700 research outputs found
New and simple algorithms for stable flow problems
Stable flows generalize the well-known concept of stable matchings to markets
in which transactions may involve several agents, forwarding flow from one to
another. An instance of the problem consists of a capacitated directed network,
in which vertices express their preferences over their incident edges. A
network flow is stable if there is no group of vertices that all could benefit
from rerouting the flow along a walk.
Fleiner established that a stable flow always exists by reducing it to the
stable allocation problem. We present an augmenting-path algorithm for
computing a stable flow, the first algorithm that achieves polynomial running
time for this problem without using stable allocation as a black-box
subroutine. We further consider the problem of finding a stable flow such that
the flow value on every edge is within a given interval. For this problem, we
present an elegant graph transformation and based on this, we devise a simple
and fast algorithm, which also can be used to find a solution to the stable
marriage problem with forced and forbidden edges.
Finally, we study the stable multicommodity flow model introduced by
Kir\'{a}ly and Pap. The original model is highly involved and allows for
commodity-dependent preference lists at the vertices and commodity-specific
edge capacities. We present several graph-based reductions that show
equivalence to a significantly simpler model. We further show that it is
NP-complete to decide whether an integral solution exists
Clusterization in the shape isomers of the 56Ni nucleus
The interrelation of the quadrupole deformation and clusterization is investigated in the example of the 56Ni nucleus. The shape isomers, including superdeformed and hyperdeformed states, are obtained as stability regions of the quasidynamical U(3) symmetry based on a Nilsson calculation. Their possible binary clusterizations are investigated by considering both the consequences of the Pauli exclusion principle and the energetic preference
Graduate HRD Programs in South Korea
The Problem To address national issues associated with societal development, many countries are recognizing the need to educate individuals who will lead developmental initiatives. While many previous studies have been conducted to examine how and what content of human resource development (HRD) has been taught in Western countries, similar research efforts have been rarely conducted in Asian countries such as South Korea. The lack of comparative study creates a research gap in understanding how HRD programs have been designed and implemented in different countries.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Barium stars as tracers of s-process nucleosynthesis in AGB stars II. Using machine learning techniques on 169 stars
We aim to analyse the abundance pattern of 169 Barium (Ba) stars, using
machine learning techniques and the AGB final surface abundances predicted by
Fruity and Monash stellar models. We developed machine learning algorithms that
use the abundance pattern of Ba stars as input to classify the initial mass and
metallicity of its companion star using stellar model predictions. We use two
algorithms: the first exploits neural networks to recognise patterns and the
second is a nearest-neighbour algorithm, which focuses on finding the AGB model
that predicts final surface abundances closest to the observed Ba star values.
In the second algorithm we include the error bars and observational
uncertainties to find the best fit model. The classification process is based
on the abundances of Fe, Rb, Sr, Zr, Ru, Nd, Ce, Sm, and Eu. We selected these
elements by systematically removing s-process elements from our AGB model
abundance distributions, and identifying those whose removal has the biggest
positive effect on the classification. We excluded Nb, Y, Mo, and La. Our final
classification combines the output of both algorithms to identify for each Ba
star companion an initial mass and metallicity range. With our analysis tools
we identify the main properties for 166 of the 169 Ba stars in the stellar
sample. The classifications based on both stellar sets of AGB final abundances
show similar distributions, with an average initial mass of M = 2.23 MSun and
2.34 MSun and an average [Fe/H] = -0.21 and -0.11, respectively. We
investigated why the removal of Nb, Y, Mo, and La improves our classification
and identified 43 stars for which the exclusion had the biggest effect. We show
that these stars have statistically significant different abundances for these
elements compared to the other Ba stars in our sample. We discuss the possible
reasons for these differences in the abundance patterns.Comment: accepted for publication in A&
Central kinematics of the globular cluster NGC 2808: Upper limit on the mass of an intermediate-mass black hole
Globular clusters are an excellent laboratory for stellar population and
dynamical research. Recent studies have shown that these stellar systems are
not as simple as previously assumed. With multiple stellar populations as well
as outer rotation and mass segregation they turn out to exhibit high
complexity. This includes intermediate-mass black holes which are proposed to
sit at the centers of some massive globular clusters. Today's high angular
resolution ground based spectrographs allow velocity-dispersion measurements at
a spatial resolution comparable to the radius of influence for plausible IMBH
masses, and to detect changes in the inner velocity-dispersion profile.
Together with high quality photometric data from HST, it is possible to
constrain black-hole masses by their kinematic signatures. We determine the
central velocity-dispersion profile of the globular cluster NGC 2808 using
VLT/FLAMES spectroscopy. In combination with HST/ACS data our goal is to probe
whether this massive cluster hosts an intermediate-mass black hole at its
center and constrain the cluster mass to light ratio as well as its total mass.
We derive a velocity-dispersion profile from integral field spectroscopy in the
center and Fabry Perot data for larger radii. High resolution HST data are used
to obtain the surface brightness profile. Together, these data sets are
compared to dynamical models with varying parameters such as mass to light
ratio profiles and black-hole masses. Using analytical Jeans models in
combination with variable M/L profiles from N-body simulations we find that the
best fit model is a no black hole solution. After applying various Monte Carlo
simulations to estimate the uncertainties, we derive an upper limit of the back
hole mass of M_BH < 1 x 10^4 M_SUN (with 95 % confidence limits) and a global
mass-to-light ratio of M/L_V = (2.1 +- 0.2) M_SUN/L_SUN.Comment: 12 pages, 9 figures, 2 tables, accepted for publication in A&
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