3,207 research outputs found
A Neural Network Gravitational Arc Finder based on the Mediatrix filamentation Method
Automated arc detection methods are needed to scan the ongoing and
next-generation wide-field imaging surveys, which are expected to contain
thousands of strong lensing systems. Arc finders are also required for a
quantitative comparison between predictions and observations of arc abundance.
Several algorithms have been proposed to this end, but machine learning methods
have remained as a relatively unexplored step in the arc finding process. In
this work we introduce a new arc finder based on pattern recognition, which
uses a set of morphological measurements derived from the Mediatrix
Filamentation Method as entries to an Artificial Neural Network (ANN). We show
a full example of the application of the arc finder, first training and
validating the ANN on simulated arcs and then applying the code on four Hubble
Space Telescope (HST) images of strong lensing systems. The simulated arcs use
simple prescriptions for the lens and the source, while mimicking HST
observational conditions. We also consider a sample of objects from HST images
with no arcs in the training of the ANN classification. We use the training and
validation process to determine a suitable set of ANN configurations, including
the combination of inputs from the Mediatrix method, so as to maximize the
completeness while keeping the false positives low. In the simulations the
method was able to achieve a completeness of about 90% with respect to the arcs
that are input to the ANN after a preselection. However, this completeness
drops to 70% on the HST images. The false detections are of the order of
3% of the objects detected in these images. The combination of Mediatrix
measurements with an ANN is a promising tool for the pattern recognition phase
of arc finding. More realistic simulations and a larger set of real systems are
needed for a better training and assessment of the efficiency of the method.Comment: Updated to match published versio
Bias at the Ballot Box? Testing Whether Candidates' Gender Affects Their Vote
Using data from all elections to the Australian House of Representatives between 1903 and 2004, we examine the relationship between candidatesâ gender and their share of the vote. We find that the vote share of female candidates is 0.6 percentage points smaller than that of male candidates (for major parties, the gap widens to 1Âœ percentage points), but find little evidence that the party preselection system is responsible for the voting bias against women. Over time, the gap between male and female candidates has shrunk considerably as a result of changes in social norms (as proxied by the gender pay gap and attitudinal data) and the share of female candidates running nationwide. We find little evidence that party-based affirmative action policies have reduced the gender penalty against female candidates.economics of gender, elections, voting behaviour
Monotop phenomenology at the Large Hadron Collider
We investigate new physics scenarios where systems comprised of a single top
quark accompanied by missing transverse energy, dubbed monotops, can be
produced at the LHC. Following a simplified model approach, we describe all
possible monotop production modes via an effective theory and estimate the
sensitivity of the LHC, assuming 20 fb of collisions at a center-of-mass
energy of 8 TeV, to the observation of a monotop state. Considering both
leptonic and hadronic top quark decays, we show that large fractions of the
parameter space are reachable and that new physics particles with masses
ranging up to 1.5 TeV can leave hints within the 2012 LHC dataset, assuming
moderate new physics coupling strengths.Comment: 17 pages, 12 figures, 3 table
Variability selected high-redshift quasars on SDSS Stripe 82
The SDSS-III BOSS Quasar survey will attempt to observe z>2.15 quasars at a
density of at least 15 per square degree to yield the first measurement of the
Baryon Acoustic Oscillations in the Ly-alpha forest. To help reaching this
goal, we have developed a method to identify quasars based on their variability
in the u g r i z optical bands. The method has been applied to the selection of
quasar targets in the SDSS region known as Stripe 82 (the Southern equatorial
stripe), where numerous photometric observations are available over a 10-year
baseline. This area was observed by BOSS during September and October 2010.
Only 8% of the objects selected via variability are not quasars, while 90% of
the previously identified high-redshift quasar population is recovered. The
method allows for a significant increase in the z>2.15 quasar density over
previous strategies based on optical (ugriz) colors, achieving a density of
24.0 deg^{-2} on average down to g~22 over the 220 deg^2 area of Stripe 82. We
applied this method to simulated data from the Palomar Transient Factory and
from Pan-STARRS, and showed that even with data that have sparser time sampling
than what is available in Stripe 82, including variability in future quasar
selection strategies would lead to increased target selection efficiency in the
z>2.15 redshift range. We also found that Broad Absorption Line quasars are
preferentially present in a variability than in a color selection.Comment: 14 pages, 21 figures, accepted for publication in A&
LHC searches for heavy neutral Higgs bosons with a top jet substructure analysis
We study the LHC searches for the heavy -odd Higgs boson and
-even Higgs boson in the context of general two-Higgs-doublet model.
Specifically, we consider the decay mode of through the or associated production channels. In the so-called
"alignment limit" of the two-Higgs-doublet model, this decay mode can be the
most dominant one. By employing the HEPTopTagger and the
multi-variable-analysis method, we present the search sensitivities for both
-odd Higgs boson and -even Higgs boson via these channels at
the high-luminosity LHC runs.Comment: 21 pages, 5 figures; v2: matches the published versio
Telling the Truth May Not Pay Off: An Empirical Study of Centralised University Admissions in Germany
We investigate the matching algorithm used by the German central clearinghouse for university admissions (ZVS) in medicine and related subjects. This mechanism consists of three procedures based on final grades from school (âAbiturbestenverfahrenâ, âAuswahlverfahren der Hochschulenâ) and on waiting time (âWartezeitverfahrenâ). While these procedures differ in the criteria applied for admission they all make use of priority matching. In priority matching schemes, it is not a dominant strategy for students to submit their true preferences. Thus, strategic behaviour is expected. Using the full data set of applicants, we are able to detect some amount of strategic behaviour which can lead to inefficient matching. Alternative ways to organize the market are briefly discussed.Matching, university admissions, strategic behaviour
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