2,519 research outputs found
Data-Optimized Coronal Field Model: I. Proof of Concept
Deriving the strength and direction of the three-dimensional (3D) magnetic
field in the solar atmosphere is fundamental for understanding its dynamics.
Volume information on the magnetic field mostly relies on coupling 3D
reconstruction methods with photospheric and/or chromospheric surface vector
magnetic fields. Infrared coronal polarimetry could provide additional
information to better constrain magnetic field reconstructions. However,
combining such data with reconstruction methods is challenging, e.g., because
of the optical-thinness of the solar corona and the lack and limitations of
stereoscopic polarimetry. To address these issues, we introduce the
Data-Optimized Coronal Field Model (DOCFM) framework, a model-data fitting
approach that combines a parametrized 3D generative model, e.g., a magnetic
field extrapolation or a magnetohydrodynamic model, with forward modeling of
coronal data. We test it with a parametrized flux rope insertion method and
infrared coronal polarimetry where synthetic observations are created from a
known "ground truth" physical state. We show that this framework allows us to
accurately retrieve the ground truth 3D magnetic field of a set of force-free
field solutions from the flux rope insertion method. In observational studies,
the DOCFM will provide a means to force the solutions derived with different
reconstruction methods to satisfy additional, common, coronal constraints. The
DOCFM framework therefore opens new perspectives for the exploitation of
coronal polarimetry in magnetic field reconstructions and for developing new
techniques to more reliably infer the 3D magnetic fields that trigger solar
flares and coronal mass ejections.Comment: 14 pages, 6 figures; Accepted for publication in Ap
Contemplative Science: An Insider's Prospectus
This chapter describes the potential far‐reaching consequences of contemplative higher education for the fields of science and medicine
Tailoring ergodicity through selective A-site doping in the Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3 system
The morphotropic phase boundary composition Bi1/2Na1/2TiO3-20 mol. % Bi1/2K1/2TiO3 was chosen as initial material to do selective A-site aliovalent doping replacing Na and K by 1 at. % La, respectively. The materials were studied macroscopically by measuring dielectric and electromechanical properties. The Na-replaced material has a lower freezing temperature Tfr, lower remanent polarization and remanent strain, and thus a higher degree of ergodicity than the K-replaced material. These results are contrasted with local poling experiments and hysteresis loops obtained from piezoresponse force microscopy. The faster relaxation of the tip-induced local polarization and the lower remanent state in bias-on and-off loops confirm the higher degree of ergodicity of the Na-replaced material. The difference in functional properties is attributed to small variations in chemical pressure achieved through selective doping. Raman results support this working hypothesis. ??? 2015 AIP Publishing LLCopen1
High-resolution Observations of the Shock Wave Behavior for Sunspot Oscillations with the Interface Region Imaging Spectrograph
We present the first results of sunspot oscillations from observations by the
Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is
identified in both the slit-jaw images and the spectra of several emission
lines formed in the transition region and chromosphere. We first apply a single
Gaussian fit to the profiles of the Mgii 2796.35 {\AA}, Cii 1335.71 {\AA}, and
Si iv 1393.76 {\AA} lines in the sunspot. The intensity change is about 30%.
The Doppler shift oscillation reveals a sawtooth pattern with an amplitude of
about 10 km/s in Si iv. In the umbra the Si iv oscillation lags those of Cii
and Mgii by about 3 and 12 s, respectively. The line width suddenly increases
as the Doppler shift changes from redshift to blueshift. However, we
demonstrate that this increase is caused by the superposition of two emission
components. We then perform detailed analysis of the line profiles at a few
selected locations on the slit. The temporal evolution of the line core is
dominated by the following behavior: a rapid excursion to the blue side,
accompanied by an intensity increase, followed by a linear decrease of the
velocity to the red side. The maximum intensity slightly lags the maximum
blueshift in Si iv, whereas the intensity enhancement slightly precedes the
maximum blueshift in Mgii. We find a positive correlation between the maximum
velocity and deceleration, a result that is consistent with numerical
simulations of upward propagating magnetoacoustic shock waves.Comment: 5 figures, in ApJ. Correction of time lags (correct values are 3 and
12s) made on June 17 201
Prevalence of Small-scale Jets from the Networks of the Solar Transition Region and Chromosphere
As the interface between the Sun's photosphere and corona, the chromosphere
and transition region play a key role in the formation and acceleration of the
solar wind. Observations from the Interface Region Imaging Spectrograph reveal
the prevalence of intermittent small-scale jets with speeds of 80-250 km/s from
the narrow bright network lanes of this interface region. These jets have
lifetimes of 20-80 seconds and widths of 300 km or less. They originate from
small-scale bright regions, often preceded by footpoint brightenings and
accompanied by transverse waves with ~20 km/s amplitudes. Many jets reach
temperatures of at least ~100000 K and constitute an important element of the
transition region structures. They are likely an intermittent but persistent
source of mass and energy for the solar wind.Comment: Figs 1-4 & S1-S5; Movies S1-S8; published in Science, including the
main text and supplementary materials. Reference: H. Tian, E. E. DeLuca, S.
R. Cranmer, et al., Science 346, 1255711 (2014
The Interface Region Imaging Spectrograph (IRIS)
The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft
provides simultaneous spectra and images of the photosphere, chromosphere,
transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s
temporal resolution and 1 km/s velocity resolution over a field-of-view of up
to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on
27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope
that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains
spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom including
bright spectral lines formed in the chromosphere (Mg II h 2803 Angstrom and Mg
II k 2796 Angstrom) and transition region (C II 1334/1335 Angstrom and Si IV
1394/1403 Angstrom). Slit-jaw images in four different passbands (C II 1330, Si
IV 1400, Mg II k 2796 and Mg II wing 2830 Angstrom) can be taken simultaneously
with spectral rasters that sample regions up to 130 arcsec x 175 arcsec at a
variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will advance
our understanding of the flow of mass and energy through an interface region,
formed by the chromosphere and transition region, between the photosphere and
corona. This highly structured and dynamic region not only acts as the conduit
of all mass and energy feeding into the corona and solar wind, it also requires
an order of magnitude more energy to heat than the corona and solar wind
combined. The IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data (after
compression) are acquired by IRIS each day and made available for unrestricted
use within a few days of the observation.Comment: 53 pages, 15 figure
Screening and brief interventions for hazardous and harmful alcohol use in primary care: a cluster randomised controlled trial protocol
A large number of randomised controlled trials in health settings have consistently reported positive effects of brief intervention in terms of reductions in alcohol use. However,although alcohol misuse is common amongst offenders, there is limited evidence of alcohol brief interventions in the criminal justice field. This factorial pragmatic cluster randomised controlledtrial with Offender Managers (OMs) as the unit of randomisation will evaluate the effectiveness and cost-effectiveness of different models of screening to identify hazardous and harmful drinkers in probation and different intensities of brief intervention to reduce excessive drinking in probation clients.
Ninety-six OMs from 9 probation areas across 3 English regions (the NorthEast Region (n = 4) and London and the South East Regions (n = 5)) will be recruited. OMs will berandomly allocated to one of three intervention conditions: a client information leaflet control condition (n = 32 OMs); 5-minute simple structured advice (n = 32 OMs) and 20-minute brieflifestyle counselling delivered by an Alcohol Health Worker (n = 32 OMs). Randomisation will be stratified by probation area. To test the relative effectiveness of different screening methods all OMs will be randomised to either the Modified Single Item Screening Questionnaire (M-SASQ) orthe Fast Alcohol Screening Test (FAST). There will be a minimum of 480 clients recruited into the trial. There will be an intention to treat analysis of study outcomes at 6 and 12 months postintervention. Analysis will include client measures (screening result, weekly alcohol consumption,alcohol-related problems, re-offending, public service use and quality of life) and implementation measures from OMs (the extent of screening and brief intervention beyond the minimum recruitment threshold will provide data on acceptability and feasibility of different models of brief intervention). We will also examine the practitioner and organisational factors associated with successful implementation.The trial will evaluate the impact of screening and brief alcohol intervention in routine probation work and therefore its findings will be highly relevant to probation teams and thus the criminal justice system in the UK
On the Origin of Cosmic Magnetic Fields
We review the literature concerning how the cosmic magnetic fields pervading
nearly all galaxies actually got started. some observational evidence involves
the chemical abundance of the light elements Be and B, while another one is
based on strong magnetic fields seen in high red shift galaxies. Seed fields,
whose strength is of order 10^{-20} gauss, easily sprung up in the era
preceding galaxy formation. Several mechanisms are proposed to amplify these
seed fields to microgauss strengths. The standard mechanism is the Alpha-Omega
dynamo theory. It has a major difficulty that makes unlikely to provide the
sole origin. The difficulty is rooted in the fact that the total flux is
constant. This implies that flux must be removed from the galactic discs. This
requires that the field and flux be separated, for otherwise interstellar mass
must be removed from the deep galactic gravitational and then their strength
increased by the alpha omega theory.Comment: 90 pages and 6 figures; accepted for publication in Reports of
Progress in Physics as an invited revie
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