7,087 research outputs found
Model of mobile agents for sexual interactions networks
We present a novel model to simulate real social networks of complex
interactions, based in a granular system of colliding particles (agents). The
network is build by keeping track of the collisions and evolves in time with
correlations which emerge due to the mobility of the agents. Therefore,
statistical features are a consequence only of local collisions among its
individual agents. Agent dynamics is realized by an event-driven algorithm of
collisions where energy is gained as opposed to granular systems which have
dissipation. The model reproduces empirical data from networks of sexual
interactions, not previously obtained with other approaches.Comment: 6 pages, 8 figure
Observational signatures of lithium depletion in the metal-poor globular cluster NGC6397
The "stellar" solution to the cosmological lithium problem proposes that
surface depletion of lithium in low-mass, metal-poor stars can reconcile the
lower abundances found for Galactic halo stars with the primordial prediction.
Globular clusters are ideal environments for studies of the surface evolution
of lithium, with large number statistics possible to obtain for main sequence
stars as well as giants. We discuss the Li abundances measured for >450 stars
in the globular cluster NGC6397, focusing on the evidence for lithium depletion
and especially highlighting how the inferred abundances and interpretations are
affected by early cluster self-enrichment and systematic uncertainties in the
effective temperature determination.Comment: 6 pages, 2 figures, conference proceedings for IAU symposium 26
Deposition of general ellipsoidal particles
We present a systematic overview of granular deposits composed of ellipsoidal
particles with different particle shapes and size polydispersities. We study
the density and anisotropy of such deposits as functions of size polydispersity
and two shape parameters that fully describe the shape of a general ellipsoid.
Our results show that, while shape influences significantly the macroscopic
properties of the deposits, polydispersity plays apparently a secondary role.
The density attains a maximum for a particular family of non-symmetrical
ellipsoids, larger than the density observed for prolate or oblate ellipsoids.
As for anisotropy measures, the contact forces show are increasingly preferred
along the vertical direction as the shape of the particles deviates for a
sphere. The deposits are constructed by means of an efficient molecular
dynamics method, where the contact forces are efficiently and accurately
computed. The main results are discussed in the light of applications for
porous media models and sedimentation processes.Comment: 7 pages, 8 figure
Scattering by nonspherical systems
Scattering by nonspherical particles with size of order of wavelength - scattering by axisymmetric penetrable particles using approximate matching of boundary condition
Basel II, External Ratings and Adverse Selection
This paper will describe and analyse the development of Basel II Capital Accord and will focus on the use of external ratings in the Standardized Approach in Basel II. Furthermore it will examine the problem of adverse selection which appears in Basel II as a result from the proposal for the use of external ratings in determining the risk weights in the standardized approach. The paper will also attempt to find possible solutions to the adverse selection problem by discussing two similar models, and derive implications from them.Basel II, external ratings, adverse selection, rating agencies, standardized approach
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Metacognition, Metamemory, and Mindreading in High-Functioning Adults With Autism Spectrum Disorder
Objectives: Metacognition refers to cognition about cognition, and encompasses both knowledge of cognitive processes and the ability to monitor and control one’s own cognitions. The current study aimed to establish whether metacognition is impaired in autism spectrum disorder (ASD). According to some theories, the ability to represent one’s own mental states (an aspect of metacognition) relies on the same mechanism as the ability to represent others’ mental states (“mindreading”). Given numerous studies have shown mindreading is impaired in ASD, there is good reason to predict concurrent impairments in metacognition. Metacognition is most commonly explored in the context of memory, often by assessing people’s ability to monitor their memory processes. The current study addressed the question of whether people with ASD have difficulty monitoring the contents of their memory (alongside impaired mindreading).
Method: Eighteen intellectually high-functioning adults with ASD and 18 IQ- and age-matched neurotypical adults participated. Metamemory monitoring ability and mindreading ability were assessed using a feeling-of-knowing task and the “animations” task, respectively. Participants also completed a self-report measure of metacognitive ability.
Results: In addition to showing impaired mindreading, participants with ASD made significantly less accurate feeling-of-knowing judgements than neurotypical adults, suggesting that metamemory monitoring (an aspect of metacognition) was impaired. Conversely, participants with ASD self-reported superior metacognitive abilities compared to those reported by neurotypical participants.
Conclusion: This study provides evidence that individuals with ASD have metamemory monitoring impairments. The theoretical and practical implications of these findings for our current understanding of metacognition in ASD and typical development are discussed
Atomic and Molecular Data for Optical Stellar Spectroscopy
High-precision spectroscopy of large stellar samples plays a crucial role for
several topical issues in astrophysics. Examples include studying the chemical
structure and evolution of the Milky Way galaxy, tracing the origin of chemical
elements, and characterizing planetary host stars. Data are accumulating from
instruments that obtain high-quality spectra of stars in the ultraviolet,
optical and infrared wavelength regions on a routine basis. These instruments
are located at ground-based 2- to 10-m class telescopes around the world, in
addition to the spectrographs with unique capabilities available at the Hubble
Space Telescope. The interpretation of these spectra requires high-quality
transition data for numerous species, in particular neutral and singly ionized
atoms, and di- or triatomic molecules. We rely heavily on the continuous
efforts of laboratory astrophysics groups that produce and improve the relevant
experimental and theoretical atomic and molecular data. The compilation of the
best available data is facilitated by databases and electronic infrastructures
such as the NIST Atomic Spectra Database, the VALD database, or the Virtual
Atomic and Molecular Data Centre (VAMDC). We illustrate the current status of
atomic data for optical stellar spectra with the example of the Gaia-ESO Public
Spectroscopic Survey. Data sources for 35 chemical elements were reviewed in an
effort to construct a line list for a homogeneous abundance analysis of up to
100000 stars.Comment: Published 30 April 2015 in Physica Script
Fe I Oscillator Strengths for the Gaia-ESO Survey
The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale
study of multi-element chemical abundances of some 100 000 stars in the Milky
Way with the ultimate aim of quantifying the formation history and evolution of
young, mature and ancient Galactic populations. However, in preparing for the
analysis of GES spectra, it has been noted that atomic oscillator strengths of
important Fe I lines required to correctly model stellar line intensities are
missing from the atomic database. Here, we present new experimental oscillator
strengths derived from branching fractions and level lifetimes, for 142
transitions of Fe I between 3526 {\AA} and 10864 {\AA}, of which at least 38
are urgently needed by GES. We also assess the impact of these new data on
solar spectral synthesis and demonstrate that for 36 lines that appear
unblended in the Sun, Fe abundance measurements yield a small line-by-line
scatter (0.08 dex) with a mean abundance of 7.44 dex in good agreement with
recent publications.Comment: Accepted for publication in Mon. Not. R. Astron. So
Cosmic Needles versus Cosmic Microwave Background Radiation
It has been suggested by a number of authors that the 2.7K cosmic microwave
background (CMB) radiation might have arisen from the radiation from Population
III objects thermalized by conducting cosmic graphite/iron needle-shaped dust.
Due to lack of an accurate solution to the absorption properties of exceedingly
elongated grains, in existing literature which studies the CMB thermalizing
process they are generally modelled as (1) needle-like spheroids in terms of
the Rayleigh approximation; (2) infinite cylinders; and (3) the antenna theory.
We show here that the Rayleigh approximation is not valid since the Rayleigh
criterion is not satisfied for highly conducting needles. We also show that the
available intergalactic iron dust, if modelled as infinite cylinders, is not
sufficient to supply the required opacity at long wavelengths to obtain the
observed isotropy and Planckian nature of the CMB. If appealing to the antenna
theory, conducting iron needles with exceedingly large elongations (10^4)
appear able to provide sufficient opacity to thermalize the CMB within the iron
density limit. But the applicability of the antenna theory to exceedingly thin
needles of nanometer/micrometer in thickness needs to be justified.Comment: 13 pages, 4 figures; submitted to ApJ
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