1,906 research outputs found
Galaxy groups in the 2dF redshift survey: The catalogue
We construct a galaxy groups catalogue from the public 100K data release of
the 2dF galaxy redshift survey. The group identification is carried out using a
slightly modified version of the group finding algorithm developed by Huchra &
Geller. Several tests using mock catalogues allow us to find the optimal
conditions to increase the reliability of the final group sample. A minimum
number of 4 members, an outer number density enhancement of 80 and a linking
radial cutoff of , are the best obtained values from the
analysis. Using these parameters, approximately 90% of groups identified in
real space have a redshift space counterpart. On the other hand the level of
contamination in redshift space reaches to 30 % including a of
artificial groups and of groups associated with binaries or triplets
in real space. The final sample comprise 2209 galaxy groups covering the sky
region described by Colless et al. spanning over the redshift range of with a mean redshift of 0.1.Comment: Accepted for publication in the MNRAS. 8 figures 8 page
Dependence of Galaxy Shape on Environment in the Sloan Digital Sky Survey
Using a sample of galaxies from the Sloan Digital Sky Survey (SDSS) Data
Release 4, we study the trends relating surface brightness profile type and
apparent axis ratio to the local galaxy environment. We use the SDSS parameter
`fracDeV' to quantify the profile type. We find that galaxies with M_r > -18
are mostly described by exponential profiles in all environments. Galaxies with
-21 < M_r < -18 mainly have exponential profiles in low density environments
and de Vaucouleurs profiles in high density environments. The most luminous
galaxies, with M_r < -21, are mostly described by de Vaucouleurs profiles in
all environments. For galaxies with M_r < -19, the fraction of de Vaucouleurs
galaxies is a monotonically increasing function of local density, while the
fraction of exponential galaxies is monotonically decreasing. For a fixed
surface brightness profile type, apparent axis ratio is frequently correlated
with environment. As the local density of galaxies increases, we find that for
-20 < M_r < -18, galaxies of all profile types become slightly rounder, on
average; for -22 < M_r < -20, galaxies with exponential profiles tend to become
flatter, while galaxies with de Vaucouleurs profiles become rounder; for M_r <
-22, galaxies with exponential profiles become flatter, while the de
Vaucouleurs galaxies become rounder in their inner regions, yet exhibit no
change in their outer regions. We comment on how the observed trends relate to
the merger history of galaxies.Comment: 23 pages, 7 figures, accepted by Ap
Lagrangian Statistics of Dark Halos in a LCDM Cosmology
New statistical properties of dark matter halos in Lagrangian space are
presented. Tracing back the dark matter particles constituting bound halos
resolved in a series of N-body simulations, we measure quantitatively the
correlations of the proto-halo's inertia tensors with the local tidal tensors
and investigate how the correlation strength depends on the proto-halo's
sphericity, local density and filtering scale. It is shown that the majority of
the proto-halos exhibit strong correlations between the two tensors provided
that the tidal field is smoothed on the proto-halo's mass scale. The
correlation strength is found to increase as the proto-halo's sphericity
increases, as the proto-halo's mass increases, and as the local density becomes
close to the critical value, delta_{ec}. It is also found that those peculiar
proto-halos which exhibit exceptionally weak correlations between the two
tensors tend to acquire higher specific angular momentum in Eulerian space,
which is consistent with the linear tidal torque theory. In the light of our
results, it is intriguing to speculate a hypothesis that the low surface
brightness galaxies observed at present epoch correspond to the peculiar
proto-halos with extreme low-sphericity whose inertia tensors are weakly
correlated with the local tidal tensors.Comment: ApJ in press, accepted version, 20 pages, 8 figures, discussion on
LSBGs improved, particle distribution of dark halos in Lagrangian space show
What country, university or research institute, performed the best on COVID-19? Bibliometric analysis of scientific literature
In this article, we conduct data mining to discover the countries,
universities and companies, produced or collaborated the most research on
Covid-19 since the pandemic started. We present some interesting findings, but
despite analysing all available records on COVID-19 from the Web of Science
Core Collection, we failed to reach any significant conclusions on how the
world responded to the COVID-19 pandemic. Therefore, we increased our analysis
to include all available data records on pandemics and epidemics from 1900 to
2020. We discover some interesting results on countries, universities and
companies, that produced collaborated most the most in research on pandemic and
epidemics. Then we compared the results with the analysing on COVID-19 data
records. This has created some interesting findings that are explained and
graphically visualised in the article
Nucleosomal composition at the centromere: a numbers game
The Centromere is a unique chromosomal locus where the kinetochore is formed to mediate faithful chromosome partitioning, thus maintaining ploidy during cell division. Centromere identity is inherited via an epigenetic mechanism involving a histone H3 variant, called centromere protein A (CENP-A) which replaces H3 in centromeric chromatin. In spite of extensive efforts in field of centromere biology during the past decade, controversy persists over the structural nature of the CENP-A-containing epigenetic mark, both at nucleosomal and chromatin levels. Here, we review recent findings and hypotheses regarding the structure of CENP-A-containing complexes
Point field models for the galaxy point pattern. Modelling the singularity of the two-point correlation function
There is empirical evidence that the two-point correlation function of the
galaxy distribution follows, for small scales, reasonably well a power-law
expression with between 1.5 and 1.9.
Nevertheless, most of the point field models suggested in the literature do not
have this property.
This paper presents a new class of models, which is produced by modifying
point fields commonly used in cosmology to mimic the galaxy distribution, but
where is too large. The points are independently and randomly
shifted, leading to the desired reduction of the value of .Comment: Inserted a missing part of the abstract; 8 pages, 6 figures, uses
aa.cls and natbib.sty (included); accepted for publication in Astronomy &
Astrophysic
Peaks in the cosmological density field: parameter constraints from 2dF Galaxy Redshift Survey data
We use the number density of peaks in the smoothed cosmological density field
taken from the 2dF Galaxy Redshift Survey to constrain parameters related to
the power spectrum of mass fluctuations, n (the spectral index), dn/d(lnk)
(rolling in the spectral index), and the neutrino mass, m_nu. In a companion
paper we use N-body simulations to study how the peak density responds to
changes in the power spectrum, the presence of redshift distortions and the
relationship between galaxies and dark matter halos. In the present paper we
make measurements of the peak density from 2dF Galaxy Redshift Survey data, for
a range of smoothing filter scales from 4-33 h^-1 Mpc. We use these
measurements to constrain the cosmological parameters, finding n=1.36
(+0.75)(-0.64), m_nu < 1.76 eV, dn/d(lnk)=-0.012 (+0.192)(-0.208), at the 68 %
confidence level, where m_nu is the total mass of three massive neutrinos. At
95% confidence we find m_nu< 2.48 eV. These measurements represent an
alternative way to constrain cosmological parameters to the usual direct fits
to the galaxy power spectrum, and are expected to be relatively insensitive to
non-linear clustering evolution and galaxy biasing.Comment: Accepted for Publication in MNRAS on Sept 25, 2009. Abstract modified
to remove LaTex markup
Dynamic real-time risk analytics of uncontrollable states in complex internet of things systems, cyber risk at the edge
The Internet of Things (IoT) triggers new types of cyber risks. Therefore,
the integration of new IoT devices and services requires a self-assessment of
IoT cyber security posture. By security posture this article refers to the
cybersecurity strength of an organisation to predict, prevent and respond to
cyberthreats. At present, there is a gap in the state of the art, because there
are no self-assessment methods for quantifying IoT cyber risk posture. To
address this gap, an empirical analysis is performed of 12 cyber risk
assessment approaches. The results and the main findings from the analysis is
presented as the current and a target risk state for IoT systems, followed by
conclusions and recommendations on a transformation roadmap, describing how IoT
systems can achieve the target state with a new goal-oriented dependency model.
By target state, we refer to the cyber security target that matches the generic
security requirements of an organisation. The research paper studies and adapts
four alternatives for IoT risk assessment and identifies the goal-oriented
dependency modelling as a dominant approach among the risk assessment models
studied. The new goal-oriented dependency model in this article enables the
assessment of uncontrollable risk states in complex IoT systems and can be used
for a quantitative self-assessment of IoT cyber risk posture
Feminine Identities
The first four essays in this volume all focus on issues of gender in the works of different English authors and thinkers. Shorter versions of each of these essays were formerly presented as papers in an autonomous section of the Research and Educational Programme on Studies of Identity at the XXth Meeting of the Portuguese Association of Anglo-American Studies (Póvoa de Varzim, 1999) and published in the proceedings of the conference. The second cluster of essays in this volume — two of which (Jennie Wang’s and Teresa Cid’s) were first presented, in shorter versions, at the joint ASA/CAAS Conference (Montréal, 1999) — addresses the work of American women variously engaged in contexts of cultural diversity and grappling with the ideas of what it means to be an American and a woman, particularly in the twentieth century. These essays approach, from different angles, the definitional quandaries and semantic difficulties encountered when speaking about the self and the United States and provide, in one way or another, a sort of feminine rewriting of American myths and history.Fundação para a Ciência e a Tecnologi
Methods for Rapidly Processing Angular Masks of Next-Generation Galaxy Surveys
As galaxy surveys become larger and more complex, keeping track of the
completeness, magnitude limit, and other survey parameters as a function of
direction on the sky becomes an increasingly challenging computational task.
For example, typical angular masks of the Sloan Digital Sky Survey contain
about N=300,000 distinct spherical polygons. Managing masks with such large
numbers of polygons becomes intractably slow, particularly for tasks that run
in time O(N^2) with a naive algorithm, such as finding which polygons overlap
each other. Here we present a "divide-and-conquer" solution to this challenge:
we first split the angular mask into predefined regions called "pixels," such
that each polygon is in only one pixel, and then perform further computations,
such as checking for overlap, on the polygons within each pixel separately.
This reduces O(N^2) tasks to O(N), and also reduces the important task of
determining in which polygon(s) a point on the sky lies from O(N) to O(1),
resulting in significant computational speedup. Additionally, we present a
method to efficiently convert any angular mask to and from the popular HEALPix
format. This method can be generically applied to convert to and from any
desired spherical pixelization. We have implemented these techniques in a new
version of the mangle software package, which is freely available at
http://space.mit.edu/home/tegmark/mangle/, along with complete documentation
and example applications. These new methods should prove quite useful to the
astronomical community, and since mangle is a generic tool for managing angular
masks on a sphere, it has the potential to benefit terrestrial mapmaking
applications as well.Comment: New version 2.1 of the mangle software now available at
http://space.mit.edu/home/tegmark/mangle/ - includes galaxy survey masks and
galaxy lists for the latest SDSS data release and the 2dFGRS final data
release as well as extensive documentation and examples. 14 pages, 9 figures,
matches version accepted by MNRA
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