250,660 research outputs found
A non-parametric and scale-independent method for cluster analysis II: the multivariate case
A general method is described for detecting and analysing galaxy systems. The
multivariate geometrical structure of the sample is studied by using an
extension of the method which we introduced in a previous paper. The method is
based on an estimate of the probability density underlying a data sample. The
density is estimated by using an iterative and adaptive kernel estimator. The
used kernels have spherical symmetry, however we describe a method in order to
estimate the locally optimal shape of the kernels. We use the results of the
geometrical structure analysis in order to study the effects that is has on the
cluster parameter estimate. This suggests a possible way to distinguish between
structure and substructure within a sample. The method is tested by using
simulated numerical models and applied to two galaxy samples taken from the
literature. The results obtained for the Coma cluster suggest a core-halo
structure formed by a large number of geometrically independent systems. A
different conclusion is suggested by the results for the Cancer cluster
indicating the presence of at least two independent structures both containing
substructure. The dynamical consequences of the results obtained from the
geometrical analysis will be described in a later paper. Further applications
of the method are suggested and are currently in progress.Comment: To appear in Monthly Notices of R.A.S., 50 pages of text, latex file,
aasms style, figures are available on request from the Autho
Water droplet excess free energy determined by cluster mitosis using guided molecular dynamics
Atmospheric aerosols play a vital role in affecting climate by influencing the properties and lifetimes of clouds and precipitation. Understanding the underlying microscopic mechanisms involved in the nucleation of aerosol droplets from the vapour phase is therefore of great interest. One key thermodynamic quantity in nucleation is the excess free energy of cluster formation relative to that of the saturated vapour. In our current study, the excess free energy is extracted for clusters of pure water modelled with the TIP4P/2005 intermolecular potential using a method based on nonequilibrium molecular dynamics and the Jarzynski relation. The change in free energy associated with the "mitosis" or division of a cluster of N water molecules into two N/2 sub-clusters is evaluated. This methodology is an extension of the disassembly procedure used recently to calculate the excess free energy of argon clusters [H. Y. Tang and I. J. Ford, Phys. Rev. E 91, 023308 (2015)]. Our findings are compared to the corresponding excess free energies obtained from classical nucleation theory (CNT) as well as internally consistent classical theory (ICCT). The values of the excess free energy that we obtain with the mitosis method are consistent with CNT for large cluster sizes but for the smallest clusters, the results tend towards ICCT; for intermediate sized clusters, we obtain values between the ICCT and CNT predictions. Furthermore, the curvature-dependent surface tension which can be obtained by regarding the clusters as spherical droplets of bulk density is found to be a monotonically increasing function of cluster size for the studied range. The data are compared to other values reported in the literature, agreeing qualitatively with some but disagreeing with the values determined by Joswiak et al. [J. Phys. Chem. Lett. 4, 4267 (2013)] using a biased mitosis approach; an assessment of the differences is the main motivation for our current study
Systematic quantum cluster typical medium method for the study of localization in strongly disordered electronic systems
Great progress has been made in the last several years towards understanding
the properties of disordered electronic systems. In part, this is made possible
by recent advances in quantum effective medium methods which enable the study
of disorder and electron-electronic interactions on equal footing. They include
dynamical mean field theory and the coherent potential approximation, and their
cluster extension, the dynamical cluster approximation. Despite their
successes, these methods do not enable the first-principles study of the
strongly disordered regime, including the effects of electronic localization.
The main focus of this review is the recently developed typical medium
dynamical cluster approximation for disordered electronic systems. This method
has been constructed to capture disorder-induced localization, and is based on
a mapping of a lattice onto a quantum cluster embedded in an effective typical
medium, which is determined self-consistently. Here we provide an overview of
various recent applications of the typical medium dynamical cluster
approximation to a variety of models and systems, including single and
multi-band Anderson model, and models with local and off-diagonal disorder. We
then present the application of the method to realistic systems in the
framework of the density functional theory.Comment: 58 pages, 46 figure
StackInsights: Cognitive Learning for Hybrid Cloud Readiness
Hybrid cloud is an integrated cloud computing environment utilizing a mix of
public cloud, private cloud, and on-premise traditional IT infrastructures.
Workload awareness, defined as a detailed full range understanding of each
individual workload, is essential in implementing the hybrid cloud. While it is
critical to perform an accurate analysis to determine which workloads are
appropriate for on-premise deployment versus which workloads can be migrated to
a cloud off-premise, the assessment is mainly performed by rule or policy based
approaches. In this paper, we introduce StackInsights, a novel cognitive system
to automatically analyze and predict the cloud readiness of workloads for an
enterprise. Our system harnesses the critical metrics across the entire stack:
1) infrastructure metrics, 2) data relevance metrics, and 3) application
taxonomy, to identify workloads that have characteristics of a) low sensitivity
with respect to business security, criticality and compliance, and b) low
response time requirements and access patterns. Since the capture of the data
relevance metrics involves an intrusive and in-depth scanning of the content of
storage objects, a machine learning model is applied to perform the business
relevance classification by learning from the meta level metrics harnessed
across stack. In contrast to traditional methods, StackInsights significantly
reduces the total time for hybrid cloud readiness assessment by orders of
magnitude
The Star Cluster System in the Local Group Starburst Galaxy IC 10
We present a survey of star clusters in the halo of IC 10, a starburst galaxy
in the Local Group based on Subaru R band images and NOAO Local Group Survey
UBVRI images. We find five new star clusters. All these star clusters are
located far from the center of IC 10, while previously known star clusters are
mostly in the main body. Interestingly the distribution of these star clusters
shows an asymmetrical structure elongated along the east and south-west
direction. We derive UBVRI photometry of 66 star clusters including these new
star clusters as well as previously known star clusters. Ages of the star
clusters are estimated from the comparison of their UBVRI spectral energy
distribution with the simple stellar population models. We find that the star
clusters in the halo are all older than 1 Gyr, while those in the main body
have various ages from very young (several Myr) to old (>1 Gyr). The young
clusters (<10 Myr) are mostly located in the H{\alpha} emission regions and are
concentrated on a small region at 2' in the south-east direction from the
galaxy center, while the old clusters are distributed in a wider area than the
disk. Intermediate-age clusters (~100 Myr) are found in two groups. One is
close to the location of the young clusters and the other is at ~4' from the
location of the young clusters. The latter may be related with past merger or
tidal interaction.Comment: 11 pages, 12 figures, 1 table; accepted for publication in Ap
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