2,991 research outputs found
Three-dimensional non-LTE radiative transfer computation of the Ca 8542 infrared line from a radiation-MHD simulation
Interpretation of imagery of the solar chromosphere in the widely used
\CaIIIR infrared line is hampered by its complex, three-dimensional and non-LTE
formation. Forward modelling is required to aid understanding. We use a 3D
non-LTE radiative transfer code to compute synthetic \CaIIIR images from a
radiation-MHD simulation of the solar atmosphere spanning from the convection
zone to the corona. We compare the simulation with observations obtained with
the CRISP filter at the Swedish 1--m Solar Telescope. We find that the
simulation reproduces dark patches in the blue line wing caused by Doppler
shifts, brightenings in the line core caused by upward-propagating shocks and
thin dark elongated structures in the line core that form the interface between
upward and downward gas motion in the chromosphere. The synthetic line core is
narrower than the observed one, indicating that the sun exhibits both more
vigorous large-scale dynamics as well as small scale motions that are not
resolved within the simulation, presumably owing to a lack of spatial
resolution.Comment: accepted as ApJ lette
Three Li-rich K giants: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952
We report on spectroscopic analyses of three K giants previously suggested to
be Li-rich: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952.
High-resolution optical spectra and the LTE model atmospheres are used to
derive the stellar parameters: (, log , [Fe/H]), elemental
abundances, and the isotopic ratio C/C. IRAS 13539-4153 shows an
extremely high Li abundance of (Li) 4.2, a value ten
times more than the present Li abundance in the local interstellar medium. This
is the third highest Li abundance yet reported for a K giant. IRAS 12327-6523
shows a Li abundances of (Li) 1.4. IRAS 17596-3952 is a
rapidly rotating ( 35 km s) K giant with
(Li) 2.2. Infrared photometry which shows the presence
of an IR excess suggesting mass-loss. A comparison is made between these three
stars and previously recognized Li-rich giants.Comment: 17 pages, 6 figures, accepted for A
Wave Propagation and Jet Formation in the Chromosphere
We present the results of numerical simulations of wave propagation and jet
formation in solar atmosphere models with different magnetic field
configurations. The presence in the chromosphere of waves with periods longer
than the acoustic cutoff period has been ascribed to either strong inclined
magnetic fields, or changes in the radiative relaxation time. Our simulations
include a sophisticated treatment of radiative losses, as well as fields with
different strengths and inclinations. Using Fourier and wavelet analysis
techniques, we investigate the periodicity of the waves that travel through the
chromosphere. We find that the velocity signal is dominated by waves with
periods around 5 minutes in regions of strong, inclined field, including at the
edges of strong flux tubes where the field expands, whereas 3-minute waves
dominate in regions of weak or vertically oriented fields. Our results show
that the field inclination is very important for long-period wave propagation,
whereas variations in the radiative relaxation time have little effect.
Furthermore, we find that atmospheric conditions can vary significantly on
timescales of a few minutes, meaning that a Fourier analysis of wave
propagation can be misleading. Wavelet techniques take variations with time
into account and are more suitable analysis tools. Finally, we investigate the
properties of jets formed by the propagating waves once they reach the
transition region, and find systematic differences between the jets in inclined
field regions and those in vertical field regions, in agreement with
observations of dynamic fibrils.Comment: 27 pages, 29 figures; accepted for publication in Astrophysical
Journa
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Review: Consumption-stage food waste reduction interventions - What works and how to design better interventions
Food waste prevention has become an issue of international concern, with Sustainable Development Goal 12.3 aiming to halve per capita global food waste at the retail and consumer levels by 2030. However there is no review that has considered the effectiveness of interventions aimed at preventing food waste in the consumption stages of the food system. This significant gap, if filled, could help support those working to reduce food waste in the developed world, providing knowledge of what interventions are specifically effective at preventing food waste.
This paper fills this gap, identifying and summarizing food-waste prevention interventions at the consumption/consumer stage of the supply chain via a rapid review of global academic literature from 2006 to 2017.
We identify 17 applied interventions that claim to have achieved food waste reductions. Of these, 13 quantified food waste reductions. Interventions that changed the size or type of plates were shown to be effective (up to 57% food waste reduction) in hospitality environments. Changing nutritional guidelines in schools were reported to reduce vegetable waste by up to 28%, indicating that healthy diets can be part of food waste reduction strategies. Information campaigns were also shown to be effective with up to 28% food waste reduction in a small sample size intervention.
Cooking classes, fridge cameras, food sharing apps, advertising and information sharing were all reported as being effective but with little or no robust evidence provided. This is worrying as all these methods are now being proposed as approaches to reduce food waste and, except for a few studies, there is no reproducible quantified evidence to assure credibility or success. To strengthen current results, a greater number of longitudinal and larger sample size intervention studies are required. To inform future intervention studies, this paper proposes a standardised guideline, which consists of: (1) intervention design; (2) monitoring and measurement; (3) moderation and mediation; (4) reporting; (5) systemic effects.
Given the importance of food-waste reduction, the findings of this review highlight a significant evidence gap, meaning that it is difficult to make evidence-based decisions to prevent or reduce consumption-stage food waste in a cost-effective manner
Accelerated particle beams in a 3D simulation of the quiet Sun. Lower atmospheric spectral diagnostics
Nanoflare heating through small-scale magnetic reconnection events is one of
the prime candidates to explain heating of the solar corona. However, direct
signatures of nanoflares are difficult to determine, and unambiguous
observational evidence is still lacking. Numerical models that include
accelerated electrons and can reproduce flaring conditions are essential in
understanding how low-energetic events act as a heating mechanism of the
corona, and how such events are able to produce signatures in the spectral
lines that can be detected through observations. We investigate the effects of
accelerated electrons in synthetic spectra from a 3D radiative
magnetohydrodynamics simulation to better understand small-scale heating events
and their impact on the solar atmosphere. We synthesised the chromospheric Ca
II and Mg II lines and the transition region Si IV resonance lines from a quiet
Sun numerical simulation that includes accelerated electrons. We calculated the
contribution function to the intensity to better understand how the lines are
formed, and what factors are contributing to the detailed shape of the spectral
profiles. The synthetic spectra are highly affected by variations in
temperature and vertical velocity. Beam heating exceeds conductive heating at
the heights where the spectral lines form, indicating that the electrons should
contribute to the heating of the lower atmosphere and hence affect the line
profiles. However, we find that it is difficult to determine specific
signatures from the non-thermal electrons due to the complexity of the
atmospheric response to the heating in combination with the relatively low
energy output (~1e21 erg/s). Even so, our results contribute to understanding
small-scale heating events in the solar atmosphere, and give further guidance
to future observations
Bombs and flares at the surface and lower atmosphere of the Sun
This research was supported by the Research Council of Norway and by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007â2013)/ERC Grant agreement no. 291058.A spectacular manifestation of solar activity is the appearance of transient brightenings in the far wings of the Hα line, known as Ellerman bombs (EBs). Recent observations obtained by the Interface Region Imaging Spectrograph have revealed another type of plasma "bombs" (UV bursts) with high temperatures of perhaps up to 8 Ă 104 K within the cooler lower solar atmosphere. Realistic numerical modeling showing such events is needed to explain their nature. Here, we report on 3D radiative magnetohydrodynamic simulations of magnetic flux emergence in the solar atmosphere. We find that ubiquitous reconnection between emerging bipolar magnetic fields can trigger EBs in the photosphere, UV bursts in the mid/low chromosphere and small (nano-/micro-) flares (106 K) in the upper chromosphere. These results provide new insights into the emergence and build up of the coronal magnetic field and the dynamics and heating of the solar surface and lower atmosphere.Publisher PDFPeer reviewe
Chromospheric emission from nanoflare heating in RADYN simulations
Heating signatures from small-scale magnetic reconnection events in the solar
atmosphere have proven to be difficult to detect through observations.
Numerical models that reproduce flaring conditions are essential in the
understanding of how nanoflares may act as a heating mechanism of the corona.
We study the effects of non-thermal electrons in synthetic spectra from 1D
hydrodynamic RADYN simulations of nanoflare heated loops to investigate the
diagnostic potential of chromospheric emission from small-scale events. The Mg
II h and k, Ca II H and K, Ca II 854.2 nm, H-alpha and H-beta chromospheric
lines were synthesised from various RADYN models of coronal loops subject to
electron beams of nanoflare energies. The contribution function to the line
intensity was computed to better understand how the atmospheric response to the
non-thermal electrons affects the formation of spectral lines and the detailed
shape of their spectral profiles. The spectral line signatures arising from the
electron beams highly depend on the density of the loop and the lower cutoff
energy of the electrons. Low-energy (5 keV) electrons deposit their energy in
the corona and transition region, producing strong plasma flows that cause both
redshifts and blueshifts of the chromospheric spectra. Higher-energy (10 and 15
keV) electrons deposit their energy in the lower transition region and
chromosphere, resulting in increased emission from local heating. Our results
indicate that effects from small-scale events can be observed with ground-based
telescopes, expanding the list of possible diagnostics for the presence and
properties of nanoflares
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