaps enhanced by lower
salinity (greater proportions of more bioavailable forms).
TBT levels in MH mussels were below OSPAR toxicity thresholds and in the Tywi
were close to zero. Phenyltins were not accumulated appreciably in Mytilus, whereas
some Nereis populations may have been subjected to localized (historical) sources.
PAHs in Nereis tended to be evenly distributed across most sites, but with somewhat
higher values at Dale for acenaphthene, fluoranthene, pyrene, benzo(a)anthracene and
chrysene; naphthalenes tended to be enriched further upstream in the mid-upper
Haven (a pattern seen in mussels for most PAHs). Whilst concentrations in MH
mussels were mostly above reference site and OSPAR backgrounds, it is unlikely that
ecotoxicological guidelines would be exceeded.
PCBs in mussels were between upper and lower OSPAR guidelines and were unusual
in their distribution in that highest levels occurred at the mouth of MH.
Condition indices (CI) of bivalves (mussels and cockles) were highest at the Tywi
reference site and at the seaward end of MH, decreasing upstream along the
Waterway. There were a number of significant (negative) relationships between CI
and body burdens and multivariate analysis indicated that a combination of
contaminants could influence the pattern in condition (and sub-lethal responses such
as MT and TOSC) across sites. Cause and effect needs to be tested more rigorously in
future assessments
Novel soft-feedback equalisation method for multilevel magnetic recording
This paper investigates the use of multilevel modulation for magnetic recording using a novel soft-feedback equalization (SFE) approach. Different aspects of investigation are 1)multilevel recording, 2) SFE, and 3) application of turbo codes. The SFE scheme is a model in which the partial response (PR) equalizer and maximum a posteriori (MAP) decoder are replaced by a linear filter with an iterative MAP decoder. Error correction codes (ECCs) are applied to the multilevel recording system in order to achieve very low error rates. Implementation of the SFE scheme for multilevel recording shows a reduction in complexity in comparison to various PRML schemes. The simulation results show a clear performance gain of multi-level-coded against binary-coded recording systems. At higher signal-to-noise ratio (SNR), the coded multilevel SFE scheme overcomes the error floor effect produced in the coded multilevel PRML scheme, which is caused by minimum distance error events. Overall, this paper proposes the use of coded multilevel recording with SFE scheme at lower rates rather than coded binary recording at higher densities in order to achieve similar performanc
Novel multi-level magnetic recording using modern error correction.
It has been shown that multilevel techniques operate closer to the channel capacity than binary for a bandwidth
limited channel experiencing Additive White Gaussian Noise (AWGN) at increased Signal to Noise Ratio (SNR)
[1]. Previous work[2] suggested that multi-level techniques, offered little, if any improvement of the magnetic recording capacity compared to the binary(two-level) system, and is eventually limited by amplitude irregularities in the magnetic channel. This paper looks at a new approach of applying powerful Error Correction Codes
(ECC) on the multi-level magnetic recording channel and investigating the improvement in the performance.
The main idea behind multilevel recording is to enable storing of more information bits per transition on
the magnetic medium. Several magnetisation levels could be used with the multi-level channel. It is known that at higher code rates for AWGN channels, binary codes tend to deviate very quickly from their theoretical performance[1]. In order to achieve very low error-rates at a particular SNR, it is necessary to use state of the art ECC like Turbo Codes. This paper examines the use of multilevel data in conjunction with Turbo codes, for a high density magnetic recording channel, to achieve increased channel capacity for a particular SNR in the operating region of the magnetic recording devices
A feasibility study of signed consent for the collection of patient identifiable information for a national paediatric clinical audit database
Objectives: To investigate the feasibility of obtaining signed consent
for submission of patient identifiable data to a national clinical
audit database and to identify factors influencing the consent process
and its success.
Design: Feasibility study.
Setting: Seven paediatric intensive care units in England.
Participants: Parents/guardians of patients, or patients aged 12-16
years old, approached consecutively over three months for signed
consent for submission of patient identifiable data to the national
clinical audit database the Paediatric Intensive Care Audit Network
(PICANet).
Main outcome measures: The numbers and proportions of admissions for
which signed consent was given, refused, or not obtained (form not
returned or form partially completed but not signed), by age, sex,
level of deprivation, ethnicity (South Asian or not), paediatric index
of mortality score, length of hospital stay (days in paediatric
intensive care).
Results: One unit did not start and one did not fully implement the
protocol, so analysis excluded these two units. Consent was obtained
for 182 of 422 admissions (43%) (range by unit 9% to 84%). Most
(101/182; 55%) consents were taken by staff nurses. One refusal (0.2%)
was received. Consent rates were significantly better for children who
were more severely ill on admission and for hospital stays of six days
or more, and significantly poorer for children aged 10-14 years. Long
hospital stays and children aged 10-14 years remained significant in a
stepwise regression model of the factors that were significant in the
univariate model.
Conclusion: Systematically obtaining individual signed consent for
sharing patient identifiable information with an externally located
clinical audit database is difficult. Obtaining such consent is
unlikely to be successful unless additional resources are specifically
allocated to training, staff time, and administrative support
Extension in the western Ross Sea region-links between Adare Basin and Victoria Land Basin
Spreading in the Adare Basin off north-western Ross Sea (43–26 Ma) and extension in the Victoria Land Basin (VLB, > 36 Ma) are used to constrain the pole of rotation for the Adare Basin, providing a rifting model for the region for the past 45 Ma. The offset from Northern Basin to VLB at about 74°S coincides with the linear Polar-3 magnetic anomaly, inferred to be caused by a major 48 - 34 Ma igneous intrusion. The style of extension apparently changed at about 34 Ma, with the end of intrusion at the Polar-3 anomaly, a change from highly asymmetric extension in Adare Basin, and the onset of major subsidence on the flanks of VLB. Ductile lower crustal and lithospheric flow is proposed as the cause of the inferred thick crust underlying southern Adare Basin, and a result of the constraining of extension to the adjacent contiguous Northern Basin
Are "EIT Waves" Fast-Mode MHD Waves?
We examine the nature of large-scale, coronal, propagating wave fronts (``EIT
waves'') and find they are incongruous with solutions using fast-mode MHD
plane-wave theory. Specifically, we consider the following properties:
non-dispersive single pulse manifestions, observed velocities below the local
Alfven speed, and different pulses which travel at any number of constant
velocities, rather than at the ``predicted'' fast-mode speed. We discuss the
possibility of a soliton-like explanation for these phenomena, and show how it
is consistent with the above-mentioned aspects.Comment: to be published in the Astrophysical Journa
Podoconiosis in East and West Gojam Zones, Northern Ethiopia
Background: Podoconiosis is a neglected tropical disease (NTD) that is prevalent in red clay soil-covered highlands of tropical Africa, Central and South America, and northern India. It is estimated that up to one million cases exist in Ethiopia. This study aimed to estimate the prevalence of podoconiosis in East and West Gojam Zones of Amhara Region in northern Ethiopia. Methodology/Principal Findings: A cross-sectional household survey was conducted in Debre Eliyas and Dembecha woredas (districts) in East and West Gojam Zones, respectively. The survey covered all 17,553 households in 20 kebeles (administrative subunits) randomly selected from the two woredas. A detailed structured interview was conducted on 1,704 cases of podoconiosis identified in the survey. Results: The prevalence of podoconiosis in the population aged 15 years and above was found to be 3.3% (95% CI, 3.2% to 3.6%). 87% of cases were in the economically active age group (15–64 years). On average, patients sought treatment five years after the start of the leg swelling. Most subjects had second (42.7%) or third (36.1%) clinical stage disease, 97.9% had mossy lesions, and 53% had open wounds. On average, patients had five episodes of acute adenolymphangitis (ALA) per year and spent a total of 90 days per year with ALA. The median age of first use of shoes and socks were 22 and 23 years, respectively. More men than women owned more than one pair of shoes (61.1% vs. 50.5%; x2 = 11.6 p = 0.001). At the time of interview, 23.6% of the respondents were barefoot, of whom about two-thirds were women. Conclusions: This study showed high prevalence of podoconiosis and associated morbidities such as ALA, mossy lesions and open wounds in northern Ethiopia. Predominance of cases at early clinical stage of podoconiosis indicates the potential for reversing the swelling and calls for disease prevention interventions
Particle abundance in a thermal plasma: quantum kinetics vs. Boltzmann equation
We study the abundance of a particle species in a thermalized plasma by
introducing a quantum kinetic description based on the non-equilibrium
effective action. A stochastic interpretation of quantum kinetics in terms of a
Langevin equation emerges naturally. We consider a particle species that is
stable in the vacuum and interacts with \emph{heavier} particles that
constitute a thermal bath in equilibrium and define of a fully renormalized
single particle distribution function. The distribution function thermalizes on
a time scale determined by the \emph{quasiparticle} relaxation rate. The
equilibrium distribution function depends on the full spectral density and
features off-shell contributions to the particle abundance. A model of a
bosonic field in interaction with two \emph{heavier} bosonic fields is
studied. We find substantial departures from the Bose-Einstein result both in
the high temperature and the low temperature but high momentum region. In the
latter the abundance is exponentially suppressed but larger than the
Bose-Einstein result. We obtain the Boltzmann equation in renormalized
perturbation theory and highlight the origin of the differences. We argue that
the corrections to the abundance of cold dark matter candidates are
observationally negligible and that recombination erases any possible spectral
distortions of the CMB. However we expect that the enhancement at high
temperature may be important for baryogenesis.Comment: 39 pages, 11 figures. Clarifying remarks. To appear in Physical
Review
- …