1,350 research outputs found
Hierarchy and Competition in CSCW applications: Model and case study
CSCW applications need to adapt themselves to the functional and organizational structures of people that use them. However they do not usually support division in groups with a certain hierarchical structure among them. In this paper, we propose and study a theoretical model of groupware appliations that reflects those hierarchical interactions. The proposed model is also intended to evaluate the effects in performance derived from competitive and collaborative relationships among the components of a hierarchy of groups. In order to demonstrate the above ideas, a groupware game, called Alymod, was designed and implemented using a modified version of a well-known CSCW Toolkit, namely Groupkit. Groupkit was modified in order to support group interactions in the same CSCW application. In Alymod, participants compete or collaborate within a hierarchical structure to achieve a common goal (completing gaps in a text, finishing numerical series, resolving University course examinations, etc.).Publicad
Signatures of the impact of flare ejected plasma on the photosphere of a sunspot light-bridge
We investigate the properties of a sunspot light-bridge, focusing on the
changes produced by the impact of a plasma blob ejected from a C-class flare.
We observed a sunspot in active region NOAA 12544 using spectropolarimetric
raster maps of the four Fe I lines around 15655 \AA\ with the GREGOR Infrared
Spectrograph (GRIS), narrow-band intensity images sampling the Fe I 6173 \AA\
line with the GREGOR Fabry-P\'erot Interferometer (GFPI), and intensity broad
band images in G-band and Ca II H band with the High-resolution Fast Imager
(HiFI). All these instruments are located at the GREGOR telescope at the
Observatorio del Teide, Tenerife, Spain. The data cover the time before,
during, and after the flare event. The analysis is complemented with
Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI)
data from the Solar Dynamics Observatory (SDO). The physical parameters of the
atmosphere at differents heights were inferred using spectral-line inversion
techniques. We identify photospheric and chromospheric brightenings, heating
events, and changes in the Stokes profiles associated to the flare eruption and
the subsequent arrival of the plasma blob to the light bridge, after traveling
along an active region loop. The measurements suggest that these phenomena are
the result of reconnection events driven by the interaction of the plasma blob
with the magnetic field topology of the light bridge.Comment: Accepted for publication in A&
Orbital characterization of superbolides observed from space: dynamical association with near-Earth objects, meteoroid streams and identification of hyperbolic meteoroids
There is an unceasing incoming flux of extraterrestrial materials reaching
the Earth's atmosphere. Some of these objects produce luminous columns when
they ablate during the hypersonic encounter with air molecules. A few fireballs
occur each year bright enough to be detected from space. The source of these
events is still a matter of debate, but it is generally accepted that they are
of sporadic origin. We studied the NASA-JPL Center for NEOs Studies (CNEOS)
fireball database to infer the dynamic origin of large bolides produced by
meter-sized projectiles that impacted our planet. These likely
meteorite-dropping events were recorded by the US Government satellite sensors.
We estimated the false-positive rate and analyzed the time evolution of
multiple orbit dissimilarity criteria concerning potential associations with
near-Earth objects and meteoroid streams. We found that at least 16% of the
large bolides could be associated with meteoroid streams, about 4% are likely
associated with near-Earth asteroids, and 4% may be linked to near-Earth
comets. This implies that a significant fraction of meter-sized impactors
producing large bolides may have an asteroidal or cometary origin. In addition,
we found at least three bolides having hyperbolic orbits with high tensile
strength values. Meter-sized meteoroids of interstellar origin could be more
common than previously thought, representing about 1% of the flux of large
bolides. The inferred bulk physical properties suggest that the interstellar
medium could bias these projectiles towards high strength rocks with the
ability to survive prolonged exposure to the harsh interstellar space
conditions.Comment: Accepted for publication in The Astronomical Journal (AAS38905R1
Fermi surface and electronic structure of Pb/Ge(111)
The electronic structure of Pb/Ge(111) has been probed along the temperature-induced phase transition ct -root 3X root 3R30 degrees double right arrow 3 X 3 using angle-resolved photoemission. The alpha-root 3X root 3R30 degrees phase is metallic due to the existence of a half-filled, dispersing surface band. The 3 X 3 phase is characterized by the appearance of an additional surface band with 3 X 3 periodicity, whose role in the phase transition is discussed. The Fermi-surface topology of the alpha-root 3X root 3R30 degrees phase has been probed using angle-resolved photoemission. Its shape is undulated, and it resembles strongly the theoretical prediction, with a Fermi momentum of 0.31 Angstrom(-1) along directions and 0.40 Angstrom(-1) along directions. These values were determined from different experimental methods, and agree with the values needed for a perfect 3 X 3 nesting. However, the Fermi surface exhibits no large flat areas suitable for electronic nesting
Bayesian Analysis of Solar Oscillations
A Bayesian probability based approach is applied to the problem of detecting
and parameterizing oscillations in the upper solar atmosphere for the first
time. Due to its statistical origin, this method provides a mechanism for
determining the number of oscillations present, gives precise estimates of the
oscillation parameters with a self-consistent statistical error analysis, and
allows the oscillatory model signals to be reconstructed within these errors.
A highly desirable feature of the Bayesian approach is the ability to resolve
oscillations with extremely small frequency separations. The code is applied to
SOHO/CDS (Solar and Heliospheric Observatory/Coronal Diagnostic Spectrometer) O
V 629A observations and resolves four distinct P4, P5, P6 and P7 p-modes within
the same sunspot transition region. This suggests that a spectrum of
photospheric p-modes is able to propagate into the upper atmosphere of the Sun
and Sun-like stars, and places precise observational constraints on models of
umbral eigen modes.Comment: Accepted for publication in The Astrophysical Journal. It is
scheduled for the ApJ July 20, 2008, v682n 1 issu
Probing the Solar Atmosphere Using Oscillations of Infrared CO Spectral Lines
Oscillations were observed across the whole solar disk using the Doppler
shift and line depth of spectral lines from the CO molecule near 4666~nm with
the National Solar Observatory's McMath/Pierce solar telescope. Power,
coherence, and phase spectra were examined, and diagnostic diagrams reveal
power ridges at the solar global mode frequencies to show that these
oscillations are solar p-modes. The phase was used to determine the height of
formation of the CO lines by comparison with the IR continuum intensity phase
shifts as measured in Kopp et al., 1992; we find the CO line formation height
varies from 425 < z < 560 km as we move from disk center towards the solar limb
1.0 > mu > 0.5. The velocity power spectra show that while the sum of the
background and p-mode power increases with height in the solar atmosphere as
seen in previous work, the power in the p-modes only (background subtracted)
decreases with height, consistent with evanescent waves. The CO line depth
weakens in regions of stronger magnetic fields, as does the p-mode oscillation
power. Across most of the solar surface the phase shift is larger than the
expected value of 90 degrees for an adiabatic atmosphere. We fit the phase
spectra at different disk positions with a simple atmospheric model to
determine that the acoustic cutoff frequency is about 4.5 mHz with only small
variations, but that the thermal relaxation frequency drops significantly from
2.7 to 0 mHz at these heights in the solar atmosphere
XPS measurements on single BiTe nanowires fabricated by electrodeposition in etched ion-track membranes
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Towards the Identification and Classification of Solar Granulation Structures Using Semantic Segmentation
Solar granulation is the visible signature of convective cells at the solar surface. The granulation cellular pattern observed in the continuum intensity images is characterised by diverse structures e.g., bright individual granules of hot rising gas or dark intergranular lanes. Recently, the access to new instrumentation capabilities has given us the possibility to obtain high-resolution images, which have revealed the overwhelming complexity of granulation (e.g., exploding granules and granular lanes). In that sense, any research focused on understanding solar small-scale phenomena on the solar surface is sustained on the effective identification and localization of the different resolved structures. In this work, we present the initial results of a proposed classification model of solar granulation structures based on neural semantic segmentation. We inspect the ability of the U-net architecture, a convolutional neural network initially proposed for biomedical image segmentation, to be applied to the dense segmentation of solar granulation. We use continuum intensity maps of the IMaX instrument onboard the Sunrise I balloon-borne solar observatory and their corresponding segmented maps as a training set. The training data have been labeled using the multiple-level technique (MLT) and also by hand. We performed several tests of the performance and precision of this approach in order to evaluate the versatility of the U-net architecture. We found an appealing potential of the U-net architecture to identify cellular patterns in solar granulation images reaching an average accuracy above 80% in the initial training experiments
Contributions to the radiogenic isotopic fingerprint of Tenerife wine from land, sea and air
We present preliminary results of a study to characterise the radiogenic isotopic fingerprint of wines across the island of Tenerife, Canary Islands, Spain, focussing initially upon Sr. The isotopically juvenile nature of Tenerife rocks supports a hypothesis that all biological material grown on Tenerife should be distinct from most other regions on Earth in terms of Sr isotopes, and especially so from the radiogenic Iberian Peninsula. Pilot data largely support this view, yet we also observe clear evidence for an isotopically evolved component in Tenerife wines. In this contribution, we consider that the unique geography of the Canary Islands may help rationalise these observations. The Canaries are adjacent to the most important atmospheric dust source on Earth, the Saharan Desert, which is largely composed of radiogenic sources of Sr. Along with contributions to the Tenerife terroir from atmospheric dust, we also consider the role that sea spray during storm events may play. Should natural processes fail to explain the patterns we observe, anthropogenic mixing during wine-making using components sourced outside the archipelago is a possibility that must be considered, which has implications for consumer confidence and, by extension, the economy of Tenerife.publishe
Response Burden and Dropout in a Probability-Based Online Panel Study â A Comparison between an App and Browser-Based Design
Survey respondents can complete web surveys using different Internet-enabled devices (PCs
versus mobile phones and tablets) and using different software (web browser versus a mobile
software application, âappâ). Previous research has found that completing questionnaires via a
browser on mobile devices can lead to higher breakoff rates and reduced measurement quality
compared to using PCs, especially where questionnaires have not been adapted for mobile
administration. A key explanation is that using a mobile browser is more burdensome and less
enjoyable for respondents. There are reasons to assume apps should perform better than
browsers, but so far, there have been few attempts to assess this empirically. In this study, we
investigate variation in experienced burden across device and software in wave 1 of a three-
wave panel study, comparing an app with a browser-based survey, in which sample members
were encouraged to use a mobile device. We also assess device/software effects on
participation at wave 2. We find that compared to mobile browser respondents, app
respondents were less likely to drop out of the study after the first wave and the effect of the
device used was mediated by subjective burden experienced during wave 1
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