737 research outputs found
Quantitative study of molecular N_2 trapped in disordered GaN:O films
The structure of disordered GaN:O films grown by ion-assisted deposition is
investigated using x-ray absorption near-edge spectroscopy and Raman
spectroscopy. It is found that between 4 and 21 % of the nitrogen in the films
is in the form of molecular N_2 that interacts only weakly with the surrounding
matrix. The anion to cation ratio in the GaN:O host remains close to unity, and
there is a close correlation between the N_2 fraction, the level of oxygen
impurities, and the absence of short-range order in the GaN:O matrix.Comment: 5 pages, 3 figure
Characterization and Photodegradation of Dissolved Organic Matter (DOM) From a Tropical Lake and Its Dominant Primary Producer, the cyanobacteria Microcystis aeruginosa
This study investigates optical and high-resolution molecular signatures and photochemical degradation of DOM from the Barra Bonita Reservoir (BB-DOM), a tropical eutrophic lake, as well as from its dominant phytoplankton species, the cyanobacteria Microcystis aeruginosa (Microcystis-DOM). Consistent with a predominantly autotrophic source, BB-DOM and Microcystis-DOM exhibited high protein-like fluorescence and contained a large number of aliphatics. Microcystis-DOM was enriched in peptide-like formulae, while BB-DOM had higher chromophoric and fluorescent DOM(CDOM and FDOM) and was enriched in moderately unsaturated formulae, indicating additions of terrigenous DOM and/or in situ processing of autochthonous material in the lake. Consistent with its higher CDOM content, BB-DOM was more photoreactive than Microcystis-DOM. For both types of DOM, photodegradation resulted in loss of CDOM, FDOM, moderately unsaturated structures, high O/C and low H/C formulae, and preservation of aliphatics. The majority of photoproducts of 0.5 d irradiation were subsequently removed by day 7, and photoproducts represented a minor fraction of the photo-irradiated DOM. For BB-DOM, molecular formula photolability increased with increasing aromaticity index values, while for Microcystis-DOM, molecular formula photolability increased with molecular mass. Photodegradation increased the proportion of molecular formulae containing N (CHO + N) in BB-DOM, while the molecular mass and the proportion of CHO + N formulae decreased upon photo-irradiation of Microcystis-DOM. In concert, these molecular shifts due to photodegradation decreased the diversity of and increased the similarity between BB-DOM and Microcystis-DOM, suggesting the selective pressure exerted by photochemistry selects for the survival of similar compounds in both samples
Distinct high-T transitions in underdoped BaKFeAs
In contrast to the simultaneous structural and magnetic first order phase
transition previously reported, our detailed investigation on an
underdoped BaKFeAs single crystal unambiguously
revealed that the transitions are not concomitant. The tetragonal (:
I4/mmm) - orthorhombic (: Fmmm) structural transition occurs at
110 K, followed by an adjacent antiferromagnetic (AFM) transition
at 102 K. Hysteresis and coexistence of the and
phases over a finite temperature range observed in our NMR
experiments confirm the first order character of the structural transition and
provide evidence that both and are strongly correlated. Our
data also show that superconductivity (SC) develops in the phase
below = 20 K and coexists with long range AFM. This new observation,
, firmly establishes another similarity between the hole-doped
BaFeAs via K substitution and the electron-doped iron-arsenide
superconductors.Comment: 4 pages, 3 figure
Electron spin resonance study of the LaIn3-xSnx superconducting system
The LaIn3-xSnx alloy system is composed of superconducting Pauli paramagnets.
For LaIn3 the superconducting critical temperature T_c is approximately 0.7 K
and it shows an oscillatory dependence as a function of Sn substitution,
presenting its highest value T_c ~ 6.4 K for the LaSn3 end member. The
superconducting state of these materials was characterized as being of the
conventional type. We report our results for Gd3+ electron spin resonance (ESR)
measurements in the LaIn3-xSnx compounds as a function of x. We show that the
effective exchange interaction parameter J_fs between the Gd3+ 4f local moment
and the s-like conduction electrons is almost unchanged by Sn substitution and
observe microscopically that LaSn3 is a conventional superconductor.Comment: 9 pages, 4 figures. Replaced with the published version and updated
the bibliographic informatio
Dynamics of Counterion Condensation
Using a generalization of the Poisson-Boltzmann equation, dynamics of
counterion condensation is studied. For a single charged plate in the presence
of counterions, it is shown that the approach to equilibrium is diffusive. In
the far from equilibrium case of a moving charged plate, a dynamical counterion
condensation transition occurs at a critical velocity. The complex dynamic
behavior of the counterion cloud is shown to lead to a novel nonlinear
force-velocity relation for the moving plate.Comment: 5 pages, 1 ps figure included using eps
Composição química e digestibilidade in vitro do pedúnculo de caju.
O presente trabalho se propõe a avaliar a composição química-bromatológica e a digestibilidade in vitro do pedúnculo de caju, um subproduto fibroso, tratado ou não tratado com ureia
Desempenho de bezerras leiteiras alimentadas com concentrado inicial contendo sais de ácidos orgânicos ou monesina.
O objetivo deste trabalho foi avaliar o efeito da inclusão de butirato de sódio, monensina sódica e propionato de cálcio no concentrado inicial sobre o desempenho de bezerras leiteiras antes e após o desaleitamento. Vinte e quatro bezerras Holandesas recém-nascidas foram alocadas em abrigos individuais até a décima semana de vida tendo livre acesso à água, alimentadas com 4L de leite/dia, em duas refeições, sendo bloqueadas em função do peso ao nascer a um dos tratamentos, de acordo com o aditivo no concentrado: 1)Butirato de sódio (0,15%); 2)Monensina sódica (30 ppm); 3)Propionato de cálcio (0,15%). Durante 10 semanas os animais receberam concentrado inicial até 2 kg/d e receberam também feno de capim-coast-cross à vontade após o desaleitamento. Semanalmente, os animais foram pesados e avaliados quanto à altura da cernelha, largura do traseiro e perímetro torácico. Não foram observados efeitos significativos entre os tratamentos para o consumo de concentrado e de feno, peso vivo e ganho de peso diário dos animais (P>0,05), entretanto foram observados efeitos de idade (P0,05). A inclusão dos aditivos resultou em desempenho satisfatório de bezerras leiteiras antes e após o desaleitamento. A monensina sódica pode ser substituída por sais de ácidos orgânicos sem prejuízo ao desempenho de bezerros
Hard X-ray spectroscopy of the itinerant magnets FeSb (Na, K, Ca, Sr, Ba)
Ordered states in itinerant magnets may be related to magnetic moments
displaying some weak local moment characteristics, as in intermetallic
compounds hosting transition metal coordination complexes. In this paper, we
report on the Fe -edge X-ray absorption spectroscopy (XAS) of the itinerant
magnets FeSb ( Na, K, Ca, Sr, Ba), aiming at exploring the
electronic and structural properties of the octahedral building block formed by
Fe and the Sb ligands. We find evidence for strong hybridization between the Fe
and Sb states at the Fermi level, giving experimental support to
previous electronic structure calculations of the FeSb
skutterudites. The electronic states derived from Fe 3 Sb mixing are
shown to be either more occupied and/or less localized in the cases of the
magnetically ordered systems, for which Na or K, connecting the local Fe
electronic structure to the itinerant magnetic properties. Moreover, the
analysis of the extended region of the XAS spectra (EXAFS) suggests that bond
disorder may be a more relevant parameter to explain the suppression of the
ferromagnetic ordered state in CaFeSb than the decrease of the
density of states.Comment: 7 pages, 5 figures, submitte
Diferentes teores de proteína metabolizável em rações com cana-de-açúcar para vacas em lactação.
O presente trabalho teve como objetivo avaliar o efeito de diferentes teores de proteína metabolizável (PM) na ração de vacas lactantes alimentadas com cana-de-açúcar
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