4,255 research outputs found
Riordan Paths and Derangements
Riordan paths are Motzkin paths without horizontal steps on the x-axis. We
establish a correspondence between Riordan paths and
-avoiding derangements. We also present a combinatorial proof
of a recurrence relation for the Riordan numbers in the spirit of the
Foata-Zeilberger proof of a recurrence relation on the Schr\"oder numbers.Comment: 9 pages, 2 figure
The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment
The fraction of stellar mass contained in globular clusters (GCs), also
measured by number as the specific frequency, is a fundamental quantity that
reflects both a galaxy's early star formation and its entire merging history.
We present specific frequencies, luminosities, and mass fractions for the
globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster
Survey, the largest homogeneous catalog of its kind. We find that 1) GC mass
fractions can be high in both giants and dwarfs, but are universally low in
galaxies with intermediate luminosities. 2) The behavior of specific frequency
across galaxy mass is dominated by the blue GCs. 3) The GC fractions of
low-mass galaxies exhibit a dependence on environment. Nearly all dwarf
galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87,
presenting the first strong evidence that GC formation in dwarfs is biased
toward dense environments. 4) GC formation in central dwarfs is biased because
their stars form earliest and most intensely. Comparisons to the Millennium
Simulation show that central dwarfs have older stellar populations and form
more stars at higher star formation rates (SFRs) and SFR surface densities. The
SFR surface density in simulated dwarfs peaks before the total SFR, naturally
producing GC populations that are older and more metal-poor than the field
stars. 5) Dwarfs within ~40 kpc of the giant ellipticals M87 and M49 are red
and have few or no GCs, suggesting that they have been tidally stripped and
have contributed their GCs to the halos of their giant neighbors. The central
dwarfs with high GC mass fractions are thus likely to be the survivors most
similar to the protogalaxies that assembled the rich M87 globular cluster
system.(Abridged)Comment: 27 pages, 21 figures, 7 tables. Accepted for publication in the
Astrophysical Journa
The ACS Fornax Cluster Survey. II. The Central Brightness Profiles of Early-Type Galaxies: A Characteristic Radius on Nuclear Scales and the Transition from Central Luminosity Deficit to Excess
We analyse HST surface brightness profiles for 143 early-type galaxies in the
Virgo and Fornax Clusters. Sersic models provide accurate descriptions of the
global profiles with a notable exception: the observed profiles deviate
systematically inside a characteristic "break" radius of R_b ~ 0.02R_e where
R_e is the effective radius of the galaxy. The sense of the deviation is such
that bright galaxies (M_B < -20) typically show central light deficits with
respect to the inward extrapolation of the Sersic model, while the great
majority of low- and intermediate-luminosity galaxies (-19.5 < M_B < -15) show
central light excesses; galaxies occupying a narrow range of intermediate
luminosities (-20 < M_B < -19.5) are usually well fitted by Sersic models over
all radii. The slopes of the central surface brightness profiles, when measured
at fixed fractions of R_e, vary smoothly as a function of galaxy luminosity in
a manner that depends sensitively on the choice of measurement radius. We show
that a recent claim of strong bimodality in slope is likely an artifact of the
galaxy selection function used in that study. To provide a more robust
characterization of the inner regions of galaxies, we introduce a parameter
that describes the central luminosity deficit or excess relative to the inward
extrapolation of the outer Sersic model. We find that this parameter varies
smoothly over the range of ~ 720 in blue luminosity spanned by the Virgo and
Fornax sample galaxies, with no evidence for a dichotomy. We argue that the
central light excesses (nuclei) in M_B > -19 galaxies may be the analogs of the
dense central cores that are predicted by some numerical simulations to form
via gas inflows. (ABRIDGED)Comment: To appear in the Astrophysical Journal, December 2007. Full
resolution paper available at
http://www.cfa.harvard.edu/~ajordan/ACSFCS/Home.htm
Prenatal Testing for Adult‐Onset Conditions: the Position of the National Society of Genetic Counselors
Advances in genetic testing and the availability of such testing in pregnancy allows prospective parents to test their future child for adult‐onset conditions. This ability raises several complex ethical issues. Prospective parents have reproductive rights to obtain information about their fetus. This information may or may not alter pregnancy management. These rights can be in conflict with the rights of the future individual, who will be denied the right to elect or decline testing. This paper highlights the complexity of these issues, details discussions that went into the National Society of Genetic Counselors (NSGC) Public Policy Task Force’s development of the Prenatal testing for Adult‐Onset Conditions position statement adopted in November 2014, and cites relevant literature on this topic through December 2015. Issues addressed include parental rights and autonomy, rights of the future child, the right not to know, possible adverse effects on childhood and the need for genetic counseling. This paper will serve as a reference to genetic counselors and healthcare professionals when faced with this situation in clinical practice.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146906/1/jgc41139.pd
Current and Nascent SETI Instruments
Here we describe our ongoing efforts to develop high-performance and
sensitive instrumentation for use in the search for extra-terrestrial
intelligence (SETI). These efforts include our recently deployed Search for
Extraterrestrial Emissions from Nearby Developed Intelligent Populations
Spectrometer (SERENDIP V.v) and two instruments currently under development;
the Heterogeneous Radio SETI Spectrometer (HRSS) for SETI observations in the
radio spectrum and the Optical SETI Fast Photometer (OSFP) for SETI
observations in the optical band. We will discuss the basic SERENDIP V.v
instrument design and initial analysis methodology, along with instrument
architectures and observation strategies for OSFP and HRSS. In addition, we
will demonstrate how these instruments may be built using low-cost, modular
components and programmed and operated by students using common languages, e.g.
ANSI C.Comment: 12 pages, 5 figures, Original version appears as Chapter 2 in "The
Proceedings of SETI Sessions at the 2010 Astrobiology Science Conference:
Communication with Extraterrestrial Intelligence (CETI)," Douglas A. Vakoch,
Edito
Investigating Graduate Education and Undergraduate Research Intentions of College Science Students
The current study examined predictors of undergraduate science students’ intentions to attend graduate school and participate in undergraduate research. We used social cognitive career theory to test our hypothesized model using a sample (N ¼ 411) of life science and physical science majors and examined basic interests in these disciplines as mediating variables. Among life science majors, results of structural equation modeling indicated that microbiology interest mediated the relationship between scientific self-efficacy (SSE) and graduate education intentions (GEIs) and the latter variable also mediated the relationship between microbiology interest and undergraduate research intentions (URIs). The model for physical science majors did not provide a good fit to the data, therefore path coefficients associated with this model were not interpreted. Implications for counseling interventions based on patterns of career intention formation in the life and physical sciences are discussed
CrackCLF: Automatic Pavement Crack Detection based on Closed-Loop Feedback
Automatic pavement crack detection is an important task to ensure the
functional performances of pavements during their service life. Inspired by
deep learning (DL), the encoder-decoder framework is a powerful tool for crack
detection. However, these models are usually open-loop (OL) systems that tend
to treat thin cracks as the background. Meanwhile, these models can not
automatically correct errors in the prediction, nor can it adapt to the changes
of the environment to automatically extract and detect thin cracks. To tackle
this problem, we embed closed-loop feedback (CLF) into the neural network so
that the model could learn to correct errors on its own, based on generative
adversarial networks (GAN). The resulting model is called CrackCLF and includes
the front and back ends, i.e. segmentation and adversarial network. The front
end with U-shape framework is employed to generate crack maps, and the back end
with a multi-scale loss function is used to correct higher-order
inconsistencies between labels and crack maps (generated by the front end) to
address open-loop system issues. Empirical results show that the proposed
CrackCLF outperforms others methods on three public datasets. Moreover, the
proposed CLF can be defined as a plug and play module, which can be embedded
into different neural network models to improve their performances
Cosmogenic 11C production and sensitivity of organic scintillator detectors to pep and CNO neutrinos
Several possible background sources determine the detectability of pep and
CNO solar neutrinos in organic liquid scintillator detectors. Among such
sources, the cosmogenic 11C nuclide plays a central role. 11C is produced
underground in reactions induced by the residual cosmic muon flux. Experimental
data available for the effective cross section for 11C by muons indicate that
11C will be the dominant source of background for the observation of pep and
CNO neutrinos. 11C decays are expected to total a rate 2.5 (20) times higher
than the combined rate of pep and CNO neutrinos in Borexino (KamLAND) in the
energy window preferred for the pep measurement, between 0.8 and 1.3 MeV.
This study examines the production mechanism of 11C by muon-induced showers
in organic liquid scintillators with a novel approach: for the first time, we
perform a detailed ab initio calculation of the production of a cosmogenic
nuclide, 11C, taking into consideration all relevant production channels.
Results of the calculation are compared with the effective cross sections
measured by target experiments in muon beams.
This paper also discusses a technique for reduction of background from 11C in
organic liquid scintillator detectors, which allows to identify on a one-by-one
basis and remove from the data set a large fraction of 11C decays. The
background reduction technique hinges on an idea proposed by Martin Deutsch,
who suggested that a neutron must be ejected in every interaction producing a
11C nuclide from 12C. 11C events are tagged by a three-fold coincidence with
the parent muon track and the subsequent neutron capture on protons.Comment: 11 pages, 6 figures; added one section detailing comparison with
previous estimates; added reference
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