1,892 research outputs found
Spatially coupled inversion of spectro-polarimetric image data I: Method and first results
When inverting solar spectra, image degradation effects that are present in
the data are usually approximated or not considered. We develop a data
reduction method that takes these issues into account and minimizes the
resulting errors. By accounting for the diffraction PSF of the telescope during
the inversions, we can produce a self-consistent solution that best fits the
observed data, while simultaneously requiring fewer free parameters than
conventional approaches. Simulations using realistic MHD data indicate that the
method is stable for all resolutions, including those with pixel scales well
beyond those that can be resolved with a 0.5m telescope, such as the Hinode
SOT. Application of the presented method to reduce full Stokes data from the
Hinode spectro-polarimeter results in dramatically increased image contrast and
an increase in the resolution of the data to the diffraction limit of the
telescope in almost all Stokes and fit parameters. The resulting data allow for
detecting and interpreting solar features that have so far only been observed
with 1m class ground-based telescopes. The new inversion method allows for
accurate fitting of solar spectro-polarimetric imaging data over a large field
of view, while simultaneously improving the noise statistics and spatial
resolution of the results significantly.Comment: A&A, accepte
Spectropolarimetry with CRISP at the Swedish 1-m Solar Telescope
CRISP (Crisp Imaging Spectro-polarimeter), the new spectropolarimeter at the
Swedish 1-m Solar Telescope, opens a new perspective in solar polarimetry. With
better spatial resolution (0.13") than Hinode in the Fe I 6302 A line and
similar polarimetric sensitivity reached through postprocessing, CRISP
complements the SP spectropolarimeter onboard Hinode. We present some of the
data which we obtained in our June 2008 campaign and preliminary results from
LTE inversions of a pore containing umbral dots.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
A reversible bifurcation analysis of the inverted pendulum
The inverted pendulum with a periodic parametric forcing is considered as a bifurcation problem in the reversible setting. Parameters are given by the size of the forcing and the frequency ratio. Normal form theory provides an integrable approximation of the Poincaré map generated by a planar vector field. Genericity of the model is studied by a perturbation analysis, where the spatial symmetry is optional. Here equivariant singularity theory is used.
Measuring the Wilson depression of sunspots using the divergence-free condition of the magnetic field vector
Context: The Wilson depression is the difference in geometric height of unit
continuum optical depth between the sunspot umbra and the quiet Sun. Measuring
the Wilson depression is important for understanding the geometry of sunspots.
Current methods suffer from systematic effects or need to make assumptions on
the geometry of the magnetic field. This leads to large systematic
uncertainties of the derived Wilson depressions.
Aims: We aim at developing a robust method for deriving the Wilson depression
that only requires the information about the magnetic field that is accessible
from spectropolarimetry, and that does not rely on assumptions on the geometry
of sunspots or on their magnetic field.
Methods: Our method is based on minimizing the divergence of the magnetic
field vector derived from spectropolarimetric observations. We focus on large
spatial scales only in order to reduce the number of free parameters.
Results: We test the performance of our method using synthetic Hinode data
derived from two sunspot simulations. We find that the maximum and the umbral
averaged Wilson depression for both spots determined with our method typically
lies within 100 km of the true value obtained from the simulations. In
addition, we apply the method to Hinode observations of a sunspot. The derived
Wilson depression (about 600 km) is consistent with results typically obtained
from the Wilson effect. We also find that the Wilson depression obtained from
using horizontal force balance gives 110 - 180 km smaller Wilson depressions
than both, what we find and what we deduce directly from the simulations. This
suggests that the magnetic pressure and the magnetic curvature force contribute
to the Wilson depression by a similar amount.Comment: 12 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysic
The role of sterol carrier protein 2 in the regulation of Leydig cell steroidogenesis
The aim of the studies described in this thesis was to
clarify the rele of SCP2 in the regulation of steroid production
in rat Leydig cells.
The ra te of steroid production in the adrenal, the ovary,
the placenta and the testis is determined by the rate of
conversion of cholesterol to pregnenolone. The complex of
reactions and the localization of the enzymes involved in this so
called cholesterol side chain cleavage are well known. The P-
450scc enzyme complex catalyzing the production of pregnenolone
from cholesterol is located in the inner mitochondria! membrane
of steroidogenic cells (Fig.l.l). Several substances that regulate steroidogenesis, regulate the
rate of pregnenolone formation via an intracellular transducing
mechanism after binding to the plasma membrane of the cell.
Different "second messengers" are involved in the transduetion of
the signal from the plasma membrane to other processesjmessengers
in the cell which are involved in regulation of steroid production.
It is also known that protein synthesis and the transfer of
cholesterol to the inner mitochondria! membrane are important in
regulation of steroidogenesis. It is not known, however, if, and
in which way the induction of secend messenger systems in
steroidogenic cells is linked with protein synthesis, cholesterol
transfer and activatien of the cholesterol side chain cleavage
reaction inside the mitochondria. In this respect, sterol carrier
protein 2 (SCP2) is one of the possible proteins that could be
involved in transduetion of the signal from the secend messengers
to the cscc enzyme complex
Vertical flows and mass flux balance of sunspot umbral dots
A new Stokes inversion technique that greatly reduces the effect of the
spatial point spread function of the telescope is used to constrain the
physical properties of umbral dots (UDs). The depth-dependent inversion of the
Stokes parameters from a sunspot umbra recorded with Hinode SOT/SP revealed
significant temperature enhancements and magnetic field weakenings in the core
of the UDs in deep photospheric layers. Additionally, we found upflows of
around 960 m/s in peripheral UDs (i.e., UDs close to the penumbra) and
600 m/s in central UDs. For the first time, we also detected
systematic downflows for distances larger than 200 km from the UD center that
balance the upflowing mass flux. In the upper photosphere, we found almost no
difference between the UDs and their diffuse umbral background.Comment: Accepted for publication in Astronomy and Astrophysic
Consultancyonderzoek naar mogelijke oorzaken uitval bij Mandevilla
Abstract Wageningen UR Greenhouse Horticulture and Marcel Lieffering Kamer- en Perkplantenadviesburo conducted exploratory research, funded by the Dutch Product Board for Horticulture, into the loss of plants in Mandevilla growing. In literature, the diseases Pythium, Phytophthora, Fusarium oxysporum, Agrobacterium and Ralstonia were mentioned. In an experimental production test, only Phytophthora was found. In this experiment, differences in crop loss were mainly related to the origin. The differences in crop loss between substrates and pH levels were clearly smaller. Origin also had a major impact on plant quality: one origin was much better than the other two
Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope
Aims: We aim to achieve high spatial resolution as well as high polarimetric
sensitivity, using an earth-based 1m-class solar telescope, for the study of
magnetic fine structure on the Sun. Methods: We use a setup with 3 high-speed,
low-noise cameras to construct datasets with interleaved polarimetric states,
particularly suitable for Multi-Object Multi-Frame Blind Deconvolution image
restorations. We discuss the polarimetric calibration routine as well as
various potential sources of error in the results. Results: We obtained near
diffraction limited images, with a noise level of approximately 10^(-3)
I(cont). We confirm that dark-cores have a weaker magnetic field and at a lower
inclination angle with respect to the solar surface than the edges of the
penumbral filament. We show that the magnetic field strength in
faculae-striations is significantly lower than in other nearby parts of the
faculae.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 11
figure
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