302 research outputs found
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
Properties of simulated sunspot umbral dots
Realistic 3D radiative MHD simulations reveal the magneto-convective
processes underlying the formation of the photospheric fine structure of
sunspots, including penumbral filaments and umbral dots. Here we provide
results from a statistical analysis of simulated umbral dots and compare them
with reports from high-resolution observations. A multi-level segmentation and
tracking algorithm has been used to isolate the bright structures in synthetic
bolometric and continuum brightness images. Areas, brightness, and lifetimes of
the resulting set of umbral dots are found to be correlated: larger umbral dots
tend to be brighter and live longer. The magnetic field strength and velocity
structure of umbral dots on surfaces of constant optical depth in the continuum
at 630 nm indicate that the strong field reduction and high velocities in the
upper parts of the upflow plumes underlying umbral dots are largely hidden from
spectro-polarimetric observations. The properties of the simulated umbral dots
are generally consistent with the results of recent high-resolution
observations. However, the observed population of small, short-lived umbral
dots is not reproduced by the simulations, possibly owing to insufficient
spatial resolution.Comment: Accepted for publication in A&
Comparison of solar photospheric bright points between SUNRISE observations and MHD simulations
Bright points (BPs) in the solar photosphere are radiative signatures of
magnetic elements described by slender flux tubes located in the darker
intergranular lanes. They contribute to the ultraviolet (UV) flux variations
over the solar cycle and hence may influence the Earth's climate. Here we
combine high-resolution UV and spectro-polarimetric observations of BPs by the
SUNRISE observatory with 3D radiation MHD simulations. Full spectral line
syntheses are performed with the MHD data and a careful degradation is applied
to take into account all relevant instrumental effects of the observations. It
is demonstrated that the MHD simulations reproduce the measured distributions
of intensity at multiple wavelengths, line-of-sight velocity, spectral line
width, and polarization degree rather well. Furthermore, the properties of
observed BPs are compared with synthetic ones. These match also relatively
well, except that the observations display a tail of large and strongly
polarized BPs not found in the simulations. The higher spatial resolution of
the simulations has a significant effect, leading to smaller and more numerous
BPs. The observation that most BPs are weakly polarized is explained mainly by
the spatial degradation, the stray light contamination, and the temperature
sensitivity of the Fe I line at 5250.2 \AA{}. The Stokes asymmetries of the
BPs increase with the distance to their center in both observations and
simulations, consistent with the classical picture of a production of the
asymmetry in the canopy. This is the first time that this has been found also
in the internetwork. Almost vertical kilo-Gauss fields are found for 98 % of
the synthetic BPs. At the continuum formation height, the simulated BPs are on
average 190 K hotter than the mean quiet Sun, their mean BP field strength is
1750 G, supporting the flux-tube paradigm to describe BPs.Comment: Accepted for publication in Astronomy & Astrophysics on May 30 201
Linear Polarization Features in the Quiet-Sun Photosphere: Structure and Dynamics
We present detailed characteristics of linear polarization features (LPFs) in
the quiet-Sun photosphere from high resolution observations obtained with
Sunrise/IMaX. We explore differently treated data with various noise levels in
linear polarization signals, from which structure and dynamics of the LPFs are
studied. Physical properties of the detected LPFs are also obtained from the
results of Stokes inversions. The number of LPFs, as well as their sizes and
polarization signals, are found to be strongly dependent on the noise level,
and on the spatial resolution. While the linear polarization with
signal-to-noise ratio covers about 26% of the entire area in the
least noisy data in our study (with a noise level of in the
unit of Stokes continuum), the detected (spatially resolved) LPFs cover
about 10% of the area at any given time, with an occurrence rate on the order
of s arcsec. The LPFs were found to be short
lived (in the range of s), relatively small structures (radii of
arcsec), highly inclined, posing hG fields, and move with an
average horizontal speed of 1.2 km s. The LPFs were observed (almost)
equally on both upflow and downflow regions, with intensity contrast always
larger than that of the the average quiet-Sun.Comment: 20 pages, 9 figures, Accepted for publication in the Solar Physics
journa
T lymphocytes from patients with primary biliary cirrhosis produce reduced amounts of lymphotoxin, tumor necrosis factor and interferon-gamma upon mitogen stimulation
Primary biliary cirrhosis (PBC) is considered an autoimmune disease characterized by destruction of small intrahepatic
bile ducts by lymphocytes. Altered functions of these lymphocytes might reflect an abnormal immune response leading
to tissue damage. We investigated lymphokine secretion by mitogen-stimulated T lymphocytes from the liver biopsies
of patients with PBC and for comparison also peripheral blood. In PBC, diminished synthesis of lymphotoxin (TNFP),
tumor necrosis factor (TNFa) and interferon-y (IFIVy) was found both in T-cell lines from liver tissue and in peripheral
blood. The reduction was most prominent for TNFP in early histological stages of PBC, and appeared to be a stable
phenomenon when T cells were tested after long-term tissue culture. Analysis of mRNA levels indicates a possible link
between reduced TNFP production and a defect in interleukin-2 transcription. The data suggest that diminished
lymphokine production in patients with PBC may play ;In important role in the immanopathogenesis of this disease
First high-resolution images of the Sun in the 2796 \AA{} Mg II k line
We present the first high-resolution solar images in the Mg II k 2796 \AA{}
line. The images, taken through a 4.8 \AA{} broad interference filter, were
obtained during the second science flight of SUNRISE in June 2013 by the SuFI
instrument. The Mg II k images display structures that look qualitatively very
similar to images taken in the core of Ca II H. The Mg II images exhibit
reversed granulation (or shock waves) in the internetwork regions of the quiet
Sun, at intensity contrasts that are similar to those found in Ca II H. Very
prominent in Mg II are bright points, both in the quiet Sun and in plage
regions, particularly near disk center. These are much brighter than at other
wavelengths sampled at similar resolution. Furthermore, Mg II k images also
show fibril structures associated with plage regions. Again, the fibrils are
similar to those seen in Ca II H images, but tend to be more pronounced,
particularly in weak plage.Comment: Accepted for publication in The Astrophysical Journal Letter
Corporate Governance, Opaque Bank Activities, and Risk/Return Efficiency: Pre- and Post-Crisis Evidence from Turkey
Does better corporate governance unambiguously improve the risk/return efficiency of banks? Or does either a re-orientation of banks' revenue mix towards more opaque products, an economic downturn, or tighter supervision create off-setting or reinforcing effects? The authors relate bank efficiency to shortfalls from a stochastic risk/return frontier. They analyze how internal governance mechanisms (CEO duality, board experience, political connections, and education profile) and external governance mechanisms (discipline exerted by shareholders, depositors, or skilled employees) determine efficiency in a sample of Turkish banks. The 2000 financial crisis was a wakeup call for bank efficiency and corporate governance. As a result, better corporate governance mechanisms have been able to improve risk/return efficiency when the economic, regulatory, and supervisory environments are more stable and bank products are more complex.corporate governance;bank risk;noninterest income;crisis;frontier
- …