7,888 research outputs found
A biased random-key genetic algorithm for the capacitated minimum spanning tree problem
This paper focuses on the capacitated minimum spanning tree(CMST)problem.Given a central
processor and a set of remote terminals with specified demands for traffic that must flow between the central processor and terminals,the goal is to design a minimum cost network to carry this demand.
Potential links exist between any pair of terminals and between the central processor and the terminals.
Each potential link can be included in the design at a given cost.The CMST problem is to design a
minimum-cost network connecting the terminals with the central processor so that the flow on any arc of the network is at most Q. A biased random-keygenetic algorithm(BRKGA)is a metaheuristic for combinatorial optimization which evolves a population of random vectors that encode solutions to the combinatorial optimization problem.This paper explores several solution encodings as well as different
strategies for some steps of the algorithm and finally proposes a BRKGA heuristic for the CMST problem.
Computational experiments are presented showing the effectivenes sof the approach:Seven newbest-
known solutions are presented for the set of benchmark instances used in the experiments.Peer ReviewedPostprint (author’s final draft
Genome sequences of 14 Firmicutes strains isolated from the human vagina
Research on vaginal infections is currently limited by a lack of available fully sequenced bacterial reference strains. Here, we present strains (now available through BEI Resources) and genome sequences for a set of 14 vaginal isolates from the phylum Firmicutes. These genome sequences provide a valuable resource for future research in understanding the role of Gram-positive bacteria in vaginal health and disease
Genome sequences of 11 human vaginal Actinobacteria strains
The composition of the vaginal microbiota is an important health determinant. Several members of the phylum Actinobacteria have been implicated in bacterial vaginosis, a condition associated with many negative health outcomes. Here, we present 11 strains of vaginal Actinobacteria (now available through BEI Resources) along with draft genome sequences
Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax Measurements
A photometric and spectroscopic analysis of 152 cool white dwarf stars is
presented. The discovery of 7 new DA white dwarfs, 2 new DQ white dwarfs, 1 new
magnetic white dwarf, and 3 weak magnetic white dwarf candidates, is reported,
as well as 19 known or suspected double degenerates. The photometric energy
distributions, the Halpha line profiles, and the trigonometric parallax
measurements are combined and compared to model atmosphere calculations to
determine the effective temperature and the radius of each object, and also to
constrain the atmospheric composition. New evolutionary sequences with C/O
cores with thin and thick hydrogen layers are used to derive masses and ages.
We confirm the existence of a range in Teff between 5000 and 6000K where almost
all white dwarfs have H-rich atmospheres. There is little evidence for mixed
H/He dwarfs, with the exception of 2 He-rich DA stars, and 5 C2H white dwarfs
which possibly have mixed H/He/C atmospheres. The DQ sequence terminates near
6500K, below which they are believed to turn into C2H stars. True DC stars
slightly above this temperature are found to exhibit H-like energy
distributions despite the lack of Halpha absorption. Attempts to interpret the
chemical evolution show the problem to be complex. Convective mixing is
necessary to account for the non-DA to DA ratio as a function of temperature.
The presence of helium in cool DA stars, the existence of the non-DA gap, and
the peculiar DC stars are also explained in terms of convective mixing,
although our understanding of how this mechanism works needs to be revised. The
oldest object in our sample is about 7.9 Gyr or 9.7 Gyr old depending on
whether thin or thick hydrogen layer models are used. The mean mass of our
sample is 0.65 +/- 0.20 Msun.Comment: Accepted by ApJ Suppl (~April 2001); 79 pages incl. 25 figure
Using Optical and Near-IR Photometry to Test MACHO Lens Candidates
We obtained new VLT/ISAAC H-band observations for five MACHO LMC source stars
and adjacent LMC field regions. After combining our near-IR photometry with
HST/PC BVRI optical photometry, we compared the MACHO objects to the adjacent
field stars in a variety of color-magnitude and color-color diagrams. These
diagnostic diagrams were chosen to be sensitive to our hypothesis that at least
some of the MACHO lenses were foreground Galactic disk or thick disk M dwarfs.
For the five lensed objects we studied, our hypothesis could be ruled out for
main sequence lens masses >= 0.1 Mo for distances out to 4 kpc. On the other
hand, the fact that LMC-MACHO-5, an object not in our study, has been recently
found to have just such a foreground lens, highlights that the remainder of the
LMC MACHO objects should be searched for the signature of their lenses using
our photometric technique, or via near-IR spectroscopy. We also constructed
diagnostic color-color diagrams sensitive to determining reddening for the
individual MACHO source stars and found that these five objects did not show
evidence for significant additional reddening. At least these five MACHO
objects are thus also inconsistent with the LMC self-lensing hypothesis.Comment: 28 pages, 8 figures, ApJ, accepted for Oct 1 issu
Genome sequences of nine gram-negative vaginal bacterial isolates
The vagina is home to a wide variety of bacteria that have great potential to impact human health. Here, we announce reference strains (now available through BEI Resources) and draft genome sequences for 9 Gram-negative vaginal isolates from the taxa Citrobacter, Klebsiella, Fusobacterium, Proteus, and Prevotella
Necessary conditions for classical super-integrability of a certain family of potentials in constant curvature spaces
We formulate the necessary conditions for the maximal super-integrability of
a certain family of classical potentials defined in the constant curvature
two-dimensional spaces. We give examples of homogeneous potentials of degree -2
on as well as their equivalents on and for which these
necessary conditions are also sufficient. We show explicit forms of the
additional first integrals which always can be chosen polynomial with respect
to the momenta and which can be of an arbitrary high degree with respect to the
momenta
Neonatal inhibition of DNA methylation disrupts testosterone-dependent masculinization of neurochemical phenotype
Many neural sex differences are differences in the number of neurons of a particular phenotype. For example, male rodents have more calbindin-expressing neurons in the medial preoptic area (mPOA) and bed nucleus of the stria terminalis (BNST), and females have more neurons expressing estrogen receptor alpha (ERα) and kisspeptin in the ventromedial nucleus of the hypothalamus (VMH) and the anteroventral periventricular nucleus (AVPV), respectively. These sex differences depend on neonatal exposure to testosterone, but the underlying molecular mechanisms are unknown. DNA methylation is important for cell phenotype differentiation throughout the developing organism. We hypothesized that testosterone causes sex differences in neurochemical phenotype via changes in DNA methylation, and tested this by inhibiting DNA methylation neonatally in male and female mice, and in females given a masculinizing dose of testosterone. Neonatal testosterone treatment masculinized calbindin, ERα and kisspeptin cell number of females at weaning. Inhibiting DNA methylation with zebularine increased calbindin cell number only in control females, thus eliminating sex differences in calbindin in the mPOA and BNST. Zebularine also reduced the sex difference in ERα cell number in the VMH, in this case by increasing ERα neuron number in males and testosterone-treated females. In contrast, the neonatal inhibition of DNA methylation had no effect on kisspeptin cell number. We conclude that testosterone normally increases the number of calbindin cells and reduces ERα cells in males through orchestrated changes in DNA methylation, contributing to, or causing, the sex differences in both cell types.Fil: Cisternas, Carla Daniela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de InvestigaciĂłn MĂ©dica Mercedes y MartĂn Ferreyra. Universidad Nacional de CĂłrdoba. Instituto de InvestigaciĂłn MĂ©dica Mercedes y MartĂn Ferreyra; ArgentinaFil: Cortese, Maria Laura. Georgia State University; Estados UnidosFil: Golynker, Ilona. Georgia State University; Estados UnidosFil: Castillo-Ruiz, Alexandra. Georgia State University; Estados UnidosFil: Forger, Nancy G.. Georgia State University; Estados Unido
The Luminosity Function of Magnitude and Proper-Motion Selected Samples. The case of White-Dwarfs
The luminosity function of white dwarfs is a powerful tool for studies of the
evolution and formation of the Milky Way. The (theoretical) white dwarf cooling
sequence provides a useful indicator of the evolutionary time scales involved
in the chronometry and star formation history of the galactic disk, therefore,
intrinsically faint (& old) white dwarfs in the immediate solar neighborhood
can be used to determine an upper limit for the age of the galactic disk.
In this paper we examine the faint-end () behavior of the disk
white dwarf luminosity function using the method, but fully
including the effects of realistic observational errors in the derived
luminosity function. We employ a Monte Carlo approach to produce many different
realizations of the luminosity function from a given data set with
pre-specified and reasonable errors in apparent magnitude, proper-motions,
parallaxes and bolometric corrections. These realizations allow us to compute
both a mean and an expected range in the luminosity function that is compatible
with the observational errors.
We find that current state-of-the art observational errors, mostly in the
bolometric corrections and trigonometric parallaxes, play a major role in
obliterating (real or artificial) small scale fluctuations in the luminosity
function. We also find that a better estimator of the true luminosity function
seems to be the median over simulations, rather than the mean. When using the
latter, an age for the disk of 10 Gyr or older can not be ruled out from the
sample of Leggett, Ruiz, and Bergeron (1998).Comment: Manuscript AAS Latex macro v4.0, 33 pages, 13 postscript figures
(Color in figs. 9 and 12). Accepted for publication in The Astrophysical
Journal. Replaced by two-column version & indication of acceptance by the Ap
The unprecedented flaring activities around Mrk 421 in 2012 and 2013: The test for neutrino and UHECR event connection
Since its mission, Fermi Collaboration reported the highest flux observed
during July - September 2012 for the BL Lac Markarian 421 (Mrk 421). The
integrated flux was eight times greater than the average flux reported in the
second Fermi catalog. During April 2013, Mrk 421 exhibited the highest TeV
-ray and optical fluxes recorded. The Telescope Array (TA)
collaboration reported the arrival of 72 ultra-high-energy cosmic rays
(UHECRs), two in temporal and positional coincidence with the flaring activity
observed in 2012 and one with the flaring activity in 2013. The IceCube
collaboration has reported around 100 neutrino events in the High-Energy
Starting Events (HESE) catalog. Although no neutrino track-like event has been
associated with this source, a neutrino shower-like event (IC31) is in temporal
and positional coincidence with the flare in 2012. Describing the broadband
spectral energy distribution during the flaring activities exhibited in 2012
and 2013 with one- and two-zone lepto-hadronic scenarios and one-zone SSC
model, we study a possible correlation between the neutrino event IC31 and the
three UHECRs. We estimate the number of neutrino and UHECR events generated
from the proposed models, and show that while the neutrino events are low to
associate the event IC31 with Mrk 421, the number of UHECRs are similar to
those reported by TA collaboration.Comment: 20 pages, 5 figures, 7 Table
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