3,510 research outputs found
Tuning the Diversity of Open-Ended Responses from the Crowd
Crowdsourcing can solve problems that current fully automated systems cannot.
Its effectiveness depends on the reliability, accuracy, and speed of the crowd
workers that drive it. These objectives are frequently at odds with one
another. For instance, how much time should workers be given to discover and
propose new solutions versus deliberate over those currently proposed? How do
we determine if discovering a new answer is appropriate at all? And how do we
manage workers who lack the expertise or attention needed to provide useful
input to a given task? We present a mechanism that uses distinct payoffs for
three possible worker actions---propose,vote, or abstain---to provide workers
with the necessary incentives to guarantee an effective (or even optimal)
balance between searching for new answers, assessing those currently available,
and, when they have insufficient expertise or insight for the task at hand,
abstaining. We provide a novel game theoretic analysis for this mechanism and
test it experimentally on an image---labeling problem and show that it allows a
system to reliably control the balance betweendiscovering new answers and
converging to existing ones
Research needs for Chagas disease prevention.
We present an overview of the two main strategies for the primary (vector control) and secondary (patient care) prevention of Chagas disease (CD). We identify major advances, knowledge gaps, and key research needs in both areas. Improved specific chemotherapy, including more practical formulations (e.g., paediatric) or combinations of existing drugs, and a better understanding of pathogenesis, including the relative weights of parasite and host genetic makeup, are clearly needed. Regarding CD vectors, we find that only about 10-20% of published papers on triatomines deal directly with disease control. We pinpoint the pitfalls of the current consensus on triatomine systematics, particularly within the Triatomini, and suggest how some straightforward sampling and analytical strategies would improve research on vector ecology, naturally leading to sounder control-surveillance schemes. We conclude that sustained research on CD prevention is still crucial. In the past, it provided not only the know-how, but also the critical mass of scientists needed to foster and consolidate CD prevention programmes; in the future, both patient care and long-term vector control would nonetheless benefit from more sharply focused, problem-oriented research
High Sensitivity Array Observations of the QSO BRI 1335-0417
We present sensitive phase-referenced VLBI results on the radio continuum
emission from the QSO BRI 1335--0417. The observations were carried out
at 1.4 GHz using the High Sensitivity Array (HSA). Our sensitive VLBI image at
mas ( kpc) resolution shows continuum
emission in BRI 1335--0417 with a total flux density of Jy,
consistent with the flux density measured with the VLA. The size of the source
at FWHM is mas ( kpc) and the derived
intrinsic brightness temperature is K. No continuum
emission is detected at the full VLBI resolution ( mas, pc), with a 4 point source upper limit of 34 Jy
beam, or an upper limit to the intrinsic brightness temperature of
K. The highest angular resolution with at least a 4.5
detection of the radio continuum emission is mas ( kpc). At this resolution, the image shows a continuum feature in BRI
1335--0417 with a size of mas ( kpc) at FWHM,
and intrinsic brightness temperature of K. The extent of
the observed continuum sources at 1.4 GHz and the derived brightness
temperatures show that the radio emission (and thus presumably the far-infrared
emission) in BRI 1335--0417 is powered by a major starburst, with a massive
star formation rate of order a few thousand M_{\odot} {\rm yr}^{-1}z=4.4$ QSO.Comment: 13 pages, 3 figures, AJ accepte
PKS 1830-211: A Face-On Spiral Galaxy Lens
We present new Hubble Space Telescope images of the gravitational lens PKS
1830-211, which allow us to characterize the lens galaxy and update the
determination of the Hubble constant from this system. The I-band image shows
that the lens galaxy is a face-on spiral galaxy with clearly delineated spiral
arms. The southwestern image of the background quasar passes through one of the
spiral arms, explaining the previous detections of large quantities of
molecular gas and dust in front of this image. The lens galaxy photometry is
consistent with the Tully-Fisher relation, suggesting the lens galaxy is a
typical spiral galaxy for its redshift. The lens galaxy position, which was the
main source of uncertainty in previous attempts to determine H_0, is now known
precisely. Given the current time delay measurement and assuming the lens
galaxy has an isothermal mass distribution, we compute H_0 = 44 +/- 9 km/s/Mpc
for an Omega_m = 0.3 flat cosmological model. We describe some possible
systematic errors and how to reduce them. We also discuss the possibility
raised by Courbin et al. (2002), that what we have identified as a single lens
galaxy is actually a foreground star and two separate galaxies.Comment: 21 pp., 4 figs., accepted by ApJ, section added to discuss related
work by Courbin et al. (astro-ph/0202026
Investigating the efficacy of network visualizations for intelligence tasks
There is an increasing requirement for advanced analytical methodologies to help military intelligence analysts cope with the growing amount of data they are saturated with on a daily basis. Specifically, within the context of terror network analysis, one of the largest problems is the transformation of raw tabular data into a visualization that is easily and effectively exploited by intelligence analysts. Currently, the primary method within the intelligence do-main is the node-link visualization, which encodes data sets by depicting the ties between nodes as lines between objects in a plane. This method, although useful, has limitations when the size and complexity of data grows. The matrix offers an alternate perspective because the two dimensions of the matrix are arrayed as an actors x actors matrix. This paper describes an experiment investigating node-link and matrix visualization techniques within social network analysis, and their effectiveness for the intelligence tasks of: 1) identifying leaders and 2) identifying clusters. The sixty participants in the experiment were all Air Force intelligence analysts and we provide recommendations for building visualization tools for this specialized group of users.Lincoln LaboratoryNational Science Foundation (U.S.) (Grant 1136996
Discovery of Molecular Gas in the Outflow and Tidal Arms around M82
We present the first fully sampled map of 12CO (1-0) emission from M82
covering the entire galaxy. Our map contains a 12 x 15 kpc^2 area. We find that
extraplanar CO emission, previously reported at short distances above the
galactic plane, extends to heights of up to 6 kpc above the disk. Some of this
emission is associated with tidal arms seen in HI, implying either that M82
contained substantial amounts of molecular gas in the outer disk, or that
molecular gas formed after the tidal features. CO emission along the direction
of the outflow extends to distances of 3 kpc above and below the disk. At this
distance, the line is shifted in velocity about 100 km/s, and has the same
sense as the galactic outflow from the central starburst. This implies that
molecular gas may be entrained into the outflow.Comment: 4 pages, 6 figures. Uses emulateapj5. Accepted by ApJ Letter
Spectroscopic Redshifts for Seven Lens Galaxies
We report VLT observations of 11 lensed quasars, designed to measure the
redshifts of their lens galaxies. We successfully determined the redshifts for
seven systems, five of which were previously unknown. The securely measured
redshifts for the lensing galaxies are: HE0047-1756 z=0.408; PMNJ0134-0931
z=0.766; HE0230-2130 z=0.522; HE0435-1223 z=0.455; SDSS0924+021 z=0.393;
LBQS1009-025 z=0.871; and WFIJ2033-472 z=0.658. For four additional systems
(BRI0952-0115, Q1017-207, Q1355-2257 and PMNJ1632-003) we estimate tentative
redshifts based on some features in their spectra.Comment: 8 pages, ApJ, submitte
First Detection of HCO+ Emission at High Redshift
We report the detection of HCO+(1-0) emission towards the Cloverleaf quasar
(z=2.56) through observations with the Very Large Array. This is the first
detection of ionized molecular gas emission at high redshift (z>2). HCO+
emission is a star formation indicator similar to HCN, tracing dense molecular
hydrogen gas (n(H_2) ~= 10^5 cm^{-3}) within star-forming molecular clouds. We
derive a lensing-corrected HCO+ line luminosity of L'(HCO+) = 3.5 x 10^9 K km/s
pc^2. Combining our new results with CO and HCN measurements from the
literature, we find a HCO+/CO luminosity ratio of 0.08 and a HCO+/HCN
luminosity ratio of 0.8. These ratios fall within the scatter of the same
relationships found for low-z star-forming galaxies. However, a HCO+/HCN
luminosity ratio close to unity would not be expected for the Cloverleaf if the
recently suggested relation between this ratio and the far-infrared luminosity
were to hold. We conclude that a ratio between HCO+ and HCN luminosity close to
1 is likely due to the fact that the emission from both lines is optically
thick and thermalized and emerges from dense regions of similar volumes. The
CO, HCN and HCO+ luminosities suggest that the Cloverleaf is a composite
AGN--starburst system, in agreement with the previous finding that about 20% of
the total infrared luminosity in this system results from dust heated by star
formation rather than heating by the AGN. We conclude that HCO+ is potentially
a good tracer for dense molecular gas at high redshift.Comment: 5 pages, 3 figures, ApJL, in press (accepted May 17, 2006
Establishment and Persistence of Yellow-Flowered Alfalfa No-Till Interseeded into Crested Wheatgrass Stands
Crested wheatgrass [Agropyron cristatum (L.) Gaertn., A. desertorum
(Fisch. ex Link) Schult., and related taxa] often exists
in near monoculture stands in the northern Great Plains.
Introducing locally adapted yellow-flowered alfalfa [Medicago
sativa L. subsp. falcata (L.) Arcang.] would complement crested
wheatgrass. Our objective was to evaluate effects of seeding
date, clethodim {(E) -2-[1-[[(3-chloro-2-propenyl)oxy]imino]
propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}
sod suppression, and seeding rate on initial establishment and
stand persistence of Falcata, a predominantly yellow-flowered
alfalfa, no-till interseeded into crested wheatgrass. Research was
initiated in August 2008 at Newcastle, WY; Hettinger, ND;
Fruitdale, SD; and Buffalo, SD. Effects of treatment factors on
plant frequency during initial establishment were influenced by
site environments. Late summer and spring were suitable seeding
dates. Clethodim sod suppression increased seedling frequency
in most cases. Seedling frequency increased as seeding
rate increased from 0.56 to 7.84 kg pure live seed (PLS) ha–1.
Specific seeding dates, clethodim sod suppression, and high
seeding rates did not greatly improve initial establishment when
site environments were poor. Residual effects of seeding date
and sod suppression post establishment were not significant
at most locations, but seeding rate effects were evident. Initial
establishment and persistence of Falcata alfalfa was successful at
Newcastle, indicating that interseeding in late summer or spring
using low seeding rates (≤3.36 kg PLS ha–1) without clethodim
can be effective. Assessing grass canopy cover, soil texture, and
management (e.g., haying) is necessary to determine the suitability
of crested wheatgrass sites for interseeding
Comparison of David V valve-sparing root replacement and bioprosthetic valve conduit for aortic root aneurysm
ObjectiveValve sparing root replacement (VSRR) is an attractive option for the management of aortic root aneurysms with a normal native aortic valve. Therefore, we reviewed our experience with a modification of the David V VSRR and compared it with stented pericardial bioprosthetic valve conduit (BVC) root replacement in an age-matched cohort of older patients.MethodsA total of 48 VSRRs were performed at our institution, excluding those on bicuspid aortic valves. We compared these cases with 15 aortic root replacements performed using a BVC during the same period. Subgroup analysis was performed comparing 16 VSRR cases and 15 age-matched BVC cases.ResultsThe greatest disparity between the VSRR and BVC groups was age (53 vs 69 years, respectively; P < .0005). The matched patients were similar in terms of baseline demographics and differed only in concomitant coronary artery bypass grafting (2 VSRR vs 7 BVC patients; P = .036). None of the VSRR and 3 of the BVC procedures were performed for associated dissection (P = .101). Postoperative aortic insufficiency grade was significantly different between the 2 groups (P = .004). The cardiopulmonary bypass, crossclamp, and circulatory arrest times were not different between the VSRR and BVC groups (174 vs 187 minutes, P = .205; 128 vs 133 minutes, P = .376; and 10 vs 13 minutes, respectively; P = .175). No differences were found between the 2 groups with respect to postoperative complications. One postoperative death occurred in the BVC group and none in the VSRR group. The postoperative length of stay and aortic valve gradients were less in the VSRR group (6 vs 8 days, P = .038; 6 vs 11.4 mm Hg, P = .001). The intensive care unit length of stay was significantly less in the VSRR group (54 vs 110 hours, P = .001).ConclusionsVSRR is an effective alternative to the BVC for aortic root aneurysm
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