EXPLORING THE STAGES OF INFORMATION SEEKING IN A CROSS-MODAL CONTEXT

Previous studies of users with visual impairments access to the web have focused on human-web interaction. This study explores the under investigated area of cross-modal collaborative information seeking (CCIS), that is, the challenges and opportunities that exist in supporting visually impaired (VI) users to take an effective part in collaborative web search tasks with sighted peers. We conducted an observational study to investigate the process with fourteen pairs of VI and sighted users in co-located and distributed settings. The study examined the effects of cross-modal collaborative interaction on the stages of the individual Information Seeking (IS) process. The findings showed that the different stages of the process were performed individually most of the time; however it was observed that some collaboration took place in the results exploration and management stages. The accessibility challenges faced by VI users affected their individual and collaborative interaction and also enforced certain points of collaboration. The paper concludes with some recommendations towards improving the accessibility of cross-modal collaborative search.Peer Reviewe

The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance

The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to mid-ultraviolet) solar radiometer onboard the European Space Agency PROBA2 mission that was launched in November 2009. LYRA acquires solar irradiance measurements at a high cadence (nominally 20 Hz) in four broad spectral channels, from soft X-ray to MUV, that have been chosen for their relevance to solar physics, space weather and aeronomy. In this article, we briefly review the design of the instrument, give an overview of the data products distributed through the instrument website, and describe the way that data are calibrated. We also briefly present a summary of the main fields of research currently under investigation by the LYRA consortium

Computer programs for calculating two-dimensional potential flow in and about propulsion system inlets

Incompressible potential flow calculations are presented that were corrected for compressibility in two-dimensional inlets at arbitrary operating conditions. Included are a statement of the problem to be solved, a description of each of the computer programs, and sufficient documentation, including a test case, to enable a user to run the program

The temporal characteristics of the early and late stages of L- and M-cone pathways that signal brightness

Flickering 560-nm light appears brighter and less saturated than steady light of the same average intensity. The changes in appearance are consistent with the visual signal's being distorted at some nonlinear site (or sites) within the visual pathway at which new temporal components, not part of the original waveform, are produced. By varying the input stimulus to manipulate these new temporal components--called distortion products--and measuring our observers' sensitivity in detecting them, we derived the temporal attenuation characteristics of the early (prenonlinearity) and late (post-nonlinearity) stages of the L- and M-cone pathway that signals brightness. We found that the early stage acts like a band-pass filter peaking at 10-15 Hz with sensitivity losses at both lower and higher frequencies, whereas the late stage acts like a two-stage low-pass filter with a corner frequency near 3 Hz. Although brightness is often associated with the fast achromatic or luminance pathway, these filter characteristics, and particularly those of the late filter, are consistent with comparable features of the L-M chromatic pathway that produce mainly chromatic distortion products (Petrova, Henning, & Stockman, 2013). A plausible site for the nonlinearity is after surround antagonism from horizontal cells. Modeling suggested the form of the nonlinearity to be initially expansive but possibly with a hard limit at the highest input levels

Detection of Extended Polarized Ultraviolet Radiation from the z = 1.82 Radio Galaxy 3C 256

We have detected spatially extended linear polarized UV emission from the high-redshift radio galaxy 3C~256 ($z=1.82$). A spatially integrated ($7.8''$ diameter aperture) measurement of the degree of polarization of the $V-$band (rest frame 0.19 $\mu$m) emission yields a value of 16.4\% ($\pm 2.2$\%) with a position angle of $42{}\rlap{\rm .}^\circ 4$ ($\pm 3{}\rlap{\rm .}^\circ 9$), orthogonal to the position angle on the sky of the major axis of the extended emission. The peak emission measured with a $3.6''$ diameter circular aperture is 11.7\% ($\pm 1.5$\%) polarized with a position angle of $42{}\rlap{\rm .}^\circ 4$ ($\pm 3{}\rlap{\rm .}^\circ 6$). An image of the polarized flux is presented, clearly displaying that the polarized flux is extended and present over the entire extent of the object. While it has been suggested that the UV continuum of 3C~256 might be due to star formation (Elston 1988) or a protogalaxy (Eisenhardt \& Dickinson 1993) based on its extremely blue spectral energy distribution and similar morphology at UV and visible wavelengths, we are unable to reconcile the observed high degree of polarization with such a model. While the detection of polarized emission from HZRGs has been shown to be a common phenomena, 3C~256 is only the third object for which a measurement of the extended polarized UV emission has been presented. These data lend additional support to the suggestion first made by di Serego Alighieri and collaborators that the ``alignment effect'', the tendency for the extended UV continuum radiation and line emission from HZRGs to be aligned with the major axis of the extended radio emission, is in large part due to scattering of anisotropic nuclear emission.Comment: 11 pages, LaTeX (aaspp style) file. Figure available by request to [email protected]

The Three Dimensional Structure of EUV Accretion Regions in AM Herculis Stars: Modeling of EUV Photometric and Spectroscopic Observations

We have developed a model of the high-energy accretion region for magnetic cataclysmic variables and applied it to {\it Extreme Ultraviolet Explorer} observations of 10 AM Herculis type systems. The major features of the EUV light curves are well described by the model. The light curves exhibit a large variety of features such as eclipses of the accretion region by the secondary star and the accretion stream, and dips caused by material very close to the accretion region. While all the observed features of the light curves are highly dependent on viewing geometry, none of the light curves are consistent with a flat, circular accretion spot whose lightcurve would vary solely from projection effects. The accretion region immediately above the WD surface is a source of EUV radiation caused by either a vertical extent to the accretion spot, or Compton scattering off electrons in the accretion column, or, very likely, both. Our model yields spot sizes averaging 0.06 R$_{WD}$, or $f \sim 1 \times 10^{-3}$ the WD surface area, and average spot heights of 0.023 R$_{WD}$. Spectra extracted during broad dip phases are softer than spectra during the out-of-dip phases. This spectral ratio measurement leads to the conclusion that Compton scattering, some absorption by a warm absorber, geometric effects, an asymmetric temperature structure in the accretion region and an asymmetric density structure of the accretion columnare all important components needed to fully explain the data. Spectra extracted at phases where the accretion spot is hidden behind the limb of the WD, but with the accretion column immediately above the spot still visible, show no evidence of emission features characteristic of a hot plasma.Comment: 30 Pages, 11 Figure

Colour and brightness encoded in a common L- and M-cone pathway with expansive and compressive nonlinearities?

Lights near 560 nm appear brighter when flickered, whereas lights near 520 or 650 nm appear yellower. Both effects are consistent with signal distortion within the visual pathway—brightness changes at an expansive nonlinearity, and hue shifts at a compressive one. We previously manipulated the distortion products generated by each nonlinearity to extract the temporal properties of stages of the L- and M-cone pathways that signal brightness and colour before (early stages) and after (late stages) each nonlinearity. We find that the attenuation characteristics of the early and late stages are virtually identical in both pathways: the early temporal stage acts like a band-pass filter peaking at 10-15 Hz, while the late stage acts like low-pass filter with a cut-off frequency near 3 Hz. We propose a physiologically-relevant model that accounts for the filter shapes and incorporates both nonlinearities within a common parvocellular pathway. The shape of the early bandpass filter is consistent with antagonism between “center” signals and more sluggish and delayed “surround” signals, while the late filter is consistent with a simple two-stage low-pass filter. Modelling suggests that the brightness-change and hue-shift are both initially caused by the half-wave rectification and partition of signals into ON and OFF components. However, the hue shift is probably caused by the additional effects of a later nonlinearity that compresses chromatic “red” and “green” signals. Plausible sites for the expansive half-wave rectifying nonlinearity are after surround antagonism, possibly from horizontal cells, but the compressive nonlinearity is likely to be after the late filter