7,979 research outputs found
The Anomalous Hall effect in re-entrant AuFe alloys and the real space Berry phase
The Hall effect has been studied in a series of AuFe samples in the
re-entrant concentration range, as well as in the spin glass range. The data
demonstrate that the degree of canting of the local spins strongly modifies the
anomalous Hall effect, in agreement with theoretical predictions associating
canting, chirality and a real space Berry phase. The canonical parametrization
of the Hall signal for magnetic conductors becomes inappropriate when local
spins are canted.Comment: 4 pages, 1 eps figur
Young stars in the periphery of the Large Magellanic Cloud
Despite their close proximity, the complex interplay between the two
Magellanic Clouds, the Milky Way, and the resulting tidal features, is still
poorly understood. Recent studies have shown that the Large Magellanic Cloud
(LMC) has a very extended disk strikingly perturbed in its outskirts. We search
for recent star formation in the far outskirts of the LMC, out to ~30 degrees
from its center. We have collected intermediate-resolution spectra of
thirty-one young star candidates in the periphery of the LMC and measured their
radial velocity, stellar parameters, distance and age. Our measurements confirm
membership to the LMC of six targets, for which the radial velocity and
distance values match well those of the Cloud. These objects are all young
(10-50 Myr), main-sequence stars projected between 7 and 13 degrees from the
center of the parent galaxy. We compare the velocities of our stars with those
of a disk model, and find that our stars have low to moderate velocity
differences with the disk model predictions, indicating that they were formed
in situ. Our study demonstrates that recent star formation occurred in the far
periphery of the LMC, where thus far only old objects were known. The spatial
configuration of these newly-formed stars appears ring-like with a radius of 12
kpc, and a displacement of 2.6 kpc from the LMC's center. This structure, if
real, would be suggestive of a star-formation episode triggered by an
off-center collision between the Small Magellanic Cloud and the LMC's disk.Comment: Accepted for publication in MNRA
In-Situ Star Formation in the Outskirts of the Large Magellanic Cloud: Gaia DR2 Confirmation
We explore the Gaia DR2 proper motions of six young, main-sequence stars,
members of the Large Magellanic Cloud (LMC) reported by Moni Bidin et al.
(2017). These stars are located in the outskirts of the disk, between 7 and 13
degrees from the LMC's center where there is very low H I content. Gaia DR2
proper motions confirm that four stars formed locally, in situ, while two are
consistent with being expelled via dynamical interactions from inner, more
gas-rich regions of the LMC. This finding establishes that recent star
formation occurred in the periphery of the LMC, where thus far only old
populations are known.Comment: Accepted for publication in Astrophysical Journal Letter
Micotoxinas: importância na alimentação e na saúde humana e animal.
Principais micotoxinas. Regulamentação de micotoxinas no Brasil e no mundo. Considerações finais.bitstream/CNPAT-2010/10830/1/Dc-110.pd
Chemical Composition of Young Stars in the Leading Arm of the Magellanic System
Chemical abundances of eight O- and B-type stars are determined from
high-resolution spectra obtained with the MIKE instrument on the Magellan 6.5m
Clay telescope. The sample is selected from 42 candidates of membership in the
Leading Arm of the Magellanic System. Stellar parameters are measured by two
independent grids of model atmospheres and analysis procedures, confirming the
consistency of the stellar parameter results. Abundances of seven elements (He,
C, N, O, Mg, Si, and S) are determined for the stars, as are their radial
velocities and estimates of distances and ages.
Among the seven B-type stars analyzed, the five that have radial velocities
compatible with membership to the LA have an average [Mg/H] of ,
significantly lower than the average of the remaining two [Mg/H] =
that are kinematical members of the Galactic disk. Among the
five LA members, four have individual [Mg/H] abundance compatible with that in
the LMC. Within errors, we can not exclude the possibility that one of these
stars has a [Mg/H] consistent with the more metal-poor, SMC-like material. The
remaining fifth star has a [Mg/H] close to MW values. Distances to the LA
members indicate that they are at the edge of the Galactic disk, while ages are
of the order of Myr, lower than the dynamical age of the LA,
suggesting a single star-forming episode in the LA. V the LA
members decreases with decreasing Magellanic longitude, confirming the results
of previous LA gas studies.Comment: 61 pages, 18 figures, 5 tables. Accepted for publication in Ap
All-optical trapping and acceleration of heavy particles
A scheme for fast, compact, and controllable acceleration of heavy particles
in vacuum is proposed, in which two counterpropagating lasers with variable
frequencies drive a beat-wave structure with variable phase velocity, thus
allowing for trapping and acceleration of heavy particles, such as ions or
muons. Fine control over the energy distribution and the total charge of the
beam is obtained via tuning of the frequency variation. The acceleration scheme
is described with a one-dimensional theory, providing the general conditions
for trapping and scaling laws for the relevant features of the particle beam.
Two-dimensional, electromagnetic particle-in-cell simulations confirm the
validity and the robustness of the physical mechanism.Comment: 10 pages, 3 figures, to appear in New Journal of Physic
Caracterização in silico de genes de expansina presentes em cafeeiro (Coffea arabica L.).
As expansinas (EXPs) são proteínas que promovem o relaxamento e extensão da parede celular em plantas, sendo codificadas por uma multifamília gênica e classificadas em: ?-expansinas, ?-expansinas, expansin-like A (EXLA) e expansin-like B (EXLB). Estas proteínas atuam no alongamento celular, maciez dos frutos, abscisão, germinação e polinização. As ?-expansinas representam a maior família e relacionam-se diretamente com o controle da extensão da parede celular em processos de desenvolvimento. Visto que a maturação uniforme dos frutos de café contribui para a qualidade da bebida, este trabalho teve por objetivo identificar e caracterizar in silico genes de expansinas envolvidas neste processo. Através da mineração dos dados do Genoma Café foram encontrados 28 contigs referentes às EXPs, sendo dois contigs de EXLB, um de EXLA e os demais pertencentes à família das ?-expansinas. Dentro desta ultima família foram identificados quatro contigs relacionados com o desenvolvimento dos frutos do cafeeiro. Comparação dos contigs obtidos nos bancos do Projeto Genoma Café e de contigs no banco de dados HarvEST Coffea permitiu a caracterização in silico da expressão dos contigs nos diferentes estádios de maturação dos frutos
The Origins of Young Stars in the Direction of the Leading Arm of the Magellanic Stream: Abundances, Kinematics, and Orbits
We explore the origins of the young B-type stars found by Casetti-Dinescu et
al.(2014) at the outskirts of the Milky-Way disk in the sky region of Leading
Arm of the Magellanic Stream. High-resolution spectroscopic observations made
with the MIKE instrument on the Magellan Clay 6.5m telescope for nine stars are
added to the previous sample analyzed by Zhang et al. (2017). We compile a
sample of fifteen young stars with well-determined stellar types, ages,
abundances and kinematics. With proper motions from Gaia DR2 we also derive
orbits in a realistic Milky-Way potential. We find that our previous
radial-velocity selected LA candidates have substantial orbital angular
momentum. The substantial amount of rotational component for these stars is in
contrast with the near-polar Magellanic orbit, thus rendering these stars
unlikely members of the LA. There are four large orbital-energy stars in our
sample. The highest orbital-energy one has an age shorter than the time to disk
crossing, with a birthplace ~kpc and ~kpc. Therefore,
the origin of this star is uncertain. The remaining three stars have disk
runaway origin with birthplaces between 12 and 25 kpc from the Galactic center.
Also, the most energetic stars are more metal poor ([Mg/H] =) and
with larger He scatter () than the inner disk ones
([Mg/H] , ). While the former group's
abundance is compatible with that of the Large Magellanic Cloud, it could also
reflect the metallicity gradient of the MW disk and their runaway status via
different runaway mechanisms.Comment: 58 pages, 17 figures, 7 tables. Accepted for publication in Ap
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