13,416 research outputs found
X-ray powder diffraction of high-absorption materials at the XRD1 beamline off the best conditions: Application to (Gd,Nd)5Si4 compounds
Representative compounds of the new family of magnetic materials Gd5-xNdxSi4
were analyzed by X-ray diffraction at the XRD1 beamline at LNLS. To reduce
X-ray absorption, thin layers of the powder samples were mounted outside the
capillaries and measured in Debye-Scherrer geometry as usual. The X-ray
diffraction analyses and the magnetometry results indicate that the behavior of
the magnetic transition temperature as a function of Nd content may be directly
related to the average of the four smallest interatomic distances between
different rare earth sites of the majority phase of each compound. The quality
and consistency of the results show that the XRD1 beamline is able to perform
satisfactory X-ray diffraction experiments on high-absorption materials even
off the best conditions.Comment: 12 pages, 3 figures, 3 table
Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy
The effect of pressure on the magnetic and the magnetocaloric properties
around the martensitic transformation temperature in NiCoMnSb Heusler alloy has
been studied. The martensitic transition temperature has significantly shifted
to higher temperatures with pressure, whereas the trend is opposite with the
application of applied magnetic field. The maximum magnetic entropy change
around the martensitic transition temperature for Ni45Co5Mn38Sb12 is 41.4 J/kg
K at the ambient pressure, whereas it is 33 J/kg K at 8.5 kbar. We find that by
adjusting the Co concentration and applying suitable pressure, NiCoMnSb system
can be tuned to achieve giant magnetocaloric effect spread over a large
temperature span around the room temperature, thereby making it a potential
magnetic refrigerant material for applications.Comment: 16 pages, 5 figure
Gravitational waves from pulsars with measured braking index
We study the putative emission of gravitational waves (GWs) in particular for
pulsars with measured braking index. We show that the appropriate combination
of both GW emission and magnetic dipole brakes can naturally explain the
measured braking index, when the surface magnetic field and the angle between
the magnetic dipole and rotation axes are time dependent. Then we discuss the
detectability of these very pulsars by aLIGO and the Einstein Telescope. We
call attention to the realistic possibility that aLIGO can detect the GWs
generated by at least some of these pulsars, such as Vela, for example.Comment: 6 pages and 4 figure
Abundance patterns in early-type galaxies: is there a 'knee' in the [Fe/H] vs. [alpha/Fe] relation?
Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in
accordance with their old ages and short formation timescales. In this
contribution we aim to resolve the enrichment histories of ETGs. This means we
study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe])
separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars
between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we
show that we can indeed recover the enrichment history per galaxy. We then
analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS
selected to be ETGs. We separate out those galaxies for which the abundance of
iron in stars grows throughout the lifetime of the galaxy, i.e. in which
[Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe]
parameters are correlated with the mass and velocity dispersion of ETGs. We
emphasize that the strongest relation is between [alpha/Fe] and age. This
relation falls into two regimes, one with a steep slope for old galaxies and
one with a shallow slope for younger ETGs. The vast majority of ETGs in our
sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly
observed in local group galaxies. This implies that for the vast majority of
ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or
formed from accreted gas. The properties of the intermediate-age stars in
accretion-dominated ETGs indicate that mass growth through late (minor) mergers
in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method
of reconstructing the stellar enrichment histories of ETGs introduced in this
paper promises to constrain the star formation and mass assembly histories of
large samples of galaxies in a unique way.Comment: 22 pages, 25 figures, accepted for publication by A&
Crescimento e qualidade química de frutos de Mangueira kent sob secamento parcial de raiz.
O objetivo deste trabalho foi avaliar o crescimento e a qualidade de frutos da mangueira ?Kent? sob secamento parcial de raiz (PRD) em condições do semiárido baiano. O estudo foi conduzido na área experimental em 0,48 ha da fazenda Boa Vista, no município de Iaçu, BA entre agosto e novembro de 2009 com 144 plantas. Os tratamentos com PRD foram baseados no percentual da lâmina bruta aplicada (LBA) pela fazenda, estimada pela evapotranspiração da cultura para irrigação localizada (ETc). O gotejamento foi o sistema de irrigação utilizado, com duas linhas laterais por fileira de plantas, entretanto, para a aplicação do PRD foi utilizada uma linha alternadamente com três emissores. O delineamento foi em blocos casualizados com três repetições, sendo oito tratamentos: T1, T2 e T3 (PRD 50% com alternância aos 7, 14 e 21 dias); T4, T5 e T6 (100% na fase de floração e 50% nas fases frutificação e estabilidade de frutos, com mesma ordem de alternância); T7 (50% fixo) e T8-testemunha (100% da LBA nos dois lados). Foram avaliados parâmetros físicos (taxa de pegamento e crescimento dos frutos) que não sofreram influência do PRD e químicos (sólidos solúveis e acidez total) que sob lâminas menores tiveram aumentos significantes
Inference of oxygen vacancies in hydrothermal Na0.5Bi0.5TiO3
A high-resolution x-ray powder diffraction study has been made of pseudo-rhombohedral and tetragonal phases in Na0.5Bi0.5TiO3 (NBT), produced via hydrothermal and conventional solidstate methods. Hydrothermal NBT exhibits significantly greater structural distortion at room
temperature than solid-state NBT. Peak widths and superstructure peak intensities show a phase
transition at 305 C, with trends suggesting that the structure tends towards cubic symmetry at this temperature. Structural refinements indicate that the transition occurs via a phase coexistence region with no clear intermediate phase. Piezoelectric data show evidence of polarisation pinning in hydrothermal NBT, interpreted as a high proportion of oxygen vacancies
Mamoeiro.
A espécie Carica papaya L. é o mamoeiro mais cultivado em todo mundo. É uma planta herbácea, tipicamente tropical, cujo centro de origem é, muito provavelmente, o Noroeste da América do Sul, vertente oriental dos Andes, ou mais precisamente, a Bacia Amazônica Superior, onde sua diversidade genética é máxima. O Brasil é o primeiro produtor mundial de mamão, situando-se entre os principais países exportadores, principalmente para o mercado europeu. A produtividade média nacional é da ordem de 40 t/ha para as variedades do grupo Solo e de 60 t/ha para as variedades do grupo Formosa. É uma fruteira cultivada em quase todo o território brasileiro, merecendo destaque os estados da Bahia, primeiro produtor, Espírito Santo e Ceará, segundo e terceiro produtores, respectivamente, responsáveis por cerca de 90% da produção nacional. O mamoeiro produz plantas masculinas, femininas e hermafroditas, que originam frutos de formatos distintos. De uma forma geral, as variedades de mamoeiros mais exploradas no Brasil são classificadas em dois grupos: Solo (ex: 'Sunrise Solo', Improved Sunrise Solo cv. 72/12', 'Baixinho de Santa Amália e 'Sunrise Golden'), mais utilizadas para a exportação, e Formosa (ex: 'Tainung nº 1', 'Tainung nº 2 e 'Caliman 1'), preferidas para agroindústria e hotelaria
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