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 $10^5$ rad m$^{-2}$. 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

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

Electro-osmosis on anisotropic super-hydrophobic surfaces

We give a general theoretical description of electro-osmotic flow at striped super-hydrophobic surfaces in a thin double layer limit, and derive a relation between the electro-osmotic mobility and hydrodynamic slip-length tensors. Our analysis demonstrates that electro-osmotic flow shows a very rich behavior controlled by slip length and charge at the gas sectors. In case of uncharged liquid-gas interface, the flow is the same or inhibited relative to flow in homogeneous channel with zero interfacial slip. By contrast, it can be amplified by several orders of magnitude provided slip regions are uniformly charged. When gas and solid regions are oppositely charged, we predict a flow reversal, which suggests a possibility of huge electro-osmotic slip even for electro-neutral surfaces. On the basis of these observations we suggest strategies for practical microfluidic mixing devices. These results provide a framework for the rational design of super-hydrophobic surfaces.Comment: 4 pages, 4 figures; submitted to PRL Revised version: several references added, typos corrected. Supplementary file was restructured, the second part of the original EPAPS was removed and is supposed to be published as a separate pape