233 research outputs found
Actin in erythrocyte ghosts and its association with spectrin. Evidence for a nonfilamentous form of these two molecules in situ.
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
Multiwavelength campaign on Mrk 509. V. Chandra-LETGS observation of the ionized absorber
We present here the results of a 180 ks Chandra-LETGS observation as part of
a large multi-wavelength campaign on Mrk 509. We study the warm absorber in Mrk
509 and use the data from a simultaneous HST-COS observation in order to assess
whether the gas responsible for the UV and X-ray absorption are the same. We
analyzed the LETGS X-ray spectrum of Mrk 509 using the SPEX fitting package. We
detect several absorption features originating in the ionized absorber of the
source, along with resolved emission lines and radiative recombination
continua. The absorption features belong to ions with, at least, three distinct
ionization degrees. The lowest ionized component is slightly redshifted (v =
+73 km/s) and is not in pressure equilibrium with the others, and therefore it
is not likely part of the outflow, possibly belonging to the interstellar
medium of the host galaxy. The other components are outflowing at velocities of
-196 and -455 km/s, respectively. The source was observed simultaneously with
HST-COS, finding 13 UV kinematic components. At least three of them can be
kinematically associated with the observed X-ray components. Based on the
HST-COS results and a previous FUSE observation, we find evidence that the UV
absorbing gas might be co-located with the X-ray absorbing gas and belong to
the same structure.Comment: 12 pages, 7 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
Activation for cell fusion in Chlamydomonas: analysis of wild-type gametes and nonfusing mutants.
Multiwavelength campaign on Mrk 509. VI. HST/COS observations of the far-ultraviolet spectrum
We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering
1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a
Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that
included observations with XMM-Newton, SWIFT, and Integral. Our high S/N
spectrum detects additional complexity in the absorption troughs from a variety
of sources in Mrk 509, including the outflow from the active nucleus, the ISM
and halo of the host galaxy, and infalling clouds or stripped gas from a merger
that are illuminated by the AGN. Variability between the STIS and COS
observation of the -400 km/s component allows us to set an upper limit on its
distance of < 250 pc. Similarly, variability of a component at +150 km/s
between two prior FUSE observations limits its distance to < 1.5 kpc. The UV
absorption only partially covers the emission from the AGN nucleus. Covering
fractions are lower than those previously seen with STIS, and are comparable to
those seen with FUSE. Given the larger apertures of COS and FUSE compared to
STIS, we favor scattered light from an extended region near the AGN as the
explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
We conclude that the outflow from the active nucleus is a multiphase wind.Comment: 21 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysics, 26 May 201
Multiwavelength campaign on Mrk 509. I. Variability and spectral energy distribution
(Abridged) Active galactic nuclei show a wealth of interesting physical
processes, some of which are poorly understood. We want to address a number of
open questions, including the location and physics of the outflow from AGN, the
nature of the continuum emission, the geometry and physical state of the X-ray
broad emission line region, the Fe-K line complex, the metal abundances of the
nucleus and finally the interstellar medium of our own Galaxy. We study one of
the best targets for these aims, the Seyfert 1 galaxy Mrk 509 with a
multiwavelength campaign using five satellites (XMM-Newton, INTEGRAL, Chandra,
HST and Swift) and two ground-based facilities (WHT and PAIRITEL). Our
observations cover more than five decades in frequency, from 2 um to 200 keV.
The combination of high-resolution spectroscopy and time variability allows us
to disentangle and study the different components. Our campaign covers 100 days
from September to December 2009, and is centred on a simultaneous set of deep
XMM-Newton and INTEGRAL observations with regular time intervals, spanning
seven weeks. We obtain a continuous light curve in the X-ray and UV band,
showing a strong, up to 60% flux increase in the soft X-ray band during the
three weeks in the middle of our deepest monitoring campaign, and which is
correlated with an enhancement of the UV flux. This allows us to study the time
evolution of the continuum and the outflow. By stacking the observations, we
have also obtained one of the best X-ray and UV spectra of a Seyfert galaxy
ever obtained. In this paper we also study the effects of the spectral energy
distribution (SED) that we obtained on the photo-ionisation equilibrium. Thanks
to our broad-band coverage, uncertainties on the SED do not strongly affect the
determination of this equilibrium.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysic
Опухоли с невыявленным первичным очагом: современные подходы к лечению
Представлены современные методы и схемы лечения разных видов рака с невыясненным очагом и получаемые результаты.Contemporary methods of treatment of various types of cancer with unrevealed focus as well as the obtained results are described
Multiwavelength campaign on Mrk 509 VIII. Location of the X-ray absorber
The bright Seyfert 1 galaxy Mrk 509 was monitored by XMM-Newton and other
satellites in 2009 to constrain the location of the outflow. We have studied
the response of the photoionised gas to changes in the ionising flux produced
by the central regions. We used the 5 discrete ionisation components A-E
detected in the time-averaged spectrum taken with the RGS. Using the ratio of
fluxed EPIC and RGS spectra, we put tight constraints on the variability of the
absorbers. Monitoring with the Swift satellite started 6 weeks before the
XMM-Newton observations, allowing to use the ionising flux history and to
develop a model for the time-dependent photoionisation. Components A and B are
too weak for variability studies, but the distance for component A is known
from optical imaging of the [O III] line to be ~3 kpc. During the 5 weeks of
the XMM-Newton observations we found no evidence of changes in the 3 X-ray
dominant ionisation components C-E, despite a huge soft X-ray intensity
increase of 60% in the middle of our campaign. This excludes high-density gas
close to the black hole. Instead, using our time-dependent modelling, we find
low density and derive firm lower limits to the distance of these components.
Component D shows evidence for variability on longer time scales, yielding an
upper limit to the distance. For component E we derive an upper limit to the
distance based on the argument that the thickness of the absorbing layer must
be less than its distance to the black hole. Combining these results, at the
90% confidence level, component C has a distance of >70 pc, component D between
5-33 pc, and component E >5 pc but smaller than 21-400 pc, depending upon
modelling details. These results are consistent with the upper limits from the
HST/COS observations of our campaign and point to an origin of the dominant,
slow (v<1000 km/s) outflow components in the NLR or torus-region of Mrk 509.Comment: 17 pages, 16 figures, accepted for publication in Astronomy and
Astrophysic
Multiwavelength campaign on Mrk 509. II. Analysis of high-quality Reflection Grating Spectrometer spectra
We study the bright Seyfert 1 galaxy Mrk~509 with the Reflection Grating
Spectrometers (RGS) of XMM-Newton using the RGS multi-pointing mode of
XMM-Newton for the first time in order to constrain the properties of the
outflow in this object. We want to obtain the most accurate spectral properties
from the 600 ks spectrum of Mrk 509 which has excellent statistical quality. We
derive an accurate relative calibration for the effective area of the RGS,
derive an accurate absolute wavelength calibration, improve the method for
adding time-dependent spectra and enhance the efficiency of the spectral
fitting by two orders of magnitude. We show the major improvement of the
spectral data quality due to the use of the new RGS multi-pointing mode of
XMM-Newton. We illustrate the gain in accuracy by showing that with the
improved wavelength calibration the two velocity troughs observed in UV spectra
are resolved.Comment: 16 pages, 13 figures, 13 tables. Submitted to Astronomy &
Astrophysics, revised version after second referee's comment
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