18,848 research outputs found
Valor nutritivo de palha de carnaúba tratada com uréia.
bitstream/item/131478/1/circular-33-Valor-nutritivo-da-palha-de-carnauba.pd
KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars
Knowing the metallicity distribution of stars in the Galactic Centre has
important implications for the formation history of the Milky Way nuclear star
cluster. However, this distribution is not well known, and is currently based
on a small sample of fewer than 100 stars. We obtained near-infrared K-band
spectra of more than 700 late-type stars in the central 4 pc^2 of the Milky Way
nuclear star cluster with the integral-field spectrograph KMOS (VLT). We
analyse the medium-resolution spectra using a full-spectral fitting method
employing the G\"ottingen Spectral library of synthetic PHOENIX spectra. The
derived stellar metallicities range from metal-rich [M/H]>+0.3 dex to
metal-poor [M/H]<-1.0 dex, with a fraction of 5.2(^{+6.0}+{-3.1}) per cent
metal-poor ([M/H]<-0.5 dex) stars. The metal-poor stars are distributed over
the entire observed field. The origin of metal-poor stars remains unclear. They
could originate from infalling globular clusters. For the metal-rich stellar
population ([M/H]>0 dex) a globular cluster origin can be ruled out. As there
is only a very low fraction of metal-poor stars in the central 4 pc^2 of the
Galactic Centre, we believe that our data can discard a scenario in which the
Milky Way nuclear star cluster is purely formed from infalling globular
clusters.Comment: 18 pages, 9 Figures, accepted for publication in MNRA
A path planning control for a vessel dynamic positioning system based on robust adaptive fuzzy strategy
The thrusters and propulsion propellers systems, as well as the operating situations, are all well-known nonlinearities which are caused less accuracy of the dynamic positioning system (DPS) of vessels in the path planning control process. In this study, to enhance the robust performance of the DPS, we proposed a robust adaptive fuzzy control model to reduce the effect of uncertainty problems and disturbances on the DPS. Firstly, the adaptive fuzzy controller with adaptive law is designed to adjust the membership function of the fuzzy controller to minimize the error in path planning control of the vessel. Secondly, the H∞ performance of robust tracking is proved by the Lyapunov theory. Moreover, compared to the other controller, a simulation experiment comprising two case studies confirmed the efficiency of the approach. Finally, the results showed that the proposed controller reaches control quality, performance and stability
On the nature of Lithium-rich giant stars: constraints from Beryllium abundances
We have derived beryllium abundances for 7 Li-rich giant (A(Li) > 1.5) stars
and 10 other Li-normal giants, with the aim of investigating the origin of the
Lithium in the Li-rich giants. In particular, we test the predictions of the
engulfment scenario proposed by Siess & Livio (1999), where the engulfment of a
brown dwarf or one or more giant planets would lead to a simultaneous
enrichment of 7Li and 9Be. We show that regardless their nature, none of the
stars studied in this paper were found to have detectable beryllium. Using
simple dilution arguments we show that the engulfment of an external object as
the sole source of Li enrichment is ruled out by the Li and Be abundance data.
The present results favor the idea that Li has been produced in the interior of
the stars by a Cameron-Fowler process and brought up to the surface by an extra
mixing mechanism.Comment: Accepted in A&
Crescimento de mamona irrigada BRS ENERGIA em neossolo flúvico sob cobertura morta no semiárido pernambucano.
Core-Level X-Ray Photoemission Satellites in Ruthenates: A New Mechanism Revealing the Mott Transition
Ru 3d core-level x-ray photoemission spectra of various ruthenates are
examined. They show in general two-peak structures, which can be assigned as
the screened and unscreened peaks. The screened peak is absent in a Mott
insulator, but develops into a main peak in the metallic regime. This spectral
behavior is well explained by the dynamical mean-field theory calculation for
the single-band Hubbard model with on-site core-hole potential using the exact
diagonalization method. The new mechanism of the core-level photoemission
satellite can be utilized to reveal the Mott transition phenomenon in various
strongly correlated electron systems, especially in nano-scale devices and
phase-separated materials.Comment: 4 pages, 5 figures, submitted to PR
Desempenho reprodutivo de vacas Nelore mantidas em pastagem nativa com suplementação na seca.
bitstream/item/131669/1/Comunicado-162-Desempenho-Reprodutivo-de-Vacas-Nelore.pd
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