3,002 research outputs found
The Massive End of the Stellar Mass Function
We derive average flux corrections to the \texttt{Model} magnitudes of the
Sloan Digital Sky Survey (SDSS) galaxies by stacking together mosaics of
similar galaxies in bins of stellar mass and concentration. Extra flux is
detected in the outer low surface brightness part of the galaxies, leading to
corrections ranging from 0.05 to 0.32 mag for the highest stellar mass
galaxies. We apply these corrections to the MPA-JHU (Max-Planck Institute for
Astrophysics - John Hopkins University) stellar masses for a complete sample of
half a million galaxies from the SDSS survey to derive a corrected galaxy
stellar mass function at in the stellar mass range
. We find that the flux corrections and the use
of the MPA-JHU stellar masses have a significant impact on the massive end of
the stellar mass function, making the slope significantly shallower than that
estimated by Li \& White (2009), but steeper than derived by Bernardi et al.
(2013). This corresponds to a mean comoving stellar mass density of galaxies
with stellar masses that is a factor of 3.36
larger than the estimate by Li \& White (2009), but is 43\% smaller than
reported by Bernardi et al. (2013).Comment: 11 pages, 8 figures, Accepted to MNRA
Parametrizing the Stellar Haloes of Galaxies
We study the stellar haloes of galaxies out to 70-100 kpc as a function of
stellar mass and galaxy type by stacking aligned and band images from a
sample of 45508 galaxies from SDSS DR9 in the redshift range
and in the mass range r. We derive surface brightness profiles to a depth of
almost . We find that the
ellipticity of the stellar halo is a function of galaxy stellar mass and that
the haloes of high concentration () galaxies are more elliptical than
those of low concentration () galaxies. The - colour profile of
high concentration galaxies reveals that the - colour of the stellar
population in the stellar halo is bluer than in the main galaxy, and the colour
of the stellar halo is redder for higher mass galaxies. We further demonstrate
that the full two-dimensional surface intensity distribution of our galaxy
stacks can only be fit through multi-component S\'{e}rsic models. Using the
fraction of light in the outer component of the models as a proxy for the
fraction of accreted stellar light, we show that this fraction is a function of
stellar mass and galaxy type. For high concentration galaxies, the fraction of
accreted stellar light rises from to for galaxies in the stellar
mass range from to . The fraction of
accreted light is much smaller in low concentration systems, increasing from
to over the same mass range. This work provides important
constraints for the theoretical understanding of the formation of stellar
haloes of galaxies.Comment: Submitted to MNRAS, 18 pages, 19 figure
A Case Study in Matching Service Descriptions to Implementations in an Existing System
A number of companies are trying to migrate large monolithic software systems
to Service Oriented Architectures. A common approach to do this is to first
identify and describe desired services (i.e., create a model), and then to
locate portions of code within the existing system that implement the described
services. In this paper we describe a detailed case study we undertook to match
a model to an open-source business application. We describe the systematic
methodology we used, the results of the exercise, as well as several
observations that throw light on the nature of this problem. We also suggest
and validate heuristics that are likely to be useful in partially automating
the process of matching service descriptions to implementations.Comment: 20 pages, 19 pdf figure
Quantifying dynamical spillover in co-evolving multiplex networks
Multiplex networks (a system of multiple networks that have different types
of links but share a common set of nodes) arise naturally in a wide spectrum of
fields. Theoretical studies show that in such multiplex networks, correlated
edge dynamics between the layers can have a profound effect on dynamical
processes. However, how to extract the correlations from real-world systems is
an outstanding challenge. Here we provide a null model based on Markov chains
to quantify correlations in edge dynamics found in longitudinal data of
multiplex networks. We use this approach on two different data sets: the
network of trade and alliances between nation states, and the email and
co-commit networks between developers of open source software. We establish the
existence of "dynamical spillover" showing the correlated formation (or
deletion) of edges of different types as the system evolves. The details of the
dynamics over time provide insight into potential causal pathways
mSPD-NN: A Geometrically Aware Neural Framework for Biomarker Discovery from Functional Connectomics Manifolds
Connectomics has emerged as a powerful tool in neuroimaging and has spurred
recent advancements in statistical and machine learning methods for
connectivity data. Despite connectomes inhabiting a matrix manifold, most
analytical frameworks ignore the underlying data geometry. This is largely
because simple operations, such as mean estimation, do not have easily
computable closed-form solutions. We propose a geometrically aware neural
framework for connectomes, i.e., the mSPD-NN, designed to estimate the geodesic
mean of a collections of symmetric positive definite (SPD) matrices. The
mSPD-NN is comprised of bilinear fully connected layers with tied weights and
utilizes a novel loss function to optimize the matrix-normal equation arising
from Fr\'echet mean estimation. Via experiments on synthetic data, we
demonstrate the efficacy of our mSPD-NN against common alternatives for SPD
mean estimation, providing competitive performance in terms of scalability and
robustness to noise. We illustrate the real-world flexibility of the mSPD-NN in
multiple experiments on rs-fMRI data and demonstrate that it uncovers stable
biomarkers associated with subtle network differences among patients with
ADHD-ASD comorbidities and healthy controls.Comment: Accepted into IPMI 202
PI-FLAME: A parallel immune system simulator using the FLAME graphic processing unit environment
Agent-based models (ABMs) are increasingly being used to study population dynamics in complex systems, such as the human immune system. Previously, Folcik et al. (The basic immune simulator: an agent-based model to study the interactions between innate and adaptive immunity. Theor Biol Med Model 2007; 4: 39) developed a Basic Immune Simulator (BIS) and implemented it using the Recursive Porous Agent Simulation Toolkit (RePast) ABM simulation framework. However, frameworks such as RePast are designed to execute serially on central processing units and therefore cannot efficiently handle large model sizes. In this paper, we report on our implementation of the BIS using FLAME GPU, a parallel computing ABM simulator designed to execute on graphics processing units. To benchmark our implementation, we simulate the response of the immune system to a viral infection of generic tissue cells. We compared our results with those obtained from the original RePast implementation for statistical accuracy. We observe that our implementation has a 13× performance advantage over the original RePast implementation
Robust Bain distortion in the premartensite phase of platinum substituted Ni2MnGa magnetic shape memory alloy
The premartensite phase of shape memory and magnetic shape memory alloys
(MSMAs) is believed to be a precursor state of the martensite phase with
preserved austenite phase symmetry. The thermodynamic stability of the
premartensite phase and its relation to the martensitic phase is still an
unresolved issue, even though it is critical to the understanding of the
functional properties of MSMAs. We present here unambiguous evidence for
macroscopic symmetry breaking leading to robust Bain distortion in the
premartensite phase of 10% Pt substituted Ni2MnGa. We show that the robust Bain
distorted premartensite (T2) phase results from another premartensite (T1)
phase with preserved cubic-like symmetry through an isostructural phase
transition. The T2 phase finally transforms to the martensite phase with
additional Bain distortion on further cooling. Our results demonstrate that the
premartensite phase should not be considered as a precursor state with the
preserved symmetry of the cubic austenite phase
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