1,146 research outputs found
A qualitative study of mothers’ perceptions of weaning and the use of commercial infant food in the United Kingdom
Background: Commercially produced infant food has a different taste profile and nutritional content to homemade baby food and its consumption is now very widespread. This change in early food experience may lead to a reduced dietary variety and a decreased microbial load exposure.Objective: The purpose of this study was to gain insight into parental perceptions of complementary feeding, specifically opinions of commercially produced baby food, using qualitative research methods. Methods: Four focus group discussions took place (n = 24), with mothers of infants aged 4-7 months. Half of participants were first time mothers and a third had experience weaning infants with symptoms of cows' milk allergy. Participants were prompted with questions about complementary feeding and shown several different products to stimulate discussion. Results: Thematic analysis of focus groups indicated that three distinctive groups of mothers exis
Statistics of counter-streaming solar wind suprathermal electrons at solar minimum : STEREO observations
Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March–December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15–20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs
Forecasting Periods of Strong Southward Magnetic Field Following Interplanetary Shocks
Long periods of strong southward magnetic fields are known to be the primary
cause of intense geomagnetic storms. The majority of such events are caused by
the passage over Earth of a magnetic ejecta. Irrespective of the interplanetary
cause, fast-forward shocks often precede such strong southward B periods.
Here, we first look at all long periods of strong southward magnetic fields as
well as fast-forward shocks measured by the \textit{Wind} spacecraft in a
22.4-year span. We find that 76{\%} of strong southward B periods are
preceded within 48 hours by at least a fast-forward shock but only about 23{\%}
of all shocks are followed within 48 hours by strong southward B periods.
Then, we devise a threshold-based probabilistic forecasting method based on the
shock properties and the pre-shock near-Earth solar wind plasma and
interplanetary magnetic field characteristics adopting a `superposed epoch
analysis'-like approach. Our analysis shows that the solar wind conditions in
the 30 minutes interval around the arrival of fast-forward shocks have a
significant contribution to the prediction of long-duration southward B
periods. This probabilistic model may provide on average a 14-hour warning time
for an intense and long-duration southward B period. Evaluating the
forecast capability of the model through a statistical and skill score-based
approach reveals that it outperforms a coin-flipping forecast. By using the
information provided by the arrival of a fast-forward shock at L1, this model
represents a marked improvement over similar forecasting methods. We outline a
number of future potential improvements.Comment: published in Space Weather, 22 Nov 201
Connecting speeds, directions and arrival times of 22 coronal mass ejections from the Sun to 1 AU
Forecasting the in situ properties of coronal mass ejections (CMEs) from
remote images is expected to strongly enhance predictions of space weather, and
is of general interest for studying the interaction of CMEs with planetary
environments. We study the feasibility of using a single heliospheric imager
(HI) instrument, imaging the solar wind density from the Sun to 1 AU, for
connecting remote images to in situ observations of CMEs. We compare the
predictions of speed and arrival time for 22 CMEs (in 2008-2012) to the
corresponding interplanetary coronal mass ejection (ICME) parameters at in situ
observatories (STEREO PLASTIC/IMPACT, Wind SWE/MFI). The list consists of
front- and backsided, slow and fast CMEs (up to ). We
track the CMEs to degrees elongation from the Sun with J-maps
constructed using the SATPLOT tool, resulting in prediction lead times of
hours. The geometrical models we use assume different CME
front shapes (Fixed-, Harmonic Mean, Self-Similar Expansion), and
constant CME speed and direction. We find no significant superiority in the
predictive capability of any of the three methods. The absolute difference
between predicted and observed ICME arrival times is hours (
value of 10.9h). Speeds are consistent to within .
Empirical corrections to the predictions enhance their performance for the
arrival times to hours ( value of 7.9h), and for the speeds
to . These results are important for Solar Orbiter
and a space weather mission positioned away from the Sun-Earth line.Comment: 19 pages, 13 figures, accepted for publication in the Astrophysical
Journa
STEREO and Wind observations of a fast ICME flank triggering a prolonged geomagnetic storm on 5-7 April 2010
On 5 April 2010 an interplanetary (IP) shock was detected by the Wind
spacecraft ahead of Earth, followed by a fast (average speed 650 km/s) IP
coronal mass ejection (ICME). During the subsequent moderate geomagnetic storm
(minimum Dst = -72 nT, maximum Kp=8-), communication with the Galaxy 15
satellite was lost. We link images from STEREO/SECCHI to the near-Earth in situ
observations and show that the ICME did not decelerate much between Sun and
Earth. The ICME flank was responsible for a long storm growth phase. This type
of glancing collision was for the first time directly observed with the STEREO
Heliospheric Imagers. The magnetic cloud (MC) inside the ICME cannot be modeled
with approaches assuming an invariant direction. These observations confirm the
hypotheses that parts of ICMEs classified as (1) long-duration MCs or (2)
magnetic-cloud-like (MCL) structures can be a consequence of a spacecraft
trajectory through the ICME flank.Comment: Geophysical Research Letters (accepted); 3 Figure
On the Spatial Coherence of Magnetic Ejecta: Measurements of Coronal Mass Ejections by Multiple Spacecraft Longitudinally Separated by 0.01 AU
Measurements of coronal mass ejections (CMEs) by multiple spacecraft at small
radial separations but larger longitudinal separations is one of the ways to
learn about the three-dimensional structure of CMEs. Here, we take advantage of
the orbit of the Wind spacecraft that ventured to distances of up to 0.012
astronomical units (au) from the Sun-Earth line during the years 2000 to 2002.
Combined with measurements from ACE, which is in a tight halo orbit around L1,
the multipoint measurements allow us to investigate how the magnetic field
inside magnetic ejecta (MEs) changes on scales of 0.005 - 0.012 au. We identify
21 CMEs measured by these two spacecraft for longitudinal separations of 0.007
au or more. We find that the time-shifted correlation between 30-minute
averages of the non-radial magnetic field components measured at the two
spacecraft is systematically above 0.97 when the separation is 0.008 au or
less, but is on average 0.89 for greater separations. Overall, these newly
analyzed measurements, combined with 14 additional ones when the spacecraft
separation is smaller, point towards a scale length of longitudinal magnetic
coherence inside MEs of 0.25 - 0.35 au for the magnitude of the magnetic field
but 0.06 - 0.12 au for the magnetic field components. This finding raises
questions about the very nature of MEs. It also highlights the need for
additional "mesoscale" multi-point measurements of CMEs with longitudinal
separations of 0.01 - 0.2 au.Comment: Published in ApJL, 6 page
Synthesis and microstructural evolution in ternary metalloceramic Ti3SiC2 consolidated via the Maxthal 312 powder route
A bulk specimen containing Ti3SiC2, TiSi2 and TiC was prepared through an in situ spark plasma sintering/solid-liquid reaction powder metallurgy method using the Maxthal 312 (nominally-Ti3SiC2) powder as a starting material. The reaction mechanism, phase constituents and evolution of the microstructure were systematically investigated by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) system, transmission electron microscopy (TEM), Raman spectroscopy, differential scanning calorimetry (DSC) and Vickers microhardness testing. Phase analysis and microstructural characterization revealed that the bulk sample contained binary ancillary phases, possibly due to Si evaporation and/or carburization. The deformed microstructure around the indents revealed evidence of plasticity, intrinsic lubricity and toughening. The Microstructural and orientation relationships between the phases contained in the bulk sample are reported
The POlarised GLEAM Survey (POGS) II: Results from an All-Sky Rotation Measure Synthesis Survey at Long Wavelengths
The low-frequency linearly-polarised radio source population is largely
unexplored. However, a renaissance in low-frequency polarimetry has been
enabled by pathfinder and precursor instruments for the Square Kilometre Array.
In this second paper from the POlarised GaLactic and Extragalactic All-Sky
Murchison Widefield Array (MWA) Survey -- the POlarised GLEAM Survey, or POGS
-- we present the results from our all-sky MWA Phase I Faraday Rotation Measure
survey. Our survey covers nearly the entire Southern sky in the Declination
range to at a resolution between around three and
seven arcminutes (depending on Declination) using data in the frequency range
169231 MHz. We have performed two targeted searches: the first covering
25,489 square degrees of sky, searching for extragalactic polarised sources;
the second covering the entire sky South of Declination ,
searching for known pulsars. We detect a total of 517 sources with 200 MHz
linearly-polarised flux densities between 9.9 mJy and 1.7 Jy, of which 33 are
known radio pulsars. All sources in our catalogues have Faraday rotation
measures in the range rad m to rad m. The
Faraday rotation measures are broadly consistent with results from
higher-frequency surveys, but with typically more than an order of magnitude
improvement in the precision, highlighting the power of low-frequency
polarisation surveys to accurately study Galactic and extragalactic magnetic
fields. We discuss the properties of our extragalactic and known-pulsar source
population, how the sky distribution relates to Galactic features, and identify
a handful of new pulsar candidates among our nominally extragalactic source
population.Comment: Replacement of previous version. Only change is minor updates to
catalogues (see ancillary files) which now contain bib code of finalised
manuscript (published in PASA). Manuscript has 31 pages, 10 figures, 5
tables. Four Appendices are included in the ancillary material, showing
further Figures, continuum spectra for a handful of selected sources, and RM
spectra for all 517 source
The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths
The low-frequency linearly polarised radio source population is largely unexplored. However, a renaissance in low-frequency polarimetry has been enabled by pathfinder and precursor instruments for the Square Kilometre Array. In this second paper from the POlarised GaLactic and Extragalactic All-Sky MWA Survey-the POlarised GLEAM Survey, or POGS-we present the results from our all-sky MWA Phase I Faraday Rotation Measure survey. Our survey covers nearly the entire Southern sky in the Declination range to at a resolution between around three and seven arcminutes (depending on Declination) using data in the frequency range 169-231 MHz. We have performed two targeted searches: the first covering 25 489 square degrees of sky, searching for extragalactic polarised sources; the second covering the entire sky South of Declination, searching for known pulsars. We detect a total of 517 sources with 200 MHz linearly polarised flux densities between 9.9 mJy and 1.7 Jy, of which 33 are known radio pulsars. All sources in our catalogues have Faraday rotation measures in the range to rad m-2. The Faraday rotation measures are broadly consistent with results from higher-frequency surveys, but with typically more than an order of magnitude improvement in the precision, highlighting the power of low-frequency polarisation surveys to accurately study Galactic and extragalactic magnetic fields. We discuss the properties of our extragalactic and known-pulsar source population, how the sky distribution relates to Galactic features, and identify a handful of new pulsar candidates among our nominally extragalactic source population
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