46 research outputs found
Spectropolarimetric NLTE inversion code SNAPI
Inversion codes are computer programs that fit a model atmosphere to the
observed Stokes spectra, thus retrieving the relevant atmospheric parameters.
The rising interest in the solar chromosphere, where spectral lines are formed
by scattering, requires developing, testing, and comparing new non-local
thermal equilibrium (NLTE) inversion codes.
We present a new NLTE inversion code that is based on the analytical
computation of the response functions. We named the code SNAPI, which is short
for spectropolarimetic NLTE analytically powered inversion. SNAPI inverts full
Stokes spectrum in order to obtain a depth-dependent stratification of the
temperature, velocity, and the magnetic field vector. It is based on the
so-called node approach, where atmospheric parameters are free to vary in
several fixed points in the atmosphere, and are assumed to behave as splines in
between. We describe the inversion approach in general and the specific choices
we have made in the implementation. We test the performance on one academic
problem and on two interesting NLTE examples, the Ca\,II\,8542 and Na\,I\,D
spectral lines. The code is found to have excellent convergence properties and
outperforms a finite-difference based code in this specific implementation by
at least a factor of three. We invert synthetic observations of Na lines from a
small part of a simulated solar atmosphere and conclude that the Na lines
reliably retrieve the magnetic field and velocity in the range .Comment: To appear in A&
Peripheral downflows in sunspot penumbrae
Sunspot penumbrae show high-velocity patches along the periphery. The
high-velocity downflow patches are believed to be the return channels of the
Evershed flow. We aim to investigate their structure in detail using Hinode
SOT/SP observations. We employ Fourier interpolation in combination with
spatially coupled height dependent LTE inversions of Stokes profiles to produce
high-resolution, height-dependent maps of atmospheric parameters of these
downflows and investigate their properties. High-speed downflows are observed
over a wide range of viewing angles. They have supersonic line-of-sight
velocities, some in excess of 20km/s, and very high magnetic field strengths,
reaching values of over 7 kG. A relation between the downflow velocities and
the magnetic field strength is found, in good agreement with MHD simulations.
The coupled inversion at high resolution allows for the accurate determination
of small-scale structures. The recovered atmospheric structure indicates that
regions with very high downflow velocities contain some of the strongest
magnetic fields that have ever been measured on the Sun.Comment: A&A, in press, 14 pages, 15 figure
Vigorous convection in a sunspot granular light bridge
Light bridges are the most prominent manifestation of convection in sunspots.
The brightest representatives are granular light bridges composed of features
that appear to be similar to granules. An in-depth study of the convective
motions, temperature stratification, and magnetic field vector in and around
light bridge granules is presented with the aim of identifying similarities and
differences to typical quiet-Sun granules. Spectropolarimetric data from the
Hinode Solar Optical Telescope were analyzed using a spatially coupled
inversion technique to retrieve the stratified atmospheric parameters of light
bridge and quiet-Sun granules. Central hot upflows surrounded by cooler fast
downflows reaching 10 km/s clearly establish the convective nature of the light
bridge granules. The inner part of these granules in the near surface layers is
field free and is covered by a cusp-like magnetic field configuration. We
observe hints of field reversals at the location of the fast downflows. The
quiet-Sun granules in the vicinity of the sunspot are covered by a low-lying
canopy field extending radially outward from the spot. The similarities between
quiet-Sun and light bridge granules point to the deep anchoring of granular
light bridges in the underlying convection zone. The fast, supersonic downflows
are most likely a result of a combination of invigorated convection in the
light bridge granule due to radiative cooling into the neighboring umbra and
the fact that we sample deeper layers, since the downflows are immediately
adjacent to the slanted walls of the Wilson depression.Comment: 10 pages, 11 figure
Recent advancements in the EST project
The European Solar Telescope (EST) is a project of a new-generation solar
telescope. It has a large aperture of 4~m, which is necessary for achieving
high spatial and temporal resolution. The high polarimetric sensitivity of the
EST will allow to measure the magnetic field in the solar atmosphere with
unprecedented precision. Here, we summarise the recent advancements in the
realisation of the EST project regarding the hardware development and the
refinement of the science requirements.Comment: accepted to Advances in Space Researc
Structure of sunspot penumbral filaments: a remarkable uniformity of properties
The sunspot penumbra comprises numerous thin, radially elongated filaments
that are central for heat transport within the penumbra, but whose structure is
still not clear. To investigate the fine-scale structure of these filaments, we
perform a depth-dependent inversion of spectropolarimetric data of a sunspot
very close to solar disk center obtained by Hinode (SOT/SP). We have used a
recently developed spatially coupled 2D inversion scheme which allows us to
analyze the fine structure of individual penumbral filaments up to the
diffraction limit of the telescope. Filaments of different sizes in all parts
of penumbra display very similar magnetic field strengths, inclinations and
velocity patterns. The similarities allowed us to average all these filaments
and to extract the physical properties common to all of them. This average
filament shows upflows associated with an upward pointing field at its inner,
umbral end and along its axis, downflows along the lateral edge and strong
downflows in the outer end associated with a nearly vertical, strong and
downward pointing field. The upflowing plasma is significantly hotter than the
downflowing plasma. The hot, tear-shaped head of the averaged filament can be
associated with a penumbral grain. The central part of the filament shows
nearly horizontal fields with strengths of ~1kG. The field above the filament
converges, whereas a diverging trend is seen in the deepest layers near the
head of the filament. We put forward a unified observational picture of a
sunspot penumbral filament. It is consistent with such a filament being a
magneto-convective cell, in line with recent MHD simulations. The uniformity of
its properties over the penumbra sets constraints on penumbral models and
simulations. The complex and inhomogeneous structure of the filament provides a
natural explanation for a number of long-running controversies in the
literature.Comment: 19 pages; 12 figures; accepted for publication in A&
Adaptation to high ethanol reveals complex evolutionary pathways
Tolerance to high levels of ethanol is an ecologically and industrially relevant phenotype of microbes, but the molecular mechanisms underlying this complex trait remain largely unknown. Here, we use long-term experimental evolution of isogenic yeast populations of different initial ploidy to study adaptation to increasing levels of ethanol. Whole-genome sequencing of more than 30 evolved populations and over 100 adapted clones isolated throughout this two-year evolution experiment revealed how a complex interplay of de novo single nucleotide mutations, copy number variation, ploidy changes, mutator phenotypes, and clonal interference led to a significant increase in ethanol tolerance. Although the specific mutations differ between different evolved lineages, application of a novel computational pipeline, PheNetic, revealed that many mutations target functional modules involved in stress response, cell cycle regulation, DNA repair and respiration. Measuring the fitness effects of selected mutations introduced in non-evolved ethanol-sensitive cells revealed several adaptive mutations that had previously not been implicated in ethanol tolerance, including mutations in PRT1, VPS70 and MEX67. Interestingly, variation in VPS70 was recently identified as a QTL for ethanol tolerance in an industrial bio-ethanol strain. Taken together, our results show how, in contrast to adaptation to some other stresses, adaptation to a continuous complex and severe stress involves interplay of different evolutionary mechanisms. In addition, our study reveals functional modules involved in ethanol resistance and identifies several mutations that could help to improve the ethanol tolerance of industrial yeasts
Neoadjuvant immunotherapy with nivolumab and ipilimumab induces major pathological responses in patients with head and neck squamous cell carcinoma
Surgery for locoregionally advanced head and neck squamous cell carcinoma (HNSCC) results in 30‒50% five-year overall survival. In IMCISION (NCT03003637), a non-randomized phase Ib/IIa trial, 32 HNSCC patients are treated with 2 doses (in weeks 1 and 3) of immune checkpoint blockade (ICB) using nivolumab (NIVO MONO, n = 6, phase Ib arm A) or nivolumab plus a single dose of ipilimumab (COMBO, n = 26, 6 in phase Ib arm B, and 20 in phase IIa) prior to surgery. Primary endpoints are feasibility to resect no later than week 6 (phase Ib) and primary tumor pathological response (phase IIa). Surgery is not delayed or suspended for any patient in phase Ib, meeting the primary endpoint. Grade 3‒4 immune-related adverse events are seen in 2 of 6 (33%) NIVO MONO and 10 of 26 (38%) total COMBO patients. Pathological response, defined as the %-change in primary tumor viable tumor cell percentage from baseline biopsy to on-treatment resection, is evaluable in 17/20 phase IIa patients and 29/32 total trial patients (6/6 NIVO MONO, 23/26 COMBO). We observe a major pathological response (MPR, 90‒100% response) in 35% of patients after COMBO ICB, both in phase IIa (6/17) and in the whole trial (8/23), meeting the phase IIa primary endpoint threshold of 10%. NIVO MONO’s MPR rate is 17% (1/6). None of the MPR patients develop recurrent HSNCC during 24.0 months median postsurgical follow-up. FDG-PET-based total lesion glycolysis identifies MPR patients prior to surgery. A baseline AID/APOBEC-associated mutational profile and an on-treatment decrease in hypoxia RNA signature are observed in MPR patients. Our data indicate that neoadjuvant COMBO ICB is feasible and encouragingly efficacious in HNSCC
Multidimensional Radiative Transfer
A multidimensional radiative transfer code is presented, using the short
characteristics scheme and the ALI method. The code uses the 2-level atom
formulation, appropriate for strong resonance lines, and can operate with
Cartesian, cylindrical and spherical coordinate systems, the last two assuming
rotational symmetry about the z-axis.
The emphasis of the code is on accurately treating large, three-dimensional
velocity fields on a large number of spatial points and with high angular resolution,
in order to deal with complete objects.
To keep the code fast and reduce memory requirements, the code was
parallelized for use on a cluster of networked PCs by using a spatial parallelization
method, where the computational domain is divided spatially in
independent subdomains. It is shown that such a method is both efficient
and reliable.
The accuracy of the code was tested at length and was found to be ~ 5%
in most cases of interest.
A spectrum synthesis code is then presented, using the long characteristics
method and an Adaptive Mesh Refinement technique. The code can
accurately calculate the emergent line profile for a specified inclination angle
on a two-dimensional structure with a specified source function assuming
rotational symmetry, in cylindrical and spherical coordinate systems. The
accuracy of the code was determined to be of the order of 1%, given the
structure and line source function.
Both codes were then applied to the problem of rotation in expanding
stellar winds. The spectroscopic effects of rotation were found to be significant
for large inclination angles only, with the largest differences with
respect to non-rotating of ~ 20%. The direction of the radiation volume
force was found to change at most by a similar amount.
Finally, the codes were applied to calculate line profiles for the disks
in cataclysmic variables. The differences due to rotation were found to be
significant, with the cores of strong resonance lines brightened by about
50% for small inclination angles. The radiation force was not found to be
strongly affected