4,597 research outputs found
Opposite polarity field with convective downflow and its relation to magnetic spines in a sunspot penumbra
We discuss NICOLE inversions of Fe I 630.15 nm and 630.25 nm Stokes spectra
from a sunspot penumbra recorded with the CRISP imaging spectropolarimeter on
the Swedish 1-m Solar Telescope at a spatial resolution close to 0.15". We
report on narrow radially extended lanes of opposite polarity field, located at
the boundaries between areas of relatively horizontal magnetic field (the
intra-spines) and much more vertical field (the spines). These lanes harbor
convective downflows of about 1 km/s. The locations of these downflows close to
the spines agree with predictions from the convective gap model (the "gappy
penumbra") proposed six years ago, and more recent 3D MHD simulations. We also
confirm the existence of strong convective flows throughout the entire
penumbra, showing the expected correlation between temperature and vertical
velocity, and having vertical RMS velocities of about 1.2 km/s.Comment: Accepted for publication in A&A (06-March-2013). Minor corrections
made in this version
Molecular characterization of autophagic and apoptotic signaling induced by sorafenib in liver cancer cells
Sorafenib is the unique accepted molecular targeted drug for the treatment of patients in advanced stage of hepatocellular carcinoma. The current study evaluated cell signaling regulation of endoplasmic reticulum (ER) stress, c-Jun-N-terminal kinase (JNK), Akt, and 5′AMP-activated protein kinase (AMPK) leading to autophagy and apoptosis induced by sorafenib. Sorafenib induced early (3–12 hr) ER stress characterized by an increase of Ser51P-eIF2α/eIF2α, C/EBP homologous protein (CHOP), IRE1α, and sXBP1, but a decrease of activating transcription factor 6 expression, overall temporally associated with the increase of Thr183,Tyr185P-JNK1/2/JNK1/2, Thr172P-AMPKα, Ser413P-Foxo3a, Thr308P-AKt/AKt and Thr32P-Foxo3a/Foxo3a ratios, and reduction of Ser2481P-mammalian target of rapamycin (mTOR)/mTOR and protein translation. This pattern was related to a transient increase of tBid, Bim EL, Beclin-1, Bcl-xL, Bcl-2, autophagy markers, and reduction of myeloid cell leukemia-1 (Mcl-1) expression. The progressive increase of CHOP expression, and reduction of Thr308P-AKt/AKt and Ser473P-AKt/AKt ratios were associated with the reduction of autophagic flux and an additional upregulation of Bim EL expression and caspase-3 activity (24 hr). Small interfering-RNA (si-RNA) assays showed that Bim, but not Bak and Bax, was involved in the induction of caspase-3 in sorafenib-treated HepG2 cells. Sorafenib increased autophagic and apoptotic markers in tumor-derived xenograft model. In conclusion, the early sorafenib-induced ER stress and regulation of JNK and AMPK-dependent signaling were related to the induction of survival autophagic process. The sustained drug treatment induced a progressive increase of ER stress and PERK-CHOP-dependent rise of Bim EL, which was associated with the shift from autophagy to apoptosis. The kinetic of Bim EL expression profile might also be related to the tight balance between AKt- and AMPK-related signaling leading to Foxo3a-dependent BIM EL upregulation.Ministerio de Economía y Competitividad BFU2016‐75352‐PInstituto de Salud Carlos III PI15/00034, PI13/ 00021, PI16/00090, PI14/01349Ministerio de Educación FPU16/05127, FPU12/01433, FPU13/01237Junta de Andalucía CTS-6264, PI-00025-2013, PI-0127-2013, PI-0198-201
Gromov hyperbolicity in strong product graphs
If X is a geodesic metric space and x1; x2; x3 2 X, a geodesic triangle T =
fx1; x2; x3g is the union of the three geodesics [x1x2], [x2x3] and [x3x1] in X. The
space X is -hyperbolic (in the Gromov sense) if any side of T is contained in a
-neighborhood of the union of the two other sides, for every geodesic triangle T
in X. If X is hyperbolic, we denote by (X) the sharp hyperbolicity constant of
X, i.e. (X) = inff > 0 : X is -hyperbolic g : In this paper we characterize the
strong product of two graphs G1 G2 which are hyperbolic, in terms of G1 and
G2: the strong product graph G1 G2 is hyperbolic if and only if one of the factors
is hyperbolic and the other one is bounded. We also prove some sharp relations
between (G1 G2), (G1), (G2) and the diameters of G1 and G2 (and we nd
families of graphs for which the inequalities are attained). Furthermore, we obtain
the exact values of the hyperbolicity constant for many strong product graphs
Dual encoding of muscle tension and eye position by abducens motoneurons
Extraocular muscle tension associated with spontaneous eye movements has a pulse-slide-step profile similar to that of motoneuron firing rate. Existing models only relate motoneuron firing to eye position, velocity and acceleration. We measured and quantitatively compared lateral rectus muscle force and eye position with the firing of abducens motoneurons in the cat to determine fundamental encoding correlations. During fixations (step), muscle force increased exponentially with eccentric eye position, consistent with a model of estimate ensemble motor innervation based on neuronal sensitivities and recruitment order. Moreover, firing rate in all motoneurons tested was better related to eye position than to muscle tension during fixations. In contrast, during the postsaccadic slide phase, the time constant of firing rate decay was closely related to that of muscle force decay, suggesting that all motoneurons encode muscle tension as well. Discharge characteristics of abducens motoneurons formed overlapping clusters of phasic and tonic motoneurons, thus, tonic units recruited earlier and had a larger slide signal. We conclude that the slide signal is a discharge characteristic of the motoneuron that controls muscle tension during the postsaccadic phase and that motoneurons are specialized for both tension and position-related properties. The organization of signal content in the pool of abducens motoneurons from the very phasic to the very tonic units is possibly a result of the differential trophic background received from distinct types of muscle fibers
A reconnection driven magnetic flux cancellation and a quiet Sun Ellerman bomb
The focus of this investigation is to quantify the conversion of magnetic to
thermal energy initiated by a quiet Sun cancellation event and to explore the
resulting dynamics from the interaction of the opposite polarity magnetic
features. We used imaging spectroscopy in the H line, along with
spectropolarimetry in the \ion{Fe}{I} 6173~{\AA} and \ion{Ca}{II} 8542~{\AA}
lines from the Swedish Solar Telescope (SST) to study a reconnection-related
cancellation and the appearance of a quiet Sun Ellerman bomb (QSEB). We
observed, for the first time, QSEB signature in both the wings and core of the
\ion{Fe}{I} 6173~{\AA} line. We also found that, at times, the \ion{Fe}{I}
line-core intensity reaches higher values than the quiet Sun continuum
intensity. From FIRTEZ-dz inversions of the Stokes profiles in \ion{Fe}{I} and
\ion{Ca}{II} lines, we found enhanced temperature, with respect to the quiet
Sun values, at the photospheric ( = -1.5; 1000 K) and lower
chromospheric heights ( = -4.5; 360 K). From the calculation
of total magnetic energy and thermal energy within these two layers it was
confirmed that the magnetic energy released during the flux cancellation can
support heating in the aforesaid height range. Further, the temperature
stratification maps enabled us to identify cumulative effects of successive
reconnection on temperature pattern, including recurring temperature
enhancements. Similarly, Doppler velocity stratification maps revealed impacts
on plasma flow pattern, such as a sudden change in the flow direction.Comment: 16 pages, 12 figures, accepted for publication in MNRA
Stokes imaging polarimetry using image restoration: A calibration strategy for Fabry-P\'{e}rot based instruments
context: The combination of image restoration and a Fabry-P\'{e}rot
interferometer (FPI) based instrument in solar observations results in specific
calibration issues. FPIs generally show variations over the field-of-view,
while in the image restoration process, the 1-to-1 relation between pixel space
and image space is lost, thus complicating any correcting for such variations.
aims: We develop a data reduction method that takes these issues into account
and minimizes the resulting errors. methods: By accounting for the time
variations in the telescope's Mueller matrix and using separate calibration
data optimized for the wavefront sensing in the MOMFBD image restoration
process and for the final deconvolution of the data, we have removed most of
the calibration artifacts from the resulting data. results: Using this method
to reduce full Stokes data from CRISP at the SST, we find that it drastically
reduces the instrumental and image restoration artifacts resulting from cavity
errors, reflectivity variations, and the polarization dependence of flatfields.
The results allow for useful scientific interpretation. Inversions of restored
data from the sunspot AR11029 using the Nicole inversion code, reveal
strong (~10 km/s) downflows near the disk center side of the umbra.
conclusions: The use of image restoration in combination with an FPI-based
instrument leads to complications in the calibrations and intrinsic limitations
to the accuracy that can be achieved. We find that for CRISP, the resulting
errors can be kept mostly below the polarimetric accuracy of ~10^-3. Similar
instruments aiming for higher polarimetric and high spectroscopic accuracy,
will, however, need to take these problems into account. keywords: Techniques:
image processing, polarimetric, imaging spectroscopy, Sun: surface magnetism,
sunspots, activityComment: Astronomy and Astrophysics (accepted
The cross helicity at the solar surface by simulations and observations
The quasilinear mean-field theory for driven MHD turbulence leads to the
result that the observed cross helicity may directly yield the
magnetic eddy diffusivity \eta_{T} of the quiet Sun. In order to model the
cross helicity at the solar surface, magnetoconvection under the presence of a
vertical large-scale magnetic field is simulated with the nonlinear MHD code
NIRVANA. The very robust result of the calculations is that \simeq 2
independent of the applied magnetic field amplitude. The
correlation coefficient for the cross helicity is about 10%. Of similar
robustness is the finding that the rms value of the magnetic perturbations
exceeds the mean-field amplitude (only) by a factor of five. The characteristic
helicity speed u_{\eta} as the ratio of the eddy diffusivity and the density
scale height for an isothermal sound velocity of 6.6 km/s proves to be 1 km/s
for weak fields. This value well coincides with empirical results obtained from
the data of the HINODE satellite and the Swedish 1-m Solar Telescope (SST)
providing the cross helicity component . Both simulations and
observations thus lead to a numerical value of \eta_{T} \simeq 10^12 cm^2 /s as
characteristic for the surface of the quiet Sun.Comment: 6 pages, 6 figure
- …