156 research outputs found
The international spine registry SPINE TANGO: status quo and first results
With an official life time of over 5years, Spine Tango can meanwhile be considered the first international spine registry. In this paper we present an overview of frequency statistics of Spine Tango for demonstrating the genesis of questionnaire development and the constantly increasing activity in the registry. Results from two exemplar studies serve for showing concepts of data analysis applied to a spine registry. Between 2002 and 2006, about 6,000 datasets were submitted by 25 centres. Descriptive analyses were performed for demographic, surgical and follow-up data of three generations of the Spine Tango surgery and follow-up forms. The two exemplar studies used multiple linear regression models to identify potential predictor variables for the occurrence of dura lesions in posterior spinal fusion, and to evaluate which covariates influenced the length of hospital stay. Over the study period there was a rise in median patient age from 52.3 to 58.6years in the Spine Tango data pool and an increasing percentage of degenerative diseases as main pathology from 59.9 to 71.4%. Posterior decompression was the most frequent surgical measure. About one-third of all patients had documented follow-ups. The complication rate remained below 10%. The exemplar studies identified "centre of interventionâ and "number of segments of fusionâ as predictors of the occurrence of dura lesions in posterior spinal fusion surgery. Length of hospital stay among patients with posterior fusion was significantly influenced by "centre of interventionâ, "surgeon credentialsâ, "number of segments of fusionâ, "age groupâ and "sexâ. Data analysis from Spine Tango is possible but complicated by the incompatibility of questionnaire generations 1 and 2 with the more recent generation 3. Although descriptive and also analytic studies at evidence level 2++ can be performed, findings cannot yet be generalised to any specific country or patient population. Current limitations of Spine Tango include the low number and short duration of follow-ups and the lack of sufficiently detailed patient data on subgroup levels. Although the number of participants is steadily growing, no country is yet represented with a sufficient number of hospitals. Nevertheless, the benefits of the project for the whole spine community become increasingly visibl
Magnetic fields inferred by Solar Orbiter: A comparison between SO/PHI-HRT and SDO/HMI
The High Resolution Telescope (HRT) of the Polarimetric and Helioseismic
Imager on board the Solar Orbiter spacecraft (SO/PHI) and the Helioseismic and
Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) both infer
the photospheric magnetic field from polarised light images. SO/PHI is the
first magnetograph to move out of the Sun--Earth line and will provide
unprecedented access to the Sun's poles. This provides excellent opportunities
for new research wherein the magnetic field maps from both instruments are used
simultaneously. We aim to compare the magnetic field maps from these two
instruments and discuss any possible differences between them. We used data
from both instruments obtained during Solar Orbiter's inferior conjunction on 7
March 2022. The HRT data were additionally treated for geometric distortion and
degraded to the same resolution as HMI. The HMI data were re-projected to
correct for the separation between the two observatories.
SO/PHI-HRT and HMI produce remarkably similar line-of-sight magnetograms, with
a slope coefficient of , an offset below G, and a Pearson correlation
coefficient of . However, SO/PHI-HRT infers weaker line-of-sight fields
for the strongest fields. As for the vector magnetic field, SO/PHI-HRT was
compared to both the -second and -second HMI vector magnetic field:
SO/PHI-HRT has a closer alignment with the -second HMI vector. In the weak
signal regime ( G), SO/PHI-HRT measures stronger and more horizontal
fields than HMI, very likely due to the greater noise in the SO/PHI-HRT data.
In the strong field regime ( G), HRT infers lower field strengths
but with similar inclinations (a slope of ) and azimuths (a slope of
). The slope values are from the comparison with the HMI -second
vector.Comment: 10 pages, 5 figures, accepted for publication in A&A; manuscript is a
part of Astronomy & Astrophysics special issue: Solar Orbiter First Results
(Nominal Mission Phase
Stereoscopic disambiguation of vector magnetograms: first applications to SO/PHI-HRT data
Spectropolarimetric reconstructions of the photospheric vector magnetic field
are intrinsically limited by the 180-ambiguity in the orientation of
the transverse component. So far, the removal of such an ambiguity has required
assumptions about the properties of the photospheric field, which makes
disambiguation methods model-dependent. The basic idea is that the unambiguous
line-of-sight component of the field measured from one vantage point will
generally have a non-zero projection on the ambiguous transverse component
measured by the second telescope, thereby determining the ``true'' orientation
of the transverse field. Such an idea was developed and implemented in the
Stereoscopic Disambiguation Method (SDM), which was recently tested using
numerical simulations. In this work we present a first application of the SDM
to data obtained by the High Resolution Telescope (HRT) onboard Solar Orbiter
during the March 2022 campaign, when the angle with Earth was 27 degrees. The
method is successfully applied to remove the ambiguity in the transverse
component of the vector magnetogram solely using observations (from HRT and
from the Helioseismic and Magnetic Imager), for the first time. The SDM is
proven to provide observation-only disambiguated vector magnetograms that are
spatially homogeneous and consistent. A discussion about the sources of error
that may limit the accuracy of the method, and of the strategies to remove them
in future applications, is also presented.Comment: 32 pages, 12 figures, accepted in A&A on 09/07/202
Magnetic fields inferred by Solar Orbiter: A comparison between SO/PHI-HRT and SDO/HMI
Context. The High Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager on board the Solar Orbiter spacecraft (SO/PHI) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) both infer the photospheric magnetic field from polarised light images. SO/PHI is the first magnetograph to move out of the SunâEarth line and will provide unprecedented access to the Sunâs poles. This provides excellent opportunities for new research wherein the magnetic field maps from both instruments are used simultaneously.
Aims. We aim to compare the magnetic field maps from these two instruments and discuss any possible differences between them.
Methods. We used data from both instruments obtained during Solar Orbiterâs inferior conjunction on 7 March 2022. The HRT data were additionally treated for geometric distortion and degraded to the same resolution as HMI. The HMI data were re-projected to correct for the 3° separation between the two observatories.
Results. SO/PHI-HRT and HMI produce remarkably similar line-of-sight magnetograms, with a slope coefficient of 0.97, an offset below 1âG, and a Pearson correlation coefficient of 0.97. However, SO/PHI-HRT infers weaker line-of-sight fields for the strongest fields. As for the vector magnetic field, SO/PHI-HRT was compared to both the 720-second and 90-second HMI vector magnetic field: SO/PHI-HRT has a closer alignment with the 90-second HMI vector. In the weak signal regime (< 600 G), SO/PHI-HRT measures stronger and more horizontal fields than HMI, very likely due to the greater noise in the SO/PHI-HRT data. In the strong field regime (âł600 G), HRT infers lower field strengths but with similar inclinations (a slope of 0.92) and azimuths (a slope of 1.02). The slope values are from the comparison with the HMI 90-second vector. Possible reasons for the differences found between SO/PHI-HRT and HMI magnetic field parameters are discussed.SecciĂłn Deptal. de Ăptica (Ăptica)Fac. de Ăptica y OptometrĂaTRUEBMWi - Bundesministerium fĂŒr Wirtschaft und Energie (Alemania)AEI/MCIN/10.13039/501100011033Ministerio de ciencia e innovaciĂłn de EspañaInstituto AstrofĂsico de AndalucĂa (España)Agencia Estatal de InvestigaciĂłn (España)Fondo Europeo de Desarrollo Regional (Fondos FEDER)Centre national d'Ă©tudes spatiales (CNES) (Francia)CSIC (Centro Superior de Investigaciones CientĂficas) (España)pu
Wavefront error of PHI/HRT on Solar Orbiter at various heliocentric distances
We use wavefront sensing to characterise the image quality of the the High
Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager (SO/PHI)
data products during the second remote sensing window of the Solar Orbiter (SO)
nominal mission phase. Our ultimate aims are to reconstruct the HRT data by
deconvolving with the HRT point spread function (PSF) and to correct for the
effects of optical aberrations on the data. We use a pair of focused--defocused
images to compute the wavefront error and derive the PSF of HRT by means of a
phase diversity (PD) analysis. The wavefront error of HRT depends on the
orbital distance of SO to the Sun. At distances \,au, the wavefront error
is small, and stems dominantly from the inherent optical properties of HRT. At
distances \,au, the thermo-optical effect of the Heat Rejection Entrance
Window (HREW) becomes noticeable. We develop an interpolation scheme for the
wavefront error that depends on the thermal variation of the HREW with the
distance of SO to the Sun. We also introduce a new level of image
reconstruction, termed `aberration correction', which is designed to reduce the
noise caused by image deconvolution while removing the aberrations caused by
the HREW. The computed PSF via phase diversity significantly reduces the
degradation caused by the HREW in the near-perihelion HRT data. In addition,
the aberration correction increases the noise by a factor of only
compared to the factor of increase that results from the usual PD
reconstructions
Intensity contrast of solar network and faculae close to the solar limb, observed from two vantage points
The brightness of faculae and network depends on the angle at which they are
observed and the magnetic flux density. Close to the limb, assessment of this
relationship has until now been hindered by the increasingly lower signal in
magnetograms. This preliminary study aims at highlighting the potential of
using simultaneous observations from different vantage points to better
determine the properties of faculae close to the limb. We use data from the
Solar Orbiter/Polarimetric and Helioseismic Imager (SO/PHI), and the Solar
Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI), recorded at
angular separation of their lines of sight at the Sun. We use
continuum intensity observed close to the limb by SO/PHI and complement it with
the co-observed from SDO/HMI, originating closer to disc centre
(as seen by SDO/HMI), thus avoiding the degradation of the magnetic field
signal near the limb. We derived the dependence of facular brightness in the
continuum on disc position and magnetic flux density from the combined
observations of SO/PHI and SDO/HMI. Compared with a single point of view, we
were able to obtain contrast values reaching closer to the limb and to lower
field strengths. We find the general dependence of the limb distance at which
the contrast is maximum on the flux density to be at large in line with single
viewpoint observations, in that the higher the flux density is, the closer the
turning point lies to the limb. There is a tendency, however, for the maximum
to be reached closer to the limb when determined from two vantage points. We
note that due to the preliminary nature of this study, these results must be
taken with caution. Our analysis shows that studies involving two viewpoints
can significantly improve the detection of faculae near the solar limb and the
determination of their brightness contrast relative to the quiet Sun
The ratio of horizontal to vertical displacement in solar oscillations estimated from combined SO/PHI and SDO/HMI observations
In order to make accurate inferences about the solar interior using
helioseismology, it is essential to understand all the relevant physical
effects on the observations. One effect to understand is the (complex-valued)
ratio of the horizontal to vertical displacement of the p- and f-modes at the
height at which they are observed. Unfortunately, it is impossible to measure
this ratio directly from a single vantage point, and it has been difficult to
disentangle observationally from other effects. In this paper we attempt to
measure the ratio directly using 7.5 hours of simultaneous observations from
the Polarimetric and Helioseismic Imager on board Solar Orbiter and the
Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. While
image geometry problems make it difficult to determine the exact ratio, it
appears to agree well with that expected from adiabatic oscillations in a
standard solar model. On the other hand it does not agree with a commonly used
approximation, indicating that this approximation should not be used in
helioseismic analyses. In addition, the ratio appears to be real-valued.Comment: Accepted for publication in Astronomy & Astrophysics. 8 pages, 8
figure
Using Phylogenomic Patterns and Gene Ontology to Identify Proteins of Importance in Plant Evolution
We use measures of congruence on a combined expressed sequenced tag genome phylogeny to identify proteins that have potential significance in the evolution of seed plants. Relevant proteins are identified based on the direction of partitioned branch and hidden support on the hypothesis obtained on a 16-species tree, constructed from 2,557 concatenated orthologous genes. We provide a general method for detecting genes or groups of genes that may be under selection in directions that are in agreement with the phylogenetic pattern. Gene partitioning methods and estimates of the degree and direction of support of individual gene partitions to the overall data set are used. Using this approach, we correlate positive branch support of specific genes for key branches in the seed plant phylogeny. In addition to basic metabolic functions, such as photosynthesis or hormones, genes involved in posttranscriptional regulation by small RNAs were significantly overrepresented in key nodes of the phylogeny of seed plants. Two genes in our matrix are of critical importance as they are involved in RNA-dependent regulation, essential during embryo and leaf development. These are Argonaute and the RNA-dependent RNA polymerase 6 found to be overrepresented in the angiosperm clade. We use these genes as examples of our phylogenomics approach and show that identifying partitions or genes in this way provides a platform to explain some of the more interesting organismal differences among species, and in particular, in the evolution of plants
Coronal voids and their magnetic nature
Context:
Extreme ultraviolet (EUV) observations of the quiet solar atmosphere reveal extended regions of weak emission compared to the ambient quiescent corona. The magnetic nature of these coronal features is not well understood.
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Aims:
We study the magnetic properties of the weakly emitting extended regions, which we name coronal voids. In particular, we aim to understand whether these voids result from a reduced heat input into the corona or if they are associated with mainly unipolar and possibly open magnetic fields, similar to coronal holes.
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Methods:
We defined the coronal voids via an intensity threshold of 75% of the mean quiet-Sun (QS) EUV intensity observed by the high-resolution EUV channel (HRIEUV) of the Extreme Ultraviolet Imager on Solar Orbiter. The line-of-sight magnetograms of the same solar region recorded by the High Resolution Telescope of the Polarimetric and Helioseismic Imager allowed us to compare the photospheric magnetic field beneath the coronal voids with that in other parts of the QS.
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Results:
The coronal voids studied here range in size from a few granules to a few supergranules and on average exhibit a reduced intensity of 67% of the mean value of the entire field of view. The magnetic flux density in the photosphere below the voids is 76% (or more) lower than in the surrounding QS. Specifically, the coronal voids show much weaker or no network structures. The detected flux imbalances fall in the range of imbalances found in QS areas of the same size.
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Conclusions:
We conclude that coronal voids form because of locally reduced heating of the corona due to reduced magnetic flux density in the photosphere. This makes them a distinct class of (dark) structure, different from coronal holes
Coronal voids and their magnetic nature
Context. Extreme ultraviolet (EUV) observations of the quiet solar atmosphere reveal extended regions of weak emission compared to the ambient quiescent corona. The magnetic nature of these coronal features is not well understood.Aims. We study the magnetic properties of the weakly emitting extended regions, which we name coronal voids. In particular, we aim to understand whether these voids result from a reduced heat input into the corona or if they are associated with mainly unipolar and possibly open magnetic fields, similar to coronal holes. Methods. We defined the coronal voids via an intensity threshold of 75% of the mean quiet-Sun (QS) EUV intensity observed by the high- resolution EUV channel (HRIEUV) of the Extreme Ultraviolet Imager on Solar Orbiter. The line-of-sight magnetograms of the same solar region recorded by the High Resolution Telescope of the Polarimetric and Helioseismic Imager allowed us to compare the photospheric magnetic field beneath the coronal voids with that in other parts of the QS.Results. The coronal voids studied here range in size from a few granules to a few supergranules and on average exhibit a reduced intensity of 67% of the mean value of the entire field of view. The magnetic flux density in the photosphere below the voids is 76% (or more) lower than in the surrounding QS. Specifically, the coronal voids show much weaker or no network structures. The detected flux imbalances fall in the range of imbalances found in QS areas of the same size. Conclusions. We conclude that coronal voids form because of locally reduced heating of the corona due to reduced magnetic flux density in the photosphere. This makes them a distinct class of (dark) structure, different from coronal holes
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