19,786 research outputs found
Searching for chemical inhomogeneities in Open Clusters: Analysis of the CN and CH Molecular Band Strengths in NGC 2158, NGC 2420, NGC 2682, NGC 7789 and Berkeley 29
Context: The total mass of a cluster, being the main parameter determining
its ability to host more than one stellar generation, may constitute a
threshold below which the cluster is able to form only a single stellar
population. AIms: Our goal is to investigate the existence of star-to-star
variations of CN and CH band strengths, related to the N and C abundances,
respectively, among the stars in five open cluster (NGC 2158, NGC 2420, NGC
2682, NGC 7789 and Berkeley 29) similar to those observed in globular clusters
and linked with the existence of multiple populations therein. Since these
systems are less massive than globulars, our results may allow us to constrain
the lower mass necessary to form more than one stellar population. Methods: We
measured the strength of the CN and CH bands, which correlate with the C and N
abundances, using four molecular indices in low-resolution SDSS/SEGUE spectra.
Results: We found that for four of the open clusters (NGC 2158, NGC 2420, NGC
2682 and Berkeley 29) all the stars studied in each of them have similar CN and
CH band strengths within the uncertainties since neither anomalous spreads nor
bimodalities have been detected in their CN and CH distributions. In contrast,
for NGC 7789 we found an anomalous spread in the strength of the CN molecular
band at 3839 \AA which is larger than the uncertainties. However, the small
number of stars studied in this cluster implies that further analysis is needed
to confirm the existence of chemical inhomogeneities in this cluster.Comment: 11 pages, 9 figures, Accepted for publication in A&A, Tables 7, 8 and
9 will be publish onlin
The influence of persuasion in opinion formation and polarization
We present a model that explores the influence of persuasion in a population
of agents with positive and negative opinion orientations. The opinion of each
agent is represented by an integer number that expresses its level of
agreement on a given issue, from totally against to totally in favor
. Same-orientation agents persuade each other with probability ,
becoming more extreme, while opposite-orientation agents become more moderate
as they reach a compromise with probability . The population initially
evolves to (a) a polarized state for , where opinions' distribution is
peaked at the extreme values , or (b) a centralized state for ,
with most opinions around . When , polarization lasts for a
time that diverges as , where is the population's size. Finally,
an extremist consensus ( or ) is reached in a time that scales as
for
Interacting social processes on interconnected networks
We propose and study a model for the interplay between two different
dynamical processes --one for opinion formation and the other for decision
making-- on two interconnected networks and . The opinion dynamics on
network corresponds to that of the M-model, where the state of each agent
can take one of four possible values (), describing its level of
agreement on a given issue. The likelihood to become an extremist ()
or a moderate () is controlled by a reinforcement parameter .
The decision making dynamics on network is akin to that of the
Abrams-Strogatz model, where agents can be either in favor () or against
() the issue. The probability that an agent changes its state is
proportional to the fraction of neighbors that hold the opposite state raised
to a power . Starting from a polarized case scenario in which all agents
of network hold positive orientations while all agents of network have
a negative orientation, we explore the conditions under which one of the
dynamics prevails over the other, imposing its initial orientation. We find
that, for a given value of , the two-network system reaches a consensus
in the positive state (initial state of network ) when the reinforcement
overcomes a crossover value , while a negative consensus happens
for . In the phase space, the system displays a
transition at a critical threshold , from a coexistence of both
orientations for to a dominance of one orientation for
. We develop an analytical mean-field approach that gives an
insight into these regimes and shows that both dynamics are equivalent along
the crossover line .Comment: 25 pages, 6 figure
Adopting BIM to Enhance Sustainability. The Saudi Arabia Construction Projects case study
Building information modelling (BIM) has become an efficient tool to contribute more effectively to achieving sustainability development goals. BIM utilities have progressively revealed efficient environments to share data amongst stakeholders. The present paper aims to evaluate levels of awareness around BIM capabilities amongst engineers and project managers, focusing on the Saudi Arabia construction industry. The study targeted individuals registered with the Saudi Council of Engineers until the year 2020, who were invited to engage with a questionnaire survey. The study targeted individuals registered with the Saudi Council of Engineers, who were invited to engage with a questionnaire survey. A sample of 940 participants was taken by the survey out of a total population of the study of 55776 engineers whose responses materialised in a robust statistical analysis. According to the survey, 61% (circa 572) have developed awareness of BIM, whereas 39% (368) confirmed that they had never heard of it. A descriptive Statistics framework with the aid of SPSS has been developed to complete the statistical study. Analyses of data indicated that the benefit of using BIM is significant in the broad sustainability realm, Life Cycle Cost (LCC), operations and maintenance, efficient use of energy, daylight analysis, thermal design, and transparency in cost
Heterogeneous pair approximation for voter models on networks
For models whose evolution takes place on a network it is often necessary to
augment the mean-field approach by considering explicitly the degree dependence
of average quantities (heterogeneous mean-field). Here we introduce the degree
dependence in the pair approximation (heterogeneous pair approximation) for
analyzing voter models on uncorrelated networks. This approach gives an
essentially exact description of the dynamics, correcting some inaccurate
results of previous approaches. The heterogeneous pair approximation introduced
here can be applied in full generality to many other processes on complex
networks.Comment: 6 pages, 6 figures, published versio
Turbulent Flow-Driven Molecular Cloud Formation: A Solution to the Post-T Tauri Problem?
We suggest that molecular clouds can be formed on short time scales by
compressions from large scale streams in the interstellar medium (ISM). In
particular, we argue that the Taurus-Auriga complex, with filaments of 10-20 pc
2-5 pc, most have been formed by H I flows in Myr,
explaining the absence of post-T Tauri stars in the region with ages Myr. Observations in the 21 cm line of the H I `halos' around the Taurus
molecular gas show many features (broad asymmetric profiles, velocity shifts of
H I relative to CO) predicted by our MHD numerical simulations, in which
large-scale H I streams collide to produce dense filamentary structures. This
rapid evolution is possible because the H I flows producing and disrupting the
cloud have much higher velocities (5-10 kms) than present in the molecular gas
resulting from the colliding flows. The simulations suggest that such flows can
occur from the global ISM turbulence without requiring a single triggering
event such as a SN explosion.Comment: 26 pages, 12 ps figures. Apj accepte
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