27,765 research outputs found
Submillimeter polarization and variability of quasar PKS 1830-211
Polarization from active galactic nuclei is interpreted as a signpost of the
role of magnetic fields in the launch and collimation of their relativistic
radio jets. Here, we report the detection of a clear polarization signal from
ALMA observations of the gravitationally lensed quasar PKS 1830-211 at
submillimeter wavelengths (Band 9, 650 GHz). Applying a
differential-polarimetry technique to the two compact lensed images of the
quasar, we estimate a fractional polarization of ~5% for one lensed image,
while the other appears nearly unpolarized, which implies that the polarization
activity varies on a timescale of a few weeks. With additional ALMA Band 7 and
8 (between 300-500 GHz) concomitant data, we constrain a Faraday rotation of a
few rad m. We also observe flux-density variability of ~10%
within one hour in Band 9. This work illustrates that a differential analysis
can extract high-accuracy information (flux-density ratio and polarimetry) free
of calibration issues from resolved sources in the submillimeter domain.Comment: 7 pages, 6 figures, accepted for publications in A&
Using gravitational lensed images to investigate the intrinsic AGN variability
We discuss about how the relative flux densities among the images of
gravitationally-lensed active galactic nuclei, AGN, can be used to study the
intrinsic AGN variability with high accuracy. Multi-frequency monitoring
observations of resolved gravitational lenses can allow us to detect signals of
very weak variability and also provide information about the jet opacity and
structure. As an example, we investigate the variability of the flux-density
ratio between the two lensed images of the blazar B0218+357, using
dual-frequency cm-wave observations. Similar to our previously reported
submm-wave observations of the lensed blazar PKS1830-211, we observe a clear
chromatic variability, starting short before an increase in the flux-density of
the blazar. The evolution of the flux-density ratios between the blazar images
shows a more clear and rich structure than that of the mere lightcurves of each
individual image. The accuracy in the ratio measurements is allowing us to see
variability episodes in the blazar that are weaker than the natural scatter in
the absolute flux-density measurements. A simple opacity model in the jet is
used to consistently explain the difference between the flux-density-ratio
evolution at the two frequencies.Comment: 5 pages, 2 figures. Accepted for publication in A&A. Final versio
Cooperative transport by small teams of molecular motors
Molecular motors power directed transport of cargoes within cells. Even if a
single motor is sufficient to transport a cargo, motors often cooperate in
small teams. We discuss the cooperative cargo transport by several motors
theoretically and explore some of its properties. In particular we emphasize
how motor teams can drag cargoes through a viscous environment.Comment: 9 pages, 1 figure, uses ws-brl.cls, presented at Bio-Systems
conference, Berlin, June 200
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Understanding needle-related distress in children with cystic fibrosis
Objective. To explore the nature and management of needle-related distress in children and adolescents with cystic fibrosis (CF).
Design. Qualitative study using semi-structured interviews.
Methods. Fourteen child–parent dyads took part. Children (5 male; 9 female) had a mean age of 12.4 years (range 7–17) and were mostly diagnosed with CF at birth (N= 11). Frequency of needle procedures ranged from once to six times a year. Parents (3 male; 11 female) had a mean age of 41.5 years and were from a variety of socio-economic backgrounds. Interviews were transcribed and analysed using thematic analysis.
Results. Most participants identified previous needle experiences and pain as related to their needle anxiety. Over half of parents and children considered ‘taking control’ to be the optimum coping strategy. The majority of parents and children thought inhaled nitrous oxide gas during needle procedures was helpful in managing needle-related distress. Parent and staff influences on needle-related distress are also examined.
Conclusions. Needle-related distress in children with CF has a substantial impact on children and their parents, and may lead to management problems and treatment refusal. Psychological and pharmacological interventions could reduce distress and aid management
Intentionality versus Constructive Empiricism
By focussing on the intentional character of observation in science, we argue that Constructive Empiricism – B.C. van Fraassen’s much debated and explored view of science – is inconsistent. We then argue there are at least two ways out of our Inconsistency Argument, one of which is more easily to square with Constructive Empiricism than the other
Photovoice methodology to promote education for sustainable development
Education for Sustainable Development is best addressed in a spontaneous, place-based context where participants have the freedom of choice. Such an opportunity occurred with the Ripple Effect, a global initiative that allows participants to indicate the role of water in their living experience. Preservice teachers embraced the chance to display their interpretation of the role of water in their lives by participating in a Photovoice project. Photovoice is a chameleon in action research as it not only provides a research methodology but can serve as a reflection tool to enhance learning. The preservice teachers concluded, after reflecting on the role of water in their daily lives, that they are citizen scientists who can utilize place-based learning opportunities. The Photovoice project allowed for affective learning as well as an opportunity to face communal problematic scenarios regarding water
UVMULTIFIT: A versatile tool for fitting astronomical radio interferometric data
The analysis of astronomical interferometric data is often performed on the
images obtained after deconvolution of the interferometer's point spread
function (PSF). This strategy can be understood (especially for cases of sparse
arrays) as fitting models to models, since the deconvolved images are already
non-unique model representations of the actual data (i.e., the visibilities).
Indeed, the interferometric images may be affected by visibility gridding,
weighting schemes (e.g., natural vs. uniform), and the particulars of the
(non-linear) deconvolution algorithms. Fitting models to the direct
interferometric observables (i.e., the visibilities) is preferable in the cases
of simple (analytical) sky intensity distributions. In this paper, we present
UVMULTIFIT, a versatile library for fitting visibility data, implemented in a
Python-based framework. Our software is currently based on the CASA package,
but can be easily adapted to other analysis packages, provided they have a
Python API. We have tested the software with synthetic data, as well as with
real observations. In some cases (e.g., sources with sizes smaller than the
diffraction limit of the interferometer), the results from the fit to the
visibilities (e.g., spectra of close by sources) are far superior to the output
obtained from the mere analysis of the deconvolved images. UVMULTIFIT is a
powerful improvement of existing tasks to extract the maximum amount of
information from visibility data, especially in cases close to the
sensitivity/resolution limits of interferometric observations.Comment: 10 pages, 4 figures. Accepted in A&A. Code available at
http://nordic-alma.se/support/software-tool
Phase diversity restoration of sunspot images I. Relations between penumbral and photospheric features
We investigate the dynamics of and the relations between small-scale
penumbral and photospheric features near the outer penumbral boundary:
penumbral grains (PGs), dark penumbral fibrils, granules, and photospheric
G-band bright points. The analysis is based on a 2 h time sequence of a sunspot
close to disc center, taken simultaneously in the G-band and in the blue
continuum at 450.7 nm. Observations were performed at the Swedish Vacuum Solar
Telescope (La Palma) in July 1999. A total of 2564 images (46 arcsec x 75
arcsec) were corrected for telescope aberrations and turbulence perturbations
by applying the inversion method of phase diversity. Our findings can by
summarized as follows: (a) One third of the outward-moving PGs pass through the
outer penumbral boundary and then either continue moving as small bright
features or expand and develop into granules. (b) Former PGs and G-band bright
points next to the spot reveal a different nature. The latter have not been
identified as a continuation of PGs escaping from the penumbra. The G-band
bright points are mostly born close to dark penumbral fibrils where the
magnetic field is strong, whereas PGs stem from the less-magnetized penumbral
component and evolve presumably to non-magnetic granules or small bright
features.Comment: Accepted by A&A, 9 pages and 5 figure
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