1,697 research outputs found
Investigation into the limits of perturbation theory at low Q^2 using HERA deep inelastic scattering data
A phenomenological study of the final combined HERA data on inclusive deep
inelastic scattering (DIS) has been performed. The data are presented and
investigated for a kinematic range extending from values of the four-momentum
transfer, , above 10 GeV down to the lowest values observable at
HERA of = 0.045 GeV and Bjorken , = 6
10. The data are well described by fits based on perturbative quantum
chromodynamics (QCD) using collinear factorisation and evolution of the parton
densities encompassed in the DGLAP formalism from the highest down to
of a few GeV. The Regge formalism can describe the data up to 0.65 GeV. The complete data set can be described by a new fit
using the ALLM parameterisation. The region between the Regge and the
perturbative QCD regimes is of particular interest.Comment: 38 pages, 13 figure
A Stellar Rotation Census of B Stars: from ZAMS to TAMS
Two recent observing campaigns provide us with moderate dispersion spectra of
more than 230 cluster and 370 field B stars. Combining them and the spectra of
the B stars from our previous investigations (430 cluster and 100
field B stars) yields a large, homogeneous sample for studying the rotational
properties of B stars. We derive the projected rotational velocity ,
effective temperature, gravity, mass, and critical rotation speed for each star. We find that the average is significantly lower
among field stars because they are systematically more evolved and spun down
than their cluster counterparts. The rotational distribution functions of
for the least evolved B stars show that lower mass B
stars are born with a larger proportion of rapid rotators than higher mass B
stars. However, the upper limit of that may separate
normal B stars from emission line Be stars (where rotation promotes mass loss
into a circumstellar disk) is smaller among the higher mass B stars. We compare
the evolutionary trends of rotation (measured according to the polar gravity of
the star) with recent models that treat internal mixing. The spin-down rates
observed in the high mass subset () agree with predictions, but
the rates are larger for the low mass group (). The faster spin
down in the low mass B stars matches well with the predictions based on
conservation of angular momentum in individual spherical shells. Our results
suggest the fastest rotators (that probably correspond to the emission line Be
stars) are probably formed by evolutionary spin up (for the more massive stars)
and by mass transfer in binaries (for the full range of B star masses).Comment: 44 pages, 10 figures, accepted for publication in Ap
Crowdsourcing malaria parasite quantification: an online game for analyzing images of infected thick blood smears
Background: There are 600,000 new malaria cases daily worldwide. The gold standard for estimating the parasite burden and the corresponding severity of the disease consists in manually counting the number of parasites in blood smears through a microscope, a process that can take more than 20 minutes of an expert microscopist’s time.
Objective: This research tests the feasibility of a crowdsourced approach to malaria image analysis. In particular, we investigated whether anonymous volunteers with no prior experience would be able to count malaria parasites in digitized images of thick blood smears by playing a Web-based game.
Methods: The experimental system consisted of a Web-based game where online volunteers were tasked with detecting parasites in digitized blood sample images coupled with a decision algorithm that combined the analyses from several players to produce an improved collective detection outcome. Data were collected through the MalariaSpot website. Random images of thick blood films containing Plasmodium falciparum at medium to low parasitemias, acquired by conventional optical microscopy, were presented to players. In the game, players had to find and tag as many parasites as possible in 1 minute. In the event that players found all the parasites present in the image, they were presented with a new image. In order to combine the choices of different players into a single crowd decision, we implemented an image processing pipeline and a quorum algorithm that judged a parasite tagged when a group of players agreed on its position.
Results: Over 1 month, anonymous players from 95 countries played more than 12,000 games and generated a database of more than 270,000 clicks on the test images. Results revealed that combining 22 games from nonexpert players achieved a parasite counting accuracy higher than 99%. This performance could be obtained also by combining 13 games from players trained for 1 minute. Exhaustive computations measured the parasite counting accuracy for all players as a function of the number of games considered and the experience of the players. In addition, we propose a mathematical equation that accurately models the collective parasite counting performance.
Conclusions: This research validates the online gaming approach for crowdsourced counting of malaria parasites in images of thick blood films. The findings support the conclusion that nonexperts are able to rapidly learn how to identify the typical features of malaria parasites in digitized thick blood samples and that combining the analyses of several users provides similar parasite counting accuracy rates as those of expert microscopists. This experiment illustrates the potential of the crowdsourced gaming approach for performing routine malaria parasite quantification, and more generally for solving biomedical image analysis problems, with future potential for telediagnosis related to global health challenges
1985 riprap tests in flood control channels
CER85-86-JFR-AS-SRA-EVR-17.Includes bibliographical references (page 42).August, 1985.Prepared for U.S. Army Corps of Engineers, Waterways Experiment Station
The Gamification of Augmented Reality Art
Augmented Reality (AR) and its applications are being used in many applications, including gaming, education, industry, research, and art. Gamification refers to the merging of games with interactive media (video games, Virtual and Augmented Realities, for example) to allow for the completion of difficult digital labour of research in a more fun, intuitive fashion. In this chapter, the merging of gamification and Augmented Reality-based art is discussed, its impact in terms of digital labour as well as examples of Augmented Reality that exhibit gamification or elements of it. Speculative design fictions of gamified Augmented Reality are examined to determine possible future outcomes of this genre. Lastly historical experiments in user interface design are mentioned to propose future solutions for Augmented Reality applications, artistic installations and gamification scenarios
Spots structure and stratification of helium and silicon in the atmosphere of He-weak star HD 21699
The magnetic star HD 21699 possesses a unique magnetic field structure where
the magnetic dipole is displaced from the centre by 0.4 +/- 0.1 of the stellar
radius (perpendicularly to the magnetic axis), as a result, the magnetic poles
are situated close to one another on the stellar surface with an angular
separation of 55 and not 180 as seen in the case of a centred dipole.
Respectively, the two magnetic poles form a large "magnetic spot".
High-resolution spectra were obtained allowing He I and Si II abundance
variations to be studied as a function of rotational phase. The results show
that the helium abundance is concentrated in one hemisphere of the star, near
the magnetic poles and it is comparatively weaker in another hemisphere, where
magnetic field lines are horizontal with respect to the stellar surface. At the
same time, the silicon abundance is greatest between longitudes of 180 -
320, the same place where the helium abundance is the weakest. These
abundance variations (with rotational phase) support predictions made by the
theory of atomic diffusion in the presence of a magnetic field. Simultaneously,
these result support the possibility of the formation of unusual structures in
stellar magnetic fields. Analysis of vertical stratification of the silicon and
helium abundances shows that the boundaries of an abundance jump (in the two
step model) are similar for each element; = 0.8-1.2 for helium
and 0.5-1.3 for silicon. The elemental abundances in the layers of effective
formation of selected absorption lines for various phases are also correlated
with the excitation energies of low transition levels: abundances are enhanced
for higher excitation energy and higher optical depth within the applied model
atmosphere.Comment: accepted by MN, 7 pagers, 10 figs, 3 table
VLBA imaging of a periodic 12.2 GHz methanol maser flare in G9.62+0.20E
The class II methanol maser source G9.62+0.20E undergoes periodic flares at
both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven
epochs over three months using the VLBA at 12.2 GHz. High angular resolution
images (beam size 1.7 x 0.6 mas) were obtained, enabling us to observe
changes in 16 individual maser components. It was found that while existing
maser spots increased in flux density, no new spots developed and no changes in
morphology were observed. This rules out any mechanism which disturbs the
masing region itself, implying that the flares are caused by a change in either
the seed or pump photon levels. A time delay of 1--2 weeks was observed between
groups of maser features. These delays can be explained by light travel time
between maser groups. The regularity of the flares can possibly be explained by
a binary system.Comment: 11 pages, accepted for publication in MNRA
Speckle Interferometry of Metal-Poor Stars in the Solar Neighborhood. I
We report the results of speckle-interferometric observations of 109 high
proper-motion metal-poor stars made with the 6-m telescope of the Special
Astrophysical Observatory of the Russian Academy of Sciences. We resolve eight
objects -- G102-20, G191-55, BD+19~1185A, G89-14, G87-45, G87-47,
G111-38, and G114-25 -- into individual components and we are the first to
astrometrically resolve seven of these stars. New resolved systems included two
triple (G111-38, G87-47) and one quadruple (G89-14) star. The ratio of
single-to-binary-to-triple-to-quadruple systems among the stars of our sample
is equal to 71:28:6:1.Comment: 8 pages, 4 figures, accepted to Astrophysical Bulleti
The Chromospheric Activity and Ages of M Dwarf Stars in Wide Binary Systems
We investigate the relationship between age and chromospheric activity for
139 M dwarf stars in wide binary systems with white dwarf companions. The age
of each system is determined from the cooling age of its white dwarf component.
The current limit for activity-age relations found for M dwarfs in open
clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for
the exploration of this relationship at ages older than 4 Gyr. The general
trend of stars remaining active for a longer time at later spectral type is
confirmed. However, our larger sample and greater age range reveals additional
complexity in assigning age based on activity alone. We find that M dwarfs in
wide binaries older than 4 Gyr depart from the log-linear relation for clusters
and are found to have activity at magnitudes, colors and masses which are
brighter, bluer and more massive than predicted by the cluster relation. In
addition to our activity-age results, we present the measured radial velocities
and complete space motions for 161 white dwarf stars in wide binaries.Comment: 22 pages including 9 figures and 5 tables. Accepted for publication
in The Astronomical Journa
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