1,293 research outputs found
The Solar Neighborhood XV: Discovery of New High Proper Motion Stars with mu >= 0.4"/yr between Declinations -47 degrees and 00 degrees
We report the discovery of 152 new high proper motion systems (mu >= 0.4"/yr)
in the southern sky (Declination = -47 degrees to 00 degrees) brighter than
UKST plate R_{59F} =16.5 via our SuperCOSMOS-RECONS (SCR) search. This paper
complements Paper XII in The Solar Neighborhood series, which covered the
region from Declination = -90 degrees to -47 degrees and discussed all 147 new
systems from the southernmost phase of the search. Among the total of 299
systems from both papers, there are 148 (71 in Paper XII, 77 in this paper) new
systems moving faster than 0.5"/yr that are additions to the classic ``LHS''
(Luyten Half Second) sample. These constitute an 8% increase in the sample of
all stellar systems with mu >= 0.5"/yr in the southern sky.
As in Paper XII, distance estimates are provided for the systems reported
here based upon a combination of photographic plate magnitudes and 2MASS
photometry, assuming all stars are on the main sequence. Two SCR systems from
the portion of the sky included in this paper are anticipated to be within 10
pc, and an additional 23 are within 25 pc. In total, the results presented in
Paper XII and here for this SCR sweep of the entire southern sky include five
new systems within 10 pc and 38 more between 10 and 25 pc. The largest number
of nearby systems have been found in the slowest proper motion bin, 0.6"/yr >
mu >= 0.4"/yr, indicating that there may be a large population of low proper
motion systems very near the Sun.Comment: 36 pages, 5 figures, accepted for publication in Astronomical Journa
The Solar Neighborhood XII: Discovery of New High Proper Motion Stars with 1.0"/yr > mu >= 0.4"/yr between Declinations -90 degrees and -47 degrees
We report the discovery of 141 new high proper motion systems (1.0"/yr > mu
>= 0.4"/yr) in the southern sky (Declination = -90 degrees to -47 degrees)
brighter than UKST plate R_{59F} = 16.5 via our SuperCOSMOS-RECONS (SCR)
search. When combined with the nine systems having mu >= 1.0"/yr and/or late
spectral type from the initial phases of this effort (Hambly et al. 2004, Henry
et al. 2004), we find that 73 of the 150 total systems are moving faster than
0.5"/yr, and are therefore new members of the classic "LHS" (Luyten Half
Second) sample. These constitute a 21% increase in the sample of stars with mu
>= 0.5"/yr in the declination region searched, thereby comprising an important
addition to this long-neglected region of the sky.
Distance estimates are provided for the entire sample, based upon a
combination of photographic plate magnitudes and 2MASS photometry, using the
relations presented in Hambly et al. (2004) for the presumed main sequence
stars. Three systems are anticipated to be within 10 pc, and an additional 15
are within 25 pc. Eight of these 18 nearby systems have proper motions falling
between 0.4"/yr and 0.6"/yr, hinting at a large population of nearby stars with
fast, but not extremely high, proper motions that have not been thoroughly
investigated.Comment: 45 pages, 6 figures, accepted for publication in Astronomical Journal
(January 2005
Factors Associated with the Diversification of the Gut Microbial Communities within Chimpanzees from Gombe National Park.
The gastrointestinal tract harbors large and diverse populations of bacteria that vary among individuals and within individuals over time. Numerous internal and external factors can influence the contents of these microbial communities, including diet, geography, physiology, and the extent of contact among hosts. To investigate the contributions of such factors to the variation and changes in gut microbial communities, we analyzed the distal gut microbiota of individual chimpanzees from two communities in Gombe National Park, Tanzania. These samples, which were derived from 35 chimpanzees, many of whom have been monitored for multiple years, provide an unusually comprehensive longitudinal depth for individuals of known genetic relationships. Although the composition of the great-ape microbiota has been shown to codiversify with host species, indicating that host genetics and phylogeny have played a major role in its differentiation over evolutionary timescales, the geneaological relationships of individual chimpanzees did not coincide with the similarity in their gut microbial communities. However, the inhabitants from adjacent chimpanzee communities could be distinguished based on the contents of their gut microbiota. Despite the broad similarity of community members, as would be expected from shared diet or interactions, long-term immigrants to a community often harbored the most distinctive gut microbiota, suggesting that individuals retain hallmarks of their previous gut microbial communities for extended periods. This pattern was reinforced in several chimpanzees sampled over long temporal scales, in which the major constituents of the gut microbiota were maintained for nearly a decade
Rotor Model Updating and Validation for an Active Magnetic Bearing Based High-Speed Machining Spindle
This paper presents an experimentally driven model updating approach to address the dynamic inaccuracy of the nominal finite element (FE) rotor model of a machining spindle supported on active magnetic bearings. Modeling error is minimized through the application of a numerical optimization algorithm to adjust appropriately selected FE model parameters. Minimizing the error of both resonance and antiresonance frequencies simultaneously accounts for rotor natural frequencies as well as for their mode shapes. Antiresonance frequencies, which are shown to heavily influence the model’s dynamic properties, are commonly disregarded in structural modeling. Evaluation of the updated rotor model is performed through comparison of transfer functions measured at the cutting tool plane, which are independent of the experimental transfer function data used in model updating procedures. Final model validation is carried out with successful implementation of robust controller, which substantiates the effectiveness of the model updating methodology for model correction
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Behavioral and epigenetic consequences of oxytocin treatment at birth.
Oxytocin is used in approximately half of all births in the United States during labor induction and/or augmentation. However, the effects of maternal oxytocin administration on offspring development have not been fully characterized. Here, we used the socially monogamous prairie vole to examine the hypothesis that oxytocin exposure at birth can have long-term developmental consequences. Maternally administered oxytocin increased methylation of the oxytocin receptor (Oxtr) in the fetal brain. As adults, oxytocin-exposed voles were more gregarious, with increased alloparental caregiving toward pups and increased close social contact with other adults. Cross-fostering indicated that these effects were the result of direct action on the offspring, rather than indirect effects via postnatal changes in maternal behavior. Male oxytocin-exposed offspring had increased oxytocin receptor density and expression in the brain as adults. These results show that long-term effects of perinatal oxytocin may be mediated by an epigenetic mechanism
Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky Data Release
Using data from the 2MASS All-Sky Point Source Catalogue, we have extended
our census of nearby ultracool dwarfs to cover the full celestial sphere above
Galactic latitute 15 degrees. Starting with an initial catalogue of 2,139,484
sources, we have winnowed the sample to 467 candidate late-type M or L dwarfs
within 20 parsecs of the Sun. Fifty-four of those sources already have
spectroscopic observations confirming them as late-type dwarfs. We present
optical spectroscopy of 376 of the remaining 413 sources, and identify 44 as
ultracool dwarfs with spectroscopic distances less than 20 parsecs. Twenty-five
of the 37 sources that lack optical data have near-infrared spectroscopy.
Combining the present sample with our previous results and data from the
literature, we catalogue 94 L dwarf systems within 20 parsecs. We discuss the
distribution of activity, as measured by H-alpha emission, in this
volume-limited sample. We have coupled the present ultracool catalogue with
data for stars in the northern 8-parsec sample and recent (incomplete)
statistics for T dwarfs to provide a snapshot of the current 20-parsec census
as a function of spectral type.Comment: Accepted for publication by the Astronomical Journa
Determinación de órbitas preliminares mediante un computador IBM-360 : Aplicación a 20 pequeños planetas no identificados
Uno de los programas que se está realizando en la Estación Astronómica de Cerro El Roble, contempla la observación de pequeños planetas recomendados. Al observar el asteroide 919-ILSEBILL (recomendado) se encontró en su placa otros 12 planetoides, lo cual fue confirmado por series de placas tomadas en 9 fechas siguientes. En estas nuevas placas pudo identificarse, con la ayuda de las "Efemérides de Pequeños Planetas para 1968" (I.T,A,)(1), los planetoides 238 HYPATIA y 153 HILDA, no logró encontrarse el 198 AMPELIA siendo que por sus efemérides debía estar en varias de las placas tomadas. Además de estas identificaciones aumentó a 20 el numero de pequeños planetas no identificados al compararlos con las efemérides del I.T.A.Asociación Argentina de Astronomí
Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?
The recently discovered sharp peak in the excitation function of the K+/pi+
ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the
framework of the Statistical Model. In this model, the freeze-out of an ideal
hadron gas changes from a situation where baryons dominate to one with mainly
mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical
potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The
calculated maximum in the K+/pi+ ratio is, however, much less pronounced than
the one observed by the NA49 Collaboration. The smooth increase of the K-/pi-
ratio with incident energy and the shape of the excitation functions of the
Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different
incident energies, is consistent with the presently available experimental
data. The measured K+/pi+ ratio exceeds the calculated one just at the incident
energy when the freeze-out condition is changing.
We speculate that at this point freeze-out might occur in a modified way. We
discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio
while most other particle ratios remain essentially unchanged. Such an early
freeze-out is supported by results from HBT studies.Comment: 8 pages, 5 figures, SQM2006 conference, Los Angeles, March 200
Determinación de órbitas preliminares mediante un computador IBM-360 : Aplicación a 20 pequeños planetas no identificados
Uno de los programas que se está realizando en la Estación Astronómica de Cerro El Roble, contempla la observación de pequeños planetas recomendados. Al observar el asteroide 919-ILSEBILL (recomendado) se encontró en su placa otros 12 planetoides, lo cual fue confirmado por series de placas tomadas en 9 fechas siguientes. En estas nuevas placas pudo identificarse, con la ayuda de las "Efemérides de Pequeños Planetas para 1968" (I.T,A,)(1), los planetoides 238 HYPATIA y 153 HILDA, no logró encontrarse el 198 AMPELIA siendo que por sus efemérides debía estar en varias de las placas tomadas. Además de estas identificaciones aumentó a 20 el numero de pequeños planetas no identificados al compararlos con las efemérides del I.T.A.Asociación Argentina de Astronomí
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